Refrigeration system

Abstract

The refrigeration system includes: indoor and outdoor units; the outdoor unit comprises a first compressor and a second compressor. The switching valve is respectively communicated with the first compressor and the second compressor, the distributor is communicated with the switching valve, and the first gas-liquid separator and the second gas-liquid separator are communicated with the control part. The control part is configured to control the first compressor and the second compressor to work according to the same operation frequency, and when the operation frequencies of the first compressor and the second compressor are the same, the first compressor and the second compressor are started based on the exhaust temperature difference between the first compressor and the second compressor. Presuming whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state or not according to the difference between the operation current of the first compressor and the operation current of the second compressor; when the non-uniform liquid level state is presumed, the operation frequency of one compressor is adjusted so that the non-uniform liquid level state can be transited to the uniform liquid level state; the non-uniform oil return and liquid return of the refrigerating system can be avoided.

Description

Technical Field

[0001] The invention relates to the technical field of air conditioning, and in particular to a refrigeration system. Background Art

[0002] Modern residential and industrial sites need to control the air parameters of indoor spaces, including but not limited to heating, cooling, ventilation, etc. The air conditioning system (HVAC) provides energy through a low-temperature heat source or a high-temperature heat source, so that the heat-exchanged air circulates indoors, or introduces outdoor air to adjust the ambient air parameters of the indoor space.

[0003] Modern air conditioning systems no longer limit the number of outdoor units and indoor units. For example, multi-split systems allow one outdoor unit to be used with multiple indoor units; modular central air conditioners allow outdoor units to be combined in a modular manner. The current capacity of the module can reach 40HP, and the capacity of the combined modules can reach 168HP. Since multi-split or modular air conditioning systems usually need to be installed on the top of a building, there is a huge height difference between the outdoor unit and the indoor unit when installed (the difference can reach 110 meters), and the length of the piping between the outdoor unit and the indoor unit is very long (the total length of the piping has reached 1,200 meters). The huge height difference and piping length require more refrigerant. The amount of refrigerant in the system has increased compared to traditional split air conditioners, and the current filling amount has reached hundreds of kilograms. At the indoor end, the capacity of the indoor unit varies greatly, ranging from 15kW to 560kW, and the ratio of indoor units to outdoor units can range from 30% to 200%.

[0004] The hardware design of modern air conditioning systems makes it impossible for traditional container components (such as gas-liquid separators) in refrigeration cycles to meet the needs. Traditional container components are usually small pressure vessels less than 30L, which cannot meet the design and use requirements even in a single module. The prior art discloses a combined gas-liquid separator to improve this problem. For example, the technical solution disclosed in the Chinese patent application (CN110470083A): "It includes two gas-liquid separators, each gas-liquid separator includes a cylinder, and the cylinder is provided with an inlet pipe and an outlet pipe; a balance pipe connected to each cylinder is provided between the side walls of each cylinder; a distribution pipe connected to each of the cylinders is provided between the bottoms of each cylinder, and an oil filling pipe is connected to the distribution pipe, so as to empty or inject the liquid refrigerant or lubricating oil in the cylinder."

[0005] However, when only one compressor is provided, the above-mentioned combined gas-liquid separator can keep the liquid level in multiple gas-liquid separators uniform. However, for modular outdoor units, there will be a hardware design that matches a four-way valve with two or more compressors, which requires the design of a distributor upstream of multiple gas-liquid separators. The distributor will cause uneven distribution of the liquid mixture in multiple gas-liquid separators; at the same time, due to the different loads of multiple compressors, the mixture of lubricating oil and liquid refrigerant will be further aggravated. The uneven distribution in each gas-liquid separator will further lead to different oil return and air return volumes for each compressor, resulting in poor oil return of the compressor, too large differences in exhaust temperatures of multiple compressors, and reduced system performance, which will further lead to compressor damage. Summary of the invention

[0006] When dual compressors or multiple compressors are used in combination with parallel gas-liquid separators, due to the design of the distributor and the different loads of each compressor, the mixture of lubricating oil and liquid refrigerant is in an uneven distribution state in each gas-liquid separator, which further leads to different return oil and return air volumes of each compressor, resulting in poor oil return of the compressor and reduced system performance. The first aspect of the present application designs and provides a refrigeration system.

[0007] The refrigeration system includes an indoor unit and an outdoor unit; the outdoor unit includes a first compressor, a second compressor, a switching valve connected to the first compressor and the second compressor respectively, a distributor connected to the switching valve, a first gas-liquid separator connected to one outlet of the distributor; and a second gas-liquid separator connected to another outlet of the distributor.

[0008] In one or more embodiments of the present application, the refrigeration system also includes a control unit, which is configured to control the first compressor and the second compressor to operate at the same operating frequency, and when the operating frequencies of the first compressor and the second compressor are the same, it is estimated whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state based on the exhaust temperature difference between the first compressor and the second compressor, and the difference in operating current between the first compressor and the second compressor; and when it is estimated to be a non-uniform liquid level state, the operating frequency of one of the compressors is adjusted to transition from the non-uniform liquid level state to the uniform liquid level state.

[0009] In one or more embodiments of the present application, the control unit is configured to infer that the first gas-liquid separator and the second separator are in a non-uniform liquid level state when the exhaust temperature difference between the first compressor and the second compressor is not lower than a first set threshold and the operating current difference between the first compressor and the second compressor is not lower than a second set threshold.

[0010] In one or more embodiments of the present application, the control unit is further configured to, after inferring that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, infer that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator when the conditions that the operating current of the second compressor is higher than the operating current of the first compressor and the exhaust temperature of the first compressor is higher than the exhaust temperature of the second compressor are met.

[0011] In one or more embodiments of the present application, the control unit is further configured to, after inferring that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, infer that the liquid level of the first gas-liquid separator is higher than the liquid level of the second gas-liquid separator when the conditions that the operating current of the first compressor is higher than the operating current of the second compressor and the exhaust temperature of the second compressor is higher than the exhaust temperature of the first compressor are met.

[0012] In one or more embodiments of the present application, the control unit is also configured to increase the operating frequency of the first compressor or reduce the operating frequency of the second compressor after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state.

[0013] In one or more embodiments of the present application, the control unit is also configured to increase the operating frequency of the second compressor or reduce the operating frequency of the first compressor after estimating that the liquid level of the first gas-liquid separator is higher than the liquid level of the second gas-liquid separator until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state.

[0014] In one or more embodiments of the present application, the control unit is also configured to obtain a frequency adjustment coefficient after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator, and increase the operating frequency of the first compressor or decrease the operating frequency of the second compressor based on the frequency adjustment coefficient until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state.

[0015] In one or more embodiments of the present application, the control unit is also configured to obtain a frequency adjustment coefficient after estimating that the liquid level of the first gas-liquid separator is higher than the liquid level of the second gas-liquid separator, and increase the operating frequency of the second compressor or reduce the operating frequency of the first compressor based on the frequency adjustment coefficient until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state.

[0016] In one or more embodiments of the present application, the frequency adjustment coefficient is obtained based on a first fitting curve generated according to the exhaust temperature difference between the first compressor and the second compressor; in the first fitting curve, the frequency adjustment coefficient corresponds one-to-one to the exhaust temperature difference between the first compressor and the second compressor.

[0017] In one or more embodiments of the present application, the outdoor unit further includes a distribution pipe having two ends respectively connected to the first gas-liquid separator and the second gas-liquid separator, and a regulating valve arranged on the distribution pipe.

[0018] In one or more embodiments of the present application, the control unit is configured to control the first compressor and the second compressor to operate at the same operating frequency, and when the operating frequencies of the first compressor and the second compressor are the same, it is estimated whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state based on the exhaust temperature difference between the first compressor and the second compressor, and the difference in operating current between the first compressor and the second compressor; and when it is estimated to be a non-uniform liquid level state, the operating frequency of one of the compressors is adjusted, and the regulating valve is driven to operate to adjust the refrigerant flow in the distribution pipe to transition from the non-uniform liquid level state to the uniform liquid level state.

[0019] In one or more embodiments of the present application, the control unit is configured to infer that the first gas-liquid separator and the second separator are in a non-uniform liquid level state when the exhaust temperature difference between the first compressor and the second compressor is not lower than a first set threshold and the operating current difference between the first compressor and the second compressor is not lower than a second set threshold.

[0020] In one or more embodiments of the present application, the control unit is further configured to, after inferring that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, infer that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator when the conditions that the operating current of the second compressor is higher than the operating current of the first compressor and the exhaust temperature of the first compressor is higher than the exhaust temperature of the second compressor are met.

[0021] In one or more embodiments of the present application, the control unit is further configured to, after inferring that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, infer that the liquid level of the first gas-liquid separator is higher than the liquid level of the second gas-liquid separator when the conditions that the operating current of the first compressor is higher than the operating current of the second compressor and the exhaust temperature of the second compressor is higher than the exhaust temperature of the first compressor are met.

[0022] In one or more embodiments of the present application, the control unit is also configured to increase the operating frequency of the first compressor or reduce the operating frequency of the second compressor after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator, and drive the regulating valve to operate until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state.

[0023] In one or more embodiments of the present application, the control unit is also configured to increase the operating frequency of the second compressor or reduce the operating frequency of the first compressor after estimating that the liquid level of the first gas-liquid separator is higher than the liquid level of the second gas-liquid separator, and drive the regulating valve to operate until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state.

[0024] In one or more embodiments of the present application, the control unit is also configured to obtain the frequency adjustment coefficient after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator, and increase the operating frequency of the first compressor or reduce the operating frequency of the second compressor based on the frequency adjustment coefficient, and drive the regulating valve to operate until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state.

[0025] In one or more embodiments of the present application, the control unit is also configured to obtain the frequency adjustment coefficient after estimating that the liquid level of the first gas-liquid separator is higher than the liquid level of the second gas-liquid separator, and increase the operating frequency of the second compressor or reduce the operating frequency of the first compressor based on the frequency adjustment coefficient, and drive the regulating valve to operate until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state.

[0026] In one or more embodiments of the present application, the frequency adjustment coefficient is obtained based on a first fitting curve generated according to the exhaust temperature difference between the first compressor and the second compressor; in the first fitting curve, the frequency adjustment coefficient corresponds one-to-one to the exhaust temperature difference between the first compressor and the second compressor.

[0027] In one or more embodiments of the present application, the regulating valve is an electronic expansion valve, and the control unit drives the regulating valve to operate to connect the distribution pipe. The operation of the regulating valve is divided into multiple continuous regulation cycles; the opening of the next regulation cycle is the sum of the opening of the current regulation cycle and the correction opening; the correction opening is the product of the maximum opening and the proportional coefficient, and the proportional coefficient is obtained based on a second fitting curve generated according to the exhaust temperature difference between the first compressor and the second compressor. In the second fitting curve, the proportional coefficient corresponds one-to-one to the exhaust temperature difference between the first compressor and the second compressor.

[0028] The present invention can effectively avoid the problem of uneven return of air and liquid caused by a set of switching valves and distributors, and improve the service life and operation stability of the compressor.

[0029] After reading the specific embodiments of the present invention in conjunction with the accompanying drawings, other features and advantages of the present invention will become more clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0031] Figure 1 A schematic block diagram of the structure of a refrigeration system provided in one or more embodiments of the present application;

[0032] Figure 2 A schematic diagram of a refrigeration cycle in a refrigeration system provided in one or more embodiments of the present application;

[0033] Figure 3 A schematic diagram of a refrigeration cycle of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0034] Figure 4 A schematic diagram of a refrigeration cycle of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0035] Figure 5 A schematic diagram of a refrigeration cycle of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0036] Figure 6 for Figure 3 A partial enlarged schematic diagram of the middle A part;

[0037] Figure 7 A schematic diagram of a refrigeration cycle of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0038] Figure 8 A schematic diagram of the structure of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0039] Fig. 9 A schematic diagram of a refrigeration cycle of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0040] Fig.10 A schematic diagram of a refrigeration cycle of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0041] Fig.11 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0042] Fig.12 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0043] Fig.13 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0044] Fig.14 A schematic diagram of a refrigeration cycle of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0045] Fig.15 A schematic diagram of the structure of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0046] Fig.16 A schematic diagram of the numerical relationship between the first set threshold and the outdoor ambient temperature in the refrigeration system provided by one or more embodiments of the present application;

[0047] Fig.17 An example diagram of a first fitting curve in a refrigeration system provided by one or more embodiments of the present application;

[0048] Fig.18 An example diagram of a second fitting curve in a refrigeration system provided by one or more embodiments of the present application;

[0049] Fig.19 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0050] In the figure, 1, refrigeration system; 10, outdoor unit; 12, outdoor unit; 20, indoor unit; 22, indoor unit; 24, indoor unit; 200, indoor heat exchanger; 201, indoor electronic expansion valve; 30, control unit; 31, liquid side connecting pipe; 32, gas side connecting pipe; 100a, first compressor; 100b, second compressor; 101a, first oil separator; 101b, second oil separator; 102, switching valve; 103, outdoor heat exchanger; 104, throttling device; 105, liquid side shut-off valve; 106, gas side shut-off valve; 107, distributor; 107a, one outlet of distributor; 107b, another outlet of distributor; 107c, inlet of distributor; 108a, first gas-liquid separator; 108b, second gas-liquid separator Separator; 109, solenoid valve; 110, high-pressure sensor; 111a, first high-pressure switch; 111b, second high-pressure switch; 112a, first compressor exhaust temperature sensor; 112b, second compressor exhaust temperature sensor; 113a, first outlet pipe; 113b, second outlet pipe; 114a, first main oil return hole; 114b, second main oil return hole; 115a, first auxiliary oil return hole; 115b, second auxiliary oil return hole 120, distribution pipe; 121, regulating valve; 130a, first shell; 130b, second shell; 131a, first inlet pipe; 131b, second inlet pipe; 140, gas connecting pipe; 150, liquid connecting pipe; 150a, first capillary tube; 150b, second capillary tube; 151, low-pressure sensor. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0052] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0053] The terms "first", "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0054] In the description of this application, it should be noted that, 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 it can be 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 this application can be understood according to specific circumstances.

[0055] In the present invention, unless otherwise clearly stipulated and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0056] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0057] Figure 1 A schematic diagram showing the structure of a refrigeration system 1 provided in one or more embodiments of the present invention; Figure 2 An example of a refrigerant circuit formed by the refrigeration system 1 according to the embodiment of the present invention is shown.

[0058] The refrigeration system 1 is installed in buildings such as apartments, hotels, office buildings, and houses, etc. The refrigeration system 1 is configured to selectively perform a heating operation or a cooling operation.

[0059] A refrigeration cycle is integrated in the refrigeration system 1. A compressor, a condenser, a throttling device 104 and an evaporator are used in the refrigeration cycle. The refrigeration cycle includes a series of processes involving compression, condensation, expansion and evaporation to cool or heat the indoor space.

[0060] From a principle perspective, low-temperature, low-pressure refrigerant enters the compressor, which compresses it into high-temperature, high-pressure refrigerant gas and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and the heat is released to the surrounding environment through the condensation process.

[0061] The throttling device 104 expands the high-temperature and high-pressure liquid refrigerant condensed in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the refrigerant expanded in the throttling device 104 and returns the refrigerant gas in a low-temperature and low-pressure state to the compressor. The evaporator can achieve a refrigeration effect by utilizing the latent heat of evaporation of the refrigerant to exchange heat with the material to be cooled. In the entire cycle, the refrigeration system 1 can adjust the temperature of the indoor space.

[0062] The refrigeration system 1 includes an outdoor unit and an indoor unit connected to each other. Figure 1 The figure shows a combination of two outdoor units (10, 12) and three indoor units (20, 22, 24). Figure 2 The combination of two outdoor units (10, 12) and five indoor units (20, 22, 24, 26, 28) is shown in FIG. In the present application, the number of outdoor units and indoor units is not particularly limited. Figure 1 and Figure 2 In the same manner as shown in the indoor unit and the outdoor unit, only one indoor unit and one outdoor unit are arranged in a refrigeration system 1, or multiple indoor units and multiple outdoor units are arranged.

[0063] The indoor unit is provided with an indoor heat exchanger (such as Figure 2 200) and an indoor throttling device (such as an indoor electronic expansion valve, such as Figure 2 201).

[0064] The indoor unit and the outdoor unit are connected by a liquid-side communication pipe 31 and a gas-side communication pipe 32. The liquid-side communication pipe 31 and the gas-side communication pipe 32 are used to allow the refrigerant to flow so that the refrigerant can form a refrigerant circuit and circulate therein.

[0065] In one or more embodiments of the present application, a liquid-side shutoff valve 105 is provided on the liquid-side connecting pipe 31, and a gas-side shutoff valve 106 is provided on the gas-side connecting pipe 32. The liquid-side shutoff valve 105 can shut off the fluid passage in the liquid-side connecting pipe 31 or, when the opening is minimum, is close to shutting off the fluid passage in the liquid-side connecting pipe 31, and the gas-side shutoff valve 106 can shut off the fluid passage in the gas-side connecting pipe 32 or, when the opening is minimum, is close to shutting off the fluid passage in the gas-side connecting pipe 32.

[0066] The basic structure and function of the outdoor unit are described exemplarily below. The number of outdoor units can be expanded to multiple, each of which constitutes a module and operates in a group manner.

[0067] Figure 3 It is a schematic diagram of the structure of the outdoor unit; Figure 4 It is a schematic diagram of the refrigeration cycle when the outdoor unit performs cooling operation; Figure 5 It is a schematic diagram of the refrigeration cycle when the outdoor unit performs heating operation; Figure 6 yes Figure 3 Enlarged view of part A in .

[0068] In one or more embodiments of the present application, the outdoor unit of the refrigeration system 1 refers to a part of the refrigeration cycle including a compressor and an outdoor heat exchanger 103, and the outdoor unit can perform heating operation or cooling operation on the outdoor side to provide energy for increasing the indoor temperature or reducing the indoor temperature to the indoor unit. Figures 3 to 6 As shown, the outdoor unit is provided with a first compressor 100a and a second compressor 100b; Figures 3 to 6 In the same manner as the first compressor 100a and the second compressor 100b shown, more compressors are arranged in the outdoor unit. The first compressor 100a and the second compressor 100b are configured to suck in and compress the refrigerant into a high temperature and high pressure state. The types of the first compressor 100a and the second compressor 100b are not further limited here, for example, they can be reciprocating compressors, screw compressors, etc. The speeds of the first compressor 100a and the second compressor 100b are controlled by a frequency converter, and the first compressor 100a and the second compressor 100b can operate independently. The discharge end of the first compressor 100a is provided with a first high pressure switch 111a, and the discharge end of the second compressor 100b is provided with a second high pressure switch 111b. The discharge side of the first compressor 100a and the second compressor 100b is also provided with a high pressure sensor 110, and the suction side of the first compressor 100a and the second compressor 100b is also provided with a low pressure sensor 151.

[0069] A first compressor exhaust temperature sensor 112a is provided at the discharge end of the first compressor 100a, and a second compressor exhaust temperature sensor 112b is provided at the discharge end of the second compressor 100b.

[0070] A first gas-liquid separator 108a is provided on the suction side of the first compressor 100a. The first gas-liquid separator 108a separates the gas and liquid of the evaporated refrigerant, and guides the separated gaseous refrigerant into the first compressor 100a. A second gas-liquid separator 108b is provided on the suction side of the second compressor 100b. The second gas-liquid separator 108b separates the gas and liquid of the evaporated refrigerant, and guides the separated gaseous refrigerant into the second compressor 100b.

[0071] The outdoor unit may also be provided with an outdoor fan (not shown) and a switching valve 102; wherein the outdoor fan may be an axial flow fan, a cross flow fan or other optional fan forms. The outdoor fan is arranged near the outdoor heat exchanger 103. The outdoor heat exchanger 103 may also exchange heat with other types of heat sources, such as water.

[0072] The outdoor unit is also provided with a first oil separator 101a and a second oil separator 101b. The first oil separator 101a is used to separate the lubricating oil from the high-temperature refrigerant vapor when the mixture of the lubricating oil and the refrigerant leaves the compressor. The second oil separator 101b is used to separate the lubricating oil from the high-temperature refrigerant vapor when the mixture of the lubricating oil and the refrigerant leaves the compressor. The first oil separator 101a is arranged in the pipeline between the first compressor 100a and the condenser. The flow velocity of the high-pressure refrigerant in the first oil separator 101a and the second oil separator 101b is reduced, so that the lubricating oil is captured in the first oil separator 101a and the second oil separator 101b. The lubricating oil with a higher density is separated from the refrigerant vapor and falls to the bottom of the first oil separator 101a and the second oil separator 101b. The lubricating oil collected in the first oil separator 101a and the second oil separator 101b returns to the first compressor 100a and the second compressor 100b through the first capillary tube 150a and the second capillary tube 150b respectively. The diameter and length of the first capillary tube 150a and the second capillary tube 150b can be used to adjust the return oil amount of the lubricating oil. A solenoid valve 109 is also provided downstream of the first oil separator 101a and the second oil separator 101b.

[0073] The switching valve 102 is exemplified by a four-way valve. The switching valve 102 is a valve used to switch the flow direction of the refrigerant in the refrigerant circuit. In the present application, there is only one switching valve 102 in one outdoor unit.

[0074] In cooling operation, the outdoor unit can form a refrigerant circuit for cooling operation (hereinafter referred to as a refrigeration cycle), wherein the switching valve 102 (for example, one passage of a four-way valve, illustratively, the fluid passage between the C port and the S port) and the distributor 107 are sequentially connected from the gas-side connecting pipe 32 to the liquid-side connecting pipe 31. The distributor 107 (the inlet is shown as 107c in the figure) is in fluid communication with the switching valve 102. Downstream of the distributor 107, that is, one outlet of the distributor 107 is connected in sequence to the first gas-liquid separator 108a and the first compressor 100a, and the other outlet of the distributor 107 is connected in sequence to the second gas-liquid separator 108b and the second compressor 100b; the mixture of refrigerant and lubricating oil flowing out of the first compressor 100a enters the first oil separator 101a, and from the first oil separator 101a, the refrigerant is again merged into the switching valve 102 (for example, another passage of the four-way valve, exemplarily the fluid passage between the D port and the E port); the mixture of refrigerant and lubricating oil flowing out of the second compressor 100b enters the second oil separator 101b, and from the second oil separator 101b, the refrigerant is again merged into the switching valve 102 (for example, another passage of the four-way valve, exemplarily the fluid passage between the D port and the E port); the refrigerant flowing out of the switching valve 102 enters the outdoor heat exchanger 103 again.

[0075] In the heating operation, the outdoor unit can form a refrigerant circuit for heating operation (hereinafter referred to as a heating cycle), wherein the outdoor heat exchanger 103, the switching valve 102 (for example, one passage of a four-way valve, exemplarily, the fluid passage between the E port and the S port) and the distributor 107 are sequentially connected from the liquid side connecting pipe 31 to the gas side connecting pipe 32. The distributor 107 is in fluid communication with the switching valve 102. Downstream of the distributor 107, that is, one outlet of the distributor 107 is sequentially connected to the first gas-liquid separator 108a, the first compressor 100a, the first oil separator 101a and the switching valve 102 (for example, one passage of a four-way valve, exemplarily, the fluid passage between the D port and the C port); the other outlet of the distributor 107 is sequentially connected to the second gas-liquid separator 108b, the second compressor 100b, the second oil separator 101b and the switching valve 102 (for example, the same passage of the four-way valve, exemplarily, the fluid passage between the D port and the C port).

[0076] The two outlets of the distributor 107 (as shown by 107a and 107b in the figure) have the same design flow rate.

[0077] The first gas-liquid separator 108a has a first shell 130a. The upper part of the first shell 130a is provided with a first inlet pipe 131a inserted therein and the inlet is located at the upper part of the first shell 130a. The first shell 130a is also provided with a first outlet pipe 113a, which is close to the bottom of the first shell 130a and bent into a roughly U-shape, and the outlet of the first outlet pipe 113a extends outward from the upper part of the first shell 130a. The first outlet pipe 113a is fluidically connected to the first compressor 100a.

[0078] The second gas-liquid separator 108b has a second shell 130b. The upper part of the second shell 130b is provided with a second inlet pipe 131b inserted therein and the inlet is located at the upper part of the second shell 130b. The second shell 130b is also provided with a second outlet pipe 113b, which is close to the bottom of the second shell 130b and bent into a roughly U-shape, and the outlet of the second outlet pipe 113b extends outward from the upper part of the second shell 130b. The second outlet pipe 113b is fluidically connected to the second compressor 100b.

[0079] When performing cooling operation or heating operation, the evaporated refrigerant is distributed by the distributor 107, and enters the first shell 130a and the second shell 130b through the first inlet pipe 131a and the second inlet pipe 131b respectively, and then produces a gas-liquid separation effect. The separated gaseous refrigerant is sucked into the first compressor 100a and the second compressor 100b from the first outlet pipe 113a and the second outlet pipe 113b; the separated liquid refrigerant is retained at the bottom of the first shell 130a and the second shell 130b, and gradually evaporates and gasifies over time, and then is sucked into the first compressor 100a and the second compressor 100b. A first main oil return hole 114a is opened at the bottom of the first outlet pipe 113a, and a second main oil return hole 114b is opened at the bottom of the second outlet pipe 113b. The lubricating oil gathered at the bottom of the first shell 130a can flow back to the first compressor 100a through the first outlet pipe 113a through the first main oil return hole 114a; similarly, the lubricating oil gathered at the bottom of the second shell 130b can flow back to the second compressor 100b through the second outlet pipe 113b through the second main oil return hole 114b.

[0080] In one or more embodiments of the present application, the first shell 130a and the second shell 130b have the same shape and volume. The upper sides of the first shell 130a and the second shell 130b can be connected through the gas connecting pipe 140, and the lower sides of the first shell 130a and the second shell 130b can be connected through the liquid connecting pipe 150.

[0081] like Figure 6As shown, in one or more embodiments of the present application, a first auxiliary oil return hole 115a higher than the first main oil return hole 114a is further provided on the first outlet pipe 113a. In one or more embodiments of the present application, the height difference between the first auxiliary oil return hole 115a and the first main oil return hole 114a can be determined by the difference between the maximum lubricating oil amount and the minimum lubricating oil amount of the first compressor 100a and the maximum refrigerant volume; wherein the difference between the maximum lubricating oil amount and the minimum lubricating oil amount represents the maximum capacity of the lubricating oil allowed to accumulate in the first shell 130a (the first compressor 100a cannot work if it is lower than the minimum lubricating oil amount), that is, the ratio of the difference between the maximum lubricating oil amount and the minimum lubricating oil amount to the cross-sectional area of ​​the first shell 130a (assuming that the first shell 130a is cylindrical) is the maximum lubricating oil height, and the ratio of the maximum refrigerant volume to the cross-sectional area of ​​the first shell 130a is the maximum refrigerant height. The sum of the maximum refrigerant volume height and the maximum lubricating oil height is the maximum liquid level height in the first shell 130a. Since the first main oil return hole 114a is set at the bottom (for example, the lowest point of the U-shaped tube), the height difference between the first auxiliary oil return hole 115a and the first main oil return hole 114a is lower than the maximum liquid level height. For example, a relatively ideal preset refrigerant volume that is smaller than the maximum refrigerant volume (for example, 60% of the maximum refrigerant volume) can be set according to the capacity of the refrigeration system 1 to ensure that both the first compressor 100a and the second compressor 100b in the refrigeration system 1 can operate stably, and the preset refrigerant height is calculated based on the ratio of the preset refrigerant volume to the cross-sectional area of ​​the first shell 130a, and the first auxiliary oil return hole 115a is opened at the set position of the first outlet pipe 113a based on the sum of the preset refrigerant height and the maximum lubricating oil height. It is also possible to evenly distribute multiple first auxiliary oil return holes 115a in an equidistant manner with the sum of the preset refrigerant height and the maximum lubricating oil height as the total height.

[0082] In one or more embodiments of the present application, the height difference between the second auxiliary oil return hole 115b and the second main oil return hole 114b can be determined by the difference between the maximum lubricating oil amount and the minimum lubricating oil amount of the second compressor 100b and the maximum refrigerant volume; wherein the difference between the maximum lubricating oil amount and the minimum lubricating oil amount represents the maximum capacity of the lubricating oil allowed to accumulate in the second shell 130b (the second compressor 100b cannot work below the minimum lubricating oil amount), that is, the ratio of the difference between the maximum lubricating oil amount and the minimum lubricating oil amount to the cross-sectional area of ​​the second shell 130b (assuming that the second shell 130b is cylindrical) is the maximum lubricating oil height, and the ratio of the maximum refrigerant volume to the cross-sectional area of ​​the second shell 130b is the maximum refrigerant height. The sum of the maximum refrigerant volume height and the maximum lubricating oil height is the maximum liquid level in the second shell 130b. Since the second main oil return hole 114b is set at the bottom (for example, the lowest point of the U-shaped tube), the height difference between the second auxiliary oil return hole 115b and the second main oil return hole 114b is lower than the maximum liquid level. For example, a relatively ideal preset refrigerant volume that is smaller than the maximum refrigerant volume (for example, 60% of the maximum refrigerant volume) and at which both the second compressor 100b and the second compressor 100b in the refrigeration system 1 can operate stably can be set according to the capacity of the refrigeration system 1, and the preset refrigerant height is calculated based on the ratio of the preset refrigerant volume to the cross-sectional area of ​​the second shell 130b, and the second auxiliary oil return hole 115b is opened at the set position of the second outlet pipe 113b based on the sum of the preset refrigerant height and the maximum lubricating oil height. It is also possible to evenly distribute multiple second auxiliary oil return holes 115b in an equidistant manner with the sum of the preset refrigerant height and the maximum lubricating oil height as the total height.

[0083] An outdoor control circuit is also provided in the outdoor unit. The outdoor control circuit is provided in an electrical box with good sealing performance and heat dissipation function. The outdoor control circuit includes components such as a processor, a storage unit, an input / output interface, and a communication interface. The processor may be a dedicated processor, a central processing unit (CPU), etc. The processor may access the storage unit to execute instructions or applications stored in the storage unit to implement related functions. The storage unit may include a volatile memory and / or a non-volatile memory. The input / output interface may be connected to various sensors provided in the outdoor unit to receive detection values ​​of various sensors provided in the outdoor unit. The input / output interface may also be connected to devices such as a frequency converter, an outdoor fan, and a four-way valve to output control instructions generated by the processor to them. The communication interface may support different wireless communication protocols, such as Wi-Fi, Bluetooth, near field communication, NB-IoT, etc., to communicate and connect with other electronic devices, including but not limited to cloud servers, computers (host computers), smart phones, tablet computers, PDAs, intelligent control tooling, wearable devices, and vehicle-mounted devices, etc.

[0084] As described in the background technology section, the refrigerant filling amount in the refrigeration system 1 has reached hundreds of kilograms. Since only one switching valve 102 is provided, the switching valve 102 must be provided corresponding to the distributor 107; however, it is difficult to ensure the similarity of the pipeline length and the pipeline diameter during long-term use downstream of the corresponding distributor 107 (such as a three-way pipe or a three-way valve), especially since there may be tiny impurities and pollutants in the refrigeration system 1, and these substances will accumulate in the pipeline near the distributor 107, gradually changing the diameter of the pipeline; and since the output of the two compressors will change with the change of load, this will aggravate the uneven distribution of liquid in the two gas-liquid separators downstream of the distributor 107, and since the lubricating oil is dissolved in the liquid refrigerant, it will further cause deviations in the return oil and return air of the first compressor 100a and the second compressor 100b.

[0085] like Figure 7 and Figure 8 As shown, to solve this problem, a control unit 30 is further provided in the refrigeration system 1. In one or more embodiments of the present application, the control unit 30 is implemented by an outdoor control circuit. In one or more embodiments of the present application, the control unit 30 can also be implemented by a cloud server or a host computer that is communicatively connected to the outdoor unit.

[0086] The control unit 30 is configured to control the first compressor 100a and the second compressor 100b to operate at the same operating frequency, and when the operating frequencies of the first compressor 100a and the second compressor 100b are the same, it is estimated whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state based on the exhaust temperature difference between the first compressor 100a and the second compressor 100b, and the difference in operating current between the first compressor 100a and the second compressor 100b. And, when it is estimated to be a non-uniform liquid level state, the operating frequency of one of the compressors is adjusted to transition from the non-uniform liquid level state to the uniform liquid level state.

[0087] More specifically, if Fig.11 As shown, the control unit 30 is configured to control the first compressor 100a and the second compressor 100b to operate at the same frequency (eg Fig.11 The operating frequency can be obtained based on the total load of the refrigeration system, for example, the total operating frequency required by the refrigeration system is obtained according to the PID algorithm or the fuzzy control algorithm; the total operating frequency is divided by the number of compressors (for example, in the present application, the total operating frequency is divided by 2 to obtain the operating frequency), and the first compressor 100a and the second compressor 100b are controlled to operate according to the obtained operating frequency, and the operating frequencies of the first compressor 100a and the second compressor 100b are the same.

[0088] The control unit 30 further samples the exhaust temperature of the first compressor 100a (eg Fig.11 Sampling the exhaust temperature of the second compressor 100b (as shown in step S112); Fig.11 Calculate the exhaust temperature difference between the first compressor 100a and the second compressor 100b (as shown in step S113); Fig.11 100a and the second compressor 100b, and whether the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than a first set threshold value (such as Fig.11 As shown in step S115): Assume that the exhaust temperature of the first compressor 100a is T d1 , the exhaust temperature of the second compressor 100b is denoted as T d2 , then calculate and determine whether there is |T d1 -T d2 |≥B+b; wherein B+b represents the first set threshold, B is a constant, and b is generated according to the outdoor ambient temperature.

[0089] For example, Fig.16 As shown, the first set threshold is the sum of a reference temperature B (pre-set and stored) and a correction temperature b. When the outdoor ambient temperature is lower than -15°C, the correction temperature is 5°C; when the outdoor ambient temperature is higher than -15°C but lower than 7°C, the correction temperature is 2°C; when the outdoor ambient temperature is higher than 7°C but lower than 20°C, the correction temperature is 0°C; when the outdoor ambient temperature is higher than 20°C, the correction temperature is -3°C.

[0090] While sampling the compressor exhaust temperature, the control unit 30 further samples the operating current of the first compressor 100a (eg Fig.11 Sampling the operating current of the second compressor 100b (as shown in step S116); Fig.11 Calculate the difference in operating current between the first compressor 100a and the second compressor 100b (as shown in step S117); Fig.11 100a and 100b); determine whether the difference in operating current between the first compressor 100a and the second compressor 100b is not less than a second set threshold value (such as Fig.11 As shown in step S119): Assuming that the operating current of the first compressor 100a is recorded as A1, the operating current of the second compressor 100b is recorded as A2, and the second set threshold is 0.5A, it is calculated and determined whether |A1-A2|≥0.5.

[0091] If the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than the first set threshold, and the operating current difference between the first compressor 100a and the second compressor 100b is not lower than the second set threshold, it is inferred that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state (such as Fig.11 ), adjusting the operating frequency of one of the compressors to transition from a non-uniform liquid level state to a uniform liquid level state (such as Fig.11 (as shown in step S121).

[0092] In one or more embodiments of the present application, Fig.12 As shown, the control unit 30 is further configured to further distinguish the liquid levels of the first gas-liquid separator 108a and the second gas-liquid separator 108b after estimating that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state.

[0093] Specifically, the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, and it is further determined whether the operating current of the second compressor 100b is higher than the operating current of the first compressor 100a, that is, whether A2>A1 (such as Fig.12 At the same time, it is determined whether the exhaust temperature of the first compressor 100a is higher than the exhaust temperature of the second compressor 100b, that is, whether T d1 >T d2 (like Fig.12 If the operating current of the second compressor 100b is higher than the operating current of the first compressor 100a and the exhaust temperature of the first compressor 100a is higher than the exhaust temperature of the second compressor 100b, that is, A2>A1 and T d1 >T d2 , it is inferred that the liquid level of the first gas-liquid separator 108a is lower than the liquid level of the second gas-liquid separator 108b (e.g. Fig. 9 As shown), that is, at this time, compared with the second compressor 100b, the exhaust temperature of the first compressor 100a is high, the current value is small, the return liquid is small, and the liquid level is low.

[0094] Alternatively, the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, and further determine whether the operating current of the first compressor 100a is higher than the operating current of the second compressor 100b, that is, determine whether A1>A2 (such as Fig.12 At the same time, it is determined whether the exhaust temperature of the second compressor 100b is higher than the exhaust temperature of the first compressor 100a, that is, whether T d2 >T d1(like Fig.12 If the operating current of the second compressor 100b is higher than the operating current of the first compressor 100a and the exhaust temperature of the first compressor 100a is higher than the exhaust temperature of the second compressor 100b, that is, A1>A2 and T d2 >T d1 , it is determined that the liquid level of the first gas-liquid separator 108a is higher than the liquid level of the second gas-liquid separator 108b (e.g. Fig.10 As shown), that is, compared with the first compressor 100a, the exhaust temperature of the second compressor 100b is high, the current value is small, the return liquid is small, and the liquid level is low.

[0095] Because during the operation of the refrigeration system, the compressor will enter different protection programs, such as electronically controlled temperature rise protection, pressure protection, current protection, etc., which will cause the compressor to operate at different frequencies, or because the pressure displacement matched by the refrigeration system is different, resulting in different return air volumes. It is easy to misjudge whether the liquid level of the first gas-liquid separator 108a and the second gas-liquid separator 108b is in a non-uniform liquid level state only by judging the compressor exhaust temperature. This problem can be solved by combining the operating current of the first compressor 100a and the operating current of the second compressor 100b.

[0096] Since the compressor operating current is proportional to the compressor suction volume, as shown in the following formula:

[0097] I=Q×v×P×η×60

[0098] Where I is the compressor operating current, Q is the compressor suction flow rate (m 3 / min), v is the specific heat capacity, P is the rated power, and η is the compressor efficiency.

[0099] By combining the compressor operating current and the compressor exhaust temperature, it can be accurately identified whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state.

[0100] like Fig.13 As shown, the control unit 30 is configured to further perform control of increasing the operating frequency of the first compressor 100a or decreasing the operating frequency of the second compressor 100b after estimating that the liquid level of the first gas-liquid separator 108a is lower than the liquid level of the second gas-liquid separator 108b (e.g. Fig.13 215), until the exhaust temperature difference between the first compressor 100a and the second compressor 100b is no less than the first set threshold and the operating current difference between the first compressor 100a and the second compressor 100b is no less than the second set threshold, it is estimated that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a uniform liquid level state (such as Fig.13The control ends.

[0101] Or, if Fig.13 As shown, the control unit 30 is configured to further perform control of increasing the operating frequency of the second compressor 100b or decreasing the operating frequency of the first compressor 100a after estimating that the liquid level of the second gas-liquid separator 108b is lower than the liquid level of the first gas-liquid separator 108a (e.g. Fig.13 225), until the exhaust temperature difference between the first compressor 100a and the second compressor 100b is no longer lower than the first set threshold and the operating current difference between the first compressor 100a and the second compressor 100b is no longer lower than the second set threshold, it is estimated that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a uniform liquid level state (such as Fig.13 The control ends.

[0102] When performing control of increasing the operating frequency of the first compressor 100a or decreasing the operating frequency of the second compressor 100b, the control unit 30 is configured to obtain a frequency adjustment coefficient (in Hz), and increase the operating frequency of the first compressor 100a or decrease the operating frequency of the second compressor 100b based on the obtained frequency adjustment coefficient until the first gas-liquid separator 108a and the second gas-liquid separator 108b transition to a uniform liquid level state. The frequency adjustment coefficient is obtained based on a first fitting curve generated according to the exhaust temperature difference between the first compressor 100a and the second compressor 100b, in which the frequency adjustment coefficient corresponds to the exhaust temperature difference between the first compressor 100a and the second compressor 100b one by one. The first fitting curve can be obtained under experimental conditions. Fig.17 An example of a first fitting curve is given.

[0103] like Fig.14 As shown, in one or more embodiments of the present application, the first gas-liquid separator 108 a and the second gas-liquid separator 108 b are also connected through a distribution pipe 120 , and a regulating valve 121 is provided on the distribution pipe 120 .

[0104] In one or more embodiments of the present application, the diameter of the distribution pipe 120 is much larger than the diameters of the gas communication pipe 140 and the liquid communication pipe 150 , so that the liquid level can be transitioned to a uniform state in a very short time.

[0105] like Fig.14 and Fig.15As shown, in one or more embodiments of the present application, the control unit 30 is configured to control the first compressor 100a and the second compressor 100b to operate at the same operating frequency, and when the operating frequencies of the first compressor 100a and the second compressor 100b are the same, it is estimated whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state based on the exhaust temperature difference between the first compressor 100a and the second compressor 100b, and the difference in operating current between the first compressor 100a and the second compressor 100b. And, when it is estimated to be a non-uniform liquid level state, the operating frequency of one of the compressors is adjusted, and the regulating valve 121 is driven to operate to adjust the refrigerant flow in the distribution pipe 120 to transition from a non-uniform liquid level state to a uniform liquid level state.

[0106] More specifically, the control unit 30 is configured to control the first compressor 100a and the second compressor 100b to operate at the same frequency. The operating frequency can be obtained based on the total load of the refrigeration system, for example, the total operating frequency required by the refrigeration system is obtained according to the PID algorithm or the fuzzy control algorithm; the total operating frequency is divided by the number of compressors (for example, in the present application, the total operating frequency is divided by 2 to obtain the operating frequency), and the first compressor 100a and the second compressor 100b are controlled to operate at the obtained operating frequency, and the operating frequencies of the first compressor 100a and the second compressor 100b are the same.

[0107] The control unit 30 further samples the exhaust temperature of the first compressor 100a; samples the exhaust temperature of the second compressor 100b; calculates the exhaust temperature difference between the first compressor 100a and the second compressor 100b; determines whether the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not less than a first set threshold value: Assuming that the exhaust temperature of the first compressor 100a is recorded as T d1 , the exhaust temperature of the second compressor 100b is denoted as T d2 , then calculate and determine whether there is |T d1 -T d2 |≥B+b; wherein B+b represents the first set threshold, B is a constant, and b is generated according to the outdoor ambient temperature.

[0108] For example, Fig.16 As shown, the first set threshold is the sum of a reference temperature B (pre-set and stored) and a correction temperature b. When the outdoor ambient temperature is lower than -15°C, the correction temperature is 5°C; when the outdoor ambient temperature is higher than -15°C but lower than 7°C, the correction temperature is 2°C; when the outdoor ambient temperature is higher than 7°C but lower than 20°C, the correction temperature is 0°C; when the outdoor ambient temperature is higher than 20°C, the correction temperature is -3°C.

[0109] While sampling the compressor exhaust temperature, the control unit 30 further samples the operating current of the first compressor 100a; samples the operating current of the second compressor 100b; calculates the difference in operating current between the first compressor 100a and the second compressor 100b; and determines whether the difference in operating current between the first compressor 100a and the second compressor 100b is not less than a second set threshold value: assuming that the operating current of the first compressor 100a is recorded as A1, the operating current of the second compressor 100b is recorded as A2, and the second set threshold value is 0.5A, then calculate and determine whether:

[0110] |A1-A2|≥0.5.

[0111] If the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than the first set threshold, and the operating current difference between the first compressor 100a and the second compressor 100b is not lower than the second set threshold, it is presumed that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, the operating frequency of one of the compressors is adjusted, and the regulating valve 121 is driven to operate the distribution pipe 120 to transition from the non-uniform liquid level state to the uniform liquid level state.

[0112] In one or more embodiments of the present application, Fig.19 As shown, the control unit 30 is further configured to further distinguish the liquid levels of the first gas-liquid separator 108a and the second gas-liquid separator 108b after estimating that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state.

[0113] Specifically, the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, and it is further determined whether the operating current of the second compressor 100b is higher than the operating current of the first compressor 100a, that is, whether A2>A1 (such as Fig.19 At the same time, it is determined whether the exhaust temperature of the first compressor 100a is higher than the exhaust temperature of the second compressor 100b, that is, whether T d1 >T d2 (like Fig.19 If the operating current of the second compressor 100b is higher than the operating current of the first compressor 100a and the exhaust temperature of the first compressor 100a is higher than the exhaust temperature of the second compressor 100b, that is, A2>A1 and T d1 >T d2 , it is judged that the liquid level of the first gas-liquid separator 108a is lower than the liquid level of the second gas-liquid separator 108b, that is, at this time, compared with the second compressor 100b, the exhaust temperature of the first compressor 100a is high, the current value is small, the return liquid is small, and the liquid level is low.

[0114] Alternatively, the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, and further determine whether the operating current of the first compressor 100a is higher than the operating current of the second compressor 100b, that is, determine whether A1>A2 (such as Fig.19 At the same time, it is determined whether the exhaust temperature of the second compressor 100b is higher than the exhaust temperature of the first compressor 100a, that is, whether T d2 >T d1 (like Fig.19 If the operating current of the second compressor 100b is higher than the operating current of the first compressor 100a and the exhaust temperature of the first compressor 100a is higher than the exhaust temperature of the second compressor 100b, that is, A1>A2 and T d2 >T d1 , it is judged that the liquid level of the first gas-liquid separator 108a is higher than the liquid level of the second gas-liquid separator 108b, that is, at this time, compared with the first compressor 100a, the exhaust temperature of the second compressor 100b is high, the current value is small, the return liquid is small, and the liquid level is low.

[0115] Because during the operation of the refrigeration system, the compressor will enter different protection programs, such as electronically controlled temperature rise protection, pressure protection, current protection, etc., which will cause the compressor to operate at different frequencies, or because the pressure displacement matched by the refrigeration system is different, resulting in different return air volumes. It is easy to misjudge whether the liquid level of the first gas-liquid separator 108a and the second gas-liquid separator 108b is in a non-uniform liquid level state only by judging the compressor exhaust temperature. This problem can be solved by combining the operating current of the first compressor 100a and the operating current of the second compressor 100b.

[0116] Since the compressor operating current is proportional to the compressor suction volume, as shown in the following formula:

[0117] I=Q×v×P×η×60

[0118] Where I is the compressor operating current, Q is the compressor suction flow rate (m 3 / min), P is the rated power, and η is the compressor efficiency.

[0119] By combining the compressor operating current and the compressor exhaust temperature, it can be accurately identified whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state.

[0120] like Fig.19As shown, the control unit 30 is configured to further perform control of increasing the operating frequency of the first compressor 100a or decreasing the operating frequency of the second compressor 100b after estimating that the liquid level of the first gas-liquid separator 108a is lower than the liquid level of the second gas-liquid separator 108b (e.g. Fig.19 The regulating valve 121 is further driven to conduct the distribution pipe 120 (as shown in step S315). Fig.19 100a and 100b) until the exhaust temperature difference between the first compressor 100a and the second compressor 100b is no less than the first set threshold and the operating current difference between the first compressor 100a and the second compressor 100b is no less than the second set threshold, it is estimated that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a uniform liquid level state (such as Fig.19 (as shown in step S317), the control ends.

[0121] Or, if Fig.19 As shown, the control unit 30 is configured to further perform control of increasing the operating frequency of the second compressor 100b or decreasing the operating frequency of the first compressor 100a after estimating that the liquid level of the second gas-liquid separator 108b is lower than the liquid level of the first gas-liquid separator 108a (e.g. Fig.19 As shown in step S325), the regulating valve 121 is further driven to conduct the distribution pipe 120 (as shown in step S326). Fig.19 2 (as shown in step S326 in the figure), until the condition that the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than the first set threshold and the operating current difference between the first compressor 100a and the second compressor 100b is not lower than the second set threshold is no longer satisfied, it is inferred that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a uniform liquid level state (such as Fig.19 (as shown in step S317), the control ends.

[0122] When performing control of increasing the operating frequency of the first compressor 100a or decreasing the operating frequency of the second compressor 100b, the control unit 30 is configured to obtain a frequency adjustment coefficient, and increase the operating frequency of the first compressor 100a or decrease the operating frequency of the second compressor 100b based on the obtained frequency adjustment coefficient until the first gas-liquid separator 108a and the second gas-liquid separator 108b transition to a uniform liquid level state. The frequency adjustment coefficient is obtained based on a first fitting curve generated according to the exhaust temperature difference between the first compressor 100a and the second compressor 100b, in which the frequency adjustment coefficient corresponds to the exhaust temperature difference between the first compressor 100a and the second compressor 100b one by one. The first fitting curve can be obtained under experimental conditions. Fig.17 An example of a first fitting curve is given.

[0123] In one or more embodiments of the present application, the regulating valve 121 can be an electronic expansion valve. The control unit 30 drives the regulating valve 121 to operate and connect the distribution pipe 120, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b transition from a uniform liquid level state to a uniform liquid level state. Among them, the operation of the regulating valve 121 is divided into multiple continuous adjustment cycles, and the opening of the next adjustment cycle is the sum of the opening of the current adjustment cycle and the correction opening. The correction opening is the product of the maximum opening and the proportional coefficient. The proportional coefficient is obtained based on a second fitting curve generated according to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. In the second fitting curve, the proportional coefficient corresponds one-to-one to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. The second fitting curve is preferably measured under experimental conditions, and an exemplary second fitting curve is such as Fig.18 As shown, ΔTd represents the exhaust gas temperature difference between the first compressor 100a and the second compressor 100b, and ΔEV represents the proportionality coefficient in percentage.

[0124] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0125] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. Refrigeration system, including: An outdoor unit comprising: The first compressor; Second compressor; A switching valve, which connects the first compressor and the second compressor respectively; a distributor connected to the switching valve; A first gas-liquid separator connected to one outlet of the distributor; a second gas-liquid separator connected to another outlet of the distributor; It is characterized by further comprising: A control unit is configured to control the first compressor and the second compressor to operate at the same operating frequency, and when the operating frequencies of the first compressor and the second compressor are the same, estimate whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state based on the exhaust temperature difference between the first compressor and the second compressor, and the difference in operating current between the first compressor and the second compressor; and when it is estimated to be a non-uniform liquid level state, adjust the operating frequency of one of the compressors to transition from the non-uniform liquid level state to the uniform liquid level state.

2. The refrigeration system according to claim 1, characterized in that: The control unit is configured to infer that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state when the exhaust temperature difference between the first compressor and the second compressor is not lower than a first set threshold and the operating current difference between the first compressor and the second compressor is not lower than a second set threshold.

3. The refrigeration system according to claim 2, characterized in that: The control unit is further configured to, after estimating that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, estimate that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator when the conditions that the operating current of the second compressor is higher than the operating current of the first compressor and the exhaust temperature of the first compressor is higher than the exhaust temperature of the second compressor are met; or, The control unit is also configured to, after inferring that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, infer that the liquid level height of the first gas-liquid separator is higher than the liquid level height of the second gas-liquid separator when the conditions that the operating current of the first compressor is higher than the operating current of the second compressor and the exhaust temperature of the second compressor is higher than the exhaust temperature of the first compressor are met.

4. The refrigeration system according to claim 3, characterized in that: The control unit is further configured to, after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator, increase the operating frequency of the first compressor or decrease the operating frequency of the second compressor until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state; or The control unit is also configured to increase the operating frequency of the second compressor or decrease the operating frequency of the first compressor until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state after estimating that the liquid level of the first gas-liquid separator is higher than the liquid level of the second gas-liquid separator.

5. The refrigeration system according to claim 4, characterized in that: The control unit is further configured to obtain a frequency adjustment coefficient after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator, and increase the operating frequency of the first compressor or decrease the operating frequency of the second compressor based on the frequency adjustment coefficient until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state; or The control unit is further configured to obtain a frequency adjustment coefficient after estimating that the liquid level of the first gas-liquid separator is higher than the liquid level of the second gas-liquid separator, and increase the operating frequency of the second compressor or decrease the operating frequency of the first compressor based on the frequency adjustment coefficient until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state; The frequency adjustment coefficient is obtained based on a first fitting curve generated according to the exhaust temperature difference between the first compressor and the second compressor; in the first fitting curve, the frequency adjustment coefficient corresponds one-to-one to the exhaust temperature difference between the first compressor and the second compressor.

6. Refrigeration system, including: An outdoor unit comprising: The first compressor; Second compressor; A switching valve, which connects the first compressor and the second compressor respectively; a distributor connected to the switching valve; A first gas-liquid separator connected to one outlet of the distributor; A second gas-liquid separator communicated with another outlet of the distributor; and a distribution pipe, two ends of which are respectively connected to the first gas-liquid separator and the second gas-liquid separator; It is characterized by further comprising: a regulating valve disposed on the distribution pipe; and A control unit is configured to control the first compressor and the second compressor to operate at the same operating frequency, and when the operating frequencies of the first compressor and the second compressor are the same, estimate whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state based on the exhaust temperature difference between the first compressor and the second compressor, and the difference in operating current between the first compressor and the second compressor; and when it is estimated to be a non-uniform liquid level state, adjust the operating frequency of one of the compressors, and drive the regulating valve to operate to adjust the refrigerant flow in the distribution pipe to transition from the non-uniform liquid level state to the uniform liquid level state.

7. The refrigeration system according to claim 6, characterized in that: The control unit is configured to infer that the first gas-liquid separator and the second separator are in a non-uniform liquid level state when the exhaust temperature difference between the first compressor and the second compressor is not lower than a first set threshold and the operating current difference between the first compressor and the second compressor is not lower than a second set threshold.

8. The refrigeration system according to claim 7, characterized in that: The control unit is further configured to, after estimating that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, estimate that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator when the conditions that the operating current of the second compressor is higher than the operating current of the first compressor and the exhaust temperature of the first compressor is higher than the exhaust temperature of the second compressor are met; or, The control unit is also configured to, after inferring that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, infer that the liquid level height of the first gas-liquid separator is higher than the liquid level height of the second gas-liquid separator when the conditions that the operating current of the first compressor is higher than the operating current of the second compressor and the exhaust temperature of the second compressor is higher than the exhaust temperature of the first compressor are met.

9. The refrigeration system according to claim 8, characterized in that: The control unit is further configured to, after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator, increase the operating frequency of the first compressor or decrease the operating frequency of the second compressor, and drive the regulating valve to operate until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state; or, The control unit is also configured to increase the operating frequency of the second compressor or reduce the operating frequency of the first compressor after estimating that the liquid level of the first gas-liquid separator is higher than the liquid level of the second gas-liquid separator, and drive the regulating valve to operate until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state.

10. The refrigeration system according to claim 9, characterized in that: The control unit is further configured to obtain a frequency adjustment coefficient after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator, and increase the operating frequency of the first compressor or decrease the operating frequency of the second compressor based on the frequency adjustment coefficient, and drive the regulating valve to operate until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state; or The control unit is further configured to obtain a frequency adjustment coefficient after estimating that the liquid level of the first gas-liquid separator is higher than the liquid level of the second gas-liquid separator, and increase the operating frequency of the second compressor or decrease the operating frequency of the first compressor based on the frequency adjustment coefficient, and drive the regulating valve to operate until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state; The frequency adjustment coefficient is obtained based on a first fitting curve generated according to the exhaust temperature difference between the first compressor and the second compressor; in the first fitting curve, the frequency adjustment coefficient corresponds to the exhaust temperature difference between the first compressor and the second compressor one by one; The regulating valve is an electronic expansion valve. The control unit drives the regulating valve to operate and connect the distribution pipe. The operation of the regulating valve is divided into multiple continuous regulation cycles. The opening degree of the next regulation cycle is the sum of the opening degree of the current regulation cycle and the correction opening degree. The correction opening degree is the product of the maximum opening degree and the proportional coefficient. The proportional coefficient is obtained based on a second fitting curve generated according to the exhaust temperature difference between the first compressor and the second compressor. In the second fitting curve, the proportional coefficient corresponds one-to-one to the exhaust temperature difference between the first compressor and the second compressor.

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