Refrigeration system

Abstract

The refrigeration system comprises an outdoor unit; the outdoor unit comprises first and second compressors; a switching valve connected with the first and second compressors respectively, a distributor connected with the switching valve, first and second gas-liquid separators, a liquid communication pipe connected with the first and second gas-liquid separators, first and second regulating branches respectively provided with first and second valve elements, and a control unit; the control unit is configured to control the first and second compressors to work at the same operating frequency, and to determine whether the first and second gas-liquid separators are in a non-uniform liquid level state based on the temperature difference between the two outlet ports of the distributor, the exhaust temperature difference between the first and second compressors, and the difference between the operating currents of the first and second compressors; when it is determined that the first and second gas-liquid separators are in the non-uniform liquid level state, the first or second valve element is driven to act to regulate the flow of the first and second regulating branches, so as to transition from the non-uniform liquid level state to a uniform liquid level state; the present application can avoid uneven oil return and liquid return.

Description

Technical Field

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

[0002] Modern residential and industrial spaces require control of indoor air parameters, including but not limited to heating, cooling, and ventilation. Air conditioning systems (HVAC) use low- or high-temperature heat sources to circulate heated air indoors, or introduce outdoor air to regulate indoor air parameters.

[0003] Modern air conditioning systems no longer limit the number of outdoor and indoor units. For example, a multi-split system allows a single outdoor unit to be used with multiple indoor units. Modular central air conditioning systems allow outdoor units to be combined in a modular fashion. Currently, module capacities reach up to 40 HP, and combined modules can reach up to 168 HP. Because multi-split or modular air conditioning systems are typically installed on top of buildings, the resulting height difference between the outdoor and indoor units (up to 110 meters) creates a significant height difference, and the piping between the two units is extremely long (total piping length reaches 1,200 meters). This significant height difference and piping length require a greater amount of refrigerant, increasing the system's refrigerant consumption compared to traditional split-type air conditioners, with current refrigerant charge levels reaching hundreds of kilograms. On the indoor side, the capacity of indoor units varies greatly, ranging from 15 kW to 560 kW, and the ratio of indoor 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 Chinese patent application (CN110470083A) is: "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 balancing 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 to facilitate the emptying or injection of liquid refrigerant or lubricating oil in the cylinder."

[0005] However, when only one compressor is installed, the above-mentioned combined gas-liquid separator can maintain a uniform liquid level in multiple gas-liquid separators. However, for modular outdoor units, there will be a hardware design that matches a four-way valve with two or more compressors. This requires a distributor to be designed upstream of the multiple gas-liquid separators. The distributor will cause uneven distribution of the liquid mixture in the multiple gas-liquid separators. At the same time, due to the different loads of the multiple compressors, the mixture of lubricating oil and liquid refrigerant will be further unevenly distributed in each gas-liquid separator, further resulting in different return oil and return air volumes for each compressor, resulting in poor oil return from the compressor, large differences in exhaust temperature between multiple compressors, reduced system performance, and further damage to the compressors. 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 outdoor unit, which 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, a second gas-liquid separator connected to another outlet of the distributor, and a liquid connecting pipe at the bottom of which both ends are connected to the first gas-liquid separator and the second gas-liquid separator respectively.

[0008] In one or more embodiments of the present application, the refrigeration system also includes a first regulating branch connecting the liquid connecting pipe and the first compressor, and a first valve element is provided on the first regulating branch; and a second regulating branch connecting the liquid connecting pipe and the first compressor, and a second valve element is provided on the second regulating branch.

[0009] 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 to infer whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state based on the temperature difference between the two outlets of the distributor, 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; when it is inferred to be a non-uniform liquid level state, the first valve element or the second valve element is driven to adjust the flow of the first regulating branch or the second regulating branch to transition from the non-uniform liquid level state to the uniform liquid level state.

[0010] 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 gas-liquid separator are in a non-uniform liquid level state when the temperature difference between the two outlets of the distributor is not lower than a first set threshold, the difference in operating current between the first compressor and the second compressor is not lower than a second set threshold, and the exhaust temperature difference between the first compressor and the second compressor is not lower than a third set threshold.

[0011] In one or more embodiments of the present application, the third set threshold is generated according to the outdoor ambient temperature, and the third set threshold is negatively correlated with the outdoor ambient temperature.

[0012] 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 height of the first gas-liquid separator is lower than the liquid level height of the second gas-liquid separator when the conditions are met 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.

[0013] 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 height of the first gas-liquid separator is higher than the liquid level height of the second gas-liquid separator when the conditions are met 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.

[0014] In one or more embodiments of the present application, the first regulating branch and the second regulating branch are respectively connected to the liquid connecting pipe through the pressure reducing element, and the first valve element can operate in the on state or the off state; the second valve element can operate in the on state or the off state.

[0015] In one or more embodiments of the present application, the control unit is further configured to drive the first valve element to operate in a conducting state until at least one set adjustment cycle ends after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator.

[0016] In one or more embodiments of the present application, the control unit is further configured to drive the second valve element to operate in a conducting state until at least one set adjustment cycle ends after estimating that the liquid level of the second gas-liquid separator is lower than the liquid level of the first gas-liquid separator.

[0017] In one or more embodiments of the present application, the duration of the set conduction period can be 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 set conduction period corresponds one-to-one to the exhaust temperature difference between the first compressor and the second compressor.

[0018] In one or more embodiments of the present application, the first regulating branch and the second regulating branch are respectively connected to the liquid connecting pipe through the regulating valve, and the opening of the regulating valve is adjustable; the first valve element can operate in the on state or the off state; the second valve element can operate in the on state or the off state.

[0019] In one or more embodiments of the present application, 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, first drive the first valve element to operate in a conducting state, and then drive the regulating valve to perform a valve opening action.

[0020] In one or more embodiments of the present application, the control unit is further configured to first drive the second valve element to operate in a conducting state after estimating that the liquid level of the second gas-liquid separator is lower than the liquid level of the first gas-liquid separator, and then drive the regulating valve to perform a valve opening action.

[0021] In one or more embodiments of the present application, the regulating valve is divided into multiple continuous regulating cycles when performing the valve opening action; the opening degree of the next regulating cycle is the sum of the opening degree of the current regulating cycle and the corrected opening degree; the corrected opening degree is the product of the maximum opening degree 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.

[0022] In one or more embodiments of the present application, the opening degree of the first valve element is adjustable, and the opening degree of the second valve element is adjustable.

[0023] In one or more embodiments of the present application, the control unit is further configured to drive the first valve element to perform a valve opening action after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator.

[0024] In one or more embodiments of the present application, the control unit is further configured to drive the second valve element to perform a valve opening action after estimating that the liquid level of the second gas-liquid separator is lower than the liquid level of the first gas-liquid separator.

[0025] In one or more embodiments of the present application, the first valve element is divided into multiple continuous adjustment cycles when performing the valve opening action; the opening degree of the next adjustment cycle is the sum of the opening degree of the current adjustment cycle and the correction opening degree; the correction opening degree is the product of the maximum opening degree 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.

[0026] In one or more embodiments of the present application, the second valve element is divided into multiple continuous adjustment cycles when performing the valve opening action; the opening degree of the next adjustment cycle is the sum of the opening degree of the current adjustment cycle and the correction opening degree; the correction opening degree is the product of the maximum opening degree 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.

[0027] 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 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, drive the first valve element or the second valve element to adjust the flow of the first regulating branch or the second regulating branch to transition from the non-uniform liquid level state to the uniform liquid level state.

[0028] 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 gas-liquid separator are in a non-uniform liquid level state when the difference in operating current between the first compressor and the second compressor is not lower than a second set threshold and the exhaust temperature difference between the first compressor and the second compressor is not lower than a third set threshold.

[0029] 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 height of the first gas-liquid separator is lower than the liquid level height of the second gas-liquid separator when the conditions are met 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.

[0030] 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 height of the first gas-liquid separator is higher than the liquid level height of the second gas-liquid separator when the conditions are met 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.

[0031] The present invention can effectively avoid the problem of uneven air and liquid return caused by a set of switching valves and distributors, thereby improving the service life and operating stability of the compressor.

[0032] Other features and advantages of the present invention will become more apparent after reading the detailed description of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to 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 any creative labor.

[0034] Figure 1 A schematic block diagram of the structure of a refrigeration system provided in one or more embodiments of the present application;

[0035] Figure 2 A schematic diagram of the structure of a refrigeration cycle in a refrigeration system provided in one or more embodiments of the present application;

[0036] Figure 3 A schematic structural diagram of an outdoor unit refrigeration cycle in a refrigeration system provided in one or more embodiments of the present application;

[0037] Figure 4 A schematic structural diagram of an outdoor unit refrigeration cycle in a refrigeration system provided in one or more embodiments of the present application;

[0038] Figure 5 A schematic structural diagram of an outdoor unit refrigeration cycle in a refrigeration system provided in one or more embodiments of the present application;

[0039] Figure 6 for Figure 3 A partial enlarged schematic diagram of part A in the middle;

[0040] Figure 7 A schematic structural diagram of an outdoor unit refrigeration cycle in a refrigeration system provided in one or more embodiments of the present application;

[0041] Figure 8 A schematic structural diagram of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0042] Figure 9 A schematic structural diagram of an outdoor unit refrigeration cycle in a refrigeration system provided in one or more embodiments of the present application;

[0043] Figure 10 A schematic structural diagram of an outdoor unit refrigeration cycle in a refrigeration system provided in one or more embodiments of the present application;

[0044] Figure 11 A schematic structural diagram of an outdoor unit refrigeration cycle in a refrigeration system provided in one or more embodiments of the present application;

[0045] Figure 12A schematic structural diagram of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0046] Figure 13 A schematic structural diagram of an outdoor unit refrigeration cycle in a refrigeration system provided in one or more embodiments of the present application;

[0047] Figure 14 A schematic structural diagram of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0048] Figure 15 A schematic diagram of the numerical relationship between the third set threshold and the outdoor ambient temperature in the refrigeration system provided in one or more embodiments of the present application;

[0049] Figure 16 An example diagram of a first fitting curve in a refrigeration system provided in one or more embodiments of the present application;

[0050] Figure 17 An example diagram of a second fitting curve in a refrigeration system provided in one or more embodiments of the present application;

[0051] 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 the distributor; 107b, another outlet of the distributor; 107c, inlet of the distributor; 108a, first gas-liquid separator; 108b, second gas-liquid 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 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; 130a, first housing; 130b, second housing; 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; 201a, first distributor outlet temperature sensor; 201b, second distributor outlet temperature sensor; 201c, distributor inlet temperature sensor; 202a-1, first valve element; 202b-1, second valve element; 202a-2, first valve element; 202b-2, second valve element; 202a-3, first valve element; 202b-3, second valve element; 203a, first regulating branch; 203b, second regulating branch; 204, pressure reducing element; 205, regulating valve. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0053] In the description of this application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply 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 a limitation on this application.

[0054] The terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified 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.

[0055] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0056] In the present invention, unless otherwise expressly specified and limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes the first feature being 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 the first feature being directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0057] The disclosure below provides many different embodiments or examples for realizing different structures of the present invention. In order to simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numbers and / or reference letters in different examples. Such repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0058] Figure 1 A schematic structural diagram of a refrigeration system 1 provided in one or more embodiments of the present invention is shown; Figure 2 An example of a refrigerant circuit formed by the refrigeration system 1 according to an embodiment of the present invention is shown.

[0059] The refrigeration system 1 is installed in buildings such as apartments, hotels, office buildings, and houses. The refrigeration system 1 is configured to selectively perform a heating operation or a cooling operation.

[0060] A refrigeration cycle is integrated into the refrigeration system 1. The refrigeration cycle uses a compressor, a condenser, a throttling device 104, and an evaporator. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation to cool or heat the indoor space.

[0061] In principle, low-temperature, low-pressure refrigerant enters the compressor, which compresses it into high-temperature, high-pressure refrigerant gas and discharges it. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, releasing heat into the surrounding environment through the condensation process.

[0062] The throttling device 104 expands the high-temperature, 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 low-temperature, low-pressure refrigerant gas to the compressor. The evaporator achieves a cooling effect by utilizing the latent heat of evaporation of the refrigerant to exchange heat with the material to be cooled. Throughout this cycle, the refrigeration system 1 can regulate the temperature of the indoor space.

[0063] 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 this application, the number of outdoor units and indoor units is not particularly limited. Figure 1 and Figure 2 In the manner shown, the indoor unit and the outdoor unit are the same, and only one indoor unit and one outdoor unit are arranged in one refrigeration system 1, or multiple indoor units and multiple outdoor units are arranged.

[0064] The indoor unit is provided with an indoor heat exchanger (such as Figure 2 200) and indoor throttling device 104 (such as indoor electronic expansion valve, as shown in FIG. Figure 2 201).

[0065] 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.

[0066] 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 at its minimum opening, can nearly shut off the fluid passage in the liquid-side connecting pipe 31. The gas-side shutoff valve 106 can shut off the fluid passage in the gas-side connecting pipe 32 or, when at its minimum opening, can nearly shut off the fluid passage in the gas-side connecting pipe 32.

[0067] The following is an exemplary description of the basic structure and function of the outdoor unit. The number of outdoor units can be expanded to multiple, each outdoor unit forming a module and operating in a group manner.

[0068] Figure 3 It is a structural diagram of the outdoor unit; Figure 4 This is a schematic diagram of the refrigeration cycle when the outdoor unit performs cooling operation; Figure 5 This is a schematic diagram of the refrigeration cycle when the outdoor unit is performing heating operation; Figure 6 yes Figure 3 Enlarged view of part A in .

[0069] 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. The outdoor unit can perform heating operation or cooling operation on the outdoor side to provide energy for increasing or decreasing 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 6In a similar manner to the first compressor 100a and second compressor 100b shown, more compressors can be installed in the outdoor unit. The first compressor 100a and the second compressor 100b are configured to draw in and compress refrigerant to a high-temperature, high-pressure state. The types of the first and second compressors 100a, 100b are not limited herein and may include, for example, reciprocating compressors, screw compressors, and the like. The speeds of the first and second compressors 100a, 100b are controlled by an inverter, allowing them to operate independently. A first high-pressure switch 111a is provided at the discharge end of the first compressor 100a, while a second high-pressure switch 111b is provided at the discharge end of the second compressor 100b. A high-pressure sensor 110 is also provided at the discharge end of the first and second compressors 100a, 100b, and a low-pressure sensor 151 is provided at the intake end of the first and second compressors 100a, 100b.

[0070] A first compressor exhaust temperature sensor 112a is provided at the outlet end of the first compressor 100a, and a second compressor exhaust temperature sensor 112b is provided at the outlet end of the second compressor 100b.

[0071] 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 evaporated refrigerant into gas and liquid, and directs 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 evaporated refrigerant into gas and liquid, and directs the separated gaseous refrigerant into the second compressor 100b.

[0072] The outdoor unit can also be equipped with an outdoor fan (not shown) and a switching valve 102. The outdoor fan can be an axial flow fan, a crossflow fan, or other optional fan types. The outdoor fan is located near the outdoor heat exchanger 103. The outdoor heat exchanger 103 can also exchange heat with other types of heat sources, such as water.

[0073] The outdoor unit is also equipped 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 as the lubricating oil-refrigerant mixture leaves the compressor. The second oil separator 101b is used to separate the lubricating oil from the high-temperature refrigerant vapor as the lubricating oil-refrigerant mixture leaves the compressor. The first oil separator 101a is located in the pipeline between the first compressor 100a and the condenser. The flow rate of the high-pressure refrigerant in the first and second oil separators 101a, 101b is reduced, trapping the lubricating oil in the first and second oil separators 101a, 101b. The denser lubricating oil separates from the refrigerant vapor and falls to the bottom of the first and second oil separators 101a, 101b. The lubricating oil collected in the first and second oil separators 101a, 101b returns to the first and second compressors 100a, 100b, respectively, through first and second capillary tubes 150a, 150b. The diameter and length of the first and second capillary tubes 150a, 150b can be used to adjust the amount of lubricating oil returned. Solenoid valves 109 are also provided downstream of the first and second oil separators 101a, 101b.

[0074] 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 one outdoor unit, there is only one switching valve 102 .

[0075] In cooling operation, the outdoor unit forms a refrigerant circuit for cooling operation (hereinafter referred to as a refrigeration cycle), wherein a switching valve 102 (e.g., one passage of a four-way valve, illustratively, the fluid passage between ports C and S) and a distributor 107 are sequentially connected from the gas-side connecting pipe 32 to the liquid-side connecting pipe 31. The distributor 107 (with its inlet 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 to the first gas-liquid separator 108a and the first compressor 100a in sequence, and the other outlet of the distributor 107 is connected to the second gas-liquid separator 108b and the second compressor 100b in sequence; the mixture of refrigerant and lubricating oil flowing out of the first compressor 100a enters the first oil separator 101a, and after 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 port D and port E); the mixture of refrigerant and lubricating oil flowing out of the second compressor 100b enters the second oil separator 101b, and after 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 port D and port E); the refrigerant flowing out of the switching valve 102 enters the outdoor heat exchanger 103 again.

[0076] During heating operation, the outdoor unit forms a refrigerant circuit for heating (hereinafter referred to as a heating cycle), wherein the outdoor heat exchanger 103, the switching valve 102 (e.g., one path of a four-way valve, illustratively, the fluid path between ports E and S), 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, i.e., at one outlet of the distributor 107, the first gas-liquid separator 108a, the first compressor 100a, the first oil separator 101a, and the switching valve 102 are sequentially connected (e.g., one path of the four-way valve, illustratively, the fluid path between ports D and C). 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 (e.g., the same path of the four-way valve, illustratively, the fluid path between ports D and C).

[0077] The two outlets of the distributor 107 (shown as 107a and 107b in the figure) have the same design flow rate.

[0078] The first gas-liquid separator 108a includes a first housing 130a. A first inlet pipe 131a is inserted into the upper portion of the first housing 130a, with its inlet located at the upper portion. A first outlet pipe 113a is also provided within the first housing 130a. The first outlet pipe 113a is curved into a roughly U-shape near the bottom of the first housing 130a, with its outlet extending outward from the upper portion of the first housing 130a. The first outlet pipe 113a is in fluid communication with the first compressor 100a.

[0079] The second gas-liquid separator 108b includes a second housing 130b. A second inlet pipe 131b is inserted into the upper portion of the second housing 130b, with its inlet located at the upper portion. A second outlet pipe 113b is also provided within the second housing 130b. The second outlet pipe 113b is curved into a roughly U-shape near the bottom of the second housing 130b, with its outlet extending outward from the upper portion of the second housing 130b. The second outlet pipe 113b is fluidically connected to the second compressor 100b.

[0080] During cooling or heating operation, the evaporated refrigerant is distributed by distributor 107 and enters the first and second shells 130a, 130b, respectively, through first and second inlet pipes 131a, 131b. This separation occurs, where the gaseous refrigerant is drawn into the first and second compressors 100a, 100b, via first and second outlet pipes 113a, 113b. The separated liquid refrigerant remains at the bottoms of the first and second shells 130a, 130b, and gradually evaporates over time before being drawn into the first and second compressors 100a, 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. Through the first main oil return hole 114a, 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; similarly, through the second main oil return hole 114b, 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.

[0081] In one or more embodiments of the present application, the first and second housings 130a, 130b have the same shape and volume. The upper sides of the first and second housings 130a, 130b can be connected via a gas communication tube 140, and the lower sides of the first and second housings 130a, 130b can be connected via a liquid communication tube 150. In other words, the ends of the gas communication tube 140 are connected to the first gas-liquid separator 108a and the second gas-liquid separator 108b, respectively.

[0082] like Figure 6 As shown, the first outlet pipe 113a is further provided with a first auxiliary oil return hole 115a higher than the first main oil return hole 114a. The second outlet pipe 113b is further provided with a second auxiliary oil return hole 115b higher than the second main oil return hole 114b.

[0083] 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 quantity and the minimum lubricating oil quantity of the first compressor 100a and the maximum refrigerant volume; wherein the difference between the maximum lubricating oil quantity and the minimum lubricating oil quantity represents the maximum capacity of lubricating oil allowed to accumulate in the first shell 130a (below the minimum lubricating oil quantity, the first compressor 100a cannot work), that is, the ratio of the difference between the maximum lubricating oil quantity and the minimum lubricating oil quantity 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 in the first shell 130a. Since the first main oil return hole 114a is located at the bottom (e.g., 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. For example, a relatively ideal preset refrigerant volume (e.g., 60% of the maximum refrigerant volume) can be set based on the capacity of the refrigeration system 1 to ensure stable operation of both the first compressor 100a and the second compressor 100b in the refrigeration system 1. 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. Based on the sum of the preset refrigerant height and the maximum lubricating oil height, the first auxiliary oil return hole 115a is opened at a predetermined position on the first outlet pipe. A plurality of first auxiliary oil return holes 115a can also be opened on the first outlet pipe to evenly divide the preset refrigerant height, and a first auxiliary oil return hole 115a is opened at each evenly divided height. The first auxiliary oil return hole 115a can assist in oil return when the outdoor ambient temperature is low, thereby avoiding oil return failure caused by condensation of lubricating oil.

[0084] 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 quantity and the minimum lubricating oil quantity of the second compressor 100b and the maximum refrigerant volume; wherein the difference between the maximum lubricating oil quantity and the minimum lubricating oil quantity represents the maximum capacity of lubricating oil allowed to accumulate in the second shell 130b (the second compressor 100b cannot work below the minimum lubricating oil quantity), that is, the ratio of the difference between the maximum lubricating oil quantity and the minimum lubricating oil quantity 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 located at the bottom (e.g., 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 (e.g., 60% of the maximum refrigerant volume) can be set based on the capacity of the refrigeration system 1, which is less than the maximum refrigerant volume and allows for stable operation of both the second compressor 100b and the second compressor 100b in the refrigeration system 1. 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. Based on the sum of the preset refrigerant height and the maximum lubricating oil height, the second auxiliary oil return hole 115b is opened at a predetermined position on the second outlet pipe. A plurality of second auxiliary oil return holes 115b can also be opened on the second outlet pipe to evenly divide the preset refrigerant height, and a second auxiliary oil return hole 115b is opened at each evenly divided height. The second auxiliary oil return hole 115b can assist in oil return when the outdoor ambient temperature is low, thereby avoiding oil return failure caused by condensation of lubricating oil.

[0085] The outdoor unit also includes an outdoor control circuit. This circuit is housed in a well-sealed, heat-dissipating electrical box. The outdoor control circuit includes components such as a processor, a storage unit, an input / output interface, and a communication interface. The processor can be a dedicated processor, a central processing unit (CPU), or the like. The processor can access the storage unit to execute instructions or applications stored therein to implement related functions. The storage unit can include volatile memory and / or non-volatile memory. The input / output interface can communicate with various sensors installed in the outdoor unit to receive their detection values. The input / output interface can also communicate with devices such as inverters, outdoor fans, and four-way valves to output control instructions generated by the processor. The communication interface can support various wireless communication protocols, such as Wi-Fi, Bluetooth, near-field communication, and NB-IoT, to connect to other electronic devices, including but not limited to cloud servers, computers (host computers), smartphones, tablets, PDAs, intelligent control tools, wearable devices, and in-vehicle devices.

[0086] 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 pipe length and pipe 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.

[0087] 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.

[0088] like Figure 7 and Figure 8As shown, refrigeration system 1 is further provided with a first regulating branch 203a and a second regulating branch 203b. First regulating branch 203a connects the liquid communicating pipe 150 and the first compressor 100a, and is provided with a first valve element 202a-1. Second regulating branch 203b connects the liquid communicating pipe 150 and the second compressor 100b, and is provided with a second valve element 202b-1.

[0089] 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 to estimate 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 temperature difference between the two outlets of the distributor 107, 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, drive the first valve element 202a-1 or the second valve element 202b-1 to adjust the flow of the first regulating branch 203a or the second regulating branch 203b to transition from the non-uniform liquid level state to the uniform liquid level state.

[0090] Regardless of whether the cooling operation or the heating operation is being executed, the evaporated refrigerant enters the first shell 130a and the second shell 130b through the inlet pipe under the distribution of the distributor 107, and a gas-liquid separation effect is generated. The gaseous refrigerant is at the upper position and the mixture of liquid refrigerant and lubricating oil is at the lower position. Since the total amount of refrigerant in the refrigeration system is constant, the flow rate at the suction end of the first compressor 100a and the second compressor 100b can be effectively adjusted through the first regulating branch 203a and the second regulating branch 203b, and further feedback is provided to improve the return liquid amount in the first gas-liquid separator 108a and the second gas-liquid separator 108b, so that the two can quickly and stably transition to a uniform liquid level state, thereby avoiding the deviation of the return liquid amount and the return oil amount from accumulating continuously over time, which affects the normal operation of the compressor.

[0091] 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 can be calculated using a PID algorithm or a fuzzy control algorithm. The total operating frequency is divided by the number of compressors (for example, in this application, the total operating frequency is divided by 2 to obtain the operating frequency). The first compressor 100a and the second compressor 100b are controlled to operate at the calculated operating frequency. The first compressor 100a and the second compressor 100b have the same operating frequency.

[0092] The control unit 30 is configured to start sampling after the first compressor 100a and the second compressor 100b operate at the same frequency for a period of time (eg, t minutes).

[0093] In one or more embodiments of the present application, the control unit 30 is configured to sample the detected temperature of the first distributor outlet temperature sensor 201a; sample the detected temperature of the second distributor 107 outlet temperature sensor 201b; calculate the temperature difference between the detected temperature of the first distributor outlet temperature sensor 201a and the detected temperature of the second distributor 107 outlet temperature sensor 201b; and determine whether the temperature difference between the detected temperature of the first distributor outlet temperature sensor 201a and the detected temperature of the second distributor 107 outlet temperature sensor 201b is not lower than a first set threshold: assuming that the detected temperature of the first distributor outlet temperature sensor 201a is recorded as T2 and the detected temperature of the second distributor 107 outlet temperature sensor 201b is recorded as T3, then calculate and determine whether |T2-T3|≥5, that is, the first set threshold can be 5°C.

[0094] The control unit 30 is further configured to sample the detected temperature of the dispenser inlet temperature sensor 201 c.

[0095] While sampling the detection temperature of the first distributor outlet temperature sensor 201a and the detection temperature of the second distributor 107 outlet temperature sensor 201b, 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 lower than a second set threshold: 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, then calculate and determine whether |A1-A2|≥0.5.

[0096] While sampling the exhaust temperature of the compressor, 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; and determines whether the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than a third 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 recorded as T d2 , then calculate and determine whether there is |T d1 -T d2|≥B+b; where B+b represents the third set threshold, B is a constant, and b is generated based on the outdoor ambient temperature. That is, the third set threshold is generated based on the outdoor ambient temperature and is negatively correlated with the outdoor ambient temperature.

[0097] For example, Figure 15 As shown, the third 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 below -15°C, the correction temperature b is 5°C; when the outdoor ambient temperature is above -15°C but below 7°C, the correction temperature b is 2°C; when the outdoor ambient temperature is above 7°C but below 20°C, the correction temperature b is 0°C; and when the outdoor ambient temperature is above 20°C, the correction temperature b is -3°C.

[0098] If the temperature difference between the two outlets of the distributor 107 is not lower than the first set threshold, the difference in operating current between the first compressor 100a and the second compressor 100b is not lower than the second set threshold, and the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than the third 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.

[0099] In one or more embodiments of the present application, 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.

[0100] 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; and 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 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 estimated 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. Figure 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 relatively small, the return liquid is small, and the liquid level is low.

[0101] 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; and at the same time determine whether the exhaust temperature of the second compressor 100b is higher than the exhaust temperature of the first compressor 100a, that is, determine whether T d2 >T d1 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. Figure 10 As shown), that is, compared with the first compressor 100a, the exhaust temperature of the second compressor 100b is higher, the current value is smaller, the return liquid is less, and the liquid level is lower.

[0102] 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 operating frequency to be different, 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 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.

[0103] Since the compressor operating current is proportional to the compressor suction volume, as shown in the following formula:

[0104] I=Q×v×P×η×60

[0105] Where I is the compressor operating current, Q is the compressor suction flow (m 3 / min), v is the specific heat capacity, P is the rated power, and η is the compressor efficiency.

[0106] By combining the compressor operating current and the compressor exhaust temperature, it can be accurately determined whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state.

[0107] like Figure 7 and Figure 8As shown, in one or more embodiments of the present application, the first valve element 202a-1 and the second valve element 202b-1 are solenoid valves, that is, the first valve element 202a-1 can operate in an on state or an off state, and the second valve element 202b-1 can operate in an on state or an off state. The first regulating branch 203a and the second regulating branch 203b are respectively connected to the liquid communication pipe 150 via a pressure reducing element (capillary tube).

[0108] The control unit 30 is configured to, after estimating that the liquid level in the first gas-liquid separator 108a is lower than the liquid level in the second gas-liquid separator 108b, drive the first valve element 202a-1 to operate in an on-state until a predetermined adjustment cycle has expired, thereby increasing the flow rate at the suction end of the first compressor 100a. If, after the predetermined adjustment cycle has expired, the temperature difference between the two outlets of the distributor 107 is no less than a first predetermined threshold, the operating current difference between the first and second compressors 100a, 100b is no less than a second predetermined threshold, and the exhaust gas temperature difference between the first and second compressors 100a, 100b is no less than a third predetermined threshold, then it is estimated that the liquid levels in the first and second gas-liquid separators 108a, 108b are uniform, and control terminates. Otherwise, the first valve element 202a-1 is again driven in an on-state until a predetermined adjustment cycle has expired. This process repeats until the liquid levels in the first and second gas-liquid separators 108a, 108b are estimated to be uniform.

[0109] Alternatively, the control unit 30 is configured to, after estimating that the liquid level in the second gas-liquid separator 108b is lower than that in the first gas-liquid separator 108a, drive the second valve element 202b-1 to operate in an on state until a set adjustment cycle has expired, thereby increasing the flow rate at the suction end of the second compressor 100b. If, after the set adjustment cycle has expired, the conditions that the temperature difference between the two outlets of the distributor 107 is no less than the first set threshold, the operating current difference between the first and second compressors 100a, 100b is no less than the second set threshold, and the exhaust gas temperature difference between the first and second compressors 100a, 100b is no less than the third set threshold are no longer met, then it is estimated that the first and second gas-liquid separators 108a, 108b are in a uniform liquid level state, and control ends. Otherwise, the second valve element 202b-1 is again driven in an on state until a set adjustment cycle has expired, and the above process is repeated until it is estimated that the first and second gas-liquid separators 108a, 108b are in a uniform liquid level state.

[0110] In one or more embodiments of the present application, the duration of the set on-cycle is obtained based on a first fitting curve generated according to the exhaust gas temperature difference between the first compressor 100a and the second compressor 100b. In the first fitting curve, the set on-cycle corresponds to the exhaust gas temperature difference between the first compressor 100a and the second compressor 100b. The first fitting curve is preferably measured under experimental conditions. An exemplary first fitting curve is as follows: Figure 16 As shown, ΔTd represents the exhaust gas temperature difference between the first compressor 100a and the second compressor 100b, and T represents the duration of the set conduction period.

[0111] like Figure 11 and Figure 12 As shown, in one or more embodiments of the present application, the first valve element 202a-2 and the second valve element 202b-2 are solenoid valves. That is, the first valve element 202a-2 can operate in an on state or an off state, and the second valve element 202b-2 can operate in an on state or an off state. The first regulating branch 203a and the second regulating branch 203b are connected to the liquid communication pipe 150 through the regulating valve 205 (electronic expansion valve).

[0112] The control unit 30 is configured to, 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, first drive the first valve element 202a-2 to operate in a conducting state, and then drive the regulating valve 205 to perform a valve opening action until the conditions that the temperature difference between the two outlets of the distributor 107 is not lower than the first set threshold, the difference in operating current between the first compressor 100a and the second compressor 100b is not lower than the second set threshold, and the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than the third set threshold are no longer met, then it is estimated that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a uniform liquid level state, and the control ends.

[0113] Alternatively, after the control unit 30 estimates that the liquid level of the second gas-liquid separator 108b is lower than the liquid level of the first gas-liquid separator 108a, it first drives the second valve element 202b-2 to operate in the on state, and then drives the regulating valve 205 to perform the valve opening action until the conditions that the temperature difference between the two outlets of the distributor 107 is not lower than the first set threshold, the difference in operating current between the first compressor 100a and the second compressor 100b is not lower than the second set threshold, and the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than the third set threshold are no longer met, then it is estimated that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a uniform liquid level state, and the control ends.

[0114] In one or more embodiments of the present application, the regulating valve 205 can be an electronic expansion valve. Among them, when the regulating valve 205 performs the valve opening action, it 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 the 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 as follows. Figure 17 As shown, ΔTd represents the exhaust gas temperature difference between the first compressor 100a and the second compressor 100b, and ΔEV represents the proportional coefficient in percentage.

[0115] like Figure 13 and Figure 14 As shown, in one or more embodiments of the present application, the opening of the first valve element 202a-3 is adjustable, and the opening of the second valve element 202b-3 is adjustable, that is, the first valve element 202a-3 is an electronic expansion valve, and the second valve element 202b-3 is an electronic expansion valve.

[0116] The control unit 30 is further configured to drive the first valve element 202 a - 3 to perform a valve opening operation after estimating that the liquid level of the first gas-liquid separator 108 a is lower than the liquid level of the second gas-liquid separator 108 b .

[0117] Among them, when the first valve element 202a-3 performs the valve opening action, it is divided into multiple continuous adjustment cycles, and the opening degree of the next adjustment cycle is the sum of the opening degree of the current adjustment 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 the 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 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 as follows. Figure 17 As shown, ΔTd represents the exhaust gas temperature difference between the first compressor 100a and the second compressor 100b, and ΔEV represents the proportional coefficient in percentage.

[0118] The control unit 30 is further configured to drive the second valve element 202b-3 to perform a valve opening operation 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.

[0119] Among them, when the second valve element 202b-3 performs the valve opening action, it is divided into multiple continuous adjustment cycles, and the opening degree of the next adjustment cycle is the sum of the opening degree of the current adjustment 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 the 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 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 as follows. Figure 17 As shown, ΔTd represents the exhaust gas temperature difference between the first compressor 100a and the second compressor 100b, and ΔEV represents the proportional coefficient in percentage.

[0120] In one or more embodiments of the present application, the control unit can also be configured to control the first compressor and the second compressor to operate at the same operating frequency, and 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, drive the first valve element or the second valve element to adjust the flow of the first regulating branch or the second regulating branch to transition from the non-uniform liquid level state to the uniform liquid level state.

[0121] Specifically, 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 difference in operating current between the first compressor and the second compressor is not lower than a second set threshold and the exhaust temperature difference between the first compressor and the second compressor is not lower than a third set threshold.

[0122] 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 height of the first gas-liquid separator is lower than the liquid level height of the second gas-liquid separator when the conditions are met 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.

[0123] Alternatively, 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 height of the first gas-liquid separator is higher than the liquid level height of the second gas-liquid separator when the conditions are met 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.

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

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

Claims

1. Refrigeration system, including: An outdoor unit comprising: First compressor; Second compressor; a switching valve connecting 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; and a liquid connecting pipe, the two ends of which are connected to the bottom of the first gas-liquid separator and the second gas-liquid separator respectively; It is characterized by further comprising: a first regulating branch connecting the liquid communicating pipe and the first compressor, wherein a first valve element is provided on the first regulating branch; a second regulating branch connected to the liquid communicating pipe and the second compressor, wherein a second valve element is provided on the second regulating branch; and, The control unit is configured to control the first compressor and the second compressor to operate at the same operating frequency, and to estimate whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state based on the temperature difference between the two outlets of the distributor, 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; when it is estimated to be a non-uniform liquid level state, the first valve element or the second valve element is driven to operate to adjust the flow of the first regulating branch or the second regulating branch to transition to a 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 temperature difference between the two outlets of the distributor is not lower than a first set threshold, the difference in operating current between the first compressor and the second compressor is not lower than a second set threshold, and the exhaust temperature difference between the first compressor and the second compressor is not lower than a third set threshold.

3. The refrigeration system according to claim 2, wherein: The third set threshold is generated according to the outdoor ambient temperature, and the third set threshold is negatively correlated with the outdoor ambient temperature.

4. The refrigeration system according to claim 2, wherein: 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 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; or 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 height of the first gas-liquid separator is higher than the liquid level height of the second gas-liquid separator when the conditions are met 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.

5. The refrigeration system according to claim 4, characterized in that: The first regulating branch and the second regulating branch are respectively connected to the liquid communicating pipe via a pressure reducing element. The first valve element can be operated in an on state or an off state; the second valve element can be operated in an on state or an off state. The control unit is further configured to drive the first valve element to operate in a conducting state until at least one set adjustment cycle ends after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator; or The control unit is further configured to drive the second valve element to operate in a conducting state until at least one set adjustment cycle ends after estimating that the liquid level of the second gas-liquid separator is lower than the liquid level of the first gas-liquid separator; Among them, the duration of the set conduction period can be 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 set conduction period corresponds one-to-one to the exhaust temperature difference between the first compressor and the second compressor.

6. The refrigeration system according to claim 4, characterized in that: The first regulating branch and the second regulating branch are connected to the liquid communicating pipe via regulating valves, respectively, and the opening of the regulating valves is adjustable; the first valve element can operate in an on state or an off state; and the second valve element can operate in an on state or an off state; 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, first drive the first valve element to operate in a conducting state, and then drive the regulating valve to perform a valve opening action; or The control unit is further configured to, after estimating that the liquid level of the second gas-liquid separator is lower than the liquid level of the first gas-liquid separator, first drive the second valve element to operate in a conducting state, and then drive the regulating valve to perform a valve opening action; In which, the regulating valve is divided into multiple continuous regulation cycles when performing the valve opening action; 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, 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.

7. The refrigeration system according to claim 4, characterized in that: The opening of the first valve element is adjustable, and the opening of the second valve element is adjustable; The control unit is further configured to drive the first valve element to perform a valve opening action after estimating that the liquid level of the first gas-liquid separator is lower than the liquid level of the second gas-liquid separator; or The control unit is further configured to drive the second valve element to perform a valve opening action after estimating that the liquid level of the second gas-liquid separator is lower than the liquid level of the first gas-liquid separator; wherein the first valve element is divided into a plurality of continuous adjustment cycles when performing a valve opening action; the opening degree of the next adjustment cycle is the sum of the opening degree of the current adjustment cycle and the correction opening degree; the correction opening degree is the product of the maximum opening degree and a proportional coefficient, the proportional coefficient being obtained based on a second fitting curve generated according to the exhaust gas temperature difference between the first compressor and the second compressor, wherein in the second fitting curve, the proportional coefficient corresponds one-to-one to the exhaust gas temperature difference between the first compressor and the second compressor; When the second valve element performs the valve opening action, it is divided into multiple continuous adjustment cycles; the opening degree of the next adjustment cycle is the sum of the opening degree of the current adjustment cycle and the correction opening degree; the correction opening degree is the product of the maximum opening degree 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.

8. Refrigeration system, including: An outdoor unit comprising: First compressor; Second compressor; a switching valve connecting 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; and a liquid connecting pipe, two ends of which are connected to the bottom of the first gas-liquid separator and the bottom of the second gas-liquid separator respectively; It is characterized by further comprising: a first regulating branch connecting the liquid communicating pipe and the first compressor, wherein a first valve element is provided on the first regulating branch; a second regulating branch connected to the liquid communicating pipe and the second compressor, wherein a second valve element is provided on the second regulating branch; and, The control unit is configured to control the first compressor and the second compressor to operate at the same operating frequency, and to 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, drive the first valve element or the second valve element to operate to adjust the flow of the first regulating branch or the second regulating branch to transition from the non-uniform liquid level state to a uniform liquid level state.

9. The refrigeration system according to claim 8, 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 difference in operating current between the first compressor and the second compressor is not lower than a second set threshold and the exhaust temperature difference between the first compressor and the second compressor is not lower than a third set threshold.

10. The refrigeration system according to claim 9, 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 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; or 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 height of the first gas-liquid separator is higher than the liquid level height of the second gas-liquid separator when the conditions are met 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.

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