Refrigeration system

Abstract

The refrigeration system comprises: indoor and outdoor units; the outdoor unit comprises a first compressor and a second compressor; a switching valve respectively connected to the first compressor and the second compressor, a distributor connected to the switching valve, a first gas-liquid separator and a control unit; 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, the control unit is configured 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 operating current difference 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; the present invention can avoid uneven oil return and liquid return in the refrigeration system.

Description

Technical Field

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

[0002] Modern residences and industrial sites require control of air parameters in indoor spaces, including but not limited to heating, cooling, ventilation, etc. An air conditioning system (HVAC) provides energy through a low-temperature heat source or a high-temperature heat source, enabling the heat-exchanged air to circulate indoors, or introducing 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, a multi-split air conditioner allows one outdoor unit to be matched with multiple indoor units for use; modular central air conditioners allow outdoor units to be combined in a modular manner. Currently, the capacity of a single module can reach 40HP, and the capacity after module combination can reach 168HP. Since multi-split or modular air conditioning systems are usually installed on the top of a building, there is a huge height difference (up to 110 meters) between the outdoor unit and the indoor unit in the installed state, and the piping length between the outdoor unit and the indoor unit is very long (the total piping length has reached 1200 meters). The huge height difference and piping length require more refrigerant volume, and the refrigerant quantity of the system has increased significantly compared with traditional split air conditioners. The current charging volume has reached hundreds of kilograms. At the indoor end, the capacity of indoor units varies greatly, with a span of 15kW to 560kW, and the ratio range of indoor units to outdoor units can reach 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 the refrigeration cycle to meet the requirements. Traditional container components are usually small pressure vessels with a volume of less than 30L, and they 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): "It includes two gas-liquid separators, each gas-liquid separator includes a cylinder body, and an inlet pipe and an outlet pipe are arranged in the cylinder body; a balance pipe communicating with each cylinder body is arranged between the side walls of each cylinder body; a distribution pipe communicating with each of the cylinder bodies is arranged between the bottoms of each cylinder body, and an oil injection pipe is connected to the distribution pipe to perform operations such as emptying or injecting liquid refrigerant or lubricating oil in the cylinder body."

[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 presuming that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, when the conditions that the operating current of the second compressor is higher than that of the first compressor and the exhaust gas temperature of the first compressor is higher than that of the second compressor are met, presume that the liquid level height of the first gas-liquid separator is lower than that of the second gas-liquid separator.

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

[0012] In one or more embodiments of the present application, the control unit is further configured to, after presuming that the liquid level height of the first gas-liquid separator is lower than that 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.

[0013] In one or more embodiments of the present application, the control unit is further configured to, after presuming that the liquid level height of the first gas-liquid separator is higher than that of the second gas-liquid separator, 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.

[0014] In one or more embodiments of the present application, the control unit is further configured to, after presuming that the liquid level height of the first gas-liquid separator is lower than that of the second gas-liquid separator, obtain a frequency adjustment coefficient, 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 further configured to, after presuming that the liquid level height of the first gas-liquid separator is higher than that of the second gas-liquid separator, obtain a frequency adjustment coefficient, 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.

[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 gas temperature difference between the first compressor and the second compressor; in the first fitting curve, the frequency adjustment coefficient corresponds one-to-one with the exhaust gas 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 further configured to increase the operating frequency of the second compressor or decrease the operating frequency of the first compressor after it is presumed that the liquid level height of the first gas-liquid separator is higher than that of the second gas-liquid separator, and drive the regulating valve to act 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 further configured to obtain a frequency adjustment coefficient after it is presumed that the liquid level height of the first gas-liquid separator is lower than that 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, while driving the regulating valve to act 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 further configured to obtain a frequency adjustment coefficient after it is presumed that the liquid level height of the first gas-liquid separator is higher than that 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, while driving the regulating valve to act 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 with 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 act to conduct the distribution pipe. When the regulating valve acts, it is divided into multiple consecutive adjustment cycles; 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 proportionality coefficient, and the proportionality 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 proportionality coefficient corresponds one-to-one with the exhaust temperature difference between the first compressor and the second compressor.

[0028] The present invention can effectively avoid the problem of uneven gas return and liquid return caused by a set of switching valves and distributors, and improve the service life and operating 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 clearer. Brief Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] Figure 1 Structural schematic block diagram of the refrigeration system provided by one or more embodiments of the present application;

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

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

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

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

[0036] Figure 6 For Figure 3 Partial enlarged schematic diagram of part A in

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

[0038] Figure 8 Structural schematic diagram of the outdoor unit in the refrigeration system provided by one or more embodiments of the present application;

[0039] Figure 9 Structural schematic diagram of the refrigeration cycle of the outdoor unit in the refrigeration system provided by one or more embodiments of the present application;

[0040] Figure 10 Structural schematic diagram of the refrigeration cycle of the outdoor unit in the refrigeration system provided by one or more embodiments of the present application;

[0041] Figure 11 Flowchart of the control unit in the refrigeration system provided by one or more embodiments of the present application;

[0042] Figure 12 Flowchart of the control unit in the refrigeration system provided by one or more embodiments of the present application;

[0043] Figure 13 Flow chart of the control unit in the refrigeration system provided by one or more embodiments of the present application;

[0044] Figure 14 Schematic structural diagram of the refrigeration cycle of the outdoor unit in the refrigeration system provided by one or more embodiments of the present application;

[0045] Figure 15 Schematic structural diagram of the outdoor unit in the refrigeration system provided by one or more embodiments of the present application;

[0046] Figure 16 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] Figure 17 Example diagram of the first fitting curve in the refrigeration system provided by one or more embodiments of the present application;

[0048] Figure 18 Example diagram of the second fitting curve in the refrigeration system provided by one or more embodiments of the present application;

[0049] Figure 19 Flow chart of the control unit in the refrigeration system provided by one or more embodiments of the present application;

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

[0051] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0052] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0053] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, unless otherwise specified, the meaning of "a plurality" is two or more.

[0054] In the description of the present application, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0055] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature.

[0056] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. 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 numerals and / or reference letters in different examples. This repetition is for the purpose of simplification 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 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 structural view of a refrigeration system 1 provided by 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.

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

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

[0060] In terms of principle, a low-temperature and low-pressure refrigerant enters the compressor, and the compressor compresses it into a high-temperature and 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 heat is released to the surrounding environment through the condensation process.

[0061] The throttling device 104 expands the high-temperature and high-pressure liquid-phase refrigerant formed by condensation in the condenser into a low-pressure liquid-phase 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 using the latent heat of evaporation of the refrigerant for heat exchange with the material to be cooled. Throughout the 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 combination form of two outdoor units (10, 12) and three indoor units (20, 22, 24) is shown, Figure 2 The combination form of two outdoor units (10, 12) and five indoor units (20, 22, 24, 26, 28) is shown. In this application, the number of outdoor units and indoor units is not particularly limited. It can be arranged in the same way as the indoor unit and outdoor unit shown in Figure 1 and Figure 2 In a set of refrigeration system 1, only one indoor unit and one outdoor unit can be arranged, or multiple indoor units and multiple outdoor units can be arranged.

[0063] An indoor heat exchanger (such as 200 shown in Figure 2 ) and an indoor throttling device (such as an indoor electronic expansion valve, such as 201 shown in Figure 2 ) are provided in the indoor unit.

[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 for 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 cutoff valve 105 is provided on the liquid-side communication pipe 31, and a gas-side cutoff valve 106 is provided on the gas-side communication pipe 32. The liquid-side cutoff valve 105 can cut off the fluid passage in the liquid-side communication pipe 31 or, when at the minimum opening degree, is close to cutting off the fluid passage in the liquid-side communication pipe 31. The gas-side cutoff valve 106 can cut off the fluid passage in the gas-side communication pipe 32 or, when at the minimum opening degree, is close to cutting off the fluid passage in the gas-side communication pipe 32.

[0066] The basic structure and functions of the outdoor unit will be exemplarily described below. The number of outdoor units can be expanded to multiple units. Each outdoor unit forms a module and operates in a grouped manner.

[0067] Figure 3 is a schematic structural diagram of the outdoor unit; Figure 4 is a schematic refrigeration cycle diagram when the outdoor unit performs refrigeration operation; Figure 5 is a schematic refrigeration cycle diagram when the outdoor unit performs heating operation; Figure 6 is Figure 3 an 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 the part of the refrigeration cycle that includes a compressor and an outdoor heat exchanger 103. The outdoor unit can perform heating operation or refrigeration operation on the outdoor side to provide energy for raising the indoor temperature or lowering the indoor temperature to the indoor unit. As Figures 3 to 6 shown, a first compressor 100a and a second compressor 100b are provided in the outdoor unit; more compressors can be provided in the outdoor unit in the same manner as the first compressor 100a and the second compressor 100b shown in Figures 3 to 6 shown. 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 herein. For example, they can be reciprocating compressors, screw compressors, etc. The rotation speeds of the first compressor 100a and the second compressor 100b are controlled by an inverter, and the first compressor 100a and the second compressor 100b can operate independently. A first high-pressure switch 111a is provided at the discharge end of the first compressor 100a, and 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 on the discharge side of the first compressor 100a and the second compressor 100b, and a low-pressure sensor 151 is also provided on the suction side of the first compressor 100a and the second compressor 100b.

[0069] A first compressor discharge temperature sensor 112a is provided at the discharge end of the first compressor 100a, and a second compressor discharge 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 evaporated refrigerant into gas and liquid 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 evaporated refrigerant into gas and liquid and guides the separated gaseous refrigerant into the second compressor 100b.

[0071] An outdoor fan (not shown) and a switching valve 102 may also be provided in the outdoor unit; the outdoor fan may be an axial flow fan, a cross flow fan, or other optional fan forms. The outdoor fan is provided 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] A first oil separator 101a and a second oil separator 101b are also provided in the outdoor unit. The first oil separator 101a is used to separate lubricating oil from the high-temperature refrigerant vapor when the mixture of lubricating oil and refrigerant leaves the compressor. The second oil separator 101b is used to separate lubricating oil from the high-temperature refrigerant vapor when the mixture of lubricating oil and refrigerant leaves the compressor. The first oil separator 101a is provided in the pipeline between the first compressor 100a and the condenser. The flow rate of the high-pressure refrigerant is reduced in the first oil separator 101a and the second oil separator 101b, so that the lubricating oil is trapped 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 diameters and lengths of the first capillary tube 150a and the second capillary tube 150b can be used to adjust the amount of lubricating oil returned. An electromagnetic valve 109 is also provided downstream of the first oil separator 101a and the second oil separator 101b.

[0073] The switching valve 102 is taken as an example of 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 one and only one switching valve 102 in one outdoor unit.

[0074] In the refrigeration operation, the outdoor unit can form a refrigerant circuit for refrigeration operation (hereinafter referred to as the refrigeration cycle), in which a switching valve 102 (for example, a path of a four-way valve, exemplarily, a fluid path between port C and port S) and a distributor 107 are sequentially connected in the direction 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 sequentially connected to a first gas-liquid separator 108a and a first compressor 100a, and the other outlet of the distributor 107 is sequentially connected to a second gas-liquid separator 108b and a second compressor 100b; the mixture of refrigerant and lubricating oil flowing out of the first compressor 100a enters a first oil separator 101a, and after leaving the first oil separator 101a, the refrigerant is again merged into the switching valve 102 (for example, another path of the four-way valve, exemplarily, a fluid path between port D and port E); the mixture of refrigerant and lubricating oil flowing out of the second compressor 100b enters a second oil separator 101b, and after leaving the second oil separator 101b, the refrigerant is again merged into the switching valve 102 (for example, another path of the four-way valve, exemplarily, a fluid path between port D and port E); 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 the heating cycle), in which an outdoor heat exchanger 103, a switching valve 102 (for example, a path of a four-way valve, exemplarily, a fluid path between port E and port S) and a distributor 107 are sequentially connected in the direction 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 a first gas-liquid separator 108a, a first compressor 100a, a first oil separator 101a and the switching valve 102 (for example, a path of the four-way valve, exemplarily, a fluid path between port D and port C); the other outlet of the distributor 107 is sequentially connected to a second gas-liquid separator 108b, a second compressor 100b, a second oil separator 101b and the switching valve 102 (for example, the same path of the four-way valve, exemplarily, a fluid path between port D and port C).

[0076] The designed flow rates of the two outlets (shown as 107a and 107b in the figure) of the distributor 107 are the same.

[0077] The first gas-liquid separator 108a has a first housing 130a. A first inlet pipe 131a is disposed in the upper part of the first housing 130a and has an inlet located in the upper part of the first housing 130a. A first outlet pipe 113a is also disposed in the first housing 130a. The first outlet pipe 113a is close to the bottom of the first housing 130a and is bent into a substantially U shape. The outlet of the first outlet pipe 113a extends outward from the upper part of the first housing 130a. The first outlet pipe 113a is in fluid communication with the first compressor 100a.

[0078] The second gas-liquid separator 108b has a second housing 130b. A second inlet pipe 131b is disposed in the upper part of the second housing 130b and has an inlet located in the upper part of the second housing 130b. A second outlet pipe 113b is also disposed in the second housing 130b. The second outlet pipe 113b is close to the bottom of the second housing 130b and is bent into a substantially U shape. The outlet of the second outlet pipe 113b extends outward from the upper part of the second housing 130b. The second outlet pipe 113b is in fluid communication with the second compressor 100b.

[0079] During refrigeration operation or heating operation, the evaporated refrigerant is distributed by the distributor 107 and enters the first housing 130a and the second housing 130b through the first inlet pipe 131a and the second inlet pipe 131b respectively, and then gas-liquid separation occurs. 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 remains in the bottoms of the first housing 130a and the second housing 130b, 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 formed at the bottom of the first outlet pipe 113a, and a second main oil return hole 114b is formed at the bottom of the second outlet pipe 113b. Through the first main oil return hole 114a, the lubricating oil accumulated at the bottom of the first housing 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 accumulated at the bottom of the second housing 130b can flow back to the second compressor 100b through the second outlet pipe 113b.

[0080] In one or more embodiments of the present application, the shapes and volumes of the first housing 130a and the second housing 130b are the same. The upper sides of the first housing 130a and the second housing 130b can be communicated through a gas communication pipe 140, and the lower sides of the first housing 130a and the second housing 130b can be communicated through a liquid communication pipe 150.

[0081] As 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 volume and the minimum lubricating oil volume of the first compressor 100a and the maximum refrigerant volume; wherein the difference between the maximum lubricating oil volume and the minimum lubricating oil volume represents the maximum capacity of the lubricating oil allowed to accumulate in the first housing 130a (the first compressor 100a cannot operate below the minimum lubricating oil volume), that is, the ratio of the difference between the maximum lubricating oil volume and the minimum lubricating oil volume to the cross-sectional area of the first housing 130a (assuming the first housing 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 housing 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 housing 130a. Since the first main oil return hole 114a is provided at the bottom (for example, the lowest point of the U-shaped pipe), 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. Exemplarily, a relatively ideal preset refrigerant volume less 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 the stable operation of both the first compressor 100a and the second compressor 100b in the refrigeration system 1. Based on the ratio of the preset refrigerant volume to the cross-sectional area of the first housing 130a, the preset refrigerant height is calculated, and 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 the set position of the first outlet pipe 113a. Multiple first auxiliary oil return holes 115a can also be evenly distributed at equal intervals 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 volume and the minimum lubricating oil volume of the second compressor 100b and the maximum refrigerant volume; wherein the difference between the maximum lubricating oil volume and the minimum lubricating oil volume represents the maximum capacity of the lubricating oil allowed to accumulate in the second housing 130b (the second compressor 100b cannot operate below the minimum lubricating oil volume), that is, the ratio of the difference between the maximum lubricating oil volume and the minimum lubricating oil volume to the cross-sectional area of the second housing 130b (assuming the second housing 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 housing 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 height in the second housing 130b. Since the second main oil return hole 114b is provided 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 height. Exemplarily, a relatively ideal preset refrigerant volume that is less 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. The preset refrigerant height can be calculated based on the ratio of the preset refrigerant volume to the cross-sectional area of the second housing 130b, and the second auxiliary oil return hole 115b can be 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. Multiple second auxiliary oil return holes 115b can also be evenly distributed at equal intervals 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 arranged 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 can be a dedicated processor, a central processing unit (CPU), etc. The processor can access the storage unit to execute instructions or application programs stored in the storage unit to implement related functions. The storage unit can include volatile memory and / or non-volatile memory. The input / output interface can be communicatively connected to various sensors arranged in the outdoor unit to receive the detection values of various sensors arranged in the outdoor unit. The input / output interface can also be communicatively connected to devices such as an inverter, an outdoor fan, and a four-way valve to output control instructions generated by the processor to them. The communication interface can support different wireless communication protocols, such as Wi-Fi, Bluetooth, near field communication, NB-IoT, etc., to be communicatively connected to other electronic devices, including but not limited to cloud servers, computers (host computers), smartphones, tablets, PDAs, intelligent control tooling, wearable devices, and vehicle-mounted devices, etc.

[0084] As described in the background art section, the refrigerant charge in the refrigeration system 1 has reached hundreds of kilograms. Since only one switching valve 102 is provided, the switching valve 102 must be correspondingly arranged with 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). In particular, there may be minute impurities and contaminants in the refrigeration system 1, and these substances will accumulate in the pipeline near the distributor 107, gradually changing the pipe diameter. Moreover, since the outputs of the two compressors change with the load, this will exacerbate the uneven liquid distribution in the two gas-liquid separators downstream of the distributor 107. Since the lubricating oil is dissolved in the liquid refrigerant, it will further cause deviations in the oil return and gas return of the first compressor 100a and the second compressor 100b.

[0085] As Figure 7 and Figure 8 shown, to solve this problem, a control unit 30 is also 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 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, based on the exhaust temperature difference between the first compressor 100a and the second compressor 100b, and the difference in the operating currents between the first compressor 100a and the second compressor 100b, estimate whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state. And, when it is estimated to be in 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 a uniform liquid level state.

[0087] More specifically, as Figure 11 shown, the control unit 30 is configured to control the first compressor 100a and the second compressor 100b to operate at the same frequency (as Figure 11 shown in step S111). The operating frequency can be obtained based on the total load of the refrigeration system. For example, the total operating frequency required for the refrigeration system is obtained according to the PID algorithm or the fuzzy control algorithm; divide the total operating frequency by the number of compressors (for example, in the present application, divide the total operating frequency by 2 to obtain the operating frequency), and control the first compressor 100a and the second compressor 100b to operate at 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 (as shown in step S112 below); samples the exhaust temperature of the second compressor 100b (as shown in step S113 below); calculates the difference in exhaust temperature between the first compressor 100a and the second compressor 100b (as shown in step S114 below); determines whether the difference in exhaust temperature between the first compressor 100a and the second compressor 100b is not lower than a first set threshold (as shown in step S115 below): Assuming the exhaust temperature of the first compressor 100a is denoted as T Figure 11 as shown below, and the exhaust temperature of the second compressor 100b is denoted as T Figure 11 as shown below, then calculates and determines whether |T Figure 11 -T Figure 11 |≥B + b; where B + b represents the first set threshold, B is a constant, and b is generated according to the outdoor ambient temperature. d1 d2 d1 d2

[0089] Exemplarily, as shown in Figure 16 below, the first set threshold is the sum of a reference temperature B (predetermined 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 exhaust temperature of the compressor, the control unit 30 also further samples the operating current of the first compressor 100a (as shown in step S116 below); samples the operating current of the second compressor 100b (as shown in step S117 below); calculates the difference in operating current between the first compressor 100a and the second compressor 100b (as shown in step S118 below); 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 (as shown in step S119 below): Assuming the operating current of the first compressor 100a is denoted as A1 and the operating current of the second compressor 100b is denoted as A2, and the second set threshold is 0.5A, then calculates and determines whether |A1 - A2|≥0.5. Figure 11 Figure 11 Figure 11 Figure 11

[0091] ​​​​​​​​If the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b is not less than the first set threshold and the difference in the operating currents between the first compressor 100a and the second compressor 100b is not less 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 (as shown in step S120 of Figure 11 ), and 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 (as shown in step S121 of Figure 11 ).

[0092] In one or more embodiments of the present application, as shown in Figure 12 , 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 presuming that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state.

[0093] Specifically, when the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, 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, to determine whether A2 > A1 (as shown in step S212 of Figure 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, to determine whether T d1 > T d2 (as shown in step S213 of Figure 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, both A2 > A1 and T d1 > T d2 , it is presumed that the liquid level height of the first gas-liquid separator 108a is lower than the liquid level height of the second gas-liquid separator 108b (as shown in Figure 9 ), that is, at this time, compared with the second compressor 100b, the first compressor 100a has a higher exhaust temperature, a smaller current value, less liquid return, and a lower liquid level.

[0094] Alternatively, when the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, it is further determined whether the operating current of the first compressor 100a is higher than the operating current of the second compressor 100b, that is, to determine whether A1 > A2 (as shown in step S222 of Figure 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, to determine whether T d2 > T d1(as shown in step S223 of Figure 12 ); if the operating current of the second compressor 100b is higher than that of the first compressor 100a and the exhaust temperature of the first compressor 100a is higher than that of the second compressor 100b, that is, when A1 > A2 and T d2 > T d1 , it is determined that the liquid level height of the first gas-liquid separator 108a is higher than that of the second gas-liquid separator 108b (as shown in Figure 10 ), that is, at this time, compared with the first compressor 100a, the second compressor 100b has a higher exhaust temperature, a smaller current value, less liquid return, and a lower liquid level.

[0095] During the operation of the refrigeration system, the compressor will enter different protection programs, such as electronic control 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 gas return volumes. It is easy to misjudge the non-uniform liquid level state of the first gas-liquid separator 108a and the second gas-liquid separator 108b only by the exhaust temperature of the compressor. Combining the operating current of the first compressor 100a and the operating current of the second compressor 100b can solve this problem.

[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] Combining the compressor operating current and the compressor exhaust temperature can accurately identify whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state.

[0100] As shown in Figure 13 , the control unit 30 is configured to further execute the control of increasing the operating frequency of the first compressor 100a or decreasing the operating frequency of the second compressor 100b (as shown in step S215 of Figure 13 ) after it is estimated that the liquid level height of the first gas-liquid separator 108a is lower than that of the second gas-liquid separator 108b, until the condition that the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not less than the first set threshold and the operating current difference between the first compressor 100a and the second compressor 100b is not less than the second set threshold is no longer satisfied, and it is estimated that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a uniform liquid level state (as shown in Figure 13as shown in step S216 in [reference], the control ends.

[0101] Alternatively, as Figure 13 shown, the control unit 30 is configured to, after estimating that the liquid level height of the second gas-liquid separator 108b is lower than that of the first gas-liquid separator 108a, further execute control to increase the operating frequency of the second compressor 100b or decrease the operating frequency of the first compressor 100a (as Figure 13 shown in step S225 in [reference]), 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 difference in operating current between the first compressor 100a and the second compressor 100b is not lower than the second set threshold is no longer satisfied, and it is estimated that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a uniform liquid level state (as Figure 13 shown in step S216 in [reference]), the control ends.

[0102] When executing the control to increase the operating frequency of the first compressor 100a or decrease 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 the first fitting curve, the frequency adjustment coefficient corresponds one-to-one with the exhaust temperature difference between the first compressor 100a and the second compressor 100b. The first fitting curve can be obtained under experimental conditions. Figure 17 Give an example of the first fitting curve.

[0103] As Figure 14 shown, in one or more embodiments of the present application, the first gas-liquid separator 108a and the second gas-liquid separator 108b 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 it can transition to a uniform liquid level state in a very short time.

[0105] As Figure 14 and Figure 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, 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, it is deduced whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state. And when it is deduced to be 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 act to adjust the refrigerant flow rate in the distribution pipe 120, so as to transition from the non-uniform liquid level state to the 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 lower than the first set threshold: assuming that the exhaust temperature of the first compressor 100a is denoted as T d1 and the exhaust temperature of the second compressor 100b is denoted as T d2 , then it is calculated and determined whether there is |T d1 -T d2 |≥B + b; where B + b represents the first set threshold, B is a constant, and b is generated according to the outdoor ambient temperature.

[0108] Exemplarily, as Figure 16 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 exhaust temperature of the compressor, 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; 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: Assuming that the operating current of the first compressor 100a is denoted as A1, the operating current of the second compressor 100b is denoted as A2, and the second set threshold is 0.5A, then calculate and determine whether there is:

[0110] |A1 - A2| ≥ 0.5.

[0111] If it simultaneously satisfies that the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b is not less than a first set threshold, and the difference in operating current between the first compressor 100a and the second compressor 100b is not less than a second set threshold, then 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, adjust the operating frequency of one of the compressors, and drive the regulating valve 121 to actuate and conduct 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, as Figure 19 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 presuming that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state.

[0113] Specifically, when the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, further determine whether the operating current of the second compressor 100b is higher than the operating current of the first compressor 100a, that is, determine whether there is A2 > A1 (as Figure 19 shown in step S312); simultaneously determine whether the exhaust temperature of the first compressor 100a is higher than the exhaust temperature of the second compressor 100b, that is, determine whether there is T d1 > T d2 (as Figure 19 shown in step S313); 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, simultaneously there is A2 > A1 and T d1 > T d2 , then it is determined that the liquid level height of the first gas-liquid separator 108a is lower than the liquid level height of the second gas-liquid separator 108b, that is, at this time, compared with the second compressor 100b, the first compressor 100a has a higher exhaust temperature, a smaller current value, less liquid return, and a lower liquid level.

[0114] Alternatively, when the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, further determine whether the operating current of the first compressor 100a is higher than that of the second compressor 100b, that is, determine whether A1 > A2 (as shown in step S322 in Figure 19 ); at the same time, determine whether the exhaust temperature of the second compressor 100b is higher than that of the first compressor 100a, that is, determine whether T d2 > T d1 (as shown in step S323 in Figure 19 ); if the operating current of the second compressor 100b is higher than that of the first compressor 100a and the exhaust temperature of the first compressor 100a is higher than that of the second compressor 100b, that is, both A1 > A2 and T d2 > T d1 , then it is determined that the liquid level height of the first gas-liquid separator 108a is higher than that of the second gas-liquid separator 108b. That is, at this time, compared with the first compressor 100a, the second compressor 100b has a higher exhaust temperature, a smaller current value, less liquid return, and a lower liquid level.

[0115] During the operation of the refrigeration system, the compressor will enter different protection programs, such as electronic control 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 gas return amounts. It is easy to misjudge the non-uniform liquid level state of the first gas-liquid separator 108a and the second gas-liquid separator 108b only by the exhaust temperature of the compressor. Combining the operating current of the first compressor 100a and the second compressor 100b can solve this problem.

[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] Combining the compressor operating current and the compressor exhaust temperature can accurately identify whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state.

[0120] Such as Figure 19As shown, the control unit 30 is configured to, after estimating that the liquid level height of the first gas-liquid separator 108a is lower than that of the second gas-liquid separator 108b, further execute control to increase the operating frequency of the first compressor 100a or decrease the operating frequency of the second compressor 100b (as shown in step S315 in Figure 19 ), and further drive the regulating valve 121 to actuate and conduct the distribution pipe 120 (as shown in step S316 in Figure 19 ), 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 difference in operating current between the first compressor 100a and the second compressor 100b is not lower than the second set threshold is no longer satisfied, and it is estimated that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a uniform liquid level state (as shown in step S317 in Figure 19 ), and the control ends.

[0121] Or, as shown in Figure 19 , the control unit 30 is configured to, after estimating that the liquid level height of the second gas-liquid separator 108b is lower than that of the first gas-liquid separator 108a, further execute control to increase the operating frequency of the second compressor 100b or decrease the operating frequency of the first compressor 100a (as shown in step S325 in Figure 19 ), and further drive the regulating valve 121 to actuate and conduct the distribution pipe 120 (as shown in step S326 in Figure 19 ), 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 difference in operating current between the first compressor 100a and the second compressor 100b is not lower than the second set threshold is no longer satisfied, and it is estimated that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a uniform liquid level state (as shown in step S317 in Figure 19 ), and the control ends.

[0122] When executing the control to increase the operating frequency of the first compressor 100a or decrease the operating frequency of the second compressor 100b, the control unit 30 is configured to obtain a frequency adjustment coefficient, and based on the obtained frequency adjustment coefficient, increase the operating frequency of the first compressor 100a or decrease the operating frequency of the second compressor 100b 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 the first fitting curve, the frequency adjustment coefficient corresponds one-to-one with the exhaust temperature difference between the first compressor 100a and the second compressor 100b. The first fitting curve can be obtained under experimental conditions. Figure 17 Give an example of the first fitting curve.

[0123] In one or more embodiments of the present application, the regulating valve 121 may be an electronic expansion valve. The control unit 30 drives the regulating valve 121 to actuate and conduct the distribution pipe 120, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b transition from the uniform liquid level state to the uniform liquid level state. Among them, when the regulating valve 121 acts, 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 proportionality coefficient. The proportionality 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 proportionality coefficient corresponds one-to-one with 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 Figure 18 shown, where ΔTd represents the exhaust 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, the 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 the 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 conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. Refrigeration system, comprising: Outdoor unit, which includes: First compressor; Second compressor; Switching valve, which is used to switch the flow direction of the refrigerant in the refrigerant circuit, and the switching valve is respectively connected to the discharge side of the first compressor and the discharge side of the second compressor; Distributor, whose inlet is connected to the switching valve; First gas-liquid separator connected to one outlet of the distributor, and the first gas-liquid separator is arranged on the suction side of the first compressor; Second gas-liquid separator connected to the other outlet of the distributor, and the second gas-liquid separator is arranged on the suction side of the second compressor; It is characterized in that it further includes: 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, 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, estimate whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state; and when it is estimated to be in 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 estimate 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 difference in operating current 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, 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, estimate that the liquid level height of the first gas-liquid separator is lower than the liquid level height of the second gas-liquid separator; 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, when 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, 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.

4. The refrigeration system according to claim 3, characterized in that: The control unit is further configured to, after estimating that the liquid level height of the first gas-liquid separator is lower than the liquid level height 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 further configured to, after estimating that the liquid level height of the first gas-liquid separator is higher than that of the second gas-liquid separator, 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.

5. The refrigeration system according to claim 4, wherein: The control unit is further configured to, after estimating that the liquid level height of the first gas-liquid separator is lower than that of the second gas-liquid separator, obtain a frequency adjustment coefficient, 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, after estimating that the liquid level height of the first gas-liquid separator is higher than that of the second gas-liquid separator, obtain a frequency adjustment coefficient, 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; wherein, the frequency adjustment coefficient is obtained based on a first fitting curve, and the first fitting curve is generated according to the exhaust temperature difference between the first compressor and the second compressor; in the first fitting curve, the frequency adjustment coefficient and the exhaust temperature difference between the first compressor and the second compressor are in one-to-one correspondence.

6. A refrigeration system, comprising: An outdoor unit, which includes: A first compressor; A second compressor; A switching valve for switching the flow direction of the refrigerant in the refrigerant circuit, and the switching valve is respectively connected to the discharge side of the first compressor and the discharge side of the second compressor; A distributor, whose inlet is connected to the switching valve; A first gas-liquid separator connected to one outlet of the distributor, and the first gas-liquid separator is arranged on the suction side of the first compressor; A second gas-liquid separator connected to the other outlet of the distributor, and the second gas-liquid separator is arranged on the suction side of the second compressor; and A distribution pipe, whose two ends are respectively connected to the first gas-liquid separator and the second gas-liquid separator; characterized in that it further includes: A regulating valve arranged on the distribution pipe; and A control unit 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, 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, estimate whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state; and when it is estimated to be in a non-uniform liquid level state, adjust the operating frequency of one of the compressors, and drive the regulating valve to act to adjust the refrigerant flow rate in the distribution pipe, so as to transition from the non-uniform liquid level state to the uniform liquid level state.

7. The refrigeration system according to claim 6, wherein: 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 value, and the difference in operating current between the first compressor and the second compressor is not lower than a second set threshold value.

8. The refrigeration system according to claim 7, wherein: 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 operating current of the second compressor is higher than that of the first compressor and the exhaust temperature of the first compressor is higher than that 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 operating current of the first compressor is higher than that of the second compressor and the exhaust temperature of the second compressor is higher than that of the first compressor.

9. The refrigeration system according to claim 8, wherein: The control unit is further configured to, after inferring that the liquid level height of the first gas-liquid separator is lower than the liquid level height 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 act 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, after inferring that the liquid level height of the first gas-liquid separator is higher than the liquid level height of the second gas-liquid separator, increase the operating frequency of the second compressor or decrease the operating frequency of the first compressor, and drive the regulating valve to act 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, wherein: The control unit is further configured to, after inferring that the liquid level height of the first gas-liquid separator is lower than the liquid level height of the second gas-liquid separator, obtain a frequency adjustment coefficient, and increase the operating frequency of the first compressor or decrease the operating frequency of the second compressor based on the frequency adjustment coefficient, while driving the regulating valve to act 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, after inferring that the liquid level height of the first gas-liquid separator is higher than the liquid level height of the second gas-liquid separator, obtain a frequency adjustment coefficient, and increase the operating frequency of the second compressor or decrease the operating frequency of the first compressor based on the frequency adjustment coefficient, while driving the regulating valve to act until the first gas-liquid separator and the second gas-liquid separator transition to a uniform liquid level state; Among them, the frequency adjustment coefficient is obtained based on the first fitting curve, and the first fitting curve is 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 with the exhaust temperature difference between the first compressor and the second compressor; The regulating valve is an electronic expansion valve, and the control unit drives the regulating valve to actuate to conduct the distribution pipe. When the regulating valve acts, 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 proportionality coefficient, and the proportionality coefficient is obtained based on the second fitting curve, and the second fitting curve is generated according to the exhaust temperature difference between the first compressor and the second compressor. In the second fitting curve, the proportionality coefficient corresponds one-to-one with the exhaust temperature difference between the first compressor and the second compressor.

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