Refrigeration system

Abstract

The refrigeration system includes an outdoor unit comprising a first compressor and a second compressor; a switching valve connecting the first compressor and the second compressor; a distributor connecting the switching valve; first and second gas-liquid separators; a distribution pipe equipped with a regulating valve; first and second detection branches; and a control unit. The first detection branch connects to a first outlet pipe via a first auxiliary oil return hole and is equipped with a first pressure-reducing element; the second detection branch connects to a second outlet pipe via a second auxiliary oil return hole and is equipped with the same second pressure-reducing element; the first and second auxiliary oil return holes are at the same height; the control unit is configured to, at the same operating frequency, estimate whether the first and second gas-liquid separators are in a non-uniform liquid level state based on the temperature changes before and after the first and second pressure-reducing elements and the temperature difference between the exhaust temperatures of the first and second compressors; and when a non-uniform liquid level state is estimated, drive the regulating valve to adjust the refrigerant flow rate in the distribution pipe; this invention can avoid uneven oil and liquid return.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, and more particularly to a refrigeration system. Background Technology

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

[0003] Modern air conditioning systems no longer limit the number of outdoor and indoor units. For example, multi-split systems allow one outdoor unit to be used with multiple indoor units; modular central air conditioning systems allow outdoor units to be combined in a modular manner. Currently, the capacity of modules can reach 40HP, and the combined capacity of modules can reach 168HP. Because multi-split or modular air conditioning systems are usually installed on the roof of a building, there is a huge height difference between the outdoor and indoor units (up to 110 meters), resulting in very long piping between them (total piping length has reached 1200 meters). This huge height difference and piping length require more refrigerant; the amount of refrigerant in the system is significantly increased compared to traditional split-type air conditioners, with current refrigerant charges reaching hundreds of kilograms. On the indoor side, the capacity of indoor units varies greatly, ranging from 15kW to 560kW, and the ratio of indoor to outdoor units can range from 30% to 200%.

[0004] The hardware design of modern air conditioning systems renders traditional container components (such as gas-liquid separators) inadequate for the needs of the refrigeration cycle. These traditional components are typically small pressure vessels less than 30L, which cannot meet design requirements even in a single module. Existing technologies disclose combined gas-liquid separators to address this issue. For example, the technical solution disclosed in Chinese patent application (CN110470083A) states: "It includes two gas-liquid separators, each comprising a cylinder with an inlet and an outlet pipe; a balance pipe connecting the side walls of each cylinder; and a distribution pipe connecting the bottoms of each cylinder, with an oil injection pipe connected to the distribution pipe for venting or injecting liquid refrigerant or lubricating oil into the cylinder."

[0005] However, when only one compressor is installed, the aforementioned combined gas-liquid separator can maintain a uniform liquid level in multiple gas-liquid separators. But for modular outdoor units, there is a hardware design where a four-way valve is matched with two or more compressors. This necessitates the design of a distributor upstream of multiple gas-liquid separators. The distributor can lead to uneven distribution of the liquid mixture within the multiple gas-liquid separators. Furthermore, due to the different loads of the multiple compressors, this further exacerbates the uneven distribution of the lubricating oil and liquid refrigerant mixture within each gas-liquid separator. This results in different oil return and gas return rates for each compressor, leading to poor oil return, excessively large differences in discharge temperatures among multiple compressors, reduced system performance, and ultimately, compressor damage. Summary of the Invention

[0006] When dual or multiple compressors are used in conjunction with parallel gas-liquid separators, the mixture of lubricating oil and liquid refrigerant is unevenly distributed in each gas-liquid separator due to the design of the distributor and the different loads of each compressor. This further leads to different oil return and gas return volumes for each compressor, resulting in poor oil return and reduced system performance. The first aspect of this 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, and a first gas-liquid separator connected to one outlet of the distributor, wherein a first outlet pipe connected to the first compressor is provided; and a second gas-liquid separator connected to the other outlet of the distributor, wherein a second outlet pipe connected to the second compressor is provided, and a distribution pipe at both ends connected to the first gas-liquid separator and the second gas-liquid separator respectively.

[0008] In one or more embodiments of this application, the refrigeration system further includes a regulating valve, a first detection branch, a second detection branch, and a control unit disposed on the distribution pipe. The first detection branch is connected to the first outlet pipe through a first auxiliary oil return hole, the first auxiliary oil return hole being higher than the bottom of the first outlet pipe, and the first detection branch is provided with a first pressure reducing element. The second detection branch is connected to the second outlet pipe through a second auxiliary oil return hole, the second auxiliary oil return hole being higher than the bottom of the second outlet pipe, and the second detection branch is provided with a second pressure reducing element. The first auxiliary oil return hole and the second auxiliary oil return hole are at the same height, and the first pressure reducing element and the second pressure reducing element are the same. 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 change before and after the first pressure reducing element and the second pressure reducing element, and the temperature difference between the exhaust temperatures of the first compressor and the second compressor; and when it is estimated to be in a non-uniform liquid level state, to drive the regulating valve to adjust the refrigerant flow in the distribution pipe to transition to a uniform liquid level state.

[0009] In one or more embodiments of this application, the first detection branch is also fluidly connected to the first compressor, and it further includes a first inlet temperature sensor, which is disposed on the inlet side of the first detection branch and close to the first auxiliary oil return hole; a first outlet temperature sensor, which is disposed on the outlet side of the first detection branch and close to the first compressor; the first inlet temperature sensor, the first pressure reducing element and the first outlet temperature sensor are arranged sequentially along the refrigerant flow direction.

[0010] In one or more embodiments of this application, the second detection branch is also fluidly connected to the second compressor and further includes: a second inlet temperature sensor, which is disposed on the inlet side of the second detection branch and close to the second auxiliary oil return hole; and a second outlet temperature sensor, which is disposed on the outlet side of the second detection branch and close to the second compressor; the second inlet temperature sensor, the second pressure reducing element, and the second outlet temperature sensor are arranged sequentially along the refrigerant flow direction.

[0011] In one or more embodiments of this application, the control unit is configured to, when the difference between the temperature detected by the first outlet temperature sensor and the temperature detected by the first inlet temperature sensor is not lower than a first set threshold, the difference between the temperature detected by the second outlet temperature sensor and the temperature detected by the second inlet temperature sensor is lower than a second set threshold, and the temperature difference between the exhaust temperatures of the first compressor and the second compressor is not lower than a third set threshold, presume that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, and the liquid level of the second gas-liquid separator is higher than the second auxiliary oil return hole, drive the regulating valve to open the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state.

[0012] In one or more embodiments of this application, the control unit is configured to presume that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state and that the liquid level of the first gas-liquid separator is higher than the first auxiliary oil return hole when the difference between the temperature detected by the first outlet temperature sensor and the temperature detected by the first inlet temperature sensor is lower than a first set threshold, the difference between the temperature detected by the second outlet temperature sensor and the temperature detected by the second inlet temperature sensor is not lower than a second set threshold, and the temperature difference between the exhaust temperatures of the first compressor and the second compressor is not lower than a third set threshold. The control unit then drives the regulating valve to open the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state.

[0013] In one or more embodiments of this application, the third set threshold is generated based on the outdoor ambient temperature, and the third set threshold is negatively correlated with the outdoor ambient temperature.

[0014] In one or more embodiments of this application, the regulating valve is a solenoid valve, and the control unit drives the regulating valve to open the distribution pipe until the end of the set opening cycle, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state; wherein, the duration of the set opening cycle is obtained based on a first fitting curve generated according to the exhaust temperature difference between the first compressor and the second compressor, and in the first fitting curve, the set opening cycle corresponds one-to-one with the exhaust temperature difference between the first compressor and the second compressor.

[0015] In one or more embodiments of this application, the regulating valve is an electronic expansion valve, and the control unit drives the regulating valve to open the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state; wherein, the operation of the regulating valve is divided into multiple continuous regulating cycles; 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 which the proportional coefficient corresponds one-to-one with the exhaust temperature difference between the first compressor and the second compressor.

[0016] In one or more embodiments of this application, 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 change before and after the first pressure reducing element and the second pressure reducing element, the temperature difference of the exhaust temperature 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 in a non-uniform liquid level state, to drive the regulating valve to adjust the refrigerant flow in the distribution pipe to transition to a uniform liquid level state.

[0017] In one or more embodiments of this application, the control unit is configured to presume that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state and the liquid level of the second gas-liquid separator is higher than the second auxiliary oil return hole when the difference between the temperature detected by the first outlet temperature sensor and the temperature detected by the first inlet temperature sensor is not lower than a first set threshold, the difference between the temperature detected by the second outlet temperature sensor and the temperature detected by the second inlet temperature sensor is lower than a second set threshold, the temperature difference between the exhaust temperatures of the first compressor and the second compressor is not lower than a third set threshold, and the difference between the operating currents of the first compressor and the second compressor is not lower than a fourth set threshold. The control unit then drives the regulating valve to open the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state.

[0018] In one or more embodiments of this application, the control unit is configured to presume that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state and the liquid level of the first gas-liquid separator is higher than the first auxiliary oil return hole when the difference between the temperature detected by the first outlet temperature sensor and the temperature detected by the first inlet temperature sensor is lower than a first set threshold, the difference between the temperature detected by the second outlet temperature sensor and the temperature detected by the second inlet temperature sensor is not lower than a second set threshold, the temperature difference between the exhaust temperatures of the first compressor and the second compressor is not lower than a third set threshold, and the difference between the operating currents of the first compressor and the second compressor is not lower than a fourth set threshold. The control unit then drives the regulating valve to open the distribution pipe, thereby transitioning the first gas-liquid separator and the second gas-liquid separator from a non-uniform liquid level state to a uniform liquid level state.

[0019] This invention identifies whether two gas-liquid separators are in a non-uniform liquid level state by measuring the temperature changes before and after the first and second pressure-reducing elements, the temperature difference between the exhaust temperatures of the two compressors, and / or the difference between the operating currents of the two compressors. It then uses a regulating valve to adjust the liquid level, which can effectively avoid the problem of uneven gas and liquid return caused by a set of switching valves and distributors, thereby improving the service life and operational stability of the compressors.

[0020] 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. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic block diagram of the structure of a refrigeration system provided for one or more embodiments of this application;

[0023] Figure 2 A schematic diagram of the refrigeration cycle in a refrigeration system provided in one or more embodiments of this application;

[0024] Figure 3 A schematic diagram of the refrigeration cycle of the outdoor unit in a refrigeration system provided in one or more embodiments of this application;

[0025] Figure 4 A schematic diagram of the refrigeration cycle of the outdoor unit in a refrigeration system provided in one or more embodiments of this application;

[0026] Figure 5 A schematic diagram of the refrigeration cycle of the outdoor unit in a refrigeration system provided in one or more embodiments of this application;

[0027] Figure 6 for Figure 3 A magnified view of part A in the middle;

[0028] Figure 7 A schematic diagram of the refrigeration cycle of the outdoor unit in a refrigeration system provided in one or more embodiments of this application;

[0029] Figure 8 A schematic diagram of the structure of the outdoor unit in a refrigeration system provided in one or more embodiments of this application;

[0030] Figure 9 A flowchart of the control unit in a refrigeration system provided for one or more embodiments of this application;

[0031] Figure 10 A flowchart of the control unit in a refrigeration system provided for one or more embodiments of this application;

[0032] Figure 11 A schematic diagram of the refrigeration cycle of the outdoor unit in a refrigeration system provided in one or more embodiments of this application;

[0033] Figure 12 A schematic diagram of the refrigeration cycle of the outdoor unit in a refrigeration system provided in one or more embodiments of this application;

[0034] Figure 13 A flowchart of the control unit in a refrigeration system provided for one or more embodiments of this application;

[0035] Figure 14 A flowchart of the control unit in a refrigeration system provided for one or more embodiments of this application;

[0036] Figure 15 A schematic diagram illustrating the numerical relationship between a third set threshold and the outdoor ambient temperature in a refrigeration system provided in one or more embodiments of this application;

[0037] Figure 16 An example diagram of a first fitted curve in a refrigeration system provided for one or more embodiments of this application;

[0038] Figure 17 An example diagram of a second fitting curve in a refrigeration system provided for one or more embodiments of this application;

[0039] In the diagram, 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 piping; 32 is the gas-side connecting piping; 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; and 103 is the indoor unit. External 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, the other outlet of the distributor; 107c, the 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 pressure... Compressor exhaust temperature sensor; 112b, Second compressor exhaust temperature sensor; 113a, First outlet pipe; 113b, Second outlet pipe; 114a, First main oil return port; 114b, Second main oil return port; 115a, First auxiliary oil return port; 115b, Second auxiliary oil return port; 116a, First detection branch; 116b, Second detection branch; 117a, First outlet temperature sensor; 117b, Second outlet temperature sensor; 118a First inlet temperature sensor; 118b, second inlet temperature sensor; 119a, first pressure reducing element; 119b, second pressure reducing element; 120, distribution pipe; 121, regulating valve; 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. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional 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, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0042] 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 number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0043] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0044] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0045] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0046] Figure 1 This diagram shows a structural schematic of a refrigeration system 1 provided by one or more embodiments of the present invention; Figure 2 An example of a refrigerant circuit formed by a refrigeration system 1 according to an embodiment of the present invention is shown.

[0047] 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 heating or cooling operation.

[0048] The refrigeration system 1 integrates a refrigeration cycle. The refrigeration cycle uses a compressor, condenser, throttling device 104, and evaporator. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation to cool or heat the indoor space.

[0049] From a principle perspective, low-temperature, low-pressure refrigerant enters the compressor, which compresses it into a high-temperature, high-pressure refrigerant gas and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and the heat is released to the surrounding environment through the condensation process.

[0050] The throttling device 104 expands the high-temperature, high-pressure liquid refrigerant that condenses in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the expanded refrigerant 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 refrigerant evaporation to exchange heat with the material being cooled. Throughout the cycle, the refrigeration system 1 regulates the temperature of the indoor space.

[0051] The refrigeration system 1 includes an outdoor unit and an indoor unit that are connected to each other. Figure 1 The image shows a combination of two outdoor units (10, 12) and three indoor units (20, 22, 24). Figure 2The diagram shows a combination of two outdoor units (10, 12) and five indoor units (20, 22, 24, 26, 28). In this application, there is no particular limitation on the number of outdoor and indoor units. It can be configured according to... Figure 1 and Figure 2 The indoor and outdoor units are arranged in the same way, with only one indoor unit and one outdoor unit in a refrigeration system 1, or multiple indoor units and multiple outdoor units.

[0052] The indoor unit is equipped with an indoor heat exchanger (such as...) Figure 2 (as shown in Figure 200) and indoor throttling devices (e.g., indoor electronic expansion valves, such as...) Figure 2 (As shown in Figure 201).

[0053] The indoor unit and the outdoor unit are connected by a liquid-side connecting pipe 31 and a gas-side connecting pipe 32. The liquid-side connecting pipe 31 and the gas-side connecting pipe 32 are used to supply refrigerant flow, so that the refrigerant can form a refrigerant loop and circulate in it.

[0054] In one or more embodiments of this application, a liquid-side shut-off valve 105 is provided on the liquid-side connecting pipe 31, and a gas-side shut-off valve 106 is provided on the gas-side connecting pipe 32. The liquid-side shut-off valve 105 can shut off the fluid passage in the liquid-side connecting pipe 31 or, at its minimum opening, nearly shut off the fluid passage in the liquid-side connecting pipe 31. The gas-side shut-off valve 106 can shut off the fluid passage in the gas-side connecting pipe 32 or, at its minimum opening, nearly shut off the fluid passage in the gas-side connecting pipe 32.

[0055] The basic structure and function of the outdoor unit are illustrated below. The number of outdoor units can be expanded to multiple, each outdoor unit constituting a module, and they operate in a group.

[0056] Figure 3 This is a structural diagram of the outdoor unit; Figure 4 This is a schematic diagram of the refrigeration cycle when the outdoor unit is performing refrigeration. Figure 5 This is a schematic diagram of the cooling cycle when the outdoor unit is in heating mode; Figure 6 yes Figure 3 Enlarged view of part A in the image.

[0057] In one or more embodiments of this application, the outdoor unit of the refrigeration system 1 refers to the portion of the refrigeration cycle that includes a compressor and an outdoor heat exchanger 103. The outdoor unit can perform heating or cooling operation on the outdoor side to provide energy to the indoor unit for raising or lowering the indoor temperature. Figures 3 to 6 As shown, the outdoor unit is equipped with a first compressor 100a and a second compressor 100b; it can be configured according to the following... Figures 3 to 6The first compressor 100a and the second compressor 100b shown are configured in the same manner, with multiple compressors installed in the outdoor unit. The first compressor 100a and the second compressor 100b are configured to draw in refrigerant and compress it to a high-temperature, high-pressure state. The type of the first compressor 100a and the second compressor 100b is not further limited here; for example, they can be reciprocating compressors, screw compressors, etc. The speeds of the first compressor 100a and the second compressor 100b are controlled by a frequency converter, and the first compressor 100a and the second compressor 100b can operate independently. A first high-pressure switch 111a is installed at the discharge end of the first compressor 100a, and a second high-pressure switch 111b is installed at the discharge end of the second compressor 100b. A high-pressure sensor 110 is also installed at the discharge end of the first compressor 100a and the second compressor 100b, and a low-pressure sensor 151 is also installed at the suction end of the first compressor 100a and the second compressor 100b.

[0058] The discharge end of the first compressor 100a is provided with a first compressor exhaust temperature sensor 112a, and the discharge end of the second compressor 100b is provided with a second compressor exhaust temperature sensor 112b.

[0059] 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 phases, 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 phases, and guides the separated gaseous refrigerant into the second compressor 100b.

[0060] The outdoor unit may also be equipped with an outdoor fan (not shown) and a switching valve 102; the outdoor fan can be an axial flow fan, a cross flow 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.

[0061] The outdoor unit also includes a first oil separator 101a and a second oil separator 101b. The first oil separator 101a separates the lubricating oil from the high-temperature refrigerant vapor as the mixture of lubricating oil and refrigerant leaves the compressor. The second oil separator 101b also separates the lubricating oil from the high-temperature refrigerant vapor as the mixture of lubricating oil and refrigerant leaves the compressor. The first oil separator 101a is located in the piping between the first compressor 100a and the condenser. The high-pressure refrigerant's flow velocity is reduced in the first oil separator 101a and the second oil separator 101b, thereby trapping the lubricating oil within them. The denser lubricating oil separates 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 via the first capillary tube 150a and the second capillary tube 150b, respectively. The diameter and length of the first capillary tube 150a and the second capillary tube 150b can be used to adjust the amount of lubricating oil returned. A solenoid valve 109 is also installed downstream of the first oil separator 101a and the second oil separator 101b.

[0062] Taking a four-way valve as an example, the switching valve 102 is used to switch the flow direction of refrigerant in the refrigerant circuit. There is one and only one switching valve 102 in an outdoor unit.

[0063] In cooling operation, the outdoor unit can form a refrigerant circuit (hereinafter referred to as the refrigeration cycle) for cooling operation, wherein a switching valve 102 (e.g., one passage of a four-way valve, exemplarily, the fluid passage between port C and port 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 (inlet shown as 107c in the figure) is in fluid communication with the switching valve 102. Downstream of distributor 107, one outlet of distributor 107 is sequentially connected to the first gas-liquid separator 108a and the first compressor 1000a, and the other outlet of distributor 107 is sequentially connected to the second gas-liquid separator 108b and the second compressor 100b. The mixture of refrigerant and lubricating oil flowing out of the first compressor 100a enters the first oil separator 101a, and from the first oil separator 101a, the refrigerant flows back into the switching valve 102 (e.g., another passage of a four-way valve, exemplarily the fluid passage between ports D and E). The mixture of refrigerant and lubricating oil flowing out of the second compressor 100b enters the second oil separator 101b, and from the second oil separator 101b, the refrigerant flows back into the switching valve 102 (e.g., another passage of a four-way valve, exemplarily the fluid passage between ports D and E). The refrigerant flowing out of the switching valve 102 flows back into the outdoor heat exchanger 103.

[0064] In heating operation, the outdoor unit can form a refrigerant circuit (hereinafter referred to as the heating cycle) for heating operation, wherein an outdoor heat exchanger 103, a switching valve 102 (e.g., one passage of a four-way valve, exemplarily, the fluid passage between port E and port S) and a distributor 107 are sequentially connected from the liquid-side connecting pipe 31 to the gas-side connecting pipe 32. The distributor 107 is in fluid communication with the switching valve 102. Downstream of the distributor 107, that is, one outlet of the distributor 107 is sequentially connected to a first gas-liquid separator 108a, a first compressor 100a, a first oil separator 101a and the switching valve 102 (e.g., one passage of a four-way valve, exemplarily, the fluid passage 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 (e.g., the same passage of a four-way valve, exemplarily, the fluid passage between port D and port C).

[0065] The two outlets of distributor 107 (as shown in 107a and 107b in the figure) are designed to have the same flow rate.

[0066] The first gas-liquid separator 108a has a first housing 130a. A first inlet pipe 131a is inserted into the upper part of the first housing 130a, with its inlet located at the upper part of the first housing 130a. A first outlet pipe 113a is also provided in the first housing 130a, the first outlet pipe 113a being near the bottom of the first housing 130a and bent into a roughly U-shape, with its outlet extending outward from the upper part of the first housing 130a. The first outlet pipe 113a is in fluid communication with the first compressor 100a.

[0067] The second gas-liquid separator 108b has a second housing 130b. A second inlet pipe 131b is inserted into the upper part of the second housing 130b, with its inlet located at the upper part of the second housing 130b. A second outlet pipe 113b is also provided in the second housing 130b, near the bottom of the second housing 130b and bent into a roughly U-shape, with its outlet extending outward from the upper part of the second housing 130b. The second outlet pipe 113b is in fluid communication with the second compressor 100b.

[0068] During cooling or heating operation, the evaporated refrigerant is distributed by 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, resulting in gas-liquid separation. The separated gaseous refrigerant is drawn 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 at the bottom of the first housing 130a and the second housing 130b and gradually evaporates and vaporizes over time, and is then drawn into the first compressor 100a and the second compressor 100b. The bottom of the first outlet pipe 113a is provided with a first main oil return hole 114a, and the bottom of the second outlet pipe 113b is provided with a second main oil return hole 114b. 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.

[0069] In one or more embodiments of this application, the first housing 130a and the second housing 130b have the same shape and volume. The first gas-liquid separator 108a and the second gas-liquid separator 108b are connected by a distribution pipe 120, on which a regulating valve 121 is provided. Outside the distribution pipe 120, the upper sides of the first housing 130a and the second housing 130b can be connected by a gas connecting pipe 140, and the lower sides of the first housing 130a and the second housing 130b can be connected by a liquid connecting pipe 150.

[0070] In one or more embodiments of this application, the diameter of the distribution pipe 120 is much larger than the diameters of the gas connecting pipe 140 and the liquid connecting pipe 150.

[0071] like Figure 6As shown, a first auxiliary oil return hole 115a, higher than the first main oil return hole 114a, is also provided on the first outlet pipe 113a. The first auxiliary oil return hole 115a is fluidly connected to the first compressor 100a through the first detection branch 116a. A second auxiliary oil return hole 115b, higher than the second main oil return hole 114b, is also provided on the second outlet pipe 113b. The second auxiliary oil return hole 115b is fluidly connected to the second compressor 100b through the second detection branch 116b. The first detection branch 116a is provided with a first inlet temperature sensor 118a and a first outlet temperature sensor 117a. A first pressure reducing element 119a (in one or more embodiments of this application, the first pressure reducing element 119a is a first oil return detection capillary) is provided between the first inlet temperature sensor 118a and the second outlet temperature sensor 117b. That is, along the refrigerant flow direction, the first inlet temperature sensor 118a, the first pressure reducing element 119a and the first outlet temperature sensor 117a are arranged in sequence. The second detection branch 116b is provided with a second inlet temperature sensor 118b and a second outlet temperature sensor 117b. A second pressure reducing element 119b (in one or more embodiments of this application, the second pressure reducing element 119b is a second oil return detection capillary) is provided between the second inlet temperature sensor 118b and the second outlet temperature sensor 117b. That is, along the refrigerant flow direction, the second inlet temperature sensor 118b, the second pressure reducing element 119b and the second outlet temperature sensor 117b are arranged in sequence. The first and second return oil detection capillary tubes can be used to regulate the flow rate in the first detection branch 116a and the second detection branch 116b, respectively. The diameter, length, and relative installation position of the first and second return oil detection capillary tubes are exactly the same.

[0072] In one or more embodiments of this 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 and 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 housing 130a (the first compressor 100a cannot work if the lubricating oil quantity is less than 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 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 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 height. For example, a relatively ideal preset refrigerant volume, less than the maximum refrigerant volume (e.g., 60% of the maximum refrigerant volume), can be set according to the capacity of the refrigeration system 1 to ensure that both the first compressor 100a and the second compressor 100b in the refrigeration system 1 can operate stably. The preset refrigerant height is calculated based on the ratio of the preset refrigerant volume to the cross-sectional area of ​​the first housing 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 set position on the first outlet pipe.

[0073] In one or more embodiments of this 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 and minimum lubricating oil quantity of the second compressor 100b and the maximum refrigerant volume; wherein the difference between the maximum and minimum lubricating oil quantity represents the maximum capacity of lubricating oil allowed to accumulate in the second housing 130b (the second compressor 100b cannot work if the lubricating oil quantity is less than the minimum lubricating oil quantity), that is, the ratio of the difference between the maximum and minimum lubricating oil quantity 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 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 height. For example, a relatively ideal preset refrigerant volume, less than the maximum refrigerant volume (e.g., 60% of the maximum refrigerant volume), can be set according to the capacity of the refrigeration system 1. This preset refrigerant volume allows both the second compressor 100b and the second compressor 100b in the refrigeration system 1 to operate stably. The preset refrigerant height is calculated based on the ratio of the preset refrigerant volume to the cross-sectional area of ​​the second housing 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 set position on the second outlet pipe.

[0074] In one or more embodiments of this application, the first auxiliary oil return hole 115a and the second auxiliary oil return hole 115b have the same height.

[0075] The outdoor unit also includes an outdoor control circuit. This circuit is housed in a well-sealed electrical box with heat dissipation capabilities. The outdoor control circuit includes components such as a processor, storage unit, input / output interfaces, and communication interfaces. The processor can be a dedicated processor, a central processing unit (CPU), etc. The processor can access the storage unit to execute instructions or applications stored therein to achieve relevant functions. The storage unit can include volatile memory and / or non-volatile memory. The input / output interfaces can communicate with various sensors installed in the outdoor unit to receive their detection values. The input / output interfaces can also communicate with devices such as frequency converters, outdoor fans, and four-way valves to output control commands generated by the processor. The communication interfaces can support different wireless communication protocols, such as Wi-Fi, Bluetooth, near-field communication, and NB-IoT, to communicate with other electronic devices, including but not limited to cloud servers, computers (host computers), smartphones, tablets, PDAs, smart control fixtures, wearable devices, and vehicle-mounted devices.

[0076] As described in the background section, the refrigerant charge in refrigeration system 1 has reached hundreds of kilograms. Since only one switching valve 102 is installed, the switching valve 102 must be set to correspond with the distributor 107. However, it is difficult to ensure the similarity of pipe length and pipe diameter in the long-term use downstream of the corresponding distributor 107 (e.g., a three-way pipe or a three-way valve). In particular, there may be tiny impurities and contaminants in refrigeration system 1. These substances will accumulate in the pipes near the distributor 107 and gradually change the pipe diameter. Furthermore, since the output of the two compressors will 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.

[0077] like Figure 7 and Figure 8As shown, to solve this problem, a control unit 30 is also provided in the refrigeration system 1. In one or more embodiments of this application, the control unit 30 is implemented by an outdoor control circuit. In one or more embodiments of this application, the control unit 30 can also be implemented by a cloud server or host computer that communicates with the outdoor unit. The control unit 30 is configured to control the first compressor 100a and the second compressor 100b to operate at the same 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 change before and after the first pressure reducing element 119a and the second pressure reducing element 119b, and the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b. When the estimated non-uniform liquid level state is determined, the control valve 121 is driven to adjust the refrigerant flow rate in the distribution pipe.

[0078] More specifically, the control unit is configured to control the first compressor and the second compressor to operate at the same frequency. The operating frequency can be obtained based on the total load of the refrigeration system, for example, by calculating the total operating frequency required by the refrigeration system using a PID algorithm or a fuzzy control algorithm; the total operating frequency is divided by the number of compressors, and the first compressor 1000a and the second compressor 100b are controlled to operate at the calculated operating frequency, with the first compressor 100a and the second compressor 100b operating at the same frequency.

[0079] Regardless of whether it is operating in cooling or heating mode, the evaporated refrigerant, distributed by the distributor 107, enters the first housing 130a and the second housing 130b through the inlet pipe, resulting in gas-liquid separation. The gaseous refrigerant is located in the upper position, while the liquid mixture of refrigerant and lubricating oil is located in the lower position.

[0080] In this case, at the same height (the opening positions of the first auxiliary oil return hole 115a and the second auxiliary oil return hole 115b), when the fluid is guided through the same pressure reducing element, the temperature difference change of the gaseous refrigerant will be much smaller than that of the liquid refrigerant (including the temperature difference change of the mixture of liquid refrigerant and lubricating oil). Therefore, the control unit 30 is configured to determine whether the substance flowing into the first detection branch 116a from the first auxiliary oil return hole 115a is a gaseous or liquid substance based on the temperature change before and after the first pressure reducing element 119a. Similarly, the temperature change before and after the second pressure reducing element 119b can determine whether the substance flowing into the second detection branch 116b from the second auxiliary oil return hole 115b is a gaseous or liquid substance.

[0081] Since the first auxiliary oil return hole 115a and the second auxiliary oil return hole 115b are at the same height, the control unit 30 can determine whether there is a situation where the liquid level of one gas-liquid separator is above the corresponding auxiliary oil return hole or the liquid level of the other gas-liquid separator is below the corresponding auxiliary oil return hole, that is, the two are in a non-uniform liquid level state.

[0082] Furthermore, the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b can be used to determine whether there is a load mismatch.

[0083] When the control unit 30 is presumed to be in a non-uniform liquid level state, it drives the regulating valve 121 to adjust the refrigerant flow in the distribution pipe, so that the liquid level in the two gas-liquid separators is maintained in a uniform liquid level state. During the adjustment process, the first main oil return hole 114a, the first auxiliary oil return hole 115a, the second main oil return hole 114b, and the second auxiliary oil return hole 115b can all play the role of oil return simultaneously or separately.

[0084] Since both the first auxiliary oil return hole 115a and the second auxiliary oil return hole 115b are located at positions designed according to the ideal preset refrigerant volume, the control unit 30 can simultaneously count the frequency at which the liquid level is higher than the first auxiliary oil return hole 115a and the second auxiliary oil return hole 115b, and thereby optimize the overall operation and hardware design of the refrigeration system 1, so that the matching performance of the indoor unit and the outdoor unit can be better.

[0085] In one or more embodiments of this application, a first inlet temperature sensor 118a and a first outlet temperature sensor 117a are further provided on the first detection branch 116a of the fluid-connected first compressor 100a. The first inlet temperature sensor 118a is located on the inlet side of the first detection branch 116a and is close to the first auxiliary oil return hole 115a. The first outlet temperature sensor 117a is located on the outlet side of the first detection branch 116a and is close to the first compressor 100a. Along the refrigerant flow direction, the first inlet temperature sensor 118a, the first pressure reducing element 119a, and the first outlet temperature sensor 117a are arranged sequentially.

[0086] Correspondingly, a second inlet temperature sensor 118b and a second outlet temperature sensor 117b are also provided on the second detection branch 116b of the fluid-connected second compressor 100b. The second inlet temperature sensor 118b is located on the inlet side of the second detection branch 116b and is close to the second auxiliary oil return hole 115b. The second outlet temperature sensor 117b is located on the outlet side of the second detection branch 116b and is close to the second compressor 100b. Along the refrigerant flow direction, the second inlet temperature sensor 118b, the second pressure reducing element 119b, and the second outlet temperature sensor 117b are arranged sequentially.

[0087] In one or more embodiments of this application, the first detection branch 116a and the second detection branch 116b have the same structural dimensions, the first inlet temperature sensor 118a is located at the same position as the second inlet temperature sensor 118b, and the first outlet temperature sensor 117a is located at the same position as the second outlet temperature sensor 117b.

[0088] Specifically, such as Figure 9 As shown, the control unit 30 is configured to sample the temperature detected by the first outlet temperature sensor 117a (e.g., ...). Figure 9 As shown in step S111), the temperature is sampled by the first inlet temperature sensor 118a (as shown in step S111). Figure 9 As shown in step S112), calculate the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a (e.g., ...). Figure 9 In step S113, it is determined whether the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a is lower than a first set threshold (e.g., ...). Figure 9 As shown in step S114), when the liquid level is below the first set threshold, it is presumed that the liquid level in the first gas-liquid separator 108a is higher than the first auxiliary oil return hole 115a (as shown in step S114). Figure 9 (as shown in step S115); or when it is not lower than the first set threshold, it is presumed that the liquid level in the first gas-liquid separator 108a is lower than the first auxiliary oil return hole 115a (as shown in step S115); Figure 9 (as shown in step S116).

[0089] Correspondingly, such as Figure 10 As shown, the control unit 30 is configured to sample the temperature detected by the second outlet temperature sensor 117b (e.g., Figure 10 As shown in step S211), the temperature is detected by the second inlet temperature sensor 118b (as shown in step S211). Figure 10 As shown in step S212), calculate the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b (e.g., ...). Figure 10 As shown in step S213, determine whether the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b is lower than a second set threshold (e.g., ...). Figure 10 As shown in step S214), when the liquid level is below the second set threshold, it is presumed that the liquid level in the second gas-liquid separator 108b is higher than the second auxiliary oil return hole 115b (as shown in step S214). Figure 10 (as shown in step S215); or, if the liquid level in the second gas-liquid separator 108b is not lower than the second set threshold, it is presumed that the liquid level is lower than the second auxiliary oil return hole 115b (as shown in step S215); Figure 10 (See step S216).

[0090] In one or more embodiments of this application, the control unit 30 is configured to presume that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state when the temperature difference between the first outlet temperature sensor 117a and the first inlet temperature sensor 118a is not lower than a first preset threshold, the temperature difference between the second outlet temperature sensor 117b and the second inlet temperature sensor 118b is lower than a second preset threshold, and the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than a third preset threshold. Furthermore, the control unit 30 also presumes that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, and the liquid level of the second gas-liquid separator 108b is higher than the second auxiliary oil return hole 115b, and the liquid level of the first gas-liquid separator 108a is lower than the first auxiliary oil return hole 115a (e.g., ...). Figure 11 As shown, the driving regulating valve 121 is activated to open the distribution pipe 120, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b can quickly transition from a non-uniform liquid level state to a uniform liquid level state in a short time.

[0091] In one or more embodiments of this application, the control unit 30 is configured to presume that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state when the temperature difference between the first outlet temperature sensor 117a and the first inlet temperature sensor 118a is lower than a first preset threshold, the temperature difference between the second outlet temperature sensor 117b and the second inlet temperature sensor 118b is not lower than a second preset threshold, and the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than a third preset threshold. Furthermore, the control unit 30 also presumes that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, and the liquid level of the first gas-liquid separator 108a is higher than the first auxiliary oil return hole 115a, and the liquid level of the second gas-liquid separator 108b is lower than the second auxiliary oil return hole 115b (e.g., ...). Figure 12 As shown, the driving regulating valve 121 is activated to open the distribution pipe 120, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b can quickly transition from a non-uniform liquid level state to a uniform liquid level state in a short time.

[0092] In one or more embodiments of this application, the third set threshold is generated based on the outdoor ambient temperature, and the third set threshold is negatively correlated with the outdoor ambient temperature.

[0093] For example, such as Figure 15As shown, the third set threshold is the sum of a reference temperature (pre-set and stored) and a correction temperature. When the outdoor ambient temperature is below -20°C, the correction temperature is 5°C; when the outdoor ambient temperature is above -20°C but below -10°C, the correction temperature is 3°C; when the outdoor ambient temperature is above -10°C but below 7°C, the correction temperature is 1°C; and when the outdoor ambient temperature is above 7°C, the correction temperature is 0°C. That is, the lower the outdoor ambient temperature, the more lenient the presupposition conditions for active liquid level adjustment. This is because the viscosity of the lubricating oil is higher at low temperatures, and the oil return characteristics of refrigeration system 1 will become worse, requiring liquid equalization to balance the distribution of the lubricating oil and improve the oil return characteristics.

[0094] In one or more embodiments of this application, the first set threshold and the second set threshold are the same, for example, both are set to 5°C.

[0095] In one or more embodiments of this application, the regulating valve 121 may be a solenoid valve. The control unit 30 drives the regulating valve 121 to open the distribution pipe 120 until the end of a set on-time period, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b transition from a non-uniform liquid level state to a uniform liquid level state. The duration of the set on-time period 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 set on-time period corresponds one-to-one with the exhaust 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 shown below. Figure 16 As shown, ΔTd represents the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b, and T represents the duration of the set conduction cycle.

[0096] In one or more embodiments of this application, the regulating valve 121 may be an electronic expansion valve. The control unit 30 drives the regulating valve 121 to open the distribution pipe 120, causing the first gas-liquid separator 108a and the second gas-liquid separator 108b to transition from a uniform liquid level state to a uniform liquid level state. The operation of the regulating valve 121 is divided into multiple continuous regulating cycles, and 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 a proportional coefficient. The proportional coefficient is obtained based on a second fitting curve generated according to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. In the second fitting curve, the proportional coefficient corresponds one-to-one 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; an exemplary second fitting curve is shown below. Figure 17As shown, ΔTd represents the temperature difference between the exhaust gases of the first compressor 100a and the second compressor 100b, and ΔEV represents the proportionality coefficient, expressed as a percentage.

[0097] In actual use, non-uniform liquid level states usually occur during the transition phase of refrigeration system 1, such as the start-up phase of the outdoor unit, the shutdown phase of the outdoor unit, the increase or decrease in the number of indoor units corresponding to the outdoor unit, defrosting, and refrigerant charging, etc. This will cause rapid changes in the gas and liquid in refrigeration system 1, resulting in instantaneous liquid level fluctuations. At this time, small liquid level changes will lead to disproportionate temperature changes, reducing the accuracy of using exhaust temperature as a liquid level judgment indicator.

[0098] To address this issue, in one or more embodiments of this application, the control unit 30 is configured 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 changes before and after the first pressure reducing element 119a and the second pressure reducing element 119b, the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b, and the operating current difference between the first compressor 100a and the second compressor 100b; and when the estimated non-uniform liquid level state is reached, to drive the regulating valve 121 to adjust the refrigerant flow rate in the distribution pipe.

[0099] Consistent with using the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b as a presupposition, a first inlet temperature sensor 118a and a first outlet temperature sensor 117a are also provided on the first detection branch 116a, which is in fluid communication with the first compressor 100a. The first inlet temperature sensor 118a is located on the inlet side of the first detection branch 116a and is close to the first auxiliary oil return hole 115a. The first outlet temperature sensor 117a is located on the outlet side of the first detection branch 116a and is close to the first compressor 100a. Along the refrigerant flow direction, the first inlet temperature sensor 118a, the first pressure reducing element 119a, and the first outlet temperature sensor 117a are arranged sequentially.

[0100] Correspondingly, a second inlet temperature sensor 118b and a second outlet temperature sensor 117b are also provided on the second detection branch 116b of the fluid-connected second compressor 100b. The second inlet temperature sensor 118b is located on the inlet side of the second detection branch 116b and is close to the second auxiliary oil return hole 115b. The second outlet temperature sensor 117b is located on the outlet side of the second detection branch 116b and is close to the second compressor 100b. Along the refrigerant flow direction, the second inlet temperature sensor 118b, the second pressure reducing element 119b, and the second outlet temperature sensor 117b are arranged sequentially.

[0101] In one or more embodiments of this application, the first detection branch 116a and the second detection branch 116b have the same structural dimensions, the first inlet temperature sensor 118a is located at the same position as the second inlet temperature sensor 118b, and the first outlet temperature sensor 117a is located at the same position as the second outlet temperature sensor 117b.

[0102] In one or more embodiments of this application, such as Figure 13 As shown in the multiple steps, the control unit 30 samples the temperature detected by the first outlet temperature sensor 117a (e.g., ...). Figure 13 As shown in step S311), the first inlet temperature sensor 118a detects the temperature (as shown in step S311). Figure 13 As shown in step S312, calculate the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a (e.g., ...). Figure 13 (as shown in step S313), and determine whether it is not lower than the first preset threshold (e.g.) Figure 13 (as shown in step S314); the second outlet temperature sensor 117b detects the temperature (e.g., ...). Figure 13 As shown in step S321), the second inlet temperature sensor 118b detects the temperature (as shown in step S321). Figure 13 As shown in step S322), calculate the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b (e.g., ...). Figure 13 (as shown in step S323), and determine whether it is lower than the second set threshold (e.g.) Figure 13 (as shown in step S324); sample the exhaust temperature of the first compressor 100a (e.g., ...). Figure 13 As shown in step S331), the discharge temperature of the second compressor 100b (as shown in step S331) Figure 13 As shown in step S332, calculate the exhaust temperature difference between the first compressor 100a and the second compressor 100b (e.g., ...). Figure 13 (as shown in step S333), and determine whether it is not lower than the third preset threshold (e.g.) Figure 13 (as shown in step S334); sample the operating current of the first compressor 100a (e.g., ...). Figure 13 As shown in step S341, the operating current of the second compressor 100b is sampled (e.g., ...). Figure 13 As shown in step S342, calculate the difference in operating current between the first compressor 100a and the second compressor 100b (e.g., ...). Figure 13 (as shown in step S343), and determine whether it is not lower than the fourth preset threshold (e.g.) Figure 13 (See step S344).

[0103] The control unit 30 is configured such that when the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a is not lower than a first set threshold, the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b is lower than a second set threshold, the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b is not lower than a third set threshold, and the difference in operating current between the first compressor 100a and the second compressor 100b is not lower than a fourth 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, and the liquid level of the second gas-liquid separator 108b is higher than that of the second auxiliary oil return hole 115b (e.g., ...). Figure 13 As shown in step S35, the driving regulating valve 121 is activated to open the distribution pipe 120 (as shown in step S35). Figure 13 As shown in step S36, this allows the first gas-liquid separator 108a and the second gas-liquid separator 108b to transition from a non-uniform liquid level state to a uniform liquid level state (as shown in step S36). Figure 13 (See step S37).

[0104] In one or more embodiments of this application, such as Figure 14 As shown in the multiple steps, the control unit 30 samples the temperature detected by the first outlet temperature sensor 117a (e.g., ...). Figure 14 As shown in step S411), the first inlet temperature sensor 118a detects the temperature (as shown in step S411). Figure 14 As shown in step S412, calculate the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a (e.g., ...). Figure 14 (as shown in step S413), and determine whether it is below the first preset threshold (e.g.) Figure 14 (as shown in step S414); the second outlet temperature sensor 117b detects the temperature (e.g., ...). Figure 14 As shown in step S421), the second inlet temperature sensor 118b detects the temperature (as shown in step S421). Figure 14 As shown in step S422), calculate the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b (e.g., ...). Figure 14 (as shown in step S423), and determine whether it is not lower than the second preset threshold (e.g.) Figure 14 (as shown in step S424); sample the exhaust temperature of the first compressor 100a (e.g., ...). Figure 14 As shown in step S431), the discharge temperature of the second compressor 100b (as shown in step S431) Figure 14 As shown in step S432, calculate the exhaust temperature difference between the first compressor 100a and the second compressor 100b (e.g., ...). Figure 14 (as shown in step S433), and determine whether it is not lower than the third preset threshold (e.g.) Figure 14 (as shown in step S434); sample the operating current of the first compressor 100a (e.g., ...). Figure 14 As shown in step S441, the operating current of the second compressor 100b is sampled (e.g., ...). Figure 14 As shown in step S442, calculate the difference in operating current between the first compressor 100a and the second compressor 100b (e.g., ...). Figure 14 (as shown in step S443), and determine whether it is not lower than the fourth preset threshold (e.g.) Figure 14 (See step S444).

[0105] In one or more embodiments of this application, the control unit 30 is configured such that when the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a is lower than a first preset threshold, the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b is not lower than a second preset threshold, the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than a third preset threshold, and the difference in operating current between the first compressor 100a and the second compressor 100b is not lower than a fourth preset 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, and the liquid level of the first gas-liquid separator 108a is higher than that of the first auxiliary oil return hole 115a (e.g., ...). Figure 14 As shown in step S45, the driving regulating valve 121 is activated to open the distribution pipe 120 (as shown in step S45). Figure 14 As shown in step S46, the first gas-liquid separator 108a and the second gas-liquid separator 108b transition from a uniform liquid level state to a uniform liquid level state (as shown in step S46). Figure 14 (See step S47).

[0106] Since non-uniform liquid level states typically occur during the transition phases of the refrigeration system 1, such as the start-up phase of the outdoor unit, the shutdown phase of the outdoor unit, the increase or decrease in the number of indoor units corresponding to the outdoor unit, defrosting, and refrigerant charging, etc., this leads to drastic changes in the gas and liquid phases within the refrigeration system 1, resulting in instantaneous liquid level fluctuations. These fluctuations are difficult to detect (even high-precision sensors cannot detect them). To address this, in this application, the control unit 30, on the one hand, uses the temperature changes of the first detection branch 116a and the second detection branch 116b to determine the distribution of gaseous and liquid refrigerant in the first gas-liquid separator 108a and the second gas-liquid separator 108b; on the other hand, it uses the complementary compressor discharge temperature difference and operating current difference to determine the impact of the workload of the first compressor 100a and the second compressor 100b on the liquid level, avoiding disproportionate temperature changes caused by small liquid level changes, thus reducing the accuracy of temperature as a liquid level judgment indicator. The compressor's operating current is directly related to its workload, especially during start-up and shutdown, where the current changes accordingly, making detection more accurate. Furthermore, the compressor discharge temperature can further identify whether the compressor itself has a fault. Multi-parameter methods offer better robustness, handling variations under different transient operating conditions and better responding to load changes, environmental changes, and even sensor failures. They are particularly useful for systems exceeding 100 HP with elevation differences exceeding 100 meters.

[0107] For example, the first and second set thresholds can both be set to 5°C, the third set threshold is generated based on the outdoor ambient temperature, and the fourth set threshold can be 1A.

[0108] In one or more embodiments of this application, the regulating valve 121 may be a solenoid valve. The control unit 30 drives the regulating valve 121 to open the distribution pipe 120 until the end of the set opening cycle, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b transition from a non-uniform liquid level state to a uniform liquid level state. The duration of the set opening cycle 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 set opening cycle corresponds one-to-one with the exhaust 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 shown in the figure, where ΔTd represents the exhaust temperature difference between the first compressor 100a and the second compressor 100b, and T represents the duration of the set opening cycle.

[0109] In one or more embodiments of this application, the regulating valve 121 may be an electronic expansion valve. The control unit 30 drives the regulating valve 121 to open the distribution pipe 120, causing the first gas-liquid separator 108a and the second gas-liquid separator 108b to transition from a uniform liquid level state to a uniform liquid level state. The operation of the regulating valve 121 is divided into multiple continuous regulating cycles, and 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 a proportional coefficient. The proportional coefficient is obtained based on a second fitting curve generated according to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. In the second fitting curve, the proportional coefficient corresponds one-to-one 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; an exemplary second fitting curve is shown in the figure, where ΔTd represents the exhaust temperature difference between the first compressor 100a and the second compressor 100b, and ΔEV represents the proportional coefficient, expressed as a percentage.

[0110] 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.

[0111] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A refrigeration system, including: Outdoor unit, which includes: First compressor; Second compressor; A switching valve is a valve used to switch the flow direction of refrigerant in a refrigerant circuit. It is connected to the discharge side of the first compressor and the discharge side of the second compressor, respectively. Distributor, the inlet of which is connected to the switching valve; A first gas-liquid separator connected to one outlet of the distributor, wherein a first outlet pipe connected to the suction side of the first compressor is provided; A second gas-liquid separator, connected to another outlet of the distributor, is provided with a second outlet pipe connected to the suction side of the second compressor; and A distribution pipe, the two ends of which are respectively connected to the first gas-liquid separator and the second gas-liquid separator; Its characteristic is that it further includes: A regulating valve is provided on the distribution pipe; The first detection branch is connected to the first outlet pipe through the first auxiliary oil return hole. The first auxiliary oil return hole is higher than the bottom of the first outlet pipe. The first detection branch is provided with a first pressure reducing element. The first detection branch is also fluidly connected to the first compressor. The second detection branch is connected to the second outlet pipe via a second auxiliary oil return hole, the second auxiliary oil return hole being higher than the bottom of the second outlet pipe. The second detection branch is equipped with a second pressure-reducing element, wherein the first and second auxiliary oil return holes are at the same height, the first and second pressure-reducing elements are identical, and the second detection branch is also fluidly connected to the second compressor. 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 changes before and after the first pressure reducing element and the second pressure reducing element, and the temperature difference between the exhaust temperatures of the first compressor and the second compressor; and when it is estimated to be in a non-uniform liquid level state, to drive the regulating valve to adjust the refrigerant flow in the distribution pipe to transition to a uniform liquid level state.

2. The refrigeration system according to claim 1, characterized in that: The first detection branch is also fluidly connected to the first compressor, and further includes: The first inlet temperature sensor is located on the inlet side of the first detection branch and is close to the first auxiliary oil return hole. The first outlet temperature sensor is located on the outlet side of the first detection branch and is close to the first compressor. Along the refrigerant flow direction, the first inlet temperature sensor, the first pressure reducing element, and the first outlet temperature sensor are arranged sequentially. The second detection branch is also fluidly connected to the second compressor, and further includes: The second inlet temperature sensor is located on the inlet side of the second detection branch and is close to the second auxiliary oil return hole. The second outlet temperature sensor is located on the outlet side of the second detection branch and is close to the second compressor. Along the refrigerant flow direction, the second inlet temperature sensor, the second pressure reducing element, and the second outlet temperature sensor are arranged in sequence.

3. The refrigeration system according to claim 2, characterized in that: The control unit is configured to, when the difference between the temperature detected by the first outlet temperature sensor and the temperature detected by the first inlet temperature sensor is not lower than a first set threshold, the difference between the temperature detected by the second outlet temperature sensor and the temperature detected by the second inlet temperature sensor is 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, presume that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, and the liquid level of the second gas-liquid separator is higher than the second auxiliary oil return hole, drive the regulating valve to open the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state; The control unit is configured to, when the difference between the temperature detected by the first outlet temperature sensor and the temperature detected by the first inlet temperature sensor is lower than a first set threshold, the difference between the temperature detected by the second outlet temperature sensor and the temperature detected by the second inlet temperature sensor 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, presume that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, and the liquid level of the first gas-liquid separator is higher than the first auxiliary oil return hole, drive the regulating valve to open the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state; The third set threshold is generated based on the outdoor ambient temperature, and the third set threshold is negatively correlated with the outdoor ambient temperature.

4. The refrigeration system according to claim 3, characterized in that: The regulating valve is a solenoid valve. The control unit drives the regulating valve to open the distribution pipe until the set opening cycle ends, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state. The duration of the set conduction period is obtained based on a first fitting curve, which is 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 with the exhaust temperature difference between the first compressor and the second compressor.

5. The refrigeration system according to claim 3, characterized in that: The regulating valve is an electronic expansion valve. The control unit drives the regulating valve to open the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state. The regulating valve operates in multiple continuous regulating cycles. 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. The proportional coefficient is obtained based on a second fitting curve, which is 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 with the exhaust temperature difference between the first compressor and the second compressor.

6. Refrigeration system, including: Outdoor unit, which includes: First compressor; Second compressor; A switching valve is a valve that switches the flow direction of refrigerant in a refrigerant circuit, and is connected to the first compressor and the second compressor respectively. Distributor, the inlet of which is connected to the switching valve; A first gas-liquid separator connected to one outlet of the distributor, wherein a first outlet pipe connected to the suction side of the first compressor is provided; A second gas-liquid separator, connected to another outlet of the distributor, is provided with a second outlet pipe connected to the suction side of the second compressor; and A distribution pipe, the two ends of which are respectively connected to the first gas-liquid separator and the second gas-liquid separator; Its characteristic is that it further includes: A regulating valve is provided on the distribution pipe; The first detection branch is connected to the first outlet pipe through the first auxiliary oil return hole. The first auxiliary oil return hole is higher than the bottom of the first outlet pipe. The first detection branch is provided with a first pressure reducing element. The first detection branch is also fluidly connected to the first compressor. The second detection branch is connected to the second outlet pipe via a second auxiliary oil return hole, the second auxiliary oil return hole being higher than the bottom of the second outlet pipe. The second detection branch is equipped with a second pressure-reducing element, wherein the first and second auxiliary oil return holes are at the same height, the first and second pressure-reducing elements are identical, and the second detection branch is also fluidly connected to the second compressor. 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 changes before and after the first pressure reducing element and the second pressure reducing element, the temperature difference of the exhaust temperature between the first compressor and the second compressor, and the difference of the operating current between the first compressor and the second compressor; and when it is estimated to be in a non-uniform liquid level state, to drive the regulating valve to adjust the refrigerant flow in the distribution pipe to transition to a uniform liquid level state.

7. The refrigeration system according to claim 6, characterized in that, The first detection branch is also fluidly connected to the first compressor, and further includes: The first inlet temperature sensor is located on the inlet side of the first detection branch and is close to the first auxiliary oil return hole. The first outlet temperature sensor is located on the outlet side of the first detection branch and is close to the first compressor. Along the refrigerant flow direction, the first inlet temperature sensor, the first pressure reducing element, and the first outlet temperature sensor are arranged sequentially. The second detection branch is also fluidly connected to the second compressor, and further includes: The second inlet temperature sensor is located on the inlet side of the second detection branch and is close to the second auxiliary oil return hole. The second outlet temperature sensor is located on the outlet side of the second detection branch and is close to the second compressor. Along the refrigerant flow direction, the second inlet temperature sensor, the second pressure reducing element, and the second outlet temperature sensor are arranged in sequence.

8. The refrigeration system according to claim 7, characterized in that, The control unit is configured to, when the difference between the temperature detected by the first outlet temperature sensor and the temperature detected by the first inlet temperature sensor is not lower than a first set threshold, the difference between the temperature detected by the second outlet temperature sensor and the temperature detected by the second inlet temperature sensor is lower than a second set threshold, the exhaust temperature difference between the first compressor and the second compressor is not lower than a third set threshold, and the difference in operating current between the first compressor and the second compressor is not lower than a fourth set threshold, presume that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, and the liquid level of the second gas-liquid separator is higher than the second auxiliary oil return hole, drive the regulating valve to open the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state; The control unit is configured to presume that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state and that the liquid level of the first gas-liquid separator is higher than the first auxiliary oil return hole when the difference between the temperature detected by the first outlet temperature sensor and the temperature detected by the first inlet temperature sensor is lower than a first preset threshold, the difference between the temperature detected by the second outlet temperature sensor and the temperature detected by the second inlet temperature sensor is not lower than a second preset threshold, the temperature difference between the exhaust temperatures of the first compressor and the second compressor is not lower than a third preset threshold, and the difference between the operating currents of the first compressor and the second compressor is not lower than a fourth preset threshold. The control unit then drives the regulating valve to open the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state.

9. The refrigeration system according to claim 8, characterized in that: The regulating valve is a solenoid valve. The control unit drives the regulating valve to open the distribution pipe until the set opening cycle ends, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state. The duration of the set conduction period is obtained based on a fitting curve, which is generated according to the exhaust temperature difference between the first compressor and the second compressor. In the fitting curve, the set conduction period corresponds one-to-one with the exhaust temperature difference between the first compressor and the second compressor.

10. The refrigeration system according to claim 8, characterized in that: The regulating valve is an electronic expansion valve. The control unit drives the regulating valve to open the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state. The regulating valve operates in multiple continuous regulating cycles. 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. The proportional coefficient is obtained based on a fitting curve, which is generated based on the exhaust temperature difference between the first compressor and the second compressor. In the fitting curve, the proportional coefficient corresponds one-to-one with the exhaust temperature difference between the first compressor and the second compressor.

Images