Refrigeration system

Abstract

The refrigeration system includes an outdoor unit; the outdoor unit includes a first and a second compressor; a first and a second outdoor heat exchanger; a first and a second outdoor throttling element; a switching valve; a distributor; and a first and a second gas-liquid separator; the control unit controls the operating frequency of the first and second compressors during heating to maintain the target discharge pressure, and controls the opening degree of the first and second outdoor throttling elements to ensure that the first and second outdoor heat exchangers are not lower than the target suction and discharge superheat; it estimates whether the correction mode start-up conditions are met based on the temperature difference between the first and second compressors' discharge temperatures; if so, it maintains heating and increases the target discharge pressure to generate a corrected target discharge pressure, increases the target suction and discharge superheat to generate a corrected target suction and discharge superheat, controls the operating frequency of the first and second compressors to maintain the corrected target discharge pressure, and controls the opening degree of the first and second outdoor throttling elements to ensure that the first and second outdoor heat exchangers are not lower than the corrected target suction and discharge superheat; this invention can solve the flow deviation problem.

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), and the piping length between the outdoor and indoor units is very long (the total piping length has reached 1200 meters). The huge height difference and piping length require more refrigerant, and the amount of refrigerant in the system is significantly increased compared to traditional split 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 units 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) includes: "two gas-liquid separators, each comprising a cylinder with an inlet and an outlet pipe; a balance pipe communicating with each cylinder between the side walls; and a distribution pipe communicating with each cylinder between the bottoms, 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 within multiple gas-liquid separators. But for modular outdoor units, there is a hardware design requiring a four-way valve to match two or more compressors, necessitating a distributor upstream of the multiple gas-liquid separators. However, from a manufacturing perspective, it's difficult to ensure complete consistency in the piping of multiple gas-liquid separators. The piping between the distributor and multiple gas-liquid separators, and between multiple gas-liquid separators and multiple compressors, may also differ in length and configuration. Furthermore, the two outlets of the distributor may be machined at an angle, all of which, under the influence of pressure loss and inertia, can cause flow deviation between the two gas-liquid separators and the two compressors. From an installation perspective, consistent installation height is also difficult to guarantee. From a usage perspective, if the outdoor heat exchanger acting as an evaporator has a weak evaporation capacity (e.g., when the indoor ambient temperature is too low during cooling operation, or the evaporator...), the evaporation capacity may be insufficient. (Dirty or clogged refrigerant; excessively low outdoor ambient temperature during heating operation, frosting or clogged outdoor heat exchangers, insufficient evaporation area of ​​outdoor heat exchangers, etc.) can lead to incomplete evaporation of the low-temperature, low-pressure two-phase refrigerant in the evaporator, resulting in a higher proportion of liquid phase in the refrigerant. This can also cause uneven liquid return from the two gas-liquid separators and the two compressors. The compressor connected to the gas-liquid separator with more liquid return will have more liquid return, and the compressor connected to the gas-liquid separator with less liquid return will have less liquid return. Over time, the operating differences between the two compressors will become significant, as will the discharge temperatures. This will greatly affect the performance and reliability of the compressor itself and the entire refrigeration system. Summary of the Invention

[0006] To address the problem that the weak evaporation capacity of the outdoor heat exchanger, which acts as an evaporator, leads to incomplete evaporation of the low-temperature, low-pressure gas-liquid two-phase refrigerant in the evaporator, resulting in a high proportion of liquid phase in the refrigerant, uneven liquid return from the two gas-liquid separators and two compressors, and thus significantly affects the performance and reliability of the compressor body and the entire refrigeration system, this invention designs and provides a refrigeration system.

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

[0008] In one or more embodiments of this application, the refrigeration system further includes a control unit configured to, during heating operation, control the operating frequency of the first compressor and the second compressor to maintain a target discharge pressure, control the opening degree of the first outdoor throttling element and the second outdoor throttling element to ensure that the first outdoor heat exchanger and the second outdoor heat exchanger are not lower than the target suction superheat and the target discharge superheat; estimate whether the correction mode start-up conditions are met based on the discharge temperature difference between the first compressor and the second compressor; and, when the correction mode start-up conditions are met, maintain heating operation and increase the target discharge pressure to generate a corrected target discharge pressure, increase the target suction superheat and the target discharge superheat to generate a corrected target suction superheat and a corrected target discharge superheat, control the operating frequency of the first compressor and the second compressor to maintain a corrected target discharge pressure, and control the opening degree of the first outdoor throttling element and the second outdoor throttling element to ensure that the first outdoor heat exchanger and the second outdoor heat exchanger are not lower than the corrected target suction superheat and the corrected target discharge superheat.

[0009] In one or more embodiments of this application, an outdoor fan is further provided in the outdoor unit, and the outdoor fan is located near the first outdoor heat exchanger or the second outdoor heat exchanger.

[0010] In one or more embodiments of this application, the control unit is further configured to control the outdoor fan to operate at a target speed according to the outdoor ambient temperature during heating operation; the target speed is negatively correlated with the outdoor ambient temperature; when the correction mode activation conditions are met, the control unit maintains the heating operation and increases the target speed to generate a correction speed; and controls the outdoor fan based on the correction speed.

[0011] In one or more embodiments of this application, the control unit is further configured to, after controlling the operating frequency of the first compressor and the second compressor based on the target exhaust pressure, controlling the opening degree of the first outdoor throttling element and the second outdoor throttling element based on the target intake superheat and the target exhaust superheat, and controlling the outdoor fan based on the corrected speed; estimate whether the correction mode exit condition is met based on the exhaust temperature difference between the first compressor and the second compressor, the outdoor ambient temperature, and the real-time current increase of the outdoor fan; and when the correction mode exit condition is met, maintain heating operation, control the operating frequency of the first compressor and the second compressor to maintain the target exhaust pressure, and control the opening degree of the first outdoor throttling element and the second outdoor throttling element so that the first outdoor heat exchanger and the second outdoor heat exchanger are not lower than the target intake superheat and the target exhaust superheat.

[0012] In one or more embodiments of this application, the control unit is configured to presume that the correction mode exit condition is met when the exhaust temperature difference between the first compressor and the second compressor is within a set temperature range, the outdoor ambient temperature is not lower than a set ambient temperature threshold, and the real-time current increase of the outdoor fan is not higher than a set current increase threshold.

[0013] In one or more embodiments of this application, the control unit is configured to perform the following steps when controlling the opening of the first outdoor throttling element to ensure that the first outdoor heat exchanger meets the target intake superheat condition and the target exhaust superheat condition: performing heating operation; sampling the detected temperature T of the gas pipe temperature sensor of the first outdoor heat exchanger. g1 The temperature T detected by the temperature sensor of the second outdoor heat exchanger pipe is sampled. g2 ; Obtain the detection pressure P of the low-pressure sensor s ; Obtain the detection pressure P of the low-pressure sensor s The corresponding saturation temperature T c_ps ; Calculate the first suction superheat T during heating operation. ssh1 Second intake superheat T ssh2 First inhalation superheat T ssh1 Satisfy T ssh1 =T g1 -T c_ps Second intake superheat T ssh2 Satisfy T ssh2 =T g2 -T c_ps Adjusting the opening of the first outdoor throttling element to achieve the first intake superheat T ssh1 The second intake superheat should not be lower than the target intake superheat a℃. Adjust the opening of the second outdoor throttling element to make the second intake superheat T... ssh2 Not lower than the target intake superheat a℃; sampling temperature T of the first compressor exhaust temperature sensor. d1 The temperature T detected by the second compressor exhaust temperature sensor is sampled. d2 ; Calculate the detected temperature T of the first compressor exhaust temperature sensor. d1 The detection temperature T of the second compressor exhaust temperature sensor d2 The mean T dave ; Obtain the detection pressure P of the high-pressure sensor d ; Obtain the detection pressure P of the high-pressure sensor d The corresponding saturation temperature T c_pd ; Calculate the first exhaust superheat T during heating operation. dsh1 First exhaust superheat T dsh1 Satisfy T dsh1 =T dave -T c_pdAdjusting the opening of the first outdoor throttling element and the opening of the second outdoor throttling element to achieve the first exhaust superheat T dsh1 Not lower than the target exhaust superheat b℃.

[0014] In one or more embodiments of this application, the control unit is configured to perform the following steps when controlling the opening of the first outdoor throttling element and the second outdoor throttling element so that the first outdoor heat exchanger and the second outdoor heat exchanger are not lower than the corrected target intake superheat and the corrected target exhaust superheat: maintaining heating operation; sampling the detected temperature T of the gas pipe temperature sensor of the first outdoor heat exchanger. g1 The temperature T detected by the temperature sensor of the second outdoor heat exchanger pipe is sampled. g2 ; Obtain the detection pressure P of the low-pressure sensor s ; Obtain the detection pressure P of the low-pressure sensor s The corresponding saturation temperature T c_ps ; Calculate the third intake superheat T when executing the correction mode. ssh3 and the fourth intake superheat T ssh4 Third intake superheat T ssh3 Satisfy T ssh3 =T g1 -T c_ps Fourth intake superheat T ssh4 Satisfy T ssh4 =T g2 -T c_ps Adjusting the opening of the first outdoor throttling element to achieve the third intake superheat T ssh3 The fourth intake superheat should be adjusted to a value not lower than the target superheat c℃, and the opening of the second outdoor throttling element should be adjusted to achieve a superheat T of not less than the target superheat c℃. ssh4 Not lower than the target intake superheat c℃; sampling temperature T of the first compressor exhaust temperature sensor. d1 The temperature T detected by the second compressor exhaust temperature sensor is sampled. d2 ; Calculate the detected temperature T of the first compressor exhaust temperature sensor. d1 The detection temperature T of the second compressor exhaust temperature sensor d2 The mean T dave ; Obtain the detection pressure P of the high-pressure sensor d ; Obtain the detection pressure P of the high-pressure sensor d The corresponding saturation temperature T c_pd ; Calculate the second exhaust superheat T when executing the correction mode. dsh2 Second exhaust superheat T dsh2 Satisfy T dsh2 =T dave -T c_pd Adjusting the opening of the first outdoor throttling element and the opening of the second outdoor throttling element to achieve the second exhaust superheat T when executing the correction mode.dsh2 Not lower than the corrected target exhaust superheat d℃.

[0015] In one or more embodiments of this application, when adjusting the opening degree of the first outdoor throttling element and the second outdoor throttling element, the control unit is configured to perform the following steps: setting a plurality of consecutive adjustment cycles; the opening degree of the first outdoor throttling element in the next adjustment cycle is the sum of the real-time opening degree of the first outdoor throttling element in the current adjustment cycle and the set change amount ΔEVO; wherein the set change amount ΔEVO satisfies ΔEVO=α×ΔEVO 排气过热度 +β×ΔEVO 吸气过热度 Where α is the influence factor of exhaust superheat on the setpoint variation, and β is the influence factor of intake superheat on the setpoint variation, α and β are constants and satisfy α + β = 1; ΔEVO 排气过热度 =a1×(T dsh2 -d)+b1,ΔEVO 吸气过热度 =a2×(T) ssh3 -c)+b2, where a1, a2, b1, and b2 are constants.

[0016] In one or more embodiments of this application, the control unit is further configured to presume that heat exchanger clogging has occurred when the real-time outdoor fan current increase exceeds a set current threshold.

[0017] In one or more embodiments of this application, the control unit is configured to presume that the correction mode start-up conditions are met when the exhaust temperature difference between the first compressor and the second compressor is higher than a set exhaust temperature difference threshold.

[0018] In one or more embodiments of this application, it further includes: a gas connecting pipe, the two ends of which are respectively connected to the upper parts of the first gas-liquid separator and the second gas-liquid separator; and a liquid connecting pipe, the two ends of which are respectively connected to the lower parts of the first gas-liquid separator and the second gas-liquid separator.

[0019] This invention can effectively avoid flow deviation problems and improve the service life and operational stability of the compressor.

[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 for Figure 3 A magnified view of part B in the middle section;

[0029] Figure 8 for Figure 3 A magnified view of part C in the middle;

[0030] Figure 9 A schematic diagram of the refrigeration cycle of the outdoor unit in a refrigeration system provided in one or more embodiments of this application;

[0031] Figure 10 A schematic diagram of the structure of the outdoor unit in a refrigeration system provided in one or more embodiments of this application;

[0032] Figure 11 A flowchart of the control unit in a refrigeration system provided for one or more embodiments of this application;

[0033] Figure 12 A flowchart of the control unit in a refrigeration system provided for 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 flowchart of the control unit in a refrigeration system provided for one or more embodiments of this application;

[0037] Figure 16 A flowchart of the control unit in a refrigeration system provided for one or more embodiments of this application;

[0038] 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; and 102 is the switching valve. 103a, First outdoor heat exchanger; 103b, Second outdoor heat exchanger; 104, Outdoor fan; 105, Liquid-side shut-off valve; 106, Gas-side shut-off valve; 107, Distributor; 107a, One outlet of the distributor; 107b, Another outlet of the distributor; 107c, Inlet of the distributor; 108a, First gas-liquid separator; 108b, Second gas-liquid separator; 109a, First outdoor throttling element; 109b, Second outdoor... Throttling element; 110, High pressure sensor; 111a, First high pressure switch; 111b, Second high pressure switch; 112a, First compressor exhaust temperature sensor; 112b, Second compressor exhaust temperature sensor; 113a, First outlet pipe; 113b, Second outlet pipe; 114a, First oil return hole; 114b, Second oil return hole; 115a, First outdoor heat exchanger gas pipe temperature sensor; 115b, Second outdoor heat exchanger gas pipe temperature sensor; 116, Outdoor ambient temperature sensor; 117a, First outdoor heat exchanger liquid pipe temperature sensor; 117b, Second outdoor heat exchanger liquid pipe temperature sensor; 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

[0039] 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.

[0040] In the description of this application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0041] 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 the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. Throughout this application, unless otherwise specified, "plurality" means two or more.

[0042] 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.

[0043] 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" of 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] The refrigeration system 1 integrates a refrigeration cycle. The refrigeration cycle uses a compressor, condenser, throttling device, and evaporator. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation to cool or heat the indoor space.

[0048] 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.

[0049] The throttling device 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 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, refrigeration system 1 regulates the temperature of the indoor space.

[0050] 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 2 The 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.

[0051] 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).

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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; Figure 7 yes Figure 3 Enlarged view of section B; Figure 8 yes Figure 3 Enlarged view of part C in the middle.

[0056] 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, as well as a first outdoor heat exchanger 103a and a second outdoor heat exchanger 103b. The first outdoor heat exchanger 103a is equipped with a first outdoor throttling element 109a, and the second outdoor heat exchanger 103b is equipped with a second outdoor throttling element 109b. It can be configured according to... 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 scroll compressors, rotary compressors, screw compressors, etc. The speeds of the first compressor 100a and the second compressor 100b are controlled by frequency converters, 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 on the discharge side of the first compressor 100a and the second compressor 100b, and a low-pressure sensor 151 is also installed on the suction side of the first compressor 100a and the second compressor 100b.

[0057] The first outdoor heat exchanger 103a is equipped with a first outdoor heat exchanger gas pipe temperature sensor 115a and a first outdoor heat exchanger liquid pipe temperature sensor 117a, and the second outdoor heat exchanger 103b is equipped with a second outdoor heat exchanger gas pipe temperature sensor 115b and a second outdoor heat exchanger liquid pipe temperature sensor 117b.

[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 104 and a switching valve 102; the outdoor fan 104 may be an axial flow fan, a cross flow fan, or other optional fan type. The outdoor fan 104 is located near the first outdoor heat exchanger 103a or the second outdoor heat exchanger 103b. The first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b may 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] The switching valve 102 is taken as a four-way valve. The switching valve 102 is used to switch the flow direction of refrigerant in the refrigerant circuit. In this application, 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 100a, 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 first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b.

[0064] In heating operation, the outdoor unit can form a refrigerant circuit (hereinafter referred to as the heating cycle) for heating operation. One path from the liquid-side connecting pipe 31 to the gas-side connecting pipe 32 is sequentially connected to a first outdoor throttling element 109a, a first outdoor heat exchanger 103a, a switching valve 102 (e.g., one path of a four-way valve, exemplarily, the fluid passage between port E and port S), and a distributor 107. The other path is sequentially connected to a second outdoor throttling element 109b, a second outdoor heat exchanger 103b, a switching valve 102 (e.g., one path of a four-way valve, exemplarily, the fluid passage between port E and port S), and a distributor 107. The distributor 107 is in fluid communication with the switching valve 102. Downstream of distributor 107, one outlet of distributor 107 is sequentially connected to a first gas-liquid separator 108a, a first compressor 100a, a first oil separator 101a, and a 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 distributor 107 is sequentially connected to a second gas-liquid separator 108b, a second compressor 100b, a second oil separator 101b, and a switching valve 102 (e.g., the same passage of a four-way valve, exemplarily, the fluid passage between port D and port C).

[0065] That is, the high-temperature and high-pressure gaseous refrigerant discharged by the first compressor 100a and the second compressor 100b flows out through the first oil separator 101a and the second oil separator 101b, and the high-temperature and high-pressure gaseous refrigerant flowing out through the first oil separator 101a and the second oil separator 101b enters the indoor unit through the switching valve 102 and the gas-side shut-off valve 106. After sufficient heat exchange in the indoor unit, the high-temperature and high-pressure gaseous refrigerant is condensed into a high-temperature and high-pressure subcooled liquid refrigerant. It then flows through the liquid-side connecting pipe 31 and enters the outdoor unit via the liquid-side shut-off valve 105. The subcooled liquid refrigerant is throttled by the first outdoor throttling element 109a and the second outdoor throttling element 109b into a low-temperature and low-pressure two-phase refrigerant. The two-phase refrigerant evaporates into a low-temperature and low-pressure superheated gaseous refrigerant in the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b. The low-temperature and low-pressure superheated gaseous refrigerant flows out from the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b, returns to the distributor through the switching valve 102, and then enters the distributor evenly into the first gas-liquid separator and the second gas-liquid separator. Finally, it enters the suction end of the first compressor 100a and the second compressor 100b, completing a normal refrigerant cycle during heating operation.

[0066] During heating operation, the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b act as evaporators. The outdoor ambient temperature is maintained in an ideal state (relatively high). No dirt blockage occurs in the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b. The outdoor air flow meets the requirements. The evaporation capacity of the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b is sufficient. The refrigerant is a superheated gaseous refrigerant after passing through the evaporator, and there will be no liquid refrigerant deviation. The operating status of the first compressor 100a and the second compressor 100b is small. At this time, normal heating operation is performed.

[0067] During normal heating operation, the switching valve 102 (exemplarily a four-way valve) is in the ON state, the outdoor fan 104 is in the ON state (the fan speed is determined by the outdoor ambient temperature), the first outdoor throttling element 109a is in a throttling state, and the second outdoor throttling element 109b is in a throttling state. The frequencies of the first compressor 100a and the second compressor 100b are controlled according to their discharge pressures, that is, by controlling the frequencies of the first compressor 100a and the second compressor 100b, the discharge pressures of the first compressor 100a and the second compressor 100b are maintained at the target discharge pressures. The opening degree of the first outdoor throttling element 109a is controlled according to the exhaust superheat and intake superheat of the first outdoor heat exchanger 103a, and the opening degree of the second outdoor throttling element 109b is controlled according to the exhaust superheat and intake superheat of the second outdoor heat exchanger 103b. That is, by controlling the opening degree of the first outdoor throttling element 109a and the second outdoor throttling element 109b, the exhaust superheat and intake superheat of the first outdoor heat exchanger 103a are maintained at the target intake superheat and target exhaust superheat, and the exhaust superheat and intake superheat of the second outdoor heat exchanger 103b are maintained at the target intake superheat and target exhaust superheat.

[0068] The two outlets of distributor 107 (as shown in 107a and 107b in the figure) are designed to have the same flow rate.

[0069] 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.

[0070] 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.

[0071] 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 oil return hole 114a, and the bottom of the second outlet pipe 113b is provided with a second oil return hole 114b. Through the first 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 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.

[0072] In one or more embodiments of this application, the first housing 130a and the second housing 130b have the same shape and volume. 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. The diameters of the gas connecting pipe 140 and the liquid connecting pipe 150 can be larger than other pipes in the refrigeration system. When the gaseous or liquid refrigerant flows out of proportion, the gas connecting pipe 140 and the liquid connecting pipe 150 can play a role in quickly equalizing the liquid.

[0073] In one or more embodiments of this application, a first auxiliary oil return hole 115a, higher than the first oil return hole 114a, is further provided on the first outlet pipe 113a. In one or more embodiments of this application, the height difference between the first auxiliary oil return hole 115a and the first 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 and 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 and 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 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 oil return hole 114a is lower than the maximum liquid level height. For example, a relatively ideal preset refrigerant volume (less than 60% of the maximum refrigerant volume) can be set according to the capacity of the refrigeration system 1, ensuring stable operation of both the first compressor 100a and the second compressor 100b in the refrigeration system 1. The preset refrigerant height is calculated based on the ratio of the preset refrigerant volume to the cross-sectional area of ​​the first 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 predetermined position on the first outlet pipe 113a. Alternatively, multiple first auxiliary oil return holes 115a can be evenly distributed at equal intervals, with the sum of the preset refrigerant height and the maximum lubricating oil height as the total height.

[0074] In one or more embodiments of this application, the height difference between the second auxiliary oil return hole 115b and the second 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 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 oil return hole 114b is lower than the maximum liquid level height. For example, a relatively ideal preset refrigerant volume (less than 60% of the maximum refrigerant volume) can be set according to the capacity of the refrigeration system 1, allowing 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 predetermined position on the second outlet pipe 113b. Alternatively, multiple second auxiliary oil return holes 115b can be evenly distributed at equal intervals, with the sum of the preset refrigerant height and the maximum lubricating oil height as the total 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 104, 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 the refrigeration system has reached hundreds of kilograms. Since only one switching valve is installed, the switching valve must be set up to correspond with the distributor. However, it is difficult to ensure the similarity of pipe length and pipe diameter downstream of the corresponding distributor (such as a three-way pipe or three-way valve) during long-term use. In particular, there may be tiny impurities and contaminants in the refrigeration system. These substances will accumulate in the pipes near the distributor and gradually change the pipe diameter. In addition, if the evaporator of the outdoor heat exchanger is weak, the low-temperature and low-pressure gas-liquid two-phase refrigerant will not evaporate completely in the evaporator. The proportion of liquid phase in the refrigerant will be large, resulting in uneven liquid return from the two gas-liquid separators and the two compressors. The compressor connected to the gas-liquid separator with more liquid return will have more liquid return, and the compressor connected to the gas-liquid separator with less liquid return will have less liquid return. Over time, the operating difference between the two compressors will be very large, and the discharge temperature difference will also be large, which will significantly affect the performance and reliability of the compressor itself and the entire refrigeration system.

[0077] like Figure 9 and Figure 10 As 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 is communicatively connected to the outdoor unit.

[0078] Control unit 30 is configured to control the refrigeration system to perform heating operation (e.g. Figure 11 As shown in step S101, the operating frequency of the first compressor 100a and the second compressor 100b is controlled to maintain the target pressure (e.g., ...). Figure 11 As shown in step S102, the opening degree of the first outdoor throttling element 109a and the second outdoor throttling element 109b is controlled so that the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b are not lower than the target intake superheat and the target exhaust superheat (e.g. Figure 11 As shown in step S103, the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b is used to determine whether the conditions for starting the correction mode are met (e.g., ...). Figure 11 As shown in step S104), when the conditions for starting the correction mode are met, the heating operation is maintained (e.g., Figure 11 As shown in step S105), the target exhaust pressure is increased to generate a corrected target exhaust pressure (e.g., ...). Figure 11 (As shown in step S106), the target intake superheat and target exhaust superheat are increased to generate corrected target intake superheat and corrected target exhaust superheat (e.g., Figure 11As shown in step S107, the operating frequency of the first compressor 100a and the second compressor 100b is controlled to maintain the corrected target discharge pressure (e.g., Figure 11 As shown in step S108, the opening degree of the first outdoor throttling element 109a and the second outdoor throttling element 109b is controlled so that the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b are not lower than the corrected target intake superheat and the corrected target exhaust superheat (e.g. Figure 11 (as shown in step S109).

[0079] During heating operation, the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b act as evaporators. If the outdoor ambient temperature is very low, or if the first outdoor heat exchanger 103a and / or the second outdoor heat exchanger 103b becomes clogged, or if the air circulation guided by the outdoor fan 104 is insufficient, the evaporation capacity is very weak. The refrigerant becomes a two-phase refrigerant after passing through the evaporator, with a higher proportion of liquid phase. At this time, the first gas-liquid separator 108a and the second gas-liquid separator 108b, as well as the first compressor 100a and the second compressor 100b, will experience flow deviation. One compressor will return more liquid, while the other will return more gas, resulting in a significant difference in the operating states of the two compressors. Specifically, this manifests as a large difference in the exhaust temperature between the first compressor 100a and the second compressor 100b. The presence of flow deviation can be deduced based on the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b.

[0080] When a flow deviation occurs, the control unit 30 is configured to maintain heating operation and increase the target exhaust pressure to generate a corrected target exhaust pressure, increase the target suction superheat and target exhaust superheat to generate corrected target suction superheat and corrected target exhaust superheat, control the operating frequency of the first compressor 100a and the second compressor 100b to maintain the corrected target exhaust pressure, and control the opening degree of the first outdoor throttling element 109a and the second outdoor throttling element 109b to ensure that the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b are not lower than the corrected target suction superheat and corrected target exhaust superheat. On the one hand, by increasing the compressor frequency, the evaporation capacity of the outdoor heat exchanger is increased; on the other hand, by adjusting (reducing) the opening degree of the first outdoor throttling element 109a and the second outdoor throttling element 109b, the amount of evaporative refrigerant is reduced, the suction superheat and exhaust superheat of the refrigerant at the evaporator outlet are increased, and the fluctuations in the refrigeration system caused by the flow deviation problem are optimized and improved.

[0081] like Figure 12 As shown, the control unit 30 is also configured to control the outdoor fan 104 to operate at a target speed (e.g., when performing heating operation) based on the outdoor ambient temperature. Figure 12As shown in step S204, the target speed is negatively correlated with the outdoor ambient temperature; and when the conditions for starting the correction mode are met, the heating operation is maintained and the target speed is increased to generate the correction speed (e.g., ...). Figure 12 As shown in step S209), the outdoor fan 104 is controlled based on the corrected rotation speed (as shown in step S209). Figure 12 (As shown in step S212). The corrected speed can be the highest speed or the speed corresponding to the highest gear of the outdoor fan 104. The outdoor fan 104 operating at the corrected speed can increase the airflow and further improve the evaporation capacity of the evaporator.

[0082] like Figure 13 As shown, the control unit 30 is further configured to, after controlling the operating frequency of the first compressor 100a and the second compressor 100b based on the target exhaust pressure, controlling the opening degree of the first outdoor throttling element 109a and the second outdoor throttling element 109b based on the target intake superheat and the target exhaust superheat, and controlling the outdoor fan 104 based on the corrected speed, estimate whether the correction mode exit condition is met based on the exhaust temperature difference between the first compressor 100a and the second compressor 100b, the outdoor ambient temperature, and the real-time current increase of the outdoor fan 104. Figure 13 (as shown in step S313), and when the exit condition for the corrected mode is met, continue to perform heating operation (e.g. Figure 13 As shown in step S314, the operating frequency of the first compressor 100a and the second compressor 100b is controlled to maintain the target discharge pressure (e.g., Figure 13 As shown in step S315, the opening degree of the first outdoor throttling element 109a and the second outdoor throttling element 109b is controlled so that the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b are not lower than the target intake superheat and the target exhaust superheat (e.g. Figure 13 (as shown in step S316).

[0083] In one or more embodiments of this application, such as Figure 14 As shown, the control unit 30 is configured to ensure that the exhaust temperature difference between the first compressor 100a and the second compressor 100b is within a set temperature range (e.g., ...). Figure 14 As shown in step S401, the outdoor ambient temperature is not lower than the set ambient temperature threshold (e.g., ...). Figure 14 As shown in step S402), and when the current increase of the outdoor fan 104 in real time does not exceed the set current increase threshold (e.g., ... Figure 14 As shown in step S403), it is presumed that the exit conditions for the modified mode are met (e.g., Figure 14 (as shown in step S404).

[0084] In one or more embodiments of this application, such as Figure 15As shown, the control unit 30 is configured to perform the following steps when controlling the opening of the first outdoor throttling element 109a so that the first outdoor heat exchanger 103a meets the target intake superheat condition and the target exhaust superheat condition:

[0085] Step S501: Perform heating operation.

[0086] Step S502: Sample the detected temperature T of the gas pipe temperature sensor 115a of the first outdoor heat exchanger. g1 The temperature T detected by the temperature sensor 115b of the second outdoor heat exchanger pipe is sampled. g2 ;

[0087] Step S503: Obtain the detection pressure P of the low-pressure sensor 151. s ;

[0088] Step S504: Obtain the detection pressure P of the low-pressure sensor 151. s The corresponding saturation temperature T c_ps ;

[0089] Step S505: Calculate the first suction superheat T during heating operation. ssh1 Second intake superheat T ssh2 First inhalation superheat T ssh1 Satisfy T ssh1 =T g1 -T c_ps Second intake superheat T ssh2 Satisfy T ssh1 =T g2 -T c_ps ;

[0090] Step S506: Adjust the opening of the first outdoor throttling element 109a to achieve the first intake superheat T. ssh1 The second intake superheat should not be lower than the target intake superheat a℃. Adjust the opening of the second outdoor throttling element 109b to make the second intake superheat T... ssh2 Not lower than the target intake superheat a℃;

[0091] Step S507: Sample the detected temperature T of the first compressor exhaust temperature sensor 112a. d1 ;

[0092] Step S508: Sample the detected temperature T of the second compressor exhaust temperature sensor 112b. d2 ;

[0093] Step S509: Calculate the detection temperature T of the first compressor exhaust temperature sensor 112a. d1 The detection temperature T of the second compressor exhaust temperature sensor 112b d2 mean T dave ;

[0094] Step S510: Obtain the detection pressure P of the high-pressure sensor 110. d ;

[0095] Step S511: Obtain the detection pressure P of the high-pressure sensor 110. d The corresponding saturation temperature T c_pd ;

[0096] Step S512: Calculate the first exhaust superheat T during heating operation. dsh1 First exhaust superheat T dsh1 Satisfy T dsh1 =T dave -T c_pd ;

[0097] Step S513: Adjust the opening of the first outdoor throttling element 109a and the opening of the second outdoor throttling element 109b to make the first exhaust superheat T dsh1 Not lower than the target exhaust superheat b℃.

[0098] In one or more embodiments of this application, such as Figure 16 As shown, the control unit 30 is configured to perform the following steps when controlling the opening degree of the first outdoor throttling element 109a and the second outdoor throttling element 109b so that the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b are not lower than the corrected target intake superheat and the corrected target exhaust superheat:

[0099] Step S601: Maintain heating operation;

[0100] Step S602: Sample the detected temperature T of the gas pipe temperature sensor 115a of the first outdoor heat exchanger. g1 The temperature T detected by the temperature sensor 115b of the second outdoor heat exchanger pipe is sampled. g2 ;

[0101] Step S603: Obtain the detection pressure P of the low-pressure sensor 151. s ;

[0102] Step S604: Obtain the detection pressure P of the low-pressure sensor 151. s The corresponding saturation temperature T c_ps ;

[0103] Step S605: Calculate the third intake superheat T when executing the correction mode. ssh3 and the fourth intake superheat T ssh4 Third intake superheat T ssh3 Satisfy T ssh3 =T g1 -T c_ps Fourth intake superheat Tssh4 Satisfy T ssh4 =T g2 -T c_ps ;

[0104] Step S606: Adjust the opening of the first outdoor throttling element 109a to achieve the third intake superheat T. ssh3 The fourth intake superheat T is adjusted to a temperature not lower than the target intake superheat c℃. ssh4 Not lower than the corrected target intake superheat temperature (c℃);

[0105] Step S607: Sample the detected temperature T of the first compressor exhaust temperature sensor 112a. d1 ;

[0106] Step S608: Sample the detected temperature T of the second compressor exhaust temperature sensor 112b. d2 ;

[0107] Step S609: Calculate the detection temperature T of the first compressor exhaust temperature sensor 112a. d1 The detection temperature T of the second compressor exhaust temperature sensor 112b d2 mean T dave ;

[0108] Step S610: Obtain the detection pressure P of the high-pressure sensor 110. d ;

[0109] Step S611: Obtain the detection pressure P of the high-pressure sensor 110. d The corresponding saturation temperature T c_pd ;

[0110] Step S612: Calculate the second exhaust superheat T when executing the correction mode. dsh2 Second exhaust superheat T dsh2 Satisfy T dsh2 =T dave -T c_pd ;

[0111] Step S613: Adjust the opening of the first outdoor throttling element 109a and the opening of the second outdoor throttling element 109b to achieve the second exhaust superheat T when the correction mode is executed. dsh2 Not lower than the corrected target exhaust superheat d℃.

[0112] In one or more embodiments of this application, when adjusting the opening degree of the first outdoor throttling element 109a and the opening degree of the second outdoor throttling element 109b, the control unit 30 is configured to perform the following steps:

[0113] Set several consecutive adjustment cycles;

[0114] In the next adjustment cycle, the opening degree of the first outdoor throttling element 109a is the sum of the real-time opening degree of the first outdoor throttling element 109a in the current adjustment cycle and the set change ΔEVO.

[0115] The change ΔEVO is set to satisfy ΔEVO=α×ΔEVO 排气过热度 +β×ΔEVO 吸气过热度 Where α is the influence factor of exhaust superheat on the setpoint variation, and β is the influence factor of intake superheat on the setpoint variation, α and β are constants and satisfy α + β = 1; ΔEVO 排气过热度 =a1×(T dsh2 -d)+b1,ΔEVO 吸气过热度 =a2×(T) ssh3 -c)+b2, where a1, a2, b1, and b2 are constants.

[0116] In one or more embodiments of this application, the control unit 30 is further configured to presume that heat exchanger clogging has occurred when the real-time increase in the current of the outdoor fan 104 is higher than a set current threshold.

[0117] More specifically, after the refrigeration system starts operating, the control unit 30 collects parameters such as temperature, pressure, and current, including but not limited to the temperature T detected by the first compressor discharge temperature sensor 112a. d1 The temperature T detected by the second compressor exhaust temperature sensor 112b d2 The high pressure sensor 110 (i.e., the exhaust pressure detection device) detects the pressure P. d The temperature T detected by the temperature sensor 115a of the first outdoor heat exchanger gas pipe g1 The temperature T detected by the temperature sensor 115b of the second outdoor heat exchanger gas pipe g2 The low-pressure sensor 151 detects the pressure P. s The outdoor ambient temperature sensor 116 detects the temperature T. a Initial outdoor fan current 104 E fan0 Real-time outdoor fan current 104E fan1 The control unit 30 determines whether to execute heating operation based on the input command. If so, it executes heating operation; otherwise, it executes cooling operation. During heating operation, it controls the operating frequency of the first compressor 100a and the second compressor 100b according to the target discharge pressure. When the pressure P detected by the high-pressure sensor 110 (i.e., the discharge pressure detection device) reaches a certain value... d Below the target exhaust pressure P d0 At that time, control is executed to increase the operating frequency of the first compressor 100a and the second compressor 100b; when the pressure P detected by the high pressure sensor 110 (i.e., the exhaust pressure detection device) is... d Higher than the target exhaust pressure Pd0 At the same time, control is implemented to reduce the operating frequency of the first compressor 100a and the second compressor 100b; the operating frequencies of both the first compressor 100a and the second compressor 100b do not exceed the upper limit frequency H. zmax1 Where 2MPa≤P d0 ≤3.5MPa, 100Hz≤H zmax1 ≤180Hz.

[0118] The wind speed of outdoor fan 104 is determined by the outdoor ambient temperature T. a The decision is that different outdoor ambient temperatures correspond to different wind speeds; the lower the outdoor ambient temperature, the higher the wind speed of the outdoor fan 104.

[0119] The first outdoor throttling element 109a and the second outdoor throttling element 109b throttle the flow, controlling the opening degree of the first outdoor throttling element 109a to achieve the first suction superheat T of the first outdoor heat exchanger 103a. ssh1 ≥a℃, where T ssh1 =T g1 -T c_ps T c_ps The detection pressure P of the low-pressure sensor 151 s The corresponding saturation temperature, which simultaneously causes the first exhaust superheat T dsh1 ≥b℃; where T dsh1 =T dave -T c_pd ,T dave =(T d1 +T d2 ) / 2, T c_pd The detection pressure P of the high-pressure sensor 110 d The corresponding saturation temperature; correspondingly, controlling the opening of the second outdoor throttling element 109b to achieve the second suction superheat T of the second outdoor heat exchanger 103b. ssh2 ≥a℃, where T ssh2 =T g2 -T c_ps T c_ps The detection pressure P of the low-pressure sensor 151 s The corresponding saturation temperature, which simultaneously causes the first exhaust superheat T dsh1 ≥b℃; where T dsh1 =T dave -T c_pd ,T dave =(T d1 +T d2 ) / 2, T c_pd The detection pressure P of the high-pressure sensor 110 d The corresponding saturation temperatures; where 0℃≤a≤20℃, 10℃≤b≤70℃.

[0120] Further determination of whether there is a T d1 -T d2 <-m℃, or whether there is a T d1 -T d2 >m℃. When the outdoor ambient temperature is high, there is no dirt or blockage in the evaporator, and the airflow of the outdoor fan 104 is large, the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b have strong evaporation capacity. The two-phase refrigerant is completely evaporated in the evaporator, and the evaporator outlet is a superheated gaseous refrigerant, which enters the first gas-liquid separator 108a and the second gas-liquid separator 108b, the first compressor 100a and the second compressor 100b evenly. The first compressor 100a and the second compressor 100b operate in the same state, and the exhaust temperature difference between the first compressor 100a and the second compressor 100b is small. Even if the above conditions are not met, heating operation is still performed; where 5℃≤m≤40℃. However, as the outdoor ambient temperature drops significantly, the outdoor heat exchanger becomes clogged, or the airflow guided by the outdoor fan 104 decreases, the evaporator's evaporation capacity is greatly reduced. The two-phase refrigerant does not evaporate completely in the evaporator, resulting in a two-phase refrigerant at the evaporator outlet. The proportion of liquid refrigerant is relatively high, and it enters the two gas-liquid separators and the two compressors unevenly, causing a flow deviation phenomenon. One compressor returns more liquid, while the other compressor returns more gas. The two compressors have different operating states, resulting in a large difference in exhaust temperature. When the above conditions are met, the heating exhaust temperature correction mode control is executed.

[0121] Maintain heating operation and increase the target exhaust pressure to generate a corrected target exhaust pressure P. d1 Increase the target intake superheat and target exhaust superheat to generate corrected target intake superheat and corrected target exhaust superheat.

[0122] The operating frequency of the first compressor 100a and the second compressor 100b is controlled according to the target discharge pressure. When the pressure detected by the high-pressure sensor 110 is lower than the target discharge pressure P, d1 At that time, control is executed to increase the operating frequency of the first compressor 100a and the second compressor 100b; when the pressure P detected by the high pressure sensor 110... d Pressure P higher than the target pressure d1 At the same time, control is implemented to reduce the operating frequency of the first compressor 100a and the second compressor 100b; the operating frequencies of both the first compressor 100a and the second compressor 100b do not exceed the upper limit frequency H in the heating exhaust temperature correction mode. zmax2 Where 2.5MPa≤Pd1≤4.0MPa.

[0123] The wind speed of outdoor fan 104 is increased to the corrected wind speed, such as the highest setting.

[0124] The first outdoor throttling element 109a and the second outdoor throttling element 109b throttle the air, controlling the opening of the first outdoor throttling element 109a so that the third intake superheat T of the first outdoor heat exchanger 103a in the heating exhaust temperature correction mode is controlled. ssh3 ≥c℃, where T ssh3 =T g1 -T c_ps , T c_ps The detection pressure P of the low-pressure sensor 151 s The corresponding saturation temperature, which simultaneously causes the second exhaust superheat T dsh2 ≥d℃; where T dsh2 =T dave -T c_pd ,T dave =(T d1 +T d2 ) / 2, T c_pd The detection pressure P of the high-pressure sensor 110 d The corresponding saturation temperature; correspondingly, controlling the opening of the second outdoor throttling element 109b so that the fourth suction superheat T of the second outdoor heat exchanger 103b in the heating exhaust temperature correction mode. ssh4 ≥c℃, where T ssh4 =T g2 -T c_ps , T c_ps The detection pressure P of the low-pressure sensor 151 s The corresponding saturation temperature, which simultaneously causes the second exhaust superheat T dsh2 ≥d℃; where T dave =(T d1 +T d2 ) / 2, T c_pd The detection pressure P of the high-pressure sensor 110 d The corresponding saturation temperatures; where 0℃≤c≤25℃, 20℃≤d≤80℃.

[0125] Further determine whether the following condition is met simultaneously: -m≤T d1 -T d2 ≤m;T a ≥e℃;E fan1 -E fan0 When all three conditions are met, it indicates that the evaporator has a high evaporation capacity, the two compressors are operating in the same state, the exhaust temperature difference is small, the heating exhaust temperature correction mode ends, and normal heating operation resumes. The preferred values ​​are -30℃≤e≤60℃ and -100≤f≤100.

[0126] 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.

[0127] 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; First outdoor heat exchanger; The first outdoor throttling element is provided in correspondence with the first outdoor heat exchanger; Second compressor; Second outdoor heat exchanger; The second outdoor throttling element is provided in correspondence with the second outdoor heat exchanger; 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, the first gas-liquid separator being disposed on the suction side of the first compressor; and A second gas-liquid separator is connected to another outlet of the distributor, and the second gas-liquid separator is disposed on the suction side of the second compressor; Its characteristic is that it further includes: The control unit is configured to, during heating operation, control the operating frequency of the first compressor and the second compressor to maintain the target discharge pressure, control the opening degree of the first outdoor throttling element and the second outdoor throttling element to ensure that the first outdoor heat exchanger and the second outdoor heat exchanger are not lower than the target suction superheat and the target discharge superheat; estimate whether the correction mode start-up conditions are met based on the discharge temperature difference between the first compressor and the second compressor; and, when the correction mode start-up conditions are met, maintain heating operation and increase the target discharge pressure to generate a corrected target discharge pressure, increase the target suction superheat and the target discharge superheat to generate corrected target suction superheat and corrected target discharge superheat, control the operating frequency of the first compressor and the second compressor to maintain the corrected target discharge pressure, and control the opening degree of the first outdoor throttling element and the second outdoor throttling element to ensure that the first outdoor heat exchanger and the second outdoor heat exchanger are not lower than the corrected target suction superheat and the corrected target discharge superheat. The control unit is configured to presume that the correction mode exit condition is met when the exhaust temperature difference between the first compressor and the second compressor is within a set temperature range, the outdoor ambient temperature is not lower than a set ambient temperature threshold, and the real-time current increase of the outdoor fan is not higher than a set current increase threshold.

2. The refrigeration system according to claim 1, characterized in that, The outdoor unit also includes: An outdoor fan is provided, which is located near the first outdoor heat exchanger or the second outdoor heat exchanger. The control unit is further configured to control the outdoor fan to operate at a target speed based on the outdoor ambient temperature during heating operation; the target speed is negatively correlated with the outdoor ambient temperature; when the correction mode activation conditions are met, the control unit maintains heating operation and increases the target speed to generate a correction speed; and controls the outdoor fan based on the correction speed.

3. The refrigeration system according to claim 2, characterized in that, The control unit is further configured to, after controlling the operating frequency of the first compressor and the second compressor based on the corrected target exhaust pressure, controlling the opening degree of the first outdoor throttling element and the second outdoor throttling element based on the corrected target intake superheat and the corrected target exhaust superheat, and controlling the outdoor fan based on the corrected speed; further, to estimate whether the correction mode exit condition is met based on the exhaust temperature difference between the first compressor and the second compressor, the outdoor ambient temperature, and the real-time current increase of the outdoor fan; and, if the correction mode exit condition is met, to maintain heating operation, control the operating frequency of the first compressor and the second compressor to maintain the target exhaust pressure, and control the opening degree of the first outdoor throttling element and the second outdoor throttling element to ensure that the first outdoor heat exchanger and the second outdoor heat exchanger are not lower than the target intake superheat and the target exhaust superheat.

4. The refrigeration system according to claim 1, characterized in that, The control unit is configured to perform the following steps when controlling the opening of the first outdoor throttling element so that the first outdoor heat exchanger meets the target intake superheat condition and the target exhaust superheat condition: Execute heating operation; The temperature T detected by the temperature sensor of the gas pipe of the first outdoor heat exchanger is sampled. g1 The temperature T detected by the temperature sensor of the second outdoor heat exchanger pipe is sampled. g2 ; Obtain the detection pressure P of the low-pressure sensor s ; Obtain the detection pressure P of the low-pressure sensor s The corresponding saturation temperature T c_ps ; Calculate the first intake superheat T during heating operation. ssh1 Second intake superheat T ssh2 First inhalation superheat T ssh1 Satisfy T ssh1 = T g1 -T c_ps Second intake superheat T ssh2 Satisfy T ssh2 = T g2 -T c_ps ; Adjusting the opening of the first outdoor throttling element to achieve the first intake superheat T ssh1 The intake superheat should not be lower than the target intake superheat a℃. Adjust the opening of the second outdoor throttling element so that the second intake superheat T is not lower than the target intake superheat a℃. ssh2 Not lower than the target intake superheat a℃; The temperature T detected by the first compressor exhaust temperature sensor. d1 ; The temperature T detected by the second compressor exhaust temperature sensor. d2 ; Calculate the detected temperature T of the first compressor exhaust temperature sensor. d1 The detection temperature T of the second compressor exhaust temperature sensor d2 The mean T dave ; Obtain the detection pressure P of the high-pressure sensor d ; Obtain the detection pressure P of the high-pressure sensor d The corresponding saturation temperature T c_pd ; Calculate the first exhaust superheat T during heating operation. dsh1 First exhaust superheat T dsh1 Satisfy T dsh1 =T dave -T c_pd ; Adjusting the opening degree of the first outdoor throttling element and the second outdoor throttling element to achieve the first exhaust superheat T dsh1 Not lower than the target exhaust superheat b℃.

5. The refrigeration system according to claim 4, characterized in that, The control unit is configured to perform the following steps when controlling the opening of the first outdoor throttling element and the second outdoor throttling element so that the first outdoor heat exchanger and the second outdoor heat exchanger are not lower than the corrected target intake superheat and the corrected target exhaust superheat: Maintain heating operation; The temperature T detected by the temperature sensor of the gas pipe of the first outdoor heat exchanger is sampled. g1 The temperature T detected by the temperature sensor of the second outdoor heat exchanger pipe is sampled. g2 ; Obtain the detection pressure P of the low-pressure sensor s ; Obtain the detection pressure P of the low-pressure sensor s The corresponding saturation temperature T c_ps ; Calculate the third intake superheat T when executing the correction mode. ssh3 and the fourth intake superheat T ssh4 Third intake superheat T ssh3 Satisfy T ssh3 = T g1 -T c_ps Fourth intake superheat T ssh4 Satisfy T ssh4 = T g2 -T c_ps ; Adjusting the opening of the first outdoor throttling element to achieve the third intake superheat T ssh3 The fourth intake superheat T is adjusted to be no less than the target intake superheat c℃. ssh4 Not lower than the corrected target intake superheat temperature (c℃); The temperature T detected by the first compressor exhaust temperature sensor. d1 ; The temperature T detected by the second compressor exhaust temperature sensor. d2 ; Calculate the detected temperature T of the first compressor exhaust temperature sensor. d1 The detection temperature T of the second compressor exhaust temperature sensor d2 The mean T dave ; Obtain the detection pressure P of the high-pressure sensor d ; Obtain the detection pressure P of the high-pressure sensor d The corresponding saturation temperature T c_pd ; Calculate the second exhaust superheat T when executing the correction mode. dsh2 Second exhaust superheat T dsh2 Satisfy T dsh2 =T dave -T c_pd ; Adjusting the opening of the first outdoor throttling element and the opening of the second outdoor throttling element to achieve the second exhaust superheat T when executing the correction mode. dsh2 Not lower than the corrected target exhaust superheat d℃.

6. The refrigeration system according to claim 5, characterized in that, When adjusting the opening degree of the first outdoor throttling element and the second outdoor throttling element, the control unit is configured to perform the following steps: Set several consecutive adjustment cycles; In the next adjustment cycle, the opening degree of the first outdoor throttling element is the sum of the real-time opening degree of the first outdoor throttling element in the current adjustment cycle and the set change ΔEVO. Where the change ΔEVO is set to satisfy ,in This is the factor influencing the change in the setpoint by the exhaust superheat. The effect factor of intake superheat on the change in setpoint. and It is a constant and satisfies ; , , , , and It is a constant.

7. The refrigeration system according to claim 1, characterized in that, The control unit is also configured to presume heat exchanger blockage when the real-time outdoor fan current increase exceeds the set current increase threshold.

8. The refrigeration system according to any one of claims 1 to 7, characterized in that, The control unit is configured to presume that the correction mode activation condition is met when the exhaust temperature difference between the first compressor and the second compressor is higher than a set exhaust temperature difference threshold.

9. The refrigeration system according to claim 1, characterized in that, Also includes: A gas connecting pipe, the two ends of which are respectively connected to the upper parts of the first gas-liquid separator and the second gas-liquid separator; and A liquid connecting pipe, the two ends of which are respectively connected to the lower parts of the first gas-liquid separator and the second gas-liquid separator.

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