Refrigeration system

Abstract

The refrigeration system comprises an outdoor unit; the outdoor unit comprises a first compressor and a second compressor. First and second outdoor heat exchangers; a first outdoor throttling element and a second outdoor throttling element; a switching valve; a distributor, a first gas-liquid separator and a second gas-liquid separator; the control part controls the operation frequency of the first compressor and the second compressor during heating so as to keep the target exhaust pressure, and controls 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 suction and exhaust superheat degree. Presuming whether a correction mode starting condition is met or not according to the exhaust temperature difference between the first compressor and the second compressor; if yes, heating is kept, the target exhaust pressure is increased to generate corrected target exhaust pressure, the target suction and exhaust superheat degree is increased to generate corrected target suction and exhaust superheat degree, and the operation frequency of the first compressor and the operation frequency of the second compressor are controlled to be kept at the corrected target exhaust pressure; the opening degrees of the first and second outdoor throttling elements are controlled so that the first and second outdoor heat exchangers are not lower than the corrected target suction and exhaust superheat degrees; the problem of bias current can be solved.

Description

Technical Field

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

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

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

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

[0005] However, when only one compressor is provided, the above-mentioned combined gas-liquid separator can keep the liquid level in multiple gas-liquid separators uniform. However, for modular outdoor units, there will be a hardware design that matches a four-way valve with two or more compressors, which requires the design of a distributor upstream of multiple gas-liquid separators. However, from a manufacturing perspective, it is difficult to ensure that the piping of multiple gas-liquid separators is completely consistent. The pipelines between the distributor and multiple gas-liquid separators, and the pipelines and pipe lengths between multiple gas-liquid separators and multiple compressors may not be consistent. In addition, the two outlets of the distributor may be tilted during processing, which will cause the two gas-liquid separators and two compressors to have flow deviation under the influence of factors such as pressure loss and inertia. From an installation perspective, it is also difficult to ensure that the installation height is consistent. From a usage perspective, if the evaporation capacity of the outdoor heat exchanger serving as the evaporator is weak (for example, when the indoor ambient temperature is too low during refrigeration operation, or the evaporator is The outdoor heat exchanger is dirty and blocked; when the heating operation is executed, the outdoor ambient temperature is too low, the outdoor heat exchanger is frosted or dirty, the evaporation area of ​​the outdoor heat exchanger is too small, etc.), which will cause the low-temperature and low-pressure gas-liquid two-phase refrigerant to be incompletely evaporated in the evaporator, and the proportion of liquid phase in the refrigerant is large. This will also cause uneven liquid return of the two gas-liquid separators and the two compressors. The compressor connected to the gas-liquid separator with more liquid return has more liquid return, and the compressor connected to the gas-liquid separator with less liquid return has less liquid return. After a long time, the operation of the two compressors is very different, and the exhaust temperature difference is also very large, which has a great impact on the performance and reliability of the compressor body and the entire refrigeration system. Summary of the invention

[0006] In view of the problem that the evaporation capacity of the outdoor heat exchanger serving as an evaporator is weak, which will lead to incomplete evaporation of the low-temperature and low-pressure gas-liquid two-phase refrigerant in the evaporator, a large proportion of liquid phase in the refrigerant, and uneven liquid return of two gas-liquid separators and two compressors, resulting in a significant impact on the performance and reliability of the compressor body and the entire refrigeration system, the present 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 respectively connected to the first compressor and the second compressor, a distributor connected to the switching valve, a first gas-liquid separator connected to one outlet of the distributor, and a second gas-liquid separator connected to another outlet of the distributor.

[0008] In one or more embodiments of the present application, the refrigeration system also includes a control unit, which is configured to control the operating frequency of the first compressor and the second compressor to maintain a target exhaust pressure when performing heating operation, 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 suction superheat and the target exhaust superheat; infer whether the correction mode start condition is met based on the exhaust temperature difference between the first compressor and the second compressor; and when the correction mode start condition is met, maintain the heating operation and increase the target exhaust pressure to generate a corrected target exhaust pressure, increase the target suction superheat and the target exhaust superheat to generate a corrected target suction superheat and a corrected target exhaust superheat, control the operating frequency of the first compressor and the second compressor to maintain the corrected 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 corrected target suction superheat and the corrected target exhaust superheat.

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

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

[0011] In one or more embodiments of the present application, the control unit is also configured to control the operating frequencies of the first compressor and the second compressor based on the corrected target exhaust pressure, control the openings of the first outdoor throttling element and the second outdoor throttling element based on the corrected target suction superheat and the corrected target exhaust superheat, and control 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 outdoor fan current increase; and when the correction mode exit condition is met, keep executing heating operation, control the operating frequencies of the first compressor and the second compressor to maintain the target exhaust pressure, and control the openings 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 suction superheat and the target exhaust superheat.

[0012] In one or more embodiments of the present application, the control unit is configured to presume that the correction mode exit condition is satisfied 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 outdoor fan current increase is not higher than a set current increase threshold.

[0013] In one or more embodiments of the present application, 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 suction superheat condition and the target exhaust superheat condition: performing heating operation; sampling the detection temperature T of the gas pipe temperature sensor of the first outdoor heat exchanger; g1 , sample the detected temperature T of the gas pipe temperature sensor of the second outdoor heat exchanger g2 ; Get the detection pressure P of the low pressure sensor s ; Get the detection pressure P of the low pressure sensor s The corresponding saturation temperature T c_ps Calculate the first suction superheat T when performing heating operation ssh1 and the second suction gas superheat T ssh2 , first suction superheat T ssh1 Meet T ssh1 =T g1 -T c_ps , Second suction superheat T ssh2 Meet T ssh2 =T g2 -T c_ps ; Adjust the opening of the first outdoor throttling element so that the first suction superheat T ssh1 The second suction superheat is not lower than the target suction superheat a℃, and the opening of the second outdoor throttling element is adjusted to make the second suction superheat T ssh2 Not less than the target suction superheat a℃; sample the detection temperature T of the first compressor exhaust temperature sensor d1 ; Sample the detection temperature T of the second compressor exhaust temperature sensor d2 ; Calculate the detection temperature T of the first compressor exhaust temperature sensor d1 and the detected temperature T of the second compressor exhaust temperature sensor d2 The mean value T dave ; Get the detection pressure P of the high pressure sensor d ; Get the detection pressure P of the high pressure sensor d The corresponding saturation temperature T c_pd Calculate the first exhaust superheat T when performing heating operation dsh1 , first exhaust gas superheat T dsh1 Meet T dsh1 =T dave -T c_pd; Adjust the opening of the first outdoor throttling element and the opening of the second outdoor throttling element so that the first exhaust superheat T dsh1 Not less than the target exhaust superheat b℃.

[0014] In one or more embodiments of the present 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 modified target suction superheat and the modified target exhaust superheat: maintaining heating operation; sampling the detected temperature T of the gas pipe temperature sensor of the first outdoor heat exchanger; g1 , sample the detected temperature T of the gas pipe temperature sensor of the second outdoor heat exchanger g2 ; Get the detection pressure P of the low pressure sensor s ; Get the detection pressure P of the low pressure sensor s The corresponding saturation temperature T c_ps ; Calculate the third suction superheat T when executing the correction mode ssh3 And the fourth suction superheat T ssh4 , the third suction superheat T ssh3 Meet T ssh3 =T g1 -T c_ps , the fourth suction superheat T ssh4 Meet T ssh4 =T g2 -T c_ps ; Adjust the opening of the first outdoor throttling element so that the third suction superheat T ssh3 The opening of the second outdoor throttling element is adjusted so that the fourth suction superheat T ssh4 Not less than the corrected target suction superheat c℃; sample the detection temperature T of the first compressor exhaust temperature sensor d1 ; Sample the detection temperature T of the second compressor exhaust temperature sensor d2 ; Calculate the detection temperature T of the first compressor exhaust temperature sensor d1 and the detected temperature T of the second compressor exhaust temperature sensor d2 The mean value T dave ; Get the detection pressure P of the high pressure sensor d ; Get 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 , the second exhaust gas superheat T dsh2 Meet T dsh2 =T dave -T c_pd ; Adjust the opening of the first outdoor throttling element and the opening of the second outdoor throttling element so that the second exhaust gas superheat T when executing the correction modedsh2 Not less than the corrected target exhaust superheat d℃.

[0015] In one or more embodiments of the present application, when adjusting the opening of the first outdoor throttling element and the opening of the second outdoor throttling element, the control unit is configured to perform the following steps: setting a number of consecutive adjustment cycles; the opening of the first outdoor throttling element in the next adjustment cycle is the sum of the real-time opening 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 set change, β is the influence factor of suction superheat on the set change, α and β are constants and satisfy α+β=1; ΔEVO 排气过热度 =a 1 ×(T dsh2 -d)+b 1 , ΔEVO 吸气过热度 =a 2 ×(T ssh3 -c)+b 2 , a 1 、a 2 , b 1 and b 2 is a constant.

[0016] In one or more embodiments of the present application, the control unit is further configured to infer that the heat exchanger is dirty and blocked when the real-time increase in the outdoor fan current is higher than a set current threshold.

[0017] In one or more embodiments of the present application, the control unit is configured to infer that the correction mode start condition is satisfied when the exhaust gas temperature difference between the first compressor and the second compressor is higher than a set exhaust gas temperature difference threshold.

[0018] In one or more embodiments of the present application, it 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.

[0019] The present invention can effectively avoid the problem of biased flow and improve the service life and operating stability of the compressor.

[0020] After reading the specific embodiments of the present invention in conjunction with the accompanying drawings, other features and advantages of the present invention will become more clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

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

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

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

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

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

[0027] Figure 6 for Figure 3 A partial enlarged schematic diagram of the middle A part;

[0028] Figure 7 for Figure 3 A partial enlarged schematic diagram of the middle B part;

[0029] Figure 8 for Figure 3 A partial enlarged schematic diagram of the middle C part;

[0030] Fig. 9 A schematic diagram of a refrigeration cycle of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0031] Fig.10 A schematic diagram of the structure of an outdoor unit in a refrigeration system provided in one or more embodiments of the present application;

[0032] Fig.11 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0033] Fig.12 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0034] Fig.13 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0035] Fig.14 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0036] Fig.15 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0037] Fig.16 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0038] In the figure, 1, refrigeration system; 10, outdoor unit; 12, outdoor unit; 20, indoor unit; 22, indoor unit; 24, indoor unit; 200, indoor heat exchanger; 201, indoor electronic expansion valve; 30, control unit; 31, liquid side connecting pipe; 32, gas side connecting pipe; 100a, first compressor; 100b, second compressor; 101a, first oil separator; 101b, second oil separator; 102, switching valve; 103a, first outdoor heat exchanger; 103b, second outdoor heat exchanger; 104, outdoor fan; 105, liquid side shutoff valve; 106, gas side shutoff valve; 107, distributor; 107a, one outlet of distributor; 107b, another outlet of distributor; 107c, inlet of distributor; 108a, first gas-liquid separator; 108b, second gas-liquid separator; 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 shell; 130b, second shell; 131a, first inlet pipe; 131b, second inlet pipe; 140, gas connecting pipe; 150, liquid connecting pipe; 150a, first capillary tube; 150b, second capillary tube; 151, low pressure sensor. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

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

[0041] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0042] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0043] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0044] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0045] Figure 1 A schematic diagram showing the structure of a refrigeration system 1 provided in one or more embodiments of the present invention; Figure 2 An example of a refrigerant circuit formed by the refrigeration system 1 according to the embodiment of the present invention is shown.

[0046] The refrigeration system 1 is installed in buildings such as apartments, hotels, office buildings, and houses, etc. The refrigeration system 1 is configured to selectively perform a heating operation or a cooling operation.

[0047] A refrigeration cycle is integrated in the refrigeration system 1. A compressor, a condenser, a throttling device and an evaporator are used in the refrigeration cycle. The refrigeration cycle includes a series of processes involving compression, condensation, expansion and evaporation to cool or heat the indoor space.

[0048] From a principle perspective, low-temperature, low-pressure refrigerant enters the compressor, which compresses it into high-temperature, high-pressure refrigerant gas and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and the heat is released to the surrounding environment through the condensation process.

[0049] The throttling device expands the high-temperature and high-pressure liquid refrigerant condensed in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the refrigerant expanded in the throttling device and returns the refrigerant gas in a low-temperature and low-pressure state to the compressor. The evaporator can achieve a refrigeration effect by utilizing the latent heat of evaporation of the refrigerant to exchange heat with the material to be cooled. In the entire cycle, the refrigeration system 1 can adjust the temperature of the indoor space.

[0050] The refrigeration system 1 includes an outdoor unit and an indoor unit connected to each other. Figure 1 The figure shows a combination of two outdoor units (10, 12) and three indoor units (20, 22, 24). Figure 2 The combination of two outdoor units (10, 12) and five indoor units (20, 22, 24, 26, 28) is shown in FIG. In the present application, the number of outdoor units and indoor units is not particularly limited. Figure 1 and Figure 2 In the same manner as shown in the indoor unit and the outdoor unit, only one indoor unit and one outdoor unit are arranged in a refrigeration system 1, or multiple indoor units and multiple outdoor units are arranged.

[0051] The indoor unit is provided with an indoor heat exchanger (such as Figure 2 200) and an indoor throttling device (such as an indoor electronic expansion valve, such as Figure 2 201).

[0052] The indoor unit and the outdoor unit are connected by a liquid-side communication pipe 31 and a gas-side communication pipe 32. The liquid-side communication pipe 31 and the gas-side communication pipe 32 are used to allow the refrigerant to flow so that the refrigerant can form a refrigerant circuit and circulate therein.

[0053] In one or more embodiments of the present application, a liquid-side shutoff valve 105 is provided on the liquid-side connecting pipe 31, and a gas-side shutoff valve 106 is provided on the gas-side connecting pipe 32. The liquid-side shutoff valve 105 can shut off the fluid passage in the liquid-side connecting pipe 31 or, when the opening is minimum, is close to shutting off the fluid passage in the liquid-side connecting pipe 31, and the gas-side shutoff valve 106 can shut off the fluid passage in the gas-side connecting pipe 32 or, when the opening is minimum, is close to shutting off the fluid passage in the gas-side connecting pipe 32.

[0054] The basic structure and function of the outdoor unit are described exemplarily below. The number of outdoor units can be expanded to multiple, each of which constitutes a module and operates in a group manner.

[0055] Figure 3 It is a schematic diagram of the structure of the outdoor unit; Figure 4 It is a schematic diagram of the refrigeration cycle when the outdoor unit performs cooling operation; Figure 5 It is a schematic diagram of the refrigeration cycle when the outdoor unit performs heating operation; Figure 6 yes Figure 3 An enlarged view of part A in FIG. Figure 7 yes Figure 3 Enlarged view of middle part B; Figure 8 yes Figure 3 Enlarged view of part C in the middle.

[0056] In one or more embodiments of the present application, the outdoor unit of the refrigeration system 1 refers to a part of the refrigeration cycle including a compressor and an outdoor heat exchanger 103, and the outdoor unit can perform heating operation or cooling operation on the outdoor side to provide energy for increasing the indoor temperature or reducing the indoor temperature to the indoor unit. Figures 3 to 6As shown, the outdoor unit is provided with a first compressor 100a and a second compressor 100b, and is also provided with a first outdoor heat exchanger 103a and a second outdoor heat exchanger 103b. The first outdoor heat exchanger 103a is correspondingly provided with a first outdoor throttling element 109a, and the second outdoor heat exchanger 103b is correspondingly provided with a second outdoor throttling element 109b; Figures 3 to 6 In the same manner as the first compressor 100a and the second compressor 100b shown, more compressors are arranged in the outdoor unit. The first compressor 100a and the second compressor 100b are configured to suck in and compress the refrigerant into a high temperature and high pressure state. The types of the first compressor 100a and the second compressor 100b are not further limited here, for example, they can be a scroll compressor, a rotor compressor, a screw compressor, etc. The speeds of the first compressor 100a and the second compressor 100b are controlled by a frequency converter, and the first compressor 100a and the second compressor 100b can operate independently. The discharge end of the first compressor 100a is provided with a first high pressure switch 111a, and the discharge end of the second compressor 100b is provided with a second high pressure switch 111b. The discharge side of the first compressor 100a and the second compressor 100b is also provided with a high pressure sensor 110, and the suction side of the first compressor 100a and the second compressor 100b is also provided with a low pressure sensor 151.

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

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

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

[0060] An outdoor fan 104 and a switching valve 102 may also be provided in the outdoor unit; wherein the outdoor fan 104 may be an axial flow fan, a cross flow fan or other optional fan forms. The outdoor fan 104 is provided 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 is also provided with a first oil separator 101a and a second oil separator 101b. The first oil separator 101a is used to separate the lubricating oil from the high-temperature refrigerant vapor when the mixture of the lubricating oil and the refrigerant leaves the compressor. The second oil separator 101b is used to separate the lubricating oil from the high-temperature refrigerant vapor when the mixture of the lubricating oil and the refrigerant leaves the compressor. The first oil separator 101a is arranged in the pipeline between the first compressor 100a and the condenser. The flow velocity of the high-pressure refrigerant in the first oil separator 101a and the second oil separator 101b is reduced, so that the lubricating oil is captured in the first oil separator 101a and the second oil separator 101b. The lubricating oil with a higher density is separated from the refrigerant vapor and falls to the bottom of the first oil separator 101a and the second oil separator 101b. The lubricating oil collected in the first oil separator 101a and the second oil separator 101b returns to the first compressor 100a and the second compressor 100b through the first capillary tube 150a and the second capillary tube 150b respectively. The diameter and length of the first capillary tube 150a and the second capillary tube 150b can be used to adjust the return oil amount of the lubricating oil. A solenoid valve 109 is also provided downstream of the first oil separator 101a and the second oil separator 101b.

[0062] The switching valve 102 is exemplified by a four-way valve. The switching valve 102 is a valve used to switch the flow direction of the refrigerant in the refrigerant circuit. In the present application, there is only one switching valve 102 in one outdoor unit.

[0063] In cooling operation, the outdoor unit can form a refrigerant circuit for cooling operation (hereinafter referred to as a refrigeration cycle), wherein the switching valve 102 (for example, one passage of a four-way valve, illustratively, the fluid passage between the C port and the S port) and the distributor 107 are sequentially connected from the gas-side connecting pipe 32 to the liquid-side connecting pipe 31. The distributor 107 (the inlet is shown as 107c in the figure) is in fluid communication with the switching valve 102. Downstream of the distributor 107, that is, one outlet of the distributor 107 is connected to the first gas-liquid separator 108a and the first compressor 100a in sequence, and the other outlet of the distributor 107 is connected to the second gas-liquid separator 108b and the second compressor 100b in sequence; the mixture of refrigerant and lubricating oil after flowing out of the first compressor 100a enters the first oil separator 101a, and after the first oil separator 101a, the refrigerant is again merged into the switching valve 102 (for example, another passage of the four-way valve, exemplarily the fluid passage between the D port and the E port); the mixture of refrigerant and lubricating oil after flowing out of the second compressor 100b enters the second oil separator 101b, and after the second oil separator 101b, the refrigerant is again merged into the switching valve 102 (for example, another passage of the four-way valve, exemplarily the fluid passage between the D port and the E port); the refrigerant flowing out of the switching valve 102 enters the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b again.

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

[0065] That is, the high-temperature and high-pressure gaseous refrigerant discharged from 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 of the first oil separator 101a and the second oil separator 101b passes through the switching valve 102 and the gas side shut-off valve 106 and enters the indoor unit. 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 supercooled liquid refrigerant, and then flows through the liquid side connecting pipe 31, and enters the outdoor unit through the liquid side shut-off valve 105. The supercooled 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 of the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b, and returns to the distributor through the switching valve 102. The superheated gaseous refrigerant evenly enters the first gas-liquid separator and the second gas-liquid separator through the distributor, and then enters the suction end of the first compressor 100a and the second compressor 100b, completing a normal refrigerant cycle during heating operation.

[0066] When performing 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), the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b are not dirty or blocked, the outdoor air flow meets the needs, 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 states of the first compressor 100a and the second compressor 100b are slightly different, and normal heating operation is performed at this time.

[0067] When performing 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 wind speed is determined by the outdoor ambient temperature), the first outdoor throttling element 109a is in the throttling state, and the second outdoor throttling element 109b is in the throttling state. The frequencies of the first compressor 100a and the second compressor 100b are controlled according to the exhaust pressures of the first compressor 100a and the second compressor 100b, that is, the exhaust pressures of the first compressor 100a and the second compressor 100b are maintained at the target exhaust pressures by controlling the frequencies of the first compressor 100a and the second compressor 100b. The opening of the first outdoor throttling element 109a is controlled according to the exhaust superheat and suction superheat of the first outdoor heat exchanger 103a, and the opening of the second outdoor throttling element 109b is controlled according to the exhaust superheat and suction superheat of the second outdoor heat exchanger 103b. That is, by controlling the opening of the first outdoor throttling element 109a and the opening of the second outdoor throttling element 109b, the exhaust superheat and suction superheat of the first outdoor heat exchanger 103a are maintained at the target suction superheat and target exhaust superheat, and the exhaust superheat and suction superheat of the second outdoor heat exchanger 103b are maintained at the target suction superheat and target exhaust superheat.

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

[0069] The first gas-liquid separator 108a has a first shell 130a. The upper part of the first shell 130a is provided with a first inlet pipe 131a inserted therein and the inlet is located at the upper part of the first shell 130a. The first shell 130a is also provided with a first outlet pipe 113a, which is close to the bottom of the first shell 130a and bent into a roughly U-shape, and the outlet of the first outlet pipe 113a extends outward from the upper part of the first shell 130a. The first outlet pipe 113a is fluidically connected to the first compressor 100a.

[0070] The second gas-liquid separator 108b has a second shell 130b. The upper part of the second shell 130b is provided with a second inlet pipe 131b inserted therein and the inlet is located at the upper part of the second shell 130b. The second shell 130b is also provided with a second outlet pipe 113b, which is close to the bottom of the second shell 130b and bent into a roughly U-shape, and the outlet of the second outlet pipe 113b extends outward from the upper part of the second shell 130b. The second outlet pipe 113b is fluidically connected to the second compressor 100b.

[0071] When performing cooling operation or heating operation, the evaporated refrigerant is distributed by the distributor 107, and enters the first shell 130a and the second shell 130b through the first inlet pipe 131a and the second inlet pipe 131b respectively, and then produces a gas-liquid separation effect. The separated gaseous refrigerant is sucked into the first compressor 100a and the second compressor 100b from the first outlet pipe 113a and the second outlet pipe 113b; the separated liquid refrigerant is retained at the bottom of the first shell 130a and the second shell 130b, and gradually evaporates and gasifies over time, and then is sucked into the first compressor 100a and the second compressor 100b. A first oil return hole 114a is provided at the bottom of the first outlet pipe 113a, and a second oil return hole 114b is provided at the bottom of the second outlet pipe 113b. The lubricating oil gathered at the bottom of the first shell 130a can flow back to the first compressor 100a through the first outlet pipe 113a through the first oil return hole 114a; similarly, the lubricating oil gathered at the bottom of the second shell 130b can flow back to the second compressor 100b through the second outlet pipe 113b through the second oil return hole 114b.

[0072] In one or more embodiments of the present application, the first shell 130a and the second shell 130b have the same shape and volume. The upper sides of the first shell 130a and the second shell 130b can be connected through the gas connecting pipe 140, and the lower sides of the first shell 130a and the second shell 130b can be connected through the liquid connecting pipe 150. 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 is biased, the gas connecting pipe 140 and the liquid connecting pipe 150 can play a role in rapid liquid equalization.

[0073] In one or more embodiments of the present 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 the present 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 lubricating oil amount and the minimum lubricating oil amount of the first compressor 100a and the maximum refrigerant volume; wherein the difference between the maximum lubricating oil amount and the minimum lubricating oil amount represents the maximum capacity of the lubricating oil allowed to accumulate in the first shell 130a (the first compressor 100a cannot work if the lubricating oil amount is lower than the minimum lubricating oil amount), that is, the ratio of the difference between the maximum lubricating oil amount and the minimum lubricating oil amount to the cross-sectional area of ​​the first shell 130a (assuming that the first shell 130a is cylindrical) is the maximum lubricating oil height, and the ratio of the maximum refrigerant volume to the cross-sectional area of ​​the first shell 130a is the maximum refrigerant height. The sum of the maximum refrigerant volume height and the maximum lubricating oil height is the maximum liquid level in the first shell 130a. Since the first oil return hole 114a is set at the bottom (for example, the lowest point of the U-shaped tube), the height difference between the first auxiliary oil return hole 115a and the first oil return hole 114a is lower than the maximum liquid level. For example, a relatively ideal preset refrigerant volume that is smaller than the maximum refrigerant volume (for example, 60% of the maximum refrigerant volume) can be set according to the capacity of the refrigeration system 1 to ensure that both the first compressor 100a and the second compressor 100b in the refrigeration system 1 can operate stably, and the preset refrigerant height is calculated based on the ratio of the preset refrigerant volume to the cross-sectional area of ​​the first shell 130a, and the first auxiliary oil return hole 115a is opened at the set position of the first outlet pipe 113a based on the sum of the preset refrigerant height and the maximum lubricating oil height. It is also possible to evenly distribute multiple first auxiliary oil return holes 115a in an equidistant manner with the sum of the preset refrigerant height and the maximum lubricating oil height as the total height.

[0074] In one or more embodiments of the present 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 lubricating oil amount and the minimum lubricating oil amount of the second compressor 100b and the maximum refrigerant volume; wherein the difference between the maximum lubricating oil amount and the minimum lubricating oil amount represents the maximum capacity of the lubricating oil allowed to accumulate in the second shell 130b (the second compressor 100b cannot work below the minimum lubricating oil amount), that is, the ratio of the difference between the maximum lubricating oil amount and the minimum lubricating oil amount to the cross-sectional area of ​​the second shell 130b (assuming that the second shell 130b is cylindrical) is the maximum lubricating oil height, and the ratio of the maximum refrigerant volume to the cross-sectional area of ​​the second shell 130b is the maximum refrigerant height. The sum of the maximum refrigerant volume height and the maximum lubricating oil height is the maximum liquid level in the second shell 130b. Since the second oil return hole 114b is set at the bottom (for example, the lowest point of the U-shaped tube), the height difference between the second auxiliary oil return hole 115b and the second oil return hole 114b is lower than the maximum liquid level. For example, a relatively ideal preset refrigerant volume that is smaller than the maximum refrigerant volume (for example, 60% of the maximum refrigerant volume) and at which both the second compressor 100b and the second compressor 100b in the refrigeration system 1 can operate stably can be set according to the capacity of the refrigeration system 1, and the preset refrigerant height is calculated based on the ratio of the preset refrigerant volume to the cross-sectional area of ​​the second shell 130b, and the second auxiliary oil return hole 115b is opened at the set position of the second outlet pipe 113b based on the sum of the preset refrigerant height and the maximum lubricating oil height. It is also possible to evenly distribute multiple second auxiliary oil return holes 115b in an equidistant manner with the sum of the preset refrigerant height and the maximum lubricating oil height as the total height.

[0075] An outdoor control circuit is also provided in the outdoor unit. The outdoor control circuit is provided in an electrical box with good sealing performance and heat dissipation function. The outdoor control circuit includes components such as a processor, a storage unit, an input / output interface, and a communication interface. The processor may be a dedicated processor, a central processing unit (CPU), etc. The processor may access the storage unit to execute instructions or applications stored in the storage unit to implement related functions. The storage unit may include a volatile memory and / or a non-volatile memory. The input / output interface may be connected to various sensors provided in the outdoor unit to receive detection values ​​of various sensors provided in the outdoor unit. The input / output interface may also be connected to devices such as a frequency converter, an outdoor fan 104, and a four-way valve to output control instructions generated by the processor to them. The communication interface may support different wireless communication protocols, such as Wi-Fi, Bluetooth, near field communication, NB-IoT, etc., to communicate with other electronic devices, including but not limited to cloud servers, computers (host computers), smart phones, tablet computers, PDAs, intelligent control tooling, wearable devices, and vehicle-mounted devices, etc.

[0076] As recorded in the background technology section, the refrigerant charge in the refrigeration system has reached hundreds of kilograms. Since only one switching valve is set, the switching valve must be set corresponding to the distributor; however, it is difficult to ensure the similarity of the pipeline length and pipeline diameter during long-term use downstream of the corresponding distributor (such as a three-way pipe or a three-way valve), especially there may be tiny impurities and pollutants in the refrigeration system, these substances will accumulate in the pipeline near the distributor, and gradually change the diameter of the pipeline; in addition, if the evaporation capacity of the outdoor heat exchanger serving as the evaporator is weak, it will cause the low-temperature and low-pressure gas-liquid two-phase refrigerant to evaporate incompletely in the evaporator, and the liquid phase ratio in the refrigerant is large, resulting in uneven liquid return of the two gas-liquid separators and the two compressors. The compressor connected to the gas-liquid separator with more liquid return has more liquid return, and the compressor connected to the gas-liquid separator with less liquid return has less liquid return. After a period of time, the operation of the two compressors is very different, and the exhaust temperature is also very different, resulting in a significant impact on the performance and reliability of the compressor body and the entire refrigeration system.

[0077] like Fig. 9 and Fig.10 As shown, to solve this problem, a control unit 30 is further provided in the refrigeration system 1. In one or more embodiments of the present application, the control unit 30 is implemented by an outdoor control circuit. In one or more embodiments of the present application, the control unit 30 can also be implemented by a cloud server or a host computer that is communicatively connected to the outdoor unit.

[0078] The control unit 30 is configured to control the refrigeration system to perform heating operation (such as Fig.11 As shown in step S101 in the figure, the operating frequencies of the first compressor 100a and the second compressor 100b are controlled to maintain the target pressure (such as Fig.11 The first outdoor throttling element 109a and the second outdoor throttling element 109b are controlled to open so that the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b are not lower than the target suction superheat and the target exhaust superheat (such as Fig.11 As shown in step S103 in the figure, it is estimated whether the correction mode start condition (such as Fig.11 As shown in step S104 in the figure), when the start condition of the correction mode is met, the heating operation is kept executed (such as Fig.11 As shown in step S105), the target exhaust pressure is increased to generate a modified target exhaust pressure (such as Fig.11 In step S106), the target intake superheat and the target exhaust superheat are increased to generate a modified target intake superheat and a modified target exhaust superheat (such as Fig.11As shown in step S107, the operating frequencies of the first compressor 100a and the second compressor 100b are controlled to maintain the corrected target exhaust pressure (eg Fig.11 The first outdoor throttling element 109a and the second outdoor throttling element 109b are controlled to open so that the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b are not lower than the modified target suction superheat and the modified target exhaust superheat (such as Fig.11 (as shown in step S109).

[0079] When performing heating operation, the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b serve as evaporators. If the outdoor ambient temperature is very low, or the first outdoor heat exchanger 103a and / or the second outdoor heat exchanger 103b are dirty or blocked, or the air circulation volume guided by the outdoor fan 104 is insufficient, the evaporation capacity is very weak, and the refrigerant is a gas-liquid two-phase refrigerant after passing through the evaporator, and the liquid phase ratio is relatively high. 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 have a bias flow phenomenon, one compressor returns more liquid, and the other compressor returns more gas, and the operating states of the two compressors are very different, which is specifically manifested in that the exhaust temperature between the first compressor 100a and the second compressor 100b is very different. According to the exhaust temperature difference between the first compressor 100a and the second compressor 100b, it can be inferred whether there is a bias flow phenomenon.

[0080] When there is a deviation phenomenon, the control unit 30 is configured to maintain the heating operation and increase the target exhaust pressure to generate a corrected target exhaust pressure, increase the target suction superheat and the target exhaust superheat to generate a corrected target suction superheat and a 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, control the opening 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 suction superheat and the corrected target exhaust superheat, on the one hand, the evaporation capacity of the outdoor heat exchanger is increased by increasing the frequency of the compressor, and on the other hand, the amount of evaporated refrigerant is reduced by adjusting (reducing) the opening of the first outdoor throttling element 109a and the second outdoor throttling element 109b, thereby increasing the suction superheat and the exhaust superheat of the refrigerant at the evaporator outlet, and optimizing and improving the refrigeration system fluctuation caused by the deviation problem.

[0081] like Fig.12 As shown, the control unit 30 is also configured to control the outdoor fan 104 to operate at a target speed (such as Fig.12As shown in step S204), the target speed is negatively correlated with the outdoor ambient temperature; and when the correction mode start condition is met, the heating operation is maintained and the target speed is increased to generate a correction speed (such as Fig.12 Based on the modified speed, the outdoor fan 104 is controlled (as shown in step S209). Fig.12 The modified speed may be the maximum speed of the outdoor fan 104 or the speed corresponding to the highest gear. The outdoor fan 104 running at the modified speed may increase the air flow rate and further improve the evaporation capacity of the evaporator.

[0082] like Fig.13 As shown, the control unit 30 is further configured to control the operating frequency of the first compressor 100a and the second compressor 100b based on the modified target exhaust pressure, control the opening of the first outdoor throttling element 109a and the second outdoor throttling element 109b based on the modified target suction superheat and the modified target exhaust superheat, and control the outdoor fan 104 based on the modified speed; and estimate whether the correction mode exit condition (such as the current increase amount of the real-time outdoor fan 104) is satisfied according to the exhaust temperature difference between the first compressor 100a and the second compressor 100b, the outdoor ambient temperature and the real-time outdoor fan 104 current increase amount. Fig.13 As shown in step S313 in the figure), and when the correction mode exit condition is met, the heating operation is continued (such as Fig.13 As shown in step S314, the operating frequencies of the first compressor 100a and the second compressor 100b are controlled to maintain the target exhaust pressure (eg Fig.13 The first outdoor throttling element 109a and the second outdoor throttling element 109b are controlled to open so that the first outdoor heat exchanger 103a and the second outdoor heat exchanger 103b are not lower than the target suction superheat and the target exhaust superheat (such as Fig.13 (as shown in step S316).

[0083] In one or more embodiments of the present application, Fig.14 As shown, the control unit 30 is configured to satisfy the exhaust temperature difference between the first compressor 100a and the second compressor 100b within the set temperature range (such as Fig.14 The outdoor ambient temperature is not lower than the set ambient temperature threshold (such as Fig.14 As shown in step S402 in FIG. 104 , and the current increase of the outdoor fan 104 in real time is not higher than the set current increase threshold value (such as Fig.14 As shown in step S403), it is inferred that the correction mode exit condition is met (such as Fig.14 (as shown in step S404).

[0084] In one or more embodiments of the present application, Fig.15As shown, the control unit 30 is configured to perform the following steps when controlling the opening degree of the first outdoor throttling element 109a so that the first outdoor heat exchanger 103a satisfies the target suction superheat condition and the target exhaust superheat condition:

[0085] Step S501, executing heating operation.

[0086] Step S502: sampling the detected temperature T of the first outdoor heat exchanger gas pipe temperature sensor 115a g1 , sampling the detected temperature T of the second outdoor heat exchanger gas pipe temperature sensor 115b g2 ;

[0087] Step S503, obtaining the detection pressure P of the low pressure sensor 151 s ;

[0088] Step S504, obtaining 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 air superheat T when performing heating operation. ssh1 and the second suction gas superheat T ssh2 , first suction superheat T ssh1 Meet T ssh1 =T g1 -T c_ps , Second suction superheat T ssh2 Meet T ssh1 =T g2 -T c_ps ;

[0090] Step S506, adjusting the opening of the first outdoor throttling element 109a so that the first suction superheat T ssh1 The second suction superheat T is not lower than the target suction superheat a℃, and the opening of the second outdoor throttling element 109b is adjusted so that the second suction superheat T ssh2 Not less than the target suction superheat a℃;

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

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

[0093] Step S509, calculating the detected temperature T of the first compressor exhaust temperature sensor 112a d1 and the detected temperature T of the second compressor discharge temperature sensor 112b d2 The mean value T dave ;

[0094] Step S510, obtaining the detection pressure P of the high pressure sensor 110 d ;

[0095] Step S511, obtaining 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 gas superheat T when performing heating operation. dsh1 , first exhaust gas superheat T dsh1 Meet T dsh1 =T dave -T c_pd ;

[0097] Step S513, adjusting the opening of the first outdoor throttling element 109a and the opening of the second outdoor throttling element 109b so that the first exhaust gas superheat degree T dsh1 Not less than the target exhaust superheat b℃.

[0098] In one or more embodiments of the present application, Fig.16 As shown, the control unit 30 is configured to perform the following steps when controlling the opening degrees 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 suction superheat and the corrected target exhaust superheat:

[0099] Step S601, keep heating operation;

[0100] Step S602: sampling the detected temperature T of the first outdoor heat exchanger gas pipe temperature sensor 115a g1 , sampling the detected temperature T of the second outdoor heat exchanger gas pipe temperature sensor 115b g2 ;

[0101] Step S603, obtaining the detection pressure P of the low pressure sensor 151 s ;

[0102] Step S604, obtaining the detection pressure P of the low pressure sensor 151 s The corresponding saturation temperature T c_ps ;

[0103] Step S605, calculating the third intake air superheat T when executing the correction mode ssh3 And the fourth suction superheat T ssh4 , the third suction superheat T ssh3 Meet T ssh3 =T g1 -T c_ps , the fourth suction superheat Tssh4 Meet T ssh4 =T g2 -T c_ps ;

[0104] Step S606, adjusting the opening of the first outdoor throttling element 109a so that the third suction air superheat T ssh3 The opening degree of the second outdoor throttling element 109b is adjusted so that the fourth suction superheat T ssh4 Not less than the corrected target suction superheat c℃;

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

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

[0107] Step S609, calculating the detected temperature T of the first compressor exhaust temperature sensor 112a d1 and the detected temperature T of the second compressor discharge temperature sensor 112b d2 The mean value T dave ;

[0108] Step S610, obtaining the detection pressure P of the high pressure sensor 110 d ;

[0109] Step S611, obtaining the detection pressure P of the high pressure sensor 110 d The corresponding saturation temperature T c_pd ;

[0110] Step S612, calculating the second exhaust gas superheat T when executing the correction mode dsh2 , the second exhaust gas superheat T dsh2 Meet T dsh2 =T dave -T c_pd ;

[0111] Step S613, adjusting the opening of the first outdoor throttling element 109a and the opening of the second outdoor throttling element 109b so that the second exhaust gas superheat T dsh2 Not less than the corrected target exhaust superheat d℃.

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

[0113] Set a number of consecutive adjustment cycles;

[0114] The opening degree of the first outdoor throttling element 109a in the next adjustment cycle 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 amount 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 set change, β is the influence factor of suction superheat on the set change, α and β are constants and satisfy α+β=1; ΔEVO 排气过热度 =a 1 ×(T dsh2 -d)+b 1 , ΔEVO 吸气过热度 =a 2 ×(T ssh3 -c)+b 2 , a 1 、a 2 、b 1 and b 2 is a constant.

[0116] In one or more embodiments of the present application, the control unit 30 is further configured to infer that the heat exchanger is dirty and blocked 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 to operate, the control unit 30 collects parameters such as temperature, pressure and current, including but not limited to the detection temperature T of the first compressor exhaust temperature sensor 112a. d1 , the detected temperature T of the second compressor exhaust gas temperature sensor 112b d2 , the detection pressure P of the high pressure sensor 110 (i.e., the exhaust pressure detection device) d , the detected temperature T of the first outdoor heat exchanger gas pipe temperature sensor 115a g1 , the detected temperature T of the second outdoor heat exchanger gas pipe temperature sensor 115b g2 , the detection pressure P of the low pressure sensor 151 s , the detected temperature T of the outdoor environment temperature sensor 116 a , Initial outdoor fan 104 current E fan0 , Real-time outdoor fan 104 current E fan1 The control unit 30 determines whether to execute the heating operation based on the input command. If yes, the heating operation is executed, otherwise the cooling operation is executed. When the heating operation is executed, the operating frequency of the first compressor 100a and the second compressor 100b is controlled according to the target exhaust pressure. When the detection pressure P of the high pressure sensor 110 (i.e., the exhaust pressure detection device) is d Lower than the target exhaust pressure Pd0 When the detection pressure P of the high pressure sensor 110 (i.e., the exhaust pressure detection device) is d Higher than the target exhaust pressure P d0 When the operating frequency of the first compressor 100a and the second compressor 100b is reduced, the operating frequency of the first compressor 100a and the second compressor 100b does not exceed the upper limit frequency H zmax1 ; Among them, 2MPa≤P d0 ≤3.5MPa, 100Hz≤H zmax1 ≤180Hz.

[0118] The wind speed of the outdoor fan 104 is determined by the outdoor ambient temperature T a Different outdoor ambient temperature ranges 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 are throttled, and the opening degree of the first outdoor throttling element 109a is controlled so that the first suction air superheat T of the first outdoor heat exchanger 103a is ssh1 ≥a℃, where T ssh1 =T g1 -T c_ps , T c_ps is the detection pressure P of the low pressure sensor 151 s The corresponding saturation temperature makes the first exhaust gas superheat T dsh1 ≥b℃; where T dsh1 =T dave -T c_pd ,T dave =(T d1 +T d2 ) / 2,T c_pd is the detection pressure P of the high pressure sensor 110 d Correspondingly, controlling the opening of the second outdoor throttling element 109b makes 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 is the detection pressure P of the low pressure sensor 151 s The corresponding saturation temperature makes the first exhaust gas superheat T dsh1 ≥b℃; where T dsh1 =T dave -T c_pd ,T dave =(T d1 +Td2 ) / 2,T c_pd is the detection pressure P of the high pressure sensor 110 d The corresponding saturation temperature; where 0℃≤a≤20℃, 10℃≤b≤70℃.

[0120] Further determine whether there is T d1 -T d2 <-m℃, or whether there is T d1 -T d2 >m℃. When the outdoor ambient temperature is high, there is no dirt blockage in the evaporator, and the air flow 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 superheated gaseous refrigerant, which evenly enters the first gas-liquid separator 108a and the second gas-liquid separator 108b, the first compressor 100a and the second compressor 100b, the first compressor 100a and the second compressor 100b have the same operating state, and the exhaust temperature difference between the first compressor 100a and the second compressor 100b is small, and the above conditions are not met, and the heating operation is still performed; wherein 5℃≤m≤40℃. However, as the outdoor ambient temperature drops significantly, the outdoor heat exchanger is dirty and blocked, or the air flow guided by the outdoor fan 104 decreases, the evaporation capacity of the evaporator is greatly reduced, the two-phase refrigerant does not evaporate completely in the evaporator, and the evaporator outlet is two-phase refrigerant with a higher proportion of liquid refrigerant. It enters the two gas-liquid separators and two compressors unevenly, resulting in a bias flow phenomenon. One compressor returns more liquid and the other returns more air. The operating states of the two compressors are very different, and the exhaust temperature difference is very large. That is, the above conditions are met and the heating exhaust temperature correction mode control is executed.

[0121] Keep executing heating operation, increase the target exhaust pressure to generate the corrected target exhaust pressure P d1 , the target intake superheat and the target exhaust superheat are increased to generate a corrected target intake superheat and a corrected target exhaust superheat.

[0122] The operating frequencies of the first compressor 100a and the second compressor 100b are controlled according to the modified target exhaust pressure. When the detected pressure of the high pressure sensor 110 is lower than the modified target exhaust pressure P d1 When the detection pressure P of the high pressure sensor 110 is d Higher than the corrected target pressure P d1 When the operating frequency of the first compressor 100a and the second compressor 100b is reduced, the operating frequency of the first compressor 100a and the second compressor 100b does not exceed the upper limit frequency H in the heating exhaust gas temperature correction mode. zmax2; Among them, 2.5MPa≤Pd1≤4.0MPa.

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

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

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

[0126] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0127] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. Refrigeration system, including: An outdoor unit comprising: The first compressor; a first outdoor heat exchanger; A first outdoor throttling element, which is arranged corresponding to the first outdoor heat exchanger; Second compressor; a second outdoor heat exchanger; a second outdoor throttling element, which is arranged corresponding to the second outdoor heat exchanger; A switching valve, which connects the first compressor and the second compressor respectively; a distributor connected to the switching valve; A first gas-liquid separator connected to one outlet of the distributor; and a second gas-liquid separator connected to another outlet of the distributor; It is characterized by further comprising: A control unit, which is configured to control the operating frequency of the first compressor and the second compressor to maintain a target exhaust pressure when performing heating operation, 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 suction superheat and the target exhaust superheat; infer whether the correction mode startup condition is met based on the exhaust temperature difference between the first compressor and the second compressor; and when the correction mode startup condition is met, keep performing heating operation and increase the target exhaust pressure to generate a corrected target exhaust pressure, increase the target suction superheat and the target exhaust superheat to generate a corrected target suction superheat and a corrected target exhaust superheat, control the operating frequency of the first compressor and the second compressor to maintain the corrected 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 corrected target suction superheat and the corrected target exhaust superheat.

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

3. The refrigeration system according to claim 2, characterized in that: The control unit is also configured to control the operating frequencies of the first compressor and the second compressor based on the corrected target exhaust pressure, control the openings 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 control 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 outdoor fan current increase, and when the correction mode exit condition is met, keep executing heating operation, control the operating frequencies of the first compressor and the second compressor to maintain the target exhaust pressure, and control the openings 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.

4. The refrigeration system according to claim 3, characterized in that: The control unit is configured to presume that the correction mode exit condition is satisfied 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.

5. The refrigeration system according to claim 1, characterized in that: The control unit is configured to perform the following steps when controlling the opening degree of the first outdoor throttle element so that the first outdoor heat exchanger satisfies a target suction superheat condition and a target exhaust superheat condition: Execute heating operation; Sample the detected temperature T of the first outdoor heat exchanger gas pipe temperature sensor g1 , sample the detected temperature T of the gas pipe temperature sensor of the second outdoor heat exchanger g2 ; Get the detection pressure P of the low pressure sensor s ; Get the detection pressure P of the low pressure sensor s The corresponding saturation temperature T c_ps ; Calculation of the first suction air superheat T during heating operation ssh1 and the second suction gas superheat T ssh2 , first suction superheat T ssh1 Meet T ssh1 =T g1 -T c_ps , Second suction superheat T ssh2 Meet T ssh2 =T g2 -T c_ps ; Adjust the opening of the first outdoor throttling element so that the first suction air superheat T ssh1 is not lower than the target suction superheat a℃, and the opening of the second outdoor throttling element is adjusted so that the second suction superheat T ssh2 Not less than the target suction superheat a℃; Sample the detected temperature T of the first compressor exhaust temperature sensor d1 ; Sample the detected temperature T of the second compressor exhaust temperature sensor d2 ; Calculate the detected temperature T of the first compressor exhaust temperature sensor d1 and the detected temperature T of the second compressor exhaust temperature sensor d2 The mean value T dave ; Get the detection pressure P of the high pressure sensor d ; Get the detection pressure P of the high pressure sensor d The corresponding saturation temperature T c_pd ; Calculation of the first exhaust gas superheat T during heating operation dsh1 , first exhaust gas superheat T dsh1 Meet T dsh1 =T dave -T c_pd ; The opening of the first outdoor throttling element and the opening of the second outdoor throttling element are adjusted so that the first exhaust gas superheat degree T dsh1 Not less than the target exhaust superheat b℃.

6. The refrigeration system according to claim 5, characterized in that: The control unit is configured to perform the following steps when controlling the opening degrees of the first outdoor throttle element and the second outdoor throttle element so 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 exhaust superheat: Keep the heating running; Sample the detected temperature T of the first outdoor heat exchanger gas pipe temperature sensor g1 , sample the detected temperature T of the gas pipe temperature sensor of the second outdoor heat exchanger g2 ; Get the detection pressure P of the low pressure sensor s ; Get the detection pressure P of the low pressure sensor s The corresponding saturation temperature T c_ps ; Calculate the third suction air superheat T when executing the correction mode ssh3 And the fourth suction superheat T ssh4 , the third suction superheat T ssh3 Meet T ssh3 =T g1 -T c_ps , the fourth suction superheat T ssh4 Meet T ssh4 =T g2 -T c_ps ; Adjust the opening of the first outdoor throttling element so that the third suction superheat T ssh3 is not lower than the modified target suction superheat c℃, and the opening of the second outdoor throttling element is adjusted so that the fourth suction superheat T ssh4 Not less than the corrected target suction superheat c℃; Sample the detected temperature T of the first compressor exhaust temperature sensor d1 ; Sample the detected temperature T of the second compressor exhaust temperature sensor d2 ; Calculate the detected temperature T of the first compressor exhaust temperature sensor d1 and the detected temperature T of the second compressor exhaust temperature sensor d2 The mean value T dave ; Get the detection pressure P of the high pressure sensor d ; Get the detection pressure P of the high pressure sensor d The corresponding saturation temperature T c_pd ; Calculate the second exhaust gas superheat T when executing the correction mode dsh2 , the second exhaust gas superheat T dsh2 Meet T dsh2 =T dave -T c_pd ; The opening degree of the first outdoor throttling element and the opening degree of the second outdoor throttling element are adjusted so that the second exhaust gas superheat T dsh2 Not less than the corrected target exhaust superheat d℃.

7. The refrigeration system according to claim 6, characterized in that: When adjusting the opening of the first outdoor throttling element and the opening of the second outdoor throttling element, the control unit is configured to perform the following steps: Set a number 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; 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 set change, β is the influence factor of suction superheat on the set change, 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, a1, a2, b1 and b2 are constants.

8. The refrigeration system according to claim 4, characterized in that: The control unit is further configured to infer that the heat exchanger is dirty and blocked when the real-time increase in the outdoor fan current is higher than the set current threshold.

9. The refrigeration system according to any one of claims 1 to 8, characterized in that: The control unit is configured to estimate that the correction mode start condition is satisfied when the exhaust gas temperature difference between the first compressor and the second compressor is higher than a set exhaust gas temperature difference threshold.

10. The refrigeration system according to claim 1, characterized in that: Also includes: a gas connecting pipe, wherein both ends of the gas connecting pipe are respectively connected to the upper parts of the first gas-liquid separator and the second gas-liquid separator; and The liquid communicating tube has two ends respectively communicating with the lower parts of the first gas-liquid separator and the second gas-liquid separator.

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