Refrigeration system

Abstract

The refrigerating system comprises an outdoor unit which comprises a first compressor and a second compressor; the system comprises a first compressor, a second compressor, a switching valve respectively communicated with the first compressor and the second compressor, a distributor communicated with the switching valve, a first gas-liquid separator, a second gas-liquid separator, a distribution pipe provided with a regulating valve, a first detection branch, a second detection branch and a control part. The first detection branch is communicated with the first eduction tube through a first auxiliary oil return hole, and the first detection branch is provided with a first pressure reduction element; the second detection branch is communicated with a second eduction tube through a second auxiliary oil return hole, and the second detection branch is provided with a same second pressure reduction element; the first auxiliary oil return hole and the second auxiliary oil return hole have the same height; the control part is configured to presume whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state or not based on the temperature change before and after the first pressure reducing element and the second pressure reducing element and the temperature difference between the exhaust temperature of the first compressor and the exhaust temperature of the second compressor when the operation frequencies are the same; when the non-uniform liquid level state is presumed, the regulating valve is driven to act so as to regulate the flow of the refrigerant in the distribution pipe; according to the invention, non-uniform oil return and liquid return can be avoided.

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 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. For example, 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. The distributor will cause uneven distribution of the liquid mixture in multiple gas-liquid separators; at the same time, due to the different loads of multiple compressors, the mixture of lubricating oil and liquid refrigerant will be further aggravated. The uneven distribution in each gas-liquid separator will further lead to different oil return and air return volumes for each compressor, resulting in poor oil return of the compressor, too large differences in exhaust temperatures of multiple compressors, and reduced system performance, which will further lead to compressor damage. Summary of the invention

[0006] When dual compressors or multiple compressors are used in combination with parallel gas-liquid separators, due to the design of the distributor and the different loads of each compressor, the mixture of lubricating oil and liquid refrigerant is in an uneven distribution state in each gas-liquid separator, which further leads to different return oil and return air volumes of each compressor, resulting in poor oil return of the compressor and reduced system performance. The first aspect of the present application designs and provides a refrigeration system.

[0007] The refrigeration system includes an indoor unit and an outdoor unit; the outdoor unit includes a first compressor, a second compressor, a switching valve 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, wherein a first outlet pipe connected to the first compressor is provided; a second gas-liquid separator connected to the other outlet of the distributor, wherein a second outlet pipe connected to the second compressor is provided, and a distributor pipe having two ends respectively connected to the first gas-liquid separator and the second gas-liquid separator.

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

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

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

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

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

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

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

[0015] In one or more embodiments of the present application, the regulating valve is an electronic expansion valve, and the control unit drives the regulating valve to operate to connect the distribution pipe so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state; wherein the regulating valve is divided into multiple continuous adjustment cycles when in operation; the opening of the next adjustment cycle is the sum of the opening of the current adjustment cycle and the corrected opening; the corrected opening is the product of the maximum opening and the proportional coefficient, and the proportional coefficient is obtained based on a second fitting curve generated according to the exhaust temperature difference between the first compressor and the second compressor, and in the second fitting curve, the proportional coefficient corresponds one-to-one to the exhaust temperature difference between the first compressor and the second compressor.

[0016] In one or more embodiments of the present application, the control unit is configured to control the first compressor and the second compressor to operate at the same operating frequency, and estimate whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state based on the temperature changes before and after the first pressure reducing element and the second pressure reducing element, the temperature difference of the exhaust temperature between the first compressor and the second compressor, and the operating current difference between the first compressor and the second compressor; and when it is estimated to be a non-uniform liquid level state, drive the regulating valve to adjust the refrigerant flow in the distribution pipe to transition to a uniform liquid level state.

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

[0018] In one or more embodiments of the present application, the control unit is configured to infer that the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state, and the liquid level of the first gas-liquid separator is higher than the first auxiliary oil return hole, when the difference between the temperature detected by the first outlet temperature sensor and the temperature detected by the first inlet temperature sensor is lower than a first set threshold, the difference between the temperature detected by the second outlet temperature sensor and the temperature detected by the second inlet temperature sensor is not lower than a second set threshold, the exhaust temperature difference between the first compressor and the second compressor is not lower than a third set threshold, and the operating current difference between the first compressor and the second compressor is not lower than a fourth set threshold, drive the regulating valve to operate and connect the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from the non-uniform liquid level state to the uniform liquid level state.

[0019] The present invention identifies whether the two gas-liquid separators are in a non-uniform liquid level state through the temperature changes before and after the first pressure reducing element and the second pressure reducing element, as well as the temperature difference between the exhaust temperatures of the two compressors and / or the difference between the operating currents of the two compressors, and uses a regulating valve to adjust them. This can effectively avoid the problem of uneven return air and liquid caused by a set of switching valves and distributors, thereby improving 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 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;

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

[0030] Fig. 9 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0031] Fig.10 A flow chart of a control unit in a refrigeration system provided by one or more embodiments of the present application;

[0032] Fig.11 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;

[0033] Fig.12 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;

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

[0037] Fig.16 An example diagram of a first fitting curve in a refrigeration system provided by one or more embodiments of the present application;

[0038] Fig.17 An example diagram of a second fitting curve in a refrigeration system provided by one or more embodiments of the present application;

[0039] In the figure, 1, refrigeration system; 10, outdoor unit; 12, outdoor unit; 20, indoor unit; 22, indoor unit; 24, indoor unit; 200, indoor heat exchanger; 201, indoor electronic expansion valve; 30, control unit; 31, liquid side connecting pipe; 32, gas side connecting pipe; 100a, first compressor; 100b, second compressor; 101a, first oil separator; 101b, second oil separator; 102, switching valve; 103, indoor external heat exchanger; 104, throttling device; 105, liquid side shut-off valve; 106, gas side shut-off valve; 107, distributor; 107a, one outlet of the distributor; 107b, another outlet of the distributor; 107c, inlet of the distributor; 108a, first gas-liquid separator; 108b, second gas-liquid separator; 109, solenoid valve; 110, high pressure sensor; 111a, first high pressure switch; 111b, second high pressure switch; 112a, first pressure compressor exhaust temperature sensor; 112b, second compressor exhaust temperature sensor; 113a, first outlet pipe; 113b, second outlet pipe; 114a, first main oil return hole; 114b, second main oil return hole; 115a, first auxiliary oil return hole; 115b, second auxiliary oil return hole; 116a, first detection branch; 116b, second detection branch; 117a, first outlet temperature sensor; 117b, second outlet temperature sensor; 118a, The first inlet temperature sensor; 118b, the second inlet temperature sensor; 119a, the first pressure reducing element; 119b, the second pressure reducing element; 120, the distribution pipe; 121, the regulating valve; 130a, the first shell; 130b, the second shell; 131a, the first inlet pipe; 131b, the second inlet pipe; 140, the gas connecting pipe; 150, the liquid connecting pipe; 150a, the first capillary tube; 150b, the second capillary tube; 151, the low pressure sensor. DETAILED DESCRIPTION

[0040] 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.

[0041] 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 referred device or element 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.

[0042] The terms "first", "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. Therefore, 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.

[0043] 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 an indirect connection 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.

[0044] In the present invention, unless otherwise clearly stipulated 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 means that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] A refrigeration cycle is integrated in the refrigeration system 1. A compressor, a condenser, a throttling device 104 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.

[0049] 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.

[0050] The throttling device 104 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 104 and returns the refrigerant gas in a low-temperature and low-pressure state to the compressor. The evaporator can achieve a refrigeration effect by 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.

[0051] 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 2The 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.

[0052] 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).

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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 Enlarged view of part A in .

[0057] 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 6 As shown, the outdoor unit is provided with a first compressor 100a and a second compressor 100b; Figures 3 to 6In the same manner as the first compressor 100a and the second compressor 100b shown in the figure, 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 reciprocating compressors, screw compressors, etc. The speeds of the first compressor 100a and the second compressor 100b are controlled by a frequency converter, and the first compressor 100a and the second compressor 100b can operate independently. 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 ends of the first compressor 100a and the second compressor 100b are also provided with a high pressure sensor 110, and the suction ends of the first compressor 100a and the second compressor 100b are also provided with a low pressure sensor 151.

[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] The outdoor unit may also be provided with an outdoor fan (not shown) and a switching valve 102; wherein the outdoor fan may be an axial flow fan, a cross flow fan or other optional fan forms. The outdoor fan is arranged near the outdoor heat exchanger 103. The outdoor heat exchanger 103 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] A four-way valve is used as an example of the switching valve 102. The switching valve 102 is a valve used to switch the flow direction of the refrigerant in the refrigerant circuit. In one outdoor unit, there is only one switching valve 102.

[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 in sequence to the first gas-liquid separator 108a and the first compressor 1000a, and the other outlet of the distributor 107 is connected in sequence 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 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 flowing out of the second compressor 100b enters the second oil separator 101b, and from 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 outdoor heat exchanger 103 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 the outdoor heat exchanger 103, the switching valve 102 (for example, one passage of a four-way valve, exemplarily, the fluid passage between the E port and the S port) and the distributor 107 are sequentially connected from the liquid side connecting pipe 31 to the gas side connecting pipe 32. The distributor 107 is in fluid communication with the switching valve 102. Downstream of the distributor 107, that is, one outlet of the distributor 107 is sequentially connected to the first gas-liquid separator 108a, the first compressor 100a, the first oil separator 101a and the switching valve 102 (for example, one passage of a four-way valve, exemplarily, the fluid passage between the D port and the C port); the other outlet of the distributor 107 is sequentially connected to the second gas-liquid separator 108b, the second compressor 100b, the second oil separator 101b and the switching valve 102 (for example, the same passage of the four-way valve, exemplarily, the fluid passage between the D port and the C port).

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

[0066] 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.

[0067] 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.

[0068] 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 main oil return hole 114a is opened at the bottom of the first outlet pipe 113a, and a second main oil return hole 114b is opened at the bottom of the second outlet pipe 113b. 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 main 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 main oil return hole 114b.

[0069] 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 first gas-liquid separator 108a and the second gas-liquid separator 108b are connected through a distribution pipe 120, and a regulating valve 121 is provided on the distribution pipe 120. Outside the distribution pipe 120, the upper sides of the first shell 130a and the second shell 130b can be connected through a gas communication pipe 140, and the lower sides of the first shell 130a and the second shell 130b can be connected through a liquid communication pipe 150.

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

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

[0072] In one or more embodiments of the present application, the height difference between the first auxiliary oil return hole 115a and the first main oil return hole 114a can be determined by the difference between the maximum lubricating oil 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 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 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 height in the first shell 130a. Since the first main 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 main oil return hole 114a is lower than the maximum liquid level height. Exemplarily, a relatively ideal preset refrigerant volume that is smaller than the maximum refrigerant volume (for example, 60% of the maximum refrigerant volume) and ensures that both the first compressor 100a 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 first shell 130a, and the first auxiliary oil return hole 115a is opened at the set position of the first outlet pipe based on the sum of the preset refrigerant height and the maximum lubricating oil height.

[0073] In one or more embodiments of the present application, the height difference between the second auxiliary oil return hole 115b and the second main oil return hole 114b can be determined by the difference between the maximum lubricating oil 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 main 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 main 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 based on the sum of the preset refrigerant height and the maximum lubricating oil height.

[0074] In one or more embodiments of the present application, the first auxiliary oil return hole 115 a and the second auxiliary oil return hole 115 b have the same 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, 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 and connect 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 described in the background technology section, the refrigerant filling amount in the refrigeration system 1 has reached hundreds of kilograms. Since only one switching valve 102 is provided, the switching valve 102 must be provided corresponding to the distributor 107; however, it is difficult to ensure the similarity of the pipeline length and the pipeline diameter during long-term use downstream of the corresponding distributor 107 (such as a three-way pipe or a three-way valve), especially since there may be tiny impurities and pollutants in the refrigeration system 1, and these substances will accumulate in the pipeline near the distributor 107, gradually changing the diameter of the pipeline; and since the output of the two compressors will change with the change of load, this will aggravate the uneven distribution of liquid in the two gas-liquid separators downstream of the distributor 107, and since the lubricating oil is dissolved in the liquid refrigerant, it will further cause deviations in the return oil and return air of the first compressor 100a and the second compressor 100b.

[0077] like Figure 7 and Figure 8As shown, in order to solve this problem, a control unit 30 is also provided in the refrigeration system 1. In one or more embodiments of the present application, the control unit 30 is implemented by an outdoor control circuit. In one or more embodiments of the present application, the control unit 30 can also be implemented by a cloud server or a host computer that is communicatively connected to the outdoor unit. The control unit 30 is configured to control the first compressor 100a and the second compressor 100b to operate at the same frequency, and to estimate whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state based on the temperature change before and after the first pressure reducing element 119a and the second pressure reducing element 119b, and the temperature difference of the exhaust temperature between the first compressor 100a and the second compressor 100b, and when it is estimated to be a non-uniform liquid level state, the regulating valve 121 is driven to operate to adjust the refrigerant flow in the distribution pipe.

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

[0079] Regardless of whether the cooling operation or the heating operation is performed, the evaporated refrigerant enters the first shell 130a and the second shell 130b through the introduction pipe under the distribution of the distributor 107, and a gas-liquid separation effect occurs. The gaseous refrigerant is at an upper position and the mixture of the liquid refrigerant and the lubricating oil is at a lower position.

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

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

[0082] Further, it is possible to determine whether there is a load mismatch based on the temperature difference between the exhaust temperatures of the first compressor 100a and the second compressor 100b.

[0083] When the control unit 30 determines that the liquid level is not uniform, the control unit 30 drives the regulating valve 121 to adjust the refrigerant flow in the distribution pipe so that the liquid levels in the two gas-liquid separators are kept in a uniform liquid level state. During the adjustment process, the first main oil return hole 114a, the first auxiliary oil return hole 115a, the second main oil return hole 114b and the second auxiliary oil return hole 115b can all play the role of returning oil simultaneously or separately.

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

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

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

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

[0088] Specifically, if Fig. 9 As shown, the control unit 30 is configured to sample the temperature detected by the first outlet temperature sensor 117a (eg Fig. 9 As shown in step S111), the first inlet temperature sensor 118a detects the temperature (as shown in step S111). Fig. 9 11), calculate the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a (as shown in step S112). Fig. 9 As shown in step S113), it is determined whether the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a is lower than a first set threshold value (such as Fig. 9 When the liquid level in the first gas-liquid separator 108a is lower than the first set threshold, it is estimated that the liquid level in the first auxiliary oil return hole 115a is higher than the first auxiliary oil return hole 115a (as shown in step S114 in FIG. 1 ). Fig. 9 or when the liquid level in the first gas-liquid separator 108a is not lower than the first set threshold, it is estimated that the liquid level in the first auxiliary oil return hole 115a is lower than that in the first auxiliary oil return hole 115a (as shown in step S115 in FIG. 1 ); Fig. 9 (as shown in step S116).

[0089] Correspondingly, such as Fig.10 As shown, the control unit 30 is configured to sample the temperature detected by the second outlet temperature sensor 117b (eg Fig.10 As shown in step S211), sampling the temperature detected by the second inlet temperature sensor 118b (as shown in step S212). Fig.10 Calculate the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b (as shown in step S212). Fig.10 As shown in step S213), it is determined whether the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b is lower than a second set threshold value (such as Fig.10 When the liquid level in the second gas-liquid separator 108b is lower than the second set threshold, it is estimated that the liquid level in the second gas-liquid separator 108b is higher than the second auxiliary oil return hole 115b (as shown in step S214 in FIG. 1 ). Fig.10 or when the liquid level in the second gas-liquid separator 108b is not lower than the second set threshold, it is estimated that the liquid level in the second gas-liquid separator 108b is lower than the second auxiliary oil return hole 115b (as shown in step S215); Fig.10 (as shown in step S216).

[0090] In one or more embodiments of the present application, the control unit 30 is configured to infer that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, and the liquid level of the second gas-liquid separator 108b is higher than the second auxiliary oil return hole 115b, and the liquid level of the first gas-liquid separator 108a is lower than the first auxiliary oil return hole 115a (such as when the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a is not lower than the first set threshold, the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b is lower than the second set threshold, and the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than the third set threshold. Fig.11 As shown), the regulating valve 121 is driven to operate and connect the distribution pipe 120, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b can quickly transition from the non-uniform liquid level state to the uniform liquid level state in a short time.

[0091] In one or more embodiments of the present application, the control unit 30 is configured to infer that the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state, and the liquid level of the first gas-liquid separator 108a is higher than the first auxiliary oil return hole 115a, and the liquid level of the second gas-liquid separator 108b is lower than the second auxiliary oil return hole 115b (such as when the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a is lower than the first set threshold, the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b is not lower than the second set threshold, and the exhaust temperature difference between the first compressor 100a and the second compressor 100b is not lower than the third set threshold. Fig.12 As shown), the regulating valve 121 is driven to operate and connect the distribution pipe 120, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b can quickly transition from the non-uniform liquid level state to the uniform liquid level state in a short time.

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

[0093] For example, Fig.15As shown, the third set threshold is the sum of a reference temperature (pre-set and stored) and a correction temperature. When the outdoor ambient temperature is lower than minus 20°C, the correction temperature is 5°C; when the outdoor ambient temperature is higher than minus 20°C but lower than minus 10°C, the correction temperature is 3°C; when the outdoor ambient temperature is higher than minus 10°C but lower than 7°C, the correction temperature is 1°C; when the outdoor ambient temperature is higher than 7°C, the correction temperature is 0°C. That is, the lower the outdoor ambient temperature, the looser the presumed condition for active adjustment of the liquid level. This is because the viscosity of the lubricating oil is higher at low temperatures, and the oil return characteristics of the refrigeration system 1 will become worse. It is necessary to balance the distribution of the lubricating oil through liquid balancing to improve the oil return characteristics.

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

[0095] In one or more embodiments of the present application, the regulating valve 121 can be a solenoid valve. The control unit 30 drives the regulating valve 121 to operate the conducting distribution pipe 120 until the end of the set conduction period, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b transition from a non-uniform liquid level state to a uniform liquid level state. The duration of the set conduction period is obtained based on a first fitting curve generated according to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. In the first fitting curve, the set conduction period corresponds one-to-one to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. The first fitting curve is preferably measured under experimental conditions, and an exemplary first fitting curve is as follows. Fig.16 As shown, ΔTd represents the exhaust gas temperature difference between the first compressor 100a and the second compressor 100b, and T represents the duration of the set conduction period.

[0096] In one or more embodiments of the present application, the regulating valve 121 can be an electronic expansion valve. The control unit 30 drives the regulating valve 121 to operate and connect the distribution pipe 120, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b transition from a uniform liquid level state to a uniform liquid level state. Among them, the operation of the regulating valve 121 is divided into multiple continuous adjustment cycles, and the opening of the next adjustment cycle is the sum of the opening of the current adjustment cycle and the correction opening. The correction opening is the product of the maximum opening and the proportional coefficient. The proportional coefficient is obtained based on a second fitting curve generated according to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. In the second fitting curve, the proportional coefficient corresponds one-to-one to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. The second fitting curve is preferably measured under experimental conditions, and an exemplary second fitting curve is such as Fig.17As shown, ΔTd represents the exhaust gas temperature difference between the first compressor 100a and the second compressor 100b, and ΔEV represents the proportionality coefficient in percentage.

[0097] During actual use, non-uniform liquid level conditions usually occur in the transition stage of the refrigeration system 1, such as the startup stage of the outdoor unit, the shutdown stage of the outdoor unit, the increase or decrease in the number of working indoor units corresponding to the outdoor unit, defrosting, and refrigerant charging, etc. This will cause drastic changes in the gas and liquid in the refrigeration system 1, and will cause instantaneous liquid level fluctuations. At this time, small liquid level changes will occur, resulting in disproportionate temperature changes, reducing the accuracy of the exhaust temperature as a liquid level judgment indicator.

[0098] To solve this problem, in one or more embodiments of the present application, the control unit 30 is configured to estimate whether the first gas-liquid separator 108a and the second gas-liquid separator 108b are in a non-uniform liquid level state based on the temperature changes before and after the first pressure reducing element 119a and the second pressure reducing element 119b, the temperature difference of the exhaust temperature between the first compressor 100a and the second compressor 100b, and the operating current difference between the first compressor 100a and the second compressor 100b; and when it is estimated to be a non-uniform liquid level state, drive the regulating valve 121 to operate to adjust the refrigerant flow in the distribution pipe.

[0099] In accordance with the use of the temperature difference of the exhaust gas temperature between the first compressor 100a and the second compressor 100b as the estimation condition, a first inlet temperature sensor 118a and a first outlet temperature sensor 117a are also provided on the first detection branch 116a that is fluidly connected to the fluid of the first compressor 100a. The first inlet temperature sensor 118a is provided on the inlet side of the first detection branch 116a and is close to the first auxiliary oil return hole 115a. The first outlet temperature sensor 117a is provided on the outlet side of the first detection branch 116a and is close to the first compressor 100a. Along the refrigerant flow direction, the first inlet temperature sensor 118a, the first pressure reducing element 119a and the first outlet temperature sensor 117a are provided in sequence.

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

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

[0102] In one or more embodiments of the present application, Fig.13 As shown in the multiple steps in the above, the control unit 30 samples the temperature detected by the first outlet temperature sensor 117a (such as Fig.13 As shown in step S311), the first inlet temperature sensor 118a detects the temperature (as shown in step S311). Fig.13 Calculate the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a (as shown in step S312). Fig.13 and determine whether it is not lower than a first set threshold (such as Fig.13 As shown in step S314); sampling the temperature detected by the second outlet temperature sensor 117b (such as Fig.13 As shown in step S321), the second inlet temperature sensor 118b detects the temperature (as shown in step S322). Fig.13 Calculate the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b (as shown in step S322). Fig.13 and determine whether it is lower than a second set threshold (such as Fig.13 Sampling the exhaust temperature of the first compressor 100a (as shown in step S324); Fig.13 As shown in step S331), the exhaust temperature of the second compressor 100b (as shown in step S332) Fig.13 Calculate the exhaust temperature difference between the first compressor 100a and the second compressor 100b (as shown in step S332). Fig.13 and determine whether it is not lower than a third set threshold value (such as Fig.13 Sampling the operating current of the first compressor 100a (as shown in step S334); Fig.13 As shown in step S341), the operating current of the second compressor 100b is sampled (as shown in step S342). Fig.13 Calculate the operating current difference between the first compressor 100a and the second compressor 100b (as shown in step S342). Fig.13 and determine whether it is not lower than the fourth set threshold (such as Fig.13 (as shown in step S344).

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

[0104] In one or more embodiments of the present application, Fig.14 As shown in the multiple steps in the above, the control unit 30 samples the temperature detected by the first outlet temperature sensor 117a (such as Fig.14 As shown in step S411), the first inlet temperature sensor 118a detects the temperature (as shown in step S412). Fig.14 ), calculate the difference between the temperature detected by the first outlet temperature sensor 117a and the temperature detected by the first inlet temperature sensor 118a (as shown in step S412). Fig.14 and determine whether it is lower than a first set threshold (such as Fig.14 As shown in step S414); sampling the temperature detected by the second outlet temperature sensor 117b (such as Fig.14 As shown in step S421), the second inlet temperature sensor 118b detects the temperature (as shown in step S422). Fig.14 Calculate the difference between the temperature detected by the second outlet temperature sensor 117b and the temperature detected by the second inlet temperature sensor 118b (as shown in step S422). Fig.14 and determine whether it is not lower than a second set threshold (such as Fig.14 Sampling the exhaust temperature of the first compressor 100a (as shown in step S424); Fig.14 As shown in step S431), the exhaust temperature of the second compressor 100b (as shown in step S432) Fig.14 Calculate the exhaust gas temperature difference between the first compressor 100a and the second compressor 100b (as shown in step S432). Fig.14 and determine whether it is not lower than a third set threshold value (such as Fig.14 Sampling the operating current of the first compressor 100a (as shown in step S434); Fig.14 As shown in step S441), the operating current of the second compressor 100b is sampled (as shown in step S442). Fig.14 ), calculate the operating current difference between the first compressor 100a and the second compressor 100b (as shown in step S442). Fig.14 and determine whether it is not lower than the fourth set threshold (such as Fig.14 (as shown in step S444).

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

[0106] Since the non-uniform liquid level state usually occurs in the transition stage of the refrigeration system 1, such as the startup stage of the outdoor unit, the shutdown stage of the outdoor unit, the increase and decrease of the number of the working indoor units corresponding to the outdoor unit, defrosting and refrigerant filling, etc., this will cause a sharp change in the gas and liquid in the refrigeration system 1, which will cause instantaneous liquid level fluctuations, which are difficult to identify (even high-precision sensors cannot identify). For this, in the present application, the control unit 30, on the one hand, identifies the distribution of gas-phase refrigerant and liquid-phase refrigerant in the first gas-liquid separator 108a and the second gas-liquid separator 108b based on the temperature change of the first detection branch 116a and the temperature change of the second detection branch 116b; on the other hand, based on the complementary compressor exhaust temperature difference and the operating current difference, the influence of the workload of the first compressor 100a and the second compressor 100b on the liquid level is identified, so as to avoid small liquid level changes causing disproportionate temperature changes and reduce the accuracy of temperature as a liquid level judgment indicator. The operating current of the compressor is directly related to its workload, especially in the start-stop stage, the current will respond to changes, and the detection is more accurate, and the compressor exhaust temperature can further identify whether the compressor itself has a fault. The multi-parameter method has better robustness and can handle changes under different transition working conditions, and can better cope with load changes, environmental changes, and even sensor failures. It is especially used for systems above 100HP and with a drop of more than 100 meters.

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

[0108] In one or more embodiments of the present application, the regulating valve 121 can be a solenoid valve. The control unit 30 drives the regulating valve 121 to conduct the distribution pipe 120 until the end of the set conduction period, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b transition from a non-uniform liquid level state to a uniform liquid level state. Wherein, the duration of the set conduction period is obtained based on a first fitting curve generated according to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. In the first fitting curve, the set conduction period corresponds to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. The first fitting curve is preferably measured under experimental conditions, and an exemplary first fitting curve is shown in the figure, where ΔTd represents the exhaust temperature difference between the first compressor 100a and the second compressor 100b, and T represents the duration of the set conduction period.

[0109] In one or more embodiments of the present application, the regulating valve 121 may be an electronic expansion valve. The control unit 30 drives the regulating valve 121 to operate and conduct the distribution pipe 120, so that the first gas-liquid separator 108a and the second gas-liquid separator 108b transition from a uniform liquid level state to a uniform liquid level state. Among them, the regulating valve 121 is divided into a plurality of continuous adjustment cycles when it is in operation, and the opening of the next adjustment cycle is the sum of the opening of the current adjustment cycle and the correction opening. The correction opening is the product of the maximum opening and the proportional coefficient. The proportional coefficient is obtained based on a second fitting curve generated according to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. In the second fitting curve, the proportional coefficient corresponds to the exhaust temperature difference between the first compressor 100a and the second compressor 100b. The second fitting curve is preferably measured under experimental conditions, and an exemplary second fitting curve is shown in the figure, where ΔTd represents the exhaust temperature difference between the first compressor 100a and the second compressor 100b, and ΔEV represents the proportional coefficient in percentage.

[0110] 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.

[0111] 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; Second compressor; 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, wherein a first outlet pipe connected to the first compressor is provided; a second gas-liquid separator connected to another outlet of the distributor, wherein a second outlet pipe connected to the second compressor is provided; and a distribution pipe, two ends of which are respectively connected to the first gas-liquid separator and the second gas-liquid separator; It is characterized by further comprising: A regulating valve, which is arranged on the distribution pipe; a first detection branch, which is connected to the first outlet pipe through a first auxiliary oil return hole, the first auxiliary oil return hole is higher than the bottom of the first outlet pipe, and the first detection branch is provided with a first pressure reducing element; a second detection branch, which is connected to the second outlet pipe through a second auxiliary oil return hole, the second auxiliary oil return hole is higher than the bottom of the second outlet pipe, the second detection branch is provided with a second pressure reducing element, wherein the first auxiliary oil return hole and the second auxiliary oil return hole have the same height, and the first pressure reducing element and the second pressure reducing element are the same; and A control unit is configured to control the first compressor and the second compressor to operate at the same operating frequency, and to estimate whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state based on the temperature changes before and after the first pressure reducing element and the second pressure reducing element, and the temperature difference of the exhaust gas temperature between the first compressor and the second compressor; and when it is estimated to be a non-uniform liquid level state, drive the regulating valve to adjust the refrigerant flow in the distribution pipe to transition to a uniform liquid level state.

2. The refrigeration system according to claim 1, characterized in that: The first detection branch is also fluidically connected to the first compressor, and further comprises: a first inlet temperature sensor, the first inlet temperature sensor being arranged at the inlet side of the first detection branch and close to the first auxiliary oil return hole; a first outlet temperature sensor, which is disposed at an outlet side of the first detection branch and is close to the first compressor; Along the refrigerant flow direction, the first inlet temperature sensor, the first pressure reducing element and the first outlet temperature sensor are arranged in sequence; The second detection branch is also fluidically connected to the second compressor, and further comprises: a second inlet temperature sensor, the second inlet temperature sensor being arranged at the inlet side of the second detection branch and close to the second auxiliary oil return hole; a second outlet temperature sensor, the second outlet temperature sensor being disposed at an outlet side of the second detection branch and close to the second compressor; Along the refrigerant flow direction, the second inlet temperature sensor, the second pressure reducing element and the second outlet temperature sensor are arranged in sequence.

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

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

5. The refrigeration system according to claim 3, characterized in that: The regulating valve is an electronic expansion valve, and the control unit drives the regulating valve to conduct the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state; Among them, the control valve is divided into multiple continuous control cycles when it is in operation; the opening of the next control cycle is the sum of the opening of the current control cycle and the correction opening; the correction opening is the product of the maximum opening and the proportional coefficient, and the proportional coefficient is obtained based on a second fitting curve generated according to the exhaust temperature difference between the first compressor and the second compressor. In the second fitting curve, the proportional coefficient corresponds one-to-one to the exhaust temperature difference between the first compressor and the second compressor.

6. Refrigeration system, including: An outdoor unit comprising: The first compressor; Second compressor; 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, wherein a first outlet pipe connected to the first compressor is provided; a second gas-liquid separator connected to another outlet of the distributor, wherein a second outlet pipe connected to the second compressor is provided; and a distribution pipe, two ends of which are respectively connected to the first gas-liquid separator and the second gas-liquid separator; It is characterized by further comprising: A regulating valve, which is arranged on the distribution pipe; a first detection branch, which is connected to the first outlet pipe through a first auxiliary oil return hole, the first auxiliary oil return hole is higher than the bottom of the first outlet pipe, and the first detection branch is provided with a first pressure reducing element; a second detection branch, which is connected to the second outlet pipe through a second auxiliary oil return hole, the second auxiliary oil return hole is higher than the bottom of the second outlet pipe, the second detection branch is provided with a second pressure reducing element, wherein the first auxiliary oil return hole and the second auxiliary oil return hole have the same height, and the first pressure reducing element and the second pressure reducing element are the same; and A control unit is configured to control the first compressor and the second compressor to operate at the same operating frequency, and estimate whether the first gas-liquid separator and the second gas-liquid separator are in a non-uniform liquid level state based on the temperature changes before and after the first pressure reducing element and the second pressure reducing element, the temperature difference of the exhaust temperature between the first compressor and the second compressor, and the operating current difference between the first compressor and the second compressor; and when it is estimated to be a non-uniform liquid level state, drive the regulating valve to adjust the refrigerant flow in the distribution pipe to transition to a uniform liquid level state.

7. The refrigeration system according to claim 6, characterized in that: The first detection branch is also fluidically connected to the first compressor, and further comprises: a first inlet temperature sensor, the first inlet temperature sensor being arranged at the inlet side of the first detection branch and close to the first auxiliary oil return hole; a first outlet temperature sensor, which is disposed at an outlet side of the first detection branch and is close to the first compressor; Along the refrigerant flow direction, the first inlet temperature sensor, the first pressure reducing element and the first outlet temperature sensor are arranged in sequence; The second detection branch is also fluidically connected to the second compressor, and further comprises: a second inlet temperature sensor, the second inlet temperature sensor being arranged at the inlet side of the second detection branch and close to the second auxiliary oil return hole; a second outlet temperature sensor, the second outlet temperature sensor being disposed at an outlet side of the second detection branch and close to the second compressor; Along the refrigerant flow direction, the second inlet temperature sensor, the second pressure reducing element and the second outlet temperature sensor are arranged in sequence.

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

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

10. The refrigeration system according to claim 8, characterized in that: The regulating valve is an electronic expansion valve, and the control unit drives the regulating valve to conduct the distribution pipe, so that the first gas-liquid separator and the second gas-liquid separator transition from a non-uniform liquid level state to a uniform liquid level state; Among them, the control valve is divided into multiple continuous control cycles when it is in operation; the opening of the next control cycle is the sum of the opening of the current control cycle and the correction opening; the correction opening is the product of the maximum opening and the proportional coefficient, and the proportional coefficient is obtained based on a fitting curve generated according to the exhaust temperature difference between the first compressor and the second compressor. In the fitting curve, the proportional coefficient corresponds one-to-one to the exhaust temperature difference between the first compressor and the second compressor.

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