Multi-connected system, multi-compressor outdoor unit multi-connected system

Abstract

The application discloses a multi-connected system, comprising one outdoor unit or multiple parallel outdoor units, multiple parallel indoor units; each outdoor unit is connected with each indoor unit; the outdoor unit comprises at least one compressor, at least one oil separator, at least one bypass branch and at least one one-way valve corresponding to the connection; the compressor comprises an exhaust port and a suction port; the oil separator is connected in series on the pipeline between the exhaust port and the one-way valve; the two ends of the bypass branch are connected with the common end of the one-way valve and the oil separator and the suction port; the outdoor unit further comprises a controller, a temperature sensor, at least one first pressure sensor and at least one second pressure sensor, which are used for detecting the ambient temperature, the exhaust pressure and the suction pressure and transmitting the same to the controller; the bypass branch is controlled to be connected and disconnected by the controller; the controller is configured to control the connection of the bypass branch and the connection duration according to the ambient temperature, the exhaust pressure and the suction pressure when the outdoor unit is stopped. The application improves the starting safety of the compressor.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, specifically to a multi-split air conditioning system and a multi-compressor outdoor unit multi-split air conditioning system. Background Technology

[0002] A multi-split air conditioning system consists of one or more outdoor units combined into a single outdoor unit, which in turn powers multiple indoor units to provide cooling and heating functions. Each outdoor unit can have one, two, or more compressors, and each compressor has a one-way valve on its discharge or refrigerant supply line. When the compressor is running, the one-way valve is open; when the compressor stops, the one-way valve is closed to prevent refrigerant from flowing back into the compressor.

[0003] When the compressor stops, some high-pressure refrigerant accumulates in the pipeline between the compressor discharge port and the one-way valve, as well as in the oil separator, while the compressor suction side remains at low pressure. When the compressor restarts shortly afterward, it needs to overcome the pressure difference between the high and low pressures before and after the compressor, as well as the high pressure after the one-way valve. If the air conditioning unit's driving capacity is insufficient, problems such as abnormal compressor stoppage, compressor malfunction, or even wear and damage may occur.

[0004] Furthermore, check valves are prone to leakage during application. If a check valve leaks, the high pressure at the compressor's discharge port will cause the compressor to start with a differential pressure the next time it starts, resulting in excessive starting resistance and potential damage to the compressor.

[0005] The information disclosed in this background section is only intended to enhance the understanding of the background technology of this application, and therefore may include prior art that is not known to those skilled in the art. Summary of the Invention

[0006] In response to the problem of compressor start-up damage caused by high pressure buildup between the one-way valve and the exhaust port as mentioned in the background art, this invention proposes a multi-split air conditioning system and a multi-compressor outdoor unit multi-split air conditioning system to solve the problem of compressor start-up damage under differential pressure, improve the safety and stability of compressor start-up in the system, and thus extend the compressor life.

[0007] To achieve the above-mentioned objectives, the present invention employs the following technical solution: A multi-split air conditioning system includes one or more outdoor units connected in parallel and multiple indoor units connected in parallel; each outdoor unit is connected to each indoor unit; each outdoor unit includes a gas-liquid separator and at least one compressor, at least one oil separator, at least one bypass branch, and at least one check valve respectively connected to it; the compressor includes an exhaust port and an intake port; the oil separator is connected in series in the pipeline between the exhaust port and the check valve; the gas-liquid separator is connected to the intake port; the two ends of the bypass branch are respectively connected to the common end of the check valve and the oil separator, and the far end of the gas-liquid separator relative to the intake port, and can be controllably connected and disconnected; The outdoor unit also includes a controller, and a temperature sensor, at least one first pressure sensor, and at least one second pressure sensor connected to the controller, which are respectively used to detect the ambient temperature, the corresponding discharge pressure of the compressor, and the suction pressure and transmit them to the controller; the bypass branch is connected to the controller and is controlled by the controller to connect and disconnect; the controller is configured to control the connection and connection duration of the corresponding bypass branch according to the ambient temperature, the discharge pressure, and the suction pressure when the outdoor unit is stopped and the bypass branch is disconnected.

[0008] In some specific embodiments, the controller is also configured with an exhaust pressure threshold, an intake pressure threshold, an ambient temperature threshold, and a first connection duration; The controller is configured to acquire the ambient temperature and the discharge pressure and suction pressure of each compressor in real time when the outdoor unit is stopped, and compare the discharge pressure with the discharge pressure threshold, the suction pressure with the suction pressure threshold, and the ambient temperature with the ambient temperature threshold; and when the discharge pressure reaches and / or exceeds the discharge pressure threshold, the suction pressure reaches and / or exceeds the suction pressure threshold, and the ambient temperature reaches and / or exceeds the ambient temperature threshold, control the bypass branch to connect to the first connection duration.

[0009] In some specific embodiments, the controller is further configured with a first threshold value for the difference between exhaust pressure and intake pressure, and a second connection duration; The controller is configured to acquire the discharge pressure and suction pressure of each compressor in real time when the outdoor unit is stopped, calculate the difference between the discharge pressure and the suction pressure, and compare the difference between the discharge pressure and the suction pressure with a first discharge pressure and suction pressure difference threshold; when the difference between the discharge pressure and the suction pressure reaches and / or exceeds the first discharge pressure and suction pressure difference threshold, the controller controls the bypass branch to connect to the second connection duration.

[0010] In some specific embodiments, the controller is further configured with an exhaust pressure threshold, an intake pressure threshold, an ambient temperature threshold, a threshold for the difference between a first exhaust pressure and an intake pressure, and a first connection duration; The controller is configured to receive the ambient temperature and the discharge pressure and suction pressure of each compressor in real time when the outdoor unit is stopped, calculate the difference between the discharge pressure and the suction pressure, and compare the discharge pressure with the discharge pressure threshold, the suction pressure with the suction pressure threshold, the ambient temperature with the ambient temperature threshold, and the difference between the discharge pressure and the suction pressure with the first discharge pressure and suction pressure difference threshold. When the discharge pressure reaches and / or exceeds the discharge pressure threshold and the suction pressure reaches and / or exceeds the suction pressure threshold and the ambient temperature reaches and / or exceeds the ambient temperature threshold, and / or the difference between the discharge pressure and the suction pressure reaches and / or exceeds the first discharge pressure and suction pressure difference threshold, the controller controls the bypass branch to connect to the first connection duration.

[0011] In some specific embodiments, the controller is configured with a power-on duration threshold and is configured to count the initial power-on duration of the outdoor unit when the outdoor unit is powered off and shut down, compare the initial power-on duration with the power-on duration threshold, and control the bypass branch to connect when the initial power-on duration is within the range of the power-on duration threshold; otherwise, control the bypass branch to disconnect.

[0012] In some specific embodiments, the controllers of each outdoor unit are communicatively connected; the controller is configured with a third threshold for the difference between exhaust pressure and intake pressure, and is configured to, when an additional outdoor unit is operating, calculate the allocated frequency of each outdoor unit, and control the compressor of the operating outdoor unit to reduce its frequency while receiving its exhaust pressure and intake pressure in real time, calculate the difference between the exhaust pressure and intake pressure, and compare the difference between the exhaust pressure and intake pressure with the third threshold for the difference between exhaust pressure and intake pressure; and when the difference between the exhaust pressure and intake pressure reaches and / or falls below the third threshold for the difference between exhaust pressure and intake pressure, control the compressor of each reduced-frequency unit to increase its frequency to the allocated frequency, and simultaneously control the compressor of the outdoor unit to be started to start and increase its frequency to the allocated frequency.

[0013] In some specific embodiments, the controller is configured with a suction pressure increase threshold and a saturation temperature difference threshold, and is configured to, when the outdoor unit is stopped, cyclically acquire the ambient temperature and the suction pressure of each compressor, and calculate the difference between the saturation temperature corresponding to the suction pressure and the ambient temperature, as well as the latest continuously acquired increase in suction pressure; compare the difference with the saturation temperature difference threshold, and the increase with the suction pressure increase threshold; when the difference reaches and / or exceeds the saturation temperature difference threshold and the increase reaches and / or exceeds the suction pressure increase threshold, control it to start first and issue a fault alarm.

[0014] A multi-compressor outdoor unit multi-split air conditioning system includes one or more outdoor units connected in parallel and multiple indoor units connected in parallel; the outdoor unit is connected to each of the indoor units; the outdoor unit includes a gas-liquid separator and multiple compressors, multiple oil separators, multiple bypass branches, and multiple one-way valves respectively connected to it; the compressor includes an exhaust port and an intake port; the oil separator is connected in series in the pipeline between the exhaust port and the one-way valve; the gas-liquid separator is connected to each of the intake ports respectively; the two ends of the bypass branch are respectively connected to the common end of the one-way valve and the oil separator, and the far end of the gas-liquid separator relative to each of the intake ports, and can be controllably connected and disconnected; The outdoor unit also includes a controller and a plurality of first pressure sensors and a plurality of second pressure sensors connected to the controller, which are respectively used to detect the discharge pressure and suction pressure of each compressor and transmit them to the controller; each bypass branch is connected to the controller and is controlled by the controller to connect and disconnect; the controller is configured to control the connection and connection duration of the corresponding bypass branch when at least one compressor of the outdoor unit is running, based on the discharge pressure and suction pressure of other compressors in the outdoor unit that are not running.

[0015] In some specific embodiments, the controller is configured with a second discharge pressure and intake pressure difference threshold and a third connection duration, and is configured to, when at least one of the compressors in the outdoor unit is running, acquire in real time the discharge pressure and intake pressure of each of the other non-running compressors, calculate the corresponding difference between the discharge pressure and intake pressure, compare it with the second discharge pressure and intake pressure difference threshold, and when the difference between the discharge pressure and intake pressure reaches and / or exceeds the second discharge pressure and intake pressure difference threshold, control the corresponding bypass branch to connect to the third connection duration.

[0016] In some specific embodiments, the controller is configured with a third threshold for the difference between exhaust pressure and intake pressure, and is configured to, when at least one of the compressors of the outdoor unit is operating and an additional compressor needs to be operated, calculate the allocated frequencies of the operating compressor and the compressor to be started, control the operating compressor to reduce its frequency while cyclically acquiring its exhaust pressure and intake pressure, calculate the difference between the exhaust pressure and the intake pressure, compare the difference between the exhaust pressure and the intake pressure with the third threshold for the difference between exhaust pressure and intake pressure, and when the difference between the exhaust pressure and the intake pressure reaches and / or is less than the third threshold for the difference between exhaust pressure and intake pressure, control the operating compressor to increase its frequency to the allocated frequency, and simultaneously control the compressor to be started to start and increase its frequency to the allocated frequency.

[0017] The multi-split air conditioning system and multi-compressor outdoor unit multi-split air conditioning system of the present invention control the connection and connection time of the bypass branch according to the ambient temperature, the discharge pressure and suction pressure of the compressor when it is stopped or stopped. Under the premise of reducing the pressure difference before and after the compressor, the connection time of the bypass branch is shortened as much as possible to prevent the compressor from starting with pressure difference, thereby improving the reliability and safety of compressor start-up and extending compressor life. In addition, shortening the connection time of the bypass branch can reduce the loss of bypass capacity and the noise generated by the connection of the bypass branch, thereby improving operating efficiency and enhancing the user experience.

[0018] Other features and advantages of the present invention will become clearer after reading the detailed embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram illustrating the composition and connection of a single-compressor outdoor unit multi-split air conditioning system according to an embodiment; Figure 2 This is a schematic diagram illustrating the composition and connection of a multi-compressor outdoor unit multi-split system according to an embodiment; Figure 3 This is a schematic diagram illustrating the composition and connection of a single-compressor outdoor unit multi-split air conditioning system according to an embodiment; Figure 4 This is a schematic diagram illustrating the composition and connection of a multi-compressor outdoor unit multi-split system according to an embodiment; Figure 5This is a schematic diagram of the control system composition and connection according to an embodiment; Figure 6 This is a schematic diagram of the bypass branch control flow when the outdoor unit of the multi-split air conditioning system is shut down according to an embodiment; Figure 7 This is a schematic diagram of the bypass branch control flow when the outdoor unit of the multi-split air conditioning system is shut down according to an embodiment; Figure 8 This is a schematic diagram of the bypass branch control flow when the outdoor unit of the multi-split air conditioning system is powered on after a power outage according to an embodiment. Figure 9 A schematic diagram of the compressor control process of the outdoor unit when starting up the multi-split air conditioning system according to the embodiment is required.

[0021] Figure 10 This is a schematic diagram of the bypass branch control flow in the outdoor unit of a multi-compressor outdoor unit multi-split system according to an embodiment; Figure 11 This is a schematic diagram of the control flow when at least one compressor in the outdoor unit of a multi-compressor outdoor unit multi-split system according to an embodiment needs to be started. Figure 12 This is a schematic diagram of the control timing when at least one compressor in the outdoor unit of a multi-compressor outdoor unit multi-split system according to an embodiment needs to be started.

[0022] Figure label, 1. Outdoor unit; 2. Indoor unit; 10. Controller; 11. Compressor; 12. Gas-liquid separator; 13. Oil separator; 14. Check valve; 15. Bypass branch; 16. Oil return branch; 17. Four-way valve; 18. Outdoor heat exchanger; 19. Temperature sensor; 110. First pressure sensor; 111. Second pressure sensor. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0025] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0026] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0027] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0028] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0029] Air Conditioner Working Principle The outdoor unit of the multi-split air conditioner in this application operates on the basic air conditioning principle, using a compressor, condenser, expansion valve, and evaporator to perform the air conditioning refrigeration cycle. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation to cool or heat the indoor space.

[0030] Low-temperature, low-pressure refrigerant enters the compressor, which compresses it into a high-temperature, high-pressure refrigerant gas and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and the heat is released to the surrounding environment through the condensation process.

[0031] The expansion valve expands the high-temperature, high-pressure liquid refrigerant that condenses in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the expanded refrigerant in the expansion valve and returns the low-temperature, low-pressure refrigerant gas to the compressor. The evaporator achieves its cooling effect by utilizing the latent heat of refrigerant evaporation to exchange heat with the material being cooled. Throughout the cycle, the outdoor unit regulates the temperature of the indoor space.

[0032] The outdoor unit refers to the part of the refrigeration cycle that includes the compressor and the outdoor heat exchanger. The outdoor unit includes the indoor heat exchanger, and the expansion valve can be provided in the outdoor unit or in the outdoor unit.

[0033] The indoor and outdoor heat exchangers function as either condensers or evaporators. When the indoor heat exchanger is used as a condenser, the air conditioner functions as a heater in heating mode; when the indoor heat exchanger is used as an evaporator, the air conditioner functions as a cooler in cooling mode.

[0034] Reference Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8The multi-split air conditioning system of the present invention includes one or more outdoor units 1 and multiple outdoor units 2; when there are multiple outdoor units 1, each outdoor unit 1 is connected in parallel; each outdoor unit 2 is connected in parallel; each outdoor unit 1 connected in parallel or each outdoor unit 1 individually is connected to each outdoor unit 2 connected in parallel, forming a refrigeration cycle from outdoor unit 1 to outdoor unit 2 and back to outdoor unit 1, so that one or more of the outdoor units 1 provide latent heat of refrigerant to one or more of the outdoor units 2. That is, when the latent heat of refrigerant required by each outdoor unit 2 is small, one of the outdoor units 1 can be operated to provide latent heat of refrigerant to each outdoor unit 2 or one or more of the outdoor units 2; when the latent heat of refrigerant required by each outdoor unit 2 is large, multiple or all of the outdoor units 1 can be operated, and the operating outdoor units 1 together provide latent heat of refrigerant to each outdoor unit 2 or one or more of the outdoor units 2.

[0035] The outdoor unit 1 includes a gas-liquid separator 12, a four-way valve 17, an outdoor heat exchanger 18, and at least one compressor 11, at least one oil separator 13, at least one bypass branch 15, at least one oil return branch 16, and at least one check valve 14, which are respectively connected to each other.

[0036] The compressor 11 includes an exhaust port and an intake port; the four-way valve 17 includes a first port, a second port, a third port, and a fourth port; the oil separator 13 is connected in series in the pipeline between the exhaust port and the one-way valve 14. That is, the exhaust port is connected to the refrigerant inlet of the oil separator 13; the refrigerant outlet of the oil separator 13 is connected to one port of the one-way valve 14; and the other port of the one-way valve 14 is connected to the first port.

[0037] The gas-liquid separator 12 is connected in series on the pipeline from each air intake to the four-way valve 17; that is, each air intake is connected to the refrigerant outlet of the gas-liquid separator 12; the refrigerant inlet of the gas-liquid separator 12 is connected to the third port; the second port and the fourth port are respectively connected to the outdoor unit 2 and the outdoor heat exchanger 18.

[0038] The two ends of the bypass branch 15 are respectively connected to the common end of the one-way valve 14 and the oil separator 13, and the far end of the gas-liquid separator 12 relative to the suction port. This allows for controllable connection and disconnection, used to control whether the high-pressure pipeline and the low-pressure pipeline are connected, thereby reducing the pressure difference before and after the compressor 11. Specifically, one end of the bypass branch 15 is connected to the pipeline connecting the one-way valve 14 and the refrigerant outlet of the oil separator 13, and the other end is connected to the pipeline connecting the refrigerant inlet and the third port of the gas-liquid separator 12.

[0039] The two ends of the oil return branch 16 are respectively connected to the far ends of the oil separator 13 and the gas-liquid separator 12 relative to the air intake port; that is, one end of the oil return branch 16 is connected to the oil return port of the oil separator 13, and the other end is connected to the pipeline connecting the refrigerant inlet and the third port of the gas-liquid separator 12, so as to realize the oil return through the oil return branch 16.

[0040] The outdoor unit 1 also includes a controller 10, which is connected to the compressor 11, the bypass branch 15, and the four-way valve 17 to control their operation or action. The outdoor unit 1 also includes a temperature sensor 19, at least one first pressure sensor 110, and at least one second pressure sensor 111, which are connected to the controller 10 and are used to detect the outdoor ambient temperature, the discharge pressure of the compressor 11, and the suction pressure, respectively, and transmit them to the controller 10.

[0041] The controller 10 is configured to control the connection and connection duration of the bypass branch 15 based on the ambient temperature, exhaust pressure and intake pressure when the outdoor unit 1 is stopped and the bypass branch 15 is disconnected.

[0042] The multi-split air conditioning system of the present invention adjusts the connection time of the bypass branch 15 of the outdoor unit 1 based on the ambient temperature, exhaust pressure, and intake pressure. While reducing the pressure difference before and after the compressor 11, the connection time of the bypass branch 15 is shortened as much as possible to prevent the compressor 11 from starting with a pressure difference when the outdoor unit 1 starts, thereby improving the reliability and safety of the compressor 11 and extending the life of the compressor 11. In addition, shortening the connection time of the bypass branch 15 can reduce the loss of bypass capacity and the noise generated when the bypass branch 15 is connected, thereby improving the operating efficiency of the outdoor unit 1 and enhancing the user experience.

[0043] The control flow and principle of the multi-unit air conditioning system of the present invention will be described in detail below through specific embodiments.

[0044] In some specific embodiments, refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 The controller 10 is configured with an exhaust pressure threshold, an intake pressure threshold, an ambient temperature threshold, and a first connection time S11. That is, the ambient temperature threshold, exhaust pressure threshold, intake pressure threshold, and first connection time S11 are set in the controller 10.

[0045] The controller 10 is configured to receive the ambient temperature of the outdoor unit 1 and the corresponding discharge pressure and suction pressure of the compressor 11 in real time when the outdoor unit 1 stops and the bypass branch 15 is disconnected (S12). It also compares the discharge pressure with the discharge pressure threshold, the suction pressure with the suction pressure threshold, and the ambient temperature with the ambient temperature threshold. When the discharge pressure reaches and / or exceeds the discharge pressure threshold, the suction pressure reaches and / or exceeds the suction pressure threshold, and the ambient temperature reaches and / or exceeds the ambient temperature threshold (S14), it controls the bypass branch 15 to connect for a first connection time (S15) to ensure that the pressure difference before and after the compressor 11 reaches a safe starting level and the bypass branch 15 connection time is minimized.

[0046] Of course, when determining whether the bypass branch 15 is connected, the exhaust pressure can be equal to or greater than the exhaust pressure threshold, or greater than or equal to the exhaust pressure threshold; the intake pressure can be equal to or greater than the intake pressure threshold, or greater than or equal to the intake pressure threshold.

[0047] The multi-split air conditioning system of this embodiment can solve the problems of high pressure difference before and after compressor 11 caused by outdoor unit 1 shutdown and high pressure difference before and after compressor 11 caused by leakage of one-way valve 14, thereby improving system stability and compressor 11 life.

[0048] In some specific embodiments, refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 7 The controller 10 is configured with a first threshold value for the difference between exhaust pressure and intake pressure, and a second connection duration S21. That is, the controller 10 is configured with a first threshold value for the difference between exhaust pressure and intake pressure, and a second connection duration S21.

[0049] The controller 10 is configured to receive the discharge pressure and suction pressure of the compressor 11 of the stopped outdoor unit 1 in real time when the outdoor unit 1 is stopped and the bypass branch 15 is disconnected (S22), calculate the difference between the discharge pressure and the suction pressure (S23), compare the difference between the discharge pressure and the suction pressure with the first threshold value for the difference between the discharge pressure and the suction pressure; and when the difference between the discharge pressure and the suction pressure reaches and / or exceeds the first threshold value for the difference between the discharge pressure and the suction pressure (S24), control the bypass branch 15 to connect for the second connection time (S25); to ensure that the pressure difference before and after the compressor 11 reaches the level for safe start-up and the connection time of the bypass branch 15 is minimized before the compressor 11 is started.

[0050] The multi-split air conditioning system of this embodiment can solve the problems of high pressure difference before and after compressor 11 caused by outdoor unit 1 shutdown and high pressure difference before and after compressor 11 caused by leakage of one-way valve 14, thereby improving system stability and compressor 11 life.

[0051] In some specific embodiments, refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 The controller 10 is configured with an exhaust pressure threshold, an intake pressure threshold, an ambient temperature threshold, a first connection time, a threshold for the difference between the first exhaust pressure and the intake pressure, and a second connection duration.

[0052] The controller 10 is configured to receive the discharge pressure, suction pressure, and ambient temperature of the compressor 11 of the stopped outdoor unit 1 when the outdoor unit 1 is stopped and the bypass branch 15 is disconnected, and compare the discharge pressure with the discharge pressure threshold, the suction pressure with the suction pressure threshold, and the ambient temperature with the ambient temperature threshold, and calculate the difference between the discharge pressure and the suction pressure; and when the discharge pressure reaches and / or exceeds the discharge pressure threshold, the suction pressure reaches and / or exceeds the suction pressure threshold, and the ambient temperature reaches and / or exceeds the ambient temperature threshold, control the bypass branch 15 to connect for a first connection duration; and when the difference between the discharge pressure and the suction pressure reaches and / or exceeds the first discharge pressure and suction pressure difference threshold, control the bypass branch 15 to connect for a second connection duration; ensuring that the pressure difference before and after the compressor 11 reaches a safe starting level and the bypass branch 15 connection duration is minimized before the compressor 11 starts.

[0053] Of course, the exhaust pressure can be compared with the exhaust pressure threshold, the intake pressure with the intake pressure threshold, and the ambient temperature with the ambient temperature threshold. When the exhaust pressure reaches and / or exceeds the exhaust pressure threshold, the intake pressure reaches and / or exceeds the intake pressure threshold, and the ambient temperature reaches and / or exceeds the ambient temperature threshold, the bypass branch 15 is controlled to connect for the first connection time, and the comparison between the difference between the exhaust pressure and the intake pressure and the first exhaust pressure and intake pressure difference threshold is no longer performed.

[0054] Alternatively, the difference between exhaust pressure and intake pressure can be compared with the first threshold for the difference between exhaust pressure and intake pressure. When the difference between exhaust pressure and intake pressure reaches and / or exceeds the first threshold for the difference between exhaust pressure and intake pressure, the duration of the second connection of the bypass branch 15 is controlled, and the comparison between exhaust pressure and exhaust pressure threshold, intake pressure and intake pressure threshold, and ambient temperature and ambient temperature threshold is no longer performed.

[0055] Alternatively, the initial comparison can be determined based on the set first and second connection durations. When the first connection duration is longer than the second connection duration, the comparisons of exhaust pressure with exhaust pressure threshold, intake pressure with intake pressure threshold, and ambient temperature with ambient temperature threshold are performed first. If the exhaust pressure reaches and / or exceeds the exhaust pressure threshold, the intake pressure reaches and / or exceeds the intake pressure threshold, and the ambient temperature reaches and / or exceeds the ambient temperature threshold, the bypass branch 15 is connected for the first connection duration, and the comparison of the difference between exhaust pressure and intake pressure with the first exhaust pressure and intake pressure difference threshold is no longer performed. If the exhaust pressure does not reach and / or exceed the exhaust pressure threshold, the intake pressure does not reach and / or exceeds the intake pressure threshold, and the ambient temperature does not reach and / or exceed the ambient temperature threshold, then the comparison of the difference between exhaust pressure and intake pressure with the first exhaust pressure and intake pressure difference threshold is performed.

[0056] When the first connection duration is less than the second connection duration, the difference between exhaust pressure and intake pressure is first compared with the threshold value for the first difference between exhaust pressure and intake pressure. If the difference between exhaust pressure and intake pressure reaches or exceeds the threshold value, the bypass branch 15 is controlled to connect to the second connection duration, and comparisons between exhaust pressure and exhaust pressure threshold, intake pressure and intake pressure threshold, and ambient temperature and ambient temperature threshold are no longer performed. If the difference between exhaust pressure and intake pressure does not reach or exceed the threshold value for the first difference between exhaust pressure and intake pressure, comparisons between exhaust pressure and exhaust pressure threshold, intake pressure and intake pressure threshold, and ambient temperature and ambient temperature threshold are performed.

[0057] In some specific embodiments, refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 The controller 10 is configured with an exhaust pressure threshold, an intake pressure threshold, an ambient temperature threshold, a first connection time, and a threshold for the difference between the first exhaust pressure and the intake pressure.

[0058] The controller 10 is configured to receive the discharge pressure, suction pressure, and ambient temperature of the compressor 11 of the stopped outdoor unit 1 when the outdoor unit 1 is stopped and the bypass branch 15 is disconnected, and compare the discharge pressure with the discharge pressure threshold, the suction pressure with the suction pressure threshold, and the ambient temperature with the ambient temperature threshold, calculate the difference between the discharge pressure and the suction pressure, and compare the difference between the discharge pressure and the suction pressure with the first discharge pressure and suction pressure difference threshold; and when the discharge pressure reaches and / or exceeds the discharge pressure threshold, the suction pressure reaches and / or exceeds the suction pressure threshold, the ambient temperature reaches and / or exceeds the ambient temperature threshold, and / or the difference between the discharge pressure and the suction pressure reaches and / or exceeds the first discharge pressure and suction pressure difference threshold, control the bypass branch 15 to connect for the first connection time; to ensure that the pressure difference before and after the compressor 11 reaches a safe starting level and the bypass branch 15 connection time is minimized before the compressor 11 starts.

[0059] In this embodiment, the multi-split air conditioning system sets the second connection duration to be equal to the first connection duration, and determines that when at least one of the conditions is met, the bypass branch 15 is connected to the first connection duration. This solves the problem of high pressure difference before and after the compressor 11 caused by the shutdown of the outdoor unit 1 and the problem of high pressure difference before and after the compressor 11 caused by leakage of the one-way valve 14, thereby improving system stability and compressor 11 lifespan.

[0060] In some embodiments, refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 8 The controller 10 is also configured with a power-on duration threshold S31, and is configured to perform an initial power-on duration calculation on the outdoor unit 1 when the outdoor unit 1 is powered off and the bypass branch 15 is disconnected S33, and compare the initial power-on duration with the power-on duration threshold. If the initial power-on duration is within the power-on duration threshold range S35, the bypass branch 15 is connected S34; otherwise, the bypass branch 15 is disconnected.

[0061] That is, when the outdoor unit 1 is powered off and then powered on again, the initial power-on time is timed for S32, and the status of the compressor 11 and the bypass branch 15 is obtained. If all compressors 11 stop and the corresponding bypass branch 15 is disconnected for S33, then each bypass branch 15 is connected for S36. And it is determined whether the power-on time reaches and / or exceeds the power-on time threshold for S35. If so, each bypass branch 15 is disconnected for S36.

[0062] If some or all of the compressors 11 start, or if some or all of the bypass branches 15 are connected, then stop timing S37.

[0063] This embodiment ensures that the pressure difference before and after the compressor 11 formed before the power failure is balanced by timing the initial duration after power-on and controlling the connection of the bypass branch 15. This solves the problem of eliminating the high pressure difference of the compressor 11 before restarting the outdoor unit 1 after a power failure, avoids the compressor 11 starting with a pressure difference, improves the safety and reliability of the compressor 11 starting, and thus improves the lifespan of the compressor 11.

[0064] In some specific embodiments, refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 9 Each outdoor unit 1 is connected to its controller 10 via communication. The controller 10 is configured with a third discharge pressure and suction pressure difference threshold S41, and is configured to calculate the allocated frequency of the operating outdoor unit 1 and the outdoor unit 1 to be started when the unit is running and needs to be started S42. The controller 10 also controls the compressor 11 of the operating outdoor unit 1 to operate at a reduced frequency while simultaneously acquiring its discharge pressure and suction pressure in real time, calculating the difference between the discharge pressure and suction pressure S44, and comparing the difference between the discharge pressure and suction pressure with the third discharge pressure and suction pressure difference threshold. When the difference between the discharge pressure and suction pressure reaches and / or is less than the third discharge pressure and suction pressure difference threshold S45, the controller controls the compressor 11 of the operating outdoor unit 1 to increase its frequency to the allocated frequency. At the same time, the controller controls the compressor 11 of the outdoor unit 1 to be started to start and increase its frequency to the allocated frequency S46.

[0065] Of course, both downclocking and upclocking can be performed in stages.

[0066] The multi-split air conditioning system in this embodiment reduces the high and low pressure difference of the system by reducing the frequency of the operating outdoor unit 1, thereby reducing the high pressure that the compressor 11 of the outdoor unit 1 to be started needs to overcome, solving problems such as compressor 11 losing synchronization and being damaged when the driving capacity is insufficient, and improving system stability.

[0067] In some specific embodiments, refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 9 The controller 10 is configured with a reference displacement and the displacement of compressor 11 in outdoor unit 1. It calculates the displacement coefficient of each compressor 11. Assuming the reference displacement is Q0, the displacement of outdoor unit 1 (N1) is Q1, and the displacement coefficient is K1 = Q1 / Q0; the displacement of outdoor unit 1 (N2) is Q2, and the displacement coefficient is K2 = Q2 / Q0. The initial operating frequency of outdoor unit 1 (N1) is Fi, and outdoor unit 1 (N2) stops. Assuming control is performed according to the actual frequency of compressor 11, when the required frequency Fd of compressor 11 increases to the point where outdoor unit 1 is started, the frequency of each outdoor unit 1 is calculated as follows: Outdoor unit 1 displacement coefficient sum: K=K1+K2=Q1 / Q0+Q2 / Q0 Therefore, the frequency of each outdoor unit 1 is: Fdi = Fd / K = Fd / (Q1 / Q0 + Q2 / Q0) Fdi represents the allocated frequency for outdoor units N1 and N2. Specifically, the frequency of outdoor unit N1 decreases from Fi to Fdi, while the frequency of outdoor unit N2 increases from 0 to Fdi. In other words, as the demand frequency increases and more outdoor units 1 are started, the frequency of compressor 11 in outdoor unit N1 decreases to the required frequency and then increases. Simultaneously, the frequency of compressor 11 in outdoor unit N2 increases, ultimately reaching Fdi for both.

[0068] In some specific embodiments, refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 The controller 10 is equipped with a suction pressure increase threshold and a saturation temperature difference threshold. When the outdoor unit 1 is stopped, it is configured to cyclically acquire the suction pressure and ambient temperature of the compressor 11 of the stopped outdoor unit 1, calculate the corresponding saturation temperature based on the suction pressure, calculate the difference between the saturation temperature and the ambient temperature, and acquire the suction pressure increase based on the latest continuously acquired suction pressure.

[0069] Compare the difference with the saturation temperature difference threshold and the increase with the intake pressure increase threshold; when the difference reaches and / or exceeds the saturation temperature difference threshold and the increase reaches and / or exceeds the intake pressure increase threshold, it is marked as high start priority, and a one-way valve 14 leakage alarm is triggered during start-up.

[0070] That is, when the difference reaches and / or exceeds the saturation temperature difference threshold and the increase reaches and / or exceeds the intake pressure increase threshold, it is determined that the one-way valve 14 is leaking; the outdoor unit 1 is marked as high start priority, so that the multi-split unit is changed to start by the outdoor unit 1 or the outdoor unit 1 is added to start, and the outdoor unit 1 gives a leak-related alarm for the one-way valve 14 when it is stopped and / or started.

[0071] In this embodiment, the multi-split air conditioning system determines that the suction pressure of the stopped outdoor unit 1 will gradually approach the refrigerant saturation pressure corresponding to the ambient temperature. If the suction pressure gradually increases and the saturation temperature corresponding to the suction pressure is higher than the ambient temperature, it determines that the one-way valve 14 has a leakage problem. After determining the leakage, it prioritizes the start of the valve and sets up an alarm to prevent the leakage from causing a high pressure difference that prevents the compressor 11 from starting and damaging it. This improves the safety and reliability of the compressor 11's start-up and extends the life of the compressor 11.

[0072] Reference Figure 2 , Figure 4 , Figure 5 The multi-compressor outdoor unit multi-split system of the present invention includes one or more outdoor units 1 and multiple outdoor units 2; each outdoor unit 1 is connected in parallel; each outdoor unit 2 is connected in parallel; each parallel-connected outdoor unit 1 is connected to each parallel-connected outdoor unit 2, forming a refrigeration cycle from each outdoor unit 1 to each outdoor unit 2 and back to each outdoor unit 1, so that one or more of each outdoor unit 1 provides latent heat of refrigerant to one or more of each outdoor unit 2. That is, when the latent heat of refrigerant required by each outdoor unit 2 is small, one of each outdoor unit 1 can be operated to provide latent heat of refrigerant to each outdoor unit 2 or one or more of them; when the latent heat of refrigerant required by each outdoor unit 2 is large, multiple or all of each outdoor unit 1 can be operated, and the operating outdoor units 1 together provide latent heat of refrigerant to each outdoor unit 2 or one or more of them.

[0073] Outdoor unit 1 includes a gas-liquid separator 12, a four-way valve 17, an outdoor heat exchanger 18, and multiple compressors 11, multiple oil separators 13, multiple bypass branches 15, multiple oil return branches 16, and multiple one-way valves 14, which are respectively connected to each other. That is, the connection of one compressor 11, one oil separator 13, one bypass branch 15, one oil return branch 16, and one one-way valve 14 in outdoor unit 1 forms a compressor 11 exhaust module; outdoor unit 1 includes multiple exhaust modules.

[0074] The compressor 11 includes an exhaust port and an intake port; the four-way valve 17 includes a first port, a second port, a third port, and a fourth port; the oil separator 13 is connected in series in the pipeline between the exhaust port and the one-way valve 14. That is, the exhaust port is connected to the refrigerant inlet of the oil separator 13; the refrigerant outlet of the oil separator 13 is connected to one port of the one-way valve 14; and the other port of the one-way valve 14 is connected to the first port.

[0075] The gas-liquid separator 12 is connected in series on the pipeline from the suction port to the four-way valve 17; that is, the suction ports of each compressor 11 are respectively connected to the refrigerant outlet of the gas-liquid separator 12; the refrigerant inlet of the gas-liquid separator 12 is connected to the third port; the second port and the fourth port are respectively connected to the outdoor unit 2 and the outdoor heat exchanger 18.

[0076] The two ends of the bypass branch 15 are connected to the common end of the one-way valve 14 and the oil separator 13, and the far end of the gas-liquid separator 12 relative to the suction port, respectively. This allows for controllable connection and disconnection, controlling whether the high-pressure and low-pressure pipelines are connected to reduce the pressure difference before and after the compressor 11. Specifically, one end of the bypass branch 15 is connected to the pipeline between the one-way valve 14 and the refrigerant outlet of the oil separator 13, and the other end is connected to the pipeline between the refrigerant inlet and the third port of the gas-liquid separator 12.

[0077] The two ends of the oil return branch 16 are respectively connected to the far ends of the oil separator 13 and the gas-liquid separator 12 relative to the air intake port; that is, one end of the oil return branch 16 is connected to the oil return port of the oil separator 13, and the other end is connected to the pipeline connecting the refrigerant inlet and the third port of the gas-liquid separator 12, so as to realize the oil return through the oil return branch 16.

[0078] The outdoor unit 1 also includes a controller 10, which is connected to each compressor 11, each bypass branch 15, and a four-way valve 17 to control their operation or action. The outdoor unit 1 also includes multiple first pressure sensors 110 and multiple second pressure sensors 111 corresponding to each compressor 11, which are respectively connected to the controller 10 and used to detect the discharge pressure and suction pressure of each compressor 11 of the outdoor unit 1 and transmit them to the controller 10.

[0079] The controller 10 is configured to control the connection and connection duration of the corresponding bypass branch 15 based on the exhaust pressure and intake pressure of the other stopped compressors 11 in the outdoor unit 1 when at least one compressor 11 of the outdoor unit 1 is running.

[0080] In the multi-compressor outdoor unit multi-split system of the present invention, when at least one compressor 11 of the outdoor unit 1 is running, the connection time of the bypass branch 15 corresponding to the stopped compressor 11 is controlled according to the discharge pressure and suction pressure of the stopped compressor 11. Under the premise of reducing the pressure difference before and after the compressor 11, the connection time of the bypass branch 15 is shortened as much as possible to prevent the stopped compressor 11 in the outdoor unit 1 from starting with a pressure difference, thereby improving the reliability and safety of the compressor 11 starting and extending the life of the compressor 11. In addition, shortening the connection time of the bypass branch 15 can reduce the loss of bypass capacity and the noise generated by the connection of the bypass branch 15, thereby improving the user experience.

[0081] The control flow and principle of the multi-compressor outdoor unit multi-split system of the present invention will be described in detail below through specific embodiments.

[0082] In some specific embodiments, refer to Figure 2 , Figure 4 , Figure 5 , Figure 10 The controller 10 is configured with a second threshold for the difference between exhaust pressure and intake pressure, and a third connection duration S51. That is, the controller 10 is configured with a second threshold for the difference between exhaust pressure and intake pressure, and a third connection duration S51.

[0083] The controller 10 is also configured to, when at least one compressor 11 in the outdoor unit 1 is running, S52, cyclically acquire the discharge pressure and suction pressure of other stopped compressors 11, calculate the difference between the discharge pressure and suction pressure S53, compare the difference between the discharge pressure and suction pressure with a second threshold for the difference between the discharge pressure and suction pressure; when the difference between the discharge pressure and suction pressure reaches and / or exceeds the second threshold for the difference between the discharge pressure and suction pressure S54, control the bypass branch 15 of the corresponding compressor 11 to connect to the third connection duration S55.

[0084] This embodiment of the multi-compressor outdoor unit multi-split system detects and judges the exhaust pressure and intake pressure of at least one compressor 11 in the outdoor unit 1 when it is stopped during startup. It solves the leakage of the corresponding one-way valve 14 and the high pressure difference generated before and after the operating compressor 11 in the outdoor unit 1. It also controls the bypass branch 15 to be connected for the shortest possible time. This not only balances the pressure difference before and after the compressor 11 caused by the stop or leakage of the one-way valve 14, preventing the compressor 11 from starting with a pressure difference when restarting, thus improving the startup safety and reliability of the compressor 11, but also reduces the noise of the bypass branch 15 connection, improving the user experience.

[0085] In some specific embodiments, refer to Figure 2 , Figure 4 , Figure 5 , Figure 11 , Figure 12The controller 10 is configured with a third discharge pressure and intake pressure difference threshold S61, that is, a third discharge pressure and intake pressure difference threshold S61 is set in the controller 10, and is configured to: S62, calculate the allocated frequency of the operating compressor 11 and the compressor to be started S63, and control the reduction of the frequency of the operating compressor 11 while receiving its corresponding discharge pressure and intake pressure in real time, calculate the difference between the discharge pressure and intake pressure S64, compare the difference between the discharge pressure and intake pressure with the third discharge pressure and intake pressure difference threshold; and when the difference between the discharge pressure and intake pressure reaches and / or falls below the third discharge pressure and intake pressure difference threshold S65, control the reduction of the frequency of the operating compressor 11 and control its frequency increase to operate at the allocated frequency, and control the compressor to be started S66 to start and continuously increase its frequency to the allocated frequency.

[0086] The multi-compressor outdoor unit module combination system of this embodiment reduces the pressure difference before and after the compressor 11 to be started by reducing the frequency of the compressor 11 in operation of the outdoor unit 1; that is, it reduces the starting pressure difference of the compressor 11 to be started, thereby improving the starting safety and reliability of the compressor 11 to be started.

[0087] In some specific embodiments, refer to Figure 2 , Figure 4 , Figure 11 , Figure 12 Compressor 11 is configured with a base displacement. The displacement of each compressor 11 in outdoor unit 1 is calculated. Assuming the base displacement is Q0, the displacement of compressor 11 N1 in outdoor unit 1 is Q1, and the displacement coefficient is K1 = Q1 / Q0. The displacement of compressor 11 N2 is Q2, and the displacement coefficient is K2 = Q2 / Q0. The initial operating frequency of compressor 11 N1 is the operating frequency Fi, and compressor 11 N2 stops. Assuming control is performed based on the actual frequency of each compressor 11, when the required frequency Fd of compressor 11 increases to the number of compressors 11, the frequency of each compressor 11 is calculated as follows: Compressor displacement coefficient sum: K = K1 + K2 = Q1 / Q0 + Q2 / Q0 Therefore, the allocated frequency for each compressor 11 is: Fdi = Fd / K = Fd / (Q1 / Q0 + Q2 / Q0) Fdi represents the allocated frequency for compressors N1 (11) and N2 (11). Specifically, the frequency of compressor N1 (11) decreases from its operating frequency Fi to the allocated frequency Fdi, while the frequency of compressor N2 (11) increases from 0 to the allocated frequency Fdi. The frequency change process of compressor 11 is described in detail below. Figure 12When the required frequency increases and the number of compressors 11 increases, the frequency of compressor 11 N1 drops to the required frequency and is then increased. At the same time as the frequency of compressor 11 N1 increases, the frequency of compressor 11 N2 increases, and eventually both frequencies are increased to the allocated frequency Fdi.

[0088] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0089] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-split air conditioning system, comprising one or more outdoor units connected in parallel, and multiple indoor units connected in parallel; each outdoor unit is connected to each indoor unit; each outdoor unit includes a gas-liquid separator and at least one compressor, at least one oil separator, at least one bypass branch, and at least one check valve respectively connected to it; the compressor includes an exhaust port and an intake port; the oil separator is connected in series in a pipeline between the exhaust port and the check valve; the gas-liquid separator is connected to the intake port; the two ends of the bypass branch are respectively connected to the common end of the check valve and the oil separator, and the far end of the gas-liquid separator relative to the intake port, and are controllably connected and disconnected; Its features are, The outdoor unit also includes a controller, and a temperature sensor, at least one first pressure sensor, and at least one second pressure sensor connected to the controller, which are respectively used to detect the ambient temperature, the corresponding discharge pressure of the compressor, and the suction pressure and transmit them to the controller; the bypass branch is connected to the controller and is controlled by the controller to connect and disconnect; the controller is configured to control the connection and connection duration of the corresponding bypass branch according to the ambient temperature, the discharge pressure, and the suction pressure when the outdoor unit is stopped and the bypass branch is disconnected; The controller is also configured with an exhaust pressure threshold, an intake pressure threshold, an ambient temperature threshold, and a first connection duration; The controller is configured to acquire the ambient temperature and the discharge pressure and suction pressure of each compressor in real time when the outdoor unit is stopped, and compare the discharge pressure with the discharge pressure threshold, the suction pressure with the suction pressure threshold, and the ambient temperature with the ambient temperature threshold; and when the discharge pressure reaches and / or exceeds the discharge pressure threshold, the suction pressure reaches and / or exceeds the suction pressure threshold, and the ambient temperature reaches and / or exceeds the ambient temperature threshold, control the bypass branch to connect to the first connection duration.

2. The multi-unit air conditioning system according to claim 1, characterized in that, The controller is also configured with a first threshold value for the difference between exhaust pressure and intake pressure, and a second connection duration; The controller is configured to acquire the discharge pressure and suction pressure of each compressor in real time when the outdoor unit is stopped, calculate the difference between the discharge pressure and the suction pressure, and compare the difference between the discharge pressure and the suction pressure with a first discharge pressure and suction pressure difference threshold; when the difference between the discharge pressure and the suction pressure reaches and / or exceeds the first discharge pressure and suction pressure difference threshold, the controller controls the bypass branch to connect to the second connection duration.

3. The multi-unit air conditioning system according to claim 1, characterized in that, The controller is also configured with an exhaust pressure threshold, an intake pressure threshold, an ambient temperature threshold, a threshold for the difference between a first exhaust pressure and an intake pressure, and a first connection duration; The controller is configured to receive the ambient temperature and the discharge pressure and suction pressure of each compressor in real time when the outdoor unit is stopped, calculate the difference between the discharge pressure and the suction pressure, and compare the discharge pressure with the discharge pressure threshold, the suction pressure with the suction pressure threshold, the ambient temperature with the ambient temperature threshold, and the difference between the discharge pressure and the suction pressure with the first discharge pressure and suction pressure difference threshold. When the discharge pressure reaches and / or exceeds the discharge pressure threshold and the suction pressure reaches and / or exceeds the suction pressure threshold and the ambient temperature reaches and / or exceeds the ambient temperature threshold, and / or the difference between the discharge pressure and the suction pressure reaches and / or exceeds the first discharge pressure and suction pressure difference threshold, the controller controls the bypass branch to connect to the first connection duration.

4. The multi-unit air conditioning system according to claim 1, characterized in that, The controller is configured with a power-on duration threshold and is configured to count the initial power-on duration of the outdoor unit when the outdoor unit is powered off and shut down, compare the initial power-on duration with the power-on duration threshold, and control the bypass branch to connect when the initial power-on duration is within the power-on duration threshold range; otherwise, control the bypass branch to disconnect.

5. The multi-unit air conditioning system according to any one of claims 1 to 4, characterized in that, The controllers of each outdoor unit are communicatively connected; each controller is configured with a third threshold for the difference between exhaust pressure and intake pressure, and is configured to, when an additional outdoor unit is operating, calculate the allocated frequency of each outdoor unit, and while controlling the compressor of the operating outdoor unit to reduce its frequency, receive its exhaust pressure and intake pressure in real time, calculate the difference between the exhaust pressure and the intake pressure, and compare the difference between the exhaust pressure and the intake pressure with the third threshold for the difference between exhaust pressure and intake pressure; and when the difference between the exhaust pressure and the intake pressure reaches and / or falls below the third threshold for the difference between exhaust pressure and intake pressure, control the compressor of each reduced-frequency unit to increase its frequency to the allocated frequency, and simultaneously control the compressor of the outdoor unit to be started to start and increase its frequency to the allocated frequency.

6. The multi-split air conditioning system according to any one of claims 1 to 4, wherein the controller is configured with a suction pressure increase threshold and a saturation temperature difference threshold, and is configured to, when the outdoor unit is stopped, cyclically acquire the ambient temperature and the suction pressure of each of the compressors, and calculate the difference between the saturation temperature corresponding to the suction pressure and the ambient temperature, and the latest continuously acquired increase in the suction pressure; compare the difference with the saturation temperature difference threshold, and the increase with the suction pressure increase threshold; when the difference reaches and / or exceeds the saturation temperature difference threshold and the increase reaches and / or exceeds the suction pressure increase threshold, control it to start first and trigger a fault alarm.

7. A multi-compressor outdoor unit multi-split system, comprising one or more outdoor units connected in parallel, and multiple indoor units connected in parallel; the outdoor unit is connected to each of the indoor units; the outdoor unit includes a gas-liquid separator and multiple compressors, multiple oil separators, multiple bypass branches, and multiple one-way valves respectively connected to it; the compressor includes an exhaust port and an intake port; the oil separator is connected in series in the pipeline between the exhaust port and the one-way valve; the gas-liquid separator is connected to each of the intake ports respectively; the two ends of the bypass branch are respectively connected to the common end of the one-way valve and the oil separator, and the far end of the gas-liquid separator relative to each of the intake ports, and can be controllably connected and disconnected; Its features are, The outdoor unit also includes a controller and a plurality of first pressure sensors and a plurality of second pressure sensors connected to the controller, which are used to detect the discharge pressure and suction pressure of each compressor and transmit them to the controller; each bypass branch is connected to the controller and is controlled by the controller to connect and disconnect; the controller is configured to control the connection and connection duration of the corresponding bypass branch when at least one compressor of the outdoor unit is running, based on the discharge pressure and suction pressure of other compressors in the outdoor unit that are not running. The controller is configured with a third threshold for the difference between exhaust pressure and intake pressure, and is configured to, when at least one of the compressors of the outdoor unit is operating and an additional compressor needs to be operated, calculate the allocated frequency of the operating compressor and the compressor to be started, control the operating compressor to reduce its frequency while cyclically acquiring its exhaust pressure and intake pressure, calculate the difference between the exhaust pressure and the intake pressure, compare the difference between the exhaust pressure and the intake pressure with the third threshold for the difference between exhaust pressure and intake pressure, and when the difference between the exhaust pressure and the intake pressure reaches and / or is less than the third threshold for the difference between exhaust pressure and intake pressure, control the operating compressor to increase its frequency to the allocated frequency, and simultaneously control the compressor to be started to start and increase its frequency to the allocated frequency.

8. The multi-compressor outdoor unit multi-split system according to claim 7, characterized in that, The controller is configured with a second threshold for the difference between exhaust pressure and intake pressure, and a third connection duration. It is configured to acquire the exhaust pressure and intake pressure of each of the other non-operating compressors in real time when at least one of the compressors in the outdoor unit is running, calculate the difference between the corresponding exhaust pressure and intake pressure, compare it with the second threshold for the difference between exhaust pressure and intake pressure, and control the corresponding bypass branch to connect to the third connection duration when the difference between the exhaust pressure and intake pressure reaches and / or exceeds the second threshold for the difference between exhaust pressure and intake pressure.

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