Control method and device for multi-connected machine liquid bypass branch and multi-connected machine air conditioning unit

Abstract

The application provides a control method and device for a liquid bypass branch of a multi-connected air conditioner and a multi-connected air conditioner. The method comprises the following steps: acquiring an outdoor environment temperature and an exhaust temperature; if the outdoor environment temperature is greater than an environment temperature threshold and the exhaust temperature is greater than a first exhaust temperature threshold, then controlling the opening degree of an expansion valve of the liquid bypass branch according to the outdoor environment temperature and the exhaust superheat; the opening degree of the expansion valve is positively correlated with the outdoor environment temperature and the exhaust superheat. According to the application, whether to open the liquid bypass branch is determined according to the outdoor environment temperature and the exhaust temperature, and the opening degree of the expansion valve of the liquid bypass branch is controlled according to the outdoor environment temperature and the exhaust superheat, so that the suction temperature and the exhaust temperature can be reduced, the refrigerating capacity can be increased, the compression efficiency of the compressor can be improved, and the reliability risk can be reduced.

Description

Technical Field

[0001] This invention relates to the field of air conditioning high-temperature operation technology, and more specifically, to a control method, device, and multi-split air conditioning unit for a liquid bypass branch. Background Technology

[0002] Multi-split air conditioning units face the problem of reduced cooling performance when operating under high-temperature conditions. This is because when the external ambient temperature is high, the compressor's suction temperature is high, the suction volume is large, and the refrigerant circulation flow is small, resulting in reduced system cooling capacity and poorer performance. Simultaneously, it also increases the discharge temperature, reduces compressor compression efficiency, and poses potential reliability risks, such as lubricant carbonization. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a control method for a liquid bypass branch in a multi-split air conditioning unit, applicable to such units. The multi-split air conditioning unit includes a liquid bypass branch connecting the refrigerant cooling side and the return gas side. The method includes: acquiring the outdoor ambient temperature and the exhaust temperature; if the outdoor ambient temperature is greater than an ambient temperature threshold and the exhaust temperature is greater than a first exhaust temperature threshold, then controlling the opening degree of the expansion valve in the liquid bypass branch based on the outdoor ambient temperature and the exhaust superheat; the opening degree of the expansion valve is positively correlated with both the outdoor ambient temperature and the exhaust superheat.

[0004] This invention determines whether to open the liquid bypass branch based on the outdoor ambient temperature and the exhaust temperature, and controls the opening of the expansion valve of the liquid bypass branch according to the outdoor ambient temperature and the exhaust superheat. This can reduce the suction temperature and exhaust temperature, increase the cooling capacity, improve the compression efficiency of the compressor, and reduce reliability risks.

[0005] Optionally, the opening degree of the expansion valve in the liquid bypass branch is calculated based on the following formula:

[0006] P2 = P1 + S1(X) 实际 -X 目标 );

[0007] Where P2 is the opening degree of the expansion valve in the current cycle, P1 is the opening degree of the electronic expansion valve in the previous cycle, S1 is the exhaust superheat correction coefficient, and X 实际 X is the actual difference between the intake temperature and the outlet temperature. 目标 S1 is the target difference between the intake temperature and the exhaust temperature; S1 is negatively correlated with the outdoor ambient temperature.

[0008] In this embodiment of the invention, the target difference between the suction temperature and the discharge temperature is used as the control target. The larger the actual difference is compared with the target difference, the more flow rate the expansion valve needs and the larger the valve opening. The target value is divided into intervals according to different external ring temperatures. The higher the external ring temperature, the higher the discharge temperature, the worse the cooling effect, the smaller the control target value, and the more liquid volume is required. The discharge superheat is used for correction. The greater the discharge superheat, the greater the correction coefficient and the faster the valve adjustment speed.

[0009] Optionally, before controlling the opening degree of the expansion valve of the liquid bypass branch according to the outdoor ambient temperature and exhaust superheat, the method further includes: determining the initial opening degree of the expansion valve of the liquid bypass branch according to the compressor operating frequency, and continuously operating for a first preset time based on the initial opening degree of the expansion valve; the initial opening degree of the expansion valve is positively correlated with the compressor operating frequency.

[0010] In this embodiment of the invention, the initial opening degree is associated with the compressor operating frequency to prevent the expansion valve from opening too large in low-frequency operation of the compressor or in the event of a liquid shortage, thus avoiding excessive bypass liquid volume.

[0011] Optionally, the initial opening of the expansion valve is calculated based on the following formula:

[0012] P0 = nf

[0013] Where f is the compressor operating frequency at the current moment, and n is the frequency correction coefficient.

[0014] In this embodiment of the invention, the initial opening degree is associated with the compressor operating frequency to prevent the expansion valve from opening too large in low-frequency operation of the compressor or in the event of a liquid shortage, thus avoiding excessive bypass liquid volume.

[0015] Optionally, the method further includes: if any of the following conditions are met and continue for a second preset duration, adjusting the opening of the expansion valve of the liquid bypass branch to zero: the exhaust superheat is less than the superheat threshold; or, the exhaust temperature is less than the second exhaust temperature threshold; or, the decrease ratio of the cold outlet temperature of the current cycle to the cold outlet temperature of the previous cycle is greater than the ratio threshold.

[0016] The embodiments of the present invention set conditions for closing the liquid bypass branch to ensure the reliability of unit operation.

[0017] Optionally, when 35℃ ≤ outdoor ambient temperature < 43℃: X 目标 The value of X is b, and the range of b is 5 < b ≤ 8; when 43℃ ≤ outdoor ambient temperature < 48℃, X 目标 The value of X is c; the range of c is 2 < c ≤ 5; when the outdoor ambient temperature is ≥ 48℃, X 目标The value is d; the range of d is 1 < d ≤ 2; or, when K1 < exhaust superheat ≤ K2, S1 is 0.5m; when K2 < exhaust superheat ≤ K3, S1 is m; when exhaust superheat > K3, S1 is 2m; where, k3 > K2 > K1, 10℃ < K1 ≤ 15℃, 15℃ ≤ K2 ≤ 20℃, 30℃ < K3 ≤ 40℃, 1 ≤ m < 1.5.

[0018] Optionally, the range of n is 1 < n ≤ 2.

[0019] Optionally, 10℃ < superheat threshold ≤ 15℃; or 65℃ ≤ second exhaust temperature threshold ≤ 75℃; or 45% ≤ decrease ratio ≤ 50%.

[0020] The embodiments of the present invention provide specific value ranges for each parameter, which can reduce the intake temperature and exhaust temperature and increase the cooling capacity.

[0021] This invention provides a control device for a liquid bypass branch in a multi-split air conditioning unit, applied to such a unit. The multi-split air conditioning unit includes a liquid bypass branch connecting the refrigerant cooling side and the return gas side. The device includes: an acquisition module for acquiring outdoor ambient temperature and exhaust temperature; and a liquid bypass control module for controlling the opening degree of the expansion valve in the liquid bypass branch based on the outdoor ambient temperature and exhaust superheat if the outdoor ambient temperature is greater than an ambient temperature threshold and the exhaust temperature is greater than a first exhaust temperature threshold. The opening degree of the expansion valve is positively correlated with both the outdoor ambient temperature and the exhaust superheat.

[0022] This invention provides a multi-split air conditioning unit, including a liquid bypass branch and a control device for the liquid bypass branch; the liquid bypass branch connects the refrigerant cooling side and the return gas side.

[0023] Optionally, one end of the liquid bypass branch is connected to the upstream side of the gas-liquid separator inlet, and the other end is connected to the downstream side of the condenser outlet.

[0024] The control device for the liquid bypass branch of the multi-split air conditioning unit, the multi-split air conditioning unit, and the computer-readable storage medium of the present invention can achieve the same technical effect as the control method for the liquid bypass branch of the multi-split air conditioning unit described above. Attached Figure Description

[0025] Figure 1 A schematic diagram of a multi-split air conditioning unit with a liquid bypass branch provided in an embodiment of the present invention is shown;

[0026] Figure 2 A schematic flowchart of a control method for a multi-unit hydraulic bypass branch according to an embodiment of the present invention is shown;

[0027] Figure 3A schematic flowchart of another control method for a multi-unit hydraulic bypass branch in an embodiment of the present invention is shown;

[0028] Figure 4 A schematic diagram of the structure of a control device for a multi-unit hydraulic bypass branch is shown in an embodiment of the present invention. Detailed Implementation

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0030] This invention provides a multi-split air conditioning unit with a liquid bypass branch. By innovatively adding a liquid bypass branch to the system, the liquid bypass branch has an electronic expansion valve to control the refrigerant flow through the branch, thereby reducing the suction temperature and exhaust temperature and increasing the cooling capacity.

[0031] Figure 1 A schematic diagram of a multi-split air conditioning unit with a liquid bypass branch provided in an embodiment of the present invention is shown. Figure 1 The liquid bypass branch is located between the refrigerant after cooling and the gas inlet. It consists of a solenoid valve, a filter, a liquid bypass electronic expansion valve, and pipelines. It cools the return gas side by taking liquid after the refrigerant is cooled, thereby reducing the suction temperature and increasing the cooling capacity.

[0032] like Figure 1 As shown, the exhaust temperature Td is detected by the exhaust temperature sensor, the intake temperature Ts is detected by the intake temperature sensor, the cold outlet temperature Te is detected by the cold outlet temperature sensor, the outer ring temperature Tao is detected by the outer ring temperature sensor, and the exhaust superheat TdSH = exhaust temperature Td - high pressure temperature (the high pressure temperature is estimated in real time from the high pressure detected by the high pressure sensor).

[0033] Figure 2 This diagram illustrates a schematic flowchart of a control method for a liquid bypass branch in a multi-split air conditioning unit according to an embodiment of the present invention. The method is applied to a multi-split air conditioning unit, which includes a liquid bypass branch connecting the refrigerant cooling side and the return gas side. The method includes the following steps:

[0034] S202, obtain the outdoor ambient temperature and exhaust temperature.

[0035] For example, based on practical experience, when the outdoor ambient temperature is ≥35℃, the cooling effect of multi-split units deteriorates significantly. Therefore, the liquid bypass electronic expansion valve can be controlled within this temperature range. If the refrigerant circulation is reduced due to excessively high outdoor ambient temperature, it will also lead to an increase in exhaust temperature. Based on these two parameters, it is possible to accurately determine whether the cooling capacity is insufficient, thereby determining whether to control the liquid bypass branch to open.

[0036] S204, if the outdoor ambient temperature is greater than the ambient temperature threshold and the exhaust temperature is greater than the first exhaust temperature threshold, then control the opening of the expansion valve of the liquid bypass branch according to the outdoor ambient temperature and the exhaust superheat.

[0037] For example, the ambient temperature threshold is 35℃, and the first exhaust temperature threshold is 95℃≤a≤105℃. The expansion valve opening is positively correlated with both the outdoor ambient temperature and the exhaust superheat; the higher the outdoor ambient temperature, the larger the expansion valve opening; and the greater the exhaust superheat, the larger the expansion valve opening.

[0038] The control method for the liquid bypass branch of a multi-split air conditioner provided in this embodiment of the invention determines whether to open the liquid bypass branch based on the outdoor ambient temperature and the exhaust temperature, and controls the opening degree of the expansion valve of the liquid bypass branch according to the outdoor ambient temperature and the exhaust superheat. This can reduce the suction temperature and the exhaust temperature, increase the cooling capacity, improve the compression efficiency of the compressor, and reduce reliability risks.

[0039] Optionally, the expansion valve opening of the liquid bypass branch can be calculated based on the following formula:

[0040] P2 = P1 + S1(X) 实际 -X 目标 );

[0041] Where P2 is the opening degree of the expansion valve in the current cycle, P1 is the opening degree of the electronic expansion valve in the previous cycle, S1 is the exhaust superheat correction coefficient, and X 实际 X is the actual difference between the intake temperature and the outlet temperature. 目标 S1 is the target difference between the intake temperature and the exhaust temperature; S1 is negatively correlated with the outdoor ambient temperature.

[0042] For example, the adjustment period is 20 seconds.

[0043] Optionally, X 目标 Different values ​​are assigned based on different outdoor ambient temperatures:

[0044] When 35℃≤Tao<43℃: X 目标 The value is b, and the range of b is 5 < b ≤ 8;

[0045] When 43℃≤Tao<48℃, X 目标 The value is c; the range of c is 2 < c ≤ 5.

[0046] When Tao ≥ 48℃, X 目标 The value is d; the range of d is 1 < d ≤ 2.

[0047] Optionally, S1 can be selected based on different exhaust superheat TdSH ranges:

[0048] When K1<TdSH≤K2, the correction factor S1 is taken as 0.5m;

[0049] When K2<TdSH≤K3, the correction coefficient S1 is taken as m;

[0050] TdSH > K3, and the correction factor S1 is set to 2m;

[0051] And k3>K2>K1, 10℃<K1≤15℃, 15℃≤K2≤20℃, 30℃<K3≤40℃, 1≤m<1.5.

[0052] In the high-temperature and high-discharge range, where the suction temperature is higher than the discharge temperature, the unit opens the liquid bypass branch, using the low-temperature refrigerant discharged to cool the suction temperature. As the suction and discharge temperatures decrease, the refrigerant circulation volume increases, thus increasing the cooling capacity. The target difference between the suction and discharge temperatures is used as the control target. The larger the actual difference compared to the target, the greater the flow rate required by the expansion valve, and the larger the valve opening. The target value is divided into ranges based on different external ambient temperatures. The higher the external ambient temperature, the higher the discharge temperature, the worse the cooling effect, the smaller the control target value, and the greater the required liquid volume. Simultaneously, discharge superheat is used for correction; the greater the discharge superheat, the larger the correction coefficient, and the faster the valve adjustment speed.

[0053] Before performing the expansion valve opening as described above, the method further includes an initial opening control step. Based on this, the method also includes:

[0054] The initial opening degree of the expansion valve in the liquid bypass branch is determined based on the compressor's operating frequency, and a first preset duration is set for continuous operation based on this initial opening degree. This initial opening degree is positively correlated with the compressor's operating frequency; the higher the compressor's operating frequency, the larger the initial opening degree of the expansion valve. Optionally, this first preset duration is 100 seconds.

[0055] Optionally, the initial opening of the expansion valve can be calculated based on the following formula:

[0056] P0 = nf

[0057] Where f is the compressor operating frequency at the current moment, and n is the frequency correction coefficient. Optionally, the value of n is in the range of 1 < n ≤ 2.

[0058] The initial opening degree is related to the compressor operating frequency to prevent the expansion valve from opening too large in low-frequency operation of the compressor or in the event of a lack of liquid, thus avoiding excessive bypass liquid volume.

[0059] Furthermore, this embodiment of the invention provides a closing condition. If any of the following conditions are met and continue for a second preset duration, the opening degree of the expansion valve in the regulating fluid bypass branch is zero:

[0060] The exhaust superheat is less than the superheat threshold; or,

[0061] The exhaust temperature is less than the second exhaust temperature threshold; or,

[0062] The rate of decrease in the current cycle's cold exit temperature compared to the previous cycle is greater than the percentage threshold.

[0063] Optionally, 10℃ < superheat threshold ≤ 15℃; or 65℃ ≤ second exhaust temperature threshold ≤ 75℃; or 45% ≤ decrease ratio ≤ 50%.

[0064] For example, if any of the following conditions are met and last for 150 seconds, the liquid bypass branch will be shut off:

[0065] ① TdSH<e, 10℃<e≤15℃;

[0066] ② Td<g, 65℃≤g≤75℃;

[0067] ③Te temperature is ↓h% lower than the previous cycle, 45≤h≤50;

[0068] When the exhaust superheat or exhaust temperature is below the above limits, the liquid bypass branch must be closed. If the exhaust superheat is low, the unit is at risk of operating with liquid present, and the liquid bypass should not be opened to reduce the exhaust temperature. Similarly, if the exhaust temperature is low, the liquid bypass should not be opened to reduce the exhaust temperature. Since the liquid bypass inlet is located at the cold outlet temperature sensor Te, if the cold outlet temperature drops too much within the same cycle, it indicates that the liquid bypass electronic expansion valve is open too wide, resulting in excessive liquid distribution. In this case, the liquid bypass branch must be closed to ensure the unit's operational reliability.

[0069] Figure 3 A schematic flowchart of a control method for a multi-unit hydraulic bypass branch according to an embodiment of the present invention is shown, including:

[0070] S301, the unit starts operating in cooling mode and automatically identifies system parameters.

[0071] S302, determine whether Tao > 35℃ and Td > a are satisfied. If yes, then execute S303; otherwise, execute S307.

[0072] For example, the system identifies that the external ambient temperature Tao = 40℃ > 35℃ and Td = 100℃ > a, where a is 95℃, which satisfies the conditions for entering the liquid bypass control.

[0073] S303, the liquid bypass electronic expansion valve enters the initial opening control mode: opening P1 = nf.

[0074] For example, P1 = nf = 2 × 50 = 100pls, the compressor's current operating frequency is 50 Hz, and n is 2. After 100s, it enters the normal opening control mode.

[0075] S304, Enter normal opening control mode: P2 = P1 + S1(X 实际 -X 目标 ).

[0076] For example, the current cycle electronic expansion valve opening P2 = P1 + S1(X) 实际 -X 目标 )=100+1×(10-6)=104pls, where, P1=100pls, K1=15℃, K2=20℃, K3=40℃, TdSH=30℃, m=1, i.e., S1=1. When the outer ring is at 40℃, X 目标 =b, where b takes the value 6, and X is at this time 实际 =10℃, one adjustment cycle is 20s.

[0077] S305, determine if any of the following conditions are met: TdSH < e, Td < g, Te temperature is ↓h% lower than the previous cycle. If yes, proceed to S306; otherwise, return to S304.

[0078] For example, if the system detects that TdSH < 15℃ (e is 15℃) for 150 seconds during operation, the electronic expansion valve will close to 0 pls until the conditions for the next opening are met.

[0079] S306, Electronic expansion valve closed.

[0080] S307 is operating under normal control mode.

[0081] This invention, in the context of high outer ring and high exhaust scenarios, utilizes a liquid bypass branch to reduce exhaust and intake temperatures, thereby increasing system cooling capacity. When controlling the opening of the liquid bypass electronic expansion valve, different correction coefficient values ​​are determined based on different exhaust superheats, and different control target values ​​are determined based on different ambient temperatures. This makes liquid bypass flow control more precise, expansion valve opening adjustment more reasonable, and adaptable to different application scenarios.

[0082] In this embodiment of the invention, the initial opening degree is correlated with the compressor operating frequency to prevent excessive opening during low-frequency compressor operation or in low-liquid-supply scenarios, thus avoiding excessive bypass fluid volume. Normal opening degree control is implemented by dividing different target values ​​according to different outer loops, making flow control more precise. Different correction coefficients are determined by dividing different exhaust superheat levels to rationally control the valve's adjustment rate.

[0083] Figure 4 This diagram illustrates a structural schematic of a control device for a liquid bypass branch in a multi-split air conditioning unit, applicable to such units. The multi-split air conditioning unit includes a liquid bypass branch connecting the refrigerant cooling side and the return gas side. The device includes:

[0084] The acquisition module 401 is used to acquire the outdoor ambient temperature and exhaust temperature;

[0085] The liquid bypass control module 402 is used to control the opening degree of the expansion valve of the liquid bypass branch according to the outdoor ambient temperature and the exhaust superheat if the outdoor ambient temperature is greater than the ambient temperature threshold and the exhaust temperature is greater than the first exhaust temperature threshold; the opening degree of the expansion valve is positively correlated with both the outdoor ambient temperature and the exhaust superheat.

[0086] The control device for the liquid bypass branch of the multi-split air conditioner provided in this embodiment of the invention determines whether to open the liquid bypass branch based on the outdoor ambient temperature and the exhaust temperature, and controls the opening degree of the expansion valve of the liquid bypass branch according to the outdoor ambient temperature and the exhaust superheat. This can reduce the suction temperature and the exhaust temperature, increase the cooling capacity, improve the compression efficiency of the compressor, and reduce reliability risks.

[0087] As a feasible approach, the liquid bypass control module is further configured to: determine the initial opening degree of the expansion valve of the liquid bypass branch according to the compressor operating frequency, and continuously operate for a first preset duration based on the initial opening degree of the expansion valve; the initial opening degree of the expansion valve is positively correlated with the compressor operating frequency.

[0088] As a feasible approach, the liquid bypass control module is further configured to: adjust the opening of the expansion valve of the liquid bypass branch to zero if any of the following conditions are met and continue for a second preset duration: the exhaust superheat is less than the superheat threshold; or, the exhaust temperature is less than the second exhaust temperature threshold; or, the decrease ratio of the cold outlet temperature of the current cycle to the cold outlet temperature of the previous cycle is greater than the ratio threshold.

[0089] This invention provides a multi-split air conditioning unit, including a liquid bypass branch and a control device for the liquid bypass branch; the liquid bypass branch connects the refrigerant cooling side and the return gas side.

[0090] As one possible approach, one end of the liquid bypass branch is connected to the upstream side of the gas-liquid separator inlet, and the other end is connected to the downstream side of the condenser outlet.

[0091] This invention also provides a computer-readable storage medium storing a computer program. When the computer program is read and executed by a processor, it implements the method provided in the above embodiments and achieves the same technical effect. To avoid repetition, further details are omitted here. The computer-readable storage medium may be a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0092] Of course, those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by computer-controlled devices. The program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the above method embodiments. The storage medium can be a memory, a disk, an optical disk, etc.

[0093] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

[0094] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0095] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the control device for the multi-split air conditioning unit's liquid bypass branch and the multi-split air conditioning unit disclosed in the embodiments, since they correspond to the control method for the multi-split air conditioning unit's liquid bypass branch disclosed in the above embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0096] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A control method for a multi-unit hydraulic bypass branch, characterized in that, The method is applied to a multi-split air conditioning unit, the multi-split air conditioning unit including a liquid bypass branch, the liquid bypass branch connecting the refrigerant cooling side and the return gas side; the method includes: Obtain outdoor ambient temperature and exhaust temperature; If the outdoor ambient temperature is greater than the ambient temperature threshold and the exhaust temperature is greater than the first exhaust temperature threshold, then the opening degree of the expansion valve of the liquid bypass branch is controlled according to the outdoor ambient temperature and the exhaust superheat; the opening degree of the expansion valve is positively correlated with both the outdoor ambient temperature and the exhaust superheat. The opening degree of the expansion valve in the liquid bypass branch is calculated based on the following formula: P2=P1+S1(X 实际 -X 目标 ); Where P2 is the opening degree of the expansion valve in the current cycle, P1 is the opening degree of the electronic expansion valve in the previous cycle, S1 is the exhaust superheat correction coefficient, and X 实际 X is the actual difference between the intake temperature and the outlet temperature. 目标 S1 is the target difference between the intake temperature and the exhaust temperature; S1 is negatively correlated with the outdoor ambient temperature.

2. The method as described in claim 1, characterized in that, Before controlling the opening degree of the expansion valve of the liquid bypass branch according to the outdoor ambient temperature and exhaust superheat, the method further includes: The initial opening degree of the expansion valve in the liquid bypass branch is determined based on the compressor operating frequency, and the expansion valve is continuously operated for a first preset duration based on the initial opening degree; the initial opening degree of the expansion valve is positively correlated with the compressor operating frequency.

3. The method as described in claim 1, characterized in that, The initial opening of the expansion valve is calculated based on the following formula: P0=nf Where f is the compressor operating frequency at the current moment, and n is the frequency correction coefficient.

4. The method according to any one of claims 1-3, characterized in that, The method further includes: If any of the following conditions are met and continue for a second preset duration, the opening of the expansion valve in the liquid bypass branch will be adjusted to zero: The exhaust superheat is less than the superheat threshold; or, The exhaust temperature is less than the second exhaust temperature threshold; or, The rate of decrease in the current cycle's cold exit temperature compared to the previous cycle is greater than the percentage threshold.

5. The method as described in claim 1, characterized in that, When the outdoor ambient temperature is between 35℃ and 43℃: X 目标 The value is b, and the range of b is 5 < b ≤ 8; When the outdoor ambient temperature is between 43℃ and 48℃, X 目标 The value is c; the range of c is 2 < c ≤ 5; When the outdoor ambient temperature is ≥48℃, X 目标 The value is d; the range of d is 1 < d ≤ 2; or, When K1 < exhaust superheat ≤ K2, S1 is taken as 0.5m; When K2 < exhaust superheat ≤ K3, S1 is taken as m; Exhaust superheat > K3, S1 is 2m; Wherein, k3>K2>K1, 10℃<K1≤15℃, 15℃≤K2≤20℃, 30℃<K3≤40℃, and 1≤m<1.

5.

6. The method as described in claim 3, characterized in that, The range of n is 1 < n ≤ 2.

7. The method as described in claim 4, characterized in that, 10℃ < superheat threshold ≤ 15℃; or 65℃ ≤ second exhaust temperature threshold ≤ 75℃; or 45% ≤ decrease ratio ≤ 50%.

8. A control device for a multi-unit hydraulic bypass branch, characterized in that, An application to a multi-split air conditioning unit, the multi-split air conditioning unit including a liquid bypass branch, the liquid bypass branch connecting the refrigerant cooling side and the return gas side; the device includes: The acquisition module is used to acquire outdoor ambient temperature and exhaust temperature; The liquid bypass control module is used to control the opening degree of the expansion valve of the liquid bypass branch according to the outdoor ambient temperature and the exhaust superheat if the outdoor ambient temperature is greater than the ambient temperature threshold and the exhaust temperature is greater than the first exhaust temperature threshold; the opening degree of the expansion valve is positively correlated with both the outdoor ambient temperature and the exhaust superheat. The opening degree of the expansion valve in the liquid bypass branch is calculated based on the following formula: P2=P1+S1(X 实际 -X 目标 ); Where P2 is the opening degree of the expansion valve in the current cycle, P1 is the opening degree of the electronic expansion valve in the previous cycle, S1 is the exhaust superheat correction coefficient, and X 实际 X is the actual difference between the intake temperature and the outlet temperature. 目标 S1 is the target difference between the intake temperature and the exhaust temperature; S1 is negatively correlated with the outdoor ambient temperature.

9. A multi-split air conditioning unit, characterized in that, It includes a liquid bypass branch and a control device for the liquid bypass branch of the multi-split air conditioner as described in claim 8; the liquid bypass branch connects the refrigerant cooling side and the return gas side.

10. The multi-split air conditioning unit as described in claim 9, characterized in that, One end of the liquid bypass branch is connected to the upstream side of the gas-liquid separator inlet, and the other end is connected to the downstream side of the condenser outlet.

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