Parallel unit oil return system and parallel unit oil return control method

Abstract

The application provides a parallel unit oil return system and a parallel unit oil return control method. The parallel unit oil return system comprises an oil separator, an oil return main line connected to the oil separator, and a plurality of oil return branches arranged in parallel on the oil return main line. The oil return branches are connected to the compressors in the parallel unit one by one, and the pipe diameters of the plurality of oil return branches are positively correlated with the pipe lengths, so that the oil amounts of the plurality of oil return branches are the same or similar. The pipe diameters of the plurality of oil return branches are positively correlated with the pipe lengths, so that the flow resistances of the oil return branches are equal, the oil return amounts among the compressors are evenly distributed, the purpose of uniform oil return is achieved, and the structure is simple and does not need complex components.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of compressors, more particularly, to a parallel compressor unit oil return system and a parallel compressor unit oil return control method. BACKGROUND

[0002] Parallel piston compressor units are widely used in various refrigeration systems, such as commercial refrigeration, air conditioning systems, and industrial refrigeration. In these systems, multiple piston compressors operate in parallel, sharing a condenser and an evaporator, and through the coordination of multiple compressors, the system achieves efficient operation. However, existing parallel piston compressor units have some problems in oil return, which seriously affect the performance and reliability of the system.

[0003] Specifically, in parallel piston compressor units, multiple compressors operate simultaneously, and the oil separator needs to handle a large amount of lubricating oil. Existing oil separators often cannot completely separate oil and refrigerant under high load, resulting in some lubricating oil not being effectively returned to the compressor, thereby affecting the lubrication effect of the compressor. Due to the different loads and operating states of each compressor, the oil level in the oil return branch is unevenly distributed, and some compressors may have insufficient oil return, while others may have excessive oil return. This uneven oil return phenomenon can lead to significant differences in lubrication effects between compressors, some compressors may overheat and wear due to oil deficiency, while others may reduce energy efficiency due to excessive oil. One direct reason for uneven oil return in parallel units is that the oil separator is at different distances from each compressor, and the along-path resistance between the oil return branches of each compressor is also different. The oil separated by the oil separator always flows preferentially to the branch with the smallest resistance, resulting in relatively sufficient oil in the compressors close to the oil separator, and the risk of insufficient lubrication in the compressors far from the oil separator.

[0004] To solve the problem of uneven oil distribution, the existing common solutions are: first, increase the oil balance pipeline and oil tank. This method requires the parallel connection of each oil return branch, adding a set of system to ensure that each compressor can effectively return oil. This not only increases the cost of the system, but also increases the difficulty of maintenance and troubleshooting. At the same time, due to the parallel operation of multiple compressors, the system needs complex control strategies to coordinate the operation of each compressor, making the system design and debugging more complex. Second, add proportional regulating valves on each oil return branch. Proportional regulating valves are expensive, and each compressor needs to add a proportional regulating valve, which has a significant impact on cost.

[0005] Therefore, how to propose a low-cost solution to the oil return effect of parallel units is a technical problem that needs to be solved in the industry. SUMMARY

[0006] The parallel unit oil return system and the parallel unit oil return control method can significantly improve the oil return effect of the parallel unit, ensure the uniform oil return among the compressors, improve the energy efficiency and reliability of the system, reduce the operation cost and maintenance difficulty, and provide protection for the stable operation of the refrigeration system.

[0007] To achieve the above object, the technical scheme adopted by the present application is:

[0008] The parallel unit oil return system comprises an oil separator, an oil return main line connected to the oil separator, and a plurality of oil return branches arranged in parallel on the oil return main line.

[0009] Further, the parallel unit is provided with a first compressor, a second compressor and a third compressor; the plurality of oil return branches are respectively a first oil return branch corresponding to the first compressor, a second oil return branch corresponding to the second compressor and a third oil return branch corresponding to the third compressor; wherein the pipe length of the first oil return branch > the pipe length of the second oil return branch > the pipe length of the third oil return branch, and the pipe diameter of the first oil return branch > the pipe diameter of the second oil return branch > the pipe diameter of the third oil return branch.

[0010] Further, an oil level gauge, an electromagnetic valve and a ball valve are arranged on each of the oil return branches.

[0011] Further, a ball valve is arranged on the oil return main line.

[0012] The present application also proposes a parallel unit oil return control method applied to the parallel unit oil return system as described above, which comprises:

[0013] Respectively judging whether each compressor in the parallel unit is started or not;

[0014] If yes, controlling the on-off of the electromagnetic valve on the oil return branch corresponding to the compressor according to the oil level parameter of the oil return branch corresponding to the compressor, or controlling the on-off of the electromagnetic valve on the oil return branch corresponding to each compressor according to the oil level parameters of the plurality of oil return branches corresponding to the plurality of compressors;

[0015] If no, disconnecting the electromagnetic valve on the oil return branch corresponding to the compressor.

[0016] Further, when only one compressor in the parallel unit is started, controlling the on-off of the electromagnetic valve on the oil return branch corresponding to the compressor according to the oil level parameter of the oil return branch corresponding to the compressor comprises:

[0017] determining whether the current oil level of the oil return branch corresponding to the compressor is within a preset oil level interval;

[0018] If yes, closing the electromagnetic valve on the oil return branch corresponding to the compressor;

[0019] If no, opening the electromagnetic valve on the oil return branch corresponding to the compressor.

[0020] Further, if the current oil level of the oil return branch corresponding to the compressor is greater than the upper limit of the preset oil level, temporarily opening the electromagnetic valve on the oil return branch corresponding to the compressor and re-closing the electromagnetic valve on the oil return branch corresponding to the compressor after the preset opening time ends.

[0021] Further, when two compressors in the parallel unit are started, the opening and closing of the electromagnetic valves on the oil return branches corresponding to the compressors is controlled according to the oil level parameters of the multiple oil return branches corresponding to the multiple compressors, including:

[0022] If the current oil level of the first oil return branch corresponding to the first compressor is less than the lower limit of the preset oil level, and the current oil level of the second oil return branch corresponding to the second compressor is greater than the lower limit of the preset oil level;

[0023] Closing the first electromagnetic valve on the first oil return branch;

[0024] Temporarily opening the second electromagnetic valve on the second oil return branch and re-closing the second electromagnetic valve on the second oil return branch after the preset opening time ends.

[0025] Further, when three compressors in the parallel unit are started, the opening and closing of the electromagnetic valves on the oil return branches corresponding to the compressors is controlled according to the oil level parameters of the multiple oil return branches corresponding to the multiple compressors, including:

[0026] If the current oil level of the first oil return branch corresponding to the first compressor is less than the lower limit of the preset oil level, and the current oil level of the second oil return branch corresponding to the second compressor is greater than the lower limit of the preset oil level, and the current oil level of the third oil return branch corresponding to the third compressor is greater than the lower limit of the preset oil level;

[0027] Comparing the current oil level of the second oil return branch with the current oil level of the third oil return branch, and obtaining that the current oil level of the third oil return branch is the largest;

[0028] Closing the first electromagnetic valve on the first oil return branch and the second electromagnetic valve on the second oil return branch;

[0029] Temporarily opening the second electromagnetic valve on the third oil return branch, and re-closing the third electromagnetic valve on the third oil return branch after the preset opening time ends.

[0030] Further, when at least two compressors in the parallel unit are started, if the current oil level of the oil return branch corresponding to all the started compressors is less than the preset lower oil level limit value, an oil return abnormality alarm is issued and all the started compressors are controlled to switch to a shutdown state.

[0031] Compared with the prior art, the parallel unit oil return system and the parallel unit oil return control method provided by the application have at least the following beneficial effects: the pipe diameter of the multiple oil return branches is positively correlated with the pipe length, so that the along-path resistance of each oil return branch is equal, the oil return amount between the compressors is uniformly distributed, the purpose of uniform oil return is achieved, and the structure is simple and does not require complex components. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0033] Figure 1 The structure diagram of the parallel unit oil return system provided by the application;

[0034] Figure 2 The gradually expanding structure profile provided by the application;

[0035] Figure 3 The flowchart of the parallel unit oil return control method provided by the application;

[0036] In the drawings, the reference signs are as follows:

[0037] 1, oil separator; 2, oil return main line; 31, first compressor; 32, second compressor; 33, third compressor; 41, first oil return branch; 42, second oil return branch; 43, third oil return branch; 51, first oil level meter; 52, second oil level meter; 53, third oil level meter; 61, first electromagnetic valve; 62, second electromagnetic valve; 63, third electromagnetic valve; 70, total ball valve; 71, first ball valve; 72, second ball valve; 73, third ball valve. DETAILED DESCRIPTION

[0038] In order to make the technical problems to be solved by the application, the technical solutions and the beneficial effects more clearly, the following will further describe the application in combination with the drawings and the embodiments. It should be understood that the specific embodiments described herein are only used to explain the application, and are not used to limit the application.

[0039] Parallel piston compressor units are widely used in various refrigeration systems, such as commercial refrigeration, air conditioning systems, and industrial refrigeration. In these systems, multiple piston compressors operate in parallel, sharing a condenser and evaporator, and through the coordination of multiple compressors, the system achieves efficient operation. However, existing parallel piston compressor units have some problems in oil return, which seriously affects the performance and reliability of the system. Specifically, in parallel piston compressor units, multiple compressors operate simultaneously, and the oil separator needs to handle a large amount of lubricating oil. The existing oil separator often cannot completely separate oil and refrigerant under high load, resulting in some lubricating oil not being effectively returned to the compressor, thereby affecting the lubrication effect of the compressor. Due to the different loads and operating states of each compressor, the oil level in the oil return branch is unevenly distributed, and some compressors may have insufficient oil return, while others may have excessive oil return. This uneven oil return phenomenon can cause significant differences in lubrication effects between compressors, some compressors may overheat and wear due to oil deficiency, while others may reduce energy efficiency due to excessive oil.

[0040] Based on this, the present application proposes a parallel unit oil return system and a parallel unit oil return control method, which solves the problems of uneven oil return, high system complexity, low energy efficiency, and poor reliability of existing parallel units at low cost, and improves the overall performance and reliability of the system.

[0041] As shown in Figure 1 The parallel unit oil return system proposed by the present application includes an oil separator 1, an oil return main path 2 connected to the oil separator 1, and multiple oil return branches arranged in parallel on the oil return main path 2, the oil return branches are connected one-to-one with the compressors in the parallel unit, and the pipe diameters of the multiple oil return branches are positively correlated with the pipe lengths, so that the oil amounts of the multiple oil return branches are the same or similar.

[0042] It should be understood that the formula for calculating the frictional resistance is: h f = f·(L / D)·(v 2 / 2g);

[0043] Where:

[0044] h f is the frictional resistance loss (unit: meter water column or meter liquid column);

[0045] f is the friction factor, dimensionless number, whose value depends on the flow state (laminar flow or turbulent flow), pipe wall roughness, etc.

[0046] L is the length of the pipeline (unit: meter);

[0047] D is the inner diameter of the pipeline (unit: meter);

[0048] v is the average flow rate of the fluid (unit: meter / second);

[0049] g is the acceleration of gravity (about 9.81 m / s 2 ).

[0050] From the above formula for calculating the flow resistance, f and g are constants, and v is approximately equal in each branch. Generally, the pipe diameters of each oil return branch are equal, and because the lengths of each oil return branch are inconsistent, the flow resistances of each oil return branch are inconsistent. At this time, the oil separated by the oil separator 1 always flows more to the oil return branch with smaller flow resistance, resulting in that the compressors close to the oil separator 1 have relatively sufficient oil, and the compressors far from the oil separator 1 have insufficient lubrication, thereby causing uneven oil return. To this end, the present application balances the influence of the length of the pipeline (also referred to as the pipe length) on the flow resistance by using the inner diameter of the pipeline (also referred to as the pipe diameter).

[0051] The advantage of the design of the present application is that the pipe diameters of the multiple oil return branches are positively correlated with the pipe lengths, so that the flow resistances of the multiple oil return branches are equal, ensuring that the oil return amounts of the multiple compressors are evenly distributed, achieving the purpose of uniform oil return, and the structure is simple and does not require complex components.

[0052] In a further preferred embodiment of the present application, the parallel unit is provided with a first compressor 31, a second compressor 32 and a third compressor 33; the multiple oil return branches are a first oil return branch 41 corresponding to the first compressor 31, a second oil return branch 42 corresponding to the second compressor 32 and a third oil return branch 43 corresponding to the third compressor 33; wherein the pipe length of the first oil return branch 41 > the pipe length of the second oil return branch 42 > the pipe length of the third oil return branch 43, and the pipe diameter of the first oil return branch 41 > the pipe diameter of the second oil return branch 42 > the pipe diameter of the third oil return branch 43.

[0053] In actual application, if the pipe length of the oil return branch is longer, the pipe diameter of the oil return branch is larger, similar to the gradually expanding structure cross-sectional view as shown in Figure 2 , and it means that the pipe diameters of the multiple oil return branches are positively correlated with the pipe lengths, and each oil return branch has only one pipe diameter and one pipe length.

[0054] The advantage of the design of the present application is that the pipe lengths and pipe diameters of the three oil return branches are not the same, and the layout and structure of the three oil return branches are optimized to satisfy that the distances between the three compressors and the oil separator 1 are not the same, and the flow resistances of the three oil return branches are equal, ensuring that each compressor can effectively return oil and reducing the load of the oil separator 1.

[0055] In further preferred embodiments of the present application, an oil level gauge, an electromagnetic valve and a ball valve are arranged on each oil return branch.

[0056] The advantage of the present application is that the current oil level of the oil return branch is detected by the oil level gauge, the on-off of the oil return branch is controlled by the opening and closing of the electromagnetic valve, and the specific part in the oil return branch is controlled and isolated by the ball valve, thereby facilitating maintenance.

[0057] In further preferred embodiments of the present application, a ball valve is arranged on the oil return main line 2.

[0058] The advantage of the present application is that the specific part in the oil return main line 2 is controlled and isolated by the ball valve, thereby facilitating maintenance.

[0059] For the sake of understanding, the parallel unit oil return system proposed by the present application will be introduced in detail below in combination with actual application scenarios.

[0060] As shown in Figure 1 The parallel unit oil return system includes an oil separator 1, three compressors, an oil return main line 2 and three oil return branches. Among them, the three compressors are a first compressor 31, a second compressor 32 and a third compressor 33, and the three oil return branches are a first oil return branch 41, a second oil return branch 42 and a third oil return branch 43.

[0061] The three oil return branches are arranged in parallel, the first oil return branch 41 is connected between the first compressor 31 and the oil separator 1, the second oil return branch 42 is connected between the second compressor 32 and the oil separator 1, and the third oil return branch 43 is connected between the third compressor 33 and the oil separator 1.

[0062] The first oil return branch 41 is provided with a first oil level gauge 51, a first electromagnetic valve 61 and a first ball valve 71; the second oil return branch 42 is provided with a second oil level gauge 52, a second electromagnetic valve 62 and a second ball valve 72; the third oil return branch 43 is provided with a third oil level gauge 53, a third electromagnetic valve 63 and a third ball valve 73, and the oil return main line 2 is provided with a total ball valve 70. Each ball valve is only used during maintenance, and is normally closed.

[0063] The length of the first oil return branch 41 > the length of the second oil return branch 42 > the length of the third oil return branch 43, and the diameter of the first oil return branch 41 > the diameter of the second oil return branch 42 > the diameter of the third oil return branch 43. Thus, the along-path resistance of the three oil return branches is balanced from the structural design of the oil return branches, ensuring that the oil return amount is evenly distributed among the three compressors.

[0064] It should be understood that in other optional embodiments, the number of oil return branches is not necessarily 3, i.e. the number of oil return branches can be flexibly selected according to actual application requirements.

[0065] It should also be understood that the compressor can be a piston compressor or a screw compressor.

[0066] Based on the structure design of the parallel unit oil return system as described above, the parallel unit oil return control method proposed by the present application includes the steps as shown in the following figure: Figure 3

[0067] respectively determine whether each compressor in the parallel unit is started;

[0068] If yes, control the on-off of the electromagnetic valve on the oil return branch corresponding to the compressor according to the oil level parameter of the oil return branch, or control the on-off of the electromagnetic valve on the oil return branch corresponding to each compressor according to the oil level parameter of the multiple oil return branches corresponding to multiple compressors;

[0069] If no, disconnect the electromagnetic valve on the oil return branch corresponding to the compressor.

[0070] The advantage of the design of the present application is that by introducing an intelligent control method, the oil return strategy is dynamically adjusted according to the on-off state of each compressor in the parallel unit and the oil level parameter of at least one oil return branch, thereby improving the energy efficiency and reliability of the system.

[0071] In a further preferred embodiment of the present application, when only one compressor in the parallel unit is started, controlling the on-off of the electromagnetic valve on the oil return branch corresponding to the compressor according to the oil level parameter of the oil return branch includes:

[0072] determine whether the current oil level of the oil return branch corresponding to the compressor is within a preset oil level interval;

[0073] If yes, close the electromagnetic valve on the oil return branch corresponding to the compressor;

[0074] If no, disconnect the electromagnetic valve on the oil return branch corresponding to the compressor.

[0075] It should be noted that the inventor has verified through a large number of experiments that the oil level of the compressor has an optimal interval, and the optimal interval is set as the preset oil level interval. If the oil level is higher than the upper limit of the preset oil level, there will be too much lubricating oil, which will affect heat exchange, and if the oil level is lower than the lower limit of the preset oil level, there will be insufficient lubricating oil, which will cause risks in the operation of the compressor.

[0076] The advantage of the design of the present application is that when only one compressor in the parallel unit is started, the on-off of the oil return branch corresponding to the compressor is controlled according to the current oil level of the oil return branch and the preset oil level interval, thereby realizing the regulation and control of the oil level of the oil return branch corresponding to the compressor, which is beneficial to ensure that the compressor can operate normally.

[0077] ​In a further preferred embodiment of the present application, if the current oil level of the oil return branch corresponding to the compressor is greater than the preset upper oil level limit, the electromagnetic valve on the oil return branch corresponding to the compressor is temporarily disconnected and the electromagnetic valve on the oil return branch corresponding to the compressor is re-closed after the preset disconnection time ends.

[0078] It should be noted that the preset disconnection time can be flexibly set according to actual application requirements, for example, the preset disconnection time is 5 seconds.

[0079] The benefit of the design is that when the current oil level of the oil return branch corresponding to the compressor that has been started is greater than the preset upper oil level limit, the oil return branch corresponding to the compressor that has been started can be controlled to be disconnected for a period of time and then re-connected, and the cycle detection and determination are performed, which more accurately realizes the regulation and control of the oil level of the oil return branch corresponding to the compressor that has been started, and is more conducive to ensuring that the compressor that has been started can operate normally.

[0080] In a further preferred embodiment of the present application, when two compressors in the parallel unit are started, the opening and closing of the electromagnetic valves on the oil return branches corresponding to the compressors is controlled according to the oil level parameters of the multiple oil return branches corresponding to the multiple compressors, which includes:

[0081] If the current oil level of the first oil return branch corresponding to the first compressor is less than the preset lower oil level limit, and the current oil level of the second oil return branch corresponding to the second compressor is greater than the preset lower oil level limit;

[0082] The first electromagnetic valve on the first oil return branch is closed;

[0083] The second electromagnetic valve on the second oil return branch is temporarily disconnected and the second electromagnetic valve on the second oil return branch is re-closed after the preset disconnection time ends.

[0084] The benefit of the design is that when two compressors in the parallel unit are started, the opening and closing of the oil return branches corresponding to the two compressors that have been started can be controlled according to the current oil level and the preset oil level interval of the oil return branches corresponding to the two compressors that have been started, the oil level of the oil return branches corresponding to all the compressors that have been started is regulated and controlled, thereby facilitating the normal operation of all the compressors that have been started; at the same time, the oil level of the oil return branch with a smaller current oil level is effectively balanced by the oil return branch with a larger current oil level.

[0085] In a further preferred embodiment of the present application, when three compressors in the parallel unit are started, the opening and closing of the electromagnetic valves on the oil return branches corresponding to the compressors is controlled according to the oil level parameters of the multiple oil return branches corresponding to the multiple compressors, which includes:

[0086] if the current oil level of the first oil return branch corresponding to the first compressor is less than the preset lower oil level limit value, and the current oil level of the second oil return branch corresponding to the second compressor is greater than the preset lower oil level limit value, and the current oil level of the third oil return branch corresponding to the third compressor is greater than the preset lower oil level limit value;

[0087] comparing the current oil level of the second oil return branch with the current oil level of the third oil return branch, obtaining that the current oil level of the third oil return branch is the largest;

[0088] closing the first electromagnetic valve on the first oil return branch and the second electromagnetic valve on the second oil return branch;

[0089] temporarily opening the second electromagnetic valve on the third oil return branch, and re-closing the third electromagnetic valve on the third oil return branch after the preset opening time ends.

[0090] The advantage of the design is that when three compressors in the parallel unit are started, the current oil level of the three compressors corresponding to the oil return branch can be controlled according to the preset oil level interval, so as to realize the regulation and control of the oil level of the oil return branch corresponding to all the started compressors, thereby facilitating the normal operation of all the started compressors; at the same time, the oil return branch with the largest current oil level is effectively utilized to balance the oil level of the oil return branch with a small current oil level.

[0091] In a further preferred embodiment of the application, when at least two compressors in the parallel unit are started, if the current oil level of the oil return branch corresponding to all the started compressors is less than the preset lower oil level limit value, an oil return abnormality alarm is issued and all the started compressors are controlled to switch to a shutdown state.

[0092] The advantage of the design is that when at least two compressors in the parallel unit are started, if the current oil level of the oil return branch corresponding to all the started compressors is not within the preset oil level interval, it reflects that the parallel unit has oil leakage and oil leakage phenomenon, and an oil return abnormality alarm is issued in time to protect the compressors.

[0093] For the sake of understanding, the parallel unit oil return control method applied to the parallel unit oil return system is introduced in detail below, taking the parallel unit oil return system including one oil separator 1, three compressors, one oil return main road 2, and three oil return branches as an example.

[0094] In the parallel unit oil return system, the three compressors are the first compressor 31, the second compressor 32 and the third compressor 33, and the three oil return branches are the first oil return branch 41, the second oil return branch 42 and the third oil return branch 43. When the loads of the compressors in the parallel unit are the same, the demand for oil return is the same, at which time the oil return is evenly divided; in the actual operation of the parallel unit, the loads among the compressors inevitably have differences, and the consistency among the compressors also has differences, and therefore a control module is needed to regulate the oil levels of the oil return branches.

[0095] The parallel unit oil return control method is as follows:

[0096] It is determined whether each compressor in the parallel unit is started or not.

[0097] If the three compressors are all stopped, the electromagnetic valves located on the three oil return branches are all turned off, so that the three oil return branches are turned off.

[0098] If only one of the three compressors is started, i.e., the first compressor 31 is started, and the second compressor 32 and the third compressor 33 are both stopped.

[0099] The second electromagnetic valve 62 and the third electromagnetic valve 63 are both turned off, so that the second oil return branch 42 and the third oil return branch 43 are turned off.

[0100] It is determined whether the current oil level of the first oil return branch 41 is within the preset oil level interval; if yes, since the first electromagnetic valve 61 is closed, the first electromagnetic valve 61 does not need to be adjusted, and the first oil return branch 41 is maintained to be turned on; if no, and the current oil level of the first oil return branch 41 is greater than the upper limit of the preset oil level, the first electromagnetic valve 61 is controlled to be turned off for 5 seconds, and after 5 seconds, the first electromagnetic valve 61 is controlled to be closed, and the cycle detection and determination are performed.

[0101] If two of the three compressors are started, i.e., the first compressor 31 and the second compressor 32 are both started, and the third compressor 33 is stopped.

[0102] The third electromagnetic valve 63 is turned off, so that the third oil return branch 43 is turned off.

[0103] It is determined whether the current oil level of the first oil return branch 41 is within the preset oil level interval;

[0104] If yes, since the first electromagnetic valve 61 and the second electromagnetic valve 62 are closed, the first electromagnetic valve 61 and the second electromagnetic valve 62 do not need to be adjusted, and the first oil return branch 41 and the second oil return branch 42 are maintained to be turned on;

[0105] If no, and the current oil level of the first oil return branch 41 is greater than the preset upper limit value of the oil level, the first electromagnetic valve 61 is controlled to be opened for 5 seconds, and then the first electromagnetic valve 61 is controlled to be closed again, the second electromagnetic valve 62 is not adjusted, and the second oil return branch 42 is maintained to be connected;

[0106] If no, and the current oil level of the first oil return branch 41 is less than the preset lower limit value of the oil level, then it is judged whether the current oil level of the second oil return branch 42 is greater than the preset lower limit value of the oil level, if no, the system appears oil running or oil leakage phenomenon, an oil return abnormality alarm is issued, and the first compressor 31 and the second compressor 32 are controlled to be stopped; if yes, the second electromagnetic valve 62 is controlled to be opened for 5 seconds, and then the second electromagnetic valve 62 is controlled to be closed, and the cycle detection and judgment are performed.

[0107] If the three compressors are all started, it is first judged whether the current oil level of the first oil return branch 41 is in the preset oil level interval;

[0108] If yes, the first electromagnetic valve 61, the second electromagnetic valve 62 and the third electromagnetic valve 63 are not adjusted, and the first oil return branch 41, the second oil return branch 42 and the third oil return branch 43 are maintained to be connected;

[0109] If no, and the current oil level of the first oil return branch 41 is greater than the preset upper limit value of the oil level, the first electromagnetic valve 61 is controlled to be opened for 5 seconds, and then the first electromagnetic valve 61 is controlled to be closed, and the second electromagnetic valve 62 and the third electromagnetic valve 63 are not adjusted, and the second oil return branch 42 and the third oil return branch 43 are maintained to be connected;

[0110] If no, and the current oil level of the first oil return branch 41 is less than the preset lower limit value of the oil level, then it is judged whether the current oil levels of the second oil return branch 42 and the third oil return branch 43 are both greater than the preset lower limit value of the oil level, if no, the system appears oil running or oil leakage phenomenon, an oil return abnormality alarm is issued, and the first compressor 31, the second compressor 32 and the third compressor 33 are controlled to be stopped; if yes, and the current oil level of the third oil return branch 43 is greater than the current oil level of the second oil return branch 42, the third electromagnetic valve 63 is controlled to be opened for 5 seconds, and then the third electromagnetic valve 63 is controlled to be closed, and the cycle detection and judgment are performed, and the second electromagnetic valve 62 is not adjusted, and the second oil return branch 42 is maintained to be connected.

[0111] The above only describes preferred embodiments of the present application and is not used to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A parallel unit oil return system, characterized in that, It includes an oil separator, a main oil return line connected to the oil separator, and multiple oil return branches arranged in parallel on the main oil return line. Each oil return branch is connected to a compressor in the parallel unit, and the pipe diameter and pipe length of the multiple oil return branches are positively correlated so that the oil volume of the multiple oil return branches is the same or similar.

2. The parallel unit oil return system as described in claim 1, characterized in that, The parallel unit is equipped with a first compressor, a second compressor, and a third compressor; the multiple oil return branches are respectively a first oil return branch corresponding to the first compressor, a second oil return branch corresponding to the second compressor, and a third oil return branch corresponding to the third compressor; wherein, the pipe length of the first oil return branch is greater than the pipe length of the second oil return branch and the pipe length of the third oil return branch, and the pipe diameter of the first oil return branch is greater than the pipe diameter of the second oil return branch and the pipe diameter of the third oil return branch.

3. The parallel unit oil return system as described in claim 1, characterized in that, Each of the aforementioned return oil branches is equipped with an oil level gauge, a solenoid valve, and a ball valve.

4. The parallel unit oil return system as described in claim 1, characterized in that, A ball valve is installed on the return oil main.

5. A method for controlling oil return in parallel generating units, characterized in that, Applied to the parallel unit oil return system as described in any one of claims 1-4, the parallel unit oil return control method includes: Determine whether each compressor in the parallel unit is running; If so, the on / off state of the solenoid valve on the oil return branch corresponding to a compressor is controlled based on the oil level parameters of the oil return branch corresponding to a compressor, or the on / off state of the solenoid valve on the oil return branch corresponding to each compressor is controlled based on the oil level parameters of multiple oil return branches corresponding to multiple compressors. If not, disconnect the solenoid valve on the oil return branch corresponding to the compressor.

6. The parallel unit oil return control method as described in claim 5, characterized in that, When only one compressor in the parallel unit is running, controlling the on / off state of the solenoid valve on the oil return branch corresponding to that compressor based on the oil level parameter of that compressor includes: Determine whether the current oil level of the return oil branch corresponding to the compressor is within the preset oil level range; If so, close the solenoid valve on the oil return branch corresponding to the compressor; If not, disconnect the solenoid valve on the oil return branch corresponding to the compressor.

7. The parallel unit oil return control method as described in claim 6, characterized in that, If the current oil level in the oil return branch corresponding to the compressor is greater than the preset upper limit of the oil level, the solenoid valve on the oil return branch corresponding to the compressor is temporarily disconnected and then re-closed after the preset disconnection time.

8. The parallel unit oil return control method as described in claim 5, characterized in that, When two compressors in a parallel unit are started, the on / off state of the solenoid valves on the oil return branches corresponding to each compressor is controlled based on the oil level parameters of the multiple oil return branches corresponding to the compressors, including: If the current oil level of the first return oil branch corresponding to the first compressor is less than the preset lower limit of oil level, and the current oil level of the second return oil branch corresponding to the second compressor is greater than the preset lower limit of oil level; Close the first solenoid valve on the first return oil branch; Temporarily disconnect the second solenoid valve on the second return oil branch and re-close the second solenoid valve on the second return oil branch after the preset disconnection time has elapsed.

9. The parallel unit oil return control method as described in claim 5, characterized in that, When three compressors in a parallel unit are started, the on / off state of the solenoid valves on the oil return branches corresponding to each compressor is controlled based on the oil level parameters of the multiple oil return branches corresponding to the compressors, including: If the current oil level of the first return oil branch corresponding to the first compressor is less than the preset lower limit of oil level, and the current oil level of the second return oil branch corresponding to the second compressor is greater than the preset lower limit of oil level, and the current oil level of the third return oil branch corresponding to the third compressor is greater than the preset lower limit of oil level; Compare the current oil level of the second return oil branch with the current oil level of the third return oil branch, and find that the current oil level of the third return oil branch is the highest. Close the first solenoid valve on the first return oil branch and the second solenoid valve on the second return oil branch; Temporarily disconnect the second solenoid valve on the third return oil branch, and re-close the third solenoid valve on the third return oil branch after the preset disconnection time has elapsed.

10. The parallel unit oil return control method as described in claim 5, characterized in that, When at least two compressors in a parallel unit are started, if the current oil level in the oil return branch corresponding to all started compressors is lower than the preset lower limit, an oil return abnormality alarm will be issued and all started compressors will be switched to the shutdown state.

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