A multi-stage variable frequency screw air compressor

Abstract

The present invention provides a multi-stage variable frequency screw air compressor, which belongs to the technical field of air compressors. It solves the technical problem of insufficient energy efficiency of existing screw compressors. The multi-stage variable frequency screw air compressor includes a primary compression main unit and a secondary compression main unit with air circuits connected in series, and the compressor also includes a variable frequency motor 1, a variable frequency motor 2, and a controller that can adjust the adaptive speed of the variable frequency motor 1 and the adaptive speed of the variable frequency motor 2 respectively according to the change of the flow rate used, the controller is electrically connected to the variable frequency motor 1 and the variable frequency motor 2, the output shaft of the variable frequency motor 1 is connected to the power input end of the primary compression main unit, and the output shaft of the variable frequency motor 2 is connected to the power input end of the secondary compression main unit. The present invention can reduce energy waste and leakage loss, thereby improving the energy efficiency of the compressor.

Description

Technical Field

[0001] The invention belongs to the technical field of compressors and relates to a multi-stage variable frequency screw air compressor. Background Art

[0002] The screw compressor consists of a cylindrical screw and two symmetrically arranged plane star wheels, which form a meshing pair and are installed in the casing. The screw groove, the inner wall of the casing and the star wheel teeth constitute a closed volume. The power is transmitted to the screw shaft, and the screw drives the star wheel to rotate. The gas enters the screw groove from the suction chamber and is discharged through the exhaust port and the exhaust chamber after being compressed. The role of the star wheel is equivalent to the piston of the reciprocating piston compressor. When the star wheel teeth move relatively in the screw groove, the closed volume gradually decreases and the gas is compressed.

[0003] The Chinese patent application with publication number CN102705238A is a seal-free tandem multi-stage screw compressor previously developed by the applicant. The motor drives the two compression main units arranged in series in the gas path to rotate synchronously, effectively realizing multi-stage supercharging, with a compact structure and convenient maintenance. In order to improve the working adaptability of the compressor, the motor speed can be adjusted to achieve the adjustment of the working flow.

[0004] However, the stable adjustment range of the two-stage compression main engine is often small during the motor adjustment process, and the working energy efficiency is also affected in the adjustment extreme value area. In order to ensure high working energy efficiency while adjusting, general technicians in this field can easily consider: 1. Setting up multiple groups of compressors that can be started and stopped, and realizing the adjustment effect by starting and stopping each compressor independently, with a large adjustment range and low loss; 2. Setting up bypass adjustment, so that part of the exhausted air flows back to the air inlet through the pipeline, adjusting the output flow and reducing energy loss. Summary of the invention

[0005] In view of the above problems existing in the prior art, the present invention provides a variable frequency medium-pressure screw air compressor. The technical problem to be solved by the present invention is: how to improve the energy efficiency of the adjustable air compressor.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A multi-stage variable frequency screw air compressor comprises a first compression main unit and a second compression main unit connected in series in an air circuit, characterized in that the compressor further comprises a variable frequency motor 1, a variable frequency motor 2 and a controller which can adjust the adaptive speed of the variable frequency motor 1 and the adaptive speed of the variable frequency motor 2 respectively according to the change of the usage flow rate, the controller is electrically connected to the variable frequency motor 1 and the variable frequency motor 2, the output shaft of the variable frequency motor 1 is connected to the power input end of the first compression main unit, and the output shaft of the variable frequency motor 2 is connected to the power input end of the second compression main unit.

[0008] The primary compression host performs preliminary compression on the inhaled air to reach the specified pressure, and the air after preliminary compression enters the secondary compression host for further compression to reach a higher specified pressure to meet the needs of industrial use; by setting the variable frequency motor 1 and the variable frequency motor 2 to respectively control the rotation of the primary compression host and the secondary compression host, when the compressor changes the constant pressure flow rate, the controller can receive the flow monitoring signal of the compressed air using equipment or the compressor's own flow monitoring related data signal and adjust the speed of the variable frequency motor 1 and the variable frequency motor 2 respectively. The primary compression host and the secondary compression host are no longer limited to the practical flow adjustment of the same speed change, and can achieve adjustment of a larger flow range. In addition, in response to different constant pressure flow requirements, the controller can adjust the constant pressure flow value according to the actual needs of the user, and the variable frequency motor 1 and the variable frequency motor 2 can be adjusted according to the controller instructions respectively, so that the compressor can achieve the most economical and stable working state after the adjustment, thereby reducing energy waste and leakage loss caused by pressure mismatch between the primary compression host and the secondary compression host after adjustment, thereby improving the energy efficiency of the compressor.

[0009] In the above-mentioned multi-stage variable frequency screw air compressor, the compressor also includes an air pressure sensor that can monitor the output pressure of the first-stage compression host and the output pressure of the second-stage compression host. The controller is electrically connected to the air pressure sensor. When the pressure monitored by the air pressure sensor is lower than the preset pressure, the controller can adjust the speed of the variable frequency motor 1 and the variable frequency motor 2 to increase. When the pressure monitored by the air pressure sensor is higher than the preset pressure, the controller can adjust the speed of the variable frequency motor 1 and the variable frequency motor 2 to decrease. In this way, when the user's flow rate increases, the output pressure of the second-stage compression host will first decrease, so that the pressure value can directly reflect the user's flow usage status. At this time, the controller can control the variable frequency motor 1 and the variable frequency motor 2 to increase the speed respectively. When the pressure values ​​reach the preset values, the speed is kept stable, thereby achieving adaptive adjustment, avoiding loss and improving energy efficiency.

[0010] As another solution, the controller stores constant-pressure flow-speed curve data corresponding to the stable speed of the variable-frequency motor one and the stable speed of the variable-frequency motor two respectively under the constant-pressure intake and constant-pressure exhaust conditions of the two-stage compression main engine. The controller can adjust the speed of the variable-frequency motor one and the speed of the variable-frequency motor two respectively when the flow rate changes according to the constant-pressure flow-speed curve data. The speeds of the variable frequency motor 1 and the variable frequency motor 2 are adjusted respectively according to the preset constant pressure usage flow-speed curve, and the constant pressure usage flow-speed curve is formed through experiments. Specifically, the test personnel first determine the rated working pressure values ​​of the intake end and the exhaust end of the two-stage compression host, and then require the compressor to work at the determined constant pressure (corresponding to the exhaust end pressure of the two-stage compression host) usage flow, and at the same time, adjust the speeds of the variable frequency motor 1 and the variable frequency motor 2 respectively so that the air pressure values ​​at the intake end and the exhaust end of the two-stage compression host are stabilized to the preset values, and then record the speed values ​​corresponding to the variable frequency motor 1 and the variable frequency motor 2 under the usage flow, and finally change the size of the constant pressure usage flow step by step to detect and record the corresponding speed values ​​of the variable frequency motor 1 and the variable frequency motor 2 under the stable voltage state, and finally form a constant pressure usage flow-speed curve within a certain constant pressure usage flow range; that is, for the constant pressure usage flow value required by the user, the variable frequency motor 1 and the variable frequency motor 2 can be adjusted respectively according to the speeds corresponding to the usage flow value in the curve data preset in the controller, so that the compressor can achieve the most economical and stable working state after the adjustment is completed, thereby improving the energy efficiency of the compressor.

[0011] In the above-mentioned multi-stage variable frequency screw air compressor, the compressor also includes a first-stage gas-liquid separator, the air inlet of the first-stage gas-liquid separator is connected to the air outlet of the first-stage compression host, and the air outlet of the first-stage gas-liquid separator is connected to the air inlet of the second-stage compression host. The controller can control the variable frequency motor 2 to accelerate first when the constant pressure usage flow increases, and control the variable frequency motor 1 to decelerate first when the constant pressure usage flow decreases. The primary gas-liquid separator is located between the primary compression host and the secondary compression host. When the compressor needs to increase the displacement, the controller controls the variable frequency motor 2 to accelerate first, so that the screw accelerates and extracts, so that the pressure at the air inlet of the secondary compression host and the primary gas-liquid separator is reduced. The primary compression host will be smoother after acceleration. At the same time, it ensures that the pressure of the closed space between the air outlet of the primary compression host and the air inlet of the secondary compression host, such as the primary gas-liquid separator, will not be too high due to the different speed change speeds during adjustment, thereby avoiding leakage loss. When the corresponding compressor needs to reduce the displacement, the controller controls the variable frequency motor 1 to decelerate first. At this time, the pressure of the closed space between the air outlet of the primary compression host and the air inlet of the secondary compression host is reduced, and then gradually recovers after the subsequent deceleration of the secondary compression host. Similarly, the leakage loss caused by the sudden increase in pressure in the closed space can be avoided, thereby improving the energy efficiency of the compressor.

[0012] As another solution, the compressor further includes a secondary gas-liquid separator, the air outlet of the compression main unit is directly connected to the air inlet of the secondary compression main unit, and the air outlet of the secondary compression main unit is connected to the air inlet of the secondary gas-liquid separator. Compared with the traditional two-stage compressor, this method omits a gas-liquid separator, which is more cost-effective.

[0013] In the above-mentioned multi-stage variable frequency screw air compressor, the variable frequency motor 1 and the variable frequency motor 2 are arranged at intervals in the horizontal direction or the vertical direction. In this way, the variable frequency motor 1 and the variable frequency motor 2 are arranged at a certain distance from each other, which facilitates the arrangement and connection between the first-stage compression host, the second-stage compression host, the first-stage gas-liquid separator and the second-stage gas-liquid separator, and at the same time reduces the vibration interference between the variable frequency motor 1 and the variable frequency motor 2, and weakens the resonance effect that may be caused when the two have the same rotation speed.

[0014] In the above-mentioned high-frequency screw air compressor, the compressor also includes a secondary gas-liquid separator, a primary filter and a secondary filter. The inlet of the primary filter and the inlet of the secondary filter are respectively connected to the discharge port of the primary gas-liquid separator and the discharge port of the secondary gas-liquid separator. The primary filter is connected to the inner cavity of the secondary compression host through an openable and closable refilling pipe 1. The middle section of the refilling pipe 1 is provided with a booster pump 1 that can drive the lubricating liquid to be transported to the secondary compression host. The secondary gas-liquid separator can dehumidify the compressed air discharged from the secondary compression host. The primary filter and the secondary filter are used to filter the separated coolant to ensure that the coolant will not cause damage to the screw and the star wheel due to impurities after circulating into the compressor. In this way, the coolant in the primary filter can enter the inner cavity of the secondary compression host after being driven by the booster pump 1 from the opened refilling pipe 1, avoiding the phenomenon of insufficient lubricating liquid in the secondary compression host due to pressure changes after speed regulation.

[0015] In the above-mentioned high-frequency screw air compressor, the compressor also includes a second refilling pipe, one end of which is connected to the air inlet of the first-stage compression host and can be opened and closed, and the other end of the second refilling pipe is connected to the outside. The middle section of the second refilling pipe is provided with a second booster pump that can drive the lubricant to be transported to the first-stage compression host. In this way, when the first-stage compression host is short of lubricant due to evaporation or replacement of water, the operator can replenish the lubricant to the first-stage compression host from the outside through the opened second refilling pipe via the second booster pump to ensure the stable adjustment state of the compressor.

[0016] In the above-mentioned high-frequency screw air compressor, the primary gas-liquid separator and the secondary gas-liquid separator are each connected to an openable and closable liquid pipe, and the inner cavity of the primary gas-liquid separator and the inner cavity of the secondary gas-liquid separator are each connected to one end of the two liquid pipes, and the other ends of the two liquid pipes are connected to the outside. In this way, the volume of pressurized coolant inside the primary gas-liquid separator and the secondary gas-liquid separator can be controlled through the liquid pipe, which is conducive to meeting the needs of different pressure regulation working states and ensuring the stability of the compressor regulation state.

[0017] In the above-mentioned high-frequency screw air compressor, the compression main unit also includes an air inlet pipe connected to the air inlet of the first-stage compression main unit and an exhaust pipe connected to the air outlet of the second-stage gas-liquid separator. The air inlet of the first-stage compression main unit is provided with an air inlet valve capable of controlling the flow cross section. In this way, the operator can perform auxiliary control of the air inlet cross section through the air inlet valve, which is beneficial to cooperate with the compressor speed adjustment to improve the working energy efficiency of the compressor.

[0018] In the above-mentioned high-frequency screw air compressor, there are two air pressure sensors, one of which is arranged on the first-level gas-liquid separator, and the other is arranged on the exhaust pipe. The pressure inside the first-level gas-liquid separator and the exhaust pipe respectively corresponds to the working pressure actually received by the first level and the user, so that the controller can control the speed according to accurate pressure data, and it is also convenient for the operator to observe the changes in working pressure and judge the adjustment state; and for the scheme of preset control curve data, continuous feedback can be formed to the controller to achieve speed control, that is, if there is a deviation in the adjusted speed during the flow adjustment process, so that the air pressure is higher or lower than the specified pressure, the speed adaptability can be controlled to increase or decrease, and auxiliary calibration can be achieved, so that the adjustment is more accurate and stable.

[0019] In the above-mentioned high-frequency screw air compressor, a minimum pressure valve is provided between the air outlet of the primary gas-liquid separator and the air inlet of the secondary compression main unit. In this way, when the compressor adjusts the flow rate, the high-pressure air in the secondary compression main unit will not flow back into the primary gas-liquid separator, further ensuring that there will be no excessively high pressure in the primary gas-liquid separator during the adjustment process, thereby avoiding leakage loss and improving working energy efficiency.

[0020] In the above-mentioned multi-stage variable frequency screw air compressor, the bottom of the first-stage compression main unit, the bottom of the second-stage compression main unit, the bottom of the variable frequency motor 1 and the bottom of the variable frequency motor 2 are all provided with vibration-damping pads. This can alleviate the influence of the working vibration of the first-stage compression main unit, the second-stage compression main unit, the variable frequency motor 1 and the variable frequency motor 2, reduce noise and ensure the working stability of the compressor.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] The multi-stage variable frequency screw air compressor controls the variable frequency motor 1 and the variable frequency motor 2 to respectively operate the two compression main units at the same or different speeds. In this way, when the compressor adjusts the flow rate, the first-stage compression main unit and the second-stage compression main unit are no longer limited to the flow rate adjustment with the same speed change. The adjustment range is larger, and in response to different flow rate requirements, the variable frequency motor 1 and the variable frequency motor 2 can be controlled to have different preset working speeds to achieve the most economical and stable working state, thereby reducing energy waste and leakage loss caused by pressure mismatch between the first-stage compression main unit and the second-stage compression main unit after adjustment, thereby improving the energy efficiency of the compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the three-dimensional structure of the first embodiment.

[0024] Figure 2 It is a schematic diagram of the three-dimensional structure of the first embodiment from another angle.

[0025] Figure 3 It is a logical schematic diagram of the controller adjusting the rotation speed in the first embodiment.

[0026] Figure 4 It is a schematic diagram of the flow-speed curve for constant pressure use in the second embodiment.

[0027] In the figure, 1. first-stage compression main unit; 2. second-stage compression main unit; 3. frequency conversion motor 1; 4. frequency conversion motor 2; 5. controller; 6. first-stage gas-liquid separator; 7. second-stage gas-liquid separator; 8. first-stage filter; 9. second-stage filter; 10. liquid replenishing pipe 1; 11. pressure pump 1; 12. liquid replenishing pipe 2; 13. pressure pump 2; 14. liquid passage pipe; 15. air pressure sensor; 16. air inlet pipe; 17. exhaust pipe; 18. air inlet valve; 19. minimum pressure valve; 20. vibration damping pad. DETAILED DESCRIPTION

[0028] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0029] Embodiment 1:

[0030] like Figure 1-3As shown, the multi-stage variable frequency screw air compressor includes a first-stage compression host 1 and a second-stage compression host 2 whose air circuits are connected in series, and also includes a variable frequency motor 1 3 and a variable frequency motor 2 4 which are respectively connected to the first-stage compression host 1 and the second-stage compression host 2 in a transmission manner. The output shaft of the variable frequency motor 1 3 is coaxially connected to the power input end of the first-stage compression host 1, and the output shaft of the variable frequency motor 2 4 is coaxially connected to the power input end of the second-stage compression host 2. The lubricating fluid of this embodiment is water lubrication, which is cleaner and has a better cooling effect. The secondary compression host 2 adds a mechanical seal to ensure high-pressure sealing. The primary compression host 1 performs preliminary compression on the inhaled air, and the air after preliminary compression enters the secondary compression host 2 for further compression to reach a specified pressure to meet industrial use needs; by setting a variable frequency motor 1 3 and a variable frequency motor 2 4 to respectively control the rotation of the primary compression host 1 and the secondary compression host 2, when the compressor uses flow adjustment, the primary compression host 1 and the secondary compression host 2 are no longer limited to the flow adjustment of the same speed change, and the adjustment range of the compressor using flow is larger. The speed of the variable frequency motor 1 3 and the variable frequency motor 2 4 can be controlled by the controller 5. The compressor also includes an air pressure sensor 15 that can monitor the output pressure of the primary compression host 1 and the output pressure of the secondary compression host 2. The controller 5 is electrically connected to the air pressure sensor 15. When the pressure monitored by the air pressure sensor 15 is lower than the preset pressure, the controller 5 can adjust the speed of the variable frequency motor 1 3 and the variable frequency motor 2 4 to increase, and when the pressure monitored by the air pressure sensor 15 is higher than the preset pressure, the controller 5 can adjust the speed of the variable frequency motor 1 3 and the variable frequency motor 2 4 to decrease. The controller 5 may be a commercially available INVT controller.

[0031] The air inlet of the primary gas-liquid separator 6 is connected to the air outlet of the primary compression host 1, and the air outlet of the primary gas-liquid separator 6 is connected to the air inlet of the secondary compression host 2. The primary gas-liquid separator 6 is located between the primary compression host 1 and the secondary compression host 2, and a minimum pressure valve 19 is provided between the air outlet of the primary gas-liquid separator 6 and the air inlet of the secondary compression host 2. In this way, when the compressor adjusts the flow rate, the high-pressure air in the secondary compression host 2 will not flow back into the primary gas-liquid separator 6, further ensuring that there will be no excessively high pressure in the primary gas-liquid separator 6 during the adjustment process, thereby avoiding leakage losses and improving working energy efficiency. Figure 1 , Figure 2As shown, the variable frequency motor 1 3 and the variable frequency motor 2 4 are arranged at intervals in the horizontal direction, and the compressor further includes a secondary gas-liquid separator 7, and the primary gas-liquid separator 6 and the secondary gas-liquid separator 7 are arranged between the variable frequency motor 1 3 and the variable frequency motor 2 4. In this way, the variable frequency motor 1 3 and the variable frequency motor 2 4 are arranged separately and spaced on both sides of the primary gas-liquid separator 6 and the secondary gas-liquid separator 7, so that the primary compression host 1 and the secondary compression host 2 are arranged and connected with the primary gas-liquid separator 6 and the secondary gas-liquid separator 7, and at the same time, the vibration interference between the variable frequency motor 1 3 and the variable frequency motor 2 4 can be reduced, and the resonance effect that may be caused when the two have the same rotation speed can be weakened. The compressor also includes a primary filter 8 and a secondary filter 9. The inlet of the primary filter 8 and the inlet of the secondary filter 9 are respectively connected to the discharge port of the primary gas-liquid separator 6 and the discharge port of the secondary gas-liquid separator 7. The primary filter 8 is connected to the inner cavity of the secondary compression host 2 through an openable and closable liquid replenishing pipe 10. The middle section of the liquid replenishing pipe 10 is provided with a booster pump 11 that can drive the lubricating liquid to be transported to the secondary compression host 2. The primary filter 8 and the secondary filter 9 are used to filter the separated coolant to ensure that the coolant will not cause damage to the screw and the star wheel due to impurities after circulating into the compressor. In this way, the coolant in the primary filter 8 can enter the inner cavity of the secondary compression host 2 after being driven by the booster pump 11 from the opened liquid replenishing pipe 10, avoiding the phenomenon of insufficient lubricating liquid in the secondary compression host 2 due to pressure changes after speed regulation. The compressor also includes a liquid replenishing pipe 12 which is connected to the air inlet of the primary compression host 1 at one end and can be opened and closed, and the other end of the liquid replenishing pipe 12 is connected to the outside world. The middle section of the liquid replenishing pipe 12 is provided with a booster pump 13 which can drive the lubricating liquid to be transported to the primary compression host 1. In this way, when the lubricating liquid is insufficient due to the pressure change after the speed regulation in the primary compression host 1, the operator can replenish the lubricating liquid to the primary compression host 1 from the outside through the opened liquid replenishing pipe 12 and the booster pump 13 to ensure the stability of the compressor adjustment state. The primary gas-liquid separator 6 and the secondary gas-liquid separator 7 are each connected to an openable and closable liquid pipe 14, and the inner cavity of the primary gas-liquid separator 6 and the inner cavity of the secondary gas-liquid separator 7 are each connected to one end of the two liquid pipes 14, and the other ends of the two liquid pipes 14 are both connected to the outside world. In this way, the capacity of the pressurized coolant inside the primary gas-liquid separator 6 and the secondary gas-liquid separator 7 can be controlled through the liquid pipe 14, which is conducive to meeting the needs of different pressure regulation working states and ensuring the stability of the compressor adjustment state. The compression host also includes an intake pipe 16 connected to the air inlet of the first-stage compression host 1 and an exhaust pipe 17 connected to the air outlet of the second-stage gas-liquid separator 7. An intake valve 18 capable of controlling the flow cross section is provided at the air inlet of the first-stage compression host 1 connected to the intake pipe 16. In this way, the operator can perform auxiliary control of the air intake cross section through the intake valve 18, which is conducive to coordination with the compressor speed adjustment to improve the working energy efficiency of the compressor. Preferably, the bottom of the first-stage compression host 1, the bottom of the second-stage compression host 2, the bottom of the variable frequency motor 1 3 and the bottom of the variable frequency motor 2 4 are all provided with a vibration damping pad 20.This can alleviate the influence of the working vibration of the primary compression host 1, the secondary compression host 2, the variable frequency motor 1 3 and the variable frequency motor 2 4, reduce noise and ensure the working stability of the compressor. Further, the two air pressure sensors 15 are respectively arranged on the primary gas-liquid separator 6 and the exhaust pipe 17, and the exhaust pipe 17 is directly connected to the user's device, which is conducive to more accurately judging the actual output pressure and ensuring accurate regulation.

[0032] Embodiment 2:

[0033] like Figure 4 As shown, this embodiment is basically the same as the first embodiment, except that: the frequency conversion motor 1 3 and the frequency conversion motor 2 4 can be adjusted by the controller 5 according to the constant pressure flow-speed curve according to the use flow requirement, so that the frequency conversion motor 1 3 and the frequency conversion motor 2 4 can reach the optimal working speed respectively and realize the most economical and stable working state; the use flow-speed curve is a smooth curve drawn by the test personnel after recording the data after the test personnel test the frequency conversion motor 1 3 and the frequency conversion motor 2 4 under various constant pressure flow conditions to reach the optimal speed respectively. For example, the test steps for forming the constant pressure flow-speed curve are as follows: a. Open the pressure The compressor and determine the output pressure of the first-stage compression host 1 to be 0.7Mpa, the output pressure of the second-stage compression host 2 to be 4Mpa, and the use flow rate to be 200L / min; b. Adjust the speed of the variable frequency motor 1 3 and the variable frequency motor 2 4 respectively, monitor and control the pressure of the two-stage compression host to be stable at 0.7Mpa and 4Mpa respectively under the condition of reaching the use flow rate, and record the corresponding speed of the variable frequency motor 1 3 and the variable frequency motor 2 4 at this time; c. Increase the use flow rate setting by 50L / min each time and repeat the above steps; d. Form a smooth curve based on the recorded constant pressure use flow value and the corresponding data of the speed. Figure 4 As shown, it is a schematic diagram of the flow-speed curve for constant pressure (4Mpa), wherein curve A corresponds to the working speed of the first-level variable frequency motor 13, and curve B corresponds to the working speed of the second-level variable frequency motor 24.

[0034] According to the constant pressure flow-speed curve, the controller 5 can directly correspond to the final speed values ​​of the variable frequency motor 1 3 and the variable frequency motor 2 4 according to the determined working flow value coordinates. After the flow rate changes, the final speeds of the variable frequency motor 1 3 and the variable frequency motor 2 4 can be directly adjusted by the controller 5, thereby reducing energy waste and leakage losses caused by pressure mismatch between the first-stage compression host 1 and the second-stage compression host 2 after adjustment, thereby improving the energy efficiency of the compressor. Further, the compressor also includes a first-stage gas-liquid separator 6 and a flow sensor for monitoring the exhaust flow of the compressor. The flow sensor is a commercially available product and can be installed at the exhaust port of the compressor or on the user-end device. The flow sensor is connected to the controller 5 for communication. The controller 5 stores the constant pressure flow-speed curve data and controls the frequency converter. Preferably, the first-stage gas-liquid separator 6 and the exhaust pipe 17 are both provided with an air pressure sensor 15 for monitoring the internal air pressure. The pressure inside the primary gas-liquid separator 6 and the secondary gas-liquid separator 7 corresponds to the primary working pressure and the secondary output pressure respectively, which makes it easy for the operator to observe the changes in the working pressure and judge the adjustment status. It is also beneficial to form continuous feedback calibration of the controller 5 to make the adjustment more accurate and stable.

[0035] Embodiment three:

[0036] This embodiment is basically the same as the first embodiment, except that: this compressor only includes one gas-liquid separator, namely the secondary gas-liquid separator 7, and the air outlet of the compression main unit 1 is directly connected to the air inlet of the secondary compression main unit 2, and the air outlet of the secondary compression main unit 2 is connected to the air inlet of the secondary gas-liquid separator 7.

[0037] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A multi-stage variable frequency screw air compressor, comprising a first-stage compression main unit (1) and a second-stage compression main unit (2) connected in series in an air circuit, characterized in that: The compressor further comprises a variable frequency motor 1 (3), a variable frequency motor 2 (4), and a controller (5) capable of adjusting the adaptive speed of the variable frequency motor 1 (3) and the adaptive speed of the variable frequency motor 2 (4) respectively according to changes in the flow rate used, the controller (5) being electrically connected to the variable frequency motor 1 (3) and the variable frequency motor 2 (4), the output shaft of the variable frequency motor 1 (3) being connected to the power input end of the first-stage compression host (1), and the output shaft of the variable frequency motor 2 (4) being connected to the power input end of the second-stage compression host (2); the compressor further comprises a first-stage gas-liquid separator (6), the air inlet of the first-stage gas-liquid separator (6) being connected to the air outlet of the first-stage compression host (1), and the first-stage gas-liquid separator (6) being connected to the air outlet of the first-stage compression host (1). The air outlet of the separator (6) is connected to the air inlet of the secondary compression main unit (2). The controller (5) can control the variable frequency motor 2 (4) to accelerate first when the constant pressure flow rate increases so as to reduce the pressure at the air inlet of the secondary compression main unit (2) and the first gas-liquid separator (6), and then the first compression main unit (1) is accelerated. When the constant pressure flow rate decreases, the variable frequency motor 1 (3) is controlled to decelerate first so as to reduce the pressure of the closed space between the air outlet of the first compression main unit (1) and the air inlet of the second compression main unit (2), and then the second compression main unit (2) is decelerated. A minimum pressure valve (19) is provided between the air outlet of the first gas-liquid separator (6) and the air inlet of the second compression main unit (2).

2. The multi-stage variable frequency screw air compressor according to claim 1, characterized in that: The compressor further comprises an air pressure sensor (15) capable of monitoring the output pressure of the first compression main unit (1) and the output pressure of the second compression main unit (2). The controller (5) is electrically connected to the air pressure sensor (15). When the pressure monitored by the air pressure sensor (15) is lower than a preset pressure, the controller (5) can adjust the rotation speeds of the first frequency conversion motor (3) and the second frequency conversion motor (4) to increase. When the pressure monitored by the air pressure sensor (15) is higher than the preset pressure, the controller (5) can adjust the rotation speeds of the first frequency conversion motor (3) and the second frequency conversion motor (4) to decrease.

3. The multi-stage variable frequency screw air compressor according to claim 1, characterized in that: The controller (5) stores constant pressure flow rate-speed curve data formed by testing different flow rates under constant pressure intake and constant pressure exhaust conditions of the two-stage compression main unit (2) and corresponding to the stable speed of the variable frequency motor 1 (3) and the stable speed of the variable frequency motor 2 (4). The controller (5) can adjust the speed of the variable frequency motor 1 (3) and the speed of the variable frequency motor 2 (4) respectively when the flow rate changes according to the constant pressure flow rate-speed curve data.

4. The multi-stage variable frequency screw air compressor according to claim 1 or 3, characterized in that: The compressor further comprises a secondary gas-liquid separator (7), a primary filter (8) and a secondary filter (9), wherein the inlet of the primary filter (8) and the inlet of the secondary filter (9) are respectively connected to the discharge port of the primary gas-liquid separator (6) and the discharge port of the secondary gas-liquid separator (7), and the primary filter (8) is connected to the inner cavity of the secondary compression main unit (2) through an openable and closable liquid replenishing pipe (10), and a pressure pump (11) capable of driving the lubricating liquid to be transported toward the secondary compression main unit (2) is provided in the middle section of the liquid replenishing pipe (10). The compressor further comprises a liquid replenishing pipe (12) having one end connected to the air inlet of the primary compression main unit (1) and being openable and closable, and the other end of the liquid replenishing pipe (12) is connected to the outside, and a pressure pump (13) capable of driving the lubricating liquid to be transported toward the primary compression main unit (1) is provided in the middle section of the liquid replenishing pipe (12).

5. The multi-stage variable frequency screw air compressor according to claim 2, characterized in that: The compressor further comprises a secondary gas-liquid separator (7), a primary filter (8) and a secondary filter (9), wherein the inlet of the primary filter (8) and the inlet of the secondary filter (9) are respectively connected to the discharge port of the primary gas-liquid separator (6) and the discharge port of the secondary gas-liquid separator (7), and the primary filter (8) is connected to the inner cavity of the secondary compression main unit (2) through an openable and closable liquid replenishing pipe (10), and a pressure pump (11) capable of driving the lubricating liquid to be transported toward the secondary compression main unit (2) is provided in the middle section of the liquid replenishing pipe (10). The compressor further comprises a liquid replenishing pipe (12) having one end connected to the air inlet of the primary compression main unit (1) and being openable and closable, and the other end of the liquid replenishing pipe (12) is connected to the outside, and a pressure pump (13) capable of driving the lubricating liquid to be transported toward the primary compression main unit (1) is provided in the middle section of the liquid replenishing pipe (12).

6. The multi-stage variable frequency screw air compressor according to claim 4, characterized in that: The first gas-liquid separator (6) and the second gas-liquid separator (7) are each connected to an openable and closable liquid passage pipe (14); the inner cavity of the first gas-liquid separator (6) and the inner cavity of the second gas-liquid separator (7) are each connected to one end of the two liquid passage pipes (14); and the other ends of the two liquid passage pipes (14) are connected to the outside.

7. The multi-stage variable frequency screw air compressor according to claim 5, characterized in that: The compressor further comprises an air intake pipe (16) connected to the air intake of the first-stage compression main unit (1) and an exhaust pipe (17) connected to the air outlet of the second-stage gas-liquid separator (7); an air intake valve (18) capable of controlling the flow cross section is provided at the air intake of the first-stage compression main unit (1).

8. The multi-stage variable frequency screw air compressor according to claim 7, characterized in that: There are two air pressure sensors (15), one of which is arranged on the primary gas-liquid separator (6), and the other of which is arranged on the exhaust pipe (17).

9. The multi-stage variable frequency screw air compressor according to claim 1, 2 or 3, characterized in that: The bottom of the first-stage compression main unit (1), the bottom of the second-stage compression main unit (2), the bottom of the first variable frequency motor (3), and the bottom of the second variable frequency motor (4) are all provided with vibration-damping pads (20).

Images