WO2020011126A1

WO2020011126A1 - Screw compressor system and heat exchange system comprising screw compressor system

Info

Publication number: WO2020011126A1
Application number: PCT/CN2019/095076
Authority: WO
Inventors: 范士则; 沈鹏飞; 森山昌幸
Original assignee: 麦克维尔空调制冷(苏州)有限公司
Priority date: 2018-07-13
Filing date: 2019-07-08
Publication date: 2020-01-16
Also published as: CN108644116A

Abstract

A screw compressor system (100) and a heat exchange system (700) comprising the screw compressor system (100). The screw compressor system (100) comprises: a speed change motor (1) , a screw compressor (2), and a controller (101); wherein the screw compressor (2) is provided with a screw main shaft (21), a screw rotor (22), a bypass housing (3), and a sliding valve (32), and the controller (101) controls movement of the sliding valve (32) and the rotating speed of a rotating shaft (5) of the speed change motor (1), wherein before the rotating speed of the rotating shaft (5) is switched from one stage to another stage, and the controller (101) controls the sliding valve (32) to move to enable the load of the screw compressor (2) to reduce to a predetermined position.

Description

Screw compressor system and heat exchange system including the screw compressor system

Technical field

The present application relates to the technical field of air conditioning equipment, and in particular, to a screw compressor system and a heat exchange system including the screw compressor system.

Background technique

Screw compressors are the most widely used form of rotary compressors. Screw compressors are divided into two types: single-screw and twin-screw compressors. Single-screw is composed of a screw and star wheel blades distributed on both sides. Twin-screw compression The machine consists of a pair of parallel, intermeshing female and male screws. In a single-screw compressor or a twin-screw compressor, the main shaft of the screw can be connected to the rotor of the motor. When the rotor of the motor rotates, the screw is driven to rotate, thereby compressing the refrigerant in the screw compressor.

The motor that drives the screw compressor may be a fixed speed electrode or a variable speed motor. Among them, the speed of the fixed speed motor is fixed, and the variable speed motor may have multiple speeds (gears).

Generally, the speed of a variable speed motor can be changed by changing the wiring mode. When the speed is switched between different levels, the wiring corresponding to the original speed is disconnected and the wiring corresponding to the new speed is closed. Therefore, during the speed switching process, it is equivalent to the motor stopping from the original speed and starting to the new speed.

It should be noted that the above description of the technical background is merely for the convenience of a clear and complete description of the technical solution of the present invention, and for the understanding of those skilled in the art. The above technical solutions should not be considered to be well known to those skilled in the art just because these solutions are explained in the background section of the present invention.

Summary of the invention

The inventor of the present application has found that during the starting process of the motor, the current flowing through the motor will be higher than the rated current of the motor. For example, the starting current of a direct start can reach 6 times the rated current. It is three times the rated current.

The starting current will impact the motor and the grid. The longer the same starting current, the longer the sustaining time, the greater the harm. For example, when the motor starts, if the load of the screw compressor is greater, the time that the motor starting current is maintained will be The longer it is, the greater the harm to the motor itself and the power grid, and it may even cause the motor to burn out.

For variable-speed motors, switching speed is equivalent to restarting the motor. Therefore, if the screw compressor load is large when the speed is switched, the starting current during switching will last longer, which will bring to the motor itself and the power grid. Greater harm.

The present application provides a screw compressor system and a heat exchange system including the screw compressor system. The load of the screw compressor is reduced before the rotation speed of the variable-speed motor is switched. Therefore, the load of the screw compressor can be reduced. Under the circumstances, the speed of the motor is switched. Therefore, the duration of the starting current during the switching of the motor is shorter, and the harm to the motor and the power grid is reduced.

According to a first aspect of the embodiments of the present application, a screw compressor system is provided, including:

A variable speed motor having a rotatable rotating shaft that can be switched between N levels of rotation speed, where N is a natural number greater than or equal to 2; a screw compressor having a screw main shaft, a screw rotor, a bypass housing, and The slide valve, wherein the screw main shaft is connected with the rotating shaft, the screw rotor rotates with the screw main shaft, the bypass rotor is provided with a bypass housing on an outer periphery, and the bypass housing is provided with A slide valve capable of moving in the axial direction of the main shaft of the screw with respect to the bypass housing, and forming a bypass port with the bypass housing when the slide valve moves away from the housing The bypass port communicates with the compression chamber and the suction end of the screw compressor; and a controller that controls the movement of the spool valve and the rotation speed of the rotating shaft of the variable speed motor, wherein, at the rotating shaft Before switching the rotation speed from one level to another, the controller controls the slide valve to move to a predetermined position that reduces the load of the screw compressor.

According to a second aspect of the embodiments of the present application, wherein the predetermined position is a position where the bypass valve opens the bypass port maximally.

According to a third aspect of the embodiments of the present application, when the controller needs to increase the screw compressor to a first predetermined load, the controller controls the variable-speed motor to maintain a current rotation speed level And controlling the slide valve to move the screw compressor to a second predetermined load.

According to a fourth aspect of the embodiments of the present application, when the screw compressor is increased to the second predetermined load, the controller: controls the slide valve to move to the predetermined position; controls the The variable speed motor is switched to a level higher than the current speed; and the slide valve is controlled to move to a position where the screw compressor is increased to the first predetermined load.

According to a fifth aspect of the embodiments of the present application, when the controller needs to reduce the load of the screw compressor to a third predetermined load, the controller controls the variable speed motor to maintain a current speed level And controlling the slide valve to move the screw compressor to a fourth predetermined load.

According to a sixth aspect of the embodiments of the present application, when the screw compressor is reduced to the fourth predetermined load, the controller: controls the slide valve to move to the predetermined position; controls the The variable speed motor is switched to a level lower than the current rotational speed; and the slide valve is controlled to move to a position where the screw compressor load reaches the third predetermined load.

According to a seventh aspect of the embodiments of the present application, wherein the controller sets a first predetermined load or a third predetermined load according to a comparison result of an outlet water temperature of the evaporator connected to the screw compressor and a predetermined temperature.

According to an eighth aspect of the embodiments of the present application, the controller determines the screw compression based on a displacement of the spool valve, or a compressor suction pressure, a compressor discharge pressure, and a current of the variable-speed motor. Whether the load is increased to the second predetermined load or reduced to the fourth predetermined load.

According to a ninth aspect of the embodiments of the present application, a maximum value of a gas flow rate discharged from the bypass port of the screw compressor is related to a maximum speed and a minimum speed of the variable speed motor.

According to a tenth aspect of the embodiments of the present application, there is provided a heat exchange system having the screw compressor system according to any one of the first aspect to the ninth aspect of the above embodiment, wherein the heat exchange system may, for example, It's a chiller.

The beneficial effect of the present application is that the starting current when the motor is switched can reduce the harm to the motor and the power grid.

With reference to the following description and drawings, specific embodiments of the present application are disclosed in detail, and the manner in which the principles of the present application can be adopted is indicated. It should be understood that the embodiments of the present application are not limited in scope. Within the spirit and terms of the appended claims, the embodiments of this application include many changes, modifications, and equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the embodiments of the present application, and constitute a part of the description, for illustrating the embodiments of the present application, and to explain the principles of the present application together with the text description. Obviously, the drawings in the following description are just some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without paying creative labor. In the drawings:

1 is a schematic diagram of a screw compressor system according to Embodiment 1 of the present application;

2 is another schematic diagram of a screw compressor system according to Embodiment 1 of the present application;

3 is another schematic diagram of a screw compressor system according to Embodiment 1 of the present application;

4 is another schematic diagram of a screw compressor system according to Embodiment 1 of the present application;

5 is a schematic diagram of a flow of a screw compressor system during startup and rotation speed switching in the example of Embodiment 1 of the present application;

6 is a schematic diagram of a compressor load curve, a slide valve moving distance curve, and a variable speed motor speed curve in the example of Embodiment 1 of the present application;

7 is a schematic diagram of a heat exchange system including the screw compressor system of Embodiment 1 of the present application;

FIG. 8 is a schematic diagram of an isentropic efficiency-load curve of a screw compressor of Embodiment 1 of the present application and a prior art screw compressor.

detailed description

The foregoing and other features of the present application will become apparent from the following description with reference to the accompanying drawings. In the description and the drawings, specific embodiments of the present application are specifically disclosed, which shows some of the embodiments in which the principles of the present application can be applied. It should be understood that the present application is not limited to the described embodiments. Instead, the present application The application includes all modifications, variations, and equivalents falling within the scope of the appended claims.

Example 1

An embodiment of the present application provides a screw compressor system. FIG. 1 is a schematic diagram of the screw compressor system of this embodiment, and FIG. 2 is another schematic diagram of the screw compressor system of this embodiment. The displacement of the spool valve is different.

In this embodiment, as shown in FIGS. 1 and 2, the screw compressor system 100 may include a variable-speed motor 1, a screw compressor 2, and a controller (not shown).

In this embodiment, the variable speed motor 2 may have a rotatable rotating shaft 5 capable of switching between N levels of speeds, where N is the number of levels of the speed and N is a natural number greater than or equal to two. For example, the rotation speed of each level can be expressed as R ₁ , R ₂ ,..., R _n ,..., R _N in order from high to low. , Where n is a natural number and 1 ≦ n ≦ N.

In this embodiment, the variable speed motor 2 may have a common stator winding coil, and the rotation speed can be switched by changing the connection mode of the stator winding. The connection mode of the stator winding can be switched by multiple sets of switches, for example: When the first group of switches is turned on and the second group of switches is turned off, the stator windings can be connected in a certain way, for example, in a delta connection. At this time, the motor can run at low speed; when the second group of switches is turned on and the first When the group switch is turned off, the stator windings can be connected in another way, for example, in a double star connection. At this time, the motor can run at high speed. Thereby, the variable speed motor 2 can be switched between two kinds of rotation speeds. When the motor needs to switch between more intermediate speeds, it can be implemented in a similar manner as described above.

In this embodiment, the screw compressor 2 may have a screw main shaft 21, a screw rotor 22, a bypass housing 3, and a slide valve 32.

As shown in FIGS. 1 and 2, the screw main shaft 21 is connected to the rotating shaft 5; the screw rotor 22 rotates with the screw main shaft 21; the bypass rotor 3 is provided on the outer periphery of the screw rotor 22; and the bypass housing 3 is provided with a bypass. Port 31 (see FIG. 2, not shown in FIG. 1), wherein, in FIG. 1, the bypass port 31 is completely covered by the slide valve 32, and in FIG. 2, the bypass valve 32 is moved to the left to make the bypass The port 31 is exposed; the bypass port 31 communicates with the compression chamber (not shown) and the suction end (not shown) of the screw compressor; the slide valve 32 may be located at the bypass port 31. The slide valve 32 is movable relative to the bypass port 31 in the axial direction of the screw main shaft 21.

As shown in Figures 1 and 2, the screw main shaft 21 is connected to the rotating shaft 5; the screw rotor 22 rotates with the screw main shaft 21; the bypass rotor 3 is provided on the outer periphery of the screw rotor 22; the bypass housing 3 is provided to be movable The slide valve 32 can move to form a bypass port 31 with the casing 3 (see FIG. 2, not shown in FIG. 1). In FIG. 1, the slide valve 32 is not moved and the bypass port is closed 31. In FIG. 2, the slide valve 32 moves to the left and forms a bypass port 31 with the bypass housing 3; the bypass port 31 communicates with the compression chamber (not shown) and the suction end (not shown) of the screw compressor. Out). The spool valve 32 can be moved relative to the housing 3 in the axial direction of the screw main shaft 21 to change the area of the bypass port 31.

In this embodiment, the controller can control the movement of the spool valve 32 and the rotation speed of the rotating shaft 5 of the variable-speed motor 1, wherein the controller controls the spool valve before the rotating speed of the rotating shaft 5 is switched from one level to another. 32 moves to a predetermined position where the load of the screw compressor 2 is reduced.

According to this embodiment, before the rotation speed of the variable speed motor is switched from the current level to another level, the load of the screw compressor is reduced by moving the slide valve. Therefore, the variable speed can be performed with a low load of the screw compressor The speed level of the motor is switched. Therefore, when the speed level is switched, the duration of the starting current is shorter, and the harm of the starting current to the variable-speed motor and the power grid supplying the variable-speed motor is reduced.

Hereinafter, the working principle of the screw compressor of the present application will be briefly described with reference to the drawings.

As shown in FIGS. 1 and 2, the rotating shaft 5 of the variable-speed motor 1 and the screw main shaft 21 may be connected by a coupling. In addition, the rotating shaft 5 of the variable speed motor 1 may also be the same shaft as the screw main shaft 21 of the screw compressor 2, that is, the rotor (not shown) of the variable speed motor 1 and the screw rotor 22 are sleeved on the same shaft, which can also achieve Same effect.

When the spool valve 32 moves to the compression chamber, the bypass port 31 gradually opens, and at the same time, the exhaust port 321 approaches the compression chamber of the screw compressor, and part of the suction volume in the screw compressor is unloaded from the bypass port 31 to the suction end. The unloaded gas does not participate in the refrigeration cycle, thereby reducing the refrigeration capacity and reducing the load of the screw compressor, that is, reducing the load; when the spool valve 32 moves to the suction end, the bypass port 31 is gradually closed, At the same time, the exhaust port 321 approaches the suction end of the screw compressor, and the load of the compressor is increased, that is, the load is increased.

The slide valve 32 can be drive-connected with a drive mechanism (not shown). The drive mechanism is, for example, a combination of a motor and a screw nut mechanism or a linear motor. As long as the slide valve 32 can be driven to move in the axial direction of the screw main shaft 21, it opens. 3. Close or adjust the opening size of the bypass port 31.

In this embodiment, the inner wall of the bypass housing 3 and the outer peripheral surface of the screw rotor 22 are arranged in close contact with each other. The bypass housing 3 is provided with an avoidance gap corresponding to the star wheel 4 provided in mesh with the screw rotor 22.

In the implementation shown in FIGS. 1 and 2, the screw compressor 2 is a single screw compressor.

In addition, this embodiment may not be limited to this, and the screw compressor 2 may be a twin screw compressor.

FIG. 3 is another schematic diagram of the screw compressor system of this embodiment, and FIG. 4 is another schematic diagram of the screw compressor system of this embodiment. In FIGS. 3 and 4, the displacement of the spool valve 32 is different.

As shown in FIG. 3 and FIG. 4, the screw rotor of the twin-screw compressor 2 may include a male rotor 221 and a female rotor 222. The rest of the components are the same as those of FIGS. 1 and 2, and are not repeated here.

The operation mode of the variable speed motor 1 and the screw compressor 2 under the control of the controller will be described below.

In this embodiment, before the variable speed motor 1 is switched from a lower rotation speed R _{n + 1} to a higher rotation speed R _n , the controller controls the spool valve 32 to move to the predetermined position so that the screw compressor 2 The load is reduced. When the spool valve moves to the predetermined position, the controller can control the variable speed motor _{1 to} switch from a lower rotation speed R _{n + 1} to a higher rotation speed R _n . In addition, after the rotation speed of the variable speed motor 1 is switched to a higher rotation speed R _{n + 1} , the controller can control the moving position of the spool valve 32 according to the target load, so that the load of the screw compressor 2 reaches the target load.

In this embodiment, before the variable speed motor 1 is switched from a higher rotation speed R _n to a lower rotation speed R _{n + 1} , the controller may control the spool valve 32 to move to the predetermined position so that the screw compressor 2 The load is reduced. When the spool valve is moved to the predetermined position, the controller can control the variable speed motor 1 to switch from a higher rotation speed R _n to a lower rotation speed R _{n + 1} . In addition, after the rotation speed of the variable speed motor 1 is switched to a lower rotation speed R _n , the controller may control the moving position of the spool valve 32 according to the target load, so that the load of the screw compressor 2 reaches the target load.

In this implementation, the controller may determine whether the spool valve moves to the predetermined position according to the detection amount of the displacement sensor connected to the spool valve 23, or according to the compressor suction pressure, compressor discharge pressure, and current of the variable speed motor. .

In the present embodiment, when the variable speed motor 1 is started from a closed state, the variable speed motor 1 may be started from the lowest rotation speed with the spool valve 32 at the predetermined position, so that when the variable speed motor is started, the screw is compressed The load of the machine is small, the duration of the starting current is short, and the damage to the motor and the power grid is small.

In addition, when the variable-speed motor 1 of this embodiment is replaced with a fixed-speed motor, the above-mentioned method may also be used to start the fixed-speed motor, so that the duration of the startup current of the fixed-speed motor is shorter to reduce the impact on the motor. And grid damage. For example, when the fixed-speed motor is started from a closed state, the slide valve 32 may be moved to the predetermined position first, and then the fixed-speed motor is started.

In this embodiment, the predetermined position may be a position that opens the bypass port more than the current position, that is, a position after the spool valve 32 is moved to the left in FIG. 2 by a distance, for example, The spool valve 32 is moved to the leftmost position in FIG. 2, where the spool valve 32 can open the bypass port 31 to the maximum extent, that is, in this position, relative to the position where the bypass port 31 is closed. The slide valve 32 has moved the maximum distance.

In the following, an example is used to describe the flow of the screw compressor system of the present application during startup and rotation speed switching.

FIG. 5 is a schematic diagram of the flow of the screw compressor system when the screw compressor system is started and the speed is switched in this example, and FIG. 6 is a schematic diagram of the compressor load curve 601, the spool movement distance curve 602, and the variable speed motor speed curve 603 in this example.

In Figure 6, the horizontal axis represents time in seconds (S); the right vertical axis represents the speed of the variable speed motor 1 in rpm; the left vertical axis represents the load on the screw compressor and the distance the spool moves. The percentage indicates that the screw compressor load is a percentage of the maximum load of the screw compressor, and a percentage of the moving distance of the spool valve 32 with respect to the maximum moving distance of the spool valve 32.

In this example, the variable speed motor 1 has two rotation speed levels, and the rotation speeds of each level are R1 and R2, wherein R1 can be 3000 revolutions per minute (rpm), and R2 can be 1500 rpm.

In this example, the predetermined position to which the spool valve is moved may be a position having a maximum moving distance.

As shown in Figures 5 and 6, the process may include the following steps:

Step 501: The spool valve is controlled to move to a position with a maximum moving distance, so that the compressor 2 is at a minimum load;

Step 502: Turn on the startup current of the compressor to start the variable-speed motor 1 to the rotation speed R2, where

steps

501 and 502 correspond to the startup phase of the screw compressor system;

The time when step 502 is completed may correspond to time t1 in FIG. 6, that is, the speed of the variable speed motor 1 is 1500 rpm, the load of the screw compressor 2 is 20% load, and the spool valve 32 is in the position with the maximum moving distance, of which 20% load It may be the minimum load of the screw compressor 2 at a speed of 1500 rpm;

Step 503: Keep the rotation speed R2 of the variable speed motor 1 unchanged, and reduce the moving distance of the spool to increase the compressor to a predetermined target load. Here, the moving distance of the spool can be reduced to 0%, for example. The target load may be the maximum load at the speed R2, for example, a 50% load. In addition, the predetermined target load may also be another small value, and the moving distance of the spool valve may be correspondingly larger than 0%.

The time when step 503 is completed may correspond to time t2 in FIG. 6, and the slide valve movement process in step 503 may correspond to the time period from time t1 to time t2 in FIG. 6, during which the speed of the variable speed motor 1 is 1500 rpm, and the slide valve The moving distance of the screw compressor is changed from 100% to 0%, so that the load of the screw compressor 2 is increased from 20% to 50%, wherein the 50% load may be the maximum load of the screw compressor 2 at a speed of 1500 rpm;

Step 504: The spool valve is moved to a position with a maximum moving distance, so that the load of the compressor becomes the minimum load at the rotation speed R2. This step 504 can be used as a preparation step before the rotation speed is switched from R2 to R1;

The time when step 504 is completed may correspond to time t3 in FIG. 6, and the process of the spool valve movement in step 504 may correspond to the time period from time t2 to time t3 in FIG. 6, during which the speed of the variable speed motor 1 is 1500 rpm, and the spool valve The moving distance is changed from 0% to 100%, so that the load of the screw compressor 2 is reduced from 50% to 20%;

Step 505: The rotation speed of the variable speed motor 1 is controlled to be switched to R1;

The time at which step 505 is completed may correspond to time t4 in FIG. 6. At this time t4, the speed of the variable speed motor 1 becomes 3000 rpm, and the load of the screw compressor 2 is 40%, that is, the minimum load at the speed of R1; During the period from t3 to t4, the spool valve 32 is maintained at the position of the maximum displacement (ie, 100%);

Step 506: Keep the rotation speed R1 of the variable speed motor 1 unchanged, and reduce the moving distance of the spool to increase the compressor to a predetermined target load. Here, the moving distance of the spool can be reduced to 0%, for example. , The target load may be the maximum load at the rotation speed R1, for example, it may be a 100% load;

The time when step 506 is completed may correspond to time t5 in FIG. 6, and the sliding valve movement process in step 506 may correspond to the time period from time t4 to time t5 in FIG. 6, during which the speed of the variable speed motor 1 is 3000 rpm, and the slide valve The moving distance is gradually reduced to 0%, so that the load of the screw compressor 2 is increased from 40% to 100%;

Step 507: Increase the moving distance of the spool valve and reduce the load to 50% of the load. Here, the 50% load can be considered as a condition for determining the speed of the variable speed motor. At 50%, the load can no longer be reduced by increasing the moving distance of the slide valve, but by switching the speed of the variable-speed motor to a lower speed. In addition, in this embodiment, the 50% load is only an example. Use a load of less than 50% as the judgment condition for the speed of the variable speed motor;

The time when step 507 is completed may correspond to time t6 in FIG. 6;

Step 508: The spool valve is moved to the position with the maximum moving distance, so that the load of the compressor becomes the minimum load at the speed R1. This step 508 can be used as a preparation step before the speed is switched from R1 to R2;

The time when step 508 is completed may correspond to time t7 in FIG. 6, and the slide valve movement process in step 508 may correspond to the time period from time t6 to time t7 in FIG. 6, during which the speed of the variable speed motor 1 is 3000 rpm, and the slide valve The moving distance is gradually increased to 100%, so that the load of the screw compressor 2 is reduced from 50% to 40%, wherein the 40% load may be the minimum load of the screw compressor 2 at a speed of 3000 rpm;

In step 509, the speed of the variable-speed motor 1 is controlled to switch to R2; the time when step 509 is completed may correspond to time t8 in FIG. 6, at this time t8, the speed of the variable-speed motor 1 becomes 1500 rpm, and the load of the screw compressor 2 is 20 % In the time period from time t7 to t8, the spool valve 2 is maintained at the position of maximum displacement;

Step 510: The spool valve is moved to increase the load of the compressor first, and then reduce the load of the compressor to the minimum load at the speed R2;

In step 510, the spool valve is loaded to time t9. At this time t9, the speed of the variable speed motor 1 is maintained at 1500 rpm, the spool valve is moved to a position with a displacement of 0%, and the load of the screw compressor 2 is 50%; The valve is deloaded to time t10, the spool valve reaches the maximum displacement, and the load of the screw compressor 2 is 20%

Step 511: Turn off the variable speed motor 1.

In this embodiment, when the control device of the screw compressor system 100 controls the rotation speed of the slide valve and the variable speed motor to adjust the load of the screw compressor system, the movement of the slide valve can be adjusted first, and when a predetermined load cannot be reached In the case of the motor, the speed level of the motor is further switched. When the speed level of the electrode is switched, the above-mentioned control method can be adopted.

In one embodiment, in a case where the controller needs to increase the screw compressor to a first predetermined load, the controller controls the level at which the variable speed motor 1 can maintain the current rotation speed, and controls the slide valve 32 to move to The screw compressor is increased to a second predetermined load.

If the load of the screw compressor does not need to further increase the load before reaching the second predetermined load, the rotation speed of the motor may not be switched. If the load of the screw compressor reaches the second predetermined load, it is necessary to continue to increase the load. The controller performs control to increase the speed of the motor, that is, the control spool 32 is moved to the predetermined position, and then the variable speed motor is controlled to switch To a speed higher than the current speed. The second predetermined load may be, for example, a maximum load at the current rotation speed. In addition, when the variable speed motor is switched to a level having a higher rotation speed, the controller may also control the spool valve 32 to move to a position where the screw compressor is increased to the first predetermined load.

In another embodiment, when the controller needs to reduce the load of the screw compressor 2 to a third predetermined load, the controller can control the variable speed motor 1 to maintain the current speed level, and control the slide valve 32 to move The screw compressor 1 is deloaded to a fourth predetermined load.

If the load of the screw compressor does not need to be further reduced before reaching the fourth predetermined load, the rotation speed of the motor may not be switched. If the load of the screw compressor needs to be further reduced when the load reaches the fourth predetermined load, the controller may perform control to reduce the rotation speed of the motor, that is, control the slide valve 32 to move to the predetermined position, and then, control The variable speed motor 1 is switched to a lower rotation speed level than the current rotation speed. That is, the fourth predetermined load may be used as a determination condition for determining whether it is necessary to switch to a lower rotation speed. The fourth predetermined load r may be, for example, less than or equal to Rn / R1 and greater than or equal to the minimum load of the screw compressor at the current speed, that is, the minimum load at the current speed ≤ r ≤ Rn / R1, where Rn Is the target speed of the variable-speed motor, that is, the speed after switching, and R1 is the maximum speed of the variable-speed motor. r is 40% ≤r≤50%, for example, r = 50%, that is, when the motor speed is R1, if the spool valve 32 moves to reduce the compressor to 50%, the controller judges that the speed can be switched to 1500rpm For the specific process of switching, refer to the foregoing description of this embodiment.

In addition, in the above description and the following description of this embodiment, the load of the screw compressor is expressed as a percentage, and its physical meaning is the actual load of the screw compressor (in kilowatts or cold tons) and the maximum load of the screw compressor. (Units are kilowatts or cold tons).

In addition, when the variable speed motor is switched to a level having a lower rotation speed, the controller may also control the spool valve 32 to move to a position where the screw compressor 1 is reduced to the third predetermined load.

In this embodiment, the controller may set the first predetermined load or the third predetermined load according to a comparison result between an outlet water temperature of the evaporator connected to the screw compressor and a predetermined temperature.

In this embodiment, the controller determines whether the screw compressor is increased to the second predetermined load or reduced to the fourth predetermined load according to the displacement of the spool valve 32. For example, the displacement of the spool valve 32 may be the current position of the spool valve With respect to the displacement at the fixed end, this displacement has a corresponding relationship with the load of the screw compressor. Therefore, the displacement of the spool valve 32 can determine the load of the screw compressor. The slide valve 32 may have a displacement sensor, and the displacement sensor may detect the displacement of the slide valve 32.

In addition, the controller can also determine whether the screw compressor is increased to load based on the compressor suction pressure Ps, compressor discharge pressure Pd, and the current of the variable speed motor 1 (for example, the current flowing through the stator of the variable speed motor 1). The second predetermined load is reduced to the fourth predetermined load. For example, the ratio of the compressor suction pressure Ps and the compressor discharge pressure Pd determines the relationship between the variable-speed motor current and the compressor load. Therefore, the calculated compressor suction pressure Ps and compressor discharge pressure are calculated. The ratio of Pd can determine the relationship curve between the current of the variable-speed motor and the load of the compressor. Combining the determined curve and the current of the variable-speed motor 1 can obtain the compressor load corresponding to the current.

In the following, an example is used to describe the method for adjusting the load of the screw compressor system of the present application in a heat exchange system.

FIG. 7 is a schematic diagram of a heat exchange system including the screw compressor system of this embodiment.

As shown in FIG. 7, the heat exchange system 700 may include: a screw compression system 100, an expansion valve 701, an evaporator 702, and a condenser 703. The screw compression system 100 may include a variable-speed motor 1, a screw compressor 2, and a controller 101. The description of the variable-speed motor 1, the screw compressor 2, and the controller 101 is the same as the foregoing description. In FIG. 7, the refrigerant compressed by the screw compressor 2 is condensed by a condenser, and then throttled by an expansion valve. The refrigerant entering the evaporator performs heat exchange with the water flowing into the evaporator, and the water after the heat exchange flows out of the evaporator to form The effluent and heat-exchanged refrigerant enter the compressor 2 for recompression.

As shown in FIG. 7, the heat exchange system 700 may be a chiller, for example. The variable speed motor 1 may be, for example, a two-speed motor, and the speeds of the two speed levels are: R1 is 3000 rpm, and R2 is 1500 rpm.

As shown in FIG. 7, the controller 101 can detect the temperature of the water output from the evaporator 702, and adjust the load of the compressor by adjusting the movement of the slide valve and the rotation speed of the motor, thereby controlling the temperature of the water output from the evaporator to stabilize at a certain value.

For example: the unit sets the evaporator outlet temperature to 7 ° C; after the compressor is started, the operating state is at a low speed of 1500 rpm and the minimum load, that is, the slide valve is at the maximum displacement; the controller 101 detects the outlet temperature of the evaporator 702. If the temperature is higher than 7 ° C, the load of the compressor needs to be increased to reduce the water temperature. Therefore, the controller 101 controls the reduction of the spool valve displacement of the compressor 2 to increase the compressor 2 load. When the spool valve is reduced to a displacement of 0%, The compressor load reaches 50% load. At this time, if the water temperature is still higher than 7 ° C, it is necessary to continue to increase the load of compressor 2. Therefore, the controller 101 switches the motor speed to a high speed of 3000 rpm, that is, first controls the slide valve 32 to move to the displacement. At the highest point, then the speed of the electrode is switched to 3000 rpm, and then, the speed is maintained, and the displacement of the slide valve is gradually reduced so that the load of the compressor reaches a level of 7 ° C.

In addition, when the compressor is running at a high speed of 3000 rpm and the load is high, for example, when the spool valve is located at the minimum displacement, if the controller 101 detects that the water temperature of the evaporator 702 is lower than 7 ° C, the compressor needs to be deloaded to increase the water temperature. The controller 101 will first control the spool valve to increase the displacement to reduce the compressor load; when the spool valve displacement is increased to the maximum, the compressor load is reduced to 50% of the load. If the water temperature is still lower than 7 ° C, the load needs to be continuously reduced. Therefore, The controller 101 switches the motor to a low speed of 1500 rpm, that is, first controls the slide valve 32 to move to the maximum displacement, then switches the speed of the electrode to 1500 rpm, and then maintains this speed, and controls the slide valve's displacement to gradually decrease to make the compression The load reached a level where the water temperature was equal to 7 ° C.

In this embodiment, the maximum value of the gas flow rate discharged from the bypass port 31 of the screw compressor is related to the maximum speed and the minimum speed of the variable speed motor 1, wherein the gas flow rate discharged from the bypass port 31 of the screw compressor is The maximum value can be expressed as the maximum bypass flow. Therefore, compared with the screw compressor system with a slide valve connected to the fixed speed motor in the prior art, the screw compressor system of the present application reduces the amount of bypass gas under the condition of the same partial load energy efficiency ratio, thereby reducing Loss of ineffective work to improve energy efficiency ratio (COP).

In one embodiment, the larger the ratio of the maximum speed to the minimum speed, the smaller the maximum bypass flow rate. For example, the relationship between the maximum bypass flow rate and the maximum and minimum speeds can be expressed as the following formula (1):

Maximum bypass flow rate = 100% -A% * (R ₁ / R _N ) (1)

Among them, A% is the minimum load of the screw compressor 2 and also the minimum load of the screw compressor 2 when the motor speed is RN; R1 is the maximum speed of the variable speed motor 1, and RN is the minimum speed of the variable speed motor 1.

In this embodiment, when the load of the screw compressor 2 is 100%, the variable speed motor 1 runs at high speed and the bypass port 31 is closed; when the load of the screw compressor is less than 100% and greater than 50%, the variable speed motor 1 is at high speed And the bypass port 31 is opened, and the degree of opening of the bypass port 31 can adjust which of the load of the screw compressor is 50% to 100%; when the load of the screw compressor is 50%, the variable speed motor 1 When the load of the screw compressor is less than 50%, the variable speed motor 1 operates at a low speed and the bypass port 31 is closed, and the bypass port 31 is opened. The opening degree of the bypass port 31 can adjust the screw compressor's Which value is less than 50% of the load.

In this embodiment, the internal volume ratio when the screw compressor load is 100% is the same as the internal volume ratio when the load is 50%, that is, the displacement of the spool valve 32 is the same; when the screw compressor load is less than 100% and greater than 50 At%, the inner volume ratio is less than the inner volume ratio of 100% load; when the screw compressor load is less than 50% and greater than 25%, the inner volume ratio is less than the inner volume ratio when the load is 50%.

Compared with the prior art screw compressor system including a constant speed motor and a slide valve, when the load of the screw compressor is low, the energy efficiency ratio of the screw compressor of this embodiment is higher than that of the prior art.

FIG. 8 is a schematic diagram of the isentropic efficiency-load curve of the screw compressor of this embodiment and the prior art screw compressor. As shown in FIG. 8, the vertical axis represents the isentropic efficiency, and the horizontal axis represents the load of the compressor. Among them, the isentropic efficiency can reflect the energy efficiency ratio of the compressor.

Curves

801 and 802 correspond to the isentropic efficiency-load curves of the screw compressor of the present embodiment and the screw compressor of the prior art, respectively. The variable-speed motor connected to the screw compressor of this embodiment may have two speed levels, for example. For example, 1500 rpm and 3000 rpm; the rotation speed of the fixed-speed motor connected to the prior art screw compressor is, for example, 3000 rpm. It can be seen from FIG. 8 that the isentropic efficiency of the screw compressor of this embodiment is higher than the isentropic efficiency of the prior art screw compressor when the load is less than 60%, that is, the screw compression of this embodiment Machine has a higher energy efficiency ratio.

According to this embodiment, before the rotation speed of the variable speed motor is switched from the current level to another level, the load of the screw compressor is reduced by moving the slide valve. Therefore, the variable speed can be performed when the load of the screw compressor is low. The speed level of the motor is switched. Therefore, the startup current lasts a short time when the speed level is switched, and the harm of the starting current to the variable-speed motor and the power grid that supplies the variable-speed motor is reduced. In addition, it is included in the prior art. Compared with the screw compressor system of the fixed speed motor and the slide valve, the compressor of this embodiment has a higher energy efficiency ratio.

Example 2

Embodiment 2 of the present application provides a heat exchange system, which includes the screw compressor system described in Embodiment 1. A schematic diagram of the heat exchange system can be shown in FIG. 7.

The heat exchange system may have a screw compressor system, an expansion valve, an evaporator, and a condenser. The heat exchange system can be a chiller unit or a heat pump unit. For descriptions of the components of the heat exchange system, reference may be made to the description of FIG. 7 in Embodiment 1.

In this embodiment, since the screw compressor system of Embodiment 1 is used, the harm of the starting current to the variable-speed motor in the screw-compressor system and the power grid supplying the variable-speed motor is reduced; in addition, the heat exchange system Higher energy efficiency.

The controller described in combination with the embodiments of the present invention may be directly embodied as hardware, a software module executed by a processor, or a combination of the two. These hardware modules can be implemented by using a field programmable gate array (FPGA) to cure these software modules.

A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art. A storage medium may be coupled to the processor so that the processor can read information from and write information to the storage medium; or the storage medium may be a component of the processor. The processor and the storage medium may reside in an ASIC. The software module can be stored in the memory of the mobile terminal or in a memory card that can be inserted into the mobile terminal. For example, if the electronic device uses a large-capacity MEGA-SIM card or a large-capacity flash memory device, the software module may be stored in the MEGA-SIM card or a large-capacity flash memory device.

The controller described in this embodiment may be implemented as a general-purpose processor, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate array (FPGA), or Other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or any suitable combination thereof. It may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP communication, or any other such configuration.

The present application has been described with reference to specific implementations, but it should be clear to those skilled in the art that these descriptions are exemplary and do not limit the scope of protection of the present application. Those skilled in the art can make various variations and modifications to this application according to the spirit and principles of this application, and these variations and modifications are also within the scope of this application.

Claims

A screw compressor system includes:

A variable speed motor having a rotatable rotating shaft that can be switched between N levels of speed, where N is a natural number greater than or equal to 2;

A screw compressor having a screw main shaft, a screw rotor, a bypass housing, and a slide valve, wherein the screw main shaft is connected to the rotating shaft, the screw rotor rotates with the screw main shaft, and an outer periphery of the screw rotor The bypass housing is provided, and a slide valve is provided on the bypass housing, and the slide valve can move in the axial direction of the screw main shaft relative to the bypass housing, and the slide valve moves away from When the bypass case moves in a direction, a bypass port is formed with the bypass case, and the bypass port communicates with the compression chamber and the suction end of the screw compressor; and

A controller that controls the movement of the spool valve and the rotation speed of the rotating shaft of the variable speed motor,

Wherein, before the rotation speed of the rotating shaft is switched from one level to another level, the controller controls the slide valve to move to a predetermined position that reduces the load of the screw compressor.
The screw compressor system of claim 1, wherein:

The predetermined position is a position where the bypass valve opens the bypass port to the maximum.
The screw compressor system of claim 1, wherein:

When the controller needs to increase the screw compressor to a first predetermined load,

The controller controls the variable speed motor to maintain a current speed level, and controls the slide valve to move the screw compressor to a second predetermined load.
The screw compressor system of claim 3, wherein:

When the screw compressor is increased to the second predetermined load,

The controller:

Controlling the slide valve to move to the predetermined position;

Controlling the variable-speed motor to switch to a higher rotation speed level than the current rotation speed; and

The slide valve is controlled to move to a position where the screw compressor is increased to the first predetermined load.
The screw compressor system of claim 1, wherein:

When the controller needs to reduce the load of the screw compressor to a third predetermined load,

The controller controls the variable speed motor to maintain a current rotation speed level, and controls the spool valve to move the screw compressor to a fourth predetermined load.
The screw compressor system according to claim 5, wherein:

When the screw compressor is reduced to the fourth predetermined load,

The controller:

Controlling the slide valve to move to the predetermined position;

Controlling the variable-speed motor to switch to a speed lower than the current speed; and

The slide valve is controlled to move to a position where the load of the screw compressor reaches the third predetermined load.
The screw compressor system according to claim 3 or 5, wherein:

The controller sets a first predetermined load or a third predetermined load according to a comparison result between an outlet water temperature of the evaporator connected to the screw compressor and a predetermined temperature.
The screw compressor system according to claim 4 or 6, wherein:

The controller determines whether the screw compressor is increased to a second predetermined load or reduced according to a displacement of the spool valve, or a compressor suction pressure, a compressor discharge pressure, and a current of the variable-speed motor Go to the fourth predetermined load.
The screw compressor system of claim 1, wherein:

The maximum value of the flow rate of the gas discharged from the bypass port of the screw compressor is related to the maximum speed and the minimum speed of the variable speed motor.
A heat exchange system, comprising: the screw compressor system according to any one of claims 1-9, an expansion valve, an evaporator, and a condenser.