Screw compressor and control method thereof

Abstract

To provide a screw compressor with improved IPLV under different loads.SOLUTION: A spool valve head end (121) of a screw compressor (100) is arranged inside a suction head end (111) of a screw rotor (110), and a suction capacity adjustment distance is formed between the spool valve head end (121) and the suction head end (111), thereby adjusting a suction capacity of the screw compressor. The suction capacity of the screw compressor (100) can be adjusted by a spool valve (120), thereby effectively solving the problems of motor temperature and exhaust gas temperature restriction of conventional variable frequency screw sets, and expanding an operating range and a load adjustment capacity of the screw compressor.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] FIELD OF THE INVENTION This application relates to screw compressors, and more particularly to an apparatus and method for regulating or controlling a screw compressor by means of a spool valve. [Background technology]

[0002] Screw compressors are common components in refrigeration units. In a screw compressor, a pair of screw rotors engage with each other through tooth grooves, resulting in a change in the volume of the elements formed by the tooth grooves, thereby achieving the suction, compression, and discharge of gas. The pair of engaged screw rotors are arranged parallel within the body of the screw compressor. One end of the screw rotor is the suction end, which is connected to the suction port of the machine body, and the other end is the exhaust end, which is connected to the exhaust port of the machine body. As the screw rotor rotates, gas is sucked in through the suction end, compressed, and discharged through the exhaust end.

[0003] The operating frequency F and the internal volume ratio Vi are two important operating parameters of a screw compressor. The suction capacity can be adjusted by changing the operating frequency F of the screw compressor. The higher the operating frequency F, the faster the screw rotor rotates and the higher the suction capacity. If the effective chamber volumes at the suction end and discharge end are set appropriately, the internal volume ratio Vi (Vi = Vs / Vd) of the screw compressor can be adjusted, where Vs is the suction chamber volume and Vd is the discharge chamber volume.

[0004] The internal volume ratio Vi of the screw compressor can be adjusted by adjusting the spool valve. Specifically, the spool valve is arranged along the axis of the screw rotor and can wrap around or cover a portion of the screw rotor along the axial direction. By moving the spool valve along the axial direction, the volume of the suction chamber and / or the volume of the discharge chamber can be changed, thereby adjusting the internal volume ratio Vi.

[0005] The integrated part load value (IPLV) is an index used to evaluate the real-time operating efficiency of a unit. When the operating frequency parameter F and the internal volume ratio parameter Vi are adjusted according to different loads, the screw compressor can operate at its most efficient point, thereby improving the overall operating performance of the unit. For example, for a unit used in a building's cooling system, the load may fluctuate widely due to seasonal changes in the indoor and outdoor temperature difference or to meet different cooling requirements on different floors, so it is necessary to adjust the screw compressor more widely accordingly. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to improve the IPLV of a screw compressor under different loads by adjusting the spool valve of the screw compressor. [Means for solving the problem]

[0007] For this purpose, the present application provides a screw compressor, which combines frequency variation and a spool valve to adjust the suction capacity, so that when the suction capacity can no longer be adjusted by lowering the frequency due to the limited operating range of the screw compressor, the spool valve is used to adjust the suction capacity. Therefore, the problems of the motor temperature and exhaust temperature limitations of the conventional variable frequency set are effectively solved, and the operating range and load adjustment capability of the screw compressor are expanded.

[0008] The present application provides a screw compressor, the screw compressor including: a screw rotor including a suction head end and an exhaust tail end, the screw rotor configured to suck gas through the suction head end and discharge compressed gas through the exhaust tail end; and a spool valve including an active side for sealing a compression chamber of the screw rotor, the active side including a spool valve head end and a spool valve tail end, the spool valve head end and the spool valve tail end being arranged in the same direction as the suction head end and the exhaust tail end of the screw rotor along an axial direction of the screw rotor, the spool valve being configured to be able to reciprocate along the axial direction of the screw rotor, particularly, the spool valve being configured to be able to move to a suction capacity adjustment position, and when the spool valve is in the suction capacity adjustment position, the spool valve head end is located inside the suction head end of the screw rotor, and a suction capacity adjustment distance is formed between the spool valve head end and the suction head end, the spool capacity adjustment distance being a distance that allows the spool valve to adjust the suction capacity of the screw compressor without changing the speed of the screw rotor.

[0009] In the above-described screw compressor, the spool valve is configured to be movable to an internal volume ratio adjustment position, and when the spool valve is in the internal volume ratio adjustment position, the spool valve head end is disposed outside or aligned with the suction head end of the screw rotor, so that the spool valve can adjust the internal volume ratio of the screw compressor.

[0010] The screw compressor according to the above further includes a position sensor, the position sensor being axially disposed between the suction head end and the exhaust tail end of the screw rotor and in contact with the spool valve, the position sensor being configured to indicate the position of the spool valve.

[0011] In the screw compressor described above, the non-working side of the spool valve has an inclined surface that is inclined axially relative to the screw rotor, and the position sensor includes a probe whose position in the axial direction is fixed, one end of the probe being in contact with the inclined surface and able to slide relative to the inclined surface as the spool valve moves, so that the probe can move in a direction perpendicular to the axis as the spool valve moves, and in particular the position sensor can determine the position of the spool valve based on the distance that the probe has moved in the direction perpendicular to the axis.

[0012] In the screw compressor described above, the non-working side of the spool valve has a groove extending along the axial direction, the bottom surface of the groove being inclined axially relative to the screw rotor, the probe has a contact end and a measuring end, the contact end extends into the groove and is in contact with the bottom surface of the groove and can slide relative to the bottom surface as the spool valve moves, and the measuring end protrudes from the groove, and in particular, the position sensor can determine the position of the spool valve based on the length of the portion of the probe protruding from the groove.

[0013] In the screw compressor described above, when the spool valve is in the first position, the spool valve head end is disposed outside the suction head end of the screw rotor, and a part of the spool valve is used to shield the part of the screw rotor extending from the suction head end to the exhaust tail end. The screw compressor has a practical minimum internal volume ratio Vi min The first position is the maximum stroke position of the spool valve toward the suction head end. When the spool valve is in the second position, the spool valve head end is aligned with the suction head end of the screw compressor, and the entire spool valve is used to shield the portion of the screw rotor extending from the suction head end to the exhaust tail end. The screw compressor has a practical maximum internal volume ratio Vi max1When the spool valve is in the third position, the spool valve head end is located inside the suction head end of the screw compressor, and the entire spool valve is used to shield the part of the screw rotor between the suction head end and the exhaust tail end, and the screw compressor has a virtual maximum internal volume ratio Vi max2 The third position is the maximum stroke position of the spool valve toward the exhaust tail end.

[0014] The screw compressor is configured such that the position of the spool valve can be adjusted between a first position and a second position to adjust the internal volume ratio Vi of the screw compressor, and the position of the spool valve can be adjusted between the second position and a third position to adjust the suction chamber volume of the screw compressor, thereby adjusting the suction capacity of the screw compressor.

[0015] The screw compressor according to the above further includes a piston rod, the piston rod being connected to the spool valve tail end and configured to be hydraulically actuable to drive the spool valve to move back and forth along the axial direction.

[0016] The screw compressor according to the above further includes a controller configured to adjust the speed of the screw rotor and to drive the piston rod via the piston rod actuator to adjust the position of the spool valve.

[0017] In another aspect, the present application also provides a control method for a screw compressor, the method including: a) setting an operating frequency parameter F and an operating internal volume ratio parameter Vi of the screw compressor based on a target load, where the operating frequency parameter F corresponds to a predetermined operating suction capacity R; b) determining whether the operating frequency parameter F is lower than an operating frequency threshold Ft, where the operating frequency threshold Ft corresponds to a threshold suction capacity Rt; and c) adjusting a position of a spool valve based on the set operating frequency parameter F and operating internal volume ratio parameter Vi. Here, c1) if the operating frequency parameter F is equal to or greater than the operating frequency threshold Ft, the operating frequency of the screw compressor is set to the operating frequency parameter F and the speed of the screw rotor of the screw compressor is adjusted, so that the suction capacity of the screw compressor is adjusted to a predetermined operating suction capacity R, and a displacement amount L1 by which the spool valve moves to an internal volume ratio adjustment position corresponding to the operating internal volume ratio parameter Vi is determined based on the set operating internal volume ratio parameter Vi, and the spool valve is moved to the internal volume ratio adjustment position based on the displacement amount L1, so that when the spool valve reaches the internal volume ratio adjustment position, the spool valve head end of the spool valve is positioned outside the suction head end of the screw rotor of the screw compressor or is aligned with the suction head end, so that the spool valve can shield a portion of the screw rotor extending from the suction head end to the exhaust tail end. c2) When the operating frequency parameter F is lower than the operating frequency threshold Ft, the operating frequency of the screw compressor is set to the operating frequency threshold Ft, and the speed of the screw rotor is adjusted. The displacement amount L2 by which the spool valve moves to a suction capacity adjustment position corresponding to a predetermined operating suction capacity R is determined based on the set operating internal volume ratio parameter Vi (virtual Vi region). The spool valve is moved to the suction capacity adjustment position based on the displacement amount L2. When the spool valve reaches the suction capacity adjustment position, the spool valve head end is located inside the suction head end of the screw rotor, and the suction capacity adjustment distance is determined based on the displacement amount L2. A threshold suction capacity Rt is formed between the head end and the sensor, and as a result, a threshold suction capacity Rt corresponding to the operating frequency threshold Ft can be adjusted to a predetermined operating suction capacity R.

[0018] In the control method for the screw compressor described above, the actual internal volume ratio reached in step c1 is equal to the set operating internal volume ratio parameter Vi, and the operating internal volume ratio parameter Vi of the compressor is equal to the actual minimum internal volume ratio Vi min and the actual maximum internal volume ratio Vi max1 The actual internal volume ratio reached in step c2 is determined by a predetermined operating suction capacity R, and the operating internal volume ratio parameter Vi of the compressor is the actual maximum internal volume ratio Vi max1 and the hypothetical maximum internal volume ratio Vi max2 It is between.

[0019] In the control method for a screw compressor according to the above, the operating frequency threshold Ft corresponds to the minimum speed for normal operation of the screw compressor.

[0020] In order to fully understand the objectives, features, and advantages of the present application, the concept, specific structure, and technical advantages of the present application will be further described below with reference to the drawings.

[0021] The present application will be better understood when the following detailed description is read in conjunction with the drawings, in which like reference numerals represent like parts throughout. [Brief explanation of the drawings]

[0022] [Figure 1A] 1 is a cross-sectional view of a screw compressor taken along the axial direction of a screw rotor in one embodiment according to the present application. FIG. [Figure 1B] 1B is a cross-sectional view of the screw compressor shown in FIG. 1A along the radial direction of the screw rotor. [Figure 2A] 1B is a simplified series of schematic diagrams of the relative positions of the spool valve and screw rotor of the screw compressor shown in FIG. 1A. [Figure 2B] 1B is a simplified series of schematic diagrams of the relative positions of the spool valve and screw rotor of the screw compressor shown in FIG. 1A. [Figure 2C] 1B is a simplified series of schematic diagrams of the relative positions of the spool valve and screw rotor of the screw compressor shown in FIG. 1A. [Figure 2D] 1B is a simplified series of schematic diagrams of the relative positions of the spool valve and screw rotor of the screw compressor shown in FIG. 1A. [Figure 2E] 1B is a simplified series of schematic diagrams of the relative positions of the spool valve and screw rotor of the screw compressor shown in FIG. 1A. [Figure 3] FIG. 1C is a simplified schematic diagram of the spool valve and probe shown in FIG. 1B. [Figure 4] 1 is a flow chart of an embodiment of a control method for a screw compressor of the present application. [Figure 5A] FIG. 1 is a block diagram of one embodiment of a control system for a screw compressor of the present application. [Figure 5B] FIG. 5B is a block diagram of the controller in FIG. 5A. DETAILED DESCRIPTION OF THE INVENTION

[0023] This application was filed on September 23, 2014, This application is related to a Chinese patent application entitled "A Screw Compressor with Male and Female Rotors" with application number 201420548889.2, filed on August 1, 2017, entitled "A Screw Compressor with Male and Female Rotors," and a PCT patent application entitled "A Screw Compressor with Male and Female Rotors" with application number PCT / CN2017 / 095491, filed on August 1, 2017, the entire texts of which are incorporated herein by reference.

[0024] Various specific embodiments of the present application are described below with reference to the drawings that form a part hereof. While directional terms such as "outer," "top," "bottom," "forward," "reverse," "proximal," "distal," "lateral," and "longitudinal" are used herein to describe structural portions and components of various examples of the present application, it should be understood that these terms are used herein for ease of explanation only and are determined based on the exemplary orientations shown in the figures. Because the embodiments disclosed herein can be implemented in a variety of orientations, these directional terms are for illustrative purposes only and should not be considered limiting.

[0025] The use of consecutive numbers such as "first" and "second" referred to in this application is for the purpose of distinction and identification only and does not have any other meaning. Unless a specific order or a specific correspondence is specified, those words do not have such meaning. For example, the term "first component" does not itself imply the existence of a "second component," and the term "second component" does not itself imply the existence of a "first component."

[0026] FIG. 1A is a cross-sectional view of a screw compressor 100 taken along the axial direction of a screw rotor 110 in one embodiment according to the present application, and FIG. 1B is a cross-sectional view of the screw compressor 100 shown in FIG. 1A taken along the radial direction of the screw rotor 110. As shown in FIGS. 1A and 1B, the screw compressor 100 includes a rotor housing 150, a screw rotor 110, and a spool valve 120 disposed within the rotor housing 150. The screw rotor 110 includes a pair of mating male and female rotors 101 and 102, which rotate under the drive of a rotor actuator (not shown). The male rotor 101 has five helical convex teeth, and the female rotor 102 has six helical grooves. The male rotor 101 and female rotor 102 form a mating structure via convex teeth and grooves, and together with the rotor housing 150 and the spool valve 120 form a compression chamber 103 .

[0027] The screw rotor 110 has a suction head end 111 and an exhaust tail end 112 along the axial direction of the screw rotor 110. Gas is sucked into the compression chamber 103 from the suction head end 111 and gradually moves toward the exhaust tail end 112 as the screw rotor 110 rotates. At the same time, as the screw rotor 110 rotates, the volume of the compression chamber 103 gradually decreases, gradually compressing the gas in the compression chamber 103. The compressed gas is released from the exhaust tail end 112.

[0028] The spool valve 120 is disposed below the screw rotor 110 and is capable of reciprocating motion along the axial direction of the screw rotor 110. Along the length of the spool valve 120 in the axial direction of the screw rotor 110, the spool valve 120 includes an operating side 125 for sealing the compression chamber 103 together with the rotor housing 150 and a non-operating side not used to seal the compression chamber 103. The operating side 125 of the spool valve 120 has a spool valve head end 121 and a spool valve tail end 122. In the axial direction of the screw rotor 110, the spool valve head end 121 and the spool valve tail end 122 are disposed in the same direction as the suction head end 111 and the exhaust tail end 112 of the screw rotor 110, i.e., the spool valve head end 121 is disposed near the suction head end 111, and the spool valve tail end 122 is disposed near the exhaust tail end 112. The sides of the spool valve 120 on the spool valve tail end 122 also extend outward from the connection end 123 .

[0029] Via the working side 125, the spool valve 120 can seal or encase a portion of the compression chamber 103 formed by the screw rotor 110. By moving the spool valve 120 to different positions along the axial direction of the screw rotor 110 (see Figures 2A-2E), the working side 125 can shield different portions of the screw rotor 110. or sealed, thereby correspondingly varying the suction chamber volume Vs and / or the discharge chamber volume Vd to adjust the internal volume ratio Vi of the screw compressor 100.

[0030] The screw compressor 100 further includes a drive device for driving and moving the spool valve 120. According to one embodiment of the present application, the drive device may be a hydraulic drive device including a piston rod 140 and a hydraulic chamber 141. One end of the piston rod 140 is disposed in the hydraulic chamber 141, and the other end of the piston rod 140 is connected to the connection end 123 of the spool valve 120, so that the piston rod 140 can reciprocate axially as the liquid pressure in the hydraulic chamber 141 changes, and can drive and reciprocate the spool valve 120.

[0031] The screw compressor 100 further includes a limiting structure for limiting the maximum axial stroke of the spool valve 120. As shown in FIG. 1A , a stop block 142 is provided on one side of the suction head end 111 of the screw rotor 110 to limit the maximum leftward stroke of the spool valve head end 121. A side wall 143 of the hydraulic chamber 141 can limit the maximum rightward stroke of the piston rod 140, thereby limiting the maximum rightward stroke of the spool valve 120. When driven by the piston rod 140, the spool valve 120 can reciprocate between left and right maximum stroke positions.

[0032] 1B, the screw compressor 100 further includes a position sensor 130 for indicating the position of the spool valve 120. The position sensor 130 is disposed axially of the screw rotor 110 between the suction head end 111 and the exhaust tail end 112 of the screw rotor 110. The position sensor 130 is in contact with the spool valve 120 and can change as the spool valve 120 moves to different positions, thereby indicating the position of the spool valve 120.

[0033] In the embodiment shown in FIGS. 1A and 1B, the spool valve 120 has an axially extending groove 126 on its non-working side, and a bottom surface 301 of the groove 126 is an inclined surface that is inclined axially relative to the screw rotor 110 (see FIG. 3 ). The position sensor 130 includes a probe 131 that is fixed in a predetermined position relative to the axial direction of the screw compressor and can reciprocate in a direction perpendicular to the axial direction (e.g., radially). For example, the probe 131 is attached to the rotor housing 150, with a bias spring provided therebetween. The probe 131 has a contact end 132 and a measuring end 133. The contact end 132 extends into the groove 126 and can maintain contact with the bottom surface 301 of the groove 126 during axial movement of the spool valve. The measuring end 133 protrudes from the groove 126. As the spool valve 120 moves axially, the contact end 132 of the probe 131 can slide against the bottom surface 301 of the groove 126 in unison with the movement of the spool valve 120, resulting in radial movement of the probe 131. In this manner, the position of the spool valve 120 can be determined based on the change in length of the portion of the probe 131 that protrudes from the groove 126.

[0034] In some embodiments, the measuring end 133 of the probe 131 includes a magnetic core around which a coil is connected in a circuit. As the probe 131 moves, the length or position of the magnetic core that extends into the coil changes, resulting in a corresponding change in the inductance of the coil and the generation of a corresponding voltage or current signal in the circuit. In this manner, these electrical signals can be used to indicate or determine the position of the spool valve 120.

[0035] 2A-2E are a series of simplified schematic diagrams of the relative positions of the spool valve 120 and the screw rotor 110 of the screw compressor 100 shown in FIG. 1A, and are used to illustrate the changes in the relative positions of the spool valve 120 and the screw rotor 110 during the movement process.

[0036] As shown in FIG. 2A , the spool valve 120 is positioned at its maximum stroke position, moving toward the suction head end 111 (to the left). This position is the first position 210 of the spool valve 120. In the first position 210, the spool valve head end 121 is positioned outside the suction head end 111 of the screw rotor 110. A portion of the working side 125 of the spool valve 120 is positioned below the screw rotor 110 to shield or seal the portion of the screw rotor 110 extending from the suction head end 111 to the exhaust tail end 112, and the remaining portion of the working side 125 of the spool valve 120 is positioned outside the suction head end 111 of the screw rotor 110. As the spool valve 120 moves during a stroke, the spool valve tail end 122 is always positioned between the suction head end 111 and the exhaust tail end 112 of the screw rotor 110, forming an exhaust capacity adjustment distance D1 between the spool valve tail end 122 and the exhaust tail end 112. When the spool valve 120 is in the first position 210 shown in FIG. 2A, the exhaust capacity adjustment distance D1 is at a maximum, so that the screw compressor 100 has a maximum discharge chamber volume Vd and, therefore, a minimum actual internal volume ratio Vi. min Generate.

[0037] As shown in Figure 2C, the spool valve head end 121 is aligned with the suction head end 111 of the screw compressor 100, which is the second position 230 of the spool valve 120. In the second position 230, the entire working side 125 of the spool valve 120 is positioned below the screw rotor 110, so that the entire working side 125 can shield the portion of the screw rotor 110 extending from the suction head end 111 to the exhaust tail end 112. When the spool valve 120 is in the second position 230 shown in Figure 2C, the exhaust capacity adjustment distance D1 reaches a minimum value without changing the suction chamber volume Vs, and therefore the actual maximum internal volume ratio Vi max1 Generate.

[0038] 2B , the spool valve 120 moves to a point between the first position 210 and the second position 230, which is the internal volume ratio adjustment position 220 of the spool valve 120. In the internal volume ratio adjustment position 220, the spool valve head end 121 is positioned outside the suction head end 111 of the screw rotor 110, a portion of the working side 125 of the spool valve 120 is positioned below the screw rotor 110 and shields the portion of the screw rotor 110 extending from the suction head end 111 to the exhaust tail end 112, and the remaining portion of the working side 125 of the spool valve 120 is positioned outside the suction head end 111 of the screw rotor 110. Compared to the first position 210 shown in FIG. 2A, in the internal volume ratio adjustment position 220 shown in FIG. 2B, the exhaust capacity adjustment distance D1 formed between the spool valve tail end 122 and the exhaust tail end 112 is smaller, resulting in a smaller exhaust chamber volume Vd, but the suction chamber volume Vs remains unchanged, resulting in a higher internal volume ratio Vi.

[0039] 2E, the spool valve 120 is positioned at a maximum stroke position moving toward the exhaust tail end 112 (to the right), which is the third position 250 of the spool valve 120. In the third position 250, the spool valve head end 121 is positioned inside the suction head end 111 of the screw compressor 100, and the entire working side 125 of the spool valve 120 is below the screw rotor 110, so that the entire working side 125 of the spool valve 120 can shield the portion of the screw rotor 110 between the suction head end 111 and the exhaust tail end 112. At this point, the exhaust capacity adjustment distance D1 formed between the spool valve tail end 122 and the exhaust tail end 112 is In addition, a suction capacity adjustment distance D2 is also formed between the spool valve head end 121 and the suction head end 111. At this point, the suction capacity adjustment distance D2 is at its maximum and the screw compressor 100 has its minimum suction chamber volume Vs.

[0040] 2D , the spool valve 120 is positioned between the second position 230 and the third position 250, which is the suction capacity adjustment position 240 of the spool valve 120. In the suction capacity adjustment position 240, the spool valve head end 121 is positioned inside the suction head end 111 of the screw compressor 100, and the entire working side 125 of the spool valve 120 is below the screw rotor 110. As a result, the entire working side 125 of the spool valve 120 can shield the portion of the screw rotor 110 between the suction head end 111 and the exhaust tail end 112. At this position, in addition to the exhaust capacity adjustment distance D1 formed between the spool valve tail end 122 and the exhaust tail end 112, a suction capacity adjustment distance D2 is also formed between the spool valve head end 121 and the suction head end 111. Compared with the second position 230 shown in Figure 2C, when the spool valve 120 is in the suction capacity adjustment position 240 shown in Figure 2D, the suction chamber volume Vs is smaller due to the existence of the suction capacity adjustment distance D2, thereby reducing the suction capacity of the screw compressor 100. Furthermore, although the suction chamber volume Vs is smaller, the exhaust capacity adjustment distance D1 is smaller and the discharge chamber volume Vd is also smaller, so the actual internal volume ratio Vi only decreases slightly and can be approximately regarded as remaining unchanged. Compared with the third position 250 shown in Figure 2E, when the spool valve 120 is located in the suction capacity adjustment position 240 shown in Figure 2D, the suction capacity adjustment distance D2 is smaller.

[0041] By adjusting the position of the spool valve 120 in the region between the first position 210 and the second position 230 (i.e., the internal volume ratio adjustment position 220), the actual internal volume ratio Vi of the screw compressor 100 can be adjusted. The adjustment range of the actual internal volume ratio Vi is min (at the first position 210) is greater than or equal to Vi max1(at second position 230): As the spool valve 120 moves through the region between the first position 210 and the second position 230, the suction chamber volume Vs remains unchanged, resulting in a one-to-one linear correlation between the actual internal volume ratio V and the position of the spool valve 120.

[0042] By adjusting the position of the spool valve 120 in the region between the second position 230 and the third position 250 (i.e., the suction capacity adjustment position 240), the suction chamber volume Vs of the screw compressor 100 can be adjusted, thereby adjusting the suction capacity of the screw compressor 100. As described above, when the spool valve 120 moves in the region between the second position 230 and the third position 250, it can be approximately assumed that the actual internal volume ratio Vi remains unchanged.

[0043] Corresponding to different loads, the screw compressor 100 has different IPLVs when operating at different operating frequencies and internal volume ratios Vi. To improve performance and efficiency, it is necessary to adjust the operating frequency and internal volume ratio Vi of the screw compressor 100 according to different load conditions so that the screw compressor 100 operates at the best possible efficiency point. Generally, the smaller the load, the smaller the required suction capacity, and the corresponding operating frequency will also be lower. For example, under the following different loads, corresponding to different internal volume ratios Vi and operating frequencies F, the IPLV of the screw compressor 100 can reach a maximum value: under 100% load, Vi = 2.3, F = 50 Hz; under 75% load, Vi = 1.8, F = 35 Hz; under 50% load, Vi = 1.65, F = 22.5 Hz; and under 25% load, Vi = 1.65, F = 12.5 Hz.

[0044] The cooling efficiency of the screw compressor 100 decreases as the operating frequency and suction capacity decrease. However, since the exhaust temperature and unit temperature become higher, the suction capacity can be adjusted by adjusting the operating frequency, but the adjustment range is limited by excessively high temperatures. Also, considering the effect of lowering the operating frequency on the unit temperature, it is not wise to reduce the suction capacity by lowering the operating frequency in order to meet the requirement for lower load when the operating frequency is lowered within a certain range.

[0045] In the present application, when the screw compressor 100 operates at the minimum operating frequency (i.e., the operating frequency threshold Ft), if the load continues to decrease, the operating frequency is no longer reduced but is maintained at the operating frequency threshold Ft, and the spool valve 120 is moved to the appropriate suction capacity adjustment position 240. In this way, it is possible to continue reducing the suction capacity to adapt to changes in the load without lowering the operating frequency, thereby eliminating the limitation of the operating frequency adjustment and expanding the application range of the screw compressor 100.

[0046] 1B , the probe 131 and the groove 126 on the spool valve 120 for accommodating the probe 131. As shown in FIG. 3 , the bottom surface 301 of the groove 126 of the spool valve 120 is an inclined surface that gradually slopes inward along the screw axis direction. As a result, the depth of the groove 126 gradually increases from the spool valve head end 121 to the spool valve tail end 122. The contact end 132 of the probe 131 extends into the groove 126 and contacts the bottom surface 301 of the groove 126, and the measuring end 133 of the probe 131 protrudes from the groove 126. As described above, when the spool valve 120 moves in the direction of the screw axis, the probe 131 cannot move in the direction of the screw axis, but moves in a direction perpendicular to the screw axis. As the spool valve 120 moves axially, the length of the portion of the probe 131 protruding from the groove 126 changes correspondingly, forming a linear correlation with the position of the spool valve 120. In other embodiments, the bottom surface 301 of the groove 126 may be sloped in the opposite direction, i.e., the depth of the groove 126 gradually increases from the spool valve tail end 122 to the spool valve head end 121.

[0047] In FIG. 3 , region A represents the region in which the probe 131 moves relative to the spool valve 120 when the spool valve 120 moves between the first position 210 and the second position 230. When the spool valve 120 moves between the first position 210 and the second position 230, the internal volume ratio Vi of the screw compressor can be adjusted. Therefore, region A can be considered as region A for adjusting the internal volume ratio Vi. Region B represents the region in which the probe 131 moves relative to the spool valve 120 when the spool valve 120 moves between the second position 230 and the third position 250. When the spool valve 120 moves between the second position 230 and the third position 250, the suction capacity of the screw compressor can be adjusted. Therefore, region B can be considered as region B for adjusting the suction capacity. The method for controlling the screw compressor in the present application will be described below with reference to region A for adjusting the internal volume ratio Vi and region B for adjusting the suction capacity, as shown in FIG. 3 .

[0048] Since the position of the spool valve 120 determines the suction volume Vs and discharge volume Vd of the screw compressor, there is a linear correlation between the internal volume ratio Vi and the position of the spool valve 120. According to the control method of the present application, based on the linear correlation between the internal volume ratio Vi and the position of the spool valve 120, whether the spool valve 120 moves within region A for adjusting the internal volume ratio Vi or within region B for adjusting the suction capacity, the position of the spool valve 120 is determined using the internal volume ratio Vi, so that the position of the spool valve 120 can be adjusted based on the value of the internal volume ratio Vi during the control process. However, when the spool valve 120 moves within region B for adjusting the suction capacity, the actual internal volume ratio Vi of the screw compressor hardly changes. Therefore, the present application uses a virtual internal volume ratio Vi to determine when the spool valve moves within region B for adjusting the suction capacity. The virtual internal volume ratio Vi and the actual internal volume ratio Vi both follow a linear correlation between the internal volume ratio Vi and the position of the spool valve 120.

[0049] Specifically, in region A for adjusting the internal volume ratio Vi, the position of the spool valve 120 is linearly correlated with the actual internal volume ratio Vi. In the first position 210, the actual minimum internal volume ratio Vi min and at the second position 230, the actual maximum internal volume ratio Vi max1 Therefore, the position of the spool valve 120 reaches [Vi min , Vi max1 ] based on the value of the internal volume ratio Vi, so that the screw compressor 100 has a corresponding actual internal volume ratio Vi.

[0050] In region B for adjusting the suction capacity, the actual internal volume ratio Vi can be approximately considered unchanged, and changes in the position of the spool valve 120 are used to adjust the suction capacity. To maintain consistency in the control method, a corresponding virtual internal volume ratio Vi can be set to the position of the spool valve 120 according to the same linear correlation in the region for adjusting the internal volume ratio Vi, so that a unified control method and control system can be used to adjust the position of the spool valve 120. The rotor profile of the screw rotor 110 can be used to calculate the suction capacity corresponding to different positions of the spool valve 120, and a correlation between the virtual internal volume ratio Vi and the suction capacity can be established. In the third position 250, the virtual maximum internal volume ratio Vi max2 Therefore, the position of the spool valve 120 is determined based on the value of the internal volume ratio Vi. max1 , Vi max2 ], so that the screw compressor 100 has a corresponding suction capacity.

[0051] The position sensor 130 can accurately determine the position of the spool valve 120, and can be used to indicate the actual internal volume ratio Vi of the screw compressor 100 in region A for adjusting the internal volume ratio Vi to suit the operating conditions in real time, and can be used to indicate changes in suction capacity in region B for adjusting the suction capacity.

[0052] Via restricting structures 142 and 143 (see FIG. 1A), spool valve 120 is in first position 210 (Vi min ) and third position 250 (Vi max2 ), which facilitates the determination and calibration of the position sensor 130 and the structural design of the position sensor 130 and the groove 126.

[0053] 4 is a flow chart of one embodiment of a method for controlling a screw compressor. As shown in FIG. 4, in step 401, when the load changes, the internal volume ratio Vi and the operating frequency F need to be adjusted to accommodate the load change.

[0054] In step 402, corresponding operating frequency parameters F and operating internal volume ratios V i are set or determined based on the target load, and then the process proceeds to step 403. Among them, the operating frequency parameter F corresponds to a predetermined operating suction capacity R. The values ​​of these parameters can be determined by a preset formula, algorithm, or scale.

[0055] In step 403, the operating frequency parameter F set in step 402 is compared with the operating frequency threshold Ft. If the operating frequency parameter F is equal to or greater than the operating frequency threshold Ft, the process proceeds to step 404. If the operating frequency parameter F is lower than the operating frequency threshold Ft, the process proceeds to step 406. The operating frequency threshold Ft corresponds to the minimum speed at which the screw compressor 100 can operate normally, and is a fixed value of the screw compressor 100. The operating frequency threshold Ft corresponds to the threshold suction capacity Rt.

[0056] In step 404, the actual operating frequency is set as the operating frequency parameter F, and the corresponding internal volume ratio adjustment position 220 of the spool valve 120 is determined based on the internal volume ratio parameter Vi, and the process proceeds to step 405. By changing the actual operating frequency to the operating frequency parameter F, the speed of the screw rotor 110 of the screw compressor 100 can be adjusted, thereby adjusting the suction capacity of the screw compressor 100 to a predetermined operating suction capacity R. Furthermore, after the corresponding internal volume ratio adjustment position 220 of the spool valve 120 is determined based on the internal volume ratio parameter Vi, the displacement amount L1 of the spool valve 120 to move to this corresponding internal volume ratio adjustment position 220 can be determined based on the current position of the spool valve 120. The current position of the spool valve 120 can be determined by the position sensor 130.

[0057] In step 405, the spool valve 120 is moved to the corresponding internal volume ratio adjustment position 220. At this point, the spool valve head end 121 is positioned outside or aligned with the suction head end 111 of the screw rotor 110, so that the spool valve 120 can shield the portion of the screw rotor 110 extending from the suction head end 111 to the exhaust tail end 112, so that the actual internal volume ratio is equal to the set internal volume ratio parameter Vi.

[0058] In step 406, the actual operating frequency is set as the operating frequency threshold Ft, and the suction capacity adjustment position 240 of the spool valve 120 corresponding to the predetermined operating suction capacity R is determined based on the internal volume ratio parameter Vi, after which the process proceeds to step 407. The speed of the screw rotor 110 can be adjusted by changing the operating frequency. Furthermore, after the suction capacity adjustment position 240 of the spool valve 120 corresponding to the predetermined operating suction capacity R is determined based on the internal volume ratio parameter Vi, the displacement amount L2 by which the spool valve 120 moves to the corresponding suction capacity adjustment position 240 can be determined based on the current position of the spool valve 120. The current position of the spool valve 120 can be determined by the position sensor 130.

[0059] In step 407, the spool valve 120 is moved to the corresponding suction capacity adjustment position 240. At this point, the spool valve head end 121 is positioned inside the suction head end 111 of the screw rotor 110, and a suction capacity adjustment distance D2 is formed between the spool valve head end 121 and the suction head end 111, thereby adjusting the threshold suction capacity Rt corresponding to the operating frequency threshold Ft to the operating suction capacity R corresponding to the operating frequency parameter Ft.

[0060] In step 408, this adjustment is completed and when the load changes again, the above steps are repeated to adjust the screw compressor 100 accordingly.

[0061] 5A shows a block diagram of one embodiment of a control system for the screw compressor of the present application. As shown in FIG. 5A, the screw compressor 100 further includes a controller 510, a rotor actuator 520 for the screw rotor 110, and a piston rod actuator 530 for the piston rod. The controller 510 is in communication with the rotor actuator 520 of the screw rotor 110 and adjusts the speed of the screw rotor 110 by adjusting its operating frequency, thereby adjusting the suction capacity of the screw compressor 100. The controller 510 is also in communication with the position sensor 130 and determines the position of the spool valve 120 based on a signal generated by the position sensor 130. The controller 510 is also in communication with the piston rod actuator 53 ... position sensor 130 and adjusts the position of the spool valve 120 based on a signal generated by the position sensor 130. The controller 510 is also in communication with the position sensor 130 and adjusts the position of the piston rod actuator 530. The piston rod 140 is driven via the piston rod actuator 530 to drive and move the spool valve 120, thereby adjusting the position of the spool valve 120. In some embodiments, the piston rod actuator 530 is a hydraulic transmission device. FIG. 5B is a block diagram of the controller 510 shown in FIG. 5A. As shown in FIG. 5B, the controller 510 includes a processor 501, an input interface 502, an output interface 503, a memory 504 with a program 505, and a bus 506. The processor 501, the input interface 502, the output interface 503, and the memory 504 are communicatively connected via the bus 506, such that the processor 501 can control the operation of the input interface 502, the output interface 503, and the memory 504. The memory 504 is used to store programs, instructions, and data. The processor 501 can read programs, instructions, and data from the memory 504 and write data to the memory 504.

[0062] The input interface 502 receives signals and data, such as a signal indicating the position of the spool valve 120 from the position sensor 130 and various manually entered parameters, via connection 507. The output interface 503 sends signals and data, such as corresponding control signals, to the rotor actuator 520 and the piston rod actuator 530 via connection 508. The memory 504 stores control programs and data, including various preset values, parameters, etc., such as the control program for the screw compressor 100, the operating frequency threshold Ft, and instructions for taking actions when a threshold is reached or a specific condition is met. The various parameters can be preset in manufacturing engineering, or can be set during use by manual input or data import. The processor 501 receives the various signals, data, programs, and instructions from the input interface 502 and the memory 504, performs corresponding processing, and outputs them via the output interface 503.

[0063] Through long-term observation and experimentation, the inventors of the present application have found that due to the limitations of the operating characteristics of screw compressors with fixed internal pressure ratios, the IPLV deviation of existing variable frequency screw sets is significantly lower than that of variable frequency centrifugal sets; existing variable frequency screw sets are subject to protection restrictions against compressor motor overheating and high exhaust temperature at low frequencies, so the operating frequency cannot be excessively low and the operating range is limited to a certain range; and two independent mechanisms are used to adjust the internal volume ratio Vi and suction capacity of existing screw compressor sets, which are complex in structure and costly.

[0064] Through the structural design and control of the spool valve 120, the screw compressor 100 of the present application can continuously adjust the internal volume ratio Vi. Furthermore, it simultaneously adjusts the suction capacity and displays the internal volume ratio Vi and suction capacity, thereby improving operating efficiency, widening the applicable adjustment range of the internal volume ratio Vi, simplifying the structure, and facilitating standardization. At the same time, the operating range and load adjustment capability of the screw compressor 100 are expanded. The coordinated control of adjusting the suction capacity via the spool valve 120 and the screw rotor 110 effectively solves the problem of excessively high operating temperatures. The screw compressor 100 of the present application can be used in air conditioning systems together with a variable frequency drive, a heat exchanger, and a throttling device. The effective combination of variable frequency adjustment of speed and suction capacity with adjustment of the internal volume ratio Vi maximizes real-time operating efficiency.

[0065] Examples are used throughout the description to disclose the present application, one or more of which are illustrated in the drawings. Each example is provided to explain the present application, not to limit it. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present application without departing from the scope or spirit of the present application. For example, features illustrated or described as part of one embodiment can be used in combination with another embodiment to yield a still further embodiment. Accordingly, it is intended that this application cover modifications and variations that come within the scope of the claims and their equivalents. [Aspect 1] In the screw compressor (100), the screw compressor (100) comprises: a screw rotor (110) including a suction head end (111) and an exhaust tail end (112), the screw rotor (110) configured to suck gas from the suction head end (111) and discharge compressed gas from the exhaust tail end (112); a spool valve (120) including an operating side (125) for sealing a compression chamber (103) of the screw rotor (110), the operating side (125) including a spool valve head end (121) and a spool valve tail end (122), the spool valve head end (121) and the spool valve tail end (122) being arranged in the same direction as the suction head end (111) and the exhaust tail end (112) of the screw rotor (110) along the axial direction of the screw rotor (110), and the spool valve (120) being configured to be reciprocable along the axial direction of the screw rotor (110); In particular, the spool valve (120) is configured to be movable to a suction capacity adjustment position (240), and when the spool valve (120) is in the suction capacity adjustment position (240), the spool valve head end (121) is disposed inside the suction head end (111) of the screw rotor (110), and a suction capacity adjustment distance (D2) is formed between the spool valve head end (121) and the suction head end (111), and the suction capacity adjustment distance (D2) is such that the suction capacity of the screw compressor (100) can be adjusted without changing the speed of the screw rotor (110). [Aspect 2] 2. The screw compressor (100) according to claim 1, wherein the spool valve (120) is configured to be movable to an internal volume ratio adjustment position (220), and when the spool valve (120) is in the internal volume ratio adjustment position (220), the spool valve head end (121) is positioned outside of or aligned with the suction head end (111) of the screw rotor (110), thereby enabling the spool valve (120) to adjust the internal volume ratio of the screw compressor (100). Aspect 3 The screw compressor (100) further comprises: 2. The screw compressor (100) according to claim 1, further comprising a position sensor (130) disposed axially between the suction head end (111) and the exhaust tail end (112) of the screw rotor (110) and in contact with the spool valve (120), the position sensor (130) being configured to indicate a position of the spool valve (120). Aspect 4 The non-working side of the spool valve (120) has an inclined surface inclined relative to the screw rotor (110) in the axial direction; the position sensor (130) includes a probe whose position in the axial direction is fixed, one end of the probe contacting the inclined surface and capable of sliding relative to the inclined surface as the spool valve (120) moves, thereby allowing the probe to move in a direction perpendicular to the axis as the spool valve (120) moves; In particular, the screw compressor (100) according to aspect 3 is characterized in that the position sensor (130) is capable of determining the position of the spool valve (120) based on the distance the probe moves in a direction perpendicular to the axis. Aspect 5 The non-operating side of the spool valve (120) has a groove extending along the axial direction, and a bottom surface of the groove is inclined in the axial direction with respect to the screw rotor (110); the probe has a contact end and a measuring end, the contact end extending into the groove, contacting the bottom surface of the groove and being slidable relative to the bottom surface as the spool valve (120) moves, and the measuring end protruding from the groove; In particular, the screw compressor (100) according to aspect 4 is characterized in that the position sensor (130) is capable of determining the position of the spool valve (120) based on the length of the portion of the probe protruding from the groove. Aspect 6 When the spool valve (120) is in the first position (210), the spool valve head end (121) is disposed outside the suction head end (111) of the screw rotor (110), a portion of the spool valve (120) is used to shield the portion of the screw rotor (110) extending from the suction head end (111) to the exhaust tail end (112), and the screw compressor (100) operates in a manner such that the actual minimum internal volume ratio Vi min the first position (210) is a maximum stroke position of the spool valve (120) toward the suction head end (111); When the spool valve (120) is in the second position (230), the spool valve head end (121) is aligned with the suction head end (111) of the screw compressor (100), the entire spool valve (120) is used to shield the portion of the screw rotor (110) extending from the suction head end (111) to the exhaust tail end (112), and the screw compressor (100) operates at a practical maximum internal volume ratio Vi max1 and When the spool valve (120) is in the third position (250), the spool valve head end (121) is disposed inside the suction head end (111) of the screw compressor (100), the entire spool valve (120) is used to shield the portion of the screw rotor (110) between the suction head end (111) and the exhaust tail end (112), and the screw compressor (100) operates at a virtual maximum internal volume ratio Vi max2 and the third position (250) is a maximum stroke position at which the spool valve (120) moves toward the exhaust tail end (112). Aspect 7 The screw compressor (100) is configured such that the internal volume ratio Vi of the screw compressor (100) can be adjusted by adjusting the position of the spool valve (120) between the first position (210) and the second position (230), Aspect 7. The screw compressor (100) according to aspect 6, wherein the screw compressor (100) is configured such that the position of the spool valve (120) can be adjusted between the second position (230) and the third position (250) to adjust the suction chamber volume of the screw compressor (100), thereby adjusting the suction capacity of the screw compressor (100). Aspect 8 The screw compressor (100) further comprises: 2. The screw compressor (100) of claim 1, comprising: a piston rod (140) connected to the spool valve tail end (122) and configured to be hydraulically actuable to drive the spool valve (120) to move back and forth along the axial direction. Aspect 9 The screw compressor (100) further comprises: 9. The screw compressor (100) according to aspect 8, comprising a controller (510) configured to adjust the speed of the screw rotor (110) and to drive the piston rod (140) via a piston rod actuator (530) to adjust the position of the spool valve (120). Aspect 10 In the control method for the screw compressor (100), the control method comprises: a) setting the operating frequency parameter F and the operating internal volume ratio parameter Vi of the screw compressor (100) based on the target load, wherein the operating frequency parameter F corresponds to a predetermined operating suction capacity R; b) determining whether the operating frequency parameter F is lower than the operating frequency threshold Ft, the operating frequency threshold Ft corresponding to a threshold suction capacity Rt; c) adjusting the position of the spool valve (120) based on the set operating frequency parameter F and the operating internal volume ratio parameter Vi; c1) if the operating frequency parameter F is equal to or greater than the operating frequency threshold Ft; (i) adjusting the speed of the screw rotor (110) of the screw compressor (100) by setting the operating frequency of the screw compressor (100) as the operating frequency parameter F, thereby adjusting the suction capacity of the screw compressor (100) to the predetermined operating suction capacity R, and determining a displacement amount L1 by which the spool valve (120) moves to the internal volume ratio adjustment position (220) corresponding to the operating internal volume ratio parameter Vi based on the set operating internal volume ratio parameter Vi; (ii) the spool valve (120) is moved to the internal volume ratio adjustment position (220) based on the displacement amount L1, and when the spool valve (120) is in the internal volume ratio adjustment position (220), the spool valve head end (121) of the spool valve (120) is positioned outside the suction head end (111) of the screw rotor (110) of the screw compressor (100) or is aligned with the suction head end (111), thereby allowing the spool valve (120) to shield a portion of the screw rotor (110) extending from the suction head end (111) to the exhaust tail end (112); c2) if the operating frequency parameter F is lower than the operating frequency threshold Ft; (i) the operating frequency of the screw compressor (100) is set to the operating frequency threshold Ft, and the speed of the screw rotor (110) is adjusted, and a displacement amount L2 by which the spool valve (120) moves to the suction capacity adjustment position (240) corresponding to the predetermined operating suction capacity R is determined based on the set operating internal volume ratio parameter Vi; (ii) the spool valve (120) is moved to the suction capacity adjustment position (240) based on the displacement amount L2, and when the spool valve (120) is at the suction capacity adjustment position (240), the spool valve head end (121) is disposed inside the suction head end (111) of the screw rotor (110), and a suction capacity adjustment distance (D2) is formed between the spool valve head end (121) and the suction head end (111), thereby adjusting the threshold suction capacity Rt corresponding to the operating frequency threshold Ft to the predetermined operating suction capacity R. Aspect 11 The actual internal volume ratio reached in step c1 is equal to the set operating internal volume ratio parameter Vi, and the operating internal volume ratio parameter Vi of the compressor is equal to the actual minimum internal volume ratio Vi min and the actual maximum internal volume ratio Vi max1 Between The actual internal volume ratio reached in step c2 is determined by the predetermined operating suction capacity R, and the operating internal volume ratio parameter Vi of the compressor is equal to the actual maximum internal volume ratio Vimax1 and the hypothetical maximum internal volume ratio Vi max2 11. The method of controlling the screw compressor (100) according to claim 10, wherein Aspect 12 11. The method for controlling the screw compressor (100) according to claim 10, wherein the operating frequency threshold Ft corresponds to a minimum speed for normal operation of the screw compressor (100).

Claims

1. A screw compressor (100), comprising: a screw rotor (110) including a suction head end (111) and an exhaust tail end (112), the screw rotor (110) configured to suck gas through the suction head end (111) and discharge compressed gas through the exhaust tail end (112); a spool valve (120) including an operating side (125) for sealing a compression chamber (103) of the screw rotor (110), the operating side (125) including a spool valve head end (121) and a spool valve tail end (122), the spool valve head end (121) and the spool valve tail end (122) being aligned in a common direction with the suction head end (111) and the exhaust tail end (112) of the screw rotor (110) along an axial direction of the screw rotor (110), the spool valve (120) being configured for reciprocating movement along the axial direction of the screw rotor (110); the spool valve (120) is configured to move to a suction capacity adjustment position (240), and when the spool valve (120) is in the suction capacity adjustment position (240), the spool valve head end (121) is disposed inside the suction head end (111) of the screw rotor (110), and a suction capacity adjustment distance (D2) is formed between the spool valve head end (121) and the suction head end (111), and the suction capacity adjustment distance (D2) is adjustable to adjust the suction capacity of the screw compressor (100) without changing the speed of the screw rotor (110); the spool valve (120) is configured to move to an internal volume ratio adjustment position (220), and when the spool valve (10) is in the internal volume ratio adjustment position (220), the spool valve head end (121) is positioned outside the suction head end (111) of the screw rotor (110) or is aligned with the suction head end (111), and an exhaust capacity adjustment position (D1) is formed between the spool valve tail end (122) and the exhaust tail end (112), and the exhaust capacity adjustment distance (D1) is configured to adjust the internal volume ratio of the screw compressor (100) without changing the suction chamber volume (Vs) of the screw compressor (100); a piston rod (140) connected to the spool valve tail end (122), the piston rod (140) configured to be hydraulically driven to drive the spool valve (120) to move back and forth along the axial direction; A controller (510), setting an operating frequency parameter (F) and an operating internal volume ratio parameter (Vi) of the screw compressor (100) based on a target load, the operating frequency parameter (F) corresponding to a predetermined operating suction capacity (R); determining whether the operating frequency parameter (F) is lower than an operating frequency threshold (Ft), the operating frequency threshold (Ft) corresponding to a threshold suction capacity (Rt); When the operating frequency parameter (F) is lower than the operating frequency threshold (Ft), setting the operating frequency threshold (Ft) as the operating frequency of the screw compressor (100); determining the suction power adjustment position (240) based on the operating internal volume ratio parameter (Vi); moving the spool valve (120) to the suction capacity adjustment position (240); When the operating frequency parameter (F) is not lower than the operating frequency threshold (Ft), setting the operating frequency parameter (F) as the operating frequency of the screw compressor (100); determining the internal volume ratio adjustment position (220) based on the operating internal volume ratio parameter (Vi); moving the spool valve (120) to the internal volume ratio adjustment position (220); a controller (510) configured to execute A screw compressor (100) comprising:

2. The screw compressor (100) 2. The screw compressor (100) of claim 1, further comprising a position sensor (130) axially disposed between the suction head end (111) and the exhaust tail end (112) of the screw rotor (110), the position sensor (130) being in contact with the spool valve (120), and the position sensor (130) being configured to indicate a position of the spool valve (120).

3. The non-working side of the spool valve (120) has an inclined surface inclined in the axial direction relative to the screw rotor (110); the position sensor (130) includes a probe having a fixed position along the axial direction, one end of the probe contacting the inclined surface and configured to slide relative to the inclined surface as the spool valve (120) moves, and the probe configured to move in a direction perpendicular to the axial direction as the spool valve (120) moves; 3. The screw compressor of claim 2, wherein the position sensor is configured to determine the position of the spool valve based on a distance the probe moves in the direction perpendicular to the axial direction.

4. The non-operating side of the spool valve (120) has a groove extending along the axial direction, and a bottom surface of the groove is inclined in the axial direction with respect to the screw rotor (110); the probe has a contact end and a measuring end, the contact end extending into the groove and contacting the bottom surface of the groove and configured to slide relative to the bottom surface as the spool valve (120) moves, and the measuring end protruding from the groove; 4. The screw compressor (100) of claim 3, wherein the position sensor (130) is configured to determine the position of the spool valve (120) based on a length of the portion of the probe that protrudes from the groove.

5. When the spool valve (120) is in a first position (210), the spool valve head end (121) is disposed outside the suction head end (111) of the screw rotor (110), and a portion of the active side of the spool valve (120) is configured to shield a portion of the screw rotor (110) extending from the suction head end (111) to the exhaust tail end (112), and the screw compressor (100) achieves a practical minimum internal volume ratio (V min ), wherein the first position (210) is a first maximum stroke position of the spool valve (120) toward the suction head end (111); When the spool valve (120) is in a second position (230), the spool valve head end (121) is aligned with the suction head end (111) of the screw compressor (100), the entire working side of the spool valve (120) is configured to shield the portion of the screw rotor (110) extending from the suction head end (111) to the exhaust tail end (112), and the screw compressor (100) operates at a practical maximum internal volume ratio (V max1 ) When the spool valve (120) is in a third position (250), the spool valve head end (121) is disposed inside the suction head end (111) of the screw compressor (100), and the entire working side of the spool valve (120) is configured to shield the portion of the screw rotor (110) between the suction head end (111) and the exhaust tail end (112), and the screw compressor (100) achieves a virtual maximum internal volume ratio (Vi max2 2. The screw compressor of claim 1, wherein the third position is a second maximum stroke position of the spool valve toward the exhaust tail end.

6. the screw compressor (100) is configured to adjust an internal volume ratio parameter (Vi) of the screw compressor (100) by adjusting the position of the spool valve (120) between the first position (210) and the second position (230); 6. The screw compressor (100) of claim 5, wherein the screw compressor (100) is configured to adjust the position of the spool valve (120) between the second position (230) and the third position (250) to adjust a suction chamber volume of the screw compressor (100), thereby adjusting the suction capacity of the screw compressor (100).

7. 2. The screw compressor of claim 1, wherein the controller is configured to adjust the speed of the screw rotor and to control a piston rod actuator to drive the piston rod to adjust the position of the spool valve.

8. 10. A control method for operating the screw compressor (100) of claim 1, comprising: a) setting the operating frequency parameter (F) and the operating internal volume ratio parameter (Vi) of the screw compressor (100) based on the target load, wherein the operating frequency parameter (F) corresponds to the predetermined operating suction capacity (R); b) determining whether the operating frequency parameter (F) is lower than an operating frequency threshold (Ft), the operating frequency threshold (Ft) corresponding to a threshold suction capacity (Rt); c) adjusting the position of the spool valve (120) based on the operating frequency parameter (F) and the operating internal volume ratio parameter (Vi), c1) when the operating frequency parameter (F) is equal to or greater than the operating frequency threshold (Ft); (i) the operating frequency parameter (F) is set as the operating frequency of the screw compressor (100), the speed of the screw rotor (110) of the screw compressor (100) is adjusted, and the suction capacity of the screw compressor (100) is adjusted toward the predetermined operating suction capacity (R), and a displacement amount (L1) of the spool valve (120) that moves to the internal volume ratio adjustment position (220) corresponding to the operating internal volume ratio parameter (Vi) is determined based on the operating internal volume ratio parameter (Vi); (ii) the spool valve (120) is moved to the internal volume ratio adjustment position (220) based on the displacement amount (L1), and when the spool valve (120) is in the internal volume ratio adjustment position (220), the spool valve head end (121) of the spool valve (120) is positioned outside of or aligned with the suction head end (111) of the screw rotor (110) of the screw compressor (100), thereby shielding the portion of the screw rotor (110) extending from the suction head end (111) to the exhaust tail end (112) of the screw rotor (110); c2) when the operating frequency parameter (F) is lower than the operating frequency threshold (Ft); (i) the operating frequency threshold (Ft) is set as the operating frequency of the screw compressor (100), and the displacement (L2) of the spool valve (120) that adjusts the speed of the screw rotor (110) and moves to the suction capacity adjustment position (240) corresponding to the predetermined operating suction capacity (R) is determined based on the operating internal volume ratio parameter (Vi); (ii) adjusting the spool valve (120) to the suction capacity adjustment position (240) based on the displacement amount (L2), and when the spool valve (120) is in the suction capacity adjustment position (240), the spool valve head end (121) is disposed inside the suction head end (111) of the screw rotor (110), and the suction capacity adjustment distance (D2) is formed between the spool valve head end (121) and the suction head end (111), thereby adjusting the threshold suction capacity (Rt) corresponding to the operating frequency threshold (Ft) to the predetermined operating suction capacity (R); A control method for operating a screw compressor (100), comprising:

9. The actual internal volume ratio reached in step c1 is equal to the operating internal volume ratio parameter (Vi), and the operating internal volume ratio parameter (Vi) of the screw compressor (100) is equal to the actual minimum internal volume ratio (Vi min ) and the actual maximum internal volume ratio (Vi max1 ) and The actual internal volume ratio reached in step c2 is determined based on the predetermined operating suction capacity (R), and the operating internal volume ratio parameter (Vi) of the screw compressor (100) is set to the actual maximum internal volume ratio (Vi max1 ) and the virtual maximum internal volume ratio (Vi max2 9. The control method for operating a screw compressor (100) according to claim 8, wherein

10. 9. The control method for operating a screw compressor (100) according to claim 8, wherein the operating frequency threshold (Ft) corresponds to a minimum speed for normal operation of the screw compressor (100).

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