Rotating body and method of controlling the same

Abstract

To provide a rotating body capable of controlling a larger thrust load by suppressing power loss of the whole magnetic bearing.SOLUTION: There are provided a main shaft 4 rotatable around an axial direction O, a plurality of thrust portions provided on the main shaft 4 and receiving a thrust load P of the main shaft 4, a pair of first magnetic bearings 81 and 82 sandwiching and supporting one first thrust portion (thrust disk 7) of the plurality of thrust portions from both sides in the axial direction O, and second magnetic bearings 83 provided on the other second thrust portion (impeller 6B portion) of the plurality of thrust portions. The first magnetic bearings 81 and 82 can actively adjust the attractive force to the thrust disk 7 so as to reduce the thrust load P. The second magnetic bearings 83 can additionally adjust the attraction force to the impeller 6B to reduce a part of the thrust load P.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a rotating body and a method for controlling a rotating body. [Background technology]

[0002] In rotating machines such as turbo compressors, centrifugal pumps, and expansion turbines, an impeller is fixed to the main shaft and compresses and expands the fluid. During this process, a thrust load, which is an axial force, is generated due to the pressure difference between the front and back of the impeller. The thrust load is received by thrust bearings, and oil bearings, gas bearings, magnetic bearings, etc. are used for bearings in high-speed rotating machines depending on the application.

[0003] Oil bearings can handle larger thrust loads than gas bearings or magnetic bearings. However, compared to hydrostatic bearings or magnetic bearings, they have higher viscosity and greater friction loss, which can lead to problems with heat generation and reduced efficiency of rotating machines. Other issues include the need for larger equipment to supply the oil and higher running costs due to regular maintenance. Furthermore, they may not be suitable for use in equipment that does not tolerate oil. Gas bearings include hydrostatic bearings, which supply a gas such as air to the bearing and support the shaft with the gas pressure, and hydrodynamic bearings, which support the shaft using the pressure difference caused by changes in the gap between the shaft and bearing. Because they are supported by gas, friction loss is small and they can be used at high speeds, but the bearing's load capacity is small, making them difficult to use in large rotating machines that generate large thrust loads.

[0004] A magnetic bearing can support a shaft by controlling the current and voltage passed through an electromagnet and using its attractive and repulsive forces. Because no highly viscous fluid such as oil is required between the shaft and the bearing, friction loss is low, similar to that of a gas bearing, and it can handle a greater thrust load than a gas bearing (see, for example, Patent Documents 1 and 2). Patent Document 1 discloses technology using a thrust magnetic bearing. Patent Document 2 describes a configuration in which an excitation shaft is provided at the tip of the rotating shaft and a coil is attached to a casing that surrounds the excitation shaft, and a configuration in which a diamagnetic material is attached to the casing so that it faces the excitation shaft. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-50334 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-17427 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the structure described in Patent Document 1, which is equipped with a thrust magnetic bearing, to obtain a large thrust capacity like that of an oil bearing, it is necessary to increase the size of the electromagnet or to increase the control current (or to increase the control voltage), which causes problems such as an increase in the size of the device and heat generation due to power loss.

[0007] Furthermore, in the case of a configuration in which a coil is attached to a casing so as to surround the excitation shaft as shown in Patent Document 2, or in the case of a configuration in which a diamagnetic body is attached to a casing so as to face the excitation shaft, passing a current through the coil causes the excitation shaft and the diamagnetic body to repel each other, thereby reducing the thrust load. However, attaching the excitation shaft, which is a heavy object, to the tip of the shaft leads to a decrease in the natural frequency of the shaft, making it difficult to rotate the shaft at high speed, and there is room for improvement in this regard.

[0008] Therefore, the present invention has been made in consideration of the above circumstances, and provides a rotating body and a method for controlling a rotating body that can suppress power loss in the entire magnetic bearing and control a larger thrust load. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention employs the following means. That is, the rotating body of the present invention comprises a rotating shaft that can rotate around the axial direction, a plurality of thrust sections that are provided on the rotating shaft and receive the thrust load of the rotating shaft, a pair of first magnetic bearings that support one first thrust section of the plurality of thrust sections by sandwiching it from both sides in the axial direction, and a second magnetic bearing that is provided on another second thrust section of the plurality of thrust sections, wherein the first magnetic bearing is capable of actively adjusting the attractive force on the first thrust section so as to reduce the thrust load, and the second magnetic bearing is capable of additionally adjusting the attractive force on the second thrust section so as to reduce part of the thrust load.

[0010] In a rotating body configured in this manner, the pair of first magnetic bearings adjust their attractive forces to reduce the thrust load on the first thrust section, and the second magnetic bearing can also adjust its attractive force on the second thrust section to additionally reduce a portion of the thrust load, thereby controlling a larger thrust load on the rotating shaft. In other words, in the present invention, the pair of first and second magnetic bearings can bear the thrust load acting on the rotating shaft by distributing it at an appropriate ratio. Therefore, the current balance can be changed by adjusting the current value of each magnetic bearing, thereby minimizing power loss across these magnetic bearings and achieving a rotating body with high energy efficiency.

[0011] In the rotating body according to the present invention, the second magnetic bearing may be controlled by feeding back a current value of the first magnetic bearing.

[0012] In a rotating body configured in this manner, the current values ​​of a pair of first magnetic bearings are detected and the current value of the second magnetic bearing is controlled based on these current values, making it easy to perform control that reduces power loss in the entire magnetic bearing.

[0013] In addition, in the rotating body according to the present invention, the current value of the second magnetic bearing may be controlled so that the power loss of the pair of first magnetic bearings and the second magnetic bearing is smaller than the power loss of the pair of first magnetic bearings.

[0014] In a rotating body configured in this manner, a highly energy-efficient rotating body can be realized by operating the rotating body while controlling the current value of the second magnetic bearing so that the total power loss of the pair of first and second magnetic bearings is smaller than the power loss of the pair of first magnetic bearings alone.

[0015] In the rotating body according to the present invention, the current value may be controlled to be distributed to each of the pair of first magnetic bearings.

[0016] In a rotating body configured in this manner, current is passed through both of the pair of first magnetic bearings to generate an attractive force, thereby preventing the rotating body from becoming difficult to operate due to an unstable support state (cantilever state) in which only one of the first magnetic bearings is attracted to the first thrust portion.

[0017] In addition, in the rotating body according to the present invention, the current value of one of the pair of first magnetic bearings, the load side magnetic bearing which attracts in a direction to reduce the thrust load of the first thrust section, may be made larger than that of the other, anti-load side magnetic bearing, while the second magnetic bearing adds attractive force.

[0018] In a rotating body configured in this manner, the current value of the load-side magnetic bearing can be made larger than the current value of the counter-load-side magnetic bearing, while also adding attractive force from the second magnetic bearing. That is, by creating a difference in the current balance between the pair of first magnetic bearings (load-side magnetic bearing and counter-load-side magnetic bearing), attractive force can be exerted so that the second magnetic bearing also bears the thrust load, which is effective in reducing the total power loss of the pair of first and second magnetic bearings. That is, the present invention prevents the second magnetic bearing from bearing the entire thrust load of the rotating shaft, which would occur if the load-side magnetic bearing and the counter-load-side magnetic bearing had the same current value and could not bear the thrust load.

[0019] In the rotating body according to the present invention, the attractive force of the second magnetic bearing may be applied in a direction that reduces the thrust load on the second thrust portion.

[0020] In a rotating body configured in this manner, the attractive force of the second magnetic bearing can be made to act in the same axial direction as the attractive forces acting on the pair of first magnetic bearings, making it easier to control the current values ​​of each.

[0021] In the rotating body according to the present invention, the attractive force of the second magnetic bearing may be applied to an end of the rotating shaft.

[0022] In a rotating body configured in this manner, even if it is not possible to place a second magnetic bearing on the anti-load side of the second thrust section, the axial end of the rotating shaft can be used as the second thrust section and the attractive force of the second magnetic bearing can be applied to this axial end, thereby distributing the thrust load acting on the rotating shaft in an appropriate ratio between the pair of first and second magnetic bearings, as described above, and the current balance can be changed by adjusting the current value of each magnetic bearing.

[0023] Furthermore, in the rotating body according to the present invention, the first thrust portion may be a thrust disk extending radially outward from the rotating shaft, and the second thrust portion may be an impeller extending radially outward from the rotating shaft.

[0024] In a rotating body configured in this manner, in addition to adjusting the attractive force to reduce the thrust load on the thrust disk using a pair of first magnetic bearings, the attractive force on the impeller can also be adjusted using the second magnetic bearing to additionally reduce part of the thrust load.

[0025] Furthermore, the control method for a rotating body according to the present invention is a control method for a rotating body as described above, which is a control method for a rotating body as described in any one of claims 1 to 8, and is characterized by comprising a step of controlling a first current value of one load side magnetic bearing of the pair of first magnetic bearings so that it is greater than a second current value of the other counter-load side magnetic bearing, and a step of controlling a third current value in the second magnetic bearing, which is the difference between the first current value and the second current value.

[0026] In this method for controlling a rotating body configured as described above, the first current value of the load-side magnetic bearing is made greater than the second current value of the counter-load-side magnetic bearing, while also adding an attractive force from the second magnetic bearing. That is, by creating a difference in the current balance (the difference between the first and second current values) between the pair of first magnetic bearings (the load-side magnetic bearing and the counter-load-side magnetic bearing), the second magnetic bearing can also exert an attractive force that reduces the thrust load, effectively reducing the total power loss of the pair of first and second magnetic bearings. That is, in this invention, if the load-side magnetic bearing and the counter-load-side magnetic bearing have exactly the same characteristics, the same attractive force is generated at the same current value, and the first magnetic bearing cannot bear the thrust load. On the other hand, if the load-side magnetic bearing and the counter-load-side magnetic bearing have different characteristics (attractive force relative to current value), the two first magnetic bearings will not be able to bear the thrust load even if the current values ​​are different, as the attractive forces of the two first magnetic bearings will be the same. In this way, the present invention can prevent the second magnetic bearing from bearing the entire thrust load of the rotating shaft, which would otherwise occur if the first magnetic bearing were unable to bear the thrust load, thereby preventing large power losses. [Effects of the Invention]

[0027] According to the rotating body and the method for controlling the rotating body of the present invention, it is possible to suppress the power loss of the entire magnetic bearing and to control a larger thrust load. [Brief explanation of the drawings]

[0028] [Figure 1]1 is a cross-sectional view of a compressor according to an embodiment of the present invention. [Figure 2] FIG. 1 is a simplified diagram of a main shaft, a thrust disk, and an impeller according to one embodiment. [Figure 3] This shows the relationship between the current I and the magnetic attraction force F of one magnetic bearing. [Figure 4] 1 is a diagram showing the control characteristics of a magnetic bearing, illustrating the relationship between current I and attractive force F. [Figure 5] 1 is a diagram showing the control characteristics of a magnetic bearing using a bypass current, showing the relationship between current I and attractive force F. FIG. [Figure 6] FIG. 3 is a simplified view of a main shaft, a thrust disk, and an impeller in a compressor according to a modified example, and corresponds to FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0029] A compressor (rotating body) and a control method for the compressor (rotating body) according to an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the drawings used in the following description may show characteristic parts enlarged for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of the components may not necessarily be the same as those in reality.

[0030] 1, the compressor 1 of this embodiment includes a high-speed motor 2 and a compressor body 3 (3A, 3B). The compressor bodies 3A, 3B are coupled to both ends of the high-speed motor 2 in the axial direction O, respectively, to form a general configuration.

[0031] The high-speed motor 2 includes a main shaft (rotating shaft) 4 having a rotor 4a at its center and rotatable around the axis, a stator 51 facing the rotor 4a, bearings 52 (52a, 52b) and bearings (a pair of first magnetic bearings 81, 82 described later) that rotatably hold the main shaft 4, a motor casing 54 that houses the main shaft 4, the stator 51, and bearings 52, 81, 83, and an impeller 6 (including the impeller designated by the symbol 6B described later) fixed to the main shaft 4.

[0032] The main shaft 4 is rotatably supported by bearings 52 (52a, 52b) and bearings 81, 82 in the motor casing 54. The length of the main shaft 4 in the axial direction O is longer than the length of the motor casing 54 in the axial direction O.

[0033] Impellers 6A and 6B are fixed to both ends 4A and 4B of the main shaft 4, respectively. As a result, the main shaft 4 functions as the main rotating shaft of the high-speed motor 2 and also as the main shaft of the compressor bodies 3A and 3B. The main shaft 4 is made of a magnetic iron-based material. A large thrust load P is generated on the main shaft 4, which tends to press the main shaft 4 toward the compressor body 3B. This thrust load P is borne by first magnetic bearings 81 and 82 and a second magnetic bearing 83, which will be described later. In this embodiment, the load acting on the opposite side of the thrust load P in the axial direction O is referred to as a thrust reaction force T.

[0034] As shown in FIG. 1, the high-speed motor 2 further includes a thrust disk (first thrust portion) 7 and an impeller (second thrust portion) 6B that are provided on the main shaft 4 and receive the thrust load P of the main shaft 4, a pair of first magnetic bearings 81, 82 that sandwich and support the thrust disk 7 from both sides in the axial direction O, and a second magnetic bearing 83 that is provided on the impeller 6B.

[0035] In the following description, when the main shaft 4, thrust disk 7, and impeller 6B are arranged in the compressor 1, a thrust load P of the main shaft 4 acts on the anti-load side O1 on the impeller 6B side (the right end side in Figure 1) along the axial direction O of the compressor 1, and a thrust reaction force T acts on the load side O2 on the opposite side to the anti-load side O1 (the left end side in Figure 1) along the axial direction O.

[0036] The thrust disk 7 is provided on the main shaft 4 so that a pair of first magnetic bearings 81, 82 can receive a load (thrust load P and thrust reaction force T) in the axial direction O. The thrust disk 7 is a disk-shaped member made of steel and disposed between the impeller 6A of the main shaft 4 and the stator 51, extending radially outward from the main shaft 4.

[0037] Impeller 6B receives a load (thrust load P and thrust reaction force T) in the axial direction O through second magnetic bearing 83. Impeller 6B is a disk-shaped member made of steel that is disposed at the tip of main shaft 4 on the anti-load side O1 relative to stator 51 and extends radially outward from main shaft 4.

[0038] As shown in Fig. 2, the first magnetic bearings 81, 82 and the second magnetic bearing 83 are made of a magnetic iron-based material. The first magnetic bearings 81, 82 and the second magnetic bearing 83 are configured so that current flows through them, and an attractive force is generated by controlling the current. That is, the magnetic force (attractive force) of each of the magnetic bearings 81, 82, 83 can be adjusted individually. The current values ​​of the magnetic bearings 81, 82, 83 are controlled by a control unit (not shown) so as to reduce the overall power loss of the magnetic bearings 81, 82, 83, as will be described later.

[0039] Furthermore, the first magnetic bearings 81, 82 and the second magnetic bearing 83 are not particularly limited as long as they are capable of supporting the thrust disk 7 and impeller 6B, which rotate together with the main shaft 4, at high speed. In this embodiment, the first magnetic bearings 81, 82 and the second magnetic bearing 83 are thrust (axial) bearings that bear the thrust load P of the thrust disk 7 and the impeller 6B, respectively.

[0040] The pair of first magnetic bearings 81, 82 are provided so as to be able to actively adjust the attractive force on the thrust disk 7 so as to reduce the thrust load P received by the second magnetic bearing 83 while allowing the thrust disk 7 to rotate. In other words, the pair of first magnetic bearings 81, 82 are controlled by controlling the current value so that the attractive force keeps the axial position O of the thrust disk 7 constant.

[0041] The pair of first magnetic bearings 81, 82 includes a load side magnetic bearing 81 that is attracted to the load side O2 that receives the thrust load P acting on the thrust disk 7, and a counter-load side magnetic bearing 82 that is attracted to the counter-load side O1 in the same direction as the thrust load P.

[0042] The load-side magnetic bearing 81 is disposed along the first surface 7a of the load side O2 of the thrust disk 7. The load-side magnetic bearing 81 is provided so as to be able to attract the thrust disk 7 to the load side O2 by an attractive force (magnetic force) due to the applied current value.

[0043] The counter-load side magnetic bearing 82 is disposed along the second surface 7b of the counter-load side O1 of the thrust disk 7 at a position facing the load side magnetic bearing 81 across the thrust disk 7 in the axial direction O. The counter-load side magnetic bearing 82 is provided so as to be able to attract the thrust disk 7 to the counter-load side O1 by an attractive force (magnetic force) due to the applied current value.

[0044] The second magnetic bearing 83 is additionally provided so as to adjust the attractive force applied to the impeller 6B so as to reduce a portion of the thrust load P on the pair of first magnetic bearings 81, 82 while allowing the impeller 6B to rotate. The second magnetic bearing 83 is arranged along the first surface 6a of the load side O2 of the impeller 6B. The second magnetic bearing 83 is arranged so as to attract the impeller 6B to the load side O2 by an attractive force (magnetic force) generated by an applied current value. Specifically, when the thrust load P of the main shaft 4 is generated in the right direction (anti-load side O1) shown in FIG. 1 , the load side magnetic bearing 81 is on the load side and the anti-load side magnetic bearing 82 is on the anti-load side, and the second magnetic bearing 83 is further arranged to reduce the thrust load P. Because the position of the thrust disk 7 is controlled by the first magnetic bearings 81, 82, position control of the second magnetic bearing 83 is not necessary.

[0045] Next, the characteristics of the current values ​​of the first magnetic bearings 81 and 82 during operation will be described in detail. Fig. 3 shows the relationship between the current I and the attractive force F of one magnetic bearing. Fig. 4 is a diagram showing the control characteristics of a magnetic bearing, showing the relationship between the current I and the attractive force F. Fig. 5 is a diagram showing the control characteristics of a magnetic bearing using a bypass current, showing the relationship between the current I and the attractive force F.

[0046] As shown in Fig. 3, the pair of first magnetic bearings 81, 82 are generally used in a range up to the maximum operating current Im (the operating range shown in Fig. 3) because the magnetic flux saturates and the attractive force no longer increases when the maximum operating current Im is exceeded. The total attractive force of the pair of first magnetic bearings 81, 82 is as shown in Fig. 4. As shown in Fig. 4, the current value of the anti-load side magnetic bearing 82 is positive in the left direction, and the attractive force is negative because it is in the opposite direction to the load side magnetic bearing 81. If the control characteristics shown in Fig. 4 are used, only one magnetic bearing is always used for the thrust load P.

[0047] Normally, to improve the stability of the magnetic bearings, control is performed using a bias current Ib so that a current always flows through the opposing first magnetic bearings 81, 82. Figure 5 shows an example of the current and attractive force F that results in a total attractive force of 0 when bias current Ib flows through the pair of first magnetic bearings 81, 82. Because the pair of first magnetic bearings 81, 82 generate attractive forces F in directions that cancel each other out, the total attractive force F in Figure 5 is the difference between the attractive forces F of each first magnetic bearing 81, 82, and has the characteristics indicated by symbol K in Figure 5.

[0048] As a method of controlling the current values ​​of the first magnetic bearings 81, 82 and the second magnetic bearing 83, the second magnetic bearing 83 is controlled by feeding back the current values ​​of the first magnetic bearings 81, 82. More specifically, the current value of the second magnetic bearing 83 is controlled so that the power loss of the pair of first magnetic bearings 81, 82 and second magnetic bearing 83 is smaller than the power loss of the pair of first magnetic bearings 81, 82 alone.

[0049] Furthermore, the current values ​​are distributed and controlled in both of the pair of first magnetic bearings 81, 82. A preferred control method is to increase the current value of one of the pair of first magnetic bearings 81, 82, the load side magnetic bearing 81, which attracts in a direction that reduces the thrust load P of the thrust disk 7 (here, the load side O2), compared to the other, anti-load side magnetic bearing 82, while controlling to add attractive force in the second magnetic bearing 83. The attractive force of the second magnetic bearing 83 at this time acts in a direction that reduces the thrust load P on the impeller 6B (here, the load side O2).

[0050] The compressor 1 configured as described above includes a main shaft 4 rotatable around the axial direction O, a plurality of thrust sections provided on the main shaft 4 and bearing a thrust load P of the main shaft 4, a pair of first magnetic bearings 81, 82 that sandwich and support one of the plurality of thrust sections, a first thrust section (thrust disk 7), from both sides in the axial direction O, and a second magnetic bearing 83 provided on the other of the plurality of thrust sections, a second thrust section (impeller 6B). The first magnetic bearings 81, 82 can actively adjust the attractive force with respect to the thrust disk 7 in response to the thrust load P. The second magnetic bearing 83 can additionally adjust the attractive force with respect to the impeller 6B so as to reduce a portion of the thrust load P of the first magnetic bearing. In the compressor 1 configured as described above, in addition to adjusting the attractive force so that the thrust load P is received by the pair of first magnetic bearings 81, 82 on the thrust disk 7, the attractive force of the second magnetic bearing 83 on the impeller 6B can also be adjusted so as to additionally reduce a portion of the thrust load P, making it possible to control a larger thrust load P on the main shaft 4. That is, in this embodiment, the pair of first magnetic bearings and second magnetic bearing 83 can receive the thrust load P acting on the main shaft 4 by distributing it at an appropriate sharing ratio. Since the current balance can be changed by adjusting the current value of each of the magnetic bearings 81, 82, 83, it is possible to keep the overall power loss of these magnetic bearings 81, 82, 83 small, and a rotating body with high energy efficiency can be realized.

[0051] Furthermore, in this embodiment, the second magnetic bearing 83 is controlled by feeding back the current values ​​of the first magnetic bearings 81 and 82. Therefore, the current values ​​of the pair of first magnetic bearings 81 and 82 are detected, and the current value of the second magnetic bearing 83 is controlled based on these current values, so that control to reduce the overall power loss of the magnetic bearings 81, 82, and 83 can be easily performed.

[0052] Furthermore, in this embodiment, the current value of the second magnetic bearing 83 is controlled so that the power loss of the pair of first magnetic bearings 81, 82 and the second magnetic bearing 83 is smaller than the power loss of the pair of first magnetic bearings 81, 82. Therefore, by operating the compressor 1 while controlling the current value of the second magnetic bearing 83 so that the total power loss of the pair of first magnetic bearings 81, 82 and the second magnetic bearing 83 is smaller than the power loss of just the pair of first magnetic bearings 81, 82, it is possible to realize a compressor 1 with high energy efficiency.

[0053] Furthermore, in this embodiment, the current value is controlled to be distributed to each of the pair of first magnetic bearings 81, 82. Therefore, current flows through both of the pair of first magnetic bearings 81, 82 to generate an attractive force, which reduces the current balance and prevents the thrust disk 7 from being attracted by the first magnetic bearing on only one side, resulting in an unstable support state (cantilever state) that makes it difficult to operate the rotor.

[0054] Furthermore, in this embodiment, the current value of one of the pair of first magnetic bearings 81, 82, the load side magnetic bearing 81, which attracts the thrust load P of the thrust disk 7 in a direction that reduces the thrust load P, is set to be larger than that of the other, anti-load side magnetic bearing 82, while an attractive force is added by the second magnetic bearing 83. Therefore, in the compressor 1 configured in this manner, the current value of the load side magnetic bearing 81 is set to be larger than the current value of the anti-load side magnetic bearing 82, while an attractive force by the second magnetic bearing 83 can also be added. In other words, by creating a difference in the current balance of the pair of first magnetic bearings (load side magnetic bearing 81 and anti-load side magnetic bearing 82), the second magnetic bearing 83 can also exert an attractive force that reduces the thrust load P, and the total power loss of the pair of first magnetic bearings 81, 82 and the second magnetic bearing 83 can be effectively reduced. In other words, in this embodiment, it is possible to prevent a situation in which the load side magnetic bearing 81 and the anti-load side magnetic bearing 82 have the same current value and the thrust load P cannot be reduced, and the second magnetic bearing 83 has to bear the entire thrust load P of the main shaft 4, resulting in large power losses.

[0055] Furthermore, in this embodiment, the attractive force of the second magnetic bearing 83 acts in a direction that reduces the thrust load P on the impeller 6B. Therefore, the attractive force of the second magnetic bearing 83 can be made to act in the same axial direction as the attractive forces acting on the pair of first magnetic bearings 81, 82, making it easier to control the current values ​​of each.

[0056] Furthermore, in this embodiment, the first thrust portion is the thrust disk 7 extending radially outward from the main shaft 4, and the second thrust portion is the impeller 6B extending radially outward from the main shaft 4. Therefore, in addition to adjusting the attractive force of the pair of first magnetic bearings to reduce the thrust load P on the thrust disk 7, the attractive force of the second magnetic bearing 83 to the impeller 6B can also be adjusted to additionally reduce a portion of the thrust load P.

[0057] Furthermore, the control method for the compressor 1 according to this embodiment includes the steps of: controlling the first current value of one load-side magnetic bearing 81 of the pair of first magnetic bearings 81, 82 so that it is greater than the second current value of the other counter-load-side magnetic bearing 82; and controlling the second magnetic bearing 83 so that it has a third current value, which is the difference between the first and second current values. With this control method for the compressor 1 configured as described above, it is possible to increase the first current value of the load-side magnetic bearing 81 greater than the second current value of the counter-load-side magnetic bearing 82, while also adding an attractive force by the second magnetic bearing 83. That is, by creating a difference (the difference between the first and second current values) in the current balance between the pair of first magnetic bearings 81, 82 (the load-side magnetic bearing 81 and the counter-load-side magnetic bearing 82), the second magnetic bearing 83 can also exert an attractive force so as to reduce the thrust load P, and this is effective in reducing the total power loss of the pair of first magnetic bearings 81, 82 and the second magnetic bearing 83. That is, in this embodiment, when the load side magnetic bearing 81 and the anti-load side magnetic bearing 82 have exactly the same characteristics, the same attractive force is obtained at the same current value, and therefore the first magnetic bearings 81, 82 cannot bear the thrust load P. In contrast to this, when the load side magnetic bearing 81 and the anti-load side magnetic bearing 82 have different characteristics (attractive force relative to current value), if the attractive forces of the first magnetic bearings 81, 82 are the same even when the current values ​​are different, they will not be able to bear the thrust load P. In this way, in this embodiment, it is possible to prevent a situation in which the second magnetic bearing 83 has to bear the entire thrust load P of the spindle 4, which would result in large power losses, as would occur in a case in which the thrust load P cannot be reduced.

[0058] Next, an example will be described below that was carried out to verify the effects of the spindle 4 (rotating body) and the method for controlling the spindle 4 (rotating body) according to the above-described embodiment.

[0059] (Example) In the examples, a pair of first and second magnetic bearings of the compressor in the above-described embodiment was used, and the power loss was calculated in three control cases (first control case (control number 1), second control case (control number 2), and third control case (control number 3)) in which the current balance of the current values ​​of each magnetic bearing was changed, and the effects were confirmed.

[0060] In this example, it is assumed that the attractive force of each magnetic bearing is 1 for a current of 1, and that the attractive force increases linearly up to a maximum operating current of 10, and the bias current of each of the pair of first magnetic bearings is controlled to 5. Table 1 shows the current values ​​and power losses of each magnetic bearing when a thrust load of 10 is applied in the control case of this example. In Table 1, the first magnetic bearing on the load side is indicated by "A," the one on the anti-load side is indicated by "A'," and the second magnetic bearing is indicated by "B." Power loss is the square of the current value.

[0061] [Table 1]

[0062] As shown in Table 1, the first control case is when the second magnetic bearing B is not used, and the current values ​​of the first magnetic bearings A and A' are 10 and 0, respectively, resulting in a cantilevered state. In the second control case, the current values ​​of the first magnetic bearings A and A' are 7.5 and 2.5, respectively, and the current value of the second magnetic bearing B is 5. In the third control case, the current values ​​of the first magnetic bearings A and A' are 5 and 5, respectively, and the current value of the second magnetic bearing B is 10. In the third control case, the first magnetic bearing is not subjected to a thrust load.

[0063] As shown in Table 1, when the second magnetic bearing 83 of the first control case (control number 1) is not used, the power loss is 100 for the first magnetic bearing A on the load side, and 0 for the first magnetic bearing A' and second magnetic bearing B on the anti-load side, totaling 100.

[0064] In the second control case (control number 2), the power loss is 56.25 for the first magnetic bearing A on the load side, 6.25 for the first magnetic bearing A' on the anti-load side, and 25 for the second magnetic bearing B, for a total of 87.5.

[0065] In the third control case (control number 3), the power loss is 25 for the first magnetic bearing A on the load side, 25 for the first magnetic bearing A' on the anti-load side, and 100 for the second magnetic bearing B, for a total of 150.

[0066] From these results, it was confirmed that in this example, even with the same thrust load, the total magnetic bearing power loss can be reduced as in the second control case by adjusting the current value of the second magnetic bearing B. Also, based on the same concept, it can be said that a greater magnetic attraction force can be obtained for the same power loss.

[0067] The assembly procedures, shapes and combinations of the components, etc. shown in the above-described embodiments are merely examples, and various modifications can be made based on design requirements, etc., within the scope of the present invention.

[0068] For example, in the above embodiment, the compressor 1 is used as an example of a rotating body, but the present invention is not limited to this and can also be applied to rotating bodies such as centrifugal pumps and expansion turbines.

[0069] Furthermore, although the impellers 6A and 6B are fixed to both ends 4A and 4B of the main shaft 4, this is not limitative. The impeller 6 may be fixed to only one of the ends 4A and 4B of the main shaft 4.

[0070] In the embodiment described above, the first thrust portion is the thrust disk 7 extending radially outward from the main shaft 4, and the second thrust portion is the impeller 6B extending radially outward from the main shaft 4, but this is not limiting. For example, the second thrust portion on which the second magnetic bearing 83 is provided may also be the thrust disk 7.

[0071] Furthermore, although the present embodiment is configured to cause the attractive force of second magnetic bearing 83 to act in a direction that reduces the thrust load on impeller 6B (second thrust portion), a configuration may also be adopted in which a radial bearing or the like is used to cause the attractive force of second magnetic bearing 83 to act on the shaft end of main shaft 4. In this case, even if second magnetic bearing 83 cannot be arranged on the anti-load direction side of impeller 6B, by using the shaft end of main shaft 4 as impeller 6B and causing the attractive force of second magnetic bearing 83 to act on this shaft end, the thrust load P acting on main shaft 4 can be distributed at an appropriate sharing ratio between the pair of first magnetic bearing and second magnetic bearing 83, as described above, and the current balance can be changed by adjusting the current value of each of magnetic bearings 81, 82, 83.

[0072] Furthermore, as in the compressor 1 (rotating body) according to a modified example shown in Fig. 6, a third magnetic bearing 84 may be provided facing the second magnetic bearing 83 across the impeller 6B in the axial direction O. The third magnetic bearing 84 may be configured to apply an attractive force to the impeller 6B (main shaft 4) when a thrust reaction force T acts on the main shaft 4 (rotating shaft), thereby moving the impeller 6B (main shaft 4) to the anti-load side O1. Furthermore, in the configuration of the modified example, the pair of first magnetic bearings 81, 82 and the pair of second magnetic bearing 83, third magnetic bearing 84 are alternately used for a predetermined period, thereby enabling long-term maintenance. [Explanation of symbols]

[0073] 1. 1A Compressor (rotating body) 4. Main shaft (rotation axis) 6,6A impeller 6B Impeller (second thrust section) 7 Thrust disc (first thrust part) 81 Load side magnetic bearing, first magnetic bearing 82 Anti-load side magnetic bearing, first magnetic bearing 83 Second magnetic bearing O Axial direction P thrust load T Thrust reaction force

Claims

1. a rotation shaft that is rotatable around an axial direction; a plurality of thrust portions provided on the rotary shaft and configured to receive a thrust load from the rotary shaft; a pair of first magnetic bearings that sandwich and support one first thrust portion of the plurality of thrust portions from both sides in the axial direction; a second magnetic bearing provided on another second thrust portion among the plurality of thrust portions, the first magnetic bearing is capable of actively adjusting an attractive force to the first thrust portion so as to reduce the thrust load; The second magnetic bearing is a rotor that can additionally adjust the attractive force to the second thrust portion so as to reduce a portion of the thrust load.

2. 2. The rotating body according to claim 1, wherein the second magnetic bearing is controlled by feeding back a current value of the first magnetic bearing.

3. 3. The rotating body according to claim 2, wherein a current value of the second magnetic bearing is controlled so that a power loss in the pair of first magnetic bearings and the second magnetic bearing is smaller than a power loss in the pair of first magnetic bearings.

4. 4. The rotating body according to claim 3, wherein the current value is controlled so as to be distributed to each of the pair of first magnetic bearings.

5. 5. The rotating body according to claim 4, wherein a current value of one of the pair of first magnetic bearings, a load side magnetic bearing that attracts in a direction to reduce the thrust load of the first thrust section, is made larger than that of the other, anti-load side magnetic bearing, while an attractive force is added by the second magnetic bearing.

6. 2. The rotating body according to claim 1, wherein the attractive force of the second magnetic bearing acts in a direction that reduces the thrust load on the second thrust portion.

7. 2. The rotating body according to claim 1, wherein the attractive force of said second magnetic bearing is applied to an end portion of said rotating shaft.

8. the first thrust portion is a thrust disk extending radially outward from the rotary shaft, The rotating body according to claim 1 , wherein the second thrust portion is an impeller extending radially outward from the rotating shaft.

9. 9. A method for controlling a rotating body according to claim 1, comprising: controlling a first current value of one of the pair of first magnetic bearings on the load side to be larger than a second current value of the other of the pair of first magnetic bearings on the counter-load side; controlling the second magnetic bearing to have a third current value that is a difference between the first current value and the second current value; A method for controlling a rotating body having the above structure.

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