CN117847087A - Asymmetric thrust-free disk three-degree-of-freedom axial-radial double-piece type hybrid magnetic bearing - Google Patents

Abstract

The invention discloses an asymmetric thrust-disk-free three-degree-of-freedom axial-radial double-plate type hybrid magnetic bearing, wherein two three-pole radial stators with the same structure and two three-pole axial stators with the same structure and positioned at two sides of a rotor center point are sleeved outside a rotor, a circular permanent magnet ring is fixedly embedded between two stator yokes, projections of six three-pole radial stator magnetic poles on the radial section of the two three-pole radial stators are uniformly distributed along the circumferential direction, and three axial stator magnetic poles and three radial stator magnetic poles of the three-pole axial stators at the same side of the rotor center point are uniformly distributed along the circumferential direction; a set of annular bias magnetic flux adjusting coils are wound between the permanent magnet ring and the rotating shaft, a topological six-pole structure of the three-pole bearing with the rotation direction difference of 60 degrees is adopted, the structure is more compact, and the critical rotating speed is improved.

Description

Asymmetric thrust-free disk three-degree-of-freedom axial-radial double-piece type hybrid magnetic bearing

Technical Field

The invention belongs to the technical field of non-contact magnetic suspension bearings, and particularly relates to a three-degree-of-freedom hybrid magnetic bearing with a thrust-free disk, which integrates radial and axial functions.

Background

The magnetic suspension bearing (magnetic bearing) is a novel high-performance bearing without mechanical contact between a rotor and a stator, and because the rotor is directly suspended in space by utilizing electromagnetic force, the magnetic suspension bearing has the advantages of no friction, long service life, high speed, high precision and the like, and is widely applied to occasions such as life science, flywheel energy storage, high-speed machine tools, aerospace and the like. The magnetic bearings can be classified into passive type, active type and hybrid type according to the way of generating magnetic flux, wherein the control magnetic flux of the hybrid magnetic bearing is generated by the energized coil, and the bias magnetic flux is generated by the permanent magnet, which is advantageous for reducing the number of turns of the coil and reducing the power loss of the driving circuit. The magnetic bearings can be divided into axial magnetic bearings (single degree of freedom), radial magnetic bearings (two degrees of freedom) and radial-axial magnetic bearings (three degrees of freedom) according to the degree of freedom of the rotor to be controlled, and the three-degree-of-freedom magnetic bearings integrating radial-axial control are more compact in structure, short in axial length, beneficial to improving the critical rotation speed of the rotor and reducing air friction loss.

In the document of Chinese patent publication No. CN101149077A, named 'permanent magnet biased axial radial magnetic bearing', a radial-axial hybrid magnetic bearing is proposed, wherein the radial magnetic bearing is fixed inside a thrust magnetic bearing, and is symmetrical about a radial plane, so that two radial degrees of freedom and two axial degrees of freedom can be controlled simultaneously. In the Chinese patent publication No. CN101832335A, named as 'permanent magnet biased axial radial magnetic bearing', a structure is proposed in which a radial stator is of a four-tooth two-pair magnetic pole structure, two bipolar or four unipolar direct current power amplifiers are needed, and the defects of high number of power electronic switches, high cost and lower power density exist.

Disclosure of Invention

The invention aims to solve the defects of the prior art and provides a novel three-degree-of-freedom axial-radial double-plate type hybrid magnetic bearing of an asymmetric thrust-free disk with compact structure, low cost and high bearing capacity.

The technical scheme adopted by the asymmetric thrust-free disk three-degree-of-freedom axial-radial double-plate type hybrid magnetic bearing is as follows: the motor comprises a rotor, two tripolar radial stators and two tripolar axial stators, wherein the rotor is sleeved with two tripolar radial stators which are respectively positioned at two sides of a rotor center point and have the same structure, and two tripolar axial stators which are respectively positioned at two sides of the rotor center point and have the same structure; a tripolar radial stator and a tripolar axial stator on the same side of the rotor center point are respectively provided with a common stator yoke; a circular permanent magnet ring is fixedly embedded between the two stator yokes, and the permanent magnet ring is magnetized in the axial direction; the projections of six tripolar radial stator magnetic poles on the radial section of the two tripolar radial stators are uniformly distributed along the circumferential direction; the three axial stator magnetic poles and the three radial stator magnetic poles on the same side of the center point of the rotor are uniformly arranged along the circumferential direction; three axial stator poles and three radial stator poles of the tripolar axial stator on the same side of the center point of the rotor are uniformly arranged along the circumferential direction; each radial stator magnetic pole is wound with a radial control coil, and one axial control coil is arranged in three axial stator magnetic poles on the same side of the center point of the rotor; a set of annular bias magnetic flux adjusting coils are wound between the permanent magnet ring and the rotating shaft, and the bias magnetic flux adjusting coils are positioned on the inner sides of the radial control coils.

Further: the axial cross section of the stator yoke part of each axial stator is U-shaped, a set of annular axial control coils are arranged in each U-shaped yoke part, and the two sets of axial control coils are connected in series in the same direction and are driven and controlled by a bidirectional direct current inverter.

Further: the bias magnetic flux adjusting coil is positioned on the inner side of the radial control coil in the same winding direction as the axial control coil.

Further: the radial control coils projected on two opposite radial stator magnetic poles on the radial section have the same winding direction, and are connected in series in pairs and then are connected in a star mode.

The invention has the advantages that:

1. compared with the combined structure of the two-degree-of-freedom radial magnetic bearing and the single-degree-of-freedom axial magnetic bearing, the motor system supported by the magnetic bearing has the advantages that the axial length of the motor system supported by the magnetic bearing is reduced, the structure is more compact, and the critical rotating speed is improved under the condition of the same power.

2. The invention adopts the topological six-pole structure of the three-pole bearing with the difference of 60 degrees in rotation direction, optimizes the nonlinearity problem caused by the asymmetry of the conventional three-pole structure, thereby reducing the coupling between the nonlinearity of the levitation force and the two radial degrees of freedom and reducing the control difficulty. The radial control coils on the two opposite radial stator magnetic poles are connected in series to form a set of three-phase windings. The three-phase inverter is adopted for driving, so that the number of switching tubes is reduced, and the power loss and the cost of a driver are reduced.

3. The invention provides a thrust-disk-free design, which enables an axial control part to directly act on a rotor through an asymmetric axial stator structural design, and solves the problems of rotor outer diameter increase and air abrasion caused by the fact that axial thrust disks are required to be arranged on a plurality of radial-axial magnetic bearings.

4. The invention adopts the hybrid magnetic bearing, provides bias magnetic flux for radial and axial components simultaneously through the axial magnetization permanent magnet, isolates radial and axial control magnetic fields, realizes radial and axial control decoupling, reduces power loss, controls the magnetic flux provided by a coil to generate dynamic levitation force, overcomes external disturbance force and load, improves bearing capacity, and effectively reduces coil current, thereby reducing power loss.

5. The invention is provided with the bias magnetic flux adjusting coil, and can adjust the magnetization state of the permanent magnet, thereby adjusting the bias flux from the permanent magnet, reducing the influence of high temperature demagnetization and other problems on the system, and being capable of replacing the permanent magnet for a short time to provide bias magnetic flux when the permanent magnet has problems, and improving the fault tolerance of the bias flux and the running stability of the magnetic bearing.

Drawings

In order to more clearly illustrate the present invention, the technical solutions and advantages of the present invention will be described in further detail below with reference to the accompanying drawings and detailed description;

FIG. 1 is a perspective view of an asymmetric thrust-free disk three degree of freedom axial-radial dual-disk hybrid magnetic bearing of the present invention;

FIG. 2 is a schematic diagram of FIG. 1 in semi-section;

FIG. 3 is a schematic view in radial plan cross-section of the present invention;

FIG. 4 is a schematic view in cross-section of the axial plane D-D of FIG. 3;

FIG. 5 is a schematic view of a radial magnetic circuit of the present invention;

fig. 6 is a schematic view of an axial magnetic circuit of the present invention.

In the figure: 1. a rotating shaft; 2. a rotor; 31. 32, a tripolar radial stator; 311. 321, a stator yoke; 312. 322 radial stator poles; 41. 42, radial control coils; 5. a radial air gap; 61. 62. tripolar axial stator; 611. 621 axial stator poles; 71. 72. axial control coils; 81. 82. axial air gap; 9. a permanent magnet ring; 10. a bias magnetic flux adjusting coil; 11. a bias magnetic flux; 12. radially controlling the magnetic flux; 13. the magnetic flux is controlled axially.

Detailed Description

As shown in fig. 1, 2, 3 and 4, the invention comprises a rotating shaft 1, a rotor 2, two three-pole radial stators 31 and 32 and two three-pole axial stators 61 and 62, wherein the rotor 2 is fixedly sleeved at the middle position outside the rotating shaft 1.

The rotor 2 is sleeved with two tripolar radial stators 31 and 32 and two tripolar axial stators 61 and 62, wherein the two tripolar radial stators 31 and 32 have the same structure and are respectively positioned at two sides of the center point of the rotor 2, and the axial distances between the two tripolar radial stators 31 and 32 and the center point of the rotor 2 are equal.

The two tripolar axial stators 61, 62 have identical structures and are respectively positioned at two sides of the center point of the rotor 2, and the axial distances between the two tripolar axial stators 61, 62 and the center point of the rotor 2 are equal.

One three-pole radial stator 31 and one three-pole axial stator 61 on the same side of the center point of the rotor 2 have a common stator yoke 311, and one three-pole radial stator 32 and one three-pole axial stator 62 have a common stator yoke 321. The two stator yokes 311, 321 have the same structure and are respectively positioned at two sides of the center point of the rotor 2, and the axial distance between the two stator yokes and the center point of the rotor 2 is equal.

A circular permanent magnet ring 9 is fixedly embedded between the two stator yokes 311, 321, the outer diameter of the permanent magnet ring 9 is the same as that of the two stator yokes 311, 321, and the inner diameter of the permanent magnet ring 9 is larger than that of the two stator yokes 311, 321.

The permanent magnet ring 9 is magnetized axially, isolates radial and axial control magnetic fields, and realizes radial and axial control decoupling.

The three radial stator poles 312 of the first three-pole radial stator 31 are uniformly arranged in the circumferential direction, the three radial stator poles 322 of the second three-pole radial stator 32 are uniformly arranged in the circumferential direction, and the two three-pole radial stators 31, 32 have six radial stator poles 312, 322 in total. The radial stator poles 312 of the first three-pole radial stator 31 are disposed to rotate 60 ° along the center line of the rotor 2 with respect to the radial stator poles 322 of the second three-pole radial stator 32, so that the two three-pole radial stators 31, 32 differ by 60 ° from each other, projections of the six three-pole radial stator poles 312, 322 on the radial cross section of the two three-pole radial stators 31, 32 are uniformly arranged in the circumferential direction, adjacent two radial stator poles 312, 322 projected on the radial cross section are separated by 60 °, one of the adjacent two radial stator poles 312, 322 projected on the radial cross section belongs to the first radial stator 31, and the other belongs to the second radial stator 32.

Similarly, the three axial stator poles 611 of the first three-pole axial stator 61 are uniformly arranged in the circumferential direction, the three axial stator poles 621 of the second three-pole axial stator 62 are uniformly arranged in the circumferential direction, and the two three-pole axial stators 61, 62 have six axial stator poles 611, 621 in total.

The three axial stator poles 611 and the three radial stator poles 312 on the same side of the center point of the rotor 2 are uniformly arranged in the circumferential direction such that the three axial stator poles 611 on one side of the center point of the rotor 2 coincide with the projected centers of the three radial stator poles 312 on the other side on the radial cross section. The axial stator pole 611 of the first three-pole axial stator 61 is placed rotated 60 ° along the centre line of the rotor 2 with respect to the axial stator pole 621 of the second three-pole axial stator 62, the two three-pole axial stators 611, 621 being 60 ° apart. The projections of the six axial stator poles 611, 621 on the radial cross section are uniformly arranged along the circumferential direction, and coincide with the projection centers of the six radial stator poles 312, 322 on the radial cross section in a one-to-one correspondence. Adjacent two axial stator poles 611, 621 projected on the radial section are separated by 60 °, one of the adjacent two axial stator poles 611, 621 projected on the radial section belongs to the first three-pole axial stator 61, the other one belongs to the second three-pole axial stator 62.

The six radial stator magnetic poles 312 and 322 of the magnetic bearing extend from the inner walls of the corresponding stator yokes 311 and 321 to the rotor 2 along the radial direction, and the same radial air gap 5 is reserved between the six radial stator magnetic poles and the rotor 2, and the distance between the six radial air gaps 5 is about 0.5 mm.

Each radial stator pole 312, 322 is wound with a radial control coil of the same turns specification. The three radial stator poles 312 of the first three-pole radial stator 31 are wound with radial control coils 41, and the three radial stator poles 322 of the second three-pole radial stator 32 are wound with radial control coils 42. The radial control coils 41 and 42 projected on the two opposite radial stator poles 312 and 322 on the radial section have the same winding direction, the radial control coils 41 and 42 projected on the two opposite radial stator poles 312 and 322 on the radial section are connected in series two by two to form a set of three-phase windings in a star-shaped linkage mode, and the three-phase windings are driven by a three-phase inverter.

As shown in fig. 3, each of the axial stators 61, 62 has a U-shaped cross section at the stator yoke 311, 321, which is a U-shaped yoke portion in which the axial control coils 71, 72 are mounted. The stator yokes 311, 321 are annular in shape, and serve as yokes of the radial stators 31, 32. The U-shaped side walls of the axial stators 61, 62 away from the center of the rotor 2 extend axially out of the axial stator poles 611, 621, respectively, toward the both end faces of the rotor 2. The six U-shaped side walls with the axial stator poles 611, 621 coincide in a one-to-one correspondence with the projected centers of the six radial stator poles 312, 322 on the radial cross section. The U-shaped side wall near the center of the rotor 2 is fixedly connected with the permanent magnet ring 9.

Axial air gaps 81 and 82 are formed between the axial stator poles 611 and 621 and the end face of the rotor 2, and the distance between the axial air gaps 81 and 82 is about 0.5 mm.

The radial distance between the axial stator poles 611, 621 and the shaft 1 should be much greater than the axial air gaps 81, 82.

An axial control coil 71, 72 is arranged in the U-shaped yoke of each tripolar axial stator 61, 62, and both sets of axial control coils 71, 72 are annular, coaxially sleeved outside the rotor 2 and are not in contact with the radial stator poles 312, 322. The two sets of axial control coils 71 and 72 are connected in series in the same direction in the winding direction, and are driven and controlled by a bidirectional direct current inverter.

A set of annular bias magnetic flux adjusting coils 10 is wound between the permanent magnet ring 9 and the rotating shaft 2, the bias magnetic flux adjusting coils 10 are coaxially sleeved outside the rotor 2, and are arranged between the permanent magnet ring 9 and the rotating shaft 2 and have the same winding direction as the axial control coils 71 and 72. The bias magnetic flux adjusting coil 10 is located inside the radial control coils 41, 42, and is not in contact with the radial control coils 41, 42.

The rotor 2 and the radial stator poles 312 and 322 are formed by laminating silicon steel sheets, the stator yokes 311 and 321 and the axial stators 61 and 62 are made of the same magnetic conduction material, and the radial control coils 41 and 42, the axial control coils 71 and 72 and the bias magnetic flux adjusting coil 10 are formed by winding insulated paint copper wires with the same specification.

The width of the axial stator poles 611, 621 along the circumferential tangential direction is smaller than the width of the radial stator poles 312, 322 along the circumferential tangential direction. The end faces of the rotor 2 are flush with the end faces of the radial stator poles 312, 322. The inner diameter of the bias flux adjusting coil 10 should be larger than the inner diameter of the radial stator poles 312, 322.

As shown in fig. 3, 4, 5 and 6, the axially magnetized permanent magnet ring 9 provides a bias magnetic flux for both the radial and axial component structures, and the path of the bias magnetic flux 11 generated by it is as follows, taking the A1 direction as an example: starting from the N pole of the permanent magnet ring 9, the permanent magnet ring passes through the stator yoke 311, the radial stator magnetic pole 312, the radial air gap 5 and the rotor 2 in sequence and then is uniformly divided into two paths, and the two paths respectively pass through the radial air gap 5, the axial stator 62 and the axial air gap 82 to reach the axial stator magnetic pole 621, and finally return to the S pole of the permanent magnet ring 9 to form a closed loop. For the A2 direction, the bias magnetic flux 11 path is as follows: after the permanent magnet ring 9 starts from the N pole, the permanent magnet ring is uniformly divided into two paths at the axial stator 61, one path passes through the axial stator magnetic pole 611 and the axial air gap 81, and the other path passes through the inner side of the axial stator 61, the radial air gap 5, the rotor 2, the radial air gap 5 and the radial stator magnetic pole 322, and finally returns to the S pole of the permanent magnet ring 9 to form a closed loop. When the bias magnetic flux adjusting coil 10 is supplied with current in the positive direction or the negative direction, a bias magnetic flux loop with the same path is generated, and the direction of the bias magnetic flux loop is the same as or opposite to that of the bias magnetic flux 11 generated by the permanent magnet ring 9, so that the magnetization state of the permanent magnet is adjusted, and the bias field state of the magnetic bearing is changed through superposition.

As shown in fig. 5, when the rotor 2 is positioned at the center position, the levitation forces generated by the bias magnetic fluxes 11 at the radial air gaps 5 of A1 and A2 are equal in magnitude and opposite in direction, and the rotor 2 is balanced. When the rotor 2 is in a radially eccentric state (for example, the A1A2 direction), a positive direction current is supplied to the radial control coil 41 in the A1 direction, and the A1 direction generated radial control magnetic flux 12 has the following paths: the magnetic flux is uniformly split into two paths from the radial stator pole 31 in the A1 direction and the radial stator yoke 311, flows to the radial stator pole 31 in the B1 direction and the C1 direction in the anticlockwise and clockwise directions respectively, passes through the radial air gap 5 and the rotor 2, merges with the radial air gap 5 at the positions from the rotor 2 to the A1 direction, and finally returns to the radial stator pole 31 in the A1 direction. When current in the same direction is supplied to the radial control coil 42 in the A2 direction, the radial air gap 5 of the generated radial control magnetic flux in the A2 direction is the same as the A1 direction. At the A1 direction radial air gap, the radial control magnetic flux 12 is superimposed with the bias magnetic flux 11, and at the A2 direction radial air gap, the radial control magnetic flux 12 is cut down with the bias magnetic flux 11, thereby generating a radial levitation force directed in the A1 direction at the rotor 2. By applying a negative current to the radial control coils 41, 42 in the direction A1, A2, a radial control flux 12 in the opposite direction is generated, thereby generating a radial levitation force at the rotor 2 directed in the direction A2. By simultaneously changing the magnitude and direction of the current in the radial control coils 41, 42, the magnetic fluxes generated by the two tripolar bearings rotating in the bearing direction in the undesired direction cancel each other, so that the coupling between the nonlinearity of the levitation force and the two radial degrees of freedom is reduced, the magnitude and direction of the radial levitation force are controlled, and the stable levitation of the rotor 2 is realized.

As shown in fig. 6, when the rotor 2 is in an axially eccentric state, the axial coils 71, 72 may be used to axially control the rotor 2. Taking the axial coil 71 at the axial stator 61 as an example, a positive current is applied to the axial coil 71, and the generated axial control magnetic flux 13 passes through the axial air gap 81 from the axial stator pole 611 to reach the rotor 2, flows through the radial air gap 5 through the rotor 2, and returns to the axial stator 61 to form a loop. The axial control flux 13 now overlaps the bias flux 11 at the axial air gap 81, so that an axial levitation force directed to the right is generated at the rotor 2. At this time, the axial control magnetic flux generated by the same current at the radial air gap 5 is opposite to the magnetic flux generated by the axial coil 71 at the radial air gap 5, and the axial control is free from interference with the radial direction, thereby realizing the structure decoupling control. When negative current is applied to the axial control coils 71, 72, the formed axial control magnetic flux 13 is reduced by the bias magnetic flux 11 at the axial air gap 82, and an axial levitation force directed to the left is generated at the rotor 2. The axial stator poles 611 and 621 arranged in an axial double-layer mode enable partial magnetic fluxes in the axial direction to directly act on the rotor 2 through the axial air gaps 81 and 82, so that an axial thrust disk structure required by a conventional axial magnetic bearing is optimized, and the radius size of the rotor 2 is shortened. By changing the magnitude and direction of the current in the axial control coils 81, 82, the magnitude and direction of the axial levitation force can be controlled, thereby achieving stable levitation of the rotor 2.

Claims (9)

1. An asymmetric thrust-free disk three-degree-of-freedom axial-radial double-piece type hybrid magnetic bearing is characterized in that: the motor comprises a rotor (2), two tripolar radial stators (31, 32) and two tripolar axial stators (61, 62), wherein the rotor (2) is sleeved with two tripolar radial stators (31, 32) with the same structure and two tripolar axial stators (61, 62) with the same structure and respectively positioned at two sides of the center point of the rotor (2);

a tripolar radial stator (31, 32) and a tripolar axial stator (61, 62) on the same side of the centre point of the rotor (2) respectively have a common stator yoke (311, 321);

a ring-shaped permanent magnet ring (9) is fixedly embedded between the two stator yokes (311, 321), and the permanent magnet ring (9) is magnetized axially;

the projections of six tripolar radial stator magnetic poles (312, 322) on the radial section of the two tripolar radial stators (31, 32) are uniformly distributed along the circumferential direction; three axial stator poles (611, 621) and three radial stator poles (312, 322) on the same side of the center point of the rotor (2) are uniformly arranged along the circumferential direction;

three axial stator poles (611, 621) and three radial stator poles (312, 322) of the tripolar axial stators (61, 62) on the same side of the center point of the rotor (2) are uniformly arranged along the circumferential direction;

each radial stator magnetic pole (312, 322) is wound with a radial control coil (41, 42), and one axial control coil (71, 72) is respectively arranged in three axial stator magnetic poles (611, 621) on the same side of the center point of the rotor (2); a set of annular bias magnetic flux adjusting coils (10) are wound between the permanent magnet ring (9) and the rotating shaft (2), and the bias magnetic flux adjusting coils (10) are positioned on the inner sides of the radial control coils (41, 42).

2. The asymmetric thrust-free disk three degree of freedom axial-radial double-disk hybrid magnetic bearing of claim 1, characterized by: the axial cross section of a stator yoke (311, 321) of each axial stator (61, 62) is U-shaped, a set of annular axial control coils (71, 72) are arranged in each U-shaped yoke part, and the two sets of axial control coils (71, 72) are connected in series in the same direction and are driven and controlled by a bidirectional direct current inverter.

3. The asymmetric thrust-free disk three degree of freedom axial-radial double-disk hybrid magnetic bearing of claim 1, characterized by: the bias magnetic flux adjusting coil (10) is positioned inside the radial control coils (41, 42) in the same winding direction as the axial control coils (71, 72).

4. The asymmetric thrust-free disk three degree of freedom axial-radial double-disk hybrid magnetic bearing of claim 1, characterized by: the axial stator poles (611, 621) have a width in the circumferential tangential direction smaller than the width in the circumferential tangential direction of the radial stator poles (312, 322), the end faces of the rotor (2) are flush with the end faces of the radial stator poles (312, 322), and the inner diameter of the bias magnetic flux adjusting coil (10) is larger than the inner diameter of the radial stator poles (312, 322).

5. The asymmetric thrust-free disk three degree of freedom axial-radial double-disk hybrid magnetic bearing of claim 1, characterized by: the axial distance between the two tripolar radial stators (31, 32) and the central point of the rotor (2) is equal, and the axial distance between the two tripolar axial stators (61, 62) and the central point of the rotor (2) is equal.

6. The asymmetric thrust-free disk three degree of freedom axial-radial double-disk hybrid magnetic bearing of claim 1, characterized by: the outer diameter of the permanent magnet ring (9) is the same as the outer diameters of the two stator yokes (311, 321), and the inner diameter of the permanent magnet ring (9) is larger than the inner diameters of the two stator yokes (311, 321) and is the same.

7. The asymmetric thrust-free disk three degree of freedom axial-radial double-disk hybrid magnetic bearing of claim 1, characterized by: radial control coils (41, 42) projected on two opposite radial stator poles (312, 322) on a radial section have the same winding direction, are connected in series two by two and then are connected in a star-shaped mode.

8. The asymmetric thrust-free disk three degree of freedom axial-radial double-disk hybrid magnetic bearing of claim 1, characterized by: the radial distance between the axial stator poles (611, 621) and the shaft (2) is greater than the axial air gap.

9. The asymmetric thrust-free disk three degree of freedom axial-radial double-disk hybrid magnetic bearing of claim 1, characterized by: the rotor (2) and the radial stator magnetic poles (312, 322) are formed by laminating silicon steel sheets, the stator yokes (311, 321) and the axial stators (61, 62) are made of the same magnetic conduction materials, and the radial control coils (41, 42), the axial control coils (71, 72) and the bias magnetic flux regulating coils (10) are formed by winding insulated paint copper wires with the same specification.