Asymmetric three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing without thrust plate

Abstract

The invention discloses an asymmetric thrust-disk-free three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing, wherein a rotor outer shell is provided with two three-pole radial stators with the same structure respectively located on both sides of a rotor center point and two three-pole axial stators with the same structure respectively located on both sides of a rotor center point, a circular permanent magnet ring is fixedly embedded between the two stator yokes, projections of a total of six three-pole radial stator magnetic poles of the two three-pole radial stators on a radial cross section are evenly arranged in a circumferential direction, and three axial stator magnetic poles and three radial stator magnetic poles of the three-pole axial stator on the same side of the rotor center point are evenly arranged in a circumferential direction; a set of circular bias flux regulating coils is wound between the permanent magnet ring and the rotating shaft, and a variable topology six-pole structure of two three-pole bearings with a rotation direction difference of 60 degrees is adopted, so that the structure is more compact and the critical speed is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of non-contact magnetic suspension bearings, and in particular relates to a three-degree-of-freedom hybrid magnetic bearing without a thrust disk which integrates radial and axial functions. Background Art

[0002] Magnetic bearings (MBs) are a new type of high-performance bearings with no mechanical contact between the rotor and the stator. Because they use electromagnetic force to directly suspend the rotor in space, they have many advantages such as no friction, long life, high speed and high precision. They are widely used in life sciences, flywheel energy storage, high-speed machine tools, aerospace and other occasions. According to the different ways of generating magnetic flux, magnetic bearings can be divided into passive, active and hybrid types. The control flux of hybrid magnetic bearings is generated by the energized coil, and the bias flux is generated by the permanent magnet, which is conducive to reducing the number of coil turns and the power loss of the drive circuit. According to the number of degrees of freedom controlled by the rotor, 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). The three-degree-of-freedom magnetic bearings that integrate radial-axial control are more compact in structure, short in axial length, and are conducive to increasing the critical speed of the rotor and reducing air friction losses.

[0003] The Chinese patent publication number CN101149077A, entitled "Permanent Magnet Biased Axial Radial Magnetic Bearing", proposes a radial-axial hybrid magnetic bearing that fixes the radial magnetic bearing inside the thrust magnetic bearing, is symmetrical about the radial plane, and can simultaneously control the radial two degrees of freedom and the axial degree of freedom. The structure uses two radially magnetized annular permanent magnets to establish a static bias magnetic field, has a long radial length, and has the problems of high cost, increased loss, poor dynamic response, and poor heat dissipation. The Chinese patent publication number CN101832335A, entitled "Permanent Magnet Biased Axial Radial Magnetic Bearing", proposes a structure in which the radial stator is a four-tooth two-pair magnetic pole structure, which requires the use of two bipolar or four unipolar DC power amplifiers, and has the disadvantages of a large number of power electronic switches, high cost, and low power density. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies of the prior art and to propose a novel three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing with compact structure, low cost and high load-bearing capacity and without a thrust disk.

[0005] The technical solution adopted by the asymmetric thrust-diskless three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing of the present invention is as follows: it includes a rotor, two three-pole radial stators and two three-pole axial stators, the rotor outer casing has two three-pole radial stators with the same structure located on both sides of the rotor center point and two three-pole axial stators with the same structure located on both sides of the rotor center point; a three-pole radial stator and a three-pole axial stator on the same side of the rotor center point respectively have a common stator yoke; a circular permanent magnet ring is fixedly embedded between the two stator yokes, and the permanent magnet ring is axially magnetized; the two three-pole radial stators have a common stator yoke. The projections of six three-pole radial stator poles on the radial section are evenly arranged in the circumferential direction; the three axial stator poles and the three radial stator poles on the same side of the rotor center point are evenly arranged in the circumferential direction; the three axial stator poles and the three radial stator poles of the three-pole axial stator on the same side of the rotor center point are evenly arranged in the circumferential direction; each radial stator pole is wound with a radial control coil, and an axial control coil is arranged in the three axial stator poles on the same side of the rotor center point; a set of annular bias flux adjustment coils is wound between the permanent magnet ring and the rotating shaft, and the bias flux adjustment coils are located on the inner side of the radial control coils.

[0006] Furthermore: the axial cross-section of the stator yoke part of each axial stator is U-shaped, and a set of annular axial control coils is arranged in each U-shaped yoke part. The two sets of axial control coils are connected in series in the same direction and driven and controlled by a bidirectional DC inverter.

[0007] Furthermore: the bias flux regulating coil has the same winding direction as the axial control coil and is located inside the radial control coil.

[0008] Furthermore: the radial control coils projected on two opposite radial stator magnetic poles on the radial cross section have the same winding direction, are connected in series in pairs and then connected in a star shape.

[0009] The advantages of the present invention are:

[0010] 1. The present invention adopts a structural design that integrates axial and radial functions. Compared with the combined structure of a two-degree-of-freedom radial magnetic bearing and a single-degree-of-freedom axial magnetic bearing, under the condition of the same power, the axial length of the motor system supported by the magnetic bearing is reduced, the structure is more compact, and the critical speed is increased.

[0011] 2. The present invention adopts a variable topology six-pole structure of two three-pole bearings with a rotational direction difference of 60 degrees, which optimizes the nonlinear problem caused by the asymmetry of the conventional three-pole structure, thereby reducing the nonlinearity of the suspension force and the coupling between the two radial degrees of freedom, and reducing the control difficulty. The radial control coils on the two opposite radial stator poles are connected in series to form a set of three-phase windings. The three-phase inverter drive is adopted to reduce the number of switch tubes, reduce power loss and driver cost.

[0012] 3. The present invention proposes a thrust plate-free design. Through the asymmetric axial stator structure design, the axial control part can directly act on the rotor. Compared with most radial-axial magnetic bearings that require an axial thrust plate, which causes the increase in rotor outer diameter and air wear problems, this structure effectively reduces the outer diameter of the rotor, thereby increasing the critical speed of the rotor and improving the dynamic performance of the rotor.

[0013] 4. The present invention adopts a hybrid magnetic bearing, which provides bias flux for radial and axial components at the same time through axially magnetized permanent magnets, and isolates the radial and axial control magnetic fields to achieve radial and axial control decoupling and reduce power loss. The control flux provided by the control coil generates a dynamic suspension force to overcome external disturbance forces and loads, improve the bearing capacity, and effectively reduce the coil current, thereby reducing power loss.

[0014] 5. The present invention is provided with a bias flux regulating coil, which can adjust the magnetization state of the permanent magnet, thereby adjusting the bias flux from the permanent magnet, reducing the impact of high-temperature demagnetization and other problems on the system. When a problem occurs with the permanent magnet, it can replace the permanent magnet in a short period of time to provide bias flux, thereby improving the fault tolerance of the bias flux and the operating stability of the magnetic bearing. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to explain the present invention more clearly, the technical solutions and advantages of the present invention are further described in detail below in conjunction with the accompanying drawings and specific embodiments;

[0016] Figure 1 It is a stereoscopic diagram of an asymmetric thrust-disk-free three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing of the present invention;

[0017] Figure 2 for Figure 1 A half-section diagram of

[0018] Figure 3 It is a schematic cross-sectional view of a radial plane of the present invention;

[0019] Figure 4 for Figure 3 Schematic diagram of axial cross-section of middle DD;

[0020] Figure 5 It is a schematic diagram of the radial magnetic circuit of the present invention;

[0021] Figure 6 It is a schematic diagram of the axial magnetic circuit of the present invention.

[0022] In the figure: 1. rotating shaft; 2. rotor; 31, 32. three-pole radial stator; 311, 321. stator yoke; 312, 322. radial stator poles; 41, 42. radial control coils; 5. radial air gap; 61, 62. three-pole axial stator; 611, 621. axial stator poles; 71, 72. axial control coils; 81, 82. axial air gap; 9. permanent magnet ring; 10. bias flux adjustment coil; 11. bias flux; 12. radial control flux; 13. axial control flux. DETAILED DESCRIPTION

[0023] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, the present invention comprises a rotating shaft 1, a rotor 2, two three-pole radial stators 31, 32 and two three-pole axial stators 61, 62, and the rotor 2 is fixedly sleeved at the middle position outside the rotating shaft 1.

[0024] Two three-pole radial stators 31, 32 and two three-pole axial stators 61, 62 are arranged outside the rotor 2, wherein the two three-pole radial stators 31, 32 have exactly the same structure and are respectively located on both sides of the center point of the rotor 2, and the axial distances between the two three-pole radial stators 31, 32 and the center point of the rotor 2 are equal.

[0025] The two three-pole axial stators 61 , 62 have completely the same structure and are respectively located on both sides of the center point of the rotor 2 . The axial distances between the two three-pole axial stators 61 , 62 and the center point of the rotor 2 are equal.

[0026] A three-pole radial stator 31 and a three-pole axial stator 61 on the same side of the center point of the rotor 2 have a common stator yoke 311, and a three-pole radial stator 32 and a three-pole axial stator 62 have a common stator yoke 321. The two stator yokes 311 and 321 have the same structure and are respectively located on both sides of the center point of the rotor 2, and the axial distance between them and the center point of the rotor 2 is equal.

[0027] 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 the outer diameter of the two stator yokes 311 , 321 , and the inner diameter of the permanent magnet ring 9 is larger than the inner diameter of the two stator yokes 311 , 321 .

[0028] The permanent magnet ring 9 is axially magnetized to isolate the radial and axial control magnetic fields, thereby achieving radial and axial control decoupling.

[0029] The three radial stator poles 312 of the first three-pole radial stator 31 are evenly arranged in the circumferential direction, and the three radial stator poles 322 of the second three-pole radial stator 32 are evenly arranged in the circumferential direction. The two three-pole radial stators 31 and 32 have a total of six radial stator poles 312 and 322. The radial stator poles 312 of the first three-pole radial stator 31 are rotated 60° relative to the radial stator poles 322 of the second three-pole radial stator 32 along the center line of the rotor 2, so that the two three-pole radial stators 31 and 32 differ by 60°. The projections of the six three-pole radial stator poles 312 and 322 of the two three-pole radial stators 31 and 32 on the radial cross section are evenly arranged in the circumferential direction. The two adjacent radial stator poles 312 and 322 projected on the radial cross section are 60° apart. One of the two adjacent radial stator poles 312 and 322 projected on the radial cross section belongs to the first radial stator 31, and the other belongs to the second radial stator 32.

[0030] Similarly, the three axial stator poles 611 of the first three-pole axial stator 61 are evenly arranged in the circumferential direction, and the three axial stator poles 621 of the second three-pole axial stator 62 are evenly arranged in the circumferential direction. The two three-pole axial stators 61 and 62 have a total of six axial stator poles 611 and 621.

[0031] 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 evenly arranged in the circumferential direction, so that the projection centers of the three axial stator poles 611 on one side of the center point of the rotor 2 and the three radial stator poles 312 on the other side on the radial cross section coincide with each other. The axial stator pole 611 of the first three-pole axial stator 61 is rotated 60° relative to the axial stator pole 621 of the second three-pole axial stator 62 along the center line of the rotor 2, and the two three-pole axial stators 611 and 621 differ by 60°. The projections of the six axial stator poles 611 and 621 on the radial cross section are evenly arranged in the circumferential direction, and coincide with the projection centers of the six radial stator poles 312 and 322 on the radial cross section in a one-to-one correspondence. Two adjacent axial stator poles 611 , 621 projected on the radial cross section are 60° apart, and one of the two adjacent axial stator poles 611 , 621 projected on the radial cross section belongs to the first three-pole axial stator 61 , and the other belongs to the second three-pole axial stator 62 .

[0032] The six radial stator poles 312, 322 of the magnetic bearing of the present invention extend radially from the inner walls of the corresponding stator yokes 311, 321 toward the rotor 2, leaving the same radial air gap 5 between them and the rotor 2, and the spacing of the radial air gap 5 is about 0.5 mm.

[0033] A radial control coil with the same number of turns is wound around each radial stator pole 312, 322. A radial control coil 41 is wound around the three radial stator poles 312 on the first three-pole radial stator 31, and a radial control coil 42 is wound around the three radial stator poles 322 on the second three-pole radial stator 32. The radial control coils 41, 42 on the two radial stator poles 312, 322 projected on the radial cross section have the same winding direction, and the radial control coils 41, 42 on the two radial stator poles 312, 322 projected on the radial cross section are connected in series in pairs and then star-linked to form a set of three-phase windings, which are driven by a three-phase inverter.

[0034] like Figure 3 As shown, the axial cross-section of each axial stator 61, 62 at the stator yoke 311, 321 is U-shaped, which is a U-shaped yoke portion, and the U-shape is used to install the axial control coils 71, 72. The rest of the stator yoke 311, 321 is annular, serving as the yoke portion 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 to the two end surfaces of the rotor 2 to form axial stator poles 611, 621. The six U-shaped side walls with axial stator poles 611, 621 coincide with the projection centers of the six radial stator poles 312, 322 on the radial cross-section in a one-to-one correspondence. The U-shaped side wall close to the center of the rotor 2 is fixedly connected to the permanent magnet ring 9.

[0035] Axial air gaps 81 , 82 are formed between the axial stator poles 611 , 621 and the end surface of the rotor 2 , and the spacing between the axial air gaps 81 , 82 is about 0.5 mm.

[0036] The radial distance between the axial stator poles 611 , 621 and the rotating shaft 1 should be much larger than the axial air gaps 81 , 82 .

[0037] An axial control coil 71, 72 is arranged in the U-shaped yoke of each three-pole axial stator 61, 62. Both sets of axial control coils 71, 72 are annular and coaxially sleeved outside the rotor 2 and do not contact the radial stator magnetic poles 312, 322. The two sets of axial control coils 71, 72 are wound in the same direction in series and driven and controlled by a bidirectional DC inverter.

[0038] A set of annular bias flux regulating coils 10 are wound between the permanent magnet ring 9 and the rotating shaft 2. The bias flux regulating coils 10 are coaxially sleeved on the outside of the rotor 2 and placed between the permanent magnet ring 9 and the rotating shaft 2, with the same winding direction as the axial control coils 71 and 72. The bias flux regulating coils 10 are located on the inner side of the radial control coils 41 and 42 and do not contact the radial control coils 41 and 42.

[0039] The rotor 2 and radial stator poles 312, 322 are all made of laminated silicon steel sheets, the stator yokes 311, 321 and the axial stators 61, 62 are made of the same magnetic conductive material, and the radial control coils 41, 42, axial control coils 71, 72 and bias flux regulating coil 10 are all wound with insulating varnished copper wires of the same specifications.

[0040] The width of the axial stator poles 611, 621 along the circumferential tangent direction is smaller than the width of the radial stator poles 312, 322 along the circumferential tangent direction. The end surface of the rotor 2 is flush with the end surface of the radial stator poles 312, 322. The inner diameter of the bias flux regulating coil 10 should be larger than the inner diameter of the radial stator poles 312, 322.

[0041] like Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, the axially magnetized permanent magnet ring 9 provides bias flux for both radial and axial component structures. Taking the A1 direction as an example, the path of the bias flux 11 generated is as follows: starting from the N pole of the permanent magnet ring 9, it passes through the stator yoke 311, the radial stator pole 312, the radial air gap 5, and the rotor 2 in sequence, and then evenly splits into two paths, passing through the radial air gap 5, the axial stator 62, and the axial air gap 82 to reach the axial stator pole 621, and finally returns to the S pole of the permanent magnet ring 9, forming a closed loop. For the A2 direction, the path of the bias flux 11 is as follows: starting from the N pole of the permanent magnet ring 9, it is evenly split into two paths at the axial stator 61, one path passes through the axial stator pole 611 and the axial air gap 81, and the other 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 pole 322, and finally returns to the S pole of the permanent magnet ring 9, forming a closed loop. When a positive or negative current is passed through the bias flux regulating coil 10, a bias flux loop with the same path will be generated, which is the same or opposite to the direction of the bias flux 11 generated by the permanent magnet ring 9, thereby adjusting the magnetization state of the permanent magnet and changing the bias field state of the magnetic bearing by superposition.

[0042] like Figure 5As shown, when the rotor 2 is located at the center position, the suspension forces generated by the bias flux 11 at the radial air gaps 5 of A1 and A2 are equal in magnitude and opposite in direction, and the rotor 2 remains balanced. When the rotor 2 is in a radial eccentric state (taking the A1A2 direction as an example), a positive current is passed through the radial control coil 41 in the A1 direction, and the path of the radial control flux 12 generated in the A1 direction is as follows: the magnetic flux is evenly divided into two paths after passing through the radial stator poles 31 and the radial stator yoke 311 in the A1 direction, and flows counterclockwise and clockwise to the radial stator poles 31 in the B1 direction and C1 direction, respectively, passes through the radial air gap 5 and the rotor 2, and flows around the rotor 2 to the A1 direction to merge with the radial air gap 5, and finally returns to the radial stator poles 31 in the A1 direction. When the same direction current is passed through the radial control coil 42 in the A2 direction, the radial control flux generated in the radial air gap 5 in the A2 direction has the same direction as that at A1. At the radial air gap in the A1 direction, the radial control flux 12 is superimposed with the bias flux 11, and at the radial air gap in the A2 direction, the radial control flux 12 is reduced with the bias flux 11, thereby generating a radial suspension force pointing in the A1 direction at the rotor 2. Passing a negative current into the radial control coils 41 and 42 in the A1 and A2 directions will generate a radial control flux 12 in the opposite direction, thereby generating a radial suspension force pointing in the A2 direction at the rotor 2. By simultaneously changing the magnitude and direction of the current in the radial control coils 41 and 42, the magnetic fluxes generated by the two three-pole bearings rotating in the bearing direction in the non-desired direction cancel each other out, thereby reducing the nonlinearity of the suspension force and the coupling between the two radial degrees of freedom, controlling the magnitude and direction of the radial suspension force, and achieving stable suspension of the rotor 2.

[0043] like Figure 6As shown, when the rotor 2 is in an axial eccentric state, the axial coils 71 and 72 can be used to perform axial control on the rotor 2. Taking the axial coil 71 at the axial stator 61 as an example, a positive current is passed into the axial coil 71, and the generated axial control magnetic flux 13 passes through the axial air gap 81 from the axial stator magnetic pole 611 to reach the rotor 2, and flows through the radial air gap 5 through the rotor 2 to return to the axial stator 61 to form a loop. At this time, the axial control magnetic flux 13 is superimposed on the bias magnetic flux 11 at the axial air gap 81, thereby generating an axial suspension force pointing to the right at the rotor 2. At this time, the axial control magnetic flux generated by passing the same current into the axial coil 72 at the radial air gap 5 is opposite to the magnetic flux generated by the axial coil 71 in the radial air gap 5, and the axial control has no interference with the radial direction, thereby realizing structural decoupling control. When a negative current is passed through the axial control coils 71 and 72, the axial control magnetic flux 13 formed is reduced by the bias magnetic flux 11 at the axial air gap 82, thereby generating an axial suspension force pointing to the left at the rotor 2. The axial stator magnetic poles 611 and 621 arranged in double layers in the axial direction allow part of the axial magnetic flux to directly act on the rotor 2 through the axial air gaps 81 and 82, thereby optimizing the axial thrust plate structure required for conventional axial magnetic bearings and shortening the radius size of the rotor 2. By changing the magnitude and direction of the current in the axial control coils 81 and 82, the magnitude and direction of the axial suspension force can be controlled, thereby achieving stable suspension of the rotor 2.

Claims

1. An asymmetric thrust-diskless three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing, characterized by: Includes a A rotor (2), two three-pole radial stators (31, 32) and two three-pole axial stators (61, 62), wherein the outer casing of the rotor (2) has two three-pole radial stators (31, 32) with the same structure and located respectively on both sides of the center point of the rotor (2) and two three-pole axial stators (61, 62) with the same structure and located respectively on both sides of the center point of the rotor (2); A three-pole radial stator (31, 32) and a three-pole axial stator (61, 62) on the same side of the center point of the rotor (2) have a common stator yoke (311, 321); A circular permanent magnet ring (9) is fixedly embedded between the two stator yokes (311, 321), and the permanent magnet ring (9) is axially magnetized; The projections of a total of six three-pole radial stator magnetic poles (312, 322) of the two three-pole radial stators (31, 32) on the radial cross section are evenly arranged in the circumferential direction; the three axial stator magnetic poles (611, 621) and the three radial stator magnetic poles (312, 322) on the same side of the center point of the rotor (2) are evenly arranged in the circumferential direction; Each radial stator magnetic pole (312, 322) is wound with a radial control coil (41, 42), and an axial control coil (71, 72) is provided in each of the 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 regulating coils (10) is wound between the permanent magnet ring (9) and the rotating shaft (2), and the bias magnetic flux regulating coils (10) are located on the inner side of the radial control coils (41, 42).

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

3. The asymmetric thrust-diskless three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing according to claim 1 is characterized by: The bias magnetic flux regulating coil (10) has the same winding direction as the axial control coils (71, 72) and is located inside the radial control coils (41, 42).

4. The asymmetric thrust-diskless three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing according to claim 1 is characterized by: The width of the axial stator magnetic poles (611, 621) along the circumferential tangent direction is smaller than the width of the radial stator magnetic poles (312, 322) along the circumferential tangent direction, the end surface of the rotor (2) is flush with the end surface of the radial stator magnetic poles (312, 322), and the inner diameter of the bias magnetic flux regulating coil (10) is larger than the inner diameter of the radial stator magnetic poles (312, 322).

5. The asymmetric thrust-diskless three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing according to claim 1 is characterized by: The axial distances between the two three-pole radial stators (31, 32) and the center point of the rotor (2) are equal, and the axial distances between the two three-pole axial stators (61, 62) and the center point of the rotor (2) are equal.

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

7. The asymmetric thrust-diskless three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing according to claim 1 is characterized by: The radial control coils (41, 42) projected on two radial stator magnetic poles (312, 322) opposite to each other on the radial cross section have the same winding direction and are connected in series in pairs in a star-shaped manner.

8. The asymmetric thrust-diskless three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing according to claim 1 is characterized by: An axial air gap is formed between the axial stator magnetic poles (611, 621) and the end surface of the rotor (2), and the radial distance between the axial stator magnetic poles (611, 621) and the rotor (2) is greater than the axial air gap.

9. The asymmetric thrust-diskless three-degree-of-freedom axial-radial double-piece hybrid magnetic bearing according to claim 1 is characterized by: The rotor (2) and radial stator magnetic poles (312, 322) are both made of laminated silicon steel sheets, the stator yokes (311, 321) and the axial stators (61, 62) are both made of the same magnetic conductive material, and the radial control coils (41, 42), the axial control coils (71, 72) and the bias flux regulating coil (10) are all wound with insulating varnished copper wires of the same specification.

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