Axial self-balancing three-degree-of-freedom magnetic bearing

Abstract

The axial self-balancing three-degree-of-freedom magnetic bearing is characterized in that a stator part comprises a stator yoke, a left attraction iron core, a right attraction iron core, a left repulsive iron core and a right repulsive iron core which are all mounted on an aluminum alloy bracket, and four poles wound with coils are uniformly distributed on the inner circumference of the stator yoke; an axial control winding is embedded in the attraction iron core, and a stator permanent magnet is embedded in the repulsive iron core. The rotor part comprises a rotor core and a rotating shaft, a radial air gap and an axial air gap are respectively arranged between the rotor core and the radial iron core, between the attraction iron core and the repulsive force iron core, rotor permanent magnets are arranged on two sides of the rotor core and at positions corresponding to the stator permanent magnets of the repulsive force iron core, and the polarities of the stator permanent magnets and the rotor permanent magnets facing the axial air gap are the same. The radial magnetic flux magnetic circuit, the axial control magnetic flux magnetic circuit and the permanent magnetic flux magnetic circuit are completely independent and free of coupling, axial static balance of the rotor is achieved, suspension is achieved in the radial direction, control is easy, and the controllable suspension force is large.

Description

Technical Field

[0001] The present invention relates to the technical field of bearing manufacturing, and particularly to an axial self-balancing three-degree-of-freedom magnetic bearing with simple control, manufacturing and assembly, independent radial control magnetic flux and bias magnetic flux generated by permanent magnets, and neither axial nor radial control magnetic flux passing through permanent magnets, which can generate greater axial and radial suspension forces. Background Art

[0002] Magnetic bearings use magnetic suspension forces to achieve stable suspension of the rotor, and magnetic bearings are used to replace traditional mechanical bearings to support the motor rotor. It not only effectively solves common problems such as vibration, wear and friction in mechanical bearings, but also avoids dependence on lubrication, making the magnetic bearing more stable and reliable during operation. The unique design principle of the magnetic bearing, especially its operating characteristics in a non-contact state, enables it to exhibit excellent performance in high-speed and high-precision working environments.

[0003] At present, three-degree-of-freedom hybrid magnetic bearings have been widely used due to their high integration and small volume, that is, they generate both radial and axial suspension forces in one unit. Its structure often uses a permanent magnet passing through both axial and radial air gaps at the same time, and then superimposes with the axial suspension magnetic flux and the radial suspension magnetic flux at the air gap respectively to generate three-degree-of-freedom suspension forces. Since the radial magnetic flux and the axial magnetic flux share the air gap, the axial suspension magnetic circuit is relatively long, resulting in large magnetic leakage and power consumption, and the amplitudes of the permanent magnetic flux and the suspension winding magnetic flux at the air gap are only 0.5 times the amplitude of the saturated air gap magnetic density. Summary of the Invention

[0004] Object of the Invention: The present invention aims to solve the limitations of existing three-degree-of-freedom magnetic bearings. Through innovative design, an axial self-balancing three-degree-of-freedom magnetic bearing is proposed, which simplifies the control, manufacturing and assembly processes, and the radial and axial control magnetic fluxes are independent of the suspension magnetic fluxes generated by permanent magnets, thereby achieving greater radial and axial suspension forces under low power consumption conditions.

[0005] Technical Solution: The present invention discloses an axial self-balancing three-degree-of-freedom magnetic bearing, including a stator part and a rotor part.

[0006] The rotor part includes a rotating shaft and a rotor core; on both sides of the rotor core near the rotating shaft side, a left inner permanent magnet ring and a right inner permanent magnet ring are embedded.

[0007] The stator part includes an aluminum alloy bracket, a stator yoke and radial stator poles; radial control windings are wound on each radial stator pole; the stator yoke is fixed inside the aluminum alloy bracket, and radial stator poles are arranged inside the stator yoke.

[0008] On the inner side of the aluminum alloy bracket, a left axial suction iron core and a right axial suction iron core are respectively fixed axially; left and right axial control windings are embedded in the left axial suction iron core and the right axial suction iron core, and a left axial control air gap and a right axial control air gap are respectively provided between them and the rotor iron core;

[0009] On the inner side of the aluminum alloy bracket opposite to the left inner permanent magnet ring and the right inner permanent magnet ring, a left axial repulsive iron core and a right axial repulsive iron core are also respectively fixed axially. Left and right outer permanent magnet rings are embedded in the left axial repulsive iron core and the right axial repulsive iron core. The left outer permanent magnet ring and the right outer permanent magnet ring are axially opposite to the left inner permanent magnet ring and the right inner permanent magnet ring, and a left permanent magnet suspension air gap and a right permanent magnet suspension air gap are provided between them;

[0010] The left outer permanent magnet ring, the right outer permanent magnet ring, the left inner permanent magnet ring, and the right inner permanent magnet ring are all magnetized axially. The opposite magnetic poles of the left outer permanent magnet ring and the left inner permanent magnet ring at the left axial offset air gap are N-N or S-S, forming a repulsive force; the opposite magnetic poles of the right outer permanent magnet ring and the right inner permanent magnet ring at the right axial offset air gap are N-N or S-S, forming a repulsive force;

[0011] A radial suspension air gap is formed between the rotor iron core and the radial stator poles.

[0012] Further, the radial control windings in each of the four directions of +X direction, -X direction, +Y direction, and -Y are connected in series to form an independent suspension winding driven by a switching power amplifier. After the suspension winding is energized, a total of four suspension winding magnetic fields are generated, and the suspension winding magnetic fields form a closed path between the radial stator poles, the stator yoke, the rotor iron core, and the radial suspension air gap.

[0013] Further, one side of the left outer permanent magnet ring and the left inner permanent magnet ring close to the left axial offset air gap is the N pole, and one side of the right outer permanent magnet ring and the right inner permanent magnet ring close to the right axial offset air gap is the N pole.

[0014] Further, the left outer permanent magnet ring, the left inner permanent magnet ring, the right outer permanent magnet ring, and the right inner permanent magnet ring form permanent magnet magnetic fields one, two, three, and four; the permanent magnet magnetic fields generated by each permanent magnet ring are divided into two at the offset working air gap and enter the permanent magnet suspension air gap along the axial direction, specifically as follows:

[0015] The permanent magnet magnetic field one starts from the N pole of the left outer permanent magnet ring, passes through the left permanent magnet suspension air gap and the left axial repulsive iron core, and then returns to the S pole of the left outer permanent magnet ring;

[0016] The permanent magnet magnetic field two starts from the N pole of the left inner permanent magnet ring, passes through the left permanent magnet suspension air gap and the rotor iron core, and then returns to the S pole of the left inner permanent magnet ring;

[0017] The permanent magnet magnetic field three starts from the N pole of the right outer permanent magnet ring, passes through the right permanent magnet suspension air gap and the right axial repulsive iron core, and then returns to the S pole of the right outer permanent magnet ring;

[0018] The permanent magnet magnetic field four starts from the N pole of the right inner permanent magnet ring, passes through the right permanent magnet suspension air gap and the rotor iron core, and then returns to the S pole of the right inner permanent magnet ring.

[0019] Furthermore, after the left and right axial control windings are energized, a left axial suspension winding magnetic field and a right axial suspension winding magnetic field are generated;

[0020] The left axial suspension winding magnetic field passes through the left axial suction iron core, the left axial control air gap, the rotor iron core, and the left axial control air gap, and then returns to the left axial suction iron core to form a closed path;

[0021] The right axial suspension winding magnetic field passes through the right axial suction iron core, the right axial control air gap, the rotor iron core, and the right axial control air gap, and then returns to the right axial suction iron core to form a closed path.

[0022] Furthermore, the stator yoke, the left and right axial repulsive iron cores, the left and right axial suction iron cores, the radial stator magnetic poles, and the rotor iron core are all made of materials with radial magnetic conductivity; the left and right outer permanent magnet rings, the left and right inner permanent magnet rings are made of rare earth permanent magnet materials.

[0023] Furthermore, the suspension force is composed of a controllable suspension force and an uncontrollable suspension force, and the range of the uncontrollable suspension force is selected to be 1.1 times - 1.2 times the axial offset bearing capacity F z , in order to reserve a control margin of 10% to 20%.

[0024] Furthermore, the parameter calculation process of the left and right outer permanent magnet rings, the left and right inner permanent magnet rings:

[0025] First, determine the axial offset bearing capacity F, and determine the axial area S of a single permanent magnet ring from the formula Then, obtain the axial magnetization length of the permanent magnet ring from the formula pm ; in the formula, B is the air gap saturation magnetic induction intensity, R max is the internal magnetic resistance of the permanent magnet ring, H pm is the coercivity of the permanent magnet ring, L c is the axial magnetization length of the permanent magnet ring. pm is the axial magnetization length of the permanent magnet ring.

[0026] Furthermore, the parameter calculation process of the radial control winding:

[0027] Determining winding parameters by controllable suspension force, the forces exerted on the rotor by two magnetic poles in a certain direction both have angles. Taking the magnetic pulling force F of the magnetic pole group in the +X direction x1 The mathematical expression is:

[0028]

[0029] In the formula, F1 is the magnetic pulling force generated by a single magnetic pole, θ represents the angle of the magnetic pole in the vertical direction, that is, 45 degrees, S represents the area of a single magnetic pole, δ represents the radial air-gap length, μ0 represents the air permeability, B0 represents the air-gap magnetic induction intensity, N represents the number of turns of the winding on each magnetic pole, and I represents the magnitude of the current flowing through the winding;

[0030] After determining the radial air-gap length δ and the area S of a single magnetic pole, the product value of the number of turns N and the current I is obtained from the radial force; the operations in the +Y direction, -X direction, and -Y direction are the same.

[0031] Compared with the prior art, the present invention has the following obvious advantages:

[0032] First: The present invention consists of four axially magnetized annular permanent magnets divided into two groups, which are used to provide permanent magnetic flux independent of the control magnetic flux. The radial control winding generates radial control magnetic flux, and two axial control windings generate axial control magnetic flux. Under the combined action of the control magnetic flux and the bias magnetic flux, it ensures the uniformity of the air gap between the stator and the rotor in the radial and axial directions, and realizes the stable suspension of the rotor. By isolating the radial and axial passive suspension parts from the active suspension parts, the bias magnetic flux and the control magnetic flux do not share the magnetic path, effectively reducing the non-linearity between the control current and the controllable bearing capacity, reducing the control difficulty of the system, improving the sensitivity of the radial and axial control currents, improving the axial bearing capacity to a certain extent, and in addition, it can also reduce the processing difficulty of the entire suspension system and reduce the production and processing costs.

[0033] Second: The permanent magnetic flux generated by each permanent magnetic ring is divided into two parts at the bias working air gap and enters the permanent magnetic suspension air gap along the axial direction, and returns to its respective permanent magnet. The radial control winding generates radial control magnetic flux passing through the radial stator magnetic poles, the radial suspension air gap, the rotor core, and the stator yoke to form a closed path. The axial control winding generates axial control magnetic flux passing through the suction core, the axial control air gap, the rotor core, and the axial control air gap back to the suction core to form a closed path, which has no coupling with the permanent magnetic flux, and has the advantages of generating a large suspension force, low power consumption, simple control, and easy processing. The magnetic flux density of the radial suspension winding magnetic field at the radial suspension air gap reaches the maximum saturation magnetic density, breaking through the limitation that the permanent magnetic flux density and the control magnetic flux density at the air gap of the traditional hybrid magnetic bearing are only 0.5 times the saturation air-gap magnetic density

[0034] Third: The present invention can be widely used in fields such as flywheel energy storage, various high-speed machine tool spindle motors, high-speed fans, centrifuges, compressors, and small hard disk drive assemblies. Description of the Drawings

[0035] Figure 1 This is a schematic diagram of the radial structure and radial control magnetic flux of an axially self - balanced three - degree - of - freedom magnetic bearing according to the present invention;

[0036] Figure 2 This is a schematic diagram of the axial structure and magnetic flux of an axially self - balanced three - degree - of - freedom magnetic bearing according to the present invention. Detailed Embodiment

[0037] The present invention will be further described below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and cannot be used to limit the protection scope of the present invention.

[0038] The present invention provides an axially self - balanced three - degree - of - freedom magnetic bearing, which includes a stator part and a rotor part.

[0039] The rotor part includes: a rotating shaft 7 and a rotor core 5. On both sides of the rotor core 5, a left - hand inner permanent magnet ring 18 and a right - hand inner permanent magnet ring 20 are placed close to the rotating shaft.

[0040] The stator part includes: an aluminum alloy bracket 25, a stator yoke 1 and radial stator poles 3. A radial control winding 4 is wound around each pole. The stator yoke 1 is fixed inside the aluminum alloy bracket 25, and the radial stator poles 3 are arranged inside the stator yoke 1.

[0041] On the inner side of the aluminum alloy bracket 25, a left - hand axial suction iron core 10 and a right - hand axial suction iron core 12 are axially fixed respectively. Left - hand and right - hand axial control windings are embedded in the left - hand axial suction iron core 10 and the right - hand axial suction iron core 12, and a left - hand axial control air gap 11 and a right - hand axial control air gap 13 are respectively provided between them and the rotor core 5.

[0042] On the inner side of the aluminum alloy bracket 25 axially opposite to the left - hand inner permanent magnet ring 18 and the right - hand inner permanent magnet ring 20, a left - hand axial repulsion iron core 14 and a right - hand axial repulsion iron core 15 are also axially fixed respectively. Left - hand and right - hand outer permanent magnet rings 17 and 19 are further embedded in the left - hand axial repulsion iron core 14 and the right - hand axial repulsion iron core 15. The left - hand outer permanent magnet ring 17 and the right - hand outer permanent magnet ring 19 are axially opposite to the left - hand inner permanent magnet ring 18 and the right - hand inner permanent magnet ring 20, and a left - hand permanent magnet suspension air gap 26 and a right - hand permanent magnet suspension air gap 6 are provided between them. All the suction iron cores and repulsion iron cores are fixed on the aluminum alloy bracket 25.

[0043] The left outer permanent magnet ring 17, the right outer permanent magnet ring 19, the left inner permanent magnet ring 18, and the right inner permanent magnet ring 20 are all magnetized axially. The opposite magnetic poles of the left outer permanent magnet ring 17 and the left inner permanent magnet ring 18 at the left permanent magnet suspension air gap 26 are N-N or S-S, forming a repulsive force. The opposite magnetic poles of the right outer permanent magnet ring 19 and the right inner permanent magnet ring 20 at the right permanent magnet suspension air gap 6 are N-N or S-S, forming a repulsive force. Refer to Figure 2 In this embodiment, the magnetic poles on one side of the left outer permanent magnet ring 17 and the left inner permanent magnet ring 18 close to the left permanent magnet suspension air gap 26 are N poles, and the magnetic poles on one side of the right outer permanent magnet ring 19 and the right inner permanent magnet ring 20 close to the right permanent magnet suspension air gap 6 are N poles.

[0044] A radial suspension air gap 8 is formed between the rotor core 5 and the radial stator poles 3.

[0045] The left outer permanent magnet ring 17, the left inner permanent magnet ring 18, the right outer permanent magnet ring 19, and the right inner permanent magnet ring 20 form permanent magnet magnetic fields one 21, two 22, three 23, and four 24; the permanent magnet magnetic fields generated by each permanent magnet ring are divided into two parts at the bias working air gap and enter the permanent magnet suspension air gap along the axial direction, specifically as follows:

[0046] The upper and lower two parts of the divided permanent magnet magnetic field one 21 start from the N pole of the left outer permanent magnet ring 17, pass through the left permanent magnet suspension air gap 26 and the left axial repulsive force core 14, and then return to the S pole of the left outer permanent magnet ring 17.

[0047] The upper and lower two parts of the divided permanent magnet magnetic field two 22 start from the N pole of the left inner permanent magnet ring 18, pass through the left permanent magnet suspension air gap 26 and the rotor core 5, and then return to the S pole of the left inner permanent magnet ring 18.

[0048] The upper and lower two parts of the divided permanent magnet magnetic field three 23 start from the N pole of the right outer permanent magnet ring 19, pass through the right permanent magnet suspension air gap 6 and the right axial repulsive force core 15, and then return to the S pole of the right outer permanent magnet ring 19;

[0049] The upper and lower two parts of the divided permanent magnet magnetic field four 24 start from the N pole of the right inner permanent magnet ring 20, pass through the right permanent magnet suspension air gap 6 and the rotor core 5, and then return to the S pole of the right inner permanent magnet ring 20.

[0050] After the left and right axial control windings are energized, a left axial suspension winding magnetic field 9 and a right axial suspension winding magnetic field 27 are generated.

[0051] The left axial suspension winding magnetic field 9 passes through the left axial suction core 10, the left axial control air gap 11, the rotor core 5, and the left axial control air gap 11, and then returns to the left axial suction core 10 to form a closed path.

[0052] The magnetic field 27 of the right - hand axial suspension winding passes through the right - hand axial suction core 12, the right - hand axial control air gap 13, the rotor core 5, and the right - hand axial control air gap 12, and then returns to the right - hand axial suction core 12 to form a closed path.

[0053] Each radial stator pole 3 is wound with a radial control winding 4. The windings in the four directions of +X, -X, +Y, and -Y are connected in series to form an independent suspension winding, which is driven by a switching power amplifier. After each suspension winding is energized, a total of four suspension winding magnetic fields 2 are generated. The suspension winding magnetic field 2 only forms a closed path among the stator pole 3, the stator yoke 1, the rotor core 5, and the radial suspension air gap 8, and has no coupling with the permanent - magnet magnetic field one 21, the permanent - magnet magnetic field two 22, the permanent - magnet magnetic field three 23, the permanent - magnet magnetic field four 24, the left - hand axial suspension winding magnetic field 9, and the right - hand axial suspension winding magnetic field 27. This can make the magnetic flux density of the radial suspension winding magnetic field 2 reach the maximum saturation magnetic density at the radial suspension air gap 8, breaking through the limitation that the permanent - magnet magnetic flux density and the control magnetic flux density at the air gap of the traditional hybrid magnetic bearing are only 0.5 times the saturation air - gap magnetic density.

[0054] The stator yoke 1, the left - hand axial repulsive core 14 and the right - hand axial repulsive core 15, the left - hand axial suction core 10 and the right - hand axial suction core 12, the radial stator pole 3, and the rotor core 5 are all made of materials with good radial magnetic - conduction performance. The left - hand outer permanent - magnet ring 17, the left - hand inner permanent - magnet ring 18, the right - hand outer permanent - magnet ring 19, and the right - hand inner permanent - magnet ring 20 are made of rare - earth permanent - magnet materials with good magnetic - conduction performance.

[0055] The suspension force is composed of a controllable suspension force and an uncontrollable suspension force. The range of the uncontrollable suspension force is selected to be 1.1 times - 1.2 times the axial offset load - bearing capacity F z , in order to reserve a control margin of 10% to 20%.

[0056] The parameter calculation process of the left - hand outer permanent - magnet ring 17, the left - hand inner permanent - magnet ring 18, the right - hand outer permanent - magnet ring 19, and the right - hand inner permanent - magnet ring 20: First, determine the axial offset load - bearing capacity F. From the formula , the axial area S of a single permanent - magnet ring can be determined pm . Then, from the formula , the axial magnetization length of the permanent - magnet ring can be obtained. In the formula, B max is the saturation magnetic induction intensity of the air gap, generally set to 1.2T, which can be adjusted appropriately according to the materials used. R pm is the internal magnetic resistance of the permanent - magnet, H c is the coercivity of the permanent - magnet, and L pm is the axial magnetization length of the permanent - magnet.

[0057] Calculation process of parameters of the radial control winding 4: Determine the winding parameters from the controllable suspension force. From the radial diagram, it can be seen that the forces exerted by two magnetic poles in a certain direction on the rotor have angles. Taking the positive direction of the X-axis as an example, the magnetic pulling force F of the upper magnetic pole group x1 The mathematical expression of is:

[0058]

[0059] In the formula, F1 is the magnetic pulling force generated by a single magnetic pole, θ represents the angle of the magnetic pole in the vertical direction, that is, 45 degrees, S represents the area of a single magnetic pole, δ represents the radial air-gap length, μ0 represents the air permeability, B0 represents the air-gap magnetic induction intensity, N represents the number of turns of the winding on each magnetic pole, and I represents the magnitude of the current flowing through the winding.

[0060] After determining the radial air-gap length δ and the area S of a single magnetic pole, the product value of the number of turns N and the current I is obtained from the radial force; the operations in the +Y direction, -X direction, and -Y direction are the same.

[0061] The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. An axially self - balanced three - degree - of - freedom magnetic bearing, comprising a stator part and a rotor part, characterized in that: The rotor part includes a rotating shaft (7) and a rotor core (5); on both sides of the rotor core (5) near the rotating shaft side, a left - hand inner permanent - magnet ring (18) and a right - hand inner permanent - magnet ring (20) are embedded; The stator part includes an aluminum - alloy bracket (25), a stator yoke (1), and radial stator poles (3); a radial control winding (4) is wound on each radial stator pole (3); the stator yoke (1) is fixed inside the aluminum - alloy bracket (25), and the radial stator poles (3) are arranged inside the stator yoke (1); On the inner side of the aluminum - alloy bracket (25) axially, a left - hand axial - suction iron core (10) and a right - hand axial - suction iron core (12) are respectively fixed; left - hand and right - hand axial control windings are embedded in the left - hand axial - suction iron core (10) and the right - hand axial - suction iron core (12), and a left - hand axial control air - gap (11) and a right - hand axial control air - gap (13) are respectively provided between them and the rotor core (5); On the inner side of the aluminum - alloy bracket (25) axially, which is opposite to the left - hand inner permanent - magnet ring (18) and the right - hand inner permanent - magnet ring (20), a left - hand axial - repulsion iron core (14) and a right - hand axial - repulsion iron core (15) are respectively fixed; a left - hand outer permanent - magnet ring (17) and a right - hand outer permanent - magnet ring (19) are also embedded in the left - hand axial - repulsion iron core (14) and the right - hand axial - repulsion iron core (15); the left - hand outer permanent - magnet ring (17) and the right - hand outer permanent - magnet ring (19) are axially opposite to the left - hand inner permanent - magnet ring (18) and the right - hand inner permanent - magnet ring (20), and a left - hand permanent - magnet suspension air - gap (26) and a right - hand permanent - magnet suspension air - gap (6) are provided between them; The left - hand outer permanent - magnet ring (17), the right - hand outer permanent - magnet ring (19), the left - hand inner permanent - magnet ring (18), and the right - hand inner permanent - magnet ring (20) are all magnetized axially. The opposite magnetic poles of the left - hand outer permanent - magnet ring (17) and the left - hand inner permanent - magnet ring (18) at the left - hand permanent - magnet suspension air - gap (26) are N - N or S - S, forming a repulsive force; the opposite magnetic poles of the right - hand outer permanent - magnet ring (19) and the right - hand inner permanent - magnet ring (20) at the right - hand permanent - magnet suspension air - gap (6) are N - N or S - S, forming a repulsive force; A radial suspension air - gap (8) is formed between the rotor core (5) and the radial stator poles (3).

2. The axial self-balancing three-degree-of-freedom magnetic bearing according to claim 1, wherein: The radial control windings (4) in the +X direction, -X direction, +Y direction, and -Y direction are connected in series to form an independent suspension winding, which is driven by a switching power amplifier. After the suspension winding is energized, a total of four suspension - winding magnetic fields (2) are generated. The suspension - winding magnetic fields (2) form a closed path among the radial stator poles (3), the stator yoke (1), the rotor core (5), and the radial suspension air - gap (8).

3. The axial self-balancing three-degree-of-freedom magnetic bearing according to claim 1, characterized in that: One side of the left - hand outer permanent - magnet ring (17) and the left - hand inner permanent - magnet ring (18) near the left - hand permanent - magnet suspension air - gap (26) is the N - pole, and one side of the right - hand outer permanent - magnet ring (19) and the right - hand inner permanent - magnet ring (20) near the right - hand permanent - magnet suspension air - gap (6) is the N - pole.

4. The axial self-balancing three-degree-of-freedom magnetic bearing according to claim 3, wherein: The left outer permanent magnet ring (17), left inner permanent magnet ring (18), right outer permanent magnet ring (19), and right inner permanent magnet ring (20) form permanent magnet magnetic fields one (21), two (22), three (23), and four (24); the permanent magnet magnetic fields generated by each permanent magnet ring are split into two at the biased working air gap and enter the permanent magnet suspension air gap along the axial direction, specifically as follows: The upper and lower parts of the split permanent magnet magnetic field one (21) start from the N pole of the left outer permanent magnet ring (17), pass through the left permanent magnet suspension air gap (26) and the left axial repulsive iron core (14), and then return to the S pole of the left outer permanent magnet ring (17); The upper and lower parts of the split permanent magnet magnetic field two (22) start from the N pole of the left inner permanent magnet ring (18), pass through the left permanent magnet suspension air gap (26) and the rotor iron core (5), and then return to the S pole of the left inner permanent magnet ring (18); The upper and lower parts of the split permanent magnet magnetic field three (23) start from the N pole of the right outer permanent magnet ring (19), pass through the right permanent magnet suspension air gap (6) and the right axial repulsive iron core (15), and then return to the S pole of the right outer permanent magnet ring (19); The upper and lower parts of the split permanent magnet magnetic field four (24) start from the N pole of the right inner permanent magnet ring (20), pass through the right permanent magnet suspension air gap (6) and the rotor iron core (5), and then return to the S pole of the right inner permanent magnet ring (20).

5. The axial self-balancing three-degree-of-freedom magnetic bearing according to claim 1, characterized in that: After the left and right axial control windings are energized, they generate a left axial suspension winding magnetic field (9) and a right axial suspension winding magnetic field (27); The left axial suspension winding magnetic field (9) passes through the left axial suction iron core (10), left axial control air gap (11), rotor iron core (5), left axial control air gap (11), and then returns to the left axial suction iron core (10) to form a closed path; The right axial suspension winding magnetic field (27) passes through the right axial suction iron core (12), right axial control air gap (13), rotor iron core (5), right axial control air gap (12), and then returns to the right axial suction iron core (12) to form a closed path.

6. The axial self-balancing three-degree-of-freedom magnetic bearing according to claim 1, wherein: The stator yoke (1), left axial repulsive iron core (14) and right axial repulsive iron core (15), left axial suction iron core (10) and right axial suction iron core (12), radial stator poles (3), and rotor iron core (5) are all made of materials with radial magnetic conductivity; the left outer permanent magnet ring (17), right outer permanent magnet ring (19), left inner permanent magnet ring (18), and right inner permanent magnet ring (20) are made of rare earth permanent magnet materials.

7. The axial self-balancing three-degree-of-freedom magnetic bearing according to any one of claims 1 to 6, characterized in that: The levitation force consists of a controllable levitation force and an uncontrollable levitation force. The range of the uncontrollable levitation force is selected to be 1.1 times to 1.2 times the axial offset bearing capacity F z , so as to reserve a control margin of 10% to 20%. Among them, the parameter calculation process of the left outer permanent magnet ring (17), the right outer permanent magnet ring (19), the left inner permanent magnet ring (18), and the right inner permanent magnet ring (20) is as follows: First, determine the axial offset bearing capacity F z , and from the formula determine the axial area S of a single permanent magnet ring pm , and then from the formula obtain the axial magnetization length of the permanent magnet ring; where B max is the air-gap saturation magnetic induction intensity, R pm is the internal magnetic resistance of the permanent magnet ring, H c is the coercivity of the permanent magnet ring, L pm is the axial magnetization length of the permanent magnet ring.

8. The axial self-balancing three-degree-of-freedom magnetic bearing according to any one of claims 1 to 6, characterized in that: The parameters of the radial control winding (4) are determined by the controllable suspension force. The forces exerted by two magnetic poles in a certain direction on the rotor have angles. The magnetic pulling force F of the magnetic pole group in the +X direction x1 has the following mathematical expression: In the formula, F1 is the magnetic pulling force generated by a single pole, θ represents the angle of the pole in the vertical direction, which is 45 degrees, S represents the area of a single pole, δ represents the radial air gap length, μ0 represents the air magnetic permeability, B0 represents the air gap magnetic induction intensity, N represents the number of turns of the winding on each pole, and I represents the magnitude of the current flowing through the winding; After determining the radial air gap length δ and the area S of a single pole, the product value of the number of turns N and the current I is obtained from the radial force; the operations in the +Y direction, -X direction, and -Y direction are the same.

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