An asymmetric rotor structure of a permanent magnet assisted bearingless synchronous reluctance motor

Abstract

The present invention discloses an asymmetric rotor structure of a permanent magnet-assisted bearingless synchronous reluctance motor. Four groups of U-shaped magnetic barriers are evenly arranged along the circumferential direction inside the rotor. Each group of U-shaped magnetic barriers is divided into an outer layer, a middle layer, and an inner layer. The openings of the three layers of magnetic barriers face outward, and a permanent magnet is embedded in the center of the bottom wall of each layer of magnetic barriers. The outer and middle layers of magnetic barriers are symmetrical about the d-axis. One of the outer sections of the U-shaped side walls of the inner layer of magnetic barriers extends a small rectangular magnetic barrier parallel to the q-axis in the q-axis direction at the end facing the q-axis. A first small rectangular permanent magnet is fixedly embedded in the small rectangular magnetic barrier. A second small rectangular permanent magnet perpendicular to the first small rectangular permanent magnet is fixedly embedded in the outer section of the U-shaped side wall with the small rectangular magnetic barrier, forming a rotor topology in which both the magnetic barriers and the permanent magnets are asymmetric. The reluctance torque and the permanent magnet torque reach peak values ​​at similar or even the same current angles, thereby increasing the output torque synthesized by the reluctance torque and the permanent magnet torque.

Description

Technical Field

[0001] The present invention belongs to the field of motor manufacturing and control, and relates to a permanent magnet assisted bearingless synchronous reluctance motor, specifically an asymmetric rotor structure of a permanent magnet assisted bearingless synchronous reluctance motor suitable for high-speed applications. Background Art

[0002] A bearingless motor is an AC motor with a novel and unique structure and principle. Its stator torque winding is stacked with a suspension winding whose pole pairs differ by one. By controlling the current flowing into these two windings, electromagnetic torque and radial suspension force can be generated simultaneously. Permanent magnet-assisted synchronous reluctance motors (PMAMs) offer advantages in torque density and efficiency, and are gaining increasing attention in industrial applications. Therefore, PMAMs combine the advantages of magnetic bearings and PMAMs, fully utilizing both reluctance torque and permanent magnet torque. Existing PMAMs have three layers of magnetic barriers, each designed with an irregular curved shape. By embedding varying numbers of block permanent magnets within the barriers, each layer of irregular magnetic barriers is filled to the maximum extent possible. This unique design alters the magnetic circuit on the rotor, affecting the direction of the motor's magnetic field lines and thus improving the motor's resistance to demagnetization. However, these designs suffer from low permanent magnet torque utilization and increased cost. After analyzing the influence of rotor geometry on torque harmonics, and based on the analysis results, the current permanent magnet assisted synchronous reluctance motor has two types of rotor laminations, namely "R"-type laminations and "J"-type laminations. These two types of laminations are combined axially asymmetrically to form a "Machaon" structure. Experimental results show that the torque ripple of the permanent magnet assisted synchronous reluctance motor with this rotor structure is only one-third of the original, but the torque performance is reduced.

[0003] The document with Chinese patent application number CN201911242920.3 discloses a permanent magnet-assisted bearingless synchronous reluctance motor that can effectively reduce torque and suspension force pulsation. The boundary line of its magnetic isolation bridge is composed of a quadratic function curve and a Bezier curve, and is no longer composed of a single curve. This makes the shape of the magnetic isolation bridge more flexible, effectively reducing torque and suspension force pulsation. However, its magnetic barrier structure and permanent magnet position distribution do not maximize the reluctance torque and permanent magnet torque, resulting in low permanent magnet utilization and low torque density. The document with Chinese patent application number CN201810623454.2 discloses a high torque density asymmetric rotor structure, whose rotor structure is composed of a unidirectional offset asymmetric rotor structure and a bidirectional offset asymmetric rotor structure. Both use ferrite permanent magnets and neodymium iron boron permanent magnets, respectively. The ferrite permanent magnets are alternately magnetized in the circumferential tangential direction, and the neodymium iron boron permanent magnets are alternately magnetized in the radial direction. The "magnetic concentration effect" is used to effectively improve the utilization rate and torque density of the permanent magnet material. However, the overall structure of the rotor adopts a block-based modular component structure, which increases the manufacturing difficulty, and the permanent magnet material uses neodymium iron boron permanent magnets, which is relatively expensive.

[0004] Therefore, while selecting suitable permanent magnet materials, how to design the rotor structure of the motor to obtain a permanent magnet assisted bearingless synchronous reluctance motor with high torque density and high power density has become a key issue for the further development of the current permanent magnet assisted bearingless synchronous reluctance motor. Summary of the Invention

[0005] The purpose of the present invention is to propose an asymmetric rotor structure of a permanent magnet assisted bearingless synchronous reluctance motor to solve the problems of low torque density and suspension force density and low power factor under high-speed operation of existing permanent magnet assisted bearingless synchronous reluctance motors, thereby achieving stable suspension and efficient operation of the motor rotor and better application in electrical transmission systems.

[0006] To achieve the above-mentioned purpose, the present invention adopts a technical solution of an asymmetric rotor structure of a permanent magnet assisted bearingless synchronous reluctance motor: the rotor is coaxially located inside the stator, and four groups of U-shaped magnetic barriers are evenly arranged inside the rotor along the circumferential direction, each group of U-shaped magnetic barriers is divided into an outer layer, a middle layer and an inner layer of magnetic barriers, the openings of the three layers of magnetic barriers face outward, and a permanent magnet is embedded in the middle of the bottom wall of each layer of magnetic barriers; the two U-shaped side walls of each layer of magnetic barriers are seamlessly connected from the inside to the outside by an inner section of the U-shaped side wall, a middle section of the U-shaped side wall and an outer section of the U-shaped side wall; the outer and middle layer magnetic barriers are symmetrical about the d axis, and one of the outer sections of the U-shaped side wall of the inner layer of magnetic barriers extends a small rectangular magnetic barrier parallel to the q axis in the direction of the q axis at the end facing the q axis, and the small rectangular magnetic barrier is fixedly embedded in the small magnetic barrier. There is a first rectangular small permanent magnet, and a second rectangular small permanent magnet perpendicular to the first rectangular small permanent magnet is fixedly embedded in the outer section of the U-shaped side wall with the rectangular small magnetic barrier. The thickness of the second rectangular small permanent magnet is the same as the thickness of the outer section of the U-shaped side wall. On the same set of U-shaped magnetic barriers, the three permanent magnets are magnetized along the inner and outer thickness directions, and the first rectangular small permanent magnet is magnetized in opposite directions along the inner and outer thickness directions. The magnetic circuits of the first and second rectangular small permanent magnets intersect at a magnetic circuit intersection point, and the magnetization directions of the first and second rectangular small permanent magnets are both away from the magnetic circuit intersection point or both close to the magnetic circuit intersection point. The corresponding three permanent magnets, the first and second rectangular small permanent magnets on the two adjacent sets of U-shaped magnetic barriers 5 are magnetized in opposite directions along the thickness direction.

[0007] Preferably, the included angles between the inner section of the U-shaped side wall and the outer section of the U-shaped side wall and the d-axis are both 45°, and the middle section of the U-shaped side wall is perpendicular to the d-axis.

[0008] Preferably, the thicknesses of magnetic barriers in the same layer are completely the same.

[0009] Preferably, the outer, middle and inner magnetic barriers have the same spacing, and their thickness increases in radial direction; the three magnetic barrier permanent magnets 3 have the same spacing, and their thickness increases in radial direction, and their tangential width increases in tangential direction.

[0010] The advantages of the present invention after adopting the above technical solution are:

[0011] 1. The present invention adopts an asymmetric structure for the rotor magnetic barrier and permanent magnet of the permanent magnet-assisted bearingless synchronous reluctance motor, forming a rotor topology in which both the magnetic barrier and the permanent magnet are asymmetric. This can maximize the output torque synthesized by the permanent magnet torque component and the reluctance torque component, increase the difference between the d-axis and q-axis inductances, further improve the utilization rate of the reluctance torque and the permanent magnet torque, enhance the motor's output torque capacity, reduce torque pulsation, reduce iron loss, and improve motor efficiency.

[0012] 2. The asymmetric rotor magnetic barrier and asymmetric permanent magnet position distribution of the present invention alter the original permanent magnet and reluctance magnetic circuits, changing the relative position of the current angle between the permanent magnet torque and the reluctance torque, and thus changing the electrical angle between the maximum reluctance torque and the maximum permanent magnet torque. By properly positioning the permanent magnets, the reluctance torque and the permanent magnet torque reach their peak values ​​at similar or even identical current angles, increasing the combined output torque of the reluctance torque and the permanent magnet torque, and improving the utilization rate of the reluctance torque and the permanent magnet torque.

[0013] 3. The permanent magnets in this invention are made of inexpensive ferrite material, and the amount of permanent magnets decreases from the inner layer to the outer layer. This improves the power factor and torque density while using a relatively small number of permanent magnets. A small number of permanent magnets facilitates field weakening at high speeds, resulting in a wider speed regulation range and expanding the application range of permanent magnet-assisted bearingless synchronous reluctance motors.

[0014] 4. The magnetic barrier in the present invention is made of epoxy resin-based composite material, which can effectively improve the mechanical strength of the rotor. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The asymmetric rotor structure of the permanent magnet assisted bearingless synchronous reluctance motor proposed in the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] Figure 1 A schematic diagram of a radial cross-section of an asymmetric rotor of a permanent magnet assisted bearingless synchronous reluctance motor according to the present invention;

[0017] Figure 2 for Figure 1 An enlarged schematic diagram of one of the magnetic barriers and the permanent magnet assembly structure thereon;

[0018] Figure 3 for Figure 1 A magnified view of the size markings of the magnetic barrier and permanent magnet in the middle part;

[0019] Figure 4 for Figure 1 Schematic diagram of the permanent magnetic circuit of the symmetrical rotor structure after removing the small rectangular magnetic barrier and two small rectangular permanent magnets;

[0020] Figure 5 Schematic diagram of the permanent magnet circuit of the asymmetric rotor structure of the present invention;

[0021] Figure 6 for Figure 1 Schematic diagram of the reluctance magnetic circuit of the symmetrical rotor structure after removing the small rectangular magnetic barrier and two small rectangular permanent magnets;

[0022] Figure 7 Schematic diagram of the reluctance magnetic circuit of the asymmetric rotor structure of the present invention;

[0023] Figure 8 for Figure 1 Schematic diagram of the torque waveform of the symmetrical rotor structure after removing the small rectangular magnetic barrier and two small rectangular permanent magnets;

[0024] Figure 9 Schematic diagram of torque waveform of the asymmetric rotor structure of the present invention;

[0025] In the figure: 1. stator, 2. rotor, 3. permanent magnet, 3-1. outer layer permanent magnet, 3-2. middle layer permanent magnet, 3-3. inner layer permanent magnet, 3-4. second rectangular small permanent magnet, 3-5. first rectangular small permanent magnet, 4. permanent magnet mounting slot, 5. U-shaped magnetic barrier, 5-1. inner section of the U-shaped magnetic barrier side wall; 5-2. middle section of the U-shaped magnetic barrier side wall, 5-3. outer section of the U-shaped magnetic barrier side wall, 5-4. rectangular small magnetic barrier; 6. rotating shaft, 7. stator teeth; 8. stator slots; 9. stator yoke; 10. torque winding; 11. suspension force winding; 12. magnetic isolation bridge. DETAILED DESCRIPTION

[0026] See also Figure 1 As shown, the permanent magnet-assisted bearingless synchronous reluctance motor comprises a stator 1, a rotor 2, and a rotating shaft 6. The rotor 2 is coaxially positioned within the stator 1. A slot is provided in the center of the rotor 2 to accommodate the rotating shaft 6. The center of the rotor 2 is coaxially fixedly connected to the rotating shaft 6. An air gap exists between the inner wall of the stator 1 and the outer wall of the rotor 2. The thickness of the air gap depends on the power rating of the motor, the selected permanent magnet material, and the processing and assembly process of the stator 1 and rotor 2. The stator 1 consists of stator teeth 7, stator slots 8, and a stator yoke 9. The stator 1 is provided with 24 stator slots 8, with a stator slot 8 formed between two adjacent stator teeth 7 and evenly spaced along the circumference. The stator slots 8 contain two layers of windings: the outer layer is the torque winding 10, and the inner layer is the suspension winding 11. Both windings adopt a distributed structure. The radial cross-section of the stator tooth 7 is T-shaped, with the top of the T adjacent to the rotor 2 and the bottom of the T integrally connected to the stator yoke 9. The stator 1 and the rotor 2 are both made of 0.35mm thick silicon steel sheets laminated together, with a lamination coefficient of 0.95. The shaft 6 is made of non-magnetic material.

[0027] Recombination Figure 2 and Figure 3 Four sets of U-shaped magnetic barriers 5 are evenly spaced along the circumference of the rotor 2. Each set of U-shaped magnetic barriers 5 is divided into three layers from the outside in: outer, middle, and inner layers. The shapes of the U-shaped magnetic barriers 5 are derived using a novel topology optimization method. This method includes a sequence-based electromagnetic actuator and uses a genetic algorithm to optimize the electromagnetic actuator core. By controlling the electromagnetic actuator's movement within the discretized rotor 2 space, a symmetrical magnetic barrier trajectory is ultimately obtained. The outer and middle magnetic barriers are symmetrical about the d-axis, while the inner magnetic barrier 5 is asymmetric.

[0028] In the radial cross-section, the opening of the U-shaped magnetic barrier 5 is facing outward. The two side walls of each layer of the magnetic barrier are seamlessly connected in sequence from the inside to the outside by the inner section 5-1 of the U-shaped side wall, the middle section 5-2 of the U-shaped side wall, and the outer section 5-3 of the U-shaped side wall. In the radial cross-section, the angles between the inner section 5-1 of the U-shaped side wall and the outer section 5-3 of the U-shaped side wall and the d-axis are both 45°, and the middle section 5-2 of the U-shaped side wall is perpendicular to the d-axis.

[0029] One of the outer sections 5-3 of the U-shaped side wall of the inner layer magnetic barrier extends a rectangular small magnetic barrier 5-4 in the direction of the q-axis at the end facing the q-axis. The rectangular small magnetic barrier 5-4 is parallel to the q-axis. Due to the structure of the rectangular small magnetic barrier 5-4, the two outer sections 5-3 of the U-shaped side wall of the same inner layer magnetic barrier are asymmetric about the d-axis, making the inner layer magnetic barrier form an asymmetric structure.

[0030] Among the outer layer, middle layer, and inner layer of these three layers of magnetic barriers, the thickness of the magnetic barrier in the same layer is exactly the same, that is, the thickness of the bottom wall of the U-shaped of the magnetic barrier in the same layer is exactly the same as that of its two side walls.

[0031] The inner and outer thicknesses of these three layers of magnetic barriers along the radial direction are different, which are h1, h2, h3 respectively, and h1 < h2 < h3, and the thickness increases in sequence. The distances between the outer layer, middle layer, and inner layer magnetic barriers 5 are the same, all of which are a.

[0032] In the middle of the bottom walls of the outer layer, middle layer, and inner layer of these three layers of magnetic barriers, a permanent magnet installation groove 4 penetrating along the radial direction is opened respectively. The permanent magnet installation groove 4 is perpendicular to the d-axis. The thicknesses of the permanent magnet installation grooves 4 on the three layers of magnetic barriers along the radial direction increase in sequence, which are h1, h2, h3 respectively; the widths in the tangential direction are l1, l2, l3 respectively, and l1 < l2 < l3, and the widths in the tangential direction also increase in sequence. Therefore, the radial cross-sectional areas increase in sequence from the outside to the inside.

[0033] Each of the permanent magnet installation grooves 4 on the three layers of magnetic barriers is fixedly embedded with a permanent magnet 3, which are the outer layer permanent magnet 3-1, the middle layer permanent magnet 3-2, and the inner layer permanent magnet 3-3 respectively. Each permanent magnet 3 is symmetric about the d-axis. The outer layer permanent magnet 3-1, the middle layer permanent magnet 3-2, and the inner layer permanent magnet 3-3 are respectively the same as the structures of the corresponding permanent magnet installation grooves 4 on the three layers of magnetic barriers, and exactly fill the corresponding permanent magnet installation grooves 4. The embedded permanent magnet 3 is flush with the surface of the corresponding magnetic barrier 5; therefore, the thicknesses of the outer layer permanent magnet 3-1, the middle layer permanent magnet 3-2, and the inner layer permanent magnet 3-3 are h1, h2, h3 respectively, increasing in sequence; the widths are l1, l2, l3 respectively, increasing in sequence, and the distances between them are the same, all of which are a.

[0034] A first rectangular small permanent magnet 3-5 is fixedly embedded within the rectangular small magnetic barrier 5-4, and the first rectangular small permanent magnet 3-5 is parallel to the rectangular small magnetic barrier 5-4. A second rectangular small permanent magnet 3-4 is fixedly embedded within the outer section 5-3 of the U-shaped side wall with the rectangular small magnetic barrier 5-4, and the second rectangular small permanent magnet 3-4 is perpendicular to the outer section 5-3 of the U-shaped side wall. The two rectangular small permanent magnets 3-5 and 3-4 have the same structure but are perpendicular to each other and are spaced apart without contact.

[0035] The thickness direction of the first rectangular small permanent magnet 3-5 is the direction parallel to the q-axis, with a thickness of h3, and the width direction is the direction perpendicular to the q-axis, with a width of l4. The thickness direction of the second rectangular small permanent magnet 3-4 is the direction perpendicular to the q-axis, with a thickness of h3, and the width direction is the direction parallel to the q-axis, with a width of l4, and l4 < l1 < l2 < l3, and the width l4 is less than the width of the outer permanent magnet 3-1.

[0036] The outer end face of the first rectangular small permanent magnet 3-5 is flush with the outer end face of the outer section 5-3 of the U-shaped side wall, and the thickness of the second rectangular small permanent magnet 3-4 is the same as the thickness of the outer section 5-3 of the U-shaped side wall, both being h3.

[0037] All the outer permanent magnets 3-1, middle permanent magnets 3-2, inner permanent magnets 3-3, first rectangular small permanent magnets 3-5, and second rectangular small permanent magnets 3-4 are magnetized along the thickness direction. The magnetization directions of the outer permanent magnets 3-1, middle permanent magnets 3-2, and inner permanent magnets 3-3 on the same set of U-shaped magnetic barriers 5 are the same, all magnetized along the inner and outer thickness directions; the magnetization direction of the first rectangular small permanent magnet 3-5 on the same set of U-shaped magnetic barriers 5 is opposite to that of the outer permanent magnets 3-1, middle permanent magnets 3-2, and inner permanent magnets 3-3, magnetized in the reverse direction along the inner and outer thickness directions, that is, when the first rectangular small permanent magnet 3-5 is magnetized in the direction from the inside to the outside along the radial direction, the first rectangular small permanent magnet 3-5 and the outer permanent magnets 3-1, middle permanent magnets 3-2, and inner permanent magnets 3-3 are magnetized in the direction from the outside to the inside along the radial direction, and vice versa. The magnetic paths of the mutually perpendicular second rectangular small permanent magnet 3-4 and first rectangular small permanent magnet 3-5 on the same set of U-shaped magnetic barriers 5 intersect at a magnetic path intersection point, and the magnetization directions of the second rectangular small permanent magnet 3-4 and first rectangular small permanent magnet 3-5 on the same set of U-shaped magnetic barriers 5 are either both away from the magnetic path intersection point or both towards the magnetic path intersection point. The corresponding two outer permanent magnets 3-!1, middle permanent magnets 3-2, inner permanent magnets 3-3, first rectangular small permanent magnets 3-5, and second rectangular small permanent magnets 3-4 on adjacent two sets of U-shaped magnetic barriers 5 are magnetized in the reverse direction along the thickness direction. <#

[0038] The three layers of magnetic barriers are filled with epoxy resin-based composite materials to enhance the mechanical strength of the rotor 2. All permanent magnets 3 and rectangular small permanent magnets 3-4 and 3-5 are made of ferrite material.

[0039] A magnetic isolation bridge 12 with a width R in the inner and outer directions is formed between the outer ends of the three-layer magnetic barrier and the outer surface of the rotor 2. The width R between the outer ends of the first rectangular small permanent magnets 3-5 and the outer surface of the rotor 2 is also R.

[0040] See also Figure 4 After removing the rectangular small magnetic barrier 5-4 and the two rectangular small permanent magnets 3-4 and 3-5, the rotor has a symmetrical structure. The permanent magnetic circuit formed by the permanent magnets 3 symmetrical about the d axis forms a loop after passing through the permanent magnets 3 between the two adjacent sets of U-shaped magnetic barriers 5. Figure 5 The permanent magnet circuit of the asymmetric rotor structure of the present invention first passes through the three layers of permanent magnets 3 in the same set of U-shaped magnetic barriers 5, then passes through the second rectangular small permanent magnets 3-4 and the first rectangular small permanent magnets 3-5 to complete the loop. The asymmetric rotor structure causes the permanent magnet circuit to shift, further changing the current angle corresponding to the maximum permanent magnet torque.

[0041] See also Figure 6 After removing the rectangular small magnetic barrier 5-4 and the two rectangular small permanent magnets 3-4 and 3-5, the rotor has a symmetrical structure, and the magnetic resistance magnetic circuit passes through the rotor 2 and the stator 1 between the two adjacent sets of U-shaped magnetic barriers 5 to form a loop. Figure 7 The asymmetric rotor structure of the present invention has a similar reluctance magnetic circuit to that of the symmetric rotor 2. However, the presence of the asymmetric rectangular magnetic barriers 5-4 blocks some of the reluctance magnetic lines of force, causing the reluctance magnetic circuit to shift to one side. This shift in the reluctance magnetic circuit further alters the current angle corresponding to the maximum reluctance torque.

[0042] See also Figure 8 After removing the rectangular magnetic barrier 5-4 and the two small rectangular permanent magnets 3-4 and 3-5, the rotor becomes a symmetrical structure. In the torque waveform of the symmetrical rotor structure, the permanent magnet torque and the reluctance torque reach their maximum values ​​at different current lead angles, resulting in the resultant output torque not being the maximum value in the ideal case. Figure 9 In the torque waveform of the asymmetric rotor structure of the present invention, the permanent magnet torque and reluctance torque simultaneously reach their maximum values ​​at the same current lead angle, maximizing the combined output torque. Due to the asymmetric rotor structure, the offset between the permanent magnet and reluctance magnetic circuits changes the current phase angles corresponding to the maximum permanent magnet torque and maximum reluctance torque. This allows the current phase angles corresponding to the maximum permanent magnet torque and reluctance torque to approximate, increasing the combined output torque of the permanent magnet torque and reluctance torque, thereby improving the utilization rate of the permanent magnet torque and reluctance torque.

[0043] During manufacturing, the present invention first determines the motor's design parameters and selects the range of values ​​for each design parameter using the finite element method. A sensitivity analysis is then performed on each parameter, with weights assigned to each objective. The weights for torque pulsation and suspension force pulsation are assigned to 0.4, and the power factor to 0.2. After performing the sensitivity analysis on each parameter, parameters with lower sensitivity are directly optimized using the finite element method. Parameters with medium sensitivity are optimized using the response surface method, and parameters with higher sensitivity are optimized using a simulated annealing particle swarm algorithm. After optimization, the optimal solution is selected, and the electromagnetic and suspension performance before and after optimization are compared to determine the final parameters. The resulting motor improves output torque and reduces torque pulsation and suspension force pulsation.

Claims

1. An asymmetric rotor structure of a permanent magnet assisted bearingless synchronous reluctance motor, wherein the rotor is coaxially located inside the stator, characterized by: Four groups of U-shaped magnetic barriers (5) are evenly arranged inside the rotor along the circumferential direction. Each group of U-shaped magnetic barriers (5) is divided into an outer layer, a middle layer and an inner layer of magnetic barriers. The openings of the three layers of magnetic barriers face outwards. A permanent magnet (3) is embedded in the middle of the bottom wall of each layer of magnetic barriers. The two U-shaped side walls of each layer of magnetic barrier are formed by seamlessly connecting the inner section (5-1) of the U-shaped side wall, the middle section (5-2) of the U-shaped side wall and the outer section (5-3) of the U-shaped side wall from the inside to the outside. The outer and middle magnetic barriers are symmetrical about the d-axis. One of the U-shaped side wall outer sections (5-3) of the inner magnetic barrier has a rectangular small magnetic barrier (5-4) extending in the q-axis direction at the end facing the q-axis and parallel to the q-axis. A first rectangular small permanent magnet (3-5) is fixedly embedded in the rectangular small magnetic barrier (5-4). A second rectangular small permanent magnet (3-4) perpendicular to the first rectangular small permanent magnet (3-5) is fixedly embedded in the U-shaped side wall outer section (5-3) with the rectangular small magnetic barrier (5-4). The thickness of the second rectangular small permanent magnet (3-4) is the same as that of the U-shaped side wall outer section (5-3). On the same set of U-shaped magnetic barriers (5), the three permanent magnets (3) are all magnetized along the inner and outer thickness directions, the first rectangular small permanent magnet (3-5) is magnetized in the opposite direction along the inner and outer thickness directions, the magnetic paths of the first and second rectangular small permanent magnets (3-5, 3-4) intersect at a magnetic path intersection, and the magnetization directions of the first and second rectangular small permanent magnets (3-5, 3-4) are both away from the magnetic path intersection or both close to the magnetic path intersection; the corresponding three permanent magnets (3) and the first and second rectangular small permanent magnets (3-5, 3-4) on two adjacent sets of U-shaped magnetic barriers (5) are magnetized in the opposite direction along the thickness direction.

2. The asymmetric rotor structure of the permanent magnet assisted bearingless synchronous reluctance motor according to claim 1 is characterized by: The included angles between the inner section (5-1) of the quasi-U-shaped side wall and the outer section (5-3) of the quasi-U-shaped side wall and the d-axis are both 45 degrees, and the middle section (5-2) of the quasi-U-shaped side wall is perpendicular to the d-axis.

3. The asymmetric rotor structure of the permanent magnet assisted bearingless synchronous reluctance motor according to claim 1 is characterized by: The thickness of the magnetic barriers in the same layer is exactly the same.

4. The asymmetric rotor structure of the permanent magnet assisted bearingless synchronous reluctance motor according to claim 3 is characterized by: The three layers of magnetic barriers (the outer layer, the middle layer and the inner layer) have the same spacing, and their thickness increases in radial direction; the three layers of magnetic barrier permanent magnets (3) have the same spacing, and their thickness increases in radial direction, and their width increases in tangential direction.

5. The asymmetric rotor structure of the permanent magnet assisted bearingless synchronous reluctance motor according to claim 1, 2 or 3, characterized in that: The first and second rectangular small permanent magnets (3-5, 3-4) have the same structure and a distance is left between them.

6. The asymmetric rotor structure of the permanent magnet assisted bearingless synchronous reluctance motor according to claim 5 is characterized by: The thickness direction of the first rectangular small permanent magnet (3-5) is parallel to the q-axis, and the width direction is perpendicular to the q-axis; the thickness direction of the second rectangular small permanent magnet (3-4) is perpendicular to the q-axis, and the width direction is parallel to the q-axis, and the widths are both smaller than the width of the permanent magnet (3) on the outer magnetic barrier.

7. The asymmetric rotor structure of the permanent magnet assisted bearingless synchronous reluctance motor according to claim 1 is characterized by: The three layers of magnetic barriers are filled with epoxy resin-based composite materials, and all permanent magnets (3) and the first and second rectangular small permanent magnets (3-5, 3-4) are made of ferrite materials.

8. The asymmetric rotor structure of the permanent magnet assisted bearingless synchronous reluctance motor according to claim 1 is characterized by: A magnetic isolation bridge (12) is formed between the outer end of the three-layer magnetic barrier and the outer cylindrical surface of the rotor.

9. The asymmetric rotor structure of the permanent magnet assisted bearingless synchronous reluctance motor according to claim 8, characterized in that: The width of the magnetic isolation bridge (12) in the inner and outer directions is 1-2 mm.

10. The asymmetric rotor structure of the permanent magnet assisted bearingless synchronous reluctance motor according to claim 9, characterized in that: The outer end surface of the first rectangular small permanent magnet (3-5) is flush with the outer end surface of the U-shaped side wall outer section (5-3).

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