Low-rare-earth permanent magnet motor rotor

Abstract

The invention discloses a less-rare-earth permanent magnet motor rotor, which comprises an annular rotor iron core (multiple layers of silicon steel sheets are axially laminated, and the outer diameter is D), and 2N magnetic poles (N is greater than or equal to 1) are uniformly and alternately arranged in the circumferential direction and have opposite polarities. Each magnetic pole comprises a first magnetic steel (the length direction is a q axis, and a d-axis area is separated) radially embedded into the rotor core, and an asymmetric permanent magnet structure positioned in the d-axis area, and the asymmetric permanent magnet structure can be (1) an asymmetric V-shaped structure formed by second and third magnetic steels (the included angle is 120-170 degrees, and the vertex is positioned at the rotating near end); (2) a double-I structure composed of a second magnetic steel and a fourth magnetic steel; and (3) a triangular structure formed by the second, third and fourth magnetic steels. Wherein the second magnetic steel is ferrite magnetic steel and is arranged at the rotating far end of the magnetic pole, the third magnetic steel and the fourth magnetic steel are rare earth magnetic steel and are located at the near end and the d axis, and all the magnetic steel are magnetized in the tangential direction and are isolated by the iron core. According to the structure, the use amount of rare earth is reduced, the torque output of unit rare earth is improved by optimizing a magnetic circuit, and the performance and the cost are both considered.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet motor rotors, and particularly to a rare-earthless permanent magnet motor rotor. Background Art

[0002] Compared with other types of motors, permanent magnet synchronous motors have higher efficiency and torque / power density. Therefore, permanent magnet synchronous motors are usually widely used in fields related to electric vehicles. However, high-performance drive motors used in electric vehicles need to use magnetic steels containing rare-earth mineral components, such as neodymium-iron-boron magnetic steels. These mineral components are rare and expensive, which increases the production cost of electric vehicles and slows down the popularization and application of electric vehicles.

[0003] Ferrite magnetic steels have rich reserves, low prices and high availability. However, the magnetic properties of ferrite magnetic steels are insufficient, and the coercivity and remanence are relatively lower than those of neodymium-iron-boron. Demagnetization is likely to occur in the application scenarios of the main drive of new energy. Therefore, ferrite magnetic steel materials are not widely used in high-power density applications such as electric vehicles.

[0004] Literature 1

Y.Chen,T.Cai,X.Zhu,D.Fan and Q.Wang,"Analysis and design of anew type of less-rare-earth hybrid-magnet motor with different rotortopologies,"IEEE Transactions onApplied Superconductivity,vol.30,no.4,pp.1-6,June 2020

[0005] Reference 2

J.Han and Z.Zhang,"Design and optimization of a low-cost hybrid-pole rotor for spoke-type permanent magnet machine," IEEE Transactions on Magnetics, vol.58, no.2, pp.1-5, Feb.2022, Art no.8103105

[0006] The present invention aims to provide a rare-earth-free permanent magnet motor rotor with asymmetric hybrid magnets different from the above-mentioned literature. While reducing the usage of rare earths, the unit rare-earth torque output is improved by optimizing the magnetic circuit, taking into account both performance and cost. The technical solution is as follows:

[0007] A rare-earth-free permanent magnet motor rotor, comprising:

[0008] A rotor core, in the shape of a circular ring, is formed by axially laminating multiple layers of silicon steel sheets, and its outer diameter is D;

[0009] 2N magnetic poles (N is an integer greater than or equal to 1) are evenly and alternately arranged along the circumferential direction of the rotor, and the polarities of adjacent magnetic poles are opposite;

[0010] Each magnetic pole includes:

[0011] A first magnet is embedded in the rotor core along the radial direction of the rotor, and its length direction is the q-axis direction of the rotor, dividing the magnetic pole into a d-axis region;

[0012] An asymmetric permanent magnet structure is located in the d-axis region of the magnetic pole and is selected from one of the following structures:

[0013] (a) An asymmetric V-shaped structure composed of a second magnet and a third magnet;

[0014] (b) A double-I structure composed of a second magnet and a fourth magnet;

[0015] (c) A triangular structure composed of a second magnet, a third magnet, and a fourth magnet;

[0016] The second magnet is located at the distal end in the rotation direction of the magnetic pole, the third magnet is located at the proximal end in the rotation direction of the magnetic pole, and the fourth magnet is located on the d-axis of the magnetic pole inside the outer edge of the rotor;

[0017] The width direction of each magnet is tangential, magnetized tangentially, and isolated by the rotor core;

[0018] The second magnetic steel is a ferrite magnetic steel, and the other magnetic steels are rare earth magnetic steels.

[0019] Furthermore, the asymmetric permanent magnet structure is an asymmetric V-shaped structure;

[0020] Both ends of the V-shaped structure extend to the inner side of the rotor outer edge, the included angle thereof is 120° to 170°, and the vertex is located at the proximal end in the magnetic pole rotation direction;

[0021] The distance between the second magnetic steel and the first magnetic steel is 2 mm to D / 30, and the distance between the third magnetic steel and the first magnetic steel is 2 mm to D / 30;

[0022] The length of the third magnetic steel is 1 / 2 to 2 / 3 of the length of the second magnetic steel, and the width is 1 / 3 to 1 / 2 of the width of the second magnetic steel.

[0023] Furthermore, the asymmetric permanent magnet structure is a double I structure;

[0024] The distance between the second magnetic steel and the first magnetic steel is 2 mm to D / 30;

[0025] The included angle between the length direction of the fourth magnetic steel and the rotor tangential direction is -10° to 10°, the included angle between its center and the d-axis is less than 5°, its length is 1 / 3 to 2 / 3 of the length of the second magnetic steel, and the width is 1 / 4 to 1 / 3 of the width of the second magnetic steel.

[0026] Furthermore, the asymmetric permanent magnet structure is a triangular structure;

[0027] The distances between the second magnetic steel, the third magnetic steel and the first magnetic steel are all 2 mm to D / 30;

[0028] The included angle between the length direction of the fourth magnetic steel and the rotor tangential direction is -10° to 10°, the included angle between its center and the d-axis is less than 5°, its length is 1 / 3 to 2 / 3 of the length of the second magnetic steel, and the width is 1 / 4 to 1 / 3 of the width of the second magnetic steel.

[0029] Furthermore, the width of the first magnetic steel is 1 / 3 to 1 / 2 of the width of the second magnetic steel.

[0030] Furthermore, the distance between each magnetic steel and the rotor outer edge is 2 mm to D / 30.

[0031] Furthermore, the rare earth magnetic steel is a neodymium iron boron magnetic steel.

[0032] Furthermore, the magnetic pole rotation direction is the circumferential rotation direction when the rotor operates, the distal end is the end of the rotation direction, and the proximal end is the starting end of the rotation direction.

[0033] Furthermore, the inner diameter of the rotor core is d, satisfying 1.5 ≤ D / d ≤ 3.

[0034] Furthermore, N is an integer from 2 to 6.

[0035] Compared with the prior art, the remarkable features of the present invention are as follows:

[0036] For the permanent magnet motor rotor of the present invention, a hybrid pole structure of a spoke type (tangential magnetization) - asymmetric permanent magnet structure is adopted. While reducing the rare earth usage, the unit rare earth torque output is improved by optimizing the magnetic circuit, taking both performance and cost into account. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a topology diagram of the spoke type asymmetric V - shaped structure rotor of the present invention;

[0038] Figure 2 It is a topology diagram of the spoke type triangular structure rotor of the present invention;

[0039] Figure 3 It is a topology diagram of the spoke type double - I structure rotor of the present invention;

[0040] Figure 4 It is a diagram showing the dimensional parameters of the triangular rotor structure used in conjunction with the spoke type structure of the present invention;

[0041] Figure 5 It is a diagram showing the dimensional parameters of the magnet 5 of the present invention;

[0042] Figure 6 It is the Pareto boundary in the multi - objective optimization process of the rotor topology proposed by the present invention;

[0043] Figure 7 It is a comparison diagram of the magnetic equipotential line distributions of the benchmark prototype and the spoke type double - I structure prototype of the present invention;

[0044] Figure 8 It is a relationship diagram of the output torque - current lead angle of the benchmark prototype and the present invention;

[0045] Figure 9 It is a torque decomposition diagram of the benchmark prototype and the present invention under peak operating conditions. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] To further illustrate the embodiments, the present invention provides drawings. These drawings are part of the disclosure of the present invention, mainly used to illustrate the embodiments and can be combined with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, those of ordinary skill in the art should be able to understand other possible implementation manners and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are usually used to represent similar components.

[0047] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0048] As Figure 1 - Figure 3 shown, the present invention provides a rare-earthless permanent magnet motor rotor, and the permanent magnet topology of the rotor adopts an asymmetric hybrid permanent magnet structure. The rotor includes a rotor core 1 and 2N magnetic poles, where N is an integer greater than or equal to 1 (preferably, N is an integer from 2 to 6). In this embodiment, the rotor is a 4-pole rotor (i.e., N = 2).

[0049] The cross-section of the rotor core 1 is in an annular shape, which is formed by laminating multiple layers of silicon steel sheets along the axial direction, with an outer diameter of D and an inner diameter of d. Preferably, 1.5 ≤ D / d ≤ 3.

[0050] The rotor structure includes 4 magnetic poles, which are uniformly and alternately arranged along the circumferential direction of the rotor, and the polarities of adjacent magnetic poles are opposite. Each magnetic pole includes: (1) magnets 2A and 2B, which are embedded in the rotor core 1 along the radial direction of the rotor, and the length direction thereof is the q-axis direction of the rotor, dividing the magnetic pole into a d-axis region; (2) an asymmetric permanent magnet structure, which is located in the d-axis region of the magnetic pole and is selected from one of the following structures:

[0051] (a) An asymmetric V-shaped structure composed of magnet 3 and magnet 4, as Figure 1 shown;

[0052] (b) A double-I structure composed of magnet 3 and magnet 5, as Figure 2 shown;

[0053] (c) A triangular structure composed of magnet 3, magnet 4 and magnet 5, as Figure 3 shown.

[0054] Magnet 3 is located at the distal end in the rotation direction of the magnetic pole, magnet 4 is located at the proximal end in the rotation direction of the magnetic pole, and magnet 5 is located on the d-axis of the magnetic pole inside the outer edge of the rotor.

[0055] In this embodiment, the length direction of each magnet is its placement direction, the width direction is the tangential direction, and the thickness direction is the axial direction of the rotor. Each magnet is tangentially magnetized and isolated by the rotor core 1 (i.e., each magnet is embedded into the corresponding slot hole on the rotor core 1, and the magnets do not directly contact each other).

[0056] In this embodiment, magnet 3 is a ferrite magnet, and the other magnets are rare-earth magnets, such as neodymium iron boron magnets.

[0057] Spoke-type structure (tangential magnetization):

[0058] This structure is an innovative design based on the spoke-type rotor structure. In the traditional spoke-type rotor structure, the magnets arranged in a spoke-type manner usually adopt radial magnetization, and the magnets are arranged on the d-axis of the rotor.

[0059] In the pole design of the motor, the d-axis is in the same direction as the rotor magnetic field and is the position with the strongest magnetic field. Under the same pair of poles, the q-axis vector lags behind the d-axis by 90 electrical degrees and is the direction with the weakest magnetic field under this pole.

[0060] In this structure, the permanent magnets 2A and 2B are arranged in a spoke-like structure and are tangentially magnetized, that is, the magnetization directions of the permanent magnets 2A and 2B are along the tangential direction of the rotor. The spoke-like arrangement structure of the rare earth permanent magnets can increase the concentration of the magnetic flux of the permanent magnets, reduce the usage of rare earth permanent magnets, and can increase the reluctance torque component on the rotor. At the same time, the rare earth permanent magnets arranged in a spoke-like manner play a supporting role in the magnetic circuit. If the supporting role of the rare earth permanent magnets in the magnetic circuit is missing, the ferrite permanent magnets will be very likely to demagnetize under the exposure of a strong magnetic field, thus affecting the safe operation of the motor.

[0061] Asymmetric permanent magnet structure:

[0062] Such as Figure 4 、 Figure 5 As shown, the spoke-like triangular structure is used to illustrate the requirements for the arrangement of the permanent magnets on the rotor of this motor.

[0063] (1) Asymmetric V-shaped structure:

[0064] Both ends of the described asymmetric V-shaped structure extend to the inner side of the rotor outer edge, and its included angle α , , , , , m , , , , ,

[0071] ,

[0070] ,

[0065] , m ,

[0069] ,

[0064] ,

[0068] ,

[0063] ,

[0067] , Figure 5 ,

[0066] is 120° to 170°, and the vertex (the virtual intersection of the lengths of magnet 3 and magnet 4) is located near the proximal end of the pole rotation direction (right side of the d-axis);

[0065] The distance between magnet 3 and magnet 2B is 2 mm to D / 30, and the distance between the third magnet and magnet 2A is 2 mm to D / 30. The length m2 of magnet 4 is 1 / 2 to 2 / 3 of the length m1 of magnet 3, and the width b2 is 1 / 3 to 1 / 2 of the width b1 of magnet 3.

[0066] (2) Double-I structure:

[0067] The distance between magnet 3 and magnet 2B is 2 mm to D / 30;

[0068] The included angle α1 between the length direction of magnet 5 and the rotor tangent is -10° to 10°, the included angle θ3 between its center and the d-axis is less than 5°, its length W3 is 1 / 2 to 2 / 3 of the length m1 of magnet 3, and the width b3 is 1 / 4 to 1 / 3 of the width b1 of magnets 2A and 2B.

[0069] (3) Triangular structure

[0070] The triangular structure is a combination of the double-I structure and the asymmetric V-shaped structure.

[0071] Both ends of the described asymmetric V-shaped structure extend to the inner side of the rotor outer edge, and its included angle α mis 120° to 170°, and the vertex (the imaginary intersection point in the length direction of magnet 3 and magnet 4) is located at the proximal end in the magnetic pole rotation direction (right side of the d-axis);

[0072] The distance between magnet 3 and magnet 2B is 2 mm to D / 30, and the distance between magnet 4 and magnet 2A is 2 mm to D / 30;

[0073] The included angle α1 between the length direction of magnet 5 and the rotor tangent is -10° to 10°, the included angle θ3 between its center and the d-axis is less than 5°, its length W3 is 1 / 3 to 2 / 3 of the length m1 of magnet 3, and its width is 1 / 4 to 1 / 3 of the width b1 of magnet 3.

[0074] In addition, the distance between each magnet and the outer edge of the rotor is 2 mm to D / 30.

[0075] Experimental data and explanations:

[0076] Table 1 gives the common design parameters of the reference motor and the rare-earth-reduced permanent magnet motor.

[0077] Table 1 Common design parameters of the reference motor and the rare-earth-reduced permanent magnet motor

[0078]

[0079] The reference prototype uses the topological structure of the main drive permanent magnet motor in Tesla Model 3.

[0080] Figures 1 - 3 The structures of the rotors of the shown rare-earth-reduced permanent magnet motors are all optimized by using the genetic algorithm on the basis of parameterization, and their common goal is to increase the output torque while reducing the usage of rare-earth magnets.

[0081] During the optimization iteration process, the NdFeB magnet of grade N52SH and the ferrite magnet of grade Y33H are used in the rotor of the rare-earth-reduced permanent magnet motor.

[0082] Figure 6 Shows the use of Figures 1 - 3 The Pareto boundary of the results obtained after optimizing the operation with the topological structure of the rare-earth-reduced rotor. The calculation results show that the three topological structures of the rotors of the rare-earth-reduced permanent magnet motors proposed in the present invention can obtain the same output torque as the design with all rare-earth magnets at a lower volume of rare-earth magnets. The performance comparison is shown in Table 2.

[0083] Table 2 Performance comparison between the rare-earth-reduced permanent magnet motor and the reference motor

[0084]

[0085] The present invention provides multiple embodiments of a permanent magnet motor rotor. The hybrid magnetic pole magnet combination with a special-shaped spoke-type asymmetric permanent magnet structure can increase the reluctance torque of the rotor. Due to its asymmetry in position, a magnetic field offset effect can be generated, shifting the reluctance torque component and the permanent magnet torque component to a similar current lead angle, thereby increasing the total average output torque of the motor.

[0086] Figure 7 The magnetic equipotential line distributions of the spoke-type double-I structure prototype of the present invention and the reference prototype under peak load conditions are given, where (1) is the reference prototype and (2) is the spoke-type double-I structure prototype of the present invention.

[0087] Figure 8 The simulation calculation results of the current lead angle - output torque shown demonstrate the variation of the average output torque of the reference prototype and the spoke-type double-I structure motor with respect to the current lead angle. Through calculation, the current lead angles for the reference prototype and the prototype of the present invention to obtain the maximum output torque are 53 degrees and 45 degrees respectively. The asymmetric magnet design of the present invention generates a magnetic field offset, aligning the reluctance torque component and the permanent magnet torque component, which reduces the current lead angle for the rare-earth-free permanent magnet motor of the present invention to obtain the maximum torque from 53 degrees to 45 degrees.

[0088] Generally, the torque T of a permanent magnet synchronous motor is composed of a reluctance torque T Rel and a permanent magnet torque T PM as follows:

[0089] T = T PM + T Rel

[0090] The advantage of adopting an asymmetric rotor structure is that it can shift and align the permanent magnet torque T PM and the reluctance torque T Rel , so as to obtain a higher torque T at the current lead angle when the permanent magnet motor operates. Through this design of the asymmetric rotor, a higher average output torque can be achieved.

[0091] Under peak operating conditions, the magnetic permeability of each grid in the finite element model of the motor is transferred to a new finite element model. The magnet material in the new model is set to air, so that the corresponding reluctance torque can be calculated. The permanent magnet torque is obtained by subtracting the reluctance torque component from the total output torque of the motor.

[0092] The results show that at a current lead angle of 53 electrical degrees, the reference prototype has a reluctance torque component of 270 Nm and a permanent magnet torque component of 166 Nm, while for the rare-earth-free permanent magnet motor of the present invention, at a current lead angle of 45 electrical degrees, it has a reluctance torque component of 287 Nm and a permanent magnet torque component of 156 Nm, as Figure 9As shown. Thus, through the magnetic field offset technology, the present invention aligns the two torque components, improving the motor torque output capacity per unit of rare earth material. Therefore, on the basis of maintaining the main characteristics of the rare earth permanent magnet motor, that is, with the same main mechanical dimensions and the same peak torque / power, the usage amount of rare earth materials in the motor rotor can be significantly reduced.

[0093] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, those skilled in the art should understand that various changes can be made to the present invention in terms of form and details without departing from the spirit and scope of the present invention defined by the appended claims, and all such changes are within the protection scope of the present invention.

Claims

1. A rare-earth-less permanent magnet motor rotor, characterized in that, Comprising: A rotor core, in an annular shape, formed by laminating multiple layers of silicon steel sheets along the axial direction, with an outer diameter of D; 2N magnetic poles (N is an integer ≥ 1), uniformly and alternately arranged along the circumferential direction of the rotor, and the polarities of adjacent magnetic poles are opposite; Each magnetic pole includes: A first permanent magnet, embedded in the rotor core along the radial direction of the rotor, with its length direction being the q-axis direction of the rotor, and separating the magnetic pole into a d-axis region; An asymmetric permanent magnet structure, located in the d-axis region of the magnetic pole, selected from one of the following structures: (a) An asymmetric V-shaped structure composed of a second permanent magnet and a third permanent magnet; (b) A double-I structure composed of a second permanent magnet and a fourth permanent magnet; (c) A triangular structure composed of a second permanent magnet, a third permanent magnet, and a fourth permanent magnet; The second permanent magnet is located at the distal end in the rotation direction of the magnetic pole, the third permanent magnet is located at the proximal end in the rotation direction of the magnetic pole, and the fourth permanent magnet is located on the d-axis of the magnetic pole inside the inner edge of the rotor; The width direction of each permanent magnet is tangential, magnetized tangentially, and isolated by the rotor core; The second permanent magnet is a ferrite permanent magnet, and the other permanent magnets are rare earth permanent magnets.

2. The rare-earth-less permanent magnet motor rotor according to claim 1, characterized in that, The asymmetric permanent magnet structure is an asymmetric V-shaped structure; Both ends of the asymmetric V-shaped structure extend to the inside of the inner edge of the rotor, with an included angle of 120° - 170°, and the vertex is located at the proximal end in the rotation direction of the magnetic pole; The distance between the second permanent magnet and the first permanent magnet is 2mm - D / 30, and the distance between the third permanent magnet and the first permanent magnet is 2mm - D / 30; The length of the third permanent magnet is 1 / 2 - 2 / 3 of the length of the second permanent magnet, and the width is 1 / 3 - 1 / 2 of the width of the second permanent magnet.

3. The rare-earthless permanent magnet motor rotor according to claim 1, wherein, The asymmetric permanent magnet structure is a double-I structure; The distance between the second permanent magnet and the first permanent magnet is 2mm - D / 30; The included angle between the length direction of the fourth permanent magnet and the tangential direction of the rotor is -10° - 10°, the included angle between its center and the d-axis is less than 5°, its length is 1 / 3 - 2 / 3 of the length of the second permanent magnet, and the width is 1 / 4 - 1 / 3 of the width of the second permanent magnet.

4. The rare-earth-less permanent magnet motor rotor according to claim 1, wherein, The asymmetric permanent magnet structure is a triangular structure; The distances between the second permanent magnet, the third permanent magnet and the first permanent magnet are all 2mm - D / 30; The included angle between the length direction of the fourth permanent magnet and the tangential direction of the rotor is -10° - 10°, the included angle between its center and the d-axis is less than 5°, its length is 1 / 3 - 2 / 3 of the length of the second permanent magnet, and the width is 1 / 4 - 1 / 3 of the width of the second permanent magnet.

5. The rare-earthless permanent magnet motor rotor according to any one of claims 1-4, characterized in that, The width of the first permanent magnet is 1 / 3 - 1 / 2 of the width of the second permanent magnet.

6. The rare-earthless permanent magnet motor rotor according to any one of claims 1-4, characterized in that, The distance between each permanent magnet and the outer edge of the rotor is 2mm - D / 30.

7. The rare-earth-deficient permanent magnet motor rotor according to any one of claims 1 to 4, characterized in that, The rare earth permanent magnet is a neodymium iron boron permanent magnet.

8. The rotor of the rare-earth-free permanent magnet motor according to any one of claims 1-4, characterized in that The rotation direction of the magnetic pole is the circumferential rotation direction when the rotor operates, the distal end is the end of the rotation direction, and the proximal end is the starting end of the rotation direction.

9. The rotor of the rare-earth-free permanent magnet motor as described in any one of claims 1-4, characterized in that, The inner diameter of the rotor core is d, satisfying 1.5 ≤ D / d ≤ 3.

10. The rare-earth-deficient permanent magnet motor rotor according to any one of claims 1 to 4, characterized in that, N is an integer from 2 to 6.

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