A stator tooth and permanent magnet structure of an outer rotor permanent magnet motor for suppressing electromagnetic vibration

Abstract

The application relates to the technical field of electric machines, in particular to a stator tooth and permanent magnet structure of an outer rotor permanent magnet motor capable of inhibiting electromagnetic vibration, which comprises an inner stator and an outer rotor, the outer rotor comprises a rotor shaft and a plurality of permanent magnets distributed in the circumferential direction of the rotor shaft, and the inner stator is provided with a plurality of stator teeth distributed in the circumferential direction of the rotor shaft; the top of the stator tooth is provided with an eccentric arc structure which is eccentric to the rotor shaft and is single-section continuous, the center of the arc line of the eccentric arc structure is not coincident with the center of the rotor shaft, the end of the permanent magnet close to the side of the stator tooth is provided with a single-section continuous convex arc structure, the convex surface direction between the eccentric arc structure at the top of the stator tooth and the convex arc structure at the end of the permanent magnet is opposite, and the arc line profiles of the eccentric arc structure and the convex arc structure are continuous and have no inflection points. The stator tooth and permanent magnet structure of the outer rotor permanent magnet motor can effectively inhibit electromagnetic vibration and reduce the cogging torque.

Description

Technical Field

[0001] This invention relates to the field of motor technology, specifically to a stator tooth and permanent magnet structure for an external rotor permanent magnet motor that suppresses electromagnetic vibration. Background Technology

[0002] As an important branch of permanent magnet motors, external rotor permanent magnet motors adopt a structure layout with the stator built-in and the rotor surrounding the stator. With advantages such as high torque-to-inertia ratio, high torque at low speeds, compact structure, and good heat dissipation, they have been widely used in fields such as hub-driven direct drive in new energy vehicles, industrial fans and pumps, smart homes, drones, and precision transmission equipment. With the rapid development of rare-earth permanent magnet materials and power electronics technology, external rotor motors have continuously improved in power density, operating efficiency, and control precision, gradually replacing traditional internal rotor and asynchronous motor solutions. However, due to structural limitations and air gap magnetic field characteristics, conventional external rotor motors still suffer from problems such as high air gap magnetic flux density harmonic content, large cogging torque and torque pulsation, and easy saturation of local magnetic circuits, making it difficult to meet the stringent requirements of high-end equipment for low vibration, low noise, and high stability. Therefore, structural optimization of the stator tooth tips and rotor permanent magnets to improve the air gap magnetic field waveform, suppress harmonic components, and enhance torque output quality has become a key research direction for the high performance of external rotor permanent magnet motors.

[0003] Currently, vibration suppression for this type of motor mainly revolves around three dimensions: electromagnetic structure optimization, control strategy improvement, and mechanical process enhancement, forming a synergistic vibration reduction technology system. Electromagnetic structure optimization includes methods such as stator tooth tip eccentricity and slot design to reduce cogging torque; the rotor improves air gap magnetic flux density through improved magnetization methods and pole arc coefficient optimization, combined with a stator-rotor air gap side protrusion collaborative structure, which can effectively weaken harmonics and suppress torque pulsation. In terms of control strategies, current harmonics and switching noise are suppressed by improving modulation algorithms, and adaptive and robust control is combined to offset vibrations caused by load disturbances and rotor imbalance, improving operational stability. At the mechanical level, structural stiffness is optimized to avoid resonance, assembly precision is strictly controlled to reduce imbalance, and damping components are added to attenuate vibration. Among these, electromagnetic structure optimization is the key to source vibration reduction; however, the existing stator tooth tip eccentricity design increases the air gap, which may reduce operating efficiency; the process of improving the rotor magnetization method is difficult to control, resulting in poor improvement effects.

[0004] like Figure 1 and Figure 2As shown, the existing external rotor permanent magnet motor includes an inner stator 100 and an outer rotor 200. The outer rotor 200 includes a rotor shaft 202 and permanent magnets 201 circumferentially distributed around the rotor shaft 202. The inner stator 100 has stator teeth 101 circumferentially distributed around the rotor shaft 202. In the prior art, the surface-mounted permanent magnets 201 of the external rotor permanent magnet motor often adopt a concentric tile-shaped structure, while the stator teeth 101 commonly adopt rectangular teeth, trapezoidal teeth, pear-shaped teeth, semi-open teeth, and closed teeth, etc. Figure 2 As shown, in existing external rotor permanent magnet motors, the top of the stator teeth 101 generally adopts an arc structure centered on the axis O of the rotor shaft 202, and the outer contour of this arc structure is concentric with the inner circle of the stator teeth 101; while the end of the permanent magnet 201 generally adopts a concave arc structure concentric with the outer circle of the external rotor 200. Furthermore, the fractional slot windings of existing surface-mounted fractional-slot external rotor permanent magnet motors generate a large number of magnetomotive force harmonics, which couple with the magnetic field of the permanent magnet to form a high-order radial electromagnetic force; this is prone to resonance with the stator core, superimposed with the effects of cogging torque and torque pulsation, causing significant electromagnetic vibration and high and low frequency noise, making it difficult to meet the application requirements of low-noise and stable operation. Summary of the Invention

[0005] In order to improve the performance of permanent magnet motors, especially to reduce the cogging torque and electromagnetic vibration generated at specific speeds, the present invention provides a stator tooth and permanent magnet structure for an external rotor permanent magnet motor that suppresses electromagnetic vibration.

[0006] The first aspect of the present invention provides a stator tooth and permanent magnet structure for an external rotor permanent magnet motor that suppresses electromagnetic vibration, including an inner stator and an outer rotor. The outer rotor includes a rotor shaft and a plurality of permanent magnets circumferentially distributed around the rotor shaft. The inner stator is provided with a plurality of stator teeth circumferentially distributed around the rotor shaft. The top of the stator teeth is provided with an eccentric arc structure that is off-center from the rotor shaft and continuous in a single segment. The center of the arc of the eccentric arc structure does not coincide with the center of the rotor shaft. The end of the permanent magnet near the stator tooth is provided with a continuous convex arc structure in a single segment. The convex surfaces of the eccentric arc structure at the top of the stator tooth and the convex arc structure at the end of the permanent magnet are opposite in direction, and the arc contours of the eccentric arc structure and the convex arc structure are continuous and without inflection points.

[0007] In this invention, the top of the stator teeth is configured as an eccentric arc structure, and the end of the permanent magnet is configured as a convex arc structure, thereby improving the performance of the external rotor permanent magnet motor. Specifically, the eccentric structure at the top of the stator teeth creates an unbalanced air gap, making the air gap structure irregular and altering the harmonics of the air gap magnetic flux density. Based on the non-uniform air gap, the convex arc structure at the end of the permanent magnet reduces the air gap and increases the weight and volume of the permanent magnet, effectively increasing the amplitude of the air gap magnetic flux density, enhancing the main magnetic flux, and improving the motor's output torque. Simultaneously, it improves the sinusoidal nature of the air gap magnetic flux density waveform, weakens harmonic components, reduces cogging torque and torque pulsation, and improves the motor's operational stability and efficiency.

[0008] Furthermore, the arc profile of the eccentric arc structure at the top of the stator teeth is characterized by the following formula: ;

[0009] in, and The coordinates of the points on the arc of the eccentric arc structure at the top of the stator teeth are given, and multiple coordinate points form a single continuous arc. The radius of the arc of the eccentric arc structure at the top of the stator teeth; Stator tooth parameter angle, stator tooth parameter angle It is a variable, and satisfies , It is half the central angle of the arc of the eccentric arc structure at the top of the stator teeth. Indicates taking the absolute value; Represents the cosine function. Represents the sine function; and The center of the arc of the eccentric arc structure at the top of the stator teeth The coordinates of the circle and the center The coordinates satisfy and All less than conditions, Let be the inner radius of the inner stator.

[0010] Furthermore, =18.05mm, , .

[0011] Furthermore, the center of the circle The distance between the rotor shaft center O and the rotor shaft is 50mm.

[0012] Furthermore, the arc profile of the convex arc structure at the end of the permanent magnet is characterized by the following formula: ;

[0013] in, and The coordinates of the points on the arc of the convex arc structure at the end of the permanent magnet are given; multiple coordinate points form a single continuous arc. The radius of the arc of the convex arc structure at the end of the permanent magnet; For the angle of the permanent magnet parameter, the angle of the permanent magnet parameter It is a variable, and satisfies , It is half the central angle of the arc of the convex arc structure at the end of the permanent magnet. Indicates taking the absolute value; Represents the cosine function. Represents the sine function; and The center of the arc of the convex arc structure at the end of the permanent magnet The coordinates of the circle and the center The coordinates satisfy conditions, is the outer radius of the outer rotor.

[0014] Furthermore, =160mm, , .

[0015] A second aspect of the present invention provides an external rotor permanent magnet motor, including the stator teeth and permanent magnet structure of the external rotor permanent magnet motor for suppressing electromagnetic vibration.

[0016] Furthermore, the external rotor permanent magnet motor is an external rotor permanent magnet synchronous motor (PMSM).

[0017] The present invention has the following beneficial effects: In this invention, the convex surfaces of the eccentric arc-shaped structure at the top of the stator teeth and the convex arc-shaped structure at the end of the permanent magnet are oriented opposite each other, and the arc contours of both the eccentric arc-shaped structure and the convex arc-shaped structure are continuous and without inflection points. This creates an asymmetrical, gradually changing, non-uniform air gap between the stator teeth and the permanent magnet. This design has the following advantages: First, the air gap magnetic field has a high sinusoidal degree and fewer harmonics, which can effectively reduce cogging torque, electromagnetic vibration, and noise. Second, the single-segment arc shape with a continuous contour without inflection points results in a simple structure, making mold processing, assembly, and dimensional control more convenient and ensuring good mass production consistency. Third, the stress distribution is uniform, resulting in strong mechanical reliability. This invention effectively reduces magnetic field distortion and air gap magnetic flux density harmonic amplitude between the stator teeth and the permanent magnet by optimizing the stator teeth and permanent magnet structure of the external rotor permanent magnet motor, improves the sinusoidal degree of the air gap magnetic field, and thus significantly suppresses electromagnetic excitation force and radial electromagnetic vibration noise during motor operation. At the same time, it greatly reduces the cogging torque caused by magnetic field pulsation, reduces torque fluctuation and low-speed pulsation, and improves the motor's running stability and electromagnetic performance. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the stator teeth and permanent magnet structure of an external rotor permanent magnet motor in the prior art.

[0019] Figure 2 This is a schematic diagram showing the shape of the outer surface of the rotor permanent magnet and the top of the stator teeth in the prior art.

[0020] Figure 3 This is a schematic diagram of the stator teeth and permanent magnet structure of an external rotor permanent magnet motor in one embodiment of the present invention.

[0021] Figure 4 This is an enlarged structural schematic diagram of the permanent magnet and stator teeth in one embodiment of the present invention.

[0022] Figure 5 This is a schematic diagram of the stator teeth dimensions in one embodiment of the present invention.

[0023] Figure 6 This is a schematic diagram of the dimensions of a permanent magnet in one embodiment of the present invention.

[0024] Figure 7 This is a flowchart of the electromagnetic noise simulation analysis of the external rotor permanent magnet motor in the implementation of this invention.

[0025] Figure 8 This is a comparison chart of the overall torque data changes of an external rotor permanent magnet motor in a prior art and an embodiment of the present invention.

[0026] Figure 9 This is a comparison diagram of the radial air gap magnetic flux density-space angle curves of an external rotor permanent magnet motor in the prior art and in one embodiment of the present invention.

[0027] Figure 10 This is a comparison diagram of the air gap magnetic flux density amplitude of an external rotor permanent magnet motor in the prior art and in one embodiment of the present invention.

[0028] Figure 11 This is a comparison diagram of the radial electromagnetic force density-space angle curves of an external rotor permanent magnet motor in the prior art and in one embodiment of the present invention.

[0029] Figure 12 This is a comparison diagram of the radial electromagnetic force amplitude of an external rotor permanent magnet motor in the prior art and in one embodiment of the present invention.

[0030] Figure 13 This is a schematic diagram of the spatiotemporal decomposition of radial electromagnetic force wave density in an external rotor permanent magnet motor in the prior art.

[0031] Figure 14 This is a schematic diagram of the spatiotemporal decomposition of the radial electromagnetic force wave density of an external rotor permanent magnet motor in one embodiment of the present invention.

[0032] Figure 15This is a comparison chart of data analysis results of cogging torque in existing technologies and one embodiment of the present invention.

[0033] Figure 16 This is a comparison chart of contrast radiometric analysis of an external rotor permanent magnet motor in cruise mode in the prior art and an embodiment of the present invention.

[0034] Figure 17 This is a schematic diagram of the mode shapes and natural frequencies of the external rotor of an external rotor permanent magnet motor obtained by calculation in one embodiment of the present invention.

[0035] Figure 18 This is a schematic diagram of the noise waterfall of an external rotor permanent magnet motor under all operating conditions in the existing technology.

[0036] Figure 19 This is a schematic diagram of the noise waterfall of the external rotor permanent magnet motor under all operating conditions in one embodiment of the present invention.

[0037] In the picture:

[0038] Inner stator 100, stator teeth 101, stator winding 102;

[0039] External rotor 200, permanent magnet 201, rotor shaft 202. Detailed Implementation

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0041] This invention changes the geometric structure of the motor stator teeth and permanent magnets, thereby altering the distribution and amplitude of the air gap magnetic flux density, ultimately achieving an effective influence on electromagnetic force.

[0042] For external rotor permanent magnet motors, electromagnetic vibration is a significant source of operating noise, primarily caused by radial electromagnetic forces acting on the inner stator 100 and outer rotor 200. Electromagnetic force waves are generated by the interaction of air gap magnetic flux density harmonics, which is crucial for energy conversion in the motor. Therefore, the present invention aims to reduce electromagnetic vibration by altering the structure of the stator teeth 101 and permanent magnet 201, thereby changing the periodic distribution of air gap magnetic permeability. This disrupts the original uniform air gap distribution between the slots (slots between adjacent stator teeth 101) and the permanent magnet 201, thus suppressing the amplitude of radial force electromagnetic harmonics, reducing cogging torque fluctuations, and minimizing periodic force abrupt changes. Effective suppression of electromagnetic force harmonics can be achieved through designs such as eccentricity at the top of the stator teeth 101 and a single-segment continuous convex arc structure on the permanent magnet 201. Furthermore, the appropriate selection of the eccentricity angle and the increment of the convex arc will produce differentiated effects on the motor's electromagnetic force characteristics and cogging torque.

[0043] By rationally designing the eccentric angle of the eccentric arc structure at the top of the stator tooth 101 and the shape of the convex arc structure at the end of the permanent magnet 201, radial electromagnetic force can be effectively suppressed, mitigating the alternating impact of radial electromagnetic force on the stator and rotor surfaces. When the outer rotor permanent magnet motor is operating, the armature magnetic field of the stator winding 102 and the excitation magnetic field of the permanent magnet 201 superimpose in the air gap to form a composite magnetic field. This composite magnetic field generates electromagnetic force on the surfaces of the inner stator 100 and the outer rotor 200. Structural optimization of the inner stator 100 and the outer rotor 200 can change the air gap state, thereby adjusting the electromagnetic force distribution and reducing the amplitude of the radial electromagnetic force.

[0044] The stator teeth and permanent magnet structure of the external rotor permanent magnet motor provided by this invention suppresses electromagnetic vibration. The top of the stator teeth 101 is configured as a single-segment continuous eccentric arc structure, offset from the rotor shaft 202. The center of the arc of the eccentric arc structure does not coincide with the axis of the rotor shaft. The end of the permanent magnet 201 near the stator teeth 101 is configured as a single-segment continuous convex arc structure. The convex surfaces of the eccentric arc structure at the top of the stator teeth 101 and the convex arc structure at the end of the permanent magnet 201 are opposite in direction, and the arc contours of both the eccentric arc structure and the convex arc structure are continuous and without inflection points. This creates an asymmetrical, gradually changing, non-uniform air gap between the stator teeth and the permanent magnet, effectively weakening the radial electromagnetic force and cogging torque, and improving the motor torque pulsation characteristics. Simultaneously, the convex arc structure at the end of the permanent magnet 201 increases the magnetization of the permanent magnet, compensating for the decrease in motor torque caused by the weakening of electromagnetic force and cogging torque, and preventing a reduction in motor efficiency.

[0045] like Figure 3 and Figure 4As shown, the external rotor permanent magnet motor in this embodiment of the invention includes an inner stator 100 and an outer rotor 200. The outer rotor 200 includes a rotor shaft 202 and a plurality of permanent magnets 201 circumferentially distributed around the rotor shaft 202. The inner stator 100 is provided with a plurality of stator teeth 101 circumferentially distributed around the rotor shaft 202. The end of the permanent magnet 201 near the stator teeth 101 (the side near the center of the rotor shaft 202) is provided with a single-segment continuous convex arc structure. The top of the stator teeth 101 of the inner stator 100 (the side away from the center of the rotor shaft 202) is provided with an eccentric arc structure that is off-center from the rotor shaft 202 and is a single-segment continuous arc structure. Specifically:

[0046] like Figure 5 As shown, the arc profile of the eccentric arc structure at the top of stator tooth 101 (on the side away from the axis of rotor shaft 202) can be characterized by the following formula: ;

[0047] in, and The coordinates of the points on the arc of the eccentric arc structure at the top of the stator teeth are given, and multiple coordinate points form a single continuous arc. The radius of the arc of the eccentric arc structure at the top of the stator teeth; Stator tooth parameter angle, stator tooth parameter angle It is a variable, and satisfies , It is half the central angle of the arc of the eccentric arc structure at the top of the stator teeth. Indicates taking the absolute value; Represents the cosine function. Represents the sine function; and The center of the arc of the eccentric arc structure at the top of the stator teeth The coordinates of the circle and the center The coordinates satisfy and All less than ; The inner radius of the inner stator, i.e., the center of the circle. It is located within the inner circle of the inner stator.

[0048] Figure 2 middle, It represents half the central angle of the arc at the tip of the stator teeth with the rotor shaft center O as the center. The radius of the arc of the concave arc structure at the end of the permanent magnet; It is half the width of the arc of the concave arc structure at the end of the permanent magnet.

[0049] The offset of the arc coordinates of the eccentric arc structure at the top of stator tooth 101 varies with the angle. (angle correspond Figure 2 The existing technology shown is a variation of half the central angle of the stator tooth tip arc with the rotor shaft center O as the center; known angle Groove angle Extreme logarithms Parameters, and angle Satisfying angle constraints: ,in, It represents the number of pole pairs (i.e., half the number of permanent magnets). This represents the slot angle; under this constraint, the arc coordinate offset of the eccentric arc structure at the top of stator tooth 101 is: ;

[0050] In the formula, This represents the coordinate offset of the eccentric arc structure at the top of the stator teeth (i.e., the coordinate offset between the arc of the eccentric arc structure at the top of the stator teeth and the corresponding point on the arc of the top of the stator teeth with the axis O of the rotor shaft as the center). Let be the radius of the arc at the top of the stator teeth, centered at the axis O of the rotor shaft. The radius of the arc of the eccentric arc structure at the top of the stator teeth. Represents the cosine function. Represents the sine function. It represents half the central angle of the arc at the tip of the stator teeth with the rotor shaft center O as the center. The number of stator teeth. Indicates the slot angle;

[0051] The slot width between adjacent stator teeth 101 (i.e., the opening width of the slot between adjacent stator teeth 101 facing the air gap) is: ;

[0052] in, Indicates the width of the groove between adjacent stator teeth; This is the groove clearance coefficient; ; The outer diameter of the inner stator (corresponding to) Figure 2 The diameter of the stator tooth tip arc with the rotor shaft center O as the center is shown in the prior art. ); This refers to the number of stator teeth.

[0053] like Figure 6 As shown, the arc profile of the convex arc structure at the end of the permanent magnet 201 can be characterized by the following formula: ;

[0054] in, and The coordinates of the points on the arc of the convex arc structure at the end of the permanent magnet are given; multiple coordinate points form a single continuous arc. The radius of the arc of the convex arc structure at the end of the permanent magnet; For the angle of the permanent magnet parameter, the angle of the permanent magnet parameter It is a variable, and satisfies , It is half the central angle of the arc of the convex arc structure at the end of the permanent magnet. Indicates taking the absolute value; Represents the cosine function. Represents the sine function; and The center of the arc of the convex arc structure at the end of the permanent magnet The coordinates of the circle and the center The coordinates satisfy ; The outer radius of the outer rotor, i.e., the center of the circle. It is located outside the outer circle of the outer rotor.

[0055] The size of permanent magnet 201 varies with width (width correspond Figure 2 The existing technology shown is a variation of half the arc width of the concave arc structure at the end of the permanent magnet; known width Circumference of the inner side of the permanent magnet Extreme logarithms The gap width between adjacent permanent magnets Parameters, and width Satisfy width constraints: ,in, The inner circumference of the permanent magnet body. It represents the number of pole pairs (i.e., half the number of permanent magnets). Let be the gap width between adjacent permanent magnets; under this constraint, the overall thickness of the permanent magnet with a convex arc structure at the end is: ;

[0056] in, The overall thickness of the permanent magnet with a concave arc-shaped structure at the end (i.e., the overall thickness of the permanent magnet in the original prototype of the prior art before the improvement). The overall thickness of the permanent magnet with a convex arc structure at the end (i.e., the overall thickness of the permanent magnet optimized in this invention). The center of the arc of the concave arc structure at the end of the permanent magnet The center of the arc of the convex arc structure at the end of the permanent magnet The distance between them, i.e. Figure 2The center of the arc of the permanent magnet near the stator tooth side shown in the prior art to Figure 6 The center of the arc of the optimized permanent magnet near the stator tooth side in the embodiment of the present invention shown The distance between them; for Figure 2 The radius of the arc of the concave arc structure at the end of the permanent magnet in the prior art shown; for Figure 6 The radius of the arc of the convex arc structure at the end of the permanent magnet in the embodiment of the present invention shown; It is half the width of the concave arc structure at the end of the permanent magnet with the axis O of the rotor shaft as the center; C is the inner circumference of the permanent magnet. This represents the gap width between adjacent permanent magnets. The center of the arc of the concave arc structure at the end of a given permanent magnet is... The center of the arc of the convex arc structure at the end of the permanent magnet Distance between And the radius of the arc of the convex arc structure at the end of the given permanent magnet. In this case, the overall thickness of the permanent magnet with a convex arc structure at the end can be calculated.

[0057] In a typical external rotor permanent magnet motor, the coordinates of the rotor shaft center O are (0, 0), the diameter of the stator tooth tip arc with the rotor shaft center O as the center is 136.1 mm, the outer diameter of the outer rotor is 145.6 mm, and the inner diameter of the concave arc structure at the end of the permanent magnet is 137.5 mm. This paper adopts a 36-slot 42-pole structure motor (i.e., a motor with 36 slots and 42 permanent magnets).

[0058] Constructing the arc of the eccentric arc structure at the top of the stator teeth: Selecting the center point coordinates When it is (50, 0), , Groove clearance coefficient The value is 0.15, and the groove width between adjacent stator teeth is... ;and ,Right now According to the stator tooth parameters angle , , The coordinates of three points on the arc of the eccentric arc structure at the top of the stator tooth can be determined. The coordinates are (67.3469, 4.9887), (68.025, 0), and (67.3469, -4.9887), respectively. Using the coordinates of these three points, the contour of the arc of the improved stator tooth top eccentric arc structure in this embodiment can be determined. Simultaneously, the slot angle between the maximum adjacent stator teeth is also determined. = ;when At that time, its corresponding =0.42mm, 0mm, 0.42mm.

[0059] Constructing the arc of the convex arc structure at the end of the permanent magnet: Select the center of the circle. coordinates When the value is (160, 0), =91.37mm, =68.75 mm, = ,and ,Right now The overall thickness of the permanent magnet with a pole arc coefficient of 0.73 and an end set as a concave arc structure. =2.1. Based on angle parameters , , The coordinates of three points on the arc line of the convex arc structure at the end of the permanent magnet can be determined. The coordinates are (68.717, 4.1), (68.63, 0), and (68.717, -4.1). Using these three points, the arc of the convex structure at the end of the permanent magnet can be constructed. Simultaneously, the maximum gap width between adjacent permanent magnets... =2.29mm; then ,when At that time, its corresponding =2.1mm, 2.22mm, 2.1mm.

[0060] The parameters of a typical external rotor permanent magnet motor in the embodiments of the present invention are analyzed and compared with those of an external rotor permanent magnet motor in the prior art. Figure 7 This paper demonstrates the process of electromagnetic noise simulation analysis for a permanent magnet motor. First, motor parameters are calculated using the finite element method. Then, a 3D structural model of the permanent magnet motor is constructed, and electromagnetic forces are applied to the stator structural model. The motor vibration characteristics are simulated using the modal superposition method. Next, the boundary element method is used to predict the motor's electromagnetic noise. Finally, the accuracy of the electromagnetic noise simulation analysis is verified through experiments. For ease of representation, "prototype" is used. Figure 1 and Figure 2 The external rotor permanent magnet motor shown in the prior art is referred to as "optimized" in the embodiments of the present invention as a typical external rotor permanent magnet motor.

[0061] Figure 8 The study demonstrates the overall torque fluctuation of the external rotor permanent magnet motor before and after structural optimization. The torque fluctuation before optimization was 0.7807 Nm, while the torque fluctuation after optimization was 0.4381 Nm, a reduction of approximately 43.88%, thus improving stability.

[0062] Figures 9-12 The spatial distribution characteristics of air gap magnetic flux density and radial electromagnetic force of the external rotor permanent magnet motor before and after structural optimization are shown. The optimization changes the spatial distribution law of air gap magnetic flux density, which in turn affects the amplitude and distribution characteristics of radial electromagnetic force. After optimization, the curves of air gap magnetic flux density and radial electromagnetic force have smoother fluctuations, and the amplitude and pulsation of radial electromagnetic force density are effectively reduced.

[0063] Figure 13 and Figure 14 The distribution of radial electromagnetic force in time and space of the optimized external rotor permanent magnet motor is shown. By comparing the two three-dimensional order spectrum diagrams of radial electromagnetic force density, it can be found that in the optimized scheme, the amplitude of radial electromagnetic force density corresponding to the middle and high order is significantly reduced and the distribution of high amplitude is sparser, which shows that the electromagnetic force excitation of the middle and high order is effectively suppressed.

[0064] Figure 15 The comparison of cogging torque before and after optimization is shown. The cogging torque before optimization was approximately 299.92 mN, and the cogging torque after optimization was approximately 139.74 mN. It can be seen that the cogging torque after optimization was reduced by approximately 53.41%.

[0065] Figure 16 The results show that the peak value of the equivalent radiated power in the low and mid-frequency bands is significantly reduced and the electromagnetic radiation noise is effectively suppressed before and after optimization, while the equivalent radiated power in the high-frequency bands tends to be consistent.

[0066] Figure 17 The results of the natural modes and natural frequency modes of the external rotor section of the external rotor permanent magnet motor are presented. Under the conditions of rated speed of 2648 RPM and number of pole pairs of 21, the natural frequencies of the 1st, 2nd, 3rd, 4th and 5th order harmonics of the external rotor permanent magnet motor are 1116.3Hz, 2085Hz, 2944.2Hz, 3999.5Hz and 5299.5Hz, respectively. The current excitation frequencies (current excitation frequency = speed × number of pole pairs ÷ 60) of the 1st, 2nd, 3rd, 4th and 5th order harmonics of the external rotor permanent magnet motor are 926.8Hz, 1853.6Hz, 2780.4Hz, 3707.2Hz and 4634Hz, respectively. It can be seen that the current excitation frequency differs from the natural frequency by more than 100Hz at the lowest, indicating that the motor does not resonate and has good stability.

[0067] Figure 18 and Figure 19 The diagram shows the noise waterfall of the external rotor permanent magnet motor under all operating conditions before and after optimization, obtained through sound field simulation calculation. The noise before optimization was 117.84dB, and the noise after optimization was 104.62dB. The noise of the external rotor permanent magnet motor after harmonic response optimization was reduced by about 11.22% compared with the original prototype.

[0068] Therefore, the proposed optimization method, which combines a single-segment continuous eccentric arc structure at the top of the stator teeth with a single-segment continuous convex arc structure at the end of the permanent magnet, can weaken the radial electromagnetic force and cogging torque of the motor and suppress torque fluctuations. By selecting appropriate stator tooth eccentricity and permanent magnet convex arc increments, this method effectively optimizes the electromagnetic force density and its distribution characteristics, reducing the excitation effect of electromagnetic force on motor vibration and noise. Simultaneously, this method addresses the problem of reduced average torque due to noise suppression, achieving a synergistic improvement in electromagnetic performance and vibration / noise performance.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An external rotor permanent magnet motor for suppressing electromagnetic vibration, comprising an inner stator and an outer rotor, the outer rotor comprising a rotor shaft and a plurality of permanent magnets circumferentially distributed around the rotor shaft, the inner stator having a plurality of stator teeth circumferentially distributed around the rotor shaft; characterized in that, The top of the stator teeth is provided with an eccentric arc structure that is off-center from the rotor shaft and is continuous in a single segment. The center of the arc of the eccentric arc structure does not coincide with the axis of the rotor shaft. The end of the permanent magnet near the stator teeth is provided with a continuous convex arc structure in a single segment. The convex surfaces of the eccentric arc structure at the top of the stator teeth and the convex arc structure at the end of the permanent magnet are opposite in direction, and the arc contours of the eccentric arc structure and the convex arc structure are continuous and without inflection points. The stator tooth top eccentric arc-shaped structure is characterized by the following formula: ； in, and The coordinates of the points on the arc of the eccentric arc structure at the top of the stator teeth are given, and multiple coordinate points form a single continuous arc. The radius of the arc of the eccentric arc structure at the top of the stator teeth; Stator tooth parameter angle, stator tooth parameter angle It is a variable, and satisfies , It is half the central angle of the arc of the eccentric arc structure at the top of the stator teeth. Indicates taking the absolute value; Represents the cosine function. Represents the sine function; and The center of the arc of the eccentric arc structure at the top of the stator teeth The coordinates of the circle and the center of the circle. The coordinates satisfy and All less than conditions, The inner radius of the inner stator; The =18.05mm, , ; The center of the circle The distance between the rotor shaft center O and the rotor shaft is 50mm; The arc profile of the convex arc structure at the end of the permanent magnet is characterized by the following formula: ； in, and The coordinates of the points on the arc of the convex arc structure at the end of the permanent magnet are given; multiple coordinate points form a single continuous arc. The radius of the arc of the convex arc structure at the end of the permanent magnet; For the angle of the permanent magnet parameter, the angle of the permanent magnet parameter It is a variable, and satisfies , It is half the central angle of the arc of the convex arc structure at the end of the permanent magnet. Indicates taking the absolute value; Represents the cosine function. Represents the sine function; and The center of the arc of the convex arc structure at the end of the permanent magnet The coordinates of the circle and the center of the circle. The coordinates satisfy conditions, The outer radius of the outer rotor; The =160mm, , .

2. The external rotor permanent magnet motor for suppressing electromagnetic vibration according to claim 1, characterized in that, The external rotor permanent magnet motor is an external rotor permanent magnet synchronous motor.

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