An electromagnetic noise optimization method for an outer-rotor axial-flux motor

Abstract

The present invention relates to an electromagnetic noise optimization method for an outer-rotor axial-flux motor. A air-gap magnetic field model after establishing and shifting the permanent magnet unequal pole arc coefficient is established, and an analytical model of the torque and vibration noise of the axial-flux motor is derived. The NSGA-II algorithm is used to optimize the electromagnetic noise of the axial-flux motor. Through the electromagnetic noise optimization method for the outer-rotor axial-flux motor based on the permanent magnet unequal pole arc coefficient and circumferential shift, the present invention can effectively reduce the vibration noise of the axial-flux motor without reducing the output torque, which is beneficial to reducing the noise of the axial-flux motor and assisting in the design of the axial-flux motor.

Description

Technical Field

[0001] The present invention belongs to the field of optimizing the electromagnetic noise of motors, especially the field of optimizing the electromagnetic noise of axial-flux motors. Background Art

[0002] Axial-flux motors get their name because the direction of their magnetic field is along the axial direction. Compared with traditional radial motors, axial motors have higher power and torque density, and a smaller length-to-diameter ratio, and have broad prospects as in-wheel motors; in order to ensure driving comfort, vehicle motors need to have a lower vibration and noise level. Therefore, it is necessary to carry out research on vibration reduction and noise reduction for axial-flux in-wheel motors. Currently, the research on motor vibration reduction and noise reduction mainly focuses on traditional radial motors. The noise of radial motors mainly comes from the resonance of the motor structure caused by electromagnetic forces with relatively low spatial orders. Therefore, the existing research mainly starts from two aspects: structure and excitation source for vibration reduction and noise reduction. However, the same method has great limitations when applied to axial-flux motors; due to the unique sector structure of the permanent magnets in axial-flux motors, it is very suitable to optimize the vibration and noise from the perspective of permanent magnets. The unequal pole arc coefficient and circumferential shift of permanent magnets have been used to reduce the torque ripple and cogging torque of axial-flux motors because of the relatively simple process; however, for the electromagnetic noise of axial-flux motors, its structure determines that it will be very time-consuming to perform finite element simulation calculations using three-dimensional finite elements. Therefore, it is unrealistic to optimize the electromagnetic noise using numerical methods, and the analytical method will be a good choice; currently, the analytical models of the vibration and noise of radial motors usually use ring or cylindrical shell models. However, the action points of axial electromagnetic force waves are on the surface of the permanent magnets, and the permanent magnets are bonded to the end covers, which causes the end covers to vibrate due to electromagnetic forces and then radiate noise outward. Therefore, the main noise radiator of axial-flux motors is the disc-shaped end cover. Therefore, the vibration and noise analytical models of radial motors are no longer applicable to axial motors. Therefore, it is necessary to design a model that can quickly and accurately predict the electromagnetic vibration and noise of axial-flux motors using the analytical method. Summary of the Invention

[0003] In order to solve the above problems, the present invention realizes the above objectives through the following technical solutions:

[0004] An electromagnetic noise optimization method for an outer-rotor axial-flux motor, comprising the following steps,

[0005] S1. Construct an analytical model between the unequal pole arc coefficient, pole pitch of the permanent magnets in the axial-flux motor and the motor radiation noise, output torque;

[0006] S2. Use the multi-objective genetic algorithm to optimize with torque and noise as the objectives, and optimize the pole arc coefficient and pole pitch of each permanent magnet of the motor.

[0007] S3. Obtain the optimal solution combination of the pole arc coefficient and the shift angle of the permanent magnet of the axial flux motor under the condition of equivalent output torque, thereby reducing the vibration and noise of the axial flux motor.

[0008] As a further optimization scheme of the present invention, the construction of the analytical model in S1 includes the following steps;

[0009] S11. Establish an air-gap magnetic field model after the pole arc coefficients of the permanent magnets are unequal and shifted;

[0010] S12. Deduce the analytical models of the torque and vibration noise of the axial flux motor.

[0011] As a further optimization scheme of the present invention, the establishment of the air-gap magnetic field model in S11 includes the following steps;

[0012] S111. Obtain the axial magnetic field and tangential magnetic field of the permanent magnet considering the unequal pole arc coefficients of the permanent magnets and the shift;

[0013] S112. Calculate the axial magnetic flux density and tangential magnetic flux density of the permanent magnet of the axial flux motor after the pole arc coefficients of the permanent magnets are unequal and shifted;

[0014] S113. Consider the influence of the edge effect and stator slotting through the radial correction function and the complex relative permeance function, and then correct the axial magnetic flux density and tangential magnetic flux density of the permanent magnet.

[0015] As a further optimization scheme of the present invention, before the axial magnetic flux density and tangential magnetic flux density of the permanent magnet are calculated and corrected, the armature reaction magnetic field caused by current harmonics needs to be considered; specifically, the axial armature reaction magnetic field and the tangential armature reaction magnetic field are respectively:

[0016]

[0017] In the formula, N t = GCD(p,Q s ) represents the number of spatial periods of the axial flux motor, Q s is the number of slots of the motor, h is the order of the current harmonic, s v,h represents the direction of the armature reaction magnetic field of the vN t order, ω r is the rotational angular frequency of the motor. Among them, and are the amplitudes of the axial and tangential armature reaction magnetic fields respectively.

[0018] As a further optimization scheme of the present invention, the axial magnetic field and tangential magnetic field of the permanent magnet in S111 are respectively

[0019]

[0020] where μ is the spatial order of the magnetic field of the permanent magnet, and θ is the spatial angle; B0, B z1u , B z2u are the amplitudes of the axial magnetic flux density, and are the amplitudes of the tangential magnetic flux density, and the specific amplitudes of B0, B z1u , B z2u can be obtained by Fourier series derivation.

[0021] As a further optimization scheme of the present invention, the complex relative air-gap permeance function in S113 is;

[0022] b s =(B mag +B arm )λ *

[0023] =(B z_mag +B z_arm +jB θ_mag +jB θ_arm )(λ a -jλ b )

[0024] =[(B z_mag +B z_arm )λ a +(B θ_mag +B θ_arm )λ b )+j[(B θ_mag +B θ_arm )λ a -(B z_mag +B z_arm )λ b

[0025] where,

[0026] λ * =λ a -jλ b

[0027]

[0028] As a further optimization scheme of the present invention, the axial and tangential magnetic flux densities at any radius in the edge effect in S113 are expressed as:

[0029]

[0030] where,

[0031] As a further optimization scheme of the present invention, the analytical model of the vibration noise in S12 is: ​

[0032]

[0033] Among them, w represents the axial displacement of the end cover, and η mn (t) is the modal participation factor, and W mn (r,θ) is the mode shape function. Specifically,

[0034]

[0035] W mn (r,θ) = [A mn J m (α mn r) + B mn I m (α mn r) + C mn Y m (α mn r) + D mn K m (α mn r)]cos(mθ + φ)

[0036] In the formula, ω m represents the frequency of the electromagnetic force, ω mn represents the natural frequency of the end cover, ξ mn is the damping ratio, φ mn is the phase angle, J m and Y m and I m and K m respectively represent the first and second kind of Bessel functions and the first and second kind of modified Bessel functions. A mn , B mn , C mn and D mn The four undetermined coefficients depend on the boundary conditions at the inner and outer boundaries.

[0037] As a further optimization scheme of the present invention, the torque analysis model of the axial motor in S12 is:

[0038]

[0039] Among them, R1 and R2 are the inner diameter and outer diameter of the permanent magnet respectively.

[0040] As a further optimization scheme of the present invention, the multi-objective genetic algorithm in S2 adopts the NSGA-II algorithm.

[0041] The beneficial effects of the present invention are as follows:

[0042] 1) The electromagnetic noise optimization method for an outer-rotor axial-flux motor based on the unequal pole arc coefficient and circumferential shift of permanent magnets in the present invention can effectively reduce the vibration noise of the axial-flux motor without reducing the output torque, which is beneficial to reducing the noise of the axial-flux motor and assisting in the design of the axial-flux motor. Description of the Drawings

[0043] Figure 1 It is a flowchart of the electromagnetic noise optimization method for the outer-rotor axial-flux motor of the present invention;

[0044] Figure 2 It is the Pareto Front diagram obtained after optimization by the NSGA-II algorithm of the present invention;

[0045] Figure 3 It is the permanent magnet distribution diagram before and after optimization of the axial-flux motor provided by the present invention;

[0046] Figure 4 It is the torque comparison diagram before and after optimization of the axial-flux motor provided by the present invention;

[0047] Figure 5 It is the electromagnetic noise spectrum diagram before and after optimization of the axial-flux motor provided by the present invention; Detailed Embodiments

[0048] The following further describes the present application in detail with reference to the drawings. It is necessary to point out here that the following detailed embodiments are only used to further illustrate the present application and cannot be understood as limiting the protection scope of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application according to the above application content.

[0049] As Figures 1 to 5 shown, an electromagnetic noise optimization method for an outer-rotor axial-flux motor is adopted. Specifically, a 30-pole 27-slot (30p27s) outer-rotor axial-flux hub motor with a rated speed of 600 rpm is used to conduct the experiment of the present invention, including the following steps:

[0050] S1. Construct an analytical model between the unequal pole arc coefficient, pole pitch of the permanent magnets in the axial-flux motor, and the radiation noise and output torque of the motor;

[0051] S2. Use a multi-objective genetic algorithm to optimize with torque and noise as the objectives, and optimize the pole arc coefficient and pole pitch of each permanent magnet of the motor;

[0052] S3. Obtain the optimal solution combination of the pole arc coefficient and shift angle of the permanent magnets of the axial-flux motor under the condition of equivalent output torque, thereby reducing the vibration noise of the axial-flux motor;

[0053] First, in step S1, generally, both the noise and torque of the motor are generated by electromagnetic forces. Therefore, to analytically calculate the noise radiated by the motor and the output torque, first, an analytical model of the motor's electromagnetic field should be established, that is, a model of the air-gap magnetic field after establishing the permanent magnet unequal pole arc coefficient and shifting it; then, based on this air-gap magnetic field model, an analytical model of the torque and vibration noise of the axial flux motor is derived.

[0054] Specifically, 1. Obtain the axial magnetic field and tangential magnetic field of the permanent magnet considering the permanent magnet unequal pole arc coefficient and shifting.

[0055] Assume the rotor is stationary and the stator rotates in the opposite direction at the same angular velocity. Then, in the rotor coordinate system, by solving the Laplace equation, the axial magnetic field and tangential magnetic field of the permanent magnet considering the permanent magnet unequal pole arc coefficient and shifting are obtained, which are respectively:

[0056]

[0057] where μ is the spatial order of the permanent magnet magnetic field, θ is the spatial angle; z1 and z2 represent the axial direction, θ1 and θ2 represent the tangential direction, B0, is the amplitude of the axial magnetic flux density, and are the amplitudes of the tangential magnetic flux density, which can be derived through Fourier series;

[0058]

[0059] where B r is the remanence of the permanent magnet, and p is the number of pole pairs of the permanent magnet;

[0060]

[0061] where h m is the thickness of the permanent magnet, R is the solution radius, L is the distance between the stator and rotor, z is the axial distance from the solution position to the rotor, and g0 is the air-gap length;

[0062] 2. Calculate the axial magnetic flux density and tangential magnetic flux density of the permanent magnet of the axial flux motor considering the permanent magnet unequal pole arc coefficient and shifting.

[0063] The amplitude of the tangential magnetic flux density of the permanent magnet magnetic field satisfies the following equation with the axial magnetic flux density:

[0064]

[0065] In the formula, R is the solution radius, L is the distance between the stator and rotor, and z is the axial distance from the solution position to the rotor;

[0066] Furthermore, by combining the above formulas, the axial magnetic flux density and tangential magnetic flux density of the permanent magnet of the axial flux motor considering the permanent magnet unequal pole arc coefficient and shifting are calculated.

[0067] Since the magnetic field of the motor includes the permanent magnet magnetic field and the armature reaction magnetic field, and the sum of the two is the total air-gap magnetic field, therefore, the armature reaction magnetic field also needs to be considered. Specifically, the axial armature reaction magnetic field and the tangential armature reaction magnetic field are respectively:

[0068]

[0069] In the formula, p is the number of pole pairs, v is a positive integer, θ is the space angle, t is the time, N t =GCD(p,Q s ) represents the space period number of the axial flux motor, Q s is the number of slots of the motor, h is the order of the current harmonic, s v,h represents the direction of the vN t th order armature reaction magnetic field, ω r is the rotational angular frequency of the motor; among them, and are respectively the amplitudes of the axial and tangential armature reaction magnetic fields;

[0070] 3. In order to obtain a more accurate air-gap magnetic field model, it is further necessary to consider the edge effect and the influence of stator slotting, and then correct the axial magnetic density and tangential magnetic density of the permanent magnet; then consider the edge effect and the influence of stator slotting through the radial correction function and the complex relative permeance function;

[0071] Specifically, the stator slotting is considered through the relative air-gap permeance function,

[0072] The complex relative air-gap permeance is expressed as: λ * =λ a -jλ b , and the real part and the imaginary part in the formula can be respectively expressed as:

[0073]

[0074] In the formula, Qs is the number of slots of the motor, ωr is the rotational angular frequency of the motor;

[0075] λ a and λ b are respectively the radial and tangential relative air-gap permeances, λ an and λ bn are respectively the amplitudes of the nth harmonic of the radial and tangential relative air-gap permeances, n is a positive integer;

[0076] Therefore, the influence of the slotting effect is considered through the relative air-gap permeance function:

[0077] b s =(B mag +B arm )λ *

[0078] = (B z_mag + B z_arm + jB θ_mag + jB θ_arm )(λ a - jλ b )

[0079] = [(B z_mag + B z_arm )λ a + (B θ_mag + B θ_arm )λ b + j[(B θ_mag + B θ_arm )λ a - (B z_mag + B z_arm )λ b

[0080] where the real part and the imaginary part are the axial and tangential magnetic flux densities of the axial flux motor respectively:

[0081]

[0082] The axial and tangential magnetic flux densities at any radius r in the edge effect are expressed as:

[0083]

[0084] where,

[0085] β is a constant, and its value is determined by the degree of magnetic flux density drop at the inner and outer radii, and can be obtained through parametric finite element analysis.

[0086] Subsequently, an analytical model of the torque and vibration noise of the axial flux motor needs to be further derived. Specifically, according to the Maxwell tensor equation, the axial and tangential electromagnetic force waves can be obtained, which are respectively expressed as:

[0087]

[0088] The tangential electromagnetic force acting on the unit area at this time:

[0089] dF t = P θ (θ, t, r)dS = rP θ (θ, t, r)dθdr

[0090] That is, the torque generated by the tangential electromagnetic force per unit area is: dT e = r × dF t

[0091] Therefore, the torque of the axial motor is:​

[0092]

[0093] Among them, R1 and R2 are the inner diameter and outer diameter of the permanent magnet respectively;

[0094] Meanwhile, the electromagnetic noise of the axial flux motor can be expressed as:

[0095]

[0096] Among them, w represents the axial displacement of the end cover, η mn (t) is the modal participation factor, and W mn (r,θ) is the mode shape function, which are respectively expressed as:

[0097]

[0098] W mn (r,θ) = [A mn J m (α mn r) + B mn I m (α mn r) + C mn Y m (α mn r) + D mn K m (α mn r)]cos(mθ + φ)

[0099] Among them, τ represents a certain moment, m represents the circumferential spatial order, φ represents the phase angle, ω ml represents the frequency of the electromagnetic force, ω m represents the frequency of the electromagnetic force, ω mn represents the natural frequency of the end cover, ξ mn is the damping ratio, φ mn is the phase angle, J m and Y m and I m and K m respectively represent the first and second kind Bessel functions and the first and second kind modified Bessel functions. A mn , B mn , C mn and D mn The four undetermined coefficients depend on the boundary conditions at the inner and outer boundaries; α mn represents the frequency constant, F mn is the generalized electromagnetic force,

[0100] Furthermore, since the vibration of the end - cover surface will radiate noise outward, the noise radiated by the end - cover can be calculated based on the vibration velocity of the end - cover surface. Therefore, taking the vibration velocity of the end - cover surface as the boundary condition, the acoustic radiation of the entire end - cover can be obtained, as shown in the following formula:

[0101] The acoustic power and acoustic power level radiated by the axial - flux motor are respectively expressed as:

[0102]

[0103] where, σ mn is the acoustic radiation efficiency, ρ0 and c0 are respectively the density and velocity of sound, S is the area of the end - cover, ∏ ref = 10 -12 W, representing the reference acoustic power;

[0104] So far, through the above steps, the analytical models between the pole - arc coefficient, pole pitch of the permanent magnet and the output torque and noise have been obtained. Further, in order to obtain the optimal solution combination of the pole - arc coefficient and the shift angle of the permanent magnet of the axial - flux motor under the condition of equivalent output torque, taking torque and electromagnetic noise as the optimization objectives, multi - objective optimization is used to reduce the vibration and noise of the motor;

[0105] Specifically, in step S2, the multi - objective genetic algorithm is used to optimize with torque and noise as the objectives, optimizing the pole - arc coefficient and pole pitch of each permanent magnet of the motor; among them, the NSGA - Ⅱ algorithm is used to optimize the vibration and noise of the axial - flux motor;

[0106] The 0 - th order electromagnetic force in space is the main source of axial - flux vibration, and the noise peak at 90 times the rotational frequency contributes greatly to the total sound pressure level. Therefore, the following two optimization objectives are determined as the fitness functions:

[0107]

[0108] Conditions: (1) The pole - arc coefficient and circumferential shift angle of each permanent magnet satisfy:

[0109]

[0110] (2) At the same time, to ensure that the permanent magnets do not collide, it should satisfy:

[0111]

[0112] (3) The pole - arc coefficient of the permanent magnet should satisfy: 0 < α p (i) < 1;

[0113] Combining the above conditions and formulas, the NSGA - Ⅱ algorithm is used to optimize the electromagnetic noise of the axial - flux motor. This optimization algorithm is implemented through MATLAB. After optimization, we get as Figure 2The Pareto Front diagram shown

[0114] After optimization by the above analytical method, the schematic diagrams of the structures of the permanent magnets before and after optimization are as Figure 3 shown. Among them, the pole arc coefficient and pole pitch of each permanent magnet in the traditional motor are the same, while in the present application, the pole arc coefficient and pole pitch of each permanent magnet are variable. The optimal pole arc coefficient and pole pitch of each permanent magnet, that is, the optimal combination, are obtained through multi-objective optimization to achieve the function of vibration and noise reduction;

[0115] And through Figure 4 the comparison diagram of the average torque of the axial flux motor before and after optimization, it can be seen that using the optimization method of the present application for optimization does not reduce the output performance of the axial motor;

[0116] Finally, the optimization results are verified through a finite element model, which specifically includes the following steps:

[0117] ① Calculate the vibration and noise of the axial flux motor before and after optimization using permanent magnets with unequal pole arc coefficients and circumferential displacement through a multi-physics field model, which mainly includes three steps: establishing an electromagnetic field model and calculating the nodal electromagnetic force acting on the surface of the permanent magnet through three-dimensional finite element;

[0118] ② Calculate the modal characteristics of the motor in workbench;

[0119] ③ Load it on the structural model in LMS virtual lab by means of nodal force transfer, and calculate the electromagnetic vibration and noise respectively according to the modal superposition method and the boundary element method;

[0120] The vibration and noise spectrograms calculated before and after optimization are as Figure 5 shown.

[0121] Each permanent magnet of the traditional axial flux motor is exactly the same, that is, the pole arc coefficient and pole pitch are equal. However, in the present application, a new permanent magnet arrangement method is proposed to optimize the noise of the motor, that is, after using permanent magnets with unequal pole arc coefficients and circumferential displacement, the pole arc coefficient and pole pitch of the permanent magnets are no longer the same; Therefore, the analytical model in this article is to establish the relationship between the technology of using permanent magnets with unequal pole arc coefficients and circumferential displacement and the noise radiated by the axial flux motor and the output torque. Finally, a multi-objective genetic algorithm is used to optimize with torque and noise as the objectives, and the optimal pole arc coefficient and displacement angle of the permanent magnet are calculated; Finally, on the premise of not reducing the output torque, the vibration and noise of the axial flux motor are effectively reduced.

[0122] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.

Claims

1. An electromagnetic noise optimization method for an outer-rotor axial-flux motor, characterized in that: Including the following steps, S1. Construct an analytical model between the unequal pole arc coefficient, pole pitch of the permanent magnet in the axial flux motor and the motor radiated noise and output torque; The construction of the analytical model includes the following steps: S11. Establish an air-gap magnetic field model after establishing and shifting the unequal pole arc coefficient of the permanent magnet. The establishment of the air-gap magnetic field model includes the following steps: S111. Obtain the axial magnetic field and tangential magnetic field of the permanent magnet considering the unequal pole arc coefficient and shift of the permanent magnet; S112. Calculate the axial magnetic flux density and tangential magnetic flux density of the permanent magnet with unequal pole arc coefficient and shift in the axial flux motor; Before calculating the axial magnetic flux density and tangential magnetic flux density of the permanent magnet and before correction, the armature reaction magnetic field considering current harmonics needs to be considered; Specifically, the axial armature reaction magnetic field and tangential armature reaction magnetic field are respectively: where p is the number of pole pairs, v is a positive integer, θ is the spatial angle, t is the time, N t = GCD(p, Q s ) represents the number of spatial periods of the axial flux machine, Q s is the number of slots of the machine, h is the order of the current harmonic, s v,h represents the direction of the vN t th order armature reaction magnetic field, ω r is the rotational angular frequency of the machine; where, and are the amplitudes of the axial and tangential armature reaction magnetic fields respectively; S113. Consider the influence of edge effect and stator slotting through the radial correction function and complex relative permeance function, and then correct the axial magnetic flux density and tangential magnetic flux density of the permanent magnet; S12. Deduce the analytical models of torque and vibration noise of the axial flux motor; The analytical model of torque is: Where, R1 and R2 are the inner diameter and outer diameter of the permanent magnet respectively; The analytical model of vibration noise is: where w represents the axial displacement of the end cover, and η mn (t) is the modal participation factor, and W mn (r, θ) is the mode shape function. Specifically, W mn (r,θ) = [A mn J m (α mn r) + B mn I m (α mn r) + C mn Y m (α mn r) + D mn K m (α mn (r)] cos(mθ + φ) where τ represents a certain moment, m represents the circumferential spatial order, φ represents the phase angle, ω ml represents the frequency of the electromagnetic force, ω mn represents the natural frequency of the end cover, ξ mn is the damping ratio, φ mn is the phase angle, J m , Y m and I m , K m respectively represent the first and second kind of Bessel functions and the first and second kind of modified Bessel functions, A mn , B mn , C mn and D mn The four undetermined coefficients depend on the boundary conditions at the inner and outer boundaries, α mn represents the frequency constant, F mn is the generalized electromagnetic force, S2. Use the multi-objective genetic algorithm to optimize with the motor torque and noise as the objectives, and obtain the optimal solution combination of the pole arc coefficient and shift angle of the permanent magnet in the axial flux motor under the condition of equivalent output torque.

2. The electromagnetic noise optimization method of an outer rotor axial flux motor according to claim 1, characterized in that: The axial magnetic field and tangential magnetic field of the permanent magnet in S111 are respectively where μ is the spatial order of the magnetic field of the permanent magnet, and θ is the spatial angle; z1 and z2 represent the axial direction, θ1 and θ2 represent the tangential direction, B0, and are the amplitudes of the axial magnetic flux density, and are the amplitudes of the tangential magnetic flux density, and B0 can be derived through Fourier series, the specific amplitude.

3. An electromagnetic noise optimization method for an outer rotor axial flux motor according to claim 1, characterized in that: The complex relative air-gap permeance function in S113 is; b s = (B mag + B arm ) λ * =(B z_mag +B z_arm +jB θ_mag +jB θ_arm )(λ a -jλ b ) = [(B z_mag + B z_arm )λ a + (B θ_mag + B θ_arm )λ b + j[(B θ_mag + B θ_arm )λ a - (B z_mag + B z_arm )λ b ​ Where, λ* = λ a -jλ b λ a and λ b are the radial and tangential relative air-gap permeances respectively, and λ an and λ bn are the amplitudes of the n-th harmonics of the radial and tangential relative air-gap permeances respectively, where n is a positive integer.

4. The electromagnetic noise optimization method for an outer rotor axial flux motor according to claim 1, wherein: The axial and tangential magnetic flux densities at any radius in the edge effect in S113 are expressed as: Among them, In the formula, r is the radius, R1 and R2 are the inner diameter and outer diameter of the permanent magnet respectively, and β is a constant.

5. The electromagnetic noise optimization method of an outer rotor axial flux motor according to claim 1, characterized in that: The multi-objective genetic algorithm in S2 adopts the NSGA-II algorithm.

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