Permanent magnet brushless direct current motor with non-uniform air gap and parameter optimization method thereof

Abstract

The invention discloses a permanent magnet brushless direct current motor with a non-uniform air gap and a parameter optimization method thereof. The permanent magnet brushless direct current motor comprises a stator core, a stator winding, a rotor core, permanent magnets, lightening holes and a rotating shaft. The non-uniform air gap is located between the stator and the rotor and is determined by the outer contour of the circular arc surface of the rotor, the outer contour of the circular arc surface of the rotor is composed of two parts including a segmented arc part and a valley-shaped non-segmented arc part, the segmented arc part is composed of eight segmented arcs, and the valley-shaped non-segmented arc part is composed of a valley-shaped non-segmented arc part and a valley-shaped non-segmented arc part. The valley-shaped non-segmented arc part is formed by superposing outer contours of third harmonics and sine waves, the two parts are sequentially connected to form an outer contour of the rotor, and parameters of the non-uniform air gap are optimized through a Taguchi method. Compared with the prior art, the sine degree of an air-gap magnetic field can be effectively improved, the torque pulsation of the permanent magnet brushless direct current motor is reduced, the harmonic content is reduced, and therefore the efficiency of the motor is improved.

Description

Technical Field

[0001] The present invention relates to motor design technology, in particular to a permanent magnet brushless DC motor with a non-uniform air gap and a parameter optimization method thereof, belonging to the field of permanent magnet brushless DC manufacturing technology. Background Art

[0002] Permanent magnet brushless DC motors (PMBLDCs), with their significant advantages such as high efficiency, low noise, and long life, are widely used in a variety of high-end fields, including aerospace, industrial automation, and electric vehicles. In electric vehicles, PMBLDCs can provide high torque and high-speed performance, which are critical to the electric vehicle's powertrain. Moreover, due to the lack of brush friction, PMBLDCs can operate at higher speeds while achieving a more compact size and lower audible noise. Furthermore, PMBLDCs are widely used in the medical device field. For example, they are used abroad to drive small blood pumps in artificial hearts, and in China, they are used in high-speed centrifuges for high-speed surgical instruments, and infrared laser modulators for thermal imagers and thermometers.

[0003] However, traditional permanent magnet brushless DC motors generally use a uniform air gap rotor structure. While its symmetrical geometric design simplifies the manufacturing process, it results in a significant non-sinusoidal distribution of the air gap magnetic field, leading to problems such as high-order harmonic content, increased torque ripple, and electromagnetic vibration noise. This seriously restricts the motor's performance in high-precision motion control scenarios. To address these issues, academia and industry have proposed a variety of optimization solutions:

[0004] Harmonic suppression technology: Improve the magnetic field distribution by optimizing the permanent magnet pole arc coefficient or using the Halbach pole array. However, this method is limited by the symmetry constraints of the magnetic circuit and is difficult to effectively suppress specific harmonics (such as the third harmonic), and it is easy to cause a decrease in average torque.

[0005] Air gap modulation technology: Introducing stator tooth slots or rotor surface salient pole design to use the magnetic permeability modulation effect to weaken harmonics, but such structures may aggravate local magnetic saturation, increase iron loss and reduce efficiency.

[0006] Control strategy optimization: Although harmonic current injection or torque observation compensation algorithms can partially suppress torque pulsation, they rely on high-precision sensors and complex control algorithms, increasing system costs and real-time challenges. Summary of the Invention

[0007] Purpose of the invention: In response to the problems in the background technology, the present invention discloses a permanent magnet brushless DC motor with a non-uniform air gap and a parameter optimization method thereof. Through segmented arc design and valley-shaped non-segmented arc design, the air gap magnetic permeability distribution is actively reconstructed to achieve the weakening of high-order harmonics and the precise enhancement of the fundamental magnetic field.

[0008] Technical solution: The present invention discloses a permanent magnet brushless DC motor with a non-uniform air gap and a parameter optimization method thereof, wherein the permanent magnet brushless DC motor with a non-uniform air gap comprises a stator and a rotor, wherein the stator comprises a stator core and a stator winding embedded in the stator core, and the rotor comprises a rotor core, permanent magnet slots, permanent magnets, a weight reduction hole and a rotating shaft passing through the rotor core; the permanent magnet slots are evenly arranged in a straight line on the inner side of the rotor core, the permanent magnets are embedded in the permanent magnet slots, and air slots are left on both sides of the permanent magnets; the outer contour of the rotor comprises segmented arc parts and valley-shaped non-segmented arc parts arranged in sequence, the weight reduction holes are evenly arranged on the inner side of the rotor, the center of the circle coincides with the center of the segmented arc, the segmented arc part and the valley-shaped non-segmented arc part are connected end to end to form a non-uniform rotor outer contour, and a non-uniform air gap structure is provided between the non-uniform rotor outer contour and the stator; the parameter optimization method of the permanent magnet brushless DC motor with a non-uniform air gap comprises the following steps:

[0009] Step 1: Design of the segmented arc part, divide the rotor arc into 8 segmented arcs, and the center of each segmented arc is the center of the weight-reducing hole O x , the radius is R1, each segmented arc curve is denoted as L x , x is a natural number from 1 to 8;

[0010] Step 2: Design the non-segmented arc part of the valley shape. Connect the two segmented arcs and take the midpoint of the line segment as P. x , with the two ends of the line segment as the starting point and the end point, and P x Point is taken as the center, and the outer contour curve of the third harmonic Q1 and the outer contour curve of the half-cycle sine wave Q2 are added at the same time. Q1 and Q2 are superimposed to form a valley-shaped non-segmented arc curve H. x ;

[0011] Step 3: Segmented arc curve L x Valley-shaped non-segmented arc curve H x They are connected in sequence to form a closed rotor outer contour, thereby forming an uneven air gap between the stator and the rotor.

[0012] Furthermore, the air gap length L of the segmented arc portion is:

[0013] L=λπR 2 -4θ1R1 2 +λδ0

[0014] Where: λ is the proportional coefficient of the segmented arc part in the rotor arc; R is the radius of the rotor circle; θ1 is the opening angle of each segmented arc; R1 is the radius of the segmented arc; δ0 is the initial air gap value;

[0015] Air gap magnetic flux density B of the segmented arc part L for:

[0016]

[0017] Where: μ0 is the vacuum permeability; μ r is the relative magnetic permeability; k δ is the air gap correlation coefficient; B r is the remanent magnetic density of the permanent magnet.

[0018] Furthermore, the air gap length H of the valley-shaped non-segmented arc is:

[0019]

[0020] Where: θ is the phase of the sine wave, 3θ is the phase of the third harmonic, sinθ is the sine wave curve, sin3θ is the third harmonic curve, and the curve H x The distance between the highest point and point O is recorded as R H , curve H x The distance between the lowest point and point O is denoted as R L ,(R H -R L ) is the amplitude of the sine wave; is the amplitude of the third harmonic; d2 is P x The distance between point θ and the rotor center point O; θ2 and θ3 are the phases of the starting and ending points of the sine wave; R is the radius of the rotor circle; δ0 is the initial air gap value; λ is the proportional coefficient of the segmented arc part in the rotor arc;

[0021] Air gap magnetic flux density B of the valley-shaped non-segmented arc part H for:

[0022]

[0023] Where μ0 is the vacuum permeability; μ r is the relative magnetic permeability; k δ is the air gap correlation coefficient; B r is the remanent magnetic density of the permanent magnet.

[0024] Furthermore, the entire rotor air gap magnetic flux density B is:

[0025]

[0026] Wherein, λ is the proportional coefficient of the segmented arc part (8) in the rotor arc; R is the radius of the rotor circle; θ1 is the opening angle of each segmented arc; R1 is the radius of the segmented arc; δ0 is the initial air gap value; μ0 is the vacuum permeability; μ r is the relative magnetic permeability; k δ is the air gap correlation coefficient; B ris the remanent magnetic density of the permanent magnet; θ is the phase of the sine wave, 3θ is the phase of the third harmonic, sinθ is the sine wave curve, sin3θ is the third harmonic curve, and the curve H x The distance between the highest point and point O is recorded as R H , curve H x The distance between the lowest point and point O is denoted as R L ,(R H -R L ) is the amplitude of the sine wave; is the amplitude of the third harmonic; d2 is P x The distance between point θ and the rotor center O; p is the number of pole pairs; θ2 and θ3 are the phases of the starting and ending points of the sine wave.

[0027] Furthermore, the Taguchi method is used to calculate the opening angle θ1 of each segmented arc and the center O of each segmented arc. x The distance between the rotor center O is recorded as the eccentricity d1, the phases of the starting and ending points of the sine wave θ2, θ3, P x The distance between point 1 and the rotor center point O is recorded as the eccentricity d2 to optimize the air gap magnetic flux sinusoidality. The process is as follows:

[0028] (1) The optimization factors are the opening angle θ1, eccentricity d1, phases θ2 and θ3 of the starting and ending points of the sine wave, and eccentricity d2 of each segmented arc. Each optimization factor takes three levels:

[0029] θ1=(30°, 35°, 40°), d1=(10, 12, 14), θ2=(0°, 15°, 30°),

[0030] θ3=(90°, 75°, 60°), d2=(15, 17, 19)

[0031] (2) Set the objective function to minimize the air gap magnetic field harmonic distortion rate THD, which is:

[0032]

[0033] Among them, B1 is the fundamental amplitude, B n is the amplitude of the nth harmonic;

[0034] (3) Design an orthogonal table and select five optimization factors, θ1, d1, θ2, θ3, and d2. Each factor has three levels, and different combinations form a 9×5 orthogonal table. Then select L9(3 5 ) orthogonal array;

[0035] (4) Carry out Maxwell finite element simulation experiment to obtain B n value;

[0036] (5) Calculate the signal-to-noise ratio and substitute the target parameters into the calculation formula:

[0037]

[0038] Where n is the number of experimental repetitions, THD i is the harmonic distortion rate of the i-th experiment;

[0039] (6) Analyze the signal-to-noise ratio, calculate the average SNR of each factor at different levels, select the level with the highest average SNR for each factor, and determine the optimal level combination;

[0040] (7) Evaluate the significant contribution of each factor to the target through variance analysis, and finally obtain the optimal combination of factors.

[0041] Furthermore, the permanent magnet is made of neodymium iron boron material and adopts radial magnetization method.

[0042] Beneficial effects:

[0043] The present invention designs a permanent magnet brushless DC motor with a non-uniform air gap by designing the rotor outer contour with a segmented arc portion and a valley-shaped non-segmented arc portion. The segmented arc portion design can optimize the waveform of the air gap magnetic field, making it closer to a sine wave, thereby reducing the harmonic content and improving the operating performance of the motor. By optimizing the sinusoidality of the air gap magnetic field, the segmented arc can effectively suppress torque pulsation, making the motor run more smoothly, thereby reducing the vibration and noise of the motor. The valley-shaped non-segmented arc portion design can effectively optimize the air gap shape and increase the fundamental air gap magnetic flux density through the superposition of the outer contour curves of the sine wave Q1 and the third harmonic Q2, thereby improving the output torque of the permanent magnet motor. By precisely controlling the angle between the third harmonic and the fundamental wave, the negative impact of other harmonics on the motor performance can be effectively suppressed, thereby optimizing the steady-state performance of the motor, and at the same time significantly improving the average torque of the motor without increasing the torque pulsation. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is the structural diagram of permanent magnet brushless DC motor;

[0045] Figure 2 This is the design diagram of the quarter rotor structure of the permanent magnet brushless DC motor;

[0046] Figure 3 Design the structural diagram for the valley-shaped non-segmented arc part of the permanent magnet brushless DC motor;

[0047] Figure 4 Algorithm flow chart for Taguchi method optimization;

[0048] Figure 5 This is a comparison diagram of the waveforms of uniform air gap magnetic flux and non-uniform air gap magnetic flux;

[0049] Figure 6 This is a comparison chart of Fourier analysis of uniform air gap magnetic flux and non-uniform air gap magnetic flux. DETAILED DESCRIPTION

[0050] The present invention will be further described below with reference to the accompanying drawings.

[0051] See also Figure 1 The present invention discloses a permanent magnet brushless DC motor with a non-uniform air gap and a parameter optimization method thereof. The permanent magnet brushless DC motor with a non-uniform air gap comprises a stator embedded with winding coils and a rotor embedded with permanent magnets. The stator comprises a stator core 1 and a stator winding 2, wherein the stator winding 2 is embedded in the stator core 1. The rotor comprises a rotor core 3, permanent magnet slots 6, permanent magnets 4, a weight-reducing hole 7, and a rotating shaft 5. The permanent magnet slots 6 are evenly arranged in a straight line inside the rotor core 3. The permanent magnets 4 are connected to the permanent magnet slots 6, with air slots left on both sides of the permanent magnets. The permanent magnets are made of neodymium iron boron material and are radially magnetized. The outer contour of the rotor includes segmented arc parts 8 and valley-shaped non-segmented arc parts 9 that are arranged in sequence. The weight-reducing holes 7 are evenly arranged on the inner side of the rotor, and their centers coincide with the centers of the segmented arcs 8. The segmented arc parts 8 and the valley-shaped non-segmented arcs 9 are connected end to end to form a non-uniform outer contour of the rotor. A non-uniform air gap structure is provided between the non-uniform outer contour of the rotor and the stator.

[0052] See also Figure 2 The non-uniform air gap structure is mainly determined by the outer contour of the rotor, which includes the segmented arc part 8 and the valley-shaped non-segmented arc part 9:

[0053] Step 1: The design of the segmented arc part 8 is to divide the rotor arc of the motor into 8 segmented arcs, and the center of each segmented arc is the center of the weight reduction hole O x (x ranges from 1 to 8), with a radius of R1. Set the center of each segmented arc to O x The distance from the rotor center O is denoted as d1, the opening angle of each segment arc is denoted as θ1, and the curve of each segment arc is denoted as L x .

[0054] Step 2: See Figure 3 The design of the valley-shaped non-segmented arc part 9 is to connect the two segmented arcs and take the midpoint of the line segment as P x (x is 1 to 8), in the valley-shaped non-segmented arc part 9, the two ends of the line segment are the starting point and the end point, with P x Point is taken as the center, and the outer contour curve of the third harmonic Q1 and the outer contour curve of the half-cycle sine wave Q2 are added at the same time. Q1 and Q2 are superimposed to form the curve H. x The valley shape. xThe distance between point d2 and the center of the rotor O is recorded as d2, and the angles of the starting and ending points of the sine wave are recorded as θ2 and θ3, then the angles of the starting and ending points of the third harmonic are 3θ2 and 3θ3, and the curve H is x The distance between the highest point and point O is recorded as R H , curve H x The distance between the lowest point and point O is denoted as R L .

[0055] Step 3: Segmented arc curve L x Valley-shaped non-segmented arc curve H x They are connected in sequence to form a closed rotor outer contour, thereby forming an uneven air gap between the stator and the rotor.

[0056] The air gap length L of the segmented arc portion 8 is:

[0057] L=λπR 2 -4θ1R1 2 +λδ0

[0058] Where: λ is the proportional coefficient of the segmented arc part in the rotor arc; R is the radius of the rotor circle; θ1 is the angle of the segmented arc; R1 is the radius of the segmented arc; δ0 is the initial air gap value.

[0059] Air gap magnetic flux density B of segmented arc part 8 L for:

[0060]

[0061] Where: μ0 is the vacuum permeability; μ r is the relative magnetic permeability; k δ is the air gap correlation coefficient; B r is the remanent magnetic density of the permanent magnet.

[0062] The air gap length H of the valley-shaped non-segmented arc portion 9 is:

[0063]

[0064] Where: A is the amplitude of the sine wave; A3 is the amplitude of the third harmonic; d2 is P x The distance between point θ and the rotor center O; p is the number of pole pairs; θ2 and θ3 are the starting angles of the sine wave.

[0065] The air gap magnetic flux density B of the valley-shaped non-segmented arc part 9 H for:

[0066]

[0067] The entire rotor air gap magnetic flux density B is:

[0068]

[0069] The air gap magnetic flux sinusoidality is optimized by using the Taguchi method for the segmented arc angle θ1, eccentricity d1, sinusoidal wave starting angles θ2, θ3, and eccentricity d2. For the optimization process, see Figure 4 , the process is as follows:

[0070] (1) Establish optimization factors and their levels. Each factor has three levels, with:

[0071] θ1=(30°, 35°, 40°)

[0072] d1=(10, 12, 14)

[0073] θ2=(0°, 15°, 30°)

[0074] θ3=(90°, 75°, 60°)

[0075] d2=(15, 17, 19)

[0076] The unit of eccentricities d1 and d2 is mm.

[0077] (2) Setting the objective function;

[0078] Target characteristics: Minimize the air gap magnetic field harmonic distortion rate THD, that is, the desired small characteristics, including:

[0079]

[0080] Among them, B1 is the fundamental amplitude, B n is the amplitude of the nth harmonic (usually calculated up to the 7th harmonic, k=7).

[0081] (3) Design an orthogonal table and select five optimization factors: θ1, d1, θ2, θ3, and d2. Each factor has three levels. Then L9(3 5 )Orthogonal array.

[0082] (4) Carry out Maxwell finite element simulation experiment to obtain B n value.

[0083] (5) Calculate the signal-to-noise ratio and substitute the target parameters into the calculation formula:

[0084]

[0085] Where n is the number of experimental repetitions (usually n = 1 or multiple experiments are performed to obtain the average value), THD i is the harmonic distortion rate of the i-th experiment.

[0086] (6) Analyze the signal-to-noise ratio, calculate the average SNR of each factor at different levels, and determine the optimal level combination (taking θ1 as an example): The average SNR of the segmented arc angle θ1 when the horizontal angle is 30°:

[0087]

[0088] Among them, SNR1, SNR2, and SNR3 are the SNR values ​​when the segmented arc angle θ1 is at a level of 30°. Correspondingly, the average SNR of the segmented arc angle θ1 at other levels is calculated, and the level with the highest average SNR in each factor is selected.

[0089] The significant contribution of each factor to the target was evaluated by analysis of variance:

[0090]

[0091] Where N is the total number of experiments (e.g. N=9 in orthogonal table L9). i is the signal-to-noise ratio of the i-th experiment; is the average value of SNR of all experiments; m is the number of levels of the factor (e.g. 3-level factor, m=3); ∑SNR k is the sum of SNRs of all experiments at the kth level of a factor; n k is the number of experiments for the kth level of a factor (usually n in an orthogonal table k equal).

[0092] Finally, the optimal combination of factors is: θ1=35°, d1=12, θ2=0°, θ3=180°, d2=19.

[0093] The following experiments are conducted with the permanent magnet brushless DC motor with uniform air gap structure and the non-uniform air gap structure of the present invention. The air gap magnetic flux density is shown in FIG. Figure 5 and Figure 6 ,according to Figure 5 Comparison of air gap flux density waveforms shows that the permanent magnet brushless DC motor with non-uniform air gap and its parameter optimization method designed by the present invention can effectively improve the sinusoidality of air gap flux density. Figure 6 The comparison of the air gap magnetic flux Fourier shows that the permanent magnet brushless DC motor with a non-uniform air gap and the parameter optimization method thereof designed in the present invention can slightly enhance the fundamental magnetic field and effectively suppress the distortion of the 3rd, 5th, 7th and 9th harmonics.

[0094] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A permanent magnet brushless DC motor with a non-uniform air gap and a parameter optimization method thereof, characterized in that: The non-uniform air gap permanent magnet brushless DC motor comprises a stator and a rotor, wherein the stator comprises a stator core (1) and a stator winding (2) embedded in the stator core (1), and the rotor comprises a rotor core (3), permanent magnet slots (6), permanent magnets (4), a weight reduction hole (7), and a rotating shaft (5) passing through the rotor core (3); the permanent magnet slots (6) are evenly arranged in a straight line on the inner side of the rotor core (3), the permanent magnets (4) are embedded in the permanent magnet slots (6), and the permanent magnets (4) are left on both sides. There are air slots; the outer contour of the rotor includes segmented arc parts (8) and valley-shaped non-segmented arc parts (9) arranged at intervals in sequence; the weight-reducing holes (7) are evenly arranged on the inner side of the rotor, and the center of the circle coincides with the center of the circle of the segmented arc (8); the segmented arc part (8) and the valley-shaped non-segmented arc part (9) are connected end to end to form a non-uniform outer contour of the rotor; a non-uniform air gap structure is provided between the non-uniform outer contour of the rotor and the stator; the parameter optimization method of the permanent magnet brushless DC motor with a non-uniform air gap comprises the following steps: Step 1: Design of the segmented arc part (8), divide the rotor arc into 8 segmented arcs, and the center of each segmented arc is the center of the weight-reducing hole O x , the radius is R1, each segmented arc curve is denoted as L x , x is a natural number from 1 to 8; Step 2: Design the valley-shaped non-segmented arc part (9). Connect the two segmented arcs and take the midpoint of the line segment as P. x , with the two ends of the line segment as the starting point and the end point, and P x Point is taken as the center, and the outer contour curve of the third harmonic Q1 and the outer contour curve of the half-cycle sine wave Q2 are added at the same time. Q1 and Q2 are superimposed to form a valley-shaped non-segmented arc curve H. x ; Step 3: Segmented arc curve L x Valley-shaped non-segmented arc curve H x They are connected in sequence to form a closed rotor outer contour, thereby forming an uneven air gap between the stator and the rotor.

2. A permanent magnet brushless DC motor with a non-uniform air gap and a parameter optimization method thereof according to claim 1, characterized in that: The air gap length L of the segmented arc portion (8) is: L=λπR 2 -4θ1R1 2 +λδ0 Where: λ is the proportional coefficient of the segmented arc part (8) in the rotor arc; R is the radius of the rotor circle; θ1 is the opening angle of each segmented arc; R1 is the radius of the segmented arc; δ0 is the initial air gap value; Air gap magnetic flux density B of segmented arc part (8) L for: Where: μ0 is the vacuum permeability; μ r is the relative magnetic permeability; k δ is the air gap correlation coefficient; B r is the remanent magnetic density of the permanent magnet.

3. A permanent magnet brushless DC motor with a non-uniform air gap and a parameter optimization method thereof according to claim 1, characterized in that: The air gap length H of the valley-shaped non-segmented arc (9) is: Where: θ is the phase of the sine wave, 3θ is the phase of the third harmonic, sinθ is the sine wave curve, sin3θ is the third harmonic curve, and the curve H x The distance between the highest point and point O is recorded as R H , curve H x The distance between the lowest point and point O is denoted as R L ,(R H -R L ) is the amplitude of the sine wave; is the amplitude of the third harmonic; d2 is the distance between point Px and the rotor center point O; θ2 and θ3 are the phases of the starting and ending points of the sine wave; R is the radius of the rotor circle; δ0 is the initial air gap value; λ is the proportional coefficient of the segmented arc part (8) in the rotor arc; Air gap magnetic flux density B of the valley-shaped non-segmented arc part H for: Where μ0 is the vacuum permeability; μ r is the relative magnetic permeability; k δ is the air gap correlation coefficient; B r is the remanent magnetic density of the permanent magnet.

4. A permanent magnet brushless DC motor with a non-uniform air gap and a parameter optimization method thereof according to claim 1, characterized in that: The entire rotor air gap magnetic flux density B is: Wherein, λ is the proportional coefficient of the segmented arc part (8) in the rotor arc; R is the radius of the rotor circle; θ1 is the opening angle of each segmented arc; R1 is the radius of the segmented arc; δ0 is the initial air gap value; μ0 is the vacuum permeability; μ r is the relative magnetic permeability; k δ is the air gap correlation coefficient; B r is the remanent magnetic density of the permanent magnet; θ is the phase of the sine wave, 3θ is the phase of the third harmonic, sinθ is the sine wave curve, sin3θ is the third harmonic curve, and the curve H x The distance between the highest point and point O is recorded as R H , the distance between the lowest point of curve Hx and point O is recorded as R L ,(R H -R L ) is the amplitude of the sine wave; is the amplitude of the third harmonic; d2 is P x The distance between point θ and the rotor center O; p is the number of pole pairs; θ2 and θ3 are the phases of the starting and ending points of the sine wave.

5. A permanent magnet brushless DC motor with a non-uniform air gap and a parameter optimization method thereof according to claim 1, characterized in that: The Taguchi method is used to calculate the opening angle θ1 of each segmented arc and the center O of each segmented arc. x The distance between the rotor center O is recorded as the eccentricity d1, the phases of the starting and ending points of the sine wave θ2, θ3, P x The distance between point 1 and the rotor center point O is recorded as the eccentricity d2 to optimize the air gap magnetic flux sinusoidality. The process is as follows: (1) The optimization factors are the opening angle θ1, eccentricity d1, phases θ2 and θ3 of the starting and ending points of the sine wave, and eccentricity d2 of each segmented arc. Each optimization factor takes three levels: θ1=(30°, 35°, 40°), d1=(10, 12, 14), θ2=(0°, 15°, 30°), θ3=(90°, 75°, 60°), d2=(15, 17, 19) (2) Set the objective function to minimize the air gap magnetic field harmonic distortion rate THD, which is: Among them, B1 is the fundamental amplitude, B n is the amplitude of the nth harmonic; (3) Design an orthogonal table and select five optimization factors, θ1, d1, θ2, θ3, and d2. Each factor has three levels, and different combinations form a 9×5 orthogonal table. Then select L9(3 5 ) orthogonal array; (4) Carry out Maxwell finite element simulation experiment to obtain B n value; (5) Calculate the signal-to-noise ratio and substitute the target parameters into the calculation formula: Where n is the number of experimental repetitions, THD i is the harmonic distortion rate of the i-th experiment; (6) Analyze the signal-to-noise ratio, calculate the average SNR of each factor at different levels, select the level with the highest average SNR for each factor, and determine the optimal level combination; (7) Evaluate the significant contribution of each factor to the target through variance analysis, and finally obtain the optimal combination of factors.

6. A permanent magnet brushless DC motor with a non-uniform air gap and an optimization method thereof according to claim 1, characterized in that: The permanent magnet is made of neodymium iron boron material and adopts radial magnetization method.

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