A low-torque pulsation hub motor and air gap magnetic field harmonic group design method

Abstract

The present invention discloses a low-torque pulsation hub motor and an air gap magnetic field harmonic group design method that introduces magnetic field modulation technology. The method analyzes the spatial and temporal orders of magnetic and armature air gap magnetic flux densities, determines whether the magnetic field harmonics can contribute to the average torque and permanent magnet torque pulsation, uses the air gap magnetic field harmonic group to analyze the permanent magnet torque pulsation, considers the contribution of the magnetic field harmonics to the average torque and permanent magnet torque pulsation, divides the magnetic field harmonic group according to the magnetic field amplitude, sets the rotor inner surface at each pole of the motor into a clipped pole arc segment, and makes the air gap at each clipped pole arc segment an air gap with non-uniform thickness on the permanent magnet side. Under the premise of maintaining the permanent magnet air gap magnetic field harmonics of the synthetic torque group, the permanent magnet air gap magnetic field harmonics of the synthetic pulsation group are suppressed. On the armature side, a star-delta winding is designed. Under the premise of maintaining the armature air gap magnetic field harmonics of the synthetic torque group, the armature air gap magnetic field harmonics of the synthetic pulsation group are suppressed, so that the motor has high torque density and low torque pulsation characteristics.

Description

Technical Field

[0001] The present invention belongs to the field of motors, and in particular relates to a design method for a hub motor and an air gap magnetic field harmonic group by introducing a magnetic field modulation technology. Background Art

[0002] In-wheel motor technology, also known as in-wheel motor technology, has the greatest advantage of integrating power, transmission, and braking within the wheel hub, significantly simplifying the overall structure of electric vehicles. To reduce motor size, address wear and heat generation issues associated with the reducer, and increase power density, magnetic field modulation in-wheel motors have been proposed. Unlike traditional in-wheel motors, magnetic field modulation in-wheel motors, due to their unique field modulation effect, break the rule that the number of rotor pole pairs must be identical to the number of armature pole pairs. This offers the advantage of high torque at low speed, giving them a distinct advantage over traditional motors in the electric vehicle sector.

[0003] For hub motors that introduce magnetic field modulation technology, the field modulation effect brings rich air gap harmonics, which gives this type of motor the advantage of high torque density, but it also brings many non-working harmonics that generate torque pulsation. The distribution of non-working harmonics in the air gap directly determines the torque pulsation in the torque. A reasonable distribution of air gap harmonics can achieve the purpose of reducing torque pulsation. For example, the document with Chinese patent application number 202110702440.1 discloses a high mechanical robustness magnetic field modulated radial permanent magnet motor and its multi-harmonic optimization design method, which takes into account the optimization of the motor's torque and torque pulsation; however, its multi-harmonic optimization has the following disadvantages: it is necessary to use sensitivity analysis methods, response surface analysis methods and multi-objective backbone particle swarm algorithms, the process is cumbersome, the method is complicated, and the optimization objects are only harmonics with greater influence, so the selected objects are not rich enough. For example, the document of Chinese patent application No. 202111485800.3 discloses a collaborative optimization design method for permanent magnet-armature dual harmonics of a magnetic field modulated permanent magnet motor, which realizes the collaborative optimization design of the permanent magnet-armature magnetic field dual harmonics, thereby improving the motor torque density and power factor; however, there are the following disadvantages: the optimization target selection method is complicated, and it is necessary to reduce the dimensions of the armature magnetic field harmonic optimization targets and design parameters through sensitivity analysis, experimental point distribution calculation and independence judgment of the armature magnetic field non-working harmonics.

[0004] Therefore, for field-modulated permanent magnet motors, the rich field harmonics not only increase torque density but also induce significant torque ripple, impacting motor performance and operation. Therefore, torque ripple must be considered not only in design but also in design. It is well known that in field-modulated permanent magnet motors, the combination of the three key elements—the magnetic source, modulator, and armature winding—determines the variation in air-gap harmonics, further impacting motor performance. To address this issue of high torque ripple, in-depth analysis of the air-gap harmonic distribution to optimize the motor's three design elements is crucial. Summary of the Invention

[0005] The purpose of the present invention is to address the shortcomings of existing magnetic field modulation hub motors in torque pulsation suppression and harmonic design, and propose a low torque pulsation hub motor and air gap magnetic field harmonic group design method to obtain an optimized synthetic magnetic field, ensuring that the motor can achieve pulsation reduction while maintaining high torque density.

[0006] The technical solution of the low torque pulsation hub motor proposed in the present invention is as follows: the rotor is coaxially sleeved outside the stator, an air gap is provided between the rotor and the stator, the stator is wound with a first winding and a second winding connected in series to form a star-delta connection, and 2P is uniformly embedded in the rotor along the circumferential direction. r For permanent magnet group, P r is the number of permanent magnet pole pairs, each pair of permanent magnet groups is composed of two permanent magnets arranged in a V-shaped structure, the center line of the V-shaped structure is along the radial direction and the V-shaped opening is inward, the radial cross-section of each permanent magnet is rectangular, the inner and outer oblique directions are the long side directions of the rectangle, the magnetization direction of each permanent magnet is perpendicular to its own long side direction, the magnetization directions of the two permanent magnets in a pair of permanent magnet groups are the same, and the magnetization directions of two adjacent pairs of permanent magnet groups are opposite; there is a pole-cutting arc segment on the inner surface of the rotor corresponding to each pair of permanent magnet groups, a total of 2P r The pole-cutting arc segments are arranged symmetrically with respect to the center line of the V-shaped structure, and the air gap at each pole-cutting arc segment is an air gap with a non-uniform thickness.

[0007] The thickness of the non-uniform air gap g min is the uniform air gap thickness at the non-pole-cut arc segment, τ p is the mechanical angle corresponding to one pole span of the rotor, θ s is the mechanical angle of the rotor, -λτ p ≤θ s ≤λτ p , 0.35≤λ≤0.425.

[0008] The angle S occupied by the pole-cutting arc segment and the mechanical angle τ p The ratio range is: 0.7≤S / τ p ≤0.85.

[0009] The star-delta connection is as follows: the three-phase currents A, B, and C enter the three-phase first end of the first winding and then flow out from the three-phase last end of the first winding; the A-phase current enters the A-phase first end and the C-phase last end of the second winding; the B-phase current enters the B-phase first end and the C-phase last end of the second winding; and the C-phase current enters the C-phase first end and the B-phase last end of the second winding, forming a star-delta connection. After the three-phase currents A, B, and C enter the second winding from the first winding, their phases are each ahead of π / 6.

[0010] The technical solution adopted by the air gap magnetic field harmonic group design method of the low torque pulsation hub motor proposed in the present invention is:

[0011] Step 1): synthesizing the composite air gap flux density of the motor under load operation according to the permanent magnet air gap flux density and the armature winding air gap flux density of the motor;

[0012] Step 2): When the spatial orders k1 and k2 of the permanent magnet air gap magnetic flux harmonics and the armature winding air gap magnetic flux harmonics are equal and the temporal orders n1 and n2 are equal, the synthetic air gap magnetic flux harmonics in the synthetic air gap magnetic flux are used as the first subgroup. When the amplitude of the harmonics in the first subgroup is greater than or equal to the set torque group reference value, the corresponding harmonic is the torque group; otherwise, it is the first low-energy group.

[0013] Step 3): When the spatial orders k1 and k2 of the permanent magnet air gap flux density and the armature winding air gap flux density are equal, and the time orders n1 and n2 are different, the synthesized air gap flux density harmonic H k_n As the second subgroup; when the amplitude of the harmonic in the second subgroup is greater than or equal to the set pulsation group reference value, the corresponding harmonic is the pulsation group, otherwise, it is the second low-energy group; when the harmonics in the pulsation group are all permanent magnet air gap magnetic density harmonics, it is the permanent magnet side pulsation group; when the harmonics in the pulsation group are all armature winding air gap magnetic density harmonics, it is the armature side pulsation group;

[0014] Step 4): For the torque group and the permanent magnet side pulsation group, the inner surface of the rotor at each pole of the motor is set to a pole-cutting arc segment, a total of 2P r Pole arc segment, P r is the number of permanent magnet pole pairs, each pole-cutting arc segment is symmetrical with respect to the radial center line of each pole of the motor, so that the air gap at each pole-cutting arc segment has a non-uniform thickness;

[0015] Step 5): For the torque group and the armature-side pulsation group, a first winding and a second winding connected in series are wound on the stator of the motor, and the first winding and the second winding are connected in star-delta.

[0016] Furthermore, after step 5), the permanent magnet air gap magnetic flux of the non-uniform air gap on the rotor side, the air gap magnetic flux generated by the first winding, and the air gap magnetic flux generated by the second winding connected in star-delta are calculated, and the air gap magnetic flux generated by the first winding and the air gap magnetic density generated by the second winding connected in star-delta are combined into the armature winding air gap magnetic flux on the stator side, and the permanent magnet air gap magnetic flux of the non-uniform air gap on the rotor side and the armature winding air gap magnetic density on the stator side are combined into an optimized synthetic magnetic field.

[0017] The beneficial effects of the present invention after adopting the above technology are:

[0018] 1. Based on the pole-slot combination and magnetic field modulation principle of the magnetic field modulation in-wheel motor, the present invention derives the harmonic expressions of the permanent magnet and armature air gap magnetic flux densities respectively. By analyzing the spatial and temporal orders of the magnetic field magnetic flux density harmonics of the two, it can quickly determine whether the magnetic field harmonics contribute to the average torque and permanent magnet torque ripple. This avoids the blindness of traditional parameter scanning analysis and design methods, points out the direction for the analysis and suppression of permanent magnet torque ripple of the in-wheel motor, reduces the workload of motor design, and shortens the motor optimization design cycle.

[0019] 2. The present invention uses the air gap magnetic field harmonic group to analyze the permanent magnet torque pulsation, considers the contribution of magnetic field harmonics to the average torque and permanent magnet torque pulsation, divides the magnetic field harmonic group according to the magnetic field amplitude, and divides the harmonics into three subgroups: the torque group that can contribute to the average torque, the pulsation group that can generate permanent magnet torque pulsation, and the low-energy group that has negligible influence on the average torque and permanent magnet torque pulsation. In this way, the harmonics that generate permanent magnet torque pulsation and the harmonics that contribute to the average torque are explored from the perspective of the air gap magnetic field harmonic group, laying a solid foundation for achieving pulsation suppression under the premise of ensuring high torque density of the motor.

[0020] 3. The present invention proposes a non-uniform air gap thickness function model that takes into account the permanent magnet air gap magnetic flux harmonics, analyzes the impact of the synchronous modulation brought by the non-uniform air gap on the permanent magnet magnetic field and its magnetic flux harmonics, and proposes a design method for the non-uniform air gap. Starting from the permanent magnet side, the air gap magnetic field harmonic group is improved, which can effectively suppress the pulsation group that generates permanent magnet torque pulsation on the basis of maintaining the torque group that contributes to the average torque, thereby achieving pulsation reduction while ensuring the high torque density of the motor.

[0021] 4. The present invention proposes a winding connection method that takes into account the harmonics of the armature air gap magnetic flux density, analyzes the influence of the star-delta winding on the armature magnetic field synthesis, and improves the air gap magnetic field harmonic group from the armature side. On the basis of maintaining the torque group that contributes to the average torque, the pulsation group that generates permanent magnet torque pulsation can be effectively suppressed, thereby achieving pulsation reduction while ensuring the high torque density of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The technical solution of the present invention is further clearly and completely described below in conjunction with the accompanying drawings in the embodiments:

[0023] Figure 1 This is a radial cross-sectional view of the magnetic field modulation hub motor structure before improvement in the embodiment;

[0024] Figure 2 for Figure 1 The uniform air gap and star winding of the magnetic field modulation hub motor shown in the figure form the time and space distribution diagram of the air gap magnetic density harmonics;

[0025] Figure 3 for Figure 1 The enlarged view of the local structure of the magnetic field modulation hub motor and the marked view of the uniform air gap thickness are shown;

[0026] Figure 4 for Figure 1 The source magnetomotive force distribution diagram of the magnetic field modulation hub motor shown;

[0027] Figure 5 for Figure 1 The uniform air gap synchronous modulation permeance distribution diagram of the magnetic field modulation type hub motor shown;

[0028] Figure 6 for Figure 1 The uniform air gap magnetomotive force distribution diagram of the magnetic field modulation hub motor shown;

[0029] Figure 7 for Figure 1 The stator asynchronous modulation magnetic permeance distribution diagram of the magnetic field modulation type hub motor shown;

[0030] Figure 8 For Figure 3 Schematic diagram of the non-uniform air gap design of the low torque pulsation hub motor of the present invention improved on the basis of the present invention;

[0031] Figure 9 This is the non-uniform air gap synchronous modulation permeance distribution diagram of the low torque pulsation hub motor of the present invention;

[0032] Figure 10 This is a diagram showing the non-uniform air gap magnetomotive force distribution of the low torque pulsation hub motor of the present invention;

[0033] Figure 11 This is a function curve diagram of the non-uniform air gap thickness of one pole of the rotor of the low torque pulsation hub motor of the present invention;

[0034] Figure 12 This is a comparison diagram of the h(x) function curve in the non-uniform air gap design process of the present invention;

[0035] Figure 13This is a comparison diagram of the uniform air gap of the magnetic field modulation hub motor before improvement and the non-uniform air gap permanent magnet air gap magnetic flux density harmonics of the improved motor of the present invention;

[0036] Figure 14 This is a schematic diagram of the star connection of the windings of the magnetic field modulation hub motor before improvement;

[0037] Figure 15 This is a star-delta connection diagram of the windings of the low-torque pulsation hub motor of the present invention;

[0038] Figure 16 This is a schematic diagram of the three-phase current phases of two windings of the low-torque pulsation hub motor of the present invention;

[0039] Figure 17 A comparison diagram of armature air gap magnetic flux harmonics between the star-connected winding of the magnetic field modulation hub motor before improvement and the star-delta connected winding of the low torque pulsation hub motor of the present invention;

[0040] Figure 18 The time-space distribution diagram of the synthetic air gap magnetic flux density harmonics of the non-uniform air gap and star-delta connection winding of the low torque pulsation hub motor of the present invention;

[0041] Figure 19 Comparison diagram of torque pulsation components between uniform air gap and star winding of the improved magnetic field modulation hub motor and non-uniform air gap and star-delta connection winding of the low torque pulsation hub motor of the present invention;

[0042] Figure 20 The uniform air gap and star winding of the improved magnetic field modulation hub motor, the non-uniform air gap and average torque and torque pulsation of the star-delta connected winding of the low torque pulsation hub motor of the present invention are compared.

[0043] In the figure: 1. Rotor; 2. Stator; 3. Permanent magnet; 4. Air gap; 5. Flux barrier; 6. First winding; 7. Second winding; 9. Stator teeth; 10. Stator slots. DETAILED DESCRIPTION

[0044] like Figure 1 The magnetic field modulation hub motor shown in the figure includes a rotor 1 and a stator 2. The rotor 1 is coaxially sleeved on the outside of the stator 2, and an air gap 4 is provided between the rotor 1 and the stator 2. The stator 2 has Z stator teeth 9, and a stator slot 10 is formed between two adjacent stator teeth 9. There are a total of Z stator slots 10, where Z is the number of stator slots. Figure 1 In the example shown, Z = 24. A first winding 6 and a second winding 7 are wound around the stator teeth 9 of the stator 2. The first winding 6 and the second winding 7 are connected in series to form a star connection. The inner surface of the rotor 1 is a smooth circular surface, and the air gap 4 has a uniform thickness along the circumference, forming a uniform air gap.

[0045] 2P are evenly embedded in the rotor 1 along the circumferential direction. r For permanent magnet group, P r is the number of permanent magnet pole pairs, Figure 1 P in the example r =13, each pair of permanent magnets consists of two permanent magnets 3 arranged in a V-shaped structure, so there are 4P in total r = 52 permanent magnets 3, with each pair of permanent magnets 3 arranged in a V-shaped configuration forming one rotor pole, for a total of 26 poles. The V-shaped opening of the V-shaped structure faces inward, with the centerline of the V-shaped structure along the radial direction. The two permanent magnets 3 are symmetrical along the centerline of the V-shaped structure.

[0046] Each permanent magnet 3 has a rectangular radial cross-section, with the inward and outward diagonal directions corresponding to the long sides of the rectangle. Each permanent magnet 3 is magnetized perpendicular to its long sides, that is, parallel to its width. The two permanent magnets 3 in a pair of permanent magnet groups forming a V-shaped structure have the same magnetization direction. In other words, both permanent magnets 3 in a rotor pole are magnetized diagonally toward the inside or outside of the motor. Adjacent pairs of permanent magnets 3 have opposite magnetization directions, alternating between poles.

[0047] Each permanent magnet 3 is provided with a flux barrier 5 at both the inner and outer ends. Figure 1 The 52 permanent magnets 3 in the example shown have a total of 104 flux barriers 5 .

[0048] against Figure 1 The air gap magnetic field harmonic group of the magnetic field modulation hub motor shown in the figure is designed. Based on the pole-slot combination and the magnetic field modulation mechanism, the temporal and spatial distributions of the permanent magnet and armature air gap magnetic field harmonics are derived. By analyzing the spatial and temporal orders of the magnetic field harmonics of both, it is quickly determined whether the magnetic field harmonics contribute to the average torque and permanent magnet torque ripple. The air gap magnetic field harmonic group is calculated based on the harmonic amplitude, and the resulting air gap magnetic field harmonics are divided into three subgroups: the torque group that contributes to the average torque, the pulsation group that generates permanent magnet torque ripple, and the remaining low-energy group with negligible impact on the average torque and permanent magnet torque ripple. A non-uniform air gap is designed on the permanent magnet side, and its regulatory effect on the permanent magnet magnetic field is analyzed. The permanent magnet air gap magnetic field harmonics of the resulting pulsation group are suppressed while maintaining the permanent magnet air gap magnetic field harmonics of the resulting torque group. A star-delta winding is designed on the armature side, and the regulating effect of the winding phase shift on the armature magnetic field is analyzed. Under the premise of maintaining the armature air gap magnetic density harmonics of the synthetic torque group, the armature air gap magnetic density harmonics of the synthetic pulsation group are suppressed. The above two effects work together to make the motor have high torque density and low torque pulsation characteristics. The present invention analyzes the mechanism of the effect of the air gap magnetic field harmonics of the hub motor introduced with magnetic field modulation technology on the average torque and permanent magnet torque pulsation, determines the air gap magnetic field harmonic group related to high torque and high pulsation, and can simultaneously directionally maintain the torque group related to high torque and directionally suppress the pulsation group related to high pulsation. The specific steps are as follows:

[0049] Step 1: Ignore the magnetic field generated by the first winding 6 and the second winding 7 on the stator 2, and only consider the number of permanent magnet pole pairs and the stator slot structure. According to the magnetic field modulation formula, deduce the permanent magnet air gap flux density B PM The expression:

[0050]

[0051] Where B k1_n1 is the permanent magnet air gap magnetic density harmonic H PM k1_n1 The amplitude of k1 is the spatial order of the permanent magnet air gap magnetic density harmonic, n1 is the time order of the permanent magnet air gap magnetic density harmonic, i is a positive odd number, j is a natural number, θ s is the mechanical angle of the air gap circle, ω is the electrical angular speed, t is the time, is the permanent magnet air gap magnetic flux harmonic phase, P r is the number of rotor permanent magnet pole pairs, and Z is the number of stator slots. Figure 1 In the magnetic field modulation hub motor shown in the figure, P r is 13, and Z is 24.

[0052] At the same time as step 1, step 2: Ignore the permanent magnetic field on the rotor 1, and only consider the tooth slot structure on the stator 2 and the connection method of the first winding 6 and the second winding 7; according to the magnetic field modulation formula, derive the armature winding air gap flux density B w expression:

[0053]

[0054] Where B k2_n2 H is the armature winding air gap magnetic density harmonic w k2_n2 The amplitude of the armature winding air gap magnetic flux harmonics, k2 is the spatial order of the armature winding air gap magnetic flux harmonics, n2 is the time order of the armature winding air gap magnetic flux harmonics, is the harmonic phase of the armature winding air gap flux density, and m is a natural number.

[0055] Based on steps 1 and 2, we can get step 3: synthesize the permanent magnet magnetic field and the armature magnetic field to obtain the permanent magnet air gap magnetic flux density B. PM and armature winding air gap flux density B w By synthesis, the synthetic air gap flux density B of the motor under load operation can be obtained. Load :

[0056]

[0057] Where B k_n is the synthetic air gap magnetic density harmonic H k_n The amplitude of k is the spatial order of the synthetic air gap magnetic density harmonic, and n is the time order of the synthetic air gap magnetic density harmonic. is the synthetic air gap magnetic density harmonic phase.

[0058] Among them, H k_n The synthetic source is H PM k1_n1 and H w k2_n2 At least one of the two is synthesized. When the synthesis source is H PM k1_n1 and H w k2_n2 When k=k1=k2,n=n1=n2。 When the synthetic source is H PM k1_n1 When k=k1, n=n1. When the synthetic source is H w k2_n2 When k=k2, n=n2. Considering that the amplitude of high time order or high space order harmonics is small, its influence on performance can be ignored. Therefore, in the design process of air gap harmonic group, the range of synthetic air gap magnetic flux harmonic time order n and space order k is pre-set as follows: -n max ≤n≤n max , 1≤k≤k max , n max is the high time order reference value, 5≤n max ≤9, k max For high spatial order reference value, 5P r ≤kmax≤9P r , P r is the number of rotor permanent magnet pole pairs. Figure 1 In the magnetic field modulation hub motor shown in the figure, n is set max =7,k max =91, see Figure 2 The time-space distribution diagram of the synthetic air gap magnetic density harmonics in the synthetic magnetic field of the magnetic field modulation hub motor shown is shown in the figure, where the horizontal axis is the spatial order k and the vertical axis is the time order n.

[0059] Step 4: Obtain the synthetic air gap flux harmonics that can contribute to the average torque. Analyze and compare the permanent magnet air gap flux B PM and armature winding air gap flux density B w The spatial order k1, k2 and time order n1, n2 of the harmonic components are as follows: PM and armature winding air gap flux density B w When the spatial order and time order of the two are equal, that is, k1 = k2 and n1 = n2, the composite air gap magnetic flux B of the two is Load The synthetic air gap magnetic density harmonic H k_n As the first subgroup, it can contribute to the average torque. PM k1_n1The time order is i or -i, and the spatial order is |iP r ±jZ|, armature winding air gap magnetic flux harmonic H w k2_n2 The time order is 1 or -1, and the spatial order is 6m+1 or 6m-1. Figure 2 , Figure 1 In the magnetic field modulation hub motor shown, the first subgroup has H 11_-1 、H 13_1 、H 35_-1 、H 37_1 、H 59_-1 、H 61_1 、H 83_-1 and H 85_1 . .

[0060] Step 5: According to the contribution capacity to the average torque, the harmonics of the first subgroup are further subdivided according to the amplitude of the harmonics in the first subgroup, and the amplitude reference value of the harmonics is preset, that is, the torque group reference value α, 0.5T≤α≤1.5T, (T: Tesla, unit of magnetic flux density). When the amplitude of the harmonics in the first subgroup is greater than or equal to the torque group reference value α, the corresponding harmonics in the first subgroup are regarded as the torque group, and the average torque contribution capacity is obvious. When the amplitude of the harmonics in the first subgroup is less than the torque group reference value α, the corresponding harmonics in the first subgroup are regarded as the first low-energy group, and the average torque contribution capacity can be ignored. In the magnetic field modulation hub motor, α is set to 0.1T, then the synthetic air gap magnetic density harmonic H in the first subgroup with an amplitude greater than or equal to 0.1T k_n As the torque group, the synthetic air gap magnetic flux harmonic H in the first subgroup with amplitude less than 0.1T k_n It is the first low-energy group. Figure 2 In the figure, the solid squares represent the torque group in the first subgroup, with H 11_-1 、H 13_1 、H 35_-1 and H 37_1 , the dotted square is the first low-energy group in the first subgroup, with H 59_-1 、H 61_1 、H 83_-1 and H 85_1 .

[0061] The torque group in the first subgroup, the torque group H in the first subgroup 11_-1 The synthetic source is H PM 5_-1 and H w 5_-1 ; Torque group H 13_1 The synthetic source is H PM 13_1 and H w 13_1 ; Torque group H 35_-1 The synthetic source is HPM 35_-1 and H w 35_-1 ; Torque group H 37_1 The synthetic source is H PM 37_1 and H w 37_1 , are all related to the permanent magnet magnetic field and the armature magnetic field.

[0062] Step 6: Obtain the synthetic air gap magnetic flux harmonics that can generate permanent magnet torque pulsation. Analyze and compare the permanent magnet air gap magnetic flux B PM and armature winding air gap flux density B w The spatial order k1, k2 and time order n1, n2 of the harmonic components are as follows: PM and armature winding air gap flux density B w The spatial orders k1 and k2 of the magnetic flux harmonics of the two are equal, k1=k2, and the time orders n1 and n2 are different, n1≠n2. At this time, the synthetic air gap magnetic flux B Load The synthetic air gap magnetic density harmonic H k_n As the second subgroup, permanent magnet torque pulsation can be generated. The time order of the permanent magnet air gap magnetic flux harmonic is i or -i, and the spatial order is |iP r ±jZ|, the time order of the armature winding air gap magnetic flux harmonic is 1 or -1, and the space order is 6m+1 or 6m-1. Figure 2 As shown, in the magnetic field modulation hub motor, the second subgroup has H 5_-1 and H 5_-7 、H 7_1 and H 7_-5 、H 17_-1 and H 17_5 、H 19_1 and H 19_7 、H 29_-1 and H 29_-7 、H 31_1 and H 31_-5 、H 41_-1 and H 41_5 、H 43_1 and H 43_7 、H 53_-1 and H 53_-7 、H 55_1 and H 55_-5 、H 65_-1 and H 65_5 、H 67_1 and H 67_7 、H 77_-1 and H 77_-7 、H 79_1 and H 79_-5 、H 89_-1 and H 89_5 、H91_1 and H 91_7 .

[0063] Step 7: Subdivide the harmonics of the second subgroup according to their contribution to the permanent magnet torque pulsation. According to the amplitude of the harmonics in the second subgroup, preset the reference value of the harmonic amplitude, that is, the pulsation group reference value β, 0.01T≤β≤0.05T. When the amplitude of the harmonics in the second subgroup is greater than or equal to the pulsation group reference value β, the corresponding harmonics in the second subgroup are used as the pulsation group, and the contribution to the permanent magnet torque pulsation is obvious; on the contrary, when the amplitude of the harmonics in the second subgroup is less than the pulsation group reference value β, the corresponding harmonics in the second subgroup are used as the second low-energy group, and the contribution to the permanent magnet torque pulsation can be ignored. In the magnetic field modulation hub motor, β is set to 0.01T, then the harmonic H with an amplitude greater than or equal to 0.01T k_n It is defined as the pulsation group, and less than 0.01T is defined as the second low energy group. Figure 2 , the solid triangle represents the pulsation group in the second subgroup, with harmonic H 5_-1 、H 7_1 、H 17_-1 、H 65_5 、H 91_7 The upper left triangle of the dotted line is the second low energy group in the second subgroup, with harmonic H 5_-7 、H 7_-5 、H 17_-1 、H 17_5 、H 19_1 、H 19_7 、H 29_-1 、H 29_-7 、H 31_1 、H 31_-5 、H 41_-1 、H 41_5 、H 43_1 、H 43_7 、H 53_-1 、H 53_-7 、H 55_1 、H 55_-5 、H 65_-1 、H 67_1 、H 67_7 、H 77_-1 、H 77_-7 、H 79_1 、H 79_-5 、H 89_-1 、H 89_5 、H 91_1 .

[0064] Harmonic H in the pulsation group 65_5 The synthetic source is H PM 65_5 ;H 91_7 The synthetic source is H PM 91_7, are all permanent magnet air gap magnetic density harmonics, which are only related to the permanent magnet magnetic field, so H 65_5 、H 91_7 As the permanent magnet side pulsation group. H 5_-1 The synthetic source is H w 5_-1 ;H 7_1 The synthetic source is H w 7_1 , H 17_-1 The synthetic source is H w 17_-1 , are all harmonics of the armature winding air gap magnetic density, which are only related to the armature magnetic field, so H 5_-1 、H 7_1 、H 17_-1 As the armature side pulsation group.

[0065] Step 8: Synthesize the air gap magnetic flux harmonic H k_n The rest of the synthetic air gap magnetic flux harmonics except the first and second subgroups are all regarded as the third subgroup. The rest of the synthetic air gap magnetic flux harmonics except the first and second subgroups are all regarded as the third subgroup. All of them are regarded as the third low-energy group, and their contribution to the average torque and permanent magnet torque ripple can be ignored. Figure 2 The lower right triangle of the middle dashed line is the third low-energy group in the third subgroup.

[0066] Step 9: For the permanent magnet side pulsation group H in the pulsation group 65_5 、H 91_7 and all torque groups H 11_-1 、H 13_1 、H 35_-1 、H 37_1 By introducing a pole-cutting arc segment on the inner surface of the permanent magnet rotor to design a non-uniform air gap, the synchronous modulation effect is changed, the magnetomotive force waveform is improved, and the permanent magnet air gap magnetic density harmonic H is reduced. PM 65_5 and H PM 91_7 amplitude, while maintaining the torque group H 11_-1 、H 13_1 、H 35_-1 、H 37_1 The permanent magnet air gap magnetic density harmonic H PM 11_-1 、H PM 13_1 、H PM 35_-1 、H PM 37_1 The purpose of keeping the amplitude constant.

[0067] The design method of the non-uniform air gap is as follows:

[0068] like Figure 3As shown, the inner surface of the rotor 1 of the magnetic field modulation hub motor is a smooth circular surface, and the thickness of the air gap 4 along the circumferential direction is uniform, and the thickness is g min , is a uniform air gap. According to the arrangement of the permanent magnet 3, we can get Figure 4 The source magnetomotive force distribution diagram shown in the figure is the mechanical angle θ. s , the vertical axis is the source magnetomotive force F s (θ s ,t), source magnetomotive force F s (θ s ,t) is expressed as:

[0069]

[0070] Where, F si is the amplitude of the i-th order component in the uniform air gap source magnetomotive force, and Ω is the mechanical speed of the rotor.

[0071] because Figure 3 The inner surface of the rotor 1 of the magnetic field modulation hub motor is smooth, and the air gap is of uniform thickness, which is g. min , so the synchronous modulation permeance is a constant Λ0. Figure 5 The uniform air gap synchronous modulation magnetic permeance distribution diagram, the vertical axis is the magnetic permeance Λ c (θ s ), so the uniform air gap synchronously modulates the magnetic permeance Λ c (θ s ) is:

[0072] Λ c (θ s )=Λ0

[0073] The uniform air gap is synchronously modulated with the magnetic permeance Λ c (θ s ) and source magnetomotive force F s (θ) and multiply it to get the uniform air gap magnetomotive force F c (θ s ,t) is:

[0074]

[0075] Where, F ci is the amplitude of the i-th order component in the uniform air gap magnetomotive force. Figure 6 The uniform air gap magnetomotive force distribution diagram, the horizontal axis represents the mechanical angle θ s , the vertical axis is the uniform air gap magnetomotive force F c (θ s ,t).

[0076] According to the structure of stator 1, we can get Figure 7 The stator asynchronous modulation permeance distribution diagram shown in the figure, the horizontal axis represents the mechanical angle θs , the vertical axis is the stator asynchronous modulation permeability Λ r (θ s ):

[0077]

[0078] Where, Λ j is the amplitude of the j-order component in the stator asynchronous modulation permeance.

[0079] The stator asynchronously modulates the magnetic permeance Λ r (θ s ) and uniform air gap magnetomotive force F c (θ s ,t) by multiplying them, we can get the permanent magnet air gap flux density B' PM :

[0080]

[0081] Where i is a positive odd number and j is a natural number, so i is the permanent magnet air gap magnetic flux density B' PM The time order of the medium harmonics, and from the formula we can know the uniform air gap magnetomotive force F c (θ s ,t) directly determines the permanent magnet air gap flux density B' PM The harmonic amplitude of the time order corresponds to the permanent magnet air gap flux density B in step 1 PM The harmonic of time order n1, |n1| = i; because it is necessary to reduce the permanent magnet air gap magnetic density harmonic H PM 65_5 and H PM 91_7 The amplitude, its time order is 5 and 7, so it can be reduced by reducing the air gap magnetomotive force F c (θ s ,t) to achieve the purpose by taking the amplitude of the 5th and 7th order components into account.

[0082] like Figure 8 , the smooth surface of the inner surface of the rotor 1 of the magnetic field modulation hub motor is changed to a pole-cut arc segment A, and the angle occupied by the pole-cut arc segment A is S. Figure 8 ,By designing a non-uniform air gap and changing the method of synchronously modulating magnetic permeance, the air gap magnetomotive force can be improved. Figure 9 The non-uniform air gap synchronous modulation permeance Λ after the pole-cut arc segment A is changed g (θ s ) distribution diagram, its maximum value is constant Λ0. The uniform air gap source magnetomotive force F s (θ s ,t) Synchronous modulation of magnetic permeance Λ with non-uniform air gap g (θ s ) and multiply them to get the non-uniform air gap magnetomotive force F g (θs ,t) expression:

[0083]

[0084] Where, F gi is the amplitude of the i-th order component in the non-uniform air gap magnetomotive force, F g5 and F g7 is 0, due to the high time order reference value n max =7, so the amplitude of the components above the 7th order can be treated as 0. Figure 10 The non-uniform air gap magnetomotive force distribution diagram shown in the figure, the horizontal axis represents the mechanical angle θ s , the vertical axis is the non-uniform air gap magnetomotive force F g (θ s ,t).

[0085] In order to obtain the non-uniform air gap thickness function expression g(θ s ), as Figure 11 Taking the air gap 4 corresponding to one pole of the rotor 1 as an example, the pole-cutting arc segment A is symmetrical about the center line of the V-shaped structure formed by the two permanent magnets 3, and is also symmetrical along the radial center of each pole of the motor. There is a pole-cutting arc segment A on the inner surface of the rotor 1 corresponding to each pair of permanent magnet groups, a total of 2P r The pole-cutting arc segments A are arranged symmetrically with respect to the center line of the V-shaped structure, and the air gap 4 at each pole-cutting arc segment A is an air gap with a non-uniform thickness.

[0086] A coordinate system is established under one pole of rotor 1, with the symmetric center line of one pole of rotor 1 as the vertical coordinate, indicating the air gap thickness g (θ s ), the intersection of the ordinate and the outer surface of the stator 2 is the coordinate origin 0, and the tangent direction of the origin 0 is the abscissa, representing the mechanical angle θ of the rotor s , that is, the tangent of the middle of the outer surface of the stator 2 in one pole is the horizontal coordinate. The dotted line is the contour line of the pole-cut arc segment A, that is, the non-uniform air gap thickness function curve. The pole pitch P is the span of one rotor pole, τ p is the mechanical angle corresponding to the rotor pole span P; because the air gap thickness is inversely proportional to the air gap permeance, and the air gap permeance is proportional to the air gap magnetomotive force, the air gap thickness is inversely proportional to the air gap magnetomotive force. According to the non-uniform air gap magnetomotive force F g (θ s ,t), we can get the non-uniform air gap thickness function g(θ s )for:

[0087]

[0088] Where g min is the initial uniform air gap thickness, that is, the uniform air gap thickness at the non-cut arc segment, and also the non-uniform air gap thickness g(θs ) is the minimum value. In the embodiment of the present invention, g min =1mm,η a is the amplitude of the first-order component in the non-uniform air gap magnetomotive force, a3, a5, and a7 are the ratios of the amplitudes of the third-, fifth-, and seventh-order components to the amplitude of the first-order component in the non-uniform air gap magnetomotive force. Therefore, setting a5 and a7 to 0 can reduce the amplitudes of the fifth- and seventh-order components in the air gap magnetomotive force, thereby reducing the permanent magnet air gap magnetic flux harmonic H. PM 65_5 and H PM 91_7 The purpose of amplitude. a To ensure that when a3 changes, g(θ s ) has a minimum value of g min θ s The range is [-λτ p ,λτ p ], λ is the mechanical angle τ corresponding to half of the angle S occupied by the pole-cutting arc segment A p The reference value of the proportion is 0.35≤λ≤0.425. Therefore, the angle S occupied by the pole-cutting arc segment A as a whole and the mechanical angle τ corresponding to the span P of one pole of the rotor are p The ratio range is: 0.7≤S / τ p ≤0.85. In the motor of the present invention, λ is set to 0.4; in order to maintain H PM 5_-1 、H PM 13_1 、H PM 35_-1 、H PM 37_1 Amplitude, its time order is 1 or -1, so it is necessary to make η a Reach the maximum value to maintain the amplitude F of the first-order component in the non-uniform air gap magnetomotive force g1 ; Let the function g(x) with x as the independent variable, which can be regarded as g(θ s )Simplified form:

[0089]

[0090] According to g(x), we can get the inverse function f(x) of g(x):

[0091] f(x)=η a [cos(x)+a3cos(3x)], -λπ≤x≤λπ,

[0092] Because f(x) is related to the non-uniform air gap magnetomotive force expression F g (θ s ,t) are in the same form, and both are accumulated by several cosine components, so in the following analysis f(x) can be equivalent to F g(θ s ,t); because g(θ) has the minimum value g min is a constant value, that is, the maximum value of f(x) is a constant value, in order to make η a To achieve the maximum value, we need to minimize the maximum value of [cos(x)+a3cos(3x)]; for this purpose, we set up the function h(x):

[0093] h(x)=cOs(x)+a3cos(3x), 0≤x≤λπ,

[0094] h(x) is an even function, so we only need to discuss [0,λπ]; because h(π / 6) is a constant √3 / 2, as long as h(x) reaches its maximum value at x=π / 6, that is, when x=π / 6, the derivative of h(x) is 0, and this point is the only point in the interval where the reciprocal is 0, it can be guaranteed that a3 is the final solution at this time, and the solution is a3=-1 / 6, and then η a =2 / √3. Figure 12 , lists the function curves of h(x) when a3 takes 0, -1 / 9, -1 / 6, -1 / 3, and -1 / 2. Function 3 corresponds to a3 = -1 / 6. It increases monotonically in the interval [0,π / 6] and decreases monotonically in the interval [π / 6,λπ]. Therefore, (π / 6,√3 / 2) is the point where the derivative of function 3 is 0 and it is also the maximum point. Figure 12 The maximum values ​​of the other functions in are all greater than √3 / 2; therefore, the non-uniform air gap thickness function expression g(θ s ):

[0095]

[0096] At this time, the expression of permanent magnet air gap flux density B1 of the non-uniform air gap on the rotor side is calculated:

[0097]

[0098] Wherein, a is 1 or 3; Figure 13 The comparison of the magnetic flux harmonics of the permanent magnet air gap with uniform air gap and non-uniform air gap is shown in Figure 2. Due to the effect of non-uniform air gap, the magnetic flux harmonics of the permanent magnet air gap H PM 65_5 and H PM 91_7 Reduced to 0, H PM 11_-1 、H PM 13_1 、H PM 35_-1 、H PM 37_1 Harmonics are effectively maintained.

[0099] Step 10: For the armature side pulsation group H 5_-1 、H 7_1 、H17_-1 and all torque groups H 11_ -1, H 13_1 、H 35_-1 、H 37_1 , the original star connection mode of the first winding 6 and the second winding 7 of the motor is changed to a star-delta connection mode, so as to reduce the armature air gap magnetic flux harmonic H w 5_-1 、H w 7_1 and H w 17_-1 amplitude, while maintaining H w 5_-1 、H w 13_1 、H w 35_-1 and H w 37_1 The purpose of amplitude.

[0100] See also Figure 14 The star connection diagram of the magnetic field modulation hub motor of the first winding 6 and the second winding 7 is shown. U, V, and W are the three-phase windings of the magnetic field modulation hub motor. The three-phase currents A, B, and C first enter the three-phase A1+, B1+, and C1+ at the head end of the first winding 6, and then flow out from the three-phase A1-, B1-, and C1- at the end of the first winding 6. Then, they enter the three-phase A2+, B2+, and C2+ at the head end of the second winding 7, and finally flow out from the three-phase A2-, B2-, and C2- at the end of the second winding 7. They meet at the neutral point to form a star connection, during which the phase of the three-phase current remains unchanged. The winding is changed to the star-delta winding of the motor of the present invention, see Figure 15 The diagram of the star-delta winding connection of the motor of the present invention is as follows: the U, V, and W three-phase windings, and the A, B, and C three-phase currents first enter the first winding 6 at the head end A1+, B1+, and C1+, respectively, and then flow out from the three-phase A1-, B1-, and C1- at the end of the first winding 6, and then enter the second winding 7. The A-phase current enters the A-phase head end A2+ and the C-phase end C2- of the second winding 7, the B-phase current enters the B-phase head end B2+ and the C-phase end C2- of the second winding 7, and the C-phase current enters the C-phase head end C2+ and the B-phase end B2- of the second winding 7, forming a star-delta connection; wherein, after the current enters the second winding 7 from the first winding 6, the three-phase phases are each ahead by π / 6, as shown in FIG. Figure 16 At this time, the phase of the armature air gap magnetic flux harmonic generated by the second winding 7 is offset. After the vector is synthesized with the armature air gap magnetic flux harmonic generated by the first winding 6, the air gap magnetic flux harmonic H in the armature magnetic field w 5_-1 、H w 7_1 and H w 17_-1Because its distribution factor decreases, its amplitude decreases, and the armature air gap magnetic density harmonic H w 11_-1 、H w 13_1 、H w 35_-1 and H w 37_1 The distribution factor of the armature air gap magnetic flux harmonics before and after the winding connection mode is changed is derived as follows:

[0101] Figure 1 The air gap flux density B generated by the first winding 6 of the magnetic field modulation type hub motor Y6 The expression is:

[0102]

[0103] Where B Y6 k3_n3 is the air gap magnetic flux density B Y6 The amplitude of the harmonics, k3 is B Y6 The spatial order of the intermediate harmonics, n3 is B Y6 The time order of the intermediate harmonics, ω is B Y6 The electrical angle speed of the harmonics, For B Y6 Phase of intermediate harmonics;

[0104] Figure 1 The air gap flux density B generated by the second winding 7 of the magnetic field modulation type hub motor Y7 The expression is:

[0105]

[0106] Wherein γ is the mechanical angle at which the first winding 6 leads the second winding 7 in spatial position. In the embodiment of the present invention, γ=π / 6.

[0107] The air gap flux density B generated by the first winding 6 Y6 The air gap flux density B generated by the second winding 7 Y7 Vector synthesis generates armature magnetic field flux density B w , where the harmonic distribution factor is calculated as:

[0108]

[0109] σ=-n3k3γ, k2=k3, n2=n3

[0110] Where K k2_n2 H in the armature magnetic field w k2_n2The distribution factor of σ is the phase difference between the first winding 6 and the second winding 7 in generating the same spatial order and the same time order harmonics in the magnetic field. After calculation, the armature air gap magnetic flux harmonic H w 5_-1 、H w 7_1 and H w 17_-1 The distribution factors of H are all 0.26. w 11_-1 、H w 13_1 、H w 35_-1 and H w 37_1 The distribution factor is 0.97.

[0111] After the first winding 6 and the second winding 7 are connected in star-delta, the air gap flux density B generated by the second winding 7 in the motor of the present invention is △7 The expression is consistent with the above air gap magnetic flux B Y7 Different, as:

[0112]

[0113] Where π / 6 is the angle of current phase advance after the winding is changed; at this time σ=-n3k3γ+π / 6, B Y6 and B △7 After the armature magnetic field is generated by vector synthesis, the armature air gap magnetic flux harmonic H is calculated. w 5_-1 、H w 7_1 and H w 17_-1 The distribution factors of H w 11_-1 、H w 13_1 、H w 35_-1 and H w 37_1 The distribution factors of are increased to 1.

[0114] At this time, the air gap flux density B generated by the first winding 6 is Y6 The air gap flux density B generated by the second winding 7 △7 The vector synthesis is the expression of the air gap flux density B2 of the armature winding of the star-delta winding on the stator side:

[0115]

[0116] k2=|6b±1|,

[0117]

[0118] Where b is a positive even number; Figure 17 The embodiment of the present invention shown in the figure shows a comparison of the armature air gap magnetic flux harmonics of the star winding and the star-delta winding. It can be seen that after the winding is changed, H w 5_-1 、H w 7_1 and H w 17_-1 The amplitude is reduced to 0, H w 11_ -1, H w 13_1 、H w 35_-1 and H w 37_1 The amplitude is maintained.

[0119] Step 11: synthesize the permanent magnet air gap flux density B1 of the non-uniform air gap on the rotor side and the armature winding air gap flux density B2 of the star-delta winding on the stator side to obtain an optimized synthetic magnetic field, thereby achieving the design purpose of the air gap magnetic field harmonic group of the present invention.

[0120] Figure 18 The distribution of synthetic air gap magnetic density harmonics in the optimized synthetic magnetic field air gap is obtained. Due to the pulsation group H 5_ -1, H 7_1 、H 17_ -1, H 65_5 、H 91_7 The synthetic source is suppressed, the pulsation group in the optimized synthetic magnetic field is effectively suppressed, and the torque group H 11_ -1, H 13_1 、H 35_-1 and H 37_1 The synthetic source is maintained, and the torque group in the optimized synthetic magnetic field is effectively maintained.

[0121] Figure 19 This is a comparison diagram of the torque pulsation components of uniform air gap and star winding, non-uniform air gap and star-delta winding in an embodiment of the present invention. The horizontal axis is the pulsation order and the vertical axis is the pulsation amplitude. It can be seen that due to the effects of non-uniform air gap and star-delta winding, the pulsation of each order is reduced to a certain extent. Figure 20 The figure shows a comparison of the average torque and torque ripple of a uniform air gap and star winding, and a non-uniform air gap and star-delta winding in an embodiment of the present invention. It can be seen that due to the effects of the non-uniform air gap and star-delta winding, the torque ripple is reduced from 2.49% to 0.35%, which is effectively suppressed, and the average torque is effectively maintained from 14.85 Nm to 14.98 Nm. The above analysis and results confirm the effectiveness of the air gap harmonic group design method of the present invention in achieving high-torque and low-pulsation motor design.

[0122] The embodiments described above with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention. Those skilled in the art will appreciate that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A low-torque pulsation hub motor, wherein the rotor is coaxially sleeved on the outside of the stator, and an air gap is provided between the rotor and the stator, characterized by: The stator is wound with the first winding and the second winding which are connected in series to form a star-delta connection. The rotor is evenly embedded with 2P r For permanent magnet group, P r is the number of permanent magnet pole pairs, each pair of permanent magnet groups is composed of two permanent magnets arranged in a V-shaped structure, the center line of the V-shaped structure is along the radial direction and the V-shaped opening is inward, the radial cross-section of each permanent magnet is rectangular, the inner and outer oblique directions are the long side directions of the rectangle, the magnetization direction of each permanent magnet is perpendicular to its own long side direction, the magnetization directions of the two permanent magnets in a pair of permanent magnet groups are the same, and the magnetization directions of two adjacent pairs of permanent magnet groups are opposite; there is a pole-cutting arc segment on the inner surface of the rotor corresponding to each pair of permanent magnet groups, a total of 2P r The pole-cutting arc segments are arranged symmetrically with respect to the center line of the V-shaped structure, and the air gap at each pole-cutting arc segment is an air gap with a non-uniform thickness; The thickness of the non-uniform air gap g min is the uniform air gap thickness at the non-pole-cut arc segment, τ p is the mechanical angle corresponding to one pole span of the rotor, θ s is the mechanical angle of the rotor, -λτ p ≤θ s ≤λτ p , 0.35≤λ≤0.

425.

2. The low torque pulsation hub motor according to claim 1, characterized in that: The angle S occupied by the pole-cutting arc segment and the mechanical angle τ p The ratio range is: 0.7≤S / τ p ≤0.

85.

3. The low torque pulsation hub motor according to claim 1, characterized in that: The star-delta connection is as follows: the three-phase currents A, B, and C enter the three-phase first end of the first winding and then flow out from the three-phase last end of the first winding; the A-phase current enters the A-phase first end and the C-phase last end of the second winding; the B-phase current enters the B-phase first end and the C-phase last end of the second winding; and the C-phase current enters the C-phase first end and the B-phase last end of the second winding, forming a star-delta connection. After the three-phase currents A, B, and C enter the second winding from the first winding, their phases are each ahead of π / 6.

4. A method for designing an air gap magnetic field harmonic group of a low torque pulsation hub motor according to claim 1, characterized in that: Step 1): synthesizing the composite air gap flux density of the motor under load operation according to the permanent magnet air gap flux density and the armature winding air gap flux density of the motor; Step 2): When the spatial orders k1 and k2 of the permanent magnet air gap magnetic flux harmonics and the armature winding air gap magnetic flux harmonics are equal and the temporal orders n1 and n2 are equal, the synthetic air gap magnetic flux harmonics in the synthetic air gap magnetic flux are used as the first subgroup. When the amplitude of the harmonics in the first subgroup is greater than or equal to the set torque group reference value, the corresponding harmonic is the torque group; otherwise, it is the first low-energy group. Step 3): When the spatial orders k1 and k2 of the permanent magnet air gap flux density and the armature winding air gap flux density are equal, and the time orders n1 and n2 are different, the synthesized air gap flux density harmonic H kn As the second subgroup; When the amplitude of the harmonics in the second subgroup is greater than or equal to the set pulsation group reference value, the corresponding harmonic is a pulsation group, otherwise, it is a second low-energy group; when the harmonics in the pulsation group are all permanent magnet air gap magnetic density harmonics, it is a permanent magnet side pulsation group; when the harmonics in the pulsation group are all armature winding air gap magnetic density harmonics, it is an armature side pulsation group; Step 4): For the torque group and the permanent magnet side pulsation group, the inner surface of the rotor at each pole of the motor is set to a pole-cutting arc segment, a total of 2P r Pole arc segment, P r is the number of permanent magnet pole pairs, each pole-cutting arc segment is symmetrical with respect to the radial center line of each pole of the motor, so that the air gap at each pole-cutting arc segment has a non-uniform thickness; Step 5): For the torque group and the armature-side pulsation group, a first winding and a second winding connected in series are wound on the stator of the motor, and the first winding and the second winding are connected in star-delta.

5. The method for designing air gap magnetic field harmonic groups according to claim 4, wherein: After step 5), the permanent magnet air gap magnetic flux of the non-uniform air gap on the rotor side, the air gap magnetic flux generated by the first winding, and the air gap magnetic flux generated by the second winding connected in star-delta are calculated, and the air gap magnetic flux generated by the first winding and the air gap magnetic flux generated by the second winding connected in star-delta are combined into the armature winding air gap magnetic flux on the stator side, and the permanent magnet air gap magnetic flux of the non-uniform air gap on the rotor side and the armature winding air gap magnetic flux on the stator side are combined into an optimized synthetic magnetic field.

6. The method for designing air gap magnetic field harmonic groups according to claim 4, wherein: The range of the torque group reference value α described in step 2) is: 0.5T≤α≤1.5T; the range of the pulsation group reference value β described in step 3) is: 0.01T≤β≤0.05T; T is the magnetic flux density unit Tesla.

7. The method for designing air gap magnetic field harmonic groups according to claim 4, wherein: The thickness of the non-uniform air gap described in step 4) g min is the uniform air gap thickness at the non-pole-cut arc segment, τ p is the mechanical angle corresponding to one pole span of the rotor, θ s is the mechanical angle of the rotor; -λτ p ≤θ s ≤λτ p , 0.35≤λ≤0.

425.

8. The method for designing air gap magnetic field harmonic groups according to claim 4, wherein: The star-delta connection described in step 5) is: the three-phase currents A, B, and C enter the three-phase of the first winding head end and flow out from the three-phase of the first winding head end, the A-phase current enters the A-phase head end and the C-phase end of the second winding, the B-phase current enters the B-phase head end and the C-phase end of the second winding, and the C-phase current enters the C-phase head end and the B-phase end of the second winding, forming a star-delta connection. After the three-phase currents A, B, and C enter the second winding from the first winding, their phases are respectively ahead of π / 6.

9. The method for designing air gap magnetic field harmonic groups according to claim 6, wherein: The expression of the permanent magnetic air gap flux density B1 of the non-uniform air gap on the rotor side is: k1=|aP r ±jZ, The air gap flux density B2 of the armature winding of the star-delta winding on the stator side is expressed as: k2=|6b±1|, B k1_n1 is the amplitude of the permanent magnet air gap magnetic density harmonic, k1 is the spatial order of the permanent magnet air gap magnetic density harmonic, n1 is the time order of the permanent magnet air gap magnetic density harmonic, θ s is the mechanical angle of the air gap circle, ω is the electrical angular speed, t is the time, is the permanent magnet air gap magnetic flux harmonic phase, P r is the number of rotor permanent magnet poles, Z is the number of stator slots; B k2_n2 is the amplitude of the armature winding air gap magnetic flux harmonic, k2 is the spatial order of the armature winding air gap magnetic flux harmonic, n2 is the time order of the armature winding air gap magnetic flux harmonic, is the harmonic phase of the armature winding air gap flux density, a is 1 or 3, b is a positive even number, and j is a natural number.

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