Unequal-air-gap bilateral permanent magnet motor and method for reducing torque ripple thereof

Abstract

The invention discloses an unequal-air-gap bilateral permanent magnet motor and a method for reducing torque pulsation of the unequal-air-gap bilateral permanent magnet motor, and relates to the technical field of motors, the unequal-air-gap bilateral permanent magnet motor comprises a stator and a rotor which are sequentially arranged from outside to inside, an air gap is formed between the rotor and the stator, the stator comprises a stator iron core, and first stator grooves and stator teeth are uniformly distributed in the stator iron core at intervals in the circumferential direction; stator armature windings are embedded in the stator slots, rotor slots and rotor teeth are uniformly distributed on the outer side of the rotor core along the circumferential direction at intervals, the tooth profile of at least one of the stator teeth and the rotor teeth is of a non-uniform geometric structure, and a non-uniform air gap is formed between the inner surface of the stator and the outer surface of the rotor. And the content of the specific secondary magnetic conductance harmonic is reduced, so that the torque ripple is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of motors, and in particular to an unequal air gap double-sided permanent magnet motor and a method for reducing the torque pulsation thereof. Background Art

[0002] Permanent magnet vernier motor (PMVM) has been widely studied due to its simple structure and high torque density. It is more suitable for low-speed and high-torque direct drive applications such as electric vehicles, ship propulsion, and wind power generation. Compared with single-sided permanent magnet vernier motors that only place permanent magnets on the stator side or rotor side, double-sided permanent magnet vernier motors (DPMVM) install permanent magnets on both sides of the stator and rotor, which can further improve the torque density. DPMVM can be regarded as a combination of stator vernier motors and rotor vernier motors. However, due to the superposition of stator-side torque and rotor-side torque, coupled with the influence of the phase relationship, this will inevitably bring about large torque pulsation, which will have an adverse effect on practical application conditions such as low-speed direct drive.

[0003] Due to the bidirectional flux modulation effect in the structure of bilateral permanent magnet excitation of DPMVM, the air gap magnetic field contains more abundant harmonics. On the one hand, for permanent magnet vernier motors, the Maxwell stress tensor method can be used to establish the relationship between the output torque and the air gap magnetic density, so that the harmonics of the air gap magnetic density are the key factors affecting the torque and torque pulsation of the permanent magnet vernier motor. On the other hand, the air gap magnetic field distribution is mainly obtained by the armature magnetomotive force and the permanent magnet magnetomotive force on the stator and rotor sides after magnetic permeability modulation, which is the result of the interaction between the two. Therefore, the air gap magnetic field distribution can be improved from the armature magnetomotive force, the permanent magnet magnetomotive force on the stator and rotor sides, and the magnetic conduction on the stator and rotor sides to achieve the effect of improving the torque pulsation. Among them, improving the permanent magnet magnetomotive force distribution has a certain effect on reducing torque pulsation, but the torque sacrifice is large. Moreover, improving the permanent magnet magnetomotive force distribution by modifying the permanent magnet will increase the processing cost and material cost. Therefore, the present invention starts from the magnetic conduction on the stator and rotor sides to improve the torque characteristics. Summary of the invention

[0004] In view of the shortcomings of the background technology, the object of the present invention is to provide an unequal air gap double-sided permanent magnet motor with low torque pulsation.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A double-sided permanent magnet motor with unequal air gaps, characterized in that it comprises a stator and a rotor arranged in sequence from outside to inside, an air gap is provided between the rotor and the stator, the stator comprises a stator core, first stator slots and stator teeth are evenly distributed along the circumferential direction in the stator core, a stator armature winding is embedded in the stator slots, rotor slots and rotor teeth are evenly distributed along the circumferential direction on the outer side of the rotor core, and the tooth profile of at least one of the stator teeth and the rotor teeth is a non-uniform geometric structure;

[0007] The non-uniform geometric structure of the stator tooth is that the end of the stator tooth extends a convex surface toward the center of the motor, the top center point of the convex surface of the stator tooth and any fixed point on the extension line of the motor center line form a reference point, and the geometric center of the convex surface of each stator tooth has an eccentricity relative to the reference point, so that a non-uniform air gap is formed between the inner surface of the stator and the outer surface of the rotor, thereby reducing the harmonic content of specific magnetic permeability and thus reducing torque pulsation.

[0008] Furthermore, the non-uniform geometric structure of the rotor teeth is that the rotor teeth have a convex surface extending toward the outside of the motor with the motor center as a reference point, the end of the rotor tooth forms a convex surface, and the geometric center of the convex surface of each rotor tooth has an eccentricity relative to the motor center.

[0009] Furthermore, the rotor comprises a rotor core, the outer surface of the rotor core is provided with rotor slots spaced circumferentially; the inner side of the stator core is provided with second stator slots spaced evenly along the circumferential direction, and the second stator slots are alternately distributed with the stator teeth.

[0010] Furthermore, stator permanent magnets and rotor permanent magnets are embedded in the second stator slots and the rotor slots respectively, so that the stator and the rotor both form an alternating pole structure, and the stator teeth and rotor teeth with non-uniform geometric structures are respectively adapted to the stator and rotor with the alternating pole structure.

[0011] Furthermore, the inner side of the stator core and the outer side of the rotor core are flux modulation poles of a double salient pole structure, forming a bidirectional flux modulation effect.

[0012] A method for reducing torque pulsation of an unequal air gap double-sided permanent magnet motor is applicable to an unequal air gap double-sided permanent magnet motor, and is characterized by comprising the following steps:

[0013] Step 101, the eccentric design of the motor stator teeth is provided with point A, point O and point O', the point A is the top center point of the stator teeth, the point O is the reference point of the stator teeth, the point O' is located on the extension line of the line connecting point A and the center of the motor circle and has an eccentricity difference from the point O, and an arc is made with O' as the center and O'A as the radius to form the eccentric design of the stator teeth, and the eccentric design of the motor rotor teeth is provided with point E, point O2 and point O2', the point E is the top center point of the rotor teeth, the point O2 is the center of the motor circle, the point O2' is located on the line connecting point E and the center of the motor circle and has an eccentricity difference from the point O2, and an arc is made with O2' as the center and O'E as the radius to form the eccentric design of the rotor teeth. The torque pulsation is minimized by parameter scanning of the eccentricity;

[0014] Step 102, using Maxwell finite element simulation to obtain the radial and tangential magnetic flux amplitudes and phases of the air gap at multiple time points;

[0015] Step 103, substituting the data obtained in step 102 into the Maxwell stress-Tenri method torque formula to obtain the torque generated by each harmonic;

[0016] Step 104, substituting the torque data obtained in step 103 into the torque pulsation formula to calculate the torque pulsation generated by each harmonic;

[0017] Step 105: Compare the changes in the amplitude of the dominant harmonics of the torque pulsation before and after the stator teeth and the rotor teeth are eccentric, and verify the result.

[0018] Furthermore, in step 101, the quantitative relationship between R, h, and OA must be: R=OA-h; wherein h is the eccentricity of the stator tooth, and R is the distance between point O' and point A; the quantitative relationship between R1, h1, and O2E must be: R1=O2E-h1; wherein h1 is the eccentricity of the rotor tooth, and R1 is the distance between point O2' and point E.

[0019] Further, in step 103, the relationship between the output torque and the air gap flux density is expressed as: (1); where T e (t) is the total output torque, r g is the air gap radius, μ0 is the vacuum permeability, l a is the motor axial length, T q (t) is the output torque generated by the qth harmonic, B Rq , B Tq are the qth radial and tangential air gap flux amplitudes, θ Rq ,θ Tq is the qth radial and tangential air gap flux phase.

[0020] Furthermore, the torque ripple is calculated according to the peak-to-peak value and average value of each order harmonic obtained in step 103. The basic calculation formula of the torque ripple is as follows: (2); where T pk2pk (t) is the peak-to-peak value of the output torque, T max (t) is the maximum output torque, T min (t) is the minimum output torque, T avg (t) is the average value of the output torque.

[0021] Furthermore, according to equations (1) and (2), the torque pulsation generated by the qth harmonic is expressed as: .

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention proposes a method for reducing the torque pulsation of a bilateral permanent magnet motor, which can significantly reduce the torque pulsation while sacrificing a small amount of output torque. There is no need to perform complex structural deformation on the motor by means of changing the magnetic permeability period, and only a simple modification design of the stator or rotor modulation teeth is required.

[0024] 2. The present invention proposes a method for reducing the torque pulsation of a bilateral permanent magnet motor. Since only the eccentric shaping design is performed on the silicon steel sheets, the processing and material costs are lower than those of the permanent magnet shaping. The modulated harmonics are the dominant harmonics of the torque pulsation. The modulated tooth eccentricity of the stator and rotor can reduce the amplitude of the modulated harmonics by reducing the amplitude of specific sub-permeability harmonics. Compared with the case where the torque pulsation is reduced by the permanent magnet shaping, the torque sacrifice is relatively small. At the same time, the optimization results show that the present method can greatly reduce the torque pulsation and the tooth slot torque of the motor, and at the same time improve the electromagnetic properties including the core loss and the power factor, which is helpful to improve the operating performance of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 It is a schematic diagram of a first embodiment of an unequal air gap double-sided permanent magnet motor of the present invention;

[0027] Figure 2 for Figure 1 A magnified view of point A;

[0028] Figure 3 It is a schematic diagram of a second embodiment of an unequal air gap double-sided permanent magnet motor of the present invention;

[0029] Figure 4 It is a schematic diagram of a third embodiment of an unequal air gap double-sided permanent magnet motor of the present invention;

[0030] Figure 5 This is a design diagram of stator teeth eccentricity of an unequal air gap double-sided permanent magnet motor of the present invention;

[0031] Figure 6 This is a design diagram of rotor teeth eccentricity of an unequal air gap double-sided permanent magnet motor of the present invention;

[0032] Figure 7 A diagram showing the relationship between each harmonic order and torque of an unequal air gap double-sided permanent magnet motor of the present invention;

[0033] Figure 8 A diagram showing the relationship between each harmonic order and torque pulsation of an unequal air gap double-sided permanent magnet motor of the present invention;

[0034] Fig. 9 A comparison diagram of the magnetic flux density amplitudes of each harmonic order of an initial structure of an unequal air gap double-sided permanent magnet motor and a modulated tooth eccentric structure of the present invention;

[0035] Fig.10 A comparison diagram of the torques at various electrical angles of an initial structure and a modulated tooth eccentric structure of an unequal air gap double-sided permanent magnet motor of the present invention;

[0036] Fig.11 A comparison diagram of back electromotive force at various electrical angles of an initial structure and a modulated tooth eccentric structure of an unequal air gap double-sided permanent magnet motor of the present invention;

[0037] Fig.12 It is a comparison diagram of the tooth slot torque at various electrical angles of an initial structure and a modulated tooth eccentric structure of an unequal air gap double-sided permanent magnet motor of the present invention.

[0038] In the figure, 101, stator core; 102, stator permanent magnet; 103, stator armature winding; 104, stator teeth; 201, rotor core; 202, rotor permanent magnet; 203, rotor teeth. DETAILED DESCRIPTION

[0039] Combine the following Figure 1-12 The present invention is described in detail.

[0040] Embodiment 1:

[0041] A double-sided permanent magnet motor with unequal air gap, such as Figure 1-2 As shown, it includes a stator and a rotor arranged in sequence from the outside to the inside, with an air gap between the rotor and the stator, the stator includes a stator core 101, the stator core 101 has first stator slots and stator teeth 104 evenly spaced in a circumferential direction, the stator slots have stator armature windings 103 embedded in them, and the outer side of the rotor core has rotor slots and rotor teeth 203 evenly spaced in a circumferential direction, the tooth profiles of the stator teeth 104 and the rotor teeth 203 are non-uniform geometric structures, and a non-uniform air gap is formed between the inner surface of the stator and the outer surface of the rotor, so as to reduce the harmonic content of specific sub-permeability and thus reduce the torque pulsation.

[0042] In this embodiment, the non-uniform geometric structure on the stator side is that the end of the stator tooth 104 extends a convex surface toward the center of the motor, the top center point of the convex surface of the stator tooth 104 and any fixed point on the extension line of the motor center line form a reference point, and the geometric center of the convex surface of each stator tooth 104 has an eccentricity relative to the reference point. The non-uniform geometric structure on the rotor side is that the rotor tooth 203 has a convex surface, and the geometric center of the convex surface of each rotor tooth 203 has an eccentricity relative to the center of the motor.

[0043] In this embodiment, the non-uniform geometric structure of the rotor tooth 203 is that the rotor tooth 203 has a convex surface extending toward the outside of the motor with the motor center as the reference point, the end of the rotor tooth 203 forms a convex surface, and the geometric center of the convex surface of each rotor tooth 203 has an eccentricity relative to the motor center.

[0044] In this embodiment, the rotor includes a rotor core 201, and the outer surface of the rotor core 201 is circumferentially spaced with rotor slots; the inner side of the stator core 101 is evenly spaced with second stator slots along the circumferential direction, and the second stator slots and the stator teeth 104 are alternately distributed. Further, the second stator slots and the rotor slots are respectively embedded with stator permanent magnets 102 and rotor permanent magnets 202, and the rotor permanent magnets 202 and the rotor teeth 203 form an array of alternating pole structures, and the stator permanent magnets 102 and the stator teeth 104 form an array of alternating pole structures. Further, the inner side of the stator core 101 and the outer side of the rotor core 201 are provided with flux modulation poles, and a non-magnetic air gap is provided between the two flux modulation poles.

[0045] In this embodiment, the structures of the motor stator permanent magnets 102 and rotor permanent magnets 202 remain unchanged, and the contour configurations of the eccentric stator teeth 104 and rotor teeth 203 change the specific subharmonic content of the flux modulation pole permeance function, thereby reducing the modulation harmonic amplitude of the dominant torque pulsation.

[0046] A method for reducing torque pulsation of an unequal air gap double-sided permanent magnet motor is applicable to an unequal air gap double-sided permanent magnet motor, comprising the following steps:

[0047] Step 101, the motor is provided with point A, point O and point O', point A is the top center point of the stator tooth, point O is the reference point, point O' is located on the extension line of the line connecting point A and the center of the motor circle and is eccentric with point O, and an arc is made with O' as the center and O'A as the radius to form an eccentric design of a bread-shaped stator tooth, and the eccentric design of the motor rotor tooth is provided with point E, point O2 and point O2', point E is the top center point of the rotor tooth, point O2 is the center of the motor circle, point O2' is located on the line connecting point E and the center of the motor circle and is eccentric with point O2, and an arc is made with O2' as the center and O'E as the radius to form an eccentric design of a bread-shaped rotor tooth. The torque pulsation is minimized by parameter scanning of the eccentricity;

[0048] Step 102, using Maxwell finite element simulation to obtain the radial and tangential magnetic flux amplitudes and phases of the air gap at multiple time points;

[0049] Step 103, substituting the data obtained in step 102 into the Maxwell stress-Tenri method torque formula to obtain the torque generated by each harmonic;

[0050] Step 104, substituting the torque data obtained in step 103 into the torque pulsation formula to calculate the torque pulsation generated by each harmonic;

[0051] Step 105 , compare the changes in the amplitude of the dominant harmonics of the torque pulsation before and after the stator teeth 104 and the rotor teeth 203 are eccentric, and verify the result.

[0052] like Figure 5-6 As shown, in step 101, the motor is further provided with a point C, which is the intersection of the line connecting point A and the center of the motor and the inner rotor, and the AC distance y is the minimum air gap distance, which is 0.75 mm.

[0053] like Figure 5 As shown, 1 is the outer contour line of the rotor, 2 is the inner contour line of the stator, point B is the top center point of any stator tooth, point D is the intersection of the line connecting point B and the center of the motor and the inner rotor, and points B and D are equivalent to points A and C; point O1 is the reference point, equivalent to point O; O1' is located on the extension line of the line connecting point B and the center of the motor and has an eccentric distance from point O1.

[0054] Further, in step 101, the quantitative relationship between R, h, and OA must be: R=OA-h; where h is the eccentricity, and R is the distance between O' and point A. The quantitative relationship between R1, h1, and O2E must be: R1=O2E-h1; where h1 is the eccentricity of the rotor tooth, and R1 is the distance between O2' and point E.

[0055] The larger the eccentricity on the stator side, the smaller R is, and the greater the eccentricity of the stator tooth 104. The design process of the stator split teeth on the other side is the same. Since point O is on the opposite side of the motor center, there is still a slight eccentricity effect when the eccentricity is 0mm. Therefore, it is necessary to select a suitable point O during optimization and fix it as a fixed point so that when the eccentricity is 0mm, the eccentricity effect can be ignored, making the subsequent parameter scanning eccentricity selection of the optimal eccentricity more accurate and reasonable. In this example, point O is 180mm away from the center of the circle.

[0056] Under the condition that the shapes of the stator teeth 104 and the rotor teeth 203 are not deformed, the stator and rotor side eccentricities in a suitable range are selected for scanning, and the optimization results are viewed with torque and torque pulsation as the main objects, and core loss and eddy current loss as the secondary objects. The low torque pulsation without excessive torque reduction is used as the selection criterion to select the optimal result.

[0057] Furthermore, in order to verify the accuracy of the stator and rotor modulated tooth eccentricity design in reducing torque pulsation, the Maxwell stress tensor method is used to calculate the torque and torque pulsation generated by each order of harmonics, and the harmonic order that contributes most to the torque and torque pulsation is obtained. At the same time, the amplitude change of the main harmonic order before and at the optimal eccentricity of the stator and rotor modulated teeth is simulated and analyzed. Finally, the relationship between the amplitude change of the main harmonic order and the dominant harmonics of the torque and torque pulsation is compared and analyzed to verify the effectiveness of the stator and rotor modulated tooth eccentricity design.

[0058] In step 102, the radial air gap flux density and the tangential air gap flux density of the motor can be expressed as: ; Among them, B Rq , B Tq are the qth radial and tangential air gap flux amplitudes, θ Rq ,θ Tq is the qth radial and tangential air gap flux phase.

[0059] The radial and tangential air gap magnetic flux can be obtained by simulating multiple time points, and the amplitude and phase of the radial and tangential air gap magnetic flux can be decomposed by FFT respectively, and finally the amplitude and phase of the radial and tangential air gap magnetic flux can be obtained.

[0060] For a permanent magnet vernier motor, the Maxwell stress tensor method can be used to establish the relationship between the output torque and the air gap flux density. In step 103, the relationship between the output torque and the air gap flux density is expressed as: (1); where T e (t) is the total output torque, r g is the air gap radius, μ0 is the vacuum permeability, l a is the motor axial length, T q (t) is the output torque generated by the qth harmonic, B Rq , B Tq are the qth radial and tangential air gap flux amplitudes, θ Rq ,θ Tq is the qth radial and tangential air gap flux phase.

[0061] Through the above analysis, the relationship between the output torque and the air gap flux density can be established through the Maxwell stress tensor method. Through simulation, the total average torque generated by each order harmonic at a single time point and the output torque of a certain order harmonic at multiple simulation time points can be obtained. The total average torque generated by each order harmonic at a single time point can be superimposed with the number of multiple time points of the simulation as the number of superpositions to obtain the average torque and torque waveform of the motor output. Similarly, the average torque and torque waveform generated by a certain order harmonic can also be obtained.

[0062] After obtaining the output torque generated by each harmonic, the torque ripple is calculated according to the peak-to-peak value and average value of each order harmonic obtained in step 103. The basic calculation formula of torque ripple is as follows: (2); where T pk2pk (t) is the peak-to-peak value of the output torque, T max (t) is the maximum output torque, T min (t) is the minimum output torque, T avg (t) is the average value of the output torque.

[0063] Furthermore, according to equations (1) and (2), the torque pulsation generated by the qth harmonic is expressed as: .

[0064] Through the above analysis, the contribution of the main order harmonics to the torque and torque ripple is obtained after ignoring the higher order harmonics and lower amplitude harmonics.

[0065] like Figure 7 As shown, it can be seen that the 38th harmonic generates 83.86Nm of torque, accounting for 69% of the average torque, and the 48th harmonic generates 26.15Nm of torque, accounting for 21% of the average torque. These two harmonics contribute most of the torque, and the remaining harmonics with higher orders or lower harmonic amplitudes contribute a total of 10% of the torque component. It can be concluded that the 38th and 48th harmonics are the dominant harmonics of the torque. The dominant harmonic order of the torque pulsation can be obtained by dividing the peak-to-peak value of each order of harmonics by the average torque of each order of harmonics.

[0066] like Figure 8 As shown in the figure, the harmonic orders that have a greater impact on torque pulsation are 34, 72, 10, and 14, which are the dominant harmonics of torque pulsation. The modulated harmonics are the dominant harmonics of torque pulsation rather than the original magnetic field harmonics. Among them, the 10th harmonic involves rotor permeability modulation, the 72nd harmonic involves stator permeability modulation, and the 14th and 34th harmonics involve stator and rotor permeability modulation. When the original magnetic field harmonic components do not change, changing the specific harmonic content of permeability is an effective way to optimize the modulated harmonics and reduce torque pulsation.

[0067] The optimization of the eccentricity through the above steps has determined the optimal eccentricity, and the main harmonic order amplitudes of the motor with the initial structure and the main harmonic order amplitudes of the motor with the optimal eccentricity are obtained through simulation.

[0068] like Fig. 9As shown in the figure, no new harmonic order is generated before and after the stator and rotor modulation teeth are eccentric, only the harmonic amplitude changes. This is because the eccentric design of the stator and rotor modulation teeth does not change the period of the magnetic permeance, but only changes the waveform of the magnetic permeance. From the magnetic field modulation theory, it can be known that both the permanent magnet magnetomotive force and the armature magnetomotive force will be modulated by the stator and rotor magnetic permeance to generate new harmonic orders. Therefore, the change in the amplitude of the magnetic permeance of each order of the stator and rotor magnetic permeance will directly affect the amplitude of the modulated harmonics. Among them, the amplitude of the 38th harmonic decreases by 7.7% at the largest rate, and the 38th harmonic torque accounts for 69%. Although the amplitudes of the 24th and 48th harmonics increase by 3.9% and 3.2% respectively, the total torque share of the two is only 28.5%, which is not enough to offset the impact of the reduction in the amplitude of the 38th harmonic on the torque. On the other hand, the amplitudes of the 34th, 72nd, 10th, and 14th harmonics are all reduced by 15%, 20%, 2.8%, and 6.5%, respectively, and these harmonics are the dominant harmonics of torque pulsation. In summary, the stator and rotor modulated tooth eccentricity design leads to changes in the air gap flux amplitude, and the changes in torque and torque fluctuation are consistent with the theoretical analysis, which verifies its effectiveness.

[0069] Taking the 24-slot 38-pole double-sided permanent magnet motor of this embodiment as an example, after the stator and rotor modulated teeth are eccentrically designed, the eccentricity is optimized for simulation to obtain the torque, back electromotive force, and cogging torque before and after the simulation, as shown in FIG. Figure 10-12 As shown:

[0070] The main performance comparison of the motor before and after the stator and rotor gear eccentricity is shown in the following table:

[0071]

[0072] From the optimization results, the torque pulsation decreased by 76.6% when the output torque decreased by 4.6%, which is a significant effect. The peak-to-peak value of the slot torque decreased by 87.3%. The core loss was reduced to a certain extent. The eccentric design of the stator and rotor modulated teeth saved the amount of silicon steel sheets and reduced the manufacturing cost of the motor.

[0073] For this example, the eccentric design of the stator and rotor teeth can significantly reduce torque fluctuations without sacrificing much output torque, while reducing losses and achieving better results.

[0074] Embodiment 2:

[0075] like Figure 3 As shown in the figure, the number of split teeth of the double-sided permanent magnet excitation vernier motor can be arbitrarily selected under the relationship between the number of slot poles. Therefore, the eccentric design can be performed for the split teeth of multiple stators. Figure 3 It is a double-sided permanent magnet vernier motor with 12 slots and 3 stator split teeth.

[0076] Embodiment three:

[0077] like Figure 4 As shown, the shape of the stator teeth 104 of the double-sided permanent magnet excitation vernier motor can be a step-type to approximate the equivalent, the essence of which is to make the sinusoidality of the stator side magnetic permeability waveform higher.

[0078] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An unequal air gap double-sided permanent magnet motor, characterized in that: The invention comprises a stator and a rotor which are sequentially arranged from the outside to the inside, an air gap is formed between the rotor and the stator, the stator comprises a stator core, first stator slots and stator teeth are evenly distributed along the circumferential direction in the stator core, a stator armature winding is embedded in the stator slots, rotor slots and rotor teeth are evenly distributed along the circumferential direction on the outer side of the rotor core, and a tooth profile of at least one of the stator teeth and the rotor teeth is a non-uniform geometric structure; The non-uniform geometric structure of the stator tooth is that the end of the stator tooth extends a convex surface toward the center of the motor, the top center point of the convex surface of the stator tooth and any fixed point on the extension line of the motor center line form a reference point, and the geometric center of the convex surface of each stator tooth has an eccentricity relative to the reference point, so that a non-uniform air gap is formed between the inner surface of the stator and the outer surface of the rotor, thereby reducing the harmonic content of specific magnetic permeability and thus reducing torque pulsation.

2. The unequal air gap double-sided permanent magnet motor according to claim 1, characterized in that: The non-uniform geometric structure of the rotor teeth is that the rotor teeth extend a convex surface toward the outside of the motor with the motor center as the reference point, the end of the rotor tooth forms a convex surface, and the geometric center of the convex surface of each rotor tooth has an eccentricity relative to the motor center.

3. The unequal air gap double-sided permanent magnet motor according to claim 1, characterized in that: The rotor comprises a rotor core, the outer surface of the rotor core is provided with rotor slots spaced circumferentially; the inner side of the stator core is provided with second stator slots spaced evenly along the circumferential direction, and the second stator slots are alternately distributed with the stator teeth.

4. The unequal air gap double-sided permanent magnet motor according to claim 3, characterized in that: Stator permanent magnets and rotor permanent magnets are embedded in the second stator slots and the rotor slots respectively, so that the stator and the rotor both form an alternating pole structure, and the stator teeth and rotor teeth with non-uniform geometric structures are respectively adapted to the stator and rotor with the alternating pole structure.

5. The unequal air gap double-sided permanent magnet motor according to claim 3, characterized in that: The inner side of the stator core and the outer side of the rotor core are flux modulation poles of a double salient pole structure, forming a bidirectional flux modulation effect.

6. A method for reducing torque pulsation of an unequal air gap double-sided permanent magnet motor, applicable to an unequal air gap double-sided permanent magnet motor as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: Step 101, the eccentric design of the motor stator teeth is provided with point A, point O and point O', the point A is the top center point of the stator teeth, the point O is the reference point of the stator teeth, the point O' is located on the extension line of the line connecting point A and the center of the motor circle and has an eccentricity difference from the point O, and an arc is made with O' as the center and O'A as the radius to form the eccentric design of the stator teeth, and the eccentric design of the motor rotor teeth is provided with point E, point O2 and point O2', the point E is the top center point of the rotor teeth, the point O2 is the center of the motor circle, the point O2' is located on the line connecting point E and the center of the motor circle and has an eccentricity difference from the point O2, and an arc is made with O2' as the center and O'E as the radius to form the eccentric design of the rotor teeth. The torque pulsation is minimized by parameter scanning of the eccentricity; Step 102, using Maxwell finite element simulation to obtain the radial and tangential magnetic flux amplitudes and phases of the air gap at multiple time points; Step 103, substituting the data obtained in step 102 into the Maxwell stress-Tenri method torque formula to obtain the torque generated by each harmonic; Step 104, substituting the torque data obtained in step 103 into the torque pulsation formula to calculate the torque pulsation generated by each harmonic; Step 105: Compare the changes in the amplitude of the dominant harmonics of the torque pulsation before and after the stator teeth and the rotor teeth are eccentric, and verify the result.

7. A method for reducing torque ripple of an unequal air gap double-sided permanent magnet motor as claimed in claim 6, characterized in that: In step 101, R, h, and OA must satisfy the quantitative relationship: R=OA-h; where h is the stator tooth eccentricity, and R is the distance between point O' and point A; R1, h1, and O2E must satisfy the quantitative relationship: R1=O2E-h1; where h1 is the rotor tooth eccentricity, and R1 is the distance between point O2' and point E.

8. A method for reducing torque ripple of an unequal air gap double-sided permanent magnet motor as claimed in claim 7, characterized in that: In step 103, the relationship between the output torque and the air gap flux density is expressed as: (1); where T e (t) is the total output torque, r g is the air gap radius, μ0 is the vacuum permeability, l a is the motor axial length, T q (t) is the output torque generated by the qth harmonic, B Rq , B Tq are the qth radial and tangential air gap flux amplitudes, θ Rq ,θ Tq is the qth radial and tangential air gap flux phase.

9. A method for reducing torque ripple of an unequal air gap double-sided permanent magnet motor as claimed in claim 8, characterized in that: The torque ripple is calculated based on the peak-to-peak value and average value of each order harmonic obtained in step 103. The basic calculation formula of the torque ripple is as follows: (2); where T pk2pk (t) is the peak-to-peak value of the output torque, T max (t) is the maximum output torque, T min (t) is the minimum output torque, T avg (t) is the average value of the output torque.

10. A method for reducing torque ripple of an unequal air gap double-sided permanent magnet motor as claimed in claim 9, characterized in that: According to equations (1) and (2), the torque ripple generated by the qth harmonic is expressed as: .

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