Outer rotor permanent magnet synchronous motor with high power density

Abstract

A high-power-density permanent magnet synchronous motor structure disclosed by the present invention comprises a stator, a rotor and a three-phase winding, the stator comprises a stator body and a plurality of T-shaped stator teeth arranged on the radial outer wall of the stator body at equal intervals, a stator slot is formed between every two adjacent stator teeth, the stator slots are arranged in a skewed slot manner in the axial direction, and the three-phase winding is arranged in the stator body. The steel wire rope slightly deviates after being longer than a certain length; the three-phase winding is arranged in a stator groove, the rotor is nested on the stator, a plurality of permanent magnets are arranged on the inner wall of the rotor at equal intervals, the permanent magnets are in a surface-mounted form, and the permanent magnets comprise three different trapezoidal permanent magnets. According to the structure, the mechanical strength of the permanent magnet synchronous motor is ensured, the air gap flux density is improved, the back electromotive force harmonic is reduced, and meanwhile, the torque output capability of the motor is improved.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic design of permanent magnet synchronous motor bodies, and specifically to an outer rotor permanent magnet synchronous motor with high power density. Background Technique

[0002] Permanent magnet synchronous motors (PMSMs) have the characteristics of long running time, high efficiency, low vibration, etc., and are widely used in fields such as aerospace, robotics, and electric vehicles. Compared with traditional motors, the structure of PMSMs is relatively simple and the power density is higher. However, the power density of permanent magnet synchronous motors currently applied in emerging fields is about 1 kW / kg. Although the power density has increased significantly compared with traditional motors, it is not sufficient for the lightweight requirements of some emerging fields. For applications in aerial drones, motors with high moment of inertia and low mass can bring greater benefits and less energy loss, thereby extending the endurance time. Therefore, the structure of an outer rotor permanent magnet synchronous motor is adopted. However, for traditional surface-mounted outer rotor permanent magnet synchronous motors, there is still room for improvement in their power density, and there are problems such as large permanent magnet losses and high harmonic content. Therefore, it is necessary to design a new structure to improve its performance to a greater extent. Summary of the Invention

[0003] Aiming at the problems of large torque ripple, high harmonic content, high motor temperature, and small power density existing in the application of the above-mentioned permanent magnet synchronous motor in the aviation field, the present invention provides an outer rotor permanent magnet synchronous motor with high power density. By optimizing the design of the motor stator and permanent magnets, the torque output ability of the motor is improved, and the cogging torque, torque ripple, and harmonic content of the motor are reduced by skewing, making the torque output of the motor more stable. This design enables the motor to have greater efficiency, stronger stability, and higher torque output ability.

[0004] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0005] An outer rotor permanent magnet synchronous motor structure suitable for small unmanned aerial vehicles in the aviation field, including a stator, a rotor, and three-phase windings. The stator includes a stator body and T-shaped stator teeth arranged in several equal parts on the radially outer wall of the stator body. The stator slots are formed by adjacent stator teeth. The stator slots use skewing technology and are slightly offset at regular intervals in the axial length. The three-phase windings are arranged in the stator slots. The rotor is sleeved outside the stator. Several permanent magnets are attached to the inner wall of the rotor. The permanent magnets are surface-mounted. The permanent magnets include three permanent magnets with different shapes, including a class I permanent magnet in the middle, a class II permanent magnet on the left, and a class III permanent magnet on the right. The class II and class III permanent magnets are attached to both sides of the class I permanent magnet, and their shapes are different but generally trapezoidal structures.

[0006] In the above technical solution, the permanent magnet is in the form of surface-mounted, and the permanent magnet uses neodymium iron boron material N50UH with good performance.

[0007] In addition, the thickness HM of the permanent magnet is 3 mm, the long bottom side L1 of the type-I permanent magnet is 4.6 - 4.7 mm, and the short bottom side L2 is 1.7 - 1.8 mm; the long bottom side L3 of the type-II permanent magnet is 5.3 - 5.4 mm, and the short bottom side L4 is 4.6 - 4.7 mm; the long bottom side L5 of the type-III permanent magnet is 6.2 - 6.3 mm, and the short bottom side L6 is 4.6 - 4.7 mm; the magnetization angle of the type-I permanent magnet is 90-degree radial magnetization, and the magnetization angle θ of the type-II and type-III permanent magnets is 25 deg.

[0008] In the above technical solution, it is designed with 30 poles and 36 slots, and the rotational speed is set to 3300 rpm, so that the frequency of the motor under rated operation is 825 Hz. The setting of the higher frequency of the motor is beneficial to the improvement of the output torque, and at the same time does not affect the sampling of the host computer and the design of the motor control process.

[0009] In the above technical solution, the stator core, stator teeth, stator slots, and three-phase fractional-slot winding form the stator part, which is located inside the motor.

[0010] In the above technical solution, the stator slots are equally divided into five segments in the axial direction, and the axial length Lt of each segment is 11.6 mm. At the same time, the offset angle γ between each segment is 1.6 degrees.

[0011] Preferably, the three-phase armature winding adopts a fractional-slot concentrated winding, and its advantage is that the length of the winding end is smaller, which can significantly improve the power density.

[0012] As a preference, the permanent magnet is axially stacked by a number of permanent magnet sheets, and its advantage is that the loss of the permanent magnet is smaller.

[0013] As a preference, the permanent magnet adopts the Halbach magnetization method. One pole of the permanent magnet is composed of type-I, type-II, and type-III permanent magnets, and the magnetization direction of the adjacent other pole of the permanent magnet is opposite to that of the permanent magnet.

[0014] As a preference, the motor rotor adopts an outer rotor structure, and its advantages are that the moment of inertia and power output are both high, and it is beneficial to heat dissipation.

[0015] As a preference, the stator is stacked by a number of silicon steel sheets, and the stacking factor of the silicon steel sheets is 0.98.

[0016] As a preference, the inner radius R1 of the stator is 46 mm, and the outer radius R2 is 63.4 mm.

[0017] As a preference, the height of the stator slot is 13 mm, the thickness of the stator yoke ST is 3 mm, the width of the stator tooth TW is 4 mm, and the opening of the stator slot is 2.8 mm.

[0018] The present invention has the following features and beneficial effects:

[0019] By adopting Halbach magnetization, the air-gap magnetic density can be increased, the magnetic flux in the rotor yoke can be reduced, the thickness of the rotor yoke can be decreased, and thus the mass of the motor can be lightened.

[0020] The magnetic flux concentrating effect of the trapezoidal permanent magnet is better. Using trapezoidal permanent magnets can increase the air-gap magnetic density, and thus improve the torque output of the motor.

[0021] The optimization of the stator slots and stator teeth can reduce the cogging torque, decrease the back electromotive force harmonics, reduce the leakage magnetic flux. At the same time, by adopting the skewed slot technology, the harmonic content can be reduced to the greatest extent, the torque ripple and motor vibration can be decreased, and the optimization of the structure is also beneficial to improving the power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0023] Figure 1 is the model diagram of the permanent magnet synchronous motor of the present invention;

[0024] Figure 2 is the schematic diagram of the permanent magnet structure of the present invention;

[0025] Figure 3 is the axial segmentation diagram of the permanent magnet of the present invention;

[0026] Figure 4 is the schematic diagram of the structure of the original permanent magnet synchronous motor;

[0027] Figure 5 is the structure size diagram of the stator of the permanent magnet motor of the present invention;

[0028] Figure 6 is the structure size diagram of the permanent magnet of the present invention;

[0029] Figure 7 Schematic diagram of the skewed slot structure of the stator of the present invention;

[0030] Figure 8 Comparison diagram of the torque output of the original permanent magnet motor and the permanent magnet motor of the present invention;

[0031] Figure 9 Comparison diagram of the air-gap magnetic density of the original permanent magnet motor and the permanent magnet motor of the present invention;

[0032] Figure 10Comparison diagram of no-load back electromotive force harmonics of the permanent magnet motor of the present invention with and without skewed slot structure;

[0033] In the figure, 1 is the rotor, 2-1 is the type I permanent magnet, 2-2 is the type II permanent magnet, 2-3 is the type III permanent magnet, 3 is the stator yoke, 4 is the three-phase winding, 5 is the stator tooth, and 6 is the stator slot. Specific embodiments

[0034] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0035] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention. In addition, terms such as "type I" and "type II" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0036] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0037] The present invention provides a high power density permanent magnet synchronous motor structure, as Figure 1 shown, including a stator 3, a rotor 1, and a winding 4. In this embodiment, the number of pole pairs of the motor is 15 pairs of poles and 36 slots, which is beneficial to reducing the 5th and 7th harmonics of the back electromotive force, reducing vibration, improving stability, and having a high torque output capacity at the same time.

[0038] Specifically, the stator 3 includes a stator body and T-shaped teeth arranged at equal intervals on the radially outer wall of the stator body. The tip part of the teeth reduces harmonics by setting the stator slot shoulder angle. Stator slots 6 are formed between adjacent stator teeth. A plurality of three-phase windings 4 are distributed in the stator slots. The rotor is nested on the stator, and an air gap is formed between the stator and the rotor. A plurality of permanent magnets are arranged at equal intervals on the inner wall of the rotor.

[0039] Among them, the three-phase winding 4 is a fractional-slot concentrated winding, which has the advantages of a smaller end length and smaller back electromotive force harmonics, and can improve stability and power density.

[0040] A further setting of this embodiment is as Figure 2 shown. The permanent magnet is in the form of surface-mounted, including three trapezoidal permanent magnets with different shapes. The middle permanent magnet is magnetized radially.

[0041] Specifically, the permanent magnet uses neodymium iron boron material with a high magnetic energy product, and the trapezoidal magnet has a better magnetic concentration effect.

[0042] Furthermore, the permanent magnet is axially segmented and optimized to reduce the eddy current loss of the permanent magnet and improve the motor efficiency.

[0043] Specifically, as Figure 6 shown, the thickness HM of the permanent magnet is 3 mm. The long bottom side L1 of the type-I permanent magnet is 4.6 - 4.7 mm, and the short bottom side L2 is 1.7 - 1.8 mm; the long bottom side L3 of the type-II permanent magnet is 5.3 - 5.4 mm, and the short bottom side L4 is 4.6 - 4.7 mm; the long bottom side L5 of the type-III permanent magnet is 6.2 - 6.3 mm, and the short bottom side L6 is 4.6 - 4.7 mm; the magnetization angle of the type-I permanent magnet is 90 degrees of radial magnetization, and the magnetization angles θ of the type-II and type-III permanent magnets are 25 deg. The pole arc coefficient of the Halbach of the present invention is the same as that of the traditional Halbach, both being 1. The permanent magnet synchronous motor of the present invention has the same number of pole slots, coil turns, current density, and stator structure as the original permanent magnet synchronous motor, and only differs in the permanent magnet configuration, which is convenient for comparison.

[0044] A further setting of this embodiment is as Figure 1 and Figure 3 shown. The stator slot is a flat-bottom slot, and the stator is laminated with silicon steel sheets, with a lamination coefficient of 0.98; the stator teeth are provided with a stator slot shoulder angle α of 11.5 - 11.6 deg, which can reduce the cogging torque.

[0045] Specifically, in this embodiment, the inner radius R1 of the stator is 46 mm, and the outer radius R2 is 63.4 mm. If the height of the stator slot is too low, the slot area will be small, resulting in a small motor torque output; if the height of the stator slot is too high, the torque ripple of the motor will increase, and the mass of the motor stator will increase, thereby reducing the power density. The stator slot opening affects the harmonic content of the back electromotive force and torque ripple of the motor, and the power output. The stator yoke thickness and tooth width affect the magnetic flux distribution and slot fill factor on the motor stator, thereby affecting the motor performance. The height HS2 of the stator slot is 13 mm, the stator yoke thickness ST is 3 mm, the stator tooth width TW is 4 mm, and the stator slot opening BS0 is 2.8 mm.

[0046] Comparative example:

[0047] As Figure 4 shown, the permanent magnet is three equally divided Halbach permanent magnets, and each permanent magnet is of a tile structure.

[0048] Figure 8 Table 1 shows the comparison of the torque output capabilities between the original permanent magnet motor and the permanent magnet synchronous motor of the present invention. It can be found that the torque output capability of the new permanent magnet structure of the present invention is 8.9% higher than that of the original magnetic pole array in terms of torque output capability, but the torque ripple is not much different.

[0049] Table 1: Comparison of electromagnetic torque output performance

[0050] Configuration Average Torque (Nm) Existing Magnetic Pole Array 26.27 New Type of Magnetic Pole Array 23.92 Comparison Effect Improved by 8.9%

[0051] In order to verify the enhancement effect of the new magnetic pole array proposed in the implementation of the present invention on the magnetic field strength, the air-gap magnetic flux density and harmonics are analyzed using ANSYS software. The radial air-gap magnetic flux density is mainly analyzed. The radial air-gap magnetic flux density waveforms of the two structures, namely the original permanent magnet synchronous motor and the permanent magnet synchronous motor of the present invention, in one electrical cycle are as Figure 9 shown. The comparison of the harmonic content and the air-gap magnetic flux density size is shown in Table 2. It can be seen that the maximum air-gap magnetic flux densities of the two structures are approximately the same, but the air-gap magnetic flux density of the new structure is more sinusoidal. By analyzing the air-gap magnetic flux density of the two structures in Table 1, it can be seen that the present invention has a smaller harmonic content, a larger air-gap magnetic flux density, and for the fifth harmonic that has the greatest impact on torque output, the fifth harmonic of the new magnetic pole array is the smallest.

[0052] Table 2: Comparison of magnetic field strength performance

[0053]

[0054] Figure 10Compare the no-load back electromotive force harmonics before and after the skew of the new magnetic pole structure. After applying the skew, the fundamental wave content decreases slightly, the third harmonic is reduced by more than half, and there are almost no harmonics of other orders, indicating that the stability of its output voltage and anti-interference ability are greatly improved.

[0055] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principle and spirit of the present invention, various changes, modifications, substitutions, and variations of these embodiments including components still fall within the protection scope of the present invention.

Claims

1. A high-power density outer-rotor permanent magnet synchronous motor, characterized in that, It includes a stator and a rotor (1). Between the inner wall of the rotor (1) and the stator, several surface-mounted permanent magnet units are provided. The several permanent magnet units are mutually attached to form an annular structure. The permanent magnet unit includes 3 permanent magnets, namely a type-I permanent magnet (2-1) and type-II permanent magnets (2-2) and type-III permanent magnets (2-3) arranged on both sides of the type-I permanent magnet (2-1). The permanent magnets adopt the Halbach magnetization method. The magnetic pole directions of adjacent three types of permanent magnets are opposite. The magnetization angle of the type-I permanent magnet is 90-degree radial magnetization, and the magnetization angles θ of the type-II and type-III permanent magnets are 25deg, and the pole arc coefficient is 1.

2. A high-power density outer-rotor permanent magnet synchronous motor according to claim 1, wherein The stator includes a stator body with an annular structure and several equally-spaced T-shaped stator teeth (5) arranged on the radially outer wall of the stator body. Between adjacent stator teeth (5), stator slots (6) are formed, and three-phase windings (4) are arranged in the stator slots (6).

3. A high-power-density outer-rotor permanent magnet synchronous motor according to claim 1, characterized in that, The stator is formed by laminating several silicon steel sheets, and the lamination coefficient is 0.98; the stator slots formed by laminating the silicon steel sheets use a continuous skewed slot process in the axial direction. It is equally divided into five sections, and the axial length Lt of each section is 11.6mm, and at the same time, the offset angle γ between each section is 1.6 degrees.

4. A high-power-density outer-rotor permanent magnet synchronous motor according to claim 1, characterized in that The permanent magnet is axially stacked by several permanent magnet sheets.

5. A high-power density outer-rotor permanent magnet synchronous motor according to claim 1, characterized in that, The inner radius R1 of the stator is 46mm, and the outer radius R2 is 63.4mm.

6. A high-power-density outer-rotor permanent magnet synchronous motor according to claim 1, characterized in that The thickness HM of the permanent magnet is 3mm.

7. A high-power density outer-rotor permanent magnet synchronous motor according to claim 1, characterized in that, The long base L1 of the type-I permanent magnet is 4.6-4.7mm, and the short base L2 is 1.7-1.8mm; the long base L3 of the type-II permanent magnet is 5.3-5.4mm, and the short base L4 is 4.6-4.7mm; the long base L5 of the type-III permanent magnet is 6.2-6.3mm, and the short base L6 is 4.6-4.7mm.

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