Slot setting method and application of fractional-slot asynchronous starting permanent magnet synchronous motor

Abstract

The present invention discloses a method for setting skew slots in a fractional-slot asynchronous-start permanent magnet synchronous motor and its application. Based on the number of pole slots in the motor and the arrangement of the stator windings, the variation period of the load cogging torque is determined, and the axial tilt angle of the stator slots is given. By rationally setting the stator slot tilt angle, the present invention can not only effectively reduce the no-load cogging torque and load cogging torque of the fractional-slot asynchronous-start permanent magnet synchronous motor, but also significantly reduce the harmonic content in the induced electromotive force of the stator winding. Simultaneously, this method does not significantly affect the magnetic circuit of the motor and has little impact on the motor's operating performance, thus facilitating the stable operation of such motors. The method has strong applicability and significant effects.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet synchronous motors, and in particular to a method for setting skew slots of a fractional slot asynchronous starting permanent magnet synchronous motor and its application. Background Art

[0002] Compared to traditional electromagnetic motors, permanent magnet motors offer advantages such as high power density, high operating efficiency, and a simple and compact structure. my country possesses abundant reserves of rare earth resources, and promoting the use of permanent magnet motors is a key measure for improving industrial production efficiency and promoting energy conservation and emission reduction. Cogging torque, an inherent issue with permanent magnet motors, has long been a research focus for scholars. Research on the cogging torque of permanent magnet motors has primarily focused on the motor's no-load condition, with a variety of effective mitigation measures investigated. However, when the motor is operating under load, the load cogging torque generated by the interaction between the permanent magnets and the saturated slotted core differs from the cogging torque when the motor is operating under no-load conditions. Therefore, direct application of mitigation measures for the cogging torque during no-load operation is difficult. Therefore, research on mitigation measures for the cogging torque of permanent magnet motors operating under load would be of greater practical value.

[0003] As a type of permanent magnet motor with self-starting capability, the asynchronous-start permanent magnet synchronous motor (ASM) is structurally similar to a conventional asynchronous motor with permanent magnets placed within the rotor core. It primarily achieves self-starting through the asynchronous torque generated by the interaction between the rotor cage winding and the stator winding's magnetomotive force. Compared to conventional asynchronous motors, ASMs offer advantages such as high power factor, high power density, and a wide economic operating range, gradually replacing asynchronous motors in various industrial applications. Similar to other types of permanent magnet motors, ASMs also suffer from cogging torque. However, due to the presence of cogging on both the stator and rotor sides of ASMs, the generation mechanism, variation characteristics, and mitigation measures for cogging torque differ from those of conventional single-sided slotted permanent magnet motors.

[0004] When a fractional-slot asynchronous-start permanent magnet synchronous motor is operating under load, the saturation level of the stator and rotor cores due to the action of the rotor permanent magnets and stator windings is non-negligible. Compared to the motor's no-load cogging torque, the distribution characteristics and variation period of its loaded cogging torque will change. Therefore, an in-depth analysis of the variation characteristics of the loaded cogging torque of fractional-slot asynchronous-start permanent magnet synchronous motors and the study of stator core skew methods that can effectively reduce the motor's loaded cogging torque have important theoretical and practical significance for the stable operation of fractional-slot asynchronous-start permanent magnet synchronous motors. This research can further promote the widespread application of permanent magnet motors and improve energy efficiency in industrial production.

[0005] As the instruction manual Figure 1As shown in the figure, when ordinary slots are used, the stator slots are tilted axially at an angle of 0°, and the number of stator slots per pole is a fraction. When the motor is running at no load, the no-load cogging torque is only related to the number of poles and slots of the motor, and has nothing to do with the distribution of the stator winding. Its variation period is Where n is is the smallest positive integer. However, when the motor is running under load, the spatial magnetomotive force generated by the stator winding no longer follows a perfect circle, and the saturation of the stator and rotor cores no longer changes with the stator tooth pitch as a period. The periodicity of the cogging torque is then related to the number of poles and slots in the motor and the distribution of the stator windings. Therefore, when a fractional-slot asynchronous-start permanent magnet synchronous motor is running under load, the periodicity and distribution of the loaded cogging torque differ from the no-load cogging torque. Existing no-load cogging torque reduction measures, including the determination of the stator skew angle, are unlikely to effectively reduce the motor's loaded cogging torque. Summary of the Invention

[0006] The object of the present invention is to provide a method for setting the skew slots of a fractional-slot asynchronous-start permanent magnet synchronous motor. This method provides a stator core skew slot angle based on the variation period of the load cogging torque of the fractional-slot asynchronous-start permanent magnet synchronous motor. While effectively weakening the motor's load cogging torque, it can also significantly weaken the motor's no-load cogging torque and reduce the harmonic content in the stator winding's induced electromotive force.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0008] The method for setting the skew slots of a fractional-slot asynchronous start permanent magnet synchronous motor is as follows: first, the number of unit motors t = GCD(Q1, p) of the motor is determined, where GCD(Q1, p) represents the greatest common divisor of the number of stator teeth Q1 and the number of motor pole pairs p;

[0009] Secondly, determine the total angle of the stator slot of the motor along the axial direction as θ s , and the A-phase, B-phase, and C-phase windings in the stator skew slots are arranged in 60° phase bands;

[0010] The first coil side of the A-phase winding in the unit motor is coil side No. 1 in the unit motor, and coil side No. 1 is located on the phase belt dividing line;

[0011] When the motor is running under load, the moment when the current of phase A winding reaches its peak is taken as the initial moment. Under the following first and second phase belt number determination methods, the magnetic field distribution in the motor is the same as that at the initial moment.

[0012] By using the first phase belt number determination method, it is determined that the number of phase belts rotated by the motor rotor when the current of the winding of a phase belt in the unit motor reaches the positive peak value is m1;

[0013] By using the second phase belt number determination method, it is determined that the number of phase belts rotated by the motor rotor when the current of the winding of a certain phase belt in the unit motor reaches a negative peak value is m2;

[0014] Finally, the minimum value of m1 and m2 is selected min , through m min Get θ s The setting algorithm is:

[0015]

[0016] Preferably, the stator skew slots are located on the inner surface of the stator core of the motor, and are arranged to be inclined along the axial direction of the stator core. Moreover, on any radial plane perpendicular to the axial direction, the stator skew slots are evenly distributed along the circumferential direction and have the same structural parameters, and the inclination angle of the stator slots along the axial direction is uniform and continuously changes.

[0017] Preferably, the method for determining the number of first phase belts includes the following steps:

[0018] If there is another phase belt in the unit motor, one of the coil sides is the coil side n1 of the unit motor, and the coil side n1 is located on the phase belt boundary line, then when the current of the winding under the phase belt reaches the positive peak, the magnetic field distribution in the motor is the same as at the initial moment; at this time, the number of phase belts m1 rotated by the motor rotor satisfies:

[0019]

[0020] in, express The remainder after dividing by 360°, m1 and n1 are positive integers that make formula (1) valid, and

[0021] Preferably, the method for determining the number of second-phase belts includes the following steps:

[0022] If there is another phase belt in the unit motor, and one of its coil sides is the coil side n2 of the unit motor, and the coil side n2 is located on the phase belt boundary line, then when the current of the winding under the phase belt reaches the negative peak, the magnetic field distribution in the motor is the same as at the initial moment; at this time, the number of phase belts m2 rotated by the motor rotor satisfies the following:

[0023]

[0024] Where m2 and n2 are positive integers that make formula (2) valid, and

[0025] Another object of the present invention is to provide an asynchronous starting permanent magnet synchronous motor, which adopts the above-mentioned inclined slot setting method.

[0026] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0027] An asynchronous start permanent magnet synchronous motor includes a stator and a rotor. The inner surface of the stator core is distributed with stator skew slots determined as described in the above method, and the number of stator skew slots per pole is a fraction. Stator windings are placed in the stator skew slots and are arranged in 60° phase bands.

[0028] Preferably, the rotor includes a rotor core, permanent magnets and a cage winding, the outer surface of the rotor core is evenly distributed with rotor slots in the circumferential direction, the rotor slots have the same structural parameters, and the number of rotor slots per pole is an integer, the inclination angle of the rotor slots along the axial direction is 0°, and a cage winding is placed in the rotor slots.

[0029] Preferably, a plurality of permanent magnet slots are distributed inside the rotor core, and one or more permanent magnets are placed in each permanent magnet slot. The permanent magnet slots and permanent magnets within each magnetic pole are symmetrically distributed with the radial center line of the magnetic pole as the symmetry axis, and the permanent magnet slots and permanent magnets within each magnetic pole are distributed in the same manner.

[0030] The beneficial effects of the present invention are:

[0031] (1) By reasonably setting the stator skew angle of the fractional slot asynchronous starting permanent magnet synchronous motor, the no-load cogging torque and load cogging torque of the motor can be effectively weakened. At the same time, the harmonic content of the induced electromotive force of the stator winding can be effectively reduced, which is beneficial to the stable operation of this type of motor. This method has strong applicability and significant effect.

[0032] (2) By reasonably setting the stator skew angle of the fractional slot asynchronous starting permanent magnet synchronous motor, it will not have a significant impact on the magnetic circuit of the motor and will have little impact on the operating performance of the motor.

[0033] (3) This method determines the variation period of the motor's cogging torque during load operation based on the number of poles and slots of the fractional slot asynchronous start permanent magnet synchronous motor and the distribution of the stator windings. By properly setting the stator skew angle, the motor's load cogging torque can be effectively weakened. While effectively weakening the motor's load cogging torque, it can also significantly weaken the motor's no-load cogging torque and reduce the harmonic content in the stator winding's induced electromotive force. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 This is a schematic diagram of the stator core of an asynchronous starting permanent magnet synchronous motor when stator skew slots are not provided.

[0036] Figure 2 This is a schematic diagram of the stator core of an asynchronous starting permanent magnet synchronous motor when the stator slots are set.

[0037] Figure 3 This is an 8-pole asynchronous start permanent magnet synchronous motor with 54 stator slots and 48 rotor slots. The curve of the no-load cogging torque changes when the relative position of the motor stator and rotor changes when the stator is not equipped with skew slots and when skew slots are equipped.

[0038] Figure 4 This is an 8-pole asynchronous start permanent magnet synchronous motor with 54 stator slots and 48 rotor slots. The load cogging torque curve changes when the relative position of the motor stator and rotor changes when the stator is not equipped with skew slots and when skew slots are equipped.

[0039] Figure 5 This is the induced electromotive force curve of the motor stator winding for an 8-pole asynchronous start permanent magnet synchronous motor with 54 stator slots and 48 rotor slots when the stator is not equipped with skew slots.

[0040] Figure 6 This is an 8-pole asynchronous start permanent magnet synchronous motor with 54 stator slots and 48 rotor slots. When the stator is set with skew slots, the induced electromotive force curve of the motor stator winding is shown.

[0041] Where 1 is the stator core, 2 is the stator skew slot, O is the center of the upper end face of the stator core, A and B are the corresponding points of the stator skew slot on the two end faces of the stator core, C is the axial projection of point B on the upper end face of the stator core, and the angle between lines OA and OC is the total axial inclination angle of the stator slot. DETAILED DESCRIPTION

[0042] The present invention provides a method and application for setting skew slots in a fractional-slot asynchronous-start permanent magnet synchronous motor. To clarify the objectives, technical solutions, and effects of the present invention, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0043] The present invention is described in detail below with reference to the accompanying drawings:

[0044] Example 1, a method for setting skew slots in a fractional-slot asynchronous start permanent magnet synchronous motor, first, determining the number of unit motors t = GCD(Q1, p), where GCD(Q1, p) represents the greatest common divisor of the number of stator teeth Q1 and the number of motor pole pairs p;

[0045] Secondly, determine the total angle of the stator slot of the motor along the axial direction as θ s , and the A-phase, B-phase, and C-phase windings in the stator skew slots are arranged in 60° phase bands;

[0046] The first coil side of the A-phase winding in the unit motor is coil side No. 1 in the unit motor, and coil side No. 1 is located on the phase belt dividing line;

[0047] When the motor is running under load, the moment when the current of phase A winding reaches its peak is taken as the initial moment. Under the following first and second phase belt number determination methods, the magnetic field distribution in the motor is the same as that at the initial moment.

[0048] By using the first phase belt number determination method, it is determined that the number of phase belts rotated by the motor rotor when the current of the winding of a phase belt in the unit motor reaches the positive peak value is m1;

[0049] By using the second phase belt number determination method, it is determined that the number of phase belts rotated by the motor rotor when the current of the winding of a certain phase belt in the unit motor reaches a negative peak value is m2;

[0050] Finally, the minimum value of m1 and m2 is selected min , through m min Get θ s The setting algorithm is:

[0051]

[0052] The stator skew slots are located on the inner surface of the stator core of the motor. The stator skew slots are arranged obliquely along the axial direction of the stator core. In addition, on any radial plane perpendicular to the axial direction, the stator skew slots are evenly distributed along the circumferential direction and have the same structural parameters. The inclination angle of the stator slots along the axial direction is uniform and continuously changes.

[0053] The method for determining the number of first-phase belts includes the following steps:

[0054] In the unit motor, if there is another phase belt, one of the coil sides of which is the coil side n1 of the unit motor, and the coil side n1 is located on the phase belt boundary line, then when the current of the winding under the phase belt reaches the positive peak, the magnetic field distribution in the motor is the same as the initial moment; at this time, the number of phase belts m1 rotated by the motor rotor satisfies

[0055]

[0056] in, express The remainder after dividing by 360°, m1 and n1 are positive integers that make formula (1) valid, and

[0057] The method for determining the number of second-phase belts includes the following steps:

[0058] If there is another phase belt in the unit motor, and one of its coil sides is the coil side n2 of the unit motor, and the coil side n2 is located on the phase belt boundary line, then when the current of the winding under the phase belt reaches the negative peak, the magnetic field distribution in the motor is the same as at the initial moment; at this time, the number of phase belts m2 rotated by the motor rotor satisfies the following:

[0059]

[0060] Where m2 and n2 are positive integers that make formula (2) valid, and

[0061] Example 2

[0062] An asynchronous start permanent magnet synchronous motor includes a stator and a rotor. The inner surface of the stator core is distributed with stator skew slots determined by the method in Example 1, and the number of stator skew slots per pole is a fraction. Stator windings are placed in the stator skew slots, and the stator windings are arranged in 60° phase bands.

[0063] The rotor includes a rotor core, permanent magnets and a cage winding. The outer surface of the rotor core is evenly distributed with rotor slots in the circumferential direction. The rotor slots have the same structural parameters, and the number of rotor slots per pole is an integer. The inclination angle of the rotor slots along the axial direction is 0°, and the cage winding is placed in the rotor slots.

[0064] There are multiple permanent magnet slots distributed inside the rotor core, and one or more permanent magnets are placed in each permanent magnet slot. The permanent magnet slots and permanent magnets within each magnetic pole are symmetrically distributed with the radial center line of the magnetic pole as the symmetry axis, and the permanent magnet slots and permanent magnets within each magnetic pole are distributed in the same way.

[0065] Example 3

[0066] An asynchronous start permanent magnet synchronous motor comprises a stator and a rotor. The inner surface of the stator core is distributed with stator skew slots, with the number of stator skew slots per pole being a fraction. Stator windings are placed within the stator skew slots, and the stator windings are arranged in 60° phase bands. The rotor comprises a rotor core, permanent magnets, and a cage winding. Rotor slots are evenly distributed along the circumference of the outer surface of the rotor core, each having identical structural parameters and an integer number of rotor slots per pole. The rotor slots are tilted axially at an angle of 0°. A cage winding is placed within the rotor slots. Multiple permanent magnet slots are distributed within the rotor core, each containing one or more permanent magnets. The permanent magnet slots and permanent magnets within each magnetic pole are symmetrically distributed about the magnetic pole's radial centerline, and the permanent magnet slots and permanent magnets within each magnetic pole are uniformly distributed.

[0067] The windings in the stator slots are arranged in 60-degree phase bands. For ease of analysis, assume that the first coil side of the phase A winding in a unit motor (coil side 1 of the unit motor) is located on the phase band boundary. When the motor is running under load, the initial moment is when the phase A winding current reaches its positive peak. In the following two cases, the magnetic field distribution in the motor remains the same as at the initial moment:

[0068] (1) If there is another phase belt in the unit motor, and its first coil side (coil side n1 of the unit motor) is also located on the phase belt boundary line, then when the current of the winding under the phase belt reaches the positive peak, the magnetic field distribution in the motor is the same as at the initial moment. At this time, the number of phase belts m1 rotated by the motor rotor satisfies in, express The remainder after dividing by 360°, m1 and n1 are positive integers that make the formula valid, and

[0069] (2) If there is another phase belt in the unit motor, and its first coil side (coil side n2 of the unit motor) is also located on the phase belt boundary line, then when the current of the winding under the phase belt reaches the negative peak, the magnetic field distribution in the motor is also the same as the initial moment. At this time, the number of phase belts m2 rotated by the motor rotor satisfies Among them, m2 and n2 are positive integers that make this formula valid, and

[0070] Determine the values ​​of m1 and m2, compare the values ​​of m1 and m2, find the minimum value between the two and name the minimum value m min , then after the rotor rotates, the rotor rotates at least m min When the phase is phased, the magnetic field distribution in the motor is the same as the initial moment, and then the cogging torque enters a new change cycle, so the total angle θ of the stator slot along the axial direction is s for In this way, by reasonably selecting the angle of the stator skew slots, the load cogging torque of the fractional-slot asynchronous-start permanent magnet synchronous motor can be significantly weakened.

[0071] Example 4

[0072] Figure 3 、 Figure 4 This figure compares the no-load cogging torque and loaded cogging torque of an 8-pole asynchronous-start permanent magnet synchronous motor with 54 stator slots and 48 rotor slots when the stator slots are not skewed and when the stator slots are skewed, as the relative position of the motor stator and rotor changes.

[0073] For this motor, the stator skew angle determined according to the variation cycle of the motor's load cogging torque can effectively weaken not only the motor's load cogging torque, but also the motor's no-load cogging torque.

[0074] Example 5

[0075] Figure 5 、 Figure 6 The induced electromotive force curves of the stator winding of an 8-pole asynchronous start permanent magnet synchronous motor with 54 stator slots and 48 rotor slots are shown in the figure below when the stator is not skewed and when the stator is skewed.

[0076] For this motor, the stator skew angle is determined according to the variation period of the motor load cogging torque. While effectively weakening the motor's no-load cogging torque and loaded cogging torque, it can also make the induced electromotive force curve of the motor's stator winding closer to an ideal sine wave, significantly reducing the harmonic content, which is more conducive to the stable operation of the motor.

[0077] Example 6

[0078] The working principle of the present invention is:

[0079] In an asynchronous start permanent magnet synchronous motor with an integer number of slots per rotor pole and an integer number of slots per stator pole, the stator winding distribution under each pair of magnetic poles is completely symmetrical, and the change cycles of the motor's no-load cogging torque and loaded cogging torque are the same, both However, in an asynchronous start permanent magnet synchronous motor with an integer number of slots per rotor pole and a fractional number of slots per stator pole, the stator windings under each pair of magnetic poles are not completely symmetrical; the no-load cogging torque of the motor is only related to the number of poles and slots of the motor, and has nothing to do with the distribution of the stator windings. Its variation period is Where n is is the smallest positive integer. When the motor is running under load, the rotation trajectory of the spatial magnetomotive force generated by the stator winding is no longer an ideal circle, and the saturation of the stator and rotor cores no longer changes with the stator tooth pitch. The period of cogging torque variation is related to the motor's number of poles and slots and the distribution of the stator windings. Stator skew is an effective measure to reduce cogging torque, and the setting of the stator skew angle is crucial for this reduction. Only when the stator skew angle matches the period of the cogging torque curve can the motor's cogging torque be significantly reduced. Therefore, by determining the period of cogging torque variation during load operation based on the number of poles and slots and the distribution of the stator windings in a fractional-slot asynchronous-start permanent magnet synchronous motor, and by appropriately setting the stator skew angle, the motor's load cogging torque can be effectively reduced.

[0080] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

[0081] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A method for setting skew slots in a fractional-slot asynchronous-start permanent magnet synchronous motor, characterized in that: First, determine the number of unit motors of the motor t = GCD (Q1, p), where GCD (Q1, p) represents the greatest common divisor of the number of stator teeth Q1 and the number of motor pole pairs p; Secondly, determine the total angle of the stator slot of the motor along the axial direction as θ s , and the A-phase, B-phase, and C-phase windings in the stator skew slots are arranged in 60° phase bands; The first coil side of the A-phase winding in the unit motor is coil side No. 1 in the unit motor, and coil side No. 1 is located on the phase belt dividing line; When the motor is running under load, the moment when the current of phase A winding reaches its peak is taken as the initial moment. Under the following first and second phase belt number determination methods, the magnetic field distribution in the motor is the same as that at the initial moment. By using the first phase belt number determination method, it is determined that the number of phase belts rotated by the motor rotor when the current of the winding of a certain phase belt in the unit motor reaches the positive peak value is m1; By using the second phase belt number determination method, it is determined that the number of phase belts rotated by the motor rotor when the current of the winding of a certain phase belt in the unit motor reaches a negative peak value is m2; Finally, the minimum value of m1 and m2 is selected min , through m min Get θ s The setting algorithm is: The method for determining the number of first-phase belts includes the following steps: If there is another phase belt in the unit motor, one of the coil sides is the coil side n1 of the unit motor, and the coil side n1 is located on the phase belt boundary line, then when the current of the winding under the phase belt reaches the positive peak, the magnetic field distribution in the motor is the same as at the initial moment; at this time, the number of phase belts m1 rotated by the motor rotor satisfies: in, express The remainder after dividing by 360°, m1 and n1 are positive integers that make formula (1) valid, and The method for determining the number of second-phase belts includes the following steps: If there is another phase belt in the unit motor, and one of its coil sides is the coil side n2 of the unit motor, and the coil side n2 is located on the phase belt boundary line, then when the current of the winding under the phase belt reaches the negative peak, the magnetic field distribution in the motor is the same as at the initial moment; at this time, the number of phase belts m2 rotated by the motor rotor satisfies the following: Where m2 and n2 are positive integers that make formula (2) valid, and 2. The method for setting skew slots of a fractional-slot asynchronous-start permanent magnet synchronous motor according to claim 1, characterized in that: The stator skew slots are located on the inner surface of the stator core of the motor. The stator skew slots are arranged obliquely along the axial direction of the stator core. In addition, on any radial plane perpendicular to the axial direction, the stator skew slots are evenly distributed along the circumferential direction and have the same structural parameters. The inclination angle of the stator slots along the axial direction is uniform and continuously changes.

3. An asynchronous start permanent magnet synchronous motor comprising a stator and a rotor, characterized in that: The inner surface of the stator core is distributed with stator skew slots determined by the method according to any one of claims 1-2, and the number of stator skew slots per pole is a fraction. Stator windings are placed in the stator skew slots, and the stator windings are arranged in 60° phase bands.

4. The asynchronous start permanent magnet synchronous motor according to claim 3, characterized in that: The rotor includes a rotor core, permanent magnets and a cage winding. The outer surface of the rotor core is evenly distributed with rotor slots in the circumferential direction. The rotor slots have the same structural parameters, and the number of rotor slots per pole is an integer. The inclination angle of the rotor slots along the axial direction is 0°, and the cage winding is placed in the rotor slots.

5. The asynchronous start permanent magnet synchronous motor according to claim 3, characterized in that: There are multiple permanent magnet slots distributed inside the rotor core, and one or more permanent magnets are placed in each permanent magnet slot. The permanent magnet slots and permanent magnets within each magnetic pole are symmetrically distributed with the radial center line of the magnetic pole as the symmetry axis, and the permanent magnet slots and permanent magnets within each magnetic pole are distributed in the same way.

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