CN114899965A - Low Pulsation Strong Fault Tolerant High Power Density Multiphase Permanent Magnet Motor - Google Patents

Abstract

The invention discloses a multi-phase permanent magnet motor with low pulsation, strong fault tolerance and high power density, comprising a modular stator, an armature winding and a rotor; the modular stator and the rotor are coaxially sleeved from outside to inside or from inside to outside, and There is an air gap between the two; the modular stator includes stator teeth and stator yoke; stator teeth include 4 n pairs of armature teeth, 4 n fault-tolerant teeth, and closed slots; each pair of armature teeth includes two Armature teeth; a large slot is formed between two armature teeth; a fault-tolerant tooth is arranged between two adjacent pairs of armature teeth; a small slot is formed between each fault-tolerant tooth and the adjacent armature teeth; the central angle of the small slot is less than the large The central angle of the slot, so that the stator teeth have unequal stator tooth pitch; each armature tooth pair and the adjacent half fault-tolerant teeth on both sides constitute a phase unit. The invention separates the stator teeth from the yoke, simplifies the winding process, improves the full rate of the stator slots, and further improves the power density. In addition, the closed slot design can suppress cogging torque and increase leakage inductance and phase self-inductance.

Description

Low Pulsation Strong Fault Tolerant High Power Density Multiphase Permanent Magnet Motor

technical field

The invention relates to the field of motor design and manufacture, in particular to a low-pulsation, strong fault-tolerant and high-power density multiphase permanent magnet motor.

Background technique

Permanent magnet motors have the advantages of high torque/power density, high efficiency, and high power factor, and have been used in many fields such as household appliances, electric vehicles, and industrial production. However, high-end equipment such as CNC machine tools and aerospace requires not only high power density and high efficiency of permanent magnet motors, but also high reliability and strong fault tolerance; the actuators are servo systems, which are very sensitive to torque ripple high demands.

Commonly used three-phase motors have poor fault tolerance. When one of the phase windings fails (such as short circuit or open circuit) and exits operation, it is difficult for the remaining two phases to meet the normal operation requirements; when two of the two-phase windings fail, the motor system cannot even run. In addition, conventional three-phase motors do not have phase-to-phase isolation of the windings (physical isolation, electromagnetic isolation, thermal isolation), which allows a faulty winding to spread the fault to adjacent windings.

In order to facilitate winding insertion, most of the existing permanent magnet motors adopt the open slot design; at the same time, in order to reduce the reluctance of the permanent magnet magnetic circuit as much as possible and increase the self-inductance of the winding phase, on the premise of satisfying the wire insertion conditions, the slot opening is designed as much as possible. Possibly small. Therefore, there are design contradictions among the slot full rate, permanent magnet utilization rate and phase self-inductance.

Therefore, the development of permanent magnet motors with low torque pulsation, strong fault tolerance and high power density has always been a hot topic in the application of motor systems to high-end equipment. It is of great significance to promote the rapid development of CNC machine tools, satellite communications, manned spaceflight and space exploration.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to aim at the above-mentioned deficiencies of the prior art, and to provide a low-pulsation strong fault-tolerant high-power density multi-phase permanent magnet motor, the low-pulsation strong fault-tolerant high power density multi-phase permanent magnet motor It is designed separately from the yoke, which simplifies the winding process, improves the full rate of the stator slots, and thus improves the power density. In addition, the closed slot design can suppress cogging torque and increase leakage inductance and phase self-inductance.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

A low-pulsation, strong fault-tolerant, high-power-density, multi-phase permanent magnet motor includes a modular stator, armature windings, and a rotor.

The modular stator and the rotor are coaxially sleeved from outside to inside or from inside to outside, and there is an air gap between them.

The modular stator includes stator teeth and a stator yoke.

The stator teeth include 4 n pairs of armature teeth, 4 n fault-tolerant teeth and closed slots; wherein, n ≥ 1.

4 n pairs of armature teeth are evenly distributed along the circumference of the stator yoke, and each pair of armature teeth includes two armature teeth; a large slot is formed between the two armature teeth.

A fault-tolerant tooth is arranged between two adjacent pairs of armature teeth; a small slot is formed between each fault-tolerant tooth and the adjacent armature teeth; the central angle of the small slot is smaller than the central angle of the large slot, so that the stator teeth have Unequal stator pitch.

The side of each armature tooth and each fault-tolerant tooth facing away from the air gap is detachably connected to the annular stator yoke.

The side of each armature tooth and each fault-tolerant tooth facing the air gap is connected by the closed slot.

Each armature tooth pair forms a phase unit with the adjacent half fault-tolerant teeth on both sides, so that the stator teeth have 4 n phase units.

The armature windings are wound on the two armature teeth of each phase unit.

The rotor includes 2i groups of rotors coaxially arranged along the axial direction, and the axial lengths of each group of rotors are equal; wherein, i≥1.

Let the number of rotor pole pairs be p, each rotor pole pair includes A magnetic pole and B magnetic pole, and at least one of the A magnetic pole and B magnetic pole is a permanent magnet pole; then the centerline of the A magnetic pole of the i group of rotors and the B of the remaining i group of rotors The centerlines of the magnetic poles are in the same circumferential position; at least one of the A magnetic pole and the B magnetic pole is a permanent magnet pole; when the A magnetic pole or the B magnetic pole is a permanent magnetic pole, the magnetization direction of the A magnetic pole or the B magnetic pole of the i group of rotors is the same as the remaining i group. The magnetization direction of the A pole or B pole is opposite.

The rotor is an alternating-pole rotor, the A magnetic pole is a permanent magnet pole, and the B magnetic pole is an iron core pole. The magnetizing direction of the A magnetic poles of the i group rotors is opposite to the magnetizing direction of the A magnetic poles of the remaining i groups.

The rotor is a permanent magnet rotor, the A magnetic pole is the first permanent magnet pole, and the B magnetic pole is the second permanent magnet pole; the magnetizing direction of the A magnetic pole of the i group rotor is opposite to the magnetizing direction of the A magnetic pole of the remaining i group, and the B magnetic pole of the i group rotor The magnetization direction is opposite to the magnetization direction of the B poles of the remaining i groups.

The rotor is a segmented oblique-pole rotor, and each set of rotors includes four rotor segments that are coaxially arranged in sequence along the axial direction. The axial length of each rotor segment is equal, and two adjacent rotor segments are circumferentially offset. The mechanical angle is set as θ, then the calculation formula of θ is: θ=360/(32×p).

Permanent magnet poles are surface-mounted permanent magnet poles or built-in permanent magnet poles.

The area of the large groove is twice the area of the small groove.

The number of phases of the armature winding is a multiple of 4.

The fundamental current and harmonic current are passed into the armature winding; among them, the fundamental current is used to do work and generate torque; the phase of the harmonic current is opposite to that of the fundamental current, and the harmonic current and the fundamental back EMF are mutually exclusive. effect, thereby generating a 4th torque pulsation, the 4th torque pulsation is opposite to the phase of the 4th torque pulsation inherent in the multi-phase permanent magnet motor, so that the 4th torque inherent in the multiphase permanent magnet motor can be suppressed or eliminated pulsation.

The harmonic current is the third harmonic current or the fifth harmonic current.

The present invention has the following beneficial effects:

1. The stator adopts the modular design of the separation of the stator teeth and the yoke, which simplifies the winding process and improves the full rate of the stator slots, thereby improving the power density. The closed slot design is not only conducive to the suppression of cogging torque (cogging torque is a part of torque ripple), but also increases the phase self-inductance by increasing the leakage inductance (which is conducive to suppressing short-circuit current).

2. The stator teeth adopt the phase-to-phase isolation design with unequal stator tooth pitch, and the mutual inductance between phases is close to 0 (low mutual inductance indicates that the failure of one phase has little impact on other phases). Combined with multi-phase windings, the reliability and fault tolerance of the motor are improved. .

3. The rotor adopts an alternate pole structure, and the reluctance of the armature magnetic circuit is reduced, which can effectively increase the phase self-inductance, thereby effectively suppressing the short-circuit current. At the same time, using the alternating pole rotor with complementary axial magnetic circuit, there are no odd harmonics of cogging torque, even harmonics of back electromotive force and unbalanced magnetic pulling force.

4. Combined with segmented sloping pole design and harmonic current injection, torque ripple is effectively suppressed.

5. The present invention is suitable for high-end equipment such as CNC machine tools, robots, and aerospace actuators, which have higher requirements on power density, fault tolerance, reliability and rotational pulsation.

Description of drawings

FIG. 1 shows a schematic structural diagram of a multi-phase permanent magnet motor with low pulsation, strong fault tolerance and high power density in Embodiment 1 of the present invention.

FIG. 2 shows a schematic diagram of the structure of the stator teeth in Embodiment 1 of the present invention.

FIG. 3 shows a schematic view of the structure of the stator yoke in Embodiment 1 of the present invention.

Figure 4-1 shows a comparative analysis diagram of rotor position mutual inductance between Embodiment 1 of the present invention and a traditional three-phase motor.

Figure 4-2 shows a comparative analysis diagram of the rotor position self-inductance of the first embodiment of the present invention and a traditional three-phase motor.

Figure 5-1 shows a schematic diagram of the magnetization directions and the magnetic pole centerlines of the first and second sets of rotors in Embodiment 1 of the present invention.

FIG. 5-2 shows a schematic diagram of the position of the center lines of the magnetic poles of the first and second groups of rotors in Embodiment 1 of the present invention.

5-3 shows a three-dimensional view of the first and second sets of rotors in Embodiment 1 of the present invention.

Figure 6-1 shows a comparison diagram between the rotor in Embodiment 1 of the present invention and the conventional rotor after only the fundamental wave current is supplied to the winding.

Figure 6-2 shows the analysis plot of a conventional rotor after injecting third and fifth harmonic currents.

FIG. 6-3 shows the analysis diagram of the segmented skew-pole rotor after injecting the third and fifth harmonic currents in Embodiment 1 of the present invention.

FIG. 7-1 shows a schematic diagram of the layout and magnetization direction of the permanent magnet pole rotor in Embodiment 2 of the present invention.

FIG. 7-2 is a schematic diagram showing the circumferential offset of two adjacent rotor segments in the permanent magnet pole rotor in Embodiment 2 of the present invention.

7-3 shows a three-dimensional view of the permanent magnet pole rotor in Embodiment 2 of the present invention.

FIG. 8 shows a schematic diagram of the magnetic field lines generated by the A-phase winding in Embodiment 1 of the present invention.

Including:

100. Modular stator;

110. stator teeth;

111. Armature tooth; 112. Fault-tolerant tooth; 113. Large slot; 114. Small slot; 115. Closed slot; 116. Plug-in protrusion;

120. stator yoke;

200. Armature winding;

300. rotor;

310. Permanent magnet pole; 311. Permanent magnet pole center line;

320. Iron core pole; 321. Iron core pole center line;

330.N permanent magnet pole; 340.S permanent magnet pole; 351. Coincidence center line 1; 352. Coincidence center line 2;

400. Phase unit.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and specific preferred embodiments.

In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "left side", "right side", "upper", "lower part", etc. are based on the orientation or positional relationship shown in the drawings, only For the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a particular orientation, be constructed and operate in a particular orientation, "first", "second", etc. importance, and therefore should not be construed as a limitation to the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution, and do not limit the protection scope of the present invention.

Example 1 Take the four-phase armature winding m=4, the number of stator slots Ns=12, the inner rotor, and the number of rotor pole pairs p =5 as an example

As shown in FIG. 1 , a multi-phase permanent magnet motor with low pulsation, strong fault tolerance and high power density includes a modular stator 100 , an armature winding 200 and a rotor 300 .

The modular stator and the rotor are coaxially sleeved from outside to inside, and there is an air gap between them. Both the modular stator core and the rotor core are preferably made of magnetically conductive material.

The modular stator includes stator teeth 110 and a stator yoke 120 .

As shown in FIG. 2 , the stator tooth portion includes 4 n armature tooth pairs, 4 n fault-tolerant teeth 112 and closed slots 115 ; wherein, n ≥1. In this embodiment, n =4 is preferred, that is, there are 4 pairs of armature teeth and 4 fault-tolerant teeth.

4 n armature tooth pairs are evenly distributed along the circumference of the stator yoke, each armature tooth pair includes two armature teeth 111, and then there are 8 armature teeth in Fig. 2; Large slot 113.

A fault-tolerant tooth is arranged between two adjacent pairs of armature teeth; a small slot 114 is formed between each fault-tolerant tooth and the adjacent armature teeth; the central angle of the small slot is smaller than the central angle of the large slot, so that the stator teeth are With unequal stator pitch.

Further, the area of the large groove is preferably twice the area of the small groove.

The side of each armature tooth and each fault-tolerant tooth facing away from the air gap is detachably connected to the annular stator yoke, and the preferred setting method is as follows: the side of each armature tooth and each fault-tolerant tooth facing away from the air gap is preferably Plugging protrusions 116 are provided, and the side of the stator yoke facing the air gap (preferably the inner ring side wall) is provided with mounting grooves 121 that are matched with all the plugging protrusions, as shown in FIG. 3 .

The side of each armature tooth and each fault-tolerant tooth facing the air gap is connected by a closed slot 115 .

Each armature tooth pair and the adjacent half fault-tolerant teeth on both sides form a phase unit 400, so that the stator tooth portion has 4 n phase units, preferably 4 phase units in this embodiment. Further, the 4n phase units of the stator teeth can be integrally manufactured or molded (that is, each unit is formed separately, and then the 4n phase units are assembled and integrated. The specific assembly process is not limited).

The armature winding is wound on the two armature teeth of each phase unit, and the number of phases is a multiple of 4. It can be 4 phases, or it can be directly changed to 8 phases or other multiples of 4 phases. The armature windings of the kth phase unit and the k+4th phase unit form the same-phase armature winding. Among them, k≥1.

The two armature windings (also called armature coils) in a phase unit constitute the same-phase armature winding, so the phase-to-phase isolation (physical isolation, electromagnetic isolation, thermal isolation) is achieved between the different phase windings through fault-tolerant teeth, and the phase-to-phase mutual inductance is almost 0 (low mutual inductance indicates that the failure of one phase has little impact on other phases), as shown in Figure 4-1, which improves the reliability and fault tolerance of the motor.

Since each phase unit has two armature coils, and there are two coil sides in the large slot between two adjacent armature teeth, there is only one coil side in the small slot between the armature tooth and the fault-tolerant tooth. Therefore, the area of the large slot is designed to be twice the area of the small slot (which can be slightly adjusted according to the specific situation), so that the winding coefficient and the slot utilization rate can be improved.

Further, the arrangement of the above-mentioned closed slot is not only beneficial to suppress the cogging torque, but also increases the phase self-inductance by increasing the leakage inductance (large self-inductance is beneficial to suppress short-circuit current). Due to the separate design of the stator teeth/stator yoke, the winding can be wound through the large slot at the separation of the stator teeth, which greatly simplifies the winding process, and is beneficial to improve the slot full rate, thereby improving the power density.

The rotor includes 2i groups of rotors arranged coaxially along the axial direction, and the axial lengths of each group of rotors are equal; wherein, i≥1, in this embodiment, preferably i=1. That is, as shown in FIGS. 5-1 , 5-2 and 5-3, the rotor includes a first set of rotors and a second set of rotors.

Each rotor pole pair includes an A magnetic pole and a B magnetic pole, and at least one of the A magnetic pole and the B magnetic pole is a permanent magnet pole. When the A magnetic pole or the B magnetic pole is a permanent magnet pole, the magnetizing direction of the A magnetic pole or the B magnetic pole of the i group rotor is opposite to the magnetizing direction of the A magnetic pole or the B magnetic pole of the remaining i group.

In this embodiment 1, the rotor is an alternating pole rotor, the A magnetic pole is a permanent magnet pole, and the B magnetic pole is an iron core pole, wherein the magnetizing direction of the A magnetic poles of the i group rotors is opposite to the magnetizing direction of the A magnetic poles of the remaining i groups. At the same time, the center line of the A magnetic pole of the rotors in the i group is in the same circumferential position as the center line of the B magnetic poles of the remaining i group of rotors, that is, the axial complementarity, which satisfies the "magnetic circuit complementary condition".

Further, the rotor is preferably a segmented slanted-pole rotor, and each set of rotors includes four rotor segments that are coaxially arranged in sequence along the axial direction. The axial length of each rotor segment is equal, and the circumferential length of two adjacent rotor segments is The offset mechanical angle is set to θ, then the calculation formula of θ is: θ=360/(32×p)=360/(32×5)=2.25°.

In Fig. 5-2, since i=1, the four rotor segments of the first rotor group and the second rotor group are respectively the first rotor segment, the second rotor segment, the third rotor segment, The fourth rotor segment, the fifth rotor segment, the sixth rotor segment, the seventh rotor segment, and the eighth rotor segment; then the centerline of the permanent magnet poles of the third rotor segment in the first group of rotors is the same as that of the second group of rotors. The centerline of the iron core pole of the sixth rotor segment in the rotor is at the same circumferential position, that is, the position of the coincident centerline 351; the centerline of the permanent magnet pole of the fourth rotor segment in the first group of rotors is the same as The centerlines of the core poles of the five rotor segments are at the same circumferential position, that is, the position where the second 352 coincident centerlines are located.

In this embodiment, the axial magnetic circuits are complementary, and since each pair of magnetic poles has only one permanent magnet pole, the magnetic resistance of the armature magnetic circuit is reduced, which can effectively increase the phase self-inductance, as shown in Figure 4-2, thereby suppressing short-circuit current.

Further, since the present invention satisfies the "complementary magnetic circuit condition": therefore, the odd harmonics of cogging torque, even harmonics of back EMF, and unbalanced magnetic pulling force generated by the i group of rotors can cancel each other out with the other i groups of rotors, and also That is, the motor using the alternating pole rotor of the present invention has no odd harmonics of cogging torque, even harmonics of back electromotive force and unbalanced magnetic pulling force.

Due to the interaction of the odd harmonics in the back EMF of the four-phase motor with the fundamental current, the 4th, 8th, 12th and 16th torque ripples will be generated. The rotor of the present invention adopts a segmented inclined-pole rotor, each group of rotors is divided into 4 segments, and the two adjacent rotor segments are circumferentially offset by 360/(32×p) mechanical angle, thereby effectively suppressing 12 and 16 torque pulsations, such as As shown in Figure 6-1.

In addition, the 4th order torque pulsation is the main pulsation component of the four-phase motor, and the present invention proposes a harmonic current injection technique to eliminate the 4th order pulsation. Specifically, in addition to the fundamental current used to perform work (torque generation), the armature winding also injects the third harmonic current or the fifth harmonic current to eliminate the fourth torque ripple. The phase of the injected third harmonic current or fifth harmonic current is opposite to that of the fundamental current, and they interact with the fundamental back EMF (that is, the back EMF generated by the rotor fundamental magnetic field in the armature winding) to produce a 4th turn. The 4th torque pulsation is opposite to the phase of the 4th torque pulsation inherent in the four-phase motor, so that the 4th torque pulsation can be suppressed or even eliminated, as shown in Figure 6-2.

Through the segmented oblique pole and harmonic current injection of the present invention, the torque ripple can be controlled to an extremely small level, as shown in Figure 6-3, which can well meet the torque stability requirements of high-end equipment and servo systems .

Further, the permanent magnet poles are surface-mounted permanent magnet poles or built-in permanent magnet poles, etc. In the present embodiment 1, they are preferably surface-mounted permanent magnet poles.

Further, the present invention can also be applied to the outer rotor. In this case, the modular stator and the rotor are coaxially sleeved from the inside to the outside, and there is an air gap between them. The rest of the arrangement is the same as that of the inner rotor.

Example 2

As shown in Figures 7-1, 7-2 and 7-3, the rotor is a conventional permanent magnet pole rotor, the A magnetic pole is a permanent magnet pole one, preferably an N permanent magnetic pole; the B magnetic pole is a permanent magnet pole two, preferably an S permanent magnetic pole; The magnetization direction of the A poles of the rotors in group i is opposite to the magnetization direction of the A poles of the remaining i groups, and the magnetization direction of the B magnetic poles of the i group rotors is opposite to the magnetization direction of the B magnetic poles of the remaining i groups; the rest of the structure is the same as the embodiment. 1.

After using the motor of Example 2, the magnetic line of force generated by the A-phase winding is shown in Figure 8, and it can be seen that it is closed through the adjacent fault-tolerant teeth, and does not pass through the teeth around which other phase windings are wound. Therefore, the present invention effectively realizes the electromagnetic isolation between phases.

The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above-mentioned embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention. These equivalent transformations All belong to the protection scope of the present invention.

Claims (10)

1. The utility model provides a multiphase permanent magnet motor of fault-tolerant high power density is strong in low pulsation which characterized in that: the modularized stator comprises a modularized stator, an armature winding and a rotor;

the modularized stator and the rotor are coaxially sleeved from outside to inside or from inside to outside, and an air gap is formed between the modularized stator and the rotor;

the modular stator includes a stator tooth and a stator yoke;

the stator teeth comprise 4nA pair of armature teeth 4nA plurality of fault-tolerant teeth and closed slots; wherein,n≥1；

4nthe armature tooth pairs are uniformly distributed along the circumferential direction of the stator yoke part, and each armature tooth pair comprises two armature teeth; a large groove is formed between the two armature teeth;

arranging an error-tolerant tooth between two adjacent armature tooth pairs; a small groove is formed between each fault-tolerant tooth and the adjacent armature tooth; the central angle of the small slot is smaller than that of the large slot, so that the stator tooth part has unequal stator tooth pitches;

one side of each armature tooth and one side of each fault-tolerant tooth, which is away from the air gap, are detachably connected with the annular stator yoke part;

one side of each armature tooth and one side of each fault-tolerant tooth, which face the air gap, are connected through the closed slot;

each armature tooth pair forms a phase unit with the adjacent half teeth on both sides, so that the stator tooth portion has 4nA phase unit;

armature windings are wound around the two armature teeth of each phase unit.

2. The low-ripple strong fault-tolerant high-power-density multiphase permanent magnet motor according to claim 1, wherein: the rotors comprise 2i groups of rotors which are coaxially arranged along the axial direction, and the axial length of each group of rotors is equal; wherein i is more than or equal to 1;

setting the number of rotor pole pairs as p, wherein each rotor pole pair comprises a magnetic pole A and a magnetic pole B, and at least one of the magnetic pole A and the magnetic pole B is a permanent magnetic pole; the central line of the magnetic pole A of the rotor in the i groups and the central line of the magnetic pole B of the rotor in the remaining i groups are at the same circumferential position; at least one of the A magnetic pole and the B magnetic pole is a permanent magnetic pole; when the A magnetic poles or the B magnetic poles are permanent magnetic poles, the magnetizing direction of the A magnetic poles or the B magnetic poles of the i groups of rotors is opposite to that of the A magnetic poles or the B magnetic poles of the remaining i groups.

3. The low-ripple strong fault-tolerant high-power-density multiphase permanent magnet motor according to claim 2, wherein: the rotor is an alternating-pole rotor, the A magnetic pole is a permanent magnetic pole, the B magnetic pole is an iron core pole, and the magnetizing direction of the A magnetic pole of the i groups of rotors is opposite to that of the A magnetic poles of the remaining i groups of rotors.

4. The low-ripple strong fault-tolerant high-power-density multiphase permanent magnet motor according to claim 2, wherein: the rotor is a permanent magnet pole rotor, the A magnetic pole is a permanent magnet pole I, and the B magnetic pole is a permanent magnet pole II; the magnetizing direction of the magnetic poles A of the i groups of rotors is opposite to that of the magnetic poles A of the remaining i groups, and the magnetizing direction of the magnetic poles B of the i groups of rotors is opposite to that of the magnetic poles B of the remaining i groups.

5. The low-ripple strong fault-tolerant high-power-density multiphase permanent magnet motor according to claim 3 or 4, wherein: the rotor is a segmented skewed-pole rotor, each group of rotors comprises 4 rotor segments which are coaxially arranged in sequence along the axial direction, the axial length of each rotor segment is equal, the circumferential offset mechanical angle of two adjacent rotor segments is set as theta, and the calculation formula of the theta is as follows: θ =360/(32 × p).

6. The low-ripple strong fault-tolerant high-power-density multiphase permanent magnet motor according to claim 3 or 4, wherein: the permanent magnet pole is a surface-mounted permanent magnet pole or a built-in permanent magnet pole.

7. The low-ripple strong fault-tolerant high-power-density multiphase permanent magnet motor according to claim 1, wherein: the area of the large grooves is twice the area of the small grooves.

8. The low-ripple strong fault-tolerant high-power-density multiphase permanent magnet motor according to claim 1, wherein: the number of phases of the armature winding is a multiple of 4.

9. The low ripple strong fault tolerant high power density multiphase permanent magnet motor of claim 8, wherein: fundamental current and harmonic current are introduced into the armature winding; the fundamental current is used for doing work and generating torque; the harmonic current has a phase opposite to that of the fundamental current, and the harmonic current interacts with the fundamental back electromotive force to generate a 4-order torque ripple, which is opposite in phase to the quartic torque ripple inherent to the multiphase permanent magnet motor, thereby suppressing or eliminating the quartic torque ripple inherent to the multiphase permanent magnet motor.

10. The low ripple strong fault tolerant high power density multiphase permanent magnet motor of claim 9, wherein: the harmonic current is a third harmonic current or a fifth harmonic current.

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