A design method of phase group modular structure for improving fault-tolerant capability of permanent magnet motor and considering low torque ripple

Abstract

The application discloses a design method of a phase group modular structure for improving fault tolerance of a permanent magnet motor and considering low torque ripple, and solves the problem that fault tolerance performance and low torque ripple are difficult to be considered simultaneously. The method comprises a design principle of phase group modularization, and the teeth and the shoe of module I, module III and module V in the phase group modularization are offset clockwise, and the teeth and the shoe of module II, module IV and module VI are offset counterclockwise. The application combines the phase group modular structure and the tooth and shoe offset, and the method is used for an 18-slot / 16-pole permanent magnet motor. Since there are fault tolerance teeth between each module, the method can effectively reduce inter-phase coupling; the winding configuration is changed, the self-induction amplitude is improved, and short-circuit current is effectively inhibited; and the teeth and the shoe of each module are offset, so that the tooth slot torque amplitude is inhibited, and torque ripple is reduced. The method realizes the improvement of fault tolerance while considering low torque ripple.

Description

Technical Field

[0001] The present invention relates to a design method for a phase group modular structure that improves the fault tolerance of a permanent magnet motor and takes low torque pulsation into consideration, and belongs to high-reliability application fields such as aerospace and electric vehicles. Background Art

[0002] Permanent magnet motors (PMMs), with their high efficiency and high power density, are widely used in defense, aerospace, and electric vehicles. However, conventional PMMs suffer from poor fault tolerance, making them unsuitable for high-reliability applications. Consequently, improving the fault tolerance of PMMs is gaining increasing attention. Fault-tolerant PMMs should possess characteristics such as good phase-to-phase isolation and low short-circuit current. Currently, improving the fault tolerance of PMMs is primarily achieved through increasing winding redundancy and designing novel stator structures. However, increasing winding redundancy increases the size of the drive, while the increased number of switching devices increases switching losses. While designing novel stator structures can effectively improve motor fault tolerance, this is often accompanied by increased cogging torque and torque ripple.

[0003] As described in the 2017 IEEE Transactions on Industrial Electronics paper "Comparative Study of Fault-tolerant Switched-Flux Permanent-Magnet Machines," C-type, E-type, and modular stator structures, compared to traditional stator structures, increase self-inductance, thereby suppressing short-circuit currents, and reduce mutual inductance, thereby improving phase isolation. However, compared to traditional structures, these structures also reduce average torque and significantly increase torque ripple.

[0004] Chinese invention patent application No. 201811432244.1 discloses a permanent magnet fault-tolerant motor based on spaced-tooth windings and unequal stator tooth pitch. Each phase of the motor's winding is separated by isolating teeth, and combined with unequal stator tooth pitch, this design enhances phase-to-phase isolation and self-inductance amplitude, effectively improving the motor's fault tolerance and short-circuit current suppression capabilities. However, this approach can increase torque ripple, impacting torque performance.

[0005] As described in the paper "Multiphase modular fault-tolerant permanent-magnet machine with hybrid single / double-layer fractional-slot concentrated winding" published in IEEE Transactions on Magnetics in 2019, a new stator structure is designed, in which the winding is in a single / double-layer hybrid configuration, the mutual inductance between phases is almost zero, effectively reducing the inter-phase coupling and improving the fault tolerance performance. However, this structure reduces the least common multiple of the slot number and the pole number, resulting in a significant increase in the amplitude of the cogging torque. SUMMARY

[0006] The purpose of the present application is to solve the defects of the above-mentioned existing technology, and to propose a design method of a phase group modular structure that improves the fault tolerance of permanent magnet motors and considers low torque ripple. This structure can effectively improve the fault tolerance performance of permanent magnet motors, and combines tooth shoe offset, while achieving improved fault tolerance and low torque ripple.

[0007] In order to achieve the above-mentioned purpose, the present application is implemented by using the following technical solution: a design method of a phase group modular structure that improves the fault tolerance of permanent magnet motors and considers low torque ripple, the specific steps are as follows:

[0008] Step 1, determine the size parameters of the traditional permanent magnet motor, including the slot-pole combination of the permanent magnet motor, the size of the stator inner and outer diameter, the pole arc coefficient of the permanent magnet, the air gap length between the stator and the rotor, and the rotor sheath thickness;

[0009] Step 2, based on the size of the traditional permanent magnet motor, design a phase group modular structure, in which each phase winding exists in an independent module and is isolated by fault-tolerant teeth; the traditional permanent magnet motor has 18 coils, each coil has 40 turns, and the total number of turns is 720. The number of coils in this structure becomes 12, and the total number of turns remains the same as the traditional motor, so the number of turns of each coil in this structure becomes 60. In order to ensure the slot area utilization rate, the slot fill rate of this structure remains the same as the traditional structure. In addition, this structure includes 6 modules: Module I-Module VI, and the mechanical angle corresponding to each module also remains the same as the traditional motor, i.e. 60°;

[0010] Step 3, on the designed phase group modular structure, the tooth shoes of modules I, III, and V are offset in the counterclockwise direction, and the tooth shoes of modules II, IV, and VI are offset in the clockwise direction by the same angle, and the tooth slot torque expression after the tooth shoe offset is derived;

[0011] Step 4, the stator tooth distribution of the phase group modular structure combined with the tooth-shoe offset and the mechanical angle spanned by the tooth tip are changed, the pitch coefficient and the distribution coefficient are changed, and the winding factor is different;

[0012] Step 5, according to the equivalent circuit diagram of the A-phase short circuit, a short-circuit current expression is derived.

[0013] Step 6, the winding number and arrangement of the phase group modular structure combined with the tooth-shoe offset are changed, a winding function is derived, and a magnetic motive force harmonic analysis and a self-inductance expression derivation are performed according to the winding function;

[0014] Step 7, by using a finite element software, performance indexes such as a magnetic motive force harmonic, a self-inductance, a mutual inductance, a short-circuit current, an average torque and a torque ripple are obtained by comparing a traditional stator structure, and the effectiveness of the application is verified.

[0015] Further, in the step 1, the motor is an 18-slot / 16-pole permanent magnet synchronous motor, which includes a stator core, an armature winding, an air gap, a rotor sheath, a rotor core and a rotor permanent magnet; the stator core contains 18 stator teeth; the armature winding adopts a double-layer fractional-slot concentrated winding; the air gap and the rotor sheath are located between the stator and the rotor, wherein the air gap length is 0.7 mm and the sheath thickness is 0.3 mm; the rotor core contains 16 grooves; 16 rotor permanent magnets are respectively embedded in the 16 grooves of the rotor core; the stator core material is B35-AH230, the rotor core material is DT4C, and the permanent magnet material is N42UH.

[0016] Further, in the step 2, in order to ensure the slot area utilization rate, the slot fill rate should be kept consistent with the traditional structure when designing the phase group modularization, and the expression of the slot fill rate K is:

[0017]

[0018] wherein n represents the parallel number of turns of the wire, S m represents the number of turns of each coil, S represents the cross-sectional area of the wire, A m represents the stator slot area.

[0019] Further, in the step 3, the expression of the cogging torque T cog (β) is:

[0020]

[0021] wherein v represents the harmonic order, T cν represents the amplitude of the cogging torque generated by the v-th harmonic, N 2pz represents the least common multiple of the slot number and the pole number, and β represents the relative position angle of the stator and the rotor.

[0022] Further, in step 3, according to the expression of cogging torque, the toothed shoes of modules I, III, V are offset counterclockwise, and the toothed shoes of modules II, IV, VI are offset clockwise. The cogging torque of the toothed shoes offset counterclockwise and clockwise can be expressed as:

[0023]

[0024]

[0025] where T cog_L (β) and T cog_R (β) represent the cogging torque of the toothed shoes offset counterclockwise and clockwise, respectively, β x represents the mechanical angle of the offset toothed shoes. Through the simultaneous equations (3) and (4), the final expression of the cogging torque is:

[0026]

[0027] Further, in step 4, the winding factor is obtained by multiplying the pitch factor and the distribution factor. The stator tooth distribution of the phase group modular structure with offset toothed shoes and the mechanical angle spanned by the tooth tips change, resulting in a change in the winding factor.

[0028] Further, in step 5, according to the equivalent circuit diagram when the A-phase is short-circuited, the following expression can be obtained:

[0029]

[0030] where ψ A represents the A-phase flux linkage, L AA represents the A-phase self-inductance, i s represents the short-circuit current, N represents the winding function amplitude, ψ m represents the flux linkage amplitude, δ represents the included angle between the short-circuit phase and the d-axis, U Δ represents the A-phase terminal voltage, R A represents the A-phase phase resistance, and t represents time.

[0031] Further, in step 6, the winding number and arrangement of the phase group modular structure with offset toothed shoes change. The winding function expression of the A-phase of this structure is:

[0032] N A (θ)=n(θ)-avg[n(θ)] (7)

[0033] where N A (θ) represents the winding function of the A-phase, n(θ) represents the number of turns function of the A-phase, avg[n(θ)] represents the average value of the number of turns function of the A-phase, and θ represents the angular position of the stator reference system relative to the A-phase axis.A The Fourier expansion expression of (θ) is:

[0034]

[0035] where a0, a ν and b ν represents the Fourier expansion coefficient, and ν represents the harmonic order.

[0036] Furthermore, in step 6, for the three-phase symmetrical winding, the synthetic magnetomotive force F s The expression is:

[0037] F s =∑(N A I A +N B I B +N C I C ) (9)

[0038] where N A 、N B and N C Represent the Fourier expansion expressions of the winding functions of phase A, phase B and phase C respectively, I A , I B and I C Represents the phase currents of phase A, phase B, and phase C respectively.

[0039] Furthermore, in step 6, the self-inductance expression is derived according to the winding function theory as follows:

[0040]

[0041] Among them L AA represents the self-inductance of phase A, μ0 represents the vacuum permeability, r represents the outer diameter of the motor stator, l represents the axial length of the stator lamination, and g represents the air gap length.

[0042] Furthermore, a phase group modular structure was designed for the target motor. In this structure, each phase winding exists in an independent module and is isolated by fault-tolerant teeth. The number of coils is reduced to 2 / 3 of that of a traditional permanent magnet motor, while the total number of turns remains unchanged. To ensure slot area utilization, the slot fill factor of this structure is consistent with that of a traditional structure. In addition, this structure contains six modules (modules I to VI), and the mechanical angle corresponding to each module is also consistent with that of a traditional motor, that is, 60 degrees.

[0043] Furthermore, the tooth boots of each module in the phase group modular structure are offset, wherein the tooth boots of module I, module III and module V are offset counterclockwise, and the tooth boots of module II, module IV and module VI are offset clockwise.

[0044] Furthermore, according to the expression of the cogging torque, the expressions of the cogging torque after the tooth shoe is offset counterclockwise and clockwise are obtained respectively, and finally the synthetic cogging torque expression is obtained.

[0045] Furthermore, according to the modular structure of the phase group, the stator tooth distribution after the tooth shoe offset and the mechanical angle spanned by the tooth top are combined to obtain the slot potential star diagram and calculate the winding factor.

[0046] Furthermore, based on the equivalent circuit diagram of phase A short circuit, the short-circuit current expression is derived.

[0047] Furthermore, in the phase group modular structure combined with tooth shoe offset, the number of turns and arrangement of the armature winding are changed, and the winding function of the structure is derived based on this.

[0048] Furthermore, the magnetomotive force harmonic analysis is performed through the winding function, and the self-inductance expression is derived based on the winding function.

[0049] Furthermore, the effectiveness of the present invention was verified by comparing the magnetomotive force, inductance, short-circuit current, cogging torque and torque of the conventional structure and the structure of the present invention through finite element simulation.

[0050] The present invention has the following benefits:

[0051] 1. The present invention designs a phase group modular structure, which can effectively suppress short-circuit current, reduce the degree of inter-phase coupling, and thus improve the fault tolerance of the motor.

[0052] 2. The present invention combines tooth shoe offset with the modular structure of the phase group to improve the fault tolerance of the motor while ensuring low torque pulsation.

[0053] 3. The present invention improves the fundamental wave winding factor, thereby improving the average torque.

[0054] In summary, the design method of the phase group modular structure of the present invention, which improves the fault tolerance capability of the permanent magnet motor and takes into account low torque ripple, overcomes the limitation of the original technology that it is difficult to take into account both improved fault tolerance performance and low torque ripple. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a schematic diagram of the traditional motor structure;

[0056] Figure 2 Schematic diagram of the motor structure of the present invention; (a) is a schematic diagram of the modular structure of the phase group; (b) is a schematic diagram of an embodiment of the present invention;

[0057] Figure 3 Schematic diagrams of the present invention; (a) is a schematic diagram of a modular phase group; (b) is a schematic diagram of an embodiment of the present invention;

[0058] Figure 4 : The slot potential star diagram; (a) is the slot potential star diagram of the traditional structure; (b) is the slot potential star diagram of the embodiment of the present invention;

[0059] Figure 5 This is the equivalent circuit diagram when phase A is short-circuited;

[0060] Figure 6 A comparison diagram of winding functions between a conventional motor structure and an embodiment of the present invention;

[0061] Figure 7 A comparison diagram of magnetomotive force harmonics between a conventional motor structure and an embodiment of the present invention;

[0062] Figure 8 The inductance comparison diagrams of the conventional motor structure and the embodiment of the present invention are shown in Figure 2. (a) is the self-inductance comparison diagram; (b) is the mutual inductance comparison diagram.

[0063] Figure 9 Comparison diagram of magnetic lines of force between a conventional motor structure and an embodiment of the present invention; (a) is a magnetic line distribution diagram of a conventional motor structure; (b) is a magnetic line distribution diagram of an embodiment of the present invention;

[0064] Figure 10 A comparison diagram of the short-circuit current of a conventional motor structure and a motor according to an embodiment of the present invention;

[0065] Figure 11 This is a schematic diagram of the cogging torque suppression principle of a motor according to an embodiment of the present invention;

[0066] Figure 12 A comparison diagram of the cogging torque between the phase group modular structure and the embodiment of the present invention;

[0067] Figure 13 This is a torque comparison diagram of the traditional structure, the phase group modular structure and the embodiment of the present invention; DETAILED DESCRIPTION

[0068] In order to illustrate the design principle, technical solution and benefit effect of the present invention in more detail, it will be described in conjunction with embodiments and related drawings.

[0069] Figure 1 This is a schematic diagram of the structure of a conventional permanent magnet motor incorporating the present invention. This motor has an 18-slot / 16-pole slot configuration. 1 represents the stator core, 2 represents the rotor core, 3 represents the armature teeth, 4 represents the armature winding, 5 represents the permanent magnets, and 6 represents the rotor sheath. The armature winding of this motor uses a double-layer fractional-slot concentrated winding, and the permanent magnets are surface-mounted. The stator core is made of B35-AH230, the rotor core is made of DT4C, and the permanent magnets are made of N42UH.

[0070] Figure 2(a) and (b) represent the modular structure of the phase group and the structural diagram of the embodiment of the present invention respectively, wherein 7 represents the auxiliary tooth, 8 represents the unshifted tooth shoe, and 9 represents the shifted tooth shoe. Figure 3 (a) and (b) in the figure represent the principles of designing phase group modularization and tooth shoe offset, respectively. When designing phase group modularization, the number of winding coils becomes 2 / 3 of the traditional structure, and the total number of coil turns remains unchanged. It can be concluded that the number of coil turns of the phase group modular structure becomes 3 / 2 of the traditional structure. In order to ensure the slot area utilization, the slot full rate should be kept consistent with the traditional structure. According to the slot full rate expression (1), it can be deduced that A2 = 1.5A1, A3 = 0.75A1. Among them, A1 represents the slot area of ​​the traditional structure, A2 represents the large slot area of ​​the phase group modular structure, and A3 represents the small slot area of ​​the phase group modular structure. Combined with the tooth slot torque expression (5) after tooth shoe offset, it can be deduced that when β x =1.875°, it has a good suppressing effect on the cogging torque.

[0071] Figure 4 The star diagram of the slot potential of the traditional structure and the embodiment of the present invention is shown in FIG. According to this diagram, the distribution coefficients of the two structures can be obtained respectively. According to the expression of the winding factor:

[0072] k ων =k pν ·k dν (10)

[0073] where k ων Indicates the winding factor, k pν represents the pitch coefficient, k dν After calculation, the fundamental wave winding factor of the conventional structure is 0.945, while the fundamental wave winding factor of the embodiment of the present invention is 0.966.

[0074] Figure 5 is the equivalent circuit diagram when phase A is short-circuited, and equation (6) can be further expressed as:

[0075]

[0076] where i s (t) represents the short-circuit current, I N Indicates rated current, ψ m(0) It can be seen from formula (11) that the short-circuit current is divided into two parts: steady-state and transient. s_steady (t) can be simplified to

[0077]

[0078] in When the phase reactance (ωL AA ) is much larger than the phase resistance (R A ), Equation (12) can be simplified to

[0079]

[0080] It can be seen from formula (13) that the amplitude of the short-circuit current is inversely proportional to the self-inductance, that is, increasing the self-inductance will be beneficial to suppressing the short-circuit current.

[0081] Figure 6 The figure is a comparison of the winding function of the traditional motor structure and the embodiment of the present invention. It can be seen from the figure that the function amplitude of the embodiment of the present invention is larger, and it can be seen that the traditional motor structure has a coupling area, while the embodiment of the present invention does not have a coupling area. Figure 6 The Fourier expansion expressions of the winding functions of the conventional structure and the embodiment of the present invention are derived from equation (8):

[0082]

[0083] where N Ac (θ) represents the winding function of the traditional structure, N c represents the amplitude of the winding function, which can be expressed as:

[0084]

[0085] where N coil Indicates the number of turns in each coil.

[0086]

[0087] where N AP represents the winding function of the embodiment of the present invention, N P1 and N P2 They represent the winding function amplitude when ν is an odd number and an even number, respectively, which can be expressed as:

[0088]

[0089] Figure 7 The figure shows the comparison of the harmonic spectrum of the magnetomotive force of the motor of the conventional structure and the embodiment of the present invention. For the three-phase symmetrical synthetic magnetomotive force, it can be derived based on the winding function obtained above and formula (9). The magnetomotive force expression of the conventional structure is:

[0090]

[0091] Where, f represents forward rotation, b represents reverse rotation, c represents the traditional structure, I represents the amplitude of the phase current, p represents the number of permanent magnet pole pairs, ω r represents the rotor angular velocity, γ drepresents the phase angle between the current vector and the rotor d-axis.

[0092] The magnetomotive force expression of the embodiment of the present invention is:

[0093]

[0094] Wherein, P represents the embodiment of the present invention, N P , N t1 and N t2 Respectively expressed as:

[0095]

[0096] According to the derivation results, it can be seen that the embodiment of the present invention has two parts due to the offset of the tooth shoe. When ν is an even number, the harmonic order of the magnetomotive force of the embodiment of the present invention and the traditional structure is the same; when ν is an odd number, the 1st, 5th, 7th, 11th, 13th, 17th and 19th order harmonics in the embodiment of the present invention do not exist in the traditional structure. As can be seen from the spectrum diagram, the harmonic content of the traditional structure and the embodiment of the present invention are consistent with the derivation results, verifying the accuracy of the theoretical derivation. In addition, the fundamental wave amplitude of the motor of the embodiment of the present invention is greater than the fundamental wave amplitude of the traditional structure, which is also consistent with the trend of the winding factor, verifying the correctness of the winding factor calculation. In addition, the increase of the fundamental wave winding factor is conducive to the improvement of torque.

[0097] Figure 8 The figure is a comparison of the inductance of the traditional structure and the embodiment of the present invention. The self-inductance can be derived by substituting the Fourier expansion of the winding function of the two structures into formula (10) to derive the self-inductance expressions of different structures. Among them, the self-inductance of phase A of the traditional structure L AAc The expression is:

[0098]

[0099] The self-inductance L of the A phase of the embodiment of the present invention AAP The expression is:

[0100]

[0101] By comparison, it can be seen that the self-inductance amplitude of the embodiment of the present invention is greater than that of the traditional structure. Furthermore, the results shown in Figure (a) are consistent with the derived results, verifying the accuracy of the theoretical derivation and demonstrating that the embodiment of the present invention has a better ability to suppress short-circuit current. As can be seen in Figure (b), the mutual inductance of the embodiment of the present invention is almost zero, indicating that the embodiment of the present invention has better fault tolerance.

[0102] Figure 9Figure 1 compares the magnetic field lines for phase A of a conventional structure and an embodiment of the present invention. Phase isolation can be demonstrated not only through mutual inductance but also through magnetic field lines. Figure (a) shows the distribution of magnetic field lines for phase A of the conventional structure. This shows that the magnetic field lines are distributed not only in phase A but also in other phases, leading to severe phase coupling. However, the magnetic field lines in Figure (b) are distributed only in phase A and not in other phases, demonstrating that the embodiment of the present invention has better phase isolation.

[0103] Figure 10 The short-circuit current comparison diagram of the conventional structure and the embodiment of the present invention shows that the amplitude of the short-circuit current is reduced from 18.4A to 12.8A, a reduction of 30.4%, indicating that the embodiment of the present invention has a better ability to suppress short-circuit current.

[0104] Figure 11 This diagram illustrates the principle behind cogging torque suppression in an embodiment of the present invention. As can be seen, as the toothed shoe shifts in different directions, the phase of the cogging torque waveform shifts accordingly. Based on the above derivation, when the shift angle is 1.875°, two cogging torque waveforms with opposite waveforms are obtained, achieving the best cogging torque suppression effect.

[0105] Figure 12 The following figure compares the cogging torque of the modular phase-group structure and an embodiment of the present invention. As can be seen, when the tooth shoe is offset by 1.875°, the amplitude of the cogging torque decreases from 290 m·Nm to 115 m·Nm, a reduction of over 60%. This demonstrates that using tooth shoe offset can effectively suppress cogging torque.

[0106] Figure 13 The following chart compares the torque of a conventional structure, a modular phase group structure, and an embodiment of the present invention. As can be seen from the chart, the modular phase group structure achieves the highest average torque, but its torque ripple reaches an unacceptable 9.02%. The embodiment of the present invention not only has greater torque than the conventional structure, but also exhibits lower torque ripple. All things considered, the embodiment of the present invention exhibits superior torque performance.

[0107] In conclusion, the application is a design method of phase group modular structure for improving fault-tolerant performance of permanent magnet motor and considering low torque ripple. Firstly, relevant parameters of the motor are determined; then, the design method of phase group modular structure and relevant features of the structure are pointed out, and the angle of tooth shoe offset is derived according to the expression of cogging torque; secondly, according to the winding distribution characteristics of the traditional structure and the embodiment of the application, the winding function expressions of the two are derived; then, the magnetic motive force harmonic analysis and inductance expression derivation are carried out according to the winding function; finally, the accuracy of the theoretical derivation is verified through finite element simulation, and it is shown that the embodiment of the application has better short-circuit current suppression ability and phase isolation ability, improves the fault-tolerant capability; and the embodiment of the application not only improves the average torque, but also has low torque ripple, realizes the combination of improving fault-tolerant capability and low torque ripple. The application can provide reference and theoretical guidance for improving motor fault-tolerant performance and suppressing torque ripple.

Claims

1. A design method for a phase group modular structure that improves the fault tolerance of a permanent magnet motor and takes into account low torque ripple, characterized in that: The specific steps are as follows: Step 1: Determine the dimensional parameters of the traditional permanent magnet motor, including the slot-pole matching of the permanent magnet motor, the inner and outer diameters of the stator, the permanent magnet pole arc coefficient, the air gap length between the stator and rotor, and the thickness of the rotor sheath; Step 2: Based on the dimensions of a conventional permanent magnet motor, a modular phase group structure was designed. Each phase winding in this structure is contained in an independent module, isolated by fault-tolerant teeth. This structure has a total of 720 turns, 12 coils, and 60 turns per coil. To ensure slot area utilization, the slot fill factor of this structure remains consistent with that of conventional structures. Furthermore, this structure contains six modules: Module I through Module VI. The mechanical angle corresponding to each module is also consistent with that of conventional motors, i.e., 60°. Step 3: On the designed phase group modular structure, the tooth shoes of modules I, III, and V and the tooth shoes of modules II, IV, and VI are offset counterclockwise and clockwise by the same angle respectively, and the cogging torque expression after the tooth shoes are offset is derived; Step 4: The stator tooth distribution and the mechanical angle spanned by the tooth top of the phase group modular structure combined with the tooth shoe offset are changed, and the pitch coefficient and distribution coefficient are changed, resulting in a different winding factor; Step 5: Derived the short-circuit current expression based on the equivalent circuit diagram of phase A short circuit; Step 6: The number of turns and arrangement of the phase group modular structure combined with the tooth shoe offset are changed. The winding function is derived, and the magnetomotive force harmonic analysis and self-inductance expression are derived based on the winding function. Step 7: Using finite element software, analyze the traditional stator structure to obtain the magnetomotive force harmonics, self-inductance, mutual inductance, short-circuit current, average torque, and torque ripple performance indicators to verify the effectiveness; In the step 1, the motor used is an 18-slot / 16-pole permanent magnet synchronous motor, which includes six parts: a stator core, an armature winding, an air gap, a rotor sleeve, a rotor core, and a rotor permanent magnet; the stator core includes 18 stator teeth; the armature winding adopts a double-layer fractional slot concentrated winding; the air gap and the rotor sleeve are located between the stator and the rotor, wherein the air gap length is 0.7 mm and the sleeve thickness is 0.3 mm; the rotor core includes 16 grooves; 16 rotor permanent magnets are respectively embedded in the 16 grooves of the rotor core; the stator core material is B35-AH230, the rotor core material is DT4C, and the permanent magnet material is N42UH.

2. A design method for a phase group modular structure that improves the fault tolerance of a permanent magnet motor and takes into account low torque ripple according to claim 1, characterized in that: In step 2, in order to ensure the utilization rate of the slot area, the slot fill rate should be kept consistent with the traditional structure when designing the phase group modularization. The expression of the slot fill rate K is: Where n represents the number of parallel turns of the wire, S m represents the number of turns of each coil, S represents the cross-sectional area of ​​the wire, A m Represents the stator slot area.

3. The design method of a phase group modular structure for improving the fault tolerance of a permanent magnet motor and considering low torque ripple according to claim 1, characterized in that: In step 3, the cogging torque T cog The expression of (β) is: Where ν represents the harmonic order, T cν Indicates the cogging torque amplitude generated by the νth harmonic, N 2pz It represents the least common multiple of the number of slots and the number of poles, and β represents the relative position angle between the stator and the rotor.

4. The design method of a phase group modular structure for improving the fault tolerance of a permanent magnet motor and considering low torque ripple according to claim 1, characterized in that: In step 3, according to the cogging torque expression, the tooth shoes of modules I, III, and V are offset counterclockwise, and the tooth shoes of modules II, IV, and VI are offset clockwise. The cogging torques after the tooth shoes are offset counterclockwise and clockwise are respectively expressed as: Where T cog_L (β) and T cog_R (β) represents the cogging torque after the tooth shoe is offset counterclockwise and clockwise, respectively, x The mechanical angle of the tooth shoe offset is represented by combining equations (3) and (4), and the final cogging torque is expressed as:

5. The design method of a phase group modular structure for improving the fault tolerance of a permanent magnet motor and considering low torque ripple according to claim 1, characterized in that: In step 4, the winding factor is obtained by multiplying the pitch coefficient and the distribution coefficient. The stator tooth distribution of the phase group modular structure combined with the tooth shoe offset and the mechanical angle spanned by the tooth top change, resulting in a change in the winding factor.

6. The design method of a phase group modular structure for improving the fault tolerance of a permanent magnet motor and considering low torque ripple according to claim 1, characterized in that: In step 5, according to the equivalent circuit diagram when phase A is short-circuited, the following expression is obtained: where ψ A Indicates the magnetic flux of phase A, L AA Indicates the self-inductance of phase A, i s represents the short-circuit current, N represents the winding function amplitude, ψ m represents the flux amplitude, δ represents the angle between the short-circuit phase and the d-axis, U Δ Indicates the terminal voltage of phase A, R A represents the phase resistance of phase A, and t represents time.

7. The design method of a phase group modular structure for improving the fault tolerance of a permanent magnet motor and considering low torque ripple according to claim 1, characterized in that: In step 6, the number of turns and arrangement of the phase group modular structure combined with the tooth shoe offset are changed. The winding function expression of phase A of this structure is: N A (θ)=n(θ)-avg[n(θ)] (7) where N A (θ) represents the winding function of phase A, n(θ) represents the number of turns function of phase A, avg[n(θ)] represents the average value of the number of turns function of phase A, θ represents the angular position relative to the phase A axis in the stator reference frame, N A The Fourier expansion expression of (θ) is: where a0, a ν and b ν represents the Fourier expansion coefficient, and ν represents the harmonic order.

8. The design method of a phase group modular structure for improving the fault tolerance of a permanent magnet motor and considering low torque ripple according to claim 1, characterized in that: In step 6, for the three-phase symmetrical winding, the synthetic magnetomotive force F s The expression is: F s =∑(N A I A +N B I B +N C I C ) (9) where N A 、N B and N C Represent the Fourier expansion expressions of the winding functions of phase A, phase B and phase C respectively, I A , I B and I C Represents the phase currents of phase A, phase B, and phase C respectively.

9. The design method of a phase group modular structure for improving the fault tolerance of a permanent magnet motor and considering low torque ripple according to claim 1, characterized in that: In step 6, the self-inductance expression is derived according to the winding function theory: Among them L AA represents the self-inductance of phase A, μ0 represents the vacuum permeability, r represents the outer diameter of the motor stator, l represents the axial length of the stator lamination, and g represents the air gap length.

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