Optimization design method of pole-changing motor based on consequent pole rotor structure

Abstract

The invention provides a pole-changing motor optimization design method based on a consequent-pole rotor structure, and the method comprises the following steps: enabling the sum of the electrical angles of windings of two pole numbers to be (2k-1) * 180 degrees, and enabling the sum of the two pole numbers to be the number of slots; comparing the two pole numbers, and carrying out armature winding phase splitting, wiring and connection according to a groove electromotive force star diagram with a large pole number; keeping the slot electromotive force star diagram with the large pole number unchanged, reversely arranging slot numbers in the slot electromotive force star diagram with the small pole number, keeping the phase belt position unchanged, and rotating the slot numbers by 180 degrees, so that the slot numbers of each phase under the two pole numbers are the same in distribution; based on winding arrangement of a slot electromotive force star diagram with a large pole number, according to whether the slot number directions of the windings in the slot electromotive force star diagram with the large pole number are the same as those in the slot electromotive force star diagram with the small pole number, the armature windings at each phase belt position are divided into two groups, namely one group with the same slot number direction and one group with the opposite slot number direction, and the current flowing direction of the group with the opposite slot number direction is changed; and any two phase sequences in the three-phase winding are exchanged to realize pole number change.

Description

Technical Field

[0001] The invention belongs to the field of motor design, and in particular relates to a pole-changing motor optimization design method based on an alternating-pole rotor structure. Background Art

[0002] With the development of rare earth materials, permanent magnet synchronous motors are widely used in high-end fields such as aerospace, new energy vehicles, and wind power generation. Compared with traditional electrically excited motors, permanent magnet synchronous motors have the advantages of high efficiency and high power density. However, because its rotor uses permanent magnets instead of adjustable excitation windings, it is difficult to adjust the air gap magnetic field of the permanent magnet motor and it cannot operate in a wide speed range. The introduction of the pole-changing permanent magnet motor (PCPM) has solved this problem well. The pole-changing motor changes the magnetization direction of the low coercive force permanent magnet by applying a reverse current pulse to achieve the purpose of changing the number of poles. By reasonably designing the stator winding and the rotor poles, the number of motor poles can be changed to achieve operation in a wide speed range, low-speed and high-torque operation can be achieved with a large number of poles, and high-speed and high-efficiency operation can be achieved with a small number of poles.

[0003] In order to solve the problem of complex pulse current application method and difficulty in accurately charging and demagnetizing permanent magnets during pole changing, a pole changing permanent magnet synchronous motor with constant winding alternating pole rotor structure is proposed. The rotor adopts an irregular alternating pole magnetic pole structure, and the pole changing process does not need to change the magnetization direction of the permanent magnet. The stator adopts a constant winding structure, and the pole changing process can be achieved by only changing the direction of part of the winding current and exchanging the phase sequence.

[0004] Harmonics in motors are the main cause of torque fluctuations. Conventional motors usually contain 6n-order torque fluctuations, while alternating-pole motors usually contain 3n-order torque fluctuations. In order to improve motor performance, the main harmonics contained in the torque of the proposed irregular alternating-pole motor with two pole numbers are analyzed, and the harmonic current injection method is used to reduce the amplitude of the main harmonics of the torque, so as to reduce the torque fluctuation of the motor and make the motor run smoothly under two pole numbers. Summary of the invention

[0005] The present invention discloses a design method of an irregular alternating pole rotor with an unchanged winding structure of a pole-changing permanent magnet synchronous motor, so as to reduce the torque fluctuation of the motor while ensuring a higher output torque. The essential feature of the present invention is that a stator unchanged winding structure is proposed, which only needs to exchange the phase sequence and change the direction of part of the winding current to realize the stator pole changing process, and an irregular alternating pole rotor is proposed, which does not need to change the magnetization direction of the permanent magnet to realize the rotor pole changing process. The harmonic current injection method is adopted, and the corresponding sub-current harmonics are injected to generate synchronous torque fluctuations opposite to the original torque fluctuations for the main sub-harmonics of the torque fluctuations, thereby reducing the amplitude of the main sub-harmonics of the torque, thereby reducing the torque fluctuations. The technical scheme of the present invention is as follows:

[0006] A pole-changing motor optimization design method based on an alternating-pole rotor structure, characterized in that:

[0007] 1) The sum of the electrical angles of the windings with two poles is (2k-1)×180°, k=1,2,3…, and the sum of the two poles is the number of slots;

[0008] 2) Compare the two pole numbers and phase, wire and connect the armature windings according to the slot EMF star diagram of the larger pole number;

[0009] 3) Keep the slot EMF star diagram of the large pole number unchanged, reverse the slot numbers in the slot EMF star diagram of the small pole number, and rotate the slot numbers 180° while keeping the phase belt position unchanged, so that the slot number distribution of each phase is the same under the two pole numbers;

[0010] 4) Based on the winding arrangement of the slot EMF star diagram with a large number of poles, the armature winding under each phase belt position is divided into two groups, namely, one group with the same slot number direction and one group with opposite slot number direction, according to whether the slot number direction is the same as that in the slot EMF star diagram with a small number of poles. The current flow direction of the group with opposite slot number direction is changed, and the phase sequence of any two phases in the three-phase winding is exchanged to realize the change of the number of poles.

[0011] Furthermore, the harmonic current injection method is used to reduce the motor torque fluctuation: the main subharmonics that mainly cause the torque fluctuation are identified, and the corresponding subharmonics are injected into the main harmonics to generate a synchronous harmonic torque opposite to the original torque fluctuation, thereby reducing the amplitude of the main subharmonics of the torque and suppressing the torque fluctuation.

[0012] Furthermore, the method of reducing the motor torque fluctuation by using the harmonic current injection method is as follows:

[0013] 1) Setting a harmonic amplitude ratio threshold, performing Fourier analysis on the electromagnetic torque waveform of the motor, defining the harmonic whose torque harmonic amplitude accounts for a ratio of the torque DC component greater than the harmonic amplitude ratio threshold as the main subharmonic that causes torque fluctuation, and defining the torque harmonic amplitude to identify the main subharmonic that mainly causes torque fluctuation;

[0014] 2) The corresponding harmonic current is injected. For the 6nth harmonic in the main harmonic of the motor torque, n=1, 2, 3…, 6n+1 or 6n-1th current harmonic is injected on the basis of the original input current; for the (2k-1)×3nth harmonic in the main harmonic of the motor torque, 3n+1th current harmonic is injected on the basis of the original input current; for the mth fractional harmonic in the main harmonic of the motor torque, m is a non-integer, and m+1th current harmonic is injected on the basis of the original input current.

[0015] Furthermore, the original input current is expressed as formula (1), where ω is the angular frequency of the original input current, I1 is the amplitude of the original input current, and α is the initial phase angle of the original input current; the injected harmonic current for the 6nth torque harmonic is expressed as formula (2), where h represents the number of injected harmonic currents, I h is the amplitude of the injected harmonic current, β h is the initial phase angle of the injected harmonic current, i represents the positive or negative of the 2π / 3 term, when h is 6n+1, the injected harmonic magnetic field has the same rotation direction as the original magnetic field of the motor, i=1, when h is 6n-1, the injected harmonic magnetic field has the opposite rotation direction to the original magnetic field of the motor, i=-1; the injected harmonic current for (2k-1)×3n and mth fractional harmonics is expressed as formula (3), the injected harmonic magnetic field has the same rotation direction as the original magnetic field of the motor, so the positive or negative of the 2π / 3 term is consistent with the original input current;

[0016]

[0017] Furthermore, the amplitude of the hth order injected harmonic current is calculated according to the torque DC component, the torque harmonic amplitude and the original input current amplitude through equation (4), where T th is the amplitude of the main harmonic of the torque, T0 is the DC component of the torque;

[0018]

[0019] Furthermore, with the goal of minimizing torque fluctuation, an exhaustive method is used to determine the initial phase angle of each injected harmonic current. The method is as follows: the interval range of the initial phase angle of the injected harmonic current is selected, and a finite element analysis is performed on the motor after the harmonic current is injected at different initial phase angles to obtain the change of the amplitude of the main harmonics of the torque with the value of the initial phase angle of the injected harmonic current, and the value of the initial phase angle when the amplitude of the main harmonics of the torque is reduced to the minimum is obtained.

[0020] Furthermore, the harmonic amplitude ratio threshold = 0.75%.

[0021] Furthermore, an irregular alternating pole rotor structure is adopted: for a variable pole permanent magnet motor with a non-integer ratio of two pole numbers, the original rotor structures under the two pole numbers are compared, and the part where the N poles overlap with the N poles is determined as the N-pole permanent magnet pole of the alternating pole rotor structure, the part where the S poles overlap with the S poles is determined as the S-pole permanent magnet pole of the alternating pole rotor structure, and the part where the N poles overlap with the S poles is determined as the iron pole pole of the alternating pole rotor structure, thereby achieving a change in the number of poles without changing the magnetization direction of the permanent magnet. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1The initial structure diagram of the traditional variable-pole permanent magnet synchronous motor; (a) is the 8-pole motor structure; (b) is the 10-pole motor structure;

[0023] Figure 2 This is the structural diagram of the 8 / 10 pole rotor overlap;

[0024] Figure 3 This is the structural diagram of the alternating pole-changing permanent magnet synchronous motor;

[0025] Figure 4 The slot electromotive force star diagram of the 8 / 10 pole 18-slot motor; (a) is the star diagram under 8 poles; (b) is the star diagram under 10 poles;

[0026] Figure 5 It is the star diagram of slot electromotive force after the 8-pole slot numbers are arranged in reverse; the inner layer is the star diagram of the 10-pole lower slot electromotive force; the outer layer is the star diagram of the 8-pole slot electromotive force after the slot numbers are arranged in reverse;

[0027] Figure 6 Fourier analysis diagram of torque harmonics; (a) is the torque harmonic analysis under 8 poles; (b) is the torque harmonic analysis under 10 poles;

[0028] Figure 7 Comparison of Fourier analysis of torque harmonics before and after optimization by harmonic current injection method; (a) is the torque harmonic analysis under 8 poles; (b) is the torque harmonic analysis under 10 poles;

[0029] Figure 8 Comparison of torque waveforms before and after optimization of harmonic current injection method; (a) is the torque under 8 poles; (b) is the torque under 10 poles; DETAILED DESCRIPTION

[0030] The following takes an 8 / 10 pole 18-slot motor as an example to describe the implementation of the present invention in detail. The parameters of the motor are shown in Table 1.

[0031] Table 1 Main parameters of the motor

[0032]

[0033]

[0034] (1) The initial structure of the pole-changing permanent magnet synchronous motor is as follows Figure 1 As shown in the figure, since the number of permanent magnets does not satisfy the integral ratio when the motor is running at 8 poles and 10 poles, the conventional rotor pole changing method cannot be used. Figure 2 As shown, part 1 is the permanent magnet pole with fixed N pole of the motor, part 2 is the permanent magnet pole with fixed S pole of the motor, and part 3 is the permanent magnet pole whose magnetization direction needs to be changed;

[0035] (2) Propose Figure 3 The alternating pole changing permanent magnet synchronous motor scheme shown replaces the three permanent magnet poles whose magnetization direction needs to be changed with iron poles without a specific magnetization direction. The rotor exhibits an alternating pole characteristic and adapts to an 8-pole magnetic circuit state under 8 poles and to a 10-pole magnetic circuit state under 10 poles. It is applicable to operation under the two pole numbers of 8 and 10 without changing the magnetization direction of the permanent magnet.

[0036] (3) The unchanged winding structure under 8 / 10 pole change is proposed. The slot electromotive force star diagrams of 8-pole 18-slot and 10-pole 18-slot under conventional winding arrangement are as follows: Figure 4 (a) and Figure 4 (b) shows that the winding phase distribution is shown in Table 2. The slot number distribution of each phase under the two pole numbers is not the same. Keeping the phase belt position unchanged, the slot number under 8 poles is reversed and rotated 180°. The winding phase distribution after reverse arrangement is shown in Table 3, and the slot number distribution of each phase under the two pole numbers is the same. Figure 5 As shown, the inner layer is the 10-pole lower slot electromotive force star diagram, and the outer layer is the 8-pole slot electromotive force star diagram after the slot numbers are arranged in reverse.

[0037] Table 2 Phase distribution of windings under 8 poles and 18 slots and 10 poles and 18 slots

[0038]

[0039] Table 3 Phase distribution of windings under 8-pole 18 slots and 10-pole 18 slots after slot number reverse arrangement

[0040]

[0041]

[0042] According to the slot electromotive force star diagram under 10 poles, the armature winding is phased, wired and connected. According to whether the slot number direction in each phase belt is the same as that in the 8-pole star diagram, the armature winding under each phase belt is divided into two groups. Taking phase A as an example, the slots 10, 12, and 14 under the 10 poles are in the same direction as the slots 10, 12, and 14 under the 8 poles, and the slots 1, 3, and 5 under the 10 poles are in the opposite direction to the slots 1, 3, and 5 under the 8 poles. Therefore, slots 10, 12, and 14 are in one group, and slots 1, 3, and 5 are in another group. When changing poles, it is only necessary to change the current flow direction of the group opposite to the slot number of 8 poles under 10 poles. The same logic can be applied to B and C to change the slot numbers 4, 6, 8 and 2, 16, and 18, so that the stator magnetic field can be changed from 10 poles to 8 poles. At this time, the rotation direction of the 8-pole magnetic field is opposite to the original direction. The complete pole change process can be achieved by exchanging the phase sequence of any two phases in the three-phase winding to change the rotation direction of the magnetic field. The proposed 8 / 10 pole-changing and unchanged winding structure can realize the operation of the motor with two poles by simply exchanging the phase sequence of any two phases in the three-phase winding and changing the direction of the current of some windings without reconstructing the winding.

[0043] (4) The harmonic current injection method is used to reduce the motor torque fluctuation. For the main subharmonics of the torque fluctuation, the corresponding subharmonic current is injected into the motor to generate synchronous torque fluctuations opposite to the original torque fluctuations, so that the torque fluctuations cancel each other out, thereby reducing the torque fluctuations while maintaining a higher output torque.

[0044] The specific steps of step (4) are as follows:

[0045] 1) The proposed constant winding universal alternating pole-changing motor is subjected to finite element simulation analysis based on 8 / 10 poles and 18 slots, and its average torque and torque fluctuation under two pole numbers are shown in Table 4. Since the winding coefficient of the motor is the same under two pole numbers and the rotor structure has not changed, the proposed constant winding universal alternating pole-changing motor has a higher average torque under 8 poles and 10 poles.

[0046] Table 4 Average torque value and torque fluctuation under 8 / 10 poles

[0047]

[0048] Table 5 Torque harmonic order and corresponding harmonic amplitude under 8 / 10 poles

[0049]

[0050] 2) Considering the low-order harmonics of 24th and below for 8 poles and 18th and below for 10 poles, as well as the harmonics with amplitudes exceeding 0.5Nm in the high-order harmonics, i.e., the 48th harmonic for 8 poles and the 38.4th harmonic for 10 poles, Fourier analysis is performed on the torque for the two pole numbers, as shown in Figure 6As shown. It can be seen that the proposed alternating pole-changing motor contains multiple complex harmonics in the torque under two pole numbers. Table 5 shows the harmonics and corresponding harmonic amplitudes analyzed under 8 / 10 poles. The harmonics under 8 poles are 1.5 and its multiple harmonics, and the 18th harmonic with the highest amplitude reaches 1.32Nm; the harmonics under 10 poles are 1.2 and its multiple harmonics, and the 14.4th harmonic with the highest amplitude reaches 1.46Nm. The harmonics whose torque harmonic amplitude accounts for a proportion of more than 0.75% of the torque DC component are selected as the main harmonics that cause torque fluctuations. Under 8 poles, the harmonics whose torque harmonic amplitude is higher than 3.64Nm are selected as the main harmonics, so the 1.5, 3, 6, 12, 15, 18, 22.5 and 48 torque harmonics are selected for harmonic current injection; under 10 poles, the harmonics whose torque harmonic amplitude is higher than 3.62Nm are selected as the main harmonics, so the 1.2, 2.4, 3.6, 4.8, 6, 7.2, 8.4, 9.6, 10.8, 12, 14.4, 18 and 38.4 torque harmonics are selected for harmonic current injection. For the 6nth harmonic in the main harmonics of the motor torque, 6n+1 or 6n-1th current harmonics are injected on the basis of the original input current; for the (2k-1)×3nth harmonic in the main harmonics of the motor torque, 3n+1th current harmonics are injected on the basis of the original input current; for the mth fractional harmonic in the main harmonics of the motor torque, m+1th current harmonics are injected on the basis of the original input current. Therefore, injecting 2.5, 4, 5, 11, 16, 17, 23.5 and 49th current harmonics under 8 poles eliminates 1.5, 3, 6, 12, 15, 18, 22.5 and 48th torque harmonics. Under 10 poles, the injection of 2.2, 3.4, 4.6, 5.8, 5, 8.2, 9.4, 10.6, 11.8, 11, 15.4, 19 and 39.4 current harmonics corresponds to the elimination of 1.2, 2.4, 3.6, 4.8, 6, 7.2, 8.4, 9.6, 10.8, 12, 14.4, 18 and 38.4 torque harmonics.

[0051] 3) According to the analysis in step 2), the values ​​of h for 8 poles are 2.5, 4, 5, 11, 16, 17, 23.5 and 49, and the values ​​of h for 10 poles are 2.2, 3.4, 4.6, 5.8, 5, 8.2, 9.4, 10.6, 11.8, 11, 15.4, 19 and 39.4. The corresponding subharmonic current is injected into the motor according to equations (1) to (3).

[0052] 4) According to formula (4), the current amplitude of the injected harmonic current is determined. The injected harmonic order and harmonic current amplitude are shown in Table 6.

[0053] Table 6 Harmonic order and current amplitude selected under 8 / 10 poles

[0054]

[0055] 5) For different initial phase angles of harmonic current, the impact on the harmonic amplitude of the motor torque varies greatly. Therefore, the initial phase angle and current amplitude within an appropriate range are selected for simulation analysis. h In one electrical cycle (0°~360°), finite element analysis is performed at different initial phase angles using the exhaustive method with a step size of 5°. The change of the amplitude of the main harmonics of the motor torque with the value of the initial phase angle of the harmonic current is obtained. The initial phase angle corresponding to the minimum amplitude of the main harmonics of the motor torque under 8-pole and 10-pole conditions is shown in Table 7.

[0056] Table 78 / 10 selected harmonic current initial phase angle

[0057]

[0058] Figure 7 This is a comparison diagram of the Fourier analysis of the torque harmonics before and after harmonic current injection. The amplitude of the main torque harmonics is significantly reduced after harmonic current injection, which verifies the feasibility of this method.

[0059] Figure 8 The torque waveform comparison diagram before and after harmonic current injection shows that when the corresponding subharmonic current is injected and the current amplitude and initial phase angle are appropriately selected, the torque fluctuation is significantly reduced compared to before injection. The average torque value and torque fluctuation after injection are shown in Table 8. The average torque of the alternating pole-changing permanent magnet synchronous motor fluctuates by no more than 1% compared to before injection. On the basis of maintaining a high torque, the torque fluctuation under 8 poles is reduced by 51.29% compared to before injection, and the torque fluctuation under 10 poles is reduced by 66.52% compared to before injection. The torque fluctuation has been significantly reduced. The results verify the effectiveness of the harmonic current injection method in reducing torque fluctuations and improve the stability of motor operation.

[0060] Table 8 Average torque and torque fluctuation at 8 / 10 poles after harmonic current injection

[0061]

[0062] In summary, the present invention proposes an irregular alternating pole-changing permanent magnet synchronous motor structure based on constant windings. The stator winding only needs to exchange the phase sequence of any two phases and change the direction of the current of some windings. The rotor does not need to change the magnetization direction of the permanent magnet to realize the motor pole changing process. The harmonic current injection method is used to reduce the torque fluctuation of the proposed pole-changing permanent magnet synchronous motor. On the basis of maintaining a higher torque average value as much as possible, the purpose of reducing the torque fluctuation is achieved, and the stability of the motor operation is improved.

Claims

1. A pole-changing motor optimization design method based on an alternating-pole rotor structure, characterized in that: 1) The sum of the electrical angles of the windings with two poles is (2k-1)×180°, k=1,2,3…, and the sum of the two poles is the number of slots; 2) Compare the two pole numbers and phase, wire and connect the armature windings according to the slot EMF star diagram of the larger pole number; 3) Keep the slot EMF star diagram of the large pole number unchanged, reverse the slot numbers in the slot EMF star diagram of the small pole number, and rotate the slot numbers 180° while keeping the phase belt position unchanged, so that the slot number distribution of each phase is the same under the two pole numbers; 4) Based on the winding arrangement of the slot EMF star diagram with a large number of poles, the armature winding under each phase belt position is divided into two groups, namely, one group with the same slot number direction and one group with opposite slot number direction, according to whether the slot number direction is the same as that in the slot EMF star diagram with a small number of poles. The current flow direction of the group with opposite slot number direction is changed, and the phase sequence of any two phases in the three-phase winding is exchanged to realize the change of the number of poles.

2. The pole-changing motor optimization design method based on the alternating-pole rotor structure according to claim 1 is characterized in that: Use harmonic current injection method to reduce motor torque fluctuation: identify the main harmonics that cause torque fluctuation, determine the main harmonics, inject corresponding current harmonics to generate synchronous harmonic torque opposite to the original torque fluctuation, reduce the amplitude of the main harmonics of the torque, and thus suppress the torque fluctuation.

3. The pole-changing motor optimization design method based on the alternating-pole rotor structure according to claim 2 is characterized in that: The method of reducing motor torque fluctuation by harmonic current injection is: 1) Setting a harmonic amplitude ratio threshold, performing Fourier analysis on the electromagnetic torque waveform of the motor, defining the harmonic whose torque harmonic amplitude accounts for a ratio of the torque DC component greater than the harmonic amplitude ratio threshold as the main subharmonic that causes torque fluctuation, and defining the torque harmonic amplitude to identify the main subharmonic that mainly causes torque fluctuation; 2) By injecting the corresponding harmonic current, for the 6nth harmonic in the main harmonic of the motor torque, n = 1, 2, 3..., inject 6n+1 or 6n-1th current harmonic on the basis of the original input current; for the (2k-1)×3nth harmonic in the main harmonic of the motor torque, inject 3n+1th current harmonic on the basis of the original input current; For the mth fractional harmonic among the main harmonics of the motor torque, m is a non-integer, and the m+1th current harmonic is injected on the basis of the original input current.

4. The pole-changing motor optimization design method based on the alternating-pole rotor structure according to claim 3 is characterized in that: The original input current is expressed as formula (1), where ω is the angular frequency of the original input current, I1 is the amplitude of the original input current, and α is the initial phase angle of the original input current; the injected harmonic current for the 6nth torque harmonic is expressed as formula (2), where h represents the number of injected harmonic currents, I h is the amplitude of the injected harmonic current, β h is the initial phase angle of the injected harmonic current, i represents the positive or negative of the 2π / 3 term, when h is 6n+1, the injected harmonic magnetic field has the same rotation direction as the original magnetic field of the motor, i=1, when h is 6n-1, the injected harmonic magnetic field has the opposite rotation direction to the original magnetic field of the motor, i=-1; the injected harmonic current for (2k-1)×3n and mth fractional harmonics is expressed as formula (3), the injected harmonic magnetic field has the same rotation direction as the original magnetic field of the motor, so the positive or negative of the 2π / 3 term is consistent with the original input current; 5. The pole-changing motor optimization design method based on the alternating-pole rotor structure according to claim 4 is characterized in that: The amplitude of the hth order injected harmonic current is calculated by equation (4) based on the torque DC component, the torque harmonic amplitude and the original input current amplitude, where T th is the amplitude of the main harmonic of the torque, T0 is the DC component of the torque; 6. The pole-changing motor optimization design method based on the alternating-pole rotor structure according to claim 4 is characterized in that: With the goal of minimizing torque ripple, an exhaustive method is used to determine the initial phase angle of each injected harmonic current. The method is as follows: the interval range of the initial phase angle of the injected harmonic current is selected, and finite element analysis is performed on the motor after the harmonic current is injected at different initial phase angles to obtain the change of the amplitude of the main harmonics of the torque with the value of the initial phase angle of the injected harmonic current, and the value of the initial phase angle when the amplitude of the main harmonics of the torque is reduced to the minimum is obtained.

7. The pole-changing motor optimization design method based on the alternating-pole rotor structure according to claim 3 is characterized in that: Harmonic amplitude percentage threshold = 0.75%.

8. The pole-changing motor optimization design method based on an alternating-pole rotor structure according to any one of claims 1 to 7, characterized in that: Adopt irregular alternating pole rotor structure: for the pole-changing permanent magnet motor with a non-integer ratio of two pole numbers, compare the original rotor structures under the two pole numbers, determine the part where the N poles overlap with the N poles as the N-pole permanent magnet pole of the alternating pole rotor structure, the part where the S poles overlap with the S poles as the S-pole permanent magnet pole of the alternating pole rotor structure, and the part where the N poles overlap with the S poles as the iron pole of the alternating pole rotor structure, so as to realize the change of pole number without changing the magnetization direction of the permanent magnet.

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