A low-pulsation inverse-cosine plus third-harmonic auxiliary salient pole type radial permanent magnet motor and a method for optimizing air gap harmonics

Abstract

The application discloses a low-pulsation inverse-cosine plus third-harmonic auxiliary salient pole type radial permanent magnet motor and a method for optimizing air gap harmonics, and belongs to the technical field of motor manufacturing. A novel radial permanent magnet synchronous motor with inverse-cosine plus third-harmonic auxiliary salient poles is provided, and the method can suppress air gap flux density harmonics and reduce torque ripple and average torque loss. The specific process is as follows: the rotor air gap flux density is proportional to the rotor magnetomotive force, and the main air gap flux density harmonic order affecting the torque ripple is determined. The inverse-cosine plus third-harmonic method is used to modify the auxiliary salient poles, so as to reduce the air gap flux density harmonics, especially the 9th, 11th, 19th and 21st harmonics causing the first and second order torque ripples, thereby reducing the torque ripple; since the third harmonic is not the main air gap flux density harmonic causing the torque ripple, the injection of the third harmonic can reduce the average torque loss.

Description

Technical Field

[0001] This invention relates to the design of radial permanent magnet synchronous motors, and in particular to a method for reducing torque ripple in radial permanent magnet synchronous motors, belonging to the technical field of motor manufacturing. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) are now widely used in numerous fields, from automotive to aerospace, playing a vital role. This is mainly due to several significant characteristics of PMSMs, including high torque density, high efficiency, and small size and weight. PMSMs utilize high-energy-product magnetic materials to replace traditional excitation windings, eliminating the negative impacts of traditional excitation windings, simplifying the motor's mechanical structure, improving operational reliability, and correspondingly reducing mechanical losses.

[0003] Permanent magnet synchronous motors, especially rare-earth permanent magnet synchronous motors with neodymium iron boron permanent magnet excitation, have significant advantages such as simple structure, reliable operation, small size, light weight, low loss, and high efficiency. As a strategic resource, the price of rare earth resources has been rising in recent years due to continuous mining and the implementation of related protection policies. This has undoubtedly had a significant impact on the further widespread application of rare-earth permanent magnet synchronous motors in industry and defense. To reduce the amount of rare-earth permanent magnet materials used in rare-earth permanent magnet synchronous motors, more and more scholars in the academic field have begun to focus on low-rare-earth permanent magnet synchronous motors. Therefore, how to ensure high power density of the motor while reducing the amount of rare-earth permanent magnet materials and how to improve the torque performance of the motor have become hot topics in motor research. Tangentially magnetized radial permanent magnet synchronous motors have a rotor structure with a magnetic focusing effect, which is beneficial to improving the torque density of the motor. Therefore, in recent years, research on radial permanent magnet synchronous motors has become a hot topic. Radial permanent magnet synchronous motors can significantly improve the utilization rate of permanent magnets, thus reducing the material cost of the motor. However, due to the special rotor permanent magnet structure, radial permanent magnet synchronous motors can experience high torque ripple. While radial permanent magnet synchronous motors (PMSMs) possess a range of advantages, they still face numerous challenges in demanding high-performance applications such as electric steering systems, servo motors, wind turbines, and electric vehicle drive systems. These applications place high demands on the motor's operational stability, requiring minimal output torque ripple to achieve smooth and precise thrust transmission. Therefore, researching methods to reduce output torque ripple is highly valuable. In conclusion, researching ways to reduce the output torque ripple of radial PMSMs is of significant value.

[0004] Currently, due to the unique structure of the rotor permanent magnets in spoke-type permanent magnet synchronous motors (PMSMs), the available technologies for reducing torque ripple in these motors are very limited and have been extensively studied. Research on suppressing torque ripple in spoke-type PMSMs mainly focuses on two aspects. Firstly, control optimization can be used to reduce steady-state error and torque ripple by suppressing harmonic currents. Secondly, optimization can be performed based on motor design. The first aspect is stator optimization. In motor design, the slot-pole combination is determined first, as it is related to the ripple period. The optimal winding configuration can result in a back EMF closer to a sinusoidal signal. Stator tooth optimization can also reduce torque ripple. Currently, due to the unique structure of the rotor permanent magnets in spoke-type PMSMs, the available technologies for reducing torque ripple in these motors are very limited and have been extensively studied. The method of axial segmentation offset for spoke-type motors reduces cogging torque and electromagnetic torque ripple; however, motor design requires building a 3D model, which is time-consuming, and manufacturing is more complex. In the circumferential direction, a three-segment arc method is proposed—the method of spoke-type motors—which can suppress air gap magnetic flux density harmonics, thereby suppressing torque ripple. Additionally, multi-objective optimization design methods can be applied, but these generally require optimizing a large number of parameters. All of the above methods are generally quite complex, and some increase manufacturing difficulty and consume a significant amount of time. Summary of the Invention

[0005] The purpose of this invention is to propose a method for optimizing torque ripple in a low-ripple anticosine plus third harmonic assisted salient pole spoke-type permanent magnet synchronous motor. Based on a novel assisted salient pole spoke-type permanent magnet synchronous motor, the method accurately analyzes the components causing torque ripple in the permanent magnet synchronous motor. Then, based on the sinusoidal air gap magnetic flux density, a modified formula for the anticosine plus third harmonic assisted salient pole configuration is derived to eliminate the 9th, 11th, 19th, and 21st harmonics that cause first and second order torque ripple, thereby reducing torque ripple. Furthermore, the third harmonic is not the primary harmonic causing torque ripple; increasing the third harmonic can improve the average torque.

[0006] The technical solution adopted in this invention is: a low-pulsation anticosine plus third harmonic assisted salient pole radial permanent magnet motor, which includes an outer stator 1, a radial inner rotor 2, and an integer slot distribution winding 4 embedded in the stator slots. The outer edge of the inner rotor 2 is provided with an anticosine plus third harmonic assisted salient pole, which is a symmetrical structure with equal pole arc angles, so that the inner rotor 2 forms 8 rotor cores and 8 permanent magnets 3. The permanent magnets 3 are built on the inner rotor, and the polarities of adjacent permanent magnets 3 are alternately distributed.

[0007] Furthermore, the auxiliary salient pole and the inner rotor 2 are connected and are made of silicon steel.

[0008] Furthermore, the motor adopts a five-phase winding arrangement, with each phase winding consisting of four coils connected in series. Each coil of the winding has 40 turns, and the motor's slot fill factor is 0.51.

[0009] The specific steps for optimizing the air gap magnetic flux density based on the use of anticosine and third harmonic type auxiliary salient poles are as follows:

[0010] Step 1: Analyze the pole-slot ratio of the target motor. Based on the relationship between the number of rotor poles and the number of stator slots, calculate the number of torque pulsation cycles within one electrical cycle and determine its overall fluctuation trend.

[0011] Step 2: A radial permanent magnet synchronous motor with symmetrical auxiliary salient poles is proposed, and based on this, the auxiliary salient poles are modified by an anticosine plus third harmonic method.

[0012] Step 3: Based on the principle of torque pulsation generation, determine the harmonic order of the rotor magnetomotive force that affects the torque pulsation of the five-phase permanent magnet synchronous motor. Then, based on the proportional relationship between the rotor air gap magnetic flux density and the rotor magnetomotive force, determine the main harmonic order of the air gap magnetic flux density that affects the torque pulsation. Since the third harmonic is not the main harmonic that causes torque pulsation, the third harmonic is injected.

[0013] Step 4: Give the formula for air gap magnetic flux density. Based on the sinusoidal air gap magnetic flux density, derive the relationship between air gap length and rotor angle. Then inject the third harmonic and select the optimal third harmonic amplitude to improve the average torque and maintain low torque pulsation.

[0014] Step 5: In order to weaken the main harmonics that cause first and second order torque pulsations, it is necessary to derive the formulas for the maximum thickness and pole arc coefficient of the anticosine plus third harmonic auxiliary salient pole, and then select the optimal maximum thickness and pole arc coefficient.

[0015] Furthermore, the formula for calculating the number of ripple cycles of torque pulsation in step 1 is as follows:

[0016]

[0017] Where v represents the number of torque pulsation cycles within one electrical cycle, S represents the number of slots in the motor, p represents the number of pole pairs in the motor, and N... 2ps N represents the least common multiple of the number of slots and poles of a motor. 2ps =LCM(S, 2p).

[0018] Furthermore, the radial permanent magnet synchronous motor with virtual poles in step 2 is a conventional radial permanent magnet synchronous motor with virtual poles added to the outer edge of the rotor. The virtual poles are connected to the conventional rotor and are made of silicon steel, so that each rotor unit forms a convex shape.

[0019] Furthermore, the formula for calculating the torque ripple of the five-phase permanent magnet synchronous motor in step 3 is as follows:

[0020]

[0021] Among them, T pul This represents the average output torque, where μ0 is the permeability of air, g is the air gap length, and r is the average output torque. g γ is the radius of the intermediate air gap, L is the stacking length of the laminations, and γ is the lamination radius of the intermediate air gap. d It is expressed as the current angle, h is the harmonic order, and F sh and F rh These are the h-order stator and rotor magnetomotive forces, respectively. Therefore, the harmonic orders of the stator and rotor magnetomotive forces that can generate torque pulsation are: h = 10m ± 1, m = 1, 2, 3… Since the rotor air gap magnetic flux density is proportional to the rotor magnetomotive force, the harmonic order of the rotor air gap magnetic flux density that affects torque pulsation is: h = 10m ± 1, m = 1, 2, 3…

[0022] Furthermore, in step 4, when the magnetic voltage drop of the ferromagnetic material is ignored, and the inner and outer surfaces of the armature under the same pole are defined as equimagnetic potential surfaces, the formula for the air gap magnetic flux density is:

[0023]

[0024] Where μ0 is the vacuum permeability, F is the air gap magnetic pressure drop, and δ(θ) is the air gap length as a function of the rotor angle;

[0025] Make the air gap magnetic flux density in the above formula follow the sinusoidal air gap magnetic flux density distribution:

[0026]

[0027] Among them, B r1 θ represents the amplitude of the sinusoidal air gap magnetic flux density, and θ is the rotor angle.

[0028] The formula for the air gap length with respect to the rotor angle is:

[0029]

[0030] When θ = 0, δ(θ) takes the minimum value δ min Therefore, the amplitude of the sinusoidal air gap magnetic flux density is obtained as follows:

[0031]

[0032] B r1 Substituting the formula into δ(θ), we obtain the simplified formula for δ(θ):

[0033]

[0034] Furthermore, a third harmonic is injected into the simplified δ(θ):

[0035]

[0036] Where c is the amplitude of the injected third harmonic, and k(c) remains constant at the minimum air gap.

[0037] When δ(θ) is taken to its minimum value, k(c) is obtained as follows:

[0038]

[0039] Furthermore, in step 5, to optimize the maximum thickness of the anticosine plus third harmonic assisted salient pole, it is necessary to add a parameter 'a', and establish the following equation with the center of the circle:

[0040]

[0041] Where R is the stator inner diameter of 49mm, and μ1 remains unchanged at the minimum air gap.

[0042] When R(θ) reaches its maximum value, the formula for calculating μ1 is:

[0043]

[0044] Furthermore, the maximum thickness h of the anticosine plus third harmonic assisted salient pole max It can be represented as:

[0045]

[0046] Where r is the rotor outer diameter, and the formulas for k(c) and μ1 have been obtained.

[0047] Furthermore, optimizing the polar arc angle requires adding parameter b and establishing parametric equations:

[0048]

[0049] Since the formula R(θ) is different for different θ m There are different shapes, so optimization is first done through θ m Select a basic shape, then use α p θ m The formula for reducing it to a single polar moment and calculating the value of b is as follows:

[0050]

[0051] Where x and y are the x-axis coordinates and y-axis coordinates, respectively, and α p For the anticosine plus third harmonic auxiliary convex pole arc angle, θ m This represents the maximum rotor angle.

[0052] The beneficial effects of this invention are:

[0053] 1. Compared with traditional spoke-type permanent magnet synchronous motors, anticosine plus third harmonic auxiliary salient poles can reduce torque pulsation.

[0054] 2. The anticosine plus third harmonic assisted salient pole optimization method of the present invention can reduce the average torque loss by injecting the third harmonic; and can reduce the main harmonics of the first and second order torque pulsation by using the anticosine assisted salient pole and reasonably selecting the pole arc angle and maximum thickness of the anticosine assisted salient pole according to the main source components of torque pulsation, thereby reducing torque pulsation.

[0055] 3. The spoke-type permanent magnet synchronous motor with anticosine and third harmonic auxiliary salient poles in this invention can not only effectively reduce the torque pulsation caused by permanent magnet torque, but also significantly reduce the peak-to-peak value of cogging torque due to the uneven air gap, thereby reducing torque pulsation. The sinusoidal nature of the back EMF is improved, resulting in a significant reduction in the final output torque pulsation. Furthermore, the injection of the third harmonic increases the average torque, thus improving the motor's performance. Attached Figure Description

[0056] Figure 1 This is a structural diagram of a traditional radial permanent magnet synchronous motor (original motor).

[0057] Figure 2 This is a schematic diagram of the auxiliary salient pole and the anticosine plus third harmonic type auxiliary salient pole modification in this invention.

[0058] Figure 3 This is a structural diagram of the radial permanent magnet motor (exemplary motor) of the anticosine plus third harmonic type auxiliary salient pole integer slot distributed winding in this invention.

[0059] Figure 4 This is a comparison diagram of the cogging torque of the original motor and the motor in the embodiment of the present invention.

[0060] Figure 5 This is a comparison diagram of the output torque of the original motor and the motor in the embodiment of the present invention.

[0061] Figure 6 The diagram shows the harmonic analysis of the output torque of the original motor and the motor in the embodiment of the present invention.

[0062] Figure 7 Comparison diagram of air gap magnetic flux density of the original motor and the motor of the embodiment in this invention.

[0063] Figure 8 Comparison diagram of air gap magnetic flux density harmonics between the original motor and the motor of the embodiment in this invention.

[0064] Figure 9 A comparison diagram of the back electromotive force of the original motor and the motor in the embodiment of the present invention.

[0065] Figure 10 Back EMF harmonic analysis diagram of the original motor and the motor in the embodiment of the present invention.

[0066] Figure 11 The output torque and torque ripple analysis diagram of the motor in the embodiment of the invention under different current angles. Detailed Implementation

[0067] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0068] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0069] like Figure 1 As shown, a conventional spoke-type permanent magnet synchronous motor includes an outer stator 1, an inner rotor 2, and permanent magnets 3; the outer stator 1 includes 40 stator slots and a single-layer integer slot distributed winding 4 embedded therein; the inner rotor 2 includes 8 rotor cores and 8 permanent magnets 4, and the excitation direction of the permanent magnets is shown in the figure.

[0070] like Figure 2 As shown, the first step is to add an auxiliary salient pole to the outer edge of the traditional spoke-type rotor core; the second step is to modify the auxiliary salient pole using the method of anticosine plus third harmonic, thereby forming an anticosine plus third harmonic type auxiliary salient pole spoke-type permanent magnet motor.

[0071] like Figure 3 As shown, the motor includes an outer stator 1, an inner rotor 2, and permanent magnets 3. The outer stator 1 includes 40 stator slots and a single-layer integer slot distribution winding 4 embedded therein. The inner rotor 2 is equipped with an anticosine plus third harmonic type auxiliary salient pole 5, forming 8 rotor core units with anticosine plus third harmonic type auxiliary salient poles and 8 permanent magnets 3. The magnetization direction of the permanent magnets is shown by the arrow in the figure.

[0072] The following is an example of a 40-slot, 8-pole radial permanent magnet synchronous motor, and the steps are as follows.

[0073] Step 1: Analyze the pole-slot ratio of the target motor. Based on the relationship between the number of rotor poles and the number of stator slots, calculate the number of torque pulsation cycles within one electrical cycle to determine its overall pulsation trend. The formula for calculating the number of torque pulsation cycles is: The calculated number of ripple cycles for the torque pulsation is v = 10. Where S = 40, p = 4; N 2ps =LCM(40,8)=40.

[0074] Step 2: A radial permanent magnet synchronous motor with symmetrical auxiliary salient poles is proposed, and based on this, the auxiliary salient poles are modified by an anticosine plus third harmonic method.

[0075] Step 3: Based on the principle of torque pulsation generation, determine the harmonic order of the rotor magnetomotive force affecting the torque pulsation of the five-phase permanent magnet synchronous motor. Then, based on the proportional relationship between the rotor air gap magnetic flux density and the rotor magnetomotive force, determine the main harmonic order of the air gap magnetic flux density affecting the torque pulsation, and determine the harmonic order to be injected based on the main harmonic order. The formula for calculating torque pulsation is:

[0076]

[0077] Among them, T pul This represents the average output torque, where μ0 is the permeability of air, g is the air gap length, and r is the average output torque. g γ is the radius of the intermediate air gap, L is the stacking length of the laminations, and γ is the lamination radius of the intermediate air gap. d It is expressed as the current angle, h is the harmonic order, and F sh and F rh These are the h-order stator and rotor magnetomotive forces, respectively. Therefore, the harmonic orders of the stator and rotor magnetomotive forces that can generate torque pulsation are: h = 10m ± 1, m = 1, 2, 3… Since the rotor air gap magnetic flux density is proportional to the rotor magnetomotive force, the harmonic order of the rotor air gap magnetic flux density that affects torque pulsation is: h = 10m ± 1, m = 1, 2, 3…

[0078] Step 4: Ignoring the magnetic voltage drop of the ferromagnetic material, and defining the inner and outer surfaces of the armature as equipotential surfaces under the same pole, the formula for the air gap magnetic flux density is:

[0079]

[0080] Where μ0 is the vacuum permeability, F is the air gap magnetic pressure drop, and δ(θ) is the air gap length as a function of the rotor angle;

[0081] Make the air gap magnetic flux density in the above formula follow the sinusoidal air gap magnetic flux density distribution:

[0082]

[0083] Among them, B r1 θ represents the amplitude of the sinusoidal air gap magnetic flux density, and θ is the rotor angle.

[0084] The formula for the air gap length with respect to the rotor angle is:

[0085]

[0086] When θ = 0, δ(θ) takes the minimum value δ min Therefore, the amplitude of the sinusoidal air gap magnetic flux density is obtained as follows:

[0087]

[0088] B r1Substituting the formula into δ(θ), we obtain the simplified formula for δ(θ):

[0089]

[0090] Furthermore, a third harmonic is injected into the simplified δ(θ):

[0091]

[0092] Where c is the amplitude of the injected third harmonic, and k(c) remains constant at the minimum air gap.

[0093] When δ(θ) is taken to its minimum value, k(c) is obtained as follows:

[0094]

[0095] Step 5: For optimizing the maximum thickness of the salient pole assisted by anticosine and third harmonic, it is necessary to add parameter 'a' and establish the following equation with the center of the circle:

[0096]

[0097] Where R is the stator inner diameter of 49mm, and μ1 remains unchanged at the minimum air gap.

[0098] When R(θ) reaches its maximum value, the formula for calculating μ1 is:

[0099]

[0100] Furthermore, the maximum thickness h of the anticosine plus third harmonic assisted salient pole max It can be represented as:

[0101]

[0102] Where r is the rotor outer diameter of 48.5 mm, and the formulas for k(c) and μ1 have been obtained.

[0103] Furthermore, optimizing the polar arc angle requires adding parameter b and establishing parametric equations:

[0104]

[0105] Since the formula R(θ) is different for different θ m There are different shapes, so optimization is first done through θ m Select a basic shape, then use α p θ m The formula for reducing it to a single polar moment and calculating the value of b is as follows:

[0106]

[0107] Through finite element simulation, the third harmonic amplitude c of the anticosine-plus-third harmonic auxiliary salient pole was selected as 0.1125, and the maximum rotor angle θ was determined. m The maximum thickness is 0.35 rad. m Choosing 1.55mm, the optimal polar arc angle (α) p The value of b is 37.3deg, which gives a value of 0.93.

[0108] Figure 4 This is a comparison diagram of the cogging torque of the original motor and the motor in the embodiment of this invention. Figure 4 As shown, the cogging torque amplitude of the original motor is 1.3 Nm, while the cogging torque amplitude of the motor in the embodiment is only 0.21 Nm. The use of an auxiliary salient pole with an anticosine and third harmonic winding introduces an uneven air gap, resulting in a significant decrease in the peak-to-peak value of the cogging torque.

[0109] Figure 5 and Figure 6 This reflects a comparison of the original motor and the motor in the embodiment regarding their final output torque and harmonics. For example... Figure 5 As shown, the torque ripple of the motor in the embodiment is significantly reduced; as Figure 6 As shown, compared with the original motor, the 10th and 20th harmonics that cause torque pulsation in the motor of the embodiment are significantly reduced. Figure 7 and Figure 8 The air gap magnetic flux density waveform and harmonics of the original motor and the motor of the embodiment were compared. Among them, the air gap magnetic flux density harmonic optimization effect was significant, with the 9th and 11th harmonics that cause first-order torque pulsation decreasing by 93.3% and 80.5%, respectively, and the 19th and 21st harmonics that cause second-order torque pulsation decreasing by 30% and 97.7%, respectively. Figure 9 and Figure 10 The comparison reflects the back EMF waveform and harmonics between the original motor and the motor of the embodiment. It can be seen that the sinusoidal nature of the back EMF waveform is significantly improved, and the main harmonics (9th, 11th, 19th, and 21st) are significantly reduced. Compared to the original motor, the torque ripple of the motor of the embodiment is reduced from 70% to 2.8%.

[0110] Modifying the auxiliary salient pole using an anticosine and third harmonic method can reduce the harmonics of the air gap magnetic flux density, especially the 9th, 11th, 19th, and 21st harmonics that cause first and second order torque pulsations, thereby reducing torque pulsations. Since the third harmonic is not the main air gap magnetic flux density harmonic that causes torque pulsations, injecting the third harmonic can reduce the average torque loss.

[0111] Figure 11 This is a graph showing the output torque and torque ripple analysis of the motor in an embodiment of the present invention under different current angles. (See graph for example.) Figure 7As shown, at a current angle of 0°, the torque ripple of the motor is minimum at 2.8%, and the torque ripple increases with the increase of the current angle, reaching a maximum of 38%; moreover, the average torque is maximum at a current angle of 0°. Therefore, the proposed method for reducing torque ripple in a spoke-type permanent magnet motor is highly effective.

[0112] In summary, this invention discloses an anticosine plus third harmonic type salient pole spoked permanent magnet motor and its torque ripple suppression method. The anticosine plus third harmonic type auxiliary salient pole reduces the motor's torque ripple and average torque loss. Specifically, it includes: deriving the Fourier expression of the rotor air gap magnetic flux density; an anticosine plus third harmonic formula for reducing the order of torque ripple based on sinusoidal air gap magnetic flux density; identifying the main air gap magnetic flux density harmonics causing torque ripple; and optimizing the harmonics causing first and second order torque ripple through the anticosine plus third harmonic type auxiliary salient pole, resulting in a significant reduction in torque ripple. The injection of the third harmonic reduces the average torque loss. Simultaneously, the non-uniform air gap introduced by the anticosine plus third harmonic type auxiliary salient pole significantly reduces the peak-to-peak value of the cogging torque, and the back EMF exhibits good sinusoidal characteristics. Ultimately, while maintaining the same amount of permanent magnets, compared to a drive motor, the average torque is reduced by 10.3%, and the torque ripple is reduced by 96.0%, achieving optimal results.

[0113] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0114] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for reducing torque pulsation in a low-pulsation anticosine and third harmonic-assisted salient-pole radial permanent magnet motor by optimizing air gap harmonics, characterized in that... The motor includes an outer stator (1), a radial inner rotor (2), and an integer slot distribution winding embedded in the stator slots. The inner rotor (2) has an anticosine and third harmonic auxiliary salient pole added to its outer edge. It is a symmetrical structure with equal pole arc angles, so that the inner rotor (2) forms (8) rotor cores and (8) permanent magnets (3). The permanent magnets (3) are built into the inner rotor, and the polarities of adjacent permanent magnets (3) are alternately distributed. The method is implemented in the following steps: Step 1: Analyze the pole-slot ratio of the target motor. Based on the relationship between the number of poles of the inner rotor (2) and the number of stator slots, calculate the number of fluctuation cycles of torque pulsation within one electric cycle and determine its overall fluctuation trend. Step 2: A radial permanent magnet synchronous motor with symmetrical auxiliary salient poles is proposed, and based on this, the auxiliary salient poles are modified by an anticosine plus third harmonic method. Step 3: Based on the principle of torque pulsation generation, determine the harmonic order of the rotor magnetomotive force that affects the torque pulsation of the permanent magnet synchronous motor. Then, based on the proportional relationship between the rotor air gap magnetic flux density and the rotor magnetomotive force, determine the harmonic order of the rotor air gap magnetic flux density that affects the torque pulsation. Since the third harmonic is not the main harmonic that causes torque pulsation, the third harmonic is determined to be injected. Step 4: The formula for air gap magnetic flux density is given. Based on the sinusoidal air gap magnetic flux density, the relationship between air gap length and rotor angle is derived. Then, the third harmonic is injected, and the optimal third harmonic amplitude is selected. Step 5: In order to weaken the main harmonics that cause first and second order torque pulsation, it is necessary to derive the formulas for the maximum thickness and pole arc coefficient of the anticosine plus third harmonic auxiliary salient pole, and then select the optimal maximum rotor angle, maximum thickness and pole arc coefficient to obtain low torque pulsation and reduce average torque loss. In step 4, when the magnetic voltage drop of the ferromagnetic material is ignored, and the inner and outer surfaces of the armature under the same pole are defined as equimagnetic potential surfaces, the formula for the air gap magnetic flux density is: ； Where μ0 is the vacuum permeability, F is the air gap magnetic pressure drop, and δ(θ) is the air gap length as a function of the rotor angle; Make the air gap magnetic flux density in the above formula follow the sinusoidal air gap magnetic flux density distribution: ； Among them, B r1 θ is the amplitude of the sinusoidal air gap magnetic flux density, θ is the rotor angle, and p represents the number of pole pairs of the motor; The formula for the air gap length with respect to the rotor angle is: ； When θ=0, δ(θ) takes the minimum value δ min Therefore, the amplitude of the sinusoidal air gap magnetic flux density is obtained as follows: ； B r1 Substituting the formula into δ(θ), we obtain the simplified formula for δ(θ): ； Inject the third harmonic into the simplified δ(θ): ； Where c is the amplitude of the injected third harmonic, and k(c) remains constant at the minimum air gap; When δ(θ) is taken to its minimum value, k(c) is obtained as follows: 。 2. The method according to claim 1, characterized in that, The auxiliary salient pole is connected to the inner rotor (2) and is made of silicon steel.

3. The method according to claim 1, characterized in that, The motor adopts a five-phase winding arrangement, with each phase winding consisting of 4 coils connected in series. Each coil has 40 turns, and the motor's slot fill factor is 0.

51.

4. The method according to claim 1, characterized in that: The formula for calculating the number of oscillation cycles of torque pulsation in step 1 is as follows: ； Where v represents the number of torque ripple cycles within one electrical cycle, S represents the number of slots in the motor, p represents the number of pole pairs in the motor, and N... 2ps N represents the least common multiple of the number of slots and poles of a motor. 2ps =LCM(S, 2p).

5. The method according to claim 1, characterized in that: The radial permanent magnet synchronous motor with auxiliary salient poles in step 2 is an auxiliary salient pole added to the outer edge of the inner rotor (2). The auxiliary salient pole is connected to the inner rotor (2) and is made of silicon steel, so that each inner rotor (2) unit forms a convex shape. Then, the auxiliary salient pole is modified by anticosine plus third harmonic.

6. The method according to claim 1, characterized in that: In step 3, the formula for calculating the torque ripple of the permanent magnet synchronous motor is: ； Among them, T pul This represents the average output torque, where μ0 is the permeability of air, g is the air gap length, p is the number of pole pairs, and r is the average output torque. g γ is the radius of the intermediate air gap, L is the stacking length of the laminations, and γ is the lamination radius of the intermediate air gap. d It is expressed as the current angle, h is the harmonic order, and F sh and F rh The stator and rotor magnetomotive forces are respectively of order h. Therefore, the harmonic orders of the stator and rotor magnetomotive forces that can generate torque pulsation are: h = 10m ± 1, m = 1, 2, 3… Since the rotor air gap magnetic flux density is proportional to the rotor magnetomotive force, the harmonic orders of the rotor air gap magnetic flux density that affect torque pulsation are also: h = 10m ± 1, m = 1, 2, 3… 7. The method according to claim 1, characterized in that: In step 5, for optimizing the maximum thickness of the salient pole assisted by anticosine and third harmonic, it is necessary to add parameter a, and establish the following equation with the center of the circle: ； Where R is the stator inner diameter, and μ1 remains constant at the minimum air gap; When R(θ) reaches its maximum value, the formula for calculating μ1 is: ； The maximum thickness h of the anticosine plus third harmonic assisted salient pole max Represented as: ； Where r is the rotor outer diameter, and the formulas for k(c) and μ1 have been obtained; optimization of the pole arc angle requires adding parameter b and establishing parametric equations: ; Since the formula R(θ) is different for different θ m There are different shapes, so optimization first involves determining θ. m Select a basic shape, then use α p θ m The formula for reducing it to a single polar moment and calculating the value of b is as follows: ； Where x and y are the x-axis coordinates and y-axis coordinates, respectively, and α p For the anticosine plus third harmonic auxiliary convex pole arc angle, θ m This represents the maximum rotor angle.

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