Permanent magnet design method with optimal permanent magnet consumption

Abstract

The permanent magnet design method comprises the following steps: dividing a permanent magnet into j units at equal angles along the circumferential direction, and analyzing the air gap flux density generated by the permanent magnet of the units and the amplitude of each harmonic wave by using an analytical method; solving an expression that the permanent magnet use amount reaches the optimal permanent magnet thickness change along with the spatial position; carrying out superposition calculation on k times of air gap flux density related to the average torque generated by the j unit permanent magnets to obtain k times of harmonic amplitude of the total air gap flux density generated by the permanent magnets; adjusting the parameters of the permanent magnet to enable the total air gap flux density amplitude of the average torque related order to reach a preset amplitude threshold value; and finally, outputting the optimal parameter of the permanent magnet to obtain the permanent magnet design with the optimal magnet consumption. By means of the permanent magnet design method, the motor outputs the preset average torque, meanwhile, the number of the permanent magnets can be effectively reduced, the utilization rate of the permanent magnets is improved, and the number of the permanent magnets in the motor and the corresponding cost are reduced.

Description

Technical Field

[0001] The invention relates to the field of permanent magnet synchronous motors, and in particular to a permanent magnet design method with an optimal permanent magnet usage. Background Art

[0002] Permanent magnet synchronous motors use permanent magnets instead of excitation windings, eliminating brush commutators, etc., which improves the reliability of motor operation while eliminating excitation losses, thereby increasing the efficiency and power density of the motor. In recent years, high-performance permanent magnet motors have been widely used in the fields of automobiles, new energy power generation, aerospace, industrial drives, etc.

[0003] The permanent magnet synchronous motor is also composed of stator, rotor, housing, end cover and other components. The stator is basically the same as the asynchronous induction motor, and generally adopts a lamination design to reduce the iron loss of the core. The rotor core can be made solid or laminated. The permanent magnet synchronous motor rotor can adopt a surface-mounted permanent magnet structure. The permanent magnet is usually tile-shaped and located on the surface of the rotor. It has the advantages of simple structure, high power density, high efficiency, etc., which can significantly improve the transmission performance of the entire system. However, the rare earth materials used to manufacture high-performance permanent magnets are expensive and account for a large proportion of the motor material cost. Moreover, the mining, production and processing of rare earth permanent magnet materials will have adverse effects on the environment. Therefore, the research on the reduction of rare earth in permanent magnet motors is of great significance for reducing the use of rare earth permanent magnets and improving the utilization rate of permanent magnets. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a permanent magnet design method with an optimal permanent magnet usage in view of the defects involved in the background technology.

[0005] The present invention adopts the following technical solutions to solve the above technical problems:

[0006] A permanent magnet design method with an optimal amount of permanent magnets, wherein the permanent magnets are embedded on the surface of a rotor core, and the rotor and the stator are coaxially distributed, comprising the following steps:

[0007] Step 1), divide the permanent magnet into j units along the circumferential direction at equal angles, and the arc length of each unit occupies the center angle θ Δm , the air gap flux density generated by the permanent magnet unit with the spatial position is analyzed by analytical method, and the harmonic amplitudes of the air gap flux density are further analyzed;

[0008] Step 2), selecting the air gap magnetic flux order k related to the average torque, superimposing and calculating the k-order air gap magnetic flux generated by j unit permanent magnets, and obtaining the k-order harmonic amplitude of the total air gap magnetic flux generated by the permanent magnets;

[0009] Step 3), deriving an expression for the change of the thickness of the permanent magnet with the spatial position when the amount of the permanent magnet reaches the optimum;

[0010] Step 4), when adjusting the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length based on the expression of the change of the permanent magnet thickness with the spatial position when the permanent magnet dosage reaches the optimal level, the thickness of the permanent magnet changes, and the center angle occupied by the arc length of the permanent magnet unit changes accordingly, and the amplitude of each harmonic of the generated air gap magnetic flux also changes accordingly, and the amplitude of the kth harmonic of the total air gap magnetic flux generated by the permanent magnet is also adjusted accordingly;

[0011] Adjust the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length so that the k-th harmonic amplitude of the total air gap magnetic flux density generated by the permanent magnet reaches a preset amplitude threshold, and use the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length at this time as the optimal thickness parameter and the optimal center angle parameter;

[0012] Step 5), output the optimal thickness parameter and the optimal center angle parameter to obtain the permanent magnet design with the optimal permanent magnet usage.

[0013] As a further optimization scheme of the permanent magnet design method with the optimal permanent magnet usage of the present invention, in step 1), the air gap magnetic flux density generated by the i-th unit permanent magnet with the spatial position is solved according to the following formula, where i is a natural number less than or equal to j:

[0014]

[0015] Among them, B δΔi (θ) is the air gap flux density generated by the i-th unit permanent magnet as its spatial position changes; θ is the spatial position angle; B r is the residual magnetic induction intensity of the permanent magnet, δ is the air gap length, θ Δm h is the angle of the center of the circle occupied by the arc length of the unit permanent magnet; Δmi is the thickness of the unit permanent magnet, is the angle between the i-th unit permanent magnet and the permanent magnet center, and n is the harmonic order.

[0016] As a further optimization scheme of the permanent magnet design method with the optimal permanent magnet dosage of the present invention, the expression of the change of the permanent magnet thickness with the spatial position when the permanent magnet dosage reaches the optimal value derived in step 2) is:

[0017]

[0018] Among them, h m (θ) is the thickness of the permanent magnet that changes with the spatial position; C is the thickness parameter of the permanent magnet; the value range of θ is 90°±θm / 2, and θm is the center angle of the permanent magnet arc length.

[0019] As a further optimization scheme of the permanent magnet design method with the best permanent magnet dosage of the present invention, in step 2), the kth harmonic amplitude of the total air gap magnetic flux density generated by the permanent magnet is solved according to the following formula:

[0020]

[0021] Among them, B δk is the kth harmonic amplitude of the total air gap flux generated by the permanent magnet; k is the order of the air gap flux related to the average torque.

[0022] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0023] The present invention uses the concept of micro-element analysis to obtain the permanent magnet thickness expression with the optimal permanent magnet dosage. By adjusting the permanent magnet parameters, the air gap flux amplitude of the order related to the average torque reaches a preset amplitude threshold, thereby reducing the motor design workload and saving motor optimization time. The motor obtained by the permanent magnet optimization method proposed in the present invention can output the expected average torque while reducing the permanent magnet dosage, and has a lower permanent magnet cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a unit permanent magnet of the present invention;

[0025] Figure 2 It is a schematic diagram of the axial cross-sectional structure of the conventional surface-mounted permanent magnet motor rotor and the permanent magnet magnetization direction, permanent magnet thickness and pole arc coefficient parameters;

[0026] Figure 3 The figure is a schematic diagram of the axial cross-sectional structure of the permanent magnet rotor designed by the present invention and the permanent magnet magnetization direction and pole arc coefficient;

[0027] Figure 4 The permanent magnet motor topology structure obtained by the permanent magnet design method of the present invention;

[0028] Figure 5 A comparison diagram of the harmonics of the permanent magnetic field of the embodiment of the present invention and the conventional surface-mounted permanent magnet motor;

[0029] Figure 6 The output torque waveform diagram of the embodiment of the present invention and the traditional surface-mounted permanent magnet motor. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings:

[0031] The present invention can be implemented in many different forms and should not be considered to be limited to the embodiments described herein. On the contrary, these embodiments are provided to make this disclosure thorough and complete, and will fully express the scope of the present invention to those skilled in the art. In the accompanying drawings, components are enlarged for clarity.

[0032] In one embodiment, taking a permanent magnet synchronous motor with a pole pair number p=4 as an example, a permanent magnet design method with an optimal amount of permanent magnets is provided, wherein the permanent magnets are embedded on the surface of a rotor core, and the rotor and the stator are coaxially distributed, and the method is characterized in that the method comprises the following steps:

[0033] Step 1), divide a lower pole permanent magnet into j units along the circumferential direction at equal angles, and the arc length of each unit permanent magnet occupies a circle center angle θ Δm , the air gap magnetic flux generated by the unit permanent magnet with the spatial position is analyzed by analytical method, and the amplitude of each harmonic of the air gap magnetic flux is further analyzed;

[0034] The schematic diagram of the unit permanent magnet is as follows Figure 1 As shown, in step 1), the air gap magnetic flux density generated by the i-th unit permanent magnet with the spatial position is solved according to the following formula:

[0035]

[0036] Among them, B δΔi (θ) is the air gap flux density generated by the i-th unit permanent magnet as the spatial position changes, i ranges from 1 to j; θ is the spatial position angle; B r is the residual magnetic induction intensity of the permanent magnet, δ is the air gap length, θ Δm h is the angle of the center of the circle occupied by the arc length of the unit permanent magnet; Δmi is the thickness of the unit permanent magnet, is the angle between the i-th unit permanent magnet and the permanent magnet center, and n is the harmonic order.

[0037] Step 2), selecting the air gap magnetic flux order k related to the average torque, superimposing and calculating the k-order air gap magnetic flux generated by j unit permanent magnets, and obtaining the k-order harmonic amplitude of the total air gap magnetic flux generated by the permanent magnets;

[0038] Taking the traditional surface-mounted permanent magnet synchronous motor with a permanent magnet thickness of 4 mm, a pole arc coefficient of 0.95, and an air gap length of 1 mm as a benchmark, the axial cross-sectional structure of the rotor and permanent magnet, the magnetization direction of the permanent magnet, the thickness of the permanent magnet, and the pole arc coefficient parameters are shown in the figure below. Figure 2 As shown. The air gap flux order k related to the average torque is 1, which is used as the preset amplitude threshold of the total air gap flux. The total air gap flux fundamental amplitude generated by the traditional surface-mounted permanent magnet is:

[0039]

[0040] Among them, B δic h is the total air gap magnetic flux fundamental amplitude generated by the traditional surface mounted permanent magnet; mc is the thickness of permanent magnets of traditional surface-mounted motors; α pc =θ mc p / π is the permanent magnet pole arc coefficient of the traditional surface-mount motor, where θ c It is the center angle of the circle occupied by the arc length of the surface mounted permanent magnet.

[0041] The axial cross-sectional structure of the permanent magnet rotor designed by the present invention and the schematic diagram of the permanent magnet magnetization direction and pole arc coefficient are shown in FIG. Figure 3 shown.

[0042] In step 2), the kth harmonic amplitude of the total air gap magnetic flux density generated by the permanent magnet is solved according to the following formula:

[0043]

[0044] Among them, B δk is the kth harmonic amplitude of the total air gap flux generated by the permanent magnet; k is the order of the air gap flux related to the average torque.

[0045] Step 3), the expression of the change of the thickness of the permanent magnet with the spatial position when the permanent magnet dosage reaches the optimal value is:

[0046]

[0047] Among them, h m (θ) is the expression of the change of permanent magnet thickness with spatial position; C is the permanent magnet thickness parameter; the value range of θ is 90°±θm / 2, and θm is the center angle occupied by the arc length of the permanent magnet.

[0048] Step 4), when adjusting the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length based on the expression of the change of the permanent magnet thickness with the spatial position when the permanent magnet dosage reaches the optimal level, the thickness of the permanent magnet changes, and the center angle occupied by the arc length of the permanent magnet unit changes accordingly, and the amplitude of each harmonic of the generated air gap magnetic flux also changes accordingly, and the amplitude of the kth harmonic of the total air gap magnetic flux generated by the permanent magnet is also adjusted accordingly;

[0049] Adjust the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length so that the k-th harmonic amplitude of the total air gap magnetic flux density generated by the permanent magnet reaches a preset amplitude threshold, and use the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length at this time as the optimal thickness parameter and the optimal center angle occupied by the permanent magnet arc length;

[0050] Step 5), output the optimal thickness parameter and the center angle occupied by the optimal permanent magnet arc length, and obtain the permanent magnet design with the optimal permanent magnet usage.

[0051] The permanent magnet motor topology structure obtained by the permanent magnet design method of the present invention is as follows: Figure 4 As shown, the permanent magnets include p pairs of permanent magnets, and the number of pairs of permanent magnets can be adjusted; each pair of permanent magnets includes two permanent magnets with different magnetization directions, and 2p permanent magnets are evenly embedded on the outer surface of the rotor core; and the rotor and the stator are coaxially distributed.

[0052] Figure 5 This is a comparison chart of the harmonics of the permanent magnetic field of the embodiment of the present invention and the conventional surface-mounted permanent magnet motor. It can be found that the air gap flux density of the embodiment of the present invention and the conventional surface-mounted permanent magnet motor is compared. The air gap flux density amplitude of the order (fundamental wave) related to the average torque reaches the preset amplitude threshold. Correspondingly, Figure 6 It is a waveform diagram of the output torque of the embodiment of the invention and the traditional surface-mounted permanent magnet motor, with average torques of 11.1Nm and 11.35Nm respectively. The average torque of the embodiment of the invention is increased by 2% compared with the traditional surface-mounted permanent magnet motor; the amount of permanent magnets used in the embodiment of the invention is reduced by 7.2% compared with the traditional surface-mounted permanent magnet motor, which proves that the proposed method can effectively reduce the amount of permanent magnets used and has a lower permanent magnet cost.

[0053] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0054] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A permanent magnet design method with optimal permanent magnet usage, wherein the permanent magnet is embedded in the surface of the rotor core, and the rotor and the stator are coaxially distributed, characterized in that: The following steps are involved: Step 1), divide the permanent magnet into j units along the circumferential direction at equal angles, and the arc length of each unit occupies the center angle θ Δm , the air gap flux density generated by the permanent magnet unit with the spatial position is analyzed by analytical method, and the harmonic amplitudes of the air gap flux density are further analyzed; Step 2), selecting the air gap magnetic flux order k related to the average torque, superimposing and calculating the k-order air gap magnetic flux generated by j unit permanent magnets, and obtaining the k-order harmonic amplitude of the total air gap magnetic flux generated by the permanent magnets; Step 3), deriving an expression for the change of the thickness of the permanent magnet with the spatial position when the amount of the permanent magnet reaches the optimum; Step 4), when adjusting the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length based on the expression of the change of the permanent magnet thickness with the spatial position when the permanent magnet dosage reaches the optimal level, the thickness of the permanent magnet changes, and the center angle occupied by the arc length of the permanent magnet unit changes accordingly, and the amplitude of each harmonic of the generated air gap magnetic flux also changes accordingly, and the amplitude of the kth harmonic of the total air gap magnetic flux generated by the permanent magnet is also adjusted accordingly; Adjust the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length so that the k-th harmonic amplitude of the total air gap magnetic flux density generated by the permanent magnet reaches a preset amplitude threshold, and use the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length at this time as the optimal thickness parameter and the optimal center angle parameter; Step 5), output the optimal thickness parameter and the optimal center angle parameter to obtain the permanent magnet design with the optimal permanent magnet usage.

2. The method for designing a permanent magnet with optimal permanent magnet usage according to claim 1, characterized in that: In step 1), the air gap magnetic flux density generated by the i-th unit permanent magnet with the spatial position is solved according to the following formula, where i is a natural number less than or equal to j: Among them, B δΔi (θ) is the air gap flux density generated by the i-th unit permanent magnet as its spatial position changes; θ is the spatial position angle; B r is the residual magnetic induction intensity of the permanent magnet, δ is the air gap length, θ Δm h is the angle of the center of the circle occupied by the arc length of the unit permanent magnet; Δmi is the thickness of the unit permanent magnet, is the angle between the i-th unit permanent magnet and the permanent magnet center, and n is the harmonic order.

3. The method for designing a permanent magnet with optimal permanent magnet usage according to claim 2, characterized in that: The expression of the change of the thickness of the permanent magnet with the spatial position when the permanent magnet dosage reaches the optimal value derived in step 2) is: Among them, h m (θ) is the thickness of the permanent magnet that changes with the spatial position; C is the thickness parameter of the permanent magnet; the value range of θ is 90°±θm / 2, and θm is the center angle of the permanent magnet arc length.

4. The method for designing a permanent magnet with optimal permanent magnet usage according to claim 3, characterized in that: In step 2), the kth harmonic amplitude of the total air gap magnetic flux density generated by the permanent magnet is solved according to the following formula: Among them, B δk is the kth harmonic amplitude of the total air gap flux generated by the permanent magnet; k is the order of the air gap flux related to the average torque.

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