A permanent magnet design method with optimal permanent magnet usage

Abstract

The present invention discloses a permanent magnet design method with optimal permanent magnet usage. The method divides a permanent magnet into j units along the circumferential direction at equal angles, uses an analytical method to analyze the air gap flux density and each harmonic amplitude generated by the unit permanent magnets; solves the expression of the change of the permanent magnet thickness with the spatial position to achieve the optimal permanent magnet usage; superimposes and calculates the k-order air gap flux density related to the average torque generated by the j unit permanent magnets to obtain the k-order harmonic amplitude of the total air gap flux density generated by the permanent magnets; adjusts the permanent magnet parameters so that the total air gap flux density amplitude of the order related to the average torque reaches a preset amplitude threshold; finally, outputs the optimal permanent magnet parameters to obtain a permanent magnet design with optimal magnet usage. Utilizing the permanent magnet design method of the present invention, the motor can output a preset average torque while effectively reducing the permanent magnet usage, thereby improving the utilization rate of the permanent magnets and reducing the permanent magnet usage and corresponding cost in the motor.

Description

Technical Field

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

[0002] Permanent magnet synchronous motors use permanent magnets instead of field windings, eliminating brushes and commutators. This improves motor reliability while reducing excitation losses, thereby increasing motor efficiency and power density. In recent years, high-performance permanent magnet motors have been widely used in automotive, renewable energy power generation, aerospace, industrial drives, and other fields.

[0003] Permanent magnet synchronous motors also consist of a stator, rotor, housing, end caps, and other components. The stator is essentially the same as an asynchronous induction motor and generally adopts a laminated design to reduce core iron loss. The rotor core can be solid or laminated. The rotor of a permanent magnet synchronous motor can utilize a surface-mounted permanent magnet structure. These magnets are typically tile-shaped and located on the rotor surface. These magnets offer advantages such as a simple structure, high power density, and high efficiency, significantly improving 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 significant proportion of the motor's material cost. Furthermore, the mining, production, and processing of rare earth permanent magnet materials can have adverse environmental impacts. Therefore, research on reducing the use of rare earth permanent magnets in permanent magnet motors is of great significance for reducing the amount of rare earth permanent magnets used and improving their utilization. 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 for optimizing permanent magnet usage, wherein the permanent magnet is embedded in the surface of a rotor core, and the rotor and stator are coaxially distributed, comprises the following steps:

[0007] Step 1) Divide the permanent magnet into j units along the circumferential direction at equal angles. The arc length of each unit occupies an angle of θ around the center of the circle. Δm , using analytical methods to analyze the air gap magnetic flux generated by the permanent magnet unit with the spatial position, and further analyze to obtain the amplitude of each harmonic of the air gap magnetic flux;

[0008] Step 2) Select the air gap flux order k related to the average torque, and perform superposition calculation on the k-order air gap flux generated by j unit permanent magnets to obtain the k-order harmonic amplitude of the total air gap flux generated by the permanent magnets;

[0009] Step 3), deriving an expression for how the thickness of the permanent magnet changes with its spatial position when the amount of the permanent magnet reaches the optimal value;

[0010] Step 4) When the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length are adjusted based on the expression of the change in 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, 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 amplitude of the kth harmonic 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 parameters and the optimal center angle parameters to obtain the permanent magnet design with the optimal permanent magnet usage.

[0013] As a further optimization scheme of the permanent magnet design method for optimizing the amount of permanent magnets 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 for achieving the optimal permanent magnet dosage of the present invention, the expression for 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 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 occupied by the arc length of the permanent magnet.

[0019] As a further optimization scheme of the permanent magnet design method for optimizing the amount of permanent magnets of the present invention, in step 2), the amplitude of the kth harmonic 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 density generated by the permanent magnet; k is the order of the air gap flux density 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 infinitesimal elements to analytically obtain an expression for the thickness of a permanent magnet with the optimal amount of permanent magnets. By adjusting the parameters of the permanent magnets, the air gap flux amplitude of the order related to the average torque reaches a preset amplitude threshold, thereby reducing the workload of motor design and saving motor optimization time. The motor obtained by using the permanent magnet optimization method proposed in the present invention can output the desired average torque while reducing the amount of permanent magnets used, thereby having a lower permanent magnet cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of a unit permanent magnet of the present invention;

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

[0026] Figure 3 A schematic diagram of the axial cross-sectional structure of the permanent magnet rotor designed using the present invention, as well as the permanent magnet magnetization direction and pole arc coefficient;

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

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

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

[0030] The technical solution of the present invention is further described in detail below with reference to 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 convey the scope of the invention to those skilled in the art. In the accompanying drawings, components are enlarged for clarity.

[0032] In one embodiment, a permanent magnet synchronous motor with a pole pair number p=4 is used as an example, and a permanent magnet design method for optimizing the amount of permanent magnets is provided. The permanent magnets are embedded on the surface of the rotor core, and the rotor and stator are coaxially distributed. The method is characterized by comprising the following steps:

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

[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 along 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, and the value of 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) Select the air gap flux order k related to the average torque, and perform superposition calculation on the k-order air gap flux generated by j unit permanent magnets to obtain the k-order harmonic amplitude of the total air gap flux generated by the permanent magnets;

[0038] Taking the traditional surface-mounted permanent magnet synchronous motor with a permanent magnet thickness of 4mm, a pole arc coefficient of 0.95, and an air gap length of 1mm as a benchmark, the axial cross-sectional structure of the rotor and permanent magnet, as well as the parameters of the permanent magnet magnetization direction, permanent magnet thickness, and pole arc coefficient 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 fundamental wave amplitude of the total air gap magnetic flux density generated by the traditional surface-mounted permanent magnet; mc is the thickness of permanent magnets in conventional surface-mount motors; α pc =θ mc p / π is the pole arc coefficient of permanent magnets in conventional surface-mount motors, where θ c It is the angle of the center 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 amplitude of the kth harmonic 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 density generated by the permanent magnet; k is the order of the air gap flux density related to the average torque.

[0045] In step 3), the expression of the change of the permanent magnet thickness 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 the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length are adjusted based on the expression of the change in 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, 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 amplitude of the kth harmonic of the total air gap magnetic flux 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 to obtain the permanent magnet design with the optimal permanent magnet usage.

[0051] The permanent magnet motor topology 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 is adjustable; 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 stator are coaxially distributed.

[0052] Figure 5 This is a comparison of the harmonics of the permanent magnetic field of the embodiment of the present invention and the traditional surface-mounted permanent magnet motor. It can be found that the air gap flux density of the embodiment of the present invention and the traditional 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. Figure 6 This is a waveform diagram of the output torque of the embodiment of the invention and the traditional surface-mounted permanent magnet motor. The average torques are 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 commonly 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 their meanings in the context of the prior art and, unless defined as such, will not be interpreted in an idealized or overly formal sense.

[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 for optimizing the amount of permanent magnets, wherein the permanent magnets are embedded in the surface of the rotor core, and the rotor and 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. The arc length of each unit occupies an angle of θ around the center of the circle. Δm , the analytical method is used to analyze the air gap magnetic flux generated by the permanent magnet unit with the spatial position, and further analyze the amplitude of each harmonic of the air gap magnetic flux; Step 2) Select the air gap flux order k related to the average torque, and perform superposition calculation on the k-order air gap flux generated by j unit permanent magnets to obtain the k-order harmonic amplitude of the total air gap flux generated by the permanent magnets; Step 3), deriving an expression for how the thickness of the permanent magnet changes with its spatial position when the amount of the permanent magnet reaches the optimal value; Step 4) When the permanent magnet thickness parameter C and the center angle θm occupied by the permanent magnet arc length are adjusted based on the expression of the change in 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, 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 amplitude of the kth harmonic 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 parameters and the optimal center angle parameters 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 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, wherein: 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: Among them, h m (θ) is the thickness of the permanent magnet that changes with 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 occupied by the arc length of the permanent magnet.

4. The method for designing a permanent magnet with optimal permanent magnet usage according to claim 3, wherein: In step 2), the amplitude of the kth harmonic 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 density generated by the permanent magnet; k is the order of the air gap flux density related to the average torque.

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