Rotor Structure for Weakening Cogging Torque of Surface Mounted Permanent Magnet Motor and Weakening Analysis Method

Abstract

The present invention provides a rotor structure and a weakening analysis method for weakening the cogging torque of a surface-mounted permanent magnet motor. In this rotor structure, the rotor permanent magnet in the prior art is divided into two parts, namely a first permanent magnet and a second permanent magnet. In this method, by assigning different characteristic value points to the second permanent magnet, the motor including this rotor structure is simulated to obtain the cogging torque, output power and air-gap magnetic flux density of the motor corresponding to the characteristic value points. After removing the unqualified characteristic value points, the motor is simulated again within the value range to analyze the change of the cogging torque of the motor. The present invention can enhance the air-gap magnetic flux density of the motor and improve the torque density; under the condition of the same motor performance, it can save motor materials and reduce the processing cost; without increasing the motor materials, the cogging torque of the motor can be reduced by 70.8%.

Description

Technical Field

[0001] The present invention belongs to the field of permanent magnet motors, and particularly relates to a rotor structure for weakening the cogging torque of a surface-mounted permanent magnet motor and a weakening analysis method. Background Art

[0002] The surface-mounted permanent magnet motor has the advantages of simple process structure, low processing cost, and the ability to improve the performance of the motor by adjusting the shape of the permanent magnet, so it is used in many occasions. However, the surface-mounted permanent magnet motor has a larger cogging torque, which is generated by the interaction between the permanent magnet and the stator teeth; since the cogging torque inevitably exists during the rotation of the permanent magnet motor, the cogging torque will affect the control accuracy of the motor at low speeds, and the cogging torque will cause vibration and noise at high speeds. The methods proposed in the industry to suppress the cogging torque mainly include: 1) On the stator side: changing the shape of the stator teeth, unequal slot widths, closed slots, skewed slots, and opening auxiliary slots, etc.; 2) On the rotor side: changing the pole arc coefficient of the magnetic pole, magnetic pole eccentricity, unequal pole arc coefficient combination, skewed poles, and unequal thickness permanent magnets, etc.

[0003] It can be seen that many methods proposed in the prior art can effectively reduce the cogging torque of the motor, but these methods have the following defects: 1) increasing the processing cost of permanent magnet materials and the scrap rate of permanent magnet materials; 2) weakening the air-gap magnetic flux density of the motor, so it will inevitably affect the torque density and other basic performance of the motor. Summary of the Invention

[0004] The purpose of the present invention is to provide a rotor structure for weakening the cogging torque of a surface-mounted permanent magnet motor and a weakening analysis method, including a motor with this rotor structure, which can achieve a reduction in the cogging torque of the motor under the same stator or the same motor materials and motor performance. At the same time, it can enhance the air-gap magnetic flux density of the motor and improve the torque density; under the condition of ensuring the same motor performance, it can save motor materials and reduce the processing cost.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A rotor structure for weakening the cogging torque of a surface-mounted permanent magnet motor, comprising: a rotor core and a plurality of magnetic steel groups arranged in sequence along the inner circumference of the rotor core; the rotor core is arranged along the outer circumference of the stator core;

[0007] The central angle corresponding to the first magnetic steel is greater than the central angle corresponding to the second magnetic steel.

[0008] Preferably, the central angle corresponding to the first magnetic steel is β, and the central angle corresponding to the second magnetic steel is in the range of: 0.05β to 0.3β.

[0009] Preferably, along the radial direction of the stator core, the length of the first permanent magnet is equal to the length of the second permanent magnet.

[0010] A method for analyzing the reduction of cogging torque of a surface-mounted permanent magnet motor, adopting the rotor structure for reducing the cogging torque of the surface-mounted permanent magnet motor, includes the following steps:

[0011] Step 1: Establish a two-dimensional simulation model of the motor;

[0012] Step 2: Set a number of characteristic value points, where one characteristic value point is 0°, and assign all the characteristic value points to the central angle α corresponding to the second permanent magnet respectively:

[0013] Step 3: Simulate the motor simulation model in Step 1 through MotorSolve motor simulation software to obtain the cogging torque, motor output power, and motor air-gap flux density corresponding to each characteristic value point;

[0014] Step 4: Sort the cogging torques of the motor corresponding to each characteristic value point;

[0015] Step 5: Compare the motor output powers corresponding to each characteristic value point, and eliminate the characteristic value points with motor output power less than the rated power;

[0016] Step 6: Compare the motor air-gap flux densities corresponding to the remaining characteristic value points, and sort the motor air-gap flux densities;

[0017] Step 7: Eliminate the characteristic value point 0°, then randomly take values within the value range formed by all the remaining characteristic value points, and assign them to the central angle α corresponding to the second permanent magnet, and then simulate the motor simulation model in Step 1 through MotorSolve motor simulation software to obtain the cogging torque of the motor corresponding to the selected characteristic value point;

[0018] Step 8: Repeat Step 7 until the cogging torque corresponding to the value range is obtained;

[0019] Step 9: Compare all the cogging torques obtained in Step 8 with the cogging torque of the motor corresponding to the characteristic value point 0° in Step 4 to analyze the cogging torque obtained in Step 8.

[0020] Preferably, in Step 2, the central angle β corresponding to the first permanent magnet and the central angle α corresponding to the second permanent magnet, where α = 0β, 0.05β, 0.1β, 0.15β, 0.2β, 0.25β, 0.3β, 0.35β.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] (1) The second magnet effectively compensates the magnetic flux concentrating effect of the first magnet, thus enhancing the air-gap magnetic flux density of the motor. At the same time, the second magnet can significantly improve the sinusoidality of the air-gap magnetic flux density. Therefore, for the motor with this rotor structure, when the stator is the same or the motor materials and motor performance are the same, the cogging torque of the motor can be reduced.

[0023] (2) Under the condition of the same motor performance, the motor materials (the lamination thickness of the stator and rotor silicon steel sheets, the length of the magnetic tile) can be saved, and the processing cost can be reduced. When the central angle of the second magnet is 0.15β, the performance of the motor remains unchanged, and the processing cost can be reduced by 2%. Specifically, the magnetic energy product of the first magnet decreases as the central angle of the second magnet increases, and the increase of the central angle of the second magnet can provide greater magnetic flux concentrating energy for the first magnet. Therefore, when the central angle of the second magnet is 0.15β, the intersection point of the two curves is the optimal point of the motor performance. At this time, a part of the motor performance can be sacrificed to reduce the cost.

[0024] (3) It can not only reduce the cogging torque of the motor, but also improve the performance of the motor to a certain extent, thus effectively avoiding the operation of inevitably reducing the motor performance in the prior art to reduce the cogging torque. Description of the Drawings

[0025] Figure 1 is a schematic diagram of the rotor structure in the prior art;

[0026] Figure 2 is a schematic diagram of the rotor structure of the surface-mounted permanent magnet motor with reduced cogging torque according to an embodiment of the present invention;

[0027] Figure 3 is Figure 2 a partial schematic diagram;

[0028] Figure 4 is including Figure 2 the air-gap magnetic flux density simulation curve diagrams of the rotor structure in

[0029] Figure 5 is including Figure 2 the cogging torque simulation curve diagrams of the rotor structure in

[0030] Figure 6 is the simulation curve diagram of the magnetic flux density when α = 0β;

[0031] Figure 7 is the simulation curve diagram of the magnetic flux density when α = 0.35β.

[0032] Among them, 1 - stator core, 2 - rotor core, 3 - magnet, 4 - first magnet, 5 - second magnet. Detailed Embodiments

[0033] The present invention will be described in more detail below with reference to the schematic diagrams, in which the preferred embodiments of the present invention are shown. It should be understood that those skilled in the art can modify the present invention described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as a broad guidance for those skilled in the art and not as a limitation on the present invention.

[0034] As Figure 2 and Figure 3 shown, this embodiment proposes a rotor structure for weakening the cogging torque of a surface-mounted permanent magnet motor, including: a rotor core 2 and a plurality of magnet groups arranged in sequence along the inner circumference of the rotor core 2 (rotor); the rotor core 2 is arranged along the outer circumference of the stator core 1 (stator). The arrangement of the first magnet 4 and the second magnet 5 is as Figure 3 shown.

[0035] Any magnet group is bonded to the rotor.

[0036] In this embodiment, the second magnet 5 is named a flux concentrating magnet. The material of the second magnet 5 is the same as that of the magnet in the prior art, but the magnetization direction is different.

[0037] In any magnet group, the central angle corresponding to the first magnet 4 is greater than the central angle corresponding to the second magnet 5 (flux concentrating magnet).

[0038] Different from the rotor structure in the prior art, the magnet group in this embodiment is equivalent to the magnet 3 in the prior art, as Figure 1 shown.

[0039] In this embodiment, the central angle corresponding to the first magnet 4 is β, and the central angle corresponding to the second magnet 5 is in the range of: 0.05β to 0.3β.

[0040] In this embodiment, along the radial direction of the stator core 1, the length of the first magnet 4 is equal to the length of the second magnet 5.

[0041] This embodiment also proposes a method for analyzing the weakening of the cogging torque of a surface-mounted permanent magnet motor. Based on a motor simulation model, the motor simulation model adopts the above rotor structure for weakening the cogging torque of a surface-mounted permanent magnet motor. Specifically, it includes the following steps:

[0042] Step 1: Establish a two-dimensional simulation model of the motor through the MotorSolve motor simulation software.

[0043] As is known to those skilled in the art, this motor simulation model is for a permanent magnet motor in the prior art ( Figure 1) The difference lies only in the rotor structure. That is, the motor simulation model includes a rotor structure for weakening the cogging torque of the surface-mounted permanent magnet motor, a stator core 1, a fixed shaft, and a hub housing. A bearing is provided between the fixed shaft and the hub housing; the stator core 1 is sleeved on the fixed shaft; the rotor core 2 is arranged on the inner wall surface of the hub housing, and the rotor core 2 can rotate relative to the fixed shaft following the hub housing.

[0044] Step 2: Set 8 characteristic value points, one of which is 0°, and assign all the characteristic value points to the central angle α corresponding to the second permanent magnet 5 respectively. That is, set the central angle α of the second permanent magnet as a variable. When the α angle is 0°, it is the normal structure of the motor. At this time, assign all the characteristic value points from 0.05β to 0.35β to the central angle corresponding to the second permanent magnet.

[0045] Specifically, the central angle β corresponding to the first permanent magnet 4 and the central angle α corresponding to the second permanent magnet 5, where α = 0β, 0.05β, 0.1β, 0.15β, 0.2β, 0.25β, 0.3β, 0.35β.

[0046] Step 3: Simulate the motor simulation model in Step 1 through MotorSolve motor simulation software to obtain the motor cogging torque, motor output power, and motor air-gap flux density corresponding to each characteristic value point. The technology of simulating through MotorSolve belongs to the prior art and will not be elaborated here.

[0047] Step 4: Sort the motor cogging torques corresponding to the 8 characteristic value points from large to small to preliminarily study the relationship between the characteristic value points and the corresponding motor cogging torques.

[0048] The motor cogging torque values corresponding to the 8 characteristic value points are T 0β 、T 0.05β 、T 0.1β 、T 0.15β 、T 0.2β 、T 0.25β 、T 0.3β and T 0.35β ; Sort the motor cogging torques of the 8 characteristic value points from small to large, then it is: T 0.35β < T 0.3β < T 0.25β < T 0.15β < T 0.2β < T 0.1β < T 0.05β < T 0β . Among them, when α = 0β, the motor simulation model in Step 1 can be regarded as the motor simulation model in Figure 1 .

[0049] Step 5: Compare the motor output powers corresponding to each characteristic value point, and eliminate the characteristic value points with motor output power less than the rated power.

[0050] Compare the motor output powers corresponding to the 8 characteristic value points. It is found that when the central angle α of the second permanent magnet 5 takes 0.35β, the motor output power is already less than the rated power. Therefore, eliminate the characteristic value point of 0.35β.

[0051] When the central angle α of the second permanent magnet 5 is 0.3β, the motor output power is basically the same as when α = 0β. When the central angle α of the second permanent magnet 5 takes 0.15β, the motor output power at this time increases by 2% compared to α = 0β; when the central angle α of the second permanent magnet 5 is 0.3β, the cogging torque of the motor is in the optimal state, and it is only 29.2% of the cogging torque when α = 0β.

[0052] Step 6: Compare the motor air-gap flux densities corresponding to the remaining characteristic value points, and sort the motor air-gap flux densities to preliminarily study the relationship between the characteristic value points and the corresponding motor air-gap flux densities.

[0053] The motor air-gap flux densities of the remaining 7 characteristic value points are B 0β 、B 0.05β 、B 0.1β 、B 0.15β 、B 0.2β 、B 0.25β and B 0.3β ; Sort the motor air-gap flux densities of the remaining 7 characteristic value points from large to small, then it is: B 0.25β >B 0.3β >B 0.2β >B 0.15β >B 0.1β >B 0.05β >B 0β . Thus, it can be seen that the presence of the second permanent magnet 5 can significantly increase the motor air-gap flux density, improve the motor air-gap flux waveform, and thus optimize the cogging torque.

[0054] Step 7: Cogging torque verification.

[0055] Eliminate the characteristic value point of 0°, take any value within the value range formed by the remaining 6 characteristic value points, and assign it to the central angle α of the second permanent magnet 5. Then, simulate the motor simulation model in Step 1 through the MotorSolve motor simulation software to obtain the motor cogging torque corresponding to the selected characteristic value point.

[0056] In this embodiment, the value range of the central angle α, that is, excluding 0β, and the value range composed of the remaining 6 characteristic value points is 0.05β to 0.3β.

[0057] Step 8: Repeat Step 7 until the cogging torque of the motor corresponding to the value range is obtained.

[0058] Step 9: Compare all the cogging torques of the motor obtained in Step 8 with the cogging torque T of the motor in Step 4 0β to analyze the other cogging torques of the motor obtained in Step 8.

[0059] As Figure 3 , 4 shown, C1 is the flux density simulation curve of the permanent magnet motor in Figure 2 , where α = 0β; C2 is the flux density simulation curve of the permanent magnet motor in Figure 2 , where α = 0.3β; It can be seen that the maximum value of the flux density of the C2 curve is 1.2 times that of the maximum value of the flux density of the C1 curve.

[0060] As Figure 5 shown, D1 is the cogging torque simulation curve of the permanent magnet motor in Figure 2 , where α = 0β; D2 is the cogging torque simulation curve of the Figure 2 permanent magnet motor, where α = 0.3β; It can be seen that the maximum value of the cogging torque of the D2 curve is 29.2% of the maximum value of the cogging torque of the D1 curve.

[0061] Based on the simulation of 6 points, it is found that the cogging torques of other magnet-concentrating magnet steel value points fluctuate within 29.2% - 76.8% of the motor cogging torque T 0β . At the same time, under the action of the magnet-concentrating effect of the second magnet 5, the performance of the motor can be improved by up to 2%, meeting the design requirements.

[0062] When the cost of the motor is the lowest, the central angle α corresponding to the second magnet 5 is 0.15β; when the cogging torque needs to be the smallest, the central angle α corresponding to the second magnet 5 is 0.3β.

[0063] Figure 6 In Figure 7 , α = 0β, and there is no second magnet 5 at this time; Figure 6 and Figure 7 It can be known by comparison: The second magnet can significantly improve the sinusoidality of the air-gap flux density of the motor. In Figure 6 and Figure 7 , the corresponding test conditions are the same, that is, the radius is 67.3 mm, the starting angle is 72°, the ending angle is 108°, and the center coordinates are (0, 0, 0) mm.

[0064] In summary, the weakening analysis method and the motor of this embodiment have the following advantages:

[0065] (1) The second permanent magnet 5 effectively compensates the magnetic flux concentrating effect of the first permanent magnet 4, so it can enhance the air-gap magnetic flux density of the motor and increase the torque density. At the same time, for the motor with this rotor structure, when the stator is the same or the motor materials and motor performance are the same, the cogging torque of the motor can be reduced.

[0066] Specifically, in the present invention, the permanent magnet in the rotor structure in the prior art is split into the first permanent magnet 4 and the second permanent magnet 5. The presence of the second permanent magnet 5 can significantly increase the air-gap magnetic flux density of the motor and improve the air-gap magnetic flux waveform of the motor, thus optimizing the cogging torque. As the central angle α of the second permanent magnet 5 increases, the cogging torque of the motor gradually decreases, and the output power of the motor first increases and then starts to decrease; when the central angle α of the second permanent magnet 5 = 0.3β, the performance of the motor is the same as that of the original motor without the second permanent magnet 5, and the cogging torque of the motor is 29.2% of the cogging torque T 0β of the original motor, as obtained from Figure 5 this.

[0067] (2) Under the condition of the same motor performance, the motor materials (the stack thickness of the stator and rotor silicon steel sheets, the length of the magnetic tile) can be saved, and the processing cost can be reduced. When the central angle α of the second permanent magnet 5 = 0.15β, the performance of the motor (such as the rated power of the motor, etc.) remains unchanged, and the processing cost can be reduced by 2%.

[0068] (3) It can not only reduce the cogging torque of the motor, but also improve the performance of the motor to a certain extent. Thus, it can effectively avoid the operation of inevitably reducing the motor performance in the prior art to reduce the cogging torque.

[0069] The above is only the preferred embodiment of the present invention, and it does not impose any limitation on the present invention. Any person skilled in the art, without departing from the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solution and technical content disclosed by the present invention, all of which belong to the content of not departing from the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. A method for analyzing and weakening the cogging torque of a surface-mounted permanent magnet motor, wherein a rotor structure is provided inside the cogging torque of the motor, and it includes: A rotor core and a plurality of magnetic steel groups arranged in sequence along the inner circumference of the rotor core; the rotor core is arranged along the outer circumference of the stator core; the center angle corresponding to the first magnetic steel is greater than the center angle corresponding to the second magnetic steel; the center angle corresponding to the first magnetic steel is β, and the center angle corresponding to the second magnetic steel has a value range of: 0.05β~0.3β; along the radial direction of the stator core, the length of the first magnetic steel is equal to the length of the second magnetic steel, characterized in that the weakening analysis method comprises the following steps: Step 1: Establish a two-dimensional simulation model of the motor; Step 2: Set a number of characteristic value points, one of which is 0°, and assign all characteristic value points to the central angle α corresponding to the second magnetic steel; Step 3: Use MotorSolve motor simulation software to simulate the motor simulation model in step 1 to obtain the motor cogging torque, motor output power and motor air gap flux density corresponding to each characteristic value point; Step 4: Sort the motor cogging torque corresponding to each characteristic value point; Step 5: Compare the motor output powers corresponding to the characteristic value points, and eliminate the characteristic value points where the motor output power is less than the rated power; Step 6: Compare the motor air gap flux densities corresponding to the remaining characteristic value points, and sort the motor air gap flux densities; Step 7: Eliminate the characteristic value point 0°, then select any value within the value range formed by all the remaining characteristic value points, and assign it to the center angle α corresponding to the second magnetic steel, and then simulate the motor simulation model in step 1 through the MotorSolve motor simulation software to obtain the motor cogging torque corresponding to the selected characteristic value point; Step 8: Repeat step 7 until the motor cogging torque corresponding to the value range is obtained; Step 9: Compare all the motor cogging torques obtained in step 8 with the motor cogging torques corresponding to the characteristic value point of 0° in step 4 to analyze the motor cogging torques obtained in step 8.

2. The method for analyzing and weakening the cogging torque of the surface-mounted permanent magnet motor according to claim 1, wherein In step 2, α=0β, 0.05β, 0.1β, 0.15β, 0.2β, 0.25β, 0.3β, 0.35β.

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