KR102062461B1 - A skew angle derivation method for reduction of cogging torque of a magnetic geared synchronous motor - Google Patents

Abstract

The present invention relates to a new method for calculating a skew angle which can easily calculate, by equation, an optimal skew angle and a peak to peak value of cogging torque to be applied to a pole piece, a secondary side low-speed rotor, in order to reduce cogging torque in a magnetic geared synchronous motor. More specifically, in the magnetic geared synchronous motor having a double rotor, the present invention relates to a cogging torque reduction type magnetic geared synchronous motor having a skew structure on a pole piece, which includes: an inner rotor composed of a permanent magnet and magnetic substance; and an outer rotor having a pole piece composed of a magnetic material, wherein the pole piece is composed of a plurality of step skews divided in an axis length direction, and a skew angle of the step skew is calculated by equation 2, θ_skew = [360/LCM (N_p, N_pp)] x 1/S = [360/LCM {N_p, (N_s/m/2 + N_p/2)} x 1/S, when applying the step skew to the pole piece of the outer rotor composed of the magnetic material in the axis direction. In equation 2, θ_skew is an optimal skew angle of a magnetic geared synchronous motor, N_pp is the number of pole pieces, m is constant, N_p is the number of rotor poles, N_s is the number of slots, and the LCM is a least common multiple.

Description

Skew angle derivation method for reduction of cogging torque of a magnetic geared synchronous motor

The present invention relates to a new skew angle derivation method which can easily calculate the optimal skew angle and the peak to peak value of the cogging torque to be applied to the pole piece which is the secondary low speed rotor to reduce the cogging torque in the magnetic geared synchronous motor. will be.

In general, in the permanent magnet synchronous motor, the cogging torque is generated due to the non-uniformity of magnetic energy (difference in magnetic resistance (reluctance)) due to the unevenness of the gap between the rotor and the stator including the permanent magnet. If the cogging torque is increased, there is a disadvantage that the noise and vibration increases when the permanent magnet synchronous motor is driven. Therefore, the cogging torque reduction technique is necessary to improve the driving characteristics of the permanent magnet synchronous motor. The same applies to the magnetic geared synchronous motor.

Fig. 1 is a cogging torque reduction type magnetic geared synchronous motor 1 to which a skew structure is not applied. Basically, the magnetic geared synchronous motor 1 has a structure in which a magnetic gear and a synchronous motor are physically coupled as shown in FIG. 1, and the gear ratio is a high speed rotor (permanent magnet 11) when the gear ratio is a reduction ratio. It consists of a 10) and a low-speed rotor 20 (pole piece made of a magnetic material), and consists of a primary side stator 30 and a secondary side high speed rotor 10 to create a magnetic field .

The pole piece (low speed rotor) 21 is located in the air gap between the primary stator 30 and the secondary high speed rotor 10, and serves to modulate the magnetic field in the air gap, and the high speed rotor To generate the torque in the same direction as shown. The speed and torque of the pole piece (low speed rotor) differ depending on the gear ratio, and at the reduction ratio, they have characteristics of low speed and high rotational power (high torque).

Therefore, when applied to propulsion systems with reduction ratios such as automobiles and railway vehicles, the pole piece (low speed rotor) is directly connected to the wheel and driven. The material of the pole piece (low speed rotor) uses ferromagnetic materials such as steel and iron. do. Generally, in case of permanent magnet synchronous motor, skew is applied to the secondary high speed rotor including permanent magnet to reduce cogging torque.

This method has been studied for a long time, and the formula can easily derive the optimal skew angle and cogging torque. However, in the case of magnetic geared synchronous motors, skewing the secondary high speed rotor with permanent magnets may cause complexity in the manufacturing process. It is advantageous.

In general, the permanent magnet synchronous motor that is applied to the traction motor for the propulsion of automobiles or railway vehicles is a large-capacity system, so the slot structure of the primary stator to which the three-phase AC power is supplied has an open structure. The nonuniformity of becomes large and is accompanied by large cogging torque. The same is true for magnetic geared synchronous motors.

2 illustrates a model in which skew is applied to a rotor including a permanent magnet. As shown in FIG. 2, in order to solve such a problem, a method of giving a step skew by dividing the permanent magnet in a predetermined number in the axial length direction to the rotor including the permanent magnet is the most common method, but the secondary rotor Dividing the core and the permanent magnet into steps has a disadvantage that the manufacturing process may be accompanied by difficulties. In addition, if the skew is applied to the permanent magnet included in the secondary rotor, the operating torque is also reduced along with the cogging torque, so it is necessary to select an appropriate skew angle.

When skew is applied to the rotor of a general permanent magnet type synchronous motor, there is a derivation method of calculating the optimum skew angle with the lowest cogging torque value and the cogging torque peak to peak value. However, in the case of magnetic geared synchronous motors, there are two rotors rotating at different speeds, and the optimum skew angle is calculated by mathematical formula in applying skew to the polepiece rotating at low speed. There was no study on the formula to predict peak to peak value.

Korea Patent Registration No. 10-1426169 Korea Patent Registration No. 10-1525222 Korea Patent Registration No. 10-1600835

Therefore, the present invention has been made to solve the above-mentioned conventional problems, according to an embodiment of the present invention as a method that can reduce the cogging torque in a simple structure structurally while minimizing the reduction of the generated torque of the magnetic geared synchronous motor The purpose is to provide a way of applying skew to the piece.

According to an embodiment of the present invention, it is an object of the present invention to provide a method for deriving an optimal skew angle for a model in which step skew is applied in an axial longitudinal direction to a pole piece of a magnetic geared.

In addition, according to an embodiment of the present invention, the optimum skew angle is calculated by a mathematical formula in applying the skew in steps to the pole piece rotating at a low speed with respect to the magnetic geared synchronous motor, and the cogging torque peak to peak generated at this time. The goal is to derive a way to predict the value.

On the other hand, the technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems that are not mentioned are clearly to those skilled in the art from the following description. It can be understood.

An object of the present invention, in the magnetic geared synchronous motor having a dual rotor, the inner rotor consisting of a permanent magnet and a magnetic body; And an outer rotor having a pole piece made of a magnetic material, wherein the pole piece is composed of a plurality of step skews divided in the axial longitudinal direction. It can be achieved as a synchronous motor.

When the step skew is applied to the pole piece of the outer rotor made of magnetic material in the axial length direction, the skew angle of the step skew may be derived by Equation 2 below.

[Equation 2]

In Equation 2, θ _skew is the optimal skew angle of the magnetic geared synchronous motor, N _pp is the number of pole pieces, m is a constant, N _p is the number of rotor poles, N _s is the number of slots, LCM is the least common multiple.

And when step skew is applied to the pole piece of the outer rotor made of the magnetic material in the axial length direction, the cogging torque function is derived by the following equation (4) reduced cogging torque having a skew structure on the pole piece Type Magnetic Geared Synchronous Motor:

[Equation 4]

In Equation 4, T _Total-cog is the cogging torque function, A is the amplitude.

When step skew is applied to the pole piece of the outer rotor made of the magnetic material in the axial length direction, the peak to peak value of the cogging torque may be derived from Equation 5 below.

[Equation 5]

In Equation 5, T _pk2pk is a peak to peak value of the cogging torque function of the magnetic geared synchronous motor.

According to an embodiment of the present invention, in a magnetic geared synchronous motor, a skew angle derivation method of a magnetic geared synchronous motor using a step skew structure is applied to a pole piece of an outer rotor made of a magnetic material rather than an inner rotor including a permanent magnet. It is possible to estimate the optimum skew angle of the pole piece skew structure of the magnetic geared synchronous motor through the presented equation, and to predict the peak to peak value of the cogging torque according to the pole piece skew angle, the present invention By using the mathematical equations presented in the embodiments of the present invention, it is possible to more easily and quickly predict the cogging torque value of the magnetic geared synchronous motor.

On the other hand, the effects that can be obtained in the present invention is not limited to the above-mentioned effects, other effects that are not mentioned will be clearly understood by those skilled in the art from the following description. Could be.

The following drawings, which are attached to this specification, illustrate one preferred embodiment of the present invention, and together with the detailed description thereof, serve to further understand the technical idea of the present invention. It should not be construed as limited.
1 is a cogging torque reduction type magnetic geared synchronous motor without a skew structure,
2 is a model of applying a skew to a rotor including a permanent magnet,
3 is a perspective view of a cogging torque reduction type magnetic geared synchronous motor having a skew structure in a pole piece according to an embodiment of the present invention;
4 is a cross-sectional view of the inner and outer rotors of the magnetic geared synchronous motor according to the embodiment of the present invention;
5 is a perspective view of the inner and outer rotors of the magnetic geared synchronous motor according to the embodiment of the present invention;
6 is a graph showing the peak to peak value variation characteristic of the cogging torque of the outer rotor according to the skew angle of the magnetic geared synchronous motor according to the experimental example of the present invention (4 poles 30 slots),
FIG. 6 is a graph illustrating peak to peak value change characteristics (4 poles and 42 slots) of the cogging torque of the outer rotor according to the skew angle of the magnetic geared synchronous motor according to the experimental example of the present invention.

Objects, other objects, features and advantages of the present invention will be readily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosure may be made thorough and complete, and to fully convey the spirit of the invention to those skilled in the art.

In the present specification, when a component is mentioned as being on another component, it means that it may be formed directly on the other component or a third component may be interposed therebetween. In addition, in the drawings, the thickness of the components are exaggerated for the effective description of the technical content.

Embodiments described herein will be described with reference to cross-sectional and / or plan views, which are ideal exemplary views of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for effective explanation of technical content. Therefore, the shape of the exemplary diagram may be modified by manufacturing techniques and / or tolerances. Accordingly, the embodiments of the present invention are not limited to the specific forms shown, but also include changes in forms generated by the manufacturing process. For example, the region shown at right angles may be round or have a predetermined curvature. Thus, the regions illustrated in the figures have properties, and the shape of the regions illustrated in the figures is intended to illustrate a particular form of region of the device and is not intended to limit the scope of the invention. Although terms such as first and second are used to describe various components in various embodiments of the present specification, these components should not be limited by such terms. These terms are only used to distinguish one component from another. The embodiments described and illustrated herein also include complementary embodiments thereof.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, the words 'comprises' and / or 'comprising' do not exclude the presence or addition of one or more other components.

In describing the specific embodiments below, various specific details are set forth in order to explain the invention more specifically and to help understand. However, one of ordinary skill in the art can understand that the present invention can be used without these various specific details. In some cases, it is mentioned in advance that parts of the invention which are commonly known in the description of the invention and which are not highly related to the invention are not described in order to prevent confusion in explaining the invention without cause.

Hereinafter, the configuration and function of the cogging torque reduction type magnetic geared synchronous motor 100 having a skew structure on the pole piece according to an embodiment of the present invention will be described. 3 is a perspective view of a cogging torque reducing magnetic geared synchronous motor having a skew structure in a pole piece according to an exemplary embodiment of the present invention. 4 is a cross-sectional view of the inner and outer rotors of the magnetic geared synchronous motor according to the embodiment of the present invention. In addition, Figure 5 shows a perspective view of the inner and outer rotor of the magnetic geared synchronous motor according to an embodiment of the present invention.

FIG. 1 mentioned above shows a magnetic geared synchronous motor having no skew structure applied to the secondary inner rotor and the outer rotor. In the case of the magnetic geared synchronous motor having such a structure, there is a limit in reducing cogging torque. Therefore, the embodiment of the present invention adopts the structure of FIG. 3 in which step skew is applied to the secondary side low speed rotor pole piece 21 to reduce cogging torque.

4 shows a cross-sectional view of the pole piece 21 of the inner rotor and outer rotor 20 composed of the secondary permanent magnet 11 and the magnetic body 12 of the magnetic geared synchronous motor 100, and the low speed rotor. It is a structure in which the pole piece 21 is divided into three in the axial length direction and skew is applied. The structure of the magnetic flux is uniformly distributed in the air gap, thereby reducing the cogging torque.

As shown in FIG. 4, the pole pieces 21 are divided into three equal parts in the axial direction, and the pole pieces 21 in the axial directions ① and ③ are stiffened with respect to 0 ° of the center pole piece ② as shown in FIG. 4. It is a structure that twists θ, -θ about the central axis. The pole piece 21 can be divided into three or more in the axial length direction.

The cogging torque optimum skew angle equation of a general synchronous motor is shown in Equation 1 below.

[Equation 1]

: 코깅토크의 1주기)(θ _O-skew : Optimal skew angle of conventional synchronous motor, N _p : Number of rotor poles, N _s : Number of slots, LCM: Minimum common multiple, S: Number of divisions in the longitudinal direction of the rotor (permanent magnet),

: 1 cycle of cogging torque)

Cogging torque occurs in the case of synchronous motors due to the difference in magnetoresistance (reluctance) in the gap between the rotor with permanent magnets and the stator with slots.

However, in the case of the magnetic geared synchronous motor 100, the low speed rotor 20 composed of the pole pieces 21 is positioned between the high speed rotor 10 including the permanent magnet 11 and the slot of the stator 30. Overall, the air gap is much larger than conventional synchronous motors.

Therefore, the nonuniformity of the magnetoresistance (reluctance) in the air gap is different from the conventional synchronous motor, and the high speed rotation in which the pole piece 21 and the permanent magnet 11 are included in the outer air gap between the stator 30 and the pole piece 21. Since it appears large in the inner gap between the electron 10, it can be confirmed that the influence of the number of slots of the stator 30 in the equation of deriving the optimal skew angle of the conventional synchronous motor does not need to be considered.

Therefore, in the embodiment of the present invention, the magnetoresistance difference in the air gap between the pole piece 21 of the secondary low speed rotor 20 of the magnetic geared synchronous motor 100 and the permanent magnet 11 of the high speed rotor 10. The following Equation 2 is proposed to derive the optimal pole piece skew angle.

[Equation 2]

In Equation 2, θ _skew is the optimal skew angle of the magnetic geared synchronous motor, N _pp is the number of pole pieces, m is a constant, N _p is the number of rotor poles, N _s is the number of slots, LCM is the least common multiple.

The number of pole pieces 21 of the magnetic geared synchronous motor 100 may be represented by the sum of the number of pole pairs of the stator 30 and the number of rotor poles, and the number of poles of the stator 30 is equal to the number of slots divided by a constant.

A general cogging torque equation may be expressed as a cosine function over time, and when converted into a function of angle, it is expressed as Equation 3 below.

[Equation 3]

(Tcog: cogging torque function, ω: angular velocity, t: time, T: period, θ: phase angle)

At this time, the pole piece 3 ② center to the pole piece and the pole piece ③ ① ② each pole piece relative to the _skew -θ, θ _skew by the skew when it is assumed that each of the movement, the geared magnetic synchronous motor (100) The cogging torque according to the skew angle of is the average of the sum of the cogging torque equations of pole pieces ②, ① and ③ can be calculated as shown in Equation 4 below.

[Equation 4]

In Equation 4, T _Total-cog is the cogging torque function, A is the amplitude.

을 상수 취급할 수 있다. Equation 4 is a linear equation in which θ and θ _skew are variables, and means a cogging torque function when the skew angle θ _skew is used. Given the skew angle θ _skew , the cogging torque function is determined.

Can be treated as a constant.

Therefore, the cogging torque function in the above equation is assumed to be a perfect sine wave, so the cogging torque value is the minimum or maximum point at the phase angle. Therefore, the maximum peak to peak value of the cogging torque according to the skew angle of the magnetic geared synchronous motor 100 is expressed by Equation 5 below.

[Equation 5]

In Equation 5, T _pk2pk is a peak to peak value of the cogging torque function of the magnetic geared synchronous motor.

Hereinafter, an experimental example of a cogging torque reduction type magnetic geared synchronous motor having a skew structure in a pole piece according to an embodiment of the present invention will be described. FIG. 6 is a graph illustrating peak to peak value change characteristics (30 poles of 4 poles) of the cogging torque of the outer rotor according to the skew angle of the magnetic geared synchronous motor according to the experimental example of the present invention, and FIG. Fig. 4 shows a graph of peak-to-peak variation of the cogging torque of the outer rotor according to the skew angle of the magnetic geared synchronous motor according to the experimental example (4 poles and 42 slots).

The cogging torques of magnetic pole geared synchronous motors of 4 poles 30 slots and 4 poles 42 slots of Surface Permanent Magnet (SPM) type were analyzed for the above mentioned equations.

6 is a graph showing the results obtained by numerical analysis (Finite Element Method, hereinafter FEM) and mathematical formula of the peak to peak value of the cogging torque according to the skew angle change in the 4-pole 30 slot model, FIG. This is a graph showing the results obtained by FEM and mathematical equations of peak to peak of cogging torque according to skew angle change in 42-pole model.

As shown in the graphs of Figs. 6 and 7, it can be seen that the cogging torque prediction value according to the skew angle change by the mathematical equation presented in the embodiment according to the present invention is similar to the result obtained using the FEM. It can be estimated that the peak to peak value of the cogging torque according to the change of the pole piece skew angle of the magnetic geared synchronous motor can be estimated similarly, and the optimum skew angle of the smallest peak to peak value of the cogging torque can be derived. Can be.

In addition, the above-described apparatus and method may not be limitedly applied to the configuration and method of the above-described embodiments, the embodiments may be a combination of all or part of each embodiment selectively so that various modifications may be made It may be configured.

1: Conventional Magnetic Geared Synchronous Motor
10: inner rotor
11: Permanent magnet
12: Magnetic material
20: Outer rotor
21: pole piece
30: stator
100: Cogging torque reduction type magnetic geared synchronous motor with skew structure on pole piece

Claims (4)

In a Makine Geared Synchronous Motor with a double rotor,
An inner rotor composed of a permanent magnet and a magnetic body; And
An outer rotor having a pole piece made of a magnetic material, the pole piece is composed of a plurality of step skew divided in the axial longitudinal direction,
When the step skew is applied to the pole piece of the outer rotor made of the magnetic material in the axial length direction, the skew angle of the step skew is derived by Equation 2 below. Cogging Torque Reduced Magnetic Geared Synchronous Motor:
[Equation 2]

In Equation 2, θ _skew is the optimal skew angle of the magnetic geared synchronous motor, N _pp is the number of pole pieces, m is a constant, N _p is the number of rotor poles, N _s is the number of slots, LCM is the least common multiple.
delete The method of claim 1,
When step skew is applied to the pole piece of the outer rotor made of the magnetic material in the axial length direction, the cogging torque function is derived from Equation 4 below. Magnetic Geared Synchronous Motor:
[Equation 4]

In Equation 4, T _Total-cog is the cogging torque function, A is the amplitude.
The method of claim 3, wherein
When step skew is applied to the pole piece of the outer rotor made of the magnetic material in the axial length direction, the peak to peak value of the cogging torque is derived from Equation 5 below. Cogging Torque Reduced Magnetic Geared Synchronous Motor:
[Equation 5]

In Equation 5, T _pk2pk is a peak to peak value of the cogging torque function of the magnetic geared synchronous motor.

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