KR101367222B1 - Permanent magnet syschronous motor - Google Patents

Abstract

The present invention relates to a permanent magnet synchronous motor, and more specifically to a permanent magnet synchronous motor using a ferrite magnet and a rare-earth magnet together. The permanent magnet synchronous motor according to the present invention comprises: a stator; and a rotor disposed within the stator and forming multiple motor poles using multiple ferrite magnets and multiple rare-earth magnets together, wherein the rotor includes: a first ferrite magnet arranged from the axis of the rotor in a first direction; a second ferrite magnet arranged from the axis of the rotor in a second direction; and a rare-earth magnet arranged at a position spaced apart from the axis of the rotor in third direction; wherein: the first direction and the second direction forms a predetermined angle with the axis of the rotor as a vertex; an angle formed by the third direction and the first direction and an angle formed by the third direction and the second direction are equal to each other and orthogonal to the axis of the rotor; the first ferrite magnet and the second ferrite magnet forms a certain angle; the rare-earth magnet is disposed between the first ferrite magnet and the second ferrite magnet; the ferrite magnet is adjacent to the axis of the rotor; and the rare-earth magnet is disposed to be adjacent to a gap formed between the stator and the rotor, thereby forming one motor pole.

Description

Permanent magnet synchronous motor {PERMANENT MAGNET SYSCHRONOUS MOTOR}

The present invention relates to a permanent magnet synchronous motor used in a drive system of an electric vehicle, and more particularly, to a permanent magnet synchronous motor using a ferrite magnet and a rare earth magnet in combination.

In general, driving motors of electric vehicles require high power density, wide speed driving range, and high efficiency. This property is well satisfied by synchronous motors using rare earth magnets.

However, rare earth magnets using neodymium (Nd) and dysprosium (Dy) are very expensive, and tend to design motors by not using rare earth magnets or reducing their usage.

One way to reduce the use of rare earth magnets is to use a ferrite magnet, which is a heterogeneous permanent magnet. However, ferrite magnets have about one third lower coercive force and residual magnetic flux density than rare earth magnets. Therefore, consideration should be given to the distribution of magnetic lines and demagnetization when used in a motor rotor simultaneously with rare earth magnets.
In addition, there is a 'permanent magnet-type synchronous motor' of the Republic of Korea Patent Publication No. 2009-0079777 (2009. 07. 22. published) as a prior art document related to the present invention to be described later.

The technical problem to be achieved by the present invention is to use a ferrite magnet and a rare earth magnet in combination with a rotor structure that can increase the pole pore ratio of the ferromagnetic with weak coercivity in the permanent magnet synchronous motor is not demagnetized, D phase inductance and Q phase inductance ratio To provide a permanent magnet synchronous motor.

In addition, another object of the present invention is to provide a permanent magnet synchronous motor that can be formed so that the magnetic flux density distribution in the gap becomes a sine wave according to the length of the ferrite magnet and the rare earth magnet.

A permanent magnet synchronous motor according to an aspect of the present invention includes a stator and a rotor disposed in the stator, the rotor including a plurality of ferrite magnets and a plurality of rare earth magnets together to form a plurality of motor poles, wherein the rotor includes: A first ferrite magnet arranged in a first direction exiting the axis of the rotor, a second ferrite magnet arranged in a second direction exiting the axis of the rotor, and arranged in a third direction at a distance from the axis of the rotor Including a rare earth magnet, the first direction and the second direction forms a predetermined angle about the axis of the rotor, the third direction and the first direction to form the angle and the third direction and the third The angles formed by the two directions are equal to each other to be orthogonal to the axis of the rotor, and the first ferrite magnet and the second ferrite magnet form a predetermined angle. The rare earth magnet is disposed between the first and second ferrite magnets, the ferrite magnet is disposed adjacent to the axis of the rotor, and the rare earth magnet is disposed adjacent to the air gap formed between the stator and the rotor. A motor pole, wherein the rotor has the ferrite magnet disposed in a V shape about the axis of the rotor, and magnetic lines of force from the ferrite magnets are transferred to the rare earth magnet toward the V-shaped opening, The magnetic field lines of the wire exit through the gap between the ferrite magnet and the rare earth magnet.

In addition, the rotor is arranged in a V shape with the ferrite magnet around the axis of the rotor, the V-shaped opening is disposed toward the voids, the rare earth magnet is disposed in the opening.

In addition, the rotor is embedded in the magnet insertion hole of the two ferrite magnets are formed in a V-shape, respectively, to form a bridge between the gap and the ferrite magnet, reducing the magnetic flux leakage to the bridge.

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In addition, the rotor forms a Q-axis magnetic flux path between the ferrite magnets that form different motor poles to form a larger Q-phase inductance than the D-phase inductance.

In addition, the length of the ferrite magnet is formed 1.5 times longer than the length of the rare earth magnet.

According to an embodiment of the present invention, the permanent magnet synchronous motor of the present invention does not demagnetize ferrite magnets with weak coercive force, and generates a reluctance torque during operation of the field weakening by increasing the pole-pole ratio, which is a ratio of D-phase inductance and Q-phase inductance. Power factor at high speed can be improved.

In addition, the present invention provides a permanent magnet synchronous motor capable of minimizing harmonic components in the air gap magnetic flux waveform by properly forming the ratio of the ferrite magnet and the rare earth magnet so that the magnetic flux density distribution in the air gap is a sine wave. .

1 is a cross-sectional view of a permanent magnet synchronous motor using a ferrite magnet and a rare earth magnet in accordance with the present invention.
2 is a view showing the magnetic flux flow of the permanent magnet synchronous motor according to the present invention.
3 is a diagram showing the magnetic flux paths of the D-phase and Q-phase magnetic fluxes of the permanent magnet synchronous motor according to the present invention.
FIG. 4 is a diagram illustrating magnet hysteresis and permeance curves of ferrite magnets and rare earth magnets.
FIG. 5 is a diagram showing magnetic force lines and magnet densities between magnets according to the length ratios of ferrite magnets and rare earth magnets.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of a permanent magnet synchronous motor using a ferrite magnet and a rare earth magnet in accordance with the present invention.

The permanent magnet synchronous motor of the present invention according to FIG. 1 includes a stator 10 and a rotor 20 disposed in the stator 10.

The rotor 20 combines ferrite magnets 30 and 32 with rare earth magnets 40 to form one or more motor poles, and in one embodiment of the invention one or more rare earths between two ferrite magnets 30 and 32. Magnets 40 are placed to form one motor pole. Here, the rare earth magnet 40 is made of neodymium (Nd) and dysprosium (Dy) according to an embodiment of the present invention.

The ferrite magnets 30 and 32 are disposed adjacent to the shaft 22 of the rotor, and the rare earth magnet 40 is disposed adjacent to the void 50 formed between the stator 10 and the rotor 20. Will form the motor pole.

That is, the rotor 20 includes a first ferrite magnet 30 arranged in a first direction exiting from the shaft 22 of the rotor, and a second ferrite magnet arranged in a second direction exiting from the shaft 22 of the rotor. 32 and rare earth magnets 40 arranged in a third direction at a predetermined distance from the shaft 22 of the rotor.

The first direction and the second direction form a predetermined angle about the axis 22 of the rotor, the angle formed by the third direction and the first direction, the third direction, and the second direction. The forming angles are the same and can be formed orthogonal to the shaft 22 of the rotor.

In addition, the first ferrite magnet 30 and the second ferrite magnet 32 forms a predetermined angle so that the rare earth magnet 40 is disposed between the first ferrite magnet 30 and the second ferrite magnet 32, the ferrite The magnet 40 is disposed adjacent to the shaft 22 of the rotor and the rare earth magnet 40 is disposed adjacent to the void 50 formed between the stator 10 and the rotor 20 to form one motor pole. Done.

Accordingly, FIG. 1 shows a part of a permanent magnet synchronous motor having eight motor poles. In the rotor 20 according to an embodiment of the present invention, two ferrite magnets 30 and 32 and one rare earth magnet are shown. Eight blocks of 40 can be formed to form eight motor poles.

The two ferrite magnets 30 and 32 may be arranged in a V shape, and one rare earth magnet 40 may be disposed in the center of the opening of the V shape. Such a V-shaped arrangement concentrates the magnetic flux of the ferrite magnets 30 and 32 in one direction so that the magnetic flux density in the cavity 50 is larger than the residual magnetic flux density of the ferrite magnets 30 and 32.

In general, the rare earth magnet 40 has a large coercive force, so that maintaining the proper thickness does not demagnetize in the proper current and temperature range. However, in the case of the ferrite magnets 30 and 32, the coercive force is only about 1/3 compared to the rare earth magnet 40, so it can be easily demagnetized.

Therefore, in the present invention, the rare earth magnet 40 having a large coercive force is disposed on the surface of the rotor 20, the ferrite magnets 30 and 32 are disposed behind the cavity 50, and the thickness thereof is made thick in a possible range. The magnets 30 and 32 have reduced the likelihood of becoming potatoes.

As such, the ferrite magnets 30 and 32 are arranged in a V shape away from the gap 50 to reduce the possibility of being demagnetized by the current in the stator 10 winding, and the coercive rare earth magnet 40 has a V shape. Place it in the opening.

In addition, the rotor 20 is embedded in the magnet insertion holes 30a and 32a in which the two ferrite magnets 30 and 32 are formed in a V-shape, respectively, and an air layer between the air gap 50 and the ferrite magnets 30 and 32. Bridges 62 and 64 are formed.

Bridges 62 and 64 reduce the leakage magnetic flux exiting between void 50 and ferrite magnets 30 and 32.

Therefore, in the present invention, the bridge 60 between the two feride magnets and the bridges 62 and 64 between the ferrite magnets and the voids are designed to be thin and long so that the magnetic flux from the ferrite magnets 30 and 32 can form a gap in the V-shaped opening. It makes it hard to escape other than (50).

As such, in the present invention, the magnetic force lines from the ferrite magnets 30 and 32 are transferred to the rare earth magnet 40 toward the V-shaped openings, and a portion of the magnetic force lines are transferred to the ferrite magnets 30 and 32 and the rare earth magnets. The air flows through the gaps 40 through the gaps 40 and minimizes the magnetic flux leaking into the bridges 62 and 64.

In addition, the present invention allows the length L1 of the ferrite magnets 30 and 32 in which the magnetic flux is generated to be at least 1.5 times the length L2 of the rare earth magnet 40. This makes it possible to minimize the amount of magnetic flux by the ferrite magnets 30 and 32 and the rare earth magnet 40 so that the magnetic flux density of the pores is distributed in the form of a sine wave, thereby minimizing harmonic components in the magnetic flux waveform of the pores.

2 is a view showing the magnetic flux flow of the permanent magnet synchronous motor according to the present invention.

According to the present invention, the ferrite magnets 30 and 32 are magnetized in parallel, and the magnetic fluxes face each other by equalizing the polarity (N pole or S pole) of the magnets in both V-shaped ferrite magnets 30 and 32, or at the same time Place it in a sucked form.

Referring to FIG. 2, magnetic lines 70 and 72 emerge from the surfaces of the ferrite magnets 30 and 32, and magnetic lines 74 enter the rare earth magnet 40.

As such, the lines of magnetic force 70 and 72 from the ferrite magnets 30 and 32 are transferred to the rare earth magnet 40 toward the V-shaped openings, and some of the lines of magnetic force 70a and 72a are transferred to the ferrite magnets 30 and 32. And through the space (a, b) between the rare earth magnet 40 and the exit to the void 50.

Therefore, the present invention can prevent the magnetic force lines of the ferrite magnets 30 and 32 from escaping to the bridges 60, 62 and 64, thereby minimizing leakage magnetic flux.

In addition, as described above, the magnetic flux density of the rare earth magnet 40 is three times higher than the magnetic flux density of the ferrite magnets 30 and 32. When the sum of the lengths of the two ferrite magnets (2 * L1) is equal to or less than three times the length (L2) of the rare earth magnets, all of the magnetic flux from the ferrite magnets is sucked into the rare earth magnets.

In this case, the magnetic field lines coming out of the sections a and b between the ferrite magnet and the rare earth magnet shown in FIG. 2 are insufficient, resulting in a decrease in the pore magnetic flux density in the sections a and b. This is because an undesired phenomenon occurs in which the rms value of the pore magnetic flux density decreases, the distribution becomes closer to a square wave away from the sine wave, and the harmonic component increases in the pore flux waveform.

Therefore, in the present invention, the length L1 of the ferrite magnets 30 and 32 in which the magnetic flux is generated is 1.5 times or more than the length L2 of the rare earth magnet 40 which absorbs the magnetic flux. This is because the amount of magnetic flux by the rare earth magnet and the ferrite magnet is appropriate, and the magnetic flux density of the void is distributed in the form of a sine wave, thereby minimizing harmonic components in the magnetic flux waveform of the void.

3 is a diagram showing the magnetic flux paths of the D-phase and Q-phase magnetic fluxes of the permanent magnet synchronous motor according to the present invention.

Fig. 3 (a) shows the magnetic flux path 80 by the D-phase coil, and Fig. 3 (b) shows the magnetic flux path 84 by the Q-phase coil.

Structurally thickening the ferrite magnets and narrowing the bridges 60, 62 and 64 of the ferrite magnets lead to very small D-phase inductance. In the magnetic flux path 80 by the D-phase coil of FIG. 3 (a), a thick ferrite magnet is located in the magnetic flux path 80 to increase the magnetoresistance, thereby reducing the D-phase inductance.

The Q-axis magnetic flux passage 82 serves as a passage of the magnetic flux path 84 by the Q-phase coil. As such, by providing the Q-phase magnetic path through the Q-axis magnetic flux path 82, the Q-phase inductance can be very large compared to the D-phase.

Therefore, in the present invention, when the Q-axis magnetic flux path 82 is made between two ferrite magnets, the Q-phase inductance is relatively large, and thus the saliency ratio increases. Here, the salient pole ratio means the ratio of the D-phase inductance and the Q-phase inductance.

In addition, the increase in the pole-pole ratio generates reluctance torque in the field weakening operation, and has the advantage of improving the power factor in the high speed operation.

Accordingly, the rotor 20 of the present invention forms a Q-axis magnetic flux path 82 between ferrite magnets formed with different motor poles, thereby forming a Q-phase inductance larger than the D-phase inductance, thereby increasing the salient pole ratio.

FIG. 4 is a diagram illustrating magnet hysteresis and permeance curves of ferrite magnets and rare earth magnets.

In FIG. 4, Hc on the horizontal axis represents coercive force, and Br on the vertical axis represents residual flux density.

It can be seen that the hysteresis curve 1 of the Nd-Fe magnet has a larger coercive force and residual magnetic density than the hysteresis curve 2 of the ferrite, and the ratio of the magnitude is about three times. Small coercive forces tend to cause permanent magnets to demagnetize when high currents are applied to the stator windings. Therefore, in consideration of the low coercive force and residual magnetic flux density of the ferrite magnet, the ferrite magnet should not be demagnetized.

In addition, the magnetic insertion hole and the bridge should be designed to minimize the leakage flux of the ferrite magnet, and the magnetic flux path should be designed so that the difference between the D-axis and Q-axis inductance is large to increase the breakthrough ratio. In case of weakening, reluctance torque can be used.

For example, as described above, the residual magnetic flux density of the rare earth magnet is three times higher than the residual magnetic flux density of the ferrite magnet. At this point, the intersections (A, B) of the permeability curve and the hysteresis curve represent the pore magnetic flux density by each magnet. The magnetic flux density (4) by the rare earth magnet is B _nd and the magnetic flux density by the ferrite magnet ( When 5) is expressed as B _fe , the relationship as in Equation 1 below is established.

Therefore, when the axial lamination length of the rotor is L, the total amount of magnetic flux emitted from the surface of the ferrite magnet is expressed by Equation 2 below, and the total amount of magnetic flux absorbed by the rare earth magnet is expressed by Equation 3.

Here, as described above, the total amount of the ferrite magnetic flux must be larger than the total amount of the rare earth magnet, that is, the floating arc as shown in Equation 4 must be satisfied to bring the magnetic flux density in the gap closer to the sine wave.

Therefore, when Equation 1 to Equation 3 is applied to Equation 4, Equation 5 below is required, which means that the length L1 of the ferrite magnet is 1.5 times greater than the length L2 of the rare earth magnet. Should be made.

Therefore, in the present invention, in order to balance the amounts of the rare earth magnet and the ferrite magnetic flux, the length of the ferrite magnet is formed to be 1,5 times or more longer than the length of the rare earth magnet.

FIG. 5 is a diagram showing magnetic force lines and magnet densities between magnets according to the length ratios of ferrite magnets and rare earth magnets.

5 (a) and 5 (b) show flux densities in flux lines and pores obtained by FEM analysis when the length ratios of ferrite magnets and rare earth magnets are different. FIG. 5 (a) is when the magnet length ratio satisfies Equation 5, and FIG. 5 (b) is not when Equation 5 is satisfied.

When satisfying Equation 5, the amount of magnetic flux (90a) coming out of the ferrite magnet is enough, and as shown in Figure 5 (a) some of the magnetic flux through the space (a, b) between the magnets. However, when the equation 5 is not satisfied, the amount of magnetic flux 92a from the ferrite magnet is not sufficient, and the magnetic flux coming out through the spaces a and b between the magnets is extremely limited as shown in FIG.

The magnetic flux densities corresponding to the amounts of magnetic flux 90a and 92a are shown in Figs. 5 (a) and 5 (b), respectively. The magnetic flux density 90b of Fig. 5 (a) is the magnetic flux density of Fig. 5 (b). Compared with (92b), it can be seen that it contributes to making the pore magnetic flux density distribution close to the sine wave.

Accordingly, the present invention provides a permanent magnet synchronous motor capable of minimizing harmonic components in the air gap magnetic flux waveform by appropriately adjusting the length ratio of the ferrite magnet and the rare earth magnet so that the magnetic flux density distribution in the air gap becomes a sine wave. .

In addition, the permanent magnet synchronous motor of the present invention can reduce the usage of rare earth magnets, and the rare earth magnets having high coercivity are arranged close to the voids, and the ferrite magnets are arranged in the V-shape on the shaft side, so that the ferrite magnets have weak coercivity. Can be reduced.

In addition, the present invention maximizes the breakthrough ratio, which is the ratio of the D-phase inductance to the Q-phase inductance by making the bridge to have a small leakage flux, thereby generating reluctance torque during weak field operation, and improving power factor at high speed.

The embodiments of the present invention described above are not implemented only by the apparatus and method, but may be implemented through a program for realizing the function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

10: stator 20: rotor
22: rotor shaft 30, 32: ferrite magnet
40: rare earth magnet 50: void
60, 62, 64: Bridge 82: Q-axis flux path

Claims (6)

In the permanent magnet synchronous motor,
Stator; And
A rotor disposed in the stator, the rotor including a plurality of ferrite magnets and a plurality of rare earth magnets to form a plurality of motor poles,
The rotor is a first ferrite magnet arranged in a first direction outgoing from the axis of the rotor, a second ferrite magnet arranged in a second direction outgoing from the axis of the rotor, and a predetermined distance from the axis of the rotor Including the rare earth magnets arranged in three directions, the first direction and the second direction forms a predetermined angle about the axis of the rotor, the angle formed by the third direction and the first direction and the third The angle formed by the direction and the second direction is the same and orthogonal to the axis of the rotor,
The first ferrite magnet and the second ferrite magnet form a predetermined angle such that the rare earth magnet is disposed between the first and second ferrite magnets, the ferrite magnet is adjacent to the axis of the rotor, and the rare earth magnet Disposed adjacent to the gap formed between the stator and the rotor to form one motor pole,
The rotor
The ferrite magnet is arranged in a V-shape around the axis of the rotor, the magnetic force lines from the ferrite magnets are transferred to the rare earth magnet toward the opening of the V-shape, a portion of the magnetic force line is the ferrite magnet and the rare earth magnet Permanent magnet synchronous motor that passes through the gap through the gap. The method of claim 1,
The rotor
The ferrite magnet is disposed in a V-shape around the axis of the rotor, the V-shaped opening is disposed to face the voids, the permanent magnet synchronous motor is disposed in the opening. 3. The method of claim 2,
The rotor
And two ferrite magnets each embedded in a V-shaped magnet insertion hole, wherein a bridge is formed between the void and the ferrite magnet to reduce the leakage magnetic flux to the bridge. delete The method of claim 3, wherein
The rotor
Permanent magnet synchronous motor that forms a Q-axis inductance larger than D-phase inductance by forming a Q-axis flux path between ferrite magnets that form different motor poles. 6. The method of claim 5,
The length of the ferrite magnet
Permanent magnet synchronous motor is formed more than 1.5 times longer than the length of the rare earth magnet.

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