KR101666931B1 - Magnetic circuit with variable magnetic flux - Google Patents

Abstract

Disclosed is a variable magnetic flux magnetic circuit having a magnet arrangement structure capable of realizing high efficiency in both a low speed and a wide rotation range through a magnetization and a potato process of a variable magnet capable of changing a magnetic flux. Wherein the variable magnetic flux magnetic circuit includes: a stator core having a plurality of winding portions arranged at regular intervals; and a stator having a plurality of coils wound around the plurality of winding portions, wherein each of the plurality of coils includes A current having a different phase is flowing; And a mover having a plurality of permanent magnets arranged at regular intervals to have a magnetic action with the plurality of coils. At least one of a coil through which a current flows in one phase among the coils through which the current having the different phases flows, or a permanent magnet aligned in the center of the winding section in which the coil through which the current flows in one phase, At least one of the permanent magnets arranged in the center between the mutually adjacent coils through which currents of two phases different from the coils flow, or the coils wound with mutually adjacent coils through which the currents of the two phases flow, Is a permanent permanent magnet.

Description

[0001] MAGNETIC CIRCUIT WITH VARIABLE MAGNETIC FLUX [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable magnetic flux magnetic circuit, and more particularly, to a variable magnetic flux circuit having a magnet arrangement structure capable of realizing high efficiency in a wide rotation range at low and high speeds through magnetization and potatoing processes of a variable magnet, To a variable magnetic flux magnetic circuit.

Devices having a magnetic circuit structure, such as a motor (motor) or a generator, are devices that have a permanent magnet and produce torque or electric power using the magnetic flux. Among the magnetic circuits, the permanent magnets and the electric motors and generators applying the permanent magnets have the advantages of high efficiency and low noise as compared with the conventional induction magnetic circuits due to no loss due to the excitation current.

However, the magnetic circuit using the permanent magnet can not exhibit the optimum characteristics in the entire operation range in terms of the rotational speed or the torque, and the efficiency may be lowered.

In order to solve the disadvantage of the magnetic circuit using the permanent magnet, a variable magnetic flux magnetic circuit capable of varying the magnetic flux of the permanent magnet according to the operating condition has been proposed. The variable magnetic flux magnetic circuit can improve the efficiency by changing the magnetic flux amount of the permanent magnet in accordance with the operating conditions by the magnetizing current in a short time.

Conventionally, permanent magnets (hereinafter, referred to as first magnets) and variable magnetic flux circuits having a high coercive force, which are difficult to change the magnetic flux, include permanent magnets having a low coercive force (hereinafter referred to as second magnets) A rotor or a mover is applied. The arrangement structure of the first magnet and the second magnet is simply a symmetric structure or a structure having a constant arrangement. Such a simple magnet arrangement structure of a conventional variable magnetic flux magnetic circuit is disclosed in Patent Registration No. 10-1276016.

On the other hand, in general, the variable magnetic flux magnetic circuit should satisfy the following requirements. First, the magnitudes of the back EMFs of the respective phases should be the same. When the instantaneous current is applied to the coil, the magnetic field should be in a region where the first magnet can be excited. The second magnet has a coercive force It should not be very variable. In addition, when the first magnet is magnetized, the electromagnetic circuit must be in a parallel state (combination of a slot and a pole), and a magnitude of the back electromotive force must be changed after the magnetizing current is applied.

Accordingly, there is a need in the art for a variable magnetic flux circuit having a magnet arrangement structure that can maximize efficiency while satisfying various conditions required for the variable magnetic flux circuit.

Registration No. 10-1276016

Accordingly, it is an object of the present invention to provide a variable magnetic flux magnetic circuit having a magnet arrangement structure capable of realizing a high efficiency in both a low speed and a high speed wide range by magnetizing and potatoing of a variable magnet capable of changing a magnetic flux To be a technical challenge.

According to an aspect of the present invention,

A stator comprising: a stator core having a plurality of winding portions arranged at regular intervals; and a stator having a plurality of coils wound on the plurality of winding portions, wherein each of the plurality of coils includes a current Flow -; And

And a mover having a plurality of permanent magnets arranged at regular intervals to perform a magnetic action with the plurality of coils,

At least one of a coil through which a current flows in one phase among the coils through which the current having the different phases flows, or a permanent magnet aligned in the center of the winding section in which the coil through which the current flows in one phase, At least one of the mutually neighboring coils through which currents of two phases different from the coils flow, or the permanent magnets arranged at the center between the coils wound with mutually adjacent coils through which the current of the other two phases flows, Wherein the variable permanent magnet magnetic circuit is a variable permanent magnet having a coercive force.

Lt; / RTI >

In one embodiment of the present invention, the variable permanent magnet may be an AlNiCo magnet (60 to 120 kA / m) or an FeCrCo magnet (about 60 kA / m) or a SmCo magnet.

’(N_spp: 매극 매상 당 슬롯수, N_ph: 상기 서로 다른 위상의 수, N_s: 가변 자속 자기 회로의 슬롯수, N_m: 복수의 영구 마그넷의 극수)에 의해 정의된 매극 매상 당 슬롯수가 0.25인 경우, 상기 가변 영구 마그넷의 수는 ‘

’(

, n은 양의 정수)일 수 있다.In one embodiment of the present invention,

(N _spp : number of slots per active pole, N _ph : number of the different phases, N _s : number of slots in the variable magnetic flux circuit, N _m : number of poles of the permanent magnets) When the number is 0.25, the number of the variable permanent magnets is "

'(

, and n is a positive integer).

In one embodiment of the present invention, when the number of slots per active pole is 0.25, the entire variable permanent magnets may have the same polarity.

’(N_spp: 매극 매상 당 슬롯수, N_ph: 상기 서로 다른 위상의 수, N_s: 가변 자속 자기 회로의 슬롯수, N_m: 복수의 영구 마그넷의 극수)에 의해 정의된 매극 매상 당 슬롯수가 0.5인 경우, 상기 가변 영구 마그넷의 수는 ‘

’(

, n은 양의 정수)일 수 있다.In one embodiment of the present invention,

(N _spp : number of slots per active pole, N _ph : number of the different phases, N _s : number of slots in the variable magnetic flux circuit, N _m : number of poles of the permanent magnets) When the number is 0.5, the number of the variable permanent magnets is "

'(

, and n is a positive integer).

In an embodiment of the present invention, when the number of slots per polarity is 0.5, the variable permanent magnets may include the same number of variable permanent magnets having different polarities.

Particularly, the present invention can be applied to a three-phase variable magnetic flux magnetic circuit that rotates, such as an electric motor or a generator. In the three-phase variable magnetic flux magnetic circuit according to the present invention,

A stator having a plurality of teeth arranged at regular intervals and a stator having a plurality of coils each wound on the plurality of teeth, wherein each of the plurality of coils has a U phase, V phase and W phase three phase current Alternating flow -; And

And a rotor having a plurality of permanent magnets arranged at regular intervals to have a magnetic action with the plurality of coils.

At least one of a coil through which the U phase current flows or a permanent magnet aligned in the center of the coil through which the coil through which the U phase current flows is wound and a coil in which the current flows through the V phase and the W phase, At least one of the permanent magnets arranged in the center between the coils of the flowing coils is a variable permanent magnet having a coercive force capable of changing its magnetization amount.

According to the present invention, by suitably arranging the variable magnet according to the phase of the coil used in the magnetic circuit, it is possible to satisfactorily satisfy the back electromotive force condition required for the variable magnetic flux magnetic circuit and to maximize the motor efficiency according to the rotation speed There is an excellent effect.

1 is an exploded perspective view briefly showing an example of a variable magnetic flux circuit according to an embodiment of the present invention.
2 is a view showing an example of a magnet arrangement structure of a variable magnetic flux magnetic circuit according to an embodiment of the present invention.
3 is a view showing another example of a magnet arrangement structure of a variable magnetic flux magnetic circuit according to an embodiment of the present invention.
Fig. 4 shows an example of an exciter circuit applied to excite a variable magnet of a variable magnetic flux magnetic circuit according to an embodiment of the present invention.
5 is a perspective view briefly showing an example of a variable magnetic flux motor to which a plurality of variable magnets implemented according to the present invention is applied.
6 is a graph showing the counter electromotive force of each phase according to the number of variable magnets of the variable magnetic flux motor shown in FIG.
FIG. 7 is a table and graph showing counter electromotive force according to an exciter of a variable magnetic flux motor to which a variable magnet according to the present invention is applied.
FIG. 8 and FIG. 9 are tables and graphs showing load evaluation results according to an exciter of a variable magnetic flux motor to which a variable magnet according to the present invention is applied.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art. In addition, in describing the present invention, the defined terms are defined in consideration of the functions of the present invention, and they may be changed depending on the intention or custom of the technician working in the field, so that the technical components of the present invention are limited It will not be understood as meaning.

1 is an exploded perspective view briefly showing an example of a variable magnetic flux circuit according to an embodiment of the present invention.

The following description describes an example of a rotating electric motor (motor) that generates torque among the variable magnetic flux magnetic circuits. However, the present invention is not limited to a rotating electric motor. Those skilled in the art will be able to understand the operation of the rotating electric motor through mutual magnetic action between the permanent magnet and the coil, such as a generator or a linear motor, It is obvious that the present invention can be applied to various magnetic circuits.

1, a variable magnetic flux circuit according to an embodiment of the present invention may include a mover 10 and a stator 20.

The stator 20 includes a stator core 21 having a plurality of winding portions for winding the coils. The winding portion of the stator core in the rotary motor or generator is also referred to as teeth. The plurality of teeth in the stator core are arranged at regular intervals.

Although not shown in Fig. 1, each of the plurality of teeth of the stator core 21 is wound with a coil. Currents having different phases flow repeatedly in the order in which the coils are wound on the coils when the motor is driven or when the tuning magnet of the variable magnet described below is turned on. For example, when the currents having different phases are three phases, the coils are repeatedly arranged in the order of 'first phase-second phase-third phase-first phase-second phase-third phase-first Prize-… Of the current flows through the plurality of coils of each.

The mover 20 is an element also called a rotor in a rotating magnetic circuit. The mover 20 may include a permanent magnet 12 arranged at regular intervals on the inner circumferential surfaces of the rotor core 11 and the rotor core 11. The variable magnetic flux motor shown as an example in FIG. 1 is an external type electric motor of 36 slots and 48 poles in particular. The rotor 20 is disposed outside the stator 20 and is connected to the magnet in the rotor 10 and the stator 20 The torque (torque) can be produced through the mutual electromagnetic action of the wound coils.

The permanent magnet 121 having a high coercive force (hereinafter referred to as a first magnet) and the variable magnetic flux circuit having a low coercive force (hereinafter referred to as " second magnet " , And a second magnet).

Generally, a permanent magnet means a magnet which keeps magnetized state continuously without flowing current from the outside, but strictly speaking, the magnetic flux density does not change at all depending on the surrounding conditions. The permanent magnet means that the magnetic flux density does not change substantially by the electric current supplied from the inverter or the like in the normal rated operating condition, not in the constant magnetic flux amount. The variable magnet applied to the embodiment of the present invention means a magnet whose magnetic flux density is changed by a current that can be provided by such an inverter or the like.

In one embodiment of the present invention, the first magnet can be applied to a neodymium magnet having a high coercive force of about 1000 kA / m. In an embodiment of the present invention, the second magnet may be a low coercive force AlNiCo magnet (60 to 120 kA / m) or a FeCrCo magnet (about 60 kA / m) or a SmCo magnet.

2 is a view showing an example of a magnet arrangement structure of a variable magnetic flux magnetic circuit according to an embodiment of the present invention. Particularly, FIG. 2 is a diagram that is linearly deformed so as to facilitate understanding of the magnet arrangement structure of the rotating electric motor.

FIG. 2 shows an example of a magnet arrangement method applied to a variable magnetic flux circuit having a slot number (N _spp ) of 0.25 per active pole phase. The number of slots per pass through can be defined as: < EMI ID = 1.0 >

[Formula 1]

In Equation 1, N _ph is the phase of the magnetic circuit, that is, the number of phases of current supplied to each coil, N _s is the number of slots, and N _m is the number of magnetic poles.

’(

, n은 양의 정수)로 결정될 수 있다.A magnetic circuit having a slot number (N _spp ) of 0.25 for each magnetic pole spot is generally used in a number of slots of 3/4, 9/12, 12/16, 15/20, 18/24, 21 / 28, and 36/48 (U-phase, V-phase, W-phase) motors. In this case, the number of variable magnets is'

'(

, and n is a positive integer).

As shown in Figs. 2 (a) and 2 (b), in one embodiment of the present invention, a coil through which a current flows in one phase or a permanent magnet And a plurality of mutually adjacent coils to which currents of two phases different from those of the coils through which the current of one phase flows, or a pair of permanent magnets At least one of them can be arranged as a variable permanent magnet having a coercive force capable of changing the magnetization amount, that is, a second magnet.

More specifically, when one second magnet 122 is aligned and disposed in the center of the coil on which the U-phase coil 22-u or the U-phase coil 22-u is wound in FIG. 2 (a) The other one of the second magnets 121 is connected to the V-phase coil 22-v and the W-phase coil 22-w immediately adjacent to the U-phase coil 22-u aligned with one second magnet 122 The immediately adjacent V-phase coil 22-v and the W-phase coil 22-w can be arranged in the center between the wound tines.

Likewise, as shown in FIG. 2 (b), one second magnet 122 is aligned and arranged in the center of the U-phase coil 22-u or the U-phase coil 22- , The other one second magnet 122 is connected to the V-phase coil 22-v and the W-phase coil 22-v spaced apart from the U-phase coil 22-u in which one second magnet 121 is aligned, w of the coil 22-v and the coil 22-w of the W-phase can be arranged in the center between the wound tines. The distance between the two second magnets is not important. In case of three phases, when one second magnet is aligned on one phase, the second magnet may be arranged such that the remaining second magnets are aligned between the remaining two phases .

In the example of Fig. 2, the polarities of the variable magnets 122 are the same.

3 is a view showing another example of a magnet arrangement structure of a variable magnetic flux magnetic circuit according to an embodiment of the present invention.

FIG. 3 shows an example of a magnet arrangement method applied to a variable magnetic flux circuit having a slot number N _spp of 0.5 for each pole track defined by the above-mentioned equation (1).

’(

, n은 양의 정수)로 결정될 수 있다.A magnetic circuit having a slot number (N _spp ) of 0.5 for each magnetic pole spot is commonly used in the case where the number of slots / poles is 3/2, 9/6, 12/8, 15/10, 18/12, 21 / 14, and 36/24 (U-phase, V-phase, W-phase) motors. In this case, the number of variable magnets is'

'(

, and n is a positive integer).

In the embodiment of the present invention shown in Figs. 3A and 3B, similarly to the example shown in Fig. 2 described above, a coil through which a current of one phase flows or a coil through which a current of one phase flows is wound And a permanent magnet arranged in the center of the portion, and a pair of adjacent coils in which currents of two phases different from those of the coil in which the one-phase current flows, or mutually adjacent coils in which two- At least one of the permanent magnets arranged at the center between the first magnet and the second magnet can be arranged as a variable permanent magnet having a coercive force capable of changing the magnetization amount, that is, a second magnet.

More specifically, when one second magnet 122 is aligned and disposed in the center of a coil in which the U-phase coil 22-u or the U-phase coil 22-u is wound in Fig. 3 (a) The other one of the second magnets 121 is connected to the V-phase coil 22-v and the W-phase coil 22-w immediately adjacent to the U-phase coil 22-u aligned with one second magnet 122 The immediately adjacent V-phase coil 22-v and the W-phase coil 22-w can be arranged in the center between the wound tines.

Likewise, as shown in FIG. 3 (b), one second magnet 122 is aligned and arranged in the center of the U-phase coil 22-u or U-phase coil 22- , The other one second magnet 122 is connected to the V-phase coil 22-v and the W-phase coil 22-v spaced apart from the U-phase coil 22-u in which one second magnet 121 is aligned, w or spaced V-phase coil 22-v and W-phase coil 22-w may be arranged in the center between the wound-up teeth.

3, the distances between the two second magnets do not matter much. In the case of three phases, when one second magnet is aligned on one phase, The second magnet may be arranged so that the two magnets are aligned.

Unlike the example of Fig. 2, the polarities of the variable magnets 122 are different from each other in the example shown in Fig.

The magnetizations and potatoes of the variable magnet shown in Figs. 2 and 3 can be implemented using an exciter circuit as shown in Fig.

Fig. 4 shows an example of an exciter circuit applied to excite a variable magnet of a variable magnetic flux magnetic circuit according to an embodiment of the present invention.

Referring to FIG. 4, the admittance circuit includes a DC power supply unit 41 for changing the polarity and switching power to provide power, and an inverter unit 42 for converting power supplied from the DC power supply unit into AC power of three phases through switching And the like. The output of each phase of the inverter section 42 can be provided as a coil of each phase of the motor 43. [

In the example shown in Fig. 4, the magnetization and the potato of the variable magnet can be made by the electric current provided to the U-phase coil. It is determined whether or not to magnetize the variable magnet to be magnetized as shown in FIG. 4, and the variable magnet is moved to the center of one coil (U phase in the example of FIG. 4) or one coil of the upper coil The polarity of the variable magnet and the polarity of the power of the proper direction according to whether the magnet is magnetized or not can be selected to temporarily provide a strong current to the coil of the corresponding phase. After one magnet of the variable magnet is made, the other magnet of the variable magnet is aligned with the coil of the upper magnetic pole or the center of the coil where the coil is wound, and then the polarity of the variable magnet and the polarity power So that an impulse generator can be achieved.

5 is a perspective view briefly showing an example of a variable magnetic flux motor to which a plurality of variable magnets are applied.

The example shown in Fig. 5 is an example of an external type motor having 36 slots and 48 pawls, in which two variable magnets (second magnets) are arranged in two, four, six, eight, ten, twelve, sixteen, 20, and 24, respectively. Although not shown in FIG. 5, the number of variable magnets may be 14, 18, and 22. In the present invention, one of the variable magnets is implemented as an even number of variable magnets, and one of the pair of variable magnets is arranged in the center of a U-phase coil or a U-phase coil, and the other is a coil of V- and W- When half of the plurality of variable magnets are aligned in the center of the U-phase coil, the other half has an arrangement structure arranged in the center between the V-phase and the W-phase.

6 is a graph showing the counter electromotive force of each phase according to the number of variable magnets of the variable magnetic flux motor shown in FIG.

As shown in FIG. 6, when various numbers of variable magnets are applied, it can be seen that the counter electromotive force of each phase is maintained at substantially the same magnitude.

FIG. 7 is a table and graph showing counter electromotive force according to an exciter of a variable magnetic flux motor to which a variable magnet according to the present invention is applied.

As shown in FIG. 7A, when the counter electromotive force according to the number of rotations of the variable magnetic flux motor is compared with the amount of potato (the magnitude of the current supplied to the coil for the potato), the magnitude of the counter electromotive force It can be confirmed that it is maintained almost constant.

7 (b), when the counter electromotive force corresponding to the magnetization amount (the magnitude of the current supplied to the coil for magnetization) is compared with the rotation number of the variable magnetic flux motor, the counter electromotive force It can be seen that the size remains almost constant.

7C shows the fluctuation range of the counter electromotive force according to the admittance when the rotation speed of the variable magnetic flux motor is 47 rpm and it is confirmed that even when the magnetic flux is changed, the fluctuation of the counter electromotive force is about 0.408 V have.

FIG. 8 and FIG. 9 are tables and graphs showing load evaluation results according to an exciter of a variable magnetic flux motor to which a variable magnet according to the present invention is applied.

8A shows the load torque, motor efficiency and inverter efficiency according to the rotor speed at the time of magnetization, and FIG. 8B shows the load torque, the motor efficiency, and the inverter efficiency according to the rotor speed at the time of magnetization. In addition, FIG. 9 shows values of motor efficiency among the values shown in FIG. 8 (a) and FIG. 8 (b) according to the rotor speed.

As shown in FIGS. 8 (a) and 8 (b) and FIG. 9, it can be seen that the motor efficiency is further improved when the motor is driven at low speed and the efficiency is further improved when the motor is driven at high speed. For example, in the case of a motor for a washing machine to which a magnetic circuit according to an embodiment of the present invention is applied, a variable magnet is magnetized and driven in a low-speed washing operation section, and a variable magnet is magnetized in a high- It is possible to improve the motor efficiency in the entire operation section.

As described above, the magnet arrangement structure of the magnetic circuit according to the embodiment of the present invention can maximally satisfy the back electromotive force condition required for the variable magnetic flux magnetic circuit while maximizing the motor efficiency according to the rotation speed .

Although the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. Therefore, the scope of the present invention should not be limited to the embodiments described, but should be determined by the scope of the following claims and equivalents thereof.

10: rotor (mover) 11: rotor core
12: Magnet 121: Fixed Magnet
122: variable magnet 20: stator
21: stator core 22-u, 22-v, 22-w: coil

Claims (7)

A stator comprising: a stator core having a plurality of winding portions arranged at regular intervals; and a stator having a plurality of coils wound on the plurality of winding portions, wherein each of the plurality of coils includes a current Flow -;
A mover having a plurality of permanent magnets arranged at regular intervals to have a magnetic action with the plurality of coils;
A first permanent magnet arranged at a center of a winding portion in which a coil through which a current flows in one phase among the coils through which the current having the different phases flow, or a coil through which the current flows in the one phase, A variable permanent magnet disposed in a second permanent magnet arranged between the mutually adjacent coils through which currents of two phases differ from each other or between the coils wound with mutually adjacent currents flowing in the other two phases, Wherein the variable permanent magnet has a coercive force capable of changing its magnetization amount and is arranged in the same arrangement pattern as the first permanent magnet and the second permanent magnet based on the number of the variable permanent magnets, Decided on mover -; And
And an exciter circuit for exciting the variable permanent magnet, the exciter circuit comprising: a DC power source for changing the polarity by switching and providing power; and a DC power source for converting power supplied from the DC power source to alternating current Comprising an inverter section for converting; / RTI >
The counter electromotive forces of the different phases are kept within the same magnitude even when the number of the variable permanent magnets, the magnetization amount of the variable permanent magnet, and the rotational speed of the mover are varied,
And controls the amount of admittance of the variable permanent magnet through the admittance circuit so that the counter electromotive force of the different phases has a specified magnitude based on the rotating speed of the mover. The method according to claim 1,
Wherein the variable permanent magnet is an AlNiCo magnet (60 to 120 kA / m) or an FeCrCo magnet (about 60 kA / m) or a SmCo magnet. The method according to claim 1,
Expression '

(N _spp : number of slots per polarity, N _ph : number of the different phases, N _s : number of slots of the variable magnetic flux circuit, N _m : number of poles of the permanent magnets) When the number of slots is 0.25, the number of the variable permanent magnets is'

'(

, and n is a positive integer). The method of claim 3,
And when the number of slots per the active pole of the magnetic pole is 0.25, the variable permanent magnets all have the same polarity. The method according to claim 1,
Expression '

(N _spp : number of slots per polarity, N _ph : number of the different phases, N _s : number of slots of the variable magnetic flux circuit, N _m : number of poles of the permanent magnets) When the number of slots is 0.5, the number of the variable permanent magnets is'

'(

, and n is a positive integer). 6. The method of claim 5,
Wherein when the number of slots per active pole is 0.5, the variable permanent magnets comprise the same number of variable permanent magnets having different polarities. A stator having a plurality of teeth arranged at regular intervals and a stator having a plurality of coils each wound on the plurality of teeth, wherein each of the plurality of coils has a U phase, V phase and W phase three phase current Alternating flow -;
A mover having a plurality of permanent magnets arranged at regular intervals to have a magnetic action with the plurality of coils;
A first permanent magnet in which a coil through which the U phase current flows or a coil through which the U phase current flows is arranged in the center of the coil, a coil through which the V phase and W phase current flows, or a V phase and W phase current A variable permanent magnet disposed in a second permanent magnet aligned in the center between the coils of the wound coil, the variable permanent magnet having a coercive force capable of changing its magnetization amount, the variable permanent magnet having a coercive force capable of changing its magnetization amount, Determining, based on the number of magnets, the mover in the same arrangement pattern as the first permanent magnet and the second permanent magnet; And
An exciter circuit for exciting the variable permanent magnet, the exciter circuit comprising: a DC power source part for changing the polarity by switching and providing power; and an inverter for converting power supplied from the DC power part to AC power of three phases through switching Including wealth -; / RTI >
The back electromotive force of each of the three phases is kept within the same magnitude even when the number of the variable permanent magnets, the magnetization amount of the variable permanent magnet, and the rotational speed of the mover are varied,
And controls the magnetization amount of the variable permanent magnet through the admittance circuit so that the three-phase counter electromotive force has a designated magnitude based on the rotating speed of the mover.

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