JP7534995B2 - Rotating Electric Machine - Google Patents

Description

The present invention relates to a rotating electric machine that is capable of switching the number of magnetic poles (number of poles).

Surface magnet vernier motors are known that increase the number of rotor poles and increase torque through the magnetic gear effect. These motors use a harmonic rotating magnetic field corresponding to the number of slots and poles, rather than the fundamental wave rotating magnetic field generated by a three-phase coil. Because a harmonic rotating magnetic field has a slow rotation speed, it is necessary to increase the drive frequency of the current passing through the three-phase coil compared to motors that use a fundamental wave rotating magnetic field (when using the fifth harmonic, the drive frequency is five times higher). As a result, torque can be increased at low speeds, but due to limitations in the drive frequency, high speed rotation is not possible, and there is a limit to the increase in output.

If it were possible to switch between the fundamental wave and the harmonics, i.e., to switch the number of poles, it would be possible to achieve both high torque and high output. As a result, there have been proposals for motors that allow the number of poles to be switched, and there are several techniques for changing the number of poles.

In Patent Documents 1 to 3, the magnetization of the rotor is changed, in Patent Document 4, the rotor magnet is mechanically moved, and in Patent Documents 5 and 6, the number of phases of the stator is changed to switch the number of poles.

JP 2015-163028 A JP 2014-168320 A JP 2014-168331 A JP 2012-130223 A Japanese Patent Application Publication No. 8-223999 JP 2012-95410 A

In order to change the magnetization of the rotor, it is necessary to pass an instantaneous pulse current, which requires a larger inverter to supply the three-phase current.

In order to mechanically move the rotor magnet, a movement mechanism and actuator are required, which increases the size.

To change the number of stator phases, a multi-phase inverter with three or more phases is required, which increases the size of the inverter.

The present invention provides a motor that can change the number of poles without adding an actuator or enlarging the size of the inverter that supplies the three-phase current.

The rotating electric machine according to the present invention has a stator core with multiple stator slots, a stator having three-phase coils arranged in the stator slots and forming a predetermined magnetic field, a rotor having a predetermined number of inner rotor poles formed on the inner diameter portion and a different number of outer rotor poles formed on the outer diameter portion, a field yoke positioned on the side of the stator core and the rotor, and a field coil that generates a field magnetic flux that circulates around a path formed by the rotor, the stator, and the field yoke, and is capable of switching the number of magnetic poles of the rotor by canceling out the magnetic field from the inner rotor poles by passing a direct current in one direction through the field coil and canceling out the magnetic field from the outer rotor poles by passing a direct current in the other direction through the field coil.

The rotor may have permanent magnets arranged at a first interval in the circumferential direction on the outer diameter portion and salient poles formed between the permanent magnets, and may have permanent magnets arranged at a second interval in the circumferential direction on the inner diameter portion and salient poles formed between the permanent magnets.

The first interval is preferably narrower than the second interval, and the number of magnetic poles in the outer diameter portion is greater than the number of magnetic poles in the inner diameter portion.

The stator generates a fundamental wave and harmonics, and the number of poles of one of the inner rotor poles or the outer rotor poles corresponds to the number of poles of the fundamental wave, and the number of poles of the other of the inner rotor poles or the outer rotor poles corresponds to the number of poles of the harmonics.

In the low speed range , a direct current in one direction is passed through the field coil to cancel out the magnetic field from the rotor poles, either the inner rotor poles or the outer rotor poles, whose number of poles corresponds to the number of poles due to the fundamental wave, thereby adjusting the harmonics to be larger, and in the high speed range, a direct current in the other direction is passed through the field coil to cancel out the magnetic field from the rotor poles, either the inner rotor poles or the outer rotor poles, whose number of poles corresponds to the number of poles due to the harmonic, thereby adjusting the fundamental wave to be larger.

According to the present invention, the number of rotor poles can be changed simply by switching the direction of the current flowing through the field coil. Therefore, the number of poles can be changed without adding an actuator or enlarging the size of the inverter that supplies the three-phase current.

1 is a circuit diagram showing a rotating electric machine system including a rotating electric machine (motor) according to an embodiment. 2 is a cross-sectional view of the motor 20 taken along a plane passing through the rotation axis thereof. FIG. 2 is a diagram showing the overall configuration of a motor 20, including an exploded view. 2 is a cross-sectional view of the motor 20 taken along a plane perpendicular to the rotation axis thereof. FIG. 2 is a diagram showing the configuration of a circumferential quarter of the rotor 40 and the stator 22. FIG. 6 is a diagram showing the state of the field current magnetic flux in the configuration shown in FIG. FIG. 6 is a diagram showing the state of magnetic flux when the field current is set to 0 in the configuration of FIG. 5 . 2 is a diagram showing an axial cross section (half) of a rotor 40, a stator 22, and a field yoke 32. FIG. In FIG. 6, the state of magnetic flux resulting from the flow of a positive field current is indicated by arrows. FIG. 9 is a diagram showing the state of magnetic flux when the field current + in FIG. 8 flows. FIG. 9 is a diagram showing the state of magnetic flux when the field current − in FIG. 8 flows. FIG. 13 is a diagram showing the state of magnetic flux when a negative field current is applied. FIG. 9 is a diagram showing the state of magnetic flux when the field current − in FIG. 8 flows. 1A and 1B are diagrams showing time waveforms of no-load interlinkage magnetic flux when the field current is changed by simulation, in which (a) shows a negative (−) field current, (b) shows a zero field current, and (c) shows a (+) field current. FIG. 15 is a diagram showing the amplitudes of the fundamental wave and the fifth harmonic in FIG. 14 . FIG. 13 is a diagram showing the results of calculating the rotation speed-torque characteristics for fundamental wave driving and fifth harmonic driving by simulation.

The following describes an embodiment of the present invention with reference to the drawings. Note that the present invention is not limited to the embodiment described here.

System Configuration
1 is a circuit diagram showing a rotating electric machine system including a rotating electric machine according to an embodiment of the present invention. In the embodiment, a rotating electric machine that converts between electrical energy and mechanical energy is called a motor.

The DC power supply 10 is a secondary battery such as a lithium ion battery, and its output is connected to a three-phase inverter 12. The three-phase inverter 12 is connected to a motor 20. This motor 20 is a permanent magnet motor, and the stator 22 has three-phase stator coils 24 (24u, 24v, 24w) in a star connection, with the three outputs of the three-phase inverter 12 connected to one end of the stator coils 24u, 24v, 24w, and the other ends of the stator coils 24u, 24v, 24w commonly connected at a neutral point. A predetermined three-phase AC current is supplied to the stator coils 24u, 24v, 24w by the three-phase inverter 12, and the rotor rotates in response to the rotating magnetic field generated by this.

The DC power supply 10 is connected to a field coil 34 via a field circuit 30. A predetermined magnetic field is applied to the stator and rotor by the field coil 34 using the DC current supplied from the field circuit 30, thereby switching the number of magnetic poles of the rotor (hereinafter referred to as the pole number) as described below.

"Configuration of motor 20"
2 is a cross-sectional view of the motor 20 taken along a plane passing through the rotation axis of the motor 20. The motor 20 has a cylindrical rotor 40 and an annular stator 22 arranged to surround the rotor 40 with a gap therebetween. A rotation shaft 28 is arranged at the center of the rotor 40 so as to pass through the rotor 40.

The rotor 40 has multiple permanent magnets arranged discretely in the circumferential direction, which forms multiple magnetic poles along its outer periphery. The stator 22 has a stator core 22a and multiple-phase stator coils 24 arranged in slots of the stator core 22a and wound around the teeth between the slots. The coil ends of the stator coils 24 are shown in the figure.

In this embodiment, a field yoke 32 is provided to cover both axial end faces of the rotor 40 and the stator 22. The field yoke 32 is annular with an open center, and has an annular recess 32a recessed in a direction away from the rotor 40 and the stator 22 to avoid the coil ends of the stator coil 24. The field coil 34, wound in an annular shape, is housed in the recess 32a radially inside the coil ends of the stator coil 24.

Figure 3 shows the overall configuration of the motor 20, including an exploded view. Thus, the field yokes 32 are arranged on both sides of the stator 22 in the axial direction. The field yoke 32 has a recess 32a, and the field coil 34, which is wound in an annular shape, is arranged relatively inside the recess 32a.

Figure 4 is a cross-sectional view of the motor 20 taken on a plane perpendicular to its axis of rotation. The field yoke 32 is not visible in this figure. The stator core 22a has an outer circumferential yoke 22a-1 and teeth 22a-2 that protrude inward from the yoke 22a-1 at equal circumferential intervals. The spaces between adjacent teeth 22a-2 are slots into which the stator coils 24 are inserted.

A number of permanent magnets are arranged on the rotor 40 to form the magnetic poles. First, on the outer periphery, the first magnets 42 that form the outer rotor magnetic poles are arranged at equal intervals (first intervals), and the space between adjacent first magnets 42 forms a first salient pole 44. In this example, 20 first magnets 42 are provided, and if the first magnet 42 is a north pole, for example, this will be the north pole, and the first salient poles 44 between the first magnets 42 will have a polarity (N, S) that corresponds to the positive or negative field current.

In addition, second magnets 46 that form the inner rotor magnetic poles are arranged at equal intervals (second intervals) on the rotor 40. The second magnets 46 are composed of multiple (two in the figure) permanent magnets inserted into magnet holes 46a, 46b that are roughly arc-shaped (outward V-shaped). The second magnets 46 are provided at four locations at equal intervals in the circumferential direction to form four magnetic poles, and four second salient poles 48 are formed between adjacent second magnets 46 in the circumferential direction. For example, if the magnetic pole formed by the second magnets 46 is an S pole, this will be an S pole, and the second salient poles 48 will have a polarity (N, S) that corresponds to the positive or negative field current.

"Pole number switching"
<Field current 0>
5 is a diagram showing the configuration of a circumferential quarter of the rotor 40 and the stator 22. In this case, one set of three-phase stator coils 24u, 24v, 24w is provided, which corresponds to an electrical angle of 360 degrees and is wound around six teeth 22a-2. The rotor 40 has five first magnets 42 and a first salient pole 44 therebetween, one second magnet 46 and a second salient pole 48 therebetween.

Figure 6 shows the state of the field current magnetic flux in the configuration of Figure 5. Each of the first magnets 42 becomes a north pole, and the first salient pole 44 between them has zero magnetic flux. Also, the second magnet 46 becomes a south pole, and the second salient pole 48 between them has zero magnetic flux.

Figure 7 shows the state of magnetic flux when the field current is set to zero in the configuration of Figure 5. In this way, five first magnets 42 form five north poles. Also, one south pole is formed by the second magnet 46. Because the field current is zero and there is no magnetic flux, the total magnetic flux obtained by adding together the magnetic flux of both the first magnet 42 and the second magnet 46 is such that the magnetic flux due to the first magnet 42 is shifted by the magnetic flux due to the second magnet 46.

<Field current +>
8 is a diagram showing an axial cross section (half) of the rotor 40, the stator 22, and the field yoke 32. The field coil 34 is annular and rotates around the rotating shaft 28, and one-way DC current flows through it as the field current (field current +). A black circle in the figure indicates that the current flows toward the front of the page, and an x indicates that the current flows toward the back of the page. Current flows in opposite directions in the field coils 34 on both sides in the axial direction.

This creates a field current magnetic flux that flows from the rotor 40, around the field yoke 32 and the stator 22, and back to the rotor 40, as shown by the arrows in the figure.

In Figure 9, the arrows show the state of the magnetic flux resulting from the flow of field current + in Figure 6. In this case, the magnetic flux passes through the first salient pole 44 between the first magnets 42, but at the second salient pole 48, the field current magnetic flux is relatively large because there is no second magnet 46, while in the area where the second magnet 46 is located, the magnetic flux is less likely to pass because of the presence of the second magnet 46, and the magnetic flux in that area is small.

Figure 10 shows the state of the magnetic flux when the field current (field current +) of Figure 8 flows. In this way, the magnetic flux formed by the five first magnets 42 and one second magnet 46 does not change, but the field current magnetic flux is newly added.

This field magnetic flux forms the south pole and is difficult to pass through the magnets, so the path that passes through both the first salient pole 44 and the second salient pole 48, which do not have magnets, produces the largest magnetic flux. Next, the path that passes through the first salient pole 44 and the second magnet 46, then the path that passes through the first magnet 42 and the second salient pole 48, and the smallest is the path that passes through the first magnet 42 and the second magnet 46.

When these magnetic fluxes are added together, the magnetic flux generated by the first magnet 42 is greatly expanded, resulting in a magnetic flux that appears to be shifted to the S side.

<Field current->
Fig. 11 is a diagram showing the state of magnetic flux when a negative (-) field current flows in Fig. 8. The negative field current forms a field current magnetic flux in the opposite direction (other direction) to that in Fig. 8.

In Figure 12, the arrows show the state of the magnetic flux when a negative field current is passed. In this case, the direction of the magnetic flux is opposite to that in Figure 9, but the magnitude of the magnetic flux is the same.

Figure 13 shows the state of the magnetic flux when the field current (-field current) of Figure 8 flows. In this way, the magnetic flux formed by the five first magnets 42 and one second magnet 46 does not change, but the field current magnetic flux is in the opposite direction to that in Figure 10, and becomes a magnetic flux that forms a north pole.

When these magnetic fluxes are added together, the magnetic flux from the second magnet is greatly expanded, resulting in a magnetic flux that appears to be shifted to the N side.

<Summary>
In this way, by passing a positive field current through the field coil 34, a magnetic flux similar to the magnetic flux of the first magnet 42 is obtained, and by passing a negative field current through the field coil 34, a magnetic flux similar to the magnetic flux of the second magnet 46 is obtained.

Therefore, depending on the direction of the DC current flowing through the field coil 34, the number of pole pairs in the rotor can be switched between 5 x 4 = 20 (40 poles) and 1 x 4 = 4 (8 poles).

The stator 22 shown in Figures 2 to 4 has 24 slots, a three-phase coil that generates a fundamental wave rotating magnetic field with 8 poles and a harmonic rotating magnetic field with 40 poles, and an annular field coil 34. The rotor 40 has a first magnet 42 that forms 40 poles and a second magnet 46 that forms 8 poles. The rotor 40 has a first salient pole 44 on its surface that is magnetized by the flow of field current magnetic flux, and a second salient pole 48 on the inner diameter of the rotor 40 that is magnetized by the flow of field current.

Therefore, in the stator 22, an 8-pole fundamental wave rotating magnetic field and a 40-pole high-frequency rotating magnetic field are generated, and by passing a negative (-) field current through the field coil 34, fundamental wave driving with 8 rotor poles can be performed, and by passing a positive (+) field current through the field coil 34, 5th harmonic driving with 40 rotor poles can be performed.

In other words, by switching the direction of the DC current flowing through the field coil 34, the number of poles of the rotor 40 can be switched between the number of poles for fundamental wave drive and the number for fifth harmonic drive, and torque can be generated in each rotating magnetic field.

"Interlinkage magnetic flux waveform"
Fig. 14 is a diagram showing the time waveform of the no-load interlinkage magnetic flux when the field current is changed by simulation, where (a) shows a negative (-) field current, (b) shows a field current of 0, and (c) shows a positive field current. Fig. 15 is a diagram showing the amplitude of the fundamental wave and the fifth harmonic at that time, where the circle ● in the diagram indicates a negative (-) field current and the square □ indicates a positive (+) field current.

In this way, when a negative (-) field current is passed through the field coil 34, the fundamental wave increases and becomes the dominant waveform, and when a positive (+) field current is passed through the field coil 34, the fifth harmonic increases and becomes the dominant waveform.

"Number of poles"
In the above-described embodiment, the slots of the stator 22 are used for a three-phase coil (stator coil 24) having eight poles, and the rotor 40 is switched between eight poles (fundamental wave) and 40 poles (fifth harmonic). However, the above-described pole number switching can be performed if the number of slots, the number of poles of the three-phase coil, and the number of poles of the rotor satisfy the following relationship.
_Z2 = _Z1 ± p
_Z1 : Number of stator slots _Z2 : Number of pole pairs on the outer diameter of the rotor p: Number of pole pairs of the three-phase coil (number of pole pairs on the inner diameter of the rotor)

In the above embodiment, Z ₁ =24, Z ₂ =20, and p=4, and switching between Z ₂ and p is possible by the field current.

"About output torque"
FIG. 16 is a diagram showing the results of calculating the rotation speed-torque characteristics for fundamental wave driving and fifth harmonic driving through a simulation, showing the characteristics when a negative (-) field current is passed and a three-phase current with a drive frequency synchronized with the rotor rotation is passed through the three-phase coil (fundamental wave driving), and the characteristics when a positive (+) field current is passed and a three-phase current with a drive frequency five times the rotor rotation is passed through the three-phase coil (fifth harmonic driving).

This confirms that by switching the direction of the field current, it is possible to achieve both high torque at low speeds and high output at high speeds.

"others"
Here, since the rotation direction of the fifth harmonic rotating magnetic field is opposite to that of the fundamental wave rotating magnetic field (which coincides with the rotor rotation direction), the rotation direction of the current command value for fifth harmonic drive is opposite to that for fundamental wave drive. Also, if the drive frequency at the maximum rotation speed in fundamental wave drive is set as the upper limit of the drive frequency, in the case of fifth harmonic drive, the rotation speed can only be 1/5 of that in fundamental wave drive.

"Effects of this embodiment"
According to this embodiment, by adjusting (switching the direction of) the field current of the field coil 34, the magnetic flux density distribution in the magnetic flux gap created by the rotor 40 can be switched between a fundamental wave and a harmonic (e.g., a fifth harmonic).

Therefore, by increasing the harmonics and increasing the frequency of the drive current of the stator coil 24 relative to the rotor synchronous frequency, high torque can be achieved through the magnetic gear effect. On the other hand, by increasing the fundamental wave, the frequency of the drive current of the stator coil 24 becomes the rotor synchronous frequency, allowing for high speed rotation and high output.

REFERENCE SIGNS LIST 10 DC power supply, 12 three-phase inverter, 20 motor, 22 stator, 24 stator coil, 28 rotating shaft, 30 field circuit, 32 field yoke, 34 field coil, 40 rotor, 42 first magnet, 44 first salient pole, 46 second magnet, 48 second salient pole.

Claims (5)

a stator having a stator core having a plurality of stator slots and a three-phase coil arranged in the stator slots to form a predetermined magnetic field;
a rotor having an inner diameter portion formed with a predetermined number of inner rotor magnetic poles and an outer diameter portion formed with a different number of outer rotor magnetic poles from the inner diameter portion;
a field yoke located on a side of the stator core and the rotor;
a field coil that generates a field flux that circulates around a path formed by the rotor, the stator, and the field yoke;
having
By passing a direct current in one direction through the field coil, the magnetic field from the inner rotor pole is cancelled, and by passing a direct current in the other direction through the field coil, the magnetic field from the outer rotor pole is cancelled, thereby making it possible to switch the number of magnetic poles of the rotor.
Rotating electric motor. 2. The rotating electric machine according to claim 1,
The rotor has permanent magnets arranged at first intervals in the circumferential direction on an outer diameter portion and salient poles formed between the permanent magnets, and has permanent magnets arranged at second intervals in the circumferential direction on an inner diameter portion and salient poles formed between the permanent magnets.
Rotating electric motor. 3. The rotating electric machine according to claim 2,
The first interval is narrower than the second interval, and the number of magnetic poles in the outer diameter portion is greater than the number of magnetic poles in the inner diameter portion.
Rotating electric motor. A rotating electric machine according to any one of claims 1 to 3,
a fundamental wave and a harmonic wave are generated by the stator, the number of poles of one of the inner rotor poles or the outer rotor poles corresponds to the number of poles of the fundamental wave, and the number of poles of the other of the inner rotor poles or the outer rotor poles corresponds to the number of poles of the harmonic wave;
Rotating electric motor. 5. The rotating electric machine according to claim 4 ,
In the low speed range , a unidirectional DC current is passed through the field coil to cancel out the magnetic field from the rotor poles whose number of poles corresponds to the number of poles of the fundamental wave among the inner rotor poles or the outer rotor poles, thereby adjusting the harmonics to be larger.
In the high speed region , a DC current in the other direction is passed through the field coil to cancel out the magnetic field from the rotor poles whose number of magnetic poles corresponds to the number of magnetic poles caused by the harmonics among the inner rotor poles or the outer rotor poles, thereby adjusting the fundamental wave to be larger.
Rotating electric motor.

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