Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-05-24
2004-09-21
Le, Dang (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156530, C310S261100
Reexamination Certificate
active
06794784
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a permanent magnet reluctance motor wherein a plurality of permanent magnets are provided in combination.
2. Description of the Related Art
A permanent magnet reluctance motor according to previous applications by the present applicants (Japanese Patent Application Number H. 11-043869 and Japanese Patent Application Number H. 11-122000) is of the construction shown in radial cross-section in FIG.
1
. In
FIG. 1
, a stator
1
is provided with an armature coil
2
, within which a rotor
3
is provided.
Rotor
3
is provided with a rotor core
4
and permanent magnet
6
. In rotor core
4
there are formed a direction where magnetization is easy and a direction where magnetization is difficult. Specifically, in order to form magnetic irregularities, rotor core
4
is constructed by laminating electromagnetic steel plates provided with eight permanent magnet embedding holes
5
in which are embedded permanent magnets
6
along the direction of easy magnetization. The eight permanent magnet embedding holes
5
form four projecting poles by being arranged in a “+” arrangement. That is, the regions sandwiched by permanent magnet embedding holes
5
which are positioned on both sides of non-magnetic portions
8
represent between-pole portions
4
b
constituting “concavities” in terms of magnetic polarity. Furthermore, permanent magnets
6
which are magnetized so as to cancel the magnetic flux of the armature current passing through adjacent between-pole portions
4
b
are arranged in permanent magnet embedding holes
5
. That is, the relationship of the permanent magnets
6
which are on both sides of pole region
4
a
is that their directions of magnetization are the same, while the relationship of the two permanent magnets
6
which are positioned on both sides of between-pole region
4
b
is that their directions of magnetization are mutually opposite in the circumferential direction of rotor
3
. Permanent magnets
6
are preferably magnetized practically in the circumferential direction and even more preferably in a direction practically perpendicular to the axis of the magnetic poles.
Next, the operation of the permanent magnet reluctance motor according to the previous application described above will be described.
FIG. 2
shows the magnetic flux &PHgr;d of the component in the direction along the axis of the magnetic pole of rotor core
4
produced by the armature current of the d axis; in order that the core of pole region
4
a
should provide a magnetic path, the magnetic construction is such that magnetic flux can easily flow, the magnetic resistance in the magnetic path in this direction being very small. Reference symbol
8
denotes a non-magnetic region.
FIG. 3
shows the magnetic flux &PHgr;q created by the armature current of the q axis of the component in the direction along the axis joining the center of between-pole region
4
b
and the center of rotor
3
. Magnetic flux &PHgr;q of this between-pole region
4
b
forms a magnetic path of non-magnetic region
8
and between-pole region
4
b
that runs transversely across permanent magnets
6
. Since the relative permeability of non-magnetic region
8
is “1” and the relative permeability of permanent magnets
6
is also practically “1”, the magnetic flux &PHgr;q produced by the armature current is lowered by the high magnetic resistance action.
The permanent magnets
6
between the magnetic poles are magnetized in the direction practically perpendicular to the axis of the magnetic pole so that, as shown in
FIG. 4
, a magnetic circuit &PHgr;ma is formed whereby the magnetic flux generated by permanent magnet
6
flows in the circumferential direction of magnetic region
7
at the boundary of the circumference of the rotor core, through pole region
4
a
, returning to the pole of opposite polarity.
Also, some of the flux of the permanent magnet
6
passes through the gap, through the pole region
4
a
of rotor
3
or permanent magnets
6
of the adjacent pole, returning to the original permanent magnets
6
and thereby also forming a magnetic circuit &PHgr;mb.
As shown in
FIG. 3
, the interlinking magnetic flux of these permanent magnets
6
is distributed in the opposite direction to the magnetic flux &PHgr;q of the component in the direction of the between-pole center axis produced by the armature current of the q axis, and repels and cancels ingress of armature flux &PHgr;q from the between-pole region
4
b
. In the gap outside between-pole region
4
b
, the gap magnetic flux density created by the armature current is lowered by the magnetic flux of permanent magnets
6
, causing it to show larger variation than the gap magnetic flux density outside pole region
4
a
. That is, the variation of the gap magnetic flux density with respect to position of rotor
3
becomes large, resulting in a large variation of magnetic energy. Furthermore, under load, at the boundary of pole region
4
a
and between-pole region
4
b
, a magnetic region
7
exists where there is magnetic short-circuiting; this is strongly magnetically saturated by the load current. As a result, the magnetic flux of permanent magnets
6
that is distributed between the poles is increased. Irregularities representing large changes in the gap flux density distribution are therefore created due to the magnetic flux of permanent magnets
6
and the high magnetic resistance of non-magnetic region
8
and permanent magnets
6
; considerable changes in magnetic energy are thereby produced, as a result of which large output is obtained.
The following effects are manifested in regard to the adjustment width of terminal voltage in order to obtain variable speed operation over a wide range. With this proposed permanent magnet reluctance motor, since permanent magnets
6
were only provided over part of the concave portion of the between-pole region
4
b
, the surface area of permanent magnets
6
was more restricted than in the case of an ordinary permanent magnet motor in which permanent magnets
6
are provided over practically the entire circumference of the surface of rotor
3
and, as a result, the amount of interlinking magnetic flux produced by the permanent magnets
6
was small.
Furthermore, in the non-excited condition, practically all of the magnetic flux of permanent magnets
6
was leakage magnetic flux within rotor core
4
passing through magnetic region
7
of the magnetic pole boundary region. Consequently, since, in this condition, the induced voltage can be made very small, core loss in the non-excited condition is small. Also, overcurrent is small even when armature coil
2
is in a short-circuited defective condition.
When loaded, terminal voltage is induced by addition of the interlinking magnetic flux created by the armature current (exciting current component and torque current component of the reluctance motor) to the interlinking magnetic flux created by the permanent magnets
6
.
In an ordinary permanent magnet reluctance, the interlinkage magnetic flux of the permanent magnets
6
represents practically all of the terminal voltage, so it is difficult to adjust the terminal voltage; however, in this permanent magnet reluctance motor, the interlinkage magnetic flux of permanent magnets
6
is small, so a large width of adjustment of the terminal voltage can be achieved by providing a large adjustment of the exciting current component. That is, since the exciting current component can be adjusted in accordance with speed so that the voltage is below the power source voltage, wide-range variable speed operation can be achieved with fixed voltage from the base speed. Also, since the voltage is not suppressed, since a weak field system is implemented under forcible control, even if control becomes inoperable when rotating at high speed, no overvoltage can be generated.
Furthermore, since permanent magnets
6
are also embedded within the core, rotor core
4
constitutes a retaining mechanism for permanent magnets
6
, preventing permanent magnet
Araki Takashi
Arata Masanori
Hashiba Yutaka
Hirano Yasuo
Kazao Yukihiko
Elkassabgi Heba Y.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Le Dang
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