Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-10-22
2001-04-03
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S162000, C310S114000
Reexamination Certificate
active
06211593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a synchronous motor utilizing a permanent magnet.
2. Description of the Related Art
One type of conventional synchronous motor is a permanent magnetic synchronous motor such as shown in FIG.
1
. Such a motor has a permanent magnet PM
1
with a N pole arranged radially outward and a permanent magnet PM
2
with a S pole arranged radially outward. The motor shown has a rotor shaft
1
, a rotor yoke
2
, and a stator (not shown) which is of a type commonly used in a three-phase induction motor, or the like.
A known example of the above conventional motor would be a permanent magnetic motor having an embedded magnet structure, such as is disclosed in such as is disclosed in Memoir D by Institute of Electrical Engineers of Japan, Vol. 114, Issue 6, 1994, pp. 668 to 673, “Wide Range Variable Speed Control for a PM Motor with Embedded Magnetic Structure”, and so on.
FIG. 2
shows an example of a three-phase and six-pole synchronous reluctance motor, provided with a thin magnetic flux path
14
for magnetically connecting magnetic poles, and a slit
10
, which is either a space or made of non-magnetic member, formed between the magnetic flux paths
14
. The motor also has a rotor shaft
1
, a rotor yoke
13
, and a link
15
in a radial direction. The link
15
is not just unnecessary from a magnetic point of view, its presence can be harmful in light of an electromagnetic operation of the motor as leakage flux passes therethrough. Nevertheless, the link
15
is required to mechanically connect the rotor yoke
13
and each magnetic flux path
14
for structural reinforcement. The link
16
on the external circumference of the rotor similarly reinforces the rotor as entirety. The rotor has a structure in which flat rolled magnetic steel sheets and strips, each having the shape as shown in
FIG. 2
, are laminated in the direction of the rotor shaft. The stator
12
has slots where an three-phase six-pole AC winding passes.
Operation of the synchronous reluctance motor
FIG. 2
will be described referring to
FIG. 3
, which shows a modeled two-pole synchronous reluctance motor, provided with thin magnetic flux paths NMP and slits SG. A magnetic flux path NMP is a path where magnetic flux passes from one magnetic pole to another. A slit SG is a space formed between adjacent thin magnetic flux paths NMP.
The rotor of
FIG. 3
has a structure in which smaller magnetic resistance is caused in the vertical (d-axis) direction of the rotor and larger magnetic resistance is caused in the horizontal (q-axis) direction. A stator
7
is also shown in the drawing.
When the rotor is excited by magnetizing current id, N and S poles are formed as indicated in the figure, thereby creating a magnetic flux MFd. When a torque current iq is then supplied in the direction of the magnetic flux MFd, force F
1
is caused. As the torque current iq additionally causes a magnetic flux MFq, force F
2
is thus caused which is proportional to a product of the magnetizing current id and the magnetic flux MFq. As a result, the motor generates a rotation torque which is proportional to the force (F
1
-F
2
).
The above operation of
FIG. 3
can be expressed using vectors, as shown in
FIG. 4
, in disregard of losses, such as winding resistance, leakage inductance, core loss, and soon, of the motor. Current i
0
, or an added current of the magnetizing current id and the torque current iq, is supplied to the motor. When the motor rotates at a rotation angle frequency &ohgr; with d-axis inductance Ld and q-axis inductance Lq, a voltage Vd=−Lq·diq/dt=−&ohgr;Lq·iq will be caused in the direction of the flow of magnetic current id, while a voltage Vq=Lq·did/dt=&ohgr;·Ld·id will be caused in the direction of the flow of torque current iq. voltage V
0
is an added voltage of the voltages Vd and Vq. Motor output power P is expressed as P=&ohgr;·Ld·id·iq−&ohgr;·Lq·iq·id=&ohgr;·(Ld−Lq)·id ·iq=v
0
·i
0
·COS(&thgr;PR), in which &thgr;PR is a phase difference between voltage V
0
and current i
0
, and COS(&thgr;PR) is a power factor.
FIG. 5
is a longitudinal cross sectional view of a three-phase six-pole synchronous motor of a hybrid type which has a pair of motors using permanent magnets and a pair of field winding.
FIG. 6A
is a lateral cross section of the rotor of
FIG. 5
along the line EF;
FIG. 6B
is a lateral cross section of the same along the line GH. A three-phase AC winding
28
passes through the respective stators ST
1
, ST
2
(
25
,
26
) of the two respective motors, winding thereabout in the same manner as a three-phase AC winding of a typical three-phase inductance motor does. A field winding
29
winds around the stator in the rotor rotation direction, and excites the magnetic flux, passing through the stators and rotors as indicated by the arrow
30
, of a magnetic field. A rotor shaft
1
is also shown in the drawing. A permanent magnet
22
constitutes a N pole of the rotor RT
1
on the left side. Three permanent magnets
22
are provided each for every electrical angle of 360° in the rotor rotation direction. The rotor RT
1
has a magnetic flux path
23
. A permanent magnet
32
constitutes a S pole of the rotor RT
2
on the right side. Three permanent magnets
32
are provided for every electrical angle of 360° in the rotor rotation direction at a position differing from that of each permanent magnet
22
by an electrical angle of 180° in the rotor rotation direction. Back yokes
24
and
27
on the rotor and stator sides, respectively, induce magnetic flux in the direction of the rotor shaft.
Magnetic flux in the magnetic poles
31
,
21
, which are made of soft magnetic material, varies due to the current flowing in the field winding
29
. Specifically, when the magnetizing current IFS for the field winding
29
is zero (IFS=0), the magnetic flux is not excited on the magnetic poles
31
,
21
, and instead is formed between the permanent magnets
22
and
32
. When the magnetizing current IFS is negative, provided that a magnetic flux is caused in the direction with the arrow
30
, the magnetic pole
31
is rendered to be a N pole, while the magnetic pole
21
is rendered to be a S pole. The magnitude of the magnetic flux is proportional to that of the field magnetizing current IFS. When the magnetizing current IFS is positive, field magnetic flux is caused in the direction opposite from that with the arrow
30
. As a result, the magnetic pole
31
is rendered a S pole, while the magnetic pole
21
is rendered a N pole. The magnitude of the magnetic flux is proportional to that of the field magnetizing current IFS. When the magnetizing current IFS is positive, respective magnetic poles of the rotor RT
1
and of the rotor RT
2
are alternately rendered to be N and S poles in the rotor rotation direction, and the motor resultantly functions like a permanent magnet synchronous motor, as shown in FIG.
1
. When the magnetizing current IFS is negative, on the other hand, the magnetic poles of the rotor RT
1
all serve as a N pole, so that a difference in magnetic flux between the magnetic poles
22
and
31
resultantly serves as a function of the motor, producing an effect similar to flux-weakening. Meanwhile, the respective magnetic poles of the rotor RT
2
all serve as a S pole, so that a difference in magnetic flux between the magnetic poles
32
and
21
resultantly serves as a function of the motor, achieving an effect similar to flux-weakening. As described above, by controlling the magnetizing current IFS by varying in a range between positive and negative, effective magnetic flux of a magnetic field can be strengthened or weakened. This enables rotation frequency control of the synchronous motor in a wider range.
Although permanent magnet synchronous motors such as shown in
FIG. 1
are widely used because of their easiness of torque control, they have a problem of incapability of constant power control through flux-weakening control whe
Nguyen Tran
Okuma Corporation
Oliff & Berridge PLC.
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