Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-03-21
2001-05-29
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S261100, C310S168000
Reexamination Certificate
active
06239526
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a synchronous reluctance motor having a plurality of flux barriers, and more particularly, to a barrier type synchronous reluctance motor with an improved flux barrier that is capable of reducing torque ripple.
2. Description of the Background Art
Generally, two axes are used for controlling a motor: one is a D axis, that is, a boundary of a magnetic pole, and the other is a Q axis, that is, a center of the magnetic pole. The D axis has a high magnetic permeability, and the Q axis has a low magnetic permeability. A torque is generated due to an inductance difference between the D axis and the Q axis.
FIG. 1
is a plan view of a synchronous reluctance motor having flux barriers in accordance with the conventional art.
For the convenience of explanation, an example is taken where there are four poles and 24 stator slots.
As shown in
FIG. 1
, a stator
10
includes a body
11
, a plurality of slots
13
and teeth
14
formed at the inner circumferential surface
12
. A rotor
20
includes a body
21
, a plurality of flux barriers
22
and a plurality of ribs.
As to the ribs, there are provided real ribs
23
(demonstrated by a circle), that is, the end portion of the flux barrier and virtual ribs
24
(demonstrated by ‘x’)., and the interval therebetween (including the actual rib
23
and the virtual rib
24
) is the same as the pole pitch of the rotator slot.
The body
21
of the rotor
20
is made of magnetic substance, and the plurality of flux barriers
22
is made of a non-magnetic substance, which are radially arranged having the Q axis as a center and D axis as a boundary.
The operation of the synchronous reluctance motor having the flux barriers in accordance with the conventional art will now be described.
First, an inductance is generated by a current applied to the winding coil of the stator
10
, and a torque is generated due to the inductance difference between the D axis and the Q axis owing to the flux barrier
22
, and the rotor is rotated by the torque.
Torque ripple is generated due to the relative position of the flux barrier and the slot opening
13
a
of the stator
10
. In other words, the torque ripple is generated due to a variation of the relative position of the slot opening
13
a
of the stator
20
and the rotor rib
23
.
FIGS. 2 and 3
are plan views of the synchronous reluctance motor in the case where the rotor
20
is placed at specific positions when the motor of
FIG. 1
is operated.
FIG. 2
shows the case where the ribs
23
and
24
of the rotor
20
face the slot opening
13
a
of the stator
10
, and
FIG. 3
shows the opposite case to that of
FIG. 2
, that is, the case where the rib
23
of the rotor
20
faces the teeth
14
of the stator
10
.
The magnetic resistances which develops in each of the first and the second cases are much different to each other, and due to the magnetic resistance, variations a substantial torque ripple is generated when the rotor
20
is rotated.
For that reason, the torque ripple is substantial when the number of the rotor ribs (the actual rib
23
and the virtual rib
24
) is the same as that of the stator slots and when the interval between the ribs is the same as that of the slots.
Since the torque ripple is determined by the arrangement structure of the flux barrier, to reduce the torque ripple, various techniques for designing the structure of the flux barrier have been developed and disclosed, which will now be described.
FIG. 4
shows a flux barrier type synchronous reluctance motor having a plurality of flux barriers in accordance with a conventional art, in which the number of the real ribs of the flux barrier
22
is greater than that of the slots
13
.
In this case, even though some of the ribs face the slots
13
, since the remaining other ribs face the teeth
14
, the average value of the overall magnetic resistance is lowered although the magnetic resistance at specific portions remains quite large.
However, as to this kind of rotor having the plurality of flux barriers, since the structure of the rotor is complicated, its mechanical strength is weakened as compared to a rotor having a few flux barriers, and its fabrication is also difficult. This problem becomes more serious as the size of the rotor is reduced.
FIG. 5
is a plan view of a flux barrier type synchronous reluctance motor where D and Q axes are mechanically unbalanced in accordance with the conventional art.
Unlike the D axis of a general motor, the D axis is slanted toward one side as much as a predetermined angle &thgr;, so that the D and Q axes are mechanically unbalanced.
With this structure, since the spacial intervals of the ribs of the flux barriers
22
and the intervals of the slots
13
are not the same, the torque ripple is reduced. However, since the D axis and the Q axis are unbalanced, it is difficult to judge electric D axis and Q axis when the motor is controlled, and the inductance values Ld and Lq according to the D and Q axes are influenced, causing a reduction of the overall torque output.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a flux barrier type synchronous reluctance motor by which the average value of the magnetic resistance generated according to the rotation of a rotor is constant regardless of the position of the rotor.
Another object of the present invention is to provide a flux barrier type synchronous reluctance motor of which the intervals between each rib, that is, the end portion of the flux barrier, are not uniform as a whole.
Still another object of the present invention is to provide a flux barrier type synchronous reluctance motor in which the rotor has a simple structure.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a flux barrier type synchronous reluctance motor in which a plurality of flux barriers are provided in a rotor, of which a plurality of ribs form the end portion of each of the flux barriers, wherein assuming that both ends of a single flux barrier are a first and a second ribs, when the first rib faces the center of a slot of a stator, the second rib faces the center of a teeth of the stator.
REFERENCES:
patent: 5818140 (1998-10-01), Vagati
patent: 5903080 (1999-05-01), Nashiki et al.
Jung Dal Ho
Oh Jae Yoon
LG Electronics Inc.
Mullins Burton
Ostrolenk Faber Gerb & Soffen, LLP
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