Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2001-08-16
2003-02-18
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
Reexamination Certificate
active
06522093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a method for driving a brushless DC motor, more particularly, to a method for driving a brushless DC motor, in which a stator of the motor selectively stops providing a magnetic field for a rotor based on the angular position of the rotor corresponding to the stator.
2. Description of the Prior Art
Motors are well known and widely used in electrical and electronic industries. A conventional motor utilizes windings as its internal rotor, in which two ends of the armature windings are continuously interchangeably coupled to external circuits through the rotating process of the rotor and thereby direction commutation for the current on the armature is ruled. Using this scheme for the motor rotation, motor brushes are apt to be worn away through mechanical rubbing against the rotating contacts. This not only causes increased impedance and bad contact with external circuits, but also gives off a spark when bad contact has occurred. In a brushless DC motor, windings are wound around the stators, and permanent magnets are used as rotors. Electronic circuits are applied instead to control current flow direction commutation through windings and thus the polarity distribution of the magnetic field is continuously interchanged. Through such a strategy, no contact switching is required, and mechanical contact attrition is effectively avoided.
The mechanism of driving the brushless DC motor is described in the flow chart of
FIG. 1. A
Hall sensor (or Hall IC) is adopted to sense the magnetic field rotor distribution (Step
101
). According to the sensing information, a driving control signal is then generated (Step
102
). The driving control signal is issued to determine the current's direction on the stator windings. The magnetic field polarities induced by the current are then interchanged with the alternated current direction (Step
103
). Since the induced magnetic field exerts a force on the permanent magnets of the rotor, the rotor is then rotated in a predetermined direction (Step
104
).
The magnetic interactions between the rotor and the stator and the rotation mechanism of the brushless DC motor are illustrated in
FIG. 2
a
to
FIG. 2
d
. In
FIG. 2
a
, the four arms
112
,
114
,
116
and
118
of the stator
110
points respectively to the four joints of the four magnetic arcs
122
,
124
,
126
and
128
of the rotor
120
, wherein every two neighboring arcs have a joint between them. A Hall sensor
130
is located on the angle bisector of the arms
112
and
114
and near the rotor
120
. The Hall sensor
130
is capable of sensing the magnetic field irradiated from the S-polar magnetic arc
124
. Based on the sensed information, a driving signal is generated to control the current's direction on the windings and thus the polarities of the four magnetic arms, which are shown in
FIG. 2
a
. Therefore, the magnetic field irradiated from the four arms of the stator will exert magnetic force on the magnetic arcs of the rotor. The force directions by the four arms of the stator on the rotor are approximately presented as the hollow arrows
131
to
138
.
As an example of the N-polar magnetic arc
122
, the N-polar magnetic arc
122
both receives an attractive force
132
by the arm
114
and a repulsive force
131
by the arm
112
. The tangent components (the forces are tangent to the rotor) of the two forces
132
and
131
on the circular rotor create a resultant force, which will drive the rotor to rotate counterclockwise in an angular acceleration motion manner (the vector of the angular acceleration is perpendicular to and penetrates through the sheet). Similarly, the S-polar magnetic arc
124
both receives an attractive force
134
by the arm
116
and a repulsive force
133
by the arm
114
. The tangent components of the two forces
134
and
133
on the circular create a resultant force, which will also drive the rotor to rotate counterclockwise in an angular acceleration motion manner. In addition, N-polar arc
126
and the S-polar arc
128
also receive the same magnetic interactive mechanism. Therefore, the motor rotor
120
will rotate counterclockwise, indicated as the direction of the arrow
139
, about the central point (the joint of the four arms) of the stator (the joint of the four arms).
As the motor rotor
120
rotates counterclockwise from
FIG. 2
a
to
FIG. 2
b
, the magnetic arms
112
,
114
,
116
and
118
of the stator
110
point to the center of the four magnetic arcs of the rotor
120
, respectively. Thus the four rotor magnetic arcs
122
,
124
,
126
and
128
will receive four centripetal magnetic forces, which points to the center of the stator as the hollow arrows
142
,
144
,
146
and
148
in
FIG. 2
b
show, by the stator
110
. Obviously, the tangent components of the magnetic force on the rotor
120
is zero, and thus the rotor
120
will not accelerate in a tangent direction. At this time, the rotor
120
will continue rotating counterclockwise owing to inertial mechanism. Now the Hall sensor is located near the joint and along the angle bisector of the S-polar
128
and N-polar
126
magnetic arcs, and thus senses a zero net magnetic field.
When the rotor
120
rotates counterclockwise to the angular position corresponding to the stator in
FIG. 2
c
from that in
FIG. 2
b
, the Hall sensor is slightly deviated from the position corresponding to the rotor
120
as compared to that in
FIG. 2
b
and thus senses magnetic force from the N-polar magnetic arc
126
. A driving control signal is in turn issued to change the direction of the current flowing though the stator windings, and thus the polarity commutation of the magnetic field induced by the direction changeover of the current is achieved. After the current's direction changeover, the stator's four arms polarities are depicted in
FIG. 2
c
. In
FIG. 2
c
, the arms
112
and
116
are S-polar, while the arms
114
and
118
are N-polar. Then, the rotor's magnetic arcs are exerted, small amounts of tangent force by the stator's arms, and the four magnetic arcs force receptive directions are indicated as the hollow arrows
152
,
154
,
156
and
158
. Thus, the rotor
120
continues rotating counterclockwise in an accelerating manner.
When the rotor
120
rotates counterclockwise to the angular position corresponding to the stator in
FIG. 2
d
from that in
FIG. 2
c
, the rotor's magnetic arcs polarity distribution and the stator's magnetic arms is just the opposite to that in
FIG. 2
a
. The repulsive force
131
and
135
in
FIG. 2
a
is now replaced by the repulsive force
161
and
165
in
FIG. 2
d
, wherein the repulsive force
161
and
165
are the same as the repulsive force
131
and
135
both in direction and quantity. The same magnetic mechanism happens to the repulsive forces
133
and
137
in
FIG. 2
a
and
163
and
167
in
FIG. 2
d
also. However, the attractive forces
134
and
138
in
FIG. 2
a
are now replaced by the attractive force
164
and
168
in
FIG. 2
d
, wherein the attractive forces
134
and
138
are the same as the attractive forces
164
and
168
both in direction and quantity.
According to the rotating mechanism described above, the rotor has the maximum angular acceleration for rotating in the case as
FIG. 2
a
. Then, the angular acceleration gets smaller and smaller and then becomes zero when it corresponding to the angular position related to the stator in
FIG. 2
b
. At that time, the angular positions of the four magnetic arcs of the rotor corresponding to the stator are called critical positions, and the angular position of the rotor is called a critical position.
In a case where the polarities of magnetic arms are kept constant, four arms of the stator generates tangent accelerations opposite to the rotating direction, after the rotor rotates across the critical position, and thus the rotating speed of the rotor is decreased. To achieve a desired continuous positive acceleration for the rotor, t
Hsu Chia-Chang
Yang Chih-Shih
Leykin Rita
Prolific Technology Inc.
Sughrue & Mion, PLLC
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