Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2001-06-15
2002-11-26
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000, C318S434000, C318S721000
Reexamination Certificate
active
06486628
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to energization control systems for a motor. More particularly, the present invention pertains to an energization control system for a motor for controlling electric current in a coil of each phase of a switched reluctance type motor (called an SR motor hereinafter) applied, for instance, to electric vehicles.
BACKGROUND OF THE INVENTION
The operational principle of SR motors in which the present invention is applied is explained in FIG.
10
. As shown in
FIG. 10
, an SR motor
1
includes a hollow cylindrical stator
2
and a cylindrical rotor
3
which is rotatably provided in the stator
2
keeping a predetermined gap with the stator
2
. On the inner periphery of the stator
2
, six radial poles
2
a
-
2
f
are formed at equal intervals. On the outer periphery of the rotor
3
, four radial poles
3
a
-
3
d
are formed at equal intervals. When two radial poles of the stator
2
(e.g.,
2
c
,
2
f
) are opposed to two radial poles of the rotor
3
(e.g.,
3
b
,
3
d
), two other radial poles
3
a
,
3
c
of the rotor
3
are located between radial poles of the stator
2
, i.e.,
2
a
,
2
b
, and
2
d
,
2
e
respectively. Each pair of opposing radial poles
2
a
and
2
d
,
2
b
and
2
e
, and
2
c
and
2
f
, shares a common circuit including coils
4
a
and
4
d
,
4
b
and
4
e
, and
4
c
and
4
f
respectively.
As shown in
FIG. 10
, when electric current I
1
is supplied to the coils
4
a
,
4
d
, magnetic flux is generated in the poles
2
a
,
2
d
of the stator
2
, and thus attracts the poles
3
a
,
3
c
of the rotor
3
. As shown in
FIG. 10
, when the electric current I
2
is supplied to the coils
4
b
,
4
e
, the magnetic flux is generated in the poles
2
b
,
2
e
of the stator
2
, and thus attracts the poles
3
d
,
3
b
of the rotor
3
. As shown in
FIG. 10
, when the electric current I
3
is supplied to the coils
4
c
,
4
f
, the magnetic flux is generated in the poles
2
c
,
2
f
of the stator
2
, and thus attracts the poles
3
c
,
3
a
of the rotor
3
. Accordingly, by supplying three-phase electric current I
1
-I
3
to the pairs of coils
4
a
-
4
c
,
4
b
-
4
e
and
4
c
-
4
f
synchronous with the rotation of the rotor
3
, the rotor
3
can be driven at a desired rotation number. By ON/OFF operation of a switching element
10
, each electric current I
1
-I
3
is switched ON and OFF. Each electric current is supplied by electric voltage from a battery
5
.
FIG. 11
shows a switching circuit for energizing the coils of SR motor by chopping control shown in FIG.
10
. The switching circuit illustrated is only for one phase. In order to drive the SR motor
1
shown in
FIG. 10
, three systems of the same switching circuit are provided.
In
FIG. 11
, the switching circuit includes a first switching element
11
, a second switching element
12
, a first diode
13
, and a second diode
14
. The first switching element
11
is connected between one end of a phase coil
15
and a high electric potential line
16
of a power source. The second switching element
12
is connected between the other end of the coil
15
and a low electric potential line
17
of a power source. The first diode
13
is connected between one end of the coil
15
and the lower electric potential line
17
. The second diode is connected between the other end of the coil
15
and the high electric potential line
16
.
The first diode
13
allows the electric current to flow from the low electric potential line
17
to one end of the coil
15
. The second diode
14
allows the electric current to flow from the other end of the coil
15
to the high electric potential line
6
. Both the first and the second diodes are flywheel diodes. A Japanese Patent Laid-Open Publication No. H07-274569 discloses a switching circuit of this kind. The switching elements
11
,
12
may be, for instance, Insulated Gate Bipolar Transistors (IGBT).
There are five methods for chopping control of the SR motor
1
by the switching circuit, which are Soft Chopping, Hard Chopping, 0V Loop (zero-volt loop), DUTY Chopping, and Three-Step OFF. The Soft Chopping is a drive method for maintaining a target electric current value by switching ON/OFF only the first switching element
11
or the second switching element
12
. In the Hard Chopping driving method, a target electric current value is maintained by switching ON/OFF both the first and the second switching elements
11
,
12
. The 0V Loop is a driving method for utilizing the energy by turning off the first switching element
11
and turning on the second switching element
12
during the condition that the electric current is already flowing. In the DUTY Chopping method, ON/OFF of the first switching element
11
is switched while the second switching element
12
is OFF, thus to utilize the electric current by degrees. The Three-step OFF is a driving method varying the operation from either one of Soft Chopping or Hard Chopping, 0V Loop, and to DUTY Chopping.
FIG. 12
shows a wave form of switching circuit operated by Soft chopping. An upper signal shown as (b) of
FIG. 12
corresponds to a drive signal for actuating the switching element
11
. A lower signal shown as (c) of
FIG. 12
corresponds to a drive signal for driving the switching element
12
. The upper signal which repeats switching ON/OFF shown in
FIG. 12
is given to a base of the switching element
11
. The lower signal which regularly maintains ON shown in
FIG. 12
is given to a base of the switching element
12
.
When both the upper signal and the lower signal are ON, the switching elements
11
,
12
are conductive, and thus the electric current flows from the high electric potential line
16
to the low electric potential line
17
via the switching element
11
, the coil
5
, and the switching element
12
. When the upper signal is switched to OFF, switching element
11
is disconnected. The lower signal maintains ON. In this condition, the second switching element
12
is conducted and the first diode
13
allows the electric current flow according to the accumulated energy in the coil
15
b
. The current flows from the coil
15
to the low electric potential line
17
via the second switching element
12
. Then, when the upper signal is switched to be ON again, the switching element
11
is conductive, and thus the electric current flows from the switching element
11
to the switching element
12
via the coil
15
.
By repeating the forgoing operation, electric current shown in
FIG. 12
flows in the coil
15
. In
FIG. 12
, rise of ripple is due to the rise of the electric current flowing in the coil
15
by conduction of the switching element
11
. Drop of ripple is due to the moderate reduction of the energy accumulated in the coil
15
by disconnection of the switching element
11
. The target value of the electric current is determined at a predetermined value in order to obtain a necessary torque in accordance with the driving condition, when the SR motor is applied, for instance, to the electric vehicle.
In the switching circuit shown in
FIG. 11
, the switching elements
11
,
12
develop heat by energization. An IGBT used as the switching elements
11
,
12
is destroyed when the temperature is greater than 150° C. Thus, a temperature sensor is positioned near the switching elements
11
,
12
to restrict the electric current flowing in the coil
15
for preventing a further increase of the temperature when the temperature detected by the temperature sensor is increased, for example, to 120° C.-130° C.
On one hand, the upper signal explained in
FIG. 12
repeats switching ON/OFF alternatively. On the other hand, the lower signal maintains ON condition. Thus, the switching element
11
repeats the switching ON/OFF and the switching element
12
is maintained to be ON. Accordingly, duration of ON period of the switching element
12
becomes longer than that of the switching element
11
and switching number of the switching element
11
becomes greater than that of the switching element
12
. Hence, switching loss of the
Honma Chiaki
Sugiyama Masanori
Aisin Seiki Kabushiki Kaisha
Dang Khanh
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