Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
1997-09-04
2001-07-03
Martin, David (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S773000
Reexamination Certificate
active
06255797
ABSTRACT:
TECHNICAL FIELD
This invention relates to a three-phase AC motor with a reactor interposed between the AC motor and a power source side for the purpose of suppressing generation of heat in a rotor and a stator by decreasing a higher harmonic component included in voltage.
BACKGROUND ART
In an AC motor which employs a three-phase alternating current drive source, in some cases, the drive of such an AC motor is controlled by supplying voltage of non-sinusoidal waveform such as stepped waveform to the motor. Such a voltage of non-sinusoidal waveform contains a higher harmonic component. A loss resulting from the higher harmonic component in the supply voltage ultimately produces heat, which causes heat operation in the motor.
In general, the AC motor has both high-speed output characteristics to generate high output at high-speed revolution and low-speed output characteristics to generate high output at low-speed revolution. The high-speed output characteristics or the low-speed output characteristics are attained by varying the number of turns of primary winding in the motor or by selecting between Y-connection and &Dgr;-connection.
Heat generated due to the higher harmonic component contained in drive voltage of the motor presents a problem particularly when the motor is operated with the connection for high-speed output characteristics. Thus, in order to suppress the generation of heat due to the higher harmonic components as described above, a reactor is interposed between the power source and the motor to attenuate the higher harmonic component contained in the drive voltage. The reactor is effective in suppressing the generation of heat in a rotor and a stator of the motor at high-speed revolution, whereas impedance of the reactor causes a decrease in the amount of current supplied to the primary winding at low-speed revolution, resulting in reduction of output.
With reference to
FIGS. 8A and 9B
, description will first be given of a method for attaining two kinds of characteristics, that is, characteristics for high-speed operation and those for low-speed operation, by switching over primary winding connection in an AC motor, which employs a three-phase alternating drive source.
Referring to
FIG. 8A
, primary winding comprises U-phase winding
1
, V-phase winding
2
and W-phase winding
3
of a motor, which are set up in the form of a Y-connection, and this Y-connection is adapted to attain the characteristics for low-speed operation. The U-phase winding
1
has U and X terminals, the V-phase winding
2
has V and Y terminals, and the W-phase winding
3
has W and Z terminals. The X, Y and Z terminals of the windings are interconnected. Then, U, V and W terminals on a power source side
31
are respectively connected to the U, V and W terminals of the windings
1
,
2
and
3
set up in the form of the Y-connection.
FIG. 8B
shows &Dgr;-connection switched over from the connection (Y-connection) of the windings shown in FIG.
8
A. This &Dgr;-connection is adapted to attain the characteristics for high-speed operation. In
FIG. 8B
, the U, V and W terminals are respectively connected to the Z, X and Y terminals. Then, the U, V and W terminals on the power source side
31
are respectively connected to the U, V and W terminals of the windings
1
,
2
and
3
in &Dgr;-connection.
Next, referring to
FIGS. 9A and 9B
, a description will now be given of a method for attaining two kinds of characteristics, that is, characteristics for high-speed operation and those for low-speed operation, by switching over a voltage application terminal of a primary winding in an AC motor, which employs a three-phase alternating drive source.
Referring to
FIG. 9A
, first and second U-phase windings
10
,
11
connected in series, first and second V-phase windings
12
,
13
connected in series and first and second W-phase windings
14
,
15
connected in series are in Y-connection. Then, a terminal U
1
of the first U-phase winding, a terminal V
1
of the first V-phase winding and a terminal W
1
of the first W-phase winding are respectively connected to U, V and W terminals on a power source side
31
. Thus, the number of turns in each phase comes to the sum of turns of two windings (
10
,
11
;
12
,
13
;
14
,
15
). This connection is suitable for attaining the characteristics for low-speed operation.
Referring to
FIG. 9B
, a terminal U
2
of the second U-phase winding, a terminal V
2
of the second V-phase winding and a terminal W
2
of the second W-phase winding in the windings in Y-connection shown in
FIG. 9A
are respectively connected to the U, V and W terminals on the power source side
31
. Thus, the number of turns in each phase becomes equal to the number of turns of a single winding (
11
,
13
,
15
), so that the number of turns in each phase is less than in the case shown in
FIG. 9A
, and as a result, this connection is suited for obtaining the characteristics for high-speed operation.
Next, referring to
FIGS. 10A and 10B
, a description will now be given of a prior art, in which a reactor is interposed between a power source and a motor in switching between Y-connection and &Dgr;-connection shown in
FIGS. 8A and 8B
.
Referring to
FIG. 10A
, a reactor
32
is interposed between U, V and W terminals on a power source side
31
and U, V and W terminals of a motor
33
. A first switch
35
is interposed between the reactor
32
and the U, V and W terminals of the motor
33
. Further, a second switch
36
is connected to Z, X and Y terminals of the motor
33
.
In
FIG. 10A
, since the first switch
35
is at an off or open or closed position and the second switch
36
is at on position, the U, V and W terminals on the power source side
31
are respectively connected to the U, V and W terminals of the motor
33
through the reactor
32
, and the X, Y and Z terminals of the motor are interconnected, so that Y-connection is formed. That is, a wiring shown in
FIG. 10A
is similar to that shown in
FIG. 8A
, except that the reactor
32
is interposed between the U, V and W terminals on the power source side
31
and the U, V and W terminals of the motor
33
.
Referring to
FIG. 10B
, the first switch
35
in
FIG. 10A
is switched over to a closed or on-position, and the second switch
36
in
FIG. 10A
is switched over to an open or off-position. As a result, the U, V and W terminals on the power source side
31
are respectively connected to U and Z, V and X and W and Y terminals of the motor
33
through the reactor
32
, so that &Dgr;-connection is set up. That is, a wiring shown in
FIG. 10B
is similar to that shown in
FIG. 8B
, except that the reactor
32
is interposed between the U, V and W terminals on the power source side
31
and the U, V and W terminals of the motor
33
.
In the foregoing, as shown in
FIGS. 10A and 10B
, the reactor
32
is interposed between the power source side
31
and the motor
33
in both the cases where switching to Y-connection (
FIG. 10A
) is made for attaining the characteristics for low-speed operation and where switching to the &Dgr;-connection (
FIG. 10B
) is made for attaining the characteristics for high-speed operation. Thus, when the characteristics for high-speed operation are attained by the &Dgr;-connection, this reactor
32
is effective in suppressing the generation of heat by decreasing the higher harmonic component. On the other hand, when an attempt to attain the characteristics for low-speed operation is made through switching to Y-connection, the reactor functions so as to reduce output.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide an improved three-phase AC motor with a reactor interposed between this AC motor and a power source side for the purpose of suppressing generation of heat in a rotor and a stator by decreasing a higher harmonic component include in voltage, wherein the reactor is inhibited from causing the fall of output when winding connection is switched over to attain the characteristics for low-speed operation, or when a voltage application terminal of a winding i
Arimatsu Yohei
Maeda Hisashi
Masuya Michi
Nakamura Kosei
Fanuc Ltd.
Martin David
Staas & Halsey , LLP
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