Electric heating – Metal heating – By arc
Reexamination Certificate
2001-11-15
2002-12-24
Shaw, Clifford C (Department: 1725)
Electric heating
Metal heating
By arc
C363S142000
Reexamination Certificate
active
06498320
ABSTRACT:
This invention relate to a power supply apparatus for arc-utilizing apparatuses, such as DC arc welders, DC arc cutters and discharge lamp ignition devices, and, more particularly, to such apparatus that can operate from any one of plural different-valued AC voltage sources.
BACKGROUND OF THE INVENTION
A power supply apparatus for an arc-utilizing apparatus sometimes needs to be used with either a high-voltage commercial AC power supply supplying a voltage of the order of, for example, 400 V or a low-voltage commercial AC power supply supplying a voltage of the order of, for example, 200 V.
There are plurality of low-voltage commercial AC power supplies, which provide an output voltage of, for example, 200 V, 208 V, 230 V and 240 V. Also, there are plural high-voltage commercial AC power supplies, which provide an output voltage of, for example, 380 V, 400 V, 415 V, 440 V and 460 V. Regions where high-voltage commercial AC power supplies are used and regions where lower-voltage commercial AC power supplies are used mingle in some area. In such area, a user must be very careful to determine an appropriate power supply apparatus.
Power supply apparatus manufacturers, too, must manufacture both high-voltage power supply apparatuses and low-voltage power supply apparatuses and store them. Sales agencies, too, must stock power supply apparatuses of both types. This is a burden on both manufacturers and sales agencies in view of manufacturing cost and stocking space.
A power supply apparatus which can operate from either of high-voltage and low-voltage power supplies has been long desired. One example of such power supply apparatuses is disclosed in Japanese (Unexamined) Patent Application Publication No. HEI 11-77302 (A) laid open for public inspection on Mar. 23, 1999. A circuit similar to this prior art apparatus is shown in
FIG. 1. A
commercial AC supply voltage applied to input supply terminals
1
a
,
1
b
and
1
c
is coupled through a switch device
2
to an input-side rectifier
4
for rectification. The rectified voltage from the input-side rectifier
4
is raised in a voltage-boosting converter
8
, which includes a reactor
10
, an IGBT
12
, a current detector
14
and a reverse-current blocking diode
16
. The boosted voltage is developed between output terminals P and N of the voltage-boosting converter
8
.
A switching unit
18
which may include a normally-open switch
20
a
, a normally-closed switch
20
b
and a normally-open switch
20
c
, is connected between the output terminals P and N. By properly opening and closing these switches
20
a
-
20
c
, smoothing capacitors
22
and
24
are connected in series or in parallel between the output terminals P and N.
Inverters
30
and
40
are connected across the smoothing capacitors
22
and
24
, respectively. The inverter
30
is a half-bridge type inverter formed of IGBTs
32
a
and
32
b
, capacitors
34
a
and
34
b
, and flywheel diodes
36
a
and
36
b
. Similarly, the inverter
40
is a half-bridge type inverter formed of IGBTs
42
a
and
42
b
, capacitors
44
a
and
44
b
, and flywheel diodes
46
a
and
46
b
. The inverters
30
and
40
develop high-frequency voltages as their output voltages, which are applied to voltage-transformers
50
and
52
, respectively.
The transformed voltages are applied to output-side rectifiers
54
and
56
, respectively, formed of diodes
54
a
and
54
b
and diodes
56
a
and
56
b
, respectively, where they are rectified. The rectified voltages are combined and smoothed in a smoothing reactor
58
before appearing between output terminals
60
P and
60
N of the power supply apparatus. The voltage developed between the output terminals
60
P and
60
N is applied to a load.
A current flowing through the load is detected by a current detector (CD)
62
, and a controller
64
controls the conduction periods of the IGBTs
32
a
,
32
b
,
42
a
and
42
b
in accordance with a current-representative signal representing the detected load current, to thereby maintain the load current constant.
A switching control unit
66
controls the switching unit
18
. The switching control unit
66
detects the voltage between the input terminals
1
a
and
1
b
and opens the normally-open switches
20
a
and
20
c
, while closing the normally-closed switch
20
b
, when it detects a high-voltage commercial AC supply being connected to the input of the apparatus. This causes the capacitors
22
and
24
to be connected in series between the terminals P and N. If the power supply connected to the input of the apparatus is a low-voltage commercial AC power supply, the switching control unit
66
closes the normally-open switches
20
a
and
20
c
and opens the normally-closed switch
20
b
, which makes the capacitors
22
and
24
connected in parallel between the terminal P and N.
The voltage boosting converter
8
is controlled by a converter control unit
68
. A reference signal source
70
a
to be used in association with higher commercial AC voltages is connected to the converter control unit
68
through a normally-closed switch
20
e
, and a reference signal source
70
b
to be used in association with lower commercial AC voltages is connected to the converter control unit
68
through a normally-open switch
20
d
. The switches
20
e
and
20
d
are also controlled by the switching control unit
66
.
The voltage appearing between the output terminal P and N is detected by a voltage detector
26
, which develops a voltage-representative signal representing the detected voltage. The voltage-representative signal is applied to the converter control unit
68
.
When one of the high-voltage commercial AC power supplies is connected to the input terminals
1
a
-
1
c
, the switching control unit
66
causes the normally-closed switch
20
e
and the normally-open switch
20
d
to be maintained closed and open, respectively. Then, the converter control unit
68
controls the voltage-boosting converter
8
in accordance with the voltage-representative signal from the voltage detector
26
and a reference signal provided by the reference signal source
70
a
, in such a manner that a voltage of about 640 V, which is equal to {square root over (2)}×460 V, can be developed between the output terminals P and N. The voltage of 460 V is the highest one of the high-voltage power supply voltages. Since the normally-open switches
20
a
and
20
c
are open, while the normally-closed switch
20
b
is closed when the high voltage is applied to the apparatus, the capacitors
22
and
24
are connected in series, and, therefore, the voltage applied to each of the inverters
30
and
40
is about 320 V.
The converter control unit
68
controls the voltage-boosting converter
8
in accordance with the current-representative signal from the current detector
14
, too, in order to improve the power factor.
When one of the low-voltage commercial AC power supplies is connected to the input terminals
1
a
-
1
c
, the switching control unit
66
opens the normally-closed switch
20
e
and closes the normally-open switch
20
d
. Then, the converter control unit
68
controls the voltage-boosting converter
8
, in accordance with the voltage-representative signal from the voltage detector
26
and the reference signal from the reference signal source
70
b
, in such a manner that a voltage of about 320 V can be developed between the output terminals P and N. Since the normally-open switches
20
a
and
20
c
are closed with the normally-closed switch
20
b
opened, the capacitors
22
and
24
are connected in parallel with each other, so that the voltage applied to each of the inverters
30
and
40
is about 320 V. In this case, too, the power factor is improved by the voltage-boosting converter
8
.
As described above, whether a high-voltage commercial AC power supply or a low-voltage commercial AC power supply is connected to the input terminals
1
a
-
1
c
, the voltage applied to each of the inverters
30
and
40
is about 320 V. Accordingly, as the IGBTs
32
a
,
32
b
,
42
a
and
42
b
of the inverters
Ikeda Tetsuro
Ishii Hideo
Moriguchi Haruo
Duane Morris LLP
Sansha Electric Manufacturing Company, Limite
Shaw Clifford C
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