Electric heating – Metal heating – By arc
Reexamination Certificate
2001-11-20
2003-01-14
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C363S142000
Reexamination Certificate
active
06507004
ABSTRACT:
This invention relates to a DC power supply apparatus useable with arc-utilizing apparatuses, such as an arc welder, an arc cutter or a discharge lamp ignition apparatus, and, more particularly, to such DC power supply apparatus operable from any one of a plurality of AC voltages.
BACKGROUND OF THE INVENTION
A DC power supply apparatus for use with an arc-utilizing apparatus is frequently operated from a commercial AC power supply. There are commercial AC power supplies supplying voltages of different magnitudes. For example, there are power supplies supplying higher voltages of, for example, 380 V, 400 V, 410 V, 460 V and 575 V, which form a higher voltage group, and there are power supplies supplying lower voltages of, for example, 200 V, 208 V, 230 V and 240 V, which form a lower voltage group. DC power supply apparatuses are designed to convert a local commercial AC voltage into a DC voltage. On the other hand, there are areas including regions where a high commercial AC voltage is supplied and regions where a low commercial AC voltage is supplied. Accordingly, a user must be very careful to determine which one of DC power supply apparatuses should be used, a high-voltage type or a low-voltage type. Therefore, a DC power supply apparatus operable either from a higher-voltage supplying commercial AC power supply or a lower-voltage supplying commercial AC power supply has been long desired.
An example of such DC power supply apparatuses is disclosed in U.S. Pat. No. 6,054,674 issued on Apr. 25, 2000 to Haruo Moriguchi et al., entitled “DC Power Supply Apparatus for Arc-Utilizing Apparatuses”, which corresponds to Japanese Patent Application Publication No. HEI 11-206123 A published on Jul. 30, 1999. The circuit diagram of the power supply apparatus disclosed in this U.S. patent is shown in FIG.
1
. The DC power supply apparatus has power supply input terminals
1
a,
1
b
and
1
c.
Let it be assumed that one of the voltages in the lower commercial AC voltage group is applied to the power supply input terminals
1
a
-
1
c.
The AC voltage is coupled to an input-side rectifier
3
through switches
2
a
,
2
b
and
2
c
, where it is rectified. A switch control unit
30
judges that the low AC voltage is being applied to the input terminals
1
a
-
1
c.
The judgment made by the switch control unit
30
is provided to a voltage-lowering converter control unit
9
, in response to which the control unit
9
sends a command to a thyristor control unit
11
for turning on a thyristor
10
. At the same time, the switch control unit
30
opens a normally-closed switch
12
a
and closes normally-open switches
12
b
and
12
c
, which causes smoothing capacitors
8
a
and
8
b
to be connected in parallel with each other. Then, the voltage resulting from the rectification of the low commercial AC voltage is smoothed by the capacitors
8
a
and
8
b
connected in parallel, and the smoothed voltages are applied to inverters
14
a
and
14
b
connected in parallel with the capacitors
8
a
and
8
b
, respectively, where they are converted into high-frequency voltages. The high-frequency voltages from the inverters
14
a
and
14
b
are transformed by of voltage transformers
18
a
and
18
b
, respectively, and the transformed voltages are rectified by output-side rectifiers
20
a
and
20
b
and smoothed by smoothing reactors
26
a
and
26
b
. The rectified and smoothed voltage appearing between output terminals
28
P and
28
N is applied to a load (not shown).
When one of the voltages in the higher commercial AC voltage group, other than the highest voltage of 575 V, is applied to the power supply input terminals
1
a
-
1
c,
it is rectified in the input-side rectifier
3
. The switch control unit
30
makes a judgment that the high commercial AC voltage other than 575 V is applied, which causes the thyristor
10
to be turned on. This causes the normally-closed switch
12
a
to be closed and causes the normally-open switches
12
b
and
12
b
to be opened. This, in turn, causes the capacitors
8
a
and
8
b
to be connected in series with each other. The high voltage resulting from rectifying the high commercial AC voltage is applied across the series combination of the capacitors
8
a
and
8
b
. In the same manner as described above with respect to the low commercial AC voltage applied to the power supply input terminals
1
a
-
1
c,
a corresponding DC voltage is developed between the output terminals
28
P and
28
N for application to a load.
When the commercial AC power supply providing a voltage of 575 V, which is the highest one of the higher AC voltage group in the example being discussed, is applied to the power supply input terminals
1
a
-
1
c
, it is rectified in the input-side rectifier
3
. The switch control unit
30
detects the 575 V commercial AC power supply being used, and the thyristor
10
is turned off. The normally-closed switch
12
a
is closed, and the normally-opened switches
12
b
and
12
c
are opened, which results in connecting the capacitors
8
a
and
8
b
in series with each other. An IGBT
5
of a voltage-lowering converter
4
, which is formed of, in addition to the IGBT
5
, a flywheel diode
6
and a smoothing reactor
7
, is so controlled by the voltage-lowering converter control unit
9
as to couple a lowered, rectified voltage across the series combination of the capacitors
8
a
and
8
b
. The magnitude of the rectified voltage across the capacitor series combination is the same as the one applied when the second highest one of the higher AC voltage group, i.e. 460 V in the example being discussed, is applied to the power supply input terminals
1
a
-
1
c
. In the same manner as described above with respect to a lower voltage applied to the power supply input terminals
1
a
-
1
c,
a DC voltage is developed between the output terminals
28
P and
28
N for application to the load.
When one of the voltages in the lower voltage group, namely, 200 V, 208 V, 230 V or 240 V, is applied to the power supply input terminals
1
a
-
1
c,
the magnitude of the voltage applied across the parallel combination of the capacitors
8
a
and
8
b
is equal to the input AC power supply voltage multiplied by {square root over (2)}. For example, the voltage applied across the parallel combination of the smoothing capacitors
8
a
and
8
b
is about 280 V when the commercial AC power supply providing a voltage of 200 V is connected to the input terminals
1
a
-
1
c
. When the input commercial AC power supply voltage is 240 V, the magnitude of the voltage applied across the capacitor parallel combination is about 340 V.
When one of the voltages in the higher voltage group except for the voltage of 575 V, namely, 380 V, 400 V, 410 V or 460 V, is applied to the power supply input terminals
1
a
-
1
c
, the magnitude of the voltage applied across each of the serially connected capacitors
8
a
and
8
b
is equal to the input AC power supply voltage multiplied by {square root over (2)}/2. For example, the voltage applied across each of the smoothing capacitors
8
a
and
8
b
connected in series is about 270 V when the commercial AC power supply providing a voltage of 380 V is connected to the input terminals
1
a
-
1
c
. When the input commercial AC power supply voltage is 460 V, the magnitude of the voltage applied across each capacitor is about 325 V.
The voltage-lowering converter
4
is so arranged as to develop an output voltage of 460 V multiplied by {square root over (2)}, which is about 650 V, when the commercial AC voltage of 575 V is applied to the power supply input terminals
1
a
-
1
c
. Therefore, a voltage of about 325 V is applied across each of the capacitors
8
a
and
8
b
connected in series with each other.
With the described arrangement, readily available general-purpose semiconductor devices which can deal with a maximum voltage of 340 V can be used as the semiconductor switching devices of the inverters
14
a
and
14
b
, for dealing with lower and higher voltages of various magnitudes.
In some countries or areas, such as U.S.A. and Japan, lower
Arai Toru
Ikeda Tetsuro
Ishii Hideo
Sansha Electric Manufacturing Company Limited
Shaw Clifford C.
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