Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-04-07
2001-01-30
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S025000, C363S098000
Reexamination Certificate
active
06181576
ABSTRACT:
This invention relates to a power supply apparatus for use with arc-utilizing apparatuses, such as an arc welder, a plasma arc welder, an arc cutter and a plasma arc cutter, which utilize an arc to process articles.
BACKGROUND OF THE INVENTION
Some such power supply apparatuses include an input-side AC-to-DC converter which converts a commercial AC voltage into a DC voltage. The DC voltage is then converted into a high-frequency voltage in an inverter, and the high-frequency voltage is voltage-transformed by a transformer. The voltage-transformed voltage is then converted back into a DC voltage in an output-side high-frequency-to-DC converter. The resulting DC voltage is applied to an arc-utilizing apparatus. The transformer can be small in size because voltage-transforming is carried out after a DC voltage is converted into a high-frequency voltage. This, in turn, enables down-sizing of the power supply apparatus.
When, for example, an input voltage is of the order of four hundred volts (400 V), a voltage as high as at least 400 V×{square root over (2)}≅565V may be applied to the inverter. Then, IGBTs or MOSFETs used in the inverter as its switching devices must have withstand voltage of 1200 V or higher. Fewer switching devices having a withstand voltage of 1200 V or higher are commercially available relative to switching devices having a withstand voltage of 600 V or so. In addition, one switching device having a withstanding voltage of the order of 1200 V is more expensive than two switching devices having a withstanding voltage of 600 V. The switching frequency at which a switching device having a withstand voltage of the order of 600 V can be switched can be higher than the switching frequency for a 1200 V withstand voltage switching device. Accordingly, a transformer succeeding such inverter formed of 600 V withstand voltage switching devices can be smaller, which, in turn, makes it possible to manufacture a smaller sized power supply apparatus.
In U.S. Pat. No. 5,272,313 issued on Dec. 21, 1993 and assigned to the same assignee as the present application, a power supply apparatus which is small in size and can be manufactured at a low cost has been proposed. The power supply apparatus disclosed in this U.S. patent can receive a high input voltage by virtue of using a series combination of two inverters formed by switching devices having a withstand voltage of the order of 600 V.
The power supply apparatus of the U.S. patent is schematically shown in
FIG. 1. A
three-phase commercial AC voltage of the order of, for example, 400 V is applied to input power supply terminals
2
a
,
2
b
and
2
c
. The input AC voltage is, then, rectified by an input-side rectifier
4
in the form of, for example, a diode-bridge configuration. Instead of the three-phase AC voltage, a single-phase AC voltage may be applied to the input power supply terminals.
The input-side rectifier
4
has two output terminals, namely, a positive output terminal P and a negative output terminal N, between which a pair of smoothing capacitors
6
a
and
6
b
are connected in series to smooth the rectifier output voltage into a DC voltage.
An inverter
8
a
is connected across the capacitor
6
a
, and an inverter
8
b
is connected across the capacitor
6
b
. The inverters
6
a
and
6
b
form a DC-to-high-frequency converter. The inverters
8
a
and
8
b
include semiconductor switching devices, e.g. IGBTs
10
a
and
12
a
, and IGBTs
10
b
and
12
b
, respectively. The IGBTs
10
a
,
10
b
,
12
a
and
12
b
have a withstand voltage of the order of, for example, 600 V. The collector-emitter paths of the IGBTs
10
a
and
12
a
of the inverter
8
a
are connected in series, and a series combination of capacitors
14
a
and
16
a
is connected in parallel with the series combination of the IGBTs
10
a
and
12
a
. Flywheel diodes
18
a
and
20
a
are connected in parallel with the collector-emitter paths of the IGBTs
10
a
and
12
a
, respectively, with their anodes connected to the emitters of the respective IGBTs and with their cathodes connected to the collectors.
The inverter
8
b
also includes capacitors
14
b
and
16
b
and flywheel diodes
18
b
and
20
b
, which are connected in the same manner as the capacitors
14
a
and
16
a
and the flywheel diodes
18
a
and
20
a
of the inverter
8
a
. The inverters
8
a
and
8
b
convert a DC voltage inputted thereto to a high-frequency voltage.
A primary winding
22
a
P of a high-frequency transformer
22
a
has its two ends connected to the junction of the IGBTs
10
a
and
12
a
, which provides an output terminal of the inverter
8
a
, and the junction of the capacitors
14
a
and
16
a
. Also, a primary winding
22
b
P of a high-frequency transformer
22
b
has its two ends connected to the junction of the IGBTs
10
b
and
12
b
, which provides an output terminal of the inverter
8
b
, and the junction of the capacitors
14
b
and
16
b
. The transformers
22
a
and
22
b
form the rest of the DC-to-high-frequency converter.
The anodes of output-side rectifying diodes
24
a
and
26
a
are connected to opposite ends of a secondary winding
22
a
S
1
of the transformer
22
a
, and the anodes of output-side rectifying diodes
24
b
and
26
b
are connected to opposed ends of a secondary winding
22
b
S
1
of the transformer
22
b
. The cathodes of the four rectifying diodes
24
a
,
24
b
,
26
a
and
26
b
are connected together to a positive load output terminal
30
P through a smoothing reactor
28
. Intermediate taps on the secondary windings
22
a
S
1
and
22
b
S
1
are connected together to a negative load output terminal
30
N. An arc-utilizing apparatus is connected between the output terminals
30
P and
30
N. With this arrangement, high-frequency voltages induced across the secondary windings
22
a
S
1
and
22
b
S
1
are converted to a DC voltage, which, in turn, is applied to the arc-utilizing apparatus.
A load current detector
32
is connected between the junction of the intermediate taps of the secondary windings and the negative load output terminal
30
N, to detect a load current and produce a load-current representative signal representing the load current. The load-current representative signal is applied to an error amplifier
34
, to which also applied is a load-current setting signal from an output-current setting device
36
. The output-current setting device
36
is used to set the level of the output current supplied to the load. The error amplifier
34
develops an error signal representing the difference between the load-current representative signal and the load-current setting signal, which is applied to inverter control units
38
a
and
38
b
. The inverter control unit
38
a
provides a control signal to the IGBTs
10
a
and
12
a
for controlling the conduction period of the IGBTs
10
a
and
12
a
, while the inverter control unit
38
b
provides a control signal to the IGBTs
10
b
and
12
b
for controlling the conduction period of the IGBTs
10
b
and
12
b
. These connections provide a feedback control to automatically make the load current equal to the load current as represented by the load-current setting signal.
The transformers
22
a
and
22
b
have another secondary windings
22
a
S
2
and
22
b
S
2
, respectively. A diode bridge formed by diodes
40
a
,
42
a
,
44
a
and
46
a
has its input terminals connected to the two ends of the secondary winding
22
a
S
2
, has its one output terminal connected through a resistor
48
a
to one end of the smoothing capacitor
6
b
and has its other output terminal connected to the other end of the capacitor
6
b
. Similarly, a diode bridge formed by diodes
40
b
,
42
b
,
44
b
and
46
b
has its input terminals connected to the two ends of the secondary winding
22
b
S
2
, has its one output terminal connected through a resistor
48
b
to one end of the smoothing capacitor
6
a
and has its other output terminal connected to the other end of the capacitor
6
a.
Input voltages to the inverters
8
a
and
8
b
would sometimes differ due to difference
Danjo Kenzo
Ikeda Tetsuro
Imahori Takamitsu
Murray William H.
Sansha Electric Manufacturing Company Limited
Vu Bao Q.
Wong Peter S.
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