Title of Invention

GENERATOR FOR ARC WELDER WITH HIGH POWER FACTOR

Abstract A generator for arc welder, of the type composed of a rectifier stage (100) followed by a PFC stage (200) and by an inverter stage (300), both of the high frequency type, the latter stage supplying power to a final rectifier stage for a welding arc (404), the PFC stage being composed of two inductors (203, 204) that are mutually magnetically coupled, two diodes (212, 213) with opposite conduction directions, two leveling capacitors (216, 217) and means for controlling the succession of the on and off switchings of the two first switches, so as to shape the current absorbed by the rectifier stage by correlating it to the waveform of the line voltage. The inverter stage comprises four triads of second controlled switches, diodes and capacitors, and there is also a control device for the four second switches for the current for the final stage that supplies power of the welding arc.
Full Text GENERATOR FOR ARC WELDER WITH HIGH POWER FACTOR
Technical Field
The present invention relates to a generator to be used in an electric
arc welder, more particularly, the present invention relates to a generator
that converts an alternating single- or three-phase mains current into a direct
current that is controlled and adapted for the welding arc.
Background Art
The problems that arise in generators for arc welders are linked
mainly to the low power factor of the current absorbed from the power
supply mains.
Additionally, another factor that has a negative effect on the
efficiency of an arc welder provided according to known layouts and
methods is the unpredictable variation of the power supply voltage.
With reference to the background art by way of example, the classic
widely used layout of an electronic Welder is shown in Figure 1.
The layout comprises, on the mains side, a first rectifier stage 1
constituted only by diodes, followed by a bank of leveling capacitors 2.
The current thus rectified and leveled supplies an inverter block 3
provided by means of high-frequency electronic switches, which supplies
the primary winding of a transformer 4.
The secondary winding of the transformer 4 is followed by a second
rectifier stage 5.
The current in output from the second rectifier stage 5 is leveled by an
inductor 6 and supplies a welding arc 7.
A generator of this kind, during operation, absorbs from the mains a
current that has a behavior of the type shown in Figure 2.
It is immediately evident that a waveform of this type has a high
harmonic content, and this entails a low power factor.
In this situation, in order to have a high useful power level in the arc
it is necessary to absorb a high RMS value from the mains.

This entails a considerable negative impact on the power supply
network, since the high harmonic content and the high RMS value of the
absorbed current cause an increase in the heating of the power supply
conductors and a considerable distortion of the waveform of the voltage of
the power supply line, which in turn causes an increase in losses in the
ferromagnetic cores of the transformers connected thereto.
Additionally, the distortion of the waveform introduces considerable
noise on the line.
Further, when the welding generators are of limited power, as occurs
for those intended to be supplied by domestic utility systems, the high
intensity of the absorbed RMS current causes the intervention of the thermal
protection of the utility system even though the power delivered on the
welding arc is lower than that of an equivalent resistive load.
Moreover, as already mentioned, a generator with a layout of the type
shown in Figure 1 inevitably is affected by the variations in the input supply
voltage, and this reduces considerably the performance of said generator.
In view of these problems, welding generators have been devised that
have additional stages that allow a mains current absorption that is as
sinusoidal as possible, i.e., render the generator equivalent to a resistive
load so as to be able to use all the active power available to the user.
"Additional stages have also been adopted which have the task of
automatically adapting the generator to the mains voltage variations,
ensuring good and stable performance of the generator.
Generators with layouts of this type can be of the type shown
schematically in Figure 3.
This layout clearly shows that with respect to the diagram of Figure 1
there is the addition of a stage 8 that is interposed between the rectifier
block 1 and the leveling block 2.
This stage, termed PFC, can be provided in various kinds.
Generators of this type are in any case expensive and complicated and

sometimes critical in the choice of the components that need to withstand
high voltages.
Disclosure of the Invention
The aim of the present invention is to provide an arc welding
generator that absorbs from the mains a current with a high power factor.
Within this aim, an object of the invention is to provide an arc
welding generator that is not sensitive to variations of the power supply
voltage drawn from the mains.
Another object is to provide a set of circuits in which it is possible to
use components that have a low cost and high efficiency.
This aim and these and other objects that will become better apparent
hereinafter are achieved by a generator for arc welder of the type composed
of a rectifier stage supplied by the mains, followed by a PFC stage and by an
inverter stage, both of the high-frequency type, the latter supplying an
output stage for supplying power to a welding arc, characterized in that:
said PFC stage is composed of: two inductors, which are mutually
magnetically coupled and are arranged in series at the output of the rectifier
stage; two first high-frequency controlled switches, which are connected
between a common node and two nodes respectively at the outputs of the
two inductors; two diodes with opposite conduction directions, which are
respectively connected to the nodes between the switches and mutual
inductors; two leveling capacitors, which are connected to the output nodes
of said diodes and the common of said first switches; means being further
provided for controlling the succession of the on and off switchings of said
two first switches, so as to shape the current absorbed by the rectifier stage,
correlating it to the waveform of the line voltage;
said inverter stage, supplied between the common of said first high-
frequency switches and the common node between said capacitors,
comprises four triads, each composed of a second controlled switch, a diode
and a capacitor, connected so as to form five nodes, respectively a central

node, two intermediate nodes and two external nodes, said external nodes
being connected to the nodes between said first switches and the respective
diodes, said intermediate nodes being connected to the common of said two
first electronic switches with the interposition of a diode respectively, a
capacitor being connected between said intermediate nodes, a control device
being further provided for the four second switches, the current for the
output stage that supplies the welding arc being drawn between the common
of the two first switches and the central node of said four triads of second
controlled switches, diodes and capacitors.
Brief description of the drawings
Further characteristics and advantages of the invention will become
better apparent from the following detailed description of a preferred
embodiment thereof, illustrated by way of non-limiting example in the
accompanying drawings, wherein:
Figures 1, 2, 3 and 4 are views of known devices and of operating
diagrams thereof;
Figure 5 is a schematic view of the four stage generator of the present
invention, illustrating in particular its connections;
Figure 6 is a detailed view of the PFC stage;
Figure 7 is a detailed view of the inverter stage.
Ways of carrying out the Invention
With reference to the figures, the generator according to the invention
can be ideally divided into four stages, which are respectively designated by
the reference numeral 100 for the mains power supply stage, by the
reference numeral 200 for the PFC stage, by the reference numeral 300 for
the inverter stage, and by the reference numeral 400 for the output and arc
supply stage.
The mains power supply stage 100 is composed of a conventional
rectifier block with diodes 101 that is supplied by a mains 102 and can be
single-phase or three-phase.

Two output conductors, designated respectively by the reference
numerals 103 and 104, lead out from the stage 101 and continue in the PFC
stage 200 in two input conductors 201 and 202.
Two inductors 203 and 204 are respectively connected to the inputs
201 and 202 and are mutually magnetically coupled.
The outputs of the two inductors 203 and 204, designated by the
reference numerals 205 and 206, are connected respectively to a first node
207 and to a second node 208.
The first terminal of a first controlled switch 209 is connected to the
node 207, and the first terminal of a second controlled switch 210 is
connected to the node 208.
The second terminal of the first controlled switch 209 and the second
terminal of the second controlled switch 210 are connected to a common
node 211.
The first terminal of a first diode 212 is connected to the node 207,
and the first terminal of a second diode 213 is connected to the node 208;
the two diodes have opposite conduction directions.
The second terminal of the first diode 212 is connected to a node 214,
and the second terminal of the second diode 213 is connected to a node 215.
The first terminal of a first leveling capacitor 216 is connected to the
node 214, and the first terminal of a second leveling capacitor 217 is
connected to the node 215.
The two capacitors 216 and 217 are arranged so as to have mutually
opposite polarities, and their second terminals are connected to a node 218
that is connected to the node 211.
The PFC stage 200 has three output conductors, respectively a
conductor 219 connected to the node 214, a conductor 220 connected to the
node 215, and a conductor 221 connected to the node 218.
The PFC stage 200 has a control device 222 that controls the on and
off switching of the switches 209 and 210, which are of the high-frequency

controlled type (IGBT or MOSFET).
The device 222 draws a voltage signal Vin from the input 201 by
means of the connection 223, a current signal Iin from the conductor 205 by
means of the connection 224, a voltage signal Vc1 from the node 214 or
from the capacitor 216 by means of the connection 225, and a voltage signal
Vc2 from the node 215 or from the capacitor 217 by means of the connection
226.
In the figure, the connections 227 and 228 designate the control of the
switches 209 and 210.
By means of a suitable control of the succession of on and off
switchings of the two switches 209 and 210, the control device 222 controls
the current absorbed by the rectified power supply stage 100, shaping it so
as to follow the waveform of the voltage line, obtained from the signal Vin,
so as to have a very low distortion and therefore a very high power factor.
By closing the switches 209 and 210, the current in the inductors 203
and 204 increases with a slope that is equal to

where M12 is a coefficient that takes into account the coupling of the
two inductors while the diodes 212 and 213 are off and L1, L2 respectively
correspond to inductors 203 and 204.
"By opening the switches 209 and 210, the current circulates in 203,
212, 216, 217, 213 and 204 so as to charge the leveling capacitors 216 and
217 and decreases with a slope equal to

By way of the connection between the node 211 and the node 218, or
between the two switches 209 and 210 with the two capacitors 216 and 217
that have equal capacitances, the voltage applied to each one of the switches
is equal to Vc/2, which is half the voltage that occurs with configurations of
normal known PFC stages.
This allows the use of switches that have a lower breakdown voltage

and for reasons linked to the manufacturing technology of electronic
switches allows to work at higher switching frequencies, consequently
allowing to reduce the values of the inductors 203 and 204 and to improve
control of the current absorbed from the mains.
As it is known, as the breakdown voltage of electronic switches rises
the proper switching times of said switches also increase, and therefore it
becomes increasingly necessary to lower the switching frequencies in order
to limit the power dissipated by said switches.
The inverter stage 300 has a high switching frequency and comprises:
a first external node 301, which is connected to the output conductor 219 of
the PFC stage; a second external node 302, which is connected to the output
conductor 220; a first intermediate node 303, which is connected to the
output conductor 221 with the interposition of a diode 304; and a second
intermediate node 305, which is connected to the output conductor 221 with
the interposition of a diode 306.
The diodes 304 and 306 are arranged so as to have opposite
conduction directions.
A first triad of components in a parallel configuration, constituted by
a controlled switch 307, a diode 308 and a capacitor 309, is provided
between the first external node 301 and the first intermediate node 303.
"A second triad of components in a parallel configuration, constituted
by a controlled switch 311, a diode 312 and a capacitor 313, is provided
between the first intermediate node 303 and a central node 310.
Likewise, a triad of components in a parallel configuration,
constituted by a third controlled switch 314, a diode 315 and a capacitor
316, is provided between the second external node 302 and the second
intermediate node 305.
A triad of components in a parallel configuration, composed of a
fourth controlled switch 317, a diode 318 and a capacitor 319, is provided
between the second intermediate node 305 and the central node 310.

There is also a capacitor 320 that is connected between the two
intermediate nodes 303 and 305.
The inverter stage 300 further has a control device 321 for switching
on and off the four controlled switches 307,311,317 and 314.
By way of the connection between the node 322, which is common to
the diodes 304 and 306, and the node 218, the maximum voltage affecting
each controlled switch is halved.
This situation allows to use components that have much higher
switching frequencies and speeds than circuits with a known layout, so that
it is possible to reduce the dimensions of the magnetic components.
In view of the connection between the PFC stage 200 and the inverter
stage 300, by means of the conductors 219, 221 and 220, by way of a
suitable on and off switching control of the switches it is possible to control
the balancing of the voltages on the capacitors 216 and 217 so as to avoid
compromising control of the welding current.
The stage 400 is supplied by the node 322 and by the node 310, with
which the primary winding of a transformer 401 is associated, said
transformer in turn supplying power to a rectifier 402, in which the output
supplies the welding arc 404 with the interposition of an inductor 403.
The disclosures in Italian Patent Application No. PD2003A000027 from
which" this application claims priority are incorporated herein by reference.

CLAIMS
1. A generator for arc welder of the type composed of a rectifier stage
supplied by the mains (100), followed by a PFC stage (200) and by an
inverter stage (300), both of the high-frequency type, the latter supplying an
output stage (400) for supplying power to a welding arc (404), characterized
in that:
said PFC stage (200) is composed of: two inductors (203, 204), which
are mutually magnetically coupled and are arranged in series at the output of
the rectifier stage (100); two first high-frequency controlled switches (209,
210), which are connected between a common node (211) and two nodes
(207, 208) respectively at the outputs of the two inductors (203, 204); two
diodes (212, 213) with opposite conduction directions, which are
respectively, connected to the nodes (207, 208) between the switches (209,
210) and mutual inductors (203, 204); two leveling capacitors (216, 217),
which are connected to the output nodes (214, 215) of said diodes (212,
213) and the common node (211) of said first switches (209, 210); means
(222) being further provided for controlling the succession of the on and off
switchings of said two first switches (209, 210), so as to shape the current
absorbed by the rectifier stage, correlating it to the waveform of the line
voltage;
'said inverter stage (300), supplied between the common node (211) of
said first high-frequency switches (209, 210) and the common node (218)
between said capacitors (216, 217), comprises four triads, each composed of
a second controlled switch (307, 311, 317, 314), a diode (308, 312, 318,
315) and a capacitor (309, 313, 319, 316), connected so as to form five
nodes, respectively a central node (310), two intermediate nodes (303, 305)
and two external nodes (301, 302), said external nodes (301, 302) being
connected to the nodes between said first switches (209, 210) and the
respective diodes (212, 213), said intermediate nodes (303, 305) being
connected to the common node (211) of said two first electronic switches

(209, 210) with the interposition of a diode (304, 306)
respectively, a capacitor (320) being connected between said
intermediate nodes (303, 305), a control device (321) being
further provided for the four second switches (307, 311, 317,
314), the current for the output stage (400) that supplies the
welding arc being drawn between the common (211) of the two
first switches (209, 210) and the central node (310) of said four
triads of second controlled switches (307, 311, 317, 314),
diodes (308, 312, 318, 315) and capacitors (309, 313, 319,
316).
2. The generator according to claim 1, wherein the mains power
supply can be single-phase or three-phase.
3. The generator according to claim 1, wherein said first two
switches (209, 210) are of the type known as insulated gate
bipolar transistor.
4. The generator according to claim 1, wherein said two first
switches (209, 210) are of the type known as metal oxide silicon
field effect transistor.
5. The generator according to claim 1, wherein said means that
control the on and off switching of said first switches (209, 210)
are constituted by a device (222) that draws voltage and current
signals (Vin, Vc1, Vc2, Iin) and controls the current absorbed by
the rectified power supply stage (100), by shaping its waveform
obtained from the signal Vin, so as to reduce distortion and
obtain a very high power factor.
6. The generator according to claim 1, wherein said two diodes
(304, 306) of the inverter stage (300), the common node (322) of
which is connected to the node (218) of the PFC stage (200),
allow to halve the maximum voltage on the four controlled
switches (307, 311, 317, 314), allowing the use of components
that have a high switching frequency and speed.

Documents:

01459-kolnp-2005-claims.pdf

01459-kolnp-2005-description complete.pdf

01459-kolnp-2005-drawings.pdf

01459-kolnp-2005-form 1.pdf

01459-kolnp-2005-form 2.pdf

01459-kolnp-2005-form 3.pdf

01459-kolnp-2005-form 5.pdf

01459-kolnp-2005-international publication.pdf

1459-kolnp-2005-correspondence.pdf

1459-kolnp-2005-examination report.pdf

1459-kolnp-2005-form 18.pdf

1459-kolnp-2005-form 26.pdf

1459-kolnp-2005-form 3.pdf

1459-kolnp-2005-form 5.pdf

1459-KOLNP-2005-FORM-27.pdf

1459-kolnp-2005-granted-abstract.pdf

1459-kolnp-2005-granted-claims.pdf

1459-kolnp-2005-granted-description (complete).pdf

1459-kolnp-2005-granted-drawings.pdf

1459-kolnp-2005-granted-form 1.pdf

1459-kolnp-2005-granted-form 2.pdf

1459-kolnp-2005-granted-specification.pdf

1459-kolnp-2005-others.pdf

1459-kolnp-2005-reply to examination report.pdf

1459-kolnp-2005-translated copy of priority document.pdf


Patent Number 247800
Indian Patent Application Number 1459/KOLNP/2005
PG Journal Number 21/2011
Publication Date 27-May-2011
Grant Date 23-May-2011
Date of Filing 27-Jul-2005
Name of Patentee SELCO S.R.L.
Applicant Address VIA PALLADIO, 19 I-35019 TOMBOLO, FRAZIONE ONARA
Inventors:
# Inventor's Name Inventor's Address
1 ROSSETTO, GIANNI VIA A. TOSCANINI, 12/B, I-35020 ALBIGNASEGO
2 MELA, FRANCO VIA ROLANDO, 101, I-35016 PIAZZOLA SUL BRENTA
3 TACCON, DANICLE VIA ASTICHELLO, 18/F, I-36100 VICENZA
PCT International Classification Number B23K 9/10
PCT International Application Number PCT/EP2004/001102
PCT International Filing date 2004-02-06
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 PD2003A00027 2003-02-14 Italy