Systems and methods providing arc re-ignition for AC arc welding processes

Systems and methods providing an energy limited arc re-ignition voltage for AC arc welding processes to re-ignite an arc during polarity transitions. In arc welding power source embodiments, configurations of bridge and superposition circuits allow for the directional switching of the welding output current through the welding output circuit path and provide a voltage between the electrode and the workpiece of the welding output circuit path that is sufficient to re-ignite the arc during polarity transition of the output current. The superposition circuit provides a capacitor for storing energy from a dedicated charging source which produces the voltage level for re-igniting the arc during the zero crossing of the output current in both polarities.

TECHNICAL FIELD

Certain embodiments of the present invention relate to arc welding. More particularly, certain embodiments of the present invention relate to systems and methods providing an energy limited arc re-ignition voltage for AC arc welding processes to re-ignite an arc during polarity transitions.

BACKGROUND

Certain prior art welding systems use bridge topologies in a welding power source to provide AC welding capability. A full bridge topology may be used with just about any power source topology, providing flexibility and the potential to be added to existing designed power sources. The full bridge topology allows easy implementation of zero cross assisting circuits. A blocking diode may be used to protect the devices in the power source from high voltage transients that occur during the zero cross. For certain welding processes such as, for example, an AC gas tungsten arc welding process (GTAW or TIG) or an AC gas metal arc welding process (GMAW or MIG), it is desirable for the arc between the electrode and the workpiece to quickly re-ignite in the opposite polarity direction when the welding current crosses zero.

A welding power source may have a maximum voltage level (e.g., 100 VDC) that it is designed to output. When an AC welding current crosses zero (i.e., changes polarity), the arc extinguishes and may not re-establish. In TIG welding (where there is no wire electrode), if the arc extinguishes, the welding power source may have to repeat the entire arc-establishment process before welding can continue, resulting in an inefficient welding process.

Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such systems and methods with embodiments of the present invention as set forth in the remainder of the present application with reference to the drawings.

SUMMARY

Embodiments of the present invention include systems and methods for providing an energy limited arc re-ignition voltage (i.e., a superposition voltage) for AC arc welding processes to re-ignite an arc during polarity transitions. The introduction of a high voltage level between the welding electrode and the workpiece for a brief period of time during a polarity transition of the welding current is provided from a superposition circuit having a dedicated charging source to readily and reliably re-ignite the arc in the opposite polarity, even though the voltage from the power source is limited. Configurations of polarity reversing bridge circuits and superposition circuits allow for the directional switching of the output welding current through the welding output circuit path while also allowing for the rapid re-igniting of the arc when the welding current changes polarity. A superposition circuit having a pre-charge capacitor and a charging source that is dedicated to charging the pre-charge capacitor provides the voltage needed during current polarity transition to quickly and reliably re-ignite the arc.

One embodiment of the present invention is a welding power source. The welding power source includes a controller, and a power conversion circuit configured to convert an input current to an output current. The power conversion circuit may include a DC output topology. The power conversion circuit may be an inverter-based circuit or a chopper-based circuit, for example. The welding power source also includes a bridge circuit operatively connected to the power conversion circuit and configured to switch a direction of the output current through a welding output circuit path operatively connected to a welding output of the welding power source at the command of the controller. The bridge circuit may be configured as a full bridge circuit, for example. The bridge circuit may include, for example, at least four switching transistors. The welding power source further includes a superposition circuit, having at least one pre-charge capacitor and at least one dedicated charging source configured to directly or indirectly charge the at least one capacitor, operatively connected to the bridge circuit and configured to provide a voltage between an electrode and a workpiece of the welding output circuit path sufficient for arc re-ignition during polarity transition of the output current. The dedicated charging source may be a current limited voltage supply. The superposition circuit may also include, for example, at least one resistor and at least one switching transistor operatively connected to the at least one capacitor, wherein the at least one switching transistor is configured to switch on and off at the command of the controller. The value of the at least one capacitor may be less than one micro-farad, in accordance with various embodiments. The power conversion circuit, the bridge circuit, and the superposition circuit may be configured to provide any of a DC positive welding operation, a DC negative welding operation, and an AC welding operation at the command of the controller of the welding power source. In accordance with an alternative embodiment, the bridge circuit and the superposition circuit may be external to the welding power source, for example, in the form of a module that operatively connects to the welding power source.

One embodiment of the present invention is a welding power source. The welding power source includes means for converting an input current to an output current and means for switching a direction of the output current through a welding output circuit path operatively connected to a welding output of the welding power source to provide at least an AC welding operation. The welding power source also includes means for applying a voltage between a welding electrode and a welding workpiece of the welding output circuit path during a polarity transition of the output current to automatically re-establish an arc between the welding electrode and the workpiece in an opposite polarity.

One embodiment of the present invention is a method. The method includes converting an input current to an output current in a welding power source and pre-charging at least one capacitor of the welding power source to an arc re-igniting voltage level from at least one dedicated charging source. The method also includes switching a direction of the output current through a welding output circuit path operatively connected to a welding output of the welding power source from a first direction to a second direction at the command of a controller of the welding power source. The method further includes applying the arc re-igniting voltage level from the at least one capacitor between a welding electrode and a workpiece of the welding output circuit path to automatically re-ignite an arc between the electrode and the workpiece in the second direction as part of switching to the second direction. The method may further include pre-charging the at least one capacitor of the welding power source to the arc re-igniting voltage level from the at least one dedicated charging source and switching a direction of the output current through the welding output circuit path from the second direction to the first direction at the command of the controller of the welding power source. The method may further include applying the arc re-igniting voltage level from the at least one capacitor between the welding electrode and the workpiece of the welding output circuit path to automatically re-ignite an arc between the electrode and the workpiece in the first direction as part of switching to the first direction. The method may further include further charging the at least one capacitor of the welding power source with energy from a load connected to the welding power source during a current decay portion of the output current to self-regulate arc re-ignition based on characteristics of the load.

One embodiment of the present invention is a welding power source. The welding power source includes a bridge circuit configured to provide an AC welding output current. The welding power source further includes a superposition circuit, including at least one capacitor and at least one dedicated charging source configured to directly or indirectly charge the at least one capacitor, operatively connected to the bridge circuit and configured to provide a voltage at a welding output of the welding power source being of sufficient magnitude to automatically re-ignite an arc in an output circuit path connected to the welding output upon reversal of a polarity of a welding output current through the output circuit path. The superposition circuit may further include at least one resistor and at least one switching transistor operatively connected to the at least one capacitor, wherein the at least one switching transistor is configured to switch on and off at the command of the welding power source.

One embodiment of the present invention is a welding power source. The welding power source includes a current switching circuit having at least one pre-charge capacitor and at least one dedicated charging source configured to directly or indirectly charge the capacitor, wherein the at least one pre-charge capacitor and the at least one dedicated charging source are configured to provide a voltage across a load connected to a welding output of the welding power source sufficient to re-ignite a welding arc across the load upon reversal of a polarity of a welding output current through the load. The current switching circuit may be configured as a full bridge circuit, for example. The current switching circuit may include at least one resistor and at least one switching transistor operatively connected to the at least one pre-charge capacitor, wherein the at least one switching transistor is configured to switch on and off at the command of the welding power source.

Details of illustrated embodiments of the present invention will be more fully understood from the following description and drawings.

DETAILED DESCRIPTION

The following are definitions of exemplary terms that may be used within the disclosure. Both singular and plural forms of all terms fall within each meaning:

“Software” or “computer program” as used herein includes, but is not limited to, one or more computer readable and/or executable instructions that cause a computer or other electronic device to perform functions, actions, and/or behave in a desired manner. The instructions may be embodied in various forms such as routines, algorithms, modules or programs including separate applications or code from dynamically linked libraries. Software may also be implemented in various forms such as a stand-alone program, a function call, a servlet, an applet, an application, instructions stored in a memory, part of an operating system or other type of executable instructions. It will be appreciated by one of ordinary skill in the art that the form of software is dependent on, for example, requirements of a desired application, the environment it runs on, and/or the desires of a designer/programmer or the like.

“Computer” or “processing element” or “computer device” as used herein includes, but is not limited to, any programmed or programmable electronic device that can store, retrieve, and process data. “Non-transitory computer-readable media” include, but are not limited to, a CD-ROM, a removable flash memory card, a hard disk drive, a magnetic tape, and a floppy disk.

“Welding tool”, as used herein, refers to, but is not limited to, a welding gun, a welding torch, or any welding device that accepts a consumable or non-consumable welding electrode for the purpose of applying electrical power to the welding electrode provided by a welding power source.

“Welding output circuit path”, as used herein, refers to the electrical path from a first side of the welding output of a welding power source, through a first welding cable (or a first side of a welding cable), to a welding electrode, to a workpiece (either through a short or an arc between the welding electrode and the workpiece), through a second welding cable (or a second side of a welding cable), and back to a second side of the welding output of the welding power source.

“Welding cable”, as used herein, refers to the electrical cable that may be connected between a welding power source and a welding electrode and workpiece (e.g. through a welding wire feeder) to provide electrical power to create an arc between the welding electrode and the workpiece.

“Welding output”, as used herein, may refer to the electrical output circuitry or output port or terminals of a welding power source, or to the electrical power, voltage, or current provided by the electrical output circuitry or output port of a welding power source.

“Computer memory”, as used herein, refers to a storage device configured to store digital data or information which can be retrieved by a computer or processing element.

“Controller”, as used herein, refers to the logic circuitry and/or processing elements and associated software or program involved in controlling a welding power source.

The terms “signal”, “data”, and “information” may be used interchangeably herein and may be in digital or analog form.

The term “AC welding” is used generally herein and may refer to actual AC welding, DC welding in both positive and negative polarities, variable polarity welding, and other hybrid welding processes.

The terms “pre-charge capacitor” and “superposition capacitor” may be used interchangeably herein.

For AC welding processes, the arc current stops and changes direction during the zero transition. Depending on the state of the arc plasma and gases surrounding the weld, the arc may or may not re-ignite. Embodiments of the present invention include a superposition circuit providing a voltage level being of sufficient magnitude to automatically re-ignite an arc upon reversal of a polarity of the welding output current. During a polarity change, the arc current decays to zero prior to advancing in the opposite polarity. During this polarity transition time, the current from the arc flows into a high voltage snubber circuit. The high voltage imposed by the snubber circuit rapidly depletes all of the arc energy. The arc re-ignition voltage is provided by a capacitor of the superposition circuit that applies the voltage across the welding load upon command by a controller, thus re-establishing the arc across the load.

FIG. 1illustrates a schematic block diagram of an exemplary embodiment of a welding power source100operatively connected to a welding electrode E and a workpiece W. The welding power source100includes a power conversion circuit110providing welding output power between the welding electrode E and the workpiece W. The power conversion circuit110may be transformer based with a half bridge rectified output topology. For example, the power conversion circuit110may be of an inverter type that includes an input power side and an output power side, for example, as delineated by the primary and secondary sides, respectively, of a welding transformer. Other types of power conversion circuits are possible as well such as, for example, a chopper type having a DC output topology. An optional wire feeder5may feed a consumable wire welding electrode E toward the workpiece W. Alternatively, as in a GTAW process, the electrode E may be non-consumable and the wire feeder5may not be used or may be used to provide a filler wire toward the workpiece W. The wire feeder5, the consumable welding electrode E, and the workpiece W are not part of the welding power source100but may be operatively connected to the welding power source100via a welding output cable.

The welding power source100further includes a waveform generator120and a controller130. The waveform generator120generates welding waveforms at the command of the controller130. A waveform generated by the waveform generator120modulates the output of the power conversion circuit110to produce the welding output current between the electrode E and the workpiece W.

The welding power source100may further include a voltage feedback circuit140and a current feedback circuit150to monitor the welding output voltage and current between the electrode E and the workpiece W and provide the monitored voltage and current back to the controller130. The feedback voltage and current may be used by the controller130to make decisions with respect to modifying the welding waveform generated by the waveform generator120and/or to make other decisions that affect safe operation of the welding power source100, for example.

The welding power source100also includes a current switching circuit180having a bridge circuit160and a superposition circuit170. The bridge circuit160is operatively connected to the power conversion circuit110and is configured to switch a direction of the output current through a low impedance welding output circuit path (including the electrode E and the workpiece W) operatively connected to a welding output of the welding power source100at the command of the controller130. The superposition circuit is an energy limited arc re-ignition circuit that provides a high voltage at the welding output (output port or terminals) of the welding power source for a brief period of time. The superposition circuit is operatively connected to the bridge circuit and is configured to provide a voltage between the electrode E and the workpiece W of the welding output circuit path that is sufficient to re-ignite the arc during a polarity transition of the output current. The superposition circuit includes a dedicated charging source that is used to pre-charge a capacitor of the superposition circuit to the sufficient voltage before polarity transition occurs. Detailed examples and operation of such bridge and superposition circuits are described in detail later herein.

FIG. 2illustrates a schematic diagram of a first exemplary embodiment of a portion of the welding power source100ofFIG. 1having a bridge circuit160and a superposition circuit170. Also illustrated inFIG. 2is a portion210of the power conversion circuit110, where the power conversion circuit110provides a DC+output (e.g., a chopper-based circuit). The current switching circuit180ofFIG. 2is in the form of a full bridge topology that may be used with almost any power source topology, providing flexibility and the potential to be added to existing designed power sources, and providing AC current switching through the welding output circuit path.

The bridge circuit160includes switching transistors211,212,213, and214. The superposition circuit170includes switching transistor215, pre-charge capacitor216, dedicated charging source217, diode218, and resistor219. In accordance with an embodiment, the switching transistors are insulated gate bipolar transistors (IGBTs). In accordance with an embodiment, the dedicated charging source is a voltage supply created off of a transformer that is current limited and is dedicated to pre-charging the capacitor216before polarity transition of the welding output current. The charging source also provides a trickle charge in the milli-amps range to initialize the snubber capacitor183. An active snubber circuit181, having a diode182and a capacitor183, is used to limit the voltage across the current switching circuit180(e.g., somewhere between 300 V and 600 V) to cause the output current through the output circuit path to decay quickly. The anti-parallel diodes of the switching transistors211,212,213, and214of the bridge circuit160complete the snubber/decay path.

The current switching circuit180ofFIG. 2provides for AC welding operation and provides a voltage at the welding output of the welding power source being of sufficient magnitude to re-establish the welding arc between the electrode E and the workpiece W during polarity reversals of the welding process, as described herein with respect toFIGS. 3A-3C. Welding output terminals191and192are shown and represent the welding output of the welding power source to which the electrode E and the workpiece W may be connected through a welding cable path.

In accordance with an embodiment, the pre-charge capacitor216has a capacitance value of less than one micro-farad and the dedicated charging source217provides a current in the range of, for example, 1-100 milli-amps. The capacitor216is sized to provide a large enough voltage between the electrode and the workpiece to quickly and reliably re-ignite the arc immediately after the arc goes out due to the output current switching direction (polarity reversal/switching). During zero current crossing (polarity reversal/switching), the arc extinguishes and the high voltage (e.g., 200 to 400 VDC) provided by the energy from the capacitor216of the superposition circuit170is used to re-establish the arc in the opposite polarity. The capacitor216provides the arc-igniting voltage level in both polarities (i.e., when crossing the zero current point from either the positive direction or the negative direction).

FIGS. 3A-3Cillustrate the operation of the welding power source inFIG. 2when implementing an AC welding output current waveform (e.g., represented as a simple square waveform). The load230shown inFIGS. 3A-3Crepresents the resistance and inductance of the arc between the electrode E and the workpiece W and the welding cable path connecting the electrode E and workpiece W to the welding power source (i.e., the welding output circuit path). The electrode E, workpiece W, and the welding cable path are not a part of the welding power source, however.

Referring to the top portion ofFIG. 3A, during the positive current portion of an AC waveform300(see thicker dark lines of the waveform300) produced by the welding power source, current flows predominantly from the power conversion circuit210, through the switching transistor211of the bridge circuit160, through the load230(in the positive direction), through the switching transistor214of the bridge circuit160, and back to the power conversion circuit210(see thick arrows). Also, a pre-charge current flows from the charging source217and charges the capacitor216to, for example, a minimum voltage for re-igniting the arc (see less thick arrow).

Referring to the bottom portion ofFIG. 3A, during the positive current decay portion of the AC waveform300(see thicker dark line of the waveform300), current flows from the load230(in the positive direction), through the anti-parallel diode of the switching transistor213of the bridge circuit160, through the active snubber181, through the anti-parallel diode of the switching transistor212, and back to the load230(see thick arrows). Also, some of the current flows through the anti-parallel diode of the switching transistor215of the superposition circuit170and may further charge the capacitor216(see less thick arrow). This further charging from the load provides a self-regulating feature by providing additional energy that may be needed to re-ignite the arc if, for example, the welding cable is a long cable having a large inductance. During current decay, the bridge circuit160changes polarity. As the current through the load drops toward zero, the arc extinguishes.

The superposition circuit applies a voltage across the load to re-ignite the arc in the opposite polarity. Current from the power conversion circuit can begin to flow again through the load in the opposite direction. The arc re-establishes quickly and any over-shoot of the welding output current is limited by the energy stored in the capacitor216of the superposition circuit. Without the superposition circuit, the power conversion circuit would attempt to re-establish the arc. However, since the voltage provided by the power conversion circuit is usually limited (e.g., to 100 VDC), re-establishment of the arc may not occur.

Referring toFIG. 3B, during the polarity transition portion of the AC waveform300(see thicker dark line of the waveform300), no significant current is provided by the power conversion circuit210. The arc between the electrode E and the workpiece W briefly extinguishes. However, energy stored in the capacitor216provides an arc-igniting voltage between the electrode E and the workpiece W. The energy from the capacitor216of the superposition circuit170is released and current flows from the capacitor216through the switching transistor215of the superposition circuit170, through the switching transistor213of the bridge circuit160, through the load230(in the negative direction), through the switching transistor212of the bridge circuit160, and back to the capacitor216(see arrows). As a result, the arc between the electrode E and the workpiece W quickly re-ignites in the negative direction.

Referring to the top portion ofFIG. 3C, during the negative current portion of the AC waveform300(see thicker dark lines of the waveform300) produced by the welding power source, current flows predominantly from the power conversion circuit210, through the switching transistor213of the bridge circuit160, through the load230(in the negative direction), through the switching transistor212of the bridge circuit160, and back to the power conversion circuit210(see thick arrows). Also, a pre-charge current flows from the dedicated charging source217and charges the capacitor216to a minimum voltage for re-igniting the arc (see less thick arrow).

Referring to the bottom portion ofFIG. 3C, during the negative current decay portion of the AC waveform300(see thicker dark line of the waveform300), current flows predominantly from the load230(in the negative direction), through the anti-parallel diode of switching transistor211of the bridge circuit160, through the snubber circuit181, through the anti-parallel diode of switching transistor214of the bridge circuit160, and back to the load230. Also, some of the current flows through the anti-parallel diode of the switching transistor215of the superposition circuit170and may further charge the capacitor216(see less thick arrow). This further charging from the load provides a self-regulating feature by providing additional energy that may be needed to re-ignite the arc if, for example, the welding cable is a long cable having a large inductance.

Upon making the transition back to the positive portion of the waveform300(i.e., the waveform is repeating), in a similar manner to that ofFIG. 3B, the capacitor216will release its stored energy through the load (but in the positive direction) via the switching transistor215of the superposition circuit170, and the switching transistors211and214of the bridge circuit160, causing the arc between the electrode E and the workpiece W to quickly re-ignite in the positive direction.

FIG. 4illustrates a schematic diagram of a second exemplary embodiment of a portion of the welding power source100ofFIG. 1having a bridge circuit160and a superposition circuit170. Also illustrated inFIG. 4is a portion210of the power conversion circuit110, where the power conversion circuit110provides a DC+output (e.g., a chopper-based circuit). The current switching circuit180ofFIG. 4is in the form of a full bridge topology that may be used with almost any power source topology, providing flexibility and the potential to be added to existing designed power sources, and providing AC current switching through the welding output circuit path.

The bridge circuit160includes switching transistors411,412,413, and414. The superposition circuit170includes switching transistor415, pre-charge capacitor416, dedicated charging source417, diode418, and resistor419. In accordance with an embodiment, the switching transistors are insulated gate bipolar transistors (IGBTs). In accordance with an embodiment, the dedicated charging source417is a voltage supply created off of a transformer that is current limited and is dedicated to pre-charging the capacitor416before polarity transition of the welding output current. The charging source also provides a trickle charge in the milli-amps range to initialize the snubber capacitor483. The superposition circuit170also includes an active snubber circuit having a diode482and a capacitor483that is used to limit the voltage across the current switching circuit180(e.g., somewhere between 300 V and 600 V) to cause the output current through the output circuit path to decay quickly. The anti-parallel diodes of the switching transistors411,412,413, and414of the bridge circuit160complete the snubber/decay current path.

The current switching circuit180ofFIG. 4provides for AC welding operation and provides a voltage at the welding output of the welding power source being of sufficient magnitude to re-establish the welding arc between the electrode E and the workpiece W during polarity reversals of the welding process, as described herein with respect toFIGS. 5A-5C. Welding output terminals191and192are shown and represent the welding output of the welding power source to which the electrode E and the workpiece W may be connected through a welding cable path.

In accordance with an embodiment, the pre-charge capacitor416has a capacitance value of less than one micro-farad and the dedicated charging source417provides a current in the range of, for example, 1-100 milli-amps. The capacitor416is sized to provide a large enough voltage between the electrode and the workpiece to quickly and reliably re-ignite the arc immediately after the arc goes out due to the output current switching direction (polarity reversal/switching). During zero current crossing (polarity reversal/switching), the arc extinguishes and the high voltage (e.g., 200 to 400 VDC) provided by the energy from the capacitor416of the superposition circuit170is used to re-establish the arc in the opposite polarity. The capacitor416provides the arc-igniting voltage level in both polarities (i.e., when crossing the zero current point from either the positive direction or the negative direction).

During pre-charging, the transistor switch415is off and the active snubber capacitor483is charged first by the dedicated charging source417. Subsequently, the capacitor416is charged off of the snubber capacitor483. That is, the pre-charge capacitor416is indirectly charged by the dedicated charging source417via the snubber capacitor483. Once the capacitor416is discharged to re-ignite the arc, additional energy may be pulled from the snubber circuit through the resistor419(e.g., about 500 ohms) which limits the current being drawn out of the snubber circuit. When the transistor switch415again shuts off, the process of pre-charging repeats. In accordance with an embodiment, an advisory circuit (not shown) monitors the active snubber capacitor483to maintain the voltage of the capacitor483at about 400 V, for example. This is accomplished by charging the snubber capacitor483from the power supply when the voltage is too low, and bleeding off energy from the capacitor483when the voltage is too high.

FIGS. 5A-5Cillustrate the operation of the welding power source inFIG. 4when implementing an AC welding output current waveform. The load230shown inFIGS. 5A-5Crepresents the resistance and inductance of the arc between the electrode E and the workpiece W and the welding cable path connecting the electrode E and workpiece W to the welding power source (i.e., the welding output circuit path). The electrode E, workpiece W, and the welding cable path are not a part of the welding power source, however.

Referring to the top portion ofFIG. 5A, during the positive current portion of an AC waveform500(see thicker dark lines of the waveform500) produced by the welding power source, current flows predominantly from the power conversion circuit210, through the switching transistor411of the bridge circuit160, through the load230(in the positive direction), through the switching transistor414of the bridge circuit160, and back to the power conversion circuit210(see thick arrows). Also, a pre-charge current flows from the dedicated charging source417. During pre-charging, the transistor switch415is off and the active snubber capacitor483is charged first by the charging source417. Subsequently, the pre-charge capacitor416is charged off of the snubber capacitor417to, for example, a minimum voltage for re-igniting the arc (see less thick arrow).

Referring to the bottom portion ofFIG. 5A, during the positive current decay portion of the AC waveform500(see thicker dark line of the waveform500), current flows predominantly from the load230(in the positive direction), through the anti-parallel diode of the switching transistor413of the bridge circuit160, through the snubber circuit, through the anti-parallel diode of the switching transistor412, and back to the load230(see thick arrows). Also, some of the current flows to the pre-charge capacitor416of the superposition circuit and may further charge the capacitor416(see less thick arrow). This further charging from the load provides a self-regulating feature by providing additional energy that may be needed to re-ignite the arc if, for example, the welding cable is a long cable having a large inductance. During current decay, the bridge circuit160changes polarity. As the current through the load drops toward zero, the arc extinguishes.

The superposition circuit applies a voltage across the load to re-ignite the arc in the opposite polarity. Current from the power conversion circuit can begin to flow again through the load in the opposite direction. The arc re-establishes quickly and any over-shoot of the welding output current is limited by the energy stored in the capacitor416of the superposition circuit. Without the superposition circuit, the power conversion circuit would attempt to re-establish the arc. However, since the voltage provided by the power conversion circuit is usually limited (e.g., to 100 VDC), re-establishment of the arc may not occur.

Referring toFIG. 58, during the polarity transition portion of the AC waveform500(see thicker dark line of the waveform500), no significant current is provided by the power conversion circuit210. The arc between the electrode E and the workpiece W briefly extinguishes. However, energy stored in the capacitor416provides an arc-igniting voltage between the electrode E and the workpiece W. The energy from the capacitor416of the superposition circuit170is released and current flows from the capacitor416through the switching transistor415of the superposition circuit170, through the switching transistor413of the bridge circuit160, through the load230(in the negative direction), through the switching transistor412of the bridge circuit160, and back to the capacitor416(see thick arrows). Additional energy may be pulled from the snubber capacitor483(see less thick arrow) through the current limiting resistor419. As a result, the arc between the electrode E and the workpiece W quickly re-ignites in the negative direction.

Referring to the top portion ofFIG. 5C, during the negative current portion of the AC waveform500(see thicker dark lines of the waveform500) produced by the welding power source, current flows predominantly from the power conversion circuit210, through the switching transistor413of the bridge circuit160, through the load230(in the negative direction), through the switching transistor412of the bridge circuit160, and back to the power conversion circuit210(see thick arrows). Also, during pre-charging, the transistor switch415is off and the active snubber capacitor483is charged first by the dedicated charging source417. Subsequently, the pre-charge capacitor416is charged off of the snubber capacitor417to, for example, a minimum voltage for re-igniting the arc (see less thick arrow).

Referring to the bottom portion ofFIG. 5C, during the negative current decay portion of the AC waveform500(see thicker dark line of the waveform500), current flows predominantly from the load230(in the negative direction), through the anti-parallel diode of the switching transistor411of the bridge circuit160, through the snubber circuit, through the anti-parallel diode of the switching transistor414of the bridge circuit160, and back to the load230(see thick arrows). Also, some of the current flows to the capacitor416of the superposition circuit and may further charge the capacitor416(see less thick arrow). This further charging from the load provides a self-regulating feature by providing additional energy that may be needed to re-ignite the arc if, for example, the welding cable is a long cable having a large inductance.

Upon making the transition back to the positive portion of the waveform500(i.e., the waveform is repeating), in a similar manner to that ofFIG. 58, the pre-charge capacitor416will release its stored energy through the load (but in the positive direction) via the switching transistor415of the superposition circuit170, and the switching transistors411and414of the bridge circuit160, causing the arc between the electrode E and the workpiece W to quickly re-ignite in the positive direction.

FIG. 6illustrates a schematic diagram of a third exemplary embodiment of a portion of the welding power source100ofFIG. 1having a bridge circuit160and a superposition circuit170. Also illustrated inFIG. 6is a portion210of the power conversion circuit110, where the power conversion circuit110provides a DC+output (e.g., a chopper-based circuit). The current switching circuit180ofFIG. 6is in the form of a full bridge topology that may be used with almost any power source topology, providing flexibility and the potential to be added to existing designed power sources, and providing AC current switching through the welding output circuit path.

The bridge circuit160includes switching transistors611,612,613, and614. The superposition circuit170includes switching transistor615, pre-charge capacitor616, dedicated charging source617, and resistor619. In accordance with an embodiment, the switching transistors are insulated gate bipolar transistors (IGBTs). In accordance with an embodiment, the dedicated charging source is a voltage supply created off of a transformer that is current limited and is dedicated to pre-charging the capacitor616before polarity transition of the welding output current. The charging source617also provides a trickle charge in the milli-amps range to initialize the snubber capacitor683. The superposition circuit170also includes an active snubber circuit having a diode682and a capacitor683that is used to limit the voltage across the current switching circuit180(e.g., somewhere between 300 V and 600 V) to cause the output current through the output circuit path to decay quickly. The anti-parallel diodes of the switching transistors611,612,613, and614of the bridge circuit160complete the snubber/decay current path.

The current switching circuit180ofFIG. 6provides for AC welding operation and provides a voltage at the welding output of the welding power source being of sufficient magnitude to re-establish the welding arc between the electrode E and the workpiece W during polarity reversals of the welding process, as described herein with respect toFIGS. 7A-7C. Welding output terminals191and192are shown and represent the welding output of the welding power source to which the electrode E and the workpiece W may be connected through a welding cable path.

In accordance with an embodiment, the pre-charge capacitor616has a capacitance value of less than one micro-farad and the dedicated charging source617provides a current in the range of, for example, 1-100 milli-amps. The capacitor is sized to provide a large enough voltage between the electrode and the workpiece to quickly and reliably re-ignite the arc immediately after the arc goes out due to the output current switching direction (polarity reversal/switching). During zero current crossing (polarity reversal/switching), the arc extinguishes and the high voltage (e.g., 200 to 400 VDC) provided by the energy from the capacitor616of the superposition circuit170is used to re-establish the arc in the opposite polarity. The pre-charge capacitor616provides the arc-igniting voltage level in both polarities (i.e., when crossing the zero current point from either the positive direction or the negative direction).

During pre-charging, the transistor switch615is off and the active snubber capacitor683is charged first by the dedicated charging source617. Subsequently, the capacitor616is charged off of the snubber capacitor683. That is, the pre-charge capacitor616is indirectly charged by the dedicated charging source617via the snubber capacitor683. Once the capacitor616is discharged to re-ignite the arc, additional energy may be pulled from the snubber circuit through the resistor619(e.g., about 500 ohms) which limits the current being drawn out of the snubber circuit. When the transistor switch615again shuts off, the process of pre-charging repeats. In accordance with an embodiment, an advisory circuit (not shown) monitors the active snubber capacitor683to maintain the voltage of the capacitor683at about 400 V, for example. This is accomplished by charging the snubber capacitor683from the power supply when the voltage is too low, and bleeding off energy from the capacitor683when the voltage is too high.

FIGS. 7A-7Cillustrate the operation of the welding power source inFIG. 6when implementing an AC welding output current waveform. The load230shown inFIGS. 7A-7Crepresents the resistance and inductance of the arc between the electrode E and the workpiece W and the welding cable path connecting the electrode E and workpiece W to the welding power source (i.e., the welding output circuit path). The electrode E, workpiece W, and the welding cable path are not a part of the welding power source, however.

Referring to the top portion ofFIG. 7A, during the positive current portion of an AC waveform700(see thicker dark lines of the waveform700) produced by the welding power source, current flows predominantly from the power conversion circuit210, through the switching transistor611of the bridge circuit160, through the load230(in the positive direction), through the switching transistor614of the bridge circuit160, and back to the power conversion circuit210(see thick arrows). Also, a pre-charge current flows from the dedicated charging source617. During pre-charging, the transistor switch615is off and the active snubber capacitor683is charged first by the charging source617. Subsequently, the pre-charge capacitor616is charged off of the snubber capacitor617to, for example, a minimum voltage for re-igniting the arc (see less thick arrow).

Referring to the bottom portion ofFIG. 7A, during the positive current decay portion of the AC waveform700(see thicker dark line of the waveform700), current flows predominantly from the load230(in the positive direction), through the antiparallel diode of the switching transistor613of the bridge circuit160, through the active snubber circuit, through the anti-parallel diode of the switching transistor612of the bridge circuit160, and back to the load230(see thick arrows). Also, some of the current flows to the capacitor616of the superposition circuit and may further charge the capacitor616(see less thick arrow). This further charging from the load provides a self-regulating feature by providing additional energy that may be needed to re-ignite the arc if, for example, the welding cable is a long cable having a large inductance. During current decay, the bridge circuit160changes polarity. As the current through the load drops toward zero, the arc extinguishes.

The superposition circuit applies a voltage across the load to re-ignite the arc in the opposite polarity. Current from the power conversion circuit can begin to flow again through the load in the opposite direction. The arc re-establishes quickly and any over-shoot of the welding output current is limited by the energy stored in the capacitor616of the superposition circuit. Without the superposition circuit, the power conversion circuit would attempt to re-establish the arc. However, since the voltage provided by the power conversion circuit is usually limited (e.g., to 100 VDC), re-establishment of the arc may not occur.

Referring toFIG. 78, during the polarity transition portion of the AC waveform700(see thicker dark line of the waveform700), no significant current is provided by the power conversion circuit210. The arc between the electrode E and the workpiece W briefly extinguishes. However, energy stored in the pre-charge capacitor616provides an arc-igniting voltage between the electrode E and the workpiece W. The energy from the capacitor616of the superposition circuit170is released and current flows from the capacitor616through the switching transistor615of the superposition circuit170, through the switching transistor613of the bridge circuit160, through the load230(in the negative direction), through the switching transistor612of the bridge circuit160, and back to the capacitor616(see thick arrows). Additional energy may be pulled from the snubber capacitor483(see less thick arrow) through the current limiting resistor619. As a result, the arc between the electrode E and the workpiece W quickly re-ignites in the negative direction.

Referring to the top portion ofFIG. 7C, during the negative current portion of the AC waveform700(see thicker dark lines of the waveform700) produced by the welding power source, current flows predominantly from the power conversion circuit210, through the switching transistor613of the bridge circuit160, through the load230(in the negative direction), through the switching transistor612of the bridge circuit160, and back to the power conversion circuit210(see thick arrows). Also, during pre-charging, the transistor switch615is off and the active snubber capacitor683is charged first by the dedicated charging source617. Subsequently, the pre-charge capacitor616is charged off of the snubber capacitor683to, for example, a minimum voltage for re-igniting the arc (see less thick arrow).

Referring to the bottom portion ofFIG. 7C, during the negative current decay portion of the AC waveform700(see thicker dark line of the waveform700), current flows predominantly from the load230(in the negative direction), through the anti-parallel diode of the switching transistor611of the bridge circuit160, through the snubber circuit, through the anti-parallel diode of the switching transistor614of the bridge circuit160, and back to the load230(see thick arrows). Also, some of the current flows to the capacitor616of the superposition circuit and may further charge the capacitor616(see less thick arrow). This further charging from the load provides a self-regulating feature by providing additional energy that may be needed to re-ignite the arc if, for example, the welding cable is a long cable having a large inductance.

Upon making the transition back to the positive portion of the waveform700(i.e., the waveform is repeating), in a similar manner to that ofFIG. 78, the pre-charge capacitor616will release its stored energy through the load (but in the positive direction) via the switching transistor615of the superposition circuit170, and the switching transistors611and614of the bridge circuit160, causing the arc between the electrode E and the workpiece W to quickly re-ignite in the positive direction.

In summary, systems and methods providing an energy limited arc re-ignition voltage for AC arc welding processes to re-ignite an arc during polarity transitions are disclosed. In arc welding power source embodiments, configurations of bridge and superposition circuits allow for the directional switching of the welding output current through the welding output circuit path and provide a voltage between the electrode and the workpiece of the welding output circuit path that is sufficient to re-ignite the arc during polarity transition of the output current. The superposition circuit provides a capacitor for storing energy from a dedicated charging source which produces the voltage level for re-igniting the arc during the zero crossing of the output current in both polarities.

In appended claims, the terms “including” and “having” are used as the plain language equivalents of the term “comprising”; the term “in which” is equivalent to “wherein.” Moreover, in appended claims, the terms “first,” “second,” “third,” “upper,” “lower,” “bottom,” “top,” etc. are used merely as labels, and are not intended to impose numerical or positional requirements on their objects. Further, the limitations of the appended claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising,” “including,” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. Moreover, certain embodiments may be shown as having like or similar elements, however, this is merely for illustration purposes, and such embodiments need not necessarily have the same elements unless specified in the claims.

While the claimed subject matter of the present application has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the claimed subject matter. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the claimed subject matter without departing from its scope. Therefore, it is intended that the claimed subject matter not be limited to the particular embodiments disclosed, but that the claimed subject matter will include all embodiments falling within the scope of the appended claims.