Modular power source for electric ARC welding and output chopper

A three stage power source for an electric arc welding process comprising an input stage having an AC input and a first DC output signal; a second stage in the form of an unregulated DC to DC converter having an input connected to the first DC output signal, a network of switches switched at a high frequency with a given duty cycle to convert the input into a first internal AC signal, an isolation transformer with a primary winding driven by the first internal high frequency AC signal and a secondary winding for creating a second internal high frequency AC signal and a rectifier to convert the second internal AC signal into a second DC output signal of the second stage; with a magnitude related to the duty cycle of the switches and, a third stage to convert the second DC output signal to a welding output for welding wherein the input stage and the second stage are assembled into a first module and the third stage is assembled into a second module connectable to the first module.

The invention relates to the field of electric arc welding and more particularly to a modular power source for such welding and a novel dual mode chopper output stage for a welder.

INCORPORATION BY REFERENCE AND BACKGROUND OF INVENTION

Electric arc welding involves the passing of an AC or DC current between a metal electrode and a workpiece where the metal electrode is normally a cored metal wire or solid metal wire. A power source is used to create a given current pattern and/or polarity between the advancing electrode wire and workpiece so that the arc will melt the end of the advancing welding wire and deposit the molten metal on the workpiece. Although various converter technologies are used for power sources, the most effective is an inverter based power source where a switching network includes switches operated at high frequency to create the desired waveform or current level for the welding process. An inverter type power source is discussed in Blankenship U.S. Pat. No. 5,278,390 where the inverter is operated in accordance with the preferred embodiment of the present invention. This preferred operating procedure involves “waveform control technology” pioneered by The Lincoln Electric Company of Cleveland, Ohio where the actual waveform is generated by a series of short pulses created at a frequency generally above 18 kHz and the group of short pulses has a profile controlled by a waveform generator. This well known type of inverter control technique is used in the preferred embodiment of the present invention and need not be described in more detail. In accordance with standard power source technology, the input signal to the inverter stage of the power source is rectified current from a sine wave power supply. An appropriate power factor correcting converter is common practice and is either a part of the inverter switching network itself, as shown in Kooken U.S. Pat. No. 5,991,169, or is located before the inverter stage, as shown in Church U.S. Pat. No. 6,177,645. Indeed, a power source with a power factor correcting converter or stage has been known in the welding art for many years. Another power source employing an input power factor correcting converter in the form of a boost converter is shown in Church U.S. Pat. No. 6,504,132. The two patents by Church and the patent by Kooken are incorporated by reference herein as background information and technology to which the present invention relates. In both Kooken U.S. Pat. No. 5,991,169 and Church U.S. Pat. No. 6,504,132 the actual welding current is regulated by an output chopper or buck converter and isolation is obtained by a transformer either in the output of the inverter stage or in the output of the input boost converter. These various topologies for power sources are common knowledge in arc welding technology. In these prior art patents, the actual welding current, voltage or power is regulated in or before the output stage of the power source, which output stage is either an inverter or a chopper. Neither the inverter, nor the chopper is unregulated to produce a fixed, lower voltage DC bus for driving a regulated welding stage as anticipated by the present invention.

Isolation of the welding operation is a characteristic of most power supplies for welding. The term “welding” includes “plasma cutting.” In Vogel U.S. Pat. No. 5,991,180, a preregulator using a boost converter is directed to a converter which is disclosed as a chopper having an output isolation transformer located after welding regulation and directly driving the welding operation. In this power source, the chopper network is controlled to create the desired regulated output welding current and isolation is provided in the output stage. In a like manner, Thommes U.S. Pat. No. 5,601,741 discloses a boost converter for driving a pulse width modulated controlled inverter providing the regulated output signal to the actual welding operation. In both Vogel and Thommes, the second stage is regulated to direct the power factor controlled current from a preregulator into a welding operation. Welding regulation is in the second stage and is normally driven by a pulse width modulator control circuit. Both Vogel and Thommes are incorporated by reference herein as background technology. In Moriguchi U.S. Pat. No. 6,278,080 an inverter type power source is regulated to control the desired welding current. Isolation is obtained by a transformer between the controlled second stage inverter and the welding output which is disclosed as a DC welding operation. A similar power source is shown in Moriguchi U.S. Pat. No. 5,926,381 and Moriguchi U.S. Pat. No. 6,069,811 wherein the isolation of the control current from the inverter stage is at the output of the inverter and directly drives the welding operation. Moriguchi U.S. Pat. No. 5,926,381 discloses the common arrangement for using the voltage at the output of the first stage boost converter to provide the controller voltage for either the regulated inverter stage or the boost converter itself. The three Moriguchi patents are incorporated by reference herein as background information showing the prior art power source where a regulated inverter is driven by an input boost converter or a DC output of a rectifier to produce a controlled welding current directed to an output transformer used for isolation. The secondary AC signal of the isolation transformer is directly used for the welding operation. There is no third stage topology as used in the novel power source of the invention.

Turning now to non-welding technology, an aspect of the invention is the use of a synchronous rectifier device at the output of a DC/DC second stage converter. Synchronous rectifiers are common practice and one such rectifier is illustrated in Boylan U.S. Pat. No. 6,618,274. Calkin U.S. Pat. No. 3,737,755, discloses a DC/DC converter for low power use where a fixed regulated current is directed to a non-regulated inverter to provide a non variable output DC signal. Any control of the non-regulated inverter is at the input side of the inverter so that the input DC signal is the only parameter that can be regulated to control the fixed output DC signal of the inverter. This is a topography that requires a control of the signal to the inverter so that the inverter provides a controlled fixed output signal. This is a different concept than anticipated by use of the present invention; however, the non-welding general background technology in Boylan and Calkin is incorporated by reference herein to show a synchronous rectifier and a version of a non-regulated inverter where any regulation is performed before the inverter by controlling the level of the input DC signal. Neither of these patents relate to a power source for welding and are only incorporated by reference as general technical concepts, such as synchronous rectifier devices and unregulated inverters. A non-welding two stage AC to DC converter is shown in Smolenski U.S. Pat. No. 5,019,952 for imparting minimum harmonic distortion to the current flowing into the converter. The load is not variable and does not require regulation as demanded in a welding operation. This patent is incorporated by reference to show general technology not related in any way to the demands of a power source for electric arc welding.

These patents constitute the background of the invention relating to a power source that must be regulated by a welding operation where such regulation is by a feedback loop of average current, average voltage, and power of the actual welding operation. Fixed load power sources are not relevant to the invention, except as general technical information.

In the past, an inverter in a power source outputted a welding current regulated by a parameter in the welding operation, such as current, voltage or power. This inverter was normally controlled by a pulse width modulator wherein the duty cycle of the switches operated at high frequency was controlled by the feedback from the welding operation so that the duty cycle was adjusted in a range substantially less than 100%. This type of PWM controlled inverter is referred to as a regulated single stage inverter. Such inverter formed the output of the power source and was the last stage of the power source. Lower duty cycles resulted in higher primary currents and more losses. The efficiency of the inverter varied according to the duty cycle adjustment caused by the requirement of regulating the output of the single stage inverter to create an output signal suitable for welding. Using a power source where the final stage is a regulated single stage inverter resulted in heat losses, lower efficiency, high cost and increased component size. For these reasons, some welding source manufacturers have marketed power sources as being better than an inverter power source because they do not use inverters with the resulting high cost and other difficulties. An inverter stage which had the dual function of isolating the output and regulating the current for the purposes of creating a current suitable for welding was to be avoided. See Hoverson U.S. Pat. No. 6,723,957 and Canales-Abarca U.S. Pat. No. 6,349,044, incorporated by reference herein as background.

The Three Stage Power Source Used in the Present Invention

The present invention is used with a power source for electric arc welding (plasma cutting) wherein the inverter of the power source is a second stage as in the past, but is unregulated so that a third stage can be added to provide the actual regulation for creating a current suitable for welding. By using this three stage concept, the inverter can operate at a very high frequency of switching whereas the output third stage can be a chopper operated at a lower frequency of switching. Consequently, the switching frequency is optimized by the function performed by the stage as opposed to the need for using high frequency in a pulse width modulated inverter stage used for actual regulation of the output welding current. Furthermore, the isolated, fixed DC voltage to the regulated third stage can be substantially lower than the DC voltage from the input converter stage and much higher than the actual welding output voltage.

The three stage power source using the invention involves a novel topography for a power source wherein the pulse width modulated inverter is merely a second stage for creating an isolated fixed output DC bus without a feedback signal to the second stage pulse width modulated inverter. This isolated bus is used in a third stage regulated by the actual welding parameters to create a current suitable for welding. Consequently, the invention involves an unregulated second stage not only providing necessary isolation but also to producing a fixed DC output bus to be used by a third stage wherein welding regulation is accomplished. The unregulated second stage inverter is operated at a very high frequency with a duty cycle that is fixed during operation of the power source. The frequency is over 18 kHz and preferably about 100 kHz. The duty cycle is fixed at various levels; however, the preferred duty cycle is close to 100% to give the maximum efficiency level obtained by use of the present invention. The use of a fixed, high duty cycle minimizes the current circulation time of the phase shift modulator controlled inverter second stage to substantially reduce heat an increase efficiency. The output of the second unregulated inverter stage is a rectifier which can use well known synchronous rectifier devices, which devices are controlled by the secondary winding of the internal isolation transformer of the second stage unregulated inverter. By using synchronous rectifier devices at the output of the second stage, there is further improvement in the total efficiency of the power source. By using the present invention, the first stage is either an input rectifier or an input rectifier with a power factor correcting converter. A first stage power factor correcting converter is preferred. This converter is after a standard rectifier or can be combined with the rectifier. Of course, this converter can be a passive power factor correcting converter or an active converter such as a boost, buck or buck+boost converter. The first stage of the invention produces a first DC bus with a fixed voltage. By using a standard first stage for the power source, the first DC output signal which is the input DC bus to the unregulated inverter can be regulated and fixed at a value of about 400-900 volts DC. The output of the unregulated, isolation inverter forming the second stage of the novel power source is a fixed DC bus having a fixed relationship with the input DC bus from the first stage. The voltage of the second DC bus or output is substantially less than the voltage of the DC bus from the first stage. The power source thus produces a second DC bus which has a fixed mathematical relationship with the input DC bus from the power factor correcting converter. In accordance with standard practice, the second stage unregulated inverter includes an isolation transformer having a primary winding and a secondary winding so that the secondary winding is isolated from the input of the power source. See Steigerwald U.S. Pat. No. 4,864,479, incorporated by reference herein. The unregulated, second stage inverter can be operated at a switching frequency to optimize the operation of the second stage inverter. Thus, extremely high switching frequency is used to reduce the size and cost of the components in the novel, unregulated second stage inverter. By utilizing a fixed duty cycle with phase shift control, voltage and current surges in the switching devices are reduced to provide a soft switching operation. Indeed, in the preferred embodiment, the duty cycle is fixed at 100% so that the switches are full on or full off. This drastically reduces the circulated current in the second stage and greatly improves the operating characteristics of the second stage inverter which also provides the function of isolating the welding output of the power source from the AC input of the power source. By having the switching devices in the second stage unregulated inverter operated at full on, this inverter has a high efficiency and is very flexible in operation. An isolation transformer determines the relationship between the fixed DC bus at the input side of the unregulated second stage (a “first DC output signal” from the first stage) and the DC output bus at the output of this second stage (a “second DC output signal”). In some prior art power sources, the duty cycle at the primary winding of the isolation transformer in the regulated inverter is regulated by the welding operation. There is no regulation by the welding operation in either the first stage or second stage of the novel power source used in the present invention.

Since the second unregulated inverter stage of the power source provides system isolation, many types of non-isolated converters can be used as the power factor correcting preregulator. A boost converter is the most popular converter due to the current shaping function and the continuous line current characteristics of this type of conversion. However, the output voltage of the boost converter is higher than the peak of the highest line voltage, which peak can be as high as 775 volts. Thus, other active power factor correcting regulators can be used with the invention, which is a three stage power source wherein the second stage is unregulated and provides isolation. One of the other options for the active power factor correcting input or first stage is a step-up/step-down converter so that the primary voltage bus or input bus to the second stage can be lower than the peak of the input AC voltage signal to the power source. This type of power factor correcting converter still produces low harmonics. One such power factor converter is referred to as a buck+boost converter. A 400 volt to 500 volt DC bus used for the second stage is obtained with an input AC voltage in the range of 115 volts to 575 volts. Irrespective of the AC voltage to the first stage, the output voltage of the active power factor converter is controlled to be at a level between 400 volts and 500 volts. Other types of active and passive power factor correcting inverters can be used in the invention. The preferred converter is active thus constituting a second switching network requiring a second control circuit. When using the term electric arc welding, it also includes other output processes, such as plasma cutting.

As so far explained, the power source using the invention involves a three stage power source for electric arc welding. A feedback control in the third stage creates an output current suitable for welding. The input first stage is normally an active power factor correcting converter requiring a second switching network and a second independent control circuit. This three stage topography is not used in the prior art. By having this topography, the added second stage is merely used to convert the high voltage DC bus at the primary side of the second stage to a lower voltage DC bus at the secondary side of the second stage isolated from the primary side. Thus, the power source involves a DC bus at the secondary side of the second stage so that the bus can be used for regulation of welding power. The term “bus” means a DC signal that has a controlled fixed level. In the present invention, there is a first DC bus from the input stage called the “first DC output” which first DC output has a controlled DC voltage. There is a second DC bus at the secondary side of the second stage called the “second DC output” which second DC output is also a controlled DC voltage level. The creation of a second DC bus at the secondary side of an unregulated inverter has advantages, other than the advantages associated with the use of the unregulated second stage inverter as so far described. The secondary DC bus or second DC output is isolated from the primary side of the second stage so that there is no isolation required in the third stage welding control circuit. In other words, the output control circuit, such as a chopper, has an input DC bus with a fixed voltage level. In practice, the chopper has a controller with a control voltage that is derived from the input DC to the chopper. This input DC signal is isolated from the input power. Consequently, the control voltage for the controller of the output stage or chopper can be derived from a non-isolated DC source. This is normally the input signal to the chopper. Separate isolation of the control voltage for the controller used in the output stage is not required. The use of a fixed DC bus from the second stage allows the DC voltage to the output third stage, which is regulated by the welding operation, to be much lower than the normal input primary DC bus (“first DC output”) of the power source. In the past, the output of the power factor converter is a relatively high level DC signal based upon the use of a boost converter. This high DC voltage was directed to the regulated inverter stage for use in outputting a current suitable for the welding. By using the present invention the high voltage from the output bus of the power factor converter is drastically reduced. It is more efficient to convert a 100 volt DC bus into a 15 volt control power than to convert a 400 volt DC bus to a 15 volt control power. This creation of a second, lower voltage DC bus is a substantial advantage of the three stage power source of the present invention.

The Invention

In accordance with the present invention there is provided a power source for an electric arc welding process wherein the power source comprises an input stage having an AC input and a first DC output signal. A second stage in the form of an unregulated DC to DC converter has an input connected to the first DC output signal and an output in the form of a second DC output signal electrically isolated from the first DC output signal with a magnitude of a given ratio to the first DC output signal. The power source includes a third stage to convert the second DC output signal to a welding current for the welding process. In accordance with another aspect of the present invention there is provided a power factor correcting converter as the first stage of the novel three stage power source. The third stage of the power source includes a regulated converter such as a chopper or inverter. When using an inverter, the output is a DC signal directed to a polarity network or switch, which switch allows DC welding by the power source. The polarity switch allows welding either DC negative, DC positive or AC. The welding process, using either a chopper or an inverter, can be performed with shielding gas, such as MIG welding, and can use any type of electrode, such as tungsten, cored wire or solid metal wire. In accordance with an aspect of the invention, the output of the unregulated DC to DC converter is substantially less than the input to the second stage. In most instances, the input and output of the second stage are DC voltages with generally fixed magnitudes. The input stage and the second stage are assembled on a first module and the third stage is a second module. This is novel. The three stages are not on a common building block. There are two power modules. The output module is preferably a chopper. However, the output stage can be changed between a DC, AC or STT circuit. The two stage input module can be paralleled to drive a high power chopper module. The advantage of such paralleling capability is explained in Stava U.S. Pat. No. 6,291,798, incorporated by reference herein.

In accordance with an aspect of the invention, the power switches of the third stage of the modularized three stage power source has a commonly used soft switching circuit of the passive type, as described in a May 1997 article by the University of California entitled Properties and Synthesis of Passive, Loseless Soft Switching PWM Converters, incorporated by reference herein. The same passive switching circuit is disclosed in Geissler U.S. Pat. No. 6,115,273 and Chen U.S. Pat. No. 5,874,826, incorporated by reference herein. See also Vogel U.S. Pat. No. 5,991,180 and Bhagwat U.S. Pat. No. 5,636,114, incorporated by reference herein.

The present invention relates to modularizing a novel three stage power source, so all three stages are not assembled onto a common base. In accordance with the invention, the first two stages are in a single module. Consequently, the input module contains the power factor correcting stage, or preregulator, and the isolation stage which second stage is an unregulated inverter operated at a fixed duty cycle by a pulse width modulator; the pulse width modulator is controlled by waveform technology using a wave shaper or waveform generator. Thus, the power factor stage and isolation stage are commonly mounted and can be used with any output stage having its own support structure. Preferably the output stage is a chopper. Use of two building blocks, instead of a single platform for the power source, allows changing of the output or chopper stage to change between various welding processes, such as DC positive, DC negative, AC or STT. By modularizing the first two stages of the novel three stage power source for welding, the modularized first stage can be paralleled to provide a higher input to drive an existing high power chopper module. This use of a first module with the first two stages and a second module with the third stage is a substantial improvement in the novel three stage welding power source to which the invention is directed. In accordance with another aspect of the invention, the chopper is provided with a somewhat common soft switching circuit so that the power switch of the chopper is soft switched both in current and in voltage. The soft switching network for the output stage is a further improvement permitted by the modularized concept.

In accordance with another aspect of the invention, the chopper is a dual mode chopper having a first power switch with a first polarity switch to produce a first polarity path in the output of the chopper. A second polarity path is formed by a second power switch and a companion polarity switch to create an opposite polarity current flow. This type of dual mode chopper constitutes a novel output stage for an electric arc welder. Consequently, the chopper design forms an aspect of the invention separate from the modularized three stage topography disclosed above.

In accordance with the present invention there is provided an output stage for a power source of an electric arc welder. This output stage is a chopper with a first polarity path having a first power switch and a polarity switch and a second polarity path having a second power switch and a polarity switch. Furthermore, this output stage includes a controller with a first mode for alternately operating the chopper between the first and second paths and a second mode operating the chopper in only one of the two polarity paths. In this manner, the single chopper output stage can be operated in DC positive, DC negative or AC by merely controlling the switching signals of the power switches and auxiliary polarity switches. This is a novel output stage for a power source used in welding and is used in a three stage power source with the first and second stages being in a single module and the third stage or chopper being in a separate and replaceable second module.

In accordance with an overall aspect of the present invention, the novel three stage power source with a center unregulated DC to DC converter is used in combination with a series of different types of welding processes such as submerged arc welding, tandem electrode welding using two three stage power sources, TIG welding and standard MIG welding. The welding processes combined with the novel three stage power source utilizes an output signal which is either DC or AC. The DC signal is a fixed voltage, fixed current signal or a pulsed signal having a specific shape determined by the use of waveform technology as pioneered by The Lincoln Electric Company of Cleveland, Ohio. The DC welding signal is either positive or negative. The AC welding signal is created by waveform technology as disclosed in many patents including Blankenship U.S. Pat. No. 5,278,390 and Stava U.S. Pat. No. 6,683,278, incorporated by reference herein. This technology involves a waveform generator or wave shaper used to control a pulse width modulator for determining the output waveform when either a DC or AC output welding signal is used in the welding process. The AC signal can have a larger energy or magnitude in either polarity. Furthermore, the electrode used in the submerged arc process and the MIG process is normally a flux cored electrode even through a solid wire electrode or alloy cored electrode can be used. The same welding processes using the novel three stage power source are performed by a welding power source having an output stage in the form of a dual mode chopper. Such chopper is unique in the welding industry and is disclosed and claimed herein. The dual mode chopper is driven by a DC input signal to produce an output welding signal, which is either DC or AC. Preferably, the DC input signal is created by a two stage input circuit having an unregulated isolation DC to DC converter just prior to the dual mode chopper. These and other combinations of the novel three stage power source and the novel dual mode chopper combined with various output welding processes is an overall aspect of the present invention.

The primary object of the present invention is the provision of a three stage power source for electric arc welding, which stages are modularized so that the first two stages are a single module and the second or output stage is a separate replaceable module.

Another object of the present invention is the provision of a three stage power source, as defined above, which power source utilizes a modularized first and second stage, which first module can be connected in parallel to drive a single output module.

Still a further object of the present invention is the provision of a three stage power source, as defined above, which three stage power source has an output module wherein the power switch of the output stage has a soft switching circuit. The soft switching circuit is passive and controls both the switching voltage and the switching current.

Yet another object of the present invention is the provision of a three stage power source, as defined above, which power source has a novel output chopper module that can be operated in DC positive, DC negative or AC to control the output welding operation for MIG welding, TIG welding, tandem welding and submerged arc welding.

Another object of the present invention is the provision of a novel dual mode chopper for the output stage of a power source used in an electric arc welding, which output stage can be shifted between DC−, DC+ or AC to control the welding operation for MIG welding, TIG welding, tandem welding and submerged arc welding.

Still a further object of the present invention is the provision of a three stage power source, as defined above, which power source can adapt to a number of different third stage modules to change the welding process.

Still an additional object of the present invention is the provision of a novel three stage power source, which three stage power source includes an unregulated second stage for isolation with this stage combined with the input first stage and used to create an output welding signal (DC+, DC− or AC) for MIG welding, TIG welding, tandem welding and submerged arc welding.

A further additional object of the present invention is the provision of a novel chopper, as defined above, which novel chopper has two power switches with passive soft switching circuits.

These and other objects and advantages will become apparent from the following description taken together with the accompanying drawings.

THREE STAGE POWER SOURCE

The present invention is a modification of a novel three stage power source for use in electric arc welding as developed by The Lincoln Electric Company and not prior art to the present invention. The new three stage power source has an input stage for converting an AC signal into a first DC output bus. This output bus has a fixed voltage level and is directed to the input of a second stage best shown inFIG. 17. This novel second stage of the three stage power source is an unregulated inverter which includes an isolation feature and has a second DC output or second DC bus which is proportional to the DC input bus. The level relationship is fixed by the construction of the unregulated inverter. The unregulated second stage inverter has a switching network wherein the switches are operated at a high switching frequency greater than 18 kHz and preferably about 100 kHz. The switching frequency of the switch network in the unregulated inverter forming the second stage of the power source allows use of small magnetic components. The isolated DC output of the unregulated inverter is directed to a third stage of the power source. This third stage can be either a chopper or inverter which is regulated by a welding parameter, such as current, voltage or power of the welding operation. In the modification this third stage is preferably a chopper. The topography of the three stage power source has an input stage to produce a first DC signal, a second unregulated DC to DC stage to provide an isolated fixed DC voltage or DC bus that is used by the third stage of the power source for regulating the current used in the welding operation. Three examples of a three stage power source to which the present invention is directed are illustrated inFIGS. 1-3. Power source PS1inFIG. 1includes first stage I, second stage II, and third stage III. In this embodiment, stage I includes an AC to DC converter10for converting AC input signal12into a first DC bus14. The input12is an one phase or three phase AC line supply with voltage that can vary between 400-700 volts. Converter10is illustrated as an unregulated device which can be in the form of a rectifier and filter network to produce DC bus14identified as (DC#1). Since the AC input signal is a line voltage, DC bus14is generally uniform in magnitude. Unregulated inverter A is a DC to DC converter with an isolation transformer to convert the DC bus14(DC#1) into a second DC bus or second DC output20(DC#2). Output20forms the power input to stage III which is converter30. The DC voltage on line20is converted by converter30into a current suitable for welding at line B. A feedback control or regulation loop C senses a parameter in the welding operation and regulates the current, voltage or power on line B by regulation of converter30. In practice, converter30is a chopper, although use of an inverter is an alternative. By having a three stage power source PS1as shown inFIG. 1, the switching network of the second stage has a frequency that is normally higher than the switching frequency of converter30. Furthermore, the DC voltage in line20(DC#2) is substantially less than the DC voltage from stage I on line14(DC#1). In practice, there is an isolation transformer in inverter A. The transformer has an input or primary section or side with substantially more turns than the secondary section or side used to create the voltage on line20. This turn ratio in practice is 4:1 so that the voltage on line20is ¼ the voltage on line14.

The general topography of three stage power source to which the present invention is directed is illustrated inFIG. 1; however,FIG. 2illustrates the preferred implementation wherein power source PS2has essentially the same stage II and stage III as power source PS1; however, input stage I is an AC to DC converter40including a rectifier followed by a regulated DC to DC converter. The converted signal is a DC signal in line14shown as a first DC bus (DC#1). The voltage on line14is regulated as indicated by feedback line42in accordance with standard technology. Thus, in power source PS2the output welding converter30is regulated by feedback loop C. The voltage on line14is regulated by feedback loop shown as line42. Since converter40is a power factor correcting converter it senses the voltage waveform as represented by line44. By using power source PS2, the first DC bus14is a fixed DC voltage with different one phase or three phase voltages at input12. Thus, output20is merely a conversion of the DC voltage on line14. DC#2is a fixed voltage with a level determined by the isolation transformer and the fixed duty cycle of the switching network in unregulated inverter A. This is the preferred implementation of the novel power source employing three separate and distinct stages with stage II being an unregulated inverter for converting a fixed first DC output or DC bus to a second fixed DC output or DC bus used to drive a regulated welding converter, such as a chopper or inverter. As another alternative, stage I could be regulated by a feedback from the DC #2bus in line20. This is represented by the dashed line46inFIG. 2.

Power source PS3inFIG. 3is another implementation of the three stage power source. This is not the preferred implementation; however, the three stage power source of the present invention can have the input converter50regulated by feedback loop52from the welding current output B. With this use of a three stage power source, converter50is regulated by the welding output and not by the voltage on line14as in power source PS2. With regulation from welding output B, converter50is both a power factor correcting stage and a welding regulator. However, this implementation of the three stage power source is disclosed for a complete technical disclosure.

As previously described, input stage I converts either a single phase or a three phase AC signal12into a fixed DC bus14(DC#1) for use by the unregulated inverter A constituting second stage II. The novel three stage power source generally employs a DC to DC converter in stage I to produce the DC voltage indicated as line14inFIGS. 1-3. The DC to DC converter of stage I can be selected to create the desired voltage on line14. Three of these converters are shown inFIGS. 4-6wherein an input rectifier60provides a DC voltage in lines60a,60bto a DC to DC converter which may be a boost converter62, a buck converter64or a buck+boost converter66, as shown inFIG. 4,FIG. 5andFIG. 6, respectively. By using these converters, the DC to DC converter of stage I incorporates a power factor correcting chip, which chip allows the power factor to be corrected thereby reducing the harmonic distortion at the input of the power source. The use of a power factor correcting input DC to DC converter is well known in the welding art and is used in many prior art two stage topographies. Converters62,64and66preferably include a power factor correcting chip; however, this is not required. The main purpose of stage I is to provide a DC bus (DC#1) in line14, which bus is indicated to be lines14a,14binFIGS. 4-6to produce a fixed DC voltage (DC#2) in line20indicated by lines20a,20bin the same figures. Power factor correction is not required to take advantage of the novel three stage topography. A non power factor correcting input stage is illustrated inFIG. 7where the output lines60a,60bof rectifier60are coupled by a large storage capacitor68to produce a generally fixed voltage in lines14a,14b. Stage I inFIG. 7does not incorporate a power factor correcting circuit or chip. However, the power source still involves three stages wherein the second stage is unregulated isolated inverter A to produce a generally fixed voltage on lines20a,20b. Another modification of input stage I is illustrated inFIG. 8where a passive power factor correcting circuit70is connected to a three phase AC input L1, L2and L3to produce a generally fixed DC voltage across lines14a,14b, which lines constitutes the DC bus14(DC#1) at the input of inverter A. The disclosures of modified stage I inFIGS. 4-8are only representative in nature and other input stages could be used with either single phase or three phase input signal and with or without power factor correcting.

By providing low fixed voltage on output bus20illustrated as lines20a,20b, the third stage of the novel three stage power source for welding can be a chopper or other converter operated at a frequency greater than 18 kHz. The switching frequencies of the unregulated inverter and the regulated output converter may be different. Indeed, normally the switching frequency of the chopper is substantially less than the frequency of unregulated inverter A. Power source PS4shown inFIG. 9illustrates the use of the present invention wherein stage III is a standard regulated converter100of the type used for electric arc welding. This converter is driven by fixed input DC bus20and is regulated by feedback from the welding operation120to provide current suitable for welding across output leads102,104. Leads102is a positive polarity lead and leads104is a negative polarity lead. In accordance with standard output technology for a two stage inverter based power sources, leads102,104are directed to a standard polarity switch110. This switch has a first position wherein lead102is directed to the electrode of the welding operation120so the output of polarity switch110has a positive polarity on output line110aand a negative polarity on output line110b. This produces an electrode positive DC welding process at weld operation120. Reversal of polarity switch network110can produce an electrode negative DC welding process at weld operation120. Thus, a DC welding process with either DC negative or DC positive can be performed according to the setting of the standard polarity switch110. In a like manner, polarity switch110can be alternated between electrode negative and electrode positive to produce an AC welding process at weld operation120. This is standard technology wherein polarity switch110drives the DC output from regulated converter100to produce either an AC welding process or a DC welding process. This process is regulated and controlled by a feedback system indicated as line or loop122directed to controller130for regulating converter100and for setting the polarity of switch110as indicated by lines132,134, respectively. By regulating the welding operation at stage III, the unregulated inverter at stage II can have a relatively higher switching frequency to reduce the component sizes within the second stage of the power source. The preferred embodiment of the three stage power source employs waveform control technology pioneered by The Lincoln Electric Company of Cleveland, Ohio. This type of control system is well known and is schematically illustrated inFIG. 9Awherein control circuit150processes a waveform profile as a voltage on line152ais outputted from waveform generator152. The waveform profile is controlled by feedback loop122as schematically illustrated by error amplifier154having an output156. Thus, the profile of the waveform from generator152is controlled by the feedback loop122and produces a signal in output line156. This line is directed to an appropriate pulse width modulator circuit160operated at a high frequency determined by the output of oscillator162. This frequency is greater than 18 kHz and is often higher than 40 kHz. The regulated converter100preferably operates under about 100 kHz. The output of the pulse width modulator, which is normally a digital circuit within controller130, is shown as line132for controlling the waveform by way of regulated converter100. In accordance with standard practice, the waveform of inverter100can have any profile, either AC or DC. This feature is schematically illustrated as waveform152b,152cand152dat the right portion ofFIG. 9A. Waveform152bis an AC waveform of the type used in AC MIG welding where a higher negative electrode amperage is provided. A higher positive amperage is also common. In waveform152c, the amperage for both electrode negative and electrode positive is essentially the same with the length of the negative electrode portion being greater. Of course, a process for AC welding can be adjusted to provide balanced AC waveforms or unbalanced AC waveforms, either in favor of electrode negative or electrode positive. When polarity switch110is set for either a DC negative or a DC positive welding operation, a pulse welding waveform, shown as waveform152d, is controlled by waveform generator152. Various other waveforms, both AC and DC, can be controlled by controller130so the welding operation120can be adjusted to be AC, or DC. Furthermore, the welding operation can be TIG, MIG, submerged arc or otherwise. Any process can be performed by power source PS4or other power sources using the present invention. The electrode can be non-consumable or consumable, such as metal cored, flux cored or solid wire. A shielding gas may or may not be used according to the electrode being employed. A modification of power source PS4to perform only DC welding is illustrated as power source PS5inFIG. 10. In this power source, welding operation120performs only a DC welding operation so that feedback loop122is directed to controller170having an output172. Regulated converter100ais preferably a chopper to produce a DC voltage across lines102a,104a. Controller170is controlled by waveform generator152, as shown inFIG. 9A. The polarity on lines102a,104ais either electrode negative or electrode positive according to the demand of the DC welding process performed at welding operation120. Regulated converter100ais more simplified than the welding output of power supply PS4shown inFIG. 9.FIGS. 9 and 10, together with the control network or circuit150shown inFIG. 9A, illustrates the versatility of the novel three stage power source.

It is necessary to provide a voltage for operating the controllers for both the regulated and unregulated switching networks used in these two types of power sources.FIG. 11illustrates the architecture and scheme employed to obtain control voltages to operate the various controllers of a three stage power source, such as power source PS6. The use of an output of a preregulator to provide the control voltage for the switching controller of the preregulator and switching controller of the second stage of a two stage power source is well known and is disclosed in Moriguchi U.S. Pat. No. 5,926,381, incorporated by reference herein. An output chopper for performing a welding operation routinely obtains the controller control voltage from the input DC voltage to the chopper. These two well known technologies are incorporated in power source PS6. The three stage power source can be operated with controllers having power supplies derived from various locations in the power source. Being more specific, power source PS6has a power supply180with an output182and inputs184,186from the first DC bus on leads14a,14b(DC#1). Power supply180includes a buck converter or flyback converter, not shown, to reduce the high voltage at the output of preregulator40ofFIG. 2to a low voltage on line182. This control voltage may be between 5 and 20 volts. Voltage on line182is directed to controller190having an output lead192for performing the operation of preregulator40in accordance with standard technology. The preregulator has regulation feedback lines42,44shown inFIGS. 2 and 3, but omitted inFIG. 11. Unregulated inverter A does not require a controller to modulate the duty cycle or the fixed relationship between the input and output voltages. However, it does require a controller194that receives controller operating voltage in line196from power supply180. This arrangement is similar to the concept disclosed in Moriguchi U.S. Pat. No. 5,926,381, except second stage controller194is not a regulating controller as used in the two stage power source of the prior art. As an alternative, power supply PS#3is driven by one phase of input12to give an optional power supply voltage shown as dashed line176. Regulated output converter30of stage III has a power supply200labeled PS#2with a controller voltage on line202determined by the voltage on DC bus20(DC#2) illustrated as including leads20a,20b. Again, power supply200includes a buck converter or flyback converter to convert the DC bus at the output of unregulated converter A to a lower voltage for use by controller210having an output212. The signal on line212regulates the output of welding converter30in accordance with the feedback signal on line C, as discussed with respect to power sources PS1, PS2inFIGS. 1 and 2, respectively. DC bus14(DC#1) and DC bus20(DC#2) provides input to power supplies180,200which are DC to DC converters to produce low level DC control voltage for controllers190,194and210. As an alternative shown by dashed line220, power supply180labeled PS#1can provide control voltage for controller210.FIG. 11has been disclosed to illustrate the versatility of using a three stage power source with controllers that can receive reduced supply voltages from various fixed DC voltage levels indicated to be PS#1and PS#2. Other arrangements could be employed for providing the controller voltage, such as a rectified connection to one phase of AC input voltage12by a transformer in a manner illustrated as PS#3.

Power source PS7inFIG. 12is similar to power source PS6with components having the same identification numbers. The output stage III is a chopper230for directing a DC current between electrode E and workpiece W. Current shunt S provides the feedback signal C to controller210. High switching speed inverter240of stage II has characteristics so far described with the isolation provided by transformer250having primary winding252and secondary winding254. The primary side of DC to DC converter240is the switching network directing an alternating current to primary winding252. The rectified output from secondary254is the secondary section or side of converter240. Converter240employs a high switching speed inverter that has a duty cycle or phase shift set by controller194. The switching frequency is about 100 kHz in the practical version of this power source. The duty cycle remains the same during the welding operation by chopper230; however, the duty cycle or phase shift of the inverter may be adjusted as indicated by “ADJ” circuit260having an output262for adjusting controller194. The duty cycle is normally close to 100% so that the switch pairs are conductive together their maximum times at the primary side of inverter240. However, to change the fixed relationship between the first DC bus14and the second DC bus20, circuit260can be used to adjust the duty cycle or phase shift. Thus, the unregulated, isolation inverter240is changed to have a different, but fixed duty cycle. However, the duty cycle normally is quite close to 100% so the switch pairs are operated essentially in unison. The duty cycle probably varies between 80-100% in normal applications of the three stage power source. In the preferred implementation of the novel power source, boost converter62shown inFIG. 4is used for a power factor correcting input stage I. This boost converter is operated in accordance with controller190having a control voltage182as previously described. In accordance with a slight modification, supply270has a transformer connected by lines272,274across one phase of a single phase or three phase AC input12. A rectifier and filter in power supply270produces a low control voltage in optimal dashed line276for use instead of the control voltage in line182if desired. These two alternatives do not affect the operating characteristics of power source PS7. Other such modifications of a three stage power source for electric arc welding can be obtained from the previous description and well known technology in the welding field.

Input stage I normally includes a rectifier and a power factor correcting DC to DC converter as disclosed inFIGS. 4-8. These input stages can be used for both three phase and single phase AC signals of various magnitudes, represented as input12. Certain aspects of an input stage for three phase AC input power are disclosed with respect to the circuits inFIGS. 13-16. Each of these circuits has a three phase input and a DC bus output (DC#1) that is obtained with a low harmonic distortion factor and a high power factor for the input stage. The disclosure inFIGS. 1-12are generally applicable to the novel three stage power source; however, the particular stage I used is relevant to both a two stage power source of the prior art or the novel three stage power source. InFIG. 13, the input circuit300of stage I includes a three phase rectifier302with output leads302a,302b. Boost switch310is in series with an inductor312, diode314and a parallel capacitor316. An appropriate circuit320which is a standard power factor correcting chip has an input322to determine the input voltage, a regulation feedback line322aand an output324for operating the boost switch to cause the current in input12to be generally in phase with the input voltage. This chip is a standard power factor correcting boost converter chip that can be used in the present invention and is also used for a normal two stage power source. In a like manner, input circuit330shown inFIG. 14has a three phase rectifier302with output leads302a,302bas previously described. A boost circuit including inductor350, diodes352,354and capacitors356,358are used in conjunction with switches340,342to provide coordination of the current at the output of circuit330and input voltage12. To accomplish this objective, a standard chip360provides gating pulses in lines362,364in accordance with the sensed voltage in input366and feedback regulation signals in lines367,368. This is standard technology to provide power factor correction of the type that forms the input of a two stage power source or the novel three stage power source. It has been found that the active three phase circuits300,330when operated on a three phase input provide an input power factor of about 0.95. The power factor of a stage I when having a single phase AC input can be corrected upwardly to about 0.99. Since a three phase power source can generally be corrected only to a lower level, it has been found that a passive circuit for the input stage I of a two stage or three stage power source is somewhat commensurate with the ability of an active power factor correcting circuit. A standard passive circuit400is shown inFIG. 15, wherein each of the three phases is rectified by three phase rectifier302which directs DC current through output leads302a,302bto a filter circuit including inductor412and capacitor414. It has been found that a passive circuit such as shown inFIG. 15can correct the power factor of the three phase input to a level generally in the range of about 0.95. This is somewhat the same as the ability of an active circuit for a three phase input circuit. A buck+boost input circuit420is shown inFIG. 16. Rectified current on lines302a,302bis first bucked by switch422using standard power factor correcting chip430having a line432having a voltage waveform signal from input12, that also steers chip434to operate boost switch440. Switches422,440are operated in unison to control the input power factor using a circuit containing inductor450, diode452and capacitor454. Circuits300,330,400and420are standard three phase passive power factor correcting circuits using standard technology and available switches controlled by the input voltage waveform and the current of DC#1.FIGS. 13-16are illustrative of certain modifications that can be made to the first stage of the three stage power source. Of course, there is other technology for improving the power factor and reducing the harmonic distortion of both DC and AC signals of the type used to drive power sources of electric arc welders.

Unregulated inverter A of stage II can use various inverter circuits. The preferred circuit is illustrated inFIG. 17wherein the inverter is divided between a primary section or side defined by the input to primary winding252of isolating transformer250and a secondary section or side defined by output of secondary winding254. Referring first to the primary section or side of inverter A, full bridge circuit500is employed wherein paired switches SW1-SW2and SW3-SW4are across capacitor548are connected by leads502,504. The switches are energized in alternate sequence by gating pulses on lines510,512,514, and516, respectively. Controller194outputs gating pulses in lines510-516and an adjusted duty cycle determined by the logic on line262from circuit260as previously discussed. The duty cycle is controlled by changing the phase shift of lines510and512and lines514and516. Circuit260adjusts the duty cycle or phse shift of the paired switches. This adjustment is fixed during the operation of inverter A. In practice, circuit500has about 50% duty cycle or phase shift, where each pair of switches has maximum periods of conduction. Preferably the duty cycle is about 100% or 80-100%. Controller194has a control voltage from an appropriate supply indicated by line196, as also previously described. In operation of circuit500, an alternating current is directed through primary winding252. This current has an ultra high frequency normally at least about 100 kHz so the components can be reduced in size, weight and cost. The high switching frequency is not dictated by the welding operation, but is selected for efficiency of unregulated stage A of the three stage power source. The secondary section or side of inverter A is a rectifier520having synchronous rectifier devices522,524. Synchronous rectifier devices are well known in the general electrical engineering art and are discussed in Boylan U.S. Pat. No. 6,618,274 incorporated by reference herein. These devices are gated by signals on lines526,528created at the opposite ends of secondary winding254in accordance with standard technology. Leads530,532, and534form the output leads of rectifier520to create a DC voltage (DC#2) across leads20a,20b. The current is smoothed by a choke544and is across capacitor546, in accordance with standard welding technology. Inverter A is unregulated which means that it is not adjusted by a real time feedback signal from the welding operation. It merely converts DC bus12(DC#1) to DC bus20(DC#2). This conversion allows a substantial reduction in the voltage directed to the regulated third stage of the power source using inverter A. The reduction in voltage is primarily determined by the turns ratio of transformer250, which ratio, in the preferred embodiment, is about 4:1. Thus, the fixed voltage on output bus20is about ¼ the fixed voltage on output bus12of the first stage. Several advantages of an unregulated stage are contained in an article entitledThe incredible Shrinking(Unregulated)Power Supplyby Dr. Ray Ridley incorporated by reference herein as background information. A basic advantage is the ability to increase the frequency to above 100 kHz to reduce the size and cost of the inverter stage.

Various circuits can be used for the unregulated inverter A constituting novel stage II of the invention. The particular type of inverter is not controlling. Several inverters have been used. Some are illustrated inFIGS. 18-21. InFIG. 18, inverter A is shown as using a full bridge circuit600on the primary side of transformer250. A switch and diode parallel circuit602,604,606and608are operated in accordance with the standard phase shift full bridge technology, as explained with respect to the inverter A version shown inFIG. 17. A modification of the internal workings for inverter A is illustrated inFIG. 19utilizing a cascaded bridge with series mounted switch circuits610,612and614,616. These switch circuits are operated similar to a half bridge and include input capacitors548a,548bproviding energy for the switching circuits which in parallel is capacitor620and is in series with diode622,624. The two switch circuits are in series so there is a reduced voltage across individual switches when a phase shift control technique similar to the technique for the full bridge inverter ofFIG. 17is used. This type of inverter switching network is illustrated in Canales-Abarca U.S. Pat. No. 6,349,044 incorporated by reference herein showing an inverter using a cascaded bridge, sometimes referred to as a three level inverter. A double forward inverter is shown inFIG. 20wherein switches630,632provide a pulse in section252aof the primary winding for transformer250a. In a like manner, switches634,636are operated in unison to provide an opposite polarity pulse in primary section252b. The alternating pulse produces an AC at the primary winding of transformer250ato produce an isolated DC output in secondary winding254. A standard half bridge circuit is shown as the architecture of inverter A inFIG. 21. This half bridge includes switches640,642alternately switched to produce an AC in primary winding252of transformer250. These and other switching circuits can be used to provide an AC signal in the primary winding of transformer250so that the secondary isolated AC signal is rectified and outputted on leads20a,20bas DC#2. The mere description of certain representative standard switching networks is not considered to be exhaustive, but just illustrative. Control of the welding current is not performed in the second stage. In this stage, a DC bus having a high voltage is converted to a fixed DC bus (DC#2) having a low voltage for the purposes of driving a third stage, which third stage is a regulated stage to provide a current suitable for electric arc welding. Electric arc welding incorporates and is intended to include other welding related applications, such as the concept of plasma cutting. The various circuits used in the three stages can be combined to construct various architectures for the basic topography which is a three stage power source.

Preferred Embodiment

The three stage power source shown and described inFIGS. 1-21constitute a substantial advance in the art of electric arc welding. The present invention involves this novel three stage power source, as generally represented inFIG. 11, formed into a modularized construction, as illustrated inFIG. 22. Power source700includes a first module702forming a fixed assembled frame on a single base. This module includes the first input stage62and the isolation or second stage, in the form of unregulated inverter A. As inFIG. 11, two controllers, shown in two stages such as controller190and controller194, direct control signals on lines192,198into the two separate stages of module702. The output of first module702are lines20a,20b(DC #2). This output voltage is directed to a separate, second module or frame704. The second frame supports the output third stage of the controller, illustrated as chopper30inFIGS. 11 and 22. Weld controller210controls the output of chopper30through a signal on input line212. This signal is generated by a pulse width modulator under the direction of a wave shaper or waveform generator in controller210. Power to controller210is provided by the second DC bus by lines204,206. A feedback current signal from shunt S is received by current sensor circuit706that creates a signal on line706a, representing the output or weld current of the welding operation. In a like manner, voltage sensor circuit708detects the voltage across the arc of the welding operation and provides a signal on line708arepresenting the welding voltage. These two signals are directed into the feedback circuit of controller210to determine the chopper input signal on line212. By mounting the output third stage on separate module704, this module can be changed to modify the power source for performing different welding operations. Furthermore different choppers can be used as the third stage of power source700. The power source is not mounted on a single module, but on an input module702and a separate last stage power module704. Other advantages of this novel modularized construction will be discussed in the implementations of the invention shown inFIGS. 28 and 29.

FIGS. 23 and 24show two output circuits for use on module704. InFIG. 23, chopper710is mounted on replaceable module704to be operated by controller210with a signal on line212. Chopper710includes power switch712controlled by high frequency signals on line212. The signal is created by a pulse width modulator in controller210. Power switch712directs current from input leads20a,20bthrough choke714to perform a welding operation between electrode E and workpiece W. Filter capacitor718is connected across the DC bus or leads20a,20bfor controlling the voltage signal to chopper710. This output chopper is releasably connected to the input leads20a,20bto the three stage power source700inFIG. 22. Thus, the three stage power source has an output chopper. An output chopper is the preferred embodiment of the invention; however, the separate module704can include another output circuit, such as the STT circuit730shown inFIG. 24. This STT circuit includes power switch732for directing current pulses through choke734to the welding operation between electrode E and workpiece W. The signal on line212forms an STT pulse profile at the welding operation. The STT waveform or profile is unique to The Lincoln Electric Company and is described in several patents, such as Parks U.S. Pat. No. 4,866,247 incorporated by reference herein. STT circuit730includes premonition switch740having an input740aactivated when the short circuit metal transfer is approaching a rupture of the metal neck between the electrode and workpiece. Just before the rupture occurs, switch740is closed to increase the current flow for the purposes of separating the short circuited molten metal. When the switch is opened, resistor742is connected in the series circuit including choke734and electrode E. Capacitor744controls the voltage across switch740when the switch is opened to transfer current flow to resistor742. Diode746prevents current flow in the reverse direction in resistor742to discharge capacitor744. Input filter capacitor738is connected between the DC bus formed by leads20a,20b. If an STT welding operation is to be performed by power source700, module730shown inFIG. 24is used to replace chopper module710shown inFIG. 23. These figures illustrate the interchageability of the output circuit on module704to perform different welding operations.

Another aspect of the present invention is a novel output chopper for use on module704. This new output chopper is shown inFIG. 25, wherein chopper750has a dual mode of operation. It has two separate and distinct polarity paths. The first path include polarity switch760operated by control pulses on line762. In series with polarity switch760and choke770is modulating switch764receiving gating pulses on line766and having free wheeling diode788. Operation of polarity switch760and modulating switch764causes current flow across the gap between electrode E and workpiece W in a first polarity direction. A second path creates a current flow across the welding arc in the opposite polarity and includes polarity switch780receiving gating pulses on line782. Corresponding modulating switch784has a gating signal line786and free wheeling diode768. The choke790in the second polarity path corresponds to choke770in the first polarity path. Switch signal control device800creates signals in line762and line766for operating the first polarity path. In a like manner, signals in line782and line786causes a current flow in the opposite polarity path. Control800has a frequency determined by oscillator802and involves a pulse width modulator in the controller in digital format. Device804selects the mode of operation. This device allows one of the polarity paths to be operated to merely provide a standard chopper circuit in either the positive or negative direction. By alternating the pulses to the two polarity paths, an AC output signal is created. The modulating switches764,784are essentially the power switches of the two chopper modes in chopper750. This is a chopper circuit to provide an AC output. A separate and distinct polarity switch as shown inFIG. 9is not required. Dual mode chopper750is novel for electric arc welding and essentially employs a chopper that can be reversed in polarity and can be operated in an AC mode. Thus, the welding operation between electrode E and workpiece W can be shifted between different modes while using the same circuit and with the advantage of a chopper concept. Chopper750, when operated in the AC mode, is a substantial improvement over the prior art AC welding power source, illustrated inFIG. 26. This prior unit is a full bridge output circuit having separate polarity paths with a double forward bias voltage drop. There is no chopper concept. Voltage810is driven by inverter812used to convert DC link820,822to output DC bus830,832. This DC bus drives the full bridge through choke834. Bridge810has switches840,842operated by leads a and switches850,852driven by leads b. The signals to the switches are created by controller860to alternate between the two sets of power switches, each of which has an anti-parallel diode840a,842a,850aand852a, respectively. The dual mode chopper shown inFIG. 25can provide not only AC operation, but also output modulating. This is a substantial improvement over bridge810and does not need an input inverter812. Any of the output modules disclosed inFIGS. 23, 24 and 25can be used in the three stage power source700, as schematically illustrated inFIG. 22. Module704with one of these circuits is used as the output stage connected to two stage input module702.

In accordance with another aspect of the present invention, the output chopper of module704is provided with a soft switching circuit900, as best shown inFIG. 27. Chopper710ofFIG. 23has power switch712driven by pulse width modulator880at a frequency controlled by oscillator882. The output880aof pulse width modulator880is controlled by input880bunder the control by comparator884that compares a command signal from a wave shaper or waveform generator on line886with the feedback circuit signal on line706a. This is the normal operation for a chopper. Soft switching circuit900is a commonly used soft switching circuit. The circuit includes an inductor902for controlling current across the power switch and diode D4. Capacitor906controls the voltage across the power switch during the switching operations. Capacitors904and906are connected as shown inFIG. 27using diodes D1, D2, D3and D4. These capacitors control the voltage across switch712. Inductor902controls the current through diode D4. Thus switch712and diode D4are soft switched in both the current and voltage during switching operations. This circuit is shown in the University of California article entitledProperties and Synthesis of Passive, Loseless Soft-Switching PWM Converters. This May 1997 article is incorporated by reference herein to explain further the operation of the commonly used circuit900. In essence, chopper710has a power switch with a soft switching circuit to control both the current and voltage during turn-on and turn-off sequences of the power switch. The same type of soft switching circuit is employed for power switches760,780of dual mode chopper750. In other words, the output chopper on module704is provided with a soft switching circuit, which soft switching circuit controls both voltage and current at the appropriate time during the switching operations.

FIGS. 28 and 29illustrate two advantages of modularizing power source700. InFIG. 28, module704is provided with output power stage920, which may be a DC chopper as shown inFIG. 23, an AC chopper as shown inFIG. 25or an STT circuit shown inFIG. 24. By using the invention, different modules704can be connected to input module702for building different types of power sources, while maintaining the novel three stage topography. Controller922combines the functions of controllers190,194shown inFIGS. 11 and 22and receives control voltage from line924. Turning now toFIG. 29, a second advantage of using the modularized three stage power source of the invention is illustrated. Two separate input modules702a,702bare connected in parallel by interconnecting the output leads20a,20bfrom each of the two input modules. Thus, chopper30has an input level which is higher than available from a single module702. Of course, more than two input modules could be employed to create a substantial amount of welding current at the input of chopper30. InFIG. 29, power source700aincludes the two input modules702a,702bwhich are controlled in unison by controller930through output lines192a,198aand output lines192band198b. Control voltage is provided by the DC bus in modules702a,702bby lines932,934, respectively. Thus, by using a modularized three stage power source of the present invention, the output stage can be selectively changed or the input stage can be parallel. Paralleling of smaller modules reduces the number of modules needed from a wide range of power levels. Two advantages of modularization are illustrated inFIGS. 28 and 29. Other advantages are apparent to create versatility while maintaining the advantage of the novel three stage power source shown inFIGS. 1-21.

Preferred Methods

The novel three stage power source disclosed inFIGS. 1-21and the novel dual mode chopper shown inFIG. 25has been developed to perform a large number of welding processes.FIGS. 30-41illustrate the combination of such power sources with these welding processes. InFIG. 30, submerged arc MIG welding process1000employs novel three stage power source1010having output leads1012,1014. Lead1014can be a ground lead in accordance with standard technology. The submerged arc welding process involves electrode E movable along workpiece WP and surrounded, at the workpiece, by a mass of granulated flux material1020. As electrode E moves with respect to workpiece WP, the electrode plows through granular flux1020to protect the welding arc and molten metal puddle prior to solidification. In accordance with an aspect of the invention the welding process is performed by the three stage power source disclosed inFIGS. 1-21. In one embodiment of the invention, electrode E is a flux cored electrode, as shown inFIG. 31wherein the electrode is a wire including an outer metal sheath1030surrounding an internal core1032containing flux. A flux cored electrode also includes granular material for alloying with the steel of sheath1030. The inclusion of alloy agents does not change the definition of the electrode as being a “flux cored” electrode. If there is no flux, the electrode can still be a “cored” electrode with metal alloying material in granular form surrounded by sheath1030. The several welding processes disclosed herein can employ a solid wire, a metal cored electrode or a flux cored electrode, the latter being preferred and schematically illustrated inFIG. 31.

In accordance with another aspect of the invention, the three stage power source ofFIGS. 1-21is used in combination with tandem welding process1050, as illustrated inFIG. 31. This process uses three stage power source1060having output leads1062,1064. A welding signal is directed to electrode E1movable in direction D along workpiece WP. The second electrode E2receives a welding signal from three stage power source180having output leads1082,1084. The output leads of both power sources are connected to workpiece WP by lead1086. By moving electrodes E1and E2along workpiece WP in direction D, a tandem welding process is performed. This process is illustrated as being a submerged arc process using granular flux1090. The MIG tandem process ofFIG. 32need not be the submerged arc process and can merely use a flux cored electrode, as shown inFIG. 31. When using the granular flux of a submerged arc welding process, the electrodes are normally solid metal or metal cored.

The three stage power source of the present invention is combined with any welding process, such as TIG welding process1100shown inFIG. 33. Power source1110has output leads1112,1114between electrode E and workpiece WIP. The TIG welding process utilizes a tungsten electrode E, which electrode is not consumed during welding. To provide additional metal for the TIG welding process, filler metal rod F can be used. A similar combination of the three stage power source for generic MIG welding process1120is illustrated inFIG. 34. Power source1122has output leads1124,1126. Electrode E is a welding wire, flux cored or otherwise stored in a supply, illustrated as spool1130. Consequently, welding wire W is moved through contact tip1132into the welding process at workpiece WP. In accordance with standard MIG technology, lead1124is connected to contact tip1132for directing a welding signal to electrode E. This generic MIG welding process uses, in combination, the three stage power source disclosed inFIGS. 1-21.

The various welding output signals shown inFIGS. 35 and 36are created by either the novel three stage power source disclosed inFIGS. 1-21or the dual mode chopper illustrated inFIG. 25. InFIG. 35, AC welding signal1200includes positive portion1202and negative portion1204. These portions are created by a series of closely spaced current pulses1210created by waveform technology, where the magnitude of each pulse is determined by a pulse width modulator under the control of a wave shaper or waveform generator. This is in accordance with standard technology pioneered by The Lincoln Electric Company of Cleveland, Ohio. The AC welding signal ofFIG. 35can be replaced by DC welding signal1250, as shown inFIG. 36. Peak current1252can be a fixed value, either positive polarity or negative polarity. In the illustrated embodiment, welding signal1250is a pulse signal, wherein peak level1252is preceded by ramp up portion1254and followed by ramp down portion1256. This provides a pulse above background level1258. In accordance with the preferred embodiment of the invention, the waveform is produced by a series of individual current pulses1260created by a pulse width modulator under the control of wave shaper or waveform generator.

The process and power source combinations illustrated inFIGS. 30-36are preferably performed by the novel dual mode chopper output stage as illustrated inFIG. 25. This concept is illustrated inFIGS. 37 and 38. InFIG. 37, MIG welding process1300, which can be a submerged arc process by using granular flux, is illustrated as being combined with three stage power source1310having an input two stage module1312directing the output signal from the unregulated isolation DC to DC converter to dual mode chopper1314. The DC signal driving chopper1314is in line1316. The output welding signal on lead1320is a signal such as shown inFIGS. 35 and 36. The welding signal is connected to contact tip1132for the MIG welding process1300. TIG welding process1350combined with power source1310is illustrated inFIG. 38. The previously used numbers for the various components are used inFIG. 38. A welding signal as shown inFIGS. 35 and 36is directed to tungsten electrode E by output lead1320. Filler metal rod F is used to provide additional metal during the DC TIG welding process. Generally this filler metal is not employed for AC TIG welding, although it is available. Generic MIG welding process1300and generic TIG welding process1350, as illustrated inFIGS. 37, 38, respectively, are novel combinations using dual mode chopper710disclosed inFIG. 25.

Dual mode chopper750, as shown inFIG. 25, can be driven by a DC signal from various isolated input power sources to perform the combined welding processes. Use of a generic DC driving signal is illustrated inFIGS. 39-41, wherein like numbers as previously used correspond to the same or like components. A MIG welding process1400is illustrated inFIG. 39, wherein generic DC input1410is converted by dual mode chopper1314to create an AC or DC welding signal at contact tip1132. The MIG welding process1400ofFIG. 39is converted to a submerged arc MIG welding process1420inFIG. 40. This conversion is accomplished by adding granular flux material1422around electrode E to protect the arc and molten metal puddle of the welding process. A dual mode chopper with a generic input DC driving signal1410is combined with a power source to provide TIG welding process1430, illustrated inFIG. 41. The AC or DC welding signal on lead1320is used by tungsten electrode E for TIG welding at workpiece WP.

As illustrated inFIGS. 30-41, the novel three stage power source shown inFIGS. 1-21and the novel dual mode chopper as disclosed inFIG. 25are combined with certain welding processes to create novel methods, which novel methods form another aspect of the present invention. The methods illustrated inFIGS. 30-41disclose the invention of combining welding processes with the novel power sources of the present invention.