Patent Publication Number: US-2018050412-A1

Title: Welding-type power supplies with adjustable ac current commutation thresholds

Description:
RELATED APPLICATIONS 
     This patent claims priority to U.S. Provisional Patent Application Ser. No. 62/375,830, filed Aug. 16, 2016, and entitled “Welding-Type Power Supplies with Adjustable AC Current Commutation Thresholds.” The entirety of U.S. Provisional Patent Application Ser. No. 62/375,830 is incorporated herein by reference. 
    
    
     BACKGROUND 
     This disclosure relates generally to alternating current welding-type systems and, more particularly, to welding-type power supplies with adjustable AC current commutation thresholds. 
     SUMMARY 
     Methods and systems are provided for welding-type power supplies with adjustable AC current commutation thresholds, substantially as illustrated by and described in connection with at least one of the figures, as set forth more completely in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary welding-type system having adjustable current commutation thresholds in accordance with aspects of this disclosure. 
         FIG. 2  is a graph illustrating an example output alternating current waveform output by the example welding-type system of  FIG. 1 , in accordance with aspects of this disclosure. 
         FIG. 3  is a flowchart illustrating example machine readable instructions which may be executed by the control circuit to implement the welding-type power supply of  FIG. 1  to output AC welding-type power based on an adjustable current commutation threshold. 
     
    
    
     The figures are not to scale. Where appropriate, the same or similar reference numerals are used in the figures to refer to similar or identical elements. 
     DETAILED DESCRIPTION 
     Conventional AC welding systems have a preset current commutation level that is tuned by the manufacturer based on the output current selected by the user. 
     In contrast to conventional AC welding systems, disclosed example welding-type power supplies enable input of a current commutation threshold to the welding-type power supply to control the current commutation timing. Disclosed examples further enable selection of the current commutation threshold independently from selection of the output current. provide the advantage of changing it to make the arc softer (less noise and intense) or more intense and driving as it is today. 
     Disclosed examples improve welding-type operations by enabling a softer arc with less puddle agitation in AC applications. Disclosed examples also provide improved wetting action of a weld puddle, less audible noise, and/or improved directional control of a welding arc. 
     Disclosed examples include an AC welding-type power source that includes control of the commutation current of the AC waveform used for control of the output power. The control of the commutation current enables changing the dynamics of a welding arc in any type of waveform chosen for control. Disclosed examples provide the operator with flexibility to control the arc independent of what output current peak is used. In some examples, the current commutation control is within a set range or an unlimited range, and/or may be tied to other variables of control on the power source such as AC frequency, current amplitude, AC current balance, an AC waveform shape, an AC pulse modulation waveform and/or any other variables. 
     Disclosed example welding-type power supplies include an interface device, a power converter, a commutator circuit, and a control circuit. The interface device receives a commutation selection input. The power converter converts input power to welding-type power. The commutator circuit outputs alternating current (AC) welding-type power and controls a polarity of the AC welding-type power. The control circuit determines a threshold output current based on the commutation selection input, determines an output current and the polarity of the AC welding-type power and, when the output current is less than the threshold output current, controls the commutator circuit to change the polarity of the AC welding-type power. 
     In some example power supplies, the control circuit determines the threshold output current based on multiplying the commutation selection input by a ratio between a positive peak current and a negative peak current of the AC welding-type power. In some examples, the commutation selection input includes a percentage of a peak current, and the control circuit is configured to determine the threshold output current based on multiplying the commutation selection input by a positive peak current setpoint or a negative peak current setpoint. In some examples, the control circuit controls a voltage level or a current level used by the power converter to output the welding-type power based on a waveform. In some examples, the commutation selection input is selectable between a first discrete commutation threshold and a second discrete commutation threshold, in which the first and second discrete commutation thresholds correspond to different arc characteristics. In some examples, the commutation selection input is selectable along a substantially continuous range of commutation threshold values. 
     In some example power supplies, the control circuit sets the threshold output current equal to a value received via the commutation selection input. In some examples, the threshold output current is a same value for a positive current or a negative current with respect to a reference current. In some examples, the threshold output current is a different value for a positive current or a negative current with respect to a reference current. In some examples, the control circuit determines the threshold output current based on at least one of an AC frequency, a current amplitude, an AC current balance, an AC waveform shape, or an AC pulse modulation waveform. 
     Disclosed example non-transitory machine readable storage devices include or store machine readable instructions which, when executed, cause a control circuit to control a commutator circuit to control a polarity of welding-type power from a power converter to output alternating current (AC), determine a threshold output current based on a commutation selection input from a user interface, determine an output current and a polarity of the AC welding-type power and, when the output current is less than the threshold output current, control the commutator circuit to change the polarity of the AC welding-type power. 
     In some examples, the instructions cause the control circuit to determine the threshold output current based on at least one of an AC frequency, a current amplitude, an AC current balance, an AC waveform shape, or an AC pulse modulation waveform. In some examples, the instructions cause the control circuit to determine the threshold output current based on multiplying the commutation selection input by a ratio between a positive peak current and a negative peak current of the AC welding-type power. In some examples, the commutation selection input includes a percentage of a peak current, and the control circuit is configured to determine the threshold output current based on multiplying the commutation selection input by a positive peak current setpoint or a negative peak current setpoint. In some examples, the commutation selection input is selectable between a first discrete commutation threshold and a second discrete commutation threshold, in which the first and second discrete commutation thresholds correspond to different arc characteristics. 
     In some examples, the threshold output current is a same value for a positive current or a negative current with respect to a reference current. In some examples, the threshold output current is different for a positive current or a negative current with respect to a reference current. In some examples, the instructions cause the control circuit to set the threshold output current equal to a value received via the commutation selection input. In some examples, the commutation selection input is selectable along a substantially continuous range of commutation threshold values. 
     Disclosed example welding-type power supplies include an interface device, a power converter, a commutator circuit, and a control circuit. The interface device receives an alternating current (AC) control variable. The power converter converts input power to welding-type power. The commutator circuit outputs alternating current (AC) welding-type power and controls a polarity of the AC welding-type power. The control circuit determines a threshold output current based on the AC control variable received via the interface device, determines an output current and the polarity of the AC welding-type power and, when the output current is less than the threshold output current, controls the commutator circuit to change the polarity of the AC welding-type power. 
     In some example power supplies, the AC control variable includes at least one of an AC frequency, a current amplitude, an AC current balance, an AC waveform shape, or a AC pulse modulation waveform. In some examples, the threshold output current is a different value for a positive current or a negative current with respect to a reference current. In some examples, the threshold output current is a same value for a positive current or a negative current with respect to a reference current. 
     Welding-type power, as used herein, refers to power suitable for welding, plasma cutting, induction heating, air carbon-arc cutting and/or gouging (CAC-A), cladding, and/or hot wire welding/preheating (including laser welding and laser cladding). 
     Welding-type system, as used herein, includes any device capable of supplying welding-type power, including inverters, converters, choppers, resonant power supplies, quasi-resonant power supplies, etc., as well as control circuitry and other ancillary circuitry associated therewith. 
     As used herein, “less than” refers to “closer to 0” when used with reference to voltages or currents and when the voltages/currents being compared have the same polarity. For example, 2 amps of current is less current than 3 amps, and −2 amps is less current than −3 amps. 
       FIG. 1  shows an exemplary welding-type system  100  having adjustable current commutation thresholds. As described below, the example system  100  of  FIG. 1  enables improved control of an AC welding-type arc compared to conventional welding power supplies. 
     The system  100  includes a user interface device  102 , a power converter  104 , a commutator circuit  106 , and a control circuit  108 . The system  100  receives input power  110  and provides welding-type AC power to a welding-type torch  112  to perform an AC welding-type operation on a workpiece  114 . 
     The example user interface device  102  receives a current selection  103  as an input. In some examples, the current selection input is a positive current commutation threshold for a positive polarity, a negative current commutation threshold for a negative polarity, and/or a current selection from which the positive and/or negative current commutation threshold(s) are derived. 
     The power converter  104  converts input power  110  to AC welding-type power. For example, the power converter  104  may be a switched mode power supply or any other type of power supply. 
     The commutator circuit  106  controls the polarity of the AC welding-type power to the welding-type torch  112  and the workpiece  114 . For example, the commutator circuit  106  may include a bridge of four insulated gate bipolar transistors (IGBTs) that are controlled by a gate drive circuit  116  to switch the polarity of the output power between positive current (e.g., electrode positive) and negative current (e.g., electrode negative). The gate drive circuit  116  is controlled by the control circuit  108 . 
     The control circuit  108  determines positive and negative commutation threshold currents based on the current selection input from the user interface device  102 . The control circuit  108  determines an output current  118  and a polarity of the AC welding-type power based on current feedback  120  from a current sensor  122 . The example current sensor  122  may be, for example, a current transformer electrically and/or magnetically coupled to the output of the commutator circuit  106  and/or the torch  112  (e.g., an electrode), which can measure the amplitude and/or polarity of the output current  118 . An analog-to-digital converter (ADC) circuit  124  converts the current feedback  120  to a digital representation for input to the control circuit  108 . 
     The control circuit  108  controls the current amplitude via a current command  126  to a power converter controller  128 . The control circuit  108  may control a voltage level and/or a current level used by the power converter  104  to output welding-type power based on the feedback  120 . In some examples, the control circuit  108  controls the voltage level or the current level based on a waveform The power converter controller  128  may be, for example, a comparator that compares the current command  126  (e.g., a desired output current) to the current feedback  120  (e.g., the measured output current) to generate an error signal  130 . The error signal  130  controls the power converter  104  to increase or decrease the output voltage and/or current (e.g., welding-type power  132 ) output to the commutator circuit  106 . 
     The control circuit  108  compares the output current to the threshold output current (e.g., the positive or negative commutation current, based on the polarity). When the output current is less than the threshold output current, the control circuit  108  controls the commutator circuit  106  to change the polarity of the output current  118 . In the example of  FIG. 1 , the control circuit  108  outputs a polarity signal  134  to the gate drive circuit  116 , which causes the gate drive circuit  116  to control the commutator circuit  106  to set or switch an output polarity of the output current  118 . 
     The current command  126  and/or the polarity signal  134  may be analog or digital output signals. In some examples, the control circuit  108  determines the current command  126  and/or the polarity signal  134  as digital signals, which are then converted to analog signals at the output by the control circuit  108  by a digital-to-analog converter (DAC) circuit. 
       FIG. 2  is a graph  200  illustrating an example AC waveform  202  output by the example welding-type system  100  of  FIG. 1 . The example AC current waveform  202  represents the output current  118  over time for the AC current waveform  202 . The graph  200  also illustrates an example positive current commutation threshold  204  and an example negative current commutation threshold  206 . 
     During a negative polarity portion  208  of the waveform  202 , the control circuit  108  monitors the current feedback  120  from the current sensor  122 . When the control circuit  108  determines that the output current  118  is less than the negative current commutation threshold  206 , the control circuit  108  controls the gate drive circuit  116 , via the polarity signal  134 , to switch the polarity of the output current  118  to a positive polarity. 
     Similarly, during a positive polarity portion  210  of the waveform  202 , the control circuit  108  monitors the current feedback  120 . When the control circuit  108  determines that the output current is less than the positive current commutation threshold  204 , the control circuit  108  controls the gate drive circuit  116 , via the polarity signal  134 , to switch the polarity of the output current  118  to a negative polarity. 
     While the thresholds  204 ,  206  of  FIG. 2  are equal with opposite polarities, in other examples the thresholds  204 ,  206  are independently selectable by the user or programmatically determined based on the input and/or one or more other control variables. Example control variables include the AC frequency, the current amplitude, an AC current balance an AC waveform shape, and/or an AC pulse modulation waveform. In still other examples, one or both of the thresholds  204 ,  206  may be adjusted based on a ratio enforced between the thresholds  204 ,  206 . For example, if the threshold  204  is set to a first current, the threshold  206  is set by applying a factor to the threshold  204 . The factor may be automatically determined and/or input via the user interface device  102 . For example, the thresholds  204 ,  206  may be determined based on a selection of one of the thresholds  204 ,  206  and calculating the other of the thresholds  204 ,  206  based on the input threshold and a ratio between the positive and negative peak currents. In some examples, the user is able to select between discrete levels of the current commutation thresholds  204 ,  206  to achieve harder or softer arc characteristics. Additionally or alternatively, the user can select the thresholds  204 ,  206  from a substantially continuous range of values A substantially continuous range of values may be implemented using relatively small incremental steps in the thresholds  204 ,  206 , such as 0.1 A, 0.5 A, 1 A, 2 A, 5 A, 10 A, or any other increment, in response to an input such as pushing a button and/or turning a dial on the user interface device  102 , receiving a communication from a remote control device, and/or receiving any other wired or wireless communication including a change in the commutation threshold(s)  204 ,  206 . 
       FIG. 3  is a flowchart illustrating example machine readable instructions  300  which may be executed by the control circuit  108  to implement the welding-type system  100  of  FIG. 1  to output AC welding-type power based on an adjustable current commutation threshold. 
     At block  302 , the control circuit  108  determines whether a selection of an output current has been received. For example, the control circuit  108  may receive an AC current amplitude selection via the user interface device  102  of  FIG. 1 . If a selection of the output current has been received (block  302 ), at block  304  the control circuit  108  sets the output current. For example, the control circuit  108  may set the current command  126  based on the output current selection  103 . 
     At block  306 , the control circuit  108  determines whether a selection of a commutation current threshold has been received. For example, the control circuit  108  may receive a selection or configuration of the positive current commutation threshold  204  and/or the negative current commutation threshold  206 , either directly or indirectly, via the user interface device  102 . If selection of a commutation current threshold has been received (block  306 ), at block  308  the control circuit  108  determines positive and/or negative current commutation threshold(s). For example, the control circuit  108  may calculate the negative current commutation threshold based on the direct selection of the positive current commutation threshold and one or more other factors, and/or vice versa. 
     At block  310 , the control circuit  108  determines whether a welding-type operation is occurring. If a welding-type operation is occurring (block  310 ), at block  312  the control circuit  108  receives the current feedback  120  for the output current  118 . For example, the control circuit  108  may read in a sample input from the ADC  124 . At block  314 , the control circuit determines a polarity of the output current. The polarity of the output current may be based on the current feedback  120  and/or based on tracking the value of the polarity signal  134 . 
     At block  316 , the control circuit  108  determines whether the output current  118  is less than the current commutation threshold for the current polarity. For example, if the control circuit  108  determines at block  314  that the current polarity is positive, the control circuit  108  compares the output current  118  (based on the feedback  120 ) to the positive current commutation threshold  204 . If the output current  118  is less than the current commutation threshold for the current polarity (block  316 ), at block  318  the control circuit  108  controls the commutator circuit  106  (e.g., via the polarity signal  134  and the gate drive circuit  116 ) to change the polarity of the welding-type power. 
     After changing the polarity of the welding-type power (block  318 ), if the output current  118  is not less than the current commutation threshold for the current polarity (block  316 ), or if a welding-type operation is not occurring (block  310 ), control returns to block  302 . 
     The present methods and systems may be realized in hardware, software, and/or a combination of hardware and software A typical combination of hardware and software may include one or more application specific integrated circuits and/or chips. Some implementations may comprise a non-transitory machine-readable (e.g., computer readable) medium (e.g., FLASH memory, optical disk, magnetic storage disk, or the like) having stored thereon one or more lines of code executable by a machine, thereby causing the machine to perform processes as described herein. As used herein, the term “non-transitory machine-readable medium” is defined to include all types of machine readable storage media and to exclude propagating signals. 
     As utilized herein the terms “circuits” and “circuitry” refer to physical electronic components (i.e. hardware) and any software and/or firmware (“code”) which may configure the hardware, be executed by the hardware, and or otherwise be associated with the hardware. As used herein, for example, a particular processor and memory may comprise a first “circuit” when executing a first one or more lines of code and may comprise a second “circuit” when executing a second one or more lines of code. As utilized herein, “and/or” means any one or more of the items in the list joined by “and/or”. As an example, “x and/or y” means any element of the three-element set {(x), (y), (x, y)}. In other words, “x and/or y” means “one or both of x and y”. As another example, “x, y, and/or z” means any element of the seven-element set {(x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means “one or more of x, y and z”. As utilized herein, the term “exemplary” means serving as a non-limiting example, instance, or illustration. As utilized herein, the terms “e.g.,” and “for example” set off lists of one or more non-limiting examples, instances, or illustrations. As utilized herein, circuitry is “operable” to perform a function whenever the circuitry comprises the necessary hardware and code (if any is necessary) to perform the function, regardless of whether performance of the function is disabled or not enabled (e.g., by a user-configurable setting, factory trim, etc.). 
     While the present method and/or system has been described with reference to certain implementations, 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 present method and/or system. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from its scope. For example, block and/or components of disclosed examples may be combined, divided, re-arranged, and/or otherwise modified. Therefore, the present method and/or system are not limited to the particular implementations disclosed. Instead, the present method and/or system will include all implementations falling within the scope of the appended claims, both literally and under the doctrine of equivalents.