Abstract:
An improved circuit and device uses a set of eight switches, four of which are connected to the positive terminal, and four of which are connected to the negative terminal of a high voltage direct current power supply. The eight switches are attached in a distributed and overlapping manner to the inputs of up to six welding transformers. Pulse width modulation is utilized to distributively control power to the six welding transformers utilizing distributed control by a single controller. Phasing of the pulse width modulated power signal enables further optimization of the distributed control and is accomplished by a single controller and based upon feedback demand from the transformers utilizing typical measured parameters.

Description:
FIELD OF THE INVENTION 
     This invention relates to a circuit and device for simultaneous control of multiple transformers and in which each transformer&#39;s power output can be individually controlled, and which is particularly useful for any transformer control but especially for welding transformers where high power control requirements normally militate toward costly independent controls. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 5 862,041 and U.S. Pat. No. 5,852,555, both to the inventor of the present invention, describe dual inverter power supplies in which a series of switches are controlled by a pair of oscillators to control a pair of separately operable input:coils of a transformer. The general technique involved control of the two oscillators by a phase controller in order to vary the timing of the two oscillators to control a transformer output. This invention had as its goal the very close control of a transformer by utilizing eight switches, two oscillators and a phasing control to achieve exact control over a transformer. 
     One of the problems in general with respect to welding transformers is that once a good high voltage direct current power supply is available, limiting a particular welding appliance to use a single output transformer and especially its own control, can be cost prohibitive. In order that welding power distribution systems could be utilized more effectively, it would be advantageous for as much of the equipment downstream of the high voltage direct current supply to work in an interrelated way to provide several welding stations depending upon a single high voltage direct current supply. Put another way, for a single high voltage direct current supply, it would be advantageous to be able to provide control to a plurality of downstream transformers with due consideration to control parameters including even power distribution, control to prevent undue power consumption by one or more users, feedback control to enable power regulation in a manner as closely approximate to individual control as possible, and a form of control which can attempt to minimize power waste. If this control can be accomplished along with the elimination of physical elements of the equipment, such as individual controllers and the like, welding power supply units can be manufactured much more inexpensively to increase the opportunities for and cost barriers to providing more inexpensive welding processes and products. 
     The problems with earlier designs relating to transformers include switching loss, combined with the saturation loss and the current density. inefficiency. Earlier controls based upon duty cycle alone, or phasing alone have been unable to address the above problem of providing a distributed control. Most of the controls involving phasing can rapidly adapt to a new current or power output set point, but concentrated rather than distributed control is the main theme of the operating solution. 
     What is therefore needed is a circuit and device which enables high current at high frequency to be distributed and controlled with an interrelated control of such distribution so as to eliminate individual controllers and their accompanying cost. The needed method should include, for the utilization of a single equipment set for conversion of the standard AC to high voltage DC power source, for multiple controlled elements of equipment, such as welding transformers. Even more importantly, the needed circuit and device should provide itself with the capability for monitoring, and feedback to provide precise voltage, or current, or power to the fusing or welding electrodes. 
     SUMMARY OF THE INVENTION 
     An improved circuit and device uses a set of eight switches, four of which are connected to the positive terminal, and four of which are connected to the negative terminal of a high voltage direct current power supply. The eight switches are attached in a distributed and overlapping manner to the inputs of up to six welding transformers. Pulse width modulation is utilized to distributively control power to the six welding transformers. Each welding transformers two port input is dependent upon four of the switches at any given time to determine its duty cycle and power output. Each of the six welding transformers two port input is dependent upon a different four of the eight switches. 
     By reducing the pulse width of one switch, two of the transformers are affected. Of the two transformers affected, the total output of each transformer depends upon four total switches, three switches of which are associated not only with the transformer being affected, but also of three other transformers. 
     A controller which controls each wave form controls the pulse width of each switches square wave, affecting the length of the pulse width control wave form pulling in the outer edges toward the center to shorten the length of duration during which each switch is in its “on” position. Affecting the pulse width of one switch affects two transformers, but the other transformer can also be affected by three other switches. 
     The controller is programmed to provide precise control by computing the pulse width duration of each of the switches in order to provide the needed power and pulse duration to each of the switches in order to deliver the power protocol demanded. Power demanded may be by feed forward control, or interactive feedback may be provided. In terms of the mathematical relationship of controlling six transformers with eight switches, only two transformers can be absolutely independently controlled at the same time. However, by utilizing a heuristic protocol controller in which the power to the six transformers can be controlled within given limits, all six of the transformers can be controlled so long as their power consumption is not grossly different, one from another. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, its configuration, construction, and operation will be best further described in the following detailed description, taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is an overall schematic of the voltage and current bearing components of the circuit of the invention including direct current components, and an array of switches electrically connected to an array of six transformers, and which facilitates identification of the logic of control; 
     FIG. 2 is a circuit diagram as but one example for each of the array of six transformers seen in FIG. 1; 
     FIG. 3 is a phase diagram for all of the switches SSSW 1 (+) through SSSW 4 (−) for controlling the six transformers of FIGS. 1 and 2 in a fully on, maximally energized condition; 
     FIG. 4 is a chart illustrating power output associated with the phase diagram of FIG. 3; 
     FIG. 5 is a phase diagram similar to that shown in FIG. 3 showing the pulse width modulation of SSSW 1 (+) &amp; SSSW 1 (−) reduced from 180° to 90° (affecting transformers  1 ,  3  and  4  during the first 180° of the cycle) and the pulse width modulation of SSSW 2 (+) &amp; SSSW 2 (−) remaining at a 100% duty cycle, and other switch settings as explained for analysis; and 
     FIG. 6 is a chart illustrating power output associated with the phase diagram of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The description and operation of the invention will be best initiated with reference to FIG.  1 . At the upper left side of FIG. 1, a three phase source supplies electricity through three lines L 1 , L 2 , &amp; L 3  to a three phase rectifier  21 . The three phase rectifier  21  has a pair of direct current outputs, including a first line  23  and a second line  25 . Between the direct current outputs and the lines  23  and  25  are pars of diodes including diodes D 11  and D 17  associated with line L 1 , diodes D 13  and D 19  associated with line L 2 , and diodes D 15  and D 21  associated with line L 3 . A filtering capacitor C 11  is connected between first direct current line  23  and second direct current line  25  to short any alternating current components still present, and provide a low impedance to an instantaneous current demand. 
     A SWITCH CONTROLLER  27  has individual control lines connected to each of a set of eight switches labeled SSSW 1 (+), SSSW 1 (−), SSSW 2 (+), SSSW 2 (−), SSSW 3 (+), SSSW 3 (−), SSSW 4 (+), and SSSW 4 (−). The switches SSSW 1 (+), SSSW 2 (+), SSSW 3 (+), and SSSW 4 (+) are connected to the positive direct current line  23 , while the switches SSSW 1 (−), SSSW 2 (−), SSSW 3 (−), and SSSW 4 (−) are connected to the negative direct current line  25 . Each of the switches SSSW 1 (+), SSSW 1 (−), SSSW 2 (+), SSSW 2 (−), SSSW 3 (+), SSSW 3 (−), SSSW 4 (+), and SSSW 4 (−) are independently controlled by the SWITCH CONTROLLER  27 . This independent control will enable the SWITCH CONTROLLER to further control individual components as will be shown. 
     To one side of the switches, the output terminals of SSSW 1 (+), SSSW 1 (−), SSSW 2 (+), SSSW 2 (−), SSSW 3 (+), SSSW 3 (−), SSSW 4 (+), and SSSW 4 (−) are connected to a series of transformers labeled T 1 , T 2 , T 3 , T 4 , T 5 , &amp; T 6 . Normally, each pair of switches, for example SSSW 1 (+) and SSSW 1 (−) would normally connect to and operate a single transformer, for example, T 1 , in order to have completely independent control. However, as has been stated, independent control requires an independent controller and its associated cost. However, in the drawing of FIG. 1, the switches connecting the transformers T 1 , T 2 , T 3 , T 4 , T 5 , &amp; T 6 , are distributed over the switches SSSW 1 (+), SSSW 1 (−), SSSW 2 (+), SSSW 2 (−), SSSW 3 (+), SSSW 3 (−), SSSW 4 (+), and SSSW 4 (−) in a manner such that control of one or more of the switches can control selected ones of the transformers. 
     As is seen, transformer T 1  is controlled by SSSW 1 (+) and SSSW 2 (−). However, SSSW 1 (+) also is connected to transformers T 1 , T 3  and T 4 . Any given transformer can be controlled using pulse width modulation by either limiting the duration of its switched on positive input or the duration of its switched on negative output. Both need not be absolutely controlled. Further, within a cycle, the phasing of the switching can be manipulated. Typically the phasing of pulse width modulation is performed around the center of the phase, that is by moving the length of the pulse width shorter by pulling it in about its center. A sophisticated SWITCH CONTROLLER  27  may not be so constrained. 
     Purely mathematically speaking, eight switches with independent controllers could operate four transformers. Using a single controller to operate eight switches which are interconnected with six transformers, in accord with the system shown in FIG. 2, can effect absolute independent control over only two transformers. 
     For example, to control transformer T 1 , switches SSSW 1 (+), SSSW 1 (−) and SSSW 2 (+), SSSW 2 (−) are required. These switches are also connected to transformers T 3 , &amp; T 4 , and to transformers T 5  &amp; T 6 , respectively, which therefore cannot be independently controlled. At the same time, to control transformer T 2 , switches SSSW 3 (+), SSSW 3 (−), &amp; SSSW 4 (+), and SSSW 4 (−) are required. These switches are also connected to transformers T 3 , T 5  &amp; T 6  and T 4  and T 6 , respectively, which cannot be independently controlled. 
     Independent control does not mean associated control. Independent control in this case is, for example, a 100% output to transformer T 1 , with a 1% output to transformer T 2 . Under this control scenario, power can be supplied to the other transformers, but some may be required to take 100% power, some may be required to take 1% power, with others having their power modulatably controllable between 100% and 1%. In the case just described, with SSSW 1 (+), SSSW 1 (−), and SSSW 2 (+); SSSW 2 (−) being operated in fully open or full pulse width modulation format, and with, SSSW 3 (+), SSSW 3 (−) and SSSW 4 (+), and SSSW 4 (−) operating at a 1% format, this case represents a nearly full take up of opposite conditions for the operation of the switches. As can be seen, transformer T 3  faces a 100% duty on one terminal and a 1% duty on its other terminal and thus can only draw 1% power. The same is true for T 5 , T 6  and T 4 . 
     Now, as an example of swing control, if transformer T 1  is operating at 100% power, and instead of transformer T 2 , it was sought to operate transformer T 3  at a 50% duty cycle, and noting that one input of transformer T 3  is connected to SSSW 1 (+), SSSW 1 (−) which is already operating at a 100% duty cycle, this can be accomplished by limiting the operation of switches SSSW 3 (+), SSSW 3 (−) at a 50% duty cycle level. Thus, although one side of transformer T 3  has a 100% duty cycle, the current through the transformer will flow based upon the limitation of the duty cycle of switches SSSW 3 (+), SSSW 3 (−). 
     Now, transformers which depend from switches SSSW 3 (+) &amp; SSSW 3 (−), transformers T 2 , T 3  and T 5 , will be limited to a 50% duty cycle. However, although these same transformers T 2 , T 3  and T 5 , may be limited to a 50% duty cycle, other switch sets from which they depend, if not in conflict with other power duty cycles, can further limit output power. Continuing in the example given, transformer T 2 , which is also dependent upon switches SSSW 4 (+) &amp; SSSW 4 (−), can have its duty cycle limited in accord with the duty cycle of SSSW 4 (+) &amp; SSSW 4 (−). Transformer T 5 , which is also dependent upon switches SSSW 2 (+) &amp; SSSW 2 (−), can also have it duty cycle limited in accord with the duty cycle of switches SSSW 2 (+) &amp; SSSW 2 (−). 
     Assuming that the duty cycles for switches SSSW 2 (+) &amp; SSSW 2 (−), and SSSW 4 (+) &amp; SSSW 4 (−), is limited to 25%, to limit the duties of transformers T 2  and T 5 , the remaining transformers T 4  and T 6  have a duty cycle based upon the other settings. Transformer T 4  has one of its inputs at 100% and the second input at 25%, so it is limited to 25%. Transformer T 6  has one of its inputs at 25% and the second input at 25%, so it is limited to 25%. As will be seen, some phasing can occur to further limit the power available. However a microprocessor controller can, even where limited to the simple logic and limitations above provide a near matching scheduling heuristic based upon demand. A dashed line format is seen to connect the switch controller to the transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6 . These lines represent feedback which can range from feedback based upon transformer operation parameters including temperature, current demand, voltage, etc. 
     Now, any transformer T 1 , T 2 , T 3 , T 4 , T 5  and T 6  which has a duty less than 100% can have the phasing of its duty temporally shifted. If the shifting is deliberate, it can allow a cycle to be shared between another one of the transformers T 1 , T 2 , T 3 , T 4 , .T 5  and T 6  which might otherwise be eliminated from operation. The temporal shifting of the phase of the pulse width modulation can be used to further limit other transformers by operating such other transformer at a reduced (less than 100% duty cycle) but shifted with respect to other duty cycles in order to result in a duty cycle which is less than the duty cycles of the switches controlling the transformer of choice. This will be illustrated in the Figures following FIG.  2 . 
     Referring to FIG. 2, a schematic view of a transformer circuit which can be utilized for the transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6  is shown. A primary winding includes terminals A and B, while a secondary winding includes legs A, D, &amp; E. Legs A and E are connected into the inputs of diodes CR 1  and CR 2  which form the positive output for welding. Leg D forms the negative ground for the welding operation. 
     FIG. 3 is a chart showing the state of the switches SSSW 1 (+), SSSW 1 (−), SSSW 2 (+), SSSW 2 (−), SSSW 3 (+), SSSW 3 (−), SSSW 4 (+), and SSSW 4 (−) as set for 100% operation to each respective one of the transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6 . The temporal operation of one of the transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6  can exclude operations of certain ones of the other transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6 , as will be seen. 
     Examples of transformer switch modulation will be illustrated. At the top, and to the right, transformer T 1  is shown to be operated by switches SSSW 1 (+) and SSSW 2 (−). For the first 180° of the full 360° cycle, switch SSSW 1 (+) can be closed as is switch SSSW 2 (−), especially for a full power delivery setting. For the second, 180° of the full 360° cycle, switch SSSW 1 (+) and switch SSSW 2 (−) are opened while switch SSSW 1 (−) and SSSW 2 (+) are closed. This action keeps current flowing through Transformer T 1 . 
     FIG. 4 illustrates the voltage output for each of the transformers based upon the settings seen in FIG. 3, even though all transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6  cannot be fully 100% operated at the same time. Each of the transformers has full voltage, shown to be ten volts. Although FIG. 3 is couched in terms of a seven hundred volt magnitude and the output of FIG. 4 is couched in terms of a ten volt magnitude, the voltage inputs and outputs of choice can vary. 
     During control times where only one or two of the transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6  are to be operated, a reduction of duty cycle may occur about the midpoint of the wave forms. When this occurs, the half cycle is occupied. For example, considering the operation of transformer T 1  by itself,. without regard to the operation of the other transformers, the first square shaped curve for SSSW 1 (+), over the first 180° of the full 360° will have the upper block wave form drawn inward toward the 90° mark from both the 0° and 180° ends. A 50% duty cycle will then include a square wave which, over the first 180° of the full 360° will begin at about 45° and terminate at the 135° mark. During the second 180° of the full 360° cycle, the second square shaped curve for SSSW 1 (−) over the second 180° of the full 360° would begin at about 225° and end at about 315°. For facilitating further discussion, we set SSSW 2 (−) and SSSW 2 (+) at a 100% duty cycle. Thus the duty cycle of the transformer T 1  is limited by the duty cycles of only SSSW 1 (−) and SSSW 1 (+) at 50%. This is shown in FIG.  5 . 
     Referring to FIG. 5, note that switches SSSW 1 (+) &amp; SSSW 1 (−) and SSSW 2 (+) &amp; SSSW 2 (−) are phase centered the same, both about the mid point of the 180° cycle phase. However, switches SSSW 1 (+) &amp; SSSW 1 (−) have a 50% duty cycle and stay on only from about 45° to about 135° in the cycle and switches SSSW 2 (+) &amp; SSSW 2 (−) remain on for the full 180° half cycle. This centered relationship, even though with different duty cycles, however represents the simplest alternative for running different duty cycles for each set of switches to get a common (strictest) limiter for the transformer having associated with it the most severely limited duty cycle. 
     Referring again to FIG. 1, and assuming that half cycles are coordinated, it can be seen that if it were desired to operate transformers T 1 , T 3  and T 5 , that during the first half cycle, with SSSW 1 (+) closed that SSSW 2 (−), SSSW 3 (−) &amp; SSSW 4 (−) are required to be closed in order to accommodate current flow. This means that the transformers T 2 , T 5 , and T 6  are inoperable during this half cycle. In the second half cycle a requirement of reversal of flow of current is such that the switch settings of the second half cycle involve a reversal of the setting of the switches in the first half cycle, namely that the closed switches are SSSW 1 (−) closed that SSSW 2 (+), SSSW 3 (+) &amp; SSSW 4 (+). 
     Where the power output for any transformer will be less than half of its maximum, there is the possibility of cycle splitting with phasing, In cycle splitting, and where other switching problems are not an issue, such as switching time, transients, etc, more than 3 of transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6  may be also be operated using the interconnect configuration seen in FIG.  1 . 
     With only a mention of cycle splitting generally, and referring again to the first wave form of FIG. 5, if instead of being centered about the 90° phase line, the 90° duration of on time of SSSW 1 (+) were to begin at 0° and end at 90°, the remaining half of the first half cycle could be used for distributing power to another transformer. Continuing to assume that SSSW 2 (−) is fully on for the second half of the first half cycle, the switch SSSW 1 (+) can now opened to allow switch SSSW 1 (−) to be closed to enable back current to flow through transformers T 1  if switch SSSW 2 (+) is closed, or transformer T 3  if switch SSSW 3 (+) is closed, or transformer T 4  if switch SSSW 4 (+) is closed. Thus where at least one of the cycles are half or less, the operation of the transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6  can be even more distributed. Put another way, where the duty of a transformer is less than 100% there exists the possibility of distributing the complement of that duty elsewhere. 
     Each wave form set seen in FIG. 5 is a composite overlap of two of the switch sets shown, even though it is impossible to operate all at the same time in accord with the logic connection scheme of FIG.  1 . It is possible for the logic of FIG. 1 to have less connectivity, i.e. where each common switch terminal connects to less than three transformers. The logic would then be less restrictive, but the degree to which distributed restrictive control can be achieved would be less. The following table illustrates the start and stop of each of the switches seen in FIG. 5, to facilitate a discussion of examples of power control which could be possible for each transformer, again not withstanding the logic of FIG. 1, in order simply to show a few grossly oversimplified examples of phasing and the effect that the limitation of only one of an output and an input of a transformer limits the operation of that transformer in order to show that distributed control is dependent partly upon the degree to which a switch is not commonly connected and partly upon differential phasing. The table is arranged in the order seen in FIG.  5 . 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Start 
                 End 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 SSSW1(+) 
                  45° 
                 135° 
               
               
                   
                 SSSW2(−) 
                  0° 
                 180° 
               
               
                   
                 T1 
               
               
                   
                 SSSW1(−) 
                 225° 
                 315° 
               
               
                   
                 SSSW2(+) 
                 180° 
                 360° 
               
               
                   
                 SSSW3(+) 
                  60° 
                 180° 
               
               
                   
                 SSSW4(−) 
                  0° 
                 120° 
               
               
                   
                 T2 
               
               
                   
                 SSSW3(−) 
                 240° 
                 360° 
               
               
                   
                 SSSW4(+) 
                 180° 
                 300° 
               
               
                   
                 SSSW1(+) 
                  45° 
                 135° 
               
               
                   
                 SSSW3(−) 
                  60° 
                 180° 
               
               
                   
                 T3 
               
               
                   
                 SSSW1(−) 
                 225° 
                 315° 
               
               
                   
                 SSSW3(+) 
                 240° 
                 360° 
               
               
                   
                 SSSW1(+) 
                  45° 
                 135° 
               
               
                   
                 SSSW4(−) 
                  0° 
                 120° 
               
               
                   
                 T4 
               
               
                   
                 SSSW1(−) 
                 225° 
                 315° 
               
               
                   
                 SSSW4(+) 
                 180° 
                 300° 
               
               
                   
                 SSSW2(+) 
                  0° 
                 180° 
               
               
                   
                 SSSW3(−) 
                  60° 
                 180° 
               
               
                   
                 T5 
               
               
                   
                 SSSW2(−) 
                 180° 
                 360° 
               
               
                   
                 SSSW3(+) 
                 240° 
                 360° 
               
               
                   
                 SSSW2(+) 
                  0° 
                 180° 
               
               
                   
                 SSSW4(−) 
                  0° 
                 120° 
               
               
                   
                 T6 
               
               
                   
                 SSSW2(−) 
                 180° 
                 360° 
               
               
                   
                 SSSW4(+) 
                 180° 
                 300° 
               
               
                   
                   
               
             
          
         
       
     
     The table and the phasing shown illustrate but some possibilities and such possibilities are illustrated without consideration of the fact that all of the transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6  cannot be on at the same time. Again, the degree of connectivity can be greater or less than that shown in FIG.  1 . 
     The output results for each transformer, given an exemplary and unrelated series of input conditions, is seen in FIG.  6 . Distributed control is first based upon not violating the logic for the interconnect configuration as seen in FIG.  1 . Where duty cycles are low enough for cycle splitting, a further level of distribution is possible. Of course, cycle splitting and total cycle time may also be affected by the lumped parameter characteristics of the transformer elements like impedance and so on. As such, another possibility is to increase the total overall power of the system so that adequate power (including voltage, current, etc.) may be derived at lower duty cycles. If enough power is available for adequate power output even in the presence of cycle skipping, it can be seen that the independent control of three transformers at any time would equate to independent control of six transformers and complete control would be had for a defined maximum power level. 
     Thus, for more distributed control, both the logic of the switch operational possibilities and phasing must occur. For a gross example of phasing only, differential phasing, that is moving a given duty cycle to one side or the other of the 180° cycle, in order to get differential overlap with other switches&#39; duty cycles. First, consider  10  a first 180° cycle of transformer T 2  where switch SSSW 3 (+) is left off for the first 60° of the cycle and where SSSW 4 (−) is left off for the last 60° of the cycle, with only the middle 60° of the cycle existing where both are turned on (and again, the possibility that some or even all of the other transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6  may be dis-enabled by the operation of these two switches is ignored for the purpose of this example and others). The same is done with switches SSSW 3 (−) and SSSW 4 (+). The duty cycle is clearly ⅓. However, the position of switches SSSW 4 (−) and SSSW 4 (+), and especially the phasing for their on times as being 66% of the 180° half cycle make available a duty cycle of up to ⅓ for other transformers (if logically possible). 
     Referring to FIG. 5, and independent of the other considerations with reference from time to time to FIG. 1, transformer T 2  is shown with its SSSW 3 (−)/SSSW 3 (+) duty cycle of ⅔ being out of phase with the settings of switches SSSW 4 (−)/SSSW 4 (+) which also have duty cycle of ⅔, but having a combined duty cycle of ⅓ due to having only a ⅓ overlap during its cycle, as discussed earlier. Other transformers are operable to the extent possible by not violating the logic of the interconnectivity. 
     In another separate example, if transformer T 3  has a 50% centered duty cycle input from SSSW 1 (−)/SSSW 1 (+) (as was used in the earlier example) in combination with its ⅔ duty cycle input from SSSW 3 (−)/SSSW 3 (+) (but occurring at the rear two thirds of each of the 180° half cycles) the result gives an overlap which begins at 60° and ends at 135° to give an “on” period of 75° of 180° or 41.6% or an output of 4.16 volts out of ten volts. 
     In a separate and unrelated example, if transformer T 4  has the temporally front loaded ⅔ duty cycle of switches SSSW 4 (−) and SSSW 4 (+), combined with a mid point centered 50% duty cycle of switches SSSW 1 (−) and SSSW 1 (+) to yield an overlap which begins at 45° and ends at 120° to give an “on” period of 75° of 180° or 41.6% or an output of 4.16 volts out of ten volts. 
     In a separate and unrelated example, if transformer T 5  has a temporally delayed ⅔ duty cycle seen before in switches SSSW 3 (−) an d SSSW 3 (+), combined with the mid point centered 100% duty cycle of switches SSSW 2 (−) and SSSW 2 (+) to yield an overlap which begins at 60° and ends at 180° to give an “on” period of 120° of 180° or 66.6% or an output of 6.66 volts out of ten volts. 
     In a separate and unrelated example, if transformer T 6  has the temporally front loaded ⅔ duty cycle of switches SSSW 4 (−) and SSSW 4 (+), combined with the mid point centered 100% duty cycle of switches SSSW 2 (−) and SSSW 2 (+) to yield an overlap which begins at 0° and ends at 120° to give an “on” period of 120° of 180° or 66.6% or an output of 6.66 volts out of ten volts. Thus it can be seen that phasing of the pulse width power modulating inputs can result in a wider variety of voltage outputs for the transformers. Where the equipment permits it, the phasing could occur at different points within the 180° cycle. 
     A good, smart, switch controller can take account of the demands on each of the six transformers T 1 , T 2 , T 3 , T 4 , T 5  and T 6  and quickly adjust switch duty cycles and phasing in order satisfy not all independent conditions as would be served by six separate controllers, but a much wider array of conditions than would otherwise be served by a single controller. This is especially realizable where the system is designed such that full power required by any given transformer is less than half and preferably a smaller fraction than the maximum energy which could be delivered. Stated differently, so long as the system is designed so that no transformer needs more than a small amount of energy represented by a pulse width less than half of the maximum pulse width applied, the power in the system described above can adequately serve more than the number of transformers which would logically otherwise be eliminated from service were the transformers required to be energized all at the same time within their cycles. 
     While the present invention has been described in terms of a circuit to be used in controlling welding transformers and any other pulse width adjusted or modulated aspects and the like, one skilled in the art will realize that the structure and techniques of the present invention can be applied to many similar devices. The present invention may be applied in any situation where a phase control or power averaging is to be used electrically to achieve desired electrical or electronic output. 
     Although the invention has been derived with reference to particular illustrative embodiments thereof, many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. Therefore, included within the patent warranted hereon are all such changes and modifications as may reasonably and properly be included within the scope of this contribution to the art.