Constant current SCR power supply method and system for a welding load

Claim 1

An SCR power supply for supplying regulated constant current to a load in which an arc is established between an electrode and workpiece comprising an SCR rectifier network interposed in series circuit relationship between said load and an input AC power line having a predetermined number of input phases with said SCR rectifier network having at least as many SCR elements as power line input phases; means for generating a first feedback signal proportional to arc current and substantially coinciding in time and phase with the arc current; means for generating a second feedback signal proportional to arc current with said second feedback signal being substantially delayed in time such that it is rendered substantially nonresponsive to the arc current fundamental ripple frequency; means for weighing said first and second feedback signals in a predetermined ratio to one another so as to produce a first and second weighted signal with the first weighted signal having an amplitude of between 10-50% of the total of said first and second weighted signals; means for generating an error feedback control in response to the summation of said first and second weighted signals and means for applying trigger signals to said SCR elements in timed synchronism with said input AC power line as a function of said error feedback control signal.

Claim 9

A method for regulating the flow of constant current from an input AC power line to an arc by an SCR power supply interposed in series between the arc and the AC power line comprising the steps of: monitoring the arc to detect arc current perturbations; generating a first feedback signal proportional to arc current which substantially coincides in time and phase with the arc current; generating a second feedback signal proportional to arc current; passing the second feedback signal through a filter network having a relatively long time constant such that the second feedback signal, is rendered substantially nonresponsive to the arc current fundamental ripple frequency; weighing the first and second feedback signals in a predetermined ratio relative to one another; generating an error feedback control signal representing the weighted output of said first and second feedback signals and controlling the firing of said SCR power supply in timed synchronism with the input AC power line as a function of said error feedback control signal.

Claim 10

A method for regulating the flow of constant current from an input AC power line to an arc by an SCR power supply interposed in series between the arc and the AC power line comprising the steps of: monitoring the arc to detect arc current perturbations; generating a first feedback signal proportional to arc current which substantially coincides in time and phase with the arc current; generating a second feedback signal proportional to arc current; passing the second feedback signal through a filter network having a relatively long time constant such that the second feedback signal, is rendered substantially nonresponsive to the arc current fundamental ripple frequency; weighing the first and second feedback signals in a predetermined ratio relative to one another; generating an error feedback control signal representing the weighted output of said first and second feedback signals and controlling the firing of said SCR power supply in timed synchronism with the input AC power line as a function of said error feedback control signal.