Steady and pulsed direct current welding with a single converter

The conventional electronically controlled power sources for steady and pul sed direct current (DC) welding are converters and transistorized power sou rces. In the case of steady direct current welding with a converter, a sing le fully or half-controlled three-phase bridge converter is commonly used. For pulsed DC welding, a single half-wave rectifier is connected in paralle l with a three-phase bridge converter to produce the desired pulsed direct current with different pulse repetition frequencies and width. The three-ph ase bridge converter provides the background current. These power sources produce harmonics in the AC mains, and, in the case of pulsed direct current welding, there is an unsymmetrical reaction in the ma ins caused by the single half-wave rectifier. In addition, the power source for pulsed DC welding is complex to operate and maintain, large in size, l ess efficient, relatively expensive and is associated with low dynamic resp onse. This investigation presents a new method of firing the thyristors, which en ables steady and pulsed direct current welding with a single fully controll ed bridge converter. A single fully controlled three-phase bridge converter was chosen as the power source as it contributes to reduction of reactive power with firing angles greater thana certain value. The distortions produ ced by the power system as a result of the new firing method can be reduced with the help of two tuned resonant line filters, if needed, although thes e filters add weight, size and cost to the power source. This was verified through simulation and the results are presented. Thus, some of the disadva ntages associated with pulsed DC welding such as low dynamic response, low efficiency and distortions in the power system can be reduced to a minimum.