Power source and its new firing method for gas metal arc welding

The electronically controlled power sources for steady and pulsed Gas Metal Arc Welding (GMAW) consist of either converters or transistors. For steady direct current welding with a converter power source, a single fully-contr olled three-phase bridge converter is widely used. As for pulsed DC welding , it is done with two parallel-connected converters: a single-phase convert er for the production of pulsed direct current with different frequencies a nd width, and a three-phase converter for the generation of the background current. Both these power sources are associated with a number of disadvant ages. They produce harmonics in the AC mains. And in the case of the power source for pulsed welding, a low dynamic response is noticeable apart from unsymmetrical reactions in the mains caused by the single-phase converter. In addition to these, it is complex to operate and maintain, large in size, less efficient and is relatively expensive. This paper presents a single f ully-controlled three-phase bridge converter with a new firing method of th e thyristors that can be used for both welding methods. The distortions pro duced in the main as a result can be reduced with the help of two tuned res onant line filters, if needed, although they add weight, size and cost to t he power source. This new method wa verified by simulation and the results are presented. Through this means, the disadvantages associated especially with pulsed DC welding can be reduced to a minimum.