A CONTROLLABLE CURRENT SUPPLY SYSTEM FOR GENERATING AN ALTERNATING POLARITY SQUARE WAVE CURRENT FOR A WELDING ARC

摘要

In a three phase welding power supply, the three phase power is connected to a welding arc by a power control circuit having three conducting paths for straight polarity current and three conducting paths for reverse polarity current. The power control circuit comprises a three phase bridge rectifier circuit having eight bridge arms each including a silicon controlled rectifier with the bridge circuit being connected between the three phase power source and the welding arc which is in turn connected to the three phase power supply neutral. An inductor is connected across the direct current terminals of the bridge circuit so that arc current flows in one direction through the inductor regardless of the polarity of the arc current. The conducting paths are selectively activated at non-zero voltage points to conduct repetitive sequences of independent numbers of straight polarity half cycles of arc current followed by independent numbers of reverse polarity half cycles of arc current to the welding arc. Pulses are generated in synchronism with each of the three power phases and counted to determine the activation sequences of the conducting paths. By controlling the generation of the pulses and the counts of the pulses at which the paths are activated, a variety of sequences are generated.