Digital control of switch-mode pulsed GMAW welding power

In this paper, development of a switch mode pulsed MIG welding machine composed of a wire feeder and DC/DC converter is described. Both control of the feeder and converter are implemented with each separated digital signal processor(DSP).To improve the stability performance and dynamic response of wire feeder, a digital control strategy consisting of outer loop of rotating speed regulation and inner loop of current regulation for wire feeding motor is proposed. As for the control of the DC/DC converter, peak current control is taken to suppress the over current across switches. To achieve constant arc length control, a triple closed loop control model including stick-out compensation, arc regulation and current control is presented to make arc length constant and welding stable during the whole process. A welding machine prototype with capacity up to 400 amperes is built. The experimental results of the prototype show that the digital control scheme either for the converter or the wire feeder is applicable for all output current range. The welding process is stable and the welding bead is also excellent with the proposed control scheme.