Design, analysis and experimental validation of a variable frequency silicon carbide-based resonant-converter for welding applications

This paper proposes a novel, reliable, efficient and cost-effective implementation of partial soft switching in a silicon carbide (SiC)-based variable-frequency phase-modulated resonant transition converter (PMRTC) used in manual metal arc welding (MMAW) applications at a peak power of 1.3 kW. The switching frequency (fsw) of the converter is increased from 100 kHz at no load to around 150 kHz for a rated power of 1.0 kW. Such an approach is not found in the existing literature. At such frequencies, a significant proportion of the output filter inductance is contributed by the inherent self-inductance of the output "lead cables". The switching losses in the semiconductor devices are reduced at no-load condition by reduction of the operating frequency. Load regulation is achieved at 150 kHz by implementing phase-shifted PWM technique. Implementation of partial soft switching without using additional components is another significant contribution of this work. The reduced size and weight of the filter inductor in turn reduces the overall size, weight and cost of the system but puts a restriction on the output lead cable length, which is another salient finding of this work. Since at high frequency the transformer model changes, design and finite-element method (FEM)-based simulation of the transformer are also presented in this paper. Loss calculations at 100 and 150 kHz are discussed. The entire converter is fabricated in the laboratory. Experimental and simulated results are found to be in excellent agreement.