Analytical and Experimental Investigation on state of the art High Frequency Power Converters for Welding Applications

Abstract

Welding is an adhesion process, used to join materials, mostly metals or thermoplastics, where two or more components are fused together using heat, pressure or both. In an arc welding the heat is generated using an electric arc. Manual metal arc (MMA) welding is most popular among other methods due to its simplicity and lower cost. Hence, it is adopted in most heavy applications like construction, aviation, heavy apparatus/ma- chines manufacture etc. newlineBefore the advent of semiconductor switching devices, the power source (PS) for arc welding were mainly generator or transformer-based. These suffered from their dis- advantages of large volume and weight. With the invention of power semiconductor switches (MOSFETs and IGBTs) inverter PS came into picture where utility grid is first converted to DC then to high-frequency (HF) AC and then again to DC. By this process, the size of the transformer used for galvanic isolation between input utility and the output has been reduced by increasing the switching frequency of the AC stage. However, due to limitations in dynamics of the semiconductor switching devices, the fre- quency could not be increased beyond a certain level. Wide band-gap (WBG) devices, invented in early 21st century, has opened up a new area of research towards increasing the portability of the welding converters by increasing the switching frequency. newlineThe present work focuses on the development of highly efficient, portable power elec- tronic converters (PECs) for MMA welding applications. Design, analysis, simulation and experimental work have been carried out on three fabricated set-ups viz., (i) Silicon (Si) device-based PEC, (ii) Silicon Carbide (SiC) device-based PEC and (iii) Gallium Nitride (GaN) device-based PEC. The initial part of this thesis deals with modelling of an arc load in FEM. This study has been conducted to determine the rating(s) of the PECs. Studies have been performed to obtain the V-I characteristics of an arc for different arc lengths and for two different standard electrode