Alternating current welding using four quadrant switches

Abstract

Welding metals such as aluminum and magnesium requires AC current. This work proposes a novel control strategy for a high-frequency rectifier built with four quadrant switches (4QSW) to transform high frequency AC current (125 kHz) into the welding arc bipolar current, controlled in amplitude, frequency and even DC offset. The rectifier is connected to the output of a resonant inverter to achieve positive and negative polarity discharges both voltage and current by operating in two quadrants, i.e. positive and negative. As long as the input power to the converter is supplied by a current source, the typical dead-time set to avoid short circuit conditions jeopardize the safe operation of the switches. A field-programmable gate array (FPGA) is selected to implement the digital control due to its high resolution for the purpose to adapt the 4QSW's drive signals without dead-time in the most accurate manner.