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Inductive heating applications like pipe welding or steel strip annealing require electrical power ratings of several megawatts at frequencies up to 100 kHz and higher. The large power-frequency product represents a significant challenge for today's semiconductor technology. As the absolute maximum rating of a single-stage inverter is often far below rated power, several inverters or several devices have to be connected in parallel. This paper presents a novel topology, consisting of parallel-connected soft-switching high-frequency inverters. Distinctive features include flexible configurations, negligible shunt currents between inverters, and equally shared power among inverters. Furthermore, compared to a single-inverter system, no additional reactive components are necessary for connecting inverters in parallel and there is no need of a high-frequency transformer to adapt the impedance of the load to the inverters.
Date of Publication: Mar/Apr 2003