Load adapting mains frequency resonant converters for supplying electrical arc-a new way in power electronics

Resonant AC-DC converters of 50 (60) Hz are described, where each half-cycle of network voltage the capacitor and inductor of an oscillatory circuit are switched from series into parallel and vice versa. The duration of series and parallel connection and also the transformer ratio are parametrically dependent on load. In case of short circuit only the parallel oscillating circuit operates. This sharply restricts the output current. The reactive power of the capacitor and the inductor compensate each other both in the case of series and parallel connection. Therefore the power factor is very high from no-load to short-circuit. This converter fits very well to supply arc furnaces. Then there is no need for the costly and fast reactive power compensator and filter circuits. The operating principle of the converter, design principles and a real operating converter rated 8.4 MW supplying steel-melting arc furnace are described.