AC-DC converter with parametric reactive power compensation

Resonant converters of 50 (60) Hz AC-DC 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 the case of short circuit, only the parallel oscillating circuit operates. This restricts sharply the output current. The reactive power of the capacitor and the inductor compensate each other, both in the cases of series and parallel connection. Therefore, the power factor is very high from no load to short circuit. This converter fits very well for supplying arc furnaces, and 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 5.4 MW supplying a steel-melting arc furnace are described.