Abstract: In a method for open-loop/closed-loop control of current converter valves of at least two load-guided parallel oscillating circuit inverters being supplied from a common direct current or direct voltage source and being connected in series on the DC side, each inverter has one induction furnace with a compensating conductor. Two diagonally opposed current converter valves are ignited at a time in one inverter to establish a flow of current from the source with a series-connected choke through the parallel oscillating circuit connected to that inverter. Load phase angles of the parallel oscillating circuit inverters are adjusted, resulting in arbitrarily specified individual powers of the parallel oscillating circuits wherein a maximum power that can be output by the source is taken into account, and attaining a specified ratio between the individual powers of the parallel oscillating circuits.

Abstract: A method for controlling current converter valves of a load-guided parallel oscillator inverter of an induction furnace includes supplying the inverter from a direct current source having positive and negative poles, and adjusting a current flow from the direct current source across the parallel oscillator by firing two diagonally opposed current converter valves of the inverter at a time. The method of the invention includes firing the two diagonally opposed current converter valves at a time with a delay between them for intermittently producing a short circuit current from the positive pole of the direct current source to the negative pole of the direct current source through two of the current converter valves being directly series-connected.

Abstract: In a half-controlled three-phase bridge for feeding an inductive load, a further, externally charged capacitor and a further thyristor are additionally connected to the conventional protective capacitor which is already in existence. The further capacitor, which is charged from an external high-impedance voltage source, has the effect of causing an increased load current to be taken over by the further thyristor so that one of the conducting thyristors of the bridge is extinguished. The capacitor recharges and its voltage is used as a blocking voltage for the thyristor of the bridge which has just been extinguished so that the energy supply from the power system is stopped. The current in the load circuit can then be removed through a free-wheeling diode.

Abstract: A configuration for starting an inverter includes a capacitor which is provided for overvoltage protection in a half-controlled 3-phase bridge, with a discharging resistor used for charging an intermediate-circuit capacitor through a switch and a diode, in such a manner that an isolating transformer at the output of an inverter is premagnetized so that the inverter reliably turns on during the starting process.