Converter device and electric power supply apparatus

Apparatus configured to supply electric power to a high-power ohmic-inductive load corresponding to an electric furnace, said apparatus comprising a plurality of power supply modules connected in parallel to each other, and further configured to be connected to a power grid and to the load, each comprising:

• a transformer connected to the power grid that supplies an alternating mains voltage and an alternating mains current, the transformer being configured to transform the alternating mains voltage and the alternating mains current into an alternating base voltage and an alternating base current;
• a plurality of rectifiers connected to the transformer and configured to transform the alternating base voltage and alternating base current into direct voltage and electric current;
• plurality of converter devices, connected on one side to the rectifiers, and on the other side configured to be connected to the load, and configured to convert direct voltage and current into a voltage and an alternating supply current, to be supplied to the load;
• control and command unit configured to control and command the functioning of the converter devices and regulate the voltage and the supply current over time,
• wherein said control and command unit is provided with regulation devices configured to regulate said electric supply frequency of said supply voltage and supply current, in a manner independent of a mains frequency of said power grid, and obtain a regulation of the reactance of said power supply apparatus and in that each converter device comprises a bank of capacitors, connectable, during use, to a direct current power supply circuit, a plurality of power semiconductors connected to the bank of capacitors and configured to be selectively turned on and off in order to allow the generation of a sinusoidal current wave toward an output, a heat sink on which said power semiconductors are installed and which is configured to dissipate the heat generated by them, and a metal casing which encloses inside it at least the bank of capacitors, the heat sink and the power semiconductors, wherein both the heat sink and the capacitors are floating with respect to the casing and to an earth connection of said casing, wherein said converter device comprises at least a first high-impedance component connected between said heat sink and said casing, and wherein said capacitors are film-type capacitors and comprise a containing body of metal material, and said converter device comprises a plurality of second high-impedance components each connected between the containing body of a respective capacitor and the earth connection connected to said casing, wherein said at least one first component and said second high-impedance components have an impedance comprised between 500Ω and 1500Ω, and wherein said apparatus comprises a low-pass electrical filter connected between an output of the converter devices and the earth, said electrical filter being an RC filter of the three-phase type inserted on the output phases which are configured to be connected to the load, the low-pass electrical filter comprising a resistive component R having a respective resistance value and a capacitive component C having a respective capacitance value,
• wherein the control and command unit is configured to modify the resistance and the capacitance values in such a way as to increase or reduce the intensity of a current that flows through the resistive component R and the capacitive component C, and
• wherein the combination of the electrical filter connected at the output of the converter devices and of the high-impedance components inserted inside the converter devices themselves, is configured to both eliminate the oscillations of the current, and also to limit or even to eliminate the peak of the current itself to earth.