Converter device and electric power supply apparatus

1 . An apparatus to supply electric power to a high-power ohmic-inductive load corresponding to an electric furnace, comprising:

a plurality of power supply modules connected in parallel to each other, connected to a power grid, and to the load;

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,

and further comprising:

a plurality of converter devices connected on one side to the rectifiers, and connected on another side 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;

a 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; and

wherein the control and command unit includes regulation devices configured to regulate said electrical supply frequency of said supply voltage and supply current in a manner independent of a mains frequency of said power grid and in that each converter device comprises a bank of capacitors connectable during use to a direct current power supply circuit, a plurality of 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 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 the casing.

2 . The electric power supply apparatus as in claim 1 , wherein said heat sink and/or said capacitors are electrically isolated with respect to said casing.

3 . The electric power supply apparatus as in claim 1 , comprising at least a first high-impedance component connected between said heat sink and said casing.

4 . The electric power supply apparatus as in claim 3 , 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.

5 . The electric power supply apparatus as in claim 1 , wherein said at least one first component and/or said second high-impedance components have an impedance comprised between 500Ω and 1500Ω.

6 . The electric power supply apparatus as in claim 1 , wherein said at least one first component and/or said second components have an impedance comprised between 800  and 1200Ω.

7 . The electric power supply apparatus of converter device as in claim 1 , comprising at least one low-pass electrical filter, connected between an output connector suitable to be connected, during use, to the load to be powered, and the earth.

8 . The electric power supply apparatus as in claim 1 , comprising a low-pass electrical filter connected between an output of the converter devices and the earth, and configured to attenuate, or eliminate, possible current fluctuations directed toward the earth.

9 . The electric power supply apparatus as in claim 8 wherein said electrical filter is an RC filter of the three-phase type, and is inserted on the output phases which are connected, during use, to the load.

10 . The electric power supply apparatus as in claim 1 , wherein said electrical filter is an RC filter provided with a resistive component and a capacitive component and comprises dissipation means configured to dissipate the thermal energy generated by one or by both the resistive and capacitive components and reduce their temperature.

11 . The electric power supply apparatus as in claim 10 , wherein said electrical filter comprises temperature measurement sensors associated with one or more of the resistive and/or capacitive components and configured to measure their temperature.

12 . The electric power supply apparatus as in claim 1 , wherein said regulation devices comprise a hysteresis modulator, or a PWM (Pulse-Width-Modulation) modulator.

13 . An electric arc furnace comprising: a container or shell into which metal material is introduced to be subsequently melted and a plurality of electrodes configured to strike an electric arc through the metal material and melt it, and further comprising the electric power apparatus as in claim 1 connected between a power grid and said electrodes.

14 . 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.