Furnace power supply, system for powering a furnace, furnace, use of a furnace power supply, and method of operation

Abstract

The present invention discloses a furnace power supply (100) for supplying electrical energy to an electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace, the furnace power supply (100) being connectable to a three-phase power network (110); the furnace power supply (100) being connectable to at least one electrode (120); the furnace power supply (100) being connectable to the three-phase power network (110); at least one AC / DC converter circuit (130) being connectable to the three-phase power network (110) and configured to rectify alternating current of at least one phase of the three-phase power network (110); and at least one DC / DC converter circuit (150) configured to handle voltage levels of -500 VDC or higher.

Description

[Technical Field]

[0001] The present invention relates to a furnace power supply, a system for powering a furnace, a furnace, the use of a furnace power supply, and a method of operation. [Background technology]

[0002] Metals, especially steels, are routinely melted and heated by electric arcs in melting units. These electrically operated melting units, especially electric arc furnaces, electric reduction furnaces, or submerged arc resistance furnaces, operate with direct current (DC), alternating current (AC), or polyphase current. Typically, for this purpose, at least one electrode is used that projects into the furnace vessel through the furnace roof, while other electrodes are provided corresponding to the first electrode or are located at the bottom of the melting vessel.

[0003] Electric arc furnaces, electric reduction furnaces or submerged arc resistance furnaces represent a highly non-linear load, which means that operation of an electric arc furnace, electric reduction furnace or submerged arc resistance furnace can result in undesirable electrical network distortions on the electrical supply network, in particular flicker, harmonic currents, etc. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention is based on the problem of providing improvements to the state of the art. [Means for solving the problem]

[0005] (A1) According to a first aspect of the present invention, the object is achieved by a furnace power supply device for supplying electrical energy to an electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace, comprising: the furnace power supply is connectable to a three-phase power network, preferably a medium-voltage three-phase power network; the furnace power supply is connectable to at least one electrode of an electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace; - Furnace power supply at least one AC / DC converter circuit connectable to a three-phase power network and configured to rectify alternating current of at least one phase of the three-phase power network, the three-phase power network having a voltage level of 1000 VAC or higher; and at least one DC / DC converter circuit configured to handle voltage levels of -500VDC or greater, the DC / DC converter circuit connected to the DC side of the AC / DC converter circuit.

[0006] Firstly, it should be clearly pointed out that in the context of this patent application, indefinite articles and numerals such as "1", "2", etc. should normally be understood as "at least" information, i.e. "at least one", "at least two", etc., unless it is clearly evident from the respective context or it is obvious to a person skilled in the art that they can only mean "exactly one", "exactly two", etc., or it is technically necessary.

[0007] In the context of this patent application, the terms "in particular" and / or "particularly" should always be understood as meaning that this term introduces an optional preferential property. This expression should not be understood as "that is."

[0008] It is proposed here to control the amount of total harmonic distortion (THD), and in particular to reduce the amount of THD by using a fully bidirectional furnace power supply, which can significantly reduce grid disturbances since THD can be minimized or prevented, and at the same time improve the power factor of the energy provided by the power network, thereby improving the efficiency of energy use.

[0009] It is further proposed herein to control the power factor, in particular to increase the power factor of the furnace power supply by using a fully bidirectional furnace power supply, preferably by using an active front end. This allows the furnace power supply to regulate the reactive power instantaneously introduced into the power network, in particular to source and / or sink reactive power, thereby reducing the need for external power compensators, such as static reactive power compensators (SVCs) or static synchronous compensators (STATCOMs). This significantly reduces the area and cost required for the installation of an electric arc furnace, electric reduction furnace, or submerged arc resistance furnace at a given plant.

[0010] Total Harmonic Distortion (THD) can be defined as the ratio of the root mean square (RMS) amplitude of a set of harmonic frequencies to the RMS amplitude of the first harmonic or fundamental frequency, which can be calculated by the following formula:

[0011]

number

[0012] The electrical load on a three-phase power network during operation of an electric arc furnace, electric reduction furnace, or submerged arc resistance furnace may be asymmetric, causing harmonic distortion of the three-phase power network. The total harmonic distortion of the three-phase power network can be affected by using a fully bidirectional furnace power supply that allows instantaneous energy flow from the three-phase power network to the load and vice versa. In particular, the total harmonic distortion can be minimized by using fully bidirectional converter components, especially active front ends.

[0013] Instantaneous apparent power (P ist ) is calculated as the instantaneous voltage (V ist ) and instantaneous current (I ist ) can be defined as: P ist =V ist * I ist During the ceremony, P ist =instantaneous apparent power V ist = instantaneous voltage I ist = instantaneous current.

[0014] The portion of instantaneous apparent power that results in a net transfer of energy in one direction is known as instantaneous "real power." The portion of instantaneous power that does not result in a net transfer of energy, but instead oscillates between source and load with each cycle due to stored energy in an AC system, is known as instantaneous "reactive power." The ratio of real power to apparent power is known as the "power factor." The higher the power factor for a given electrical energy transfer, the higher the net transfer of energy for a given transfer of apparent power, and therefore the more efficient that net energy transfer.

[0015] An "electric arc furnace" is a furnace that uses electrical energy provided and / or processed by a "furnace power supply" to generate an electric arc to melt ingot metal, in particular scrap metal and / or scrap metal mixture and / or direct reduced iron (DRI) and / or hot briquetted iron (HBI) and / or hot metal and / or flux material in the electric arc furnace. The electric arc furnace may be a ladle furnace.

[0016] An electric arc is formed between the charged material and the electrode. The charge in an electric arc furnace is heated both by the current passing through the charge and by the radiant energy emitted by the arc. Electric arc temperatures can reach over 3,000°C.

[0017] An "electroreduction furnace" is a furnace that uses electrical energy provided and / or processed by a furnace power supply to generate an electric arc to melt scrap metal and / or scrap metal mixtures of ingot metals, particularly ferroalloys such as, but not limited to, ferronickel (FeNi), ferromanganese (FeMn), ferroaluminum (FeAl), ferrotungsten (FeW), ferrochromium (FeCr), ferrotitanium (FeTi), and ferromagnesium (FeMg) in the electroreduction furnace.

[0018] A "submerged arc resistance furnace" is a furnace that uses electrical energy provided and / or processed by a furnace power supply to generate an arc between an electrode and the charge material or to heat the charge material by resistance heating (Joule effect). The charge materials are typically non-ferrous metals, ores and materials, reducing agents, but can also be ferrous alloys, waste recycle, slag, and slag washing.

[0019] The electric arc furnace, electric reduction furnace, or submerged arc resistance furnace may have a charge capacity of 1 ton or more, preferably 20 ton or more, particularly preferably 50 ton or more. More advantageously, the electric arc furnace or submerged arc resistance furnace may have a charge capacity of 100 ton or more, preferably 200 ton or more, particularly preferably 400 ton or more.

[0020] The furnace power supply may be connected to an electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace. In particular, the furnace power supply may be connected to the electrodes of the electric arc furnace, the electric reduction furnace, or the submerged arc resistance furnace by bus bars or bus tubes, cables, or other suitable power transmission media, such as copper or aluminum, that can be cooled with air, gas, water, or another suitable cooling medium other than water or gas. The furnace power supply may particularly preferably include less than one furnace transformer. In other words, the furnace power supply may be directly connectable to at least one electrode of the electric arc furnace, the electric reduction furnace, or the submerged arc resistance furnace.

[0021] A "three-phase power network" is a polyphase system used for generating, transmitting, and distributing electricity. A three-phase power network provides alternating current (AC), specifically three ACs, each AC having a +120 degree phase difference with one of the other two ACs and a -120 degree phase difference with each of the other ACs.

[0022] The three-phase power network may be a high-voltage three-phase power network, a medium-voltage three-phase power network, or a low-voltage three-phase power network.

[0023] The high voltage can be 36 kV or more, preferably 60 kV or more, particularly preferably 100 kV or more. More advantageously, the high voltage can be 150 kV or more, preferably 200 kV or more, particularly preferably 300 kV or more. Even more advantageously, the high voltage can be 400 kV or more, preferably 700 kV or more, particularly preferably 1100 kV or more.

[0024] The medium voltage can be less than or equal to 36 kV, more advantageously less than or equal to 30 kV, preferably less than or equal to 20 kV, particularly preferably less than or equal to 15 kV.

[0025] The medium voltage can be 1 kV or more, preferably 2 kV or more, particularly preferably 10 kV or more, and more advantageously 15 kV or more, preferably 20 kV or more, particularly preferably 30 kV or more.

[0026] The low voltage may be 50 V or more, preferably 60 V or more, particularly preferably 100 V or more. Even more advantageously, the low voltage may be 120 V or more, preferably 220 V or more, particularly preferably 240 V or more.

[0027] The low voltage can be 1,000 V or less, particularly preferably 900 V or less, and more advantageously 600 V or less, preferably 240 V or less, particularly preferably 220 V or less.

[0028] Preferably, the voltage levels may be defined in accordance with IEC 60038.

[0029] An "electrode" is a conductor used to contact a part of a circuit, particularly an electric arc furnace, electric reduction furnace, or submerged arc resistance furnace circuit, particularly a non-metallic part of the circuit. In the case of an electric arc furnace, electric reduction furnace, or submerged arc resistance furnace, the non-metallic part of the circuit may correspond to the atmosphere within the electric arc furnace, electric reduction furnace, or submerged arc resistance furnace.

[0030] The electrodes can be made of high density graphite and / or Wolfram. They can be designed to transmit electrical energy, forming an arc between the tip and the charge material. They can be pre-fired or self-fired (Söderberg) electrodes, and / or extruded / composite electrodes, which are a combination of a pre-fired electrode with a Söderberg electrode as the core, and / or hollow electrode systems that allow for the filling of fine powder through the center hole (pre-fired, self-fired), whereby the choice of electrode type can depend on the size of the electrode, the material / metallurgy from which it is manufactured, and economic aspects such as operating costs.

[0031] The electrodes of the electric arc furnace, electric reduction furnace, or submerged arc resistance furnace may be located at the top of the electric arc furnace, electric reduction furnace, or submerged arc resistance furnace. Preferably, the top-located electrodes are connected to height adjustment means, which allow the distance of the electrodes to the designated scrap and / or designated molten metal in the electric arc furnace or submerged arc resistance furnace to be varied. Such variation may be controlled and / or adjusted by an electrode regulator.

[0032] The second electrode may be disposed within the furnace vessel of the electric arc furnace, electric reduction furnace, or submerged arc resistance furnace, or may be a component of the interior wall of the furnace vessel.

[0033] The second electrode may also be placed at the top of the electric arc furnace, electric reduction furnace, or submerged arc resistance furnace, and may preferably be connected to a height adjustment means.

[0034] The electric arc furnace, electric reduction furnace or submerged arc resistance furnace may also have three, four or more electrodes, each of which may be connected to a height adjustment means.

[0035] Electric arc furnaces, electric reduction furnaces, or submerged arc resistance furnaces can be operated with direct current (DC) or with alternating current (AC).

[0036] In electric arc furnaces, electric reduction furnaces, or submerged arc resistance furnaces operating with direct current, the electrodes are sometimes referred to as anodes and cathodes. The cathode may be located at the top of the furnace. The anode may also be divided into several segments. The anode, preferably the bottom electrode, comprises a metal and / or conductive material at the bottom of the furnace, and an arc is formed between the charge material and the cathode from the top, preferably made of graphite, carbon, or Wolfram.

[0037] Electric arc furnaces, electric reduction furnaces or submerged arc resistance furnaces operated by alternating current can be powered by a single-phase or a polyphase power supply, in particular a three-phase power supply.

[0038] An "AC / DC converter circuit" is an electrical device that converts alternating current into direct current.

[0039] The AC / DC converter circuit is capable of providing a DC voltage level on the DC side of the AC / DC converter circuit that is greater than or equal to the root mean square (RMS) value of the AC voltage level on the AC side of the AC / DC converter circuit, preferably greater than or equal to the root mean square of two multiplied by the AC voltage level on the AC side of the AC / DC converter circuit.

[0040] The AC / DC converter circuit is capable of providing a DC voltage level on the DC side of the AC / DC converter circuit that is at least 0.1 times the root mean square of the AC voltage level on the AC side of the AC / DC converter circuit, preferably at least 0.2 times the root mean square, and most preferably at least 0.5 times the root mean square.

[0041] The AC / DC converter circuit may provide a DC voltage level on the DC side of the AC / DC converter circuit that is greater than or equal to 1.0 times the root mean square of the AC voltage level on the AC side of the AC / DC converter circuit, preferably greater than or equal to 1.5 times the root mean square, particularly preferably greater than or equal to 2 times the root mean square, and especially preferably greater than or equal to 3 times the root mean square.

[0042] The AC / DC converter circuit may comprise at least one AC / DC converter unit. An "AC / DC converter unit" is an electrical device that converts alternating current into direct current.

[0043] The AC / DC converter unit may be an integrated component. The AC / DC converter unit may comprise at least one circuit board.

[0044] The AC / DC converter circuit may include multiple AC / DC converter units connected in parallel with each other, thereby increasing the upper current limit of the AC / DC converter circuit.

[0045] The AC / DC converter circuit may include a plurality of AC / DC converter units connected in series with each other, thereby increasing the upper voltage limit of the AC / DC converter circuit.

[0046] The AC / DC converter circuit may comprise an AC / DC housing, which is a housing in the context of the present invention.

[0047] A "housing" in the context of the present invention is designed to protect the designated components therein from external influences, in particular mechanical and / or electrical influences. Furthermore, the housing may be provided with an electrical ground connection, thereby increasing in a certain way the safety for personnel in the vicinity of the electrical components enclosed by the housing.

[0048] The housing may include a bottom, a top, and at least one side. The bottom, top, and at least one side may at least partially limit the housing volume. The bottom, top, and at least one side may be connected to one another to form a unitary component.

[0049] The AC / DC housing may be configured to house at least one AC / DC converter unit, and preferably multiple AC / DC converter units, within the housing volume.

[0050] The AC / DC converter circuit may be an integrated component. The AC / DC converter circuit may comprise at least one circuit board.

[0051] Two parts that form an "integral component" in the context of the present invention are interconnected to each other by at least one mechanical connection. In other words, the two parts that form the integral component change their relative spatial position with respect to each other within the limits of their mechanical connection when the integral component is moved from one spatial position to another.

[0052] In a preferred embodiment of the present invention, the mechanical connection of the integral component is fixed, in other words, the relative position of two parts forming the integral component, where the mechanical connection between the two parts is fixed, remains constant during changes in the spatial position of the integral component.

[0053] The AC / DC converter unit may comprise a unit housing, which may be the housing in the context of the present invention.

[0054] A plurality of AC / DC converter units connected in parallel and / or in series to one another can be disposed within the housing volume of the AC / DC housing. In this way, the AC / DC converter circuit can be formed as an integrated component. In this way, the AC / DC converter circuit can be replaced for maintenance or repair in an easier manner. Furthermore, individual AC / DC converter units can be replaced from the AC / DC converter circuit for maintenance or repair in an easier manner, resulting in an increased modularity of the AC / DC converter circuit.

[0055] The AC / DC converter circuit and / or the AC / DC converter unit may comprise at least one capacitor and / or at least one inductor for storing electrical energy, thus providing an isolation between the three-phase power network and the at least one electrode.

[0056] The AC / DC converter circuit and / or AC / DC converter unit may include at least one half H-bridge circuit. An H-bridge circuit is an electronic circuit that converts direct current to alternating current. A half H-bridge includes two switching elements. A full H-bridge includes four switching elements.

[0057] The upper limit voltage of the half H-bridge circuit may be 0.5 kV or more, preferably 1.0 kV or more, and particularly preferably 1.5 kV or more.

[0058] The AC / DC converter circuit and / or the AC / DC converter unit may include at least one full H-bridge circuit, the upper voltage limit of which may be 0.5 kV or more, preferably 1.0 kV or more, and particularly preferably 1.5 kV or more.

[0059] The AC / DC converter circuit and / or AC / DC converter unit may include multiple full H-bridge circuits and / or half H-bridge circuits connected in series with each other, thereby increasing the upper voltage limit of the AC / DC converter circuit and / or AC / DC converter unit.

[0060] The AC / DC converter circuit and / or AC / DC converter unit may include multiple full H-bridge circuits and / or half H-bridge circuits connected in parallel to each other, thereby increasing the upper current limit of the AC / DC converter circuit and / or AC / DC converter unit.

[0061] The upper current limit of the AC / DC converter circuit and / or AC / DC converter unit may be 750 A or more, preferably 1500 A or more, preferably 2000 A or more, particularly preferably 2500 A or more, and especially preferably 3000 A or more.

[0062] The AC / DC converter circuit may comprise exactly one AC / DC converter unit.

[0063] The AC / DC converter circuit may be configured to rectify alternating current of at least one phase of a three-phase power network, where the three-phase power network is a high-voltage three-phase power network, a medium-voltage three-phase power network, or a low-voltage three-phase power network.

[0064] The AC / DC converter circuit may be configured to rectify alternating current on all phases of a three-phase power network.

[0065] The AC / DC converter circuit may be indirectly connectable to a three-phase power network. In other words, additional components may be interposed between the AC / DC converter circuit and the three-phase power network. The additional components may include, but are not limited to, one or more transformers, one or more capacitors, one or more inductors, etc.

[0066] The AC / DC converter circuit may be directly connectable to a three-phase power network, i.e., there may be less than one intervening component between the AC / DC converter circuit and the three-phase power network, other than one or more power cables for transporting electrical energy.

[0067] The AC / DC converter circuit and / or AC / DC converter unit may have a switching frequency of 1 kHz or more, preferably 2 kHz or more, particularly preferably 5 kHz or more. Advantageously, the AC / DC converter circuit and / or AC / DC converter unit may have a switching frequency of 10 kHz or more, preferably 15 kHz or more, particularly preferably 20 kHz or more.

[0068] In this way, instantaneous power factor correction that improves the power factor can be achieved, which may also be called dynamic power factor correction (DPFC).

[0069] The AC / DC converter circuit and / or AC / DC converter unit may provide 6 impulse modulation and / or any multiple of 6 impulse modulation, i.e. 12 impulse modulation or 18 impulse modulation, etc. In this way, harmonics higher than the fundamental are significantly reduced, and therefore THD can be significantly reduced.

[0070] A "DC / DC converter circuit" is an electrical device that converts direct current having a first voltage level into direct current having a second voltage level.

[0071] A "first voltage level" in the context of the present invention is the voltage level of a current entering the DC / DC converter circuit in the direction of electrical energy transport of that current. The current entering the DC / DC converter circuit may transport electrical energy from a three-phase power network and / or another DC power source to a load, or from a load to a three-phase power network and / or another DC power source.

[0072] A "second voltage level" in the context of the present invention is the voltage level of a current exiting the DC / DC converter circuit in the direction of electrical energy transport of that current. The current exiting the DC / DC converter circuit may transport electrical energy from a three-phase power network and / or another DC power source to a load, or from a load to a three-phase power network and / or another DC power source.

[0073] The first voltage level may be higher or lower than the second voltage level, or alternatively, the first voltage level may be equal to the second voltage level.

[0074] The DC / DC converter circuit can be configured to provide a constant second voltage level. The constant second voltage level can vary from a nominal second voltage level by 80% or less, or 60% or less, or 50% or less, or 40% or less, or 30% or less, or 20% or less, or 15% or less, or 10% or less, or 5% or less. The voltage variation can be measured as an average voltage value of a given number of predetermined time intervals that must fall within a specific range around the nominal voltage level. For example, for a 20% deviation of the second voltage level from a specified nominal voltage level, 95% of the one-minute averages of the measured voltage values ​​over a one-hour interval must be within the 20% deviation limit from the nominal voltage level. The time interval can be varied. The required number of average voltage values ​​can be varied. Alternatively or additionally, the voltage fluctuations can be measured according to one of the measurement principles of DIN EN 50160, DIN EN 61000-2-2 or DIN EN 61000-2-4 or any other standard suitable for the field of application.

[0075] The DC / DC converter circuit may include at least one DC / DC converter unit. A "DC / DC converter unit" is an electrical device that converts direct current having a first voltage level into direct current having a second voltage level.

[0076] The DC / DC converter unit may include a unit housing, the DC / DC converter unit may be an integrated component, or the DC / DC converter unit may include a circuit board.

[0077] The DC / DC converter circuit may comprise a DC / DC housing, which is a housing in the context of the present invention, configured to house at least one DC / DC converter unit within a housing volume.

[0078] The DC / DC converter circuit may be an integrated component. The DC / DC converter circuit may comprise a circuit board.

[0079] The DC / DC converter circuit may comprise a plurality of DC / DC converter units connected in parallel with each other, thereby increasing the upper current limit of the DC / DC converter circuit.

[0080] The DC / DC converter circuit may include a plurality of DC / DC converter units connected in series with each other, thereby increasing the upper voltage limit of the DC / DC converter circuit.

[0081] A plurality of DC / DC converter units connected in parallel and / or in series with one another can be arranged within the housing volume of a DC / DC housing of the DC / DC converter circuit. In this way, the DC / DC converter circuit can be formed as a single integrated component that can be replaced for maintenance or repair in an easier manner. Furthermore, individual DC / DC converter units can be replaced from the DC / DC converter circuit for maintenance or repair in an easier manner, resulting in an increased modularity of the DC / DC converter circuit.

[0082] The DC / DC converter circuit and / or the DC / DC converter unit may comprise at least one capacitor and / or at least one inductor for storing electrical energy and smoothing the current and / or voltage having the second voltage level, whereby higher order harmonics are reduced from the current.

[0083] The DC / DC converter circuit and / or the DC / DC converter unit may include at least one half H-bridge circuit, the upper voltage limit of which may be 0.5 kV or more, preferably 1.0 kV or more, particularly preferably 1.5 kV or more.

[0084] The DC / DC converter circuit and / or the DC / DC converter unit may include at least one full H-bridge circuit, the upper voltage limit of which may be 0.5 kV or more, preferably 1.0 kV or more, and particularly preferably 1.5 kV or more.

[0085] The DC / DC converter circuit and / or the DC / DC converter unit may include multiple full H-bridge circuits and / or half H-bridge circuits connected in series with each other, thereby increasing the upper voltage limit of the DC / DC converter unit.

[0086] The DC / DC converter circuit and / or the DC / DC converter unit may include multiple full H-bridge circuits and / or half H-bridge circuits connected in parallel to each other, thereby increasing the upper current limit of the DC / DC converter unit.

[0087] The DC / DC converter circuit may comprise exactly one DC / DC converter unit.

[0088] The DC / DC converter circuit may be configured to handle voltage levels of 300 VDC or higher, preferably 500 VDC or higher, particularly preferably 800 VDC or higher. In preferred embodiments, the DC / DC converter circuit may be configured to handle voltage levels of 1000 VDC or higher, preferably 1500 VDC or higher, particularly preferably 2000 VDC or higher. (A2) According to a preferred embodiment, the furnace power supply comprises less than one transformer, preferably less than one step-down transformer, arranged between the three-phase power network and at least one electrode.

[0089] Eliminating the transformer, preferably a step-down transformer, can further increase system efficiency and reduce overall costs. The presence of current harmonics in the transformer can lead to larger eddy currents in the transformer's magnetic core. Eddy current losses typically reduce the efficiency of the transformer.

[0090] The furnace power supply may comprise less than one transformer, preferably less than one step-down transformer, arranged between the three-phase power network and the at least one AC / DC converter circuit.

[0091] The furnace power supply may include less than one transformer disposed between the at least one AC / DC converter circuit and the at least one electrode.

[0092] The furnace power supply may include less than one transformer disposed between the at least one DC / DC converter circuit and the at least one electrode.

[0093] The furnace power supply may include less than one transformer disposed between the at least one DC / AC converter circuit and the at least one electrode.

[0094] (A3) According to a preferred embodiment, the AC / DC converter circuit comprises at least one bidirectional AC / DC converter unit, preferably an active front-end circuit.

[0095] A "bidirectional" AC / DC converter unit essentially allows electrical energy to flow in both directions, i.e., electrical energy can flow from the three-phase power network and / or other DC power source to the load, and from the load to the three-phase power network and / or other DC power source. In this way, the AC / DC converter can instantaneously supply or compensate for reactive power, thereby increasing the power factor of the furnace power supply.

[0096] The "active front-end circuit" comprises a controllable semiconductor device, preferably an insulated-gate bipolar transistor (IGBT).

[0097] The AC / DC converter circuit may comprise exactly one AC / DC converter unit, preferably an active front-end circuit, the AC / DC converter circuit and the AC / DC converter unit forming an integrated component.

[0098] (A4) According to a preferred embodiment, the at least one DC / DC converter circuit comprises at least one bidirectional DC / DC converter unit.

[0099] A "bidirectional" DC / DC converter unit allows electrical energy to flow essentially in both directions, i.e., electrical energy can flow from the three-phase power network and / or other DC power source to the load, and from the load to the three-phase power network and / or other DC power source.

[0100] (A5) According to a preferred embodiment, the at least one DC / DC converter circuit comprises at least one galvanically isolated DC / DC converter unit.

[0101] "Galvanic isolation" is the avoidance of electrical conduction between two electrical circuits between which power or signals are exchanged. The two circuits can be separated by a non-conductive coupling element. In the case of galvanic isolation, the electrical potentials are separated from each other and the circuits have no potential between them. In this way, the propagation of ground faults can be prevented.

[0102] Galvanic isolation can be achieved by several means such as magnetic flux and / or optical means, preferably light.

[0103] A transformer can be used as galvanic isolation.

[0104] The at least one DC / DC converter circuit comprises at least one galvanically isolated DC / DC converter unit, and is capable of providing galvanic isolation between the AC / DC converter circuit and at least one electrode when the furnace power supply is connected to an electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace, thereby preventing propagation of ground faults, particularly without the use of additional transformers in and / or connected to the furnace power supply.

[0105] (A6) According to a preferred embodiment, the at least one DC / DC converter circuit comprises at least one switching DC / DC converter unit.

[0106] A "switching DC / DC converter unit" converts one DC voltage level to another, which may be higher or lower, by temporarily storing energy and then releasing that energy at a different voltage level. In this way, the efficiency of power conversion can be increased, especially compared to non-switching DC / DC converter units.

[0107] The DC / DC converter circuit and / or the DC / DC converter unit may have a switching frequency of 1 kHz or more, preferably 2 kHz or more, particularly preferably 5 kHz or more. Advantageously, the DC / DC converter circuit and / or the DC / DC converter unit may have a switching frequency of 10 kHz or more, preferably 15 kHz or more, particularly preferably 20 kHz or more. In this way, the power factor can be improved instantly.

[0108] (A7) According to a preferred embodiment, at least one first buffer circuit of direct current is interposed between the AC / DC converter circuit and the DC / DC converter circuit, connecting the AC / DC converter circuit and the DC / DC converter circuit, the first buffer circuit being configured to store energy and to create isolation between the three-phase power network and at least one electrode.

[0109] A "first buffer circuit" is an electrical circuit that transmits and / or stores electrical energy.

[0110] The first buffer circuit can create isolation between the three-phase power network and at least one electrode. The isolation can be electrical isolation due to electrical energy stored in the first buffer circuit. The electrical energy stored in the first buffer circuit can absorb fluctuations, particularly instantaneous fluctuations, in the supply and / or demand of electrical energy. For example, if the electrical energy demand of an electrical load directly or indirectly connected to the first buffer circuit drops, the first buffer circuit can store an excess electrical energy supply, preferably from the three-phase power network connected to the first buffer circuit. For example, if the electrical energy supply, preferably from the three-phase power network connected to the first buffer circuit, drops, the first buffer circuit can supply electrical energy from the electrical energy stored in the first buffer circuit to the electrical load directly or indirectly connected to the first buffer circuit. In other words, the first buffer circuit can create electrical isolation between the three-phase power network and at least one electrode. In this way, the effects, particularly adverse effects, of fluctuations in the electrical energy supply from the three-phase power network to at least one electrode can be reduced.

[0111] The first buffer circuit may include at least one capacitor configured to store energy. The first buffer circuit may include multiple capacitors connected in parallel and / or series with each other. In this way, improved isolation between the three-phase power network and the at least one electrode may be achieved.

[0112] The first buffer circuit may include at least one inductor configured to store energy. The first buffer circuit may include multiple inductors connected in parallel and / or series with each other. In this manner, improved isolation between the three-phase power network and the at least one electrode may be achieved.

[0113] The first buffer circuit may include at least one battery configured to store energy. The first buffer circuit may include multiple batteries connected in parallel and / or series with each other. In this way, improved isolation between the three-phase power network and the at least one electrode can be achieved.

[0114] The first buffer circuit may provide isolation between the AC / DC converter circuit and the DC / DC converter circuit.

[0115] The first buffer circuit may have a voltage level of 1 kV or more, preferably 10 kV or more, particularly preferably 100 kV or more, and especially preferably 150 kV or more. Advantageously, the first buffer circuit may have a voltage level of 300 kV or more, preferably 500 kV or more, particularly preferably 900 kV or more, and especially preferably 1500 kV or more. The first buffer circuit may also be referred to as an HV DC link. In this way, the first buffer circuit may provide an increased power supply to at least one electrode.

[0116] The first buffer circuit voltage level may depend on the AC voltage level of the AC voltage on the AC side of the AC / DC converter circuit. The first buffer circuit voltage level may be adjusted, preferably by an electronic control unit.

[0117] (A8) According to a preferred embodiment, at least one DC power source, preferably a renewable DC power source, is connectable to the first buffer circuit.

[0118] A "DC power supply" is an electrical device that provides direct current (DC).

[0119] The DC power source may be a renewable DC power source such as a wind turbine and / or a wind turbine power plant and / or a solar power plant and / or a geothermal power plant and / or a wave power plant. The DC power source may be a battery.

[0120] The DC power source may be other power plant types that at least indirectly provide DC power, such as nuclear power plants, coal power plants, gas power plants, and / or oil power plants.

[0121] The DC power source may be at least indirectly connectable to the first buffer circuit and / or the plurality of first buffer circuits. In this way, a stable energy supply for the furnace power supply may be provided even in the event of disturbances and / or faults in the three-phase power network.

[0122] Alternatively or additionally, the DC power source may be at least indirectly connectable to the second buffer circuit and / or to a plurality of second buffer circuits. In this way, a stable energy supply for the furnace power supply may be provided even in the event of disturbances and / or failures in the three-phase power network and / or in the DC power source connected to the at least one first buffer circuit.

[0123] The DC power supply can directly or indirectly provide a voltage level that is essentially the same as that of the first buffer circuit, thus providing electrical energy to the first buffer circuit with less disturbance.

[0124] The DC power source can be indirectly connected to the first buffer circuit and / or the second buffer circuit via one or more DC / DC converter circuits configured to provide a first voltage level and / or a second voltage level that match the voltage levels of the DC power source and / or the first buffer circuit and / or the second buffer circuit, depending on the direction of electrical energy transport. In other words, when electrical energy flows from the DC power source to the first buffer circuit and / or the second buffer circuit, the DC / DC converter circuit can process the first voltage level, which is essentially the same voltage level as that provided by the DC power source, and provide a second voltage level, which is essentially the same voltage level as that of the first buffer circuit and / or the second buffer circuit. When electrical energy flows from the first buffer circuit and / or the second buffer circuit to the DC power source, the DC / DC converter circuit can process the first voltage level, which is essentially the same voltage level as that provided by the first buffer circuit and / or the second buffer circuit, and provide a second voltage level, which is essentially the same voltage level as that of the DC power source.

[0125] At least one AC / DC converter circuit may be connectable to multiple three-phase power networks. In this way, a stable energy supply for the furnace power supply may be provided even in the event of a disturbance and / or a failure in one of the three-phase power networks.

[0126] (A9) According to a preferred embodiment, the furnace power supply device comprises a plurality of AC / DC converter circuits connected in parallel with each other, and the AC / DC converter circuits are connected to a common first buffer circuit, preferably a plurality of first buffer circuits.

[0127] The multiple first buffer circuits may be connected in parallel with each other.

[0128] The multiple AC / DC converter circuits and the multiple first buffer circuits may be the same. In other words, the number of AC / DC converter circuits and the number of first buffer circuits may be the same. Each first buffer circuit may be interposed between one AC / DC converter circuit and one DC / DC converter circuit, establishing a one-to-one connection between exactly one AC / DC converter circuit and exactly one DC / DC converter circuit. A one-to-one connection means that one AC / DC converter circuit is connected to only one DC / DC converter circuit, and one DC / DC converter circuit is connected to only one AC / DC converter circuit. In this way, even if one AC / DC converter circuit or one DC / DC converter circuit is switched off or malfunctions, it is still possible to have an energy supply with an expected current level, voltage level, and / or frequency.

[0129] According to some embodiments of the present invention, a "common first buffer circuit" connects two or more AC / DC converter circuits with one or more DC / DC converter circuits.

[0130] According to some embodiments of the present invention, a common first buffer circuit connects one AC / DC converter circuit to two or more DC / DC converter circuits.

[0131] The common first buffer circuit can transport electrical energy between multiple AC / DC converters and / or multiple DC / DC converters, thus enabling large amounts of energy to be transported while at the same time achieving constant current levels and keeping installation costs low.

[0132] Preferably, the common first buffer circuit may have a voltage level of 1 kV or more, preferably a voltage level of 36 kV or more, particularly preferably a voltage level of 100 kV or more. Advantageously, the common first buffer circuit may have a voltage level of 300 kV or more, preferably a voltage level of 500 kV or more, particularly preferably a voltage level of 900 kV or more, and especially preferably a voltage level of 1500 kV or more.

[0133] (A10) According to a preferred embodiment, at least one second buffer circuit of direct current is interposed between the DC / DC converter circuit and the at least one electrode, at least indirectly connecting the DC / DC converter circuit and the at least one electrode, the second buffer circuit being configured to store energy and to create isolation between the three-phase power network and the at least one electrode.

[0134] A "second buffer circuit" is an electrical circuit that transmits and / or stores electrical energy.

[0135] The second buffer circuit can create isolation between the DC / DC converter circuit and the at least one electrode. The isolation can be electrical isolation due to electrical energy stored in the second buffer circuit. The electrical energy stored in the second buffer circuit can absorb fluctuations, particularly instantaneous fluctuations, in the supply and / or demand of electrical energy. In other words, the second buffer circuit can create electrical isolation between the DC / DC converter circuit and the at least one electrode. In this way, the effects, particularly adverse effects, of fluctuations in the electrical energy supply from the DC / DC converter circuit to the at least one electrode can be reduced.

[0136] The second buffer circuit may include at least one capacitor configured to store energy. The second buffer circuit may include multiple capacitors connected in parallel and / or series with each other. In this way, improved isolation between the three-phase power network and the at least one electrode may be achieved.

[0137] The second buffer circuit may include at least one inductor configured to store energy. The second buffer circuit may include multiple inductors connected in parallel and / or series with each other. In this manner, improved isolation between the three-phase power network and the at least one electrode may be achieved.

[0138] The second buffer circuit may include at least one battery connected in series and / or parallel to the second buffer circuit and configured to store energy. The second buffer circuit may include multiple batteries connected in parallel and / or series to each other and / or to the second buffer circuit. In this way, improved isolation between the three-phase power network and the at least one electrode can be achieved.

[0139] The second buffer circuit may have a voltage level of 1500 kV or less, preferably a higher voltage level of 900 kV or less, particularly preferably a voltage level of 500 kV or less, and especially preferably a voltage level of 300 kV or less. Advantageously, the second buffer circuit may have a voltage level of 150 kV or less, preferably a voltage level of 100 kV or less, particularly preferably a voltage level of 10 kV or less, and especially preferably a voltage level of 1 kV or less. The second buffer circuit may also be referred to as a DC link. In this way, the second buffer circuit may provide an increased power supply to at least one electrode.

[0140] The second buffer circuit voltage level may depend on the DC voltage level of the first buffer circuit. The second buffer circuit voltage level may be lower than the first buffer circuit voltage level.

[0141] The second buffer circuit voltage level can preferably be adjusted by an electronic control unit.

[0142] (A11) According to a preferred embodiment, the furnace power supply comprises an electronic control unit, which is connectable to the AC / DC converter circuit and configured to regulate the active power flow of the furnace power supply.

[0143] An "electronic control unit" is any electronic system adapted to receive signals, store signals, process signals, and / or control or regulate a furnace power supply in response to at least one signal.

[0144] The furnace power supply may include one or more sensors for providing information regarding harmonic distortion and / or flicker and / or the ratio of active to reactive power flow in the power network. The electronic control unit may be operatively connected to one or more such sensors and may receive the sensor signals, process them, and use them to control or regulate the furnace power supply.

[0145] The electronic control unit may include a storage element configured to store sensor signals received by the plurality of sensors from the furnace power supply.

[0146] The electronic control unit may include a housing. The electronic control unit may be an integrated component.

[0147] The electronic control unit may be connectable to a DC / DC converter circuit, in particular to a plurality of DC / DC converter circuits.

[0148] The electronic control unit may be configured to control or regulate the AC / DC converter circuit, in particular to reduce or prevent harmonic distortion and / or flicker in the power network, in particular to mitigate flicker.

[0149] The electronic control unit may be configured to control or regulate the AC / DC converter circuit, in particular to optimize the ratio of active to reactive power flow in the power network.

[0150] The electronic control unit may be configured to control or regulate the DC / DC converter circuit, in particular to reduce or prevent harmonic distortion and / or flicker in the power network, in particular to mitigate flicker.

[0151] The electronic control unit may be configured to control or regulate the DC / DC converter circuit, in particular to achieve a constant second voltage level.

[0152] The electronic control unit may be adapted to control the current loop and / or the voltage loop and / or the impedance loop and / or the active power loop and / or the active power loop with hysteresis of the furnace power supply.

[0153] The electronic control unit may be connectable to a DC / AC converter circuit, in particular to a plurality of DC / AC converter circuits.

[0154] The electronic control unit may be connectable to a DC chopper circuit, in particular to a plurality of DC chopper circuits.

[0155] The electronic control unit may be configured to control or regulate DC chopper circuits and / or DC / AC converter circuits in the power network, in particular to reduce or prevent harmonic distortion and / or flicker, in particular to mitigate flicker, particularly by applying a pulse width modulation strategy algorithm.

[0156] The electronic control unit may be connectable to the DC power source and may be configured to control or regulate the DC power source, in particular to optimize electrical energy transferred from the DC power source to the at least one first buffer circuit and / or from the at least one first buffer circuit to the DC power source, in particular to increase efficiency of electrical energy transfer.

[0157] The furnace power supply may comprise an electrode regulator, preferably a plurality of electrode regulators. The furnace power supply may comprise one electrode regulator per electrode. The furnace power supply may be connectable to an electrode regulator, preferably to a plurality of electrode regulators, particularly preferably to one electrode regulator per electrode.

[0158] The "electrode regulator" may be configured to control and / or adjust the position of the electrode. The electrode may be automatically raised and lowered by height adjustment means, which may be an electric winch hoist, a hydraulic cylinder, a pneumatic cylinder, or the like.

[0159] Electrode conditioners may pursue different objectives individually or in combination, in particular maintaining a nearly constant voltage and / or constant current and / or power input during melting of the charge, even though the scrap may move under the electrode as it melts. The length of the arc may increase with increasing voltage supplied to an electric arc furnace, electric reduction furnace, or submerged arc resistance furnace.

[0160] The electrode regulator may be operatively connected to one or more electronic control units and may receive signals from the one or more electronic control units, process them, and use them to control or adjust one or more electrode height adjustment means of an electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace.

[0161] The electronic control unit is connectable to the electronic coordination and regulation unit, and the electronic control unit is operably connected to the at least one AC / DC converter circuit and / or the at least one DC / DC converter circuit and / or the at least one DC / AC converter circuit and / or the at least one DC chopper circuit and adapted to regulate the active power flow of the furnace power supply.

[0162] An "electronic coordination and conditioning unit" is any electronic system adapted to communicate with one or more electronic control units. Preferably, the electronic coordination and conditioning unit is adapted to communicate with one or more electrode regulators, in particular for the purposes of reducing harmonic distortion and / or reducing flicker, in particular mitigating flicker and / or improving power factor.

[0163] The electronic coordination and regulation unit may comprise a housing. The electronic coordination and regulation unit may be an integrated component. The electronic coordination and regulation may comprise a memory element configured to store a plurality of setting values.

[0164] The electronic coordination and regulation unit may be configured to take over superior control or regulation of the electrode regulators of the electronic control units and one or more furnace power supplies to which it is connected.

[0165] The electronic coordination and regulation unit may be configured to take over higher level control or regulation of some of the connected regulators in the system of the furnace power supply, in particular one or more connected electronic control units and / or one or more electrode regulators.

[0166] The electronic coordination and regulation unit is operably connected to the electronic control unit and / or the electrode regulator, and may preferably be operably connected to each electronic control unit and / or each electrode regulator.

[0167] The electronic coordination and regulation unit may control or regulate the voltage and / or current set points of one or several furnace power supplies.

[0168] The electronic coordination and regulation unit can control or regulate the active and / or reactive power setpoints of one or several furnace power supplies.

[0169] The electronic coordination and regulation unit can control or regulate the frequency setpoint of one or several furnace power supplies. In particular, the electronic coordination and regulation unit can control multiple frequency setpoints for one or several furnace power supplies, preferably different frequency setpoints for different melting stages during operation of an electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace.

[0170] The electronic coordination and regulation unit can control or regulate the impedance or resistance setpoint of one or several furnace power supplies.

[0171] The electronic coordination and regulation unit may control or regulate the electrode height setting of one or several electrodes of one or several electric arc furnaces, electric reduction furnaces, or submerged arc resistance furnaces.

[0172] (A12) According to a preferred embodiment, the furnace power supply comprises at least one DC / AC converter circuit configured to supply electrical energy to the at least one electrode, the at least one DC / DC converter circuit being connected to the at least one DC / AC converter circuit.

[0173] A "DC / AC converter circuit" is an electrical device that converts direct current into alternating current.

[0174] The DC / AC converter circuit may comprise a DC / AC housing, the DC / AC converter circuit may be an integrated component, or the DC / AC converter circuit may comprise a circuit board.

[0175] The DC / AC converter circuit may comprise at least one DC / AC converter unit. A "DC / AC converter unit" is an electrical device that converts direct current into alternating current.

[0176] The DC / AC converter unit may include a unit housing, the DC / AC converter unit may be an integrated component, or the DC / AC converter unit may include a circuit board.

[0177] The DC / AC housing may be configured to house at least one DC / AC converter unit, and preferably multiple DC / AC converter units, within the housing volume.

[0178] The DC / AC converter circuit may include multiple DC / AC converter units connected in parallel with each other, thereby increasing the upper current limit of the DC / AC converter circuit.

[0179] The DC / AC converter circuit may include multiple DC / AC converter units connected in series with each other, thereby increasing the upper voltage limit of the DC / AC converter circuit.

[0180] A plurality of DC / AC converter units connected in parallel and / or in series to one another can be disposed within the housing volume of the DC / AC housing. In this way, the DC / AC converter circuit can be formed as a single integrated component. In this way, the DC / AC converter circuit can be replaced for maintenance or repair in an easier manner. Furthermore, individual DC / AC converter units can be replaced from the DC / AC converter circuit for maintenance or repair in an easier manner, resulting in an increased modularity of the DC / AC converter circuit.

[0181] The DC / AC converter circuit may comprise two or more DC / AC converter units connected in parallel and / or in series with one another, preferably four or more DC / AC converter units, particularly preferably ten or more DC / AC converter units. Advantageously, the DC / AC converter circuit may comprise twenty or more DC / AC converter units, preferably thirty or more DC / AC converter units, particularly preferably forty or more DC / AC converter units, connected in parallel and / or in series with one another.

[0182] The DC / AC converter circuit and / or the DC / AC converter unit may comprise at least one capacitor and / or at least one inductor for storing electrical energy, thus providing an isolation between the three-phase power network and the at least one electrode.

[0183] The DC / AC converter circuit and / or the DC / AC converter unit may include at least one half H-bridge circuit, the upper voltage limit of which may be 0.5 kV or more, preferably 1.0 kV or more, and particularly preferably 1.5 kV or more.

[0184] The DC / AC converter circuit and / or the DC / AC converter unit may include at least one full H-bridge circuit, the upper voltage limit of which may be 0.5 kV or more, preferably 1.0 kV or more, and particularly preferably 1.5 kV or more.

[0185] The DC / AC converter circuit and / or the DC / AC converter unit may include multiple full H-bridge circuits and / or half H-bridge circuits connected in series with each other, thereby increasing the upper voltage limit of the DC / AC converter circuit and / or the DC / AC converter unit.

[0186] The DC / AC converter circuit and / or the DC / AC converter unit may include multiple full H-bridge circuits and / or half H-bridge circuits connected in parallel to each other, thereby increasing the upper current limit of the DC / AC converter circuit and / or the DC / AC converter unit.

[0187] The upper current limit of the DC / AC converter circuit and / or DC / AC converter unit may be 750 A or more, preferably 1500 A or more, preferably 2000 A or more, particularly preferably 2500 A or more, and especially preferably 3000 A or more.

[0188] The DC / AC converter circuit may comprise exactly one DC / AC converter unit.

[0189] The DC / AC converter circuit and / or the DC / AC converter unit may have a switching frequency of 1 kHz or more, preferably 2 kHz or more, particularly preferably 5 kHz or more. Advantageously, the DC / AC converter circuit and / or the DC / AC converter unit may have a switching frequency of 10 kHz or more, preferably 15 kHz or more, particularly preferably 20 kHz or more. In this way, instantaneous power factor correction, which improves the power factor, can be achieved. Such power factor correction may also be called dynamic power factor correction (DPFC).

[0190] The DC / AC converter circuit may be indirectly connectable to one or more electrodes. In other words, additional components may be interposed between the DC / AC converter circuit and one or more electrodes. The additional components may include, but are not limited to, one or more transformers, one or more capacitors, one or more inductors, etc.

[0191] The DC / AC converter circuit may be directly connectable to one or more electrodes, that is, there may be less than one intervening component between the DC / AC converter circuit and one or more electrodes, other than one or more power cables for transporting electrical energy.

[0192] The DC / AC converter circuit may be connectable to at least one electrode, preferably a plurality of electrodes, and configured to supply electrical energy to the electrodes.

[0193] The DC / AC converter circuit may be connectable to exactly one electrode and configured to supply electrical energy to this electrode.

[0194] The furnace power supply may include multiple DC / AC converter circuits connected in parallel with each other, each DC / AC converter circuit configured to supply electrical energy to one or more electrodes.

[0195] The furnace power supply comprises a plurality of DC / AC converter circuits connected in parallel to one another, the DC / AC converter circuits being connectable to the same electrode and configured to supply electrical energy to the same electrode, in this way, even if one DC / AC converter circuit is switched off or has a malfunction, it is still possible to have an energy supply with the expected current and / or voltage levels and / or frequency.

[0196] (A13) According to a preferred embodiment, the furnace power supply comprises at least one DC chopper circuit configured to supply electrical energy to the at least one electrode, and the at least one DC / DC converter circuit is connected to the at least one DC chopper circuit.

[0197] A "DC chopper circuit" is an electrical device that directly converts direct current having a fixed voltage into direct current having a variable voltage.

[0198] Because the switching elements in the DC chopper circuit and / or DC chopper unit are either fully on or fully off, their losses are low, and the DC chopper circuit and / or DC chopper unit can provide high efficiency at switching speeds of 1 kHz or more, preferably 2 kHz or more, and particularly preferably 5 kHz or more. Advantageously, the DC chopper circuit and / or DC chopper unit can have a switching frequency of 10 kHz or more, preferably 15 kHz or more, and particularly preferably 20 kHz or more. In this way, the electric arc can be advantageously stabilized, while at the same time protecting the furnace power supply from possible drift.

[0199] The DC chopper circuit may include a DC chopper housing, the DC chopper circuit may be an integrated component, or the DC chopper circuit may include a circuit board.

[0200] The DC chopper circuit may include at least one DC chopper unit. A "DC chopper unit" is an electrical device that directly converts direct current having a fixed voltage into direct current having a variable voltage.

[0201] The DC chopper unit may include a unit housing, the DC chopper unit may be an integrated component, or the DC chopper unit may include a circuit board.

[0202] The DC chopper housing may be configured to accommodate at least one DC chopper unit, and preferably multiple DC chopper units, within the housing volume.

[0203] The DC chopper circuit may comprise multiple DC chopper units connected in parallel to each other, thus increasing the upper current limit of the DC chopper circuit.

[0204] The DC chopper circuit may include multiple DC chopper units connected in series with each other, thus increasing the upper voltage limit of the DC chopper circuit.

[0205] A plurality of DC chopper units connected in parallel and / or in series to one another can be disposed within the housing volume of the DC chopper housing. In this way, the DC chopper circuit can be formed as one integrated component that can be replaced for maintenance or repair in an easier manner. Furthermore, individual DC chopper units can be replaced from the DC chopper circuit for maintenance or repair in an easier manner, thereby increasing the modularity of the DC chopper circuit.

[0206] The DC chopper circuit and / or the DC chopper unit may comprise at least one capacitor and / or at least one inductor for storing electrical energy, thus providing a separation between the three-phase power network and the at least one electrode.

[0207] The upper current limit of the DC chopper circuit and / or DC chopper unit may be 750 A or more, preferably 1500 A or more, preferably 2000 A or more, particularly preferably 2500 A or more, and especially preferably 3000 A or more.

[0208] The DC chopper circuit may comprise exactly one DC chopper unit.

[0209] The DC chopper circuit may be indirectly connectable to one or more electrodes. In other words, additional components may be interposed between the DC chopper circuit and one or more electrodes. The additional components may include, but are not limited to, one or more capacitors, one or more inductors, etc.

[0210] The DC chopper circuit may be directly connectable to one or more electrodes, i.e., there may be less than one component between the DC chopper circuit and the one or more electrodes, other than one or more power cables for transporting electrical energy.

[0211] A DC chopper circuit may be connectable to at least one electrode, preferably a plurality of electrodes, and configured to supply electrical energy to the electrodes.

[0212] The DC chopper circuit may be connectable to exactly one electrode and configured to supply electrical energy to this electrode.

[0213] The furnace power supply may include a plurality of DC chopper circuits connected in parallel with each other, each DC chopper circuit configured to supply electrical energy to one or more electrodes.

[0214] The furnace power supply comprises a plurality of DC chopper circuits connected in parallel to one another, the plurality of DC chopper circuits being connectable to the same electrode and configured to supply electrical energy to the same electrode, in this way, even if one DC chopper circuit is switched off or has a malfunction, it is still possible to have an energy supply with an expected current level and / or voltage level and / or frequency.

[0215] The AC / DC converter unit and / or the DC / DC converter unit and / or the DC / AC converter unit and / or the DC chopper unit may comprise at least one semiconductor element, preferably a plurality of semiconductor elements, comprising silicon carbide.

[0216] "Semiconductor devices" include conductivity values ​​that fall between conductors, such as metallic copper, and insulators, such as glass. Semiconductor devices can be used for amplification, switching, and energy conversion.

[0217] The semiconductor element may be a diode, a thyristor, such as a silicon controlled rectifier (SCR), a gate turn-off thyristor (GTO), an integrated gate commutated thyristor (IGCT), a metal-oxide semiconductor controlled thyristor (MCT), a transistor, such as a bipolar junction transistor (BJT), a metal-oxide semiconductor field-effect transistor (MOSFET), an injection enhanced gate transistor (IEGT), or an insulated gate bipolar transistor (IGBT), or other suitable semiconductor element. The semiconductor element may comprise silicon and / or carbon, preferably silicon carbide (SiC).

[0218] A DC second buffer circuit may be interposed between the DC / DC converter circuit and the DC / AC converter circuit or between the DC / DC converter circuit and the DC chopper circuit, the second buffer circuit being configured to store energy and provide isolation between the three-phase power network and the electrodes.

[0219] The second buffer circuit can create isolation between the DC / DC converter circuit and the DC / AC converter circuit or the DC chopper circuit. The isolation can be electrical isolation due to the electrical energy stored in the second buffer circuit. The electrical energy stored in the second buffer circuit can absorb fluctuations, particularly instantaneous fluctuations, in the supply and / or demand of electrical energy. In other words, the second buffer circuit can create electrical isolation between the DC / DC converter circuit and the DC / AC converter circuit or the DC chopper circuit connected to the second buffer circuit. In this way, the effects, particularly adverse effects, of fluctuations in the electrical energy supply on the DC / AC converter circuit or the DC chopper circuit can be reduced.

[0220] The second buffer circuit may provide isolation between the DC / DC converter circuit and the DC / AC converter circuit, or between the DC / DC converter circuit and the DC chopper circuit.

[0221] The furnace power supply may include a common second buffer circuit. The common second buffer circuit may connect a DC / DC converter circuit with two or more DC / AC converter circuits or two or more DC chopper circuits. Alternatively, the common second buffer circuit may connect two or more DC / DC converter circuits with one DC / AC converter circuit or one DC chopper circuit. The common second buffer circuit may transport electrical energy between multiple DC / DC converters and / or multiple DC / AC converters and / or multiple DC chopper circuits, thus transporting large amounts of energy while simultaneously achieving a constant current level and keeping installation costs low.

[0222] The furnace power supply may include a plurality of second buffer circuits connected in parallel with each other.

[0223] The multiple DC / DC converter circuits, the multiple second buffer circuits, and the multiple DC / AC converter circuits or DC chopper circuits may be the same. In other words, the number of DC / DC converter circuits, the number of second buffer circuits, and the number of DC / AC converter circuits or DC chopper circuits may be the same. Each second buffer circuit may be interposed between one DC / DC converter circuit and one DC / AC converter circuit, or between one DC / DC converter circuit and one DC chopper circuit, establishing a one-to-one connection between exactly one DC / DC converter circuit and exactly one DC / AC converter circuit, or exactly one DC / DC converter circuit and one DC chopper circuit, to form a power sub-module. In this way, even if one DC / DC converter circuit, one DC / AC converter circuit, or one DC chopper circuit is switched off or malfunctions, it is still possible to have an energy supply with an expected current level, voltage level, and / or frequency.

[0224] The power sub-module may include a housing. The power sub-module may be an integrated component.

[0225] The furnace power supply may comprise a plurality of power sub-modules connected in parallel with one another. Each power sub-module may be connected to exactly one separate electrode and generate an independent power supply for that electrode. In other words, there is a one-to-one assignment between one power sub-module and one electrode.

[0226] According to a preferred embodiment of the furnace power supply, the AC / DC converter circuit, the first buffer circuit, the DC / DC converter circuit, the second buffer circuit, and the DC / AC converter circuit or the DC chopper circuit may form a power module.

[0227] The power module may include a housing. The power module may be an integrated component.

[0228] Preferably, the furnace power supply comprises a plurality of power modules connected in parallel to one another. Each power module can be connected to exactly one separate electrode, generating an independent power supply for each of the electrodes. In other words, there is a one-to-one assignment between one power module and one electrode. In this way, electrical disturbances at one electrode do not affect the other electrodes.

[0229] (A14) According to a second aspect of the present invention, the present task is solved by a system for supplying electrical energy to at least one electric arc furnace and / or electric reduction furnace and / or submerged arc resistance furnace, - the system is connectable to at least one three-phase power network; the system is connectable to at least one electrode of at least one electric arc furnace and / or electric reduction furnace and / or submerged arc resistance furnace, - the system comprises a plurality of furnace power supplies according to the first aspect of the invention; The furnace power supply devices are connected in parallel with one another.

[0230] It will be appreciated that the advantages of the furnace power supply according to the first aspect of the invention, as described above, transfer directly to a system comprising a furnace power supply according to the first aspect of the invention.

[0231] The system may preferably comprise an electrode adjuster operatively connected to each electronic control unit and / or each height adjustment means.

[0232] The system may comprise an electronic coordination and regulation unit operably connected to the electronic control unit and / or electrode regulator, preferably operably connected to each electronic control unit and / or each electrode regulator.

[0233] (A15) According to a third aspect of the present invention, this problem is solved by an electric arc furnace, an electric reduction furnace or a submerged arc resistance furnace, characterized in that the electric arc furnace, the electric reduction furnace or the submerged arc resistance furnace comprises a furnace feeding device according to the first aspect of the present invention and / or a system according to the second aspect of the present invention.

[0234] An electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace may comprise a plurality of furnace power supplies according to the first aspect of the invention and / or a plurality of systems according to the second aspect of the invention. Each furnace power supply according to the first aspect of the invention and / or each system according to the second aspect of the invention is connectable to exactly one electrode and is configured to supply polyphase electrical energy to that electrode. In this way, a stable energy supply for the electric arc furnace, the electric reduction furnace, or the submerged arc resistance furnace can be provided even in the event of disturbances and / or failures in one of the furnace power supplies and / or systems.

[0235] It will be appreciated that the advantages of the furnace power supply apparatus according to the first aspect of the invention and / or the system for supplying electrical energy to one or more electrodes of an electric arc furnace or an electric reduction furnace or a submerged arc resistance furnace according to the second aspect of the invention are directly transferred to an electric arc furnace, an electric reduction furnace or a submerged arc resistance furnace comprising such a system according to the second aspect of the invention, as described above.

[0236] It is noted that the subject matter of the third aspect may be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination.

[0237] Alternatively, an electric arc furnace, an electric reduction furnace or a submerged arc resistance furnace may comprise a plurality of furnace power supplies according to the first aspect of the invention and / or a plurality of systems according to the second aspect of the invention, each furnace power supply according to the first aspect of the invention and / or each system according to the second aspect of the invention being connectable to a plurality of electrodes and configured to supply polyphase electrical energy to the plurality of electrodes.

[0238] (A16) According to a fourth aspect of the present invention, this problem is solved by the use of a furnace power supply device according to the first aspect of the present invention for supplying electrical energy to at least one electric arc furnace and / or electric reduction furnace and / or submerged arc resistance furnace.

[0239] (A17) According to a fifth aspect of the present invention, the problem is solved by a method for operating an electric arc furnace, an electric reduction furnace or a submerged arc resistance furnace, in particular an electric arc furnace, an electric reduction furnace or a submerged arc resistance furnace according to the third aspect of the present invention, wherein the ratio of active power flow to reactive power flow is controlled and / or regulated by influencing controlled variables of an AC / DC converter circuit and / or a DC / DC converter circuit and / or a DC / AC converter circuit and / or a DC chopper circuit, in particular the reactive power flow is minimized by influencing controlled variables of the AC / DC converter circuit and / or the DC / AC converter circuit.

[0240] It will be appreciated that the advantages of an electric arc furnace, electric reduction furnace or submerged arc resistance furnace according to the third aspect of the invention, as described above, transfer directly to the method for operating an electric arc furnace, electric reduction furnace or submerged arc resistance furnace according to the third aspect of the invention.

[0241] It is noted that the subject matter of the fifth aspect may be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination.

[0242] Further advantages, details and properties of the present invention are explained in the following description of embodiments. [Brief explanation of the drawings]

[0243] [Figure 1] 1 shows a schematic diagram of a first embodiment of a furnace power supply; [Figure 2] 1 shows a schematic diagram of a second embodiment of a furnace power supply; [Figure 3]1 shows a schematic diagram of a third embodiment of a furnace power supply; [Figure 4] 1 shows a schematic diagram of a fourth embodiment of a furnace power supply; [Figure 5] 10 shows a schematic diagram of a fifth embodiment of a furnace power supply. [Figure 6] 10 shows a schematic diagram of a sixth embodiment of a furnace power supply; [Figure 7] 1 shows a schematic diagram of a first embodiment of a system for supplying electrical energy to an electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace. [Figure 8] 1 shows a schematic diagram of a second embodiment of a system for supplying electrical energy to an electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace. DETAILED DESCRIPTION OF THE INVENTION

[0244] In the following description, the same reference numbers describe the same elements and the same characteristics, respectively, so that a description of one element made with reference to one figure is valid for the other figures, so that repetition of the respective characteristics is omitted.

[0245] The furnace power supply device 100 of FIG. 1 includes an AC / DC converter circuit 130 and a DC / DC converter circuit 150 connected to the DC side of the AC / DC converter circuit 130.

[0246] The furnace power supply 100 is connectable to a three-phase power network 110 and to an electrode 120 .

[0247] The AC / DC converter circuit 130 is configured to rectify alternating current of at least one phase of the three-phase power network 110 .

[0248] The furnace power supply 100 of Figure 2 further includes a DC / AC converter circuit 170. This furnace power supply is intended for use with an AC-powered electric arc furnace or electric reduction furnace, or a submerged arc resistance furnace (not shown).

[0249] The furnace power supply 100 further comprises a DC first buffer circuit 140 interposed between and connecting the AC / DC converter circuit 130 and the DC / DC converter circuit 150. The first buffer circuit 140 may be configured to store energy and provide isolation between the three-phase power network 110 and the electrodes 120.

[0250] The furnace power supply 100 further comprises an electronic control unit 200 connected to the AC / DC converter circuit 130. The electronic control unit 200 is configured to regulate the active power flow of the furnace power supply 100.

[0251] The electronic control unit 200 is connected to the DC / DC converter circuit 150 and is configured to control or regulate the DC / DC converter circuit 150 .

[0252] The electronic control unit 200 is connected to the DC / AC converter circuit 170 and is configured to control or regulate the DC / AC converter circuit 170 .

[0253] The furnace power supply 100 is further connectable to a DC power supply 300. The DC power supply 300 is connected to the first buffer circuit 140.

[0254] The electronic control unit 200 is connected to the DC power supply 300 and is configured to control and / or regulate the DC power supply 300 .

[0255] The furnace power supply 100 further comprises a DC second buffer circuit 160 interposed between the DC / DC converter circuit 150 and the DC / AC converter circuit 170. The second buffer circuit 160 is configured to store energy and provide isolation between the three-phase power network 110 and the electrodes 120.

[0256] An alternative embodiment (not shown) to the embodiment of the furnace power supply 100 of Figure 2 includes a DC chopper circuit 180 instead of the DC / AC converter circuit 170. This furnace power supply is intended for use with a DC-powered electric arc furnace or electric reduction furnace, or a submerged arc resistance furnace (not shown).

[0257] All other characteristics of the embodiment of the furnace power supply according to FIG. 2 apply to this alternative embodiment of the furnace power supply.

[0258] The furnace power supply device 100 of Fig. 3 includes three DC / DC converter circuits 150 connected in parallel to each other. Each DC / DC converter circuit 150 is connected to the DC side of the same AC / DC converter circuit 130 via a common first buffer circuit 140.

[0259] The furnace power supply 100 further includes three DC / AC converter circuits 170 .

[0260] A DC / AC converter circuit 170 can be connected to the same electrode 120 .

[0261] An electronic control unit 200 is connected to each of the DC / DC converter circuits 150. The electronic control unit 200 is configured to separately control or regulate each DC / DC converter circuit 150, allowing independent control or regulation of each DC / DC converter circuit 150.

[0262] An electronic control unit 200 is connected to each of the DC / AC converter circuits 170. The electronic control unit 200 is configured to separately control or regulate each DC / AC converter circuit 170, allowing for independent control or regulation of each DC / AC converter circuit 170.

[0263] The furnace power supply 100 further includes three DC second buffer circuits 160. Each second buffer circuit 160 is interposed between one DC / DC converter circuit 150 and one DC / AC converter circuit 170, thereby forming three electrically separate power sub-modules 510. Each power sub-module 510 includes one DC / DC converter circuit 150, one DC / AC converter circuit 170, and one second buffer circuit 160 interposed between one DC / DC converter circuit 150 and one DC / AC converter circuit 170.

[0264] An alternative embodiment (not shown) to the embodiment of the furnace power supply 100 of Figure 3 includes three DC chopper circuits 180 instead of the three DC / AC converter circuits 170. This furnace power supply is intended for use with a DC-powered electric arc furnace or electric reduction furnace, or a submerged arc resistance furnace (not shown).

[0265] An alternative embodiment of the furnace power supply 100 further includes three DC / DC converter circuits 150 connected in parallel with each other, each connected to the DC side of the same AC / DC converter circuit 130 via a common first buffer circuit 140.

[0266] A DC chopper circuit 180 can be connected to the same electrode 120 .

[0267] An electronic control unit 200 is connected to each of the DC / DC converter circuits 150. The electronic control unit 200 is configured to separately control or regulate each DC / DC converter circuit 150, allowing independent control or regulation of each DC / DC converter circuit 150.

[0268] An electronic control unit 200 is connected to each of the DC chopper circuits 180. The electronic control unit 200 is configured to separately control or regulate each DC chopper circuit 180, allowing for independent control or regulation of each DC chopper circuit 180.

[0269] An alternative embodiment of the furnace power supply 100 further includes three DC second buffer circuits 160. Each second buffer circuit 160 is interposed between one DC / DC converter circuit 150 and one DC chopper circuit 180, thereby forming three electrically separate power sub-modules 510. Each power sub-module 510 includes one DC / DC converter circuit 150, one DC chopper circuit 180, and one second buffer circuit 160 interposed between one DC / DC converter circuit 150 and one DC chopper circuit 180.

[0270] 4 is connectable to three electrodes 120. Each power sub-module 510 is connectable to exactly one separate electrode 120, resulting in an independent power supply for each of the electrodes 120. In other words, there is a one-to-one assignment between one power sub-module 510 and one electrode 120.

[0271] An alternative embodiment (not shown) to the embodiment of the furnace power supply 100 of Figure 4 is connectable to three electrodes 120. Each power sub-module 510 includes one DC chopper circuit 180 instead of one DC / AC converter circuit 170. Each power sub-module 510 is connectable to exactly one separate electrode 120, resulting in an independent power supply for each of the electrodes 120. In other words, there is a one-to-one assignment between one power sub-module 510 and one electrode 120.

[0272] 5 comprises three AC / DC converter circuits 130 connected in parallel to one another. The AC / DC converter circuits 130 are connectable to a three-phase power network 110.

[0273] The AC / DC converter circuit 130 is connected to a DC / DC converter circuit 150 via a common first buffer circuit 140 .

[0274] An electronic control unit 200 is connected to each of the AC / DC converter circuits 130. The electronic control unit 200 is configured to separately control or regulate each AC / DC converter circuit 130, allowing for independent control or regulation of each AC / DC converter circuit 130. In this manner, the active power flow of the furnace power supply 100 can be better regulated.

[0275] In an alternative embodiment (not shown) to the embodiment of the furnace power supply 100 of FIG. 5, the power sub-modules 510 each include one DC chopper circuit 180 instead of one DC / AC converter circuit 170 .

[0276] An alternative embodiment of the furnace power supply 100 comprises three AC / DC converter circuits 130 connected in parallel to one another. The AC / DC converter circuits 130 are connectable to the three-phase power network 110.

[0277] The AC / DC converter circuit 130 is connected to a DC / DC converter circuit 150 via a common first buffer circuit 140 .

[0278] An electronic control unit 200 is connected to each of the AC / DC converter circuits 130. The electronic control unit 200 is configured to separately control or regulate each AC / DC converter circuit 130, allowing for independent control or regulation of each AC / DC converter circuit 130. In this manner, the active power flow of the furnace power supply 100 can be better regulated.

[0279] 6 includes three first buffer circuits 140. Each first buffer circuit 140 is interposed between one AC / DC converter circuit 130 and one DC / DC converter circuit 150, and establishes a one-to-one connection between exactly one AC / DC converter circuit 130 and exactly one DC / DC converter circuit 150.

[0280] The AC / DC converter circuit 130, the first buffer circuit 140, the DC / DC converter circuit 150, the second buffer circuit 160, and the DC / AC converter circuit 170 constitute a power module 500. The first buffer circuit 140 is interposed between the AC / DC converter circuit 130 and the DC / DC converter circuit 150. The second buffer circuit 160 is interposed between the DC / DC converter circuit 150 and the DC / AC converter circuit 170. Therefore, the furnace power supply apparatus 100 includes three power modules 500.

[0281] Each power module 500 is connectable to exactly one separate electrode 120, resulting in an independent power supply for each of the electrodes 120. In other words, there is a one-to-one assignment between one power module 500 and one electrode 120.

[0282] 6 includes three first buffer circuits 140. Each first buffer circuit 140 is interposed between one AC / DC converter circuit 130 and one DC / DC converter circuit 150, establishing a one-to-one connection between exactly one AC / DC converter circuit 130 and exactly one DC / DC converter circuit 150.

[0283] The AC / DC converter circuit 130, the first buffer circuit 140, the DC / DC converter circuit 150, the second buffer circuit 160, and the DC chopper circuit 180 form a power module 500. The first buffer circuit 140 is interposed between the AC / DC converter circuit 130 and the DC / DC converter circuit 150. The second buffer circuit 160 is interposed between the DC / DC converter circuit 150 and the DC chopper circuit 180. Thus, the furnace power supply apparatus 100 includes three power modules 500.

[0284] Each power module 500 is connectable to exactly one separate electrode 120, resulting in an independent power supply for each of the electrodes 120. In other words, there is a one-to-one assignment between one power module 500 and one electrode 120.

[0285] The system (not marked) for the supply of electrodes 120 of an electric arc furnace, an electric reduction furnace or a submerged arc resistance furnace of FIG. 7 comprises two or more furnace power supplies 100 connected in parallel with each other.

[0286] The system further comprises an electronic coordination and regulation unit 400. The electronic coordination and regulation unit 400 is connected to the furnace power supply 100.

[0287] The system further comprises an electrode adjuster 410 connectable to an electrode height adjustment means (not shown).

[0288] The electronic coordination and regulation unit 400 is configured to communicate with the electronic control unit 200 of the furnace power supply 100 and the electrode regulator 410 .

[0289] The system for supplying a plurality of electrodes 120 of an electric arc furnace, an electric reduction furnace or a submerged arc resistance furnace of Figure 8 (not marked) comprises a plurality of electrode regulators 410. Preferably, one electrode regulator 410 is connectable to only one height adjustment means (not shown) and each electrode 120 is provided with one height adjustment means.

[0290] Multiple power supplies 100 correspond to multiple electrodes 120. In other words, one power supply 100 can be connected to only one electrode 120, resulting in a one-to-one assignment between one furnace power supply 100 and one electrode 120. [Explanation of symbols]

[0291] 100 Furnace power supply device 110 Three-phase power network 120 electrodes 130 AC / DC converter circuit 140 first buffer circuit 150 DC / DC converter circuit 160 Second buffer circuit 170 DC / AC converter circuit 180 DC Chopper Circuit 200 Electronic Control Unit 300 DC power supply 400 Electrical Coordination and Coordination Unit 410 Electrode Adjuster 500 Power Module 510 Power Submodule

Claims

1. A furnace power supply (100) for supplying electrical energy to an electric arc furnace, an electric reduction furnace, or a submerged arc resistance furnace, comprising: - the furnace power supply (100) is connectable to a three-phase power network (110), preferably a medium-voltage three-phase power network (110); - the furnace power supply (100) is connectable to at least one electrode (120) of the electric arc furnace, the electric reduction furnace or the submerged arc resistance furnace; said furnace power supply (100) at least one AC / DC converter circuit (130) connectable to said three-phase power network (110) and configured to rectify alternating current of at least one phase of said three-phase power network (110), said three-phase power network (110) having a voltage level of 1000 VAC or greater; and at least one DC / DC converter circuit (150) configured to handle voltage levels of -500 VDC or greater, the DC / DC converter circuit (150) being connected to a DC side of the AC / DC converter circuit (130).

2. 2. The furnace power supply (100) according to claim 1, characterized in that the furnace power supply (100) comprises less than one transformer, preferably less than one step-down transformer, arranged between the three-phase power network (110) and at least one electrode (120).

3. 3. The furnace power supply (100) according to claim 1 or 2, characterized in that the AC / DC converter circuit (130) comprises at least one bidirectional AC / DC converter unit, preferably an active front-end circuit.

4. Furnace power supply (100) according to any one of claims 1 to 3, characterized in that the at least one DC / DC converter circuit (150) comprises at least one bidirectional DC / DC converter unit.

5. Furnace power supply (100) according to any one of claims 1 to 4, characterized in that at least one DC / DC converter circuit (150) comprises at least one galvanically isolated DC / DC converter unit.

6. Furnace power supply (100) according to any one of claims 1 to 5, characterized in that the at least one DC / DC converter circuit (150) comprises at least one switching DC / DC converter unit.

7. At least one first buffer circuit (140) of direct current is interposed between the AC / DC converter circuit (130) and the DC / DC converter circuit (150); 7. The furnace power supply (100) of claim 1, wherein the first buffer circuit (140) connects the AC / DC converter circuit (130) and the DC / DC converter circuit (150), and is configured to store energy and provide isolation between the three-phase power network (110) and the at least one electrode (120).

8. 8. The furnace power supply (100) according to any one of claims 1 to 7, characterized in that at least one DC power source (300), preferably a renewable DC power source (300), is connectable to the first buffer circuit (140).

9. The furnace power supply (100) according to any one of claims 1 to 8, characterized in that the furnace power supply (100) comprises a plurality of AC / DC converter circuits (130) connected in parallel with each other, and the AC / DC converter circuits (130) are connected to a common first buffer circuit (140), preferably to a plurality of first buffer circuits (140).

10. 10. The furnace power supply system (100) of claim 1, wherein at least one second buffer circuit (160) of direct current is interposed between the DC / DC converter circuit (150) and the at least one electrode (120) and at least indirectly connects the DC / DC converter circuit (150) and the at least one electrode (120), the second buffer circuit (160) being configured to store energy and to provide isolation between the three-phase power network (110) and the at least one electrode (120).

11. 11. The furnace power supply system (100) according to claim 1, further comprising an electronic control unit (200), the electronic control unit (200) being connectable to the AC / DC converter circuit (130) and configured to regulate the active power flow of the furnace power supply system (100).

12. 12. The furnace power supply (100) according to claim 1, characterized in that the furnace power supply (100) comprises at least one DC / AC converter circuit (170) configured to supply electrical energy to at least one electrode (120), and the at least one DC / DC converter circuit (150) is connected to the at least one DC / AC converter circuit (170).

13. 12. The furnace power supply (100) according to claim 1, characterized in that the furnace power supply (100) comprises at least one DC chopper circuit (180) configured to supply electrical energy to at least one electrode (120), and at least one DC / DC converter circuit (150) is connected to the at least one DC chopper circuit (180).

14. 1. A system for supplying electrical energy to at least one electric arc furnace and / or electric reduction furnace and / or submerged arc resistance furnace, comprising: - said system is connectable to at least one three-phase power network (110); - said system is connectable to at least one electrode (120) of at least one electric arc furnace and / or electroreduction furnace and / or submerged arc resistance furnace; - the system comprises a plurality of furnace power supplies (100) according to any one of claims 1 to 13, a plurality of said furnace power supplies (100) are connected in parallel with one another.

15. 15. An electric arc furnace, an electric reduction furnace or a submerged arc resistance furnace, characterized in that the electric arc furnace, the electric reduction furnace or the submerged arc resistance furnace is provided with a furnace power supply (100) according to any one of claims 1 to 13 and / or a system according to claim 14.

16. Use of a furnace power supply (100) according to any one of claims 1 to 13 for supplying electrical energy to at least one electric arc furnace and / or electric reduction furnace and / or submerged arc resistance furnace.

17. 16. A method for operating an electric arc furnace or an electroreduction furnace or a submerged arc resistance furnace, in particular an electric arc furnace or an electroreduction furnace or a submerged arc resistance furnace according to claim 15, characterized in that the ratio of active power flow to reactive power flow is controlled and / or regulated by influencing controlled variables of the AC / DC converter circuit (130) and / or the DC / DC converter circuit (150) and / or the DC / AC converter circuit (170) and / or the DC chopper circuit (180), in particular the reactive power flow is minimized by influencing controlled variables of the AC / DC converter circuit (130) and / or the DC / AC converter circuit (170).

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