Device for supplying an electric furnace with electrical energy, system, electric furnace and method for controlling an electric furnace

Abstract

The invention relates to a device (1) for supplying an electric oven (2) with electrical energy, wherein the device (1) comprises a first DC / DC converter (10) and a second DC / DC converter (20), wherein the first and the second DC / DC converter (10, 20) are electrically connected to each other in a series circuit, and wherein exactly one electrical pole of the output side of the first DC / DC converter (10) is electrically connected without load to exactly one electrical pole of the output side of the second DC / DC converter (20), the two electrical poles being configured to have the same polarity. The invention further relates to a system (100), an electric oven (2), and a method for controlling an electric oven (2).

Description

The present invention relates to a device for supplying an electric oven with electrical energy, a system for supplying an electric oven with electrical energy, an electric oven and a method for controlling an electric oven. Metals, especially steel, are regularly heated and melted by an electric arc in electric furnaces. Such an electric furnace can be operated with direct current (DC), alternating current (AC), or multi-phase alternating current. Typically, at least one electrode is used, which protrudes through the furnace lid into the crucible of the electric furnace. Additional electrodes can be arranged either adjacent to this electrode or in the base of the crucible of the electric furnace. Electric furnaces represent a highly nonlinear electrical load, meaning that operating an electric furnace can lead to undesirable stresses on the electrical supply network. These stresses can cause electrical network distortions, particularly flicker, higher harmonic currents, and similar issues. One of the problems underlying the present invention is to provide a device with which the aforementioned undesirable network feedback can be reduced or prevented. This problem underlying the present invention is achieved by a device according to claim 1. Preferred embodiments are described in the dependent claims. More precisely, the problem underlying the present invention is solved according to a first aspect of the invention by a device for supplying an electric oven with electrical energy, wherein the device comprises a first DC / DC converter unit configured to provide two electrical poles at its output side; a second DC / DC converter unit configured to provide two electrical poles at its output side; wherein the first and the second DC / DC converter units are electrically connected to each other in a series circuit; and wherein exactly one electrical pole of the output side of the first DC / DC converter unit is electrically connected without load to exactly one electrical pole of the output side of the second DC / DC converter unit, wherein the two electrical poles are configured to have the same polarity. When the intended use of the device is mentioned below, this refers to the use of the device to supply an electric oven with electrical energy. Such a device offers the advantage that, when used as intended, unwanted network feedback from the operation of an electric furnace can be reduced. In particular, it is possible to reduce the total harmonic distortion, thus simultaneously increasing energy efficiency by improving the power factor of the electrical power transmission, in addition to reducing unwanted network feedback. Finally, the device can provide alternating current by having only one of the two DC / DC converter units provide a second voltage level at any given time.Because the first and second DC / DC converter units are each electrically connected to each other with a pole of the same polarity in a load-free manner, the device can, for example, initially provide a second voltage level with the shape of the first half-wave of a sine wave when used as intended. At the same time, the second DC / DC converter unit merely provides a freewheeling path for the current. To generate a complete sine wave, the second DC / DC converter unit can then immediately generate a second voltage level with the shape of the second half-wave of the sine wave, while the first DC / DC converter unit again provides a freewheeling path for the current.In other words, during the operation of an electric oven, only the switching elements of one DC / DC converter unit are in regular switching operation, while the switching elements of the other DC / DC converter unit are in a constant switching state. During these constant switching states, the switching elements can also be cooled more effectively due to the lower thermal stress, thus further increasing the overall efficiency of the electrical power transfer of the device. A DC / DC converter is an electrical device that converts a direct current with a first voltage level into a direct current with a second voltage level. Specifically, a DC / DC converter can vary the second voltage level between 0 V and a maximum operating value, where the maximum operating value is a positive voltage. Alternatively, a DC / DC converter can vary the second voltage level between 0 V and a minimum operating value, where the minimum operating value is a negative voltage. In other words, a single DC / DC converter cannot provide an alternating current, especially not a voltage with a zero crossing. In this invention, a first voltage level is the voltage level of a current entering a DC / DC converter in the direction of electrical energy transport. In other words, the first voltage level is the voltage level present at an input side of the DC / DC converter. The current entering the DC / DC converter can transport electrical energy from an electrical energy source, for example, a three-phase power grid and / or a direct current source (DC source), to a load, for example, an electric oven. The input side of a DC / DC converter is preferably oriented towards an electrical energy source. In other words, the input side of a DC / DC converter is located upstream of the output side of the DC / DC converter in the current flow direction from an electrical energy source through the DC / DC converter to a load. In this invention, a second voltage level is the voltage level of a current exiting a DC / DC converter in the direction of electrical energy transport. In other words, the second voltage level is the voltage level present at the output side of the DC / DC converter. The current exiting the DC / DC converter can transport electrical energy from an electrical energy source, for example, a three-phase power grid and / or a DC power source, to a load, for example, an electric oven. The output side of a DC / DC converter is preferably located away from an electrical energy source. In other words, in the current flow direction from an electrical energy source through the DC / DC converter to a load, the output side of a DC / DC converter is located downstream of the input side of the DC / DC converter. A first voltage level can be higher or lower than a second voltage level. Alternatively, a first voltage level can be equal to a second voltage level. A second voltage level can vary over time. For example, a second voltage level can exhibit the shape of a half-sine wave. A DC / DC converter device can have a variety of switching elements and / or a variety of non-switching elements. These switching elements and / or non-switching elements can be connected in series and / or parallel. A switching element and / or a non-switching element can be a semiconductor device. A switching element can be 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-strengthened gate transistor (IEGT), and / or an insulated-gate bipolar transistor (IGBT). A non-switching element can be a diode. Since a switching element in a DC / DC converter is either completely on or off, its losses are low, allowing the DC / DC converter to have high efficiency. The switching frequency of a DC / DC converter can be greater than or equal to 1 kHz, preferably greater than or equal to 2 kHz, and particularly preferably greater than or equal to 5 kHz. Advantageously, a DC / DC converter can have a switching frequency greater than or equal to 10 kHz, preferably greater than or equal to 15 kHz, and particularly preferably greater than or equal to 20 kHz. This allows for advantageous arc stabilization. The switching frequency is preferably the switching rate at which a switching element can be moved between its open and closed positions within a given time interval. An electrical pole is one of two points between which an electrical voltage exists. Polarity is the assignment of electrical poles between which a voltage exists. In other words, polarity determines which of the two electrical poles is the positive pole and which is the negative pole. The polarity of one electrical pole of a DC / DC converter device is preferably determined with respect to the other electrical pole of the same DC / DC converter device. If two DC / DC converter devices are electrically connected to each other via one electrical pole without a load, preferably no electrical load, such as an electric oven, is arranged between these two electrical poles. In other words, two electrically connected poles without a load are preferably directly connected to each other by means of cables and / or busbars. The two electrically conductive poles of the first and second DC / DC converter units, when connected without a load, preferably have the same polarity. For example, the two electrically conductive poles connected without a load are configured as either the positive or the negative pole. When two DC / DC converter devices are electrically connected in a series circuit, an electric current preferably always flows through both DC / DC converter devices, at least section by section, during the intended use of the device during the operation of an electric oven. A DC / DC converter device can be designed as a galvanically isolated converter device and / or have galvanic isolation. A DC / DC converter device can have a housing that at least partially, and preferably completely, isolates the DC / DC converter device from its environment. In other words, the DC / DC converter device can be an integral component. The device can be electrically connectable to, or be electrically connected to, an electrical power source and at least one electrode of an electric furnace. An electrical power source can have, or be configured as, a three-phase power supply. A three-phase power supply provides alternating current (AC), in particular three alternating currents, each alternating current having a phase difference of +120 degrees to one of the other two alternating currents and a phase difference of -120 degrees to the other alternating current. The three-phase power supply can be a high-voltage three-phase network, a medium-voltage three-phase network, or a low-voltage three-phase network. High voltage can be greater than or equal to 36 kV, preferably greater than or equal to 60 kV, and particularly greater than or equal to 100 kV. Furthermore, high voltage can advantageously be greater than or equal to 150 kV, preferably greater than or equal to 200 kV, and particularly preferably greater than or equal to 300 kV. More advantageously, high voltage can be greater than or equal to 400 kV, preferably greater than or equal to 700 kV, and particularly preferably greater than or equal to 1100 kV. Medium voltage can be less than or equal to 36 kV. Furthermore, medium voltage can advantageously be less than or equal to 30 kV, preferably less than or equal to 20 kV, and particularly preferably less than or equal to 15 kV. Medium voltage can be greater than or equal to 1 kV, preferably greater than or equal to 2 kV, and particularly preferably greater than or equal to 10 kV. Furthermore, medium voltage can advantageously be greater than or equal to 15 kV, preferably greater than or equal to 20 kV, and particularly preferably greater than or equal to 30 kV. Low voltage can be greater than or equal to 50 V, preferably greater than or equal to 60 V, and particularly preferably greater than or equal to 100 V. Further advantageously, low voltage can be greater than or equal to 120 V, preferably greater than or equal to 220 V, and particularly preferably greater than or equal to 240 V. Low voltage can be less than or equal to 1,000 V, particularly preferably less than or equal to 900 V. Furthermore, low voltage can advantageously be less than or equal to 600 V, preferably less than or equal to 240 V, and particularly preferably less than or equal to 220 V. Preferably, the voltage levels can be defined according to IEC 60038. Particularly preferably, the voltage levels can be defined according to Table 1, Table 3 and Table 4 of IEC 60038. Alternatively or additionally, an electrical energy source can be, or include, a direct current (DC) source. The DC source can include, or be configured as, one or more batteries. An electric furnace can be an electric arc furnace, an electric reduction furnace, an immersion arc resistance furnace and / or any other electric furnace suitable for melting metallic or non-metallic materials. An electrode is an electrical conductor used to establish contact with a part of an electrical circuit, in particular an electric furnace, and especially with a non-metallic part of the circuit. The non-metallic part of the circuit may correspond to the atmosphere of the electric furnace. An electrode of an electric arc furnace can be arranged on the top of the furnace. Preferably, a top-mounted electrode is connected to a height adjustment device, allowing the distance of the electrode to a metal material and / or a molten metal material in the electric arc furnace to be varied. Such a change can be controlled and / or regulated by an electrode controller. The device can include an electrode controller and be data-connected to it. A second electrode can be arranged in a furnace vessel of an electric furnace or be a component of the inner wall, in particular a bottom wall, of the furnace vessel. The second electrode can also be arranged on the top of the electric furnace and preferably also be connected to a height adjustment device. An electric oven can also have three, four, or more electrodes. Each electrode can be connected to a height adjustment device. An electric oven can be operated with direct current (DC) or with alternating current (AC), preferably with multi-phase alternating current. Preferably, the other electrical pole of the output side of the first DC / DC converter is electrically connectable to, or electrically conductively connected to, an electric oven. Preferably, the other electrical pole of the output side of the second DC / DC converter is electrically connectable to, or electrically conductively connected to, an electric oven. In particular, the first DC / DC converter and the second DC / DC converter are electrically connectable to, or electrically conductively connected to, an electric oven via their electrical poles. Preferably, the first DC / DC converter and the second DC / DC converter are electrically connected to each other without a load solely via one of their electrical poles. The other electrical pole of each DC / DC converter is preferably electrically conductively connected to each other via an electrical load, for example, an electric oven. The device is preferably configured to supply an electric oven with an alternating voltage, preferably a single-phase alternating voltage. The device can also be configured to supply an electric oven with a multi-phase alternating voltage. Preferably, the device is designed such that it has a first DC source which is electrically conductively connected to the first DC / DC converter device; and a second DC source which is electrically conductively connected to the second DC / DC converter device; wherein the first DC source is galvanically isolated from the second DC source. A device designed in this way has the advantage that, when used as intended, it offers improved protection against short circuits caused by a common earth potential. Galvanic isolation can be achieved by means of a first and a second galvanically isolated DC / DC converter, wherein the first galvanically isolated DC / DC converter is electrically conductively connected to the first DC / DC converter unit and the second galvanically isolated DC / DC converter is electrically conductively connected to the second DC / DC converter unit. Galvanic isolation can be achieved by means of one or more magnetic fields. In this application, the terms DC source and direct current source are used synonymously. One of the DC / DC converter devices may have a half-bridge circuit. A device designed in this way has the advantage of being particularly cost-effective to manufacture. A half-bridge circuit is a common basic component available in many different and, in particular, standardized configurations, making it possible to manufacture a DC / DC converter device incorporating a half-bridge circuit very cost-effectively. A half-bridge circuit has at least two switching elements, preferably two semiconductor components. Preferably, a DC / DC converter device comprises a plurality of half-bridge circuits connected in series and / or parallel to each other. Preferably, a DC / DC converter device consists of a single half-bridge circuit. Preferably, a DC / DC converter device consists of a plurality of half-bridge circuits connected in series and / or parallel to each other. According to a preferred embodiment, the first DC / DC converter device and the second DC / DC converter device each have a half-bridge circuit, preferably a plurality of half-bridge circuits. One of the DC / DC converter devices may include a buck converter circuit. A device designed in this way has the advantage that it can be manufactured even more cost-effectively. A buck converter circuit is a common basic circuit that is available as a finished component. According to a preferred embodiment, the first DC / DC converter device and the second DC / DC converter device each have a buck converter circuit, preferably a plurality of buck converter circuits. Preferably, each DC / DC converter device has one or more coils on its output side for smoothing a current. The buck converter circuit can have at least two switching elements. A device designed in this way has the advantage that, when used as intended, a free-running path for current flow in both directions is ensured. This allows unwanted network feedback from the operation of an electric furnace to be significantly reduced. Preferably, the device is designed such that the device has a first DC source which has a first rectifier circuit, wherein the first rectifier circuit is electrically connected to the first DC / DC converter device; and a second DC source which has a second rectifier circuit, wherein the second rectifier circuit is electrically connected to the second DC / DC converter device. A rectifier circuit can be configured as a unidirectional or a bidirectional converter. A unidirectional converter allows electrical energy to flow in one direction and blocks electrical energy in the opposite direction. This means that electrical energy can flow from an electrical energy source, for example, a three-phase power grid, to a load, preferably an electric oven, but cannot flow from a load to an electrical energy source. Alternatively, electrical energy can flow from a load, preferably an electric oven, to an electrical energy source, preferably a three-phase power grid, but cannot flow from an electrical energy source to a load. A bidirectional converter allows electrical energy to flow in essentially both directions.For example, electrical energy can flow from an electrical energy source, such as a three-phase power grid, to a load, preferably an electric oven, and from a load, preferably an electric oven, to an electrical energy source, preferably a three-phase power grid. A rectifier circuit designed as a bidirectional converter can also be called an Active Front End (AFE). Such a rectifier circuit can have a variety of switching elements and / or non-switching elements, in particular semiconductor components. A rectifier circuit can include an uncontrolled diode bridge. Such a unidirectional converter can also be referred to as a diode front end (DFE). In particular, a rectifier circuit can be configured as a three-phase rectifier circuit, preferably as a 6-pulse rectifier circuit, and more preferably as a B6 bridge circuit. Preferably, the device is designed such that the first DC source has a first DC intermediate circuit comprising a capacitor and / or an inductor, which electrically connects the first rectifier circuit and the first DC / DC converter device; and / or the second DC source has a second DC intermediate circuit comprising a capacitor and / or an inductor, which electrically connects the second rectifier circuit and the second DC / DC converter device. Such a device offers the advantage that, when used as intended, unwanted network feedback can be further reduced. Electrical energy can be stored in the DC link, thus achieving electrical decoupling between an electric furnace connected via the device and an electrical power source. The electrical energy stored in the DC link can then act as a buffer between the electric furnace and the power source, temporarily compensating for fluctuations in the furnace's power supply caused by its operation. The first and / or second DC link can contain a number of capacitors and / or inductors. The capacitors and / or inductors can be connected in series and / or parallel to each other. Preferably, the device is designed such that the device has a three-phase transformer, wherein the three-phase transformer has a first secondary winding which is electrically conductively connected to the first DC / DC converter device; and has a second secondary winding which is electrically conductively connected to the second DC / DC converter device. A device designed in this way has the advantage that, when used as intended, it offers improved protection against short circuits caused by a common earth potential. The first secondary winding is preferably galvanically isolated from the second secondary winding. The first and second secondary windings are preferably galvanically isolated from a primary winding of the three-phase transformer. The first secondary winding can be electrically connected to the first DC source. The second secondary winding can be electrically connected to the second DC source. Preferably, the device is designed such that the device has a first and a second three-phase transformer, wherein the first three-phase transformer has a first secondary winding which is electrically conductively connected to the first DC / DC converter device; and the second three-phase transformer has a second secondary winding which is electrically conductively connected to the second DC / DC converter device. A device designed in this way has the advantage that, when used as intended, it offers even better protection against short circuits caused by a common earth potential. The first secondary winding of the first three-phase transformer is preferably electrically connected to the first DC source. The second secondary winding of the second three-phase transformer is preferably electrically connected to the second DC source. One of the DC / DC converter devices may include a semiconductor device, wherein the semiconductor device comprises silicon and / or gallium. A device designed in this way has the advantage that, when used as intended, an electric oven can be supplied with electrical energy at an increased voltage. Semiconductor components containing silicon and / or gallium can be operated at an increased voltage and also exhibit increased temperature resistance. The semiconductor device can contain silicon carbide (SiC) and / or gallium nitride (GaN). Preferably, the device is configured such that it comprises a third DC / DC converter unit configured to provide two electrical poles at its output side; a fourth DC / DC converter unit configured to provide two electrical poles at its output side; wherein the third and fourth DC / DC converter units are electrically connected to each other in a series circuit; wherein exactly one electrical pole of the output side of the third DC / DC converter unit is electrically connected without load to exactly one electrical pole of the output side of the fourth DC / DC converter unit, wherein the two electrical poles are configured to have the same polarity; and wherein the third and fourth DC / DC converter units are connected in parallel and / or in series with the first and second DC / DC converter units. A device designed in this way has the advantage that, when used as intended, an electric oven can be supplied with an increased amount of electrical energy. By connecting the third and fourth DC / DC converter units in series with the first and second DC / DC converter units, the voltage level at which the electric oven is supplied with electrical energy via the device can be increased. By connecting the third and fourth DC / DC converter units in parallel with the first and second DC / DC converter units, the current at which the electric oven is supplied with electrical energy via the device can be increased. The two electrically conductive poles of the third and fourth DC / DC converter units, which are connected to each other without a load, preferably have the same polarity. For example, both electrical poles are configured as either the positive or the negative pole. The first DC / DC converter device, the second DC / DC converter device, the third DC / DC converter device and the fourth DC / DC converter device are preferably configured to supply an equal electrode of an electric furnace with a single-phase alternating electrical voltage and a single-phase alternating electrical current. Preferably, the device is designed such that it has a control and regulating device which is operatively connected to the DC / DC converter devices, wherein the control and regulating device is configured to control the DC / DC converter devices in such a way that the device can supply an electric oven with an alternating voltage. A device designed in this way has the advantage that, when used as intended, an electric furnace can be supplied with alternating current using DC / DC converters, which are normally used to supply electric furnaces with direct current. The associated standardization and scaling effects allow such a device to be manufactured more cost-effectively. Preferably, the control device is configured to alternately activate and deactivate the first DC / DC converter and the second DC / DC converter, so that one of the DC / DC converters is activated and the other deactivated at any given time. This makes it possible to provide alternating current. When a DC / DC converter is activated, its switching elements are in switching mode, meaning they are moved between their open and closed positions at a specific switching frequency. When a DC / DC converter is deactivated, its switching elements are in a constant switching state. In other words, for example, while a DC / DC converter is deactivated, one switching element is in its open position and another is in its closed position. The problem underlying the present invention is further solved according to a second aspect by a system for supplying an electric oven with electrical energy; wherein the system is electrically connectable to an electrical energy source and an electrode of the electric oven; wherein the system comprises a plurality of devices according to the first aspect; and wherein the devices are interconnected in a star connection or in a delta connection. A system designed in this way offers the advantage that, when used as intended, unwanted network feedback from the operation of an electric furnace can be reduced. In particular, it is possible to reduce the total harmonic distortion, thus simultaneously increasing energy efficiency by improving the power factor of the electrical power transmission, in addition to reducing unwanted network feedback. Finally, such a system can reduce the thermal load on the switching elements of the DC / DC converter devices, thereby enabling increased overall efficiency of the electrical power transmission. The system is preferably configured such that the devices are interconnected in a star or delta connection on the output side. An output side of a device is preferably located away from an electrical power source. In other words, the output side of a device is located downstream of an input side of the device in the direction of current flow from an electrical power source through the device to a load. Conversely, the input side of a device is preferably located towards an electrical power source. In other words, the input side of a device is located upstream of the output side of the device in the direction of current flow from an electrical power source through the device to a load. If the devices are connected in a star configuration at the output, the supply voltage to an electric oven can be increased. If the devices are connected in a delta configuration at the output, the supply current to an electric oven can be increased. Preferably, the system is connectable to or connected with more than one electrode, in particular with two or three electrodes of the electric furnace. According to a preferred embodiment, the system comprises at least three devices according to the first aspect of the invention, wherein each device is electrically connectable to or connected with exactly one electrode of the electric furnace, and wherein each electrode of the electric furnace is electrically connectable to or connected with at least one device. The system can be connected to an electric oven using either a three-cable or a four-cable system. It should be noted that features of the first aspect of the invention can also be combined with the second aspect of the invention, both individually and cumulatively. Accordingly, advantages described for the first aspect of the invention also apply to the second aspect of the invention. The problem underlying the present invention is further solved according to a third aspect by an electric oven, wherein the electric oven has one or more than one device according to the first aspect, or a system according to the second aspect, wherein the electric oven is operable with an alternating current. An electric furnace designed in this way offers the advantage of reducing unwanted network feedback during operation. In particular, it is possible to reduce the total harmonic distortion, thus simultaneously increasing energy efficiency by improving the power factor of the electrical power transmission. Finally, such an electric furnace reduces the thermal stress on the switching elements of the DC / DC converter devices, thereby enabling increased overall efficiency of the electrical power transmission. It should be noted that features of the first aspect and / or the second aspect of the invention can also be combined with the third aspect of the invention, both individually and cumulatively. Advantages described for the first aspect and / or the second aspect of the invention accordingly also apply to the third aspect of the invention. The problem underlying the present invention is further solved according to a fourth aspect by a method for controlling an electric oven according to the third aspect wherein the second DC / DC converter device is deactivated when the first DC / DC converter device is activated. It should be noted that features of the first aspect and / or the second aspect and / or the third aspect of the invention can also be combined with the fourth aspect of the invention, both individually and cumulatively. Accordingly, advantages achieved for the first aspect and / or the second aspect and / or the third aspect of the invention also apply to the fourth aspect of the invention. Further advantages, details and features of the present invention are explained in the description of the following embodiments: Fig. 1: a schematic representation of a device according to a first embodiment; and Fig. 2: a schematic representation of a system according to a second embodiment. In the following description, identical reference symbols denote identical features, so that the description of a feature with reference to one figure also applies to the other figures and the repetition of the respective feature is omitted. Fig. 1 shows a device 1 for supplying electrical energy to an electric oven 2 (not shown in Fig. 1), comprising a first DC / DC converter 10, which is configured to provide two electrical poles at its output side, and a second DC / DC converter 20, which is configured to provide two electrical poles at its output side. The first and the second DC / DC converter 10, 20 are electrically connected to each other in a series circuit, wherein exactly one electrical pole of the output side of the first DC / DC converter 10 is electrically connected without load to exactly one electrical pole of the output side of the second DC / DC converter 20, wherein the two electrical poles are configured to have the same polarity, in this case a positive polarity. Fig. 2 shows a system 100 for supplying an electric furnace 2 with electrical energy, wherein the system 100 is electrically connected to an electrical energy source 60 and an electrode of the electric furnace 2, wherein the system 100 has three devices 1, wherein the devices 1 are connected to each other in a star connection on the output side. Each device 1 has a first DC source 30 comprising a first rectifier circuit 31 and a first DC link 32, which electrically connects the first rectifier circuit 31 to the first DC / DC converter unit 10. Each device 1 also has a second DC source 40 comprising a second rectifier circuit 41 and a second DC link 42, which electrically connects the second rectifier circuit 41 to the second DC / DC converter unit 20. Each device 1 has a three-phase transformer 50, wherein each three-phase transformer 50 has a first secondary winding and a second secondary winding. The first secondary winding is electrically conductively connected to the first rectifier circuit 31 and the second secondary winding is electrically conductively connected to the second rectifier circuit 41. The electrical positive terminal of the output side of the first DC / DC converter device 10 of a device 1 is electrically conductively connected to the electrical positive terminal of the output side of the second DC / DC converter device 20 of the same device 1 without load. Reference symbol list 1 Device 2 Electric oven 10 First DC / DC converter unit 20 Second DC / DC converter unit 30 First DC source 31 First rectifier circuit 32 First DC link 40 Second DC source 41 Second rectifier circuit 42 Second DC link 50 Three-phase transformer 60 Electrical power source 100 System

Claims

Device (1) for supplying an electric oven (2) with electrical energy, comprising: - a first DC / DC converter device (10) configured to provide two electrical poles at its output side; - a second DC / DC converter device (20) configured to provide two electrical poles at its output side; - wherein the first and the second DC / DC converter devices (10, 20) are electrically connected to each other in a series circuit; and - wherein exactly one electrical pole of the output side of the first DC / DC converter device (10) is electrically connected without load to exactly one electrical pole of the output side of the second DC / DC converter device (20), wherein the two electrical poles are configured to have the same polarity. Device (1) according to claim 1, characterized in that the device (1)- has a first DC source (30) which is electrically conductively connected to the first DC / DC converter device (10); and- has a second DC source (40) which is electrically conductively connected to the second DC / DC converter device (20);- wherein the first DC source (30) is galvanically isolated from the second DC source (40). Device (1) according to one of the preceding claims, characterized in that one of the DC / DC converter devices (10, 20) has a half-bridge circuit. Device (1) according to one of the preceding claims, characterized in that one of the DC / DC converter devices (10, 20) has a buck converter circuit. Device (1) according to claim 4, characterized in that the buck converter circuit has at least two switching elements. Device (1) according to one of the preceding claims, characterized in that the device (1)- has a first DC source (30) comprising a first rectifier circuit (31), wherein the first rectifier circuit is electrically connected to the first DC / DC converter device (10); and- has a second DC source (40) comprising a second rectifier circuit (41), wherein the second rectifier circuit is electrically connected to the second DC / DC converter device (20). Device (1) according to claim 6, characterized in that: - the first DC source (30) has a first DC intermediate circuit (32) comprising a capacitor and / or an inductor, which electrically connects the first rectifier circuit (31) and the first DC / DC converter device (10); and / or - the second DC source (40) has a second DC intermediate circuit (42) comprising a capacitor and / or an inductor, which electrically connects the second rectifier circuit (41) and the second DC / DC converter device (20). Device (1) according to one of the preceding claims characterized in that the device (1) has a three-phase transformer (50), wherein the three-phase transformer (50) has a first secondary winding which is electrically conductively connected to the first DC / DC converter device (10); and a second secondary winding which is electrically conductively connected to the second DC / DC converter device (20). Device (1) according to one of claims 1 to 7, characterized in that the device (1) has a first and a second three-phase transformer (50), wherein - the first three-phase transformer (50) has a first secondary winding which is electrically conductively connected to the first DC / DC converter device (10); and - the second three-phase transformer (50) has a second secondary winding which is electrically conductively connected to the second DC / DC converter device (20). Device (1) according to one of the preceding claims, characterized in that one of the DC / DC converter devices (10, 20) has a semiconductor device, wherein the semiconductor device has silicon and / or gallium. Device (1) according to one of the preceding claims, characterized in that the device (1) - comprises a third DC / DC converter device configured to provide two electrical poles at its output side; - comprises a fourth DC / DC converter device configured to provide two electrical poles at its output side; - wherein the third and the fourth DC / DC converter devices are electrically connected to each other in a series circuit; - wherein exactly one electrical pole of the output side of the third DC / DC converter device is electrically connected without load to exactly one electrical pole of the output side of the fourth DC / DC converter device, wherein the two electrical poles are configured to have the same polarity; and - wherein the third and the fourth DC / DC converter devices are connected in parallel and / or in series with the first and the second DC / DC converter devices (10, 20). Device (1) according to one of the preceding claims, characterized in that the device (1) has a control and regulating device which is operatively connected to the DC / DC converter devices (10, 20), wherein the control and regulating device is configured to control the DC / DC converter devices (10, 20) in such a way that the device (1) can supply an electric oven (2) with an alternating voltage. System (100) for supplying an electric furnace (2) with electrical energy,- wherein the system (100) is electrically connectable to an electrical energy source (60) and an electrode of the electric furnace (2);- wherein the system (100) comprises a plurality of devices (1) according to one of the preceding claims; and- wherein the devices (1) are interconnected in a star connection or in a delta connection. Electric oven (2), wherein the electric oven (2) comprises one or more than one device (1) according to one of claims 1 to 12, or a system (100) according to claim 13, characterized in that the electric oven (2) is operable with alternating current. Method for controlling an electric oven (2) according to claim 14, characterized in that the second DC / DC converter device (20) is deactivated when the first DC / DC converter device (10) is activated.

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