Device for supplying an electric oven with electrical energy, electric oven and use of a device

Abstract

The invention relates to a device (10) for supplying an electric oven (90) with electrical energy, wherein the device (10) is electrically connectable to a power grid (100), preferably a three-phase power grid, and to at least one electrode (91) of the electric oven (90); wherein the device (10) comprises at least one power module (20), the power module (20) comprising a rectifier stage (30) configured to be electrically connected to fewer than three phases, in particular fewer than three different phases, of the power grid (100); an inverter stage (40) electrically connectable to at least one electrode of the electric oven (90); and a DC link (50), the DC link (50) electrically connecting the rectifier stage (30) to the inverter stage (40) of the power module (20).

Description

[0001] The present invention relates to a device for supplying an electric oven with electrical energy, an electric oven comprising this device, and a use of such a device for supplying an electric oven with electrical energy.

[0002] Metals, especially steel and metal ores, are regularly melted and heated by an electric arc in an electric furnace. These electric furnaces are 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 roof into the furnace vessel, while the other electrodes are positioned according to the first electrode or are located in the base of the furnace vessel.

[0003] Electric furnaces are typically operated with specialized power supply systems to provide the required amount of electrical energy and to mitigate the highly nonlinear loads on the power grid during furnace operation. To reduce these nonlinear loads, power supply systems for electric furnaces are typically designed to provide at least partial isolation between the furnace and the supplying power grid. This helps to reduce unwanted electrical grid distortions, particularly flicker and higher harmonic currents, and to minimize reactive power injection and similar issues on the grid.

[0004] The invention is based on the objective of providing an improvement to the prior art.

[0005] According to a first aspect of the invention, the problem is solved by a device for supplying an electric oven with electrical energy, wherein the device is electrically connectable to a power grid, preferably a three-phase power grid and at least one electrode of the electric oven; wherein the device comprises at least one power module, the power module comprising a rectifier stage configured to be electrically connected to fewer than three phases, in particular fewer than three different phases of the power grid; an inverter stage electrically connectable to at least one electrode of the electric oven; and a DC link, wherein the DC link electrically connects the rectifier stage to the inverter stage of the power module.

[0006] In the following, the term “intended use of the device” is used to describe the use of the device to supply an electric oven with electrical energy during the operation of the electric oven.

[0007] A device designed in this way offers the advantage of increased resilience to fluctuations in power consumption during the operation of an electric furnace, leading to increased furnace availability. When used as intended, an electric furnace generates significant power fluctuations due to arc instabilities during the melting process. These arc instabilities often affect more than one electrode of the electric furnace. In the event of an arc interruption between one electrode and the metal, the impact on arcs at other electrodes is reduced because each arc is supplied by at least one other phase of the power supply. Furthermore, such a device requires fewer switching devices, particularly compared to a conventional three-phase system for supplying an electric furnace.In this way, the complexity of controlling the device when supplying an electric oven with electrical energy can be reduced even further.

[0008] A power grid is preferably a multi-phase system used for electricity generation, transmission, and distribution. A power grid preferably supplies alternating current (AC). The power grid can be a three-phase grid supplying 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.

[0009] The power grid can be a high-voltage grid, a medium-voltage grid, or a low-voltage grid.

[0010] High voltage can be greater than or equal to 36 kV, preferably greater than or equal to 60 kV, and particularly preferably 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. Moreover, high voltage can advantageously 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.

[0011] 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.

[0012] The 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, the 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.

[0013] 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.

[0014] Low voltage can be less than or equal to 1,000 V and 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.

[0015] 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.

[0016] An electric furnace can be an electric arc furnace, an electric reduction furnace, an immersion arc furnace and / or any other electric furnace suitable for melting metallic or non-metallic materials.

[0017] An electrode is an electrical conductor used to make 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 inside the electric furnace.

[0018] An electrode can be made of high-density graphite and / or tungsten. An electrode can be designed to transfer electrical energy and form arcs between the tip and the charge material. An electrode can be a pre-fired electrode or a self-baking electrode (Soederberg electrode) and / or an extrusion / composite electrode, which is a combination of a Soederberg electrode with a pre-fired electrode as its core and / or a hollow electrode system that allows the charging of fines through the central hole (pre-fired, self-baking). The choice of electrode type may depend on factors such as electrode size, the material / metallurgy used, and economic aspects like operating costs.

[0019] An electrode of an electric arc furnace can be arranged at 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 molten metal material located in a furnace vessel of the electric arc furnace to be varied. Such a change can be controlled and / or regulated by an electrode controller.

[0020] A second and / or a third electrode can be arranged in a furnace vessel of an electric furnace. The second and / or the third electrode can also be arranged on the top of the electric furnace and preferably be connected to a height adjustment mechanism. An electric furnace can have four or more electrodes. Each electrode can be connected to a height adjustment device.

[0021] An electric oven can be operated with alternating current (AC), in particular with single-phase alternating current and / or with multi-phase alternating current, preferably with three-phase alternating current.

[0022] Preferably, the device is electrically connected to the mains power supply and / or to the at least one electrode of the electric oven.

[0023] A power module according to the present invention is preferably a functional unit comprising a rectifier stage, an inverter stage and a DC link that electrically connects the rectifier stage to the inverter stage.

[0024] A rectifier stage configured to be electrically connected to fewer than three phases, in particular fewer than three different phases of the power grid, can be understood as a rectifier stage that cannot be electrically connected to three or more different phases of the power grid.

[0025] The rectifier stage can be configured to rectify an alternating current, in particular two different alternating currents, into a direct current. The rectifier stage can also be configured to rectify an alternating voltage, in particular two different alternating voltages, into a direct voltage.

[0026] Preferably, the rectifier stage is electrically connected to fewer than three phases, in particular fewer than three different phases of the power grid.

[0027] An inverter stage can be electrically connected to at least one electrode of the electric oven.

[0028] The DC link can include one or more capacitors and / or inductors connected in series and / or parallel to each other to store energy and provide electrical isolation between the rectifier and inverter stages. This electrical isolation can be achieved by electrical energy stored in the DC link and / or its capacitors.

[0029] Electrical isolation can be achieved through magnetic energy stored in coils of the DC link. This stored electrical isolation can compensate for fluctuations, especially instantaneous fluctuations, in the electrical energy supply and / or demand.

[0030] The DC link may include or consist of power cables and / or busbars. The DC link may be made of an alloy containing copper, silver, and / or another metal with high electrical conductivity. The DC link may be made of copper and / or silver. The DC link may include at least one section containing a superconducting material.

[0031] A superconducting material within the meaning of the invention can be a semi-ceramic or ceramic material defined as HTS (High Temperature Superconductivity), or a metallic material defined as LTS (Low Temperature Superconductivity). These materials, when heated to a critical temperature specific to each, exhibit the property of having essentially no resistance to current flow. In particular, the superconducting material in question can be defined as such according to the BCS (Bardeen-Cooper-Schrieffer) theory of ceramic-, metal-, or salt-based superconductivity.

[0032] The device can be electrically connected to one or more additional energy sources, wherein the additional energy source can be electrically connected to the DC link, in particular directly to the DC link.

[0033] The additional energy source can be a renewable energy source, in particular a photovoltaic energy source, a wind energy source, a hydropower source, or similar. The additional energy source can be a fossil fuel-based energy source, in particular a gas-fired power plant, a coal-fired power plant, or similar. The additional energy source can supply electrical energy in direct current (DC) or alternating current (AC). In particular, the additional energy source can include one or more batteries.

[0034] The additional power source can be connected to the DC link via a connecting circuit. The connecting circuit can include at least one converter configured to provide an output voltage level that is essentially the same as the DC link voltage level. The converter can include a rectifier circuit and / or a DC / DC converter circuit.

[0035] A power module within the meaning of the invention can be understood as a functional unit that receives an alternating current with an alternating voltage and a frequency on the input side and provides an alternating current with an alternating voltage and a frequency on the output side, wherein the alternating current, the alternating voltage and / or the frequency on the output side can be essentially independent of the alternating current, the alternating voltage and / or the frequency on the input side.

[0036] A power module can have a power module housing that at least partially limits the power module housing volume.

[0037] The power module enclosure can have or be one or more cabinets, in particular a control cabinet.

[0038] A housing according to the present invention is designed to protect components arranged within a housing volume from external influences, in particular from mechanical and / or electrical influences, and to provide a defined climatic condition within the housing volume, in particular a defined temperature and humidity. A housing can comprise a lower part, an upper part, and at least one side part, preferably four side parts. The lower part, the upper part, and the at least one side part at least partially define the housing volume. The lower part, the upper part, and the at least one side part can be connected to one another and form an integral component. Furthermore, a housing can be provided with an electrical grounding connection so that the housing can appropriately increase the safety of persons in the vicinity of the electrical components enclosed by the housing.

[0039] Two parts that form an integral component within the scope of the present invention are connected to each other by at least one mechanical connection. In other words, two parts that form an integral component change their relative spatial position to each other within the limits of their mechanical connection when the integral component is moved from one spatial position to another.

[0040] In a preferred embodiment of the invention, the mechanical connection of an integral component is fixed. In other words, the relative position of two parts forming an integral component, wherein the mechanical connection between the two parts is fixed, remains constant when the spatial position of the integral component changes.

[0041] The rectifier stage and / or the inverter stage and / or the DC link can be arranged within the power module housing volume.

[0042] The device may include an electronic control unit. An electronic control unit is any electronic system capable of receiving and / or storing signals and / or processing signals and / or controlling or regulating a device based on at least one signal. The device may include one or more sensors that provide information about harmonic distortion and / or flicker and / or the ratio of active power flux to reactive power flux in the power grid. The electronic control unit may be operationally connected to one or more such sensors and may receive, process, and use sensor signals to control and / or regulate the device.

[0043] An electronic control unit can be configured to control and / or regulate a rectifier stage, in particular a rectifier circuit, especially to reduce or prevent harmonic distortion and / or flicker, and / or to reduce reactive power in the power grid. An electronic control unit can also be configured to control and / or regulate an inverter stage, in particular an inverter circuit, especially to reduce or prevent harmonic distortion and / or flicker in the power grid, and / or to optimize the ratio of active power flow to reactive power flow in the power grid, and in particular to minimize reactive power flow into the power grid.An electronic control unit can be configured to control and / or regulate an inverter circuit, in particular to reduce or prevent harmonic distortion and / or flicker, especially flicker, in the power grid, particularly to mitigate flicker, preferably by applying an algorithm for a pulse width modulation strategy.

[0044] The device may include a cooling system. The cooling system may be configured to provide cooling capacity for the device to dissipate heat losses, particularly for one or more power modules of the device. The cooling system may be located within the power module housing. Alternatively, the cooling system may be located in a separate cooling system housing.

[0045] The cooling system may include a cooling circuit configured to circulate a cooling fluid to and from the power module.

[0046] A device designed in this way offers the advantage of improved cooling. When used as intended, it is now possible to supply individual electrical components, especially switching devices, with cooling power. In this way, heat losses can be dissipated with a further increased efficiency.

[0047] The cooling system may include a primary coolant pump configured to circulate coolant through the cooling circuit. The cooling system may also include a secondary coolant pump. This secondary pump may be a backup pump configured to automatically activate if the primary pump fails or malfunctions. Both the primary and secondary coolant pumps may be of the same type. The coolant pump may be located within the cooling system housing.

[0048] The cooling system can include a filter system, preferably a deionization system, configured to regulate and / or control the electrical conductivity of the cooling fluid. The filter system can be configured to regulate and / or control the electrical conductivity of the cooling fluid to a range of ≥ 1 µS / cm and ≤ 50 µS / cm, preferably to a range of ≥ 0.5 µS / cm and ≤ 1 µS / cm, and more preferably to a range of ≥ 0.1 µS / cm and ≤ 0.5 µS / cm. Particularly preferably, the filter system can be configured to regulate and / or control the electrical conductivity of the cooling fluid to a range of ≥ 0.055 µS / cm and ≤ 0.1 µS / cm. A device designed in this way has the advantage of increased protection against unwanted electrical currents and / or electrical voltages in the cooling circuit.

[0049] The cooling system may include at least one air conditioning system. The air conditioning system may be configured to supply cooling capacity to the power module. In particular, the air conditioning system may be configured to remove heat and moisture from the air within the power module housing volume.

[0050] The cooling system can be configured to supply cooling capacity to the power module via the cooling circuit and the air conditioning system. The cooling capacity can be provided such that a portion is supplied by the cooling circuit and the other portion by the air conditioning system. Specifically, the cooling capacity supplied by the cooling circuit can be ≥ 70% of the total cooling capacity, and the cooling capacity supplied by the air conditioning system can be ≤ 30% of the total cooling capacity. Alternatively, the cooling capacity supplied by the cooling circuit can be ≥ 80% of the total cooling capacity, and the cooling capacity supplied by the air conditioning system can be ≤ 20% of the total cooling capacity.In a preferred embodiment, the proportion of cooling capacity provided by the cooling circuit can be ≥ 90% of the total cooling capacity, and the proportion of cooling capacity provided by the air conditioning system can be ≤ 10% of the total cooling capacity. The total cooling capacity is the amount of cooling capacity that the cooling system provides to the power module at any given time.

[0051] The cooling system may include a temperature and humidity control device configured to regulate and / or control the temperature of the power module housing and / or the humidity of the power module housing volume. A temperature and humidity control device is any electronic system capable of receiving and / or storing and / or processing signals and / or controlling and / or regulating the temperature of the power module housing and / or the humidity of the power module housing volume of the device based on at least one signal.

[0052] The device may have one or more sensors that provide information about the temperature of the power module and / or the humidity of the power module housing volume. The temperature and humidity control unit may be operationally connected to one or more of the sensors and may receive, process, and use sensor signals to control and / or regulate the temperature of the power module housing and / or the humidity of the power module housing volume. The temperature and humidity control unit may be operationally connected to the cooling system, in particular to the coolant pump and the air conditioning system.

[0053] The sensor can be a temperature and / or humidity sensor. The sensors can be located at the rectifier stage, the DC link, the inverter stage, and / or in the power module housing.

[0054] The temperature and humidity control unit can be configured to individually regulate and / or control the temperature of the rectifier stage and / or the DC link and / or the inverter stage. In particular, the temperature and humidity control unit can be configured to regulate and / or control the temperature and / or humidity of the power module housing volume.

[0055] The temperature and humidity control unit can be configured to regulate and / or control the temperature of the rectifier stage and / or the DC link and / or the inverter stage and / or the temperature and humidity of the power module housing volume, depending on the control and / or regulation of the electronic control unit. If a high amount of electrical energy is required during the intended use of the device, e.g., at the beginning and during a melting process in an electric furnace, a higher cooling capacity is necessary.The temperature and humidity control device is therefore designed to receive and process at least one sensor signal and use it to control and / or regulate the cooling system in order to provide high cooling capacity to the power module housing volume, the rectifier stage, the DC link, and / or the inverter stage, in particular by increasing the cooling fluid flow rate and / or by reducing the cooling fluid temperature of the at least one cooling circuit and / or by increasing the air flow rate and / or by reducing the air temperature and / or by reducing the water content of the air flow rate of the air conditioning system.

[0056] Preferably, the power module has exactly one DC intermediate circuit that electrically connects the rectifier stage to the inverter stage of the power module.

[0057] A device designed in this way has the advantage that, when used as intended, it creates a separation between the power grid and the electric oven with fewer DC intermediate circuits, thus reducing the overall cost of the device. Furthermore, it can mitigate the risk of current imbalance between multiple DC intermediate circuits, which can occur when using power modules with a large number of DC intermediate circuits.

[0058] The power module can have more than one DC link, with the DC links connected in parallel. This allows a larger amount of electrical energy to be transferred between the rectifier stage and the inverter stage.

[0059] Preferably, the device has fewer than six power modules.

[0060] A device designed in this way has the advantage that, when used as intended, an electric furnace can be supplied with multiphase current, particularly three-phase current, using fewer power modules, thus reducing the overall cost of the device. Furthermore, using fewer than six power modules reduces the complexity of the entire device, especially the complexity of its control system during normal operation. This increases the reliability of the device.

[0061] In a preferred embodiment, the device has exactly three power modules.

[0062] Preferably, the rectifier stage comprises one or more rectifier circuits, wherein the rectifier circuit has electrical input connections for fewer than three different phases of an alternating current supplied to an input side of the rectifier circuit.

[0063] A device designed in this way has the advantage that, when the device is used as intended, the effect of an arc interruption between an electrode and the metal material on arcs of other electrodes is reduced by the fact that each arc is supplied by at least one other phase of the power grid.

[0064] The input side of a rectifier circuit is the side of the rectifier circuit to which an alternating current is electrically connected in order to be rectified by the rectifier circuit.

[0065] A rectifier circuit that has input terminals for fewer than three different phases of an alternating current supplied to one input side of the rectifier circuit cannot be electrically connected to three or more than three different phases of an alternating current.

[0066] The rectifier circuit can be configured to convert alternating current and voltage into direct current and voltage. Preferably, the rectifier circuit is configured to convert two different phases of a multiphase alternating current into direct current.

[0067] In a preferred embodiment, the rectifier circuits are connected in parallel and / or in series with each other.

[0068] A rectifier circuit can include an uncontrolled diode bridge. A rectifier stage with such a rectifier circuit can also be called a diode front end (DFE). A DFE is a unidirectional converter.

[0069] A unidirectional converter allows electrical energy to flow in only one direction and blocks electrical energy in the opposite direction. This means that electrical energy can flow from a power grid to a load, preferably an electric oven, but cannot flow from a load to a power grid. Alternatively, electrical energy can flow from a load, preferably an electric oven, to a power grid, but cannot flow from a power grid to a load.

[0070] A rectifier circuit and / or an inverter circuit can comprise a plurality of switching devices connected in parallel and / or in series, wherein the switching devices may include semiconductors, diodes, in particular uncontrolled diodes, thyristors such as silicon-controlled rectifiers (SCR), gate turn-off thyristors (GTO), integrated gate-commutated thyristors (IGCT), metal-oxide semiconductor controlled thyristors (MCT), transistors such as bipolar junction transistors (BJT), metal-oxide semiconductor field-effect transistors (MOSFET) and / or insulated-gate bipolar transistors (IGBT).

[0071] A rectifier stage and / or an inverter stage can be a bidirectional converter. A bidirectional converter allows the flow of electrical energy essentially in both directions; that is, electrical energy can flow from a power grid to a load, preferably an electric oven, and from a load, preferably an electric oven, to a power grid. A bidirectional rectifier stage can also be referred to as an Active Front End (AFE).

[0072] The switching devices of a rectifier circuit can be connected to each other in a half-bridge or full-bridge configuration. A half-bridge and / or a full-bridge can be capable of supplying a direct current with a current of ≥ 2500 A, in particular ≥ 3000 A, preferably ≥ 3500 A, and most preferably ≥ 5000 A.

[0073] Preferably, the rectifier circuit is a single-phase rectifier circuit or a two-phase rectifier circuit.

[0074] A single-phase rectifier circuit is configured to rectify a single alternating current and a single alternating voltage into a direct current. The single alternating current and voltage can be the current and voltage of one phase of a multi-phase alternating current or voltage. Specifically, a single-phase rectifier circuit cannot rectify more than one phase of a multi-phase alternating current or voltage. A single-phase rectifier circuit is typically connected to a single alternating current phase and a neutral phase of the power grid. Such a device has the advantage of reducing the output voltage of the rectifier stage. This allows the use of components, particularly switching devices, with lower voltage ratings, thus reducing costs.

[0075] A two-phase rectifier circuit is configured to rectify two alternating currents of two different phases and two alternating voltages of two different phases of a multi-phase current and voltage into one direct current and one direct voltage. Specifically, a two-phase rectifier circuit cannot rectify more than two phases of a multi-phase alternating current or voltage. Such a device has the advantage of reducing the output current of the rectifier stage. This allows the use of components, particularly switching devices, with lower current ratings, thus reducing costs.

[0076] Preferably, the rectifier circuit has a first electrical input terminal and a second electrical input terminal, wherein the first electrical input terminal is configured to be electrically connected to a first phase of the power grid, and the second electrical input terminal is configured to be electrically connected to a second phase of the power grid, wherein the second phase of the power grid is different from the first phase of the power grid.

[0077] The rectifier circuit can have a first plurality of electrical input terminals. These first input terminals can be connected in parallel. The rectifier circuit can also have a second plurality of electrical input terminals. These second input terminals can also be connected in parallel. In this way, the current of the rectifier circuit can be increased.

[0078] According to one embodiment, the rectifier circuit has fewer than three electrical input terminals, with one electrical input terminal being configured to be connected to exactly one phase of the power grid.

[0079] The device can have one or more step-down transformers, the primary winding of which is electrically connectable to the power grid and the secondary winding of which is electrically connected to the rectifier stage, particularly to an input side of the rectifier stage, preferably to the rectifier circuit. The step-down transformer is preferably a high- to medium-voltage transformer. In other words, the step-down transformer is preferably configured to transform a voltage with a high voltage level at its primary winding into a voltage with a medium voltage level at its one or more secondary windings. The step-down transformer is preferably an oil-cooled transformer. The step-down transformer can be a high- to low-voltage transformer.

[0080] Preferably, the step-down transformer is a three-phase transformer having one primary winding per phase and one or more secondary windings per phase. The step-down transformer can be a phase-shifting transformer.

[0081] A phase-shifting transformer is a special type of transformer that can be configured to adjust the phase relationship between its primary and secondary windings.

[0082] The phase angle between the primary and secondary sides of a transformer is a function of the transformer's winding group. A winding group, defined elsewhere by a terminal symbol, is the International Electrotechnical Commission's (IEC) method for categorizing the configurations of the primary winding, preferably the high-voltage (HV) winding, and the secondary winding, preferably the medium-voltage (MV) or low-voltage (LV) winding, of three-phase transformers. The winding group designation indicates the winding configurations and the difference in phase angle between them.

[0083] A connection group provides a simple way to specify how the terminals of a transformer are arranged. Various configurations are possible for how the primary and secondary windings are connected. In particular, they can be connected in delta, star, or zigzag configurations, with the primary and secondary windings being connected differently, resulting in a phase shift between the primary and secondary sides of a phase-shifting transformer.

[0084] For example, a star primary winding and a delta secondary winding can be combined into a switching group, resulting in a phase shift of 30 degrees between the primary and secondary sides.

[0085] A three-phase transformer can have one or more sets of secondary windings. If the transformer has more than one set of secondary windings, the power can be distributed among the available sets of secondary windings. Advantageously, a different switching group can be chosen between the primary windings, preferably high-voltage (HV) or medium-voltage (MV) windings, and each set of secondary windings, preferably MV or low-voltage (LV) windings, so that the electrical power can be transmitted with different phase shifts.

[0086] The portion of instantaneous power that results in a net transfer of energy in one direction is called instantaneous active power. The portion of instantaneous power that does not result in a net transfer of energy, but instead oscillates between source and load in each cycle due to stored energy, is called instantaneous reactive power.

[0087] Preferably, the DC link is designed for a voltage level of ≥ 1500 VDC, in particular ≥ 3000 VDC and preferably ≥ 5000 VDC.

[0088] A device designed in this way has the advantage that large amounts of electrical energy can be supplied at comparatively low currents.

[0089] The DC link can be designed for a voltage level of ≥ 10 kVDC, preferably ≥ 30 kVDC, more preferably ≥ 60 kVDC, and particularly preferably ≥ 90 kVDC. According to a preferred embodiment, the DC link can be designed for a voltage level of ≥ 100 kVDC.

[0090] The DC link can include a cooling unit, in particular a cooling unit connected to the device's cooling system. The cooling unit can have a cooling jacket that surrounds the DC link, in particular the power cables and / or busbars of the DC link.

[0091] Preferably, the inverter stage comprises a plurality of inverter circuits connected in parallel and / or in series, each inverter circuit being designed to provide a single-phase alternating current.

[0092] A device designed in this way has the advantage of reducing the complexity of controlling such a device for supplying electrical energy to an electric oven. An inverter stage configured to provide single-phase alternating current has fewer switching elements than an inverter stage configured to provide multi-phase alternating current, thus reducing the complexity of its control during operation.

[0093] The inverter circuits can be connected to each other in a star or delta configuration at their respective electrical output terminals. In this way, a multi-phase alternating current, in particular a three-phase alternating current, can be provided at the output of the inverter stage.

[0094] Preferably, the inverter stage comprises a plurality of inverter circuits connected in parallel and / or in series, each inverter circuit being designed to provide a three-phase alternating current.

[0095] A device designed in this way has the advantage that, when used as intended, in the event of a malfunction in an inverter circuit, all electrodes of an electric oven can continue to be supplied with alternating current.

[0096] The inverter circuits can be connected in parallel at their respective electrical output terminals. In this way, a three-phase alternating current with an increased current intensity can be provided at the output of the inverter stage.

[0097] Preferably, at least one power module has a transformer, in particular a three-phase current transformer, wherein a primary winding of the transformer is electrically connected to the inverter stage of this power module and a secondary winding of the transformer is electrically connectable to the electric furnace, in particular to at least one electrode of the electric furnace.

[0098] A device designed in this way has the advantage that, when used as intended, large amounts of electrical energy can be transmitted to the transformer at comparatively high voltages, resulting in comparatively low currents that need to be transmitted through the rectifier stage, the DC link and the inverter stage, leading to lower overall costs for the device components.

[0099] A secondary winding of the transformer can be electrically connected to the electric furnace, in particular to at least one electrode of the electric furnace.

[0100] Preferably, the three-phase current transformer has one primary winding per phase and one or more secondary windings per phase. Preferably, the three-phase current transformer is a phase-shifting transformer.

[0101] Preferably, the transformer is a medium-voltage (MV) to low-voltage (LV) transformer. In other words, the transformer is preferably configured to convert a voltage at a medium-voltage level across its primary winding into a voltage at a low-voltage level across its one or more secondary windings. The transformer may be oil-cooled.

[0102] In one embodiment, the three-phase current transformer is a dry-type transformer. A dry-type transformer is a transformer that uses neither a liquid as a cooling medium nor as an insulating medium for its windings and core. Instead, a dry-type transformer uses a gaseous fluid, preferably air, as the cooling medium and a solid material, preferably an epoxy resin, polyester resin, and / or aramid material, as the insulating medium. Such a device has the advantage of simplifying initial installation and reducing the fire potential in the event of a failure due to ignition of the cooling medium.

[0103] Preferably, the inverter stage supplies an alternating voltage with a voltage level of ≥ 1700 VAC at its output side.

[0104] A device designed in this way has the advantage that a comparatively large amount of electrical energy can be transmitted with comparatively low currents, resulting in lower overall costs for the need for copper or other conductive materials.

[0105] The inverter stage can provide an AC voltage at its output side with a voltage level of ≥ 10,000 VAC, preferably ≥ 20,000 VAC, and particularly preferably ≥ 30,000 VAC. According to a preferred embodiment, the inverter stage can provide an AC voltage at its output side with a voltage level of ≥ 33,000 VAC, preferably ≥ 40,000 VAC, and particularly preferably ≥ 66,000 VAC.

[0106] An inverter circuit of the inverter stage can comprise one or more switching devices, in particular two switching devices, connected in series and / or parallel to each other, each switching device being capable of withstanding a voltage level of ≥ 1700 VAC, preferably ≥ 2000 VAC, and particularly preferably ≥ 5000 VAC. According to a preferred embodiment, the switching device is capable of withstanding a voltage level of ≥ 10000 VAC, preferably ≥ 20000 VAC, particularly preferably ≥ 33000 VAC, and further preferably ≥ 66000 VAC. The switching devices of an inverter circuit can be connected to each other in a half-bridge or a full-bridge configuration. A half-bridge and / or a full-bridge may be able to supply an alternating current with a current strength of ≥ 2500 A, particularly preferably ≥ 3000 A, preferably ≥ 3500 A and particularly preferably ≥ 5000 A.

[0107] Preferably, two or more than two power modules are connected in parallel.

[0108] 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 current.

[0109] Preferably, the power modules are interconnected in a star or triangular configuration.

[0110] In a triangular configuration, a higher voltage level can be achieved between the power modules, while in a star configuration an asymmetric load can be better balanced.

[0111] In particular, the power modules are connected to each other in a star or triangular configuration at their respective electrical output sides.

[0112] Preferably the device has two or more than two power modules, wherein the rectifier stages of the two or more than two power modules each have a single-phase rectifier circuit, wherein the power modules can be connected to different phases of the power grid, preferably are connected.

[0113] A device designed in this way has the advantage of increased reliability and availability due to its modular topology.

[0114] Preferably, the device has two or more than two power modules, wherein at least one phase of the power grid, to which a rectifier stage of a first power module can be connected, differs from at least one of the phases to which a rectifier stage of a second power module can be connected.

[0115] A device designed in this way has the advantage of increased reliability and availability due to its modular topology.

[0116] Preferably, the device has two or more than two power modules, wherein at least one phase of the power grid to which a rectifier stage of a first power module is connected differs from at least one of the phases to which a rectifier stage of a second power module is connected.

[0117] According to a second aspect of the invention, the problem is solved by using a device according to the first aspect of the invention to supply an electric oven with electrical energy.

[0118] It should be noted that the features described in relation to the first aspect of the invention can be combined with the second aspect of the invention both independently and cumulatively. Thus, the advantages described in relation to the first aspect of the invention also apply to the second aspect of the invention.

[0119] According to a third aspect of the invention, the problem is solved by an electric oven which has one or more than one device according to the first aspect of the invention.

[0120] An electric furnace designed in this way has the advantage of increased resilience to fluctuations in power consumption during operation, leading to increased furnace availability. During the operation of an electric furnace, significant power fluctuations occur due to arc instabilities during the melting process. These arc instabilities often occur between several electrodes of the electric furnace. In the event of an arc interruption between one electrode and the metal material, the impact on the arcs of other electrodes is reduced by ensuring that each arc is supplied by at least one other phase of the power grid.

[0121] It should be noted that the features described in relation to the first and second aspects of the invention can be combined both independently and cumulatively with the third aspect of the invention. Thus, the advantages described in relation to the first and second aspects of the invention also apply to the third aspect of the invention.

[0122] Preferably the electric furnace has two or more electrodes, preferably exactly three electrodes.

[0123] Preferably, the electric oven is designed for operation at a voltage of ≥ 1200 VAC, in particular ≥ 1800 VAC, preferably ≥ 3000 VAC and especially preferably ≥ 5000 VAC.

[0124] It should be noted that the features described in relation to the first, second, and third aspects of the invention can be combined both independently and cumulatively with the fourth aspect of the invention. Thus, the advantages described in relation to the first, second, and third aspects of the invention also apply to the fourth aspect of the invention.

[0125] Further advantages, details and features of the present invention are explained in the description of the following embodiments, wherein: Fig. : shows a schematic view of a first embodiment of a device; Fig. : shows a schematic view of a second embodiment of a device; and Fig. Figure 1 shows a schematic view of a third embodiment of a device.

[0126] In the following description, identical numbers denote identical elements or identical features, so that the description of an element with reference to one figure also applies to the other figures and the repetition of the respective feature is omitted.

[0127] Fig. Figure 1 shows a device 10 for supplying an electric oven 90 with electrical energy according to a first embodiment of the invention, wherein the device 10 is electrically connected to a three-phase power grid 100 and three electrodes 91 of the electric oven 90; wherein the device 10 has three power modules 20, each power module 20 having a rectifier stage 30 which is connected to fewer than three different phases R, S, T of the power grid 100, in particular to exactly one phase of the power grid 100; an inverter stage 40 which is electrically connected to at least one electrode 91 of the electric oven 90; and a DC link 50, wherein the DC link 50 electrically connects the rectifier stage 30 to the inverter stage 40 of the power module 20.

[0128] The rectifier stages 30 of the three power modules 20 each have a single-phase rectifier circuit, with the power modules 20 being connected to different phases R, S, T of the power grid 100. Each single-phase rectifier circuit is connected to the neutral conductor N of the power grid 100.

[0129] The inverter stages 40 of the three power modules 20 feature a plurality of inverter circuits connected in parallel and / or in series, each inverter circuit being configured to provide a three-phase alternating current with phases R, S, T at the output side of the inverter circuit. The power modules 20 are connected in parallel at their respective electrical outputs.

[0130] Fig. Figure 2 shows a device 10 for supplying an electric oven 90 with electrical energy according to a second embodiment of the invention, wherein the rectifier stages 30 of the power modules 20 each have a two-phase rectifier circuit, wherein at least one phase of the power grid 100, to which a rectifier stage 30 of a power module 20 is connected, is different from at least one of the phases to which a rectifier stage 30 of another power module 20 is connected.

[0131] Each power module 20 has a three-phase current transformer 60, wherein a primary winding of the three-phase current transformer 60 is electrically connected to the inverter stage 40 of this power module 20 and a secondary winding of the three-phase current transformer 60 is electrically connected to the electrodes 91 of the electric furnace 90.

[0132] Fig.Figure 3 shows a device 10 for supplying an electric oven 90 with electrical energy according to a third embodiment of the invention, wherein the inverter stage 40 of each power module 20 has a plurality of inverter circuits connected in parallel and / or in series to each other, wherein each inverter circuit is configured to provide a single-phase alternating current.

[0133] The power modules 20 are connected in a star configuration at their respective electrical outputs, with the star point connected to a common neutral conductor N. The electric oven 90 is also connected to the neutral conductor N. Reference symbol list 10 Device 20 Power module 30 Rectifier stage 40 Inverter Stage 50 DC intermediate circuit 60 transformer 90 Electric oven 91 Electrode of the electric oven 100 Power grid R First Phase Second Phase Third Phase N Neutral conductor

Claims

Device (10) for supplying an electric oven (90) with electrical energy, wherein the device (10) is electrically connectable to a power grid (100), preferably a three-phase power grid, and to at least one electrode (91) of the electric oven (90); wherein the device (10) comprises at least one power module (20), the power module (20) comprising: a rectifier stage (30) configured to be electrically connected to fewer than three phases, in particular fewer than three different phases, of the power grid (100); an inverter stage (40) electrically connectable to at least one electrode of the electric oven (90); and a DC link (50), wherein the DC link (50) electrically connects the rectifier stage (30) to the inverter stage (40) of the power module (20). Device (10) according to claim 1, characterized in that the power module (20) has exactly one DC intermediate circuit (50) which electrically connects the rectifier stage (30) to the inverter stage (40) of the power module (20). Device (10) according to claim 1 or 2, characterized in that the device has fewer than six power modules (20). Device (10) according to one of the preceding claims, characterized in that the rectifier stage (30) has one or more than one rectifier circuit, wherein the rectifier circuit has electrical input connections for fewer than three different phases of an alternating current supplied to an input side of the rectifier circuit. Device (10) according to claim 4, characterized in that the rectifier circuit is a single-phase rectifier circuit or a two-phase rectifier circuit. Device (10) according to claim 4 or claim 5, characterized in that the rectifier circuit has a first electrical input terminal and a second electrical input terminal, wherein the first electrical input terminal is configured to be electrically connected to a first phase of the power grid (100), and the second electrical input terminal is configured to be electrically connected to a second phase of the power grid (100), wherein the second phase of the power grid (100) is different from the first phase of the power grid (100). Device (10) according to one of the preceding claims, characterized in that the DC intermediate circuit (50) is designed for a voltage level of ≥ 1500 VDC, in particular of ≥ 3000 VDC and preferably of ≥ 5000 VDC. Device (10) according to one of the preceding claims, characterized in that the inverter stage (40) has a plurality of inverter circuits connected in parallel and / or in series to each other, wherein each inverter circuit is configured to provide a single-phase alternating current. Device (10) according to one of the preceding claims 1 to 7, characterized in that the inverter stage (40) has a plurality of inverter circuits connected in parallel and / or in series to each other, wherein each inverter circuit is configured to provide a three-phase alternating current. Device (10) according to one of the preceding claims, characterized in that at least one power module (20) has a transformer (60), preferably a three-phase current transformer, wherein a primary winding of the transformer (60) is electrically connected to the inverter stage (40) of this power module (20) and a secondary winding of the transformer (60) is electrically connectable to the electric furnace (90), in particular to at least one electrode (91) of the electric furnace (90). Device (10) according to one of the preceding claims, characterized in that the inverter stage (40) provides an alternating voltage with a voltage level of ≥ 1700 VAC at its output side. Device (10) according to one of the preceding claims, characterized in that two or more than two power modules (20) are connected in parallel to each other. Device (10) according to one of the preceding claims, characterized in that the power modules (20) are interconnected in a star or triangular configuration. Device (10) according to one of the preceding claims, characterized in that the device (10) has two or more than two power modules (20), wherein the rectifier stages (30) of the two or more than two power modules (20) each have a single-phase rectifier circuit, wherein the power modules (20) can be connected to different phases of the power grid (100), preferably are connected. Device (10) according to one of the preceding claims, characterized in that the device (10) has two or more than two power modules (20), wherein at least one phase of the power grid (100), to which a rectifier stage (30) of a first power module (20) can be connected, differs from at least one of the phases, to which a rectifier stage (30) of a second power module (20) can be connected. Use of a device (10) according to one of the preceding claims for supplying an electric oven (90) with electrical energy. Electric oven (90) comprising one or more than one device (10) according to any one of claims 1 to 15 . Electric oven (90) according to claim 17, characterized in that the electric oven (90) has two or more electrodes (91), preferably exactly three electrodes (91). Electric oven (90) according to claim 17 or claim 18, characterized in that the electric oven (90) is designed for operation at a voltage of ≥ 1200 VAC, in particular ≥ 1800 VAC, preferably ≥ 3000 VAC and particularly preferably ≥ 5000 VAC.

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