Converter device and power supply device

Abstract

The converter device is configured to convert a DC voltage and a DC current into an AC voltage and an AC current that is supplied to a load (L). The converter device comprises a bank (11) of capacitors (12), a plurality of power semiconductors (13), a heat sink (14), and a casing (15).

Description

[Technical Field]

[0001] The embodiments described herein relate to converter devices or inverters suitable for converting a quantity of direct current to a quantity of alternating current. In particular, the invention relates to high power converter devices of a type that can be used advantageously in medium voltage applications, but not exclusively.

[0002] The embodiments described herein also relate to a power supply using one or more of the above converters or inverters and suitable for powering a load requiring high power, such as an electric arc furnace. [Background technology]

[0003] It is known to use converter devices to convert a quantity of direct current into a quantity of alternating current that can be more or less constant or variable and that can be used to power a given load.

[0004] Depending on the needs and different applications, the converter devices can be used independently or connected to each other.

[0005] From EP 3124903 in the name of the applicant there is known a power supply for an electric arc furnace, comprising a device for positioning the electrodes and a regulating unit comprising a number of selectively controllable converters for regulating the supply voltage and current of the electrodes.

[0006] The power supply device described in EP 3124903 therefore operates as an adjustable current generator and is able to generate the power required to power an electric arc furnace according to the process step in the operation (piercing, melting, refining), which distinguishes the solution according to EP 3124903 from typical solutions in which the converter operates as a voltage generator and the current is not controllable but is only limited by the parameters of an equivalent circuit which vary according to the process step.

[0007] Furthermore, the power supply described in EP 3124903 makes it possible to separately regulate the current and voltage of the arc in a way that significantly limits current fluctuations in the first step of the process, i.e. the piercing step, and makes the current practically stable in the subsequent melting and refining steps.

[0008] One of the most obvious advantages obtained is the stability of electrode adjustment, in contrast to conventional plants where the electrode moves continuously due to the instability of the supplied current, forcing an uncontrolled current to ensure the continuity of the arc.

[0009] The limitation in the power supply described in EP 3124903 is given by the maximum current that can be provided by the current control.

[0010] The power is modified by adjusting the voltage of the arc depending on the current supplied, and the arc can then be modified mechanically by raising and lowering the electrode with a positioning device, and also by manipulating the PWM (pulse width modulation) to control the converter device.

[0011] A typical high-power converter or inverter for medium-voltage applications generally comprises a bank of series- and / or parallel-connected capacitors suitable for storing energy in the form of DC, a heat sink, and a number of power semiconductors connected to the bank of capacitors and mounted on the heat sink. The converter components are usually enclosed in a metal casing, which is provided with input and output connectors connectable respectively to an upstream circuit, e.g., a power supply grid, and a downstream circuit, e.g., a powered load or user device.

[0012] For example, converters are known which comprise power semiconductors, for example IGBT modules (insulated gate bipolar transistors), which are alternately switched depending on the passage of a positive or negative current half-wave.

[0013] The capacitor bank and heat sink are normally connected to earth, the earth connection being integral with the converter casing, which is also generally earthed for safety reasons.

[0014] Each IGBT module is operated by a circuit board that switches on and off a static semiconductor switch, which allows current to flow towards the load. With a defined on-off pulse profile, the semiconductor switch powers the load with rectangular pulses of varying amplitude.

[0015] A sinusoidal envelope is obtained by appropriately applying PWM (Pulse-Width Modulation) to an ohmic-inductive circuit. Indeed, this digital modulation makes it possible to obtain a variable average voltage that depends on the ratio between the duration of the positive pulse (ON) and the total duration of the pulse (ON+OFF), this ratio being defined as the duty cycle.

[0016] An IGBT module consists of appropriately doped silicon chips mounted on a thermally conductive but electrically insulating substrate, which is welded to a tinned copper base. The chips are then encapsulated in a plastic case, inside which they are protected with a filler gel, and connected by a wire connection system to external terminals to which cables, i.e., power and signal bars, are connected to control the on / off switching of the IGBTs.

[0017] The IGBTs are mounted on an appropriately sized heat sink to dissipate the heat generated during functioning, and the heat sink can be cooled by forced air or water.

[0018] The IGBT base and the heat sink constitute two opposing flat surfaces with a dielectric placed between them, in particular a thermal paste that serves to improve the heat transfer between the two surfaces, resulting in the formation of a parasitic capacitance for each power semiconductor present in the module.

[0019] The above-described configuration of the converter or inverter causes parasitic capacitances to occur, in particular between the power semiconductors and the heat sink connected to the converter casing, and between the capacitor housing and the converter casing.

[0020] When the switches are turned on and off to generate a sine wave towards the load, i.e. when current flows in the converter and positive and negative half waves are formed, in the case of an application in an electric arc furnace power supply, the voltage is switched from 1800 V to 0 V and back again with switching times of the order of a few hundred nanoseconds, which therefore results in very large voltage variations with time dv / dt of the order of 5 kV / microsecond, and the parasitic capacitances therefore cause the generation of currents to earth.

[0021] The strength of the current towards earth can in fact be calculated using the formula i=C*((ΔV) / (ΔT)), where ΔV is the voltage fluctuation (given by the difference between 1800V and 0V or vice versa), ΔT is the period during which the fluctuation occurs, equal to approximately 250 nanoseconds, and C is the parasitic capacitance created between the base of the IGBT module and the heat sink.

[0022] For example, if the parasitic capacitance for an IGBT module is about 2nF, then the total parasitic capacitance for, say, four IGBT modules is about 8nF, which is added to the total capacitance of the capacitor, resulting in a capacitance for one converter device of about 25-30nF.

[0023] If a power supply system has several converter devices, for example 60 modules, the total capacitance can be very high, about 1.5-1.8 μF. Each time an IGBT module is switched to define a sine wave, the total capacitance generates a current to ground, the peak of which can also be well above 200-250 A.

[0024] Furthermore, each interconnection to each converter device, defined by a conductor having a given length, has a parasitic inductance, which causes damped oscillations in the development of current generated by the parasitic capacitance.

[0025] In power supply systems of the type mentioned above, the parasitic current peaks and oscillations generated can lead to accidental interventions in various protections or desaturations, or to failure of the programmed switching states of the module drivers, resulting in risks of disconnection, auxiliary power supply failure, overvoltage, undervoltage, AC failure, etc. Some of these interventions are not due to real alarms, but are merely signal disturbances that are interpreted as such by the control system.

[0026] However, in some cases the disturbance may be such as to cause a real malfunction or "failure" in, for example, the auxiliary power supply.

[0027] U.S. Patent Application Publication No. 2014 / 268570 discloses an inverter including a housing assembly, a capacitor assembly, multiple arm assemblies, multiple heat sinks, and a support assembly. The housing assembly includes multiple side walls defining an enclosed space. The capacitor assemblies are coupled to the housing assembly. Each arm assembly includes multiple electrical components and multiple electrical buses. Each arm assembly is coupled to a capacitor assembly and is electrically connected to the capacitor assemblies. The support assembly includes a non-conductive frame assembly. The support assembly is configured to electrically support each heat sink in an insulating manner. A sealant is applied to each electrical bus and a limited number of electrical components. Therefore, the limited number of electrical components are substantially sealed from the atmosphere, and components not enclosed by the sealant can be repaired or replaced in the field.

[0028] DE 10 2017 206 774 A1 discloses an electrical control device comprising a number of components to be cooled and a heat sink arranged in a housing, the heat sink being electrically insulated from a reference potential and the components to be cooled being thermally conductively connected to the heat sink.

[0029] JP 2016-123235 A discloses a power conversion circuit that reduces the effect of electromagnetic noise applied to a control circuit by a DC power supply and prevents the inverter device from becoming large in size when a DC power supply connector, a control circuit of the power conversion circuit, and the power conversion circuit are arranged in order in a direction perpendicular to the arrangement surface on which the power conversion circuit is arranged.

[0030] U.S. Pat. No. 6,274,851 discloses a controller for an electric arc furnace that includes dampers each having a low-pass filter coupled to an output phase, with the resistive and capacitive components being fixed and non-variable.

[0031] Therefore, there is a need to develop a converter device that can overcome at least one of the drawbacks of the prior art.

[0032] In particular, it is an object of the present invention to provide a converter device that can limit, if not eliminate, the parasitic capacitance and hence the generation of parasitic currents to ground.

[0033] Another object of the present invention is to provide an efficient and reliable converter device that can be used independently or in combination with other converter devices and that limits the generation of possible parasitic currents.

[0034] Another object of the invention is to provide a method for the production of electric arc furnaces, which is applicable for example to power electric arc furnaces. Na, negative To perfect a device for supplying power to a load, which is simple to manufacture and can prevent the generation of undesirable currents to earth that interfere with alarm and control signals and make them inefficient, or at least reduce their presence to the point where they can be ignored.

[0035] Applicant has conceived, tested and embodied the present invention to overcome the shortcomings of the prior art and to obtain these and other objects and advantages. Summary of the Invention

[0036] The invention is set forth and characterized in the independent claims, while the dependent claims describe other features of the invention or variations of the main idea of ​​the invention.

[0037] In accordance with the above objects, a converter device or inverter is provided that is suitable for converting DC voltage and current into AC supply voltage and current supplied to a load and that can be used in medium voltage applications requiring high power.

[0038] A converter device according to the present invention may be used in combination with multiple converter devices of substantially the same type in a power supply to provide a voltage and current suitable for powering a load requiring high power, such as, by way of example only, the electrodes of an electric arc furnace.

[0039] In some embodiments, the converter device comprises a bank of capacitors adapted to be connected in use to a power supply circuit and to store electrical energy in direct current, and a plurality of power semiconductors connected to the bank of capacitors and configured to be selectively switched on and off to generate a sinusoidal current towards an output, and a heat sink on which the power semiconductors are mounted and configured to dissipate heat generated by the power semiconductors during functioning.

[0040] The converter device also comprises a casing or metal shell that encloses the capacitor bank, the heat sink and the power semiconductor unit.

[0041] The casing is provided with input and output connectors which are connectable in use to a power circuit or grid and a powered load.

[0042] In some embodiments, the casing of the converter device may be connected to earth for safety reasons.

[0043] In one aspect of the invention, at least one of the heat sink and / or the bank of capacitors has a floating potential relative to the casing of the converter device, ie, the floating potential is not at the same reference potential as the casing of the converter device.

[0044] In some embodiments, both the heat sink and the bank of capacitors are floating relative to the casing.

[0045] In some embodiments, the heat sink and / or the bank of capacitors are electrically isolated from the casing and therefore from the earth connection connected to the casing, thereby substantially preventing direct current from flowing between the two components.

[0046] In a further embodiment, the heat sink and / or bank of capacitors are connected to the casing by high impedance components or circuits, which significantly limits the generation of parasitic currents to earth.

[0047] In some embodiments, the converter device includes at least a first high impedance component connected between the heat sink and a ground of the casing of the converter device.

[0048] In this way, the heat sink is substantially insulated with respect to the casing of the converter device and therefore with respect to earth, which greatly limits the generation of parasitic currents to earth, at least in relation to peak values.

[0049] In some embodiments, the converter device comprises a plurality of second high impedance components each connected between the capacitor housing and an earth connection of the casing of the converter device.

[0050] In this way, the capacitor is advantageously substantially insulated and isolated from the casing of the converter device, so that any parasitic currents generated towards earth will have negligible peak values.

[0051] Thanks to the presence of the first high-impedance component and the second high-impedance component, both the heat sink and the capacitor are insulated from the casing of the converter device, making it possible to substantially eliminate the parasitic capacitance generated by them and therefore significantly reduce the peaks of the current flowing to earth.

[0052] This advantage is particularly evident when using multiple converter devices connected together.

[0053] In a further embodiment, the converter device comprises at least one low-pass electrical filter connected between an output connector suitable for connection to a load to be powered and an earth connection, the low-pass electrical filter being configured to remove possible oscillations in the current to earth due to distributed parasitic inductances and capacitances having frequencies higher than the operating frequency.

[0054] In some embodiments, the low pass electrical filter is an RC electrical filter connected between the output connection and the earth connection, with a resistive component and a capacitive component arranged in series with each other.

[0055] In some embodiments, the resistive and capacitive components can be sized according to the application of the converter device and the characteristics of the load being powered, and these components can potentially be modified to accommodate changes in the overall electrical system.

[0056] In some embodiments, the resistive and capacitive components can be adjusted to change their respective resistive and capacitive values ​​to increase or decrease the magnitude of the current flowing through them.

[0057] In some embodiments, the RC electrical filter may include dissipation means configured to reduce the temperature of the resistive and / or capacitive components.

[0058] In some embodiments, the RC electrical filter may also comprise temperature measurement means, for example associated with one or more of the resistive or capacitive components.

[0059] Some embodiments described herein are particularly suitable for high power loads of the ohmic inductive type. Electric arc furnaces are used as loads. It also relates to an apparatus for supplying power.

[0060] The power supply device is a converter connected to a power grid providing an AC mains voltage and an AC mains current, the converter being configured to convert the AC mains voltage and current into an AC base voltage and an AC base current; - a plurality of rectifiers connected to the converter and configured to convert AC base voltages and AC base currents into DC voltages and DC currents; - One side is connected to the rectifier and the other side into the electric arc furnace The plurality of converter devices connected together convert DC voltage and DC current , electric arc furnace Supplied power supply a plurality of converter devices configured to convert the voltage and the AC power supply current; - Control and command the functionality of the converter device , power supply pressure and AC power a control and command unit configured to adjust the source current over time.

[0061] In some embodiments, an apparatus for powering a load according to the present invention comprises a low pass electrical filter connected downstream of the converter device and configured to attenuate or possibly eliminate oscillations in the current to earth.

[0062] In some embodiments, the low pass electrical filter comprises an RC electrical filter connected between the output of the converter device and an earth connection.

[0063] In some embodiments, the presence of an RC filter connected to earth can also damp possible oscillations due to parasitic capacitances generated by other components of the power supply that can be connected to earth, such as transformers, cables, pipes, etc.

[0064] In some embodiments, there is a single RC electrical filter of the three-phase type connected to the three output phases of the power supply.

[0065] In some embodiments, when the power supply is used to power an electric arc furnace, RC electric filters are connected to the three phases that are connected to the electrodes of the furnace.

[0066] The above and other aspects, features and advantages of the present invention will become apparent from the following description of some embodiments thereof, given by way of non-limiting example with reference to the accompanying drawings, in which:

[0067] For ease of understanding, the same reference numerals have been used in the figures in some instances to designate the same common elements, it being understood that elements and features of one embodiment may be advantageously incorporated in other embodiments without further explicit recitation. [Brief explanation of the drawings]

[0068] [Figure 1] 1A and 1B are schematic diagrams of converter devices according to some embodiments described herein, where (1a) is a schematic diagram of a first embodiment of a component of the converter device of FIG. 1; (1b) is a schematic diagram of a variation of a component of the converter device of FIG. 1; (1c) is a schematic diagram of a first embodiment of another component of the converter device of FIG. 1; and (1d) is a schematic diagram of a variation of another component of the converter device of FIG. 1. [Figure 2] 1 is a schematic diagram of an apparatus for powering a high power load applied as an electric arc furnace; DETAILED DESCRIPTION OF THE INVENTION

[0069] Reference will now be made in detail to possible embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided to illustrate the invention and should not be construed as limiting the invention. For example, one or more features illustrated or described as part of one embodiment can be changed or employed in or associated with other embodiments to make up further embodiments. It is understood that the invention includes all such modifications and variations.

[0070] The embodiments described with reference to FIG. 1 relate to a converter device, generally designated 10, suitable for converting DC voltages and currents into AC voltages and currents.

[0071] The converter device 10 can be used, for example, in medium voltage applications requiring high power.

[0072] The converter device 10 according to the present invention can advantageously be used independently and in combination with a number of other converter devices 10.

[0073] Additionally, some embodiments described herein are generally designated by the reference numeral 20 (FIG. 2), and are particularly suitable for use with high power loads of the ohmic inductive type. Electric arc furnace 2 The present invention relates to a power supply device configured to provide an alternating current and voltage suitable for powering a power supply unit.

[0074] FIG. 2 shows an example of the application of the power supply 20 to a load corresponding to an electric arc furnace 21, but the power supply 20 can also be used to power different types of loads, such as a ladle furnace or a submerged arc furnace.

[0075] In some embodiments, the converter device 10 comprises a capacitor bank 11 including a plurality of capacitors 12 connected in series and / or parallel to one another and configured to store electrical energy in the form of direct current.

[0076] The converter device 10 also includes a plurality of power semiconductors 13 connected to the capacitor bank 11 and configured to be selectively turned on and off to generate a sinusoidal current towards the output.

[0077] The converter device 10 also comprises a dissipation device 14, on which the power semiconductors 13 are mounted and installed, the dissipation device 14 being configured to dissipate heat generated by the power semiconductors 13 during functioning.

[0078] In some embodiments, the heat sink 14 is water-cooled, although this does not preclude the use of a forced air cooled heat sink 14 for certain applications.

[0079] According to one possible solution, the power semiconductor 13 comprises a device selected from the group consisting of an SCR (Silicon Controlled Rectifier), a GTO (Gate Turn-Off Thyristor), an IGCT (Integrated Gate Commutated Thyristor), an MCT (Metal Oxide Semiconductor Controlled Thyristor), a BJT (Bipolar Junction Transistor), a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and an IGBT (Insulated Gate Bipolar Transistor).

[0080] The converter device 10 also includes a casing 15, or metal shell, that encloses the capacitor bank 11, the heat sink 14, and the power semiconductors 13.

[0081] The casing 15 contains an upstream circuit, e.g., a power supply grid, and a downstream circuit, e.g., a load to be powered. L and , and an input connector 15a and an output connector 15b are provided.

[0082] In some embodiments, the casing 15 may be connected to an earth connection G for safety reasons during use.

[0083] Depending on the requirements, the earth connection can be a real safety earth or a functional earth, which ensures the functionality of the electronic device and is sized according to the device to be protected but does not ensure operator safety according to regulations.

[0084] In one aspect of the invention, at least one of the heat sink 14 or the capacitor bank 11 has a floating potential relative to the casing 15 and therefore relative to the earth connection G connected thereto.

[0085] In a further embodiment, both the heat sink 14 and the capacitor bank 11 are "floating" relative to the casing 15 and therefore relative to the earth connection G.

[0086] The terms "floating" or "floating potential" mean that the heat sink 14 and / or the bank 11 of capacitors 12 are at least partially insulated from the casing 15, i.e., they are electrically isolated from the casing 15 and therefore from the earth connection G connected to the casing 15, or that the heat sink 14 and / or the bank 11 of capacitors 12 are connected to the casing 15 by high impedance components or circuits, which prevent or at least significantly limit the generation of parasitic currents to earth G.

[0087] In some embodiments, at least one of the heat sink 14 or the bank 11 of capacitors 12 is electrically isolated from the casing 15, i.e., no direct current flows circulating between them and the casing 15 (FIGS. 1(a) and 1(c)).

[0088] In a possible variant, at least one of the heat sink 14 or the bank of capacitors 12 is connected to the casing 15 by a high impedance component (FIGS. 1(1b) and (1d)).

[0089] In some embodiments, the converter device 10 comprises at least a first high impedance component 16 connected between the heat sink 14 and an earth connection G to which the casing 15 is connected (FIG. 1( 1 d)).

[0090] In some embodiments, the first high impedance component 16 can have an impedance between 500 ohms and 1500 ohms.

[0091] In a further embodiment, the first high impedance component 16 may have an impedance between 800 ohms and 1200 ohms.

[0092] In some embodiments, capacitor 12 is a film-type capacitor with a housing 17 made of a metallic material, such as aluminum.

[0093] In some embodiments, the converter device 10 includes a plurality of second high-impedance components 18 each connected between the casing 15 of the housing 17 of the capacitor 12 and an earth connection G to which the casing 15 is connected (FIG. 1(1b)).

[0094] In this way, the capacitor 12 is substantially insulated relative to the casing 15 of the converter device 10, so that any possible undesirable currents to ground G that may be generated have a substantially negligible peak value.

[0095] In some embodiments, the second high impedance components 18 can each have an impedance between 500 ohms and 1500 ohms.

[0096] In a further embodiment, the second high impedance components 18 may each have an impedance between 800 ohms and 1200 ohms.

[0097] In some embodiments, both the heat sink 14 and the capacitor 12 are connected to the casing 15, and therefore to ground G, by respective high impedance components 16, 18.

[0098] In a further embodiment, the converter device 10 comprises at least one electrical filter 19 connected between an output connection of the converter device 10 connectable in use to a load L to be powered and an earth connection G.

[0099] The electrical filter 19 comprises an RC filter having a resistive component R and a capacitive component C arranged in series with each other and is configured to act as a low pass filter, thereby removing possible current oscillations due to distributed parasitic inductances and capacitances.

[0100] Referring to Figure 2, Gas arc furnace 21 comprises a vessel 22 or shell into which the metallic material M is introduced which will then be melted.

[0101] Also, electricity Gas arc furnace 21 is also provided with a number of electrodes 23 (three electrodes 23 in the illustrated example) which are configured to generate an electric arc across the metallic material M to melt it.

[0102] In some embodiments of the present invention, the electrode 23 is mounted on a movement device 24 configured to selectively move the electrode 23 towards and away from the metal material M.

[0103] The movement device 24 may be selected from the group including at least one of a mechanical actuator, an electric actuator, a pneumatic actuator, a hydraulic actuator, an articulated mechanism, a kinematic mechanism, a similar equivalent member, or any conceivable combination thereof.

[0104] According to one possible solution of the invention, if there are three electrodes 23, each of them is connected to a respective power supply phase L1, L2, L3 of the power supply device 20.

[0105] In some embodiments of the present invention, the power supply 20 comprises at least one converter 25 connected to a power grid 26 for supplying a voltage and an AC mains current, the converter 25 being configured to convert the voltage and the AC mains current into a voltage and an AC base current.

[0106] According to one possible solution of the present invention, the power grid 26 may be three-phase.

[0107] In some embodiments of the invention, the mains voltage Ur and the mains current Ir have a predetermined mains frequency fr.

[0108] According to a possible solution, the mains frequency fr is a value chosen between 50 Hz and 60 Hz, i.e. a value chosen based on the frequency of the power grid of the country in which the furnace is installed.

[0109] According to a possible solution of the invention, the converter 25 may comprise a converter primary 27 magnetically coupled to at least one converter secondary 28 .

[0110] According to one possible solution of the invention, the converter 25 can comprise a number of converter secondaries 28 magnetically coupled to a converter primary 27. This solution allows the combination of the converter 25 and the rectifier 29 to reduce the grid side effects of disturbances, i.e. to reduce the harmonic content and reactive power exchanged with the grid.

[0111] Preferably, three phases are connected to the converter secondary 28, although fewer or more phases may be connected. In some embodiments, the number of phases may vary from 1 to n, where n may be an integer up to or greater than 20, for example.

[0112] The base electrical energy supplied by the converter 25 has a base voltage Ub, a base current Ib, and a base frequency fb, which are predetermined and set by the design characteristics of the converter 25 itself.

[0113] In particular, the base frequency fb is substantially equal to the mains frequency fr indicated above.

[0114] On the other hand, the base voltage Ub and the base current Ib are correlated with the mains voltage Ur and the mains current Ir, respectively, depending on the transformation ratio of the converter 25 itself.

[0115] For example, a multi-tap type transformer 25 may include an adjusting device (not shown) provided for selectively adjusting the electrical transformation ratio of the transformer 25 in relation to particular requirements.

[0116] The device 20 according to the present invention also comprises a plurality of rectifiers 29 connected to the converter 25 and adapted to convert the voltage and AC base current into a DC voltage and DC current.

[0117] In particular, the rectifier 29 makes it possible to rectify the voltage Ub and the AC base current Ib into a respective DC voltage and DC current.

[0118] The rectifier 29 may be selected from the group consisting of a diode bridge and a thyristor bridge.

[0119] According to one possible solution, the rectifier 29 comprises, for example, a device selected from the group consisting of a diode, an SCR (Silicon Controlled Rectifier), a GTO (Gate Turn-Off Thyristor), an IGCT (Integrated Gate Commutated Thyristor), an MCT (Metal Oxide Semiconductor Controlled Thyristor), a BJT (Bipolar Junction Transistor), a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and an IGBT (Insulated Gate Bipolar Transistor).

[0120] In another aspect of the invention, the apparatus 20 comprises a plurality of converter devices 10 connected to a rectifier 29 and configured to convert DC voltage and DC current to voltage and AC current for powering the electrodes 23.

[0121] The converter device may be a converter device 10 according to the invention, configured such that the capacitor 12 and / or the heat sink 14 are floating with respect to the earth connection G of the casing 15 of the respective converter device 10 .

[0122] Converter Device 10 Electric arc furnace 2 The converter device 10 is connected to one of the electrodes 23 and to a control and command unit 31 which is configured to control and command the functioning of the converter device 10 and to regulate the AC power supply to the electrodes 23 over time.

[0123] In some embodiments, the apparatus 20 may be configured to receive the output of the converter device 10 and the Electric Arc Furnace and an electric filter 30 connected between the power supply 10 and the powered load, which is the electrode 23 of the converter device 10, the electric filter 30 acting as a low pass filter and configured to attenuate or eliminate possible oscillations in the ground current during the switching of the semiconductor device 13, which may be generated by parasitic capacitance and inductance components of the converter device 10 or possibly by other components of the apparatus 20.

[0124] In some embodiments, the electrical filter 30 may be an RC filter connected correspondingly to the output of the converter device 10 .

[0125] In some embodiments, the electrical filter 30 can be used as an alternative to a possible electrical filter 19 of the individual converter devices 10 .

[0126] According to a possible solution, an electrical filter 30 may also be provided which is used in addition to a possible electrical filter 19 associated with the respective converter device 10 .

[0127] In some embodiments, the electrical filter 30 is of the three-phase type and Electric arc furnace 21 as a load It is inserted relative to the connected output phases L1, L2, L3, that is, the electrode 23.

[0128] The combination of an electrical filter 30 connected at the output of the converter device 10 and high impedance components 16, 18 inserted inside the converter device 10 itself makes it possible to eliminate current oscillations and, if they are not eliminated, also to limit the peaks of the current itself to earth.

[0129] This configuration therefore allows for the use of a large number of converter devices, such as more than 60, without the risk of malfunctioning of the control device due to high current peaks generated by parasitic currents, thus making the power supply 20 efficient and reliable.

[0130] In some embodiments, the resistive component R and / or the capacitive component C of the electrical filters 19, 30 may be sized according to the application of the converter device 10 and the characteristics of the load being powered.

[0131] In some embodiments, the resistive component R and the capacitive component C can be adjusted by the control and command unit 31 to modify their respective resistive and capacitive values ​​in such a way as to increase or decrease the intensity of the current flowing through them.

[0132] In some embodiments, the electrical filters 19, 30 may comprise dissipation means 36 configured to reduce the temperature of the components of the RC filter.

[0133] By way of example, the dissipation means 36 may comprise a fan or other means for moving air, dissipation fins, or the like.

[0134] In some embodiments, the electrical filters 19, 30 may also comprise temperature measurement means, for example a sensor 37 associated with one or more of the resistive component R and / or the capacitive component C.

[0135] By way of example, the temperature measurement sensor 37 may include a thermocouple associated with one or both of a resistive component R or a capacitive component C.

[0136] In some embodiments, the control and command unit 31 may be configured to receive detected data from the sensors 37 and, in some cases, command the activation / deactivation of the ventilation device 36 depending on the received data to maintain suitable thermal conditions to ensure effective functioning of the electric filters 19, 30.

[0137] In some embodiments, the control and command unit 31 also controls the converter device 10 to selectively set the voltage and AC mains current parameters as described above.

[0138] In one aspect of the invention, the control and command unit 31 comprises a regulating device 32 configured to regulate the power supply frequency fa of the voltage and of the AC power supply current to obtain a simultaneous variation of the reactance value of the power supply circuit of the electrodes.

[0139] Specifically, the power supply voltage and current comprise a power supply voltage Ua and a power supply current Ia, which are selectively adjusted in relation to the required melting power.

[0140] According to a possible solution of the invention, the regulating device 32 may comprise, by way of example only, a hysteresis modulator or a PWM (Pulse Width Modulation) modulator.

[0141] These types of modulators can be used to command the semiconductor devices of the rectifier 29 and the converter device 10. These modulators are suitably controlled to generate voltage or current values ​​to be driven to the electrodes 23. In particular, the modulators are configured to process such voltage and current values ​​and generate commands to drive at least the rectifier 29 and the converter 10 so that the voltage and current values ​​required by the control device are present at the terminals for connection to the electrodes 23. The voltage and current to be driven are the result of actions performed by the control and command unit 31 based on quantities read by the process and on a process model.

[0142] According to a possible solution, the rectifier 29 can be connected to the converter device 10 by means of at least one intermediate circuit 33 which works with direct current.

[0143] The intermediate circuit 33 stores DC energy and in this particular case is the power consumption of the electric arc furnace 21, which is the load. Kiwami 2 3 and 29 and therefore the power grid 26.

[0144] In particular, rapid power fluctuations resulting from the process are partially filtered by the intermediate circuit 33, thereby reducing their impact on the power grid 26 side.

[0145] The control and command unit 31 may also be configured to adjust the parameters of the supply voltage Ua and the supply current Ia generated by the converter device 10 and supplied to the electrodes 23 .

[0146] According to some solutions of the invention, the control and command unit 31 is also connected to the movement device 24 in order to allow adjustment of the position of the electrode 23 in relation to the different steps of the melting process.

[0147] In particular, the electrode 23 is moved by a moving device 24 in order to track the position of the material and therefore modify the length of the arc.

[0148] In this way, the control and command unit 31 is able to manage and command at least the following parameters in relation to a particular step of the process: the supply voltage Ua, the supply current Ia, the supply frequency fa and the position of the electrode 23. The high possibility of controlling different parameters makes it possible to optimize the transfer of energy to the process, while at the same time reducing the impact on the power grid 26 of rapid power fluctuations on the furnace side.

[0149] According to a possible solution, the converter 25 , the rectifier 29 connected to the converter 25 and the converter device 10 together define a power supply module 34 .

[0150] According to one possible embodiment of the present invention, the device 20 is connected to a power grid 26 and electric arc furnace 2 There may be a plurality of power supply modules 34 connected together and in parallel with one another.

[0151] The combination of multiple power supply modules 34 Gas arc furnace It is possible to obtain a device 20 that is scalable in size relative to the specific size of 21.

[0152] In embodiments, the number of power supply modules 34 may vary from 2 to m, where m may be 10, 12, 20, 40, 60, or an integer greater than 60.

[0153] The power supply modules 34 may each be connected to an electrode 23 for supplying electrical energy to the electrode 23. Multiple power supply modules 34 may be provided for each electrode 23.

[0154] Thus, depending on the number of power supply modules 34, the apparatus 20 can include a large number of converter devices 10, up to 60 or more.

[0155] According to one possible solution, the control and command unit 31 is connected to all power supply modules 34 for controlling at least each converter device 10, so that each module delivers the same values ​​of supply voltage Ua, supply current Ia and supply frequency fa. Electric arc furnace 21 provided as a load In this way, malfunction of the entire system can be prevented.

[0156] According to one possible solution, the device 20 may comprise an inductor 35 configured to obtain a desired overall reactance of the device.

[0157] Inductor 35 may be connected downstream of converter device 10 and sized to achieve a desired total equivalent reactance. In this way, the contribution of inductor 35 and the load on the system are determined. Electric arc furnace 21 provided as a load and the reactances introduced by the connecting conductors, we obtain the overall reactance.

[0158] In some embodiments, an inductor 35 may be connected downstream of the low pass electrical filter 30 .

[0159] In general, inductance is a (design) parameter that cannot be modified once the component is constructed.

[0160] By modifying the frequency (e.g., relative to the grid's 50 Hz), the inductance remains the same, but the reactance values ​​that the components have in the circuit can be changed, thus arriving at the desired total equivalent reactance value.

[0161] Therefore, by adjusting the frequency during different steps of the process, the present invention makes it possible to optimize the electrical parameters at each step: First, the substance (and therefore the cost) of the inductance can be reduced, and its capacity can be maximized during refining.

[0162] Furthermore, the electrical topology adopted in the converter makes it possible to protect the power grid from disturbances caused by the melting process (flicker reduction, harmonics, power factor, etc.) while guaranteeing arc stability at every step.

[0163] Furthermore, the ability to modify the electrode power supply frequency relative to the mains frequency facilitates sizing of inductive components under space / cost constraints and improves conductor utilization, thereby reducing resistance and therefore system losses.

[0164] For example, in an electric arc furnace with the same arc impedance, increasing the frequency increases the inductive reactance, To the electric arc furnace provided as a load The equivalent power factor of the arc is reduced, which improves the stability of the arc (useful, for example, when the scrap is not yet molten and the arc is not very protected) and can prevent the arc from extinguishing.

[0165] It will be apparent that modifications and / or additions of components may be made to the converter device 10 and power supply 20 described above without departing from the field and scope of the present invention.

[0166] Furthermore, although the present invention has been described with reference to some specific examples, it will be clear to those skilled in the art that many other equivalent forms of converter device 10 and power supply 20 can be achieved which have the features recited in the claims and are therefore within the scope of protection specified thereby.

[0167] In the following claims, the sole purpose of reference signs in parentheses is to facilitate reading and they should not be considered as limiting elements with regard to the scope of protection claimed in a particular claim.

Claims

1. 1. A converter device configured to convert a DC voltage and a DC current into an AC voltage and an AC current supplied to a load (L), comprising: The converter device a bank (11) of a plurality of capacitors (12) connectable in use to a direct current power supply circuit; a plurality of power semiconductors (13) connected to the bank of capacitors (12), the plurality of power semiconductors (13) being configured to be selectively turned on and off to enable generation of a sinusoidal current towards an output connector (15b); a heat sink (14) on which the power semiconductor (13) is mounted and configured to dissipate heat generated by the power semiconductor (13); a casing (15) configured to enclose at least the bank (11) of capacitors (12), the heat sink (14) and the power semiconductors (13) therein, the casing having a ground connection (G); The converter device, wherein the heat sink (14) or the housing (17) of each of the plurality of capacitors (12) is electrically insulated with respect to the casing (15).

2. 1. A converter device configured to convert a DC voltage and a DC current into an AC voltage and an AC current supplied to a load (L), comprising: The converter device a bank (11) of a plurality of capacitors (12) connectable in use to a direct current power supply circuit; a plurality of power semiconductors (13) connected to the bank of capacitors (12), the plurality of power semiconductors (13) being configured to be selectively turned on and off to enable generation of a sinusoidal current towards an output connector (15b); a heat sink (14) on which the power semiconductor (13) is mounted and configured to dissipate heat generated by the power semiconductor (13); a casing (15) configured to enclose at least the bank (11) of capacitors (12), the heat sink (14), and the power semiconductor (13); at least one first component (16) connected between the heat sink (14) and the casing (15); Equipped with the first component (16) has an impedance between 500 ohms and 1500 ohms; The capacitor (12) is a film-type capacitor, The heat sink (14) or the housing (17) of each of the plurality of capacitors (12) is made of a metal material; The converter device further comprises a plurality of second components (18) each connected between the housing (17) of a respective one of the capacitors (12) and a ground connection (G) connected to the casing (15); The converter device, wherein the plurality of second components (18) have an impedance between 500 ohms and 1500 ohms.

3. 3. The converter device of claim 2, wherein the at least one first component (16) and / or the second component (18) has an impedance between 800 ohms and 1200 ohms.

4. at least one low-pass electrical filter (19) connected between said output connector (15b) suitable for connection in use to said load (L) to be powered and said earth connection (G); 4. The converter device according to claim 1, wherein the low-pass electric filter (19) has one end connected to a circuit connecting the output connector (15b) and the load (L) and another end connected to the earth connection (G).

5. A power supply for powering an electric arc furnace (21), which is a high power ohmic inductive load, comprising: a converter (25) connected to a power grid (26) supplying an AC mains voltage (Ur) and an AC mains current (Ir), the converter (25) being configured to convert the AC mains voltage (Ur) and the AC mains current (Ir) into an AC base voltage (Ub) and an AC base current (Ib); a plurality of rectifiers (29) connected to the converter (25) and configured to convert the AC base voltage (Ub) and the AC base current (Ib) into a DC voltage and a DC current; The power supply device is a plurality of converter devices (10) according to any one of claims 1 to 4, one side of which is connected to the rectifier (29) and the other side of which is connected to the electric arc furnace (21), the plurality of converter devices (10) being configured to convert a DC voltage and a DC current into a power supply voltage (Ua) and an AC power supply current (Ia) to be supplied to the electric arc furnace (21); a control and command unit (31) configured to control and command the functioning of the converter device (32) and to regulate the power supply voltage (Ua) and the AC power supply current (Ia) over time, The AC base voltage (Ub) and the AC base current (Ib) are parameters of the base electrical energy supplied by the converter (25) that are preset according to a transformation ratio of the converter (25) itself, and are correlated with the AC mains voltage (Ur) and the AC mains current (Ir), respectively.

6. 6. The power supply according to claim 5, comprising a low-pass electrical filter (30) connected between the output of the converter device (10) and the earth connection (G), the low-pass electrical filter (30) being configured to attenuate or eliminate fluctuations in the current to the earth connection (G).

7. 7. The power supply device according to claim 6, wherein the electric filter (30) is a three-phase type RC filter and is inserted for the output phases (L1, L2, L3) connected in use to the electric arc furnace (21).

8. 8. The power supply device according to claim 6 or 7, wherein the electric filter (30) is an RC filter comprising a resistive component (R) and a capacitive component (C), and comprises dissipation means (36) configured to dissipate thermal energy generated by one or both of the resistive component (R) and the capacitive component (C) to reduce their temperatures.

9. 9. The power supply device of claim 8, wherein the electric filter (30) comprises a temperature measurement sensor (37) associated with one or more of the resistive components (R) and / or the capacitive components (C) and configured to measure the temperature thereof.

10. 10. The power supply apparatus according to claim 5, wherein the control and command unit (31) is provided with a regulating device (32) configured to regulate the supply frequency (fa) of the supply voltage (Ua) and of the alternating current supply current (Ia) independently of the mains frequency (fr) of the power grid (26) and to effect regulation of the reactance of the power supply apparatus (10).

11. 11. The power supply of claim 10, wherein the regulating device (32) comprises a hysteresis modulator or a PWM (Pulse Width Modulation) modulator.

12. a plurality of power supply modules (34) each including the converter (25), the rectifier (29), and the converter device (10); 12. The power supply device according to claim 5, wherein the plurality of power supply modules (34) are connected in parallel with each other and are connected to the power grid (26) and the electric arc furnace (21).

13. a container (22) or shell into which the metallic material (M) to be subsequently melted is introduced; a plurality of electrodes (23) configured to generate an arc across the metal material (M) to melt the metal material (M); and a power supply device (20) according to any one of claims 5 to 12 connected between the power grid (26) and the electrodes (23).

Images