EP4307834A1 - Procédé et système de commande d'un four à arc électrique - Google Patents

Procédé et système de commande d'un four à arc électrique Download PDF

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Publication number
EP4307834A1
EP4307834A1 EP22184832.8A EP22184832A EP4307834A1 EP 4307834 A1 EP4307834 A1 EP 4307834A1 EP 22184832 A EP22184832 A EP 22184832A EP 4307834 A1 EP4307834 A1 EP 4307834A1
Authority
EP
European Patent Office
Prior art keywords
converter
electric arc
arc furnace
voltage
controller
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22184832.8A
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German (de)
English (en)
Inventor
Jean-Philippe Hasler
Alexandre CHRISTE
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hitachi Energy Ltd
Original Assignee
Hitachi Energy Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hitachi Energy Ltd filed Critical Hitachi Energy Ltd
Priority to EP22184832.8A priority Critical patent/EP4307834A1/fr
Publication of EP4307834A1 publication Critical patent/EP4307834A1/fr
Pending legal-status Critical Current

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B7/00—Heating by electric discharge
    • H05B7/02—Details
    • H05B7/144—Power supplies specially adapted for heating by electric discharge; Automatic control of power, e.g. by positioning of electrodes

Definitions

  • the present disclosure generally relates to a method and a system for controlling an electric arc furnace.
  • An Electric Arc Furnace may be supplied by a power supply system having a converter device, such as a Static Frequency Converter (SFC), which connects the Alternating Current (AC) grid to the EAF.
  • SFC Static Frequency Converter
  • An advantage of such a power supply system is to optimize the production of melted metal without requiring a tap-changer on the EAF transformer nor additional series reactors as in previous power supply systems, which decrease the electrode consumption.
  • a prior art solution using a converter device is dislosed in the patent US10470259B2 , which shows an electric arc furnace system with a Multi-Modular Converter (MMC) arranged to supply power from the AC grid to the EAF.
  • MMC Multi-Modular Converter
  • the MMC is controlled by a control device, which receives a reference signal constituting a reference current value and/or a reference voltage value from an electrode controller.
  • the control device is configured to control the MMC to generate an output current feeding the EAF, via the EAF transformer, to meet the reference current and/or reference voltage.
  • the present disclosure seeks to at least partly remedy the above discussed issues. To achieve this, a method of operating an electric arc furnace and an electric arc furnace operation system, as defined by the independent claims are provided. Further embodiments are provided in the dependent claims.
  • a method of operating an electric arc furnace by means of an electric arc furnace operation system connectable with the electric arc furnace to form an electric arc furnace system wherein the electric arc furnace operation system comprises a converter device connectable with the AC grid for supplying the electric arc furnace with electric power, an electrode controller controlling electrodes of the electric arc furnace, and a converter controller, the method comprising:
  • the method may comprise measuring a load voltage and a load current between the converter device and the electric arc furnace.
  • the operation of controlling the converter may be further based on the load voltage and the load current.
  • the method may comprise comparing the load current with a threshold, and determining, when the electrode current exceeds the threshold, a virtual resistance arranged to decrease the electrode current below the threshold.
  • the method may comprise generating the reference impedance and the reference voltage by means of the electrode controller.
  • the physical inductance may be predetermined.
  • an electric arc furnace operation system connectable to an electric arc furnace to form an electric arc furnace system.
  • the electric arc furnace operation system comprises:
  • the electric arc furnace operation system comprises a voltage measurement device configured to measure a load voltage between the converter device and the electric arc furnace, and a current measurement device configured to measure a load current between the converter device and the electric arc furnace, wherein the load voltage and the load current measurement devices are connected with the converter controller, and wherein the converter controller is configured to additionally base the converter control on the load voltage and the load current.
  • the converter controller is configured to compare the load current with a threshold, wherein the converter controller is configured to determine, when the load current exceeds the threshold, a virtual resistance which is arranged to decrease the load current below the threshold.
  • the electric arc furnace operation system comprises a supply voltage measurement device and a supply current measurement device for measuring a supply voltage and a supply current.
  • the converter controller is configured to additionally base the control of the converter device on the measured supply voltage and supply current.
  • the converter device has an input and an output and comprises a first converter part connected with the input, a second converter part connected with output, and a mid converter part interconnecting the first and second parts.
  • the converter device is a back-to-back converter
  • An exemplifying embodiment of the present electric arc furnace operation system 100 comprises a converter device 101, connected with an electric arc furnace (EAF) 102 for supplying electric power to the EAF 102, an electrode controller 103, connected with electrodes 104 of the EAF 102 for controlling the position of the electrodes 104, and a converter controller 105, connected with the converter device 101 and controlling the converter device 101.
  • the converter device 101 is connected to an AC grid 106, at an input 110 of the converter device 101, and more particularly to grid power lines 107 via a grid transformer 108 and intermediate power lines 109 extending between the grid transformer 108 and the converter device 101.
  • the converter controller 105 is, additionally, connected with the electrode controller 103. More particularly, the converter device 101 is connected with the EAF 102 at an output 111 of the converter device 101 via load power lines 112, an EAF transformer 113 and electrode power lines 114 extending between the EAF transformer 113 and the electrodes 104.
  • the total system comprising the electric arc furnace operation system 100 and the electric arc furnace 104 is defined as an electric arc furnace system 150.
  • the electric arc furnace operation system 100 is operated as follows.
  • the converter device 101 supplies electric power from the AC grid 106 to the EAF 102, and more particularly to the electrodes 104 of the EAF 102.
  • the electrode controller 103 controls the arc impedance by means of adjusting the electrode positions in the EAF 102 to obtain an efficient melting process in the EAF 102, which requires different impedances at different stages of the melting process.
  • the converter controller 105 controls the converter device 101 to provide the required output voltage based on input from at least the electrode controller 103.
  • the electrode controller 103 additionally determines a reference voltage U REF , and a reference impedance Z REF comprising a reference inductance L REF and a reference resistance R REF , which provides a desired electrode current I EL through the electrodes 104.
  • a reference voltage U REF and a reference impedance Z REF comprising a reference inductance L REF and a reference resistance R REF , which provides a desired electrode current I EL through the electrodes 104.
  • the reference impedance Z REF may be constructed as a virtual impedance representing a total impedance of the electric arc furnace system 150.
  • the reference inductance L REF may be constructed as a virtual inductance
  • reference resistance R REF may be constructed as a virtual resistance
  • the reference voltage U REF may be constructed as a virtual voltage which, when applied across the whole electric furnace system, generates a desired electrode current I EL .
  • the electrode controller 103 may, for example, use a predetermined schedule which is related to the stage at which the melting process in the electric arc furnace presently is.
  • the present electrode voltage U EL and the present electrode current I EL may be measured by means of suitable voltage and current measurement devices 115, 116, connected with the electrode controller 105.
  • the electrode controller 103 uses the measurements to adjust the reference impedance Z REF and/or the reference voltage U REF .
  • the electrode controller 103 may emulate a tap-changer system, where different tap-changer positions are related with different source impedances and voltages, to be represented by a virtual controller impedance and a physical impedance of, inter alia, the converter device 101 and the EAF transformer 113, and by a converter voltage.
  • the converter controller 105 receives, from the electrode controller 103, the reference voltage U REF , and the reference impedance Z REF .
  • the reference inductance L REF may be regarded to comprise a virtual control inductance L C and a physical inductance L F of the electric arc furnace system 150, such that the sum of the physical inductance L F and the virtual control inductance Lc equals the reference inductance L REF , or, if desired, matches some other appropriate relation between the virtual control inductance L C and the reference inductance L REF .
  • the converter controller 105 is configured to determine a converter reference voltage U CREF on basis of at least the reference voltage U REF , the reference impedance Z REF , both received from the electrode controller 103, the physical inductance L F , which is predetermined, and an electrode voltage U EL , which can be the above-mentioned electrode voltage and is received from the electrode controller 103 as well or measured in some other way.
  • the converter controller 105 controls the converter device 101 to generate an output voltage U CON on basis of the converter reference voltage U CREF .
  • FIG. 2 shows a schematic diagram of the electric arc furnace system 150 illustrating the control principle.
  • the physical inductance L F of the electric arc furnace system 150 is represented in the diagram by a first inductor denoted L F .
  • the physical inductance L F of the electric arc furnace system 150 is a sum of physical inductances of the converter device 101, the EAF transformer 113, the electrodes 104, electrode power cables, etc.
  • the virtual control inductance Lc is represented by a second inductor denoted Lc.
  • the reference resistance R REF is represented by a resistor denoted R REF .
  • the operations performed by the converter controller 105 include determining the converter reference voltage U CREF This determination can be expressed mathematically as follows.
  • the converter voltage reference U CREF is defined as the converter voltage output behind the physical reactance, or the converter voltage at no load, and it can be expressed as follows:
  • the measured electrode voltage U EL is the electrode voltage measured at the secondary side of the EAF transformer 114, as shown in Figure 2 .
  • a converter output voltage U CON at the output 111 of the converter device 101 is the converter reference voltage U CREF minus a voltage drop across phase reactors at the output end of the converter device 101, such as for example illustrated by inductors 127 in Figure 4 .
  • a load voltage U L and a load current I L may be measured, by means of suitable voltage and current measurement devices 128, 129, between the converter output 111 and the EAF 102. For instance, as shown in Figure 2 , the measurements are performed between the converter device 101 and the EAF transformer 113.
  • the voltage and current measurement devices 128, 129 are connected with the converter controller 105, which uses the values of the load voltage U L and load current I L for feedback control of the converter output voltage U CON , and thus of the converter reference voltage U CREF .
  • the load voltage U L may be the same as the above-mentioned electrode voltage U EL
  • the load current I L may be the same as the above-mentioned electrode current I EL .
  • the method operating an electric arc furnace may contain the following main operations.
  • the converter device 101 may be a Back to Back (B2B) converter, as shown in Figure 3 . While being an AC-AC converter as a whole, looking at the input 110 and output 111 of the converter device 101, on a more detailed level it is an AC-DC-AC converter having a first Voltage Source Converter (VSC) part 117 connected with the input 110 of the converter device 101, a second VSC part 118, connected with the output 111 of the converter device 101, and an intermediate DC part 119 interconnecting the first and second VSC parts 117, 118.
  • VSC Voltage Source Converter
  • An advantage of this kind of converter is that it can be used for controlling reactive power on the AC grid side to minimize flicker, voltage variations, etc.
  • the converter controller 105 additionally uses measurements of the supply voltage Is and the supply current Us, measured by means of suitable supply voltage and supply current measurement devices 120, 121. Furthermore, the converter controller 105, in addition to voltage magnitudes controls the phase angle of the voltages in order to obtain the reactive power control, such that the converter device 101, and more particularly the first VSC part 117 in conjunction with the second DC part 118, either consumes reactive power from or generates reactive power to the AC grid 106.
  • Each VSC part 117, 118 comprises two converter units 122 arranged in parallel in two branches, which in turn are connected with the DC part 119.
  • Each converter unit 122 has three modules 123 each.
  • the modules 123 of the first VSC part 117 are connected with one phase each of the 3-phase AC grid 106 via phase reactors 127, and the modules 123 of the second VSC part 118 are connected with one phase each of the output lines via phase reactors 127.
  • Each module 123 comprises several cells 124 connected in series, where each cell 124 comprises several switches 125 and a capacitor element 126.
  • Each cell 124 can be switched between a state where it is inserted and contributes to a total voltage across the module 123 and a state where it is bypassed and provides no contribution.
  • the converter device 101 may be a Matrix Modular Multi-level Converter (MMMC) 201 as shown in Figure 5 .
  • the MMMC 201 comprises three converter units 202 connected in parallel.
  • Each converter unit 202 comprises three modules 203, one for each phase.
  • An input end of each module 203 is connected to a phase line 206 at the input 204 of the MMMC 201, and an output end of each module 203 is interconnected with the output ends of the other two modules of the converter unit 202 and connected to one of the phase lines 207 at the output 205 of the MMMC.
  • the converter units 202 are connected to one phase each at the output 205 of the MMMC 201.
  • the converter controller 105 comprises the ordinary units for detailed control of the converter device 101, i.e. cell selection units, such as e.g. one or more pwm units for determining how many cells to insert or bypass in each module, one or more cell selector units for determining which cells within each module to insert or bypass, gate units for operating the individual switches of the cells, etc., in order to generate the converter output voltage U CON . Since this is well known to the person skilled in the art no further description thereof will be made.
  • cell selection units such as e.g. one or more pwm units for determining how many cells to insert or bypass in each module, one or more cell selector units for determining which cells within each module to insert or bypass, gate units for operating the individual switches of the cells, etc.
  • the converter controller 105 may additionally receive a reference frequency F REF from the electrode controller 103.
  • the converter controller 105 is configured to use the reference frequency F REF for optimizing the melting down process of the EAF 102 and for reducing the electrode power consumption. For example, the frequency may be increased at the beginning of the process and then a lower frequency can be used when the arc is more stable to increase the metal production.
  • the converter controller 105 may additionally be configured to compare the load current I L with a threshold, and to determine whether the load current I L exceeds the threshold or not. When the load current I L exceeds the threshold, the converter controller 105 will determine a virtual resistance which is added to the reference resistance to decrease the electrode current below the threshold.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Discharge Heating (AREA)
EP22184832.8A 2022-07-13 2022-07-13 Procédé et système de commande d'un four à arc électrique Pending EP4307834A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP22184832.8A EP4307834A1 (fr) 2022-07-13 2022-07-13 Procédé et système de commande d'un four à arc électrique

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EP22184832.8A EP4307834A1 (fr) 2022-07-13 2022-07-13 Procédé et système de commande d'un four à arc électrique

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EP4307834A1 true EP4307834A1 (fr) 2024-01-17

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2926182A1 (fr) * 2008-01-08 2009-07-10 Toulouse Inst Nat Polytech Dispositif d'alimentation electronique de puissance pour four a arc alimente en courant alternatif.
US20110176575A1 (en) * 2008-09-30 2011-07-21 Hoerger Wolfgang Power supply system for a polyphase arc furnace with an indirect converter between a mains connection and a furnace transformer
EP3124903A1 (fr) * 2015-07-30 2017-02-01 Danieli Automation SPA Appareil et procédé pour l'alimentation électrique d'un four à arc électrique
US10470259B2 (en) 2014-05-19 2019-11-05 Siemens Aktiengesellschaft Power supply for a non-linear load with multilevel matrix converters

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2926182A1 (fr) * 2008-01-08 2009-07-10 Toulouse Inst Nat Polytech Dispositif d'alimentation electronique de puissance pour four a arc alimente en courant alternatif.
US20110176575A1 (en) * 2008-09-30 2011-07-21 Hoerger Wolfgang Power supply system for a polyphase arc furnace with an indirect converter between a mains connection and a furnace transformer
US10470259B2 (en) 2014-05-19 2019-11-05 Siemens Aktiengesellschaft Power supply for a non-linear load with multilevel matrix converters
EP3124903A1 (fr) * 2015-07-30 2017-02-01 Danieli Automation SPA Appareil et procédé pour l'alimentation électrique d'un four à arc électrique

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