EP2276323A1 - Elektrische Netzteilschaltung - Google Patents

Elektrische Netzteilschaltung Download PDF

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Publication number
EP2276323A1
EP2276323A1 EP09425287A EP09425287A EP2276323A1 EP 2276323 A1 EP2276323 A1 EP 2276323A1 EP 09425287 A EP09425287 A EP 09425287A EP 09425287 A EP09425287 A EP 09425287A EP 2276323 A1 EP2276323 A1 EP 2276323A1
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EP
European Patent Office
Prior art keywords
phase
power circuit
circuit according
frequency converter
voltage
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.)
Withdrawn
Application number
EP09425287A
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English (en)
French (fr)
Inventor
Marco Passoni
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.)
Calamari SpA
Original Assignee
Calamari SpA
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 Calamari SpA filed Critical Calamari SpA
Priority to EP09425287A priority Critical patent/EP2276323A1/de
Publication of EP2276323A1 publication Critical patent/EP2276323A1/de
Withdrawn legal-status Critical Current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
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/06—Control, e.g. of temperature, of power
    • H05B6/067—Control, e.g. of temperature, of power for melting furnaces

Definitions

  • the present invention relates to an electrical power supply circuit to supply and control at least one load, for example an induction heating element for industrial machines for the extrusion of metal section bars.
  • a metal billet is fed longitudinally through an electric induction furnace capable of heating it to increase the plasticity and facilitate deformation thereof during extrusion through a die which defines the final section.
  • furnaces suitable for the purpose some are known which are divided longitudinally into subsequent sections controlled with different temperatures dictated by the plastic deformation requirements of the billet material along the extrusion path thereof.
  • each section to a respective pair of phases means that areas are divided preferably into multiples of three, as by using fewer the system would be unbalanced.
  • the object of the invention is therefore to provide an electrical power circuit able to substantially overcome the aforesaid drawbacks.
  • Another object of the present invention is to provide a power circuit able to regulate the power supplied to each heating element separately.
  • a further object of the present invention is to provide a power circuit which is flexible and simple to use for multiple power distribution configurations to more than one furnace.
  • Yet another object of the present invention is to provide a power circuit which is able to achieve a high power factor cos ⁇ , also for low supply powers of the heating elements.
  • One more object of the present invention is to provide an electrical power circuit with a configuration suitable to allow cooling of the components of which it is composed, in a simple and inexpensive manner, while ensuring safe electrical insulation.
  • a further object of the present invention is to provide a power circuit which is able to ensure high reliability and duration in time.
  • a power circuit to supply and control at least one heating element as claimed in the attached claim 1.
  • heating elements 5 comprising coils 19 wound in the form of solenoid and arranged aligned upstream of the die, inside which the billet is fed to heat it through the known mechanism of electromagnetic induction.
  • the power circuit 10 comprises an electrical power source 6, of the alternating current three phase type, a rectifier 3 suitable to transform the alternating voltage of the three-phase source 6 into a single-phase direct voltage downstream of the rectifier 3, a frequency converter 4, arranged downstream of the rectifier 3, suitable to transform the single-phase direct voltage downstream of the rectifier 3 into single-phase alternating voltage downstream of the converter 4, suitable to supply the heating element.
  • the circuit 10 also comprises a PLC, not shown in the figure, suitable to control the frequency converter 4, in such a manner as to supply downstream of the converter 4 a desired value of frequency and of single-phase effective voltage to supply the heating element 5.
  • a PLC not shown in the figure, suitable to control the frequency converter 4, in such a manner as to supply downstream of the converter 4 a desired value of frequency and of single-phase effective voltage to supply the heating element 5.
  • the circuit 10 comprises a three-phase transformer 1 suitable to adapt the power supply voltage of the source 6 to a voltage value suitable to supply the furnace 5.
  • the three-phase transformer 1 also performs the function of galvanic separation between the power supply of the source 6 and the supply circuit 10.
  • the three-phase transformer 1 has a double secondary and therefore has two separate secondary windings, one of which is star, or "Y”, connected, and one delta, or "D", connected, from which a first three-phase line 7 and a second three-phase line 8 extend respectively at the same voltage, which share the line power equally, and which reunite upstream of the rectifier 3.
  • Y star
  • D delta
  • each line 7 and 8 has a respective switch 9.
  • each line can have respective precharge resistors 12.
  • a three-phase transformer 1 of the rectifiable type with 12 pulses is selected, in order to achieve a substantially sinusoidal waveform downstream of the transformer 1, as shown in Fig. 2 , where the wave 21 output from the transformer is compared with the ideal sinusoidal wave 20.
  • the three-phase voltage output from the two lines 7 and 8, is thus input to the rectifier 3.
  • This rectifier 3 advantageously comprises uncontrolled diodes 13, connected as shown in Fig. 1 in order to obtain the maximum angle of flow and minimum harmonic pollution coming from the three-phase voltage upstream. In this manner, a constant direct voltage 22 proportional to the input three-phase line voltage 23 is output from the rectifier 3, as shown in Fig. 3 .
  • the frequency converter 4, shown in Fig. 1 advantageously comprises at least one semiconductor transistor 14 of IGBT type (Insulated Gate Bipolar Transistor), with switch on and switch off controllable through a signal sent by said PLC. These transistors are connected in an H-shaped bridge configuration, in such a manner as to selectively and alternately connect the positive and negative pole of the single-phase direct voltage output from the rectifier 3 to a respective end of the resistive load of the heating element 5.
  • IGBT type Insulated Gate Bipolar Transistor
  • each transistor 14 is equivalent to a switch which can be closed or opened through an electrical open/close signal sent by the PLC.
  • the converter 4 of Fig. 1 can be schematized as in Fig. 4 , in which Vin is the direct voltage downstream of the rectifier 8, Vout is the single-phase alternating voltage sent to the heating element 5, and the switches 15 represent the transistors 14.
  • the heating element 5 besides having a coil 19, also comprises two reactors 16 and 17 and a capacitor 18, suitable to adapt the stepped alternating voltage output from the convertor to a sinusoidal alternating voltage input to the coil 19.
  • Fig. 5 shows the voltage 25 and current 24 trend output from the converter 4
  • Fig. 6 shows the corresponding voltage 27 and current 26 trend output from the power factor correction reactors in input to the coil 19.
  • the circuit 10 is provided with a plurality of frequency converters 4 connected in parallel downstream of the rectifier 3, each frequency converter supplying a respective heating element 5.
  • the PLC is capable of controlling each single converter 4, and therefore each heating element 5, separately.
  • FIG. 8 An example of such configuration is described in Fig. 8 , in which twelve heating elements 5 are provided, divided into two groups 42 and 43 of six elements each.
  • Each group 42 and 43 is managed by a respective PLC 40 and 41 capable of controlling the heating groups 5 separately by means of a respective frequency converter 4.
  • the system is supplied by a single source with three-phase alternating voltage 6, and comprises a three-phase transformer 1 with double secondary, of which one is star connected and the other delta connected.
  • a respective three-phase line 7 and 8 at the same voltage, i.e. 520V, extends from each secondary, and reunite in the rectifier 3.
  • a single-phase direct voltage line, i.e. at 780V extends downstream of the rectifier 3, and on which all the frequency converters 4 are connected.
  • the PLC 40 and 41 supplies these converters 4 with a preset sequence of pulses on which the frequency and effective voltage supplied to each heating element 5 depends, according to a function described below.
  • the aforesaid two groups of six heating elements can each belong to two separate furnaces, allowing high flexibility in the possibility of multiple distribution of the power, applying it simultaneously to more than one furnace.
  • high powers are fed through the components of such circuit, they tend to become hot due to power losses, and therefore require a continuous cooling process.
  • the largest losses and consequently the most heat are localized in the power transformer 1, in the rectifier 3, in the converter or inverter 4 and in the filter reactors 16 and 17.
  • the transformer 1 must be maintained at a temperature of around 40-45 °C, while the PLC and the regulation electronics must be maintained at a temperature of 30-35°C.
  • this object is achieved by integrating several components in a single block 50 in such a manner as to use a single heat exchanger.
  • the rectifier 3 and the frequency converter 4 are contained in a same sealed container 51 electrically insulated and provided on a first face 52 with a electrically insulated and thermally conductive heat sink layer 55 which can face a heat exchanger, not shown.
  • a second face of the sealed container comprises the electrical connections 53, 54 and 56.
  • the layer 55 comprises a thin layer of electrically insulating material interposed between the components contained and the outside, externally coated by a copper or aluminium heat sink substrate.
  • a copper or aluminium heat sink substrate for example the rectifier and the converter, to be buried directly in an insulating matrix, for example made of plastic or ceramic materials, which forms the container 51.
  • the present invention can also be implemented in other embodiments, in which the sealed container 51 can also include other components therein, selected from the three-phase transformer, filter reactors or yet other components.
  • Operation of a circuit according to the invention and in particular of the frequency converter 4, the structure of which is described above, is as follows. With reference to Figs. 1 and 4 , analyzing the converter 4, commonly known as "inverter”, each of the four transistors 14, schematized with a switch 15, has two possible states, ON and OFF, for a total of sixteen theoretical configuration combinations.
  • An inversion of the output voltage corresponds to each alternation of the two active configurations, so as to achieve an alternating voltage, but in steps. In this manner, if the two configurations are cyclically altered with the same duration a null, or alternating, mean output voltage is achieved, the frequency of which is variable simply by varying the period of the cycle and therefore the duration of the configurations.
  • FIG. 7 shows, in a first graph, an instantaneous voltage trend 29 corresponding to active phases 31 and 32 of maximum duration and recirculation phase 33 of null duration, and, in the second graph, an instantaneous voltage trend 30 with active phases 31 and 32 of lesser duration and recirculation phase of greater duration, of the same period 28 with respect to the first graph.
  • the first graph corresponds to a maximum power supplied to the heating element, while the second corresponds to an intermediate power.
  • switching from one active configuration 31 to the other 32 passes through a recirculation configuration 33 which introduces a null level on the instantaneous output voltage 29, 30, which has a total of three levels: the null level 33, where the instantaneous voltage is equal to zero and two active levels 31 and 32 of an amplitude equal to the output voltage of the rectifier 3 and with opposite polarity.
  • the four possible configurations of the transistors are alternated with the operating frequency of the furnace, which is thus established unequivocally through the cycle period 28.
  • the effective output voltage is reduced. In this way, it is possible to vary the effective voltage output from the inverter 4 from zero to a maximum equal to the rectified input voltage. Therefore, the inverter 4 performs the two effective frequency and voltage regulations of the system.
  • the invention achieves important advantages.
  • the power circuit according to the invention allows all the heating elements of a furnace for extrusion machines to be controlled separately, in such a manner as to optimize the temperatures in the different subsequent sections in complete freedom, without causing unbalances in the system.
  • Another important advantage of the present invention is that of being able to use any number of heating elements and not necessarily multiples of three.
  • An important advantage of the present invention is to allow high flexibility and simple implementation for configurations of multiple distribution of the power generated, applying it simultaneously to more than one furnace.
  • a further advantage of the present invention is that of allowing simple and inexpensive cooling of the components through an air/water heat exchanger which does not require high qualities of the water used, due to a large surface of the heat sink layer.
  • One more advantage of the present invention is the fact that it achieves a high power factor cos ⁇ , between 0.98 and 1, which makes the use of a bank of power factor correction capacitors unnecessary.
  • Another advantage of the present invention is that of reaching the nominal cos ⁇ value already at 20% of the power regulation.
  • an advantage of the present invention is reduced harmonic distortion.
  • furnaces can be synchronized so that each one, or each group, has a high power heating period and a temperature maintenance period at a lower power, in particular around one fifth of the high power.
  • Said heating and maintenance periods are preferably alternated, so that while one group of furnaces, or a single furnace, is in heating mode, a second group of furnaces, or single furnace, is in maintenance mode.
  • induction furnaces for billets require a first heating period at maximum power, during which the whole billet is heated homogeneously, and a second maintenance period, during which only some areas of the billets are heated, while other areas are maintained at a constant temperature.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Induction Heating (AREA)
EP09425287A 2009-07-16 2009-07-16 Elektrische Netzteilschaltung Withdrawn EP2276323A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP09425287A EP2276323A1 (de) 2009-07-16 2009-07-16 Elektrische Netzteilschaltung

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP09425287A EP2276323A1 (de) 2009-07-16 2009-07-16 Elektrische Netzteilschaltung

Publications (1)

Publication Number Publication Date
EP2276323A1 true EP2276323A1 (de) 2011-01-19

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Family Applications (1)

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EP09425287A Withdrawn EP2276323A1 (de) 2009-07-16 2009-07-16 Elektrische Netzteilschaltung

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EP (1) EP2276323A1 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3790180A1 (de) 2019-09-04 2021-03-10 IAS GmbH Vorrichtung und verfahren zur induktiven erwärmung von metallgut

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1511457A (fr) * 1966-02-15 1968-01-26 Heraeus Hochvakuum Gmbh Procédé de fusion de métal dans un four à induction sans noyau suivie d'un brassage du métal fondu et four à induction pour la mise en oeuvre de ce procédé
WO2000051410A2 (en) * 1999-03-05 2000-09-08 Abb Metallurgy Resonant frequency induction furnace system using capacitive voltage division
US20060118549A1 (en) * 2004-12-08 2006-06-08 Inductotherm Corp. Electric induction control system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1511457A (fr) * 1966-02-15 1968-01-26 Heraeus Hochvakuum Gmbh Procédé de fusion de métal dans un four à induction sans noyau suivie d'un brassage du métal fondu et four à induction pour la mise en oeuvre de ce procédé
WO2000051410A2 (en) * 1999-03-05 2000-09-08 Abb Metallurgy Resonant frequency induction furnace system using capacitive voltage division
US20060118549A1 (en) * 2004-12-08 2006-06-08 Inductotherm Corp. Electric induction control system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3790180A1 (de) 2019-09-04 2021-03-10 IAS GmbH Vorrichtung und verfahren zur induktiven erwärmung von metallgut

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