EP1935213B1 - Method for operating an induction heating device - Google Patents

Method for operating an induction heating device Download PDF

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Publication number
EP1935213B1
EP1935213B1 EP06806263A EP06806263A EP1935213B1 EP 1935213 B1 EP1935213 B1 EP 1935213B1 EP 06806263 A EP06806263 A EP 06806263A EP 06806263 A EP06806263 A EP 06806263A EP 1935213 B1 EP1935213 B1 EP 1935213B1
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EP
European Patent Office
Prior art keywords
voltage
wave
induction coil
transistor
intermediate circuit
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EP06806263A
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German (de)
French (fr)
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EP1935213A1 (en
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Wilfried Schilling
Ralf Dorwarth
Martin Volk
Tobias SCHÖNHERR
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EGO Elektro Geratebau GmbH
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EGO Elektro Geratebau GmbH
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Priority to SI200630281T priority Critical patent/SI1935213T1/en
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    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00Heating by electric, magnetic or electromagnetic fields
    • H05B6/02Induction heating
    • H05B6/06Control, e.g. of temperature, of power
    • H05B6/062Control, e.g. of temperature, of power for cooking plates or the like

Definitions

  • the invention relates to a method for operating an induction heating device according to the preamble of claim 1.
  • an induction coil is subjected to an alternating voltage or an alternating current, whereby eddy currents are induced in a cookware to be heated, which is magnetically coupled to the induction coil.
  • the eddy currents cause heating of the cookware.
  • the mains input voltage is usually first rectified by means of a rectifier into a DC supply voltage or intermediate circuit voltage and then processed to generate the high-frequency drive voltage by means of one or more switching means, generally insulated gate bipolar transistors (IGBT) ,
  • IGBT insulated gate bipolar transistors
  • a first converter variant forms a converter in full bridge circuit, in which the induction coil and a capacitor are connected in series between two so-called half bridges.
  • the half bridges are each looped between the intermediate circuit voltage and the reference potential.
  • the induction coil and the capacitor form a series resonant circuit.
  • Another converter variant forms a half-bridge circuit of two IGBTs, wherein the induction coil and two capacitors, which are connected in series between the intermediate circuit voltage and the reference potential, form a series resonant circuit.
  • the induction coil is connected to a connection to a connection point of the two capacitors and to its other connection to a connection point of the two IGBTs forming the half-bridge.
  • a variant optimized from a cost point of view uses only one switching means or an IGBT, wherein the induction coil and a capacitor form a parallel resonant circuit. Between the output terminals of the rectifier, parallel to the DC link capacitor, the parallel resonant circuit of induction coil and capacitor are connected in series with the IGBT.
  • Allen mentioned inverter variants have in common that the link capacitor charges during a first half-wave to an open circuit voltage with an amount of peak value of the AC line voltage, for example, to 325V at a mains AC voltage of 230V, as soon as they are supplied with mains voltage.
  • the invention is therefore based on the object to provide a method for operating an induction heater with a converter available that allows reliable, component-saving and quiet operation of the induction heater with low noise radiation.
  • the intermediate circuit capacitor is discharged to a threshold value by driving the switching means in a time range before a zero crossing of the AC mains voltage before the induction coil is driven to produce an adjustable heating power, which already during discharge a small heating power supply in an optionally existing cookware.
  • the discharge of the intermediate circuit capacitor causes that at a start of a heating process, ie when the induction coil is to deliver heating power to a cookware, the intermediate circuit capacitor is substantially discharged. If at this time the switching means is turned on or conductive, there is no or only a small current pulse through the switching means and the resonant circuit of induction coil and capacitor. Consequently, there is no switch-on noise and the pulse current load of the power components is reduced, which increases their life.
  • the actual heating process can be carried out in a conventional manner, for example, the or the switching means can be controlled with a square wave signal with a working frequency and an associated Hätastfood.
  • the inverter is consequently started up with small currents or voltages in the area of the zero crossing. With the rise of the half-wave after the zero crossing, the inverter can adjust to its, the set heating power corresponding operating point with a working frequency and a duty cycle.
  • the converter is a single-transistor converter.
  • the at least one switching means preferably forms the switching means of the single-transistor converter.
  • the inverter is designed in full-bridge circuit or half-bridge circuit, wherein the at least one switching means is part of a bridge.
  • the time range starts from 1 ms to 5 ms, preferably 2.5 ms, before the zero crossing of the mains alternating voltage.
  • the threshold is in a range of 0V to 20V.
  • the intermediate circuit capacitor is discharged to 0V. This allows a practically impuls current-free starting of the inverter.
  • the at least one switching means is a transistor, in particular an IGBT.
  • the transistor for discharging the intermediate circuit capacitor is driven during the discharge such that a linear operating state of the transistor is established. Since the transistor does not completely switch through in this operating mode or this operating state, the DC link capacitor is discharged slowly along the mains half-cycle. The resulting currents through the parallel resonant circuit and the transistor remain relatively low, whereby noise is avoided or significantly reduced.
  • the switching means for discharging the DC link capacitor is driven with a pulse width modulated square wave signal.
  • the square-wave voltage signal preferably has a frequency in the range from 20 kHz to 50 kHz, in particular 39 kHz, and / or an on / off ratio in the range from 1/300 to 1/500, in particular 1/378.
  • the frequency and / or the on / off ratio is preferably adapted to a used IGBT type, its drive voltage, a driver circuit used for generating the drive voltage and / or to a capacitance value of the DC link capacitor.
  • the adjustable heating power is generated by means of a half-wave pattern, wherein the intermediate circuit capacitor is discharged before activation of a half-wave.
  • a heating power generation With the aid of the half-wave pattern, individual half-waves of the mains alternating voltage are completely blanked out or deactivated, ie not used for heating power generation.
  • 1/3-Netzraumwellen Say example, only one of three consecutive half-waves for power supply to the resonant circuit or the induction coil is used or activated. During the remaining two half-cycles, the switching means remains open, ie no power is fed into the resonant circuit.
  • a 2/3 mains half-wave operation two out of three consecutive half-waves are used or activated for supplying power to the oscillating circuit or the induction coil.
  • power adjustment is done in a conventional manner.
  • Line half-wave operation allows finer resolution of power levels over a wide power setting range.
  • Such a power setting is particularly advantageous for single-transistor converters.
  • an open-circuit voltage for example, 325V at 230V mains voltage, turns on the intermediate circuit capacitor during an inactive half-wave, during which no power is fed into the resonant circuit.
  • Fig. 1 shows a circuit diagram of an induction heater in the form of a Eintransistorumrichters EU.
  • the induction heating device may also include further, not shown, identically constructed single-transistor converter EU and additional conventional components, such as control elements for power adjustment, etc.
  • the single-transistor converter EU comprises a bridge rectifier GL, which generates a DC link voltage UG from an AC input voltage UN of 230V and 50Hz, a buffer or DC link capacitor C1 for stabilizing or buffering the intermediate DC voltage UG connected between output terminals N1 and N2 of the rectifier GL Induction coil L1 and a capacitor C2, which are connected in parallel and form a parallel resonant circuit, a controllable switching means in the form of an IGB transistor T1, which is looped in series with the resonant circuit between the output terminals N1 and N2 of the rectifier GL, a freewheeling diode D1, the is connected in parallel with a collector-emitter path of the IGB transistor T1, and a control unit SE, for example in the form of a microprocessor or a digital signal processor.
  • a control unit SE for example in the form of a microprocessor or a digital signal processor.
  • the control unit SE carries out the invention, hereinafter with reference to Fig. 2 described operating method for operating the Eintransistorumrichters EU and may include other, not shown actuators and / or sensors, for example, for mains voltage monitoring, include or be coupled with these.
  • Fig. 2 does not show true-to-scale timing diagrams of signals from the single-pole converter EU of Fig. 1 , Due to the mains frequency of the input mains AC voltage UN of 50 Hz, a zero crossing takes place every 10 ms between adjacent mains half-waves H1 to H3 of the input mains AC voltage UN.
  • the single-transistor converter EU is operated in 2/3 mains half-wave operation, ie power is fed into the parallel resonant circuit or into the induction coil L1 only during two out of three mains half-cycles.
  • Fig. 1 Due to the mains frequency of the input mains AC voltage UN of 50 Hz, a zero crossing takes place every 10 ms between adjacent mains half-waves H1 to H3 of the input mains AC voltage UN.
  • the single-transistor converter EU is operated in 2/3 mains half-wave operation, ie power is fed into the parallel resonant circuit or into the induction coil L1 only during two out of three mains half-cycles
  • the half-waves H2 and H3 are the active half-waves during which power is applied, and the mains half-wave H1 is the inactive half-wave during which no power feed takes place.
  • the IGB transistor T1 blocks, except for a transition region or predefinable discharge time range INT, during which the intermediate circuit capacitor C1 is discharged.
  • UC is a voltage at the collector of the IGB transistor T1 with respect to a reference potential applied to the terminal N1 of the rectifier GL.
  • an open circuit voltage with an amount of a peak value of the mains AC voltage UN at the collector, i. in the illustrated embodiment about 325V.
  • the active half waves H2 and H3 power is fed into the induction coil L1.
  • This can be effected in a conventional manner, for example by driving the IGB transistor T1 with a square-wave voltage signal having a frequency and a duty cycle, which are adjusted depending on the power to be injected during the half-wave.
  • the IGB transistor T1 is driven by a rectangular voltage signal, not shown, with a frequency of about 39 kHz and an on / off ratio of about 1/378.
  • the drive pulses are so short that they are insufficient to clear the charge on the IGB transistor gate.
  • the IGB transistor T1 is therefore not completely turned on, but goes into a linear operation mode.
  • the voltage UC at the collector of the IGB transistor T1 which in this case corresponds to the voltage UG at the intermediate circuit capacitor C1, thereby drops as shown slowly along the network half-wave as an envelope to about 0V.
  • the signal UC is shown with greater temporal resolution. From this the switching frequency of the IGBT of approx. 39kHz becomes visible during the discharging process.
  • the IGB transistor T1 is driven in a conventional manner with a square-wave voltage signal, not shown.
  • Fig. 2 is the envelope of the resulting voltage UC and a partial enlargement of the signal UC shown with greater temporal resolution.
  • the voltage UC increases due to the vibration in the parallel resonant circuit to values well above the open circuit voltage.
  • the envelope has a sinusoidal shape, which follows the rectified input AC voltage UN.
  • the course of the voltage UC shown repeats during the half wave H3.
  • the frequency of the drive signal of the IGBT T1 in this operating state is approximately 22 kHz.
  • the IGB transistor T1 is deactivated, whereby the voltage UC rises again to its no-load value of approximately 325V.
  • the discharge process is repeated, as shown for the half-wave H1. The processes described are repeated periodically.
  • the converter circuit can start with small voltages and currents and adjust with the increase of the mains half-wave to its actual operating point of suitable frequency and duty cycle.
  • the discharge frequency and duty cycle can be adjusted to operate the IGB transistor in linear mode during discharge.
  • Fig. 3 shows a circuit diagram of an inverter HU in half-bridge circuit, which is operated with the operating method according to the invention.
  • Components with compared to Fig. 1 identical function are the same Provided with reference numerals. Regarding their functional description is on Fig. 1 directed.
  • a half-bridge is formed of IGBTs T2 and T3, which are serially connected between the output terminals N1 and N2 of the rectifier GL.
  • Freewheeling diodes D2 and D3 are connected in parallel to an associated collector-emitter path of the IGBTs T2 and T3, respectively.
  • Capacitors C3 and C4 are also serially connected between the output terminals N1 and N2. Between a connection node N3 of the IGBTs T2 and T3 and a connection node N4 of the capacitors C3 and C4, the induction coil L1 is looped. It forms a series resonant circuit together with the capacitors C3 and C4.
  • the IGBTs T2 and T3 are driven by the control unit SE.
  • a power setting can be done in a conventional manner, for example by a frequency adjustment of the control signals generated by the control unit SE IGBTs.
  • the intermediate circuit capacitor C1 and the capacitors C3 and C4 are discharged by driving the IGBTs T2 and T3.
  • This is done analogously to that with reference to Fig. 2 described method by driving the IGBTs T2 and T3 with rectangular voltage signals with a suitable frequency and suitable on / off ratio. Again, the drive pulses are so short that they are insufficient to clear the charge at the respective IGB transistor gate. The IGB transistors T2 and T3 are therefore not completely turned on, but go into a linear operation mode.
  • Fig. 4 shows a circuit diagram of an inverter VU in full bridge circuit, which is operated with the operating method according to the invention.
  • Components with compared to Fig. 1 identical function are provided with the same reference numerals. Regarding their functional description is on Fig. 1 directed.
  • a first half-bridge is formed of IGBTs T4 and T5 and a second half-bridge of IGBTs T6 and T7, which are respectively connected in series between the output terminals N1 and N2 of the rectifier GL.
  • Free-wheeling diodes D4 to D7 are connected in parallel with in each case one associated collector-emitter path of the IGBTs T4 to T7.
  • the induction coil L1 and a capacitor C5 are connected in series.
  • the inductor L1 and the capacitor C5 form a series resonant circuit.
  • the IGBTs T4 to T7 are driven by the control unit SE.
  • a power setting can be done in a conventional manner, for example by a frequency adjustment of the control signals generated by the control unit SE IGBTs.
  • the DC link capacitor C1 is discharged by driving the IGBTs T4 to T7.
  • This is done analogously to that with reference to Fig. 2 described method by driving the IGBTs T4 to T7 with square wave signals with a suitable frequency and suitable on / off ratio.
  • the drive pulses are again so short that they are not sufficient to clear the charge at the respective IGB transistor gate.
  • the IGB transistors T4 to T7 are therefore not completely turned on, but go into a linear operation mode.
  • all the IGBTs T4 to T7 or only certain IGBTs can be driven in such a way that a current path for discharging the DC link capacitor C1 is formed.
  • a current path for discharging the DC link capacitor C1 is formed.
  • only T4 and T5 only T6 and T7, only T4 and T7 or only T6 and T5 for discharge can be controlled.
  • the mains voltage is 230V and the mains frequency is 50Hz.
  • the operating method shown can be adapted to other mains voltages and mains frequencies.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Inverter Devices (AREA)
  • General Induction Heating (AREA)
  • Control Of High-Frequency Heating Circuits (AREA)
  • Rectifiers (AREA)

Abstract

The invention relates to a method for operating an induction heating device. The induction heating device comprises an induction coil and a frequency converter for producing a control voltage for the induction coil. The frequency converter comprises a rectifier rectifying an alternating supply voltage (UN), an intermediate circuit capacitor, looped in between output terminals of the rectifier and equalizing the rectified voltage (UG), and at least one controllable switching element, looped in between the output terminals of the rectifier. According to the invention, in a predetermined discharge interval (INT) before a zero crossing (ND) of the alternating supply voltage (UN), the intermediate circuit capacitor is discharged to a threshold value by controlling the at least one switching element before the induction coil is controlled in order to produce an adjustable heating capacity.

Description

Die Erfindung betrifft ein Verfahren zum Betrieb einer Induktionsheizeinrichtung nach dem Oberbegriff des Anspruchs 1.The invention relates to a method for operating an induction heating device according to the preamble of claim 1.

Bei Induktionsheizeinrichtungen wird eine Induktionsspule mit einer Wechselspannung bzw. einem Wechselstrom beaufschlagt, wodurch in einem magnetisch mit der Induktionsspule gekoppelten, zu erhitzenden Kochgeschirr Wirbelströme induziert werden. Die Wirbelströme bewirken eine Erhitzung des Kochgeschirrs.In induction heating devices, an induction coil is subjected to an alternating voltage or an alternating current, whereby eddy currents are induced in a cookware to be heated, which is magnetically coupled to the induction coil. The eddy currents cause heating of the cookware.

Zur Ansteuerung der Induktionsspule sind unterschiedliche Schaltungsanordnungen und Ansteuerverfahren bekannt. Allen Schaltungs- bzw. Verfahrensvarianten ist gemeinsam, dass sie aus einer niederfrequenten Netzeingangsspannung eine hochfrequente Ansteuerspannung für die Induktionsspule erzeugen. Derartige Schaltungen werden als Umrichter bezeichnet.For controlling the induction coil, different circuit arrangements and control methods are known. All circuit or process variants have in common that they produce a high-frequency drive voltage for the induction coil from a low-frequency power input voltage. Such circuits are referred to as converters.

Zur Umrichtung bzw. Frequenzwandlung wird üblicherweise zunächst die Netzeingangsspannung mit Hilfe eines Gleichrichters in eine Versorgungsgleichspannung bzw. Zwischenkreisspannung gleichgerichtet und anschließend zur Erzeugung der hochfrequenten Ansteuerspannung mit Hilfe von einem oder mehreren Schaltmitteln, im allgemeinen Insulated-Gate-Bipolar-Transistoren (IGBT), aufbereitet. Am Ausgang des Gleichrichters, d.h. zwischen der Zwischenkreisspannung und einem Bezugspotential, ist üblicherweise ein so genannter Zwischenkreiskondensator zur Pufferung der Zwischenkreisspannung vorgesehen.For conversion or frequency conversion, the mains input voltage is usually first rectified by means of a rectifier into a DC supply voltage or intermediate circuit voltage and then processed to generate the high-frequency drive voltage by means of one or more switching means, generally insulated gate bipolar transistors (IGBT) , At the output of the rectifier, ie between the intermediate circuit voltage and a reference potential, a so-called DC link capacitor for buffering the DC link voltage is usually provided.

Eine erste Umrichtervariante bildet ein Umrichter in Vollbrückenschaltung, bei dem zwischen zwei so genannten Halbbrücken die Induktionsspule und ein Kondensator seriell eingeschleift sind. Die Halbbrücken sind jeweils zwischen die Zwischenkreisspannung und das Bezugspotential eingeschleift. Die Induktionsspule und der Kondensator bilden einen Serienschwingkreis.A first converter variant forms a converter in full bridge circuit, in which the induction coil and a capacitor are connected in series between two so-called half bridges. The half bridges are each looped between the intermediate circuit voltage and the reference potential. The induction coil and the capacitor form a series resonant circuit.

Eine weitere Umrichtervariante bildet eine Halbbrückenschaltung aus zwei IGBTs, wobei die Induktionsspule und zwei Kondensatoren, die seriell zwischen die Zwischenkreisspannung und das Bezugspotential eingeschleift sind, einen Serienschwingkreis bilden. Die Induktionsspule ist mit einem Anschluss mit einem Verbindungspunkt der beiden Kondensatoren und mit ihrem anderen Anschluss mit einem Verbindungspunkt der beiden die Halbbrücke bildenden IGBTs verbunden.Another converter variant forms a half-bridge circuit of two IGBTs, wherein the induction coil and two capacitors, which are connected in series between the intermediate circuit voltage and the reference potential, form a series resonant circuit. The induction coil is connected to a connection to a connection point of the two capacitors and to its other connection to a connection point of the two IGBTs forming the half-bridge.

Sowohl die Variante mit Vollbrücke als auch die Variante mit Halbbrücke sind aufgrund der großen Anzahl benötigter Bauteile, insbesondere von IGBTs, jedoch vergleichsweise teuer.However, both the variant with full bridge and the variant with half bridge are relatively expensive due to the large number of components required, in particular of IGBTs.

Eine aus Kostengesichtspunkten optimierte Variante verwendet daher nur ein Schaltmittel bzw. einen IGBT, wobei die Induktionsspule und ein Kondensator einen Parallelschwingkreis bilden. Zwischen die Ausgangsanschlüsse des Gleichrichters, parallel zum Zwischenkreiskondensator sind der Parallelschwingkreis aus Induktionsspule und Kondensator seriell mit dem IGBT eingeschleift.Therefore, a variant optimized from a cost point of view uses only one switching means or an IGBT, wherein the induction coil and a capacitor form a parallel resonant circuit. Between the output terminals of the rectifier, parallel to the DC link capacitor, the parallel resonant circuit of induction coil and capacitor are connected in series with the IGBT.

Allen genannten Umrichtervarianten ist gemeinsam, dass sich der Zwischenkreiskondensator während einer ersten Netzhalbwelle auf eine Leerlaufspannung mit einem Betrag eines Scheitelwerts der Netzwechselspannung auflädt, beispielsweise auf 325V bei einer Netzwechselspannung von 230V, sobald diese mit Netzspannung versorgt werden.Allen mentioned inverter variants have in common that the link capacitor charges during a first half-wave to an open circuit voltage with an amount of peak value of the AC line voltage, for example, to 325V at a mains AC voltage of 230V, as soon as they are supplied with mains voltage.

Wenn keine Ansteuerspannung zur Leistungserzeugung der Induktionsspule erzeugt wird, d.h. das oder die Schaltmittel bzw. IGBTs sperren, bleibt die am Zwischenkreiskondensator anstehende Spannung in etwa konstant. Beim Starten des Umrichters, d.h. wenn die Induktionsspule zur Erzeugung einer einstellbaren Heizleistung angesteuert bzw. mit einer Wechselspannung beaufschlagt wird, fließt beim Einschalten des oder der IGBTs zunächst ein hoher Strom aus dem Zwischenkreiskondensator in den Schwingkreis und durch den oder die IGBTs. Dies verursacht ein hörbares Geräusch in einem durch die Induktionsheizeinrichtung beheizten Kochgeschirr, beispielsweise in einem Topfboden. Weiterhin reduziert sich die Lebensdauer der mit dem hohen Einschaltstrom beaufschlagten Bauelemente.
US4438311 offenbart ein Verfahren nach der Stand der Technik.
If no drive voltage for generating power of the induction coil is generated, that is to block the switching means or IGBTs, the voltage present at the intermediate circuit capacitor remains approximately constant. When starting the inverter, that is, when the induction coil is driven to generate an adjustable heating power or applied with an AC voltage flows when turning on the IGBTs or first, a high current from the DC link capacitor in the resonant circuit and by the IGBTs or. This causes audible noise in a cookware heated by the induction heater, for example, in a pot bottom. Furthermore, reduces the life of the acted upon by the high inrush current components.
US4438311 discloses a method according to the prior art.

Aufgabe und LösungTask and solution

Der Erfindung liegt daher die Aufgabe zugrunde, ein Verfahren zum Betrieb einer Induktionsheizeinrichtung mit einem Umrichter zur Verfügung zu stellen, das einen zuverlässigen, bauteileschonenden und geräuscharmen Betrieb der Induktionsheizeinrichtung mit geringer Störabstrahlung ermöglicht.The invention is therefore based on the object to provide a method for operating an induction heater with a converter available that allows reliable, component-saving and quiet operation of the induction heater with low noise radiation.

Die Erfindung löst diese Aufgabe durch ein Verfahren mit den Merkmalen des Anspruchs 1. Vorteilhafte sowie bevorzugte Ausgestaltungen der Erfindung sind Gegenstand der weiteren Ansprüche und werden im folgenden näher erläutert. Der Wortlaut der Ansprüche wird durch ausdrückliche Bezugnahme zum Inhalt der Beschreibung gemacht.The invention solves this problem by a method having the features of claim 1. Advantageous and preferred embodiments of the invention are the subject of the other claims and are explained in more detail below. The wording of the claims is incorporated herein by express reference.

Erfindungsgemäß wird in einem Zeitbereich vor einem Nulldurchgang der Netzwechselspannung der Zwischenkreiskondensator bis auf einen Schwellenwert durch Ansteuerung des Schaltmittels entladen, bevor die Induktionsspule zur Erzeugung einer einstellbaren Heizleistung angesteuert wird, wobei bereits bei der Entladung eine geringfügige Heizleistungseinspeisung in ein gegebenenfalls vorhandenes Kochgeschirr erfolgt. Die Entladung des Zwischenkreiskondensators bewirkt, dass bei einem Start eines Heizvorgangs, d.h. wenn die Induktionsspule Heizleistung an ein Kochgeschirr abgeben soll, der Zwischenkreiskondensator im wesentlichen entladen ist. Wenn zu diesem Zeitpunkt das Schaltmittel durchgeschaltet bzw. leitend wird, entsteht kein bzw. lediglich ein geringer Stromimpuls durch das Schaltmittel und den Schwingkreis aus Induktionsspule und Kondensator. Es entsteht folglich kein Einschaltgeräusch und die Impulsstrombelastung der Leistungsbauteile wird reduziert, wodurch sich deren Lebensdauer erhöht. Nach dem Entladen des Zwischenkreiskondensators, kann der eigentliche Heizvorgang in herkömmlicher weise erfolgen, beispielsweise kann das bzw. die Schaltmittel mit einem Rechtecksignal mit einer Arbeitsfrequenz und einem zugehörigen Arbeitstastverhältnis angesteuert werden. Der Umrichter wird folglich mit kleinen Strömen bzw. Spannungen im Bereich des Nulldurchgangs angefahren. Mit dem Anstieg der Halbwelle nach dem Nulldurchgang kann sich der Umrichter auf seinen, der eingestellten Heizleistung entsprechenden Arbeitspunkt mit einer Arbeitsfrequenz und einem Arbeitstastverhältnis einregeln.According to the invention, the intermediate circuit capacitor is discharged to a threshold value by driving the switching means in a time range before a zero crossing of the AC mains voltage before the induction coil is driven to produce an adjustable heating power, which already during discharge a small heating power supply in an optionally existing cookware. The discharge of the intermediate circuit capacitor causes that at a start of a heating process, ie when the induction coil is to deliver heating power to a cookware, the intermediate circuit capacitor is substantially discharged. If at this time the switching means is turned on or conductive, there is no or only a small current pulse through the switching means and the resonant circuit of induction coil and capacitor. Consequently, there is no switch-on noise and the pulse current load of the power components is reduced, which increases their life. After discharging the DC link capacitor, the actual heating process can be carried out in a conventional manner, for example, the or the switching means can be controlled with a square wave signal with a working frequency and an associated Arbeitstastverhältnis. The inverter is consequently started up with small currents or voltages in the area of the zero crossing. With the rise of the half-wave after the zero crossing, the inverter can adjust to its, the set heating power corresponding operating point with a working frequency and a duty cycle.

In einer Weiterbildung ist der Umrichter ein Eintransistorumrichter. Das mindestens eine Schaltmittel bildet hierbei bevorzugt das Schaltmittel des Eintransistorumrichters. Alternativ ist der Umrichter in Vollbrückenschaltung oder Halbbrückenschaltung ausgeführt, wobei das mindestens eine Schaltmittel Teil einer Brücke ist.In a further development, the converter is a single-transistor converter. The at least one switching means preferably forms the switching means of the single-transistor converter. Alternatively, the inverter is designed in full-bridge circuit or half-bridge circuit, wherein the at least one switching means is part of a bridge.

In einer Weiterbildung beginnt der Zeitbereich 1 ms bis 5ms, bevorzugt 2,5ms, vor dem Nulldurchgang der Netzwechselspannung. Dies ermöglicht eine zuverlässige Entladung des Zwischenkreiskondensators, bei vergleichsweise geringer Verlustleistungserzeugung im Schaltmittel durch den Entladevorgang.In a further development, the time range starts from 1 ms to 5 ms, preferably 2.5 ms, before the zero crossing of the mains alternating voltage. This allows a reliable discharge of the DC link capacitor, with comparatively low loss power generation in the switching means by the discharge.

In einer Weiterbildung liegt der Schwellenwert in einem Bereich von 0V bis 20V. Bevorzugt wird der Zwischenkreiskondensator auf 0V entladen. Dies ermöglicht ein praktisch impulsstromfreies Anfahren des Umrichters.In a further development, the threshold is in a range of 0V to 20V. Preferably, the intermediate circuit capacitor is discharged to 0V. This allows a practically impuls current-free starting of the inverter.

In einer Weiterbildung ist das mindestens eine Schaltmittel ein Transistor, insbesondere ein IGBT. Bevorzugt wird der Transistor zur Entladung des Zwischenkreiskondensators während der Entladung derart angesteuert, dass sich ein linearer Betriebszustand des Transistors einstellt. Da der Transistor in dieser Betriebsart bzw. diesem Betriebszustand nicht vollständig durchschaltet, wird der Zwischenkreiskondensator langsam, entlang der Netzhalbwelle entladen. Die entstehenden Ströme durch den Parallelschwingkreis und den Transistor bleiben vergleichsweise gering, wodurch eine Geräuschentwicklung vermieden bzw. deutlich verringert wird.In a development, the at least one switching means is a transistor, in particular an IGBT. Preferably, the transistor for discharging the intermediate circuit capacitor is driven during the discharge such that a linear operating state of the transistor is established. Since the transistor does not completely switch through in this operating mode or this operating state, the DC link capacitor is discharged slowly along the mains half-cycle. The resulting currents through the parallel resonant circuit and the transistor remain relatively low, whereby noise is avoided or significantly reduced.

In einer Weiterbildung wird das Schaltmittel zur Entladung des Zwischenkreiskondensators mit einem pulsweitenmodulierten Rechteckspannungssignal angesteuert. Bevorzugt weist das Rechteckspannungssignal eine Frequenz im Bereich von 20kHz bis 50kHz, insbesondere 39kHz, und/oder ein An/Aus-Verhältnis im Bereich von 1/300 bis 1/500, insbesondere 1/378, auf. Auf diese Weise kann ein kontrolliertes Entladen des Zwischenkreiskondensators bewirkt werden, ohne dass ein zu großer Entladestrom fließt. Die Frequenz und/oder das An/Aus-Verhältnis wird vorzugsweise an einen verwendeten IGBT-Typ, dessen Treiberspannung, eine verwendete Treiberschaltung zur Erzeugung der Treiberspannung und/oder an einen Kapazitätswert des Zwischenkreiskondensators angepasst.In a development, the switching means for discharging the DC link capacitor is driven with a pulse width modulated square wave signal. The square-wave voltage signal preferably has a frequency in the range from 20 kHz to 50 kHz, in particular 39 kHz, and / or an on / off ratio in the range from 1/300 to 1/500, in particular 1/378. In this way, a controlled discharge of the DC link capacitor can be effected without an excessive discharge current flows. The frequency and / or the on / off ratio is preferably adapted to a used IGBT type, its drive voltage, a driver circuit used for generating the drive voltage and / or to a capacitance value of the DC link capacitor.

In einer Weiterbildung wird die einstellbare Heizleistung mit Hilfe eines Halbwellenmusters erzeugt, wobei der Zwischenkreiskondensator vor einer Aktivierung einer Halbwelle entladen wird. Bei einer Heizleistungserzeugung mit Hilfe des Halbwellenmusters werden einzelne Halbwellen der Netzwechselspannung vollständig ausgeblendet bzw. deaktiviert, d.h. nicht zur Heizleistungserzeugung verwendet. Bei einem so genannten 1/3-Netzhalbwellenbetrieb wird beispielsweise lediglich eine von drei aufeinanderfolgenden Halbwellen zur Leistungseinspeisung in den Schwingkreis bzw. die Induktionsspule verwendet bzw. aktiviert. Während der verbleibenden beiden Halbwellen bleibt das Schaltmittel geöffnet, d.h. es wird keine Leistung in den Schwingkreis eingespeist. Bei einem 2/3-Netzhalbwellenbetrieb werden zwei von drei aufeinanderfolgenden Halbwellen zur Leistungseinspeisung in den Schwingkreis bzw. die Induktionsspule verwendet bzw. aktiviert. Während einer aktiven Halbwelle erfolgt eine Leistungseinstellung in herkömmlicher Weise. Der Netzhalbwellenbetrieb ermöglicht eine feinere Auflösung von Leistungsstufen über einen großen Leistungseinstellungsbereich. Eine derartige Leistungseinstellung ist insbesondere für Eintransistorumrichter vorteilhaft. Wenn bei einem herkömmlichen Betriebsverfahren des Eintransistorumrichters ein Halbwellenbetrieb zur Leistungseinstellung verwendet wird, stellt sich während einer inaktiven Halbwelle, d.h. einer Halbwelle, während der keine Leistung in den Schwingkreis eingespeist wird, eine Leerlaufspannung, beispielsweise 325V bei 230V Netzspannung, am Zwischenkreiskondensator ein.In a development, the adjustable heating power is generated by means of a half-wave pattern, wherein the intermediate circuit capacitor is discharged before activation of a half-wave. In a heating power generation With the aid of the half-wave pattern, individual half-waves of the mains alternating voltage are completely blanked out or deactivated, ie not used for heating power generation. In a so-called 1/3-Netzhalbwellenbetrieb example, only one of three consecutive half-waves for power supply to the resonant circuit or the induction coil is used or activated. During the remaining two half-cycles, the switching means remains open, ie no power is fed into the resonant circuit. In a 2/3 mains half-wave operation, two out of three consecutive half-waves are used or activated for supplying power to the oscillating circuit or the induction coil. During an active half cycle, power adjustment is done in a conventional manner. Line half-wave operation allows finer resolution of power levels over a wide power setting range. Such a power setting is particularly advantageous for single-transistor converters. When a half-wave operation is used for power adjustment in a conventional operating method of the single-transistor converter, an open-circuit voltage, for example, 325V at 230V mains voltage, turns on the intermediate circuit capacitor during an inactive half-wave, during which no power is fed into the resonant circuit.

Wenn beim Übergang von einer nicht aktiven zu einer aktiven Halbwelle das Schaltmittel erstmalig durchgeschaltet wird, fließt daher kurzzeitig ein hoher Strom durch den Schwingkreis und das Schaltmittel, wodurch, wie bereits ausgeführt, ein Geräusch verursacht wird. Bei dem 1/3- und dem 213-Netzhalbwellenbetrieb entsteht auf diese Weise alle 30ms ein Geräusch. Dies ist einem Benutzer nicht zuzumuten. Daher wird bei herkömmlichen Eintransistorumrichtern üblicherweise keine Halbwellensteuerung zur Leistungseinstellung verwendet. Bei Verwendung des erfindungsgemäßen Entladens des Zwischenkreiskondensators vor dem Aktivieren einer Halbwelle, d.h. beim Übergang von einer deaktivierten zu einer aktivierten Halbwelle, entsteht bei einem Übergang kein hoher Einschaltstrom, d.h. es kann auch beim Eintransistorumrichter eine Halbwellensteuerung zur Leistungseinstellung verwendet werden. Bevorzugt wird eine von drei oder zwei von drei Halbwellen aktiviert, d.h. der 1/3- oder der 2/3-Netzhalbwellenbetrieb eingestellt.Therefore, when the switching means is turned on for the first time during the transition from a non-active to an active half-wave, a high current flows through the oscillating circuit and the switching means for a short time, as a result of which a noise is caused. With 1/3 and 213 half-wave operation, this produces a noise every 30ms. This is unreasonable for a user. Therefore, conventional single-transistor inverters typically do not use half-wave control for power adjustment. When using the inventive discharge of the DC link capacitor before activating a half-wave, ie the transition from a deactivated to an activated half-wave, resulting in a transition no high inrush current, ie it can also be used in Eintransistorumrichter a half-wave controller for power adjustment. Preferably one of three or two out of three half-waves is activated, ie the 1/3 or 2/3 half-wave operation is set.

Diese und weitere Merkmale gehen außer aus den Ansprüchen auch aus der Beschreibung und den Zeichnungen hervor, wobei die einzelnen Merkmale jeweils für sich alleine oder zu mehreren in Form von Unterkombinationen bei einer Ausführungsform der Erfindung und auf anderen Gebieten verwirklicht sein und vorteilhafte sowie für sich schutzfähige Ausführungen darstellen können, für die hier Schutz beansprucht wird. Die Unterteilung der Anmeldung in einzelne Abschnitte und Zwischen-Überschriften beschränkt die unter diesen gemachten Aussagen nicht in ihrer Allgemeingültigkeit.These and other features will become apparent from the claims and from the description and drawings, wherein the individual features in each case alone or more in the form of sub-combinations in an embodiment of the invention and in other fields be realized and advantageous and protectable Represent embodiments for which protection is claimed here. The subdivision of the application into individual sections and intermediate headings does not limit the statements made thereunder in their generality.

Kurzbeschreibung der ZeichnungenBrief description of the drawings

Ausführungsformen der Erfindung sind in den Zeichnungen schematisch dargestellt und werden im folgenden näher erläutert. Hierbei zeigen:

Fig. 1
ein Schaltbild eines Eintransistorumrichters, der mit dem erfindungsgemäßen Betriebsverfahren betrieben wird,
Fig. 2
Zeitablaufdiagramme von Signalen des Eintransistorumrichters von Fig. 1,
Fig. 3
ein Schaltbild eines Umrichters in Halbbrückenschaltung, der mit dem erfindungsgemäßen Betriebsverfahren betrieben wird, und
Fig.4
ein Schaltbild eines Umrichters in Vollbrückenschaltung, der mit dem erfindungsgemäßen Betriebsverfahren betrieben wird.
Embodiments of the invention are shown schematically in the drawings and are explained in more detail below. Hereby show:
Fig. 1
a circuit diagram of a Eintransistorumrichters, which is operated with the operating method according to the invention,
Fig. 2
Timing diagrams of signals of the Eintransistorumrichters of Fig. 1 .
Fig. 3
a circuit diagram of a converter in half-bridge circuit, which is operated with the operating method according to the invention, and
Figure 4
a circuit diagram of an inverter in full bridge circuit, which is operated with the operating method according to the invention.

Detaillierte Beschreibung der AusführungsbeispieleDetailed description of the embodiments

Fig. 1 zeigt ein Schaltbild einer Induktionsheizeinrichtung in Form eines Eintransistorumrichters EU. Die Induktionsheizeinrichtung kann auch weitere, nicht gezeigte, identisch aufgebaute Eintransistorumrichter EU und zusätzliche herkömmliche Komponenten, beispielsweise Bedienelemente zur Leistungseinstellung usw. umfassen. Fig. 1 shows a circuit diagram of an induction heater in the form of a Eintransistorumrichters EU. The induction heating device may also include further, not shown, identically constructed single-transistor converter EU and additional conventional components, such as control elements for power adjustment, etc.

Der Eintransistorumrichter EU umfasst einen Brückengleichrichter GL, der aus einer Eingangsnetzwechselspannung UN von 230V und 50Hz eine Zwischenkreisgleichspannung UG erzeugt, einen Puffer- oder Zwischenkreiskondensator C1 zur Stabilisierung bzw. Pufferung der Zwischenkreisgleichspannung UG, der zwischen Ausgangsanschlüsse N1 und N2 des Gleichrichters GL eingeschleift ist, eine Induktionsspule L1 und einen Kondensator C2, die parallel geschaltet sind und einen Parallelschwingkreis bilden, ein ansteuerbares Schaltmittel in Form eines IGB-Transistors T1, der in Serie mit dem Schwingkreis zwischen die Ausgangsanschlüsse N1 und N2 des Gleichrichters GL eingeschleift ist, eine Freilaufdiode D1, die parallel zu einer Kollektor-Emitter-Strecke des IGB-Transistors T1 geschaltet ist, und eine Steuereinheit SE, beispielsweise in Form eines Mikroprozessors oder eines digitalen Signalprozessors.The single-transistor converter EU comprises a bridge rectifier GL, which generates a DC link voltage UG from an AC input voltage UN of 230V and 50Hz, a buffer or DC link capacitor C1 for stabilizing or buffering the intermediate DC voltage UG connected between output terminals N1 and N2 of the rectifier GL Induction coil L1 and a capacitor C2, which are connected in parallel and form a parallel resonant circuit, a controllable switching means in the form of an IGB transistor T1, which is looped in series with the resonant circuit between the output terminals N1 and N2 of the rectifier GL, a freewheeling diode D1, the is connected in parallel with a collector-emitter path of the IGB transistor T1, and a control unit SE, for example in the form of a microprocessor or a digital signal processor.

Die Steuereinheit SE führt das erfindungsgemäße, nachfolgend unter Bezugnahme auf Fig. 2 beschriebene Betriebsverfahren zum Betrieb des Eintransistorumrichters EU aus und kann weitere, nicht gezeigte Aktoren und/oder Sensoren, beispielsweise zur Netzspannungsverlaufsüberwachung, umfassen bzw. mit diesen gekoppelt sein.The control unit SE carries out the invention, hereinafter with reference to Fig. 2 described operating method for operating the Eintransistorumrichters EU and may include other, not shown actuators and / or sensors, for example, for mains voltage monitoring, include or be coupled with these.

Fig. 2 zeigt nicht maßstäbliche Zeitablaufdiagramme von Signalen des Eintransistorumrichters EU von Fig. 1. Aufgrund der Netzfrequenz der Eingangsnetzwechselspannung UN von 50Hz findet alle 10ms ein Nulldurchgang zwischen benachbarten Netzhalbwellen H1 bis H3 der Eingangsnetzwechselspannung UN statt. Der Eintransistorumrichter EU wird im 2/3-Netzhalbwellenbetrieb betrieben, d.h. lediglich während zwei von drei Netzhalbwellen wird Leistung in den Parallelschwingkreis bzw. in die Induktionsspule L1 eingespeist. In Fig. 2 sind die Halbwellen H2 und H3 die aktiven Halbwellen, während denen Leistung eingespeist wird, und die Netzhalbwelle H1 ist die inaktive Halbwelle, während der keine Leistungseinspeisung stattfindet. Während der inaktiven Halbwelle H1 sperrt der IGB-Transistor T1, bis auf einen Übergangsbereich bzw. vorgebbaren Entladezeitbereich INT, während dem der Zwischenkreiskondensator C1 entladen wird. Fig. 2 does not show true-to-scale timing diagrams of signals from the single-pole converter EU of Fig. 1 , Due to the mains frequency of the input mains AC voltage UN of 50 Hz, a zero crossing takes place every 10 ms between adjacent mains half-waves H1 to H3 of the input mains AC voltage UN. The single-transistor converter EU is operated in 2/3 mains half-wave operation, ie power is fed into the parallel resonant circuit or into the induction coil L1 only during two out of three mains half-cycles. In Fig. 2 For example, the half-waves H2 and H3 are the active half-waves during which power is applied, and the mains half-wave H1 is the inactive half-wave during which no power feed takes place. During the inactive half cycle H1, the IGB transistor T1 blocks, except for a transition region or predefinable discharge time range INT, during which the intermediate circuit capacitor C1 is discharged.

UC ist eine Spannung am Kollektor des IGB-Transistors T1 in Bezug auf ein am Anschluss N1 des Gleichrichters GL anliegendes Bezugspotential. Während inaktiver Halbwellen, bei gesperrtem IGB-Transistors T1, liegt eine Leerlaufspannung mit einem Betrag eines Scheitelwert der Netzwechselspannung UN am Kollektor an, d.h. im gezeigten Ausführungsbeispiel ca. 325V.UC is a voltage at the collector of the IGB transistor T1 with respect to a reference potential applied to the terminal N1 of the rectifier GL. During inactive half-cycles, when the IGBT transistor T1 is turned off, an open circuit voltage with an amount of a peak value of the mains AC voltage UN at the collector, i. in the illustrated embodiment about 325V.

Während der aktiven Halbwellen H2 und H3 wird Leistung in die Induktionsspule L1 eingespeist. Dies kann in herkömmlicher Weise bewirkt werden, beispielsweise durch Ansteuerung des IGB-Transistors T1 mit einem Rechteckspannungssignal mit einer Frequenz und einem Tastverhältnis, welche in Abhängigkeit von der einzuspeisenden Leistung während der Halbwelle eingestellt werden.During the active half waves H2 and H3 power is fed into the induction coil L1. This can be effected in a conventional manner, for example by driving the IGB transistor T1 with a square-wave voltage signal having a frequency and a duty cycle, which are adjusted depending on the power to be injected during the half-wave.

Um einen Einschaltstromimpuls beim Übergang von der Halbwelle H1 zur Halbwelle H2 zu verhindern, wird während des Entladezeitbereichs bzw. Zeitintervalls INT beginnend bei einem Zeitpunkt T0, ca. 2,5ms vor einem Nulldurchgang ND zwischen der Halbwelle H1 und H2 und dem Nulldurchgang ND der Zwischenkreiskondensator C1 kontinuierlich bis auf ca. 0V durch Ansteuerung des IGB-Transistors T1 entladen. Hierzu wird der IGB-Transistor T1 mit einem nicht gezeigten Rechteckspannungssignal mit einer Frequenz von ca. 39kHz und einem An/Aus-Verhältnis von ca. 1/378 angesteuert. Die Ansteuerimpulse sind so kurz, dass sie nicht ausreichen, die Ladung am IGB-Transistor-Gate auszuräumen. Der IGB-Transistor T1 wird daher nicht vollständig durchgeschaltet, sondern geht in einen Linearbetriebsmodus. Die Spannung UC am Kollektor des IGB-Transistors T1, die für diesen Fall der Spannung UG am Zwischenkreiskondensator C1 entspricht, fällt dadurch wie gezeigt langsam entlang der Netzhalbwelle als Hüllkurve bis auf ca. 0V ab. In der in Fig. 2 gezeigten Ausschnittvergrößerung ist das Signal UC mit größerer zeitlicher Auflösung dargestellt. Hieraus wird die Schaltfrequenz des IGBTs von ca. 39kHz während des Entladevorgangs sichtbar.In order to prevent a switch-on current pulse during the transition from the half-wave H1 to the half-wave H2, during the discharge time range or time interval INT, starting at a time T0, about 2.5 ms a zero crossing ND between the half-wave H1 and H2 and the zero crossing ND of the DC link capacitor C1 continuously discharged to about 0V by driving the IGB transistor T1. For this purpose, the IGB transistor T1 is driven by a rectangular voltage signal, not shown, with a frequency of about 39 kHz and an on / off ratio of about 1/378. The drive pulses are so short that they are insufficient to clear the charge on the IGB transistor gate. The IGB transistor T1 is therefore not completely turned on, but goes into a linear operation mode. The voltage UC at the collector of the IGB transistor T1, which in this case corresponds to the voltage UG at the intermediate circuit capacitor C1, thereby drops as shown slowly along the network half-wave as an envelope to about 0V. In the in Fig. 2 shown section enlargement, the signal UC is shown with greater temporal resolution. From this the switching frequency of the IGBT of approx. 39kHz becomes visible during the discharging process.

Da der IGBT T1 nicht vollständig leitet bzw. durchgeschaltet wird, ergibt sich lediglich ein geringer Strom durch die Induktionsspule L1. Durch den Spulenstrom hervorgerufene Geräusche werden somit verhindert bzw. deutlich reduziert.Since the IGBT T1 is not completely conducted or switched through, only a small current through the induction coil L1 results. Noise caused by the coil current is thus prevented or significantly reduced.

Wahrend der Halbwellen H2 und H3 wird der IGB-Transistor T1 mit einem nicht gezeigten Rechteckspannungssignal in herkömmlicher Weise angesteuert. In Fig. 2 ist die Hüllkurve der entstehenden Spannung UC und eine Ausschnittvergrößerung des Signal UC mit größerer zeitlicher Auflösung dargestellt. Die Spannung UC steigt aufgrund der Schwingung im Parallelschwingkreis auf Werte deutlich über der Leerlaufspannung an. Die Hüllkurve weist einen sinusförmigen Verlauf auf, der der gleichgerichteten Eingangsnetzwechselspannung UN folgt. Der gezeigte Verlauf der Spannung UC wiederholt sich während der Halbwelle H3. Die Frequenz des Ansteuersignals des IGBTs T1 in diesem Betriebszustand liegt bei ca. 22kHz.During the half-waves H2 and H3, the IGB transistor T1 is driven in a conventional manner with a square-wave voltage signal, not shown. In Fig. 2 is the envelope of the resulting voltage UC and a partial enlargement of the signal UC shown with greater temporal resolution. The voltage UC increases due to the vibration in the parallel resonant circuit to values well above the open circuit voltage. The envelope has a sinusoidal shape, which follows the rectified input AC voltage UN. The course of the voltage UC shown repeats during the half wave H3. The frequency of the drive signal of the IGBT T1 in this operating state is approximately 22 kHz.

In einer nicht gezeigten, auf die Halbwelle H3 folgenden Halbwelle wird der IGB-Transistor T1 deaktiviert, wodurch die Spannung UC wieder auf ihren Leerlaufwert von ca. 325V ansteigt. Beim Übergang auf eine nachfolgende, aktive Halbwelle wiederholt sich der Entladevorgang, wie für die Halbwelle H1 gezeigt. Die beschriebenen Vorgänge wiederholen sich periodisch.In a half-wave, not shown, following the half wave H3, the IGB transistor T1 is deactivated, whereby the voltage UC rises again to its no-load value of approximately 325V. During the transition to a subsequent, active half cycle, the discharge process is repeated, as shown for the half-wave H1. The processes described are repeated periodically.

Die Umrichterschaltung kann folglich mit kleinen Spannungen und Strömen anfahren und sich mit dem Anstieg der Netzhalbwelle auf ihren eigentlichen Arbeitspunkt aus geeigneter Frequenz und Tastverhältnis einregeln.Consequently, the converter circuit can start with small voltages and currents and adjust with the increase of the mains half-wave to its actual operating point of suitable frequency and duty cycle.

In Abhängigkeit von dem verwendeten IGB-Transistor, einer zu seiner Ansteuerung verwendeten Treiberspannung, der Kapazität des Zwischenkreiskondensators und der Schwingkreisdimensionierung kann die Entladefrequenz und das Tastverhältnis angepasst werden, um den IGB-Transistor während der Entladung im Linearbetrieb zu betreiben.Depending on the IGB transistor used, a drive voltage used to drive it, the capacitance of the link capacitor and the resonant circuit sizing, the discharge frequency and duty cycle can be adjusted to operate the IGB transistor in linear mode during discharge.

Durch die erfindungsgemäße Entladung des Zwischenkreiskondensators wird, wie gezeigt, eine Leistungssteuerung mit Halbwellenmustern des Eintransistorumrichters EU möglich, ohne dass eine Geräuschbelästigung verursacht wird. Wenn in diesem Fall in einer Halbwelle Leistung abgegeben werden soll, wird der Zwischenkreiskondensator am Ende der vorhergehenden, nicht aktiven Halbwelle entladen. Dies ermöglicht einen großen Leistungseinstellbereich, ohne dass Einschaltstromspitzen den IGB-Transistor T1 übermäßig beanspruchen. Insgesamt erhöht sich folglich die Lebensdauer der Bauelemente.As a result of the discharge according to the invention of the intermediate circuit capacitor, power control with half-wave patterns of the single-turn converter EU is possible, without any noise being caused. If, in this case, power is to be output in a half-wave, the DC link capacitor is discharged at the end of the previous, non-active half-cycle. This allows a large power adjustment range without inrush current peaks overstressing the IGB transistor T1. Overall, therefore, increases the life of the components.

Fig. 3 zeigt ein Schaltbild eines Umrichters HU in Halbbrückenschaltung, der mit dem erfindungsgemäßen Betriebsverfahren betrieben wird. Bauelemente mit im Vergleich zu Fig. 1 identischer Funktion sind mit gleichen Bezugszeichen versehen. Hinsichtlich ihrer funktionalen Beschreibung wird auf Fig. 1 verwiesen. Fig. 3 shows a circuit diagram of an inverter HU in half-bridge circuit, which is operated with the operating method according to the invention. Components with compared to Fig. 1 identical function are the same Provided with reference numerals. Regarding their functional description is on Fig. 1 directed.

Eine Halbbrücke ist aus IGBTs T2 und T3 gebildet, die seriell zwischen die Ausgangsanschlüsse N1 und N2 des Gleichrichters GL eingeschleift sind. Freilaufdioden D2 bzw. D3 sind parallel zu jeweils einer zugehörigen Kollektor-Emitter-Strecke der IGBTs T2 bzw. T3 geschaltet. Kondensatoren C3 und C4 sind ebenfalls seriell zwischen die Ausgangsanschlüsse N1 und N2 eingeschleift. Zwischen einen Verbindungsknoten N3 der IGBTs T2 und T3 und einen Verbindungsknoten N4 der Kondensatoren C3 und C4 ist die Induktionsspule L1 eingeschleift. Sie bildet zusammen mit den Kondensatoren C3 und C4 einen Serienschwingkreis.A half-bridge is formed of IGBTs T2 and T3, which are serially connected between the output terminals N1 and N2 of the rectifier GL. Freewheeling diodes D2 and D3 are connected in parallel to an associated collector-emitter path of the IGBTs T2 and T3, respectively. Capacitors C3 and C4 are also serially connected between the output terminals N1 and N2. Between a connection node N3 of the IGBTs T2 and T3 and a connection node N4 of the capacitors C3 and C4, the induction coil L1 is looped. It forms a series resonant circuit together with the capacitors C3 and C4.

Die IGBTs T2 und T3 werden durch die Steuereinheit SE angesteuert. Eine Leistungseinstellung kann in herkömmlicher Weise erfolgen, beispielsweise durch eine Frequenzverstellung der durch die Steuereinheit SE erzeugten Ansteuersignale der IGBTs.The IGBTs T2 and T3 are driven by the control unit SE. A power setting can be done in a conventional manner, for example by a frequency adjustment of the control signals generated by the control unit SE IGBTs.

Nach einem Einschalten des Umrichters HU und vor einer Heizleistungserzeugung wird der Zwischenkreiskondensator C1 und die Kondensatoren C3 und C4 durch Ansteuerung der IGBTs T2 und T3 entladen. Dies geschieht analog zu dem unter Bezugnahme auf Fig. 2 beschriebenen Verfahren durch Ansteuerung der IGBTs T2 und T3 mit Rechteckspannungssignalen mit geeigneter Frequenz und geeignetem An/Aus-Verhältnis. Die Ansteuerimpulse sind hierbei wiederum so kurz, dass sie nicht ausreichen, die Ladung am jeweiligen IGB-Transistor-Gate auszuräumen. Die IGB-Transistoren T2 und T3 werden daher nicht vollständig durchgeschaltet, sondern gehen in einen Linearbetriebsmodus.After switching on the converter HU and before generating a heating power, the intermediate circuit capacitor C1 and the capacitors C3 and C4 are discharged by driving the IGBTs T2 and T3. This is done analogously to that with reference to Fig. 2 described method by driving the IGBTs T2 and T3 with rectangular voltage signals with a suitable frequency and suitable on / off ratio. Again, the drive pulses are so short that they are insufficient to clear the charge at the respective IGB transistor gate. The IGB transistors T2 and T3 are therefore not completely turned on, but go into a linear operation mode.

Auf diese Weise können auch bei einem Umrichter in Halbbrückenschaltung störende Knack-Geräusche bei einem Einschaltvorgang oder nach einer Deaktivierung der Heizleistung und anschließender erneuter Aktivierung wirksam verhindert werden.In this way, even with a converter in a half-bridge circuit, annoying cracking noises can be effectively prevented during a switch-on process or after a deactivation of the heating power and subsequent renewed activation.

Fig. 4 zeigt ein Schaltbild eines Umrichters VU in Vollbrückenschaltung, der mit dem erfindungsgemäßen Betriebsverfahren betrieben wird. Bauelemente mit im Vergleich zu Fig. 1 identischer Funktion sind mit gleichen Bezugszeichen versehen. Hinsichtlich ihrer funktionalen Beschreibung wird auf Fig. 1 verwiesen. Fig. 4 shows a circuit diagram of an inverter VU in full bridge circuit, which is operated with the operating method according to the invention. Components with compared to Fig. 1 identical function are provided with the same reference numerals. Regarding their functional description is on Fig. 1 directed.

Eine erste Halbbrücke ist aus IGBTs T4 und T5 und eine zweite Halbbrücke aus IGBTs T6 und T7 gebildet, die jeweils seriell zwischen die Ausgangsanschlüsse N1 und N2 des Gleichrichters GL eingeschleift sind. Freilaufdioden D4 bis D7 sind parallel zu jeweils einer zugehörigen Kollektor-Emitter-Strecke der IGBTs T4 bis T7 geschaltet. Zwischen einen Verbindungsknoten N5 der IGBTs T4 und T5 und einen Verbindungsknoten N6 der IGBTs T6 und T7 ist die Induktionsspule L1 und ein Kondensator C5 seriell eingeschleift. Die Induktionsspule L1 und der Kondensator C5 bilden einen Serienschwingkreis.A first half-bridge is formed of IGBTs T4 and T5 and a second half-bridge of IGBTs T6 and T7, which are respectively connected in series between the output terminals N1 and N2 of the rectifier GL. Free-wheeling diodes D4 to D7 are connected in parallel with in each case one associated collector-emitter path of the IGBTs T4 to T7. Between a connection node N5 of the IGBTs T4 and T5 and a connection node N6 of the IGBTs T6 and T7, the induction coil L1 and a capacitor C5 are connected in series. The inductor L1 and the capacitor C5 form a series resonant circuit.

Die IGBTs T4 bis T7 werden durch die Steuereinheit SE angesteuert. Eine Leistungseinstellung kann in herkömmlicher Weise erfolgen, beispielsweise durch eine Frequenzverstellung der durch die Steuereinheit SE erzeugten Ansteuersignale der IGBTs.The IGBTs T4 to T7 are driven by the control unit SE. A power setting can be done in a conventional manner, for example by a frequency adjustment of the control signals generated by the control unit SE IGBTs.

Nach einem Einschalten des Umrichters VU und vor einer Heizleistungserzeugung wird der Zwischenkreiskondensator C1 durch Ansteuerung der IGBTs T4 bis T7 entladen. Dies geschieht analog zu dem unter Bezugnahme auf Fig. 2 beschriebenen Verfahren durch Ansteuerung der IGBTs T4 bis T7 mit Rechteckspannungssignalen mit geeigneter Frequenz und geeignetem An/Aus-Verhältnis. Die Ansteuerimpulse sind hierbei wiederum so kurz, dass sie nicht ausreichen, die Ladung am jeweiligen IGB-Transistor-Gate auszuräumen. Die IGB-Transistoren T4 bis T7 werden daher nicht vollständig durchgeschaltet, sondern gehen in einen Linearbetriebsmodus.After switching on the converter VU and before a heating power generation, the DC link capacitor C1 is discharged by driving the IGBTs T4 to T7. This is done analogously to that with reference to Fig. 2 described method by driving the IGBTs T4 to T7 with square wave signals with a suitable frequency and suitable on / off ratio. The drive pulses are again so short that they are not sufficient to clear the charge at the respective IGB transistor gate. The IGB transistors T4 to T7 are therefore not completely turned on, but go into a linear operation mode.

Zur Entladung des Zwischenkreiskondensators C1 können alle IGBTs T4 bis T7 oder nur bestimmte IGBTs derart angesteuert angesteuert werden, dass sich ein Strompfad zur Entladung des Zwischenkreiskondensators C1 bildet. Beispielsweise können nur T4 und T5, nur T6 und T7, nur T4 und T7 bzw. nur T6 und T5 zur Entladung angesteuert werden.For discharging the DC link capacitor C1, all the IGBTs T4 to T7 or only certain IGBTs can be driven in such a way that a current path for discharging the DC link capacitor C1 is formed. For example, only T4 and T5, only T6 and T7, only T4 and T7 or only T6 and T5 for discharge can be controlled.

Auf diese Weise können auch bei einem Umrichter in Vollbrückenschaltung störende Knack-Geräusche bei einem Einschaltvorgang oder nach einer Deaktivierung der Heizleistung und anschließender erneuter Aktivierung wirksam verhindert werden.In this way, annoying cracking noises can be effectively prevented at a power-up or after a deactivation of the heating power and subsequent re-activation even in a converter in full bridge circuit.

In den gezeigten Ausführungsbeispielen beträgt die Netzspannung 230V und die Netzfrequenz 50Hz. Selbstverständlich kann das gezeigte Betriebsverfahren auf andere Netzspannungen und Netzfrequenzen angepasst werden.In the embodiments shown, the mains voltage is 230V and the mains frequency is 50Hz. Of course, the operating method shown can be adapted to other mains voltages and mains frequencies.

Claims (12)

  1. Method for operating an induction heating device comprising:
    - an induction coil (L1), and
    - a frequency converter (ET, HU, VU) for generating a control voltage for the induction coil (L1) comprising:
    - a rectifier (GL) which rectifies an alternating supply voltage (UN),
    - an intermediate circuit capacitor (C1) coupled between output terminals (N 1, N2) of the rectifier (GL) and buffering the rectified voltage (UG), and
    - at least one controllable switching element (T1 to T7) coupled between the output terminals (N1, N2) of the rectifier (GL),
    characterized in that
    - in a predeterminable discharge time range (INT) prior to a zero passage (ND) of the alternating supply voltage (UN) the intermediate circuit capacitor (C1) is discharged to a threshold value by controlling the at least one switching element (T1 to T7) before the induction coil (L1) is controlled for generating an adjustable heating power.
  2. Method according to claim 1, characterized in that the frequency converter is a single transistor converter (EU).
  3. Method according to claim 1, characterized in that the frequency converter is a converter in full bridge circuit (VU) or half-bridge circuit (HU), the at least one switching element (T1 to T7) forming part of the bridge.
  4. Method according to one of the preceding claims, characterized in that the discharge time range (INT) commences 1 ms to 5 ms prior to the zero passage (ND) of the alternating supply voltage (UN).
  5. Method according to one of the preceding claims, characterized in that the threshold value is between 0 and 20 V.
  6. Method according to one of the preceding claims, characterized in that the at least one switching element is a transistor, particularly an IGB transistor (T1 to T7).
  7. Method according to claim 6, characterized in that, for discharging the intermediate circuit capacitor (C1) during the discharge the IGB transistor (T1 to T7) is controlled such that the IGB transistor (T1 to T7) operates in a linear operating state.
  8. Method according to one of the preceding claims, characterized in that the at least one switching element (T1 to T7) is controlled by a pulse-width modulated square-wave voltage signal for discharging the intermediate circuit capacitor (C1).
  9. Method according to claim 8, characterized in that the square-wave voltage signal has a frequency of 20 to 50 kHz.
  10. Method according to claim 8 or 9, characterized in that the square-wave voltage signal has an on/off ratio in the range of 1/300 to 1/500.
  11. Method according to one of the preceding claims, characterized in that the adjustable heating power is generated using a half-wave pattern, the intermediate circuit capacitor (C1) being discharged prior to an activation of a half-wave.
  12. Method according to claim 11, characterized in that one of three or two of three half-waves are activated.
EP06806263A 2005-10-14 2006-10-13 Method for operating an induction heating device Active EP1935213B1 (en)

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PCT/EP2006/009916 WO2007042318A1 (en) 2005-10-14 2006-10-13 Method for operating an induction heating device

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ES2320594T3 (en) 2009-05-25
WO2007042318A1 (en) 2007-04-19
US8415594B2 (en) 2013-04-09
DE102005050038A1 (en) 2007-05-24
SI1935213T1 (en) 2009-08-31
CN101326857A (en) 2008-12-17
JP2009512147A (en) 2009-03-19
CA2625765A1 (en) 2007-04-19
DE502006002762D1 (en) 2009-03-19
US20080203087A1 (en) 2008-08-28
CN101326857B (en) 2011-11-23
ATE422146T1 (en) 2009-02-15
EP1935213A1 (en) 2008-06-25
CA2625765C (en) 2015-06-16

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