AN INDUCTION HEATING COOKER

Description

[0001] The present invention relates to an induction heating cooker comprising the electronic elements that carry high current.

[0002] The induction heating cooker functions according to the principle of heating a cast iron or steel ferromagnetic cooking container with the magnetic field effect generated by the induction coil. The energy efficiency of induction heating cookers is considerably high since the heat required for cooking is not generated in the gas or electric burners on the cooker but directly in the cooking container. In order to drive the induction coils generating magnetic field, high amount of electric current is conducted through electronic switching elements like the power switch (IGBT-Insulated Gate Bipolar Transistor or Mosfet) and the diode bridge on the circuit board. In the state of the art, for driving the induction coils, the quasi resonant converter circuit realized by one IGBT and one resonant capacitor that provides cost advantage is used besides the half bridge series resonant converter realized by using two switches and two resonant capacitors. In this circuit, the resonant capacitor is connected in parallel with the induction coil in contrast to the half bridge series resonant converter circuit wherein the induction coils and the resonant capacitors are connected in series. One end of the IGBT switch is connected in series to one end of the parallel connected coil and capacitor and the other end is connected to the reference output point of the rectified voltage. This structure that is connected in series is connected to the intermediate circuit voltage. The disadvantage of this drive circuit is that it can work in narrower power frequency range and the maximum value thereof is limited. The basic parameter limiting the operating range is that in low load conditions, the voltage occurring on the switch during switching does not to fall to zero and results in high losses on the switches and the drawing of high value capacitor charge currents in the IGBT switch. The transmission operating conditions in the quasi resonant structure having low cost single IGBT and single resonant capacitor is determined largely by the load itself. The control and switching electronics are expected to energize the load at suitable moments.

[0003] In the state of the art European Patent No. EP 0 888 033 B1, the control circuit and the control method used in an induction heating cooker is explained.

[0004] The aim of the present invention is the realization of an induction heating cooker wherein the power losses are decreased.

[0005] The induction heating cooker realized in order to attain the aim of the present invention, explicated in the first claim and the respective claims thereof, comprises at least one additional capacitor parallel to the resonant capacitor and the induction coil connected parallel to each other. The induction coil is provided to operate in a wide power range by activating or deactivating the additional capacitor by the control unit.

[0006] When the voltage passing through the induction coil gets near the upper limit, the additional capacitor is activated by the control unit and provides the induction coil to be able to operate at higher power level. When the voltage passing through the induction coil gets near the lower limit, the additional capacitor is deactivated by the control unit, thereby providing the induction coil to operate at lower power level.

[0007] In an embodiment of the present invention, the induction heating cooker comprises two additional capacitors and the induction coil is operated at three different levels. The resonant capacitor is conducting at all levels. In the high power level, both of the additional capacitors are conducting. In the middle power level only one of the additional capacitors is conducting.

[0008] In the induction heating cooker, the operating range of the induction coil and the highest and lowest power levels of usability are increased by making the total capacity value of the capacitors connected parallel to the induction coil variable.

[0009] The induction heating cooker realized in order to attain the aim of the present invention is illustrated in the attached figures, where:

Figure 1 - is the schematic view of an induction heating cooker.

[0010] The elements illustrated in the figures are numbered as follows:

1. Induction heating cooker

2. Mains filtering circuit

3. Diode bridge rectifier

4. Filtering circuit

5. Power switch

6. Resonant capacitor

7. Induction coil

8. , 108. Additional capacitor

9. , 109. Switch

10. Voltage detecting circuit

11. Control unit

12. Current detecting circuit

13. Power switch drive circuit

[0011] The induction heating cooker (1) comprises a mains filtering circuit (2), a diode bridge rectifier (3) providing the alternative current received from the mains to be converted to direct current, a filtering circuit (4) that cleans the voltage signal delivered by the diode bridge rectifier (3) from high frequency noises, a power switch (5) that drives the voltage received from the filtering circuit (4) to high frequency voltage, an induction coil (7) connected in series to the end of the power switch (5), providing the ferromagnetic cooking container placed thereon to be heated with the magnetic field generated and a resonant capacitor (6) connected parallel to the induction coil (7).

[0012] The induction heating cooker (1) comprises at least one additional capacitor (8, 108) connected in parallel to the induction coil (7).

[0013] The induction heating cooker (1) furthermore comprises a voltage detecting circuit (10), one end connected to the collector point (K) prior to the power switch (5) and that measures the voltage (V1) at the collector point (K) and a control unit (11) that compares the voltage (V1) at the collector point (K) measured by the voltage detecting circuit (10) with the voltage upper limit value (Vu) and the voltage lower limit value (Va) prerecorded in its memory by the producer, that activates or deactivates the additional capacitors (8, 108) if the voltage (V1) at the collector point (K) is around the voltage upper limit value (Vu) and the voltage lower limit value (Va).

[0014] As the conducting time of the power switch (5) increases, the amount of energy delivered to the induction coil (7) increases in direct proportion. The induction coil (7) can be operated at different power levels by an adjustment means (not shown in the figures) that is actuated by the user.

[0015] The induction heating cooker (1) furthermore comprises a switch (9, 109) that is connected in series to each additional capacitor (8, 108).

[0016] If the user drives the induction coil (7) at high power level, the voltage (V1) measured at the collector point (K) gets closer to the voltage upper limit value (Vu). In this case, the control unit (11) activates at least one of the switches (9, 109) and provides current to be conducted through at least one of the additional capacitors (8, 108). The total capacity value increases and the induction coil (7) can be driven at high power level since the additional capacitor (8, 108) that starts conducting and the resonant capacitor (6) are connected in parallel.

[0017] If the user drives the induction coil (7) at low power level, the voltage (V1) measured at the collector point (K) gets closer to the voltage lower limit value (Va). In this case, the control unit (11) provides to cut off the current conducted through at least one of the additional capacitors (8, 108) by deactivating at least one of the switches (9, 109). The total capacity value decreases and the induction coil (7) can be operated at low power level since the switched off additional capacitor (8, 108) and the resonant capacitor (6) are connected in parallel.

[0018] In an embodiment of the present invention, the induction heating cooker (1) comprises a current detecting circuit (12) that measures the current at the output of the power switch (5) and a power switch drive circuit (13) that activates or deactivates the power switch (5). The current detecting circuit (12) detects the momentary peaks in the current (I) when the voltage (V1) measured at the collector point (K) reaches the voltage lower limit value (Va) if the induction coil (7) is driven at low power level. The current detecting circuit (12) transmits the detected momentary current (I) peaks to the control unit (11). The control unit (11) deactivates the additional capacitors (8, 108) at the momentary current (I) peaks.

[0019] In an embodiment of the present invention, the induction heating cooker (1) comprises two additional capacitors (8, 108) and two switches (9, 109). The induction coil (7) is operated at three different levels (A1, A2, A3) and at three different power scales at each level (A1, A2, A3), in total nine different power scales by means of an adjustment means (not shown in the figures) that is actuated by the user. Only the resonant capacitor (6) is activated while the induction coil (7) is operated at low power level (A1). The control unit (11) does not activate the additional capacitors (8, 108). The resonant capacitor (6) and the first additional capacitor (8) are conducting while the induction coil (7) is operated at middle power level (A2). The control unit (11) does not activate the other additional capacitor (108). The resonant capacitor (6) and the additional capacitors (8, 108) are conducting while the induction coil (7) is operated at high power level (A3).

[0020] In the induction heating cooker (1), the induction coil (7) is provided to be driven electrically safely and in a wide range of power by means of activating or deactivating the additional capacitors (8, 108) connected in parallel to the induction coil (7) by the control unit (11) depending on the power value whereat the induction coil (7) is operated. By means of the additional capacitors (8, 108) connected parallel to the resonant capacitor (6), passing of momentary high voltage through the power switch (5) and damaging of the power switch (5) are prevented.

[0021] It is to be understood that the present invention is not limited by the embodiments disclosed above and a person skilled in the art can easily introduce different embodiments. These should be considered within the scope of the protection postulated by the claims of the present invention.

Claims

1. An induction heating cooker (1) comprising a mains filtering circuit (2), a diode bridge rectifier (3) providing the alternative current received from the mains to be converted to direct current, a filtering circuit (4) that cleans the voltage signal delivered by the diode bridge rectifier (3) from high frequency noises, a power switch (5) that drives the voltage received from the filtering circuit (4) to high frequency voltage, an induction coil (7) connected in series to the end of the power switch (5), providing the ferromagnetic cooking container placed thereon to be heated with the magnetic field generated and a resonant capacitor (6) connected parallel to the induction coil (7), wherein at least one additional capacitor (8, 108) is connected parallel to the induction coil (7) and wherein a switch (9, 109) is connected in series to each additional capacitor (8, 108),
characterized by a voltage detecting circuit (10), one end connected to the collector point (K) prior to the power switch (5) and that measures the voltage (V1) at the collector point (K) and a control unit (11) that compares the voltage (V1) at the collector point (K) measured by the voltage detecting circuit (10) with a voltage upper limit value (Vu) and a voltage lower limit value (Va) prerecorded in its memory by the producer, that activates or deactivates the additional capacitors (8, 108) if the voltage (V1) at the collector point (K) is around the voltage upper limit value (Vu) and the voltage lower limit value (Va) in that the control unit (11) activates at least one of the switches (9, 109) and thus provides current to be conducted through at least one of the additional capacitors (8, 108) when the voltage (V1) measured at the collector point (K) gets closer to the voltage upper limit value (Vu) and deactivates at least one of the switches (9, 109) and thus provides to cut off the current conducted through at least one of the additional capacitors (8, 108) when the voltage (V1) measured at the collector point (K) gets closer to the voltage lower limit value (Va).

2. The induction heating cooker (1) as in Claim 1,
characterized by two additional capacitors (8, 108) and two switches (9, 109) and the induction coil (7) that is operated at three different levels (A1, A2, A3) and at three different power scales at each level (A1, A2, A3), in total nine different power scales.

3. The induction heating cooker (1) as in Claim 2, characterized by the control unit (11) that activates only the resonant capacitor (6), not activating the additional capacitors (8, 108) while the induction coil (7) is operated at low power level (A1), that activates the resonant capacitor (6) and the first additional capacitor (8), not activating the other additional capacitor (108) while the induction coil (7) is operated at middle power level (A2), and that activates the resonant capacitor (6) and the additional capacitors (8, 108) while the induction coil (7) is operated at high power level (A3).

Ansprüche

1. Induktionsherd (1), umfassend eine Netzstromfilterschaltung (2), einen Diodenbrückengleichrichter (3), der es ermöglicht, dass Wechselstrom vom Stromnetz in Gleichstrom umgewandelt wird, eine Filterschaltung (4), die Hochfrequenzrauschen aus dem Spannungssignal vom Diodenbrückengleichrichter (3) entfernt, einen Leistungsschalter (5), der die Spannung von der Filterschaltung (4) auf Hochfrequenzspannung treibt, eine Induktionsspule (7), die in Reihe mit dem Ende des Leistungsschalters (5) verbunden ist und ermöglicht, dass der darauf abgestellte ferromagnetische Kochbehälter mit dem erzeugten Magnetfeld erwärmt wird, und einen Resonanzkondensator (6), der parallel mit der Induktionsspule (7) verbunden ist, wobei wenigstens ein Zusatzkondensator (8, 108) parallel mit der Induktionsspule (7) verbunden ist und wobei ein Schalter (9, 109) in Reihe mit jedem Zusatzkondensator (8, 108) verbunden ist,
gekennzeichnet durch eine Spannungsdetektionsschaltung (10), deren eines Ende vor dem Leistungsschalter (5) mit dem Kollektorpunkt (K) verbunden ist und die die Spannung (V1) an dem Kollektorpunkt (K) misst, und eine Steuereinheit (11), die die Spannung (V1) an dem Kollektorpunkt (K), die von der Spannungsdetektionsschaltung (10) gemessen wird, mit einem oberen Spannungsgrenzwert (Vu) und einem unteren Spannungsgrenzwert (Va) vergleicht, die im Voraus vom Hersteller in ihrem Speicher aufgezeichnet wurden, und die Zusatzkondensatoren (8, 108) aktiviert oder deaktiviert, wenn die Spannung (V1) an dem Kollektorpunkt (K) bei dem oberen Spannungsgrenzwert (Vu) und dem unteren Spannungsgrenzwert (Va) liegt, indem die Steuereinheit (11) wenigstens einen der Schalter (9, 109) aktiviert und dadurch ermöglicht, dass Strom durch wenigstens einen der Zusatzkondensatoren (8, 108) geleitet wird, wenn die Spannung (V1), die an dem Kollektorpunkt (K) gemessen wird, sich dem oberen Spannungsgrenzwert (Vu) nähert, und wenigstens einen der Schalter (9, 109) deaktiviert und dadurch ermöglicht, dass der Strom, der durch wenigstens einen der Zusatzkondensatoren (8, 108) geleitet wird, unterbrochen wird, wenn die Spannung (V1), die an dem Kollektorpunkt (K) gemessen wird, sich dem unteren Spannungsgrenzwert (Va) nähert.

2. Induktionsherd (1) nach Anspruch 1, gekennzeichnet durch zwei Zusatzkondensatoren (8, 108) und zwei Schalter (9, 109) und dadurch, dass die Induktionsspule (7) auf drei verschiedenen Pegeln (A1, A2, A3) und drei verschiedenen Leistungsstufen auf jedem Pegel (A1, A2, A3), insgesamt auf neun verschiedenen Leistungsstufen, betrieben wird.

3. Induktionsherd (1) nach Anspruch 2, dadurch gekennzeichnet, dass die Steuereinheit (11) nur den Resonanzkondensator (6) aktiviert und nicht die Zusatzkondensatoren (8, 108) aktiviert, während die Induktionsspule (7) auf dem Niedrigleistungspegel (A1) betrieben wird, den Resonanzkondensator (6) und den ersten Zusatzkondensator (8) aktiviert und den anderen Zusatzkondensator (108) nicht aktiviert, während die Induktionsspule (7) auf dem mittleren Leistungspegel (A2) betrieben wird, und den Resonanzkondensator (6) und die Zusatzkondensatoren (8, 108) aktiviert, während die Induktionsspule (7) auf dem Hochleistungspegel (A3) betrieben wird.

Revendications

1. Une table de cuisson à chauffage d'induction (1) comprenant un circuit de filtrage de réseau (2), un redresseur de pont de diode (3) qui convertit le courant alternatif reçu du réseau en courant continu, un circuit de filtrage (4) qui vide le signal de tension transmis par le redresseur de pont de diode (3) de bruits de haute fréquence, un interrupteur d'alimentation (5) qui entraîne la tension reçue du circuit de filtrage (4) à la tension de haute fréquence, une bobine d'induction (7) qui est connectée en série à l'extrémité de l'interrupteur d'alimentation (5) et qui permet le chauffage du récipient de cuisson ferromagnétique placé sur celle-ci et un condensateur de résonance (6) qui est connecté en parallèle à la bobine d'induction (7), où au moins un condensateur supplémentaire (8, 108) est connecté en parallèle à la bobine d'induction (7) et où un interrupteur (9, 109) est connecté en série à chaque condensateur supplémentaire (8, 108),
caractérisée par un circuit de détection de tension (10) dont une extrémité est connectée au point de collecteur (K) avant l'interrupteur d'alimentation (5) et qui mesure la tension (V1) au point de collecteur (K), et une unité de commande (11) qui compare la tension (V1) au point de collecteur (K) mesurée par le circuit de détection de tension (10) avec une valeur supérieure limite de tension (Vu) et une valeur inférieure limite de tension (Va) préenregistrées dans sa mémoire par le fabricant, qui active ou désactive les condensateurs supplémentaires (8, 108) si la tension (V1) au point de collecteur (K) est autour de la valeur supérieure limite de tension (Vu) et la valeur inférieure limite de tension (Va) en ce que l'unité de commande (11) active au moins un des interrupteurs (9, 109) et donc permet la conduction du courant à travers au moins un des condensateurs supplémentaires (8, 108) lorsque la tension (V1) mesurée au point de collecteur (K) s'approche de la valeur supérieure limite de tension (Vu) et désactive au moins un des interrupteurs (9, 109) et donc permet l'interruption du courant conduite à travers au moins un des condensateurs supplémentaires (8, 108) lorsque la tension (V1) mesurée au point de collecteur (K) s'approche de la valeur inférieure limite de tension (Va).

2. Une table de cuisson à chauffage d'induction (1) selon la Revendication 1, caractérisée par deux condensateurs supplémentaires (8, 108) et deux interrupteurs (9, 109) et la bobine d'induction (7) qui est fonctionnée à trois niveaux différentes (A1, A2, A3) et à trois échelles de puissance à chaque niveau, au total neuf échelles de puissance différentes.

3. Une table de cuisson à chauffage d'induction (1) selon la Revendication 2, caractérisée par l'unité de commande (11) qui active seulement le condensateur de résonance (6) mais n'active pas les condensateurs supplémentaires (8, 108) lorsque la bobine d'induction (7) est fonctionnée à l'échelle de puissance basse (A1), qui active le condensateur de résonance (6) et le premier condensateur supplémentaire (8) mais n'active pas l'autre condensateur supplémentaire (108) lorsque la bobine d'induction (7) est fonctionnée à l'échelle de puissance intermédiaire (A2) et qui active le condensateur de résonance (6) et les condensateurs supplémentaires (8, 108) lorsque la bobine d'induction (7) est fonctionnée à l'échelle de puissance élevée (A3).

Drawing