INDUCTION HEATING COOKER POWER CONTROL CIRCUIT

Description

[0001] The present invention relates to a power control circuit that detects the presence of the vessel placed on an induction heating cooker.

[0002] The induction heating cooker functions according to the principle of heating a cast iron or steel ferromagnetic cooking vessel with the magnetic field generated by the induction coil. In order to drive the induction coils generating the magnetic field, a high-level electric current is passed through the powerswitch (such as IGBT (Insulated Gate Bipolar Transistor), diode, MOSFET, etc.) on the electronic circuit. In the state of the art, half bridge series resonant (HBSR) circuit formed by using two power switches and two resonant capacitors, and single switch quasi-resonant (SSQR) circuits formed by one power switch and again two resonant capacitors are used for driving a single induction coil.

[0003] Using a vessel produced from a metal that is not ferromagnetic or the absence of the vessel on the induction heating cooker may cause damage in terms of the power control circuit. If vessels with a small diameter or kitchen utensils such as forks, spoons, etc. are placed on the induction heating cooker, the system is required to quickly detect that "no appropriate vessel is present" and to cut the current passing through the induction coil. If the situation that there is no vessel suitable for induction heating is not quickly detected, problems in terms of user safety may arise. In the state of the art, whether there is a suitable vessel is detected by transmitting a current signal or in other words a "pulse" by the induction coil; however, since the induction coil is energized with the mains current, the latter causes excessive energy consumption just for the detection process and moreover, a noise disturbing the user is generated during the detection process.

[0004] The European Patent No. EP2282606 relates to an induction heating appliance control method. By comparing the resonance voltage with a constant reference voltage predetermined by the control unit, the presence or absence of a vessel present on the induction coil, and the resistivity and the amplitude thereof is determined.

[0005] In the European Patent No. EP1629698, an induction cooking system comprising a power inverter, a microprocessor, a protection circuit and a pan detection circuit is explained.

[0006] The European Patent No. EP1542508 relates to the determination of the location of the cooking utensils on the induction cooking hob.

[0007] The European Patent No. EP2177076 relates to the method for operation an induction heating cooker the cooking surface of which is covered with induction coils.

[0008] An induction heating cooker of the prior art can be seen in US 2011/233199.

[0009] The aim of the present invention is the realization of a power control circuit that detects the presence of the vessel placed on the induction heating cooker without energizing the induction coil.

[0010] The induction heating cooker power control circuit realized in order to attain the aim of the present invention, explicated in the first claim and the respective claims thereof, comprises an electronic oscillator, preferably a Colpitts oscillator, that is connected to the microcontroller, that transmits signals by electrically connecting to the induction coil at the beginning of the operation when the induction coil has not been energized, yet, before the user sets the power and that produces sinusoidal output voltage according to the serial resistance and inductor values of the induction coil - vessel pair. According to the data received from the Colpitts oscillator, the microcontroller detects whether there is a vessel on the induction coil and if there is, whether the ferromagnetic characteristics thereof are suitable.

[0011] The power control circuit furthermore comprises at least one oscillator switch that provides the activation of the Colpitts oscillator by connecting to the induction coil and the deactivation thereof by cutting the connection thereof with the induction coil. During the beginning time where the induction heating coil is started but the power setting has not been selected for heating the vessel, yet, the Colpitts oscillator is electrically connected to the induction coil and transmits signals to the induction coil for the detection of the vessel. When the presence of the vessel is detected, the oscillator switch cuts the connection of the Colpitts oscillator with the induction coil and enables the induction coil to be connected to the power control circuit.

[0012] The power control circuit furthermore comprises a peak voltage monitoring circuit that enables the peak voltage values of the sinusoidal current generated in the Colpitts oscillator to be read by the microcontroller, and a zero crossing monitoring circuit that converts the sinusoidal current generated in the Colpitts oscillator into square wave form and enables the amplitude of the signal to be read by the microcontroller.

[0013] In the induction heating cooker wherein the power control circuit of the present invention comprising the Colpitts oscillator is used, the presence of the vessel is detected before energizing the induction coil, thus decreasing the energy consumption and preventing the power switches from being damaged from high current. Moreover, noises that may disturb the user during the detection of the vessel are eliminated.

[0014] The induction heating cooker power control circuit 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 the induction heating cooker power control circuit

[0015] The elements illustrated in the figure are numbered as follows:

1 - Power control circuit

2 - Bridge rectifier

3 - Filter inductor

4- Filter capacitor

5 - Induction coil

6 - Resonant capacitor

7 - Power switch

8 - Drive circuit

9 - Microcontroller

10 - Electronic oscillator

11 - Oscillator switch

12 - Peak voltage monitoring circuit

13 - Zero crossing monitoring circuit

14 - Vessel

R: Resistance

L: Inductor

AC: Mains current (alternative current) input

[0016] The power control circuit (1) (also referred to as the inverter circuit) that is suitable to be used in induction heating cookers and that provides the generation of magnetic energy for heating a vessel (14) placed onto the induction heating cooker surface, comprises a filter circuit (not shown in the figures) that filters the AC mains current; a bridge rectifier (2) that converts the alternative current received from the mains into direct current; a filter inductor (3) and a filter capacitor (4) that are disposed at the outlet of the bridge rectifier (2) on the DC line; an induction coil (5) that is energized for heating the vessel (14) placed onto the induction heating cooker so that the coil current passes therethrough; at least one resonant capacitor (6) that energizes the induction coil (5); at least one power switch (7), for example an IGBT (Insulated Gate Bipolar Transistor) that enables the resonant capacitor (6) to be charged/discharged and that provides the transmission of power from the induction coil (5) to the vessel (14); a drive circuit (8) that enables the power switch (7) to be driven with a drive voltage at the desired level, and a microcontroller (9) that regulates the operation of the power switch (7) by means of the drive circuit (8).

[0017] The induction heating cooker is operated by means of an on-off button (not shown in the figures) and first electronic components such as the microcontroller (9) and the user interface (not shown in the figures) are activated, the induction coil (5) is not energized at the beginning. Afterwards, in order to heat the vessel (14) at the desired power setting, the heating setting is selected by the user and the induction coil (5) is energized.

[0018] The power control circuit (1) of the present invention comprises an electronic oscillator (10) that is connected to the microcontroller (9), that transmits signals by electrically connecting to the induction coil (5) at the beginning of the operation of the induction heating cooker when the induction coil (5) has not been energized, yet, and that produces an output voltage according to the serial resistance and inductor (R, L) values of the induction coil (5) - vessel (14) pair, and the microcontroller (9) that, according to the data received from the electronic oscillator (10), detects whether there is a vessel (14) on the induction coil (5) and if there is a vessel (14), whether the ferromagnetic characteristics thereof are suitable.

[0019] In the preferred embodiment of the present invention, the electronic oscillator (10) is a Colpitts oscillator that generates a current in sinusoidal wave form.

[0020] The electronic oscillator (10) enables the detection of whether the vessel (14) is present on the induction heating cooker surface before the induction coil (5) is energized. The electronic oscillator (10) generates signals in form of a sinusoidal voltage with low amplitude such as 3 - 3.5 V by means of a low voltage generator (not shown in the figures), and applies the said signals to the induction coil (5). As in the state of the art embodiments, the induction coil (5) - vessel (14) pair is modeled as serial resistance and inductor (R, L) and the said resistance (R) and inductance (L) values vary depending on the presence of absence of the vessel (14) and on the type of the vessel (14). In case of the absence of the vessel (14), the inductor (L) value is high and the resistance (R) value is low. In case of the presence of the ferromagnetic vessel (14) suitable for induction heating, the inductor (L) value is low and the resistance (R) value is high. If a vessel (14) produced from aluminum, Teflon, copper, etc. not suitable for induction cooking is placed, both the resistance (R) and the inductor (L) values are low. The electronic oscillator (10) applies the sinusoidal input voltage (current) to the induction coil (5) whereto the oscillator (10) is electrically connected at the beginning of the operation. The electronic oscillator (10) generates a sinusoidal output voltage (current) according to the status of the induction coil (5) - vessel (14) pair and transmits the same to the microcontroller (9). According to the data received from the electronic oscillator (10), the microcontroller (9) detects whether the vessel (14) is on the induction coil (5) and if the vessel (14) is thereon, whether the ferromagnetic characteristics thereof are suitable.

[0021] In an embodiment of the present invention, the power control circuit (1) comprises at least one oscillator switch (11) that is controlled by the microcontroller (9), that provides the activation of the electronic oscillator (10) by connecting to the induction coil (5) when the induction coil (5) is energized and the deactivation of the electronic oscillator (10) by cutting the connection thereof when the induction coil (5) is energized.

[0022] At the beginning of the operation of the induction heating cooker, the oscillator switch (11) cuts the connection between the induction coil (5) and the power control circuit (1) when the power switches (7) are non-conducting and the induction coil (5) is not energized. The oscillator switch (11) provides the electrical connection between the electronic oscillator (10) and the induction coil (5) when the induction coil (5) is not energized and the electronic oscillator (10) transmits signals to the induction coil (5) for detecting the vessel (14). When the presence of the vessel (14) is detected, the oscillator switch (11) enable the induction coil (5) to be connected to the power control circuit (1) while providing the deactivation of the electronic oscillator (10).

[0023] In another embodiment of the present invention, the power control circuit (1) comprises a peak voltage monitoring circuit (12) that enables the microcontroller (9) to read the peak voltage values of the sinusoidal current generated in the electronic oscillator (10) according to the status of the induction coil (5) - vessel (14) pair.

[0024] In another embodiment of the present invention, the power control circuit (1) comprises a zero crossing monitoring circuit (13) that converts the sinusoidal current generated in the electronic oscillator (10) to square wave form according to the status of the induction coil (5) - vessel (14) pair and enables the signal amplitude to be read by the microcontroller (9).

[0025] According to the data received from the peak voltage monitoring circuit (12) and the zero crossing monitoring circuit (13), the microcontroller (9) detects whether the vessel (14) is on the induction coil (5) and if the vessel (14) is thereon, whether the ferromagnetic characteristics thereof are suitable.

[0026] In another embodiment of the present invention, the power control circuit (1) is a half bridge series resonant (HBSR) circuit comprising a pair of resonant capacitors (6) and a pair of power switches (7).

[0027] In another embodiment of the present invention, the power control circuit (1) is a single switch quasi resonant (SSQR) circuit comprising a single resonant capacitor (6) and a single power switch (7). In some embodiments, it is known as single-ended inverter circuit.

[0028] In the induction heating cooker wherein the power control circuit (1) of the present invention comprising the electronic oscillator (10) is used, at the beginning of the operation when only the microcontroller (9) and the user interface are activated and before the induction coil (5) is not energized, the presence and absence of the vessel (14), and, if the vessel (4) is present, whether the ferromagnetic characteristics thereof are suitable is detected. Thus, the energy consumption is reduced and the power switches (7) energizing the induction coil (5) are prevented from being damaged from high current and generation of noise that may disturb the user during the detection of the vessel (14) is eliminated.

Claims

1. A power control circuit (1) that is suitable to be used in induction heating cookers, comprising a bridge rectifier (2) that converts the alternative current received from the mains into direct current; a filter inductor (3) and a filter capacitor (4) that are disposed at the outlet of the bridge rectifier (2); an induction coil (5) that is energized for heating a vessel (14) placed onto the induction heating cooker so that the coil current passes therethrough; at least one resonant capacitor (6) that energizes the induction coil (5); at least one power switch (7) that enables the resonant capacitor (6) to be charged/discharged and that provides the transmission of power from the induction coil (5) to the vessel (14); a drive circuit (8) that enables the power switch (7) to be driven with a drive voltage at the desired level, and a microcontroller (9) that regulates the operation of the power switch (7) by means of the drive circuit (8), characterized by

- an electronic oscillator (10) that is connected to the microcontroller (9), that transmits signals by electrically connecting to the induction coil (5) at the beginning of the operation of the induction heating cooker when the induction coil (5) has not been energized, yet, and that produces an output voltage according to the serial resistance and inductance (R, L) values of the induction coil (5) - vessel (14) pair, and

- the microcontroller (9) that, according to the data received from the electronic oscillator (10), detects whether there is a vessel (14) on the induction coil (5) and if there is a vessel (14), whether the ferromagnetic characteristics thereof are suitable.

2. A power control circuit (1) as in Claim 1, characterized by the electronic oscillator (10) that is a "Colpitts oscillator" that generates current in sinusoidal wave form.

3. A power control circuit (1) as in Claim 1 or 2, characterized by at least one oscillator switch (11) that is controlled by the microcontroller (9), that provides the activation of the electronic oscillator (10) by connecting to the induction coil (5) when the induction coil (5) is energized and the deactivation of the electronic oscillator (10) by cutting the connection thereof when the induction coil (5) is energized.

4. A power control circuit (1) as in Claim 1 or 2, characterized by a peak voltage monitoring circuit (12) that enables the microcontroller (9) to read the peak voltage values of the sinusoidal current generated in the electronic oscillator (10).

5. A power control circuit (1) as in Claim 1 or 2, characterized by a zero crossing monitoring circuit (13) that converts the sinusoidal current generated in the electronic oscillator (10) to square wave form and enables the signal amplitude to be read by the microcontroller (9).

6. A power control circuit (1) as in Claim 1 or 2, characterized by being a half bridge series resonant circuit comprising a pair of resonant capacitors (6) and a pair of power switches (7).

7. A power control circuit (1) as in Claim 1 or 2, characterized by being a single switch quasi resonant circuit comprising a single resonant capacitor (6) and a single power switch (7).

8. An induction heating cooker (1), characterized by a power control circuit (1) as in Claim 1 or 2.

Ansprüche

1. Eine Leistungssteuerschaltung (1), die zur Verwendung in Induktionsherden geeignet ist, umfasst einen Brückengleichrichter (2), der den vom Netz empfangenen Wechselstrom in Gleichstrom umwandelt; eine Filterinduktivität (3) und einen Filterkondensator (4), die am Ausgang des Brückengleichrichters (2) angeordnet sind; eine Induktionsspule (5), die betrieben wird, um ein Gefäß (14) zu erwärmen, welches auf dem Induktionsherd abgelegt ist, so dass der Spulenstrom dadurch fließen kann; mindestens einen Resonanzkondensator (6), der die Induktionsspule (5) betreibt; mindestens einen Leistungsschalter (7), der das Laden / Entladen des Resonanzkondensators (6) ermöglicht und die Übertragung von Leistung von der Induktionsspule (5) zum Gefäß (14) ermöglicht; eine Ansteuerschaltung (8), die es ermöglicht, den Leistungsschalter (7) mit einer Ansteuerspannung auf dem gewünschten Pegel anzusteuern, und einen Mikrocontroller (9), der den Betrieb des Leistungsschalters (7) mittels der Ansteuerschaltung (8) durchführt; gekennzeichnet ist es durch

- einen elektronischen Oszillator (10), der mit dem Mikrocontroller (9) verbunden ist und zu Beginn des Betriebs des Induktionskochers Signale durch elektrische Verbindung mit der Induktionsspule (5) überträgt, wenn die Induktionsspule (5) nicht in Betrieb war, es noch zu erregen, und somit eine Ausgangsspannung erzeugt, gemäß den Werten für den Serienwiderstand und die Induktivität (R, L) des Paares Induktionsspule (5) - Gefäß (14), und

- den Mikrocontroller (9), der anhand der vom elektronischen Oszillator (10) empfangenen Daten erkennt, ob sich ein Gefäß (14) auf der Induktionsspule (5) befindet und ob es ein Gefäß (14) gibt, ob die ferromagnetischen Eigenschaften davon geeignet sind.

2. Eine Leistungssteuerschaltung (1), wie in Anspruch 1 aufgeführt, ist dadurch gekennzeichnet, dass der elektronische Oszillator (10) ein "Colpitts-Oszillator" ist, der Strom in Sinuswellenform erzeugt.

3. Eine Leistungssteuerschaltung (1), wie in Anspruch 1 oder 2 aufgeführt, ist dadurch gekennzeichnet, dass mindestens einer vom Mikrocontroller (9) gesteuerten Oszillatorschalter (11) die Aktivierung des elektronischen Oszillators (10) durch Verbindung mit der Induktionsspule (5) bei bestromter Induktionsspule (5) ermöglicht und die Deaktivierung des elektronischen Oszillators (10) durch Unterbrechen seiner Verbindung, wenn die Induktionsspule (5) erregt wird.

4. Eine Leistungssteuerschaltung (1), wie in Anspruch 1 oder 2 aufgeführt, ist dadurch gekennzeichnet, dass eine Spitzenspannungsüberwachungsschaltung (12) es dem Mikrocontroller (9) ermöglicht, die Spitzenspannungswerte des im elektronischen Oszillator (10) erzeugten Sinusstroms zu lesen.

5. Eine Leistungssteuerschaltung (1), wie in Anspruch 1 oder 2 aufgeführt, ist dadurch gekennzeichnet, dass eine Nulldurchgangsüberwachungsschaltung (13) den im elektronischen Oszillator (10) erzeugten Sinusstrom in eine Rechteckform umwandelt und das Lesen der Signalamplitude durch den Mikrocontroller (9) ermöglicht.

6. Eine Leistungssteuerschaltung (1), wie in Anspruch 1 oder 2 aufgeführt, ist dadurch gekennzeichnet, dass sie ein Halbbrücken-Serienresonanzkreis ist, der ein Paar Resonanzkondensatoren (6) und ein Paar Leistungsschalter (7) besitzt.

7. Eine Leistungssteuerschaltung (1), wie in Anspruch 1 oder 2 aufgeführt, ist dadurch gekennzeichnet, dass es sich um einen Einzelschalter-Quasi-Resonanzkreis handelt, der einen einzelnen Resonanzkondensator (6) und einen einzelnen Leistungsschalter (7) umfasst.

8. Ein Induktionsherd (1) ist durch einen Leistungssteuerschaltung (1) nach Anspruch 1 oder 2 gekennzeichnet.

Revendications

1. Un circuit de commande et de puissance (1) qui peut être utilisé dans les cuisinières à chauffage par induction, comprenant un pont redresseur (2) qui convertit le courant alternatif reçu par le secteur en courant continu; un inducteur de filtre (3) et un condensateur de filtrage (4) qui est disposé à la sortie du pont redresseur (2) ; une bobine d'induction (5) qui est alimentée pour chauffer un récipient (14) placé sur la cuisinière à chauffage par induction de sorte que le courant de la bobine passe à travers celui-ci; au moins un condensateur résonnant (6) qui alimente la bobine d'induction (5); au moins un interrupteur d'alimentation (7) qui permet de charger/décharger le condensateur résonnant (6) et qui assure la transmission de la puissance de la bobine d'induction (5) au récipient (14) ; un circuit de commande (8) qui permet de commander l'interrupteur d'alimentation (7) avec une tension de commande au seuil souhaité, et un microcontrôleur (9) qui régule le fonctionnement de l'interrupteur d'alimentation (7) au moyen du circuit de commande (8) caractérisé par

- un oscillateur électronique (10) qui est connecté au microcontrôleur (9), qui transmet les signaux en se connectant électriquement à la bobine d'induction (5) au début du fonctionnement de la cuisinière à chauffage par induction lorsque la bobine d'induction (5) n'a pas encore été alimenté et qui produit une tension de sortie en accord avec les valeurs de résistance en série et d'inductance (R, L) de la paire bobine d'induction (5) - récipient (14), et

- le microcontrôleur (9) qui, en fonction des données reçues de l'oscillateur électronique (10), détecte s'il y a un récipient (14) sur la bobine d'induction (5) et si les caractéristiques ferromagnétiques de celui-ci sont appropriées lorsqu'il y a un récipient (14),

2. Un circuit de commande et de puissance (1) selon la Revendication 1, caractérisé par l'oscillateur électronique (10) qui est un «oscillateur Colpitts » qui génère le courant sous forme d'onde sinusoïdale.

3. Un circuit de commande et de puissance (1) selon la Revendication 1 ou 2, caractérisé par au moins un interrupteur d'oscillateur (11) qui est contrôlé par le microcontrôleur (9), qui assure l'activation de l'oscillateur électronique (10) en se connectant à la bobine d'induction (5) lorsque la bobine d'induction (5) est alimentée et la désactivation de l'oscillateur électronique (10) en coupant la connexion de celui-ci lorsque la bobine d'induction (5) est alimentée.

4. Un circuit de commande et de puissance (1) selon la Revendication 1 ou 2, caractérisé par un circuit de contrôle de tension de crête (12) qui permet au microcontrôleur (9) de lire les valeurs de tension de crête du courant sinusoïdal généré dans l'oscillateur électronique (10).

5. Un circuit de commande et de puissance (1) selon la Revendication 1 ou 2, caractérisé par un circuit de contrôle de passage par zéro (13) qui convertit le courant sinusoïdal généré dans l'oscillateur électronique (10) en une forme d'onde carrée et qui permet à l'amplitude du signal d'être lue par le microcontrôleur (9).

6. Un circuit de commande et de puissance (1) selon la Revendication 1 ou 2, caractérisé en ce que le circuit soit un circuit résonnant en série en demi-pont comprenant une paire de condensateurs résonnants (6) et une paire d'interrupteurs d'alimentation (7).

7. Un circuit de commande et de puissance (1) selon la Revendication 1 ou 2, caractérisé en ce que le circuit soit un circuit quasi résonnant à interrupteur unique comprenant un seul condensateur résonnant (6) et un seul interrupteur d'alimentation (7).

8. Une cuisinière à chauffage par induction (1), caractérisée par un circuit de commande et de puissance (1) selon la Revendication 1 ou 2.

Drawing