EP3424269A1

EP3424269A1 - Induction heating cooker power control circuit

Info

Publication number: EP3424269A1
Application number: EP17708509.9A
Authority: EP
Inventors: Metin OZTURK; Atakan SARIOGLU; Ulas OKTAY; Sercan SINIRLIOGLU; Bekir DUMLU
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2016-03-04
Filing date: 2017-03-03
Publication date: 2019-01-09
Anticipated expiration: 2037-03-03
Also published as: TR201602883A2; WO2017149126A1; EP3424269B1

Abstract

The present invention relates to a power control circuit (1) 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, 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); at least one resonant capacitor (6); at least one power switch (7); a drive circuit (8), and a microcontroller (9) that regulates the operation of the power switch (7) by means of the drive circuit (8), whereon the power control circuit (1) detects the presence of the vessel (14) on the induction heating cooker.

Description

INDUCTION HEATING COOKER POWER CONTROL CIRCUIT

The present invention relates to a power control circuit that detects the presence of the vessel placed on an induction heating cooker.
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.
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.
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.
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.
The European Patent No. EP1542508 relates to the determination of the location of the cooking utensils on the induction cooking hob.
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.
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.
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.
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.
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.
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.
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
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
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).
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.
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.
In the preferred embodiment of the present invention, the electronic oscillator (10) is a Colpitts oscillator that generates a current in sinusoidal wave form.
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.
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.
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).
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.
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).
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.
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).
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.
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

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