WO2013064331A1

WO2013064331A1 - An induction heating cooker

Info

Publication number: WO2013064331A1
Application number: PCT/EP2012/069850
Authority: WO
Inventors: Namik Yilmaz; Metin OZTURK; Hakan Suleyman YARDIBI; Ibrahim Niyazi Ulgur; Burcak Aytekin
Original assignee: Arcelik Anonim Sirketi
Priority date: 2011-11-03
Filing date: 2012-10-08
Publication date: 2013-05-10
Also published as: EP2774452A1

Abstract

The present invention relates to an induction heating cooker (1) comprising a bridge rectifier (3) that converts the alternative current to direct current, a DC-line inductor (4) and a DC-line capacitor (5) disposed at the output of the bridge rectifier (3), a parallel resonant circuit (8) having an induction coil (6) that provides the vessel (K) placed thereon to be heated with the magnetic field it generates and a resonant capacitor (7) connected in parallel to the induction coil (6), a power switch (9) that drives the parallel resonant circuit (8), a collector node (10) whereon the resonant voltage (Vce) is generated in the open position of the power switch (9) during the non-conducting time (Toff), a control unit (13) that regulates the operation of the power switch (9) and a drive circuit (12) that provides the power switch (9) to be driven with the drive voltage (Vge), and wherein the presence of the vessel (K) on the induction coil (6) and the characteristic features thereof are detected in case of variable AC mains voltage conditions.

Description

AN INDUCTION HEATING COOKER

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

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. In order to drive the induction coils generating magnetic field, high amount of electric current is passed through the power switch (IGBT-Insulated Gate Bipolar Transistor, diode or Mosfet) on the circuit board. In the state of the art, the half bridge series resonant (HBSR) circuits realized by using two power switches and two resonant capacitors, and the single switch quasi resonant (SSQR) circuits realized by one power switch and one resonant capacitor are used for driving a single induction coil. The single switch quasi resonant circuits (SSQR) are preferred due to cost advantage however they function in narrower energy frequency range and can deliver power to the cooking container only within a certain voltage and power range. In the induction heating cookers, before transmitting power to the cooking container for the heating process, vessel detection process is realized in order to determine the initial conditions and it is detected if there is a vessel on the induction coil and when a vessel is present if the ferromagnetic features and dimensions thereof are appropriate. If this detection process is not carried out properly, energy is transmitted to the induction coil when no vessel is present thereon or when there is a vessel without appropriate ferromagnetic features, thus the electronic components shortcircuit due to high currents. In the case the mains input voltage is irregular, for example the mains input voltage oscillates between 100 and 300 volts, detection and analysis of the cooking container pose a serious problem in the said quasi resonant structure. Vessel detection process is not carried out properly due to the changing mains input voltage and the power switch is damaged due to high currents.

The European Patent Application No. EP2282606 relates to an induction device control method. The presence of the vessel on the induction coil, the resistivity and the dimensions thereof are detected by comparing the resonant voltage with a predetermined fixed reference voltage in the control unit.

The aim of the present invention is the realization of an induction heating cooker wherein the vessel placed onto the induction coil is properly detected in variable mains input voltage conditions.

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 a bridge rectifier that converts the alternative mains current to direct current, a quasi resonant circuit having an induction coil and a resonant capacitor, a power switch, for example an IGBT, that drives the quasi resonant circuit, a collector node whereon the resonant voltage is generated, a drive circuit that provides the power switch to be driven and a comparator that compares the DC-line voltage at the output of the bridge rectifier with the resonant voltage at the collector node. By evaluating the signals at the output of the comparator, the control unit detects if a vessel is present on the induction coil, and when a vessel is present, detects if the ferromagnetic features and dimensions thereof are appropriate, moreover if the vessel is properly aligned on the induction coil.

In an embodiment of the present invention, the induction heating cooker comprises a first voltage divider disposed between the quasi resonant circuit and the ground, having resistors connected in series, connected in parallel to the power switch and a second voltage divider disposed between the DC line and the ground, having resistors connected in series. In this embodiment, the comparator compares the low-level reference resonant voltage generating at the connection node between the resistors in the first voltage divider with the low-level reference DC voltage generating at the connection nodes between the resistors in the second voltage divider.

The control unit decides that a vessel with appropriate ferromagnetic features is placed on the induction coil, if a single square wave signal is observed at the output of the comparator or if there is no square wave signal. The control unit decides that no vessel is present on the induction coil, if a high number of successive square wave signals is observed at the output of the comparator. The control unit decides that the diameter of the vessel is smaller than what is allowed or the vessel is not ferromagnetic, if a smaller number of square wave signals compared to the situation where no vessel is present, is observed at the output of the comparator.

In the induction heating cooker of the present invention, the control unit, furthermore, compares the period of the square wave signal at the output of the comparator with limit values prerecorded in its memory and decides if the vessel is properly aligned on the induction coil. The control unit updates the non-conducting time where the power switch is in the open position according to the period of the square wave signal, if the period of the square wave signal changes on the condition that it remains between the limit values.

In the induction heating cooker, in the unfavorable conditions where the AC mains input voltage is variable, the presence of vessel on the induction coil, the ferromagnetic features of the vessel and the alignment state thereof on the induction coil are detected in a secure manner, and initial conditions suitable for the characteristics of the vessel are applied while the initial energy is delivered when the heating process is started.

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.

Figure 2 – is the graph showing the change of the resonant voltage at the collector node and the square wave signals at the output of the comparator, with respect to time, when the drive voltage is applied to the power switch of an induction heating cooker.

The elements illustrated in the figures are numbered as follows:

Induction heating cooker
Mains filtering circuit
Bridge rectifier
DC-line inductor
DC-line capacitor
Induction coil
Resonant capacitor
Parallel resonant circuit
Power switch
Collector node
Voltage measuring unit
Drive circuit
Control unit
Comparator
First voltage divider
Second voltage divider

The induction heating cooker (1) comprises a filtering circuit (2) that filters the AC mains voltage, a bridge rectifier (3) that converts the alternative current received from the mains to direct current, a DC-line inductor (4) and a DC-line capacitor (5) disposed at the output of the bridge rectifier (3) and which deliver DC voltage in a certain frequency range by filtering the voltage generated in the DC-line, a parallel resonant circuit (8) having an induction coil (6) that provides the vessel (K) placed thereon to be heated and a resonant capacitor (7) connected in parallel to the induction coil (6), a power switch (9), for example an IGBT (Insulated Gate Bipolar Transistor), that drives the parallel resonant circuit (8), that changes to the conducting state in the closed position and that provides the resonant capacitor (7) to be charged during the conducting time (Ton), that stops conducting in the open position and that provides the resonant capacitor (7) to be discharged during the non-conducting time (Toff), also providing the delivery of the energy to the vessel (K) from the induction coil (6), a collector node (10) whereon the resonant voltage (Vce) is generated in the open position of the power switch (9) during the non-conducting time (Toff), a voltage measuring unit (11) that detects the resonant voltage (Vce) on the collector node (10), a drive circuit (12) that provides the power switch (9) to be driven with the required level of drive voltage (Vge) and a control unit (13), preferably a microcontroller, that regulates the operation of the power switch (9) by controlling the drive circuit (12).

The conducting time (Ton) where the power switch (9) is in the closed position, is determined by power level adjustment performed by the user. The non-conducting time (Toff) where the power switch (9) is in the open position is determined by the control unit (13) according to the characteristic features of the vessel (K) placed on the induction coil (6), alignment of the vessel (K) on the induction coil (6), AC mains voltage conditions and the temperature of the vessel (K). During the conducting time (Toff) of the power switch (9), the resonant capacitor (7) is first charged then discharged, the resonant voltage (Vce) is generated at the collector node (10) and energy is delivered to the vessel (K) from the induction coil (6). At the lowermost level of the resonant voltage (Vce), the power switch (9) is changed from the open position to the closed position, in other words from the non-conducting state to the conducting state and energy is stored in the induction coil (6) during the conducting time (Ton) of the power switch (9).

The induction heating cooker (1) of the present invention comprises a comparator (14) that compares the DC line voltage (Vdc) at the output of the bridge rectifier (3) with the resonant voltage (Vce) generating at the collector node (10) and the control unit (13) that evaluates the signals (S) at the output of the comparator (14) and detects if the vessel (K) is present on the induction coil (6) and when the vessel (K) is present, if the characteristic features, for example ferromagnetic features and dimensions thereof and its alignment on the induction coil (6) are appropriate (Figure 1).

When the induction heating cooker (1) is operated, the control unit (13) applies a short term drive voltage (Vge) (input signal or “pulse”), for example in a value of 15V to the power switch (9) through the drive circuit (12) in order to detect the vessel (K), the power switch (9) is changed to the closed position and then back to the open position, the resonant capacitor (7) is discharged during the non-conducting time (Toff) where the power switch (9) is in the open position and the resonant voltage (Vce) is generated at the collector node (10). The comparator (14) compares the collector node (10) voltage (Vce) with the DC line voltage (Vdc) and generates square wave signals (S) with variable number or period according to the difference between the two voltage values (Vdc, Vce). By evaluating the signals (S) at the output of the comparator (14), the control unit (13) detects if a vessel (K) is present on the induction coil (6), and when a vessel (K) is present, detects if the ferromagnetic features and dimensions thereof are appropriate, if the vessel (K) is properly aligned on the induction coil (6). The control unit (13) adjusts the non-conducting time (Toff) of the power switch (9) according to the result of the vessel (K) detection. The conducting time (Ton) of the power switch (9) is determined by power level adjustment performed by the user. In the induction heating cooker (1), in the cases where the AC mains voltage is variable, for example the AC mains voltage varies between 100 volts and 300 volts, the DC line voltage (Vdc) changes in synchronization with the AC mains voltage, and the resonant voltage (Vce) and the variable DC line voltage (Vdc) are compared (Figure 2). Thus, in the cases where the AC mains voltage is variable, a secure comparison is realized and the erroneous detection of the vessel (K) is prevented. For example, in low mains input voltage conditions, it is prevented that the vessel (K) is detected as non-present although the vessel (K) is present on the induction coil (6).

In an embodiment of the present invention, the induction heating cooker (1) comprises a first voltage divider (15) disposed between the parallel resonant circuit (8) and the ground (GND), having resistors (R1, R2) connected in series, connected in parallel to the power switch (9) and applying an easily-measurable low level reference resonant voltage (Vce-ref) to the comparator (14) by dividing the resonant voltage (Vce) at the collector node (10) and a second voltage divider (16) disposed between the DC line and ground (GND), having resistors (R3, R4) connected in series and applying an easily-measurable low level reference DC voltage (Vdc-ref) to the comparator (14) by dividing the DC voltage (Vdc) (Figure 1).

The comparator (14) compares the reference resonant voltage (Vce-ref) generating at the connection node (N1) between the resistors (R1, R2) in the first voltage divider (15) with the reference DC voltage (Vdc-ref) generating at the connection node (N2) between the resistors (R3, R4) in the second voltage divider (16) (Figure 1).

When the drive voltage (Vge) is applied by the drive circuit (12) for the vessel (K) detection process, the control unit (13) decides that a vessel (K) with appropriate characteristic features is present on the induction coil (6) if a single square wave signal (S) is observed at the output of the comparator (14) or if no square wave signal is observed. No square wave signal (S) is generated at the output of the comparator (14) even if a vessel (K) is placed on the induction coil (6), the number of the drive voltage (Vge) is increased until a square wave signal (S) generation is observed. The control unit (13) determines the non-conducting time (Toff) where the power switch (9) is in the open position, according to the period (Ts) of the square wave signal (S) at the output of the comparator (14).

If a high number (for example 10) of square wave signals (S) are observed at the output of the comparator (14), the control unit (13) decides that the resonant voltage (Vce) is higher than the DC voltage (Vdc) since the resonant voltage (Vce) encounters any resistance generated by the vessel (K), and decides that no vessel (K) is present on the induction coil (6).

If more than one square wave signal (S) and a lower number of square wave signals (S) compared to the situation where no vessel (K) is present on the induction coil (6) at the output of the comparator (14) are observed, the control unit (13) decides that the diameter of the vessel (K) is smaller than what is allowed or that the vessel (K) is not of ferromagnetic characteristic.

In another embodiment of the present invention, the control unit (13) compares the period (Ts) of the square wave signal (S) at the output of the comparator (14) with a lower limit (Ts-min) and a upper limit (Ts-max) prerecorded in its memory and, if the period (Ts) of the square wave signal (S) is between the lower limit (Ts-min) and the upper limit (Ts-max) (Ts-min < Ts < Ts-max), decides that the vessel (K) is properly aligned on the induction coil (6) (Figure 2).

If the period (Ts) of the square wave signal (S) is not between the lower limit (Ts-min) and the upper limit (Ts-max) (Ts < Ts-min veya Ts > Ts-max), the control unit (13) decides that the vessel (K) is not properly aligned on the induction coil (6), in other words the vessel (K) is “slid” or “lifted” from over the induction coil (6) more than the desired amount.

The control unit (13) updates the non-conducting time (Toff) where the power switch (9) is in the open position according to the period (Ts) of the square wave signal (S), if the period (Ts) of the square wave signal (S) changes on the condition that it remains between the limit values (Ts-min, Ts-max). For example, in the case that the vessel (K) is not properly aligned on the induction coil (6), but slid a little bit within the allowed limits, the period (Ts) of the square wave signal (S) at the output of the comparator (14) changes according to the new position of the vessel (K) and the non-conducting time (Toff) of the power switch (9) is updated depending on the period (Ts) of the square wave signal (S) at the output of the comparator (14),

In the induction heating cooker (1) of the present invention, in the cases where the AC mains input voltage is variable, the vessel (K) placed on the induction coil (6) is detected, and it is controlled in a secured manner if the vessel (K) is present, if the vessel (K) is of ferromagnetic characteristics or if the vessel (K) is properly aligned on the induction coil (6).

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

An induction heating cooker (1) comprising a bridge rectifier (3) that converts the alternative current to direct current, a DC-line inductor (4) and a DC-line capacitor (5) disposed at the output of the bridge rectifier (3), a parallel resonant circuit (8) having an induction coil (6) and a resonant capacitor (7) connected in parallel to the induction coil (6), a power switch (9) that provides the resonant capacitor (7) to be charged by conducting the current in the closed position and that provides the resonant capacitor (7) to be discharged by cutting off the current in the open position, a collector node (10) whereon the resonant voltage (Vce) is generated in the open position of the power switch (9) during the non-conducting time (Toff), a control unit (13) that regulates the operation of the power switch (9) and a drive circuit (12) that provides the power switch (9) to be driven with the drive voltage (Vge), characterized by a comparator (14) that compares the DC line voltage (Vdc) at the output of the bridge rectifier (3) with the resonant voltage (Vce) at the collector node (10) and the control unit (13) that evaluates the signals (S) at the output of the comparator (14) and detects if the vessel (K) is present on the induction coil (6) and when the vessel (K) is present, if the characteristic features thereof and its alignment on the induction coil (6) are appropriate
An induction heating cooker (1) as in Claim 1, characterized by a first voltage divider (15) disposed between the parallel resonant circuit (8) and the ground (GND), having resistors (R1, R2) connected in series, connected in parallel to the power switch (9) and a second voltage divider (16) disposed between the DC line and ground (GND), having resistors (R3, R4) connected in series.
An induction heating cooker (1) as in Claim 2, characterized by the comparator (14) that compares the reference resonant voltage (Vce-ref) generating at the connection node (N1) between the resistors (R1, R2) in the first voltage divider (15) with the reference DC voltage (Vdc-ref) generating at the connection node (N2) between the resistors (R3, R4) in the second voltage divider (16).
An induction heating cooker (1) as in any one of the above claims, characterized by the control unit (13) that decides that a vessel (K) with appropriate characteristic features is present on the induction coil (6) if a single square wave signal (S) is observed at the output of the comparator (14) or if no square wave signal is observed.
An induction heating cooker (1) as in any one of the above claims, characterized by the control unit (13) that decides that no vessel (K) is present on the induction coil (6) if a number of square wave signals (S) is observed at the output of the comparator (14).
An induction heating cooker (1) as in any one of the above claims, characterized by the control unit (13) that decides that the diameter of the vessel (K) is smaller than what is allowed or that the vessel (K) is not of ferromagnetic characteristics, if more than one square wave signal (S) and a lower number of square wave signals (S) compared to the situation where no vessel (K) is present on the induction coil (6) at the output of the comparator (14) are observed.
An induction heating cooker (1) as in any one of the above claims, characterized by the control unit (13) that compares the period (Ts) of the square wave signal (S) at the output of the comparator (14) with a lower limit (Ts-min) and a upper limit (Ts-max) prerecorded in its memory and, if the period (Ts) of the square wave signal (S) is between the lower limit (Ts-min) and the upper limit (Ts-max), decides that the vessel (K) is properly aligned on the induction coil (6), and if not between the lower limit (Ts-min) and the upper limit (Ts-max), decides that the vessel (K) is not properly aligned on the induction coil (6).
An induction heating cooker (1) as in Claim 7, characterized by the control unit (13) that updates the non-conducting time (Toff) where the power switch (9) is in the open position according to the period (Ts) of the square wave signal (S), if the period (Ts) of the square wave signal (S) changes.