EP2932793A1

EP2932793A1 - An induction heating cooktop

Info

Publication number: EP2932793A1
Application number: EP13818991.5A
Authority: EP
Inventors: Metin OZTURK; Namik Yilmaz; Hakan Suleyman YARDIBI; Metin ASTOPRAK
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2012-12-12
Filing date: 2013-12-11
Publication date: 2015-10-21
Anticipated expiration: 2033-12-11
Also published as: EP2932793B1; ES2606687T3; CN105191489A; WO2014090874A1

Abstract

The present invention relates to an induction heating cooktop (1) comprising a resonant circuit (6) having an induction coil (4) and a resonant capacitor (5) connected in parallel to the induction coil (4), a power switch (7), for example an IGBT, that drives the resonant circuit (6), a collector node (8) whereon resonance voltage (Vce) is generated during the non-conduction (turn-on) times of the power switch (7), a drive circuit (9) that provides the power switch (7) to be driven, and a control unit (11) that regulates the operation of the power switch (7) by controlling the drive circuit (9), and wherein the presence of the vessel (K) placed on the induction coil (4) and appropriate position thereof is determined in different heating settings and under variable AC mains voltage and temperature conditions.

Description

AN INDUCTION HEATING COOKTOP

The present invention relates to an induction heating cooktop wherein it is detected whether or not the vessel placed thereon is at the appropriate position.
The induction heating cooktop functions according to the principle of heating a cast iron or steel ferromagnetic cookware, for example a pot, with the magnetic field effect generated by the induction coil. In the state of the art, single switch quasi-resonant (SSQR) circuits formed 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 operate in a narrower energy frequency range and can deliver power to the cookware only within a certain voltage and power range. In induction heating cooktops wherein the single switch quasi-resonant circuits (SSQR) are used, problems are encountered in detecting different kinds of cookware and the changes in position of the cookware on the cooktop burner. Furthermore, difficulties arise in detecting the position of the cookware in mains voltage fluctuations and at different temperature conditions. In some induction heating cooktops, multi coil – multi zone structure is used, heating can be maintained on the entire cooktop surface and flexibility is provided for the user. In this type of induction heating cooktops, induction coils of various shapes and sizes are situated on the cooktop surface. Under variable mains voltage, input voltage depending on the power setting and at variable temperature conditions, the detection of the cookware position and furthermore the characteristic features like the diameter, type and the ferromagnetic properties during power transmittance to the cookware is quite critical for products wherein multi coil and also the single switch quasi-resonant circuits (SSQR) are used. In the induction heating cooktops, the position of the vessel placed on the induction coil is generally defined by circular border lines drawn on the cooktop surface. If aligned with the induction coil according to the predetermined border lines, the vessel can be heated efficiently. The user is allowed to slide the vessel outside the said border lines a little and the vessel can be heated at the desired power setting as long as it is in the efficient heating zone. With the condition of being in the efficient heating zone, the vessel should be heated according to the power setting selected by the user and without being affected by variable mains voltage and temperature conditions and if the vessel is slid outside the efficient heating zone, this situated should be detected and energy transmitted to the vessel should be interrupted. If it is not detected that the vessel is slid outside the efficient heating zone, the vessel cannot be heated according to the selected power setting and the circuit board can be damaged.
The European Patent Application No. EP2282606 relates to an induction apparatus control method. The presence or absence of the vessel on the induction coil, the resistivity and the dimensions thereof are detected by comparing the resonance voltage with a predetermined fixed reference voltage in the control unit.
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.
In the Japanese patent application no. JP4371108, an induction heating cooking device that comprises a cookware detection circuit is explained.
In the Japanese patent application no. JP2011023163, a rice cooker is explained wherein existence or nonexistence of a pan on the induction heater or whether or not the pan is located at a designated position is detected under unstable power source voltage conditions.
In the Japanese Patent Application No. JP2007066837, a rice cooker is explained wherein the presence of kitchenware such as spoon, knife on the induction heater is detected under fluctuating power source voltage conditions.
The aim of the present invention is the realization of an induction heating cooktop wherein the position of the vessel placed on the induction coil is detected under variable mains input voltage and temperature conditions.
The induction heating cooktop 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 into direct current, a resonant circuit having an induction coil and a resonant capacitor, a power switch, for example an IGBT, that drives the resonant circuit, a collector node whereon resonance voltage is generated, a current monitoring circuit, connected in series to the induction coil, that provides the coil current, passing through the induction coil, to be monitored by converting it into voltage data, and a voltage monitoring circuit that provides the monitoring of the resonant voltage (power switch voltage) generated on the collector node.
In an embodiment of the present invention, the current monitoring circuit comprises a current detection resistor connected in series to the induction coil, and in another embodiment of the present invention comprises a current transformer connected in series to the induction coil and a current detection resistor connected in parallel to the secondary side of the current transformer.
In an embodiment of the present invention, the voltage monitoring circuit comprises a voltage divider that decreases the resonant voltage, thus enabling easy measurement thereof.
The control unit decides that the vessel is inside the efficient heating zone on the upper plate of the cooktop, wherein the vessel is allowed to be slid a little off the level of the induction coil, if the coil current changes monitored by means of the current monitoring circuit are greater than the limit coil current changes prerecorded in its memory for different power scales selected via the user interface.
Upon detecting that the vessel is inside the efficient heating zone, the control unit keeps the resonant voltage, monitored by means of the voltage monitoring circuit, constant by increasing the resonant voltage if low or decreasing it if high, thus the power transferred to the vessel is enabled to be kept constant as long as the vessel is inside the efficient heating zone even if slid a little off the level of the induction coil.
Upon detecting that the vessel is slid outside the efficient heating zone, the control unit stops the operation of the induction heating cooktop.
In the induction heating cooktop of the present invention, the control unit keeps the power transferred to the vessel constant in variable mains voltage and temperature conditions in accordance with the heating settings selected via the user interface. By precisely detecting the alignment of the vessel on the induction coil, the power switch that drives the induction coil, and other electronic components are prevented from being damaged.
The induction heating cooktop realized in order to attain the aim of the present invention is illustrated in the attached figures, where:
Figure 1 – is the top schematic view of an induction heating cooktop.
Figure 2 – is the schematic view of the control circuit of an induction heating cooktop.
Figure 3 – is the schematic view of the control circuit of an induction heating cooktop in an embodiment of the present invention.
The elements illustrated in the figures are numbered as follows:

Induction heating cooktop
Bridge rectifier
Filter circuit
Induction coil
Resonant capacitor
Resonant circuit
Power switch
Collector node
Drive circuit
User interface
Control unit
Voltage monitoring circuit
Current monitoring circuit
Current detection resistor
Current transformer
Voltage divider

The induction heating cooktop (1) comprises a bridge rectifier (2) that converts the alternating current received from the mains into direct current, a high frequency filter circuit (3) at the outlet of the bridge rectifier (2) and one or more than one induction coil (4) through which the coil current (I_L) passes during the heating of the vessel (K) placed on the upper plate (P) of the induction heating cooktop (1) so as to be inside the efficient heating zone (B).
Onto the upper plate (P) of the induction heating cooktop (1), the vessel (K) or other ferromagnetic cooking containers are placed so as to be inside an efficient heating zone (B) that allows them to go a little beyond the border line (S) defining the position thereof at the induction coil (4) level and that provides the efficient heating thereof (Figure 1).
The induction heating cooktop (1) comprises a resonant circuit (6) having a resonant capacitor (5) connected in parallel to the induction coil (4), a power switch (7), for example an IGBT (Insulated Gate Bipolar Transistor), having a collector, an emitter and a freewheeling diode, that drives the resonant circuit (6), that is in conducting state in the turned-off position, providing the resonant capacitor (5) to be charged during the conduction time, that interrupts conduction in the turned-on position, providing the resonant capacitor (5) to be discharged during the non-conduction time and that provides the power to be delivered from the induction coil (4) to the vessel (K), a collector node (8) whereon resonance voltage (Vce) or in other words the collector-emitter voltage of the power switch (7) is generated during the non-conduction (turn-on) times of the power switch (7), a drive circuit (9) providing the power switch (7) to be driven with the drive voltage (Vge) at the required level, a user interface (10) that provides the heating of the vessel (K) at the desired power level and whereby the user adjust the heating setting, and a control unit (11), for example a microcontroller, that regulates the operation of the power switch (7) by means of the drive circuit (9) in accordance with the heating setting selected via the user interface (10) (Figure 2, Figure 3).
As long as the vessel (K) placed on the upper plate (P) of the induction heating cooktop (1) stays inside the efficient heating zone (B) having a diameter greater than the border line (S) marked on the upper plate (P), the vessel (K) is heated by receiving constant power in accordance with the heating setting (power scale) selected via the user interface (10). The user is allowed to slide the vessel (K) a little off the induction coil (4) level. If the vessel (K) is slid outside the efficient heating zone (B), the power being transferred from the induction coil (4) to the vessel (K) is interrupted.
In the induction heating cooktop (1), the conduction times wherein the power switch (7) is in the turned-off position are determined by the heating setting selected via the user interface (10). The non-conduction times wherein the power switch (7) is in the turned-on position are determined by the control unit (11) depending on the characteristic features of the vessel (K) placed on the induction coil (4), alignment of the vessel (K) on the induction coil (4), mains voltage conditions and the temperature of the vessel (K). During the non-conduction times of the power switch (7), resonance voltage (Vce) is generated at the collector node (8), the coil current (I_L) passes through the induction coil (4) and energy is transferred to the vessel (K).
The induction heating cooktop (1) of the present invention comprises,
- a voltage monitoring circuit (12) connected to the collector node (8) and providing the monitoring of the resonant voltage (Vce) during power transmission to the vessel (K), and
- a current monitoring circuit (13) connected in series to the induction coil (4) and providing the monitoring of the coil current (I_L) by converting it into voltage data during power transmission to the vessel (K),
- the control unit (11) that decides that the vessel (K) is inside the efficient heating zone (B) if the coil current changes (ΔI_L) monitored by means of the current monitoring circuit (13) are greater than the limit coil current changes (ΔI_L-lim) prerecorded in its memory for different power scales selected via the user interface (10) and that keeps the resonant voltage (Vce) constant by intervening in the resonant voltage (Vce) monitored by means of the voltage monitoring circuit (12), thus enables the power transferred to the vessel (K) to be kept constant..
If the coil current changes (ΔI_L) monitored by means of the current monitoring circuit (13) are smaller than the limit coil current changes (ΔI_L-lim) prerecorded in its memory for different power scales, the control unit (11) decides that the vessel (K) is slid outside the efficient heating zone (B), interrupts the coil current (I_L) and stops the operation of the induction heating cooktop (1).
In the induction heating cooktop (1), when the vessel (K) is slid a little off over the induction coil (4), whether or not the vessel (K) is inside the efficient heating zone (B) is determined by means of the current monitoring circuit (13). If the vessel (K) is inside the efficient heating zone (B), the control unit (11) keeps the resonant voltage (Vce) and hence the power transferred to the vessel (K) constant in variable mains voltage and temperature conditions by means of the voltage monitoring circuit (12) and the drive circuit (9). Even if slid a little off the level of the induction coil (4), the vessel (K) is enabled to be heated inside the efficient heating zone (B) in accordance with the heating setting selected via the user interface (10).
In an embodiment of the present invention, the control unit (11) compares the constant resonant voltage (Vce-sb) values prerecorded in its memory and corresponding to the heating setting selected via the user interface (10) with the actual resonant voltage (Vce) values monitored by means of the voltage monitoring circuit (12), intervenes in the power switch (7) by means of the drive circuit (9) and enables the actual resonant voltage (Vce) to be equalized with the constant resonant voltage (Vce-sb), thus enables the power transferred from the induction coil (4) to the vessel (K) to be kept constant.
In an embodiment of the present invention, the current monitoring circuit (13) comprises a current detection resistor (14) that is connected in series to the induction coil (4) and that converts the coil current (I_L) into voltage data (Figure 3). The control unit (11) receives the voltage data relating to the coil current (I_L) from the terminals of the current detection resistor (14).
In another embodiment of the present invention, the current monitoring circuit (13) comprises a current transformer (15) connected in series to the induction coil (4) and decreasing the coil current (I_L) to a level that can be detected by the control unit (11) and the current detection resistor (14) connected in parallel to the secondary side of the current transformer (15) (Figure 2).
In another embodiment of the present invention, the voltage monitoring circuit (12) comprises a voltage divider (16) that has resistors (R1, R2) connected in series to the collector node (8) and that applies an easy-to-measure, low level resonant voltage (Vce) to the control unit (11) by dividing the resonant voltage (Vce) (Figure 2, Figure 3).
In the induction heating cooktop (1) of the present invention, constant power is transferred to the vessel (K) in the efficient heating zone (B) wherein the vessel (K) is allowed to be slid a little off the induction coil (4) level and the vessel (K) being slid causes change in the coil current (I_L). In order to detect the position of the vessel (K) placed onto the upper plate (P), the resonant voltage (Vce) is kept constant and the coil current (ΔI_L) that changes as the vessel (K) is slid off over the induction coil (4) is monitored. In order to keep the power transferred to the vessel (K) constant in the heating settings selected via the user interface (10), the control unit (11) keeps the resonant voltage (Vce) constant and detects whether or not the vessel (K) is present or the alignment of the vessel (K) on the induction coil (4) is appropriate by monitoring the coil current changes (ΔI_L) caused by the vessel (K) being slid. The power switch (7) and the other electronic circuit components are prevented from being damaged. In different heating settings, the position of the vessel (K) placed on the induction coil (4) is detected precisely under variable mains input voltage and temperature conditions, and the vessel (K) is provided to be heated with a constant power.
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 cooktop (1) comprising a bridge rectifier (2) that converts the alternating current into direct current, a filter circuit (3) disposed at the outlet of the bridge rectifier (2), one or more than one induction coil (4) through which the coil current (I_L) passes during the heating of the vessel (K) placed on the upper plate (P) of the induction heating cooktop (1) so as to be inside the efficient heating zone (B), a resonant circuit (6) having a resonant capacitor (5) connected in parallel to the induction coil (4), a power switch (7) that drives the resonant circuit (6), a collector node (8) whereon resonance voltage (Vce) is generated during the non-conduction times of the power switch (7), a drive circuit (9) providing the power switch (7) to be driven, a user interface (10), and a control unit (11) that regulates the operation of the power switch (7) by means of the drive circuit (9) in accordance with the heating setting selected via the user interface (10), characterized in that

- a voltage monitoring circuit (12) connected to the collector node (8) and providing the monitoring of the resonant voltage (Vce), and

- a current monitoring circuit (13) connected in series to the induction coil (4) and providing the monitoring of the coil current (I_L), and

- the control unit (11) that decides that the vessel (K) is inside the efficient heating zone (B) if the coil current changes (ΔI_L) monitored by means of the current monitoring circuit (13) are greater than the limit coil current changes (ΔI_L-lim) prerecorded in its memory for different power scales selected via the user interface (10) and that keeps the resonant voltage (Vce) monitored by means of the voltage monitoring circuit (12) and the power transferred to the vessel (K) constant..
An induction heating cooktop (1) as in Claim 1, characterized in that the control unit (11) that decides that the vessel (K) is slid outside the efficient heating zone (B) and stops the operation of the induction heating cooktop (1) if the coil current changes (ΔI_L) monitored by means of the current monitoring circuit (13) are smaller than the limit coil current changes (ΔI_L-lim).
An induction heating cooktop (1) as in Claim 1 or 2, characterized in that the control unit (11) that compares the constant resonant voltage (Vce-sb) prerecorded in its memory and corresponding to the heating setting selected via the user interface (10) with the actual resonant voltage (Vce), that intervenes in the power switch (7) by means of the drive circuit (9) and that enables the actual resonant voltage (Vce) to be equalized with the constant resonant voltage (Vce-sb).
An induction heating cooktop (1) as in any one of the above claims, characterized in that the current monitoring circuit (13) comprising a current detection resistor (14) that is connected in series to the induction coil (4) and that converts the coil current (I_L) into voltage data.
An induction heating cooktop (1) as in any one of the Claims 1 to 3, characterized in that the current monitoring circuit (13) comprising a current transformer (15) connected in series to the induction coil (4) and decreasing the coil current (I_L), and the current detection resistor (14) connected in parallel to the current transformer (15).
An induction heating cooktop (1) as in any one of the above claims, characterized in that the voltage monitoring circuit (12) that comprises a voltage divider (16) that has resistors (R1, R2) connected in series to the collector node (8) and that applies an easy-to-measure, low level resonant voltage (Vce) to the control unit (11) by dividing the resonant voltage (Vce).