WO2016010493A1

WO2016010493A1 - Induction heating cooker enabling improved power setting control

Info

Publication number: WO2016010493A1
Application number: PCT/TR2014/000284
Authority: WO
Inventors: Metin ASTOPRAK; Metin ÖZTÜRK; Namik Yilmaz; Bekir DUMLU; Selçuk SOYYIĞIT
Original assignee: Arçeli̇k Anoni̇m Şi̇rketi̇
Priority date: 2014-07-15
Filing date: 2014-07-15
Publication date: 2016-01-21
Also published as: EP3170364A1

Abstract

The present invention relates to a method for operating an induction heating cooker (1) comprising a plurality of induction coils (2) in association with induction resonant inverters (4) to provide multi-zone induction coils (3), a power switch driving circuit (14) driving power switching devices associated with the induction resonant inverters (4), a pan detection circuit (13) and a user interface (8) having a graphic display (16), the induction heating cooker (1) further comprising a vitro-ceramic glass surface containing no surface indication as to suggestible placement of a pan (15).

Description

INDUCTION HEATING COOKER ENABLING IMPROVED POWER

SETTING CONTROL

The present invention relates to a method for operating an induction heating cooker by which power supplied to a larger container can be set to a minimal power setting.

It is well-known that an induction heating cooker operates based on the process of heating a ferromagnetic material by electromagnetic induction where eddy currents are to be induced and resistance provides heat dissipation within the ferromagnetic material, i.e. a cooking vessel in the form of a pot or pan.

By induction heating, high-frequency alternating current is passed through a coil upon which a magnetic field of the same frequency is induced. The internal resistance of the pan causes heat dissipation due to Joule effect and energy transfer is interrupted once the pan is removed from the cooktop. The energy efficiency of induction heating cookers is considerably high since there is no transfer of heat energy between the hob and the cookware and heat energy lost in the air is minimal.

A resonant converter in an induction heater circuit topology typically consists of a capacitor, an inductor and resistance. To this end, when power is supplied to the resonant tank, electric energy is stored in the inductor and transferred to the capacitor. Resonance therefore occurs while the inductor and the capacitor involve in energy exchange. The resonant converter can be a half-bridge series resonant converter or a quasi-resonant converter.

A quasi-resonant converter exhibits certain advantages over a half-bridge series resonant converter especially due to its simpler circuit design having only one power switching device compared to the half-bridge series resonant converter whose overall operation is more complex. The circuit design parameters in a quasi-resonant converter are regarded as a serious cost advantage in this regard. In order to drive the resonant inductor generating magnetic field and in turn inducing eddy currents on the skin depth of a cooking vessel, a high-frequency power switch such as an IGBT is accordingly used.

Among others, a prior art publication in the technical field of the invention may be referred to as EP 1 629 698 B l , which discloses an induction cooking system including a power inverter, a microprocessor, a protection circuit and a pan detection circuit.

The present invention provides a simple yet effective method by which a number of sufficiently small cooking zones are created to provide a flexible-distribution cooking surface to correspond to a cooking container of any size.

The present invention provides a plurality of distinct induction coils driven by respective resonant inverters such that a plurality of flexible cooking zones can be created with a minimal number of induction coils whereby a cooking container of any size can be heated by induction heating. The method of operation according to the invention ensures that while a smaller size cooking pan of standard shape can be heated by a single induction coil alone, a larger size pan or a non-standard, non-circular larger pan can be heated by a plurality of induction coils such that power suppliable to such a larger container can be set to a minimal power setting. As is known, the level of lowered power setting can be an important parameter in cooking practice.

The present invention provides a method for operating an induction heating cooker by which power setting for heating a cooking container on a plurality of induction coils can be set to a minimal level as provided by the characterizing features defined in Claim 1. Primary object of the present invention is to provide a method for operating an induction heating cooker by which a cooking container of any size is heatable by a limited number of induction coils sufficiently small to obtain flexible cooking zones and the power level for heating a cooking container on a plurality of inductions coils can be set to a minimal level.

The present invention proposes a method for operating an induction heating cooker by which a pan detected on multiple induction coils is heated by apportioning the total power of the cooking zone as set by the user to the induction coils of said cooking zone. In this regard, a number of induction coils less than the total number defined in association with the cooking zone can be powered depending on the lowest safe and effective power level of each induction coil and the adjusted power level of the cooking zone. Induction coils of said cooking zone are therefore powered in a successively interrupted manner such that a certain number of induction coils less than the total number in the cooking zone are energized at a given time so that power transferred to the cooking zone at any time corresponds to the power setting defined by the user.

If the power setting of said cooking zone with multiple induction coils allows that a single coil can supply alone the adjusted power, the induction coils forming the cooking zone are operated in a successively interrupted manner such that only one induction coil is energized at a given time. Heating energy can also be controlled by driving a respective power switching device at a certain duty cycle.

Accompanying drawings are given solely for the purpose of exemplifying an induction heating cooker, whose advantages over prior art were outlined above and will be explained in brief hereinafter.

The drawings are not meant to delimit the scope of protection as identified in the Claims, nor should they be referred to alone in an effort to interpret the scope identified in said Claims without recourse to the technical disclosure in the description of the present invention. Fig. 1 demonstrates a general circuit diagram of an induction heating cooker system according to the present invention.

Fig. 2 demonstrates a general top view of the induction heating cooker with different size food containers and cooking zones according to the present invention.

Fig. 3 demonstrates another general top view of the induction heating cooker with different size food containers and cooking zones according to the present invention.

Fig. 4 demonstrates power distribution profiles of different induction coils powered for heating the pan PI shown in Fig. 3 according to the present invention.

The following numerals are assigned to different part numbers used in the detailed description:

1) Induction heating cooker

2) Induction coil

3) Multi-zone coil system

4) Induction resonant inverter

5) Filter Inductance

6) Leveling capacitor

7) Power switching device

8) User interface

9) Resonant capacitor 10) Full-wave rectifier

11) Freewheeling diode

12) Control circuitry

13) Pan detection circuit

14) Power switch driving circuit

15) Pan

16) Graphic display

17) Cooking zone

18) Control buttons

19) DC bus

20) Collector mode

21) Current sensing resistance

The present invention proposes an induction heating cooker (1) having a plurality of induction coils (2) in the form of a multi-zone coil system (3). An induction resonant inverter (4) stage in relation with each induction coil (2) provides that heat energy is induced within a magnetically responsive cooking container or pan (15) placed above the induction coils (2) of the induction heating cooker (1 ). The induction heating cooker (1) of the present invention is supplied with a source of AC voltage. A full-wave bridge rectifier (10) is connected between the AC source and power stage of the induction coil (2). The induction coil (2) is connected between the output of said rectifier and a power switching device (7). The resonant capacitor (9) is parallel to the induction coil (2) and an anti-parallel diode, i.e. a freewheeling diode (1 1 ) is connected parallel to said power switching device (7). A plurality of induction resonant inverter (4) stages associated with a respective induction coil (2) therefore provides a multi-zone coil system (3).

The induction heating cooker (1) also conventionally comprises an AC signal filtering circuit. Power passing through a leveling capacitor (6) serves to the purpose of filtering high frequency current. The voltage of the leveling capacitor

(6) is converted into a square wave by the high-frequency power switching device

(7) . According to Ampere's Law, the square wave provides resonance creating a magnetic field around an associated induction coil (2). The resonant capacitor (9) provided in parallel with the induction coil (2) therefore compensates the inductive nature of the latter.

The quasi-resonant converter's power switching device (7) is an insulated gate bipolar transistor (IGBT). The operating principle of the quasi-resonant converter typically relies on the storage of energy in the induction coil (2) when the power switching device (7) is turned on, and on the transfer of energy from the induction coil (2) to a cooking container or pan (15) when the power switching device (7) is turned off. More particularly, when the power switching device (7) is turned off, the resonant voltage (V_ce) increases on the collector node (20) as the resonant capacitor (9) is being discharged. When the resonant voltage (V_ce) is equal to the voltage at the DC bus (19), the energy stored in the induction coil (2) begins to be transferred to the resonant capacitor (9). The resonant current gradually decreases to zero when the resonant voltage reaches its maximum, meaning that energy transfer from the induction coil (2) to the resonant capacitor (9) is terminated. Thereupon, the resonant capacitor (9) starts discharging the energy to the induction coil (2). The current completes its cycle by passing through the freewheeling diode (1 1) connected in parallel to the IGBT.

According to the present invention, a control circuitry (12) monitors and controls the operation of the induction heating cooker (1). To detect cookware presence on a vitro-ceramic glass surface of the induction heating cooker (1 ) and also to detect its position accurately, a pan detection circuit (13) sensing cookware positioning is used. The microcontroller of the control circuitry (12) monitors voltages (V_cc) of the collector nodes (20) together with voltages at DC buses (19) and a power switch driving circuit (14) drives the respective power switching devices (7) in correspondence to the current feedback signal from a respective current sensing resistance (21) and also depending on the associated power 'setting as defined by the user. Pan detection techniques in induction heating cookers (1 ) are extensively used in the state of the art and being known to the skilled worker will as such not be further discussed herein.

According to the invention, a user interface (8) with control buttons (18) and a graphic display (16) being controlled by a display driver circuit are provided to enable the user to operate the induction heating cooker (1) functioning according to the method as described hereinafter.

In accordance with the invention, the vitro-ceramic glass contains no surface indication as to suggested placement of a cookware or utensil and a user can place a pan (15) anywhere on the vitro-ceramic glass surface he/she wishes. To this end, the pan detection circuit (13) detects presence of at least one cooking pan (15) on the vitro-ceramic glass and the user interface (8) generates a graphic representation of the detected cookware placement as currently placed on the graphic display (16).

It is known that cooking utensils are manufactured in certain standard sizes such as having base diameters of 105, 145, 180, 210 or 288 mm. According to the present invention, it is established that a single induction coil (2) itself can supply alone sufficient power to a smaller size pan (15), while at the same time providing a sufficiently small cooking zone (17) to provide a distributed-configuration cooking surface. Such a flexible cooking surface allows simultaneous powering of a certain number of induction coils (2) to provide versatile cooking zones (17) corresponding to cooking pans (15) of different sizes, including those with nonstandard, i.e. non-circular shapes. Therefore, a flexible surface configuration can be maintained with a limited number of induction coils (2), those being sufficiently small in size to provide flexible cooking zones (17) and sufficiently large to keep the total number of induction coils (2) limited, while at the same time creating optimum size cooking zones (17) for powering cooking pans (15) of different sizes, including non-standard ones. If the size of individual cooking zones (17) is too small, although more efficient cooking with more accurate cooking zones (17) can be obtained, a large number of induction coils (2) with respective induction resonant inverters (4) will be necessary. On the other hand, if substantially large induction coils (2) are provided, the efficiency will again be low. Therefore, an induction heating cooker (1) being versatile and flexible, yet having a reduced number of induction coils (2) creating, when combined, cooking zones (17) corresponding to the existing standard sizes of the cooking equipment is proposed in the manner that while a single cooking zone (17) can feed power to a smaller size container, a larger size container is heatable in an efficient manner in the event that a lower power setting is selected, as described hereinafter.

In accordance with the invention, if the pan detection circuit (13) detects presence of a pan (15) occupying a surface area corresponding to the effect area of more than one induction coil (2), the control circuitry (12) will apportion the requested power to each induction coil (2), the power transferred to the coils being determined depending on the power setting of the respective cooking zone (17) as defined by the user. As exemplified in Fig. 4, a cooking container PI placed on the coils Al, A2, A3 and A4 as shown in Fig. 3 can be heated by powering the respective coils Al, A2, A3 and A4 in an apportioned manner depending on the specific power setting.

This apportionment may also require that all of the induction coils (2) or only a certain number of them is operated at a given time. If the power setting of the respective cooking zone (17) is set to a level which can be suppliable by a single induction coil (2), than the induction coils (2) forming the cooking zone (17) are operated in a successive manner, that is, only one the plurality of induction coils (2) is powered at a given time.

According to the present invention, the largest distance between two portions of an induction coil (2) is between 100 and 140 mm, preferably between 1 10 and 130 mm and more preferably 120 mm. The method of operation according to the invention ensures that while a smaller size cooking pan (15) of standard shape can be heated by a single induction coil (2) alone, a larger size pan (15) or a nonstandard, non-circular larger pan (15) can be heated by a plurality of induction coils (2) such that power suppliable to such a larger container can be set to a minimal power setting. To reduce power delivered to a single larger pan (15) on a cooking zone (17) of multiple induction coils (2), the minimal power setting is achievable by powering each induction coil (2) at the lowest safe and effective power level in a successive manner, which also ensures homogeneous heating. According to the invention, it is further proposed that an induction coil (2) can be operated at a lowered duty cycle so that a lower power setting is achievable. For instance, in the case of a cooking zone (17) having a single induction coil (2), the lowest power level supplied can be changed by driving the respective power switching device (7) at a certain lowered duty cycle.

In a nutshell, the present invention proposes an induction heating cooker (1 ) comprising a plurality of induction coils (2) in association with induction resonant inverters (4) to provide multi-zone induction coils (3), a power switch driving circuit (14) driving power switching devices (7) associated with the induction resonant inverters (4) and a pan detection circuit (13) for detecting presence of at least one pan (15).

The induction heating cooker (1 ) of the invention comprises a control circuitry (12) effecting: a) detection of presence of at least one cooking pan (15) associated with a cooking zone (17) having at least one induction coil (2) by means of the pan detection circuit (8) and, b) apportioning of total power being adjusted for the cooking zone (17) to a plurality of induction coils (2) if presence of a cooking pan (15) on more than one induction coil (2) is detected.

In one embodiment of the present invention, the plurality of induction coils (2) of the cooking zone (17) are powered in a successively interrupted manner such that the number of induction coils (2) powered at a given time corresponds to the power setting of the respective cooking zone (17) as defined. In other words, number of the plurality of induction coils (2) of the cooking zone (17) powered at a given time may be less than the total number of the induction coils (2) of the cooking zone (17), therefore providing an advantageous power management by which lower heating levels can be delivered to the cooking pan (15).

In a further embodiment of the present invention, if the power setting of the cooking zone (17) having the plurality of induction coils (2) is set to a power level suppliable by a single induction coil (2) of the cooking zone (17), the induction coils (2) forming the cooking zone (17) are operated in a successively interrupted manner such that only one induction coil (2) is powered at a given time.

In a still further embodiment of the present invention, power supplied to an induction coil (2) is changed by driving a respective power switching device (7) at a certain duty cycle if presence of a cooking pan (15) on a single induction coil (2) is detected. Therefore, it is also possible to transfer lowered power to a cooking zone (17) having only one induction coil (2). In a yet still further embodiment of the present invention, the largest distance between two different portions of an induction coil (2) is between 100 and 140 mm.

In a yet still further embodiment of the present invention, each induction coil (2) is comprised of a plurality of separately powerable sub-coils. In a yet still further embodiment of the present invention, the induction heating cooker (1 ) comprises at least nine induction coils (2) in the form of a 3x3 induction coil (2) matrix.

In a yet still further embodiment of the present invention, each induction coil (2) is structured to have a rectangular, triangular or circular form.

In a yet still further embodiment of the present invention, the largest distance between two different portions of an induction coil (2) is between 1 10 and 130 mm and preferably 120 mm.

The present invention provides a plurality of distinct induction coils (2) driven by respective resonant inverters such that a plurality of flexible cooking zones (17) can be created with a minimal number of induction coils (2) such that a smaller size cooking pan (15) can be heated by a single induction coil (2) alone and a larger size pan (15) can be heated by a plurality of induction coils (2), in the manner to be capable of receiving a reduced amount of power.

Claims

1 ) An induction heating cooker (1 ) comprising a plurality of induction coils (2) in association with induction resonant inverters (4) to provide multi-zone induction coils (3), a power switch driving circuit (14) driving power switching devices (7) associated with the induction resonant inverters (4) and a pan detection circuit (13) for detecting presence of at least one pan (15) characterized in that a control circuitry (12) configured to effect:

- detection of presence of at least one cooking pan (15) associated with a cooking zone ( 17) having at least one induction coil (2) by means of said pan detection circuit (8) and

- apportioning of total power being adjusted for said cooking zone (17) to a plurality of induction coils (2) if presence of a cooking pan (15) on more than one induction coil (2) is detected.

2) An induction heating cooker (1) as in Claim 1, characterized in that the plurality of induction coils (2) of the cooking zone (17) are powered in a successively interrupted manner such that the number of induction coils (2) powered at a given time corresponds to the power setting of the respective cooking zone ( 7) as defined.

3) An induction heating cooker (1) as in Claim 2, characterized in that number of the plurality of induction coils (2) of the cooking zone (17) powered at a given time is less than total number of the induction coils (2) of the cooking zone (17).

4) An induction heating cooker (1 ) as in Claim 2, characterized in that if the power setting of the cooking zone (17) having the plurality of induction coils (2) is set to a power level suppliable by a single induction coil (2) of the cooking zone (17), the induction coils (2) forming the cooking zone (17) are operated in a successively interrupted manner such that only one induction coil (2) is powered at a gi ven time.

5) An induction heating cooker (1 ) as in Claim 1 , characterized in that power supplied to an induction coil (2) is changed by driving a respective power switching device (7) at a certain duty cycle if presence of a cooking pan (15) on a single induction coil (2) is detected.

6) An induction heating cooker (1) as in Claim 1 or 2, characterized in that the largest distance between two different portions of an induction coil (2) is between 100 and 140 mm.

7) An induction heating cooker (1) as in Claim 6, characterized in that each induction coil (2) is comprised of a plurality of separately powerable sub-coils.

8) An induction heating cooker (1) as in Claim 6 or 7, characterized in that the induction heating cooker (1) comprises at least nine induction coils (2) in the form of a 3x3 induction coil (2) matrix. 9) An induction heating cooker (1) as in Claim 6, 7 or 8, characterized in that each induction coil (2) is structured to have a rectangular, triangular or circular form.

10) An induction heating cooker (1) as in Claim 6, characterized in that the largest distance between two different portions of an induction coil (2) is between 110 and 130 mm.

1 1 ) An induction heating cooker (1 ) as in Claim 0, characterized in that the largest distance between two different portions of an induction coil (2) is 120 mm.