COOKING HOB

Abstract

The invention relates to a cooking hob comprising at least one heating power transferring element (2) including multiple concentrically arranged windings (2.1-2.n), one or more heating power energy units (3.1-3.n) for powering said windings (2.1-2.n) of the heating power transferring element (2) and a control unit (4) configured to control said one or more heating power energy units (3.1-3.n), wherein the cooking hob (1) comprises detection means configured to determine the coverage of the windings (2.1-2.n) of the heating power transferring element (1) by a cookware item (5), wherein the control unit (4) is configured to balance the heat provided to the cookware item (5) by determining a rescaled electric power for the windings (2.1-2.n) of the heating power transferring element (2) based on power requests and information regarding the coverage of the windings (2.1-2.n) and to establish an operating cycle by determining a duty cycle for one or more windings (2.1-2.n) of the heating power transferring element (2), said duty cycle defining the activation time of the respective winding (2.1-2.n), wherein the duty cycle is chosen such that the mean electric power provided to the respective winding (2.1-2.n) within the operating cycle is equal or essentially equal to the rescaled electric power associated with said winding (2.1-2.n).

Claims

1. Cooking hob comprising at least one heating power transferring element including multiple concentrically arranged windings, one or more heating power energy units for powering said windings of the heating power transferring element and a control unit configured to control said one or more heating power energy units, wherein the cooking hob comprises detection means configured to determine the coverage of the windings of the heating power transferring element by a cookware item, wherein the control unit is configured to balance heat provided to the cookware item by determining a rescaled electric power for the windings of the heating power transferring element based on power requests and information regarding the coverage of the windings and to establish an operating cycle by determining a duty cycle for one or more windings of the heating power transferring element, said duty cycle defining an activation time of the respective winding, wherein the duty cycle is chosen such that a mean electric power provided to the respective winding within the operating cycle is equal or essentially equal to the rescaled electric power associated with said winding.

2. Cooking hob according to claim 1, comprising a storage including power scale information, said power scale information indicating a fraction of power provided to the respective winding depending on a certain operating scenario.

3. Cooking hob according to claim 2, wherein the operating scenario is associated with coverage information indicating the coverage of the windings of the heating power transferring element.

4. Cooking hob according to claim 2, wherein the control unit is configured to add the power requests associated with all windings of said heating power transferring element in order to obtain total requested power and distribute said total requested power among the windings according to said power scale information.

5. Cooking hob according to claim 1, wherein the windings of the heating power transferring element are powered by an AC current having the same or essentially the same frequency.

6. Cooking hob according to claim 1, comprising means for evaluating inductive coupling between a cookware item and one or more windings of the heating power transferring element.

7. Cooking hob according to claim 6, comprising assessment means adapted to establish information regarding power decrease caused by a poorly-coupled winding and adapted to compare said information regarding the power decrease with a threshold value in order to exclude said poorly-coupled winding.

8. Method for controlling a cooking hob, the cooking hob comprising at least one heating power transferring element comprising multiple concentrically arranged windings, one or more heating power energy units powering said windings of the heating power transferring element and a control unit for controlling said one or more heating power energy units, the method comprising the steps of: determining coverage of the windings of the heating power transferring element by a cookware item; determining a rescaled electric power for the windings of the heating power transferring element based on power requests and information regarding the coverage of the windings, thereby balancing heat provided by the windings to the cookware item; establishing an operating cycle by determining a duty cycle for one or more windings of the heating power transferring element, said duty cycle defining an activation time of the respective winding, wherein the duty cycle is chosen such that mean electric power provided to the respective winding within the operating cycle is equal or essentially equal to the rescaled electric power associated with said winding.

9. Method according to claim 8, wherein the windings of the heating power transferring element are powered by an AC current having the same or essentially the same frequency.

10. Method according to claim 8, wherein the operating cycle is segmented in multiple time slots and a length of a first time slot of the operating cycle is determined such that the rescaled electric power associated with at least one said winding is obtained based on the electric power provided to said at least one winding in the first time slot multiplied by a quotient of durations of said first time slot and said operating cycle.

11. Method according to claim 8, wherein at a beginning of the operation cycle, a number of activated windings is greatest and then decreases in subsequent time slots.

12. Method according to claim 8, wherein a total electric power is established and said total electric power is distributed among the active windings.

13. Method according to claim 8, wherein windings with the same rescaled electric power are powered simultaneously and with a same duration in the operating cycle.

14. Method according to claim 8, wherein the operating cycle is segmented in multiple time slots, wherein a number of time slots included in one operating cycle corresponds to a number of different rescaled electric power values associated with said windings.

15. Method according to claim 8, wherein inductive coupling between the cookware item and at least one said winding is evaluated and the at least one said winding is deactivated if a power decrease caused by a poor coupling is above a certain threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

[0061] FIG. 1 shows an example top view of cookware item placed above a heating power transferring element comprising multiple concentrically arranged windings;

[0062] FIG. 2 shows an example schematic diagram of a cooking hob;

[0063] FIG. 3 shows the percentage of total requested power provided to the respective windings in an operation cycle according to a first example power request;

[0064] FIG. 4 shows the electric power provided to the respective windings in an operation cycle according to the first example power request;

[0065] FIG. 5 shows the electric power provided to the respective windings in an operation cycle according to a second example power request; and

[0066] FIG. 6 shows the frequency dependency of consumed electric power of a certain winding for different cookware items.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0067] The present invention will now be described more fully with reference to the accompanying drawings, in which example embodiments are shown. The embodiments in the figures may relate to preferred embodiments, while all elements and features described in connection with embodiments may be used, as far as appropriate, in combination with any other embodiment and feature as discussed herein, in particular related to any other embodiment discussed further above. However, this invention should not be construed as limited to the embodiments set forth herein. Throughout the following description similar reference numerals have been used to denote similar elements, parts, items or features, when applicable.

[0068] The features of the present invention disclosed in the specification, the claims, examples and/or the figures may both separately and in any combination thereof be material for realizing the invention in various forms thereof.

[0069] FIG. 1 illustrates a heating power transferring element 2 which is partly covered by a cookware item 5 placed above the heating power transferring element 2. The heating power transferring element 2 may be, for example, an induction coil of a cooking hob, specifically an induction hob.

[0070] The heating power transferring element 2 comprises multiple windings 2.1-2.n. Said windings 2.1-2.n are concentrically arranged, i.e. a first winding 2.1 forms an inner winding which is circumferentially surrounded by one or more further windings 2.2-2.n. Such arrangement of windings 2.1-2.n is advantageous because by activating only some of the inner windings, a cookware item with a small-sized base area can be heated, whereas powering all windings 2.1-2.n allows for a heating of cookware items with a large-sized base area.

[0071] FIG. 2 shows a schematic diagram of a cooking hob 1 including a heating power transferring element 2 similar to the one shown in FIG. 1.

[0072] The cooking hob 1 comprises multiple heating power energy units 3.1-3.n. Each heating power energy unit 3.1-3.n may be coupled with one of the windings 2.1-2.n in order to provide electric power to said winding 2.1-2.n. As shown in FIG. 2, the heating power energy units 3.1-3.n are connected to a line 6 via which rectified mains voltage may be provided to the heating power energy units 3.1-3.n.

[0073] The cooking hob 1 further comprises a control unit 4. Said control unit 4 is coupled with said heating power energy units 3.1-3.n in order to provide control information from the control unit 4 to the heating power energy units 3.1-3.n. Based on said control information, the operation conditions of the winding 2.1-2.n (winding active/inactive, electric power provided through the winding, AC-frequency etc.) are controlled.

[0074] The control unit 4 may be coupled with a user interface 7 via which user requests are received.

[0075] A heating power transferring element 2 comprising multiple concentrically arranged windings 2.1-2.n may suffer from a nonuniform heat distribution in radial direction, i.e. an inner winding 2.1 may have a higher power density and therefore may provide more heating power to the cookware item 5 than an outer winding 2.2-2.n. In addition, in order to avoid or reduce noise occurring due to a mismatch of operating conditions, the cooking hob 1 performs a power redistribution algorithm which balances the provision of heat to the cookware item 5 and leads to noise reduction due to a noise reduction algorithm.

[0076] As an overview, the cooking hob 1 comprises a control unit (which may be a dedicated control unit or a control unit included in the user interface 7 or formed by a controller of a master heating power energy unit). The control unit is configured to collect power requests associated with the concentric windings 2.1-2.n of a single heating power transferring element 2 in order to obtain total requested power and redistribute said total requested power to the windings 2.1-2.n according to power scale information stored in the cooking hob 1. The operation of the cooking hob, specifically of the windings 2.1-2.n is performed according to an operation cycle including multiple time slots. The electric power provided to the respective winding 2.1-2.n and the duty cycle associated with said winding 2.1 is chosen such that the mean electric power provided to the respective winding within an operation cycle is equal or essentially equal to the requested power.

[0077] In the following, the power redistribution algorithm is described in closer detail. The control unit 4 may have access to a storage in which power scale information is stored. The power scale information may determine which portion of total requested power should be provided to a certain winding 2.1-2.n of a heating power transferring element 2. The power scale information associated with a certain winding 2.1-2.n may be different for various coverage scenarios of the heating power transferring element 2. In case that all windings 2.1-2.n of the heating power transferring element 2 are covered, the portion of total requested power provided to a certain covered winding may be smaller than in case of covering only some inner windings.

[0078] The following table shows example power scale information associated with a heating power transferring element 2 comprising three windings 2.1-2.3 for different coverage conditions.

TABLE-US-00001 Power scale Power scale Power scale Windings factor factor factor coverage winding 2.1 winding 2.2 winding 2.3 Windings 2.1-2.3  25% 35% 40% Windings 2.1-2.2  40% 60%  0% (2.3 not active) Windings 2.1 100%  0%  0% (2.2 and 2.3 not active) No winding active  0%  0%  0%

[0079] Based on upper-mentioned table including power scale information, an example of power rescaling is provided. According to the example, all three windings 2.1-2.3 may be covered. The user may provide a power request of 500 W per each winding 2.1-2.3. Therefore, the total requested power of the heating power transferring element 2 is 1500 W.

[0080] In order to balance the heating power over the cross-sectional area of the cookware item 5, the total requested power (e.g. 1500 W according to the present example) is multiplied with the power scale information associated with the respective winding 2.1-2.3 thereby obtaining a rescaled electric power associated with each winding 2.1-2.3.

[0081] In the present example of total requested power of 1500 W and a coverage of all windings 2.1-2.3, the inner winding 2.1 may be powered with 375 W, the middle winding 2.2 may be powered with 525 W and the outer winding 2.3 may be powered with 600 W.

[0082] According to a second example, only windings 2.1 and 2.2 may be covered and the power request per each winding may be 500 W. Thus, the total requested power is 1000 W.

[0083] According to the second example, the inner winding 2.1 may be powered with 400 W, the middle winding 2.2 may be powered with 600 W and the outer winding 2.3 is deactivated, i.e. no electric power is provided to the outer winding 2.3.

[0084] Thereby, a higher uniformity of heat distribution over the cross-section of the cookware item is obtained.

[0085] In the following, the power distribution over an operating cycle is explained which leads to a mean value of electric power provided to a respective winding which coincides with the rescaled electric power obtained by upper-mentioned power redistribution algorithm. The operating cycle may be a repetitive time frame which may have a duration in the range of 1 sec to 20 sec, preferably, 3 sec to 10 sec, specifically 4 sec, 5 sec, 6 sec, 7 sec, 8 sec or 9 sec. Also other durations may be possible. The operating cycle may be segmented into multiple time slots.

[0086] According to one aspect, acoustic noise interferences are avoided by using equal or essentially equal AC-frequencies for all active windings 2.1-2.n. So, in other words, the electric current provided to the active windings 2.1-2.n comprises the same frequency.

[0087] In order to power the windings 2.1-2.n with the rescaled electric power without frequency changes, at least some windings 2.1—2.n may not be powered during the whole operating cycle. So, in other words for at least some windings 2.1-2.n, a duty cycle may be defined, said duty cycle indicating, for example, a portion of the operating cycle in which the respective winding 2.1-2.n is powered.

[0088] In the following, a method for determining a duty cycle for at least some windings 2.1-2.n is explained in closer detail.

[0089] In a first step, the number of time slots is determined, based on which the operating cycle is segmented.

[0090] The number of time slots N.sub.Slots may be chosen equal to the number of different power requests N.sub.PowerRequest, specifically rescaled electric power requests obtained based on upper-mentioned power redistribution algorithm:

N.sub.slots=N.sub.PowerRequest;  (formula 1)

[0091] The total requested power Tot.sub.Pwr is given by the sum of power requests associated with all active windings 2.1-2.n:

Tot.sub.Pwr=Σ.sub.i=0.sup.N.sup.zaPwr.sub.Zi;  (formula 2)

wherein
N.sub.Za is the number of active windings (i.e. number of windings for which a power request is received from the user interface); and
Pwr.sub.Zi is the power request associated with a certain winding Z.sub.i (e.g. received via the user interface).

[0092] The power requested for each winding, specifically the rescaled electric power request, may be sorted into a power array Sort.sub.Pwr, wherein the requested power values may increase with the length of the array. Windings with the same power request may be only considered once in the array, but a weight array W may be associated with the power array Sort.sub.Pwr, the entries of the weight array W indicating the number of windings having a power request according to the corresponding position in the power array Sort.sub.Pwr.

Sort.sub.Pwr={Pwr.sub.s0,Pwr.sub.s1,Pwr.sub.s2, . . . };  (formula 3)

wherein
Pwr.sub.si indicates a rescaled power request associated with one or more windings and wherein Pwr.sub.si+1>Pwr.sub.si.

[0093] As mentioned before, the weight array W may include weighting values w.sub.1, . . . , w.sub.n indicating the number of windings having a power request according to the corresponding position in the power array Sort.sub.Pwr:

W={w.sub.0,w.sub.1,w.sub.2, . . . };  (formula 4)

[0094] The power provided to each winding 2.1-2.n per time slot and the duty cycle of each time slot (i.e. the share of the time slot with respect to the whole operating cycle) can be calculated as follows:

[0095] The number of active windings 2.1-2.n per time slot ts.sub.i is:

N.sub.ts.sub.0=N.sub.Za;  (formula 5)

N.sub.ts.sub.i=N.sub.ts.sub.(i−1)−W[i−1]; where i>1;  (formula 6)

wherein
N.sub.ts0 is the number of active windings in the first time slot of an operating cycle;
N.sub.Za is the number of active windings (i.e. number of windings for which a power request is received from the user interface);
N.sub.tsi is the number of active windings in the i.sup.th timeslot of an operating cycle; and
W[i] is the weighting value at position i of the weight array.

[0096] The average power of each time slot ts.sub.i is given by formulas:

P.sub.tS.sub.0=Pwr.sub.s0.Math.N.sub.ts.sub.0;  (formula 7)

P.sub.ts.sub.i=(Pwr.sub.si−Pwr.sub.si−1).Math.N.sub.ts.sub.i; where i>1;  (formula 8)

wherein
Pwr.sub.s0 is the power value included in the first position of the power array Sort.sub.Pwr; and
Pwr.sub.si is the power value included in the i.sup.th position of the power array Sort.sub.Pwr.

[0097] The duty cycle t.sub.si % of time slot t.sub.si is given by formula:

[00001]$\begin{array}{cc}{t}_{si\%}=\frac{P_{t{s}_i}}{{\mathrm{Tot}}_{\mathrm{Pwr}}};& \left(\mathrm{formula}9\right)\end{array}$

[0098] The percentage of total power for each winding in the respective time slot ts.sub.i is given by formula:

[00002]$\begin{array}{cc}{P}_{siZ\%}=\frac{1}{N_{t{s}_i}};& \left(\mathrm{formula}10\right)\end{array}$

[0099] In the following, the distribution of power over the active windings within an operating cycle is explained based on examples.

[0100] FIGS. 3 and 4 illustrate diagrams which show the percentage of total requested power Tot.sub.Pwr provided to each winding 2.1-2.4 over an operating cycle, in the present example represented as duty cycle.

[0101] In a first example, power requests are received for a heating power transferring element 2 comprising four windings 2.1-2.4, wherein the power request for the first winding 2.1 is Z1=500 W, the power request for the second winding 2.2 is Z2=500 W, the power request for the third winding 2.3 is Z3=1000 W and the power request for the fourth winding 2.4 is Z4=1000 W. The power request may be the power request provided by the user via the user interface or, preferably, the rescaled power request obtained by upper-mentioned power redistribution algorithm.

[0102] Based on formula 1, the number of time slots included in one operating cycle is N.sub.Slots=2. According to formula 2, the total requested power is Tot.sub.Pwr=3000 W.

[0103] So, in other words, the operating cycle shown in FIGS. 3 and 4 comprises two time slots t.sub.s0 and t.sub.s1, wherein the total power of 3000 W has to be distributed over the windings 2.1-2.4 of the heating power transferring element 2 within the operating cycle.

[0104] According to formula 3, the power array Sort.sub.Pwr includes the following values: Sort.sub.Pwr={Pwr.sub.s0,Pwr.sub.s1}{500,1000}.

[0105] The weight array W includes, according to formula 4, the values: W={w.sub.0,w.sub.1} {2, 2}.

[0106] According to formula 5, N.sub.ts0=N.sub.Za=4. So, in other words, at the beginning, all windings 2.1-2.4 for which a power request has been received are powered.

[0107] According to formula 6, in the second time slot t.sub.s1, the number of activated windings is reduced as follows:

N.sub.ts.sub.1=N.sub.ts.sub.0−W[0]=2;

[0108] So, in other words, in the second time slot t.sub.s1, the number of activated windings is reduced from four to two (windings 2.1 and 2.2 are deactivated). It is worth mentioning that in the second time slot t.sub.s1, those windings remain activated for which higher power requests have been received.

[0109] Based on formulas 7 and 8, the average power provided to the cookware item in the respective time slot is calculated:

P.sub.ts.sub.0=Pwr.sub.s0.Math.N.sub.ts.sub.0=2000 W;

P.sub.ts.sub.1=(Pwr.sub.s1−Pwr.sub.s0).Math.N.sub.ts.sub.1=(1000 W−500 W).Math.N.sub.ts.sub.1=500 W.Math.2=1000 W;

[0110] The length of the time slots t.sub.s0 and t.sub.s1 is calculated based on formula 9:

[00003]$t_{s0\%}=\frac{P_{{\mathrm{ts}}_0}}{To{t}_{Pwr}}=\frac{2000W}{3000W}=0,\stackrel{\_}{66};$$t_{s1\%}=\frac{P_{{\mathrm{ts}}_1}}{To{t}_{Pwr}}=\frac{1000W}{3000W}=0,\stackrel{\_}{33};$

[0111] According to formula 10, the portions of power provided by active windings in the respective time slots t.sub.s0 and t.sub.s1 are:

[00004]$P_{s0Z\%}=\frac{1}{N_{{\mathrm{ts}}_0}}=\frac{1}{4};$$P_{s1Z\%}=\frac{1}{N_{{\mathrm{ts}}_1}}=\frac{1}{2};$

[0112] So, summing up, the total requested power is distributed over the operating cycle which is segmented in multiple time slots wherein the number of time slots is determined based on the number of different power requests or rescaled power requests. In the first time slot, all windings for which power requests have been received are powered by the same electric power value and, at the transition to the next time slot, at least one winding is deactivated. So in other words, the number of active windings decreases within an operating cycle. In addition, also in subsequent time slots, the electric power provided to active windings is equal or essentially equal. Thereby, the windings can be operated with the same AC-frequency and interferences between the windings leading to audible noise can be decreased.

[0113] Referring again to FIGS. 3 and 4, the power provided to the windings 2.1 to 2.4 in the first time slot is 750 W per each winding. Due to the duty cycle of 66% of the first and second winding 2.1, 2.2, the mean power provided to the first and second winding 2.1, 2.2 is 500 W, as requested. Similarly, the power provided to the third and fourth winding 2.3, 2.4 in the first time slot is 750 W per each winding and in the second time slot 1500 W. Thus, again taking the duty cycle of the first and second time slot (66%, 33%) into account, the mean power provided to the third and fourth winding 2.3, 2.4 is (750 W*66%)+(1500 W*33%)=1000 W, as requested.

[0114] FIG. 5 illustrates an example power distribution provided to a heating power transferring element 2 comprising for windings 2.1—2.4 over an operating cycle. In the shown example, four different power requests or rescaled power requests have been received, namely a power request of 200 W for winding 2.1, a power request of 400 W for winding 2.2, a power request of 600 W for winding 2.3 and a power request of 800 W for winding 2.4.

[0115] Based on formula 1, the number of time slots included in one operating cycle is N.sub.Slots=4. According to formula 2, the total requested power is Tot.sub.Pwr=2000 W.

[0116] So, in other words, the operating cycle shown in FIG. 5 comprises four time slots t.sub.s0 to t.sub.s4, wherein the total power of 2000 W has to be distributed over the windings 2.1-2.4 of the heating power transferring element 2 within the operating cycle. According to formula 3, the power array Sort.sub.Pwr includes the following values: Sort.sub.Pwr={Pwr.sub.s0, Pwr.sub.s1, Pwr.sub.s2, Pwr.sub.s3}={200, 400, 600, 800}.

[0117] The weight array W includes, according to formula 4, the values: W={w.sub.0,w.sub.1,w.sub.2,w.sub.3}={1,1,1,1}.

[0118] According to formula 5, N.sub.ts.sub.0=N.sub.Za=4. So, in other words, at the beginning, all windings 2.1-2.4 for which a power request has been received are powered.

[0119] According to formula 6, in the second time slot t.sub.s1, the number of activated windings is reduced as follows:

N.sub.ts1=N.sub.ts.sub.0−W[0]=3;

[0120] So, in other words, in the second time slot t.sub.s1, the number of activated windings is reduced from four to three (winding 2.1 is deactivated). It is worth mentioning that in the second time slot t.sub.s1, those windings remain activated for which higher power requests have been received.

[0121] Similarly, in the following time slots t.sub.s2, t.sub.s3 also one winding is deactivated per each time slot.

N.sub.ts.sub.2=N.sub.ts.sub.1−W[1]=2;

N.sub.ts.sub.3=N.sub.ts.sub.2−W[1]=1;

[0122] Based on formulas 7 and 8, the average power provided to the cookware item in the respective time slot is calculated:

P.sub.ts.sub.0=Pwr.sub.s0.Math.N.sub.ts.sub.0=800 W;

P.sub.ts.sub.1=(Pwr.sub.s1−Pwr.sub.s0).Math.N.sub.ts.sub.1=(400 W−200 W).Math.N.sub.ts.sub.1=200 W.Math.3=600 W;

P.sub.ts.sub.2=(Pwr.sub.s2−Pwr.sub.s1).Math.N.sub.ts.sub.2=(600 W−400 W).Math.N.sub.ts.sub.2=200 W.Math.2=400 W;

P.sub.ts.sub.3=(Pwr.sub.s3−Pwr.sub.s2).Math.N.sub.ts.sub.3=(800 W−600 W).Math.N.sub.ts.sub.3=200 W.Math.1=200 W;

[0123] The length of the time slots t.sub.s0 to t.sub.s3 is calculated based on formula 9:

[00005]$t_{s0\%}=\frac{P_{{\mathrm{ts}}_0}}{To{t}_{Pwr}}=\frac{800W}{2000W}=0,4;$$t_{s1\%}=\frac{P_{{\mathrm{ts}}_1}}{To{t}_{Pwr}}=\frac{600W}{2000W}=0,3;$$t_{s2\%}=\frac{P_{{\mathrm{ts}}_2}}{To{t}_{Pwr}}=\frac{400W}{2000W}=0,2;$$t_{s3\%}=\frac{P_{{\mathrm{ts}}_3}}{To{t}_{Pwr}}=\frac{200W}{2000W}=0,1;$

[0124] Thus, in the first time slot t.sub.s0, all windings 2.1-2.4 are powered with 500 W, in the second time slot t.sub.s1, windings 2.2-2.4 are powered with 660 W, whereas winding 2.1 has been deactivated.

[0125] In the third time slot t.sub.s2, windings 2.3 and 2.4 are powered with 1000 W (windings 2.1 and 2.2 deactivated) and in the fourth time slot t.sub.s3, only winding 2.4 is powered at 2000 W.

[0126] FIG. 6 schematically illustrates the decrease of electric power consumed by a winding of a heating power transferring element 2 depending on different cookware items placed above said winding. The higher the frequency, the lower the power consumption of the winding.

[0127] In case of a bad coupling of a cookware item with a certain winding, for example because of a bad coverage of said winding, the electric power provided to said winding has to be reduced, which can be obtained by an increase of AC-frequency.

[0128] However, due to isofrequenciality, i.e. the target to power all windings with the same or essentially the same frequency in order to reduce acoustic noise, not only the partly covered winding but all windings have to be powered with a higher frequency, which leads to a decrease of power of all windings.

[0129] In order to avoid an excessive power decrease of the whole heating power transferring element 2 caused by a single, badly-covered winding, the electric power provided to the respective winding may be evaluated. The electric power value obtained by said evaluation may be compared with a power threshold value. If the evaluated power value is below said power threshold value, the badly-covered winding may be excluded, i.e. not powered despite having received a power request for said winding in order to avoid a power reduction of all windings.

[0130] According to a more sophisticated embodiment, the power consumed by the badly-covered winding may be compared with the power decrease of all other windings which may be negatively affected due to the badly-covered winding. More in detail, the power decrease of well-covered windings may be summed-up and said summation value may be compared with the power consumed by the badly-covered winding. If the summation value increases the power consumed by the badly-covered winding, it is advantageous to exclude/deactivate the badly-covered winding. Accordingly, it may be a more flexible possibility for excluding a winding.

[0131] It should be noted that the description and drawings merely illustrate the principles of the proposed invention. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the invention.

LIST OF REFERENCE NUMERALS

[0132] 1 cooking hob [0133] 2 heating power transferring element [0134] 2.1-2.n winding [0135] 3.1-3.n heating power energy unit [0136] 4 control unit [0137] 5 cookware item [0138] 6 line [0139] 7 user interface