EP4250873A1 - Method for operating an induction hob and induction hob - Google Patents

Abstract

To operate an induction hob with a hob plate, at least two induction heating coils underneath, a hob control, and a power section for power supply to the induction heating coils, the two induction heating coils are supplied with power together and each operated with a power density spectrum with exactly one maximum. In a first operating mode, the power density spectra are measured and it is determined how their respective maxima are related to one another and their sum is formed. Then the difference in power density between a local minimum of the sum, which lies between the two maxima of the sum, and the two maxima of the sum is reduced. For this purpose, the switch-on time and/or the switch-off time of at least one of the power switches are varied in order to actively change the power density spectrum of the power supply.

Description

FIELD OF APPLICATION AND STATE OF TECHNOLOGY

The invention relates to a method for operating an induction hob and an induction hob designed to carry out this method, whereby the resulting noise should be as low as possible.

From the WO 2016/010492 A1 An induction hob is known which has a hob plate and underneath it a plurality of induction heating coils. Furthermore, a hob control and a power unit are provided for supplying power to the induction heating coils, which has several power switches. An LC filter is provided to prevent unwanted noise as so-called noise due to certain frequencies for their operation. Furthermore, when operating several induction heating coils, an attempt is made to find a common switching frequency.

TASK AND SOLUTION

The invention is based on the object of creating a method mentioned at the beginning and an induction hob mentioned at the beginning, with which problems of the prior art can be solved and, in particular, it is possible to avoid noise development when operating such an induction hob, in particular with several induction heating coils next to one another are arranged to improve.

This object is achieved by a method with the features of claim 1 and by an induction hob with the features of claim 12. Advantageous and preferred embodiments of the invention are the subject of the further claims and are explained in more detail below. Some of the features are only described for the method or only for the induction hob. However, they should be able to apply independently and independently of each other to both the process and such an induction hob. The wording of the claims is incorporated into the content of the description by express reference.

The induction hob has a hob plate and at least two induction heating coils underneath. It is advantageous to have a larger number of induction heating coils, preferably six, eight or up to twenty induction heating coils. Furthermore, the induction hob has a hob control, in particular with a display and an operating device for an operator and a power unit with which power is supplied to the induction heating coils. The power section is controlled by the hob control and has several power switches, which in turn can be controlled using parameters such as switch-on time and/or switch-off time. This can be done in a known manner. The power section can be connected to a mains voltage and designed to generate a higher-frequency control voltage from the mains voltage for the power supply to the induction heating coils using the power switches mentioned.

Interference occurs between the power density spectra of the coupled induction heating coils due to coupling via a common intermediate circuit voltage or due to the magnetic field of the inductors. If the power spectra overlap without a distinct minimum, broadband interference noise occurs, which is usually not perceived as disturbing by a user. If, on the other hand, the power density spectra have a pronounced local minimum between them, frequency ranges in the spectrum of audible interference are missing, which is usually perceived by a user as a disturbing, unpleasant noise. If the maxima of the power density spectra of the induction heating coils are several kHz apart, there is no low-frequency interference.

Human hearing is particularly sensitive to sound pressure levels in the range between 1 kHz and 5 kHz. Narrow-band noises are perceived as more intense than broad-band noises. The lack of frequencies in an otherwise broadband noise is also subjectively perceived as disturbing.

According to the invention, the power density spectra of the power supply of the at least two induction heating coils that are to be operated simultaneously are estimated or measured. They can be intended for different cooking vessels placed on the hob plate, or possibly for the same one. In this case, they can heat the two cooking vessels set up together with other induction heating coils. Each of the power density spectra has a maximum, in particular exactly a single maximum. Then, in a first operating mode, the switch-on time and/or the switch-off time of at least one of the power switches are varied in order to actively change the power density spectrum of the power supply of at least one induction heating coil, in particular exactly a single induction heating coil, so that the two power density spectra of the power supply overlap more or that the two maxima come closer to each other and therefore have a smaller distance or a smaller frequency difference between them. Alternatively or additionally, a resulting sum of the two power density spectra can be formed. This is relatively easy to do. Then the difference in power density between a local minimum of the sum, which lies between the two maxima of the sum, and the two maxima of the sum. This can be done, for example, in such a way that the two power density spectra are shifted closer to one another, in particular the power density spectrum with the maximum at the higher frequency is shifted towards lower frequencies. This automatically increases the intermediate minimum power density of the resulting sum.

In this way it can be achieved that the minimum or a frequency drop between the two maximums becomes smaller. The smaller the difference between the minimum and the maximum, the lower the noise will be, as has been shown in the context of the invention. The difference between the minimum and one of the maximums should be a maximum of 40 dB and advantageously less, preferably a maximum of 20 dB. It is particularly advantageous that they are at least 5 dB or 10 dB, so that they have a certain relevant size. A resulting sum of the at least two different power density spectra of the power supply is formed with a local minimum of the curve of the sum that lies between the two maxima of the sum. At least one of the power density spectra of the power supply is actively changed as described above with regard to the difference.

In principle, it is possible to change only one of the two power density spectra, i.e. in a power supply for only one of the induction heating coils. Alternatively, both can be changed, especially towards each other. At the usual operating points of induction heating coils, the power output can be increased by lower frequencies, i.e. a longer sum of on and off times. By simultaneously reducing the switch-on time, the power can be reduced again so that the power can remain approximately constant by balancing both measures. Wobbling, i.e. a periodic variation of the frequency, creates a power density spectrum that can be determined, for example, by measuring the current curve through an induction heating coil or the voltage curve on the resonance capacitor over a wobbling period.

In one embodiment of the invention, provision can be made to actively change the power density spectra of the power supply in the said first operating mode in such a way that, as a result, there is no longer a local minimum of the power density spectra between the two maxima. For this purpose, it can be provided that the two maxima are different by a maximum of 10%, advantageously should be the same size or similar, or their difference from one another is smaller than the difference from the local minimum. This means that under certain circumstances a frequency shift can occur in such a way that the two maxima are identical.

It is possible that the two induction heating coils are supplied with power together and are each operated with a power density spectrum with exactly a single maximum, as explained above. The power density spectra of the power supply for the two induction heating coils are measured or estimated to determine whether the two power density spectra overlap or how these two power density spectra relate to each other in relation to their respective maximum. A distinction can then be made between two cases.

In a first case, the two power density spectra are such that the two maxima are far apart by more than 5 kHz, in particular by more than 2 kHz. The power supply to the induction heating coils is not changed. It is then assumed that the noise development is not too great or not very disturbing.

In a second case, the two maxima are closer to each other, so that the two maxima are not more than 5 kHz apart, but less, in particular not more than 2 kHz. But they shouldn't be identical either. A local minimum or a frequency reduction between the two maxima then arises in the common power density spectrum or in the aforementioned sum of the two power density spectra. This only creates a single local minimum. Then, in this second case, the power supply to the induction heating coils is changed, and a so-called wobble is generated for at least one power density spectrum, as mentioned above, for which purpose the parameters of the switch-on time and/or switch-off time of at least one of the power switches are changed, preferably changed periodically. Such wobbling is known from the EP 1734789 A1 , to which explicit reference is made here. Wobbling is the periodic or recurring change in the frequency of an oscillator or resonant circuit over an adjustable range, sometimes used for measurement purposes, but here simply for variation. The aim of this is to ensure that the power density spectra, including their maxima, change in such a way that their relationship to one another in relation to their respective maximum corresponds to the first case, in order to avoid a frequency reduction or a minimum in between. In this embodiment, it can generally be provided that a minimum is defined by being at least 20% below the maximum or one of the two maxima, preferably at least 40% below.

In a possible embodiment of the invention, an active change in the power supply to the induction heating coils in the second case mentioned can take place in such a way that a change occurs from a single higher frequency to a single lower frequency. In this way, a measured frequency reduction or a minimum can be reduced and/or eliminated.

In an advantageous possible embodiment of the invention, it can be provided that the aforementioned first case is still considered to be present even if the maxima of the two power density spectra are more than 2 kHz to 4 kHz apart, i.e. the frequency difference is so large. With such small differences between the maxima, changing one of the power density spectra can be saved. Experience has shown that there is no need to fear any significant noise development.

In one embodiment of the invention it can be provided that the method is used for three induction heating coils, i.e. three induction heating coils are operated, which are arranged adjacent to one another without further induction heating coils in between, i.e. directly adjacent. The parameters of the circuit breakers intended or used for them are varied accordingly so that there are no maxima that are more than 5 kHz apart with a frequency reduction or with a minimum between the maxima. For this purpose, three maxima are then considered relative to each other.

In a further development of the invention, an active change in the power supply to the induction heating coils in the second case can be a change in the power density spectrum of the induction heating coil operated with the higher-frequency control from higher frequency components to lower frequency components in such a way that the local minimum based on two maxima of the resulting sum is reduced and / or is eliminated. This creates a simple and practical procedure.

In a further development of the invention, a predetermined target value for the power for the induction heating coil can also be changed. Preferably, the change in the setpoint for the power is limited to less than 15%, since a small change is usually not perceived as relevant by a user. A cooktop control can also reduce the output of an induction heating coil more if noise optimization is prioritized over performance accuracy. In this way it can be achieved that the power density spectra overlap in such a way that they correspond to the first case. However, this should advantageously only be done after other influences have been made, for example if these have too little effect. A change in the power of at least one of the induction heating coils is a certain interference in the operation of the induction heating coils, which may be more disruptive than noise development. If there is a change in the power of one of the induction heating coils, this should be done for the induction heating coil with the higher nominal value of the power, i.e. its power should be reduced so that the frequency difference between the two maxima corresponds to the first case. This is less dangerous or critical than increasing the power of the other induction heating coil.

In an embodiment of the invention, the at least two induction heating coils can be arranged adjacent to one another, in particular without a further induction heating coil in between, the at least two induction heating coils preferably being rectangular or polygonal. They can run next to each other and approximately parallel to each other with at least one side or long side. The at least two induction heating coils are preferably designed identically, particularly preferably all induction heating coils of an induction hob are designed identically.

Advantageously, the method operates three induction heating coils, which are arranged adjacent to one another without any further induction heating coil in between. The parameters of their power switches are varied accordingly, so that the maxima of the three power density spectra of the power supply of the three induction heating coils are no more than 5 kHz apart, with exactly one local minimum between each two maxima of the three maxima.

In a further development of the invention, the power density spectra can be determined by measuring the voltage of a capacitor connected in parallel to the induction heating coil or by measuring the current through the induction heating coil. This can be done in practice.

The induction hob according to the invention is therefore designed as described above and has an aforementioned power section and a hob control, which are designed to carry out the method according to one of the preceding claims. In this way, the power density spectra can be monitored and, if necessary, influenced after the case distinction described has been carried out.

The power section has a parallel resonant circuit with at least one power switch, which can in particular be a transistor or an IGBT. The power section is designed as a quasi-resonant converter for operating the at least one circuit breaker. It is possible to use half-bridge circuits as well as full-bridge circuits.

In a further embodiment, the power section can have a rectifier that is connected to a mains voltage. Two or more identical circuit branches are connected to the rectifier, each of which has an LC element, with an induction heating coil, an oscillating circuit coil and a power switch being connected thereto, in particular a power switch described above.

In yet another embodiment, it can be provided that the circuit branches are separated from the rectifier by means of an inductor. Exactly one inductance can be provided between the rectifier and the circuit branch for each rectifier.

These and other features emerge not only from the claims but also from the description and the drawings, with the individual features being implemented individually or in groups in the form of subcombinations in one embodiment of the invention and in other areas and being advantageous and protectable in their own right may represent versions for which protection is claimed here. The division of the application into individual sections and subheadings does not limit the general validity of the statements made under them.

Brief description of the drawings

Fig. 1

ein erfindungsgemäßes Induktionskochfeld mit mehreren Induktionsheizspulen,

Fig. 2

ein Leistungsdichtespektrum 1 der Leistungsversorgung für eine Induktionsheizspule 1 mit einem Maximum bei f1,

Fig. 3

ein Leistungsdichtespektrum 2 der Leistungsversorgung für eine Induktionsheizspule 2 mit einem Maximum bei f2,

Fig. 4

die Leistungsdichtespektren 1 und 2 sowie die Summe der Leistungsdichtespektren gemeinsam,

Fig. 5

die Kurve der Summe der Leistungsdichtespektren alleine,

Fig. 6

ein Flussdiagramm zur Beschreibung des erfindungsgemäßen Verfahrens,

Fig. 7

die Kurve der Summe der Leistungsdichtespektren 1 und 2`, wobei das Leistungsdichtespektrum 2 auf das Leistungsdichtespektrum 1 verschoben worden ist, und

Fig. 8

die Kurve der Summe der Leistungsdichtespektren 1 und 2`, wobei das Leistungsdichtespektrum 2 nicht ganz bis auf das Leistungsdichtespektrum 1 verschoben worden ist.

Embodiments of the invention are shown schematically in the drawings and are explained in more detail below. Shown in the drawings:

Fig. 1

an induction hob according to the invention with several induction heating coils,

Fig. 2

a power density spectrum 1 of the power supply for an induction heating coil 1 with a maximum at f1,

Fig. 3

a power density spectrum 2 of the power supply for an induction heating coil 2 with a maximum at f2,

Fig. 4

the power density spectra 1 and 2 as well as the sum of the power density spectra together,

Fig. 5

the curve of the sum of the power density spectra alone,

Fig. 6

a flowchart for describing the method according to the invention,

Fig. 7

the curve of the sum of the power density spectra 1 and 2', whereby the power density spectrum 2 has been shifted to the power density spectrum 1, and

Fig. 8

the curve of the sum of the power density spectra 1 and 2', whereby the power density spectrum 2 has not been completely shifted to the power density spectrum 1.

Detailed description of the exemplary embodiments

In the Fig. 1 an induction hob 11 according to the invention is shown with a hob plate 12 and a plurality of induction heating devices 14 underneath, which are designed as conventional induction heating coils. Eight induction heating devices 14 are arranged in a regular pattern, all of which are the same size or identical. The induction hob 11 has a hob control 16, a power supply 18 and an operating device 20, which also has display functions, as is generally known. The power section 18 is designed as explained at the beginning and essentially as known from the prior art, i.e. with power switches, for example IGBT. The power section 18 has a usual design. It can have several bridge circuits of the type mentioned at the beginning and is connected to each of the induction heating devices 14 to supply their power.

A pot T1 is placed on the two left front induction heaters 14, with the coverage on the front induction heater 14 being slightly larger than on the middle induction heater. The pot T1 should be heated together by both heating devices 14. For this purpose, an operator has set a power level P1 via the operating device 20. Because of the different coverings, different working frequencies occur despite similar power specifications and unpleasant interference noise can occur between the two heating devices 14. This should be reduced if possible. However, it does not matter to the invention whether the frequency differences between heating devices 14 are caused by differences in coverage of a single pot T1 with the same power level P1 or by several pots T1, T2 with different power levels P1, P2 and/or coverages.

In the Fig. 2 the power density spectrum 1 of the power supply for the front left induction heating device 14 is shown below the pot T1. The power density spectrum 1 has a maximum of 40 dB at the frequency f1 = 43 kHz.

In a similar form to Fig. 2 is in Fig. 3 the power density spectrum 2 of the power supply for the middle and also for the rear induction heating device 14 is shown. Here there is a maximum of around 48 dB at a frequency f2 = 46 kHz. Regarding the pure form, the two power density spectra 1 and 2 see the Figs. 2 and 3 similar, but not quite the same. Furthermore, they are not mirror-symmetrical to the vertical axis at the frequency of the maximum. These curves of the Fig. 2 and Fig. 3 are either the envelopes of spectra actually obtained via FFT. Alternatively, the spectra mentioned can also be smoothed.

In the Fig. 4 For clarification, the power density spectra 1 and 2, together with the resulting curve of the sum of the power density spectra, are shown again in a diagram. For better illustration, in the Fig. 5 only the sum of the power density spectra is shown. It has two relative maxima at f1 and f2, the frequency difference here is about 3 kHz. Between f1 and f2 there is a local minimum at fmin of around 44 kHz. At about -10 dB, it is about 50 dB below the maximum at f1 and about 58 dB below the maximum at f2. The two maxima f1 and f2 are about 3 kHz apart.

According to the flowchart of the Fig. 6 starts the process for operating the induction hob 11 with the induction heating devices 14. Two specifications of the power levels P1 and P2 for heating the pots T1 and T2 are entered via the operating device 20, as explained above. Then the power supply 18 and the hob control 16 determine the frequency spectra 1 and 2 of the power densities, i.e. the power density spectra 1 and 2, for the power density in the two operated induction heating devices 14. This corresponds to each Figs. 2 and 3 .

In the next step, a difference between the maxima f1 and f2 is determined, see Fig. 4 . In the present case, this is 3 kHz, and therefore the magnitude value of 3 is smaller than the 5 mentioned in the condition above as the magnitude of 5 kHz difference between the maxima. If the difference in magnitude was greater than 5, the two maxima would be so far apart that the noise would be perceived as relatively low anyway. Then no intervention would have to be made, so that the power supply remains the same and in particular the switch-on times and the switch-off times as well as the power density spectra remain unchanged.

However, since, as explained above, the difference value of 3 is smaller than a value of 5, the process continues by calculating the total power density or the sum accordingly Fig. 5 is determined. The next condition is then to check whether a local minimum between the two maxima f1 and f2, i.e. fmin, is more than 40 dB below f1 and/or f2. This is at the Fig. 5 This is obviously the case, as it is actually more than 50 dB lower. If this were not the case, there would be no need to make any changes to the power supply. Since this is the case here, there is an active change in the switch-on times and the switch-off times of the power switches (not shown) in the power section 18. An attempt is made to keep the power P1 and the power P2 approximately constant or not to change them too much. Here is The procedure has been such that the power density spectrum 2 for the induction heating coils 14 has been changed below the pot T2, namely the frequencies have been lowered or the second maximum f2 has been combined with the first maximum f1 or has also been shifted to 43 kHz. This means there is no longer any difference or at least no measurable difference. The first condition from the flowchart Fig. 6 is still fulfilled, but there is then clearly no longer any significant local minimum of the common sum, especially none with a difference of at least 40 dB from the maximum. Further operation can therefore take place with this performance specification, which has been changed according to the invention. Noise reduction has been successfully carried out. This is in Fig. 7 shown with the power density spectra 1 and 2', whereby the power density spectrum 2' has been shifted to the left up to the power density spectrum 1. So they are congruent. In practice, this will only be difficult or rarely possible. However, it serves to illustrate the general possibility of shifting a power density spectrum to reduce the frequency difference between the local minimum and the two neighboring maxima. Here there is no longer any local minimum for the sum.

Another possibility for shifting a power density spectrum is shown by: Fig. 8 . Here the power density spectrum 2 has been shifted to the left by approximately 1.5 kHz. The original power density spectrum 2 is shown in dashed lines, the shifted power density spectrum 2 'is actually to the left of it. The sum of the power density spectra 1 and 2' is shown in solid lines. Here it can be clearly seen that there is still a local minimum between the two maxima at the frequencies f1 and f2', but the difference to the two maxima is significantly smaller than the sum according to Fig. 5 . It is approximately 18 dB to the maximum of the power density spectrum f1 and approximately 23 dB of the power density spectrum f2'. The two maxima at frequencies f1 and f2' are approximately 1.8 kHz apart, i.e. less than 2 kHz. This case the Fig. 8 is considerably more realistic than that of Fig. 7 , see the explanation above.

Based on the difference between the maxima at f1 and f2 and determining the presence and size of the local minimum between them, it is very easy to measure and calculate. This makes the process advantageous and practical.

In general, the term power spectral density can also be used instead of the power density spectrum. As an alternative to evaluating a power density spectrum or a spectral power density, a signal spectrum can also be evaluated. The signals are RMS measurements (square mean value of the measured signal) of voltage at the induction heating coil or of the current through the induction heating coil. Using of signal spectra instead of the power density spectra, the dB limit values mentioned must be halved according to the well-known logarithm rule to dB signal versus dB power.

A power density spectrum represents the distribution of the power components of a signal over frequency and can be determined by FFT over a period of time, preferably a periodic period of time. This time period can be a whole, half or a multiple of a period of the mains voltage.

Claims (15)

Method for operating an induction hob, the induction hob comprising: - a hob plate, - at least two induction heating coils under the hob plate, - a hob control, - a power section for a power supply for the induction heating coils, the power section: + is controlled by the hob control, + has several circuit breakers that can be controlled using the switch-on time and/or switch-off time parameters, + is designed to generate a higher-frequency control for the power supply of the induction heating coils from the mains voltage using the circuit breakers, characterized in that - the power density spectra of the power supply of the two induction heating coils are estimated or measured, each power density spectrum having a maximum at a frequency, in particular having a single maximum at a frequency, - In a first operating mode, the switch-on time and/or the switch-off time of at least one of the power switches is varied in order to actively change the power density spectrum of the power supply, so that the two power density spectra of the power supply for the two induction heating coils overlap more or that the frequency difference between the two Maxima is reduced and / or that a resulting sum of the two power density spectra is formed and the difference in the power density between a local minimum of the sum, which lies between the two maxima of the sum, and the maxima of the sum is reduced. Method according to claim 1, characterized in that the resulting sum of the two power density spectra is used instead of the individual power density spectra. Method according to claim 1 or 2, characterized in that a resulting sum of the two different power density spectra of the power supply is formed with a local minimum of the sum that lies between the two maxima of the sum, and that at least one of the power density spectra of the power supply is actively changed so that the difference between the local minimum and the maximum is a maximum of 40dB or less, preferably a maximum of 20dB or less, and in particular a minimum of 5 dB or a minimum of 10 dB. Method according to claim 1 or 2, characterized in that in the first operating mode the power density spectra of the power supply are actively changed such that, as a result, there is no pronounced local minimum between the two maxima of the power density spectra, preferably the two maxima of the power density spectra being different by a maximum of 10% are, in particular are the same size or are smaller than the difference to the local minimum. Method according to one of claims 1 to 3, characterized in that the two induction heating coils are supplied with power at the same time and are each operated with a power density spectrum with exactly one maximum of the power density, - wherein the power density spectra for the two induction heating coils are measured or estimated and it is determined whether these two power density spectra each overlap or how these two power density spectra relate to one another in relation to the frequency of their respective maximum, - wherein in a first case in which the two power density spectra are such that the two maxima are more than 5 kHz apart, the power supply to the induction heating coils is not changed, - whereby in a second case, in which the two power density spectra are located such that the two maxima are no more than 5 kHz apart and in which a pronounced local minimum between the two maxima arises in a resulting sum of the two power density spectra, the power supply to the induction heating coils is changed and a wobble is generated in the power supply of at least one induction heating coil and the switch-on time parameter and/or the switch-off time parameter of at least one of the circuit breakers is changed in such a way that the sum of the power density spectra with the maxima changes in such a way that the local minimum between the two maxima is increased or a difference in the power density at the local minimum to the power densities of the two maxima becomes smaller. Method according to claim 5, characterized in that the first case is still considered to be present if the frequency difference between the two maxima is more than 2 kHz to 4 kHz. Method according to claim 5 or 6, characterized in that an active change in the power supply of the induction heating coils in the second case is a change in the power density spectrum of the induction heating coil operated with the higher-frequency control from higher frequency components to lower frequency components such that the local minimum is related to two maxima the resulting sum is reduced and/or eliminated. Method according to one of claims 5 to 7, characterized in that a predetermined target value of the power for at least one of the induction heating coils is changed to enable overlapping in the second case, if this would otherwise occur without changing the instantaneous power by more than 2%, preferably more than 15% is not possible. Method according to one of claims 5 to 7, characterized in that the setpoint of the power of one of the two induction heating coils, in particular the induction heating coil with the higher setpoint of the power, is changed so that the frequency difference between the two maxima corresponds to the first case. Method according to one of the preceding claims, characterized in that three induction heating coils are operated, which are arranged adjacent to one another without any further induction heating coil in between, the parameters of their power switches being varied accordingly, so that the maxima of the three power density spectra of the power supply of the three induction heating coils do not are more than 5 kHz far apart with exactly one local minimum between two of the three maxima. Method according to one of the preceding claims, characterized in that the determination of the power density spectra by measuring the voltage of a to Induction heating coil connected in parallel with the capacitor or by measuring the current through the induction heating coil. Induction hob with: - a hob plate, - at least two induction heating coils under the hob plate, - a hob control, - a power section for a power supply to the induction heating coils, which is controlled by the hob control, the power section having a plurality of circuit breakers which can be controlled by means of the switch-on time and/or switch-off time parameters, and is connected to a mains voltage and is designed to be switched off by means of the circuit breaker to generate a higher-frequency control for the power supply of the induction heating coils using the mains voltage, characterized in that the power unit and the hob control are designed to carry out the method according to one of the preceding claims. Induction hob according to claim 12, characterized in that the power part has a parallel resonant circuit with at least one power switch per induction heating coil, in particular with a transistor or an IGBT, the power part preferably being designed for operation of the at least one power switch as a quasi-resonant converter. Induction hob according to claim 12 or 13, characterized in that the power section has a rectifier for connection to a mains voltage, two identical circuit branches being connected to the rectifier, each of which has an LC element, with an induction heating coil, a resonant circuit capacitor and a circuit breaker attached to it , in particular a power semiconductor switch, are connected, wherein preferably the circuit branches are each separated from the rectifier by means of an inductance or filter choke, with preferably exactly one separate inductance being provided between the rectifier and each circuit branch. Induction hob according to one of claims 12 to 14, characterized in that the at least two induction heating coils are arranged adjacent to one another, in particular without a further induction heating coil in between, wherein preferably the at least two induction heating coils are rectangular or polygonal and with at least one side or long side next to each other and approximately parallel to each other, the at least two induction heating coils preferably being designed identically.

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