EP2506663B1 - Cooking device - Google Patents

Description

The invention is based on a cooking device device according to the preamble of claim 1.

The publication EP 1 951 003 A1 discloses an induction hob having at least two heating frequency units operated according to a particular method to at least substantially avoid intermodulation noise. According to this method, both heating-frequency units are operated at an identical and fixed first frequency in a first time interval. In a second time interval, a heating frequency unit is switched off, while the other heating frequency unit is operated at a fixed second frequency. The two frequencies and the relative lengths of the two time intervals are adjusted so that an average output power of each heating frequency unit corresponds to an operator selected heating power. At the same time, a flicker characteristic is minimized. Further induction hobs according to the prior art are known from the documents WO 2005/043737 A2 . WO 2006/117182 A1 . US 2010/237065 A1 and US 2006/289489 A1 known. The object of the invention is in particular to provide a generic Gargerätevorrichtung that allows an advantageously flexible adjustment of a mean output power. The object is achieved by the features of claim 1 and the method claim 8, while advantageous embodiments and modifications of the invention can be taken from the dependent claims.

The invention is based on a cooking appliance device with at least one first and at least one second heating frequency unit and with at least one control unit, which is provided to operate the first heating frequency unit continuously and at least a first time interval with a fixed first frequency, the second heating frequency unit in the first To operate time interval and turn off in at least a second time interval and to minimize at least one Flickerkenngröße.

It is proposed that the control unit is provided to operate the second heating frequency unit in the first time interval with at least one frequency differing by at least 14 kHz, preferably by at least 15 or 16 kHz and particularly advantageously by at least 17 kHz from the first frequency. It can be provided in particular to operate the first heating frequency unit in the second time interval with a changing frequency. Preferably, however, it is provided to operate the first heating frequency unit in the second time interval likewise with a fixed frequency and preferably at a frequency different from the first frequency. It can be provided in particular to operate the second heating frequency unit in the first time interval with a changing frequency. Preferably, however, it is provided to operate the second heating frequency unit in the first time interval with a fixed frequency. The cooking device device is preferably designed as a hob device and particularly advantageously as an induction hob device. A "first time interval" and a "second" time interval are to be understood as meaning, in particular, two temporally successive time intervals of a length greater than 0. The designations "first" and "second" time intervals are intended exclusively for distinguishing the time intervals and, in particular, no statement about a time interval The term "provided" should in particular be understood to mean specially programmed and / or designed and / or equipped.

A "heating frequency unit" should in particular be understood to mean an electrical unit which generates an oscillating electrical current, preferably with a frequency of at least 1 kHz, in particular of at least 10 kHz and advantageously of at least 20 kHz, for operation of at least one heating unit. A "heating unit" is to be understood in particular as meaning a unit which is intended to convert electrical energy into heat, at least to a large extent, and thus in particular to heat a food to be cooked. In particular, the heating unit comprises a radiant heater, a resistance heater and / or preferably an induction heater provided for this purpose is to convert electrical energy into heat indirectly via induced eddy currents. The heating frequency unit comprises in particular at least one inverter, which preferably comprises two switching units. A "switching unit" is to be understood in particular as meaning a unit which is intended to interrupt a conduction path comprising at least part of the switching unit. Preferably, the switching unit is a bidirectional unipolar switch which in particular allows a current flow through the switch along the conduction path in both directions and in particular short-circuits an electrical voltage in at least one polarity direction. Preferably, the inverter comprises at least two bipolar transistors with insulated gate electrode and particularly advantageously at least one damping capacitor. A "conduction path" is to be understood as meaning, in particular, an electrically conductive conductor piece between two points. The term "electrically conductive" is to be understood in particular with a specific electrical resistance of at most 10 ^-4 Ωm, in particular of at most 10 ^-5 Ωm, advantageously of at most 10 ^-6 Ωm and particularly advantageously of not more than 10 ^-7 Ωm at 20 ° C.

A "control unit" is to be understood in particular as meaning an electronic unit which is preferably at least partially integrated in a control and / or regulating unit of a cooking appliance, in particular an induction hob, and which preferably has an arithmetic unit and in particular in addition to the arithmetic unit a storage unit with a stored therein Control program includes. Preferably, the control unit is provided to control and / or regulate the heating frequency units by means of control signals and preferably electrical control signals. A "control signal" should be understood in particular to mean a signal which, in particular in at least one operating state, triggers a switching operation of a heating frequency unit, in particular also indirectly. An "electrical control signal" is to be understood in particular to mean a control signal having an electrical potential of at most 30 V, preferably of at most 20 V, particularly advantageously of at most 10 V and in particular of at least 5 V relative to a reference potential. Preferably, the control signal has a periodicity at least at times, in particular with a period of at most 1 ms, in particular of at most 0.1 ms and advantageously of at most 0.05 ms. Particularly advantageously, the control signal is at least substantially a rectangular signal, which in particular has two discrete values, preferably a switch-on value and a switch-off value. Preferably, each of the two values corresponds to a switching position of the heating frequency units and in particular their inverter. A "frequency" of a heating frequency unit is to be understood in particular as the frequency of the control signal controlling the heating frequency unit.

By the fact that a heating frequency unit is "operated" should be understood in particular that the frequency of the heating frequency unit is different from zero. By the fact that a heating frequency unit is operated "continuously" should be understood in particular that the heating frequency unit is operated continuously during a heating mode, wherein the non-zero frequency of the control signal can change. The fact that a heating frequency unit is operated with a "fixed" frequency should in particular be understood to mean that the heating frequency unit is operated with a frequency that is at least substantially constant during a heating mode. An "at least largely immutable frequency" should be understood in particular to mean a frequency which during the heating mode has a fluctuation of at most 10%, in particular of at most 5%, preferably of at most 1% and particularly advantageously of 0%. The fact that a heating frequency unit is "switched off" in a time interval should in particular be understood to mean that the heating frequency unit has at least substantially a negligibly low output power in the relevant time interval. A "at least substantially negligibly low output power in the relevant time interval" shall be understood to mean in particular an output power which is at most 100 W, in particular at most 50 W, preferably at most 25 W and particularly advantageously 0 W, and / or during the time interval exclusively during a period of time not more than 50%, in particular not more than 25%, preferably not more than 15%. and most advantageously corresponds to at most 10% of a length of the time interval. The control unit is provided to control and / or regulate the at least two heating frequency units by means of the control signals in such a way that an average output power of one of the at least two heating frequency units corresponds at least largely to a nominal power selected by an operator. In this case, a relative deviation of the set by the control unit average output power of the target power should be at most 20%, preferably at most 10% and more preferably at most 5%. An "output power" of one of the at least two heating-frequency units should in particular be understood to mean a power which is supplied by the heating-frequency unit in at least one heating operating state. A "mean output power" is to be understood in particular a time-averaged output power. In a simultaneous operation of the at least two Heizfrequenzeinheiten the control unit is in particular provided to make an adjustment of the average output power to the desired power while largely avoiding Intermodulationsgeräuschen. A "substantial avoidance of intermodulation noise" is to be understood in particular as meaning that intermodulation noises having a frequency of less than 17 kHz, in particular less than 16 kHz and preferably less than 14 kHz at a distance of 1 m from the cooking appliance device have a maximum sound pressure level 20 dB, in particular of at most 10 dB, preferably of at most 5 dB, and particularly advantageously have a maximum of 0 dB. Preferably, the intermodulation sounds are inaudible by an average hearing operator.

A "flicker characteristic" is to be understood in particular as a parameter that represents a measure of flicker. By "flicker" is meant, in particular, a subjective impression of an instability of a visual perception, which is caused in particular by a light stimulus whose luminance and / or spectral distribution varies with time. In particular, flicker can be caused by a voltage drop of a mains voltage. In particular, the patch parameter is a total output power difference, preferably between two points in time of two time intervals and particularly advantageously two adjacent time intervals. A "total output" is understood to mean, in particular, a sum of output powers of all heating-frequency units at a particular point in time. A "total output power difference" is to be understood in particular as a difference of the total output powers at two different points in time. Preferably, the control unit is provided to lower the flicker characteristic below a threshold. The limit value is preferably a value defined by at least one statutory requirement and / or standard, in particular the standard DIN EN 61000-3-3.

By means of such an embodiment, an advantageously flexible adjustment of the average output powers of the heating frequency units can be achieved, in particular since the frequency of the second heating frequency unit in the first time interval can be selected to be greater or smaller than the first frequency and the frequency of the first heating frequency unit in the second time interval and the frequency the second heating frequency unit may be variable in the first time interval. Furthermore, a further control option can be provided, which can additionally be used in combination with other known control options.

It is also proposed that the control unit is provided to operate the first heating frequency unit in the second time interval at least temporarily with a frequency which is smaller than the first frequency. Advantageously, it is provided to operate the first heating frequency unit during the entire second time interval with a preferably fixed frequency, which is smaller than the first frequency. As a result, a minimization of the patch characteristic can be made particularly advantageous.

Advantageously, the frequencies are at least 14 kHz, preferably at least 17 kHz and particularly advantageously at least 20 kHz. This can be intermodulation noises be minimized. Furthermore, switching losses in the heating frequency units can be reduced.

In a preferred embodiment of the invention, it is proposed that the control unit is provided to continuously operate the heating frequency unit with the highest setpoint power. As a result, a minimization of the patch characteristic can be achieved particularly advantageously. Furthermore, ease of use can be increased advantageously, since just as possible for the heating frequency unit with the highest target power as even as possible power output.

In a particularly preferred embodiment of the invention it is proposed that the control unit is provided in at least one operating state to periodically operate the at least two Heizfrequenzeinheiten with a period corresponding to a sum of a length of the first time interval and a length of the second time interval. As a result, a simple and easily implemented in a software controller can be provided.

In a further embodiment of the invention, it is proposed that the control unit is provided to control and / or regulate the at least two heating frequency units in each case by means of a control signal and to adapt a duty cycle of at least one of the control signals in at least one operating state. In particular, a ratio of a time duration in which the control signal assumes the switch-on value within a period duration to the period duration of the control signal is to be understood as a "duty cycle". Preferably, at a fixed frequency of one of the heating frequency units by changing the duty cycle, an output of the heating frequency unit can be changed. By the fact that the control unit is intended to "adapt a duty cycle of at least one of the control signals" should be understood in particular that the control unit is provided to change the duty cycle of at least one of the control signals, preferably thereby changing a power output at fixed frequency of a heating frequency unit to reach. Preferably, the control unit is provided by changing the duty cycle of at least one control signal of at least two Heizfrequenzeinheiten a total output of the at least two Heizfrequenzeinheiten in at least one operating state temporally as constant as possible and particularly advantageous a maximum difference of total output power at two different times under a law and / or value prescribed by standards. In this way, further adjustment options for the control unit can be developed, whereby an ease of use can be advantageously increased.

Advantageously, the control unit is provided to adapt the time intervals to desired powers of the at least two heating frequency units after a selection of the frequencies that minimize the flicker characteristic. It is intended, in particular, that a "length of the time intervals is adapted, so that the average output power of one of the at least two heating frequency units comes as close as possible to the nominal power of this heating frequency unit, and preferably identical to this one. This ensures that legal requirements and / or standards regarding flicker are complied with.

It is also proposed that the control unit is provided to prioritize in favor of minimizing intermodulation noise and / or flicker, if operation of the at least two heating frequency units with selected target powers while largely avoiding Intermodulationsgeräuschen and / or flicker is impossible. The fact that the control unit is intended to "prioritize in favor of minimizing intermodulation noise and / or flicker", if operation of the at least two Heizfrequenzeinheiten with selected target powers while largely avoiding Intermodulationsgeräuschen and / or flicker is impossible, should be understood in particular that is provided, an operation of at least one of the at least two Heat frequency units with a different average output power from a target power, thereby minimizing intermodulation noise and / or flicker. Preferably, it is provided to minimize flicker under specified in the standard DIN EN 61000-3-3 prescribed limits. As a result, an ease of use can be advantageously increased, as can be avoided by an operator as unpleasant noises and / or flicker. Preferably, the average output power is always less than or equal to the target power. As a result, unsafe operating conditions can be avoided.

Furthermore, a method is proposed with a cooking device device with at least one first and at least one second heating frequency unit in which the first heating frequency unit is operated continuously and in at least a first time interval with a fixed first frequency, the second heating frequency unit operated in the first time interval and in at least one second Time interval is turned off and at least a flicker characteristic is minimized, wherein the second heating frequency unit is operated in the first time interval with a by at least 14 kHz, preferably at least 16 kHz and more preferably at least 17 kHz from the first frequency different frequency. In this way, an advantageously flexible adjustment of the average output power of the heating frequency units can be achieved.

Furthermore, a cooking appliance, in particular a hob, proposed with a Gargerätevorrichtung invention. Preferably, the hob is an induction hob.

Further advantages emerge from the following description of the drawing. In the drawing, an embodiment of the invention is shown. The drawing, the description and the claims contain numerous features in combination.

Fig. 1

ein Induktionskochfeld mit einer erfindungsgemäßen Gargerätevorrichtung mit zwei Heizfrequenzeinheiten,

Fig. 2

ein beispielhaftes, nicht maßstabsgetreues Steuersignal einer der zwei Heizfrequenzeinheiten,

Fig. 3

beispielhafte, nicht maßstabsgetreue Leistungs-Frequenz-Kurven für die zwei Heizfrequenzeinheiten,

Fig. 4

je eine beispielhafte, nicht maßstabsgetreue Leistungs-Zeit-Kurve für die zwei Heizfrequenzeinheiten und

Fig. 5

beispielhafte, nicht maßstabsgetreue Leistungs-Frequenz-Kurven einer der zwei Heizfrequenzeinheiten bei unterschiedlichen Tastgraden eines Steuersignals.

Show it:

Fig. 1

an induction hob with a cooking appliance device according to the invention with two heating frequency units,

Fig. 2

an exemplary, not to scale, control signal of one of the two heating frequency units,

Fig. 3

exemplary, not to scale true power frequency curves for the two heating frequency units,

Fig. 4

each an exemplary, not to scale true power-time curve for the two heating frequency units and

Fig. 5

exemplary, not to scale power frequency curves of one of the two heating frequency units at different duty cycles of a control signal.

Hierbei bezeichnen P₁(t) die Ausgangsleistung der ersten Heizfrequenzeinheit 10 zur Zeit t und P₂(t) die Ausgangsleistung der zweiten Heizfrequenzeinheit 12 zur Zeit t. Die Steuereinheit 14 steuert die erste Heizfrequenzeinheit 10 mittels eines Steuersignals V₁(t) und die zweite Heizfrequenzeinheit 12 mittels eines Steuersignals \/₂(t). FIG. 1 shows a trained as induction hob 16 cooking appliance. The induction hob 16 comprises a hob plate 18, in particular of a glass ceramic, on the two heating zones 20, 22 are marked in a known manner. The hob plate 18 is arranged horizontally in an operational state of the induction hob 16 and provided for setting up cooking utensils. Furthermore, touch-sensitive operating elements 26 and display elements 28 of an operating and display unit 30 of the induction hob 16 are marked on the hob plate 18 in a known manner. The induction hob 16 further comprises a cooking device device having a first and a second heating frequency unit 10, 12 arranged below the hob plate 18 and having a control unit 14 arranged underneath the hob plate 18 FIG. 1 are components which are arranged below the hob plate 18, drawn schematically and dashed, with functional relationships are marked with arrows. The control unit 14 is integrated in a control and regulation unit 32 of the induction hob 16. One of the heating zone 20 associated and disposed below this induction heating unit is powered by the first heating frequency unit 10 with energy. One of the heating zone 22 associated and arranged below this induction heating unit is powered by the second heating frequency unit 12 with energy. An operator can by means of the operating and Display unit 30 select a heating stage for each of the heating zones 20, 22, resulting in each case a target power P _obj1 , P _obj2 for the two heating frequency units 10, 12 results. The control unit 14 is provided to _adapt a respective average output power P _ave1 , P _{ave2 of} the heating frequency units 10, 12 to the desired powers P _obj1 , P _obj2 while largely avoiding intermodulation noise, so that the selected heating levels of the heating zones 20, 22 can be achieved. In addition, the control unit 14 is provided to minimize a flicker characteristic F. The flicker characteristic F is a maximum difference between two total output powers P ₁ + P _{2 of} the two heating-frequency units 10, 12 at two different times t ₁ and t ₂ : $$\mathrm{F}=\left|{\mathrm{P}}_{\mathrm{1}}\left({\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="imgf0001.png"\; state="\{\{state\}\}">t</figure-callout>}}_{\mathrm{1}}\right)+{\mathrm{P}}_{\mathrm{2}}\left({\mathrm{t}}_{\mathrm{1}}\right)-{\mathrm{P}}_{\mathrm{1}}\left({\mathrm{t}}_{\mathrm{2}}\right)-{\mathrm{P}}_{\mathrm{2}}\left({\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{\mathrm{2}}\right)\right|\mathrm{,}$$

Here, P ₁ (t) designates the output power of the first heating frequency unit 10 at time t and P ₂ (t) the output power of the second heating frequency unit 12 at time t. The control unit 14 controls the first heating frequency unit 10 by means of a control signal V ₁ (t) and the second heating frequency unit 12 by means of a control signal \ / ₂ (t).

FIG. 2 shows by way of example a not to scale control signal V ₂ (t) of the second heating frequency unit 12 in a Cartesian coordinate system. An ordinate axis 36 has a control voltage V ₂ and an abscissa axis 38 a time t. The control signal V ₂ (t) is during a first time interval T _A a period T a square wave signal with a switch-V ₀ and a switch-off of 0 volts. The switch-on value V ₀ is held during a switch-on time t ₀ . A period of the rectangular signal is T ₀ . During a period of time (T ₀ -t ₀ ), the turn-off value is held. A frequency f _{2A of} the control signal V ₂ (t) is calculated from a reciprocal of the period T ₀ . The frequency f _2A is typically between 20 kHz and 100 kHz. A duty cycle D _{2A of} the control signal V ₂ (t) is calculated from a quotient of the switch-on time t ₀ divided by the period T ₀ . While V ₂ (t) is the shape of the square wave signal, a first of two switching units of the second heating frequency unit 12 is periodically switched in accordance with a periodic change of the ON value V ₀ and the OFF value. A second switching unit of the second heating frequency unit 12 is periodically switched in an analogous, but time-shifted manner, so that a high-frequency alternating current to an operation of the heating zone 22 associated induction heating unit arises. During a second sub-interval T _{B of} the period T with T _B = T -T _A , the control signal V ₂ (t) is identical to zero. A time x separates the first time interval T _A and the second time interval T _B. After the period T has elapsed, the control signal V ₂ (t) is repeated.

FIG. 3 shows in a Cartesian coordinate system by way of example two not-to-scale power frequency curves P ₁ (f) and P ₂ (f). The output powers P ₁ and P _{2 of} the heating frequency units 10, 12 are plotted on an ordinate axis 42. On an abscissa axis 44, the frequency f is plotted. The target powers P _obj1 and P _{obj2 of} the heating frequency units 10, 12 are set by an operator. Without limiting the generality, let it be assumed that the first heating frequency unit 10 has the highest setpoint power P _obj1 . This is then operated continuously by the control unit 14, in the first time interval T _A with a fixed first frequency f _1A and in the second time interval T _B with a fixed second frequency f _1B . The second Heizfrequenzeinheit 12 is operated by the control unit 14 in the first time interval T _A at a fixed frequency f _2A, which is to at least 17 kHz higher than the first frequency f _1A. Since the output power P _{2 of} the second heating frequency unit 12 at the frequency f _2A exceeds the setpoint power P _{obj2 of} the second heating frequency unit 12, the second heating frequency unit 12 is switched off in the second time interval T _B. The frequencies f _1A , f _2A and f _1B are each at least 20 kHz.

$${\mathrm{P}}_{\mathrm{1}}\left(\mathrm{0}\le \mathrm{t}\le \mathrm{x}\right)\le {\mathrm{P}}_{\mathrm{obj}\mathrm{1}}\le {\mathrm{P}}_{\mathrm{1}}\left(\mathrm{x}<\mathrm{t}\le \mathrm{T}\right),$$

$$\left|{\mathrm{f}}_{\mathrm{1}\mathrm{A}}-{\mathrm{f}}_{\mathrm{2}\mathrm{A}}\right|\ge \mathrm{17}\mathrm{kHz}$$

und $${\mathrm{f}}_{\min \mathrm{1}/\mathrm{2}}\le {\mathrm{f}}_{\mathrm{1}\mathrm{A}},{\mathrm{f}}_{\mathrm{2}\mathrm{A}},{\mathrm{f}}_{\mathrm{1}\mathrm{B}}\le {\mathrm{f}}_{\max }\mathrm{.}$$

FIG. 4 shows in a Cartesian coordinate system by way of example two not-to-scale power-time curves P ₁ (t) and P ₂ (t). The output powers P ₁ and P _{2 of} the heating frequency units 10, 12 are plotted on an ordinate axis 46. The time t is plotted on an abscissa axis 48. One in figure 4 illustrated course of the power-time curves P ₁ (t) and P ₂ (t) is in a heating operating state of the heating frequency units 10, 12 periodically through the period T. Ideally, the control unit 14, the frequencies f _{1 A,} f _2A and _1B as well as the lengths of the time intervals T _A and T _B so that the average output powers P _ave1 and P _AVE2 of the two Heizfrequenzeinheiten 10, 12 respectively to the target powers P _obj1 and P _obj2 correspond, intermodulation _noises are largely avoided and the flicker characteristic F identically becomes zero. This is possible under the following conditions: $${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{2}}\left(\mathrm{0}\le \mathrm{t}\le \mathrm{x}\right)\ge {\mathrm{<figure-callout\; id="2"\; label="P\; obj"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">P\; </figure-callout>}}_{\mathrm{obj}}.$$

$${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{1}}\left(\mathrm{0}\le \mathrm{t}\le \mathrm{x}\right)\le {\mathrm{P}}_{\mathrm{obj}\mathrm{1}}\le {\mathrm{P}}_{\mathrm{1}}\left(\mathrm{x}<\mathrm{t}\le \mathrm{T}\right).$$

$$\left|{\mathrm{f}}_{\mathrm{1}\mathrm{A}}-{\mathrm{f}}_{\mathrm{2}\mathrm{A}}\right|\ge \mathrm{17}\mathrm{kHz}$$

and $${\mathrm{<figure-callout\; id="1"\; label="f\; min"\; filenames="imgf0001.png"\; state="\{\{state\}\}">f\; </figure-callout>}}_{\min }\le {\mathrm{f}}_{\mathrm{1}\mathrm{A}}.{\mathrm{f}}_{\mathrm{2}\mathrm{A}}.{\mathrm{<figure-callout\; id="1B"\; label="f"\; filenames="imgf0002.png"\; state="\{\{state\}\}">f</figure-callout>}}_{\mathrm{1}\mathrm{B}}\le {\mathrm{f}}_{\mathrm{Max}}\mathrm{,}$$

The last condition takes into account additional limits for the frequencies f _1A , f _2A and f _1B . On the one hand there exists in each case a curve-specific minimum frequency f _min1 and f _min2 and thus a maximum achievable output power P ₁ , P ₂ for each heating frequency unit 10, 12. Furthermore, there is a maximum frequency f _max given by electronic restrictions and thus minimal in a continuous operation achievable output power P ₁ , P ₂ for each heating frequency unit 10, 12. The second condition is that the first heating frequency unit 10 is to operate in the second time interval T _B with a frequency f _1B , which is smaller than the frequency f _1A , with the first Heizfrequenzeinheit 10 is operated in the first time interval T _A.

To determine the frequencies f _1A , f _2A and f _1B and the lengths of the time intervals T _A and T _B , the control unit 14 first determines the frequencies f _1A , f _2A and f _1B , by means of which flicker-free operation with F = 0 is possible. This is done by gradually lowering the frequencies f _1A , f _2A and f _1B and thus by gradually increasing the output power P ₁ , P _{2 of} the relevant heating frequency unit 10, 12. The lowering of the frequencies f _1A , f _2A and f _1B can be used for both Heizfrequenzeinheiten 10, 12 separated or carried out simultaneously. If a sentence of frequencies f _1A , f _2A and f _1B satisfying the above conditions, the time intervals T _A and T _{B are} adjusted until the average output _powers P _ave1 and P _{ave2 of} the two heating-frequency units 10, 12 respectively correspond to the target powers P _obj1 and P _obj2 . During operation of the heating frequency units 10, 12, if necessary, a correction can be made in real time, in order to respond to power fluctuations caused, for example, by heating.

$${\mathrm{P}}_{\mathrm{1}}\left(\mathrm{0}\le \mathrm{t}\le \mathrm{x},{\mathrm{D}}_{\mathrm{1}\mathrm{A}}\right)\le {\mathrm{P}}_{\mathrm{obj}\mathrm{1}}\le {\mathrm{P}}_{\mathrm{1}}\left(\mathrm{x}<\mathrm{t}\le \mathrm{T},{\mathrm{D}}_{\mathrm{1}\mathrm{B}}\right),$$

$$\left|{\mathrm{f}}_{\mathrm{1}\mathrm{A}}-{\mathrm{f}}_{\mathrm{2}\mathrm{A}}\right|>\mathrm{17}\mathrm{kHz}$$

und $${\mathrm{f}}_{\min \mathrm{1}/\mathrm{2}}\le {\mathrm{f}}_{\mathrm{1}\mathrm{A}},{\mathrm{f}}_{\mathrm{2}\mathrm{A}},{\mathrm{f}}_{\mathrm{1}\mathrm{B}}\le {\mathrm{f}}_{\max }\mathrm{.}$$

FIG. 5 shows in a Cartesian coordinate system example, not to scale power frequency curves P ₂ (f, d _j ) for different duty cycles D _2A = d _j (j = 1, ..., n) of the control signal V ₂ (t) of the second Heating frequency unit 12 (see also FIG. 2 ). On an ordinate axis 50, the output power P _{2 of} the second heating frequency unit 12 is plotted. On an abscissa axis 52, the frequency f is plotted. By adapting the duty cycle D _2A , for example from 0.5 to smaller values, the control unit 14 can adjust the output power P _{2 of} the second heating frequency unit 12. In this way, in particular a lowering of the output power P ₂ at a fixed frequency f _{2A of} the second heating frequency unit 12 can be achieved. The same applies to an adaptation of duty cycles D _1A and D _1B for the first heating frequency unit 10. The control unit 14 may additionally be provided to adapt the duty cycles D _1A , D _2A and D _1B to fulfill the above conditions. Generalized then the conditions are: $${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{2}}\left(\mathrm{0}\le \mathrm{t}\le \mathrm{x}.{\mathrm{D}}_{\mathrm{2}\mathrm{A}}\right)\ge {\mathrm{<figure-callout\; id="2"\; label="P\; obj"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">P\; </figure-callout>}}_{\mathrm{obj}}.$$

$${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{1}}\left(\mathrm{0}\le \mathrm{t}\le \mathrm{x}.{\mathrm{D}}_{\mathrm{1}\mathrm{A}}\right)\le {\mathrm{P}}_{\mathrm{obj}\mathrm{1}}\le {\mathrm{P}}_{\mathrm{1}}\left(\mathrm{x}<\mathrm{t}\le \mathrm{T}.{\mathrm{<figure-callout\; id="1B"\; label="D"\; filenames="imgf0002.png"\; state="\{\{state\}\}">D</figure-callout>}}_{\mathrm{1}\mathrm{B}}\right).$$

$$\left|{\mathrm{f}}_{\mathrm{1}\mathrm{A}}-{\mathrm{f}}_{\mathrm{2}\mathrm{A}}\right|>\mathrm{17}\mathrm{kHz}$$

and $${\mathrm{<figure-callout\; id="1"\; label="f\; min"\; filenames="imgf0001.png"\; state="\{\{state\}\}">f\; </figure-callout>}}_{\min }\le {\mathrm{f}}_{\mathrm{1}\mathrm{A}}.{\mathrm{f}}_{\mathrm{2}\mathrm{A}}.{\mathrm{<figure-callout\; id="1B"\; label="f"\; filenames="imgf0002.png"\; state="\{\{state\}\}">f</figure-callout>}}_{\mathrm{1}\mathrm{B}}\le {\mathrm{f}}_{\mathrm{Max}}\mathrm{,}$$

If at selected target power P _obj1 and P _obj2 no set of frequencies f _1A , f _2A , f _1B exists, for which the above conditions are met, then the control unit 14 is provided, at least one of the two heating frequency units 10, 12 with a lower the setpoint power P _obj1 , P _obj2 lying average output power P _ave1 , P _ave2 in order to avoid intermodulation _noise and to keep flicker under a limit prescribed by the DIN EN 61000-3-3 standard. That is, at least one of the target powers P _obj1 , P _{obj2 is lowered} by the control unit 14 to _satisfy the above conditions.

Alternatively, an induction hob can also have more than two induction heating units, wherein a plurality of induction heating units can be connected via a switching unit with a heating frequency unit. Furthermore, it is also conceivable that frequencies of Heizfrequenzeinheiten always differ in a first time interval by exactly 17 kHz. Furthermore, the control method described here can be combined with other control methods which are known to a person skilled in the art and appear reasonable. Thus, it is conceivable, for example, for time intervals T _A and T _{B to be followed by} a further time interval T _C in which all or even only part of the heating frequency units are switched off or operated at a further common frequency f _C. reference numeral 10 heating frequency unit f _2A frequency 12 heating frequency unit fc frequency 14 control unit f _min1 minimum _frequency 16 induction hob f _min2 minimum _frequency 18 hob plate f _{max maximum} frequency 20 heating zone P ₁ output power 22 heating zone P ₁ (f) power frequency curve 26 control element P ₁ (t) power-time curve 28 indicator P ₂ output power 30 operating and display unit P ₂ (f) power frequency curve 32 control unit P ₂ (f, d _j ) power frequency curve 36 ordinate axis P ₂ (t) power-time curve 38 abscissa axis P _ave1 Average output power 42 ordinate axis P _ave2 Average output power 44 abscissa axis P _obj1 target power 46 ordinate axis P _obj2 target power 48 abscissa axis T period 50 ordinate axis T ₀ period 52 abscissa axis T _A time interval d _j duty cycle (j = 1, ..., n) T _B time interval D _1A duty cycle Tc time interval D _1B duty cycle t time D _2A duty cycle t ₀ switch-on time Fickle characteristic t ₁ time f frequency t ₂ time f _1A frequency V ₀ switch-on value f _1B frequency V ₁ (t) control signal V ₂ control voltage V ₂ (t) control signal x time

Claims (9)

1. Cooking device having at least one first and at least one second heat frequency unit (10, 12) and having at least one control unit (14), which is provided to operate the first heat frequency unit (10) continuously and with a fixed first frequency (f _1A ) in at least one first time interval (T_A ), to operate the second heat frequency unit (12) in the first time interval (T_A ), and to switch off said second heat frequency unit in at least one second time interval (T_B ), wherein the control unit (14) is provided to operate the second heat frequency unit (12) in the first time interval (T_A ) with at least one frequency (f _2A ) which differs by at least 14 kHz from the first frequency (f _1A ), characterised in that the control unit (14) is provided to control and/or regulate the at least two heat frequency units (10, 12) using a control signal (V ₁ (t), V ₂ (t)) in each case and in at least one operating state to adjust a pulse duty factor (D _1A , D _2A , D _1B ) of at least one of the control signals (V ₁ (t), V ₂ (t)) and to minimise at least one flicker parameter (F), wherein the control unit (14) is provided to change the pulse duty factor of at least one of the control signals (V ₁ (t), V ₂ (t)) in order in this way to achieve a change in an output power with a fixed frequency of a heat frequency unit (10, 12).
2. Cooking device according to claim 1, characterised in that the control unit (14) is provided to operate the first heat frequency unit (10) in the second time interval (T_B ) at least at times with a frequency (f _1B ), which is lower than the first frequency (f _1A ).
3. Cooking device according to claim 1 or 2, characterised in that the frequencies (f _1A ,f _2A ,f _1B ) amount to at least 14 kHz.
4. Cooking device according to one of the preceding claims, characterised in that the control unit (14) is provided to continuously operate the heat frequency unit (10) with the highest setpoint power (P _obj1).
5. Cooking device according to one of the preceding claims, characterised in that in at least one operating state the control unit (14) is provided to operate the at least two heat frequency units (10, 12) periodically with a cycle duration (T) which corresponds to a sum of a length of the first time interval (T_A ) and a length of the second time interval (T_B ).
6. Cooking device according to one of the preceding claims, characterised in that the control unit (14) is provided to adjust the time intervals (T_A,T_B ) to setpoint powers (P _obj1,P _obj2) of the at least two heat frequency units (10, 12) following a selection of the frequencies (f _1A , f _{2 A}, f _1B ) that minimise the flicker parameter (F).
7. Cooking device according to one of the preceding claims, characterised in that the control unit (14) is provided to perform a prioritisation favouring a minimisation of intermodulation noises and/or flickers, if an operation of the at least two heat frequency units (10, 12) with selected setpoint powers (P _obj1,P _obj2) is impossible while simultaneously largely avoiding intermodulation noises and/or flickers.
8. Method with a cooking device having at least one first and at least one second heat frequency unit (10, 12), in particular according to one of the preceding claims, in which the first heat frequency unit (10) is operated continuously and with a fixed first frequency (f _1A ) in at least one first time interval (T_A ), the second heat frequency unit (12) is operated in the first time interval (T_A ) and is switched off in at least one second time interval (T_B ), wherein in the first time interval (T_A ) the second heat frequency unit (12) is operated with a frequency (f _{2 A}) which differs by at least 14 kHz from the first frequency (f _1A ), characterised in that at least one flicker parameter (F) is minimised and the at least two heat frequency units (10, 12) are each controlled and/or regulated using a control signal (V ₁ (t), V ₂(t)) and in at least one operating state a pulse duty factor (D _1A , D _2A , D _1B ) of at least one of the control signals (V ₁ (t), V ₂ (t)) is adjusted, wherein the pulse duty factor of at least one of the control signals (V ₁ (t), V ₂ (t)) is changed by the control unit (14), in order in this way to achieve a change in output power with a fixed frequency of a heat frequency unit (10, 12).
9. Cooking appliance, in particular hob, with a cooking device according to one of claims 1 to 7.

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