EP2469971B1 - 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 B1 discloses an induction hob with at least two heating frequency units operated according to a particular method to prevent intermodulation noises. According to this method, both heating-frequency units are operated at an identical first frequency in a first time period. In a second period of time, one heating frequency unit is switched off, while the other heating frequency unit is operated at a second frequency. The two frequencies as well as the relative lengths of the two time segments are adjusted so that a mean output power of each heating frequency unit corresponds to an operator selected heating power.

The publication EP 2 200 398 A1 describes a Gargerätevorrichtung according to the preambles of claims 1 and 12th

The object of the invention is in particular to provide a generic Gargerätevorrichtung with a continuous power output possible. The object is achieved by the features of claim 1 and the method claim 9, while advantageous embodiments and refinements of the invention can be taken from the dependent claims.

The invention is based on a cooking device device with at least two heating frequency units and with at least one control unit, which is provided to set in each case an average output power of the heating frequency units.

According to the invention, the control unit is provided for effecting an adjustment of the mean output power of at least one of the heating frequency units using a duty cycle of a control signal. Preferably the cooking device device is designed as a hob device and particularly advantageous as an induction hob device. By "provided" is intended to be understood in particular specially programmed and / or designed and / or equipped. A "heating frequency unit" is to be understood as meaning 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 as a unit which is intended to at least partially convert electrical energy into heat 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, which is intended to convert electrical energy indirectly via induced eddy currents into heat. The heating frequency unit comprises at least one inverter, which preferably comprises two switching units. A "switching unit" is to be understood as a unit which is intended to interrupt a line 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.

A "control unit" is to be understood as 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. Preferably, the control unit comprises a computing unit and in particular in addition to the computing unit, a memory unit with a control program stored therein. Preferably, the control unit is provided to the Heizfrequenzeinheiten to control and / or regulate by means of electrical control signals. An electrical "control signal" is to be understood in particular a signal having an electrical voltage of at most 30 V, preferably of at most 20 V and more preferably of at most 10 V, which is supplied to the inverters of the heating frequency units in particular in at least one operating state. 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 a square-wave signal, which in particular can assume two values, preferably a switch-on value and a switch-off value. Preferably, each of the two values corresponds to a switching position of the inverters. 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. An "output power" is to be understood, in particular, as meaning an electrical power which, in at least one operating state, is transmitted from a heating frequency unit to a heating unit. Preferably, the output power is transmitted by an electric current. The output power is preferably converted in the heating unit at least partially and particularly advantageously at least to a large extent into a heat flow. A "mean output power" is to be understood in particular a time-averaged output power. Preferably, the control unit is provided to set the average output power such that a selected by an operator heating power is achieved, in particular for each heating zone of a hob.

A "duty cycle" should be understood to mean 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. Preferably, at a fixed frequency of one of the heating frequency units by changing the duty cycle, the output power can be changed. Assuming that the control unit is intended to "set the average output power of at least one of the heating frequency units using a duty cycle a control signal ", it should be understood that the control unit is arranged to change the duty cycle of at least one of the heating frequency units at a setting of the average output power, thereby achieving a change in the instantaneous output power Modification of the duty cycle of at least one of the two heating frequency units to keep a total output of both heating frequency units as constant in time as possible in at least one operating state and particularly advantageous to suppress an overall output power difference at two different time points below a legal and / or prescribed by standards value In particular, "total output" A sum of the output powers of all heating-frequency units at a certain point in time is to be understood by a "total output power difference" in particular a difference of the total benefits at two different times.

By such a configuration, a power output as continuous as possible can be made possible. Furthermore, an output power of the heating rate units selected by an operator can be advantageously delivered accurately. Furthermore, a simple algorithm can be provided. Furthermore, energy efficiency can be increased because operation of the heating frequency units close to a resonance frequency is enabled.

Advantageously, the control unit is provided to use the duty cycle of the heating frequency unit, which requires a highest frequency to achieve the average output power in a continuous operation. As a result, an advantageously continuous power output can be achieved. Furthermore, flicker can be minimized. By "flicker" is meant in particular a subjective impression of instability of a visual perception, which is caused in particular by a light stimulus whose luminance or spectral distribution varies with time. In particular, flicker can be caused by a voltage drop of a mains voltage.

It is also proposed that the control unit is provided to reduce a patch parameter using the duty cycle. A "flicker characteristic" is to be understood in particular as a parameter that represents a measure of flicker. The flicker characteristic is preferably the total output power difference, preferably between two times of two time ranges and particularly advantageously two adjacent time ranges. Preferably, the control unit is provided to reduce the flicker characteristic under a legal and / or by standards, in particular by the standard DIN EN 61000-3-3 prescribed limit. As a result, flicker can be advantageously reduced.

In a preferred embodiment of the invention, it is proposed that the control unit is provided to permanently operate at least one of the heating frequency units. By the fact that the control unit is intended to "permanently operate" at least one of the heating frequency units, it should be understood in particular that at least one of the heating frequency units has a non-zero instantaneous output power in at least one operating state at all times. As a result, an advantageously uniform power output can be achieved.

In a particularly preferred embodiment of the invention it is proposed that the control unit is provided to operate the heating frequency unit continuously with a first frequency. By the fact that the control unit is intended to "continuously operate the heating frequency unit with a first frequency", should be understood in particular that the heating frequency unit is operated in at least one operating state at any time with the same, non-zero, first frequency. Preferably, an output power of the heating frequency unit in the operating state is constant and particularly advantageously identical to the mean output power of the heating frequency unit. In this way, a particularly advantageous uniform power output can be achieved.

Advantageously, the control unit is provided to permanently operate the one heating frequency unit which requires a minimum frequency to achieve the average output power in a continuous operation. As a result, a control algorithm can advantageously be simplified. Furthermore, flicker can be reduced.

It is also proposed that the control unit is provided to operate at least one of the heating frequency units at least temporarily with a second frequency. This allows a high degree of flexibility can be achieved. Preferably, the first frequency and the second frequency are identical. As a result, intermodulation noises can be excluded. If the first frequency is different from the second frequency, a frequency spacing between the first frequency and the second frequency is preferably at least 15 kHz, in particular at least 16 kHz and particularly advantageously at least 17 kHz. If the first frequency is different from the second frequency, both frequencies are preferably greater than 30 kHz, in particular greater than 32 kHz and particularly advantageously greater than 34 kHz. As a result, intermodulation noises can be advantageously reduced.

In a further embodiment of the invention, it is proposed that the control unit is provided to switch off at least one of the heating frequency units at least temporarily. By the fact that the control unit is provided to "at least temporarily turn off at least one of the heating frequency units" should be understood in particular that at least one of the Heizfrequenzeinheiten in at least one operating state alternately at least substantially has an output power of zero and a substantially nonzero output power. In particular, in the case of the vanishing output power, the control signal has the switch-off value. As a result, an adaptation to any average output power can be made possible.

Furthermore, a method is proposed with a cooking appliance device with at least two heating frequency units, in each of which an average output power of the heating frequency units is set, wherein an adjustment of the mean output power of at least one of the heating frequency units is made using a duty cycle of a control signal. This allows the most continuous power output possible.

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 Heizfrequenzeinheiten,

Fig. 3

je eine beispielhafte Leistungs-Frequenz-Kurve für die zwei Heizfrequenzeinheiten,

Fig. 4

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

Fig. 5

eine beispielhafte Leistungs-Frequenz-Kurvenschar für verschiedene Tastgrade für eine der Heizfrequenzeinheiten.

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 heating frequency units,

Fig. 3

one exemplary power frequency curve for the two heating frequency units,

Fig. 4

each an exemplary power-time curve for the two heating frequency units and

Fig. 5

an exemplary power-frequency waveform for different duty cycles for one of the heating frequency units.

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, are marked in the known manner three heating zones 20, 22, 24. 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 with two heating frequency units 10, 12 arranged below the hob plate 18 and with a control unit 14 arranged below the hob plate 18 Fig. 1 are components which are arranged below the cooking plate 18, dashed lines, wherein functional relationships are indicated by means of 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 heating frequency unit 10 with energy. One of the heating zone 22 associated and arranged below this induction heating unit and another of the heating zone 24 associated and arranged below this induction heating unit are supplied via a switching unit 34 of the cooking appliance by the heating frequency unit 12 with energy. The switching unit 34 is provided for operating the two induction heating units assigned to the two heating zones 22, 24 in a known manner in a time division multiplex controlled by the control unit 14. An operator can select a heating level for each of the heating zones 20, 22, 24 by means of the operating and display unit 30. The control unit 14 is designed to set a respective average output power P _0A , P _{0B of} the heating frequency units 10, 12, so that the selected heating levels of the heating zones 20, 22, 24 are achieved, in particular using the time multiplex, and intermodulation noises are avoided. The control unit 14 controls the heating frequency unit 10 by means of a control signal V _A (t) and the heating frequency unit 12 by means of a control signal V _B (t).

Fig. 2 shows an example of a non-to-scale control signal V _B (t) in a Cartesian coordinate system. On an ordinate axis 36 is a control voltage V _B and plotted on an abscissa axis 38 a time t. The control signal V _B (t) during a sub-interval T _{2 of} a time interval T is a rectangular signal with a switch-on value V ₀ and a switch-off value 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 of the control signal V _B (t) is calculated from a reciprocal of the period T ₀ . The frequency f is usually between 30 kHz and 100 kHz. A duty cycle D _{B of} the control signal V _B (t) is calculated from a quotient of the switch-on time t ₀ divided by the period T ₀ . An envelope 40 of the control signal V _B (t) is shown in dashed lines. While V _B (t) takes the form of the square wave signal, an inverter of the heating frequency unit 12 is periodically switched in accordance with a periodic change of the turn-on value V ₀ and the turn-off value. This results in a high-frequency alternating current to an operation of the heating zones 22, 24 associated Induktionsheizeinheiten. During a subinterval T _{1 of} the time interval T with T ₁ = TT ₂ , the control signal V _B (t) is identical to zero. After expiration of the time interval T, the control signal V _B (t) is repeated.

In the following it is assumed that the heating frequency unit 12 in a continuous operation requires a higher frequency for generating the average output power P _0B than the heating frequency unit 10 for generating the average output power P _0A in a likewise continuous operation. However, the reverse case would also be conceivable. Fig. 3 shows in a Cartesian coordinate system by way of example two power-frequency curves P _A (f) and P _B (f). On an ordinate axis 42 output powers P _A and P _{B of} the heating frequency units 10, 12 are plotted. On an abscissa axis 44, the frequency f is plotted. The heating frequency unit 10, which requires a smaller frequency f to achieve the average output power P _0A in a continuous operation, is operated continuously at a fixed frequency f ₀ . The heating frequency unit 12 is switched off in the partial interval T ₁ and is also operated in the partial interval T ₂ with the frequency f ₀ .

Fig. 4 shows in a Cartesian coordinate system by way of example two power-time curves P _A (t) and P _B (t). On an ordinate axis 46, the output power P _A and P _B of the Heizfrequenzeinheiten 10, applied 12th The time t is plotted on an abscissa axis 48. Fig. 4 shows how the heating frequency unit 10 in the first sub-interval T _{1 is operated} at the frequency f ₀ , while the heating frequency unit 12 is turned off. In the second sub-interval T ₂ both Heizfrequenzeinheiten 10, 12 are operated at the same frequency f ₀ . As a result, intermodulation hum can be effectively avoided. For the heating frequency unit 10, the instantaneous output power P _{A is} always identical to the mean output power P _0A . For the heating frequency unit 12, the instantaneous output power P _B during the sub-interval T _{2 is} always greater than the average output power P _0B . The mean output power P _0B results from the product of the output power P _B with the quotient of the subinterval T ₂ divided by the time interval T: $${\mathrm{P}}_{\mathrm{0}\mathrm{B}}={\mathrm{P}}_{\mathrm{B}}\times {\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">T</figure-callout>}}_{\mathrm{2}}/\mathrm{T}\mathrm{,}$$

Accordingly, the control unit 14 is provided to set a time x, which divides the time interval T in the sub-intervals T ₁ and T ₂ , such that the heating frequency unit 12 in a pulsed operation with a pulse interval corresponding to the sub-interval T ₂ , the average output power P _0B supplies.

Fig. 5 shows in a Cartesian coordinate system by way of example a power frequency curve family P _B '(f). On an ordinate axis 50, the output power P _{B of} the heating frequency unit 12 is plotted for different duty cycles D _B = d _j (j = 1,..., N). On an abscissa axis 52, the frequency f is plotted. Fig. 5 shows how by adjusting the duty cycle D _B at a fixed frequency f, an adjustment of the output power P _B can be made. Let D _{A be} a duty cycle of the heating frequency unit 10 and D _B a duty cycle of the heating frequency unit 12 during the sub-interval T ₂ . Then, the control unit 14 is provided to make an adjustment of the duty D _A and D _B , thereby reducing a flicker characteristic F, in particular one in the European standard EN 61000-3-3 prescribed limit. The patch characteristic F is a total output power difference F = (P _A + P _B ) -P _A = P _B between the two subintervals T ₁ and T ₂ . For this purpose, in the case of a continuous operation of the heating frequency unit 10, the duty cycle D _{B of} the heating frequency unit 12 is lowered, in order thereby to achieve an extension of the second subinterval T ₂ .

In an alternative embodiment, an adaptation of the duty cycle D _A can be made in addition. Alternatively, an induction hob can also have four induction heating units, wherein two of the induction heating units are each connected via a switching unit to a heating frequency unit. As an alternative or in addition to operation in a time multiplex, two induction heating units assigned to a heating frequency unit can also be operated by any other method that appears appropriate to a person skilled in the art. Furthermore, it is also conceivable that more than two induction heating units are assigned to a heating frequency unit. reference numeral 10 Heizfrequenzeinheit V _B (t) control signal 12 Heizfrequenzeinheit V ₀ Switch-on 14 control unit V _B control voltage 16 Induction hob t Time 18 Hotplate t ₀ on time 20 heating zone T time interval 22 heating zone T ₀ period 24 heating zone T ₁ subinterval 26 operating element T ₂ subinterval 28 display element x time 30 Operating and display unit P _A output 32 Control unit P _B output 34 switching unit f frequency 36 axis of ordinates f ₀ frequency 38 abscissa f ₁ frequency 40 envelope f ₂ frequency 42 axis of ordinates F Flickerkenngröße 44 abscissa P _A (f) Power-frequency curve 46 axis of ordinates P _B (f) Power-frequency curve 48 abscissa P _B '(f) Load frequency curves 50 axis of ordinates P _A (t) Power-time curve 52 abscissa P _B (t) Power-time curve P _0A average output power P _0B average output power D _A duty cycle D _B duty cycle d _j duty cycle

Claims (13)

1. Cooking device having at least two heat frequency units (10, 12), each of which comprises at least one inverter, and having at least one control unit (14), which is provided to adjust a mean power output (P _{0 A}, P _0B ) of the heat frequency units (10, 12) and to minimise a flicker parameter (F), which is the overall power output difference between two time instants of two time domains, characterised in that the control unit (14) is provided to perform an adjustment of the mean power output (P _0B ) of at least one of the heat frequency units (12) using a pulse duty factor (D_B ) of a control signal (V_B (t)) and to reduce the flicker parameter (F) using the pulse duty factor (D_B ), wherein the control unit (14) is provided to lower the pulse duty factor (D_B ) of the second heat frequency unit (12) when the first heat frequency unit (10) is operated continuously.
2. Cooking device according to claim 1, characterised in that the overall power output difference is a difference between the overall power outputs, which each represent a total of the power outputs of all heat frequency units (10, 12) at a specific time instant, at two different time instants.
3. Cooking device according to one of the preceding claims, characterised in that the control unit (14) is provided to keep an overall power output of both heat frequency units (10, 12) in at least one operating state as constant as possible over time by changing the pulse duty factor of at least one of the two heat frequency units (12) and to reduce an overall power output difference at two different time instants to below a value prescribed by law and/or standards.
4. Cooking device according to one of the preceding claims, characterised in that the control unit (14) is provided to use the pulse duty factor (D_B ) of the heat frequency unit (12) which requires the highest frequency in order to reach the mean power output (P _0B ) during continuous operation.
5. Cooking device according to one of the preceding claims, characterised in that the control unit (14) is provided to operate constantly at one of the heat frequency units (10).
6. Cooking device according to claim 5, characterised in that the control unit (14) is provided to operate the heat frequency unit (10) continuously with a first frequency (f ₁).
7. Cooking device at least according to claim 5, characterised in that in at least one operating state, at least one of the heat frequency units (10) has a momentary power output which differs from zero at each time instant.
8. Cooking device at least according to claim 6, characterised in that a power output of the heat frequency unit (10) is constant in the operating state and identical to the mean power output of the heat frequency unit (10).
9. Cooking device according to claim 5 or 6, characterised in that the control unit (14) is provided to operate constantly the heating frequency unit (10) which requires the smallest frequency in order to reach the mean power output (P _0A ) during continous operation.
10. Cooking device according to one of the preceding claims, characterised in that the control unit (14) is provided to operate at least one of the heat frequency units (12) at least temporarily with a second frequency (f ₂).
11. Cooking device according to one of the preceding claims, characterised in that the control unit (14) is provided to at least temporarily switch off at least one of the heat frequency units (12).
12. Method with a cooking device having at least two heat frequency units (10, 12), in particular according to one of the preceding claims, in which a mean power output (P _0A , P _0B ) of the heat frequency units (10, 12) is adjusted in each case and a flicker parameter (F), which is the overall power output difference between two time instants of two time domains, is reduced, characterised in that an adjustment of the mean power output (P _0B ) of at least one of the heat frequency units (12) is performed by using a pulse duty factor (D_B) of a control signal (V_B (t)) and the flicker parameter (F) is reduced using the pulse duty factor (D_B ), wherein during a continuous operation of the first heat frequency unit (10), the pulse duty factor (D_B ) of the second heat frequency unit (12) is lowered.
13. Cooking apparatus, in particular hob, having a cooking device according to one of claims 1 to 11.

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