Cooking appliance

Abstract

The invention relates to a cooking appliance (10), in particular an induction hob device, comprising at least one control unit (12) which is provided, in at least one periodic timed heating mode (50) associated with at least one operating time (16), for repetitively controlling and supplying power to at least one induction zone (18) and for operating the induction zone (18) with heating power in at least one ON time interval (26, 44) of the operating time (16). In order to propose a cooking appliance having improved control-related properties, the control unit (12) is provided for operating the induction zone (18) at a substantially constant heating current frequency during the ON interval (26, 44) and for varying a duty cycle (30).

Description

[0001] Cooking appliance device

[0002] The invention relates to a cooking appliance according to the preamble of claim 1 and a method for operating a cooking appliance according to the preamble of claim 12.

[0003] Cooking appliances, in particular hobs, with cooking appliance devices are already known from the prior art, which have inductors which are operated for heating various cooking utensils, wherein in order to avoid intermodulation noise, complex control schemes are used to control inductors for heating cooking utensils as a result of increased customer requirements regarding, for example, noise levels and cooking temperatures, which leads to more difficult compliance with flicker and EMC (electromagnetic compatibility) standards, which in turn increases the complexity of the control scheme.

[0004] In this context, EP 3001773 B1 discloses an induction hob device with two inverters, each operating an inductor, and with a control unit that jointly operates two inverters in a time window of a continuous operating state and divides the time window into two time intervals, wherein the control unit continuously changes a total achieved heating power of the at least two inverters in a transition time interval of the two time intervals.

[0005] In this context, the document US 8686321 B2 discloses a method for supplying induction targets, each comprising an inductor, wherein in one method step all inductors are supplied with a heating power based on a previously determined control sequence in order to comply with an operator input.

[0006] The object of the invention is, in particular, to provide a generic cooking appliance with improved control properties. This object is achieved according to the invention by the features of claims 1 and 12, while advantageous embodiments and further developments of the invention can be found in the subclaims. The invention is based on a cooking appliance, in particular an induction hob, with at least one control unit which is provided to repetitively control and supply with energy at least one induction target in at least one periodic continuous heating operating state, to which at least one operating period is assigned, and to operate the induction target with a heating output in at least one switch-on interval of the operating period.

[0007] It is proposed that the control unit is provided to operate the induction target in the switch-on interval of the operating period with a substantially constant heating current frequency and to vary a duty cycle.

[0008] The inventive design makes it possible to provide a generic cooking appliance with improved control properties. In particular, compliance with EMC standards can be achieved while simultaneously precisely achieving the desired heating output. Furthermore, the occurrence of flicker can be advantageously reduced, in particular minimized. A cooking appliance with particularly advantageous properties with regard to low-noise operation can be provided. The inventive design makes it advantageously possible to reduce, in particular eliminate, the need for EMC filters, thereby making it possible to provide a cost-effective cooking appliance. Furthermore, an energy-efficient cooking appliance can also be provided.Advantageously, low-noise and EMC-compliant operation of the cooking appliance can be achieved, particularly when multiple induction targets are operated simultaneously. Furthermore, a reliable design with respect to a target heating output requested by an operator can be achieved. Furthermore, intermittent operation of induction targets can be advantageously prevented. Furthermore, rapid perturbations, for example, due to shifting of cooking utensils and / or ferromagnetic saturation, can be advantageously avoided. Advantageously, the cooking appliance can be operated independently of a number of induction targets while reliably adhering to EMC standards.

[0009] A "cooking appliance device," advantageously an "induction hob device," is understood to mean at least one part, in particular a subassembly, of a cooking appliance, in particular an oven, for example an induction oven, and advantageously a hob, preferably an induction hob. A cooking appliance comprising the cooking appliance device can be designed, for example, as an oven and / or as a microwave and / or as a grill and / or as a steamer. Advantageously, a cooking appliance comprising the cooking appliance device is designed as a hob and preferably as an induction hob.

[0010] A "control unit" is to be understood as an electronic unit which is preferably at least partially integrated into the cooking appliance, in particular the induction hob, and which is intended to control and / or regulate at least one inverter unit of the cooking appliance. The control unit preferably comprises a computing unit and, in particular, in addition to the computing unit, a memory unit with a control and / or regulating program stored therein, which is intended to be executed by the computing unit. The cooking appliance preferably has at least one inverter unit for controlling and supplying energy to the at least one induction target, which inverter unit can be designed, in particular, as a resonant inverter and preferably as a dual half-bridge inverter.The inverter unit preferably comprises at least two switching elements, in particular inverter switching elements, which can be individually controlled by the control unit. A “switching element” is to be understood as an element that is intended to establish and / or break an electrically conductive connection between two points, in particular contacts of the switching element. The switching element preferably has at least one control contact via which it can be switched. The switching element is preferably designed as a semiconductor switching element, in particular as a transistor, for example as a metal oxide semiconductor field-effect transistor (MOSFET) or organic field-effect transistor (OFET), advantageously as a bipolar transistor with a preferably insulated gate electrode (IGBT). Alternatively, it is conceivable for the switching element to be designed as a mechanical and / or electromechanical switching element, in particular as a relay.

[0011] The cooking appliance device preferably comprises at least one resonant capacitor unit, which has at least one, preferably two, resonant capacitors. The control unit is preferably designed to operate the unit having the induction target as a resonant circuit in the continuous heating operating state. A resonant circuit having the induction target is formed from at least one inverter switching element, in particular precisely one inverter switching element, the inverter unit, at least one inductor, a cooking utensil, and at least one resonant capacitor, in particular precisely one resonant capacitor.

[0012] An "induction target" is understood to mean an inductor or a plurality of inductors, which is / are in particular part of the cooking appliance, with a cooking utensil placed above the inductor and / or the plurality of inductors, wherein the inductor or the plurality of inductors are provided, in particular jointly, in at least one continuous heating operating state to inductively heat the cooking utensil placed above the inductor or the plurality of inductors. In this case, the inductors of the induction target can each provide the same heating power compared to one another in at least the continuous heating operating state. Preferably, the control unit controls the inductors of an induction target with the same heating current frequency. Furthermore, the inductor, in particular precisely a single inductor, of the induction target can provide a different heating power over time during at least the continuous heating operating state.The control unit is particularly provided to define at least one induction target. In particular, the control unit can define multiple induction targets. The cooking appliance device has, in particular, at least one inductor, in particular a plurality of inductors. An “inductor” is to be understood here in particular as an element which, in at least one continuous heating operating state, supplies energy to at least one cooking utensil for the purpose of heating the cooking utensil, in particular in the form of an alternating magnetic field which is intended to induce eddy currents and / or magnetization reversal effects in a metallic, preferably at least partially ferromagnetic heating means, in particular a cooking utensil, which are converted into heat.The inductor, in particular, has at least one induction coil and is particularly designed to supply energy to the cooking utensil in the form of an alternating magnetic field with a heating current frequency, in particular a short-term variable one. The inductor is arranged, in particular, below and advantageously in the vicinity of at least one support plate of a cooking appliance, in particular a hob, having the cooking appliance device. In particular, the plurality of inductors can be arranged in a matrix, wherein the matrix-like inductors can form a variable cooking surface.

[0013] In particular, the inductors can be combined with one another to create induction targets of any size, particularly with different contours. Alternatively or additionally, inductors can also be arranged in the form of a classic cooking surface, in particular with two, three, four or five heating zones, particularly those that are highlighted compared to the remaining surface of the installation plate designed as a matrix hob. A "installation plate" should be understood to mean at least one, in particular plate-like, unit that is intended for placing at least one item of cooking utensil on it and / or for placing at least one item of cooking food on it. The installation plate could, for example, be made at least largely from glass and / or glass ceramic and / or Neolith and / or Dekton and / or wood and / or marble and / or stone, in particular natural stone, and / or laminate and / or plastic and / or ceramic.

[0014] A "heating current frequency" is understood to mean, in particular, a frequency of an alternating electrical current in a range from 20 kHz to 100 kHz, preferably 30 kHz to 75 kHz, which, in the continuous heating operating state, is provided by the inverter unit and applied to an inductor to generate an alternating magnetic field. The heating current frequency differs from the mains frequency of an alternating mains voltage of the energy source, in particular a power supply network. Preferably, the control unit is provided to select and / or adjust the heating current frequency in a range from 20 kHz to 100 kHz, preferably 30 kHz to 75 kHz, and to keep it substantially constant.

[0015] A "substantially constant" operating parameter is understood to mean that the operating parameter, for example the heating frequency and / or a real conductance and / or a complex conductance and / or an impedance and / or another operating parameter of the cooking appliance device and / or of a cooking appliance having the cooking appliance device, has a constant value, except for deviations of a maximum of 10%, preferably a maximum of 8%, particularly preferably a maximum of 5%, over at least 70%, preferably at least 80%, particularly preferably at least 90% of a corresponding period of time. Operating parameters can be kept constant by the control unit, either directly or indirectly, i.e., by controlling at least one further operating parameter.The phrase “supplying an object with energy” is to be understood in particular as providing electrical energy in the form of an electrical voltage, an electrical current and / or an electrical and / or electromagnetic field from at least one energy source for the object. An “energy source” is to be understood in particular as a unit which provides electrical energy in the form of an electrical voltage, an electrical current and / or an electrical and / or electromagnetic field to at least one further unit and / or at least one electrical circuit. The energy source can in particular be an electrical current phase of a power supply network. An inverter unit is preferably arranged between the energy source and at least one induction target, preferably all induction targets.

[0016] A "continuous heating operating state" is understood to mean an operating state of the cooking appliance in which the control unit continuously operates the at least one induction target with a heating power. The continuous heating operating state lasts at least 10 ms, preferably at least 1 s, advantageously at least 60 s, preferably at least 90 s, and particularly preferably at least 120 s.

[0017] The term "repetitive control" of a unit or "repetitively controlling" a unit should be understood here in particular to mean a periodically repeated control of a unit in at least one continuous heating operating state, in particular with an electrical signal. Preferably, the induction target is repetitively controlled in the continuous heating operating state with the operating period. Preferably, the control unit repeats the control from an individual operating period of at least one induction target within an individual continuous heating operating state, in particular until this continuous heating operating state is terminated by an operator input. In particular, the operating period, in particular the control of the induction targets of an operating period, is repeated over the entire duration of the continuous heating operating state.Preferably, the duration of an operating period corresponds to half a period of the mains alternating voltage, which lasts, for example, 10 ms at a mains frequency of 50 Hz.

[0018] A "duty cycle" is a control parameter of the inverter unit that specifies the ratio between a pulse duration, during which an inverter switching element of the inverter unit is closed and at least one induction target is subjected to an electrical alternating current pulse, and a period duration of the operating period. The duty cycle can assume values ​​between 0% and 100% or, alternatively, be specified as a dimensionless parameter with values ​​between 0.0 and 1.0.

[0019] The control unit is designed to vary the duty cycle within the switch-on interval in order to reduce, preferably minimize, interference that can be caused in the continuous heating mode of the cooking appliance, for example by individual peaks in the heating current frequency. Interference can be influences that are perceptible to a user and perceived as undesirable and / or influences that are prohibited by law. For example, interference could take the form of flicker. Alternatively or additionally, interference could be undesirable acoustic influences, in particular in a frequency range between 20 Hz and 20 kHz that is perceptible to the average human ear. Interference could be caused in particular by intermodulation and manifest itself in acoustically perceptible intermodulation noise."Intermodulation" refers to the sum and / or difference products of individual alternating current frequencies or their nth harmonics, where n represents an integer greater than zero. Interference can also be caused, alternatively or additionally, by the occurrence of a ripple current, i.e., an alternating current of any frequency and waveform superimposed on a direct current, resulting in an unwanted hum. Interference in this context does not include technical malfunctions and / or defects.

[0020] In this document, numerals such as "first" and "second," which precede certain terms, serve only to distinguish between objects and / or to correlate objects with each other and do not imply a total number and / or ranking of the objects. In particular, a "second object" does not necessarily imply the presence of a "first object."

[0021] "Intended" should be understood as specifically programmed, designed, and / or equipped. The fact that an object is intended for a specific function should be understood as meaning that the object fulfills and / or performs this specific function in at least one application and / or operating state.

[0022] It is further proposed that the control unit be configured to maintain at least one real conductance of at least one resonant circuit having the induction target at least substantially constant within the switch-on interval in the continuous heating operating state by varying the duty cycle. This advantageously makes it possible to provide a cooking appliance with improved electromagnetic compatibility. A "real conductance" is understood to be the inverse of a real component of an impedance.

[0023] Furthermore, it is proposed that the control unit be configured to keep at least one complex conductance of at least one resonant circuit having the induction target at least substantially constant within the switch-on interval in the continuous heating operating state by varying the duty cycle. This can advantageously further improve electromagnetic compatibility. A "complex conductance" is understood to be the inverse of an imaginary part of the impedance.

[0024] Furthermore, it is proposed that the control unit be configured to keep at least one impedance of at least one resonant circuit having the induction target at least substantially constant within the switch-on interval in the continuous heating operating state by varying the duty cycle. Such a configuration can advantageously further improve electromagnetic compatibility.

[0025] It is further proposed that the control unit be configured to vary the duty cycle during at least one first switch-on interval within a first duty cycle range, with duty cycles less than or equal to a maximum power duty cycle. Furthermore, it is proposed that the control unit be configured to vary the duty cycle during at least one second switch-on interval within a second duty cycle range, with duty cycles greater than or equal to the maximum power duty cycle. Such a configuration can advantageously improve energy efficiency.In particular, switching losses of inverter switching elements of the inverter unit can be reduced if they are arranged in a dual half-bridge configuration and the control unit varies the duty cycle during the at least one first switch-on interval within the first duty cycle range, with duty cycles less than or equal to the maximum power duty cycle, and during the at least one second switch-on interval within the second duty cycle range, with duty cycles greater than or equal to the maximum power duty cycle. With a dual half-bridge configuration of the inverter switching elements, the maximum power duty cycle corresponds to a duty cycle of 50% or 0.5. At the maximum power duty cycle, the inverter unit provides maximum power at a specific heating current frequency.

[0026] It is also proposed that the control unit be configured to continuously change the duty cycle during the switch-on interval in the continuous heating operating state. This advantageously enables reliable control of at least one operating parameter, in particular reliably maintaining the real conductance and / or the complex conductance and / or the impedance of the at least one resonant circuit having the induction target constant. In this context, "continuously changing" is understood to mean that the duty cycle is changed, in particular adjusted, at least ten times, preferably at least twenty times, more preferably at least twenty-five times, and particularly preferably at least fifty times, during the switch-on interval at constant intervals.

[0027] Furthermore, it is proposed that the control unit be configured to repetitively control and supply energy to at least one further induction target in the continuous heating operating state, and to operate the further induction target with a heating output in at least one further activation interval of the operating period. This advantageously provides a cooking appliance with a high degree of flexibility.

[0028] Furthermore, it is proposed that the control unit is provided to operate a further heating current frequency for the second induction target in the further switch-on interval of the operating period with a substantially constant further heating current frequency and to vary a further duty cycle. Such a configuration makes it possible to achieve an advantageous cooking environment with the simultaneous operation of several induction targets and while simultaneously complying with EMC standards. Furthermore, it is proposed that the control unit is provided to at least minimize intermodulation noise between the induction target and the further induction target in the continuous heating operating state. This advantageously enables simultaneous operation of at least two induction targets while complying with EMC standards.

[0029] The invention also relates to a cooking appliance, in particular a hob, comprising at least one cooking device according to one of the previously described embodiments. Such a cooking appliance is characterized in particular by the advantageous properties of the cooking device described above.

[0030] The invention further relates to a method for operating a cooking appliance, in particular an induction hob device, in particular according to one of the previously described embodiments, wherein in at least one periodic continuous heating operating state, to which at least one operating period is assigned, at least one induction target is repeatedly controlled and supplied with energy and the induction target is operated with a heating power in at least one switch-on interval of the operating period.

[0031] It is proposed that, in the continuous heating operating state, the heating current frequency be kept substantially constant during the switch-on interval of the operating period, and a duty cycle be varied. Such a configuration can provide an improved method for operating the cooking appliance with regard to control. The cooking appliance can advantageously be operated with particularly low noise and with minimal interference.

[0032] The cooking appliance device is not intended to be limited to the application and embodiment described above. In particular, the cooking appliance device may have a number of individual elements, components, and units that differs from the number stated herein to fulfill a functionality described herein.

[0033] Further advantages are shown in the following drawing description.

[0034] The drawing shows an embodiment of the invention. The drawing, the description, and the claims contain numerous features in combination. Those skilled in the art will expediently consider the features individually and combine them into further meaningful combinations.

[0035] They show:

[0036] Fig. 1 shows a cooking appliance with a cooking appliance device in a schematic representation,

[0037] Fig. 2 is a schematic electrical diagram of the cooking appliance device with a control unit, several inverter units, resonance capacitor units and induction targets,

[0038] Fig. 3 is a schematic electrical diagram of an inverter unit of the cooking appliance, a resonance capacitor unit and an induction target,

[0039] Fig. 4a is a schematic diagram showing a curve of a real conductance of an oscillating circuit having the induction target without variation of a duty cycle by the control unit and when reducing a power at the beginning and at the end of an operating period,

[0040] Fig. 4b is a schematic diagram illustrating a time course of a theoretical power provided by the inverter unit when operating a purely resistive load and a real power provided by the inverter unit when operating the induction target without variation of the duty cycle by the control unit and when reducing the power at the beginning and end of the operating period,

[0041] Fig. 4c is a schematic diagram illustrating a time course of a variation of the duty cycle by the control unit in a first switch-on interval of the operating period,

[0042] Fig. 5 is a schematic diagram of a time course of the real conductance of the at least one resonant circuit having the induction target within the first switch-on interval when the duty cycle is varied by the control unit,

[0043] Fig. 6a is a schematic diagram illustrating a curve of the real conductance of an oscillating circuit having the induction target without variation of a duty cycle by the control unit and when reducing a power at the maximum value of a rectified AC mains voltage within the operating period,

[0044] Fig. 6b is a schematic diagram illustrating a time course of a theoretical power provided by the inverter unit when operating a purely resistive load and a real power provided by the inverter unit when operating the induction target without variation of the duty cycle by the control unit and when reducing at the maximum amount of the rectified AC mains voltage within the operating period,

[0045] Fig. 6c is a schematic diagram illustrating a time course of a variation of the duty cycle by the control unit in a second switch-on interval of the operating period,

[0046] Fig. 7 is a schematic diagram of a time course of the real conductance of the at least one resonant circuit having the induction target within the second switch-on interval when the duty cycle is varied by the control unit,

[0047] Fig. 8 is a schematic diagram of a time profile of a complex conductance of the at least one resonant circuit having the induction target within the first switch-on interval when the duty cycle is varied by the control unit and

[0048] Fig. 9 is a schematic process flow diagram of a method for operating the cooking appliance device.

[0049] Figure 1 shows a schematic representation of a cooking appliance 50. In this case, the cooking appliance 50 is designed as a hob 52, specifically an induction hob.

[0050] The cooking appliance 50 has a mounting plate 80, which in this case is designed as a cooking plate of the cooking surface 52.

[0051] The cooking appliance 50 has a cooking appliance device 10. In the present case, the

[0052] Cooking appliance 10 is designed as an induction hob. Cooking appliance 10 has a control unit 12. Figure 1 shows, by way of example, three cooking utensils 66, 68, 70 placed on the support plate 80.

[0053] Figure 2 shows a schematic electrical circuit diagram of the cooking appliance device 10.

[0054] In the present embodiment, the cooking appliance 10 has four inductors 58, 60, 62, 64. Alternatively, however, the cooking appliance 10 could have any other number of inductors 58, 60, 62, 64 that is greater than or equal to one.

[0055] In an assembled state of the cooking appliance device 10, the inductors 58, 60, 62, 64 are arranged below the mounting plate 80 of the cooking appliance 50 (see Figure 1).

[0056] In an operating state of the cooking appliance 10, a first inductor 58 with a first cooking utensil 66 forms an induction target 18.

[0057] The control unit 12 is provided to repetitively control and supply with energy at least the induction target 18 in at least one periodic continuous heating operating state, to which at least one operating period 16 (cf. Figure 4a) is assigned, and to operate the induction target 18 with a heating power in at least one switch-on interval 26, 44 (cf. Figures 4c and 6c) of the operating period 16.

[0058] In this case, the operating period 16 corresponds to half the period of an AC mains voltage of a power supply network (not shown), by means of which the cooking appliance device 10 is supplied with energy in the continuous heating mode. The period of the AC mains voltage corresponds to an inverse of the mains frequency and lasts, for example, 20 ms at a mains frequency of 50 Hz, so that the operating period 16 has a duration of, for example, 10 ms.

[0059] The control unit 12 is provided to operate the induction target 18 in at least one switching-on interval 26, 44 of the operating period 16 with a substantially constant heating current frequency (not shown) and to vary a duty cycle 30 (cf. Figure 4c).

[0060] In the operating state of the cooking appliance 10, a second inductor 60 forms a first further induction target 20 with a second cooking utensil 68, a third inductor 62 forms a second further induction target 22 with a third cooking utensil 70, and a fourth inductor 64 forms a third further induction target 24 with a fourth cooking utensil 72.

[0061] The control unit 12 is provided to repetitively control and supply energy to at least one of the further induction targets 20, 22, 24 in the continuous heating operating state, and to operate the further induction target 20 with a heating output in at least one further switching-on interval (not shown) of the operating period 16. In the present case, the control unit 12 is provided to repetitively control and supply energy to the first further induction target 20, the second further induction target 22, and the third further induction target 24 in the continuous heating operating state, and to operate each of them with a heating output in at least one further switching-on interval (not shown) of the operating period 16.

[0062] The cooking appliance 10 has at least one inverter unit 74 with a first inverter switching element 76 and a second inverter switching element 78. In the present case, the cooking appliance 10 has a total of four inverter units 74, each with a first inverter switching element 76 and a second inverter switching element 78. In the present case, each of the inductors 58, 60, 62, 54 is assigned an inverter unit 74.

[0063] Of objects that exist multiple times, only one is provided with a reference symbol in the figures.

[0064] The cooking appliance 10 has at least one resonant capacitor unit 82 with a first resonant capacitor 84 and a second resonant capacitor 86. In the present case, the cooking appliance 10 has a total of four resonant capacitor units 82, each with a first resonant capacitor 84 and a second resonant capacitor 86. In the present case, each of the inverter units 74 is assigned a resonant capacitor unit 82.

[0065] The control unit 12 is provided to operate the first further induction target 20 in the further switch-on interval of the operating period 16 with a substantially constant further heating current frequency (not shown) and to vary a further duty cycle (not shown). The control unit 12 is provided to at least minimize intermodulation noise between the induction target 18 and at least one of the further induction targets 20, 22, 24 in the continuous heating operating state.The minimization of the intermodulation noise between the induction target 18 and at least one of the further induction targets 20, 22, 24 is achieved by varying the duty cycle 30 and the at least one further duty cycle, wherein the control unit 12 is provided to coordinate the variations of the duty cycle 30 and the at least one further duty cycle such that intermodulation noise between the induction target 18 and at least one of the further induction targets 20, 22, 24 is at least minimized, preferably completely prevented.

[0066] Figure 3 shows a schematic electrical circuit diagram of the inverter unit 74 of the cooking appliance 10 with the resonance capacitor unit 82 and the induction target 18.

[0067] The control unit 12 is provided to keep at least one real conductance 32 (cf. Figures 4a and 5) of at least one oscillating circuit 34 having the induction target 18 at least substantially constant within a first switch-on interval 26 by varying the duty cycle 30 in the continuous heating operating state.

[0068] In the continuous heating state, the inverter unit 74 forms the at least one resonant circuit 34 with the induction target 18 and the resonant capacitor unit 82. Within an operating period 16, i.e., during half a period of the AC mains voltage, the control unit 12 controls the first inverter switching element 76 of the inverter unit 74 to operate the induction target 18 at the substantially constant heating frequency, so that a voltage Vo drops across the inverter switching element, which corresponds to half of a bus capacitor voltage V buscorresponds to the voltage to which a bus capacitor (not shown), which is arranged electrically in parallel with the inverter unit 74, is charged at the beginning of the operating period 16. An amount of the bus capacitor voltage V bus at the beginning of the operating period corresponds to a peak value of a rectified AC mains voltage (not shown). During the operating period 16, the first inverter switching element 76 of the inverter unit 74 forms the resonant circuit 34 with the induction target 18 and the first resonant capacitor 84. A voltage V is applied across the induction target 18 during the operating period 16. RLand an alternating current l flows within the resonant circuit 34. During a further operating period (not shown), i.e. during a further half period of the mains alternating voltage, the second inverter switching element 76 of the inverter unit 74 forms a further resonant circuit (not shown) with the induction target 18 and the second resonant capacitor 86 of the resonant capacitor unit 82.

[0069] Figure 4a shows a schematic diagram illustrating a curve of the real conductance 32 of the resonant circuit 34 having the induction target 18 for the case where the duty cycle 30 does not vary in the first switch-on interval 26 and the power provided via the inverter unit 74 is reduced at the beginning and end of the operating period 16 when an amount of the rectified AC mains voltage is minimal. A time in seconds is plotted on an abscissa 54 of the diagram. A conductance in milliohms is plotted on an ordinate 56 of the diagram. -1 As can be seen from the diagram, the conductance 32 within the first switch-on interval 26, the duration of which in this case corresponds to the duration of the operating period 16, has a curved temporal progression with maximum values ​​of approximately 100 milliohms -1 and a minimum value of about 50 milliohms -1if the duty cycle 30 is not varied in the first switching interval 26.

[0070] Figure 4b shows a time curve of a theoretical power 28 provided by the inverter unit 74 during operation of a purely resistive load and a real power 38 provided by the inverter unit 74 during operation of the induction target 18 for the case where the duty cycle 30 does not vary in the first switch-on interval 26 and a power provided via the inverter unit 74 is reduced at the beginning and end of the operating period 16 when an amount of the rectified AC mains voltage is minimal. A time in seconds is plotted on an abscissa 88. A power in watts is plotted on an ordinate 90. As can be seen from the diagram in Figure 4b, the theoretical power 28 is lower than the real power 38 because inductive and capacitive reactive power losses occur in the resonant circuit 34 shown in Figure 3.The aim of the present invention is to achieve an almost purely ohmic behavior by varying the duty cycle 30 and thereby to minimize these reactive power losses within the first switch-on interval 26.

[0071] Figure 4c shows a time course of a variation of the duty cycle 30 by the

[0072] Control unit 12 in the first switch-on interval 26. On an abscissa 92 of the

[0073] A time in seconds is plotted on the diagram. A duty cycle 30 is plotted as a dimensionless parameter on an ordinate 94 of the diagram. The control unit 12 is provided to vary the duty cycle 30 during at least a first switch-on interval 26 within a first duty cycle range 40, with duty cycles 30 less than or equal to a maximum power duty cycle 42. In the present case, the control unit 12 is provided to continuously change the duty cycle 30 in the first switch-on interval 26 in the continuous heating operating state.

[0074] Figure 5 shows a schematic diagram of a time course of the real conductance 32 of at least one resonant circuit 34 having the induction target 18 (cf.

[0075] Figure 3) within the first switch-on interval 26 when the duty cycle 30 is varied by the control unit 12. A time in milliseconds is plotted on an abscissa 96 of the diagram. A conductance in milliohms is plotted on an ordinate 98 of the diagram. -1 As can be seen from the diagram, the real conductance 32 of the at least one resonant circuit 34 having the induction target 18 can be kept at least substantially constant within the first switch-on interval 26 by the variation of the duty cycle 30 shown in Figure 4c.

[0076] Figure 6a shows a schematic diagram illustrating a curve of the real conductance 32 of the resonant circuit 34 having the induction target 18 for the case where the duty cycle 30 does not vary in a second switch-on interval 44 and the power provided via the inverter unit 74 is reduced at the maximum value of the rectified AC mains voltage within the operating period 16. A time in seconds is plotted on an abscissa 100 of the diagram. A conductance in milliohms is plotted on an ordinate 102 of the diagram. -1 As can be seen from the diagram, the conductance 32 within the second switch-on interval 44 has a curve-shaped time profile with maximum values ​​of approximately 120 milliohms -1 and a minimum value of about 70 milliohms -1 if the duty cycle 30 is not varied in the second switching interval 44.

[0077] Figure 6b shows a time curve of the theoretical power 28 provided by the inverter unit 74 during operation of a purely resistive load and a real power 38 provided by the inverter unit 74 during operation of the induction target 18 for the case where the duty cycle 30 does not vary in the second switch-on interval 44 and the power provided via the inverter unit 74 is reduced at the maximum amount of the rectified AC mains voltage within the operating period 16. A time in seconds is plotted on an abscissa 104. A power in watts is plotted on an ordinate 106. As can be seen from the diagram in Figure 6b, the theoretical power 28 is much lower than the real power 38, since inductive and capacitive reactive power losses again occur in the resonant circuit 34 shown in Figure 3.

[0078] Figure 6c shows a temporal progression of a variation of the duty cycle 30 by the control unit 12 in the second switch-on interval 44. A time in seconds is plotted on an abscissa 108 of the diagram. A duty cycle is plotted as a dimensionless parameter on an ordinate 110 of the diagram. The control unit 12 is provided to vary the duty cycle 30 during the at least one second switch-on interval 44 within a second duty cycle range 46, with duty cycles greater than or equal to the maximum power duty cycle 42. In the present case, the control unit 12 is provided to continuously change the duty cycle 30 in the second switch-on interval 44 in the continuous heating operating state.

[0079] By alternately varying the duty cycle 30 within the first duty cycle range 40 (cf. Figure 4c) in the first switch-on interval 26 and within the second duty cycle range 46 in the second switch-on interval 44, switching losses in the inverter switching elements 76, 78, which are arranged in a dual half-bridge configuration (cf. Figure 3), can advantageously be reduced, wherein in the periodic continuous heating operating state, the heating power can be kept constant, since the heating powers that can be achieved with the duty cycles 30 within the first duty cycle range 40, which are less than or equal to the maximum power duty cycle 42, are equivalent to the heating powers that can be achieved with the duty cycles 30 within the second duty cycle range 46, which are greater than or equal to the maximum power duty cycle 42.

[0080] Figure 7 shows a schematic diagram of a time course of the real conductance 32 of at least one resonant circuit 34 having the induction target 18 (cf.

[0081] Figure 3) within the second switch-on interval 44 when the duty cycle 30 is varied by the control unit 12. A time in milliseconds is plotted on an abscissa 112 of the diagram. A conductance in milliohms is plotted on an ordinate 114 of the diagram. 1 As can be seen from the diagram, the real conductance 32 of the at least one resonant circuit 34 having the induction target 18 can be kept at least substantially constant within the second switch-on interval 44 by the variation of the duty cycle 30 shown in Figure 6c.

[0082] The control unit 12 is provided to keep at least one complex conductance 36 of the at least one resonant circuit 34 having the induction target 18 (see Figure 3) at least substantially constant within the first switch-on interval 26 (see Figure 4c) by varying the duty cycle 30 in the continuous heating operating state. Figure 8 shows a schematic diagram of a time profile of the complex conductance 36 of the at least one resonant circuit 34 having the induction target 18 within the first switch-on interval 26 when the duty cycle 30 (see Figure 4c) is varied by the control unit 12. A time in milliseconds is plotted on an abscissa 116 of the diagram. A conductance in milliohms is plotted on an ordinate 118 of the diagram. -1As can be seen from the diagram, the complex conductance 36 of the at least one resonant circuit 34 having the induction target 18 is kept at least substantially constant within the first switch-on interval 26 by varying the duty cycle 30 as shown in Figure 4c.

[0083] The control unit 12 is further provided to keep at least one impedance (not shown) of the at least one resonant circuit 34 having the induction target 18 at least substantially constant within the first switch-on interval 26 by varying the duty cycle 30 in the continuous heating operating state. Since the real conductance 32 (cf.Figure 5) represents the inverse of the real part of the impedance of the at least one resonant circuit 34 having the induction target 18 and the complex conductance 36 represents the inverse of the imaginary part of the impedance of the at least one resonant circuit 34 having the induction target 18 and both the real conductance 32 and the complex conductance 36 are kept at least substantially constant by varying the duty cycle 30 within the first switch-on interval 26, the impedance of the at least one resonant circuit 34 having the induction target 18 also remains at least substantially constant within the first switch-on interval 26 due to the variation in the duty cycle 30.

[0084] Figure 9 shows a schematic process flow diagram of a method for operating the cooking appliance 10. The method comprises at least two method steps 120, 122. In a first method step 120 of the method, in the at least one periodic continuous heating operating state, to which the at least one operating period 16 is assigned, at least one induction target 18 is repeatedly controlled and supplied with energy, and the induction target 18 is operated with a heating power in at least one switch-on interval 26, 44 of the operating period 16, wherein the heating current frequency is kept substantially constant. In a second method step 122 of the method, in the continuous heating operating state, the duty cycle 30 is varied in at least one of the switch-on intervals 26, 44 of the operating period 16.

[0085] Reference symbol

[0086] 10 Cooking appliance device

[0087] 12 Control unit

[0088] 16 operating period

[0089] 18 Induction target

[0090] 20 first further induction target

[0091] 22 second additional induction target

[0092] 24 third additional induction target

[0093] 26 first switch-on interval

[0094] 28 theoretical performance

[0095] 30 duty cycle

[0096] 32 real conductance

[0097] 34 resonant circuit

[0098] 36 complex conductance

[0099] 38 real performance

[0100] 40 duty cycle range

[0101] 42 Maximum power duty cycle

[0102] 44 second switch-on interval

[0103] 46 second duty cycle range

[0104] 50 cooking appliance

[0105] 52 hob

[0106] 54 Abscissa

[0107] 56 ordinates

[0108] 58 first inductor

[0109] 60 second inductor

[0110] 62 third inductor

[0111] 64 fourth inductor

[0112] 66 first cooking utensils

[0113] 68 second cooking utensil third cooking utensil fourth cooking utensil

[0114] Inverter unit first inverter switching element second inverter switching element

[0115] mounting plate

[0116] Resonance capacitor unit first resonance capacitor second resonance capacitor

[0117] abscissa

[0118] ordinate

[0119] abscissa

[0120] ordinate

[0121] abscissa

[0122] ordinate

[0123] abscissa

[0124] ordinate

[0125] abscissa

[0126] ordinate

[0127] abscissa

[0128] ordinate

[0129] abscissa

[0130] ordinate

[0131] abscissa

[0132] Ordinate first process step second process step

Claims

Claims Cooking appliance device (10), in particular induction hob device, with at least one control unit (12) which is provided to repetitively control and supply with energy at least one induction target (18) in at least one periodic continuous heating operating state, to which at least one operating period (16) is assigned, and to operate the induction target (18) with a heating power in at least one switch-on interval (26, 44) of the operating period (16), characterized in that the control unit (12) is provided to operate the induction target (18) in the switch-on interval (26, 44) of the operating period (16) with a substantially constant heating current frequency and to vary a duty cycle (30).Cooking appliance device (10) according to claim 1, characterized in that the control unit (12) is provided to keep at least one real conductance (32) of at least one oscillating circuit (34) having the induction target (18) at least substantially constant within the switch-on interval (26, 44) by varying the duty cycle (30) in the continuous heating operating state. Cooking appliance device (10) according to claim 1 or 2, characterized in that the control unit (12) is provided to keep at least one complex conductance (36) of at least one oscillating circuit (34) having the induction target (18) at least substantially constant within the switch-on interval (26, 44) by varying the duty cycle (30). Cooking appliance device (10) according to one of the preceding claims, characterized in that the control unit (12) is provided to keep at least one impedance of at least one resonant circuit (34) having the induction target (18) at least substantially constant within the switch-on interval (26, 44) by varying the duty cycle (30). Cooking appliance device (10) according to one of the preceding claims, characterized in that the control unit (12) is provided to vary the duty cycle (30) during at least a first switch-on interval (26) within a first duty cycle range (40), with duty cycles (30) less than or equal to a maximum power duty cycle (42).Cooking appliance device (10) according to claim 5, characterized in that the control unit (12) is provided to vary the duty cycle (30) during at least one second switch-on interval (44) within a second duty cycle range (46), with duty cycles greater than or equal to the maximum power duty cycle (42). Cooking appliance device (10) according to one of the preceding claims, characterized in that the control unit (12) is provided to continuously change the duty cycle (30) in the switch-on interval (26, 44) in the continuous heating operating state. Cooking appliance device (10) according to one of the preceding claims, characterized in that the control unit (12) is provided to repetitively control and supply with energy at least one further induction target (20, 22, 24) in the continuous heating operating state and to operate the further induction target (20, 22, 24) with a heating power in at least one further switch-on interval of the operating period (16).Cooking appliance (10) according to claim 8, characterized in that the control unit (12) is provided to operate the further induction target (20, 22, 24) in the further switch-on interval (44) of the operating period (16) with a substantially constant further heating current frequency in the continuous heating operating state and to vary a further duty cycle. Cooking appliance (10) according to claim 8 or 9, characterized in that the control unit (12) is provided to at least minimize intermodulation noise between the induction target (18) and the further induction target (20, 22, 24) in the continuous heating operating state. Cooking appliance (50), in particular a hob (52), comprising at least one cooking appliance (10) according to one of the preceding claims.Method for operating a cooking appliance (10), in particular an induction hob device, in particular according to one of claims 1 to 10, wherein in at least one periodic continuous heating operating state, to which at least one operating period (16) is assigned, at least one induction target (18) is repetitively controlled and supplied with energy and the induction target (18) is operated with a heating power in at least one switch-on interval (26, 44) of the operating period (16), characterized in that in the continuous heating operating state, a heating current frequency is kept substantially constant in the switch-on interval (26, 44) of the operating period (16) and a duty cycle (30) is varied.

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