Domestic appliance device

Abstract

The invention relates to a domestic appliance device (10a-e), in particular a cooking appliance device, comprising at least one control unit (12a-e) which is provided to control at least one induction target (14a-e) repetitively with a switching frequency (16a-e) and to supply same with power. According to the invention, in order to provide a generic device with improved efficiency, the control unit (12a-e), in an operating state, modulates the switching frequency (16a-e) within a modulation period (18a-e) which corresponds to an integer multiple of a half period duration (20a-e) of a mains AC voltage (22a-e), by means of at least one frequency modulation.

Description

[0001] The invention relates to an induction cooktop according to the preamble of claim 1 and a method for operating an induction cooktop according to the preamble of claim 9.

[0002] A household appliance with a control unit is already known from the prior art. This unit is designed to repeatedly control and energize an induction target using a switching frequency. To minimize electromagnetic interference, the control unit modulates the switching frequency within a modulation period, which corresponds to a maximum of half a period of a mains AC voltage, using frequency modulation. Due to the very short duration of the modulation period, performing the frequency modulation is computationally intensive, necessitating the use of high-performance, application-specific integrated circuits and thus increasing costs. Documents WO 2018 / 116050 A1, CN 101 848 566 B, FR 2 726 704 A1, US 2010 / 237065 A1, and JP 2010 080359 A disclose induction cooktops according to the prior art.

[0003] The object of the invention is, in particular but not limited to, providing a generic device with improved efficiency characteristics. This object is achieved according to the invention by the features of claims 1 and 9, while advantageous embodiments and further developments of the invention can be found in the dependent claims.

[0004] The invention relates to a household appliance device, in particular a cooking appliance device, with at least one control unit which is designed to repeatedly control and supply energy to at least one induction target at a switching frequency.

[0005] It is proposed that, in an operating state, the control unit modulates the switching frequency within a modulation period, which corresponds to an integer multiple of half a period of a mains AC voltage, by means of at least one frequency modulation.

[0006] Such a design allows for the provision of a household appliance of this type with improved characteristics regarding safe and / or convenient operation, in particular quiet operation and / or compliance with EMC standards and / or flicker conformity, while increasing efficiency. Preferably, the spectral power density of the switching frequency can be reduced by means of frequency modulation. Preferably, flicker can be avoided, at least to a large extent, and in particular substantially completely, according to a flicker standard, in particular according to DIN EN 61000-3-3 and / or IEC 1000-3-3, especially by advantageous control of single or multiple induction targets.Furthermore, adverse acoustic stress on the operator can be avoided, resulting in a high level of user comfort and a positive user experience, particularly with regard to acoustic quality. Additionally, the requirements for an EMC filter can be advantageously reduced, thereby lowering material costs. By increasing the modulation period compared to the prior art and making it an integer multiple of half the period of the mains AC voltage, the temporary computational effort required for frequency modulation can also be advantageously reduced. This makes it conceivable that, for many household appliance applications, an application-specific integrated circuit (ASIC chip) can be replaced by simpler and more cost-effective circuits.The resulting cost savings can, in turn, allow users to be provided with particularly inexpensive household appliances with the aforementioned advantageous features regarding safety and / or comfort.

[0007] The term "household appliance device," particularly "cooking appliance device," advantageously "cooktop device," and especially advantageously "induction cooktop device," refers to at least a part, particularly a subassembly, of a household appliance, especially a cooking appliance, advantageously a cooktop, and particularly advantageously an induction cooktop. Advantageously, the household appliance comprising the household appliance device is a cooking appliance. A household appliance designed as a cooking appliance could, for example, be an oven and / or a microwave and / or a grill and / or a steam cooker. Preferably, a household appliance designed as a cooking appliance is a cooktop, and particularly preferably an induction cooktop.

[0008] A "control unit" is defined as an electronic unit that is at least partially integrated into the household appliance and is designed to repeatedly control and energize at least one induction target at a switching frequency. Preferably, the control unit includes at least one inverter unit for controlling and energizing the at least one induction target. This inverter unit may be configured, in particular, as a resonant inverter and / or a dual half-bridge inverter. The inverter unit preferably comprises at least two switching elements that can be individually controlled by the control unit. A "switching element" is defined as an element designed to establish and / or disconnect an electrically conductive connection between two points, in particular contacts of the switching element.Preferably, the switching element has at least one control contact via which it can be switched. Preferably, the switching element is 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 that the switching element is designed as a mechanical and / or electromechanical switching element, in particular as a relay. Preferably, the control unit comprises a processing unit and, in particular, in addition to the processing unit, a storage unit with at least one control program stored therein, which is intended to be executed by the processing unit.

[0009] An "induction target" is defined as an inductor or a plurality of inductors, which is / are part of the household appliance and which can be jointly controlled by the control unit, with at least one receiving element positioned above the inductor and / or the plurality of inductors, which may in particular be part of an external unit. An "inductor" is understood here to be an element that has at least one induction coil and is designed to supply energy, in particular in the form of an alternating magnetic field, to the at least one receiving element during operation. In the case of a household appliance designed as an induction cooker, an induction target may be designed to supply energy to the receiving element for the purpose of heating.In this case, the receiving element could, for example, be designed as a cooking vessel and include at least one secondary coil as a receiving element for receiving the energy provided by the inductor. Alternatively or additionally, the receiving element could also be designed as a metallic heating element, in particular as an at least partially ferromagnetic heating element, for example as a ferromagnetic base of a cooking vessel, in which, during operation, eddy currents and / or remagnetization effects are induced by the inductor, which are at least partially converted into heat. The plurality of inductors can be arranged in a matrix, with the matrix-arranged inductors forming a variable cooking surface. Preferably, at least one inverter unit is assigned to each of the induction targets.

[0010] According to the invention, the control unit continuously modulates the switching frequency during operation within an operating period, which corresponds to at least one modulation period, preferably a plurality of successive modulation periods. It is conceivable that the operating period of the induction target corresponds to the entire operating time of the household appliance, i.e., a period during which the household appliance is continuously operated. It is also conceivable that the control unit operates several induction targets and / or several inductors of the induction target alternately in a time-division multiplex operation. In time-division multiplex operation, the operating period corresponds to the duration during which the control unit continuously and without interruption simultaneously drives and energizes a specific induction target or a plurality of specific induction targets at the switching frequency.Preferably, the control unit controls at least one inductor of the induction target, to generate an alternating magnetic field and to supply electrical energy, with an alternating electric current, the switching frequency of which is preferably in a range of 20 kHz to 150 kHz and particularly preferably in a range of 30 kHz to 75 kHz.

[0011] A "modulation period" is defined as the time span during which the control unit modulates the switching frequency using at least one frequency modulation. The modulation period is an integer multiple of half the period of a mains AC voltage, where the period of the mains AC voltage is the reciprocal of the mains frequency. In Europe, mains AC voltage is typically supplied at a mains frequency of 50 Hz, so half a period of the mains AC voltage is 10 ms in this case. In cases where the household appliance is supplied with mains AC voltage at a mains frequency other than 50 Hz, the control unit is designed to adjust the duration of the modulation period to the correspondingly altered period of the mains AC voltage and to select it as a corresponding integer multiple of half the altered period.

[0012] Frequency modulation refers to a modulation method by which the control unit varies the switching frequency. Preferably, frequency modulation includes at least one method known as "frequency spreading" or "spread spectrum clocking." Frequency modulation is intended to reduce, and preferably minimize, interference that can occur during the operation of the household appliance, for example, due to individual peaks in the switching frequency. Interference can be perceptible to a user and perceived as undesirable, and / or prohibited by law. For example, interference could manifest as flicker.Alternatively or additionally, interference could consist of unwanted acoustic influences, particularly in the frequency range perceptible to the average human ear, between 20 Hz and 20 kHz. Interference could be caused, in particular, by intermodulation and manifest itself as audibly perceptible noise. "Intermodulation" is defined as sum and / or difference products of individual alternating current frequencies or their nth harmonics, where n represents an integer greater than zero. Furthermore, 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, manifesting as an unwanted hum.In this context, disruptive influences do not include technical malfunctions, defects and / or other undesirable phenomena, such as uneven heat distribution.

[0013] The term "intended" means specifically programmed, designed, and / or equipped. The fact that an object is intended for a specific function means that the object fulfills and / or executes this specific function in at least one application and / or operating state.

[0014] Furthermore, it is proposed that the modulation period comprises at least two modulation intervals, which are particularly distinct from one another and each correspond to an integer multiple of half a period of an AC mains voltage. This advantageously allows for particularly precise frequency modulation. Preferably, the modulation period comprises a plurality of modulation intervals, which are particularly distinct from one another and each correspond to an integer multiple of half a period of an AC mains voltage. It would be conceivable for the at least two modulation intervals to correspond to different multiples of half a period of the AC mains voltage. For example, a first modulation interval could correspond to twice and a second modulation interval to four times half a period of the AC mains voltage.Preferably, all modulation intervals within a modulation period correspond to the same multiple, particularly preferably twice, half the period of the AC mains voltage. The modulation intervals can differ from each other, for example, with respect to the magnitude and / or sign of a variation in the switching frequency. For example, the control unit could vary the switching frequency by a certain initial amount in the first modulation interval and vary the switching frequency by a further amount in a subsequent modulation interval, which is, for example, greater or less than the initial amount and / or has the opposite sign to the initial amount.

[0015] Furthermore, it is proposed that the control unit modulates the switching frequency in its operating state using at least one predefined modulation profile. This allows for the targeted reduction of interference. It also advantageously reduces the computational effort required by the control unit. The predefined modulation profile can be understood as a fundamental temporal pattern of frequency modulation within a modulation period, which is stored in the control unit's memory. For example, the predefined modulation profile could define a frequency range within which the control unit modulates the switching frequency during the modulation period. For instance, the predefined modulation profile could include a maximum and / or minimum switching frequency that the control unit cannot exceed or fall below.Alternatively or additionally, the modulation profile could, for example, include a maximum and / or minimum percentage variation of an output switching frequency. Furthermore, it is conceivable that the modulation profile comprises specific switching frequency values, particularly those determined experimentally, and especially specific switching frequency values ​​of individual, and in particular all, modulation intervals of the modulation period. Preferably, a plurality of different predefined modulation profiles are stored in the memory unit of the control unit, which can be automatically recalled by the control unit, in particular based on a user's selection of a specific operating mode and / or a target power supplied via the induction target.The phrase "the control unit modulates the switching frequency based on at least one predefined modulation profile" means that the control unit at least considers the predefined modulation profile in relation to the frequency modulation. The predefined modulation profile can serve as a template for the frequency modulation to be performed by the control unit, whereby the control unit can modify the frequency modulation based on the predefined modulation profile and, in particular, adapt it to an individual operating situation, for example, to a specific operating mode and / or to a number of induction targets to be operated simultaneously and / or to a set power selected by a user, or the like.

[0016] The modulation profile could, for example, be a rectangular or sawtooth profile and exhibit discontinuities with larger jumps in switching frequency.

[0017] According to the invention, it is proposed that the modulation profile can be described by an essentially continuous mathematical function. This advantageously reduces, and preferably minimizes, the occurrence of flicker. Since changes in switching frequencies in electrical components are discrete and therefore cannot occur in infinitesimally small steps, as would be required according to a strict mathematical definition of continuity, the at least essentially continuous modulation profile is considered continuous in this context within the framework of a resolution of the switching frequency, i.e., a minimum step of change between two immediately successive switching frequencies.Preferably, the minimum step between two immediately successive switching frequencies of the modulation profile, which can be described by a substantially continuous switching frequency, is at least 1 Hz, advantageously at least 2 Hz, particularly advantageously at least 4 Hz, and at most 8 Hz.

[0018] Furthermore, it is proposed that the modulation profile exhibit at least a section-by-section linear response within the modulation period. Such a section-by-section linear modulation profile advantageously reduces, and preferably minimizes, interference during the operation of the household appliance, such as acoustic noise or the like. "At least a section-by-section linear response" here means that the modulation profile includes at least one section consisting of a plurality of at least three consecutive modulation intervals, in which the switching frequency is changed by the control unit by the same amount each time. For example, the modulation period could include a section consisting of at least three consecutive modulation intervals in which the control unit increases the switching frequency by 1 Hz each time.The modulation profile can have several sections, each with a linear progression, whereby the linear sections could have different slopes relative to each other. For example, the control unit could increase the switching frequency in a first linear section of the modulation profile, consisting of at least three consecutive modulation intervals, by 1 Hz in each of the modulation intervals, and in a subsequent second linear section of the modulation profile, consisting of at least three further consecutive modulation intervals, increase it by 2 Hz in each of the modulation intervals.

[0019] Furthermore, it is proposed that the modulation profile exhibit at least a piecewise exponential curve within the modulation period. Such a piecewise exponential modulation profile advantageously reduces, and preferably minimizes, interference during the operation of the household appliance, such as acoustic noise or the like. Here, "at least a piecewise exponential curve" means that the modulation profile has a plurality of at least three consecutive modulation intervals, in which the switching frequency is changed by the control unit by an amount that can be described by an exponential function.For example, the modulation period could include a section consisting of at least three consecutive modulation intervals, in which the control unit increases the switching frequency by 2 Hz in the first of the consecutive modulation intervals, by 4 Hz in the second of the consecutive modulation intervals, and by 8 Hz in the third of the consecutive modulation intervals.

[0020] Furthermore, it is proposed that the modulation profile be at least section-wise mirror-symmetric within the modulation period. This advantageously reduces the occurrence of interference effects, particularly flicker. Moreover, it allows for particularly precise adjustment of the desired target power of the induction source. The at least section-wise mirror-symmetric modulation profile could, for example, have a first section in which the switching frequency exhibits a curve, such as linear or exponential, which can be described by a first mathematical function, and a second section immediately following the first, which can be described by a second mathematical function that can be represented by reflection across an axis of symmetry.

[0021] Furthermore, it is proposed that the control unit be designed to vary the modulation profile based on at least one parameter relating to the induction target. This allows the frequency modulation to be advantageously adapted to an individual operating situation. It is conceivable that the control unit includes at least one sensor unit for detecting the parameter relating to the induction target. The parameter relating to the induction target could, for example, include the temperature of the induction target and / or a near-area of ​​the induction target and / or the operating time of the induction target, or the like. In the case of a household appliance designed as an induction cooktop, for example, it would be conceivable that the control unit could vary the modulation profile based on a measured temperature in a near-area of ​​the induction target, such as on a cooktop element.Preferably, the parameter relating to the induction target is an electrical parameter of the induction target and / or at least of a component connected to the induction target in at least one electrical circuit. The electrical parameter relating to the induction target could, for example, include an inductance and / or an electrical resistance and / or an impedance and / or a capacitance and / or an electrical voltage and / or current and / or an electrical power and / or a resonant frequency, or the like. In an advantageous embodiment, it is proposed that the parameter includes at least one electrical conductance of the induction target. This allows a desired target power of the induction target to be set with particular precision. Preferably, the control unit varies the modulation profile such that the electrical conductance of the induction target remains constant on average over the modulation period.The electrical conductance of the induction target can be a real conductance and / or a complex conductance of the induction target.

[0022] Furthermore, it is proposed that the control unit, in its operating state, additionally modulates the switching frequency within an intermediate modulation period, which corresponds to a maximum of half the period of the mains AC voltage, by means of at least one further frequency modulation. This can advantageously reduce and preferably minimize the occurrence of interference effects, which can be caused in particular by harmonics of an AC current in the supply network.

[0023] The invention further relates to a method for operating a household appliance, in particular a cooking appliance, with at least one induction target that can be controlled with a switching frequency.

[0024] It is proposed that the switching frequency be modulated within a modulation period, which corresponds to an integer multiple of half a period of a mains AC voltage, by means of at least one frequency modulation. Such a design allows the household appliance to be operated with particular efficiency. Furthermore, the household appliance can be operated with particular safety and / or convenience, especially quietly and in compliance with EMC and flicker standards.

[0025] The household appliance device is not to be limited to the application and embodiment described above. In particular, the household appliance device may, to fulfill a function described herein, have a different number of individual elements, components, and units than specified herein.

[0026] Further advantages become apparent from the following description of the drawings. The drawings illustrate five exemplary embodiments of the invention. The drawings, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and combine them into meaningful further combinations.

[0027] They show: Fig. 1 a schematic representation of a household appliance with a household appliance device comprising an induction target and a control unit, Fig. 2 a schematic electrical circuit diagram of the household appliance with the household appliance device, Fig. 3 a schematic diagram to represent a modulation period within which the control unit modulates a switching frequency, Fig. 4 a schematic diagram to represent a modulation profile according to which the control unit modulates the switching frequency, Fig. 5 another embodiment of a modulation profile according to which a control unit of a household appliance device modulates a switching frequency, in a schematic diagram, Fig. 6 another embodiment of a modulation profile according to which a control unit of a household appliance device modulates a switching frequency, in a schematic diagram, Fig.Figure 7 shows a further embodiment of a modulation profile by which a control unit of a household appliance modulates a switching frequency, in two schematic diagrams, and Figure 8 shows a further embodiment of a modulation profile by which a control unit of a household appliance modulates a switching frequency, in two schematic diagrams.

[0028] Figure 1 Figure 40a shows a household appliance 40a with a household appliance device 10a. The household appliance 40a is designed as an induction cooktop. The household appliance device 10a has a control unit 12a and an induction target 14a.

[0029] The control unit 12a is designed to repeatedly control the induction target 14a with a switching frequency 16a (see below). Fig 3 ) to control and supply with energy.

[0030] Figure 2Figure 1 shows a schematic electrical circuit diagram of the household appliance 40a. The household appliance 40a is connected to a mains AC voltage source 34a. The mains AC voltage source 34a provides a mains AC voltage 22a or a mains AC current 36a with a period of 46a. The household appliance 40a has an EMC filter unit 38a, which is electrically connected to the mains AC voltage source 34a. The household appliance has a rectifier unit 42a, which is electrically connected to the mains AC voltage source 34a via the EMC filter unit 38a. The rectifier unit 42a is designed to convert the mains AC voltage 22a into a periodically pulsating DC voltage 44a, the period of which corresponds to half a period 20a of the mains AC voltage 22a.

[0031] The control unit 12a is designed to repeatedly control and energize the induction target 14a at a switching frequency 16a. The control unit 12a comprises an inverter unit 48a. The inverter unit 48a is electrically connected to the rectifier unit 42a of the household appliance 40a. In an operating state of the household appliance 10a, the inverter unit 48a of the control unit 12a converts the DC voltage 44a provided by the rectifier unit 12a of the household appliance 40a into a supply voltage 50a at a switching frequency 16a through a multitude of successive switching operations, each lasting one switching period 52a. In an operating state of the household appliance 10a, the control unit 12a supplies the induction target 14a with electrical energy in the form of a supply current 54a.

[0032] In Figure 3A diagram is shown schematically representing a modulation period 18a. Time is plotted on the abscissa 56a of the diagram. The switching frequency 16a and the supply current 54a are plotted on the ordinate 58a. In its operating state, the control unit 12a modulates the switching frequency 16a within a modulation period 18a by means of frequency modulation. The modulation period 18a corresponds to an integer multiple of half the period 20a of the AC mains voltage 22a. Averaged over the modulation period 28a, the switching frequency 16a corresponds to an average switching frequency 60a.

[0033] Figure 4 Figure 1 shows a diagram illustrating a modulation profile 28a within the modulation period 18a. Time is plotted on the abscissa 62a of the diagram. The switching frequency 16a is plotted on the ordinate 64a.

[0034] The modulation period 18a comprises a plurality of successive modulation intervals 24a, 26a, each corresponding to an integer multiple of half the period 20a of the mains AC voltage 22a. In the Figure 4 Two of the modulation intervals 24a and 26a are shown as examples. Within modulation interval 24a, the switching frequency 16a increases. Within modulation interval 26a, the switching frequency 16a decreases.

[0035] In its operating state, the control unit 12a modulates the switching frequency 16a according to the predefined modulation profile 28a. The modulation profile 28a can be described by an essentially continuous mathematical function. Within the modulation period 18a, the modulation profile 28a exhibits at least a piecewise linear response. Within a first section 68a of the modulation period 18a, the modulation profile 28a exhibits a linear and essentially continuous response with an increasing switching frequency 16a. Within a second section 70a, the modulation profile 28a exhibits a linear and essentially continuous response with a decreasing switching frequency 16a. The modulation profile 28a is at least piecewise mirror-symmetric.In the present case, the modulation profile 28a is mirror-symmetric with respect to an axis of symmetry 66a, so that the course of the modulation profile 28a in the first section 68a by reflection across the axis of symmetry 66a results in the course of the modulation profile 28a in the second section 70a.

[0036] After the modulation period 18a has elapsed, this is repeated again and the control unit 12a modulates the switching frequency 16a again based on the modulation profile 28a.

[0037] In a method for operating the household appliance device 10a, the switching frequency 16a is modulated within the modulation period 18a, which corresponds to an integer multiple of half a period 20a of the mains alternating voltage 22a, by means of frequency modulation.

[0038] In the Figures 5 to 8Four further embodiments of the invention are shown. The following descriptions are essentially limited to the differences between the embodiments, whereby with regard to components, features and functions that remain the same, reference is made to the description of the embodiment of the Figures 1 to 4 Reference can be made to. To distinguish the embodiments, the letter a in the reference numerals of the embodiment is used in the Figures 1 to 4 by the letters b to e in the reference numerals of the exemplary embodiments of the Figures 5 to 8 replaced. With regard to identically designated components, especially those with the same reference numerals, reference can generally also be made to the drawings and / or the description of the embodiment of the Figures 1 to 4 be referred.

[0039] Figure 5Figure 1 shows a diagram illustrating a modulation profile 28b, which is used by a control unit 12b of a household appliance 10b for frequency modulation of a switching frequency 16b. Time is plotted on the abscissa 62b of the diagram. A switching frequency 16b is plotted on the ordinate 64b of the diagram.

[0040] The household appliance device 10b differs from the household appliance device 10a of the previous embodiment essentially with regard to the modulation profile 28b used by the control unit 12b for frequency modulation. In an operating state of the household appliance device 10b, the control unit 12b modulates the switching frequency 16b based on the modulation profile 28b by means of frequency modulation within a modulation period 18b, which corresponds to an integer multiple of half a period 20b of a mains AC voltage 22b.

[0041] The modulation profile 28b can be described by a mathematical function that is at least essentially continuous. Within the modulation period 18b, the modulation profile 28b exhibits a linear progression, at least piecewise. Within a first subsection 72b of a first section 68b of the modulation period 18b, the modulation profile 28b exhibits a linear and essentially continuous progression with an increasing switching frequency 16b. Within a second subsection 74b of the first section 68b of the modulation period 18b, the modulation profile 28b exhibits a linear and essentially continuous progression with a shallower increase in the switching frequency 16b compared to the first subsection 72b.Within a third subsection 76b of the first section 68b of the modulation period 18b, the modulation profile 28b has a linear and essentially continuous course with a flatter increase in the switching frequency 16b compared to the second subsection 74b.

[0042] The modulation profile 28b is at least partially mirror-symmetric. In this case, the modulation profile 28b is mirror-symmetric with respect to an axis of symmetry 66b, such that the course of the modulation profile 28b in the first section 68b, reflected across the axis of symmetry 66b, results in a course of the modulation profile 28b in a second section 70b.

[0043] Figure 6Figure 1 shows a diagram illustrating a modulation profile 28c, which is used by a control unit 12c of a household appliance 10c for frequency modulation of a switching frequency 16c. Time is plotted on the abscissa 62c of the diagram. A switching frequency 16c is plotted on the ordinate 64c of the diagram.

[0044] The household appliance device 10c differs from the household appliance devices 10a and 10b of the preceding embodiments essentially with regard to the modulation profile 28c used by the control unit 12c for frequency modulation. In an operating state of the household appliance device 10c, the control unit 12c modulates the switching frequency 16c based on the modulation profile 28c by means of frequency modulation within a modulation period 18c, which corresponds to an integer multiple of half a period 20c of a mains AC voltage 22c.

[0045] The modulation profile 28c can be described by a mathematical function that is at least essentially continuous. Within the modulation period 18c, the modulation profile 28c exhibits at least a piecewise exponential curve. Within a first section 68c of the modulation period 18c, the modulation profile 28c exhibits an essentially continuous curve with an exponentially increasing switching frequency 16b. Within a second section 70c of the modulation period 18c, the modulation profile 28c exhibits an essentially continuous curve with an exponentially decreasing switching frequency 16c.

[0046] The modulation profile 28c is at least section-wise mirror-symmetric. In this case, the modulation profile 28c is mirror-symmetric with respect to an axis of symmetry 66c, such that the course of the modulation profile 28c in the first section 68c, reflected across the axis of symmetry 66c, results in a course of the modulation profile 28c in a second section 70c.

[0047] Figure 7 Figure 1 shows two diagrams illustrating a modulation profile 28d, which is used by a control unit 12d of a household appliance 10d for frequency modulation of a switching frequency 16d. A time is plotted on the abscissa 62d of the lower diagram. A switching frequency 16d is plotted on the ordinate 64d of the lower diagram. A time is plotted on the abscissa 78d of the upper diagram. A power 82d is plotted on the ordinate 80d of the upper diagram.

[0048] The household appliance device 10d differs from the household appliance devices 10a-c of the preceding embodiments essentially with regard to the modulation profile 28d used by the control unit 12d for frequency modulation. In an operating state of the household appliance device 10b, the control unit 12d controls an induction target 14d of the household appliance device 10d with the switching frequency 16d and modulates this on the basis of the modulation profile 28d by means of frequency modulation within a modulation period 18d, which corresponds to an integer multiple of half a period 20d of a mains AC voltage 22d.

[0049] The control unit 12d is designed to vary the modulation profile 28d based on at least one parameter 30d relating to the induction target 14d. In the present embodiment, the parameter 30d relating to the induction target 14d is a target power set by a user, which is to be provided by the induction target 14d. A general course of the modulation profile 28d is at least substantially continuous, piecewise linear, and can be considered the inverse of a general course of the modulation profile 28b (cf. Fig. 5Based on the parameter 30d relating to the induction target 14d, the control unit 12d varies a frequency range 84d of the modulation profile 28d in an operating state such that the power curve 82d shown in the upper diagram results. Due to the frequency modulation of the switching frequency 16d, the power 82d changes and exhibits a surplus 86d in some sections and a deficit 88d in others, so that the power 82d, considered over the modulation period 18d, corresponds on average to the target power set by the user.

[0050] Figure 8Figure 1 shows two diagrams illustrating a modulation profile 28e, which is used by a control unit 12e of a household appliance 10e for frequency modulation of a switching frequency 16e. A time is plotted on the abscissa 62e of the lower diagram. The switching frequency 16e is plotted on the ordinate 64e of the lower diagram. A time is plotted on the abscissa 78e of the upper diagram. An electrical conductance 90e is plotted on the ordinate 80e of the upper diagram.

[0051] The household appliance device 10e differs from the household appliance device 10d of the previous embodiment with respect to a parameter 30e relating to an induction target 14e, which the control unit 12e uses as the basis for varying the modulation profile 28e. The parameter 30e comprises at least one electrical conductance of the induction target 14e. In this case, the parameter 30e relating to the induction target 14e is an average actual conductance of the induction target 14e. Based on the parameter 30e relating to the induction target 14e, the control unit 12e varies the modulation profile 28e in an operating state such that the course of the electrical conductance 90e shown in the diagram above results. Due to the frequency modulation of the switching frequency 16e, the electrical conductance 90e changes and exhibits a section-by-section excess 86e and a section-by-section deficit 88e.The control unit 12d varies the modulation profile 28e in such a way that the electrical conductance 90e is constant on average over the modulation period 18e.

[0052] In an operating state of the household appliance device 10e, the control unit 12e controls an induction target 14e of the household appliance device 10e with the switching frequency 16e and modulates it according to the modulation profile 28e by means of frequency modulation within a modulation period 18e, which corresponds to an integer multiple of half a period 20e of a mains AC voltage 22e.

[0053] Household appliance device 10e differs from household appliance devices 10a-d in that the control unit 12e, in its operating state, additionally modulates the switching frequency 16e within an intermediate modulation period 32e, which corresponds to a maximum of half the period 20e of the mains AC voltage 22e, by means of at least one further frequency modulation. In addition to the frequency modulation described above based on the modulation profile 28e, the control unit 12e also briefly varies the switching frequency 16e within the intermediate modulation period 32e, specifically within half the period 20e of the mains AC voltage 22e, based on the profile described in the Figure 8 The intermediate modulation profile 92e shown is used to prevent flicker. Reference sign

[0054] 10 Household appliance device 12 Control unit 14 Induction target 16 Switching frequency 18 Modulation period 20 Half period duration 22 Mains AC voltage 24 Modulation interval 26 Further modulation interval 28 Modulation profile 30 Parameters 32 Intermediate modulation period 34 Mains AC voltage source 36 Mains AC current 38 EMC filter unit 40 Household appliance 42 Rectifier unit 44 DC voltage 46 Period duration 48 Inverter unit 50 Supply voltage 52 Switching period 54 Supply current 56 Abscissa 58 Ordinate 60 Average switching frequency 62 Abscissa 64 Ordinate 66 Axis of symmetry 68 First section 70 Second section 72 First subsection 74 Second subsection 76 Third subsection 78 Abscissa 80 Ordinate 82 Power 84 Frequency range 86 Excess 88 Deficit 90 Electrical conductance 92 Intermodulation profile

Claims

1. Induction hob with one control unit (12a-e) which is provided to control at least one induction target (14a-e) repetitively with a switching frequency (16a-e) and to supply said induction target with energy, wherein the induction hob is connected to a mains AC voltage source (34a-e) and wherein the mains AC voltage source (34a-e) provides a mains AC voltage (22a-e) with a period (46a-e), characterised in that in an operating state the control unit (12a-e) modulates the switching frequency (16a-e) within a modulation period (18a-e) which corresponds to an integer multiple of a half period (20a-e) of a mains AC voltage (22a-e), by means of at least one frequency modulation, wherein in the operating state the control unit (12a-e) modulates the switching frequency (16a-e) using at least one predefined modulation profile (28a-e), and wherein the modulation profile (28a-e) is able to be described by a substantially continuous mathematical function.

2. Induction hob according to claim 1, characterised in that the modulation period (18a-e) comprises at least two modulation intervals (24a-e, 26a-e) which are, in particular, different from one another and which in each case correspond to an integer multiple of a half period (20a-e) of a mains AC voltage (22a-e).

3. Induction hob according to claim 1 or 2, characterised in that the modulation profile (28a; 28b; 28d; 28e) within the modulation period (18a; 18b; 18d; 18e) has a path which is linear at least in some portions.

4. Induction hob according to claim 3, characterised in that the modulation profile (28c) within the modulation period (18c) has a path which is exponential at least in some portions.

5. Induction hob according to one of claims 3 or 4, characterised in that the modulation profile (28a-e) within the modulation period (18a-e) is mirror- symmetrical at least in some portions.

6. Induction hob according to claim 3 to 5, characterised in that the control unit (12a; 12e) is provided to vary the modulation profile (28a; 28e) using at least one parameter (30d; 30e) relating to the induction target (14d; 14e).

7. Induction hob according to claim 6, characterised in that the parameter (30e) comprises at least one electrical conductance value (90e) of the induction target (14e).

8. Induction hob according to one of the preceding claims, characterised in that in the operating state the control unit (12e) additionally modulates the switching frequency (16e) within an intermediate modulation period (32e) which corresponds to a maximum of the half period (20e) of the mains AC voltage (22e), by means of at least one further frequency modulation.

9. Method for operating an induction hob, in particular according to one of claims 1 to 8, with at least one induction target (14a-e) which can be controlled by a switching frequency (16a-e), wherein the induction hob is connected to a mains AC voltage source (34a-e) and wherein a mains AC voltage (22a-e) with a period (46a-e) is provided by the mains AC voltage source (34a-e), characterised in that the switching frequency (16a-e) is modulated by means of at least one frequency modulation within a modulation period (18a-e) which corresponds to an integer multiple of a half period (20a-e) of a mains AC voltage (22a-e), wherein in the operating state the switching frequency (16a-e) is modulated by the control unit (12a-e) using at least one predefined modulation profile (28a-e), and wherein the modulation profile (28a-e) is able to be described by a substantially continuous mathematical function.

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