Induction hob device

Abstract

The invention relates to an induction hob device (10) comprising at least one inductor (12), at least one inverter unit (14) which comprises at least two inverter switching elements (16, 18) for supplying energy to the inductor (12), at least one bus capacitor (20) which is arranged electrically parallel to the inverter switching elements (16, 18), and a detection unit (22) for detecting cooking utensils placed above the inductor (12) within a detection interval (24, 24'). In order to increase comfort, the invention proposes that the detection unit (22) comprises a discharge unit (26) which is designed to at least partially discharge the bus capacitor (20) in order to obtain an adjustable detection voltage (28, 28') for the detection interval (24, 24').

Description

[0001] Induction hob device

[0002] The invention relates to an induction hob device according to the preamble of claim 1 and a method for operating an induction hob device according to the preamble of claim 14.

[0003] Induction hobs with sensors for detecting cooking utensils are already known from the prior art. In some prior art induction hobs, an additional, separate sensor circuit, also known as a Colpitts oscillator, is used to detect cooking utensils. In addition to simply detecting the presence of a cooking utensil above an inductor, this can also detect the degree of coverage of one or more inductors by the cooking utensil by measuring an oscillation frequency of the sensor circuit, which changes depending on the material of the cooking utensil and / or the degree of coverage of the cooking utensil.However, such designs are cost-intensive due to the separate sensor circuit, which is why other known designs use an existing circuit comprising an inductor and inverter switching elements as a sensor for detecting cooking utensils on the induction field. Cooking utensils placed above an inductor are detected by operating at least one inverter switching element at a high frequency outside of a heating period, and the inductor is subjected to a voltage that corresponds to at least half the voltage applied to a bus capacitor arranged parallel to the inverter switching element. A change in at least one electrical parameter of the circuit comprising the inductor and inverter switching element, for example a change in inductance, is then used to determine whether cooking utensils are present above the inductor.A disadvantage of such designs is that high current peaks occur during detection, since at least half the voltage to which the bus capacitor is charged is applied to the load, which leads to audible acoustic noise and, consequently, to reduced electromagnetic compatibility and, in particular, to reduced comfort. The object of the invention is, in particular but not limited to, to provide a generic device with improved properties with regard to comfort. This object is achieved according to the invention by the features of claims 1 and 14, while advantageous embodiments and further developments of the invention can be found in the subclaims.

[0004] The invention is based on an induction hob device, with at least one inductor, with at least one inverter unit which comprises at least two inverter switching elements for supplying energy to the inductor, with at least one bus capacitor which is arranged electrically in parallel with the inverter switching elements, and with a detection unit for detecting cooking utensils placed above the inductor within a detection interval.

[0005] It is proposed that the detection unit comprises a discharge unit which is intended to at least partially discharge the bus capacitor in order to obtain an adjustable detection voltage for the detection interval.

[0006] Such a configuration advantageously makes it possible to provide an induction hob device with improved comfort characteristics. It is also possible to provide an induction hob device with improved electromagnetic compatibility. Noise interference, which can occur in generic induction hob devices during detection of cooking utensils, can be advantageously reduced, preferably minimized, if the detection unit comprises a discharge unit designed to at least partially discharge the bus capacitor in order to obtain an adjustable detection voltage for the detection interval. Furthermore, it is advantageously possible to relieve the load on the inverter switching elements if the bus capacitor is at least partially discharged.Furthermore, the lowest possible heating of cooking utensils and / or inductively heatable foreign objects, such as metallic cutlery and the like, can advantageously be ensured during detection. An "induction hob device" is understood to mean at least a part, in particular a subassembly, of an induction hob, wherein, in particular, accessory units for the hob can also be included, such as a sensor unit for externally measuring the temperature of a cooking utensil and / or a food item. In particular, the hob device, in particular the induction hob device, can also comprise the entire hob, in particular the entire induction hob.

[0007] The induction hob device comprises at least one inductor, which, in at least one operating state, provides energy in the form of an alternating electromagnetic field to at least one object, in particular to a cooking utensil. The induction hob device can have at least two, in particular at least three, preferably at least four, and particularly preferably at least five inductors. The inductors can be distributed, for example, in one or more rows and / or in the form of a matrix, and can be provided to form one or more flexible and / or freely definable heating zones, depending on the configuration.

[0008] The induction hob device comprises at least one inverter unit with at least two inverter switching elements for supplying power to the at least one inductor, wherein each two inverter switching elements of the inverter unit form, in particular, a resonant inverter and preferably a dual half-bridge inverter. The inverter switching elements of the inverter unit are preferably designed as semiconductor switching elements, in particular as transistors, for example, as a metal-oxide-semiconductor field-effect transistor (MOSFET) or an organic field-effect transistor (OFET), advantageously as a bipolar transistor with preferably an insulated gate electrode (IGBT). The inverter unit preferably has two inverter switching elements for supplying power to each inductor of the induction hob device.Alternatively, it is also conceivable that several inductors can be supplied with energy simultaneously by two of the inverter switching elements each.

[0009] The detection unit is designed to detect cooking utensils placed above the inductor within the detection interval and, for this purpose, in particular to detect at least one electrical parameter, for example an inductance and / or impedance and / or resonant frequency, of a circuit comprising at least the inductor and to compare it with at least one stored reference value. The electrical parameter detected by the detection unit within the detection interval is preferably a characteristic, in particular a change in the amplitude and / or frequency of an alternating current flowing, in particular oscillating, through the inductor during the detection interval. The detection unit can be at least partially integral with a control unit of the induction hob device and / or the induction hob having the induction hob device.A “control unit” is to be understood as an electronic unit that is preferably at least partially integrated into a control and / or regulating unit of an induction hob and that is preferably intended to control and / or regulate at least the inverter unit. 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. A detection interval is to be understood as a period in which the detection unit detects cooking utensils located above the inductor. The duration of the detection interval preferably corresponds to a maximum of half the period of an alternating mains voltage of a power supply network, which lasts, for example, 10 ms at a mains frequency of 50 Hz.The fact that two units are “partially integral” is to be understood as meaning that the units have at least one, in particular at least two, advantageously at least three common elements which are a component, in particular a functionally important component, of both units.

[0010] The discharge unit is provided to at least partially or completely discharge the at least one bus capacitor. The discharge unit comprises at least one switching element, preferably a semiconductor switching element, for example a transistor, which is controllable by the detection unit by means of a control signal, for example by applying a gate voltage, and which, in a closed and / or conductive state, is provided to enable at least one discharge path for partially or completely discharging the bus capacitor. The discharge unit can have at least one, preferably high-ohmic, discharge resistor, which is arranged in the discharge path, preferably electrically parallel to the bus capacitor, and is provided to dissipatively discharge the bus capacitor at least partially or completely.Alternatively or additionally, it is conceivable that the switching element is provided to enable a discharge path for at least partial or complete discharge of the bus capacitor into a power supply network. The induction hob device can have a plurality of bus capacitors. In particular, the induction hob device can have a bus capacitor for each two inverter switching elements of the inverter unit, which are each provided to supply power to at least one inductor, which bus capacitor is arranged electrically parallel to these two inverter switching elements. In the case of an induction hob device with more than one bus capacitor, the discharge unit is preferably provided to at least partially discharge all bus capacitors, preferably with a time offset from one another.In the case of an induction hob device with more than one bus capacitor, the discharge unit preferably has at least one switching element for each bus capacitor, wherein each of the switching elements can be controlled by the detection unit, preferably with a time delay. The adjustable detection voltage for the detection interval, which is obtained by the at least partial discharge of the bus capacitor by the discharge unit, is preferably continuously adjustable. The adjustable detection voltage corresponds to an electrical voltage to which the bus capacitor is charged before the detection interval is initiated by the detection unit. The detection unit could be provided to apply the detection voltage present at the bus capacitor at the beginning of the detection interval to the inductor.The induction hob device preferably has at least two resonant capacitors, wherein each of the resonant capacitors is arranged electrically in parallel with one of the inverter switching elements, so that the at least two resonant capacitors are arranged electrically in series with one another and electrically in parallel with the bus capacitor. In the case of an induction hob device with more than one bus capacitor, the induction hob device preferably has two resonant capacitors for each bus capacitor, wherein each two of the resonant capacitors are arranged electrically in series with one another and electrically in parallel with at least one of the bus capacitors.Preferably, the resonant capacitors have the same capacitance, so that an electrical voltage applied to each of the resonant capacitors in an operating state of the induction hob device corresponds to half the detection voltage simultaneously applied to the bus capacitor arranged electrically parallel thereto. The detection unit is then preferably provided to apply an electrical voltage to the inductor during the detection interval that corresponds to an electrical voltage applied to one of the resonant capacitors and in particular to half the detection voltage applied to the bus capacitor.

[0011] 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."

[0012] "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.

[0013] It is further proposed that the discharge unit is provided to discharge the bus capacitor to a predetermined detection voltage before the start of the detection interval. This enables low-noise detection using particularly simple technical means. The predetermined detection voltage is lower than the maximum voltage to which the bus capacitor can be charged, wherein the maximum voltage corresponds in particular to a peak value of a rectified AC mains voltage of a power supply network with which the induction hob device is supplied in an operating state. The predetermined detection voltage corresponds in particular to at most 80%, advantageously at most 70%, particularly advantageously at most 60%, preferably at most 50%, more preferably at most 40% and particularly preferably at most 30% of the maximum voltage to which the bus capacitor can be charged.The discharge unit is preferably provided to discharge the bus capacitor to the predetermined detection voltage before the start of the detection interval by appropriately selecting a discharge interval in which the bus capacitor is partially discharged. The detection unit is preferably provided to determine a duration of the discharge interval by controlling the at least one switching element of the discharge unit before the start of the detection interval, wherein the discharge interval corresponds to a period of time between the closing of the switching element of the discharge unit by the detection unit and the opening of the switching element of the discharge unit by the detection unit.The duration of the discharge interval could be stored in a memory unit of the detection unit and / or the control unit of the induction hob device and / or of the induction hob having the induction hob device, in particular as a factory setting. It is also conceivable for the duration of the discharge interval to be variably adjustable by the detection unit, in particular depending on at least one current operating parameter, for example, a current electrical voltage to which the bus capacitor is charged and / or an AC mains voltage with which the induction hob device is operated, in order to enable a partial discharge of the bus capacitor to the predetermined detection voltage before the start of the detection interval.

[0014] In an alternative advantageous embodiment, it is proposed that the discharge unit is provided to completely discharge the bus capacitor before the start of the detection interval. Such a configuration can advantageously enable a discharge of the bus capacitor using particularly simple technical means. Preferably, the detection unit is provided to define a duration of a discharge interval before the start of the detection interval by controlling the at least one switching element of the discharge unit such that the bus capacitor is completely discharged by the discharge unit during the discharge interval. Furthermore, it is proposed that the detection unit is provided to initiate the detection interval after a complete discharge and partial recharging of the bus capacitor to a predetermined detection voltage.This advantageously enables a particularly precise setting of the predetermined detection voltage. The detection unit is preferably designed to select a starting time of the detection interval after complete discharge such that the bus capacitor is recharged to the predetermined detection voltage at the starting time.

[0015] It is also proposed that the detection unit at least initiate the detection interval by controlling at least one of the inverter switching elements. Such a configuration advantageously enables detection of cooking utensils placed above the inductor using particularly simple technical means and therefore at a particularly low cost. Preferably, the detection unit initiates the detection interval by controlling precisely one of the inverter switching elements. Preferably, the detection unit operates at least one, preferably precisely one, of the inverter switching elements during the detection interval at a detection frequency that differs from a heating frequency.For example, the control unit of the induction hob device and / or of the induction hob having the induction hob device can be provided to operate the at least two inverter switching elements of the inverter unit to supply energy to the at least one inductor in a heating mode at a heating frequency of at least 15 kHz and at most 70 kHz, and the detection unit can be provided to operate at least one of the inverter switching elements, preferably exactly one of the inverter switching elements, in the detection interval at a detection frequency of at least 75 kHz. This can advantageously reduce, preferably minimize, unwanted heating of the cooking utensil and / or other inductively heatable objects located above the inductor during the detection interval.

[0016] Furthermore, it is proposed that the discharge unit be provided to periodically at least partially discharge the bus capacitor. This advantageously enables regular detection and / or checking of the presence of cooking utensils placed above the inductor. The discharge unit is provided to periodically at least partially discharge the bus capacitor, in particular within a period of at most 2,000 ms, advantageously within a period of at most 1,5000 ms, particularly advantageously within a period of at most 1,250 ms, preferably within a period of at most 1,000 ms, preferably within a period of at most 750 ms, and particularly preferably within a period of at most 500 ms.The discharge unit is provided to at least partially discharge the bus capacitor periodically, in particular within a period of at least 50 ms, advantageously within a period of at least 100 ms, particularly advantageously within a period of at least 150 ms, preferably within a period of at least 200 ms, preferably within a period of at least 225 ms and particularly preferably within a period of at least 250 ms.

[0017] Furthermore, it is proposed that the detection unit is provided to initiate the detection interval periodically at a repetition rate of at least 0.50 Hz and at most 5.50 Hz. This advantageously makes it possible to regularly check for the presence of cooking utensils placed above the inductor. In particular, moving and / or removing cooking utensils can be detected in good time, which advantageously increases safety and ease of use. The detection unit is provided to initiate the detection interval periodically at a repetition rate of in particular at least 0.75 Hz, advantageously at least 1.00 Hz, particularly advantageously at least 1.25 Hz, preferably at least 1.50 Hz, preferably at least 1.75 Hz and particularly preferably at least 2.00 Hz.The detection unit is provided to initiate the detection interval periodically with a repetition rate of in particular at most 5.25 Hz, advantageously at most 5.00 Hz, particularly advantageously at most 4.75 Hz, preferably at most 4.50 Hz, preferably at most 4.25 Hz and particularly preferably at most 4.00 Hz.

[0018] It is further proposed that the detection unit comprise a computing unit designed to detect cooking utensils placed above the inductor based on an alternating current flowing through the inductor during the detection interval. This advantageously enables particularly reliable detection of cooking utensils placed above the inductor. The computing unit of the detection unit could be partially formed integrally with the control unit of the induction hob device and / or the induction hob having the induction hob device. The computing unit of the detection unit is preferably designed as an application-specific integrated circuit (ASIC).

[0019] It is also proposed that the detection unit have an analog-to-digital converter unit which is provided for converting the alternating current flowing through the inductor during the detection interval into a digital measurement signal and transmitting it to the computing unit. Such a configuration can advantageously enable particularly precise and reliable detection. The analog-to-digital converter unit has at least one input which is connected to a circuit comprising the inductor during the detection interval and is provided for detecting the alternating current flowing through the inductor during the detection interval as an analog measurement signal. The analog-to-digital converter unit has at least one output which is connected to the computing unit during the detection interval and is provided for transmitting the digital measurement signal to the computing unit.Preferably, the analog-to-digital converter unit is designed as a sigma-delta converter. Alternatively, other types of analog-to-digital converters can also be used as the analog-to-digital converter unit.

[0020] Furthermore, it is proposed that the analog-to-digital converter unit have a sampling rate of at least 1.0 MS / s (mega samples per second). This advantageously enables detection of cooking utensils placed above the inductor with sufficient accuracy. In particular, the analog-to-digital converter unit has a sampling rate of at least 1.1 MS / s, advantageously of at least 1.3 MS / s, particularly advantageously of at least 1.5 MS / s, preferably of at least 2.0 MS / s, and more preferably of at least 2.5 MS / s.

[0021] Furthermore, it is proposed that the analog-to-digital converter unit have a resolution of at least 8 bits. This can advantageously further improve the accuracy in detecting cooking utensils placed above the inductor. The analog-to-digital converter unit preferably has a resolution of at least 10 bits, more preferably at least 12 bits. Although the use of an analog-to-digital converter unit with a resolution of at least 8 bits is sufficient for use within the induction hob device according to the invention, the use of high-performance analog-to-digital converters with higher resolutions of 24 bits or more as the analog-to-digital converter unit is of course also conceivable.

[0022] It is further proposed that the detection unit comprise a driver unit for impedance matching for the analog-to-digital converter unit. Such a configuration can advantageously further improve the accuracy of detecting cookware placed above the inductor. Furthermore, the analog-to-digital converter unit can be advantageously protected from voltage spikes. The driver unit preferably comprises a voltage follower and an operational amplifier.

[0023] The invention further relates to an induction hob with at least one induction hob device according to one of the previously described embodiments. Such an induction hob is characterized in particular by the advantageous properties that can be achieved by the previously described features of the induction hob device. The induction hob can have several of the previously described induction hob devices.

[0024] The invention further relates to a method for operating an induction hob device, in particular according to one of the previously described embodiments, with an inverter unit which comprises at least two inverter switching elements for supplying energy to the inductor, with at least one bus capacitor which is arranged electrically in parallel with the inverter switching elements, wherein cooking utensils placed above the inductor are detected based on a complete or partial activation of at least one of the inverter switching elements within a detection interval.

[0025] It is proposed that the bus capacitor be at least partially discharged before the detection interval. Such a method can advantageously enable particularly convenient operation of the induction hob device. In particular, electromagnetic compatibility can be improved and noise emissions during the detection of cooking utensils can be reduced, in particular minimized. The induction hob device is not intended to be limited to the application and embodiment described above. In particular, the induction hob device can have a number of individual elements, components, and units that differs from the number stated herein to fulfill a function described herein.

[0026] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an exemplary embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will also expediently consider the features individually and combine them into useful further combinations.

[0027] They show:

[0028] Fig. 1 shows an induction hob with an induction hob device in a schematic plan view,

[0029] Fig. 2 is a schematic electrical circuit diagram of the induction hob device with at least one inductor, at least one inverter unit, at least one bus capacitor, a detection unit and a discharge unit for at least partially discharging the bus capacitor,

[0030] Fig. 3 is a schematic diagram illustrating a functioning of the detection unit in a first configuration,

[0031] Fig. 4 is a schematic diagram illustrating a functioning of the detection unit in a second configuration,

[0032] Fig. 5 is a schematic diagram showing a temporal sequence of several detection processes by the detection unit in the second configuration and

[0033] Fig. 6 is a schematic process flow diagram illustrating a method for operating the induction hob device.

[0034] Figure 1 shows an induction hob 40 in a schematic plan view. The induction hob 40 comprises at least one induction hob device 10. The induction hob device 10 has at least one inductor 12. In the present case, the induction hob device 10 has a first inductor 12, a second inductor 42, and three further inductors 44, 46, 48.

[0035] The induction hob 40 includes a hob plate 50 for placing cooking utensils (not shown). When the induction hob 40 is assembled, the inductors 12, 42, 44, 46, 48 of the induction hob device 10 are mounted below the hob plate 50 of the induction hob 40.

[0036] The induction hob device 10 has at least one inverter unit 14, which comprises at least two first inverter switching elements 16, 18 for supplying power to the first inductor 12 (see Figure 2). In the present case, the inverter unit 14 comprises two second inverter switching elements 76, 78 (see Figure 2) for supplying power to the second inductor 42, as well as two further inverter switching elements (not shown) for supplying power to the further inductors 44, 46, 48. The first inverter switching elements 16, 18, the second inverter switching elements 76, 78, and the further inverter switching elements of the inverter unit 14 are arranged together on a printed circuit board (not shown).

[0037] In the present case, the induction hob 10 comprises an additional induction hob device 80 with a first additional inductor 82, a second additional inductor 84, and three further additional inductors 86, 88, 90. In the assembled state of the induction hob 40, the additional inductors 82, 84, 86, 88 of the additional induction hob device 80 are mounted below the hob plate 50 of the induction hob 40. The additional induction hob device 80 has an additional inverter unit (not shown) with additional inverter switching elements (not shown) for supplying power to the additional inductors 82, 84, 86, 88, 90, which are arranged together on an additional printed circuit board (not shown). The additional induction hob device 80 is designed essentially identically to the induction hob device 10.The following description is therefore limited to the operation of the induction hob device 10, but can be applied analogously to the additional induction hob device 80. The induction hob 40 has a control unit 38. The control unit 38 is provided for controlling the inverter unit 14 (see Figure 2) for operating the inductors 12, 42, 44, 46, 48 of the induction hob device 10 and for controlling the additional inverter unit (not shown) for operating the additional inductors 82, 84, 86, 88, 90.

[0038] Figure 2 shows a simplified and schematic electrical diagram of the induction hob device 10.

[0039] The induction hob device 10 includes a mains connection 52 for connection to a power supply network (not shown) and for supplying power to the induction hob device 10. The induction hob device 10 further includes a filter unit 54. The filter unit 54 is connected downstream of the mains connection 52 and is provided to reduce interference.

[0040] The induction hob device 10 also includes a rectifier unit 56. The rectifier unit 56 is designed to rectify an AC mains voltage provided by the power supply network and applied to the mains connection 52. In an operating state of the induction hob device 10, the rectifier unit 56 converts the AC mains voltage into a rectified AC mains voltage 62 (see Figures 3 and 4).

[0041] Figure 2 shows the inverter unit 14 with the first inverter switching elements 16, 18 for supplying power to the first inductor 12. In this case, the first inverter switching elements 16, 18 are arranged in a dual half-bridge circuit. In a heating mode of the induction hob device 10, the first inverter switching elements 16, 18 are designed to operate at a heating frequency in order to supply the first inductor 12 with a high-frequency alternating current. The induction hob device 10 comprises two first resonance capacitors 116, 118, wherein a first resonance capacitor 116 is arranged electrically parallel to the first inverter switching element 16, and a further first resonance capacitor 118 is arranged electrically parallel to the further first inverter switching element 18.In the heating operation, the first resonance capacitor 116 forms a resonant circuit with the first inductor 12 and the first inverter switching element 16 and the further first resonance capacitor 118 forms a resonant circuit with the first inductor 12 and the further first inverter switching element 18.

[0042] The induction hob device 10 further comprises at least one bus capacitor 20. In the present case, the induction hob device 10 comprises a first bus capacitor 20, which is arranged electrically parallel to the first inverter switching elements 16, 18.

[0043] The induction hob device 10 also has a detection unit 22. The detection unit 22 is provided for detecting cooking utensils (not shown) placed above the first inductor 12 within a detection interval 24 (see Figure 3). The detection unit 22 is also provided for detecting cooking utensils (not shown) placed above the second inductor 42 and / or above the further inductors 44, 46, 48 within a second detection interval 98 (see Figure 5) or within further detection intervals 100 (see Figure 5).

[0044] The detection unit 22 comprises a discharge unit 26. The discharge unit 26 is provided to at least partially discharge the first bus capacitor 20 in order to obtain an adjustable detection voltage 28 (see Figure 3) for the detection interval 24 (see Figure 3). The discharge unit 26 here comprises a discharge resistor 58 and a switching element 60, which are each arranged electrically parallel to the first bus capacitor 20. The switching element 60 is here designed as a semiconductor switching element, for example as a transistor or the like, and can be controlled by the detection unit 22 by means of a discharge signal 72 (see Figure 3). The discharge signal 72 can be, for example, a gate voltage, which can be applied by the detection unit 22 to a gate of the switching element 60 designed as a semiconductor switching element.

[0045] The detection unit 22 comprises a computing unit 30, which is designed to detect cooking utensils placed above the first inductor 12 based on an alternating current 32 flowing through the inductor 12 during the detection interval 24 (see Figure 3). In the present case, the computing unit 30 is designed as an application-specific integrated circuit (ASIC). The detection unit 22 has at least one analog-to-digital converter unit 34. The first analog-to-digital converter unit 34 of the detection unit 22 is designed to convert the alternating current 32 flowing through the first inductor 12 during the detection interval 24 into a digital measurement signal (not shown) and transmit it to the computing unit 30. The first analog-to-digital converter unit 34 has a sampling rate of at least 2.0 MS / s. In the present case, the first analog-to-digital converter unit 34 has a sampling rate of at least 2.5 MS / s.

[0046] The first analog-to-digital converter unit 34 has a resolution of at least 8 bits. In the present case, the first analog-to-digital converter unit 34 has a resolution of at least 12 bits.

[0047] The detection unit 22 has at least one first driver unit 36 ​​for impedance matching for the first analog-to-digital converter unit 34. The driver unit 36 ​​is comprised of a voltage follower (not shown) and an operational amplifier (not shown).

[0048] In Figure 2, in addition to the inductor 12, the second inductor 42 is also shown together with the second inverter switching elements 76, 78 of the inverter unit 14, which are provided for supplying energy to the second inductor 42. In the heating mode of the induction hob device 10, the second inverter switching elements 76, 78 are provided for operation at a heating frequency in order to supply the second inductor 42 with a high-frequency alternating current. The induction hob device 10 here comprises two second resonance capacitors 120, 122, wherein a second resonance capacitor 120 is arranged electrically parallel to the second inverter switching element 76 and a further second resonance capacitor 122 is arranged electrically parallel to the further second inverter switching element 78.In heating mode, the second resonant capacitor 120 forms a resonant circuit with the second inductor 42 and the second inverter switching element 76, and the further second resonant capacitor 122 forms a resonant circuit with the second inductor 42 and the further second inverter switching element 78. The induction cooktop device 10 comprises a second bus capacitor 92, which is arranged in parallel with the second inverter switching elements 76, 78 and connected to the rectifier unit 56. For discharging the second bus capacitor 92, the discharge unit 26 comprises a second discharge resistor (not shown) and a second switching element (not shown), each of which is arranged electrically parallel to the second bus capacitor 92. The second switching element can be controlled by the detection unit 22 using a second discharge signal (not shown).

[0049] The computing unit 30 is provided to detect cooking utensils (not shown) placed above the second inductor 42 on the basis of an alternating current (not shown) flowing through the second inductor 42 during a second detection interval 98 (cf. Figure 5).

[0050] For this purpose, the detection unit 22 has a second analog-to-digital converter unit 94. The second analog-to-digital converter unit 94 is designed essentially identically to the first analog-to-digital converter unit 34 and is intended to convert the alternating current flowing through the second inductor 42 during the second detection interval 98 into a digital measurement signal and transmit it to the computing unit 30. For impedance matching for the second analog-to-digital converter unit 94, the detection unit 22 accordingly has a second driver unit 96, which is designed essentially identically to the first driver unit 36.

[0051] For the sake of clarity, the simplified and schematic electrical circuit diagram of Figure 2 includes only the first inductor 12 with the associated first inverter switching elements 16, 18 and the associated first bus capacitor 20, and the second inductor 42 with the associated second inverter switching elements 76, 78 and the second bus capacitor 92, as well as the detection unit 22 with the associated subunits and elements for detecting cooking utensils placed above the first inductor 12 and / or above the second inductor 42. The induction hob device 10 includes at least two further inverter switching elements (not shown) that are part of the inverter unit 14 for supplying power to each of the further inductors 44, 46, 48 (cf. Figure 1), as well as further bus capacitors (not shown) that are electrically connected in parallel therewith.The discharge unit 26 comprises additional discharge resistors (not shown) and additional switching elements (not shown) for discharging these additional bus capacitors, each of which is arranged in parallel with one of the additional bus capacitors. The detection unit 26 also comprises an additional analog-to-digital converter unit (not shown) for each of the additional inductors 44, 46, 48. These converter units are each designed essentially identically to the first analog-to-digital converter unit 34 and are provided for converting the alternating currents (not shown) flowing through the additional inductors 44, 46, 48 during additional detection intervals 100 into digital measurement signals (not shown) and for transmitting them to the computing unit 30.For impedance matching for the further analog-to-digital converter units, the detection unit 22 has corresponding further driver units (not shown), which are designed essentially identically to the first driver unit 36.

[0052] Figure 3 shows a schematic diagram illustrating the mode of operation of the detection unit 22 in a first configuration. The diagram shows the temporal progression of the rectified AC mains voltage 62, which the rectifier unit 56 (see Figure 2) provides in the operating state of the induction hob device 10. As can be seen from the diagram in Figure 3, the rectified AC mains voltage 62 in this case is a pulsating DC voltage which, within half a period 66, rises from a value of zero to a peak value 68 and then falls back to the value of zero. One period corresponds to the inverse of a mains frequency of the power supply network. At a mains frequency of 50 Hz, the period corresponds to a period of 20 ms, and half the period 66 corresponds to a period of 10 ms.

[0053] The diagram in Figure 3 shows a time profile of a capacitor voltage 64, which is applied to the first bus capacitor 20 in the operating state of the induction hob device 10. When the induction hob device 10 is started up, the first bus capacitor 20 is fully charged within a first half period 66, specifically up to the peak value 68 of the rectified AC mains voltage 62. The capacitor voltage 64 of the bus capacitor 20 then remains constant at the peak value 68 of the rectified AC mains voltage 62 until the discharge unit 26 is activated. In the first configuration of the detection unit 22 shown in Figure 3, the discharge unit 26 is provided to discharge the first bus capacitor 20 down to a predetermined detection voltage 28 before the start of the detection interval 24.

[0054] To discharge the first bus capacitor 20, the detection unit 22 activates the discharge unit 26 by controlling the switching element 60 using a discharge signal 72. The discharge signal 72 closes the switching element 60 of the discharge unit 26 or makes it conductive along a collector-emitter path, and the first bus capacitor 20 is discharged via the discharge resistor 58. In this case, the detection unit 22 activates the discharge unit 26 within a discharge interval 70. At the end of the discharge interval 70, the switching element 60 of the discharge unit 26 is closed again, or its collector-emitter path becomes non-conductive. In the first configuration, the detection unit 22 is configured such that the discharge interval 70 lasts until the first bus capacitor 20 is discharged to the predetermined detection voltage 28.The detection voltage 28 can, for example, be predetermined to 100 V, although other predetermined detection voltages 28 are also conceivable.

[0055] Figure 3 shows the detection interval 24. The detection unit 22 initiates the detection interval 24 by controlling at least one of the inverter switching elements 16, 18. In this case, the detection unit 22 initiates the detection interval 24 by activating the first inverter switching element 16. During the detection interval 24, the first inductor 12 is therefore subjected to a voltage to which the first resonant capacitor 116 is charged at the beginning of the detection interval 24.In the present case, the first resonance capacitor 116 and the further first resonance capacitor 118 have the same capacitance, so that the voltage to which the first resonance capacitor 116 is charged at the beginning of the detection interval 24 corresponds to half of the predetermined detection voltage 28, in the present case, for example, 50 V, to which the discharge unit 26 has discharged the first bus capacitor 20 before the beginning of the detection interval 24.

[0056] The detection interval 24 follows the discharge interval 70 and is separated from the discharge interval 70 by less than half a period 66. In the detection interval 24, the detection unit 22 controls the first inverter switching element 16 by means of a control signal 74. The control signal 74 closes the first inverter switching element 16, or makes its collector-emitter path conductive, and the first inductor 12 is supplied with half of the predetermined detection voltage 28 applied to the first bus capacitor 20. As a result, the alternating current 32 flows through the inductor 12, which is tapped by the first analog-to-digital converter unit 34, converted into the digital measurement signal, and transmitted to the computing unit 30 of the detection unit 22.The computing unit 30 detects cooking utensils placed above the first inductor 12 based on at least one characteristic of the alternating current 32, for example based on a change in an amplitude and / or frequency of the alternating current 32.

[0057] Figure 4 shows a schematic diagram illustrating the functionality of the detection unit 22 in an alternative second configuration. The diagram again shows the time profile of the rectified AC mains voltage 62, which the rectifier unit 56 (see Figure 2) provides in the operating state of the induction hob device 10. In contrast to the first configuration shown in Figure 3, the discharge unit 26 in the second configuration is designed to completely discharge the first bus capacitor 20 before the start of a detection interval 24'.

[0058] To fully discharge the first bus capacitor 20, the detection unit 22 activates the discharge unit 26 by controlling the switching element 60 using a discharge signal 72' within a discharge period 70'. In the second configuration, the detection unit 22 is configured such that the discharge interval 70' lasts until the first bus capacitor 20 is fully discharged. Accordingly, the discharge interval 70' for fully discharging the first bus capacitor 20 in the second configuration of the detection unit 20 lasts longer than the discharge interval 70 shown in Figure 3 for partially discharging the first bus capacitor 20 in the first configuration.

[0059] In the second configuration, the detection unit 22 is also provided to initiate the detection interval 24' after a complete discharge and partial recharging of the first bus capacitor 20 to a predetermined detection voltage 28'. The detection unit 22 initiates the detection interval 24' by controlling at least one of the inverter switching elements 16, 18. In the present case, the detection unit 22 initiates the detection interval 24' by activating the first inverter switching element 16. The detection interval 24' follows the discharge interval 70' and is separated from the discharge interval 70' by less than half a period 66. In the detection interval 24', the detection unit 22 controls the first inverter switching element 16 by means of a control signal 74'.The control signal 74' closes the first inverter switching element 16 or makes its collector-emitter path conductive, and the first inductor 12 is supplied with half of the predetermined detection voltage 28' applied to the first bus capacitor 20. The detection unit 22 initiates the detection interval 24' within a half-wave of the rectified AC mains voltage 62 following the complete discharge of the bus capacitor 20, at a time at which the first bus capacitor 20 is recharged to the predetermined detection voltage 28'. In the detection interval 24', an alternating current 32' flows through the first inductor 12, which is tapped by the first analog-to-digital converter unit 34, converted into a digital measurement signal, and transmitted to the computing unit 30 of the detection unit 22.The computing unit 30 detects cooking utensils placed above the inductor 12 based on at least one characteristic of the alternating current 32', for example a change in a frequency and / or amplitude of the alternating current 32'.

[0060] Figure 5 shows a schematic diagram illustrating a temporal sequence of detection processes by the detection unit 22 in the second configuration. The diagram shows a detection cycle 106 of the detection unit 22. Within the detection cycle 106, the detection unit checks successively whether cooking utensils are placed above one of the inductors 12, 42, 44, 46, 48. The detection cycle is composed of several detection sub-cycles 108, 110, wherein a number of the detection sub-cycles 108, 110 corresponds to a number of inductors 12, 42, 44, 46, 48 of the induction cooktop device 10. A first detection sub-cycle 108 begins after a complete discharge of the first bus capacitor 20 after the discharge interval 70'. The detection interval 24' lies within the first detection sub-cycle 108. The first detection sub-cycle 108 can last, for example, 50 ms to 100 ms.At the end of the first detection sub-cycle 108, the second bus capacitor 92 is fully discharged within a second discharge interval 102. Following the second discharge interval 102, a second detection sub-cycle 110 begins, within which the second discharge interval 98 lies, in which the computing unit 30 detects whether cooking utensils are placed above the second inductor 42 or not. At the end of the second detection sub-cycle 110, a bus capacitor (not shown) assigned to the further inductor 44 is fully discharged within a further discharge interval 104. In a further detection sub-cycle (not shown) following the further discharge interval, a further detection interval 100 occurs, in which the computing unit 30 detects whether cooking utensils are placed above the further inductor 44 or not.Corresponding further detection sub-cycles (not shown) follow for the other inductors 46, 48. At the end of the detection cycle 106, the first bus capacitor 20 is again discharged in the discharge interval 70.

[0061] The discharge unit 26 is provided to at least partially discharge the bus capacitor 20 on a periodic, recurring basis. In the second configuration of the detection unit 22, the discharge unit 26 is provided to completely discharge the bus capacitor 20 on a periodic, recurring basis. A period duration of a recurring periodic discharge of the first bus capacitor 20 corresponds to a duration of the detection cycle 106. In this case, the detection cycle 106 can last, for example, 250 ms to 500 ms. Analogous to the detection cycle 106 in the second configuration, the detection unit 22 can have a corresponding detection cycle (not shown) for the first configuration.

[0062] In the first configuration, the detection unit 22 is designed to initiate the detection interval 24 (see Figure 3) periodically at a repetition rate of at least 0.5 Hz and at most 5 Hz. In the second configuration, the detection unit 22 is likewise designed to initiate the detection interval 24' periodically at a repetition rate of at least 0.5 Hz and at most 5 Hz.

[0063] Figure 6 shows a schematic process flow diagram of a method for operating the induction hob device 10. In the method, the first bus capacitor 20 is at least partially discharged before the detection interval 24. The method comprises at least two method steps 112, 114. In a first method step 112 of the method, the first bus capacitor 20 is partially discharged before the detection interval 24, specifically by means of the discharge unit 26 to the predetermined detection voltage 28 (cf. Figure 3). Alternatively, the first bus capacitor 20 can also be completely discharged in the first method step 112 of the method before the detection interval 24' and then partially recharged to the predetermined detection voltage 28' (cf. Figure 4). In a second method step 114 of the method, the detection interval 24 (cf. Figure 3) or alternatively the detection interval 24' (cf.Figure 4) in order to detect cooking utensils placed above the first inductor 12 (see Figures 1 and 2).

[0064] Reference symbol

[0065] 10 Induction hob device

[0066] 12 Inductor

[0067] 14 Inverter unit

[0068] 16 first inverter switching element

[0069] 18 further first inverter switching element

[0070] 20 first bus capacitor

[0071] 22 Detection unit

[0072] 24 detection interval

[0073] 26 Discharge unit

[0074] 28 Detection voltage

[0075] 30 computing units

[0076] 32 alternating current

[0077] 34 first analog-to-digital converter unit

[0078] 36 first driver unit

[0079] 38 Control unit

[0080] 40 induction hob

[0081] 42 second inductor

[0082] 44 additional inductor

[0083] 46 additional inductor

[0084] 48 additional inductor

[0085] 50 hob plate

[0086] 52 Mains connection

[0087] 54 Filter unit

[0088] 56 Rectifier unit

[0089] 58 Discharge resistance

[0090] 60 switching element

[0091] 62 rectified AC mains voltage

[0092] 64 Capacitor voltage half period

[0093] Peak value

[0094] Discharge interval

[0095] discharge signal

[0096] Control signal second inverter switching element further second inverter switching element additional induction hob device additional inductor second additional inductor further additional inductor further additional inductor further additional inductor second bus capacitor second analog-to-digital converter unit second driver unit second detection interval further detection interval second discharge interval further discharge interval

[0097] Detection cycle first detection sub-cycle second detection sub-cycle first process step second process step first resonance capacitor further first resonance capacitor second resonance capacitor further second resonance capacitor

Claims

Claims 1. Induction hob device (10), with at least one inductor (12), with at least one inverter unit (14) which comprises at least two inverter switching elements (16, 18) for supplying energy to the inductor (12), with at least one bus capacitor (20) which is arranged electrically in parallel with the inverter switching elements (16, 18), and with a detection unit (22) for detecting cooking utensils placed above the inductor (12) within a detection interval (24, 24'), characterized in that the detection unit (22) comprises a discharge unit (26) which is provided for at least partially discharging the bus capacitor (20) in order to obtain an adjustable detection voltage (28, 28') for the detection interval (24, 24').

2. Induction hob device (10) according to claim 1, characterized in that the discharge unit (26) is provided to discharge the bus capacitor (20) to a predetermined detection voltage (28) before the start of the detection interval (24).

3. Induction hob device (10) according to claim 1, characterized in that the discharge unit (26) is provided to completely discharge the bus capacitor (20) before the start of the detection interval (24').

4. Induction hob device (10) according to claim 3, characterized in that the detection unit (22) is provided to initiate the detection interval (24') after a complete discharge and partial recharging of the bus capacitor (20) to a predetermined detection voltage (28').

5. Induction hob device (10) according to one of the preceding claims, characterized in that the detection unit (22) at least initiates the detection interval (24, 24') by controlling at least one of the inverter switching elements (16, 18).

6. Induction hob device (10) according to one of the preceding claims, characterized in that the discharge unit (26) is provided to at least partially discharge the bus capacitor (20) periodically.

7. Induction hob device (10) according to one of the preceding claims, characterized in that the detection unit (22) is provided to initiate the detection interval (24, 24') periodically recurring with a repetition rate of at least 0.50 Hz and at most 5.50 Hz.

8. Induction hob device (10) according to one of the preceding claims, characterized in that the detection unit (22) comprises a computing unit (30) which is provided to detect cooking utensils placed above the inductor (12) on the basis of an alternating current (32) flowing through the inductor (12) during the detection interval (24, 24').

9. Induction hob device (10) according to claim 8, characterized in that the detection unit (22) has at least one analog-digital converter unit (34) which is provided to convert the alternating current (32) flowing through the inductor (12) during the detection interval (24, 24') into a digital measurement signal and to transmit it to the computing unit (30).

10. Induction hob device (10) according to claim 9, characterized in that the analog-digital converter unit (34) has a sampling rate of at least 1.0 MS / s.

11. Induction hob device according to claim 9 or 10, characterized in that the analog-digital converter unit (34) has a resolution of at least 8 bits.

12. Induction hob device (10) according to one of claims 9 to 11, characterized in that the detection unit (22) has at least one driver unit (36) for impedance matching for the analog-digital converter unit (34).

13. Induction hob (40) with at least one induction hob device (10) according to one of the preceding claims.

14. A method for operating an induction hob device (10), in particular according to one of claims 1 to 12, with at least one inductor (12), with an inverter unit (14) which comprises at least two inverter switching elements (16, 18) for supplying energy to the inductor (12), with at least one bus capacitor (20) which is arranged electrically in parallel with the inverter switching elements (16, 18), wherein cooking utensils placed above the inductor (12) are detected based on a complete or partial activation of at least one of the inverter switching elements (16, 18) within a detection interval (24, 24'), characterized in that the bus capacitor (20) is at least partially discharged before the detection interval (24, 24').

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