EP2638777B1 - Heating apparatus - Google Patents

Description

The invention relates to a heating device according to the preamble of claim 1.

Heater heaters are known which comprise a larger number of heating elements than frequency units. An assignment of the heating elements to the frequency units via a switching arrangement of the heater.

From the international patent application WO 2006/072765 A1 already a controller for a heating cable is known. The heating cable comprises at least first and second conductors and a separating layer (4) arranged between the conductors. The conductors and the separating layer extend along the length of the cable and an electrical resistance developed by the separating layer between adjacent partial regions of the conductors has a negative thermal coefficient. The regulator comprises a first switch electrically connected in series to connect the first and second conductors and disposed at one end of the cable such that when the first and second conductors at the other end of the cable are connected to respective poles of a power supply, currents are in opposite directions Directions through adjacent portions of the conductors flow. The controller further includes a second switch arranged for connection in series between the first conductor and a pole of the power supply at the other end of the cable. The regulator further includes a first resistor connected in parallel with the second switch and with a voltmeter configured to measure the voltage across the first resistor, wherein when both switches are open, the voltage across the first resistor is subject to changes in electrical resistance the separation layer depends. The controller is configured to control the power supply to the cable as a function of the voltage measured across the first resistor when both switches are open.

The British patent application GB 2 162 384 A discloses an induction heater. The induction heating apparatus has a rectifier circuit for rectifying an AC voltage from a source, an inverter circuit for converting a DC output current from the rectifier circuit to a high-frequency current and transmitting to a heating coil, and a circuit for detecting a fluctuation in the AC power source through a low-voltage conversion section which is coupled to the source. The circuit has a detection characteristic that can maintain the detection status at least for a constant period of time, and keeps the inverter circuit in the stopped state or the drive state depending on the presence or absence of a detection output from the circuit to prevent unstable operation and protect the inverter ,

The European patent application EP 1 517 091 A2 discloses an electric cooking appliance and a method of controlling it. The electric cooking appliance includes heating units, a switching unit, a current detection unit and a control unit. The heating units each have a heating element and electrodes connected to the heating element. The switching unit switches a voltage to be applied to the electrodes. The current detection unit detects values of output current from the heating units. The control unit operates a predetermined number of heating units, which is determined depending on the current values detected after operation of the heating units by the current detection unit.

From the international patent application WO 2008/031714 A1 is already a cooking device, namely for induction cookers, known with a computing unit having at least one waiting mode, which is activated when removing a cookware from a cooking zone. In order to achieve increased safety for an operator of the cooktop apparatus, the cooktop apparatus has a warning signal output unit which emits an output of a warning signal a re-installation of the cookware is provided with activated waiting mode on the cooking zone.

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

The invention is based on a heating device, in particular a cooktop heating device, with at least one heating connection for at least one heating element and at least one frequency unit.

It is proposed that the heating device has a protection unit which is provided to detect the existence of a line path between the frequency unit and the heating connection. By "provided" is intended to be understood in particular specifically designed and / or equipped and / or programmed. A "heating element" is to be understood in particular an element which is intended to convert electrical energy into heat. In particular, the heating element consists of a resistance heater or a radiant heater or preferably an induction heater, which is intended to convert electrical energy indirectly via induced eddy currents into heat. A "frequency unit" is to be understood in particular as meaning an electrical unit which supplies the heating element with electrical power Energy supplied. Preferably, the frequency unit is intended to generate an oscillating electrical signal, preferably with a frequency of at least 1 kHz, in particular of at least 10 kHz and advantageously of at least 20 kHz. The frequency unit preferably comprises at least one inverter, which particularly advantageously has two switching units. A "switching unit" is to be understood in particular as meaning a unit which is intended to interrupt a line path comprising the switching unit. Preferably, the switching unit is a bidirectional unipolar switch which in particular allows a current flow through the switch along the conduction path in both directions and in particular short-circuits an electrical voltage in at least one polarity direction. Preferably, the inverter comprises at least two insulated-gate bipolar transistors, and in particular at least one damping capacitor. A "conduction path" is to be understood in particular as an electrically conductive path between two points for direct current. A specific electrical resistance of the line path at 20 ° C. is preferably at most 10 ^-4 Ωm, in particular at most 10 ^-5 Ωm, advantageously at most 10 ^-6 Ωm and particularly advantageously at most 10 ^-7 Ωm. Preferably, the conduction path is free of heating elements. Preferably, the conduction path comprises at least one further component which is different from a conductor piece and a heating element, preferably a switching element of a switching arrangement and particularly advantageously a relay. A "heating connection" of a heating element should in particular be understood to mean an electrical connection point of the heating element. Preferably, the electrical connection point is a connection point between a power supply line of the heating element, in particular a power supply cable of the heating element, and a further power supply line, in particular a conductor track of a circuit board. Preferably, the heating connection is provided on a side facing away from the frequency unit in the direction of the line path between the frequency unit and the heating connection to an electrical connection of the heating element. A "protection unit" is to be understood in particular as meaning a unit, in particular an electronic unit, which assumes a protective function. Preferably, the protective function includes recognizing a line path and passing this information to a controller.

By such a configuration, a reliability can be increased, in particular when the heater has a switching arrangement with switching elements, preferably in the form of electromechanical relays, and these are provided for a periodic switching in a time division multiplex method. A "time-division multiplexing" is to be understood in particular as a control method in which individual time segments are defined, which are preferably run through one after the other, periodically recurring. In particular, in the case of a transition from a first to a second time segment, a switching state of the switching arrangement changes, preferably such that at least one first heating element is supplied with energy in the first time segment and at least one second heating element in the second time segment. In particular, a power supplied to the heating elements during a period of time is greater than an average time power supplied to the heating elements. Preferably, a period of the control method is 1 s to 5 s. By means of the protection unit, an operating safety can be increased, since a faulty existence of a line path can be detected. As a result, it can be prevented, in particular in the case of a hob, that heating elements are operated without load or with empty cooking utensils. Furthermore, it can be prevented, in particular in the case of induction hobs, that magnetic fields propagate freely from the heating elements in the vicinity of the induction hob.

It is further proposed that the protection unit is provided to determine the existence of the conduction path based on a potential curve. A "potential profile" should be understood in particular to be a time profile of an electrical potential, preferably at a point of the line path. An "electrical potential" at a point is to be understood in particular as a path integral via an electric field from a reference point to the point. Preferably, the reference point is for the electrical potential a point of a ground line of the frequency unit. As a result, costs can be significantly reduced because expensive measuring devices for high-frequency alternating currents can be dispensed with.

Advantageously, the protection unit is provided to evaluate the potential profile at the heating connection. Including that the protection unit is intended to "evaluate the potential profile at the heating connection" should be understood in particular that the protection unit supplied an electrical voltage between the heating connection or a point with a substantially same electrical potential as the heating connection and the reference point as an input voltage gets and processes internally. An "essentially the same electrical potential" should be understood to mean in particular an electrical potential with a deviation of at most 1% and preferably at most 0.1%. Preferably, an output voltage of the protection unit is a digital output signal, which in particular can assume only two values. This can reliably determine the existence of the line path.

In a preferred embodiment, it is proposed that the protection unit is provided to determine the existence of the conduction path based on a frequency spectrum of the potential profile. A "frequency spectrum" of the potential curve is to be understood, in particular, as a frequency-dependent mathematical function which describes a composition of the potential profile from signal components of different frequencies. By the fact that the protection unit is intended to "determine the existence of the conduction path based on a frequency spectrum of the potential profile", it should be understood in particular that the output signal and preferably the output voltage of the protection unit depends on the frequency spectrum. In particular, the protection unit recognizes a presence of high-frequency signals of a certain intensity in the frequency spectrum, in particular above a cut-off frequency, that a conduction path between the frequency unit and the heating connection exists. As a result, the existence of the line path can be determined particularly reliably.

Advantageously, the protection unit comprises at least one high-pass filter, which is provided to make a discrimination of potential gradients. A "high-pass filter" should in particular be understood to mean an electronic filter unit which is intended to allow signals with a frequency above a cut-off frequency to pass through at least substantially unattenuated and to attenuate signals at a lower frequency. By "at least substantially unattenuated" is to be understood in particular that a signal attenuation is at most 15%, in particular at most 10%, advantageously at most 5% and particularly advantageously at most 1%. Preferably, the high-pass filter comprises at least one capacitor. This can be achieved in a simple and cost-effective manner discrimination of potentials.

In a further embodiment of the invention it is proposed that the protection unit comprises a current sensor which is provided to determine the existence of the conduction path. A "current sensor" should be understood in particular to mean a unit which is intended to detect at least the presence of an electrical current. As a result, costs compared to an embodiment with a current measuring device, which is designed for measuring a high-frequency alternating current, can be saved.

The heating device comprises a control unit, which is provided to receive connection information from the protection unit and, in the event of a faulty existence of the line path, to initiate at least one safety measure. A "control unit" should in particular be understood to mean an electronic unit which is preferably at least partially integrated in a control and / or regulating unit of an induction hob and which is preferably provided to control and / or regulate at least the frequency unit and a switching arrangement. Preferably the control unit comprises a computing unit and in addition to the computing unit a memory unit. A "connection information" is to be understood in particular a connection status between the frequency unit and the heating connection. Preferably, the connection information is encoded in a digital signal, which preferably can assume only two values. A "faulty existence of the line path" is to be understood in particular an existence of the line path between the frequency unit and the heating connection, which exists erroneously and deviates from an adjustment made by the control unit of the switching arrangement. In particular, a faulty existence of a line path can be due to a defective switching element, in particular a stuck electromechanical relay, and / or to a faulty control of the switching element. A "security measure" should be understood in particular as a measure that is triggered in response to the faulty existence of the line path and that preferably aims at securing the heating device. The security measure preferably includes a shutdown of all frequency units. The security measure preferably includes issuing an error message and / or a maintenance request. By such a configuration, an operating safety can be increased particularly advantageous.

Advantageously, a total number of all heating elements is greater than a total number of all frequency units. A "total number of all heating elements" should be understood in particular the total number of all heating elements of a hob. A "total number of frequency units" should be understood in particular the total number of all frequency units of the hob. This can reduce material and costs. Advantageously, the total number of frequency units is two in a hob with at least three heating elements. Advantageously, the total number of frequency units is four in a matrix cooktop. A "matrix cooking field" is to be understood, in particular, as a cooking surface in which the heating elements are arranged in a regular grid under a hob plate, and a region which can be heated by means of the heating elements the cooktop panel preferably comprises at least 60%, in particular at least 70%, advantageously at least 80% and particularly advantageously at least 90% of a total area of the cooktop panel. In particular, the matrix cooking field comprises at least 10, in particular at least 20, advantageously at least 30 and particularly advantageously at least 40 heating elements. In this way, despite a limited number of frequency units, in particular in matrix cooking fields, where experience teaches that usually a maximum of four cookware are heated, a high level of operating comfort can be ensured.

Furthermore, a method is proposed with a heating device according to the invention, in particular a cooktop device, with at least one heating connection for at least one heating element, at least one frequency unit and a protection unit, in which the protection unit determines that a line path exists between the frequency unit and the heating connection. As a result, operational reliability can be increased, in particular if the heating device has switching elements, preferably in the form of electromechanical relays. Furthermore, an operating security can be increased since a faulty existence of a line path can be detected. In this way, in particular in the case of a hob, it is possible to prevent heating elements from being operated without load. Furthermore, it can be prevented, in particular with induction hobs, that magnetic fields propagate freely from the heating elements in the vicinity of the induction hob.

Further advantages can be found in the following drawing descriptions. In the drawings, two embodiments of the invention are shown. The drawings, the descriptions and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into meaningful further combinations.

Fig. 1a

ein Induktionskochfeld mit vier Heizzonen in einer Draufsicht,

Fig. 1b

eine Heizvorrichtung des Induktionskochfelds aus Fig. 1 a,

Fig. 2

einen Potentialverlauf bei einer bestehenden Verbindung,

Fig. 3

einen Potentialverlauf bei einer getrennten Verbindung,

Fig. 4a

ein Induktionskochfeld mit drei Heizzonen in einer Draufsicht und

Fig. 4b

eine Heizvorrichtung des Induktionskochfelds aus Fig. 4a.

Show it:

Fig. 1a

an induction hob with four heating zones in a plan view,

Fig. 1b

a heater of the induction hob off Fig. 1 a,

Fig. 2

a potential course in an existing connection,

Fig. 3

a potential course in a separate connection,

Fig. 4a

an induction hob with three heating zones in a plan view and

Fig. 4b

a heater of the induction hob off Fig. 4a ,

Fig. 1a shows a plan view of an induction hob with a cooktop plate 34a made of glass ceramic, on the four heating zones 36a, 38a, 40a, 42a are marked in a known manner. A heating device ( Fig. 1b ) of the induction hob has four heating elements 18a, 20a, 22a, 24a designed as inductor coils, all of which can be operated simultaneously at different power levels. Each of the heating elements 18a, 20a, 22a, 24a is associated with one of the cooking zones 36a, 38a, 40a, 42a, so that when using the induction hob each heating element 18a, 20a, 22a, 24a exactly one cookware element, ie z. As a pot or pan, heated. The heating device has two frequency units 26a, 28a, by means of which the heating elements 18a, 20a, 22a, 24a can be supplied with energy via heating connections 10a, 12a, 14a, 16a of the heating device. Thus, a total number of all heating elements 18a, 20a, 22a, 24a is greater than a total number of all frequency units 26a, 28a. The two frequency units 26a, 28a each include an inverter 44a, 46a and a snubber bank 48a, 50a. The inverter 44a includes a first insulated gate bipolar transistor (hereinafter abbreviated to "IGBT") 52a and a second IGBT 54a. In addition, the inverter 46a has a first IGBT 56a and a second IGBT 58a. Alternatively, instead of the IGBTs, any other switching unit that appears expedient to the person skilled in the art can be used, but preferably a bidirectional unipolar switch.

Furthermore, the heating device has a country-specific AC voltage source 60a, which supplies a mains voltage with an effective value of 230 V and a frequency of 50 Hz. The described heater is intended in particular for operation in Germany. For heaters intended for US operation, a corresponding AC power source supplies a 60 Hz power line voltage. The voltage of AC power source 60a first passes through a heater filter 62a, which eliminates high frequency noise and is essentially a low pass filter. A voltage filtered by the filter 62a is rectified by a rectifier 64a of the heater, which may be formed as a bridge rectifier, so that a rectified voltage U ₀ is output at an output of the rectifier 64a between a collector of the IGBT 52a and an emitter of the IGBT 54a is present. The rectified voltage U ₀ is also applied between a collector of the IGBT 56 a and to an emitter of the IGBT 58 a. The snubber capacitor banks 48a, 50a each consist of two capacitors, wherein a first capacitor is connected in parallel with the first IGBT 52a, 56a and a second capacitor is connected in parallel with the second IGBT 54a, 58a of the respective frequency unit 26a, 28a.

Furthermore, the heating device has a switching arrangement 66a. The switching arrangement 66a comprises six switching elements 68a, 70a, 72a, 74a, 76a, 78a. The switching elements 68a, 70a, 72a, 74a, 76a, 78a are SPDT relays and identical. Each of the switching elements 68a, 70a, 72a, 74a, 76a, 78a has a first, a second and a third contact and a coil, wherein the first contact is conductively connectable to the second or the third contact by a corresponding control of the coil , The first contact of the switching element 68a is conductively connected to the emitter of the IGBT 52a. Further, the second contact of the switching element 68a is connected to the first contact of the switching element 70a. The third contact of the switching element 68a is conductively connected to the first contact of the switching element 72a. The second contact of the switching element 70a is conductively connected to the heating terminal 10a. The third contact of the switching element 70a is conductively connected to the heating terminal 12a. The second contact of the switching element 72a is conductively connected to the heating terminal 14a. The third contact of the switching element 72a is conductively connected to the heating port 16a. In addition, the first contact of the switching element 74a is conductively connected to the emitter of the IGBT 56a. Further, the second contact of the switching element 74a is connected to the first contact of the switching element 76a. The third contact of the switching element 74a is conductively connected to the first contact of the switching element 78a. The second contact of the switching element 76a is conductively connected to the heating terminal 10a. The third contact of the switching element 76a is conductively connected to the heating terminal 12a. The second contact of the switching element 78a is conductively connected to the heating terminal 14a. The third contact of the switching element 78a is conductively connected to the heating terminal 16a.

The heating element 18a is connected to a first contact with the heating connection 10a. The heating element 20a is connected to a first contact with the heating connection 12a. The heating element 22a is connected to a first contact with the heating connection 14a. The heating element 24a is connected to a first contact with the heating connection 16a. A second contact of the heating element 18a is conductively connected to a second contact of the heating element 20a. Further, a second contact of the heating element 22a is conductively connected to a second contact of the heating element 24a. The heater further includes resonant capacitors 80a, 82a, 84a, 86a. The second contact of the heating element 18a is conductively connected to a first contact of the resonance capacitor 80a and to a first contact of the resonance capacitor 82a. The second contact of the heating element 22a is conductively connected to a first contact of the resonance capacitor 84a and to a first contact of the resonance capacitor 86a. Second contacts of the two resonant capacitors 80a, 84a are conductively connected to the collector of the IGBT 52a. Further, second contacts of the two resonance capacitors 82a, 86a are conductively connected to the emitter of the IGBT 58a.

The heating device comprises a control unit 32a, which is provided to control the switching arrangement 66a and the frequency units 26a, 28a by means of drive signals for the inverters 44a, 46a and a predetermined heating power regulate. The control unit 32a is designed to perform a time-division multiplexing method, wherein different operating modes can be used in the individual defined time segments of the time-division multiplexing method. The operating modes used include a "dedicated mode", a "booster mode" and a "phase drive mode". The control mechanisms may be executed sequentially at different time slots of the time division multiplexing process.

In the "dedicated mode", a frequency unit 26a, 28a supplies exactly one of the heating elements 18a, 20a, 22a, 24a with energy. Due to the shared resonant capacitors 80a, 82a of the heating elements 18a, 20a and the shared resonant capacitors 84a, 86a of the heating elements 22a, 24a, there are limitations in associating the heating elements 18a, 20a, 22a, 24a with the frequency units 26a, 28a. Thus, a simultaneous operation of several heating elements 18a, 20a, 22a, 24a in the dedicated mode is only possible for the heating elements 18a, 20a, 22a, 24a, which are connected to different resonance capacitors 80a, 82a, 84a, 86a. The drive signals for the inverters 44a, 46a of the frequency units 26a, 28a are independent in this mode of operation.

In booster mode, one heating element 18a, 20a, 22a, 24a is operated in parallel by both frequency units 26a, 28a in order to achieve a higher heating power. The drive signals for the inverters 44a, 46a of the frequency units 26a, 28a are identical in this operating mode for both inverters 44a, 46a.

In the phase drive mode, two heating elements 18a, 20a, 22a, 24a with common resonant capacitors 80a, 82a, 84a, 86a are respectively energized by a frequency unit 26a, 28a. The drive signals for the inverters 44a, 46a of the frequency units 26a, 28a have the same frequency in this operating mode, whereby a total power of the two heating elements 18a, 20a, 22a, 24a is fixed. A relationship of the individual Heating powers of the two heating elements 18a, 20a, 22a, 24a to each other is determined by a phase shift between the drive signals. Further, the driving signals are adjusted so as to ensure zero-voltage switching of the IGBTs 52a, 54a, 56a, 58a of the inverters 44a, 46a of the frequency units 26a, 28a. As a result, switching losses can be minimized.

Due to frequent switching of the switching elements 68a, 70a, 72a, 74a, 76a, 78a of the time division multiplexing circuitry 66a, it is important to detect malfunctions of the switching device 66a or to drive the switching device 66a. During a lifetime of the induction hob some hundreds of thousands of switching operations per switching element 68a, 70a, 72a, 74a, 76a, 78a are to be expected. To minimize malfunctions, the frequency units 26a, 28a are turned off during the switching operations, so that the switching elements 68a, 70a, 72a, 74a, 76a, 78a are de-energized during the switching operation. Nevertheless, a malfunction can never be completely ruled out. Possible malfunctions include on the one hand malfunction of the switching elements 68a, 70a, 72a, 74a, 76a, 78a, such as a stuck relay or a defective component in a control circuit of the relay, or on the other malfunction of the control software of the switching elements 68a, 70a, 72a, 74a, 76a , 78a.

In the case of the heating device according to the invention, a method is used in which the existence of a line path between a frequency unit 26a, 28a and a heating connection 10a, 12a, 14a, 16a is determined by a protective unit 30a of the heating device. In at least one operating state, the protection unit 30a determines the existence of the conduction path between one of the two frequency units 26a, 28a and one of the four heating connections 10a, 12a, 14a, 16a on the basis of a potential curve which it evaluates at the heating connections 10a, 12a, 14a, 16a.

Fig. 2 shows in a Cartesian coordinate system a typical potential profile V ₁ (t) at a heating connection 10 a, 12 a, 14 a, 16 a in the presence of a Conduction paths between the heating port 10a, 12a, 14a, 16a and a frequency unit 26a, 28a. The ordinate axis 88a shows the electrical potential V ₁ at the heating connection 10a, 12a, 14a, 16a. The abscissa axis 90a shows a time t. The potential profile V ₁ (t) essentially has the form of a rectangular signal with steep flanks. Due to sharp edges, high-frequency signal components whose frequency is above a switching frequency of the frequency units 26a, 28a are contained in a frequency spectrum of the potential profile V ₁ (t).

Fig. 3 shows in a Cartesian coordinate system a typical potential profile V ₂ (t) at a heating connection 10a, 12a, 14a, 16a in the absence of a line path between the heating connection 10a, 12a, 14a, 16a and a frequency unit 26a, 28a. The ordinate axis 92a shows the electrical potential V ₂ at the heating connection 10a, 12a, 14a, 16a. The abscissa axis 94a shows a time t. The potential curve V ₂ (t) has substantially the shape of a U to _0/2 shifted in the direction of the axis of ordinates 92a sinusoidal signal. The potential profile V ₂ (t) at the heating connection 10a, 12a, 14a, 16a is with a potential profile on a side facing away from the heating connection 10a, 12a, 14a, 16a side of the heating connection 10a, 12a, 14a, 16a associated heating element 18a, 20a, 22a , 24a, in the absence of a conduction path between the heating port 10a, 12a, 14a, 16a and the frequency unit 26a, 28a, current flow through the heating element 18a, 20a, 22a, 24a is zero. Due to an approximately sinusoidal course, only a few signal components are contained in a frequency spectrum of the potential course V ₂ (t). Their frequencies are in the vicinity of the switching frequency of the frequency units 26a, 28a.

In order to distinguish the two different potential profiles V ₁ (t), V ₂ (t), the protection unit 30a comprises a high-pass filter for each heating connection 10a, 12a, 14a, 16a with a cutoff frequency above the switching frequency of the frequency units 26a, 28a. Signal components of the potential profiles V ₁ (t), V ₂ (t) with frequencies below the cutoff frequency are strongly attenuated, while signals with frequencies above the cutoff frequency are left virtually unchanged. This results in a discrimination of the potential curves V ₁ (t), V ₂ (t) in terms of their frequency spectrum and the protection unit 30a can determine whether the conduction path exists between the heating port 10a, 12a, 14a, 16a and a frequency unit 26a, 28a. In the case of the existence of the line path, the protection unit 30a outputs a logic "0". In the case of the absence of the line path, the protection unit 30a outputs a logical "1".

In one example, assume that the two heaters 18a, 24a are to be operated in the dedicated mode. With a correct switch position of the switching arrangement 66a, the two switching elements 68a, 70a in the upper position and the switching elements 74a, 78a in the lower position. The protection unit 30a passes on to the control unit 32a corresponding connection information, which compares the control unit 32a with a desired switch position. In the present case, the protection unit 30a gives a "0" for the heating connection 10a, a "1" for the heating connection 12a, a "1" for the heating connection 14a and a "0" for the heating connection 16a. Assume that the switching element 70a is in the wrong position in the lower position instead of the upper position. In this case, the protection unit 30a gives a "1" for the heating connection 10a, a "0" for the heating connection 12a, a "1" for the heating connection 14a and a "0" for the heating connection 16a to the control unit 32a. In this failure mode, the heating element 20a is erroneously energized, potentially resulting in an operator-dangerous operating condition. The control unit 32a detects this misalignment and shuts off all the frequency units 26a, 28a. In addition, the control unit 32a issues a warning message and a maintenance request to an operator. Assume that the switching element 68a is in the wrong position, namely in the lower position instead of the upper position. In this case, the protection unit 30a for the heating terminal 10a gives a "1", for the heating terminal 12a a "1", for the heating terminal 14a depending on a switch position of the switching element 72a either a "0" or a "1" and for the Heating terminal 16a a "0" to the control unit 32a on. When the switching element 72a is in the up position, the heating element 22a is erroneously energized, potentially resulting in a dangerous operating state for an operator can lead. If the switching element 72a in the lower position, both frequency units 26a, 28a are connected in parallel with the heating element 24a and it can in the case of different drive signals, in particular in the case of different phase positions, for the inverters 44a, 46a of the frequency units 26a, 28a to a Short circuit of the inverters 44a, 46a and their destruction come. The control unit 32a detects this misalignment and shuts off all the frequency units 26a, 28a. In addition, the control unit 32a issues a warning message and a maintenance request to an operator.

In another example, assume that the heating element 18a is to be operated in booster mode. With a correct switch position of the switching arrangement 66a, the four switching elements 68a, 70a, 74a, 78a are in the upper position. The protection unit 30a passes on to the control unit 32a corresponding connection information, which compares the control unit 32a with a desired switch position. In the present case, the protection unit 30a gives a "0" for the heating connection 10a, a "1" for the heating connection 12a, a "1" for the heating connection 14a and a "1" for the heating connection 16a. Assume that the switching element 76a is in the wrong position, in the lower position instead of the upper position. In this case, the protection unit 30a gives a "0" for the heating connection 10a, a "0" for the heating connection 12a, a "1" for the heating connection 14a and a "1" for the heating connection 16a to the control unit 32a. In this failure mode, the two heating elements 18a, 20a are operated in a phase drive mode with unpowered drive signals of the inverters 44a, 46a of the frequency units 26a, 28a. This can lead to higher switching losses and more heating of the inverters 44a, 46a. Furthermore, the heating element 20a is erroneously energized, which can potentially lead to a dangerous operating state for an operator. The control unit 32a detects this misalignment and shuts off all the frequency units 26a, 28a. In addition, the control unit 32a issues a warning message and a maintenance request to an operator. Assume that the switching element 74a is in the wrong position, in the lower position instead of the upper position. In this case, the protection unit 30a outputs a "0" for the heating connection 10a, a "1" for the heating connection 12a and a "0" for the heating connection 14a or a "1" for the heating connection 16a, depending on a switch position of the switching element 78a. or for the heating connection 14a a "1" and for the heating connection 16a a "0" to the control unit 32a on. In this failure mode, depending on the switching state of the switching element 78a, either the heating element 22a or the heating element 24a is energized, which may result in a potentially hazardous operating condition for an operator. The control unit 32a detects this misalignment and shuts off all the frequency units 26a, 28a. In addition, the control unit 32a issues a warning message and a maintenance request to an operator.

In a final example, assume that the two heaters 18a, 20a are to be operated in the phase drive mode. With a correct switch position of the switching arrangement 66a, the three switching elements 68a, 70a, 74a in the upper position and the switching element 76a in the lower position. The protection unit 30a passes on to the control unit 32a corresponding connection information, which compares the control unit 32a with a desired switch position. In the present case, the protection unit 30a gives a "0" for the heating connection 10a, a "0" for the heating connection 12a, a "1" for the heating connection 14a and a "1" for the heating connection 16a. Assume that the switching element 76a is in the wrong position, in the upper position instead of the lower position. In this case, the protection unit 30a for the heating connection 10a gives a "0", for the heating connection 12a a "1", for the heating connection 14a a "1" and for the heating connection 16a a "1" to the control unit 32a. In this fault mode, the two frequency units 26a, 28a are connected in parallel with the heating element 18a and, in the case of different drive signals, in particular in the case of different phase positions, for the inverters 44a, 46a of the frequency units 26a, 28a, the inverters 44a, 46a short-circuit and their destruction is coming. The control unit 32a detects this misalignment and shuts off all the frequency units 26a, 28a. In addition, the control unit 32a issues a warning message and a maintenance request to an operator. Assume that the switching element 74a is in the wrong position, in the lower position instead of the upper position. In this case, the protection unit 30a outputs a "0" for the heating connection 10a, a "1" for the heating connection 12a and a "0" for the heating connection 14a or a "1" for the heating connection 16a, depending on a switch position of the switching element 78a. or for the heating connection 14a a "1" and for the heating connection 16a a "0" to the control unit 32a on. In this failure mode, depending on a switch position of the switching element 78a, either the heating element 22a or the heating element 24a is erroneously energized, which may result in a potentially hazardous operating condition for an operator. The control unit 32a detects this misalignment and shuts off all the frequency units 26a, 28a. In addition, the control unit 32a issues a warning message and a maintenance request to an operator.

Alternatively or additionally, the protection unit 30a may also include a current sensor to determine the existence of the conduction path in at least one operating state. Alternatively or additionally, the heating device may comprise at least one ammeter provided for measuring an electric current through the conduction path.

In the Fig. 4a and 4b a further embodiment of the invention is shown. The following descriptions are essentially limited to the differences between the embodiments, with respect to the same components, features and functions on the description of the other embodiments, in particular the Fig. 1a and 1b , can be referenced. To distinguish the embodiments, the letter a in the reference numerals of the embodiment in the Fig. 1a and 1b by the letter b in the reference numerals of the embodiment of Fig. 4a and 4b replaced. With regard to identically designated components, in particular with regard to components with the same reference numerals, can in principle also to the drawings and / or the description of the other embodiment, in particular the Fig. 1a and 1b , to get expelled.

Fig. 4a shows a second induction hob with a hob plate 34b made of a glass ceramic in a plan view. On the hob plate 34b three circular heating zones 36b, 38b, 40b are marked in a known manner. Fig. 4b shows an electrical circuit diagram of a second heating device of the second induction hob. The heating device comprises only three heating elements 18b, 20b, 22b, which can be connected via a switching arrangement 66b with two frequency units 26b, 28b. To minimize production costs by reducing a number of different types of heaters, the heater comprises Fig. 4b furthermore, a heating connection 16b for a fourth heating element, which can be connected via the switching element 72b to the frequency unit 26b and via the switching element 78b to the frequency unit 28b. In this way, a further fault situation becomes possible, namely that one of the two switching elements 72b, 78b establishes a conduction path between one of the frequency units 26b, 28b and the heating connection 16b. An inverter 44b, 46b of the frequency unit 26b, 28b would then have as its sole load a damping capacitor bank 48b, 50b belonging to the frequency unit 26b, 28b. The inverters 44b, 46b can survive this mode of operation for a short time without damage. It is the task of a protection unit 30b of the heating device to recognize this mode of operation in good time. For a detailed description of an operation of the protection unit 30b, reference is made to the description of the previous embodiment.

In principle, it is conceivable that a heating device has further switching elements and more than four heating elements which are connected to frequency units by means of the further switching elements. In principle, it is conceivable that the switching elements, which are designed as SPDT relays, are each replaced by two SPST relays. reference numeral 10a heating connection 38a heating zone 10b heating connection 38b heating zone 12a heating connection 40a heating zone 12b heating connection 40b heating zone 14a heating connection 42a heating zone 14b heating connection 44a inverter 16a heating connection 44b inverter 16b heating connection 46a inverter 18a heating element 46b inverter 18b heating element 48a Snubber capacitor bank 20a heating element 48b Snubber capacitor bank 20b heating element 50a Snubber capacitor bank 22a heating element 50b Snubber capacitor bank 22b heating element 52a IGBT 24a heating element 52b IGBT 26a frequency unit 54a IGBT 26b frequency unit 54b IGBT 28a frequency unit 56a IGBT 28b frequency unit 56b IGBT 30a protection unit 58a IGBT 30b protection unit 58b IGBT 32a control unit 60a AC voltage source 32b control unit 60b AC voltage source 34a Hotplate 62a filter 34b Hotplate 62b filter 36a heating zone 64a rectifier 36b heating zone 64b rectifier 66a switching arrangement V ₂ (t) potential curve 66b switching arrangement V ₁ potential 68a switching element V ₂ potential 68a switching element t Time 70a switching element 70b switching element 72a switching element 72b switching element 74a switching element 74b switching element 76a switching element 76b switching element 78a switching element 78b switching element 80a resonant capacitor 80b resonant capacitor 82a resonant capacitor 82b resonant capacitor 84a resonant capacitor 84b resonant capacitor 86a resonant capacitor 86b resonant capacitor 88a axis of ordinates 90a abscissa 92a axis of ordinates 94a abscissa U ₀ Rectified voltage V ₁ (t) potential curve

Claims (9)

1. Heating apparatus having at least one heating element (18a, 20a, 22a, 24a; 18b, 20b, 22b), which has at least one heating connection (10a, 12a, 14a, 16a; 10b, 12b, 14b, 16b), and having at least one frequency unit (26a, 28a; 26b, 28b), characterised by a protective unit (30a; 30b), which is provided to determine the existence of a conducting path between the frequency unit (26a, 28a; 26b, 28b) and the heating connection (10a, 12a, 14a, 16a; 10b, 12b, 14b, 16b) and by a control unit (32a; 32b), which is provided to receive connection information from the protective unit (30a; 30b) and to initiate at least one safety measure in the event of the erroneous existence of a conducting path.
2. Heating apparatus according to claim 1, characterised in that the protective unit (30a; 30b) is provided to determine the existence of the conducting path based on a potential profile.
3. Heating apparatus according to claim 2, characterised in that the protective unit (30a; 30b) is provided to analyse the potential profile at the heating connection (10a, 12a, 14a, 16a; 10b, 12b, 14b, 16b).
4. Heating apparatus according to claim 2 or 3, characterised in that the protective unit (30a; 30b) is provided to determine the existence of the conducting path based on a frequency spectrum of the potential profile.
5. Heating apparatus according to one of claims 2 to 4, characterised in that the protective unit (30a; 30b) comprises at least one high-pass filter, which is provided to discriminate between potential profiles.
6. Heating apparatus according to one of the preceding claims, characterised in that the protective unit (30a; 30b) comprises a current sensor, which is provided to determine the existence of the conducting path.
7. Heating apparatus as claimed one of the preceding claims, characterised in that a total number of all heating elements (18a, 20a, 22a, 24a; 18b, 20b, 22b) is greater than a total number of all frequency units (26a, 28a; 26b, 28b).
8. Method with a heating apparatus having at least one heating element (18a, 20a, 22a, 24a; 18b, 20b, 22b), which has at least one heating connection (10a, 12a, 14a, 16a; 10b, 12b, 14b, 16b), and having at least one frequency unit (26a, 28a; 26b, 28b), a protective unit (30a; 30b) and a control unit (32a; 32b), wherein the protective unit (30a; 30b) determines the existence of a conducting path between the frequency unit (26a, 28a; 26b, 28b) and the heating connection (10a, 12a, 14a, 16a; 10b, 12b, 14b, 16b), wherein connection information from the protective unit (30a; 30b) is received by the control unit (32a; 32b) and at least one safety measure is initiated by the control unit (32a; 32b) in the event of the erroneous existence of the conducting path.
9. Cooktop having a heating apparatus according to one of claims 1 to 7.

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