EP2789208B1 - Induction heating device - Google Patents

Description

The invention is based on an induction heating device according to the preamble of claim 1.

It's from documents like EP-A-0888033 Induction cooking furnaces are known having inverters connected in parallel to an inductor.

The object of the invention is in particular to provide a generic device with improved heating properties. The object is achieved by the features of claim 1, while advantageous embodiments and modifications of the invention can be taken from the dependent claims.

The invention is based on an induction heating device, in particular an induction hob device, having at least two switching elements which are connected in parallel in at least one operating mode and intended to generate a high-frequency alternating current for supplying an induction heating element, and with at least one control unit.

It is proposed that the control unit be provided to actuate at least two of the at least two switching elements with different activity parameters, at least in the operating mode. A "switching element" is to be understood, in particular, as an electrical component which is intended to produce and / or to separate at least one electrical connection between at least two power contacts of the switching element. In particular, the switching element is designed as a semiconductor switching element, preferably as a transistor, in particular as an IGBT. Preferably, the switching element has at least one control contact, which is merely provided to enable an adjustment of a switching state of the switching element, in particular by a control unit. Including that two switching elements are "connected in parallel", should be understood in particular that poles of the same name, in particular at least similar power contacts, the switching elements are connected to each other directly. Under a "direct connection" should In particular, an electrical connection can be understood which, at least in an operating state with a current flow of alternating current via the connection with a frequency between 1 kHz and 100 kHz has an impedance which is smaller in magnitude than 10 V / A, in particular smaller than 1 V / A, preferably less than 0.1 V / A, and the amount thereof in particular over a frequency range of 1 kHz to 100 kHz by a maximum of 100%, in particular a maximum of 40%, preferably a maximum of 10%, preferably a maximum of 3%, fluctuates ,

An "induction heating element" is to be understood in particular a heating element with at least one induction heating, which is provided by induction effects, in particular induction of electric current and / or Ummagnetisierungseffekte in a, preferably ferromagnetic, in particular metallic, heating means, in particular in a cooking utensil, in an oven wall and / or in a radiator, which is arranged in an oven to cause heating of the heating medium. In particular, the induction heating element is provided to transmit in at least one operating mode in which the induction heating is connected to a supply electronics, a power of at least 100 W, in particular at least 500 W, advantageously at least 1000 W, preferably at least 2000 W, in particular electrical energy into electromagnetic field energy, which is finally converted into heat in a suitable heating medium. An "induction heating line" is to be understood as meaning, in particular, an electrical line which is intended to carry an electric current which is intended to induce induction effects in a suitable heating means. Preferably, the induction heating is as inductance, in particular as a coil, advantageously as a flat coil, preferably at least substantially in the form of a circular disc, alternatively in the form of an oval or a rectangle formed. In particular, the induction heating line, in particular with a coupled heating means, has an inductance of at least 0.1 μT, in particular at least 0.3 μT, advantageously at least 1 μT. In particular, the induction heating line, in particular without a coupled heating means, has an inductance of not more than 100 mT, in particular not more than 10 mT, advantageously not more than 1 mT. Preferably, the induction heating is intended, at least in an operating state of high-frequency alternating current, in particular an alternating current having a frequency of at least 1 kHz, in particular at least 3 kHz, advantageously at least 10 kHz, preferably at least 20 kHz, in particular at most 100 kHz, in particular with a current of at least 0.5 A, in particular at least 1 A, advantageously at least 3 A, preferably at least 10 A, to be traversed. A "control unit" is to be understood, in particular, as an electronic unit which is preferably at least partially integrated in a control and / or regulating unit of a domestic appliance having the induction heating device. Preferably, the control unit is at least provided to control and / or regulate the switching elements. 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.

By "provided" is intended to be understood in particular specially programmed, designed and / or equipped. An "activity parameter" should in particular be understood to mean at least one switch-on instant, one duration and / or one switch-off instant of a drive, in particular a phase and / or a duty cycle of a regular, preferably at least substantially periodic, drive. In particular, the induction heating device has at least one sensor arrangement which is provided to provide operating values, as a function of which the control unit determines the activity parameters.

Due to the configuration according to the invention, in particular a heating behavior adapted to operating values can be achieved. In particular, a duration that can be heated with maximum heating power before an emergency regulation due to overheating of the switching elements takes place can be extended.

Furthermore, it is proposed that the at least two switching elements are connected in parallel independently of the operating state. Alternatively, it is conceivable that the switching elements are provided, for example, to a boost mode to be connected in parallel via a further, in particular electromechanical, switching element, in particular a relay. By continuously switching elements in parallel increased efficiency can be made possible by reduced line losses in the switching elements, even at low power.

It is also proposed that the control unit is provided to operate at least two of the switching elements with different duty cycles, at least in the operating mode. A duty cycle is to be understood in particular the ratio of turn-on time to total time. A duty cycle of 100% corresponds to a constantly established connection, while a duty cycle of 0% corresponds to a constantly disconnected connection. In particular, an effective value of currents flowing through the different switching elements can be adapted, whereby in particular line losses of the different switching elements can be changed.

Furthermore, it is proposed that the control unit be provided to activate the at least two switching elements at least substantially simultaneously, at least in the operating mode. The term "substantially simultaneously" should in particular be understood to mean that a distance of switch-on edges of the control currents for the different switching elements is at most 1 μs, advantageously at most 0.1 μs, preferably at most 10 ns. Preferably, in this case, a sampling rate for the correspondingly switched off switching element is selected such that a current through the switching element is zero before the correspondingly different switching element is switched off. In particular, high efficiency can be achieved. In particular, a power loss can be avoided by switching losses on the switching element, which is turned off earlier accordingly. Alternatively, it is conceivable that the control unit is provided to switch off the switching elements at least substantially simultaneously, whereby an allocation of the switching losses is achieved, but line losses are redistributed.

It is also proposed that the induction heating device has at least one current sensor arrangement which is provided to determine currents flowing through the at least two switching elements. In particular, it is conceivable that each of the switching elements, in particular exactly one, current sensor is connected in series. A "current sensor" is to be understood, in particular, as a sensor, in particular an ammeter, which measures at least the alternating current component, in particular by inductive means. Alternatively, it is conceivable that at least one current sensor is provided which measures the total current flowing through all the switching elements. In particular, it may be an accurate determination of a performance in the Induction heating element is implemented to be performed. In particular, a loss performance determination of the line losses can be carried out for each of the switching elements.

In particular, the control unit is provided to determine the activity parameters of the at least two switching elements as a function of values of the current sensor arrangement. In particular, the control unit is provided to equalize rms values of the currents through different ones of the at least two switching elements by decreasing the sampling rate of a high rms switching element over a low rms switching element. In particular, the control unit is provided to adjust the activity parameters when a minimum effective value of the at least two switching elements is less than 100%, in particular less than 80%, advantageously none is 60%, preferably less than 40% of a maximum effective value of the at least two switching elements. In particular, the control unit is provided to adjust the activity parameters when a minimum effective value of the at least two switching elements is at most 20%; in particular at most 40%, advantageously at most 60%, preferably at most 80%, of a maximum effective value of the at least two switching elements. In particular, it is possible to achieve a distribution of occurring power losses of the switching elements which arise as a result of line losses.

Furthermore, it is proposed that the induction heating device has at least one temperature sensor arrangement which is provided to determine temperatures of the at least two switching elements. In particular, the temperature sensor arrangement has at least two temperature sensors which are arranged on at least one heat sink, in particular divided by the switching elements, wherein the control unit is provided to determine temperatures of the switching elements on the basis of measured values of these temperature sensors. Alternatively, it is conceivable that at least one, in particular a plurality, preferably each, of the switching elements has an integrated temperature sensor. In particular, a temperature monitoring of the switching elements can be achieved.

In particular, the control unit is provided to adjust the activity parameters of the at least two switching elements as a function of values of the To determine temperature sensor arrangement. In particular, the control unit is provided to adjust the activity parameters when a temperature of at least one of the switching elements exceeds a temperature of 160 ° C, in particular of 150 ° C, advantageously of 140 ° C. In particular, the control unit is provided to adapt the activity parameters when a minimum of the temperatures of the at least two switching elements deviates by at least 5 K, in particular by at least 10 K, advantageously by at least 15 K, from a maximum of the temperatures of the at least two switching elements. In particular, regulation of the activity parameters as a function of values of the temperature sensor arrangement takes precedence over regulation of the activity parameters as a function of values of the current sensor arrangement.

Further advantages emerge from the following description of the drawing. In the drawing, an embodiment of the invention is shown. The drawing, the description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into meaningful further combinations.

Fig. 1

ein erfindungsgemäßes Kochfeld in einer schematischen Ansicht von oben,

Fig. 2

eine erfindungsgemäße Induktionsheizvorrichtung in einem schematischen Schaltbild,

Fig. 3

ein erster Betriebszustand eines ersten Ausgangsbetriebsmodus,

Fig. 4

ein erster erfindungsgemäßer Betriebsmodus als Reaktion auf den ersten Betriebszustand,

Fig. 5

ein zweiter Betriebszustand des ersten Ausgangsbetriebsmodus,

Fig. 6

ein zweiter erfindungsgemäßer Betriebsmodus als Reaktion auf den zweiten Betriebszustand und

Fig. 7

ein Temperatur- und Leistungsverlauf einer erfindungsgemäßen Induktionsheizvorrichtung bei Hochleistungsbetrieb.

Show it:

Fig. 1

an inventive hob in a schematic view from above,

Fig. 2

an induction heating device according to the invention in a schematic diagram,

Fig. 3

a first operating state of a first output operating mode,

Fig. 4

a first operating mode according to the invention in response to the first operating state,

Fig. 5

a second operating state of the first output operating mode,

Fig. 6

a second operating mode according to the invention in response to the second operating state and

Fig. 7

a temperature and performance curve of an induction heater according to the invention in high-power operation.

FIG. 1 shows a designed as an induction hob home appliance 10 with an induction heater designed as an induction heater 12. The induction heater 12 has four induction heating 20, 22, 24, 26 on. The induction heating elements 20, 22, 24, 26 are arranged under a hob plate 18.

FIG. 2 1 shows an embodiment of the induction heating device 12 in an exemplary circuit of the induction heating element 20. The induction heating device 12 has a voltage source 30. Furthermore, the induction heating device 12 has four switching elements 42, 44, 46, 48. The switching elements 42, 44, and 46, 48 are connected in parallel to each other in pairs, independently of an operating mode. The switching elements 42, 44, 46, 48 are part of an inverter 40. The switching elements 42, 44, 46, 48 are designed as IGBTs. The inverter 40 and the switching elements 42, 44, 46, 48 are provided to generate a high-frequency alternating current for supplying the induction heating element 20. The inverter 40 is connected to the voltage source 30 and draws on this energy to supply the induction heating element 20. The voltage source 30 has, among other things, a rectifier, a filter electronics and a buffer capacity (not shown). and furthermore, the induction heating device 12 has a control unit 14, which is provided to control the switching elements 42, 44, 46, 48. The control unit 14 is provided to periodically control the switching elements 42, 44, 46, 48 for generating the high-frequency alternating current. The control unit 14 is provided, in operating modes in which operating parameters of the parallel-connected switching elements 42, 44, and 46, 48 differ from each other, the parallel switching elements 42, 44, and 46, 48 to drive with different activity parameters. The control unit 14 is provided to operate in such an operating mode, the switching elements 42, 44, and 46, 48 with different duty cycles. Furthermore, the control unit 14 is provided to activate the parallel-connected switching elements 42, 44, and 46, 48 at the same time in such an operating mode. The control unit 14 is provided to turn on the switching elements 42, 44, 46, 48 under zero voltage conditions (ZVS). The induction heating element 20 is connected in a half-bridge circuit with resonance. The induction heating element 20 is schematically represented here by a series connection of an inductance and a resistance corresponding to a load.

Alternatively, it is conceivable that an induction heating element is connected in full bridge circuit or in one-switch topology.

The induction heater 12 further includes a heat sink 16 which is arranged to dissipate heat generated by the switching elements 42, 44, 46, 48 during operation.

Furthermore, the induction heating device 12 has a temperature sensor arrangement 50. The temperature sensor arrangement 50 has four temperature sensors 52, 54, 56, 58, which are provided to measure temperatures of the heat sink 16 at different positions. The control unit 14 is provided to calculate temperatures of the temperature sensor arrangement 50 from temperatures ₄₂ , ₄₄ , ₄₆ , _{48 of} the switching elements 42, 44, 46, 48. Furthermore, the induction heating device 12 has a current sensor arrangement 60. The current sensor arrangement 60 has four current sensors 62, 64, 66, 68. The current sensors 62, 64, 66, 68 are each connected in series in a parallel branch of the switching elements 42, 44, 46, 48 to the respective switching element 42, 44, 46, 48. The current sensor arrangement 60 is provided to measure currents I ₄₂ , I ₄₄ , I ₄₆ , I ₄₈ flowing through the switching elements 42, 44, 46, 48.

In FIG. 3 are exemplary illustrated at the switching elements 42, 44, schematic courses of different operating variables over an activity period during a switching period of a first initial operating mode of the switching elements 42, 44 as a function of the time t shown. In the first mode of operation, the switching elements 42, 44 are turned on simultaneously and at the same frequency and later switched off again. They have the same phase and the same duty cycle. The upper two graphs show a profile of a voltage U ₂₀ and a current I _{20 of} the induction heating element 20. The third and fourth graph or the seventh and eighth graph show curves of voltages U ₄₂ , U ₄₄ and of currents I ₄₂ , I, respectively _{44 of} the switching elements 42, 44. The fifth and ninth graph from above show switching states S ₄₂ , S _{44 of} the switching elements 42, 44, wherein a value other than zero corresponds to an on state. The switching elements 42, 44 are switched on at a time t ₁ simultaneously and switched off at a time t ₂ simultaneously. The sixth and tenth graphs each show a course of a power loss P ₄₂ , P _44, which results from switching losses when switching off the switching elements 42, 44. In the lowermost graph, a temperature θ _{44 of} the switching element 44 is shown. The corresponding ones Graphs of the switching elements 42, 44 have a substantially same course. The temperature θ _{44 of} the switching element 44, for example due to a defect, increases more than a temperature θ _{42 of} the switching element 42 connected in parallel.

The control unit 14 is provided to determine the activity parameters of the switching elements 42, 44, 46, 48 as a function of values of the temperature sensor arrangement 50. The control unit 14 is intended to adjust the activity parameters of a switching element 42, 44 whose temperature θ ₄₂ , θ ₄₄ exceeds a limit temperature. The limit temperature is 135 ° C. The control unit 14 is provided, for example, to adjust the activity parameters of the switching element 44 when its temperature θ ₄₄ exceeds the limit temperature in order to avoid switching losses in the switching element 44 having an elevated temperature θ ₄₄ . Furthermore, an effective value I _{eff44 of} the current I _{44 of} the switching element 44 and thus line losses are thereby reduced. The control unit 14 is provided to reduce a duty cycle of the switching element 44 and thus turn off earlier than the parallel switching element 42.

In FIG. 4 For example, schematic diagrams of the various operating variables over an activity period during a switching period of an operating mode that is used in response to the overheating of the switching element 44 are shown. In this mode of operation, the switching elements 42, 44 are turned on simultaneously and at the same frequency. The switching elements 42, 44 are switched on at a time t ₁ at the same time. At a time t ₂ ', the switching element 44 is switched off prematurely. The control unit 14 controls the time t ₂ 'of the shutdown so that a current I _{44 of} the switching element 44 reaches zero before the parallel-connected switching element 42 is turned off at a regular time t ₂ . After switching off the switching element 44, the current I _{42 of} the parallel-connected switching element 42 increases to compensate for the premature shutdown. The switching element 42 carries only a power loss P ₄₂ when switching off. The temperature θ _{44 of} the switching element 44 decreases due to the reduced power loss. If the temperature θ _{44 of} the switching element 44 continues to increase, the time t ₂ 'of switching off can be further advanced by lowering the clock ratio.

In FIG. 5 Again graphs of the first mode of operation are shown in an alternative case. In this alternative case, there is an effective value I _{eff42 of} the current I ₄₂ , for example, by an increased resistance of the switching element 42, lower than an effective value I _{eff44 of} the current I _44th This results for the switching element 44 connected in parallel, a higher power loss P ₄₄ by switching losses and increased line losses.

The control unit 14 is provided to determine the activity parameters of the switching elements 42, 44, 46, 48 in dependence on values of the current sensor arrangement 60. The control unit 14 is provided to adjust the activity _parameters when the effective values I _eff42 , I _{eff44 of} the switching elements 42, 44 differ by more than 50%. The control unit 14 is provided to shorten the duty cycle of the switching element 44 with the higher effective value I _{eff44 of} the current I ₄₄ .

In FIG. 6 the graphs obtained by adjusting the activity parameters are shown. The switching element 44 with the formerly higher effective value I _eff44 is prematurely switched off at the _instant t ₂ "The switching element 42 connected in parallel with the formerly low effective value I _eff42 has an increased current I ₄₂ from the _instant t ₂ " in order to prevent premature switching off of the other switching element 44 to compensate. The control unit 14 is provided to select the time t ₂ "of the shutdown so that an effective value I _eff42 'and an effective value I _eff44 ' _differ less than 20%, alternatively they are equal.

In FIG. 7 is a time course of a power P _{20 of} the induction heating _element 20, of RMS I _eff42 , I _eff44 of currents I ₄₂ , I ₄₄ through the switching elements 42, 44 and of temperatures θ ₄₂ , θ _{44 of} the switching elements 42, 44 shown, from the beginning a heating operation with high performance P ₂₀ until after reduction of the power P ₂₀ due to overheating. Starting from room temperature, the temperatures θ ₄₂ , θ _{44 of} the switching elements 42, 44 continue to rise, until a time t _10, a first of the switching elements 42 reaches the limit temperature. Rather than now reducing the power P ₂₀ to reduce power dissipation of the switching elements 42, 44 and prevent further increase in temperature, the inventive method is used to reduce the power dissipation across the first of the switching elements 42 and to keep the power P ₂₀ constant , The control unit 14 is designed to switch between the different operating modes, the operating mode with the same activity parameters and the operating mode with different activity parameters, whenever the temperatures θ ₄₂ , θ ₄₄ require a high To achieve overall efficiency. The temperature θ ₄₂ fluctuates minimally around the maximum temperature. Achieved at a time t _20, the temperature θ _{44 of} the second switching element 44, the limit temperature, the power P _{20 is} reduced in order to reduce the power losses across the switching elements 42, 44 and to avoid further heating. Compared to a classic mode of operation in which the switching elements are operated with the same activity parameters, so a longer time with high power is heated.

Should temperatures θ ₄₆ , θ ₄₈ or currents I ₄₆ , I _{48 of} the switching elements 46, 48 have increased values, as explained with reference to the example of the switching elements 42, 44, corresponding to FIGS FIGS. 4 and 6 , proceed.

Furthermore, any numbers of parallel switching elements are conceivable. Furthermore, it is conceivable that a control unit is provided to delay a switch-on time of a switching element and to prefer a switch-off time of a switching element connected in parallel, whereby an operating mode with different phases is effectively produced. Furthermore, a combination of the operating mode with different phases with the operating mode with different duty cycles is conceivable in order to achieve a fine-tuning of the power losses.

reference numeral

10 household appliance I ₄₂ electricity 12 induction heating I ₄₄ electricity 14 control unit I ₄₆ electricity 16 heatsink I ₄₈ electricity 18 Hotplate I _eff42 RMS 20 induction heating I _eff42 ' RMS 22 induction heating I _eff44 RMS 24 induction heating I _eff44 ' RMS 26 induction heating P ₂₀ power 30 voltage source P ₄₂ power loss 40 inverter P ₄₄ power loss 42 switching element S ₄₂ switching status 44 switching element P ₄₄ switching status 46 switching element U ₂₀ tension 48 switching element U ₄₂ tension 50 Temperature sensor arrangement U ₄₄ tension 52 temperature sensor t ₁ time 54 temperature sensor t ₁₀ time 56 temperature sensor t ₂ time 58 temperature sensor t ₂₀ time 60 Flow sensor assembly t ₂ ' time 62 current sensor t ₂ " time 64 current sensor θ ₄₂ temperature 66 current sensor θ ₄₄ temperature 68 current sensor θ ₄₆ temperature I ₂₀ electricity θ ₄₈ temperature

Claims (9)

1. Induction heating device having at least two switching elements (42, 44, 46, 48) which are connected in parallel in at least one operating mode and are provided to generate a high frequency alternating current to supply an induction heating element (20, 22, 24, 26), and having at least one control unit (14), characterised in that the control unit (14) is provided to actuate at least two of the at least two switching elements (42, 44, 46, 48) with different activity parameters in at least the first operating mode.
2. Induction heating device according to claim 1, characterised in that the at least two switching elements (42, 44, 46, 48) are connected in parallel independently of the operating state.
3. Induction heating device according to one of the preceding claims, characterised in that the control unit (14) is provided to operate at least two of the switching elements (42, 44, 46, 48) with different pulse duty factors at least in the operating mode.
4. Induction heating device according to claim 3, characterised in that the control unit (14) is provided to at least essentially simultaneously activate at least two switching elements (42, 44, 46, 48) at least in the operating mode.
5. Induction heating device according to one of the preceding claims, characterised by a current sensor arrangement (60), which is provided to determine currents (I _42, I₄₄ , I ₄₆, I ₄₈) flowing through the at least two switching elements (42, 44, 46, 48).
6. Induction heating device according to claim 5, characterised in that the control unit (14) is provided to determine the activity parameter of the at least two switching elements (42, 44, 46, 48) as a function of values of the current sensor arrangement (60).
7. Induction heating device according to one of the preceding claims, characterised by a temperature sensor arrangement (50), which is provided to determine temperatures (ϑ₄₂, ϑ₄₄, ϑ₄₆, ϑ₄₈) of the at least two switching elements (42, 44, 46, 48).
8. Induction heating device according to claim 7, characterised in that the control unit (14) is provided to determine the activity parameter of the at least two switching elements (42, 44, 46, 48) as a function of values of the temperature sensor arrangement (50).
9. Domestic appliance, in particular hob, having an induction heating device (12) according to one of the preceding claims.

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