EP2494846B1 - Cook top comprising at least two heating elements and a power electronics arrangement - Google Patents

Description

The invention relates to a hob with at least two heating elements and a power electronics assembly according to the preamble of claim 1.

From the EP 0 986 287 B1 from the EP 193177 A1 , from the WO 2005/043737 and from the EP 0 971 562 B1 Cooking hobs are known which comprise a plurality of heating elements and a power electronics assembly for connecting the hob to one or more phases of a household power grid. It is common to use separate power electronics assemblies each with a filter and a rectifier for each phase of a household power grid. Hobs, which are connected to only one phase of the household electricity network, are usually of low cost and simple design and have due to the power limitation of the household electricity network over a limited heating capacity, which may be, for example, a maximum of 4.6 kW.

On the other hand, there is a trend to provide cooktops with a plurality of heating elements that can be flexibly used and can be switched on or off depending on a size and / or position of a cookware element placed on the cooktop. In such cooktops independently operable power supply units are used, which are each used for heating a cooking utensil element and can be flexibly connected via a switch arrangement with the heating elements, which are associated with the respective cookware element. It is also known to use electromechanical relays for the realization of such switch arrangements, which can establish or disconnect a connection between the power supply units and the heating elements.

Such switch assemblies typically combine a large number of heating elements, for example, small inducers of a matrix cooktop, with a much smaller number of power supply units, such as inverters. The switch assembly therefore branches in the direction of the heating elements and each heating element is usually associated with the end of a branch of the branching tree structure. Each of the heating elements can therefore be connected in exactly one way to a power supply unit get connected. Exceptions to this rule can be found in cooktops with a so-called booster mode, in which two power supply units can be interconnected to operate a single heating element. A corresponding electromechanical relay opens or closes a bridge between the two power supply units, in particular between two inverters of an induction hob. Since the heating power is to be concentrated in the booster mode just on a heating element, in each case a further switch is disposed between this switch bridge and the heating elements, which can separate the heating elements not to be heated from the power supply.

In order to tap cost-saving potential, it is important to be able to use the available resources flexibly for different heating elements. It should be noted that the simultaneous use of all the heating elements of a hob with a large number of heating elements is unlikely and that even if all heating zones or heating elements are used, only in the rarest cases, each of the heating elements must be operated with the maximum power.

The invention is therefore based on the object of making the association between power supply units and heating elements more flexible, reducing the number of switching operations necessary for the alternating use of a power supply unit for a plurality of heating elements and simplifying the fulfillment of standards for electromagnetic compatibility. Furthermore, the invention has the object to enable emergency operation of the hob even if one of the switches in the switch assembly is rendered inoperable by a defect.

The object is achieved in particular by a hob with the features of claim 1. Further advantageous embodiments of the invention will become apparent from the dependent claims.

The invention relates to a hob with at least two heating elements and a power electronics assembly for connection to a single phase of a household electricity network. The power electronics assembly includes a plurality of power supply units for supplying each one or more heating elements with heating currents. Furthermore, the hob comprises a switch assembly with a plurality of electromechanical Relay for connecting and / or disconnecting the power supply units to and from the heating elements.

The invention relates to cooking fields with at least three heating zones or at least three heating elements, which are fed by a single phase of the household electricity network and which are arranged, for example, under a cover plate with edge lengths between 60 and 80 cm.

It is proposed that at least one of the heating elements is fixedly connected to one of at least two output terminals of at least two of the electromechanical relays. As a result, a redundant switch arrangement is realized, in which the heating element can be supplied with heating current optionally via two different paths, wherein each of the paths comprises one of the two relays. The number of switching options and the number of possible assignments between power supply units and heating elements is significantly increased, thereby increasing the flexibility of the hob.

Due to the short response times of induction hobs compared to radiant fields, induction hobs are particularly suitable for time division multiplexing. Therefore, the advantages of the invention in its application to induction cooktops come especially to fruition. In this case, the heating elements are inductors and the power supply units comprise an inverter which can generate a high-frequency heating current from the rectified and possibly filtered current from the household power grid. The frequencies of heating currents in induction hobs are typically between 20 kHz and 100 kHz.

Since the distribution of the available energy to the heating elements or heating zones can be simplified by the invention, a satisfactory result can be achieved even with a lower nominal power of the power electronics assembly. In particular, the sum of the nominal outputs of the heating elements can be selected greater than the nominal power of the power electronics assembly. The nominal power of the power electronics assembly is usually just below the maximum available power of a phase of the household power grid and can be, for example, 4.6 kW for Germany. The maximum power consumed by the power electronics can also be made adjustable depending on the available power. This setting can be used in combination with other country settings, such as a time zone and / or language.

It is also proposed that in the no-current state or in the "normally closed" (NC) state of the two relays, exactly one of the two relays connects the heating element to one of the power supply units while the other relay disconnects the connection to the same power supply unit or other power supply unit , As a result, an operation of the heating element can also be realized if due to a defect, the switching currents are not available.

It is also proposed that each of the heating elements is fixedly connected to one of at least two output terminals of at least two of the electromechanical relays. The redundant power supply can thus be realized for each of the heating elements. Alternatively, one or more heating elements may be connected to one of at least two output terminals of only a single electromagnetic relay.

Cost saving potentials through the sharing of hardware can be realized if the power electronics assembly includes a low pass filter and a rectifier shared for all power supply units.

In particular, single-pole changeover switches can be used as electromechanical relays, wherein the two output poles can be connected to different heating elements. In this case, it is further proposed that a common center terminal of the relay is connected to a power supply unit and the two output poles of the relay are each arranged with a heating element or in the connection between the heating element and the power supply unit in the corresponding direction.

A further increased flexibility of the switch arrangement can be realized by a plurality of series-connected relays in a connection between a power supply unit and a heating element. The switch arrangement may in particular comprise a plurality of branch layers.

The number of branch layers or the number of relays connected in series can also be designed differently for different heating elements. For example, it may be useful to design the switch assembly so that centrally located heating elements can be connected to a particularly large number of power supply units or inverters, while heating elements, which are arranged at the edge of the hob, can be connected to a smaller number of power supply units , As a result, the centrally arranged heating elements can be very flexibly combined with other heating elements to heating zones, which is not necessary for heating elements which are arranged at the edge of the heating zone to the same extent.

Fig. 1

zeigt schematisch den Aufbau eines Kochfelds mit mehreren Heizelementen und einer Leistungselektronikanordnung zum Anschluss an eine einzige Phase eines Haushaltsstromnetzes,

Fig. 2

zeigt schematisch den Aufbau eines Kochfelds nach einer alternativen Ausgestaltung der Erfindung,

Fig. 3

zeigt schematisch den Aufbau eines Kochfelds nach einer weiteren alternativen Ausgestaltung der Erfindung, und

Fig. 4

zeigt schematisch den Aufbau eines Kochfelds in einer Verallgemeinerung des Erfindungsgedankens.

Further advantages emerge from the following description of the drawing. In the drawings, embodiments of the invention are 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

shows schematically the construction of a hob with a plurality of heating elements and a power electronics assembly for connection to a single phase of a household electricity network,

Fig. 2

shows schematically the structure of a hob according to an alternative embodiment of the invention,

Fig. 3

shows schematically the structure of a hob according to a further alternative embodiment of the invention, and

Fig. 4

schematically shows the structure of a hob in a generalization of the inventive concept.

Fig. 1 schematically shows a hob with four heating elements 10a-10d and a power electronics assembly 12. The power electronics assembly is used to connect the hob to a single phase 14 of a household power network and supplies the entire hob from the flow of this phase fourteenth

The power electronics assembly includes a filter 16 and a rectifier 18 which filter the AC drawn from the household power grid and in a DC current convert, which undergoes further filtering by a damping capacitor 20. The filter 16 is a low-pass filter that prevents damage to the hob by strong pulses from the household power grid and flicker amplifying feedback from the hob in the household power grid.

In the in Fig. 1 1, the power electronics module further comprises two power supply units 22a, 22b, which are designed as inverters and which are operated by a control unit, not shown here, so that a heating current is generated at a desired heating frequency. The two inverters 22a, 22b can generate heating currents with different heating frequencies, different amplitudes and / or different load cycles or phases in order to generate the desired heating power in the heating elements 10a-10d. The heating elements 10a-10d are inductors that generate a high-frequency magnetic field at the frequency of the heating current. The magnetic field induces eddy currents in a ferromagnetic bottom of a cooking utensil element placed on the hob in the region of the relevant heating element 10a-10d, which is heated thereby.

Between the power supply units 22a, 22b and the heating elements 10a-10d, a switch arrangement 24 with electromechanical relays 26a-26d is arranged. The relays 26a-26d are unipolar changeover switches whose common center connection is connected to a respective pole of two further relays 28a, 28b. The further relays 28a, 28b are connected via their center connection to a respective power supply unit 22a, 22b. Each of the power supply units 22a, 22b may be connected to each of the heating elements 10a-10d by appropriate switching of the relays 26a, 26b, 28a-28d. The heating elements 10a-10d are in turn fixedly connected to two output terminals of two different relays 26a-26d of the second relay layer of the switch arrangement 24. Thereby, each of the heating elements 10a-10d can be connected to both power supply units 22a, 22b at the same time in order to concentrate the total available energy on the heating element 10a-10d in question. In this case, the two power supply units 22a, 22b designed as inverters should generate heating currents with the same heating frequency in order to avoid destructive interference.

The output poles of the relays 26a-26d, to which one of the heating elements 10a-10d is connected, are selected so that in the non-switching state of the relay 26a-26d exactly one of the two relays connects the heating element 10a-10d to one of the power supply units 22a, 22b while the other relay 26a-26d disconnects the connection to the other power supply unit 22a, 22b. The heating element 10a is thus connected, for example, to the normally closed (NC) output terminal of the relay 26b and to the normally open (NO) output terminal of the relay 26c.

The sum of the nominal powers of the heating elements 10a-10d is greater than the nominal power of the power electronics assembly 12 and the phase 14 of the household power grid. For example, the sum of the nominal outputs of the heating elements 10a-10d can be 7.2 kW and the nominal power of the power electronics assembly 4.6 kW.

By the in Fig. 1 illustrated two-layer structure of the switch assembly 24 are arranged in the connections between the heating elements 10a-10d and the power supply units 22a, 22b each have two series-connected relay 28a, 28b, 26a-26d.

Fig. 2 shows a further embodiment of the invention. In order to avoid repetition, the following description is limited essentially to differences from those in Fig. 1 illustrated embodiment, while with regard to consistent features on the description in Fig. 1 is referenced.

In the in Fig. 2 illustrated embodiment, the hob comprises three heating elements 10a-10c and the switch assembly 24 includes only a total of four relays 28a, 28b, 26a, 26b. The heating element 10a is connected to the power supply units 22a, 22b via only one relay 28a, 28b, while the heating elements 10b, 10c are connected to the power supply units 22a, 22b via two series-connected relays 26a, 28a and 26b, 28b, respectively.

Fig. 3 shows a further alternative embodiment of the invention with only two relays 26a, 26b and three heating elements 10a, 10b, 10c. Of the heating elements, only the middle heating element 10b is connected to output terminals of both relays 26a, 26b, while the heating elements 10a are connected to the output terminal of only one relay 26a, 26b, respectively.

Fig. 4 shows a generalization of the structure of an induction hob according to the invention with M power supply units 22.1-22.M or inverters and N heating elements 10.1-10.N, which are connected via a switch assembly 24 to the power supply units 22.1-22.M. It is M <N. The number K of the branching stages 30.1-30.K of the array 24 is at least as large as the smallest integer larger than the two logarithm of the number of power supply units M.

The switch assembly 24 may be mounted on a separate board or together with the power supplies 22.1-22.M on a single board. The same applies to the low-pass filter 16 and the rectifier 18. These elements can also be mounted on a separate board or together with the power supply units 22.1-22.M on a large board.

The invention can be used both for traditional well mirrors with four fixed heating zones and for matrix hobs with a large number of heating elements arranged in a grid and flexibly combined to heat a single pot. The topology in Fig. 3 is particularly suitable for troughs with so-called paella heating zones in which in the middle of the hob with the help of the central heating element 10b, a large heating zone for heating a Paellapfanne is generated.

reference numeral

10

heating element

12

Power electronics arrangement

14

phase

16

filter

18

rectifier

20

snubber capacitor

22

Power supply unit

24

switch arrangement

26

relay

28

relay

30

branching stage

Claims (11)

1. Cook top having at least three heating elements (10a-10d) and a power electronics arrangement (12) for connection to a single phase (14) of a domestic AC supply, wherein the power electronics arrangement (12) comprises a plurality of power supply units (22a, 22b) each supplying one or more heating elements (10a-10d) with heating currents, and having a switch arrangement (24) with a plurality of electromechanical relays (26a-26d; 28a, 28b) for connecting and/or disconnecting the power supply units to/from the heating elements (10a-10d), wherein the number of power supply units (22a, 22b) is less than the number of heating elements (10a-10d) connected to the power supply units (22a, 22b) by way of the switch arrangement (24),
   wherein at least one of the heating elements (10a-10d) is permanently connected to one of at least two output poles of at least two of the electromechanical relays (26a-26d) in each case.
2. Cook top according to claim 1, characterised in that the heating elements (10a-10d) are inductors and the power supply units (22a, 22b) each comprise an inverter.
3. Cook top according to one of the preceding claims, characterised in that the sum of the nominal outputs of the heating elements (10a-10d) is greater than the nominal output of the power electronics arrangement.
4. Cook top according to one of the preceding claims, characterised in that, in the unenergised state of the two relays (26a-26d), just one of the two relays connects the heating element (10a-10d) to one of the power supply units (22a, 22b), while the other relay (26a-26d) breaks the connection to another power supply unit (22a, 22b).
5. Cook top according to one of the preceding claims, characterised in that each of the heating elements (10a-10d) is permanently connected to one of at least two output poles of at least two of the electromechanical relays (26a-26d) in each case.
6. Cook top according to one of claims 1 - 3, characterised in that at least one of the heating elements (10a-10d) is connected to one of at least two output poles of only one electromechanical relay (26a-26d).
7. Cook top according to one of the preceding claims, characterised in that the power electronics arrangement comprises a low-pass filter (16) and a rectifier (18) shared by all the power supply units (22a, 22b).
8. Cook top according to one of the preceding claims, characterised in that the electromechanical relays (26a-26d) are single-pole double-throw switches.
9. Cook top according to claim 8, characterised in that a common central terminal of the relay (26a-26d) is connected to a power supply unit (22a, 22b) and the two output poles of the relay (26a-26d) are each connected to a heating element (10a-10d).
10. Cook top according to one of the preceding claims, characterised in that the switch arrangement (24) comprises a plurality of series-connected relays (26a-26d; 28a, 28b) in a connection between a power supply unit (22a, 22b) and a heating element (10a-10d).
11. Cook top according to claim 10, characterised in that a different number of series-connected relays (26a-26d; 28a, 28b) is disposed in the connections between two heating elements (10a-10d) and one or two power supply units (22a, 22b).

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