Patent Publication Number: US-2009230123-A1

Title: Device and method for driving the induction heating means of an induction hob

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to DE 10 2008 015 036.3, filed on Mar. 14, 2008, the contents of which are incorporated by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a device and a method for driving or supplying power to the induction heating means of an induction hob, called induction coils herein. Power is supplied to these induction heating means via the electric power grid or a grid phase thereof, a filter unit being provided thereon and a rectifier unit with at least one converter and one intermediate circuit being provided on the filter unit. In one case, a rectifier unit, with in each case having two converters in the rectifier unit, is advantageously connected to a filter unit, such that one induction heating means is driven or is supplied with power per converter. 
     BACKGROUND OF THE INVENTION 
     Conventional induction generators or previously described devices for hobs are optimized for two or four induction coils or cooking rings. Devices with one or three cooking rings are produced by omitting one converter or by operating a two-circuit cooking zone using twin converters. Systems with four rings are produced by parallel construction of two twin units. Five or six ring systems accordingly use three twin units or a quad unit together with a twin unit. 
     A generator contains in principle the converters, which produce the high frequency, and a filter. Filters and converters may be constructed on a printed circuit board or separately, but one converter unit with one or more induction coils, typically two induction coils, is always allocated to one filter unit. Each filter unit may be connected separately to one grid phase. If fewer grid phases are available than filter units, the filter units are always connected together on the grid side. 
     It is additionally known for an individual converter to be connected alternately by means of relay switching to a plurality of induction coils or a plurality of heating circuits of one induction coil. It is likewise known for two or more converters, which may even be located in different converter units, to be permanently connected to different sub-coils of a multi-circuit induction coil. 
     In the case of alternate use of a converter for two induction coils, it is possible to cut down on one converter. Then, however, it is only ever possible for one induction coil to be supplied with power at any one time. 
     If the converter is alternately connected at short intervals to the two induction coils, as known from EP 286044 A2, disadvantages arise with regard to cooking performance, such as for example water may go on and off the boil. Furthermore, mechanical switching of the relay brings about regular troublesome clicking noises. The flickering, which arises on switching, is also disadvantageous. 
     On the other hand, if the converter is firmly allocated to one induction coil via a relay, as is known from EP 1194008 A2 and U.S. Pat. No. 7,227,103 A1, such that a further induction coil is completely without a converter connection, the induction coil cannot be supplied with power and the corresponding ring remains cold. An advantage of this solution is that no regularly occurring clicking noise arises and the operating noise is quieter, provided that the two converters of the multi-circuit induction heating means are frequency-synchronized with one another. 
     The problem on which the present invention is based is that of providing an above-mentioned device and a method for supplying power to or driving induction heating means, with which prior art problems may be avoided and in particular a further induction heating means may advantageously be driven with the least possible effort. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are illustrated schematically in the drawings and explained in more detail below. In the drawings: 
         FIG. 1  shows a representation of the connection of an additional rectifier unit for an additional induction heating means via switching means to the two existing filter units, 
         FIG. 2  shows a modification of the representation of  FIG. 1  with connection via the switching means to the intermediate circuits of two existing rectifier units, 
         FIG. 3  shows the connection of an additional induction heating means in the form of a two-circuit coil with one induction coil connected to an existing rectifier unit and the other induction coil to an additional converter, 
         FIG. 4  shows a further modification, in which an additional twin converter unit is connected via switching means to intermediate circuits of two existing rectifier units for two additional induction heating means and 
         FIG. 5  shows a modification of the representation of  FIG. 4 , in which two separate additional converters for in each case one additional induction heating means are connected via in each case their own switching means to the two intermediate circuits of the two existing rectifier units. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     This problem is solved in one embodiment by a device having the features of claim  1  and a method having the features of claim  13 . Advantageous and preferred configurations of the invention are the subject matter of the further claims and are explained in greater detail below. Some of the features listed below are described only with reference to the device or only with reference to the method. However, they may apply irrespectively both to the device and to the method. The wording of the claims is incorporated by express reference into the content of the description. 
     The invention provides for an additional converter, which is connected downstream of one of the existing filter units, to be provided for a further induction heating means, which is designed to be driven by the device or the method and supplied with power. According to one embodiment of the invention, no further filter unit is therefore provided for an additional converter of a further induction heating means even if the filter units are in themselves already fully occupied, but rather this additional converter is connected downstream thereof. In an advantageous configuration of the invention, a total of two filter units are provided, each of them supplying one rectifier unit having in each case two converters. An existing induction heating means is connected to each of these converters. 
     In a basic configuration of one embodiment of the invention the additional converter may be connected, in particular directly connected, without a rectifier to an intermediate circuit of an existing rectifier unit connected to the filter unit. Moreover, this connection may again be effected via switching means as previously described. In a still further embodiment of the invention, the additional converter may be connected without a rectifier via switching means to a plurality of intermediate circuits of a plurality of rectifier units. Varying power supply of the additional converter via the connection from various intermediate circuits may proceed according to the same principles as described before for connection of the additional converter to a filter unit. 
     Furthermore, it is also possible with the above-stated configuration of the invention not only for one additional converter for one additional induction heating means, but rather for a plurality of additional converters for in each case one additional induction heating means, to be connected to the intermediate circuits of existing rectifier units. This may advantageously again proceed via switching means, since this is an advantageous possibility for power supply from a plurality of rectifier units or a plurality of filter units. 
     In another embodiment of the invention, provision may be made for the additional converter for the additional induction heating means to be connected, together with a rectifier unit for it, between a filter unit and an existing rectifier unit with converters. In particular, the additional converter may here be connected directly to a connection between filter unit and rectifier unit. In this case, it is advantageously possible to connect the additional converter via a switching means, for example a relay, to such a connection between filter unit and rectifier unit. It is particularly advantageously possible to connect the additional converter via the switching means not just to one connection between one filter unit and one rectifier unit, but rather to the connections between a plurality of filter units and in each case their firmly associated rectifier units. It is thus possible, as is explained below in greater detail, for the additional converter as it were to be connected via the switching means, to one or another filter unit, depending on the reserve capacity of the filter unit still available. In particular, the additional converter for the additional induction heating means may in each case be connected to that filter unit which at that moment has a lower power output for its existing induction heating means, i.e., still a relatively large reserve capacity. 
     In this case it is moreover still possible, if even this filter unit under lower load has insufficient residual power, for the additional induction heating means to be operated with reduced power, so as to comply with a maximum admissible power, in particular also a temporarily maximum admissible power, of the filter unit. In a still further configuration of the invention, such a power reduction may indeed mainly take place at the additional induction heating means, but additionally also at one of the existing induction heating means of the filter unit. In this way, the virtually absolutely necessary power reduction may be spread over a plurality of induction heating means, such that it does not have a particularly significant or negative effect on any of them. Possible methods of achieving such a power reduction are known to a person skilled in the art from DE 10 2005 045 875 A1, the content of which in this regard is hereby incorporated by express reference into the content of the present description. 
     In a further embodiment of the invention, it is possible to apply power in such a way to additional heating means, which in each case comprise two or even more associated induction coils as “two-circuit heating means” or “multi-circuit heating means”, wherein the power for a first induction coil comes from an existing first rectifier unit. For a second or further induction coil, which is advantageously a heating means usually connectable to the first induction coil, the power may come from a previously described additional converter, which is connected by switching means to one of the intermediate circuits of the existing rectifier units. Alternatively, power may be supplied to the second induction coil via an additional converter with rectifier unit, which is connected to an existing filter unit. 
     In a still further embodiment of the invention, provision may advantageously be made for the converters to be operated in a frequency-synchronized manner. In this way, interference noise between the induction heating means may be avoided. 
     These and further features follow not only from the claims but also from the description and the drawings, the individual features being realized in each case alone or several together in the form of sub-combinations in an embodiment of the invention and in other fields and may constitute advantageous, per se protectable embodiments, for which protection is here claimed. Subdivision of the application into individual sections and intermediate headings does not limit the general applicability of the statements made thereunder. 
       FIG. 1  shows a device  11   a  for driving induction heating means  14   a  to  17   a . These induction heating means  14   a  to  17   a  are constituent parts of an induction hob  12   a  represented by broken lines, as is known in principle for example from the above-mentioned U.S. Pat. No. 7,227,103 A1. The induction heating means  14   a  to  17   a  in each case comprise schematically illustrated induction coils  14 ′ a  to  17 ′ a  or are formed thereof This construction does not present any problem to a person skilled in the art. 
     The device  11   a  comprises two filter units  23   a  and  24   a , which are connected to an electric power grid  21 , in particular a two-phase electric power grid. Although the filter units  23   a  and  24   a  are illustrated as belonging together, they may be separate components or structural units. Advantageously and conventionally, they are arranged on the same printed circuit board or in the same housing. A first rectifier unit  26   a  is connected to the left-hand filter unit  23   a . This comprises a rectifier  27   a , which powers two converters  28   a  and  29   a , and does this via an intermediate circuit which is not shown, which is conventionally achieved in this way however and is also revealed by the above-stated prior art. The converter  28   a  powers the induction heating means  14   a  and the converter  29   a  powers the induction heating means  15   a  or the converters are each responsible for power supply of the induction heating means. 
     The right-hand filter unit  24   a  accordingly powers a second rectifier unit  31   a  having a rectifier  32   a  and two converters  33   a  and  34   a , which in turn supply the induction heating means  16   a  and  17   a  with power. To this extent, the device described corresponds to the prior art for driving the four induction heating means  14   a  to  17   a  via four converters  28   a ,  29   a ,  33   a  and  34   a.    
     However, if in the case of the induction hob  12   a  an additional induction heating means  18   a  with corresponding induction coil  18 ′ a  needs to be supplied with power, this is per se difficult. It could be connected via a switching means to an output of one of the converters, but then the other induction heating means usually supplied by this converter could no longer be supplied with power. 
     Therefore, according to one embodiment of the invention, a switching means  36   a  is connected to the connections between the two rectifier units  26   a  and  31   a  and their respective filter units  23   a  and  24   a , i.e. downstream of the filter units. The switching means  36   a  may connect to the supply of one of the filter units, depending on the power requirements at the time. The switching means  36   a  powers an additional converter  38   a . This in turn ensures power supply for the additional induction heating means  18   a . In the case illustrated in  FIG. 1  the switching means  36   a  is connected to the right-hand filter unit  24   a . This means that the total power needed by the induction heating means  16   a ,  17   a  and  18   a  may not be above the maximum total power which the filter unit  24   a  can make available, for example even in the short term. In this case, the above-described methods of sharing power between the three induction heating means take effect, the latter being in each case adjusted by the converters  33   a ,  34   a  and  38   a . Alternatively, in the case of an overloaded filter unit  24   a , it is possible to switch to the left-hand filter unit  23   a , which may still have reserves. 
     An additional converter thus connects via the switching means in principle to the filter unit or rectifier unit, which is more suitable at that moment. By means of frequency or phase control, the desired power of each induction heating means may be adjusted by the converter. 
       FIG. 2  shows a modification of the device from  FIG. 1  as device  11   b . The difference is that the additional switching means  36   b  is no longer connected directly to the filter units  23   b  and  24   b , but rather to the intermediate circuits (not shown) of the first rectifier unit  26   b  and the second rectifier unit  31   b . This means that then the additional rectifier according to  FIG. 1  is no longer necessary either, since connection takes place directly to the intermediate circuits of the existing rectifier units. Otherwise, the function and use of the switching means  36  is the same as before. In addition, however, it is also still necessary to take account of the maximum available total power of the rectifier units or indeed of the associated intermediate circuits. 
       FIG. 3  shows a further modification of a device  11   c , which again corresponds substantially to that of  FIG. 2 , i.e. with the additional switching means  36   c  connected to the intermediate circuits of the first rectifier unit  26   c  and second rectifier unit  31   c . Furthermore, in  FIG. 3  the existing induction heating means  17   c  or the corresponding induction coil is the inner part of a two-circuit heating means. The outer part surrounding the inner part is formed by the additional induction heating means  18   c  with the corresponding induction coil. This additional induction heating means  18   c  is powered by an additional converter  38   c . Although, in the case of an induction hob, the two induction heating means  17   c  and  18   c  thus form virtually the same cooking ring, they are powered from different converters and, if the additional converter  38   c  is connected to the left-hand rectifier unit  26   c  via the switching means  36   c , even via different filter units and different rectifier units. Precisely in this case, however, the distribution of power may be advantageous, since in the case of two-circuit operation of the two-circuit heating unit a large amount of power is required and then the induction heating means  16   c  belonging to the same rectifier unit  31   c  could probably not be operated or only with very low power. Otherwise, the same power distribution rules apply here as previously described. 
     In the further device  11   d  according to  FIG. 4 , two additional converters  38   d  and  39   d  are connected to a switching means  36   d . In this case the additional converter  38   d  powers the additional induction heating means  18   d  and the additional converter  39   d  powers the additional induction heating means  19   d . Thus an induction hob may here be constructed with six induction heating means  14   d  to  19   d  and thus also six cooking rings. The two additional induction heating means  18   d  and  19   d  may thus be connected via additional converters  38   d  and  39   d  and the switching means  36   d  to one of the intermediate circuits of the existing rectifier units  26   d  and  31   d . In this respect, power management is precisely here also of great importance. 
       FIG. 5  finally shows a device  11   e . In a modification of the device of  FIG. 4 , two additional switching means  36   e  and  40   e  are provided here, which are connected in each case to two intermediate circuits of the existing rectifier units  26   e  and  31   e . The switching means  36   e  is connected to an additional converter  38   e , which powers an additional induction heating means  18   e  from the intermediate circuit of one of the rectifier units. The additional switching means  40   e  connects the additional converter  39   e  to one of the intermediate circuits of the existing rectifier units to supply power to the additional induction heating means  19   e.    
     With the device  11   e  according to  FIG. 5 , it is thus more advantageously possible than with the device  11   d  in  FIG. 4  for each of the converters  38   e  and  39   e  for the induction heating means  18   e  and  19   e  to be connected as required via the switching means  36   e  and  40   e  to one of the intermediate circuits of the existing rectifier units  26   e  and  31   e . In this respect it is also possible for both converters  38   e  and  39   e  to be connected to the same intermediate circuit, if this is allowed by the adjusted powers and the reserve capacities of the relevant rectifier unit.