Patent Publication Number: US-10772161-B2

Title: Method for controlling an induction cooking hob including a number of induction coils

Description:
The present invention relates to a method for controlling an induction cooking hob including a number of induction coils. Further, the present invention relates to an induction cooking hob including a number of induction coils. 
     Many current induction cooking hobs include number of induction coils forming flexible cooking zones. Said flexible cooking zones may be adapted to the shapes of different cookware. The induction coils are driven by induction generators. The frequency of the induction generator depends on the power of the induction coil. If adjacent induction coils work with a frequency difference within the audible range, then an acoustic interference noise may occur. 
     It is an object of the present invention to provide a method for controlling an induction cooking hob including a number of induction coils, wherein said method allows the formation of cooking zones by one or more induction coils with a suitable heat distribution, and wherein an acoustic interference noise is avoided. 
     The object is achieved by the method according to claim  1 . 
     The present invention provides a method for controlling an induction cooking hob including a number of induction coils, wherein a heating process includes a plurality of subsequent fixed time cycles subdivided into one or more flexible time slots, and wherein each induction coil is driven by at least one dedicated induction generator, and wherein the method comprises the following steps:
         setting a requested power for each induction coil to be activated by a user,   defining at least one group of one or more induction coils, wherein the induction coils of one group have the same requested power,   determining a number of time slots for each time cycle, wherein the number of time slots is given by the number of groups of induction coils having the same requested power,   activating all groups of induction coils to be activated during a first time slot at a same current power for a calculated duration, and   activating a part of groups of induction coils to be activated during at least one further time slot at the same current powers in each time slot for a calculated duration, if more than one group of induction coils are defined,   so that an average current power of each induction coil within the time cycle corresponds with the requested power for said induction coil.       

     The core of the present invention is the division of the fixed time cycles into one or more flexible time slots, wherein the induction coils within one time slot work at the same frequency, and wherein the number of time slots is given by the number of groups of induction coils having the same requested power. The same frequencies avoid acoustic interference noise, while the flexible time slots allow that the average current power of each induction coil within the time cycle corresponds with the requested power for said induction coil. 
     Preferably, the method is provided for controlling an induction cooking hob, wherein the induction coils are arranged as a matrix. 
     In particular, an array of different requested powers is defined, in which said different requested powers increase, wherein the number of said different requested powers corresponds with the number of time slots in each time cycle, and wherein a corresponding weight array is defined in order to indicate the number of induction coils having the same requested power. 
     Further, the number of activated induction coils in the first time slot may be given by the number of induction coils to be activated, and the numbers of activated induction coils in the further time slots may be given by:
 
 Nic (1)= Num  zones active
 
 Nic ( i )= Nic ( i− 1)− w ( i− 1), wherein  i&gt; 1,
 
and wherein w(i) is the number of activated induction coils in the i-th time slot.
 
     The average power (aP( 1 )) in the first time slot may be given by:
 
 aP (1)= rP (1)* Nic (1),
 
wherein rP( 1 ) is the lowest requested power and Nic( 1 ) is the number of activated induction coils in the first time slot, and the average power in the further time slots i is given by:
 
 aP ( i )=[ rP ( i )− rP ( i− 1)]* Nic ( i ), wherein  i&gt; 1.
 
     The durations of the time slots i may be given by:
 
 T ( i )= aP ( i )/ rP,  
 
wherein aP(i) is the average power of the induction coils and rP is the total requested power.
 
     The percentage power for each induction coil within one time slot i may be given by:
 
 pP ( i )=1/ Nic ( i ),
 
wherein Nic(i) is the number of activated induction coils in the i-th time slot.
 
     For example, an estimated power for each induction coil is determined and compared with the requested power for said induction coil, wherein the induction coil is excluded, if the relation between the estimated power and the requested power exceeds a high threshold value and/or falls below a low threshold value. 
     Furthermore, a power loss for each induction coil may be determined, wherein said power loss is given by the difference between the requested power and the estimated power. 
     Moreover, the power losses of the induction coils may form a is power loss array, wherein said power loss array is periodically updated. 
     Preferably, the duration of each time cycle is between three seconds and ten seconds, in particular six seconds. 
     Further, the present invention relates to an induction cooking hob including a number of induction coils, wherein a heating process performed by said induction cooking hob includes a plurality of subsequent fixed time cycles subdivided into one or more flexible time slots, and wherein the induction cooking hob includes at least one induction generator for each induction coil, so that each induction coil is driven by at least one dedicated induction generator, wherein the induction cooking hob is provided for the method mentioned above. 
     In particular, the induction coils are arranged as a matrix. 
     Further, the induction cooking hob may include at least one control unit for controlling the induction generators. 
     Additionally, the induction cooking hob may include at least one user interface connected or connectable to the control unit. 
     At last the present invention relates to a computer program stored in a computer usable medium, comprising computer readable program means for causing a computer to perform the method mentioned above. 
     Novel and inventive features of the present invention are set forth in the appended claims. 
    
    
     
       The present invention will be described in further detail with reference to the drawing, in which 
         FIG. 1  illustrates a schematic top view of an induction cooking hob according to a preferred embodiment of the present invention, 
         FIG. 2  illustrates a further schematic top view of the induction cooking hob according to the preferred embodiment of the present invention, 
         FIG. 3  illustrates a schematic block diagram of the induction cooking hob according to the preferred embodiment of the present invention, 
         FIG. 4  illustrates a schematic top view of the induction cooking hob according to a further embodiment of the present invention, 
         FIG. 5  illustrates a schematic diagram of the relationships between the frequency and the power of an induction heating generator according to the preferred embodiment of the present invention, 
         FIG. 6  illustrates a schematic flow chart diagram of an algorithm for evaluating estimated powers of the inductions coils according to the preferred embodiment of the present invention, and 
         FIG. 7  illustrates a schematic flow chart diagram of an algorithm for a convergence power routine according to the preferred embodiment of the present invention. 
     
    
    
       FIG. 1  illustrates a schematic top view of an induction cooking hob  10  according to a preferred embodiment of the present invention. In this example, the induction cooking hob  10  comprises four induction coils  12 ,  14 ,  16  and  18  arranged as a two-by-two matrix. In general, the induction cooking hob  10  may comprise an arbitrary number of induction coils arranged in matrix from. In this example, the induction coils  12 ,  14 ,  16  and  18  have elliptic base areas. In general, the induction coils  12 ,  14 ,  16  and  18  may have arbitrary base areas. For example, the induction coils  12 ,  14 ,  16  and  18  may have circular, square or rectangular base areas. 
     A frying pan  20  is arranged above the second induction coil  14  and the fourth induction coil  18 . In this case, the second induction coil  14  and the fourth induction coil  18  are activated, while the first induction coil  12  and the third induction coil  16  remain deactivated. The heated area of the induction cooking hob  10  can be adapted to the size of the frying pan  20 . 
       FIG. 2  illustrates a further schematic top view of the induction cooking hob  10  according to the preferred embodiment of the present invention. The induction cooking hob  10  comprises the four induction coils  12 ,  14 ,  16  and  18  arranged as two-by-two matrix. In this case, the frying pan  20  is arranged above the induction coils  12 ,  14 ,  16  and  18 . All four induction coils  12 ,  14 ,  16  and  18  are activated. The frying pan  20  in  FIG. 2  is bigger than the frying pan  20  shown in  FIG. 1 . 
       FIG. 3  illustrates a schematic block diagram of the induction cooking hob  10  according to the preferred embodiment of the present invention. 
     The induction cooking hob  10  comprises the four induction coils  12 ,  14 ,  16  and  18 . Each of the induction coils  12 ,  14 ,  16  and  18  is connected to a dedicated induction generator  22 ,  24 ,  26  or  28 , respectively. For example, the induction generators  22 ,  24 ,  26  or  28  are half-bridge inverters. Each induction generator  22 ,  24 ,  26  and  28  is connected to a power supply line  34 . Said power supply line  34  provides rectified mains voltage for the induction generators  22 ,  24 ,  26  and  28 . 
     Further, the induction generators  22 ,  24 ,  26  and  28  are connected to a control unit  30  via control lines  36 . Each induction generator  22 ,  24 ,  26  and  28  may be separately controlled and activated. Moreover, the control unit  30  is connected to a user interface  32 . 
     As mentioned above, the four induction coils  12 ,  14 ,  16  and  18  are arranged as two-by-two matrix. One or more induction coils  12 ,  14 ,  16  and  18  form a group of induction coils. The induction coils  12 ,  14 ,  16  and  18  of one group work at the same power setting. In doing so induction coils  12 ,  14 ,  16  and  18  of one group are activated at the same working frequency in order to avoid acoustic interference noise. The acoustic interference noise would occur, if adjacent induction coils have got a frequency difference, which is within the audible range of the human ear. 
     The four induction coils  12 ,  14 ,  16  and  18  arranged as two-by-two matrix may form five different group configurations. Firstly, the four induction coils  12 ,  14 ,  16  and  18  work with a single power setting in each case. Secondly, the four induction coils  12 ,  14 ,  16  and  18  form one group. Thirdly, two groups are formed by two induction coils  12 ,  14 ,  16  and/or  18  in each case. Fourthly, one group is formed by three induction coils  12 ,  14 ,  16  and/or  18  and another one group is formed by one induction coil  12 ,  14 ,  16  or  18 . Fifthly, one group is formed by two induction coils  12 ,  14 ,  16  and/or  18  and two groups are formed by one induction coil  12 ,  14 ,  16  or  18  in each case. 
     An algorithm of the present invention manages the activation of each group of induction coils  12 ,  14 ,  16  and/or  18  according to the user&#39;s request, wherein acoustic interference noise is avoided. The heating or cooking process includes a plurality of subsequent fixed time cycles, so that each time cycle has the same time period. The time cycle takes between three seconds and ten seconds, preferably six seconds. The time cycle is subdivided into one or more flexible time slots, so that the number and time period of said time slots are variable. 
     The user sets a requested power rPj for each induction coil  12 ,  14 ,  16  and/or  18  to be activated, wherein j denotes the number of the induction coil  12 ,  14 ,  16  and  18 . The induction coils  12 ,  14 ,  16  and/or  18  having the same requested power rPj form a group. The number of groups of induction coils  12 ,  14 ,  16  and/or  18  defines the number Nts of the time slots within one time cycle. In other words, the number Nts of time slots is given by the number of inductions coils  12 ,  14 ,  16  and/or  18  having different requested powers rP(i) bigger than zero. For example, if the requested powers rPj for the induction coils  12 ,  14 ,  16  and  18  are rP 1 =500 W, rP 2 =500 W, rP 3 =1000 W and rP 4 =1000 W, then the number of time slots is Nts=2 in each time cycle and the different requested powers are rP( 1 )=500 W and rP( 2 )=1000 W. In this example, the total requested power is rP=3000 W. The total requested power rP is the sum of the requested powers rPj of all induction coils  12 ,  14 ,  16  and  18  to be activated. 
     The different requested powers rP(i) of the induction coils  12 ,  14 ,  16  and  18  to be activated are ordered in an array of requested powers
 
{ rP (1), rP (2), rP (3), . . . , rP ( Nts )}, wherein  rP ( i+ 1)&gt; rP ( i ),
 
and wherein Nts is the number of time slots in each time cycle. In the example mentioned above the array of requested powers is given by
 
{ rP 1 =rP 2 ,rP 3 =rP 4}={500 W,1000 W}.
 
     Further a corresponding weight array
 
{ w (1), w (2)}={2,2}
 
is defined in order to indicate the number of induction coils  12 ,  14 ,  16  and/or  18  having the same requested power rP(i). In this example, the weight array {2, 2} and the array of different requested powers {500 W, 1000 W} indicate that the requested power rP(i) for two induction coils is rP( 1 )=rP 1 =rP 2 =500 W and for the other two induction coils is rP( 2 )=rP 3 =rP 4 =1000 W.
 
     A current power cPj of each induction coil  12 ,  14 ,  16  and/or  18  in each time slot and the duration T of each time slot is calculated on the basis of the number of time slots Nts, the array of requested powers and the weight array. 
     The number Nic(i) of activated induction coils  12 ,  14 ,  16  and/or  18  in the time slot i is given by:
 
 Nic (1)= Nic,  
 
 Nic ( i )= Nic ( i− 1)− w ( i− 1), wherein  i&gt; 1,
 
and wherein Nic is the number of induction coils  12 ,  14 ,  16  and/or  18  to be activated. The average power aP(i) of each time slot i is given by
 
 aP (1)= rP (1)* Nic (1),
 
 aP ( i )=[ rP ( i )− rP ( i− 1)]* Nic ( i ), wherein  i&gt; 1.
 
     The durations T(i) of the time slots i are given by
 
 T ( i )= aP ( i )/ rP  
 
     The percentage power pP(i) for each induction coil  12 ,  14 ,  16  and/or  18  within one time slot i is given by
 
 pP ( i )=1/ Nic ( i ).
 
     For the example mentioned above the percentage powers pP(i) for each induction coil in each time slot i are given by: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 time slot 1 
                 time slot 2 
               
               
                   
                 T(1) = 0.66 
                 T(2) = 0.33 
               
               
                 rPj 
                 pP(1) 
                 pP(2) 
               
               
                   
               
             
            
               
                  500 W 
                 0.25 
                   
               
               
                  500 W 
                 0.25 
               
               
                 1000 W 
                 0.25 
                 0.5 
               
               
                 1000 W 
                 0.25 
                 0.5 
               
               
                   
               
            
           
         
       
     
     The total requested power rP=3000 W is delivered in two time slots, wherein the duration of the first time slot is T( 1 )=0.66 and the duration of the second time slot is T( 2 )=0.33 of the total time cycle. In the first time slot the total power is splitted equally on four induction coils  12 ,  14 ,  16  and  18 , wherein each induction coil  12 ,  14 ,  16  and  18  receives 25% of the total power. In the second time slot the total power is splitted equally on two induction coils  12 ,  14 ,  16  and/or  18 , wherein said two induction coils  12 ,  14 ,  16  and/or  18  receives 50% of the total power. 
     The current powers cP(i) for each induction coil in the first and second time slots are given by: 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                   
                 time slot 1 
                 time slot 2 
                   
               
               
                   
                   
                 T(1) = 0.66 
                 T(2) = 0.33 
               
               
                   
                 rPj 
                 cP(1) 
                 cP(2) 
                 aPj 
               
               
                   
                   
               
             
            
               
                   
                  500 W 
                 750 W 
                   
                  500 W 
               
               
                   
                  500 W 
                 750 W 
                   
                  500 W 
               
               
                   
                 1000 W 
                 750 W 
                 1500 W 
                 1000 W 
               
               
                   
                 1000 W 
                 750 W 
                 1500 W 
                 1000 W 
               
               
                   
                   
               
            
           
         
       
     
     According to another example one group of four induction coils  12 ,  14 ,  16  and  18  is formed. The requested powers for each induction coil  12 ,  14 ,  16  and  18  is rP 1 =rP 2 =rP 3 =rP 4 =500 W. 
     The percentage powers pP(i) for each induction coil  12 ,  14 ,  16  and  18  in the time slot are given by: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                   
                 time slot 1 
               
               
                   
                   
                 T(1) = 1.0 
               
               
                   
                 rPj 
                 pP(1) 
               
               
                   
                   
               
             
            
               
                   
                 500 W 
                 0.25 
               
               
                   
                 500 W 
                 0.25 
               
               
                   
                 500 W 
                 0.25 
               
               
                   
                 500 W 
                 0.25 
               
               
                   
                   
               
            
           
         
       
     
     In this special case the time cycle includes only one time slot  1 . The current powers cP(i) for each induction coil in the one time slot  1  are given by: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 time slot 1 
                   
               
               
                   
                 T(1) = 1.0 
               
               
                 rPj 
                 cP(1) 
                 aPj 
               
               
                   
               
             
            
               
                 500 W 
                 500 W 
                 500 W 
               
               
                 500 W 
                 500 W 
                 500 W 
               
               
                 500 W 
                 500 W 
                 500 W 
               
               
                 500 W 
                 500 W 
                 500 W 
               
               
                   
               
            
           
         
       
     
     According to the next example four induction coils  12 ,  14 ,  16  and  18  have different requested powers rP 1 =200 W, rP 2 =400 W, rP 3 =600 W and rP 4 =800 W. The percentage powers pP(i) for each induction coil  12 ,  14 ,  16  and  18  in each time slot i are given by: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 time slot 1 
                 time slot 2 
                 time slot 3 
                 time slot 4 
               
               
                   
                 T(1) = 0.4 
                 T(2) = 0.3 
                 T(3) = 0.2 
                 T(4) = 0.1 
               
               
                 rPj 
                 pP(1) 
                 pP(2) 
                 pP(3) 
                 pP(4) 
               
               
                   
               
             
            
               
                 200 W 
                 0.25 
                   
                   
                   
               
               
                 400 W 
                 0.25 
                 0.33 
               
               
                 600 W 
                 0.25 
                 0.33 
                 0.5 
               
               
                 800 W 
                 0.25 
                 0.33 
                 0.5 
                 1.0 
               
               
                   
               
            
           
         
       
     
     The current powers cP(i) for the activated induction coils  12 ,  14 ,  16  and/or  18  in each time slot i are given by: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                   
                 time slot 1 
                 time slot 2 
                 time slot 3 
                 time slot 4 
                   
               
               
                   
                 T(1) = 0.4 
                 T(2) = 0.3 
                 T(3) = 0.2 
                 T(4) = 0.1 
               
               
                 rPj 
                 cP(1) 
                 cP(2) 
                 cP(3) 
                 cP(4) 
                 aPi 
               
               
                   
               
             
            
               
                 200 W 
                 500 W 
                   
                   
                   
                 200 W 
               
               
                 400 W 
                 500 W 
                 660 W 
                   
                   
                 400 W 
               
               
                 600 W 
                 500 W 
                 660 W 
                 1000 W 
                   
                 600 W 
               
               
                 800 W 
                 500 W 
                 660 W 
                 1000 W 
                 2000 W 
                 800 W 
               
               
                   
               
            
           
         
       
     
     In the next example one induction coil  12 ,  14 ,  16  or  18  has the requested power rP 1 =500 W and one group with three induction coils  12 ,  14 ,  16  and/or  18  have the requested powers rP 2 =rP 3 =rP 4 =1000 W. The percentage powers pP(i) for the activated induction coils  12 ,  14 ,  16  and/or  18  in each time slot are given by: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 time slot 1 
                 time slot 2 
               
               
                   
                 T(1) = 0.57 
                 T(2) = 0.43 
               
               
                 rPi 
                 pP(1) 
                 pP(2) 
               
               
                   
               
             
            
               
                  500 W 
                 0.25 
                   
               
               
                 1000 W 
                 0.25 
                 0.33 
               
               
                 1000 W 
                 0.25 
                 0.33 
               
               
                 1000 W 
                 0.25 
                 0.33 
               
               
                   
               
            
           
         
       
     
     The current powers cP(i) for activated induction coils  12 ,  14 ,  16  and/or  18  in each time slot i are given by: 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                   
                 time slot 1 
                 time slot 2 
                   
               
               
                   
                   
                 T(1) = 0.57 
                 T(2) = 0.43 
               
               
                   
                 rPi 
                 cP(1) 
                 cP(2) 
                 aPj 
               
               
                   
                   
               
             
            
               
                   
                  500 W 
                 875 W 
                   
                  500 W 
               
               
                   
                 1000 W 
                 875 W 
                 1155 W 
                 1000 W 
               
               
                   
                 1000 W 
                 875 W 
                 1155 W 
                 1000 W 
               
               
                   
                 1000 W 
                 875 W 
                 1155 W 
                 1000 W 
               
               
                   
                   
               
            
           
         
       
     
     According to a further example two single induction coils  12 ,  14 ,  16  and/or  18  have the requested power rP 1 =500 W and rP 2 =700 W and one group with two induction coils  12 ,  14 ,  16  and/or  18  have the requested power rP 3 =rP 4 =1000 W. The percentage powers pP(i) for the activated induction coils  12 ,  14 ,  16  and/or  18  in each time slot are given by: 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                   
                 time slot 1 
                 time slot 2 
                 time slot 2 
               
               
                   
                   
                 T(1) = 0.625 
                 T(2) = 0.188 
                 T(3) = 0.187 
               
               
                   
                 rPj 
                 pP(1) 
                 pP(2) 
                 pP(2) 
               
               
                   
                   
               
             
            
               
                   
                  500 W 
                 0.25 
                   
                   
               
               
                   
                  700 W 
                 0.25 
                 0.33 
               
               
                   
                 1000 W 
                 0.25 
                 0.33 
                 0.5 
               
               
                   
                 1000 W 
                 0.25 
                 0.33 
                 0.5 
               
               
                   
                   
               
            
           
         
       
     
     The current powers cP(i) for activated induction coils  12 ,  14 ,  16  and/or  18  in each time slot i are given by: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 time slot 1 
                 time slot 2 
                 time slot 2 
                   
               
               
                   
                 T(1) = 0.625 
                 T(2) = 0.188 
                 T(3) = 0.187 
               
               
                 rPj 
                 cP(1) 
                 cP(2) 
                 cP(3) 
                 aPj 
               
               
                   
               
             
            
               
                  500 W 
                 800 W 
                   
                   
                  500 W 
               
               
                  700 W 
                 800 W 
                 1056 W 
                   
                  700 W 
               
               
                 1000 W 
                 800 W 
                 1056 W 
                 1600 W 
                 1000 W 
               
               
                 1000 W 
                 800 W 
                 1056 W 
                 1600 W 
                 1000 W 
               
               
                   
               
            
           
         
       
     
       FIG. 4  illustrates a schematic top view of the induction cooking hob  10  according to a further embodiment of the present invention. The induction cooking hob  10  comprises six induction coils  12 ,  14 ,  16 ,  18 ,  38  and  40  arranged as a two-by-three matrix. 
     According to an example the induction coils  12 ,  14 ,  16 ,  18 ,  38  and  40  have the requested powers rP 1 =200 W, rP 2 =200 W, rP 3 =300 W, rP 4 =300 W, rP 5 =400 W and rP 6 =700 W. Thus, the total requested power of the induction coils  12 ,  14 ,  16 ,  18 ,  38  and  40  is rP=2100 W. Since two pairs of induction coils  12  and  14  as well as  16  and  18  have the same requested powers rPj in each case, the power array is given by
 
{200 W,300 W,400 W,700 W},
 
and the weight array is given by
 
{ w (1), w (2), w (3), w (4)}={2,2,1,1}.
 
     There are four groups of induction coils  12 ,  14 ,  16 ,  18 ,  38  and  40 . The number of time slots corresponds with said number of groups:
 
 Nts= 4.
 
     The numbers Nic(i) of activated induction coils  12 ,  14 ,  16 ,  18 ,  38  and/or  40  for the time slots i are given by:
 
 Nic (1)= Nic= 6,
 
 Nic (2)= Nic (1)− w (1)=6−2=4,
 
 Nic (3)= Nic (2)− w (2)=4−2=2,
 
 Nic (4)= Nic (3)− w (3)=2−1=1.
 
     The average powers aP(i) for the time slots i are given by
 
 aP (1)= rP (1)* Nic (1)=200 W*6=1200 W,
 
 aP (2)=[ rP (2)− rP (1)]* Nic (2)=(300 W−200 W)*4=400 W,
 
 aP (3)=[ rP (3)− rP (2)]* Nic (3)=(400 W−300 W)*2=200 W,
 
 aP (4)=[ rP (4)− rP (3)]* Nic (4)=(700 W−400 W)*1=300 W.
 
     The durations T(i) of the time slots i are given by
 
 T (1)= aP (1)/ rP= 1200 W/2100 W=0.57,
 
 T (2)= aP (2)/ rP= 400 W/2100 W=0.19,
 
 T (3)= aP (3)/ rP= 200 W/2100 W=0.09,
 
 T (4)= aP (4)/ rP= 300 W/2100 W=0.15.
 
     The percentage powers pPi for each induction coil in each time slot are given by:
 
 pP (1)=1/ Nic (1)=1/6=0.16,
 
 pP (2)=1/ Nic (2)=1/4=0.5,
 
 pP (3)=1/ Nic (3)=1/2=0.25,
 
 pP (4)=1/ Nic (4)=1/1=1.
 
     The percentage powers pPi for each induction coil in each time slot are shown in detail below: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 time slot 1 
                 time slot 2 
                 time slot 3 
                 time slot 4 
               
               
                   
                 T(1) = 0.57 
                 T(2) = 0.19 
                 T(3) = 0.09 
                 T(4) = 0.15 
               
               
                 rPj 
                 pP(1) 
                 pP(2) 
                 pP(3) 
                 pP(4) 
               
               
                   
               
             
            
               
                 200 W 
                 0.16 
                   
                   
                   
               
               
                 200 W 
                 0.16 
               
               
                 300 W 
                 0.16 
                 0.25 
               
               
                 300 W 
                 0.16 
                 0.25 
               
               
                 400 W 
                 0.16 
                 0.25 
                 0.5 
               
               
                 700 W 
                 0.16 
                 0.25 
                 0.5 
                 1.0 
               
               
                   
               
            
           
         
       
     
     The current powers cP(i) for the activated induction coils in each time slot are given by: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                   
                 time slot 1 
                 time slot 2 
                 time slot 3 
                 time slot 4 
                   
               
               
                   
                 T(1) = 0.57 
                 T(2) = 0.19 
                 T(3) = 0.09 
                 T(4) = 0.15 
               
               
                 rPj 
                 cP(1) 
                 cP(2) 
                 cP(3) 
                 cP(4) 
                 aPj 
               
               
                   
               
             
            
               
                 200 W 
                 336 W 
                   
                   
                   
                 200 W 
               
               
                 200 W 
                 336 W 
                   
                   
                   
                 200 W 
               
               
                 300 W 
                 336 W 
                 525 W 
                   
                   
                 300 W 
               
               
                 300 W 
                 336 W 
                 525 W 
                   
                   
                 300 W 
               
               
                 400 W 
                 336 W 
                 525 W 
                 1050 W 
                   
                 400 W 
               
               
                 700 W 
                 336 W 
                 525 W 
                 1050 W 
                 2100 W 
                 700 W 
               
               
                   
               
            
           
         
       
     
       FIG. 5  illustrates a schematic diagram of the relationships  42  and  44  between the frequency f and the power P of an induction heating generator  22 ,  24 ,  26  and/or  28  according to the preferred embodiment of the present invention. 
     A first diagram  42  shows the relationship between the frequency f and the power P of the induction heating generator  22 ,  24 ,  26  and/or  28  for the case, in which a cooking pot substantially covers the corresponding induction coil. A second diagram  44  shows the relationship between the frequency f and the power P of the induction heating generator  22 ,  24 ,  26  and/or  28  for the case, in which the cooking pot has a bad coverage of the corresponding induction coil. In the latter case the power delivered to the cooking pot is lower than expected. Adjacent induction coils have the same requested powers and run at the same frequencies, so that the performances of adjacent induction coils could be limited. 
     In order to avoid the bad coverage of the cooking pot on the corresponding induction coil  12 ,  14 ,  16 ,  18 ,  38  and/or  40  a power estimation and adjustment loop is provided. 
       FIG. 6  illustrates a schematic flow chart diagram of an algorithm for evaluating estimated powers of the inductions coils  12 ,  14 ,  16 ,  18 ,  38  and/or  40  according to the preferred embodiment of the present invention. 
     In a first step  50  the real powers ePj of each induction coil j are estimated. In a next step  52  the relation between the estimated power ePj and requested power rPj of each induction coil j is compared with a predetermined high threshold value ThrH. For example, said high threshold value ThrH is about 70%. If the relation between the estimated power ePj and requested power rPj of the induction coil j is bigger than the high threshold value ThrH, then step  50  is activated again. If the relation between the estimated power ePj and requested power rPj of the induction coil j is smaller than the high threshold value ThrH, then a further step  54  is activated. 
     In the step  54  the relation between the estimated power ePj and requested power rPj of the induction coil j is compared with a predetermined low threshold value ThrL. For example, said low threshold value ThrL is about 30%. If the relation between the estimated power ePj and requested power rPj of the induction coil j is smaller than the low threshold value ThrL, then the induction coil j is excluded in step  56 . If the relation between the estimated power ePj and requested power rPj of the induction coil j is bigger than the low threshold value ThrL, then a convergence power routine is performed in step  58 . 
       FIG. 7  illustrates a schematic flow chart diagram of an algorithm for a convergence power routine  58  according to the preferred embodiment of the present invention. 
     As a first step  60  a time warp is performed. In this example, the time wrap extends two time cycles. In a next step  62  a power loss lPj of each induction coil j is calculated. A total power loss is given by the sum of power losses lPj of all activated induction coils j. In a further step  64  the power losses lPj are ordered into a power loss array
 
{ lP 1, lP 2, lP 3, . . . , lP ( Nic )},
 
wherein the power losses lPj are ordered from the highest to the lowest values of the power losses lPj. The power loss array is ordered and updated again after a certain time in particular every two time cycles. In a next step  66  a decrease of the power loss lPj after two time cycles is checked. If said decrease is smaller than a threshold value Thr, then the convergence power routine returns to step  60 . If the decrease of the power loss lPj is bigger than the threshold value Thr, then the requested power rPj is reduced in a step  68 . In the step  68  the requested power rPj is reduced of a quantity equal to a certain percentage quotation of the power loss of the induction coil j. The decrement of the requested power of the induction coil j is stopped, when lPj is decreasing within the threshold value Thr. Further, the original requested power is checked periodically in order to avoid a permanent reduction of power.
 
     Although an illustrative embodiment of the present invention has been described herein with reference to the accompanying drawing, it is to be understood that the present invention is not limited to that precise embodiment, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims. 
     LIST OF REFERENCE NUMERALS 
     
         
           10  induction cooking hob 
           12  first induction coil 
           14  second induction coil 
           16  third induction coil 
           18  fourth induction coil 
           20  frying pan 
           22  first induction generator 
           24  second induction generator 
           26  third induction generator 
           28  fourth induction generator 
           30  control unit 
           32  user interface 
           34  power supply line 
           36  control line 
           38  fifth induction coil 
           40  sixth induction coil 
           42  diagram of frequency as function of the delivered power 
           44  diagram of frequency as function of the delivered power 
           50  step of estimating the power 
           52  step of comparing the estimated power 
           54  step of further comparing the estimated power 
           56  step of excluding the induction coil 
           58  step of performing the convergence power routine 
           60  step of time warp 
           62  step of calculating the power loss 
           64  step of updating the power loss array 
           66  step of checking the decrease of power 
           68  step of reducing the requested power 
         P power of an induction coil 
         rP total requested power of the induction coils 
         rPj requested power of the j-th induction coil 
         pP(i) percentage power of each induction coil in the time slot i 
         cP(i) current power of each induction coil in the time slot i 
         aPj average power of the j-th induction coil 
         Nts number of time slots 
         Nic number of induction coils to be activated 
         Nic(i) number of activated induction coils in the time slot i 
         ts time slot 
         T(i) duration of time slot i 
         f frequency 
         ePj estimated power of the j-th induction coil 
         ThrH high threshold value 
         ThrL low threshold value 
         lPj power loss of the j-th induction coil 
         Thr threshold value for the decrease of power loss