Method for controlling an induction cooking hob with a plurality of induction coils and an induction cooking hob

A method for controlling a cooking hob with one or more induction coils covered by a cookware and forming a cooking zone. All induction coils of the cooking zone are alternately activated. The method includes setting an average power to be transferred to the cookware by a user, determining a frequency, estimating a maximum average power if all induction coils of the cooking zone would be activated with said frequency, estimating a percentage power defined as quotient between the set average power and the estimated maximum average power, estimating a calculated number of coils defined as product of the number of coils within the cooking zone and the percentage power, defining a minimum number of simultaneously activated coils within the cooking zone by an integer value of the calculated number, and defining a temporal activation of a further one of the coils by a fractional part of the calculated number.

The present invention relates to a method for controlling an induction cooking hob with a plurality of induction coils according to the preamble of claim1. Further, present invention relates to an induction cooking hob with a plurality of induction coils according to the preamble of claim9.

An induction cooking hob includes a plurality of induction coils. The induction coils are arranged below a cooking surface. For example, the cooking surface is formed by a glass ceramic panel. The induction coils are arranged as a matrix below the glass ceramic panel. Typically, a standard size cookware covers multiple induction coils. The power transferred to the cookware has to be controlled. The induction coils covered by the same piece of cookware are grouped together into a zone-group. A detection system identifies those induction coils, which are covered by the same cookware.

Adjacent induction coils generate interference between each other, if their frequencies are different. This may result in an audible noise, if the difference between the frequencies is in the audible range. The induction coils of the same zone-group are powered by the same frequency. However, adjacent zone-groups may have different frequencies in order to obtain different powers.

WO 2005/069688 A2 discloses a method for controlling heating elements of a subarea on a cooking hob. The power of each heating element is released with discrete power stages. Some heating elements are operated at maximum power, while one heating element is operated in a clocked mode. The remaining heating elements are deactivated.

It is an object of the present invention to provide an improved method for controlling an induction cooking hob with a plurality of induction coils and a corresponding induction cooking hob, which overcomes the problem of interference.

The object of the present invention is achieved by the method according to claim1.

According to the present invention the method comprises the further steps of:estimating a percentage power defined as quotient between the set average power and the estimated maximum average power, andestimating a calculated number of induction coils defined as product of the number of induction coils within the cooking zone and the percentage power,wherein a minimum number of simultaneously activated induction coils within the cooking zone is defined by an integer value of the calculated number,and wherein a temporal activation of a further one of the induction coils is defined by a fractional part of the calculated number,and wherein the determined frequency depends on the cooking zone with the highest set power on the induction cooking hob.

The core of the present invention is the operation of the induction cooking hob at a determined frequency, wherein the power of the cooking zone is controlled by activating and deactivating the induction coils of said cooking zone. The maximum average power corresponds with the determined frequency. Said maximum average power occurs then, if all induction coils of the cooking zone would be activated with said frequency. The integer value of the calculated number defines the minimum number of simultaneously activated induction coils within the cooking zone. The fractional part of the calculated number defines the temporal activation of the further one of the induction coils. The determined frequency depends on the cooking zone with the highest set power on the induction cooking hob.

Preferably, the induction coils of the cooking zone are activated and deactivated according to a time schedule including a plurality of subsequent cycles, wherein each cycle corresponds with a combination of activated induction coils.

In particular, during the cycle at least the minimum number of simultaneously activated induction coils is really activated.

In a similar way, during the cycle at most the minimum number of simultaneously activated induction coils and the further one of the induction coils is really activated.

Further, the number of cycles with the further one of the induction coils and the number of cycles without the further one of the induction coils may correspond with the fractional part of the calculated number.

Preferably, the time of a cycle following another cycle with the same number of activated induction coils is between 0.3 s and 0.6 s.

However, the time of a cycle following another cycle with a different number of activated induction coils may be between 1.2 s and 1.8 s, preferably 1.5 s.

Further, in subsequent cycles with the same number of activated induction coils the activated induction coils may be cyclically interchanged. This contributes to an even power distribution.

The present invention relates further to an induction cooking hob with a plurality of induction coils, wherein one or more induction coils are covered by a cookware and form a cooking zone, and wherein all induction coils of said cooking zone are at least alternately activated, wherein the induction cooking hob is provided for method mentioned above.

Preferably, the induction coils are arranged as a matrix on a cooking surface of the induction cooking hob.

In particular, the induction coils on the cooking surface of the induction cooking hob have the same sizes.

Novel and inventive features of the present invention are set forth in the appended claims.

FIG. 1illustrates a schematic top view of an induction cooking hob10according to a preferred embodiment of the present invention.

The induction cooking hob10comprises a cooking surface12and a user interface14. The user interface14may be a touch-key panel or a touch screen. The induction cooking hob10comprises a control unit, which is not explicitly shown inFIG. 1. The control unit is electrically connected to the user interface14. A cookware16is put on the cooking surface12. The cookware16may be a pot or pan.

A plurality of induction coils20is arranged below the cooking surface12. The induction coils20are arranged as a matrix. The induction coils20are relative small. In this example, the induction coils20have the same diameters. Further, the induction coils20of this embodiment have a diameter of about 70 mm in each case.

In this example, the induction cooking hob10comprises 43 induction coils20at all. A first front line of the matrix comprises four serial induction coils20, wherein said first front line is interrupted by the user interface14. A second front line of the matrix comprises six serial induction coils20, wherein said second front line is also interrupted by the user interface14. Three lines in a central portion of the cooking surface12comprise nine serial induction coils20in each case. A rear line of the matrix comprises six serial induction coils20.

The cookware16shown inFIG. 1covers four induction coils20, namely a first induction coil22, a second induction coil24, a third induction coil26and a fourth induction coil28. The induction coils22,24,26and28below the cookware16are the same as the other induction coils20, but they are denoted by special reference numbers. The induction coils22,24,26and28below the cookware16form a cooking zone. In other words, the cooking zone includes the induction coils22,24,26and28covered by the same cookware16.

The power transferred to the cookware16is adjustable by varying the frequency of the induction coils22,24,26and28. Typically, the frequency is between 18 kHz and 60 kHz, wherein the highest frequency provided the lowest power. In general, the frequencies of the induction coils20are higher than the audible frequencies of the human ear. Otherwise, the currents in the induction coils20would stimulate physical movements resulting in audible noise. Further, different frequencies of adjacent inductions coils20would cause audible noise at the frequency difference.

The induction coils20of adjacent cooking zones are running at the same frequency in order to prevent interference and audible noise. In a similar way, the induction coils22,24,26and28below the cookware16are also running at the same frequency in order to prevent interference and audible noise. The frequency depends on the cooking zone with the highest set power on the cooking hob10. The variation of the frequency cannot be used to vary the power of the cooking zone. The power of the cooking zone is adjusted by switching on and off the induction coils22,24,26and28below the cookware16according to a predetermined time schedule.

The table below shows an example of the time schedule for activating and deactivating the induction coils22,24,26and28below the cookware16. The time schedule includes a number of subsequent cycles. During each cycle only a part of the induction coils22,24,26and28below the cookware16is activated. The activated induction coils22,24,26and28are denoted by x.

In the first cycle0the three induction coils22,24and26are activated. During the second cycle1the three induction coils24,26and28are activated. In the third cycle2only two induction coils26and28are activated. During the fourth cycle3the both induction coils22and28are activated. In the fifth cycle4the two induction coils22and24are activated.

During the next group of the five cycles0,1,2,3and4the same scheme is performed, wherein the second induction coil24plays now the same role of the first induction coils22before. In a similar way, the third induction coil26plays now the same role of the second induction coils24before, and so on. In other words, the activated induction coils22,24,26and28are rotating counter-clockwise. The activation and deactivation of the induction coils22,24,26and28allow the adjusting of the set power, wherein the same frequency is maintained.

In the above example, the power regulation is performed by reducing the activated induction coils20with the cooking zone. The activated induction coils20are rotated around the complete number of induction coils20covered by the cookware16, so that an even power distribution at the bottom of the cookware16is obtained. Since the rotation of the activated induction coils20does not create any flicker, the activation and deactivation of the induction coils20may be relative fast. For example, the time of one cycle may be 0.3 s to 0.6 s. In this case no significant boil-up and boil-down effect occurs.

The power of one induction coil20is variable between 50 W and 500 W. Typically, the cookware may cover between two and eight induction coils20.

In the above example, the number of activated induction coils20during the first and second cycle is three, while during the third, fourth and fifth cycle the number of activated induction coils20is only two. The variation of the number of activated induction coils20allows a fine tuning of the average power. When the number of activated induction coils20has been changed from one to the next cycle, then the time of this cycle is about 1.5 s, since flicker and a limited boil-up and boil-down effect are created.

In the above example, the number of the induction coils22,24,26and28with the cooking zone is four. The set average power P for the cooking zone is 270 W. The maximum average power PM generated by the cooking zone at the predetermined frequency is 450 W, when all four induction coils22,24,26and28are activated. Thus, the percentage power PP is
PP=P/PM=270 W/450 W=0.6=60%.

The calculated number CN of induction coils20is given by the product of the percentage power PP and the number N of induction coils22,24,26and28within the cooking zone
CN=4*PP=4*0.6=2.4.

The calculated number CN of 2.4 means that two of the induction coils22,24,26and28have to be activated the full time, while a further one of the induction coils22,24,26and28has to be activated 40% of the time. The timely part for activating the further one of the induction coils22,24,26and28corresponds with the fractional part of the calculated number CN.

The method for controlling the induction cooking hob with the plurality of induction coils according to the present invention allows an operation at a constant frequency, wherein all activated induction coils22,24,26and28are working at said same frequency.

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.

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