METHOD AND ARRANGEMENT FOR SUPPLYING POWER TO SEVERAL INDUCTION COILS IN AN INDUCTION APPARATUS

• US 20080087661A1
• Filed: 11/02/2007
• Published: 04/17/2008
• Est. Priority Date: 05/04/2005
• Status: Active Grant

• Current Assignee: EGO Elektro-Gerã¤Tebau GmbH (EGO Blanc und Fischer & Company GmbH)
• Original Assignee: EGO Elektro-Gerã¤Tebau GmbH (EGO Blanc und Fischer & Company GmbH)
• Inventors: Friedrich, Hartmut, Haag, Thomas, Bogel, Jorg
• Granted Patent: US 7,910,865 B2
• Time in Patent Office: Days
• US Class Current: 219/620
• CPC Class Codes: H05B 6/065 using coordinated control of multiple induction coils

Abstract

An arrangement for controlling induction coils of an induction cooking hob so as to minimize noise production resulting from intermodulation of certain frequencies of operation. The induction coils are operated in two modes, with a first mode at the same frequency f_g so to produce a low intermodulation or differential frequency, or at a second mode having a high differential frequency of about 18 kHz. Alternating back and forth between said modes of operation makes it possible to reach predefined average values for the power of the induction coils for a given time period, while at the same time minimizing development of disturbing noise.

Claims

1. A method for supplying power to a plurality of induction coils in an induction apparatus, each said induction coil having a respective frequency converter and being supplied with said power by means of said respective frequency converter operating at a given frequency, wherein during simultaneous operation of the plurality of said induction coils, said frequencies of said frequency converters are set as a function of said power provided with respect to a frequency difference between said frequencies according to one of the following operating modes:

a) said frequency difference is less than 10 Hz,

b) said frequency difference is less than 1 kHz, or

c) said frequency difference is between 15 kHz and 25 kHz.

2. The method according to claim 1, wherein two induction coils are operated according to one of said aforementioned operating modes a) to c).

3. The method according to claim 1, wherein said plurality of induction coils are operated in a frequency range of approximately 16 kHz to 100 kHz.

4. The method according to claim 1, wherein at a start of operation of said plurality of induction coils said induction coils are operated

a) with the requisite values for individual power levels and a total power of said induction apparatus initially with a high frequency, and

b) subsequently accompanied by reduction of said frequency and a rise of said power wherein a total power for said induction coils is set at said requisite value, one said induction coil having more power than required as an increased power and another said induction coil having less power than required, said induction coils having up to then a same common frequency, and

c) subsequently said induction coil with said increased power is moved upwards in frequency by a frequency difference according to operating mode c), and

d) then said frequencies of said induction coils with said fixed mutual frequency difference are lowered to an extent that said total power of said induction coils corresponds to said requisite value for said total power.

5. The method according to claim 4, wherein at said start of operation said induction coils are operated with said high frequency in a mode as saucepan detection coils.

6. The method according to claim 4, wherein a subsequently alternating operation of said induction coils takes place with either said aforementioned common frequency for a first specific time or with said aforementioned frequency difference for a second specific time, said first specific time being equal to:

7. The method according to claim 1, wherein said frequency difference for operating mode b) is a maximum of 500 Hz.

8. The method according to claim 1, wherein said frequency difference for operating mode c) is approximately 18 kHz.

9. A system for controlling an induction hob having at least two separately controllable induction coils comprising:

a first induction coil associated with a first frequency converter capable of being supplied with a first power level;

a second induction coil associated with a second frequency converter capable of being supplied with a second power level;

a power source configured to supply said first power level and said second power level;

a controller configured to control over a first time period a first frequency of said first frequency converter and a second frequency of said second frequency converter, wherein the first frequency and said second frequency are set so that the first power level and the second power level add to a desired total power level, wherein further maintaining a frequency difference between said first frequency and said second frequency such that said frequency difference is;

a) less than 1 khz, or

b) between 15 kHz and 25 kHz.

10. The system of claim 9 wherein said first induction coil and said second induction coil are respectively incorporated into a first hotplate element and a second hotplate element on the induction hob.

11. The system of claim 9 wherein said first induction coil and said second induction coil are incorporated into a single hotplate element on the induction hob.

12. The system of claim 9 wherein said controller is further configured to maintain the frequency difference less than 1 kHz for the first time period, and maintain the first power level at a lower level for a second time period simultaneously with an increase in the second power level wherein a second frequency difference during the second time period is between 15 kHz and 25 kHz.

13. The system of claim 10 wherein the controller is configured so that an average power produced over the first time period and the second time period is equal to the desired power level.

14. The system of claim 10 wherein the controller is configured to repeat the first time period and the second time period in sequence.

15. A controller comprising computer readable software configured to perform the steps of:

controlling a first frequency converter associated with a first induction coil to supply a first power level (P₁(f_g1)) to the first induction coil at a first frequency (f_g1) during a first time period (t_g);

controlling a second frequency converter associated with a second induction coil to supply a second power level (P₂(f_g2)) to the second induction coil at a second frequency (f_g2) during said first time period (t_g);

controlling the first frequency converter to supply a third power level (P₁(f_v1)) to the first induction coil at a third frequency (f_v1) during a second time period (t_v);

controlling the second frequency converter to supply a fourth power level (P₂(f_v2)) to the second induction coil during the second time period (t_v), wherein

a difference between the first frequency (f_g1) associated with the first induction coil and the second frequency (f_g2) associated with the second induction coil in the first time period (t_g) is less than 1 kHz, and

a difference between the third frequency associated with the first induction coil (f_v1) and the fourth frequency (f_v2)associated with the second induction coil in the second time period (t_v) is between 15 kHz and 25 kHz.

16. The computer readable medium of claim 15 wherein the sum of the first power level and the second power level correspond to the sum of the third power level and the fourth power level.