COOKING APPLIANCE

Abstract

A cooking appliance device includes a control and/or regulating unit which is provided such that in a periodic continuous heating operation state, which is allocated at least one operating period, an induction target is repetitively controlled, supplied with energy, and operated in a switched-on interval of the operating period with a heating power, and that in the continuous heating operating state a heating current frequency for the induction target in the switched-on interval of the operating period is varied.

Claims

1-12. (canceled)

13. A cooking appliance device, comprising a control and/or regulating unit provided such that in a periodic continuous heating operation state, which is allocated at least one operating period, an induction target is repetitively controlled, supplied with energy and operated in a switched-on interval of the operating period with a heating power, and that in the continuous heating operating state a heating current frequency for the induction target in the switched-on interval of the operating period is varied

14. The cooking appliance device of claim 13, constructed in the form of an induction hob device.

15. The cooking appliance device of claim 13, wherein the control and/or regulating unit is provided to maintain in the continuous heating operating state an impedance of a unit, which has the induction target, essentially constant within the switched-on interval.

16. The cooking appliance device of claim 13, wherein the control and/or regulating unit is provided to maintain in the continuous heating operating state an actual conductance of a unit, which has the induction target, essentially constant within the switched-on interval.

17. The cooking appliance device of claim 13, wherein the control and/or regulating unit is provided to maintain in the continuous heating operating state a complex conductance of a unit, which has the induction target, essentially constant within the switched-on interval.

18. The cooking appliance device of claim 13, wherein the control and/or regulating unit is provided to control and/or regulate the heating current frequency in the continuous heating operating state.

19. The cooking appliance device of claim 13, wherein the control and/or regulating unit is provided to constantly vary in the continuous heating operating state the heating current frequency in the switched-on interval.

20. The cooking appliance device of claim 19, wherein the control and/or regulating unit is provided to apply in the continuous heating operating state a frequency spread by using a reference curve of an actual conductance and/or a complex conductance of a unit that has the induction target to a harmonic of one of the heating current frequencies.

21. The cooking appliance device of claim 13, wherein the control and/or regulating unit is provided such that in the continuous heating operating state a second induction target is repetitively controlled, supplied with energy, and operated in a second switched-on interval of the operating period with a heating power.

22. The cooking appliance device of claim 21, wherein the control and/or regulating unit is provided to vary in the continuous heating operating state a second heating current frequency for the second induction target in the second switched-on interval of the operating period.

23. The cooking appliance device of claim 21, wherein the control and/or regulating unit is provided to avoid in the continuous heating operating state intermodulation noise of the first and second induction targets.

24. A cooking appliance, comprising a cooking appliance device, said cooking appliance comprising a control and/or regulating unit provided such that in a periodic continuous heating operation state, which is allocated at least one operating period, an induction target is repetitively controlled, supplied with energy and operated in a switched-on interval of the operating period with a heating power, and that in the continuous heating operating state a heating current frequency for the induction target in the switched-on interval of the operating period is varied.

25. The cooking appliance of claim 24, constructed in the form of a hob.

26. A method for operating a cooking appliance device, said method comprising: repetitively controlling an induction target in a periodic continuous heating operating state, which is allocated an operating period; supplying the induction target with energy; operating the induction target in a switched-on interval of the operating period with a heating power; and varying in the continuous heating operating state a heating current frequency for the induction target in the switched-on interval of the operating period

27. The method of claim 26 for operating an induction hob device.

28. The method of claim 26, further comprising maintaining in the continuous heating operating state an impedance of a unit that has the induction target essentially constant within the switched-on interval.

29. The method of claim 26, further comprising maintaining in the continuous heating operating state an actual conductance of a unit, which has the induction target, essentially constant within the switched-on interval.

30. The method of claim 26, further comprising maintaining in the continuous heating operating state a complex conductance of a unit, which has the induction target, essentially constant within the switched-on interval.

31. The method of claim 26, further comprising controlling and/or regulating the heating current frequency in the continuous heating operating state.

32. The method of claim 26, further comprising constantly varying in the continuous heating operating state the heating current frequency in the switched-on interval.

33. The method of claim 32, further comprising applying in the continuous heating operating state a frequency spread by using a reference curve of an actual conductance and/or a complex conductance of a unit that has the induction target to a harmonic of one of the heating current frequencies.

34. The method of claim 26, further comprising: repetitively controlling in the continuous heating operating state a second induction target; supplying the second induction target with energy; and operating the second induction target in a second switched-on interval of the operating period with a heating power.

35. The method of claim 34, further comprising varying in the continuous heating operating state a second heating current frequency for the second induction target in the second switched-on interval of the operating period.

36. The method of claim 34, further comprising avoiding in the continuous heating operating state intermodulation noise of the first and second induction targets.

Description

[0042] In the drawings:

[0043] FIG. 1 shows a hob with a cooking appliance device and as an example with items of cookware placed thereon,

[0044] FIG. 2 shows the cooking appliance device with four induction targets that are defined by a control and/or regulating unit,

[0045] FIG. 3 shows a schematic illustration of a control for one of the induction targets,

[0046] FIG. 4 shows an exemplary schematic illustration of the resistance curve and the induction curve of one of the induction targets in an operating period,

[0047] FIG. 5 shows a schematic illustration of a distorted supply current in comparison to an ideal supply current and a schematic illustration of the spacing of the individual harmonics of the supply current from corresponding EMC limit values,

[0048] FIG. 6 shows a schematic illustration of a control with a frequency spread and the actual conductance for one of the induction targets being maintained constant,

[0049] FIG. 7 shows a schematic illustration of a control with a frequency spread and the actual conductance constant for one of the induction targets being maintained constant,

[0050] FIG. 8 shows a schematic illustration of a control with a frequency spread for one of the induction targets,

[0051] FIG. 9 shows a schematic illustration of a control at a maximum frequency and a minimum frequency with respect to the actual conductance for one of the induction targets being maintained constant,

[0052] FIG. 10 shows a schematic illustration of a control with a frequency spread with the actual conductance for one of the induction targets being maintained constant,

[0053] FIG. 11 shows a schematic illustration of a control with a frequency spread with the complex conductance for one of the induction targets being maintained constant,

[0054] FIG. 12 shows a schematic illustration of a control with respect to a low-noise operation with the actual conductance for two of the induction targets being maintained constant,

[0055] FIG. 13 shows a schematic illustration of a control with respect to a low-noise operation with the actual conductance for two induction targets being maintained constant,

[0056] FIG. 14 shows a schematic illustration of a frequency spectrum of EMC emissions in the case of a fixed heating current frequency (a) and in the case of a variable heating current frequency (b) and

[0057] FIG. 15 shows a schematic illustration of a method for operating the cooking appliance device.

[0058] Where more than one object appears in the figures in part only one of said objects is provided with a reference numeral.

[0059] FIG. 1 illustrates a cooking appliance 20 that is embodied as a hob 12, in particular as an induction hob, and three items of cookware 14, 14′, 14″ that are placed thereon.

[0060] The cooking appliance 20 has a resting plate 16. The resting plate 16 is provided for the cookware 14, 14′, 14″ to be placed thereon. The resting plate 16 is embodied as a hob plate. In the illustrated exemplary embodiment, the cooking appliance 20 has four classic cooking zones 18. However, it is also conceivable as an alternative that the cooking appliance 20 is embodied as a matrix hob. An item of cookware 14, 14′ 14″ is arranged respectively on three of the four cooking zones 18.

[0061] The cooking appliance 20 has a cooking appliance device 10 that is embodied as an induction hob device.

[0062] The cooking appliance device 10 has a multiplicity of inductors 22, 22′, 22″, 22′″. FIG. 2 illustrates as an example a cooking appliance device 10 having respectively an inductor 22, 22′, 22″, 22′″ for each cooking zone 18 or for each item of cookware 14, 14′, 14″, 14′″. An inductor 22, 22′, 22″, 22′″ is allocated precisely to one cooking zone 18. It is conceivable that in the case of a matrix hob the inductors 22, 22′, 22″, 22′″ are arranged in a matrix-like manner below the resting plate 16 in order to create a uniform cooking zone 18. It is likewise conceivable that in the case of a matrix hob multiple inductors 22, 22′, 22″, 22′″ are arranged in individual regions of the resting plate 16 in order to create different cooking zones for example rapid cooking zones, wherein the matrix hob renders it possible to continue to use the entire surface of the resting plate 16 for cooking. In the present example, the cooking appliance device 10 has four inductors 22, 22′, 22″, 22′″.

[0063] The inductors 22, 22′, 22″, 22′″ are arranged in the installed state below the resting plate 16, in particular within the cooking appliance device 10. The inductors 22, 22′, 22″, 22′″ are each provided so as in a periodic continuous heating operating state 50 to heat, in particular inductively, an item of cookware 14, 14′, 14″, 14′″ that is placed on the resting plate 16 over the inductors 22, 22′, 22″, 22′″.

[0064] The cooking appliance device 10 comprises a control panel 24 for an operator to input and/or select operational parameters. For example, an operational parameter can be embodied as a desired heating power 30, 30′ and/or as a cooking duration, wherein the operational parameter can be adjusted in particular as a discrete and/or an abstract value for example in quantized intervals or from a pool of an essentially continuous value range. The control panel 24 can be embodied as a display 28, in particular a touch screen display. The control panel 24 is provided so as to output to the operator at least one operational parameter.

[0065] The cooking appliance device 10 has a control and/or regulating unit 26. The control and/or regulating unit 26 is provided so as in dependence upon the operational parameter that is input by the operator, such as the desired heating power 30, 30′ or a cooking duration, to perform programs, actions and/or algorithms and/or to vary the settings of the cooking appliance device 10.

[0066] Based on the cookware 14, 14′, 14″, 14′″ that is placed on the resting plate 16, the control and/or regulating unit 26 defines in this case for example multiple induction targets 32, 32′, 32″, 32′″. In FIG. 1, two induction targets 32, 32′ are defined by the control and/or regulating unit 26 based on the cookware 14, 14′ that is placed on the resting plate 16 and defines the inductors 22, 22′ that are arranged below the resting plate 16. In FIG. 2, four induction targets 32, 32′, 32″, 32′″ are defined by the control and/or regulating unit. An induction target 32, 32′, 32″, 32′″ has precisely one inductor 22, 22′, 22″, 22′″. An induction target 32, 32′, 32″, 32′″ has at least one item of cookware 14, 14′, 14″, 14″. In particular, in dependence upon the configuration of the hob 12 and the cookware 14, 14′, 14″, 14′″ that is located thereon, the control and/or regulating unit 26 can define a multiplicity of induction targets 32, 32′, 32″, 32′″.

[0067] The control and/or regulating unit 26 heats an item of cookware 14, 14′, 14″, 14′″ by applying a heating current frequency 36 to the respective inductor 22, 22′, 22″, 22′″. A particularly momentarily achieved output heating power 34 of each induction target 32, 32′, 32″, 32′″ is significantly dependent upon the heating current frequency 36 that is applied to the induction target 32, 32′, 32″, 32′″. In a ZVS-mode the output heating power 34 of an induction target 32, 32′, 32″, 32′″ increases with a reducing heating current frequency 36. In a ZCS-mode the output heating power 34 of an induction target 32, 32′, 32″, 32′″ reduces with a reducing heating current frequency 36. The control and/or regulating unit 26 operates the cooking appliance device 10 as an example in the ZVS-mode.

[0068] In the continuous heating operating state 50, an energy source supplies the induction targets 32, 32′, 32″, 32′″ with electrical energy. The energy source is an electrical current phase of a current supply network. The cooking appliance device 10 has at least one inverter unit 38 for providing at least one heating current frequency 36 for the respective induction target 32, 32′, 32″, 32′″ (cf. FIG. 2).

[0069] FIG. 2 illustrates the cooking appliance device 10 having four induction targets 32, 32′, 32″, 32′ that are defined by a control and/or regulating unit 26 of the cooking appliance device 10. The cooking appliance device 10 has four resonant inverter units 38. The inverter units 38 provide a heating current frequency 36 for the induction targets 32, 32′, 32″, 32′″. The inverter units 38 supply the induction targets 32, 32′, 32″, 32′ with electrical energy independently of one another. Each inverter unit 38 is allocated respectively to one of the induction targets 32, 32′, 32″, 32′″. Each inverter unit 38 comprises in FIG. 2 as an example an inverter 64.

[0070] The control and/or regulating unit 26 is provided so as in the periodic continuous heating operating state 50, which is allocated one operating period 42, to repetitively control and supply energy to the at least one induction target 32, 32′, in particular from the energy source. The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to periodically control and supply energy to the induction target 32, 32′. The control and/or regulating unit 26 is provided so as in a switched-on interval 40, 40′ of the operating period 42 to operate the induction target 32, 32′, 32″, 32′″ with a heating power, in particular a desired heating power 30, 30′ or excess power with respect to the desired heating power 30, 30′. In particular in the absence of a changed desired heating power 30, 30′ that has been set by an operator, the control and/or regulating unit 26 repetitively runs through the operating period 42 for at least one induction target 32, 32′, 32″, 32′″ in the continuous heating operating state 50.

[0071] The cooking appliance device 10 has an electromechanical switching element 60 for each induction target 32, 32′, 32″, 32′. The switching element 60 is embodied as a relay 62. The induction targets 32, 32′, 32″, 32′″ can be connected to the electrical energy supply by the relay 62. The cooking appliance device 10 has in each case one resonance capacitor unit 44 for each induction target 32, 32′, 32″, 32′. Each induction target 32, 32′, 32″, 32′ can be controlled individually with a respective heating current frequency 36.

[0072] FIG. 3 shows a section of FIG. 2 with schematically illustrated voltages vi and currents i.sub.i, wherein the subscript i is inserted as a placeholder for the respective reference character. A rectified supply voltage v.sub.bus is applied by way of the inverter unit 38, in particular by way of the inverter 64. A voltage v.sub.0 is applied by way of one, in particular each, part 66 of the inverter 64. The voltage v.sub.RL is applied by way of the inductor 22, in particular the induction target 32. The voltage v.sub.c is applied by way of one, in particular each, capacitor 68 of the resonance capacitor unit 44. The control and/or regulating unit 26 can measure the voltage v.sub.0 by way of a part 66 of the inverter 64, in particular the voltages v.sub.bus, v.sub.RL, v.sub.c. The control and/or regulating unit 26 can measure the current strength i.sub.L. The control and/or regulating unit 26 can store measured values. Over each half of a period duration of an alternating voltage supply, in particular period durations during which rectified alternating voltage is supplied, for example 10 ms, the control and/or regulating unit 26 can measure the voltage v.sub.0 at least ten times, preferably at least twenty times, particularly preferably at least a hundred times. Over the course of each half of a period duration of an alternating voltage supply, in particular a period duration during which the rectified alternating voltage is supplied, for example 10 ms, the control and/or regulating unit 26 can measure the voltage v.sub.0 a maximum of seven hundred and fifty times. The control and/or regulating unit 26 can calculate average values over an arbitrary number N of measured values, in particular for voltages and current strengths. The control and/or regulating unit 26 can perform an error calculation for each calculated average value and/or determine whether an average value is within or outside predetermined error tolerances. If an average value lies outside the error tolerances, it is conceivable that the control and/or regulating unit 26 takes into consideration further values when calculating an average, in particular until the value is within the error tolerances. It is conceivable that so as to determine an average value the control and/or regulating unit 26 takes into consideration a lower limit and an upper limit for a number N of values by way of inclusion when calculating an average value. In the case of error tolerances not being achieved for an arbitrary value, in particular a calculated average value, within the lower and the upper limit for the number N of values, it is conceivable that the control and/or regulating unit 26 rejects this value for the average calculation and moves ahead so as to determine the next value. The number N is in particular an arbitrary natural number. In the case of unreliable measurements or calculations, the control and/or regulating unit 26 can cease, in particular temporarily, the control, in particular for the heating current frequency 36 of an induction target 32, 32′, 32″, 32′″. The unit 80 that has the induction target 32, 32′, 32″, 32′″ comprises at least one induction target 32, 32′, 32″, 32′″ and in each case at least one capacitor 68 of the resonance capacitor unit 44, which is connected in series to the induction target 32, 32′, 32″, 32′″.

[0073] FIG. 4a illustrates the curve of the rectified voltage v.sub.bus over a period duration, in particular of 10 ms. The time is plotted in milliseconds on an abscissa 88. The rectified voltage v.sub.bus is plotted in volts on an ordinate 90. FIGS. 4b and 4c illustrate how within the period duration of the rectified voltage v.sub.bus the resistance, which is plotted in particular on an ordinate 92, (cf. FIG. 4b), and the inductivity, which is plotted in particular on an ordinate 94 (cf. FIG. 4c) of the controlled induction target 32, 32′, 32″, 32′″ or of a unit 80 that comprises the induction target 32, 32′, 32″, 32′″, vary over time in particular in dependence upon the signal level of the rectified voltage, wherein in particular the time is plotted in milliseconds on the abscissa 88. In particular, as the inductivity varies, an impedance, in particular a complex conductance, of the induction target 32, 32′, 32″, 32′″ also changes within the period duration of the rectified voltage v.sub.bus. In particular, as the resistance varies, the actual conductance of the induction target 32, 32′, 32″, 32′″ also changes within the period duration of the rectified voltage v.sub.bus. The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to vary a heating current frequency 36 for the induction target 32, 32′, 32″, 32′″ in the switched-on interval 40, 40′ of the operating period 42. In the continuous heating operating state 50, the control and/or regulating unit 26 can vary the heating current frequency 36 in particular so as to maintain constant the impedance and/or the actual conductance and/or of the complex conductance of a unit 80 that has the induction target 32, 32′, 32″, 32′″. The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to maintain at least one impedance at least of one unit 80 that has the induction target 32, 32′, 32″, 32′″ at least essentially constant within the switched-on interval 40, 40′. The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to constantly vary the heating current frequency 36 in the switched-on interval 40, 40′. In particular, the control and/or regulating unit 26 varies the heating current frequency 36 at least ten times in an operating period 42.

[0074] FIG. 5 illustrates a distorted alternating current supply in the case of the operation of an induction target 32, 32′, 32″, 32′″ with a constant heating current frequency 36 in the continuous heating operating state 50. In FIG. 5a, the time is plotted in milliseconds on the abscissa 88. In FIG. 5a, the current strength is plotted in amps on an ordinate 96. FIG. 5 illustrates in addition that individual harmonics 78 (harmonics) have a greater amplitude than other harmonics 78, in particular on account of the dependency of the waveform of the supply current on the signal level, in particular on the amplitude, and on the temperature. As a consequence, individual harmonics 78, in this example the third harmonic 78, cannot comply with the EMC standards. FIG. 5a illustrates in particular an example of how the alternating current supply is distorted on account of the dependency of the impedance of the unit 80 that has the induction target 32, 32′, 32″, 32′″ on the signal level of the alternating voltage supply. In FIG. 5b, the alternating current supply is broken down into its in particular first forty onwards from the second harmonic 78, alternatively also referred to as harmonics, wherein each harmonic 78 has a specific current strength and for each harmonic 78 a current strength limit applies that is laid down in particular by EMC standards. In FIG. 5b, the order of the harmonics is plotted without a unit on an abscissa 98. In FIG. 5b, the current strengths, in particular the difference of the current strengths, is plotted in amps on the ordinate 96. In FIG. 5b, in particular the differences of the current strengths of the individual harmonics 78 are plotted after the second order up to their limits, wherein a positive difference indicates that the value is not within the limit. For example, it is illustrated that the third harmonic 78, for example of 2.77 A, lies above its limit, wherein the limit is in particular 2.3 A, and the EMC standards are not complied with. In this example, the induction target 32, 32′, 32″, 32′″ is controlled and operated with a constant heating current frequency 36 of 60 kHz.

[0075] FIG. 6 illustrates schematically a curve of a control for an induction target 32, 32′, 32″, 32′″ performed by the control and/or regulating unit 26. The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to maintain at least the actual conductance at least of the unit 80 that has the induction target 32, 32′, 32″, 32′″ in particular essentially constant within the switched-on interval 40, 40′. In the continuous heating operating state 50, the control and/or regulating unit 26 maintains at least the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″ essentially constant within the switched-on interval 40, 40′. FIG. 6a illustrates the curve of the actual conductance G of the unit 80 that has the induction target 32, 32′, 32″, 32′″ in the operating period 42, for example 10 ms, corresponding to half a period duration of the alternating voltage supply. In FIG. 6a, the time is plotted in milliseconds on the abscissa 88. In FIG. 6a, the actual conductance is plotted in (mΩ.sup.−1), in particular milliohm.sup.−1, on an ordinate 100. FIG. 6b illustrates in the same operating period 42 of the heating current frequency 36 the curve that is required so as to maintain the actual conductance G constant and is achieved by the control and/or regulating unit 26. In FIG. 6b, the time is plotted in milliseconds on the abscissa 88. In FIG. 6b, the frequency is plotted in kHz on an ordinate 102. In particular, the control and/or regulating unit 26 changes the heating current frequency 36, in particular of the induction target 32, 32′, 32″, 32″, in particular at least five times per millisecond. It is illustrated that the control and/or regulating unit 26 can control the heating current frequency 36 at times without any changes. The control and/or regulating unit 26 controls and/or regulates the heating current frequency 36 to a constant value in the first and last approximately 0.2 milliseconds of the operating period 42. In particular, the control and/or regulating unit 26 can determine measurement data outside error tolerances and therefore avoid an adjustment of the heating current frequency 36.

[0076] FIG. 6c illustrates the curve of the squared rectified alternating voltage supply v.sub.bus in the operating period 42. In FIG. 6c, the time is plotted in milliseconds on the abscissa 88. In FIG. 6c, the squared voltage is plotted in mV.sup.2, in particular millivolt, on an ordinate 104. FIG. 6d illustrates the curve of the heating power that is achieved, in particular required by the unit 80 that has the induction target 32, 32′, 32″, 32″, in particular by the induction target 32, 32′, 32″, 32′″, in the operating period 42. In FIG. 6d, the time is plotted in milliseconds on the abscissa 88. In FIG. 6d, the power is plotted in W, in particular watts, on an ordinate 106. In FIG. 6e, the curves shown in FIGS. 6c and 6d are standardized and illustrated placed over one another. In the ideal case of a constant actual conductance, the power is proportional to the square of the voltage and both curves that are illustrated in FIG. 6e should fall precisely on top of each another (cf. the following equation).

P=U.sup.2.Math.G

[0077] wherein P is a power, U is a voltage and G is the actual conductance. In FIG. 6e, the time is plotted in milliseconds on the abscissa 88. In FIG. 6e, a standardizing variable is plotted without units on an ordinate 108. FIG. 6e illustrates that the control and/or regulating unit 26 controls and/or regulates the actual conductance so as to achieve a match between the curves of the squared rectified alternating voltage supply v.sub.bus and of the power, in particular the heating power, which arises by way of the unit 80 that has the induction target 32, 32′, 32″, 32′″. By maintaining constant the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″, the control and/or regulating unit 26 reduces the distortion of the supply current. The control and/or regulating unit 26 achieves compliance with EMC standards by maintaining constant the actual conductance, in particular the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″. In particular, the value of the complex conductance, to which the complex conductance is maintained constant by the control and/or regulating unit 26 in the operating period 42, is the desired heating power 30, 30′ that is desired in particular by an operator.

[0078] FIG. 7 illustrates schematically a curve of a control for the induction target 32, 32′, 32″, 32′″ performed by the control and/or regulating unit 26. In FIGS. 7a to 7e, the time is plotted in milliseconds on the abscissa 88. In FIG. 7a, the actual conductance is plotted in (mΩ.sup.−1), in particular milliohm.sup.−1 on the ordinate 100. In FIG. 7b, the frequency is plotted in kHz on the ordinate 102. In FIG. 7c, the squared voltage is plotted in mV.sup.2, in particular millivolt, on the ordinate 104. In FIG. 7d, the power is plotted in W, in particular in watts, on the ordinate 106. In FIG. 7e, a standardizing variable is plotted without units on the ordinate 108.

[0079] The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to maintain at least the actual conductance (G), at least of the unit 80 that has the induction target 32, 32′, 32″, 32′″ in particular essentially constant within the switched-on interval 40, 40′. In the continuous heating operating state 50, the control and/or regulating unit 26 maintains at least the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″ essentially constant within the switched-on interval 40,40′. FIG. 7a illustrates the curve of the actual conductance G of the unit 80 that has the induction target 32, 32′, 32″, 32′″ in the operating period 42, for example 10 ms, corresponding to a half period duration of the alternating voltage supply. FIG. 7b illustrates in the same operating period 42 the curve of the heating current frequency 36 that is necessary in order to maintain the actual conductance G constant and is achieved by the control and/or regulating unit 26. In particular, the control and/or regulating unit 26 changes the heating current frequency 36, in particular of the induction target 32, 32′, 32″, 32′″ at least ten times per millisecond. It is illustrated that the control and/or regulating unit 26 can control the heating current frequency 36 at times without any changes. The control and/or regulating unit 26 controls and/or regulates the heating current frequency 36 to different values in the first and last approximately 0.2 milliseconds of the operating period 42. In particular, the control and/or regulating unit 26 can determine measurement data within error tolerances and therefore control and/or regulate an adjustment of the heating current frequency 36.

[0080] FIG. 7c illustrates the curve of the squared rectified alternating voltage supply v.sub.bus in the operating period 42. FIG. 7d illustrates the curve of the heating power that is achieved, in particular consumed, by the unit 80 that has the induction target 32, 32′, 32″, 32′″, in particular by the induction target 32, 32′, 32″, 32′″, in the operating period 42. In FIG. 7e, the curves shown in FIGS. 7c and 7d are illustrated standardized and placed above one another. FIG. 7e illustrates that the control and/or regulating unit 26 controls and/or regulates the actual conductance so as to achieve a match between the curves of the squared rectified alternating current supply v.sub.bus and of the power, in particular heating power, which arises by way of the unit 80 that has the induction target 32, 32′, 32″, 32′″. By maintaining constant the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″, the control and/or regulating unit 26 reduces the distortion of the supply current. The control and/or regulating unit 26 achieves compliance with EMC standards by maintaining constant the actual conductance, in particular the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″. In particular, the value of the complex conductance, to which the complex conductance is maintained constant by the control and/or regulating unit 26 in the operating period 42, is the desired heating power 30, 30′ that is desired in particular by an operator.

[0081] FIG. 8 illustrates schematically a curve of a control for an induction target 32, 32′, 32″, 32′″ performed by the control and/or regulating unit 26. The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to maintain the complex conductance, at least of the unit 80 that has the induction target 32, 32′, 32″, 32′″, in particular essentially constant within the switched-on intervals 40, 40′. In FIGS. 8a to 8e, the time is plotted in milliseconds on the abscissa 88. In FIG. 8a, the complex conductance is plotted in (mΩ.sup.−1), in particular milliohm.sup.−1, on an ordinate 110. In FIG. 8b, the frequency is plotted in kHz on the ordinate 102. In FIG. 8c, the voltage is plotted in V, in particular volts, on the ordinate 112. In FIG. 8d, the current strength is plotted in A, in particular in amps, on the ordinate 114. In FIG. 8e, a standardizing variable is plotted without units on the ordinate 108.

[0082] In the continuous heating operating state 50, the control and/or regulating unit 26 maintains the complex conductance of a unit 80 that has the induction target 32, 32′, 32″, 32′″ essentially constant within the switched-on interval 40, 40′ (cf. FIG. 8a). FIG. 8a illustrates the curve of the complex conductance Y of the unit 80 that has the induction target 32, 32′, 32″, 32′″ in the operating period 42, for example 10 ms, corresponding to half a period duration of the alternating voltage supply.

[0083] FIG. 8b illustrates in the same operating period 42 the curve of the heating current frequency 36 that is necessary so as to maintain the complex conductance Y constant and is achieved by the control and/or regulating unit 26. In particular, the control and/or regulating unit 26 changes the heating current frequency 36, in particular of the induction target 32, 32′, 32″, 32′″, at least five times per millisecond. It is illustrated that the control and/or regulating unit 26 can control the heating current frequency 36 at times without any changes. The control and/or regulating unit 26 controls and/or regulates the heating current frequency 36 to different values in the first and last approximately 0.2 milliseconds of the operating period 42. In particular, the control and/or regulating unit 26 can avoid measurement data outside error tolerances and therefore adjust the heating current frequency 36.

[0084] FIG. 8c illustrates the curve of the rectified alternating voltage supply v.sub.bus in the squared average in the operating period 42. FIG. 8d illustrates the curve of the heating current in the squared average, said heating current being applied, in particular consumed, by the unit 80 that has the induction target 32, 32′, 32″, 32′″, in particular by the induction target 32, 32′, 32″, 32′″, in the operating period 42. FIG. 8e illustrates the curves of the parameters from FIGS. 8c and 8d standardized and placed above one another.

[0085] FIG. 8e illustrates that the control and/or regulating unit 26 controls and/or regulates the actual conductance so as to achieve a match between the curves of the squared rectified alternating voltage supply v.sub.bus in the squared average and of the current strength i.sub.L, in particular of the heating current that is applied to the unit 80 that has the induction target 32, 32′, 32″, 32′″. The control and/or regulating unit 26 reduces the distortion of the supply current by maintaining constant the complex conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″. The control and/or regulating unit 26 achieves compliance with EMC standards by maintaining constant the complex conductance, in particular of the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″. In particular, the value of the complex conductance, to which the complex conductance is maintained constant by the control and/or regulating unit 26 in the operating period 42, is the desired heating power 30, 30′ that is desired in particular by an operator.

[0086] FIG. 9 illustrates schematically a curve of a control for an induction target 32, 32′, 32″, 32′″ performed by the control and/or regulating unit 26. In FIGS. 9a to 9d, the time is plotted in milliseconds on the abscissa 88. In FIGS. 9a and 9c, the actual conductance is plotted in (mΩ.sup.−1), in particular milliohm.sup.−1, on the ordinate 100. In FIGS. 9b and 9d, the frequency is plotted in kHz on the ordinate 102. The 26 is provided so as in the continuous heating operating state 50 to maintain at least the actual conductance, at least of the unit 80 that has the induction target 32, 32′, 32″, 32′″, in particular essentially constant within the switched-on interval 40, 40′. In particular, the control and/or regulating unit 26 changes the heating current frequency 36 of the induction target 32, 32′, 32″, 32′″. The control and/or regulating unit 26 varies the heating current frequency 36 of the induction target 32, 32′, 32″, 32′″ within a maximum frequency 82 and a minimum frequency 84 that are permissible according to technical limitations. FIG. 9a illustrates a curve of the actual conductance of a unit 80 that has the induction target 32, 32′, 32″, 32′″ in the switched-on interval 40, 40′, in particular of an operating period 42. FIG. 4b illustrates the curve of the heating current frequency 36 that corresponds to FIG. 4a. The control and/or regulating unit 26 changes the heating current frequency 36 within the permissible frequency limits, such as a maximum frequency 82 and a minimum frequency 84. The control and/or regulating unit 26 controls and/or regulates the actual conductance on account of a necessary change in the heating current frequency 36 above the maximum frequency 82 in the time interval of 0 to 2.5 ms and from 7.5 ms to 10 ms of the operating period 42 to a constant value, in particular to the maximum frequency 82 (cf. FIGS. 4a and 4b).

[0087] FIG. 9c illustrates a curve of the actual conductance of a unit 80 that has the induction target 32, 32′, 32″, 32′″ in the switched-on interval 40, 40′ in particular of an operating period 42. FIG. 4d illustrates the curve of the heating current frequency 36 that corresponds to FIG. 4c. The control and/or regulating unit 26 controls and/or regulates the actual conductance on account of a necessary change in the heating current frequency 36 below the minimum frequency 84 in the time interval of 0 to 2.5 ms and from 7.5 ms to 10 ms of the operating period 42 to a constant value, in particular to the minimum frequency 84 (cf. FIGS. 4c and 4d).

[0088] FIG. 10 illustrates schematically a curve of a control for an induction target 32, 32′, 32″, 32′″ performed by the control and/or regulating unit 26 as shown in FIG. 7 with an additional frequency spread 74. In FIGS. 10a to 10d, the time is plotted in milliseconds on the abscissa 88. In FIG. 10a, the actual conductance is plotted in (mΩ.sup.−1), in particular milliohm.sup.−1 on the ordinate 100. In FIG. 10b, the frequency is plotted in kHz on the ordinate 102. In FIG. 10c, the squared voltage is plotted in mV.sup.2, in particular in millivolts, on the ordinate 104. In FIG. 10d, the power is plotted in W, in particular watts, on the ordinate 106. In FIG. 10e, a standardizing variable is plotted without units on the ordinate 108.

[0089] The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to apply a frequency spread 74 by means of a reference curve 70 of the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″ to at least one harmonic 78, in particular at least to one of the heating current frequencies 36. The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to maintain the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″ in particular essentially constant within the switched-on interval 40, 40′. In a middle region 72 of the operating period 42, in particular of 3 ms to 7 ms, the control and/or regulating unit 26 carries out a frequency spread 74 by means of a wavy reference curve 70 for the actual conductance on the heating current frequency 36. The reference curve 70 in order to achieve a frequency spread 74 has a sinusoidal curve. The reference curve 70 is constant outside the middle region 72, in particular corresponds to the reference curve 70 outside the middle region 72 of a temporally constant function. In particular for the duration of the entire operating period 42, in particular at least for the duration of the switched-on intervals 40, 40′ of an operating period, the reference curve 70 is centered around the value of the actual conductance at which the induction target 32, 32′, 32″, 32′″ achieves the desired heating power 30, 30′. In the middle, the control and/or regulating unit 26 achieves in the induction target 32, 32′, 32″, 32′″ for the duration of the frequency spread 74, for example in the middle region 72, in particular also for the duration of the operating period 42 having a frequency spread 74 the desired heating power 30, 30′, in particular the heating current frequency 36 that the control and/or regulating unit 26 maintains constant during the remainder of the operating period 42. In the continuous heating operating state 50, the control and/or regulating unit 26 maintains at least the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″ essentially constant within the switched-on interval 40, 40′ outside the middle region 72. FIG. 10a illustrates the curve of the actual conductance G of the unit 80 that has the induction target 32, 32′, 32″, 32′″ in the operating period 42, for example 10 ms, corresponding to a half period duration of the alternating voltage supply. FIG. 10b illustrates in the same operating period 42 the curve of the heating current frequency 36 that is required so as to maintain the actual conductance G constant and is achieved by the control and/or regulating unit 26. In particular, the control and/or regulating unit 26 changes the heating current frequency 36, in particular of the induction target 32, 32′, 32″, 32′″, at least five times per millisecond. In particular, the control and/or regulating unit 26 controls and/or regulates the heating current frequency 36 outside the middle region 72 of the switched-on interval 40, 40′ so as to achieve a constant actual conductance. In particular, the constant actual conductance is predetermined outside the middle region 72 by means of a constant reference curve 70. In particular, the switched-on interval 40, 40′ has two regions from 0 ms to 3 ms and from 7 ms to 10 ms outside the middle region 72 from 3 ms to 7 ms. In particular, the control and/or regulating unit 26 controls and/or regulates the heating current frequency 36 for 6 ms in order to achieve a constant actual conductance and for 4 ms to create a sinusoidal curve of the actual conductance. FIG. 10c illustrates the curve of the squared rectified alternating voltage supply v.sub.bus in the operating period 42. FIG. 10d illustrates the curve of the heating power that is achieved, in particular consumed, by the unit 80 that has the induction target 32, 32′, 32″, 32′″, in particular by the induction target 32, 32′, 32″, 32′″, in the operating period 42. In FIG. 10e, the curves of the FIGS. 10c and 10d are illustrated standardized and placed over one another. FIG. 10e illustrates that the control and/or regulating unit 26 controls and/or regulates the actual conductance, in particular the heating current frequency 36, so as to achieve a match between the curves of the squared rectified alternating voltage supply v.sub.bus and of the power, in particular the heating power, which arises by way of the unit 80 that has the induction target 32, 32′, 32″, 32′″. By maintaining constant the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″, the control and/or regulating unit 26 reduces the distortion of the supply current. In addition by virtue of the frequency spread 74, the control and/or regulating unit 26 achieves compliance with EMC standards for critical heating current frequencies 36 (cf. FIG. 14) by maintaining constant the actual conductance, in particular the actual conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″. In particular, the value of the complex conductance, to which the complex conductance is maintained constant by the control and/or regulating unit 26 in the operating period 42, is the desired heating power 30, 30′ that is desired in particular by an operator. It is conceivable that the control and/or regulating unit 26 extends the region of the operating period 42 with a frequency spread 74 by a wavy reference curve 70 for the duration of the entire operating period 42. It is likewise conceivable that the control and/or regulating unit 26 has at least two regions with a frequency spread 74 distributed in the operating period 42.

[0090] FIG. 11 illustrates schematically a curve of a control for an induction target 32, 32′, 32″, 32′″ performed by the control and/or regulating unit 26 as in FIG. 8 with an additional frequency spread 74 in a similar manner to the combination which is described in FIG. 10, wherein the control and/or regulating unit 26 controls the frequency spread 74 by means of a reference curve 70 for the complex conductance. In FIGS. 11a to 11d, the time is plotted in milliseconds on the abscissa 88. In FIG. 11a, the complex conductance is plotted in (mΩ.sup.−1), in particular in milliohm.sup.−1, on the ordinate 110. In FIG. 11b, the frequency is plotted in kHz on the ordinate 102. In FIG. 11c, the voltage is plotted in V, in particular in volts, on the ordinate 112. In FIG. 11d, the current strength is plotted in A, in particular in amps, on the ordinate 114. In FIG. 11e, a standardizing variable is plotted without units on the ordinate 108.

[0091] In particular, the control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to apply a frequency spread 74 by means of a reference curve 70 of the complex conductance at least of a unit 80 that has the induction target 32, 32′, 32″, 32′″ to at least one harmonic 78, in particular at least one of the heating current frequencies 36. The control and/or regulating unit 26 achieves the frequency spread 74 by means of a reference curve 70 in a similar manner to the example of FIG. 10, wherein the reference curve 70 applies for the complex conductance. It is conceivable that the control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to control and/or to regulate the heating current frequency 36 by a target frequency, in particular with the aid of a reference curve 70 with tolerances, in particular in order to achieve the desired heating power 30, 30′ in the induction target 32, 32′, 32″, 32′″ for the duration of the operating period 42.

[0092] FIG. 12 illustrates schematically a curve of a noise-free control for two units 80 that have an induction target 32, 32′, 32″, 32′″ performed by the control and/or regulating unit 26. In FIGS. 12a to 12d, the time is plotted in milliseconds on the abscissa 88. In FIG. 12a, the actual conductance is plotted in (mΩ.sup.−1), in particular in milliohm.sup.−1, on the ordinate 100. In FIG. 12b, the frequency is plotted in kHz on the ordinate 102. In FIG. 12c, the squared voltage is plotted in mV.sup.2, in particular in millivolt, on the ordinate 104. In FIG. 12d, the power is plotted in W, in particular in watts, on the ordinate 106. In FIG. 12e, a standardizing variable is plotted without units on the ordinate 108.

[0093] In the illustrated example, the operating period 42 corresponds to a multiplicity, in particular ten, of the halves of the period duration of the alternating voltage supply, in particular of the period duration of the rectified alternating current supply. The operating period 42 has for example a duration of 10 ms. FIG. 12a illustrates the respective curves of the actual conductance for each of the two units 80 that have an induction target 32, 32′, 32″, 32′″ and the sum of the actual conductances of the two units 80 that have an induction target 32, 32′, 32″, 32′″ in an operating period 42, in particular for an operating period 42.

[0094] The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to repetitively control at least a second induction target 32, 32′, 32″, 32′″ and to supply said second induction target with energy and to operate the induction target 32, 32′, 32″, 32′″ in at least one second switched-on interval 86, 86′ of the operating period 42 with a heating power, in particular a desired heating power 30, 30′ or an excess power with respect to a desired heating power 30, 30′. The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to vary a second heating current frequency 36′ for the second induction target 32, 32′, 32″, 32′″ in the second switched-on interval 86, 86′ of the operating period 42. The control and/or regulating unit 26 is provided so as in the continuous heating operating state 50 to avoid intermodulation noise at least of two different induction targets 32, 32′, 32″, 32′″.

[0095] FIG. 12b illustrates the respective curves of the heating current frequencies 36 that are controlled by the control and/or regulating unit 26 at the units 80 that have an induction target 32, 32′, 32″, 32′″, in particular for an operating period 42.

[0096] FIG. 12c illustrates the respective curves of the squared rectified alternating voltage supply v.sub.bus that are controlled by the control and/or regulating unit 26 at the units 80 that have an induction target 32, 32′, 32″, 32′″, in particular for an operating period 42.

[0097] FIG. 12d illustrates the respective curves, which are controlled by the control and/or regulating unit 26, of the heating powers that are achieved, in particular consumed, at the units 80 that have an induction target 32, 32′, 32″, 32′″ and also the curve of the sum of the heating powers, in particular for an operating period 42.

[0098] In FIG. 12e, the respective curves of FIGS. 12c and 12d that are controlled by the control and/or regulating unit 26 are standardized and placed above one another. FIG. 12e illustrates that the control and/or regulating unit 26 controls and/or regulates the sum of the actual conductance of the controlled units 80 that have an induction target 32, 32′, 32″, 32′″ so as to achieve a match between the curves of the squared rectified alternating voltage supply v.sub.bus and of the sum of the powers, in particular heating powers, that arise by way of the units 80 that have the induction target 32, 32′, 32″, 32′″.

[0099] By maintaining constant the sum of the actual conductance of the units 80 that have the induction target 32, 32′, 32″, 32′″, the control and/or regulating unit 26 reduces the distortion of the supply current. The control and/or regulating unit 26 achieves compliance with EMC standards by maintaining constant the sum of the actual conductance, in particular of the actual conductance of the units 80 that have the induction target 32, 32′, 32″, 32′″. In particular, the curves of the actual conductance for each unit 80 that has an induction target 32, 32′, 32″, 32′″ deliver the desired heating power 30, 30′ that is desired in particular by an operator.

[0100] The control and/or regulating unit 26 can apply the control whilst maintaining constant the actual and/or complex conductances in the switched-on interval 40, 40′ of the operating period 42 for one unit 80 that has an induction target 32, 32′, 32″, 32′″ for multiple units 80 that have an induction target 32, 32′, 32″, 32′″.

[0101] For example, the mathematical correlations of the control performed by the control and/or regulating unit 26 for multiple units 80 that have an induction target 32, 32′, 32″, 32′″ are illustrated below.

[0102] In order to achieve compliance with EMC standards, the control and/or regulating unit 26 can maintain the sum of the actual conductances of all the units 80 that have an induction target 32, 32′, 32″, 32′″ essentially constant. The sum of the actual conductance of all units 80 that have an induction target 32, 32′, 32″, 32′″ is described by the following equation. The control and/or regulating unit 26 can by means of the following equation also calculate the sum of the actual conductances that is associated in each case with a target frequency, in particular a desired heating power 30, 30′.

[00003]$\Sigma G=G_1+G_2=\frac{P_1}{v_{0,1\mathrm{rms}}^2}+\frac{P_2}{v_{0,2\mathrm{rms}}^2}$

[0103] wherein ΣG represents the sum of the actual conductaces. Since all the units 80 that have an induction target 32, 32′, 32″, 32′″ share the same voltage, in particular v.sub.01,rms.sup.2=v.sub.02,rms.sup.2, the control and/or regulating unit 26 can calculate the sum of the actual conductances directly and by way of variations of the heating current frequencies 36 maintain said sum constant over each switched-on interval 40, 40′ of each operating period 42. In particular, the control and/or regulating unit 26 can maintain the sum of the actual conductances essentially constant by way of variations of the heating current frequencies 36 of each controlled unit 80 that has an induction target 32, 32′, 32″, 32′″ over each switched-on interval 40, 40′ of each operating period 42, in particular the entire operating period 42, in particular the half of the period duration of the alternating voltage supply. In particular, so as to maintain constant the sum of all the actual conductances, the control and/or regulating unit 26 can control each unit 80 that has an induction target 32, 32′, 32″, 32′″ individually in a similar manner to the control for only one unit 80 that has an induction target 32, 32′, 32″, 32′″.

[0104] In order to control multiple units 80 that have an induction target 32, 32′, 32″, 32′″, the control and/or regulating unit 26 calculates a linear equation system that is described mathematically below:

[00004]$\mathrm{Gx}=g;G=\left[\begin{array}{cccc}{G}_{11}& G_{12}& \mathrm{.Math.}& G_{1N}\\ G_{21}& G_{22}& \mathrm{.Math.}& G_{2N}\\ \mathrm{.Math.}& \mathrm{.Math.}& \mathrm{.Math.}& \mathrm{.Math.}\\ G_{M1}& G_{M2}& \mathrm{.Math.}& G_{\mathrm{MN}}\end{array}\right];x=\frac{1}{T_{\mathrm{cs}}}\left[\begin{array}{c}{t}_1\\ t_2\\ \mathrm{.Math.}\\ t_N\end{array}\right];g=\left[\begin{array}{c}{G}_{T1}\\ G_{T2}\\ \mathrm{.Math.}\\ G_{\mathrm{TM}}\end{array}\right]$

[0105] wherein G is the matrix of the actual conductances, x is a vector with the switched-on times t.sub.i and g is a vector with actual conductances G.sub.ti of the units 80 that have an induction target 32, 32′, 32″, 32′″, said actual conductances corresponding to the desired heating powers.

[0106] The columns of the matrix G are the actual conductances for a noiseless modulation for the different induction target 32, 32′, 32″, 32′″, in particular of the units 80 that have an induction target 32, 32′, 32″, 32′″ at each switched-on interval 40, 40′. The rows of the matrix G are the actual conductances for in each case an induction target 32, 32′, 32″, 32′″, in particular a unit 80 that has an induction target 32, 32′, 32″, 32′″, in each switched-on interval 40, 40′.

[0107] The control and/or regulating unit 26 is provided so as to embody at least two time intervals, in particular switched-on intervals 40, 40′, in an operating period 42 in the case of the operation of multiple induction targets 32, 32′, 32″, 32′″.

[0108] The control and/or regulating unit 26 is provided so as in each respective switched-on interval 40, 40′ in an operating period 42 to operate in each case one induction target 32, 32′, 32″, 32′″ with an excess power and another induction target 32, 32′, 32″, 32′″ with a power deficit with respect to a desired heating power 30, 30′. The control and/or regulating unit 26 is provided so as in each respective switched-on interval 40, 40′ in an operating period 42 to operate in each case one induction target 32, 32′, 32″, 32′″ with a greater actual and/or complex conductance and another induction target 32, 32′, 32″, 32′″ with a smaller actual and/or complex conductance with respect to an actual and/or complex conductance that corresponds to a desired heating power 30, 30′.

[0109] The control and/or regulating unit 26 is provided so as in a further switched-on interval 40, 40′ in an operating period 42 to operate in each case the one induction target 32, 32′, 32″, 32′″ with a power deficit and the other induction target 32, 32′, 32″, 32′″ with an excess power with respect to a desired heating power 30, 30′.

[0110] For the individual switched-on times 40, 40′ of an operating period 42, the limitations apply that the sum of all switched-on intervals 40, 40′ of an operating period 42 can be a maximum length equal to the operating period 42 itself, wherein each switched-on interval 40, 40′ must be greater than/equal to zero.

[0111] So as to achieve the noiseless control of multiple units 80 that have an induction target 32, 32′, 32″, 32′″, the control and/or regulating unit 26 varies the heating current frequencies 36 at each unit 80 that has an induction target 32, 32′, 32″, 32′″ to a difference 48 of in each case at least 20 kHz, preferably at least 16 kHz or to an infinitesimally small difference 48. FIG. 12 illustrates that an operating period 42 comprises 100 ms. For example, an operating period 42 comprises five period durations of the alternating voltage supply, in particular ten halves of the period duration of the alternating voltage supply.

[0112] In each switched-on interval 40, 40′, the control and/or regulating unit 26 maintains constant the sum of the respective actual and/or complex conductances, in particular desired conductances, of the units 80 that have an induction target 32, 32′, 32″, 32′″. An actual and/or complex desired conductance corresponds in this case to the conductance that corresponds to a desired heating power 30, 30′ of the unit 80 that has an induction target 32, 32′, 32″, 32′″. The control and/or regulating unit 26 varies in each switched-on interval 40, 40′ the heating current frequency 36 at the units 80 that have an induction target 32, 32′, 32″, 32′″ so as to maintain constant the sum of all actual conductances of the operated units 80 that have an induction target 32, 32′, 32″, 32′″, for example for two units 80 that have an induction target 32, 32′, 32″, 32′″ (FIGS. 12a and 12b).

[0113] The operating period 42 has for example two different switched-on intervals 40, 40′. The first switched-on interval 40, 40′ goes from 0 ms to 40 ms of the operating period 42 of 100 ms in total. The second switched-on interval 40, 40′ goes from 40 ms to 100 ms of the operating period 42 of 100 ms in total.

[0114] In this example, in the first switched-on interval 40, 40′ of 0 ms to 40 ms of the operating period 42 of 100 ms in total (cf. FIG. 12a), the actual conductance G.sub.11 of a unit 80 that has an induction target 32, 32′, 32″, 32′″ is approximately 185 mΩ.sup.−1. In this example, in the first switched-on interval 40, 40′ of 0 ms to 40 ms of the operating period 42 of 100 ms in total (cf. FIG. 12a), the actual conductance G.sub.21 of a further unit 80 that has an induction target 32, 32′, 32″, 32′″ is approximately 45 mΩ.sup.−1.

[0115] In this example, in the second switched-on interval 86, 86′ of 40 ms to 100 ms of the operating period 42 of 100 ms in total (cf. FIG. 12a), the actual conductance G.sub.12 of the unit 80 that has an induction target 32, 32′, 32″, 32′″ is approximately 80 mΩ.sup.−1. In this example, in the first switched-on interval 40, 40′ of 40 ms to 100 ms of the operating period 42 of 100 ms in total (cf. FIG. 12a), the actual conductance G.sub.22 of a further unit 80 that has an induction target 32, 32′, 32″, 32′″ is approximately 150 mΩ.sup.−1.

[0116] The control and/or regulating unit 26 maintains constant the sum of the two conductances of approximately 230 mΩ.sup.−1 for the entire operating period 42, in particular for the duration of each switched-on interval 40, 40′.

[0117] The control and/or regulating unit 26 can determine from the desired heating power 30, 30′ for both units 80 that have an induction target 32, 32′, 32″, 32′″ a corresponding heating current frequency 36 and the actual conductances that match this. The control and/or regulating unit 26 can determine a switched-on interval distribution in the operating period 42 from the actual conductances.

[0118] The average conductances that are to be achieved over the duration of the operating period 42 are in this example approximately 122 mΩ.sup.−1 for the unit 80 that has an induction target 32, 32′, 32″, 32′″ and approximately 108 mΩ.sup.−1 for the further unit 80 that has an induction target 32, 32′, 32″, 32′″.

[0119] The control and/or regulating unit 26 controls the heating current frequencies 36 of the units 80 that have an induction target 32, 32′, 32″, 32′″ to a difference 48 of at least 20 kHz, in particular at least 16 kHz, in this example to a difference 48 of approximately 30 kHz in the first switched-on interval 40, 40′.

[0120] The control and/or regulating unit 26 controls the heating current frequencies 36 of the units 80 that have an induction target 32, 32′, 32″, 32′″ to a difference 48 of at least 0 kHz, in particular to an identical curve, in the second switched-on interval 86, 86′ of the operating period 42.

[0121] The control and/or regulating unit 26 can perform a variation of the heating current frequencies 36 for maintaining constant the sum of all actual conductances of the units 80 that have an induction target 32, 32′, 32″, 32′″. In the case of the variation of at least two simultaneously controlled heating current frequencies 36, the control and/or regulating unit 26 avoids a difference 48 of the heating current frequencies 36 of below 16 kHz, in particular below 20 kHz, so as to maintain constant the sum of all actual conductances of the units 80 that have an induction target 32, 32′, 32″, 32′″.

[0122] It is conceivable that, so as to maintain said sum constant in the best possible manner, the control and/or regulating unit 26 must correct one heating current frequency 36 to a greater extent that another, wherein the control and/or regulating unit 26 checks whether a difference 48 of at least 16 kHz, in particular at least 20 kHz, remains guaranteed.

[0123] The control and/or regulating unit 26 achieves compliance with EMC standards in the case of the low noise operation of multiple, in particular two, induction targets 32, 32′, 32″, 32′″.

[0124] FIG. 13 illustrates schematically a further example of a noise-free control for two units 80 that have an induction target 32, 32′, 32″, 32′″ performed by the control and/or regulating unit 26. In this example, the operating period 42 is precisely the same length as half the duration of the period of the alternating voltage supply. In FIGS. 13a to 13d, the time is plotted in milliseconds on the abscissa 88. In FIG. 13a, the actual conductance is plotted in (mΩ.sup.−1), in particular milliohm.sup.−1, on the ordinate 100. In FIG. 13b, the frequency is plotted in kHz on the ordinate 102. In FIG. 13c, the squared voltage is plotted in mV.sup.2, in particular in millivolt, on the ordinate 104. In FIG. 13d, the power is plotted in W, in particular watt, on the ordinate 106. In FIG. 13e, a unitless standardization variable is plotted on the ordinate 108.

[0125] The operating period 42 has nine switched-on intervals 40, 40′. In four of the nine switched-on intervals 40, 40′, the control and/or regulating unit 26 controls the heating current frequencies 36 of the two units 80 that have an induction target 32, 32′, 32″, 32′″ to a difference 48 of at least 20 kHz, in particular at least 16 kHz. In the other five of the nine switched-on intervals 40, 40′, the control and/or regulating unit 26 controls the heating current frequencies 36 of the two units 80 that have an induction target 32, 32′, 32″, 32′″ to a difference 48 of 0 kHz. In particular, the control and/or regulating unit 26 avoids intermodulation noises between the units 80 that have an induction target 32, 32′, 32″, 32′″. The control and/or regulating unit 26 maintains constant the sum of the actual conductances of the units 80 that have an induction target 32, 32′, 32″, 32′″ over the entire operating period 42, in a similar manner to the example in FIG. 12.

[0126] FIG. 14 illustrates a frequency spectrum of an induction target 32, 32′, 32″, 32′″ that is operated with a constant heating current frequency 36 (FIG. 14a) and that is operated with a variable heating current frequency 36 (FIG. 14b). In the FIGS. 14a and 14b, the frequency is plotted in kHz on the abscissa 116. In the FIGS. 14a and 14b, the voltage is plotted in (dBμV), in particular in decibel microvolts, on an ordinate 118. The frequency spectrum illustrates the harmonics 78 which respectively form peaks. The permissible limit values for the amplitudes of the harmonics 78 are illustrated respectively in the two illustrated spectra (FIGS. 14a and 14b) by a limit line 76. The control and/or regulating unit 26 changes the heating current frequency 36 so as to maintain the actual or complex conductance constant and meets the requirements of the EMC standards in the best possible manner. A constant heating current frequency 36 of 60 kHz is illustrated in FIG. 14a. In FIG. 14, the control and/or regulating unit 26 varies the heating current frequency 36 so as to minimize the extent to which the desired heating power 30, 30′ is not maintained over the operating period 42. In particular the control and/or regulating unit 26 achieves a best possible compliance with the EMC standard.

[0127] It is conceivable that an operating period 42 has multiple mutually different switched-on intervals 40, 40′ and/or switched-off intervals 46. It is thereby conceivable that the control and/or regulating unit 26 varies the heating current frequency 36 so as to maintain the actual and/or complex conductance constant in each switched-on interval 40, 40′ of the operating period 42. It is likewise conceivable that the control and/or regulating unit 26 maintains constant the actual or complex conductance for one harmonic 78, in particular the first harmonic 78. In particular, the control and/or regulating unit 26 can perform a frequency analysis, in particular a signal analysis, such as for example a Fourier analysis, and determine the actual or complex conductance for one harmonic 78, in particular the first harmonic 78, by way of the following equations. For example, the following equations are disclosed for the first harmonic 78.

[00005]$G_H=\frac{P_H}{v_{\mathrm{OH},\mathrm{rms}}^2},$

[0128] wherein G.sub.H is the actual conductance with respect to the first harmonic 78 and P.sub.H is the desired heating power in the case of the first harmonic 78 and v.sub.0H is the voltage in the operating period 42, said voltage being applied in this case by way of the unit 80 that has the induction target 32, 32′, 32″, 32′″.

[00006]$Y_H=\frac{I_H}{v_{\mathrm{OH}}},$

[0129] wherein Y.sub.H is the complex conductance with respect to the first harmonic 78 and I.sub.H is the current strength in the case of the first harmonic 78 and v.sub.0H is the voltage in the operating period 42, said voltage being applied in this case by way of the unit 80 that has the induction target 32, 32′, 32″, 32′″. As a result, the control and/or regulating unit 26 can advantageously quickly adjust the heating current frequency 36.

[0130] It is conceivable that the control and/or regulating unit 26 performs a variation of the heating current frequency 36 so as to maintain constant an actual and/or complex conductance as soon as a measured average value for calculating the complex and/or actual conductance lies within the predetermined error tolerances. In particular, different algorithms are conceivable for finding a best possible adjustment of the heating current frequencies 36, in particular in the case of multiple operated induction targets 32, 32′, 32″, 32′″.

[0131] It is conceivable that the control and/or regulating unit 26 determines, stores and recalls a variation of the heating current frequency 36 so as to maintain constant an actual and/or complex conductance for different desired values 30, 30′ of an item of cookware 14, 14′ 14″. In particular, the impedance of the unit 80 that has the induction target 32, 32′, 32″, 32′″ depends upon the type of material, in particular of the item of cookware 14, 14′, 14″ and the inductor 22, 22′, 22″, 22′″ and the capacitor 68.

[0132] It is conceivable that the control and/or regulating unit 26 performs a variation of the heating current frequency 36, in particular so as to maintain constant the actual and/or complex conductance, as a “closed-loop” action such as a feedback loop or any other algorithm, irrespective of the number of units 80 that have induction targets 32, 32′, 32″, 32′″ or an induction target 32, 32′, 32″, 32′″.

[0133] It is conceivable that the control and/or regulating unit 26 can achieve a reduction of the distortion of the supply current by adjusting the heating current frequency 36.

[0134] A procedure of controlling the actual conductance or complex conductance can be interpreted as a procedure of controlling the power or the current strength.

[0135] Advantageously, the actual and complex conductance are not dependent upon the amplitude of the rectified supply voltage and equivalent electrical parameters of the item of cookware 14, 14′, 14″.

[0136] It is conceivable that in a frequency sweep state the control and/or regulating unit 26 determines and/or stores critical heating current frequencies 36, in particular harmonics 78 and/or resonance frequencies, for each item of cookware 14, 14′, 14′″ of an induction target 32, 32′, 32″, 32′″, in particular for each unit 80 that has an induction target 32, 32′, 32″, 32′″. It is furthermore conceivable that the control and/or regulating unit 26 exerts a frequency spread 74, in particular by means of the reference curve in the case of each control of a unit 80 that has an induction target 32, 32′, 32″, 32′″, on the critical frequencies, in particular harmonics 78 and/or resonance frequencies. It is conceivable that, in the case of maintaining an actual and/or complex conductance constant, the control and/or regulating unit 26 varies the heating current frequency 36 to an extent that the control and/or regulating unit 26 can avoid an additional frequency spread 74 by means of a reference curve 70. In particular, the control and/or regulating unit 26 can correct the heating current frequency 36 at any point in time to higher and lower values. It is conceivable that the control and/or regulating unit 26 performs the frequency spread 74, wherein the waveform of the supply current remains undistorted.

[0137] It is conceivable that the control and/or regulating unit 26 applies a power factor control such as maintaining the actual or complex conductance constant for any imaginable scenario, such as the number of items of cookware 14, 14′, 14′″ to be heated and/or the design of the hob 12 of a cooking appliance device 10. It is conceivable that, in the case of maintaining an actual and/or complex conductance constant, the control and/or regulating unit 26 can vary the heating current frequency 36 irrespective of the duration of the operating period 42. It is particularly advantageous that the control and/or regulating unit 26 can maintain the actual and/or complex conductance constant over the entire duration of half of the period duration of the alternating voltage supply. It is preferred that the duration of operating period 42 corresponds to the duration of half the period duration of the alternating voltage supply.

[0138] The control and/or regulating unit 26 can be embodied as an actual conductance controller or as a complex conductance controller. The control and/or regulating unit 26 can counteract a variation of the impedance of an induction target 32, 32′, 32″, 32′″ or of a unit 80 that has an induction target 32, 32′, 32″, 32′″ in an operating period 42, in particular can maintain the impedance constant. In particular, the control and/or regulating unit 26 can as an actual conductance controller control and/or regulate the achieved heating power over each operating period 42 so as to imitate the waveform of the squared rectified supply voltage.

[0139] It is conceivable that the control and/or regulating unit 26 selects an average value of the reference curve 70 of the frequency spread 74 as the value of the actual and/or complex conductance of the unit 80 that has the induction target 32, 32′, 32″, 32′″ that corresponds to the desired heating power 30, 30′.

[0140] It is conceivable that the control and/or regulating unit 26 can switch individual inverter units 38, in particular inverters 64, on and/or off.

[0141] It is conceivable that the control and/or regulating unit 26 can maintain the actual or complex conductance constant irrespective of the resonance frequency of a unit 80 that has an induction target 32, 32′, 32″, 32′″. It is conceivable that, so as to maintain the actual or complex conductance constant, the control and/or regulating unit 26 must vary the heating current frequency 36, 36′ in a surrounding area of the resonance frequency to a greater extent than when at a greater distance from the resonance frequency.

[0142] FIG. 15 illustrates schematically a flow diagram for a method for operating a cooking appliance device 10, in particular an induction hob device.

[0143] In at least one periodic continuous heating operating state 50, which is allocated an operating period 42, at least one induction target 32, 32′, 32″, 32′″ is repetitively controlled and supplied with energy.

[0144] In the at least one continuous heating operating state 50, the at least one induction target 32, 32′, 32″, 32′″ is operated in at least one switched-on interval 40, 40′ of the operating period 42 with a heating power, in particular a desired heating power 30, 30′ or with an excess power with respect to a desired heating power 30, 30′.

[0145] In the at least one continuous heating operating state 50, the heating current frequency 36 varies in the switched-on interval 40, 40′ of the operating period 42.

[0146] The at least one continuous heating operating state 50 comprises at least four part states, in particular at least one inputting state 52, at least one determining state 54, at least one controlling state 56 and at least one heating state 58.

[0147] In the at least one inputting state 52, a desired heating power 30, 30′ is input by an operator for at least one induction target 32, 32′, 32″, 32′″.

[0148] In the at least one inputting state 52, the target frequency for the at least one induction target 32, 32′, 32″, 32′″ is calculated in particular from a desired heating power 30, 30′ that is set by the operator. In the at least one inputting state 52, the actual and/or complex conductance is calculated for the at least one induction target 32, 32′, 32″, 32′″, in particular from a desired heating power 30, 30′ that is set by the operator, in particular from the target frequency.

[0149] In the at least one determining state 54 that in particular follows on from the at least one inputting state 52, the switched-on intervals 40, 40′ of each induction target 32, 32′, 32″, 32′″ are calculated. In the at least one determining state 54, the actual and/or complex conductances are calculated, in particular the sum of the actual and/or complex conductances, of each induction target 32, 32′, 32″, 32′″.

[0150] In the at least one controlling state (56) that follows on from the at least one determining state 54, the switched-on intervals 40, 40′ and switched-off intervals 46 are calculated for each induction target 32, 32′, 32″, 32′″, which is to output a desired heating power 30, 30′ in an operating period 42, so as to avoid intermodulation noises and distributed over the operating period 42 so as to comply with EMC standards.

[0151] In the at least one heating state 58 that in particular follows on from the at least one controlling state 56, each induction target 32, 32′, 32″, 32′″ is operated over at least one operating period 42 with the selected switched-on intervals 40, 40′ and/or switched-off intervals 46 so as to provide the set desired heating power 30, 30′. In the at least one heating state 58, the heating current frequency 36 is varied in at least one switched-on interval 40, 40′ for at least one induction target 32, 32′, 32″, 32′″, in particular a unit 80 that has an induction target 32, 32′, 32″, 32′″. In particular, in the at least one heating state 58, the actual conductance and/or the complex conductance and/or the impedance is maintained constant in at least one switched-on interval 40, 40′ for at least one induction target 32, 32′, 32″, 32′″, in particular a unit 80 that has an induction target 32, 32′, 32″, 32′″.

[0152] In the at least one continuous heating state 50, the part states are performed repetitively, wherein the parameters that are selected/calculated and/or determined in the part states are maintained in the absence of a desired heating power 30, 30′ that has been changed by an operator for at least one induction target 32, 32′, 32″, 32′″.

LIST OF REFERENCE NUMERALS

[0153] 10 Cooking appliance device [0154] 12 Hob [0155] 14 Cookware [0156] 16 Resting plate [0157] 18 Cooking zone [0158] 20 Cooking appliance [0159] 22 Inductor [0160] 24 Control panel [0161] 26 Control and/or regulating unit [0162] 28 Display [0163] 30 Desired heating power [0164] 32 Induction target [0165] 34 Output heating power [0166] 36 Heating current frequency [0167] 38 Inverter unit [0168] 40 Switched-on interval [0169] 42 Operating period [0170] 44 Resonance capacitor unit [0171] 46 Switched-off interval [0172] 48 Difference [0173] 50 Continuous heating operating state [0174] 52 Inputting state [0175] 54 Determining state [0176] 56 Controlling state [0177] 58 Heating state [0178] 60 Switching element [0179] 62 Relay [0180] 64 Inverter [0181] 66 Part [0182] 68 Capacitor [0183] 70 Reference curve [0184] 72 Middle region [0185] 74 Frequency spread [0186] 76 Limit line [0187] 78 Harmonic(s) [0188] 80 Unit [0189] 82 Maximum frequency [0190] 84 Minimum frequency [0191] 86 Switched-on interval [0192] 88 Abscissa [0193] 90 Ordinate [0194] 92 Ordinate [0195] 94 Ordinate [0196] 96 Ordinate [0197] 98 Abscissa [0198] 100 Ordinate [0199] 102 Ordinate [0200] 104 Ordinate [0201] 106 Ordinate [0202] 108 Ordinate [0203] 110 Ordinate [0204] 112 Ordinate [0205] 114 Ordinate [0206] 116 Abscissa [0207] 118 Ordinate