EP3809800A1 - Method for controlling the power of at least one induction unit and induction cooking appliance for implementing the method - Google Patents

Abstract

A method for controlling the power of at least one inductor (L) covered with a container and supplied with alternating current by an inverter power supply device (20) controlled by a periodic control signal comprises the following steps: - choice a frequency for the periodic control signal from among a set of N predefined frequency values, N being equal to or greater than two; and adjustment of a duty cycle of the periodic control signal at the frequency chosen to obtain a power induced in the receptacle. Use in induction hobs, in particular without a predefined cooking zone in the hob.

Description

The present application relates to a method for controlling the power of at least one inductor covered with a container.

It also relates to an induction cooking appliance suitable for implementing this control method.

In general, the present invention relates to the field of the alternating electric current supply of an inductor by an inverter power supply device controlled by a periodic control signal.

It finds its application in particular in induction cooking appliances, such as an induction hob, comprising one or more cooking zones each equipped with one or more inductors.

It concerns not only hobs with predefined cooking zones in the hob but also so-called matrix hobs, without predefined cooking zones and in which the cooking zones are defined on a case-by-case basis, depending on the position of. 'a receptacle placed on the cooking surface and covering a sub-assembly of inductors.

An alternating current is thus generated by the inverter power supply device and circulates in the inductor (s).

Conventionally, an induced current is then generated in a receptacle placed above this inductor, the receptacle itself heating up by the Joule effect due to its resistance.

The power induced in the receptacle depends in particular, for a given receptacle, on the alternating current flowing in the inductor and generated by the inverter power supply device.

Power control methods are known in the state of the art, suitable for modifying the power induced in the receptacle by varying the frequency of the periodic control signal controlling the inverter power supply device.

Thus, for a given receptacle, to each restored power corresponds a frequency of the periodic control signal of the inverter power supply device.

The slaving of the power induced in the vessel to the frequency of the periodic control signal requires the use of a wide range of frequencies. This operating mode can become problematic when certain frequencies generate electromagnetic compatibility (EMC) problems on the electrical supply network of the cooking appliance.

When the inverter power supply device comprises two power elements, of the type two IGBT transistors (acronym for the English term Insulated Gate Bipolar Transistor ), mounted in a half-bridge, the periodic control signal is generally a square signal. The control signal thus makes it possible to control the supply of the two power elements in phase opposition. In the operation described above, in which the power is restored as a function of the frequency, the duty cycle of the periodic control signal is generally equal to 50%, which makes it possible to supply the two power elements in symmetry.

It is also possible, but in a limited manner, to vary the power induced in the vessel by changing the duty cycle of the periodic control signal at a given frequency.

The variation of the duty cycle of the periodic control signal generates an induced power in the container less than the induced power obtained when the duty cycle is equal to 50%.

This operating mode is used when several inverter power supply devices are controlled simultaneously to respectively power several inductors or cooking zones and it is necessary to control the inverter power supply devices by a periodic control signal of the same frequency. in order to avoid the appearance of unpleasant whistling in the receptacles covering the inducers.

Indeed, parasitic noises can appear when two inductors are put into operation by power supply devices with inverter controlled by periodic control signals of different frequency.

This problem is particularly important in so-called matrix hobs in which the inductors are placed next to each other in a two-dimensional distribution in the hob and simultaneously controlled to heat a container placed on the hob and covering several inductors. .

However, this solution of varying the duty cycle at a given frequency is complex to implement. In particular, it is necessary to use a single frequency which is suitable for controlling the inverter power supply devices of each inductor and generally to periodically switch off the alternating current supply of one or both inductors to reach the set power requested for each container.

An example of such an operation is described in the document EP 2,200,398 .

The aim of the present invention is to resolve at least one of the aforementioned drawbacks and to provide a method for controlling the power of at least one inductor covered with a less complex container.

According to a first aspect, the present invention relates to a method for controlling the power of at least one inductor covered with a container and supplied with alternating current by an inverter power supply device controlled by a periodic control signal.

• choix d'une fréquence pour le signal de commande périodique parmi un ensemble de N valeurs de fréquences prédéfinies, N étant égal ou supérieur à deux ; et
• ajustement d'un rapport cyclique du signal de commande périodique à la fréquence choisie pour obtenir une puissance induite dans le récipient.

According to the invention, this control method comprises the following steps:

• choosing a frequency for the periodic control signal from among a set of N predefined frequency values, N being equal to or greater than two; and
• adjusting a duty cycle of the periodic control signal at the selected frequency to obtain induced power in the vessel.

Thanks to the invention, it is possible to vary the power induced in the container by using only values of frequencies predefined in a set and varying only the duty cycle of the periodic control signal.

It is thus possible to choose predefined frequency values so as not to generate acoustic or electromagnetic disturbances and to comply with electromagnetic compatibility standards.

The limited number of N predefined frequency values makes it possible to considerably reduce the risk of the appearance of resonance phenomena in the receptacle.

In practice, at the adjustment step, the duty cycle is chosen from an interval between a minimum duty cycle and a maximum power duty cycle, the maximum power duty cycle being equal to 50%.

Alternatively, in the adjustment step, the duty cycle is chosen from an interval between a maximum power duty cycle and a maximum duty cycle, the maximum power duty cycle being equal to 50%.

Thus, at each frequency of the periodic control signal, there corresponds a maximum induced power in the container when the selected duty cycle is equal to 50%. Adjusting this duty cycle within an interval above or below this value of 50% makes it possible to vary the power induced in the receptacle and thus to achieve a requested setpoint power.

According to an advantageous characteristic of the invention, the assembly comprises an increasing ordered series of N predefined frequency values, and, to any pair of adjacent predefined frequencies of said assembly corresponds a pair of power values induced in the receptacle when the device d The inverter power supply is controlled by a periodic control signal at one of said predefined frequencies of said torque and a duty cycle of 50%, the power induced in the vessel when the inverter power supply device is controlled by a periodic control signal at the highest frequency of said pair of frequencies and a duty cycle by 50% being greater than the power induced in the vessel when the inverter power supply device is controlled by a periodic control signal at the lower frequency of said pair of frequencies and a duty cycle equal to the minimum duty cycle or the ratio maximum cyclic.

The set of N predefined frequency values is thus determined so as to be able to sweep the set of powers between a maximum power and a minimum power induced in a receptacle.

In a practical embodiment, the predefined frequency values of said set are between 20 and 150 KHz.

As an exemplary embodiment, the number N of predefined frequency values is between 2 and 10, and preferably between 4 and 8 and preferably equal to 6.

According to another embodiment, at least two inductors are supplied with alternating current respectively by an inverter power supply device controlled by a periodic control signal, the frequency of the periodic control signal of each inverter power supply device being chosen from among the same set of N predefined frequency values.

Thanks to a judicious choice of the predefined frequency values, it is possible to operate several inductors simultaneously without generating electromagnetic disturbances.

According to an advantageous characteristic, said same set comprises an increasing ordered sequence of N predefined frequency values, the difference between two values of a pair of adjacent predefined frequencies of said same set being less than a minimum threshold frequency and greater than a threshold frequency maximum, the frequencies between the minimum threshold frequency and the maximum threshold frequency corresponding to frequencies audible to the human ear.

Thus, the inductors can be simultaneously supplied with current by an inverter power supply device controlled by a periodic control signal of different frequencies as soon as this frequency is chosen from the same set of predefined frequency values, without generate the appearance of parasitic noises and whistles in the receptacles covering each inducer.

In practice, the minimum threshold frequency is equal to 2 kHz and the maximum threshold frequency is equal to 14 kHz.

According to a second aspect, the present invention relates to an induction cooking appliance comprising at least one inductor supplied with alternating current by an inverter supply device controlled by a periodic control signal.

According to the invention, the cooking appliance comprises means for controlling the inverter power supply device suitable for implementing the power control method according to the invention.

This cooking appliance has characteristics and advantages similar to those described above in relation to the power control method according to the invention.

The present invention finds its application in particular when the inverter power supply device comprises two power switches of the IGBT type mounted in a half-bridge.

Other features and advantages of the invention will become apparent in the description below.

• [Fig. 1A] la figure 1A représente schématiquement un appareil de cuisson à induction conforme à un mode de réalisation de l'invention ;
• [Fig. 1B] la figure 1B représente schématiquement un appareil de cuisson à induction conforme à un autre mode de réalisation de l'invention ;
• [Fig. 2] la figure 2 est un schéma illustrant le montage de deux éléments de puissance en demi-pont dans un appareil de cuisson à induction selon un mode de réalisation de l'invention ;
• [Fig. 3] la figure 3 est un schéma bloc illustrant un dispositif de commande des deux éléments de puissance de la figure 2, selon un mode de réalisation de l'invention ;
• [Fig. 4A] la figure 4A illustre schématiquement des signaux de pilotage d'une topologie demi-pont à partir d'un signal de commande périodique, le rapport cyclique du signal de commande périodique étant égal à 50% ;
• [Fig. 4B] la figure 4B illustre schématiquement des signaux de pilotage d'une topologie demi-pont à partir d'un signal de commande périodique, le rapport cyclique du signal de commande périodique étant égal à 30%.
• [Fig. 5] la figure 5 illustre schématiquement la variation d'un rapport cyclique du signal de commande périodique de la figure 4 ;
• [Fig. 6] la figure 6 illustre schématiquement la variation de puissance restituée dans un récipient en fonction de la variation du rapport cyclique du signal de commande périodique à une fréquence donnée ;
• [Fig. 7] la figure 7 illustre schématiquement la variation de puissance restituée dans un récipient en fonction de la fréquence du signal de commande périodique ; et
• [Fig. 8] la figure 8 illustre schématiquement la variation continue de la puissance restituée dans un récipient recouvrant un inducteur commandé selon le procédé de commande en puissance conforme à un mode de réalisation de l'invention.

In the accompanying drawings, given by way of non-limiting examples:

• [ Fig. 1A ] the figure 1A schematically shows an induction cooking appliance according to one embodiment of the invention;
• [ Fig. 1B ] the figure 1B schematically shows an induction cooking appliance according to another embodiment of the invention;
• [ Fig. 2 ] the figure 2 is a diagram illustrating the assembly of two half-bridge power elements in an induction cooking appliance according to one embodiment of the invention;
• [ Fig. 3 ] the figure 3 is a block diagram illustrating a device for controlling the two power elements of the figure 2 , according to one embodiment of the invention;
• [ Fig. 4A ] the figure 4A schematically illustrates control signals of a half-bridge topology from a periodic control signal, the duty cycle of the periodic control signal being equal to 50%;
• [ Fig. 4B ] the figure 4B schematically illustrates control signals of a half-bridge topology from a periodic control signal, the duty cycle of the periodic control signal being equal to 30%.
• [ Fig. 5 ] the figure 5 schematically illustrates the variation of a duty cycle of the periodic control signal of the figure 4 ;
• [ Fig. 6 ] the figure 6 schematically illustrates the variation in power restored in a receptacle as a function of the variation in the duty cycle of the periodic control signal at a given frequency;
• [ Fig. 7 ] the figure 7 schematically illustrates the variation in power restored in a receptacle as a function of the frequency of the periodic control signal; and
• [ Fig. 8 ] the figure 8 schematically illustrates the continuous variation of the power restored in a receptacle covering an inductor controlled according to the power control method according to one embodiment of the invention.

We will first describe with reference to figure 1A a cooking appliance according to one embodiment of the invention.

In this example, the electric cooking appliance is an induction hob 10 comprising four cooking zones F1, F2, F3, F4.

Each cooking zone F1, F2, F3, F4 comprises an inductor formed from one or more coils in which an electric current flows.

The hob 10 is supplied electrically by a mains supply 11, for example 230V and 32 Amps.

A power control and command card 12 is suitable for supporting all the electronic and computer means necessary for controlling the hob 10.

In practice, electrical connections 13 are provided between the control and command card 12 and each inductor of the cooking zones F1, F2, F3, F4.

Each inductor of the cooking zones F1, F2, F3, F4 is supplied with alternating current, via the electrical connections 13, by an inverter power supply device provided on the control and command board 12.

Conventionally, the inductors and the control and command card 12 are placed under a flat cooking surface, generally formed from a glass-ceramic plate.

The cooking zones F1, F2, F3, F4 can be identified by a silkscreen printing on the glass-ceramic plate opposite the inductors placed under the cooking surface.

Finally, the induction hob 10 comprises control and interface means 14 with the user, in particular allowing the user to control the power and duration of the operation of each cooking zone F1, F2, F3, F4.

The structure of such a hob and the mounting of the inductors need not be described in more detail here.

Of course, this example of a cooking appliance is not limiting. In particular, the power control method which will be described below can be applied to any type of induction cooking appliance, and to any configuration of an induction hob, regardless of the number of hotplates, the number of inductors, the number of coils per hearth and the arrangement of the cooking zones.

In particular, the power control method described below is particularly advantageous for a so-called matrix hob.

An exemplary embodiment of such a hob is illustrated on figure 1B .

The hob 15 comprises a hob 16 intended to receive containers on the hob 15.

This hob 15 comprises heating means consisting of inductors 17 distributed in the hob 16.

These inductors 17 are distributed in a two-dimensional grid under the hob 16 of the hob 15.

They are arranged side by side so as to cover the entire surface of the hob 16.

In this example, the inductors 17 are staggered.

In other embodiments, the inductors can be arranged in a distribution in rows and columns, that is to say in a matrix arrangement.

When a receptacle is placed on the cooking surface 16, a heating zone Z is formed from the detection of the inductors 17 covered by the receptacle.

Each inductor 17 of the hob 15 can thus be controlled independently and put into operation only when a receptacle covers at least part of this inductor.

The hob 15 comprises in a known manner, as in the embodiment of the figure 1A , both a control and power command card adapted to support all the electronic and computer means necessary for the control of the hob 15, and control and interface means with the user, allowing in particular the user to control the power and duration of the operation of each Z cooking zone.

The structure of such a hob and the mounting of the inductors need not be described in more detail here.

We will describe below with reference to figure 2 an exemplary embodiment of an inverter power supply device 20, each inductor of the cooking zones F1, F2, F3, F4 of the hob 10 illustrated in figure 1A or the Z heating zones of the hob 15 shown in figure 1B being supplied with electric current by an identical inverter power supply device 20.

In this embodiment, the inverter power supply device 20 comprises two power elements, and for example two voltage-controlled transistors of the IGBT type (acronym for the English term Insulated Gate Bipolar Transistor).

In this exemplary embodiment, the two power switches T1, T2 of the IGBT type are mounted as a half-bridge.

Of course, the invention is not limited to this half-bridge topology but can also be applied to a full bridge topology of four power switches.

In the example shown in figure 2 , an inductor L schematically represents the induction cooking zone and may correspond to one or more inductor coils connected in series, thus constituting a cooking zone F1, F2, F3, F4 of the hob 10 illustrated in figure 1A or to one of the inductors 17 of the heating zone Z of the hob 15 illustrated in figure 1B .

The two power switches T1, T2 mounted in a half-bridge are controlled to generate an alternating electric current in the inductor L, hereinafter called inductor current I.

The inverter power supply device 20 with half-bridge assembly of the two power switches T1, T2 is conventional and is presented briefly below.

Each power switch T1, T2 is connected in parallel between its collector C and its emitter E to a freewheeling diode D1, D2 and a switching aid capacitor C1, C2.

Resonance capacitors, C3, C4 are mounted to constitute a resonant circuit with the inductor L to which is associated a resistance R representing the resistance of a container placed on a cooking zone, above the inductor L.

In a known manner, the control of the two power switches T1, T2 by a control signal at a given frequency F, makes it possible to position the two power switches T1, T2 alternately in an on state and in a blocked state, and to generate thus an alternating current circulating in the inductor L.

An induced current is thus generated in the container which heats up by the Joule effect due to its resistance R.

The control of the power switches T1, T2 is carried out using control means 30 as illustrated in detail on figure 3 .

Thus, control signals Com1, Com2 respectively addressed to the power switches T1, T2 are generated by the control means 30.

The control means 30 comprise in this embodiment a controller 31 (also called in English terminology “Driver ”), itself controlled by a microprocessor 32.

The microprocessor 32 controls the controller 31 by a periodic control signal having a frequency F.

The periodic control signal is an alternating signal between a high state and a low state.

In this embodiment, the periodic control signal is a square signal of frequency F as illustrated in figures 4A and 4B .

We have thus illustrated figures 4A and 4B , on time t, the alternating operation of the power switches T1, T2 placed respectively in an ON state and an OFF blocked state as a function of the periodic control signal at a given frequency F.

Thus, when the control signal Com1 from the first power switch T1 sends an ON state to the first power switch T1, the control signal Com2 from the second power switch T2 sends a blocked OFF state to the second power switch T2, and vice versa.

When the periodic frequency control signal F switches from a high state to a low state, the control signals Com1, Com2 are alternated in order to switch each power switch from an ON state to a blocked OFF state, and vice versa. versa.

The inverter power supply device 20 is thus controlled by a periodic control signal of given frequency F.

By way of example, we have illustrated figures 4A and 4B a periodic control signal with the same frequency F but with a different duty cycle Δ: at the figure 4A , the duty cycle Δ is equal to 50%, both power switches T1, T2 being supplied symmetrically with electric current.

On the other hand, at the figure 4B , the duty cycle Δ is equal to 30%, the second power switch T2 being in this embodiment kept in an ON state for 70% of the period of the periodic control signal of frequency F and the first power switch T1 being kept in an ON state for 30% of the period of the periodic control signal of frequency F.

Depending on the alternating current thus generated in the inductor L, a heating power is supplied to the receptacle.

As shown in figures 5 and 6 , it is possible to vary the power P delivered to the receptacle by modifying the duty cycle of the periodic control signal of given frequency Fx.

The variation of the duty cycle Δ of the periodic control signal of given frequency Fx is illustrated in figure 5 , between a minimum duty cycle Δmin and a maximum duty cycle Δmax.

By way of nonlimiting example, the minimum duty cycle Δmin is between 15 and 25% and the maximum duty cycle Δmax is between 75 and 85%.

For a given frequency Fx, the power P supplied to the receptacle when the duty cycle is different from 50% is less than the power Px, obtained for a duty cycle equal to 50%.

The power control method implemented in the control means 30 of the inverter power supply device 20 will now be described.

The power control method firstly comprises a step of choosing a frequency Fx for the periodic control signal from among a set S of N predefined frequency values, N being equal to or greater than two.

In a nonlimiting manner, the predefined frequency values of the set S are between 20 and 150 kHz.

We have illustrated at the figure 7 an example of such a set S of predefined frequencies, Fi with i belongs to {1, 2, ..., 6}.

The values of the predefined frequencies Fi are selected and stored in a memory associated with the microprocessor 32 so as not to generate electromagnetic disturbances on the general electrical supply network of the induction cooking appliance.

Each frequency Fi corresponds to a heating power Pi induced in a given container.

In a known manner, the higher the value of the frequency Fi, the lower the heating power Pi induced in the container, and vice versa.

In this example, the number N of predefined frequencies Fi is equal to 6.

Of course, this number N of predefined frequencies can vary and is typically between 2 and 10, and preferably between 4 and 8.

It is determined so as to cover a range of induced powers Pi sufficient to cover the setpoint powers which can be chosen by the user of the induction cooking appliance.

The difference ΔF between the predefined frequency values Fi of the set S is here greater than or equal to 17 kHz.

The difference ΔF between two values of adjacent frequencies Fi, Fi + 1, illustrated in figure 7 by the intervals ΔF12, ΔF23, ΔF34, ΔF45, ΔF56, can be identical or different.

The set S thus comprises an increasing ordered sequence of N values of predefined frequencies Fi.

To any pair of adjacent predefined frequencies Fi, Fi + 1 of this set S corresponds to a pair of induced power values Pi, Pi + 1 in the receptacle when the inverter power supply device 20 is controlled by a periodic control signal at one of these two predefined frequencies Fi, Fi + 1 and a duty cycle Δ of 50%

The predefined frequencies Fi are also selected so that for any pair of adjacent predefined frequencies Fi, Fi + 1, it is possible to scan all of the induced power values between the induced power values Pi and Pi + 1, and this by varying only the duty cycle Δ of the periodic control signal at one of the two frequencies Fi, Fi + 1.

Thus, the power control method comprises a step of adjusting a duty cycle Δ of the periodic control signal at the chosen frequency Fx to obtain a power induced in the container.

We have illustrated at the figure 8 the possibility of scanning all the powers between P1 and P6 in this exemplary embodiment.

To do this, for each pair of adjacent predefined frequencies Fi, Fi + 1, the induced power Pi + 1 in the container when the inverter power supply device 20 is controlled by a periodic control signal at the highest frequency Fi +1 of the frequency torque and a duty cycle of 50% is greater than the induced power Pi in the container when the inverter power supply device 20 is controlled by a periodic control signal at the lowest frequency Fi of the torque of frequencies and a duty cycle equal to a minimum duty cycle Δmin.

• P6 (F6 ; 50%) ≥ P5 min (F5 ; Δmin)
• P5 (F5 ; 50%) ≥ P4 min (F4 ; Δmin)
• P4 (F4 ; 50%) ≥ P3 min (F3 ; Δmin)
• P3 (F3 ; 50%) ≥ P2 min (F2 ; Δmin)
• P2 (F2 ; 50%) ≥ P1 min (F1 ; Δmin)

Indeed, it will be noted that the powers:

• P6 (F6; 50%) ≥ P5 min (F5; Δmin)
• P5 (F5; 50%) ≥ P4 min (F4; Δmin)
• P4 (F4; 50%) ≥ P3 min (F3; Δmin)
• P3 (F3; 50%) ≥ P2 min (F2; Δmin)
• P2 (F2; 50%) ≥ P1 min (F1; Δmin)

In this embodiment, during the adjustment step, the duty cycle Δ is chosen from an interval between a minimum duty cycle Δmin and the maximum power duty cycle equal to 50%.

It is thus possible to obtain an induced power in the container by adjusting the duty cycle Δ.

The variation of the power and obtaining a setpoint power could also be done by using a maximum duty cycle different from the maximum power duty cycle equal to 50%. However, as indicated previously with reference to the figure 6 , the heating power returned to the receptacle at a given frequency is maximum for a duty cycle Δ equal to 50% and decreases when the duty cycle Δ decreases or increases.

It is thus advantageous to vary the heating power in the container by adjusting the duty cycle Δ around the value of 50%.

Of course, a similar adjustment step could be implemented by choosing the duty cycle Δ from an interval between the maximum power duty cycle equal to 50% and a maximum duty cycle Δmax.

Thus, with this power control method, it is possible, by judiciously choosing a set S of predefined frequencies Fi and by adjusting only the duty cycle Δ of operation of the inverter power supply device 20, to vary the power by the value P6 to P1 without discontinuity.

When the limit of the heating power which can be restored to the vessel is reached for a given frequency of the periodic control signal, the power control method chooses another frequency from the set S and adjusts the duty cycle Δ to obtain the power set point requested for the container.

On the other hand, when the inductors of the induction cooking appliance are simultaneously supplied with alternating current, each by an inverter power supply device 20 controlled by a periodic control signal, the frequency for the periodic control signal of each device power supply to inverter 20 is chosen from the same set S of N predefined frequency values Fi.

Thus, each inverter power supply device is independent and can operate simultaneously without generating electromagnetic disturbances since the predefined frequencies Fi have been chosen so as not to generate electromagnetic disturbances.

Thus, the difference ΔF between two values of a pair of adjacent predefined frequencies Fi, Fi + 1 of the set S is less than a frequency minimum threshold Fmin or greater than a maximum threshold frequency Fmax, the frequencies between the minimum threshold frequency Fmin and the maximum threshold frequency Fmax corresponding to frequencies audible to the human ear.

In practice, the minimum threshold frequency Fmin is equal to 2 kHz and the maximum threshold frequency Fmax is equal to 14 kHz.

The set S of predefined frequencies Fi is thus chosen in order to avoid the appearance of audible noises and whistles when inductors of the induction cooking appliance 10 are simultaneously controlled respectively by an inverter power supply device 20.

In the embodiment described above, in which the difference ΔF is equal to 17 kHz, parasite noises produced when two inductors operate simultaneously are eliminated when the frequencies of the periodic control signals are chosen from the whole. S of pre-finite frequencies Fi.

The power control method of the invention thus makes it possible to obtain a simplified power control of one or more inductors while avoiding any electromagnetic disturbance and / or any parasitic noise between receptacles when it is implemented at starting from a limited number N of predefined frequencies, and by varying only the duty cycle Δ of the periodic control signal (s).

It is in particular well suited to simultaneously controlling inductors of a heating zone in a so-called matrix hob, without a predefined cooking zone in the hob.

Claims (11)

Method for controlling the power of at least one inductor (L) covered with a container and supplied with alternating current by an inverter power supply device (20) controlled by a periodic control signal, characterized in that it comprises the following steps: - choice of a frequency (Fx) for the periodic control signal from among a set (S) of N values of predefined frequencies (Fi), N being equal to or greater than two; and - adjustment of a duty cycle (Δ) of the periodic control signal at the selected frequency (Fx) to obtain an induced power (Px) in the container. Power control method according to claim 1, characterized in that in the adjusting step, the duty cycle (Δ) is chosen from an interval between a minimum duty cycle (Δmin) and a power duty cycle maximum, the maximum power duty cycle being equal to 50%. Power control method according to claim 1, characterized in that in the adjusting step, the duty cycle (Δ) is chosen from an interval between a maximum power duty cycle and a maximum duty cycle (Δmax ), the maximum power duty cycle being equal to 50%. Power control method according to one of claims 2 or 3, characterized in that said set (S) comprises an increasing ordered sequence of N predefined frequency values (Fi), and in that at any pair of frequencies adjacent predefined (Fi, Fi + 1) of said set (S) corresponds to a pair of induced power values (Pi, Pi + 1) in the container when the inverter power supply device (20) is controlled by a control signal periodic at one of said predefined frequencies (Fi, Fi + 1) of said torque and a duty cycle of 50%, the induced power (Pi + 1) in the container when the inverter power supply device (20) is controlled by a periodic control signal at the highest frequency (Fi + 1) of said pair of frequencies and a duty cycle (Δ) of 50% being greater than the induced power (Pi) in the vessel when the inverter power supply device (20) is controlled by a periodic control signal at the lowest frequency (Fi) of said pair of frequencies and a duty cycle (Δ) equal to the minimum duty cycle (Δmin) or to the maximum duty cycle (Δmax). Power control method according to one of claims 1 to 4, characterized in that the predefined frequency values (Fi) of said assembly (S) are between 20 and 150 kHz. Power control method according to one of claims 1 to 5, characterized in that the number N of predefined frequency values (Fi) is between 2 and 10, and preferably between 4 and 8, and preferably equal to 6. Power control method according to one of the preceding claims, at least two inductors (L) being supplied with alternating current respectively by an inverter supply device (20) controlled by a periodic control signal, characterized in that the frequency (Fx) for the periodic control signal of each inverter power supply device (20) is chosen from the same set (S) of N predefined frequency values (Fi). Power control method according to claim 7, characterized in that said same set (S) comprises an increasing ordered sequence of N values of predefined frequencies (Fi), the difference (ΔF) between two values of a torque of adjacent predefined frequencies (Fi, Fi + 1) of said same set (S) being less than a minimum threshold frequency (Fmin) or greater than a maximum threshold frequency (Fmax), the frequencies between said minimum threshold frequency (Fmin) and said maximum threshold frequency (Fmax) corresponding to frequencies audible to the human ear. Power control method according to Claim 8, characterized in that the minimum threshold frequency (Fmin) is equal to 2 kHz and the maximum threshold frequency (Fmax) is equal to 14 kHz. Induction cooking appliance comprising at least one inductor (L) supplied with alternating current by an inverter power supply device (20) controlled by a periodic control signal, characterized in that it comprises control means (30) of the inverter power supply device (20) adapted to implement the power control method according to one of the preceding claims. Induction cooking appliance according to Claim 10, characterized in that the inverter power supply device (20) comprises two power switches (T1, T2) of the IGBT type mounted in half-bridge.

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