EP2200398A1 - Method for supplying power to two induction units and cooking device implementing said method - Google Patents

Abstract

The method involves supplying power to inductors in cyclic predetermined periods, where the power supply process comprises a mixed power supply phase constituted of a power supply phase in parallel with the inductors and another power supply phase in alternating with the inductors on each predetermined period. The inductors are respectively supplied by two inverters controlled in a same operating frequency in the parallel power supply phase. The inductors respectively associated with containers to be heated are analyzed during power supplying of the inductors. An independent claim is also included for an electric cooking appliance comprising two boiling plates respectively comprising two inductors mounted in parallel in a single phase of an electrical power supply.

Description

The present invention relates to a power supply method of two inductors connected in parallel on the same power phase of a power supply.

It also relates to a cooking appliance implementing this power supply method of two inductors.

In general, the present invention relates to the power supply of the inductors of a cooking appliance, and in particular of a domestic hob using induction heating.

Conventionally, in these cooking appliances, the inductors are respectively powered by inverters controlled at a working frequency according to the set power assigned to each inductor.

When the working frequency of the inverter is equal to the resonant frequency of the resonant circuit formed by the inductor and a kitchen utensil placed thereon, the inductor generates in the kitchen utensil as much power as possible and when the inverter is controlled to move the operating frequency away from this resonant frequency, the power generated by the inductor decreases.

Depending on the container to be heated disposed on the inductor (size of the container, material, position relative to the inductor), the power delivered by the inductor or the power output varies.

In practice, as described in the document FR 2 783 370 to control the power delivered by the inductor to a target power, the power delivered at the inductor is measured by measuring a mean current flowing in the resonant circuit formed by the inductor and the container and multiplying the value of the average current by the value of the supply voltage.

This restored power is compared to the requested power demand and the working frequency of the inverter is modified to approach by the value of the power restored by the inductor, the value of the nominal power.

However, when these inductors are close to each other, the operation of the inverters at a different working frequency has the disadvantage of creating interference between adjacent inductors operating at different and neighboring frequencies, and generating audible and annoying noise for the user.

One solution to avoid the generation of noise is to mount the inductors in parallel on the same power phase of a power supply and to supply these inductors by inverters controlled by the same frequency generator.

Thus, hobs are known in which the inductors are powered by inverters controlled by a signal of identical frequency.

However, when the inductors are supplied in parallel, it is not possible to obtain significant power variations between the two inductors.

This mode of operation is therefore only well suited when the reference powers assigned by the user to the two inductors are close to one another.

Such a feeding device is known in the document FR 2 773 014 , in which each inductor is continuously supplied by an inverter, the adjustment of the consumed power being achieved by changing the operating frequency of the inverter.

However, such an assembly does not make it possible to vary significantly the power delivered by each inductor.

Also known devices designed to use a single inverter supplying multiple inductors, these devices providing for supplying each inductor cyclically, that is to say one after the other, for example by means of a relay.

During a phase of alternating power supply, the inductors are powered on a pro rata temporis of the requested power demand.

When an inductor is energized, the instantaneous power is slaved to the sum of the reference power values associated with the two inductors, the sum of the nominal power values being limited in this case by the permissible power by an inductor.

However, it is impossible to obtain by the alternating power mode certain power combinations.

The object of the present invention is to solve the abovementioned drawbacks and to propose a power supply method for two inductors connected in parallel, making it possible to optimize the power operating range of these two inductors, powered by inverters controlled by a same frequency generator.

For this purpose, the present invention relates to a power supply method with reference power values of two inductors connected in parallel on the same power phase of a power supply and powered respectively by two inverters controlled by the same generator. frequency.

According to the invention, the supply method comprises a cyclic power supply step over predetermined periods, the power supply step comprising, on each predetermined period, a mixed feed phase composed of a phase of supply in parallel of the two inductors in which the two inductors are respectively powered by said two inverters controlled at the same working frequency and alternating supply phase of the two inductors.

Thus, by coupling during the mixed supply phase a parallel supply and alternating inductors, it is possible to optimally supply two inductors to very different setpoint power values.

In the parallel supply phase, the power control is performed from the sum of the average powers delivered by the inductors, so that it is close to the sum of the set power values.

However, the average powers delivered by each inductor may themselves be remote from the value of the desired power associated with each inductor.

By coupling a supply phase in parallel with an alternating power supply phase, it is possible to obtain, over a predetermined period of the power supply, a mean power delivered by each inductor close to the value of the power of the power supply. setpoint requested on this inductor.

The parallel power supply phase smooths the power delivered by the inductors and the alternating power phase enables idle phases to be given during the operation of each inverter, avoiding overheating and premature wear of the electronic components used. artwork.

In practice, a first duration of the parallel power supply phase, a second duration of the alternating power supply phase and instantaneous power supply powers of the inductors during the parallel and alternating power supply phases are determined so that that the average powers delivered over said predetermined period by the inductors associated respectively with containers to be heated are substantially equal respectively to the reference power values respectively associated with the two inductors.

The power supply method in accordance with the invention thus makes it possible to guarantee that the average powers delivered by the inductors are as close as possible to the reference power values associated with each inductor by adjusting the times and the instantaneous powers of power on the inductors. two feeding phases, in parallel and alternating.

According to an advantageous characteristic of the invention, the instantaneous power admitted by each inductor fed by an inverter being between a minimum continuous power and a maximum continuous power, the mixed feed phase is implemented at least when the sum of the values setpoint power is greater than the maximum continuous power and at least one of the setpoint power values is less than a predetermined threshold value, greater than or equal to the value of the minimum continuous power.

As soon as the sum of the desired power values is greater than the maximum continuous power, an alternating power phase alone can not be implemented, alternately delivering to each inductor the sum of the reference powers.

Since the instantaneous power delivered must be less than the maximum continuous power, an alternating power supply mode would necessarily lead to at least one of the inductors not reaching the desired reference power value.

By coupling an alternating power supply phase to a parallel power supply phase during the mixed power supply phase, it is possible to obtain the nominal power values at the average power levels delivered by the two inductors, on each predetermined period of the cyclic feeding step.

In practice, the predetermined threshold value is substantially equal to a maximum value of minimum continuous power admitted by the two inductors.

In this case, at least one of the setpoint power values associated with an inductor is less than the minimum DC power value, a supply phase in parallel with an instantaneous power value necessarily greater than the continuous power value. minimum would then exceed the setpoint value associated with this inductor.

The combination of an alternating power supply phase and the parallel power supply phase thus makes it possible, over a predetermined period, to obtain on average a power delivered by each inductor close to the desired power value.

In practice, if the target power values are lower than the predetermined threshold value, the two inductors are supplied with several alternating pulses during the alternating power supply phase.

It is thus possible to smooth the power delivered by each inductor over time on the alternating power supply phase and to avoid having a period of excessive duration during which one of the inductors is not powered, leading to heating by blow of the container, generally badly felt by the user and giving bad culinary results.

According to another characteristic of the invention, the method comprises a preliminary step of determining the predetermined period as a function of the instantaneous powers of supply of the inductors during the phase of supply in parallel and alternately.

This preliminary step makes it possible to modify the value of the predetermined period during the supply of two inductors associated with containers to be heated, in order to better take into account instantaneous power differences during the supply step.

According to another characteristic of the invention, the method comprises a step of analyzing the inductors associated respectively with containers to be heated, this step being adapted to determine a function between the period of the chopper signal generated by the frequency generator controlling said inverters and instantaneous power supplying each inductor, said analysis step comprising measurements implemented for a sample of target power values allocated to said two inductors.

This analysis step makes it possible to know the power distribution during a phase of supply in parallel of the two inductors, this distribution being dependent in particular on the type of container (size, material) and its positioning above each inductor .

According to another aspect of the invention, a cooking appliance, and in particular a cooking hob, comprising at least two cooking hobs respectively comprising two inductors connected in parallel on the same power phase of a power supply and respectively powered respectively. two inverters controlled by the same frequency generator, comprises a processing unit adapted to to control at one and the same operating frequency said inverters and to implement a method of supplying power to power values of said two inductors according to the invention.

This cooking appliance has characteristics and advantages similar to those described above in relation to the power supply method used.

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

• la figure 1 représente schématiquement un appareil de cuisson conforme à un premier mode de réalisation de l'invention;
• la figure 2 représente schématiquement un appareil de cuisson conforme à un second mode de réalisation de l'invention ;
• la figure 3 est un circuit électronique illustrant le montage de deux inducteurs et de deux onduleurs sur une phase de puissance d'une alimentation électrique ;
• les figures 4A et 4B sont des schémas illustrant un algorithme du procédé d'alimentation en puissance selon un mode de réalisation de l'invention;
• la figure 5 illustre schématiquement différents modes d'alimentation de deux inducteurs sur une période prédéterminée d'une alimentation en puissance ; et
• la figure 6 illustre des courbes de variation de puissance en fonction de la période d'un signal de découpage.

In the accompanying drawings, given as non-limiting examples:

• the figure 1 schematically represents a cooking appliance according to a first embodiment of the invention;
• the figure 2 schematically represents a cooking appliance according to a second embodiment of the invention;
• the figure 3 is an electronic circuit illustrating the mounting of two inductors and two inverters on a power phase of a power supply;
• the Figures 4A and 4B are diagrams illustrating an algorithm of the power supply method according to one embodiment of the invention;
• the figure 5 schematically illustrates different modes of supplying two inductors over a predetermined period of a power supply; and
• the figure 6 illustrates power variation curves as a function of the period of a chopping signal.

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

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

Each cooking zone F1, F2, F3, F4 respectively comprises an inductor mounted on a power phase of a power supply 11, typically a mains power supply. Conventionally, the hob is powered by 32 amps that can provide a maximum power of 7200 W at the hob 10, a power of 3600 W per phase.

It will be noted that each inductor of the firing heaters F1, F2, F3, F4 can in practice be made from one or more coils in which the electric current flows.

A control and power control card 12 makes it possible to support all the electronic and computer means necessary for controlling the hob 10.

In practice, electrical connections 13 are provided between this control and control board 12 and each cooking zone F1, F2, F3, F4.

Conventionally, in such a hob, all of the inductors and the control and control board 12 are placed under a flat cooking surface, generally made from a glass-ceramic plate.

The cooking hobs can also be identified by screen printing vis-à-vis the inductors placed under the cooking surface.

Finally, the hob 10 also comprises control and interface means 14 with the user, in particular enabling the user to control in power and in duration the operation of each focus F1, F2, F3, F4.

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

We also illustrated at the figure 2 a second embodiment of a cooking appliance according to the invention.

This cooktop has similar features and the same numerical references as the cooktop shown in figure 1 .

Unlike the four-focus embodiment of the figure 1 , the embodiment of the figure 2 has only three foci, F1 foci, F2 identical to those previously described, and a larger F5 dual focus.

This double F5 fireplace is usually made of a central inductor and an annular inductor.

The central inductor is operated in isolation when a small container is placed on the F5 and the two inductors are operated simultaneously with larger containers.

In both embodiments illustrated in Figures 1 and 2 , the inductors of each home are mounted in pairs in parallel on the same power phase of the power supply.

Thus, in the embodiment illustrated in FIG. figure 1 the inductors associated with the first two foci F1, F2 are connected in parallel with a first power phase of the power supply, and the inductors associated with the other two foci F3, F4 are connected in parallel with the second power phase of the power supply. power supply.

Similarly, figure 2 the inductors associated with the first two foci F1, F2 are connected in parallel on a first phase of the power supply, and the concentric inductors associated with the focal point F5 are connected in parallel with a second power phase of the power supply.

We will describe the assembly by pair of these inductors with reference to the figure 3 .

We have illustrated in this way figure 3 two inductors I1, I2 which can correspond to the inductors of the foci F1, F2, or foci F3, F4, or F5 focus.

As well illustrated at the figure 3 these two inductors I1, I2 are connected in parallel on a power phase of the power supply and controlled respectively by two inverters 31, 32.

Each inductor I1, I2 is connected in parallel with a capacitor C1, C2.

The inductor I1, I2 and the capacitor C1, C2 then form a resonant circuit whose resonant frequency varies as a function of the receptacle disposed above the inductor I1, I2.

Each inverter 31, 32 can operate from any electronic switching means, and for example, from a voltage-controlled transistor type switch, known as IGBT (acronym for the term " Insulated Gate Bipolar Transistor "). This switch is associated with a freewheeling diode.

Such an inverter is conventionally used in an induction cooktop and need not be described in more detail here.

In a conventional manner, each inverter 31, 32 is controlled at a frequency F _T1 , F _T2 .

This frequency command is managed by a processing unit 33.

Thus, the processing unit 33 is adapted to control the frequency at which the transistors of the inverters 31, 32 are conductive or lock.

As indicated previously, in the present invention, it is considered that the frequency signals F _T1 , F _T2 are identical for each inductor I1, I2 and hereinafter called working frequency F _T.

The operation of the inverters 31, 32 at an identical working frequency F _T thus makes it possible to eliminate the interference at the level of the inductors I1, I2, and thus to avoid the generation of annoying audible noise for the user.

The processing unit 33 is thus adapted to control a frequency generator 34 adapted to generate an identical working frequency F _T for each inverter 31, 32.

We also illustrated at the figure 3 measuring means 35, 36 respectively adapted to measure the current flowing between each inverter 31, 32 and the associated inductors I1, I2.

These measuring means 35, 36 make it possible in particular to measure the peak current Imax1, Imax2 and the switched current Icom1, Icom2 at the output of each inverter 31, 32.

In particular, the peak current Imax is deduced from the instantaneous current flowing in each inverter 31, 32.

Similarly, the switching current Icom, current for which the switch or associated freewheeling diode becomes conductive, is also deduced from the instantaneous current measured at the output of the inverter.

The determination of the peak current Imax and the Icom switching current is known and need not be described in more detail here.

It is notably described in the document US 4,847,746 .

We will now describe with reference to Figures 4A and 4B the power supply method of the two inductors I1, I2 implemented in accordance with the invention in the device described in figure 3 .

The processing algorithm described below makes it possible to distribute the power on each inductor I1, I2 taking into account different parameters.

In principle, the power distribution performed by the processing algorithm must make it possible to obtain at each inductor I1, I2 a power output close to the desired power demanded by the user.

This restored power corresponds. the power restored by each inductor I1, I2 over a predetermined period of time, hereinafter referred to as the Tprog program period.

Recall that the standard EN-61000-3-3 on the electrical network (Flicker standard) sets a maximum number of variations of the voltage per minute, depending on the amplitude of the variation.

In known manner, the value of the program period Tprog is determined according to a maximum number of power variations allowed in one minute.

We consider here, by way of non-limiting example, a Tprog program period of fixed duration, of the order of 10 s.

When operating the cooking hobs, a setpoint power is defined by the user for the one and / or the other inductor I1, I2.

Thus P1d is defined as the power demanded on the inductor I1 and P2d, the power demanded on the inductor I2.

A test step E41 first makes it possible to check whether the power at the hob 10 is requested only on one of the two inductors I1, I2.

If so, it is checked whether the requested power is lower than a minimum continuous power admitted by an inductor I1, I2.

In the following, it is considered that when only one of the two inductors I1, I2 is in operation, it is the first inductor I1.

Of course, the following description applies identically to the second inductor I2.

It is thus verified in a test step E42 whether the requested power P1d on the inductor I1 is less than a minimum continuous power allowed PminCont1.

The minimum continuous power allowed PminCont1, PminCont2 on each inductor I1, I2 depends in particular on the inverter 31, 32, and in particular the operation of the IGBT switch, that is to say, its switching possibilities.

The permissible minimum continuous power value PminCont1, PminCont2 can be between 600 and 1800 W depending on the operating temperature, the type of container and its size, and the size of the inductor.

By way of nonlimiting example, the minimum continuous power admitted PminCont can be here equal to 1400 W.

At the minimum continuous power allowed PminCont1, PminCont2 for each inductor I1, I2 corresponds, for the period of the switching signal T generated by the frequency generator 34, a minimum value Tmin1, Tmin2 allowed.

If the requested power P1d is less than the minimum permissible continuous power PminCont1, then the supply of the inductor I1 is carried out in a simple cut-off mode.

This simple cut mode is illustrated in the figure 5 . The inductor I1 is thus powered by controlling the inverter 31 with a decoding signal. period Tmin1, corresponding to the minimum allowed value, dependent on the minimum continuous power allowed PminCont1.

For each program period Tprog, the inductor I1 is supplied on a pro rata temporis of this period to reach the value of the requested power P1d.

By thus alternating a switching period and a non-switching period of the inverter 31 over the program period Tprog, it is possible to reach the setpoint value at the requested power P1d on the inductor I1.

On the other hand, if, at the end of the test step E42, the requested power P1d is greater than the minimum permissible continuous power PminCont1, the supply of the inductor I1 can be carried out according to a simple continuous mode illustrated in FIG. figure 5 .

In this case, the inductor I1 is continuously supplied by switching of the inverter 31 according to a working frequency F _T associated with the requested power P1d.

Note further that the requested power P1d on the inductor I1 must also be less than a maximum allowed continuous power PmaxCont1 by the inductor I1, also dependent on the components of the inverter 31, and in particular the IGBT switch.

For example, this maximum continuous power admitted PmaxCont1 can be of the order of 2300 W.

As previously, at the maximum continuous power allowed PmaxCont1, PmaxCont2 by each inductor I1, I2 corresponds to a maximum value Tmax1, Tmax2 allowed for the period of the switching signal T sent by the frequency generator 34 to the inverter 31, 32.

If a power is requested on the two inductors I1, I2 at the end of the test step E41, two test steps E43, E44 are successively checked if each receptacle associated with each inductor I1, I2 accepts a mode operation. parallel.

It will be recalled that in a parallel mode, the two inductors I1, I2 are supplied simultaneously with a respective control signal associated with the same period of the switching signal T, equal to the value Tp in this parallel mode.

In this case, the processing unit 33 is adapted to control the power so that the two powers measured on each inductor I1, I2 are not too far respectively from the setpoint value P1d, P2d and the sum of the measured powers. are not too far from the sum of the setpoints P1d + P2d.

If one of the two receptacles does not accept the parallel mode, only an alternating power supply can be implemented.

The acceptance by each container of the parallel mode is determined during the characterization of the behavior of the container and will be described later with reference to the figure 6 .

If the two receptacles accept the parallel mode, a comparison step E45 also makes it possible to check whether the sum of the requested powers P1d + P2d is greater than the maximum continuous power allowed PmaxCont1, PmaxCont2 by each inductor I1, I2.

In the following, the permissible maximum continuous power PmaxCont will be noted as the maximum value of the maximum continuous power allowed PmaxCont1 by the inductor I1 and the maximum continuous power allowed PmaxCont2 by the inductor I2: $$\mathrm{PmaxCont}=\mathrm{Max}\left(\mathrm{PmaxCont}1,\mathrm{PmaxCont}2\right)$$

If the sum of the requested powers P1d + P2d is not greater than the permissible maximum continuous power PmaxCont, the supply of the two inductors I1, I2 is carried out alternately as illustrated in FIG. figure 5 .

In this case, a test step E46 also makes it possible to check whether the sum of the powers requested P1d + P2d is less than the minimum continuous power allowed PminCont1, PminCont2 on each inductor I1, I2.

In the following, the permissible minimum continuous power PminCont will be noted as the minimum value of the minimum continuous power admitted PminCont1 by the inductor I1 and the minimum continuous power admitted PminCont2 by the inductor I2: $$\mathrm{PminCont}=\min \left(\mathrm{PminCont}1,\mathrm{PminCont}2\right)$$

If the sum of the requested powers P1d + P2d is less than the minimum permissible continuous power PminCont, the supply of the two inductors I1, I2 is implemented according to an incomplete alternating mode.

In the negative, the supply of the two inductors I1, I2 is implemented in a complete alternating mode.

These alternate modes complete or incomplete are illustrated in figure 5 .

In the incomplete alternating mode, the alternating power supply power Palt of each inductor I1, I2 is fixed at the minimum permissible continuous power PminCont.

The operating time of the inverters 31, 32 supplying each inductor I1, I2 is determined, over each program period Tprog, so that the average power P1m, P2m over this program period Tprog, restored by each inductor I1, I2, is the as close as possible to the requested power P1d, P2d.

Rather than supplying one of the inductors I1 for a first duration, then for a second duration the second inductor I2, it is preferable to supply the two inductors I1, I2 with several alternating pulses during the program period Tprog in order to homogenise the time the power supplied to each inductor I1, I2.

This alternation of operation of the two inductors I1, I2 during the program period Tprog smooths the power supplied during this period and is less visible at the container by the user.

In practice, to determine the distribution in the incomplete alternating power mode, consider the length of the smallest possible pulse to perform the alternating operation of the inverters 31, 32.

This length of the smallest pulse τ is set by the processing unit 33 and corresponds to the minimum time necessary to alternate the operation of the two inverters 31, 32 at the level of the processing unit 33.

By way of example, this smaller pulse length τ may be of the order of 100 milliseconds.

Considering in the example shown in figure 5 the requested power P2d on the inductor I2 is lower than the requested power P1d on the inductor I1, the requested power P2d controls the number of pulses of smaller length τ.

In practice, we consider the overall operating time of the inductor I2 over the program period Tprog, calculated prorata temporis to obtain the requested power P2d by providing an instantaneous power Palt of the order of PminCont, and we divide this duration of overall operation by the duration of pulses τ of smaller length.

A number n of pulses τ of alternation is thus obtained. Then dividing the overall operating time of the inductor I1 over the program period Tprog, calculated pro rata temporis to obtain the requested power P1d on the inductor I1 by addressing the instantaneous power Palt on the inductor I1, by the number n pulses τ, it is possible to determine the length of each operating pulse of the first inductor I1.

The complete alternating mode is implemented in the same way, preferably by alternating pulses τ over the program period Tprog. In this case, the alternating power Palt supplied to each inductor I1, I2 is for example equal to the sum of the requested powers P1d + P2d since this sum of the reference powers is well between the minimum value of the maximum permissible continuous powers PmaxCont1 , PmaxCont2 and the maximum value of the permissible minimum continuous powers PminCont1, PminCont2 by the inductors I1, I2.

As before, the lowest power demand on the two inductors I1, I2 determines the number n of pulses τ of alternation over the program period Tprog, the length of each pulse τ of alternation depending on the power demanded on each inductor I1, I2.

At the end of the comparison step E45, if the sum of the requested powers P1d + P2d on each inductor I1, I2 is greater than the maximum allowed continuous power PmaxCont, a power supply phase alternating as described above does not provide all the power necessary to achieve the setpoints P1d, P2d.

According to the invention, it is then envisaged to implement a power supply step, on each program period Tprog, in which a mixed power phase is implemented, composed of a power supply phase. parallel of the two inductors I1, I2 and an alternating supply phase of the two inductors I1, I2.

We must therefore first of all check the possibility of simultaneously implementing the supply of two inductors I1, I2 covered by containers.

In parallel mode, the total power consumed is controlled by the power supplied by the mains supply, and for example, is equal to 3600 W.

By considering the period of the switching signal Tp when the two inductors I1, I2 are supplied in parallel, that is to say simultaneously, a relation makes it possible to know the instantaneous power P1p, P2p distributed on each inductor I1, I2, and which depends in particular on the container placed on this inductor (size of the container, material, positioning with respect to the inductor).

Thus, in a parallel mode, the sum of the instantaneous powers P1p, P2p by each inductor I1, I2 corresponds to the power absorbed on the network: $$\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{+}\mathrm{P}\mathrm{2}\mathrm{p}\mathrm{=}\mathrm{3600}\mathrm{W}\mathrm{.}$$

On the other hand, each power P1p and P2p is not necessarily equal although the working frequency F _T of the inverters 31, 32, corresponding to the period of the switching signal Tp, is identical.

It is possible to characterize the power absorbed by each inductor I1, I2 during a parallel operation, prior to the implementation of the distribution step.

This characterization will be described later with reference to figure 6 .

$$\mathrm{P}\mathrm{2}\mathrm{p}\mathrm{=}\mathrm{A}2\mathrm{\times }{\mathrm{T}}_{\mathrm{p}}\mathrm{+}\mathrm{B}2$$

In practice, a linear relation connects the instantaneous power P1 p, P2p by each inductor I1, I2 to the period of the switching signal Tp according to the following equations: $$\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{=}\mathrm{AT}\mathrm{1}\mathrm{\times }{\mathrm{T}}_{\mathrm{p}}\mathrm{+}\mathrm{B}\mathrm{1}$$

$$\mathrm{P}\mathrm{2}\mathrm{p}\mathrm{=}\mathrm{AT}2\mathrm{\times }{\mathrm{T}}_{\mathrm{p}}\mathrm{+}\mathrm{B}2$$

It can thus be calculated in a calculation step E47 illustrated in FIG. Figure 4B the value of the period of the clipping signal Tp by knowing the coefficients A1, B1, A2, B2 determined during the characterization of the containers.

A test step E48 then makes it possible to compare the period of the switching signal Tp during parallel operation to the minimum value Tmin allowed for the period of the switching signal T and to the maximum value Tmax allowed for the period of the switching signal. T.

As indicated above, these maximum and minimum values Tmin and Tmax depend on the electronic components and are related to the powers PminCont1, PminCont2 and PmaxCont1, PmaxCont2 that can be delivered by switching the inverters 31, 32.

$$\mathrm{Tmax}=\min \left(\mathrm{Tmax}1,\mathrm{Tmax}2\right)$$

The minimum value Tmin allowed for the period of the chopper signal T is the maximum value of the minimum values Tmin1, Tmin2 allowed for the period of the chopping signal T on each inverter 31, 32 and the maximum value Tmax allowed for the period of the chime signal. switching T is the minimum value of the maximum values Tmax1, Tmax2 allowed for the period of the switching signal T on each inverter 31, 32: $$\mathrm{Tmin}=\max \left(\mathrm{Tmin}1,\mathrm{Tmin}2\right)$$

$$\mathrm{Tmax}=\min \left(\mathrm{Tmax}1,\mathrm{Tmax}2\right)$$

If the period of the parallel switching signal Tp is not greater than the minimum allowed value Tmin and less than the maximum allowed value Tmax, the parallel mode can not be implemented and, at the end of the step E48 test, the complete alternating mode is implemented as described above.

However, this complete alternate mode will not achieve the requested power P1d, P2d on each inductor I1, I2.

On the other hand, if at the end of the test step E48, the period of the parallel switching signal Tp lies between the minimum value Tmin and the maximum value Tmax allowed for the period of the switching signal, it is determined for one first inductor, and for example the inductor I1, the instantaneous power on this inductor according to the characterization of the container described above.

In practice, a calculation step E49 makes it possible to determine this instantaneous power P1p by the following formula: $$\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{=}\mathrm{AT}\mathrm{1}\mathrm{\times }{\mathrm{T}}_{\mathrm{p}}\mathrm{+}\mathrm{B}\mathrm{1.}$$

A comparison step E50 again makes it possible to verify that the value of the instantaneous power P1p during the parallel phase is much greater than the minimum continuous power allowed PminCont1 by the inductor I1 and lower than the maximum continuous power allowed PmaxCont1 by the inductor. I1.

In the negative, the parallel mode can not be implemented and the power supply method of the two inductors I1, I2 implements as indicated above the complete alternating mode.

In the positive, calculation steps E51 and comparison E52 are implemented in a similar manner to the calculation steps E49 and comparison E50 for the second inductor I2.

If at the comparison step E52, the value of the instantaneous power P2p in the parallel phase is not greater than the minimum continuous power admitted PminCont2 or less than the maximum continuous power allowed PmaxCont2 by the inductor I2, the parallel mode can not be implemented and the power supply method of the two inductors I1, I2 implements as indicated above the complete alternating mode.

If the test at the end of the comparison step E52 is positive, comparing in a comparison step E53 the values of the requested powers P1d, P2d on each inductor I1, I2 with a threshold value Vs.

The threshold value Vs is greater than or equal to the minimum permissible continuous power value PminCont1, PminCont2 for each inductor I1, I2.

The threshold value Vs is preferably greater than the values of the permissible minimum continuous power PminCont1, PminCont2 in order to artificially increase the power demanded on each inductor I1, I2 so as to limit the temperature rise of the IGBT switches.

The threshold value Vs may also be equal to the maximum value of the permissible minimum continuous power PminCont1 for the inductor I1 and the minimum continuous power admitted PminCont2 for the inductor I2.

In this embodiment where the values PminCont1 and PminCont2 are substantially identical and equal to 1400 W, the threshold value Vs may be between 1400 W and 1700 W.

By way of nonlimiting example, this threshold value Vs may be equal to 1650 W.

In practice, the mixed feed phase is implemented when at least one of the set power values P1d, P2d is lower than this threshold value Vs.

In this practical embodiment, the maximum value of the reference power values P1d, P2d at the threshold value Vs is compared with the comparison step E53.

If this maximum value is not greater than the threshold value Vs, that is to say that the two desired power values P1d, P2d are lower than the threshold value Vs, then a mixed feed phase can be implemented in an alternating parallel mode which will be described below with reference to the figure 5 .

If at the output of the comparison step E53, one of the set power values P1d, P2d is lower than the threshold value Vs and the other of the set power values P1d, P2d is greater than the threshold value Vs a mixed feed phase can be implemented in an incomplete parallel mode which will be described later with reference to the figure 5 .

On the other hand, if the sum of the requested powers P1d + P2d is greater than the maximum allowed continuous power PmaxCont, but the two requested powers P1d, P2d are greater than the threshold value Vs and are close to one another, a Parallel power supply in a complete parallel mode is implemented to feed simultaneously during the entire program period Tprog the two inductors I1, I2.

In practice, it is verified in two successive test steps E54, E55 if the tolerances on the requested powers P1d, P2d and the instantaneous powers P1p, P2p during the parallel phase make it possible to use the complete parallel mode without going too far from the powers requested by the user.

In the first test step E54, it is verified that the difference in absolute value between each requested power value P1d, P2d and an average value of 1800 W remains less than 150 W.

If not, the complete parallel mode can not be implemented, and the incomplete parallel mode is then implemented as will be described later with reference to FIG. figure 5 .

If so, it is verified in the second test step E55 whether the difference in absolute value between the instantaneous power values P1 p, P2p during the parallel phase and a mean power value of 1800 W remains low, and for example less than 200 W.

If not, the complete parallel mode can not be implemented without departing too far from the user-requested setpoint values P1d, P2d and the incomplete parallel mode is then implemented.

If so, the parallel power supply can then be used to supply the two inductors I1, I2 simultaneously during the entire program period Tprog.

We will now describe with reference to the figure 5 the calculation of the parameters necessary to implement the mixed power supply in which a parallel mode and an alternating mode are implemented over a program period Tprog.

It is recalled that this mixed feed is implemented when the sum of the two requested powers P1d and P2d is greater than the maximum continuous power admitted PmaxCont by the inductors I1, I2, and here substantially equal to 2300 W, and when at least 1 one of the two requested powers P1d, P2d is less than a predetermined threshold value Vs, of the order of the minimum continuous power admitted PminCont by the inductors I1, I2.

An exemplary embodiment in which the two requested powers P1 d, P2d are below the threshold value Vs, for example less than 1400 W., will be described below.

In this case, returning to the figure 5 , the mixed feed phase implements an alternating parallel mode during a program period Tprog.

In this operating mode, on each Tprog program period, there is a parallel supply phase followed by a phase in alternating power supply.

The program period Tprog is a succession of sector periods.

As indicated previously, according to the Flicker standard, the number of sector periods which constitute the program period Tprog is determined as a function of the power difference existing between the instantaneous power P1 p, P2p supplying the inductors I1, I2 during the parallel phase and the instantaneous power Palt supplying the inductors I1, I2 during the alternating phase.

In practice, during the parallel supply phase, the sum of the two absorbed powers P1p + P2p by each inductor I1, I2 is equal to the power available on the supply phase, and here 3600 W.

During the alternating power phase, the powers absorbed by each inductor I1, I2 are equal and between a value of 1800 W and 2300 W.

Thus, in view of the electrical network, the system consisting of the inductors I1, I2 absorbs 3600 W during the phase parallel feeding phase. mixed feed, then the instantaneous power Palt sent alternately on the two inductors I1, I2.

This power difference thus makes it possible to determine beforehand the maximum length of the program period Tprog.

It is possible to set the value of the program period Tprog in such a way that it complies with the Flicker standard irrespective of the difference existing between the instantaneous powers P1 p, P2p, the supply voltage of the inductors I1, I2 during the parallel phase and the alternating phase.

It suffices to consider a Tprog program period of sufficiently long length, for example equal to 15 seconds, likely to be suitable for the largest power difference, of the order of 1800 W.

According to another embodiment, the duration of the program period Tprog can be variable and determined case by case as a function of the actual difference between the instantaneous powers P1p, P2p.

It is therefore possible, from the Flicker standard, setting a maximum number of voltage variations per minute as a function of the value of the voltage variation, to deduce a minimum program period duration Tprog for a given instantaneous power deviation. It is thus possible to define the length of the program period Tprog as a function of the difference existing between the instantaneous power P1p, P2p, here 3600 W, during the parallel phase and the instantaneous power Palt during the alternating phase of the phase of mixed feeding.

By way of example, for a power deviation that can vary between 1300 and 1800 W, the program period Tprog can vary between 4 and 15 s.

By optimally adjusting the length of the program period Tprog away from power, it avoids oversizing the program period Tprog.

Indeed, the shorter the Tprog program period, the faster the power distribution pattern is repeated over time.

The user thus has a feeling of regularity in the power delivered to the container.

On the contrary, if the length of the program period Tprog is long, large power deviations will occur from one program period Tprog to another, giving an impression of irregularity in the power delivered to the container.

In practice, the duration Np of the parallel supply phase, the duration Nalt of the alternating power supply phase and the instantaneous powers P1 p, P2p, the supply voltage of the inductors I1, I2 during the supply phases in parallel and alternately are determined such that the average powers P1m, P2m delivered over the program period Tprog by the inductors I1, I2 associated respectively with containers to be heated are close to the desired power values P1d, P2d respectively associated with the two inductors I1, I2 and requested by the user.

In order to determine the respective durations Np, Nalt of each phase of parallel and alternating power supply and the instantaneous powers P1p, P2p, Palt supplying each inductor I1, I2, the method implements calculation means making it possible to determine the duration Np of the parallel feeding phase.

$$\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{=}\mathrm{A}\mathrm{1}\mathrm{\times }{\mathrm{T}}_{\mathrm{p}}\mathrm{+}\mathrm{B}\mathrm{1}$$

$$\mathrm{P}\mathrm{2}\mathrm{p}\mathrm{=}\mathrm{A}2\mathrm{\times }{\mathrm{T}}_{\mathrm{p}}\mathrm{+}\mathrm{B}2$$

As indicated previously, during the phase of parallel power supply, the instantaneous powers P1p, P2p sent on each inductor I1, I2 correspond to the following equations: $$\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{+}\mathrm{P}\mathrm{2}\mathrm{p}\mathrm{=}\mathrm{3600}\mathrm{W}$$

$$\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{=}\mathrm{AT}\mathrm{1}\mathrm{\times }{\mathrm{T}}_{\mathrm{p}}\mathrm{+}\mathrm{B}\mathrm{1}$$

$$\mathrm{P}\mathrm{2}\mathrm{p}\mathrm{=}\mathrm{AT}2\mathrm{\times }{\mathrm{T}}_{\mathrm{p}}\mathrm{+}\mathrm{B}2$$

It is possible to determine by these equations the value of the instantaneous powers P1p and P2p.

où $$\mathrm{N}\mathrm{1}\mathrm{alt}\mathrm{+}\mathrm{N}\mathrm{2}\mathrm{alt}\mathrm{=}\mathrm{Nalt}\mathrm{,}$$

Moreover, for the duration Nprog of the program period Tprog, we have the following equation: $$\mathrm{NPROG}\mathrm{=}\mathrm{np}\mathrm{+}\mathrm{NOT}\mathrm{1}\mathrm{alt}\mathrm{+}\mathrm{NOT}\mathrm{2}\mathrm{alt}$$

or $$\mathrm{NOT}\mathrm{1}\mathrm{alt}\mathrm{+}\mathrm{NOT}\mathrm{2}\mathrm{alt}\mathrm{=}\mathrm{NALT}\mathrm{,}$$

N1alt and N2alt being the respective duration of supply during the alternating phase of each inductor I1, I2, that is to say the overall duration of supply of each inductor I1, I2.

$$\mathrm{P}\mathrm{2}\mathrm{m}\mathrm{=}\left(\mathrm{Np}\mathrm{\times }\mathrm{P}\mathrm{2}\mathrm{p}\mathrm{+}\mathrm{N}\mathrm{2}\mathrm{alt}\mathrm{\times }\mathrm{Palt}\right)\mathrm{/}\mathrm{Nprog},$$

The average power P1m, P2m thus restored by each inductor I1, I2 corresponds to the following equations: $$\mathrm{P}\mathrm{1}\mathrm{m}\mathrm{=}\left(\mathrm{np}\mathrm{\times }\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{+}\mathrm{NOT}\mathrm{1}\mathrm{alt}\mathrm{\times }\mathrm{Palt}\right)\mathrm{/}\mathrm{NPROG}$$

$$\mathrm{P}\mathrm{2}\mathrm{m}\mathrm{=}\left(\mathrm{np}\mathrm{\times }\mathrm{P}\mathrm{2}\mathrm{p}\mathrm{+}\mathrm{NOT}\mathrm{2}\mathrm{alt}\mathrm{\times }\mathrm{Palt}\right)\mathrm{/}\mathrm{NPROG},$$

Combining the previous equations, we arrive at the following equation: $$\mathrm{np}\mathrm{=}\mathrm{NPROG}\mathrm{\times }\left({\mathrm{Palt}}^{\mathrm{2}}\mathrm{-}\mathrm{Palt}\mathrm{\times }\left(\mathrm{P}\mathrm{1}\mathrm{m}\mathrm{+}\mathrm{P}\mathrm{2}\mathrm{m}\right)\right)\mathrm{/}\left({\mathrm{Palt}}^{\mathrm{2}}\mathrm{-}\mathrm{Palt}\mathrm{\times }\left(\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{+}\mathrm{P}\mathrm{2}\mathrm{p}\right)\right)\mathrm{.}$$

P1p and P2p are known by the calculation and P1 m and P2m are equal to the requested setpoints P1d and P2d.

The duration Np of the parallel supply phase is thus determined as a function of the duration Nprog of the program period Tprog, of the power Palt in the alternating phase, of the reference powers P1d, P2d requested on each inductor I1, I2 and instantaneous powers P1 p, P2p absorbed by each inductor I1, I2 during the parallel supply phase.

This defines a value of the power Palt during the alternating phase.

The value of the power Palt is necessarily between the maximum value of the minimum permissible continuous powers PminCont1, PminCont2 by the inductors I1, I2 and the minimum value of the maximum permissible continuous powers PmaxCont1, PmaxCont2 by the inductors I1, I2, that is, that is, between approximately 1400 W and 2300 W.

It is preferable to choose a value of the high power Palt, for example at least 1800 W.

By way of example, this value of the instantaneous power Palt can be set to the minimum value of the maximum permissible continuous powers PmaxCont1, PmaxCont2.

Knowing the value of the power Palt during the alternating phase, it is possible to determine by the Flicker standard the value of the duration Nprog of the program period Tprog by the difference between the power consumed during the parallel phase (here 3600 W corresponding to the power of the mains phase) and the power consumed during the alternating power phase Palt.

As indicated above, this value of the duration Nprog can also be fixed and equal for example to 10 s.

Knowing the value Nprog, the previous equation allows to know the duration Np of the parallel power phase.

$$\mathrm{N}\mathrm{2}\mathrm{alt}\mathrm{=}\left(\mathrm{P}\mathrm{2}\mathrm{d}\mathrm{\times }\mathrm{Nprog}\mathrm{-}\mathrm{P}\mathrm{2}\mathrm{p}\mathrm{\times }\mathrm{Np}\right)\mathrm{/}\mathrm{Palt}$$

It is possible to deduce from the preceding equations the overall durations N1alt and N2alt of supply of the inductors I1, I2 during the alternate feeding phase according to the following formulas: $$\mathrm{NOT}\mathrm{1}\mathrm{alt}\mathrm{=}\left(\mathrm{P}\mathrm{1}\mathrm{d}\mathrm{\times }\mathrm{NPROG}\mathrm{-}\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{\times }\mathrm{np}\right)\mathrm{/}\mathrm{Palt}$$

$$\mathrm{NOT}\mathrm{2}\mathrm{alt}\mathrm{=}\left(\mathrm{P}\mathrm{2}\mathrm{d}\mathrm{\times }\mathrm{NPROG}\mathrm{-}\mathrm{P}\mathrm{2}\mathrm{p}\mathrm{\times }\mathrm{np}\right)\mathrm{/}\mathrm{Palt}$$

One solution during the alternating feed phase is successively supplying the inductor I1 for a duration N1alt then the inductor I2 for a duration N2alt, or vice versa.

A second solution as illustrated in figure 5 consists of cutting into several pulses each duration N1alt, N2alt of the alternate feeding phase of each inductor I1, I2 in order to smooth the power distribution on the containers and to obtain a better average of the power in the container.

As described previously during the alternating power phase, the distribution of the power supply on several alternating pulses is implemented starting from the minimum power demanded on one or the other of the two inductors I1, I2 and the minimum length of each pulse τ, composed of a number of periods mains.

It is possible to define the number n of supply pulses τ for each inductor I1, I2 during the alternating power supply phase.

In practice, considering the duration N1alt associated with the inductor I1 for which the requested power P1d is the smallest and the length of each mains pulse, it is possible by division to know the number n of supply pulses τ.

From this number n of pulses τ and the duration N2alt associated with the second inductor I2 for which the requested power P2d is greater, it is possible by division to know the duration of each supply pulse for the second inductor I2.

It will be noted in particular that, as a function of the relative values of the minimum length of each pulse and the duration N1alt of the alternate supply phase of the first inductor I1, the number n of pulses τ of minimum length obtained by division can not not be integer, so that, for example, the last building pulse τ of the first inductor I1 is greater than the minimum length.

Similarly, the duration of each pulse τ for the alternate supply phase of the second inductor I2, obtained by division, may also not correspond to an integer so that the duration of certain pulses τ are prolonged to distribute the duration global N2alt on the alternating power phase.

In all cases, the sum of the duration of the pulses τ is equal to the overall duration N1alt, N2alt calculated for each inductor I1, I2 during the alternate feeding phase.

As illustrated in figure 5 if at least one value of the requested powers P1d, P2d is greater than the predetermined threshold value Vs, here the value P2d associated with the second inductor I2, only one of the inductors I1, I2 is supplied during the alternating power supply phase.

In this case, the mixed feed phase implements an incomplete parallel mode and comprises a parallel feed phase followed by an alternating feed phase in which only one of the inductors I1, I2 is fed, that is, ie the inductor I1, I2 for which the reference power P1d, P2d is greater than the predetermined threshold value Vs.

This mixed feed mode coupling a parallel power supply and alternating power supply inductors I1, I2 makes it possible to obtain at best on each inductor I1, I2 the requested reference power P1d, P2d during each program period Tprog.

We will now describe with reference to the figure 6 , an example of characterization of the behavior of a container placed on an inductor I1, I2, for determining a function, for example an affine function, connecting the period of the switching signal T of the inverter 31, 32 supplying this inductor I1 , I2 and the instantaneous power P absorbed by this inductor I1, I2.

An analysis step is carried out prior to a parallel supply phase or a mixed feed phase of inductors I1, I2.

In practice, this analysis step is carried out regularly during the power supply of the two inductors I1, I2, since the position of the pan on the furnace F1, F2 can vary during cooking and that the behavior The resonant of the system constituted by the inductor I1, I2 and the pan can be modified in time, as the temperature rise in the container.

In principle, the analysis step comprises for each inductor I1, I2 a series of measurements implemented for a sample of target power values assigned to each inductor I1, I2.

The sample of nominal power values may comprise in particular a minimum reference power value Pmin equal to the minimum continuous power value admitted PminCont1, PminCont2 by each inductor I1, I2 and a maximum reference power value Pmax equal to the permissible maximum continuous power value PmaxCont1, PmaxCont2 by each inductor I1, I2.

For each of these setpoint values Pmin, Pmax, the instantaneous power P supplying each inductor I1, I2 and the period of the switching signal T generated by the frequency generator 34 during this measurement are determined.

Samples of desired power values may also include intermediate command power values between the minimum setpoint power value Pmin and the maximum setpoint power value Pmax used previously.

All of these values and measurements can then reliably determine a curve, and here a straight line as illustrated in FIG. figure 6 , connecting the instantaneous power P and the period of the switching signal T for the inductor-container system considered, depending in particular on each inductor I1, I2 and the container R1-R6 deposited vis-à-vis.

A relationship of the type P = A x T + B is thus defined for each inductor I1, I2 covered with a container.

As indicated above, this relationship makes it possible to know the instantaneous power distribution on each inductor I1, I2, in particular when it operates in parallel with a period of the switching signal Tp.

In particular, if at the end of the analysis step, the maximum setpoint power values Pmax and minimum Pmin are very close to each other, that is to say that the curve illustrated in FIG. the figure 6 is a straight segment of very small dimensions, or even reduced to a point, the operation of this system in parallel with another inductor-container system will not be possible.

In this case, only a supply according to an alternating mode of the two inverters 31, 32 can be implemented.

If a phase of supply in parallel is possible on the two inductors I1, I2 associated with the containers, the working frequency F _T can be determined from the functions determined during the analysis step, connecting the period of the signal of cutting T _p generated by the frequency generator 34 controlling the two inverters 31, 32 and the instantaneous power P1 p, P2p supplying each inductor I1, I2, the sum of the instantaneous powers P1p, P2p supplying each inductor I1, I2 during the parallel mode being equal to the maximum power provided by the power phase of the power supply.

As illustrated in figure 6 it will be noted for example that it is possible to operate in parallel a container R1 (white triangle curve) with a container R4 (black round curve). In this case, it is also necessary that the sum of the instantaneous powers P1p, P2p on each inductor I1, I2 does not exceed the maximum power supplied by the phase of the mains supply, here equal to 3600 W.

In contrast, a parallel supply phase can not be implemented for a container R2 (white square curve) and a container R6 (black diamond curve).

Indeed, for a given period of the clipping signal Tp, at least one of the instantaneous powers P1p, P2p can be outside the limits of authorized powers, for example between 1400 and 2300 Watts.

In addition, it is possible that for certain containers, and in particular in the example illustrated in FIG. figure 6 , for a container R7, that the line connecting the instantaneous power P to the period of the switching signal T is outside the authorized power range.

This type of container can be powered at low power.

Of course, the present invention is not limited to the embodiments described above.

In particular, the invention can be implemented with a half-bridge generator structure.

Claims (13)

Power supply method with reference power values (P1d, P2d) of two inductors (I1, I2) connected in parallel on the same power phase of a power supply and powered respectively by two inverters (31, 32). ) controlled by the same frequency generator (34), characterized in that it comprises a step of supplying power, cyclic over predetermined periods (Tprog), said power supply step comprising, on each predetermined period ( Tprog), a mixed power supply phase consisting of a parallel supply phase of said two inductors (I1, I2) in which said two inductors (I1, I2) are respectively powered by said two inverters (31, 32) controlled at the same working frequency (F _T ), and an alternating power supply phase of said two inductors (I1, I2). Power supply method according to claim 1, characterized in that a first duration (Np) of said parallel power supply phase, a second duration (Nalt) of said alternating power supply phase and instantaneous power supply powers (P1p, P2p, Palt) of said inductors (I1, I2) during said parallel and alternating power supply phases are determined so that the average powers (P1m, P2m) delivered over said predetermined period (Tprog) by said inductors ( I1, I2) respectively associated with containers to be heated are substantially equal respectively to said reference power values (P1d, P2d) respectively associated with said two inductors (I1, I2). Power supply method according to one of claims 1 or 2, characterized in that in said parallel supply phase, the sum of the instantaneous powers of supply (P1p, P2p) of said inductors (I1, I2) is substantially equal to the maximum power delivered by said power phase of the power supply, and in that a duration (Np) of said parallel supply phase is determined according to a duration (Nprog) of said predetermined period (Tprog), of an instantaneous feed power (Palt) in said alternating feeding phase, said reference powers (P1d, P2d) for said two inductors (I1, I2) and instantaneous power supplies (P1p, P2p) of each inductor (I1, I2) during said parallel supply phase. Power supply method according to one of claims 1 to 3, characterized in that , the instantaneous power admitted by each inductor (I1, I2) supplied by an inverter (31, 32) being between a minimum continuous power (PminCont ) and a maximum continuous power (PmaxCont), said mixed supply phase is implemented at least when the sum of said set power values (P1d, P2d) is greater than said maximum continuous power (PmaxCont) and at least one set power values (P1d, P2d) are less than a predetermined threshold value (Vs), greater than or equal to the value of said minimum continuous power (PminCont). Power supply method according to claim 4, characterized in that said predetermined threshold value (Vs) is substantially equal to a maximum value of the minimum continuous power (PminCont1, PminCont2) admitted by said two inductors (I1, I2). Power supply method according to one of Claims 4 or 5, characterized in that an instantaneous power supply power (Palt) in said alternating power supply phase is substantially equal to a minimum value of the maximum continuous power ( PmaxCont1, PmaxCont2) admitted by said two inductors (I1, I2). Power supply method according to one of Claims 4 to 6, characterized in that if at least one value of said reference powers (P1d, P2d) is greater than said predetermined threshold value (Vs), only one of said inductors (I1, I2) is fed during said alternating power phase. Power supply method according to one of Claims 4 to 7, characterized in that, if said target power values (P1d, P2d) are lower than said predetermined threshold value (Vs), said two inductors (I1, I2) are fed with several alternating pulses during said alternate feeding phase. Power supply method according to one of claims 1 to 8, characterized in that it comprises a preliminary step of determining said predetermined period (Tprog) as a function of the instantaneous power supply powers (P1p, P2p, Palt) of said inductors (I1, I2) during said alternating power supply phase. Feeding method according to one of claims 1 to 9, characterized in that it comprises a step of analyzing said inductors (I1, I2) associated respectively with containers to be heated, said analysis step being adapted to determining a function between the period of the switching signal (T) generated by the frequency generator (34) controlling said inverters (31, 32) and an instantaneous power (P) supplying each inductor (I1, I2), said step of analysis comprising measurements implemented for a sample of target power values assigned to said two inductors (I1, I2). Feeding method according to claim 10, characterized in that said analyzing step is carried out regularly during power supply of the two inductors (I1, I2). Power supply method according to one of Claims 1 to 11, characterized in that the instantaneous power admitted by each inductor (I1, I2) supplied by an inverter (31, 32) is between a minimum permissible continuous power (PminCont ) and a maximum allowable continuous power (PmaxCont), and in that it comprises a parameterization step of a power supply in which the sum of the reference power values (P1d, P2d) respectively associated with said two inductors (I1 , I2) is compared to said maximum allowable continuous power (PmaxCont), the power supply step comprising only an alternating power supply phase of said two inductors (I1, I2) when said sum of said set power values ( P1d, P2d) is less than the maximum allowable continuous power (PmaxCont), and the power supply stage comprising only a phase of supply in parallel of said two inductors (I1, I2) when the sum of said set power values (P1d, P2d) is greater than said permissible maximum continuous power (PmaxCont) and said target power values (P1d, P2d) are greater than a predetermined threshold value (Vs), greater than or equal to the value of the permissible minimum continuous power (PminCont). Electric cooking appliance, and in particular an induction hob (10), comprising at least two cooking hobs (F1, F2, F3, F4, F5) respectively comprising two inductors (I1, I2) connected in parallel on the same phase power supply of a power supply and respectively powered by two inverters (31, 32) controlled by the same frequency generator (34), characterized in that it comprises a processing unit (33) adapted to control at the same frequency working (F _T ) said inverters (31, 32) and to implement the power supply method according to one of claims 1 to 12.

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