EP2200397A1 - Power supply process of at least one heating element and cooking apparatus using this process - Google Patents

Abstract

The method involves supplying power to an electrical element i.e. inductor, of an electrical boiling plate (F1) of an electrical cooking apparatus e.g. induction cooktop (10), over a program time period with instantaneous supply power, in a cyclic manner. The program time period is determined based on instantaneous variation of power supplied to the electrical element during cyclic supplying of the power to the electrical element. An independent claim is also included for an electrical cooking apparatus comprising an inductor.

Description

The present invention relates to a method of supplying power to a target power value of at least one electrical element.

It also relates to a cooking appliance using this power supply method.

In general, the present invention relates to the power supply of electrical elements of the electric resistance type in an electric cooking appliance, or of the inductor type, in particular in a domestic hob using induction heating.

Conventionally, such a power supply method of an electric element, implemented to obtain a desired power value, comprises a cyclic power supply step over a program period so that the power value of on average over this program period.

During the cyclic feeding step, an instantaneous power supply is delivered to the electric element. Thus, the instantaneous power is applied to the electrical element in a repeating pattern, identical from one program period to another.

When an electrical element is powered, each power up causes a current draw on the general power supply network of the cooking appliance.

This current draw is responsible for a drop in the mains voltage due to the power line impedance.

When the instantaneous power applied during each program period of the cyclic power supply is greater than the target power value, this instantaneous power is applied only over part of the duration of the program period.

This power cut over the program period is responsible for a voltage variation on the power supply network, periodically.

However, the electrical standard EN-61000-3-3 (Flicker standard) fixes for a power supply network a maximum number of variations of the voltage per minute as a function of the amplitude of this variation.

It is known to set a program period length sufficiently long, for example equal to 15 seconds, suitable for any power deviation that may occur during the cyclic power supply of an electrical element of a cooking appliance.

However, the longer the duration of the program period relative to the desired power demand on the electrical element, the longer the period during which the electrical element is not powered.

The user thus has an unpleasant impression of irregularity in the power delivered to the electrical element.

This disadvantage is particularly amplified when the electric element is an inductor associated with a container to be heated.

In the case of a pot of water brought to a boil, the boiling intensity varies during the program period, which is badly felt by the user.

The present invention aims to provide a power supply method for solving the aforementioned drawbacks and to provide a power supply method ensuring a better regularity in the power delivered.

In this regard, the present invention relates, according to a first aspect, to a power supply method with a target power value of at least one electrical element, comprising a step of cyclically feeding a program period of said at least one element. at least one instant power supply.

According to the invention, the method comprises a preliminary step of determining a program period duration as a function of the variation of instantaneous power supplying said at least one electrical element during the cyclic feeding step.

Thus, the duration of the program period can be variable during the power supply of an electrical element, depending in particular on the instantaneous power supplying this electric element in order to better adjust the duration of the program period.

Indeed, by optimally adjusting the length of the program period away from power, it avoids oversizing the program period.

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

The user thus has a feeling of regularity in the power delivered by the electric element.

In practice, the preliminary determination step is carried out on the basis of a pre-established relationship connecting the minimum duration of a program period to a given instantaneous power deviation.

Thus, the duration of the program period is determined so as to be as short as possible for a given instantaneous power deviation supplying the electric element during the cyclic power supply step.

In practice, the predetermined relationship is determined from a standard setting a number of permissible voltage variations per minute on an electrical supply network of said at least one electrical element, as a function of the value of the voltage variation.

The supply method according to the invention finds particular application when the instantaneous power is greater than the desired power value, an operating time of said at least one electrical element during the program period being such that the average power restored by said at least one electrical element during the program period is substantially equal to the target power value.

In a practical embodiment of the invention, said at least one electrical element is an inductor powered by an inverter controlled by a frequency generator.

Indeed, when an inductor is associated with a container to be heated, the instantaneous power supplying this system can not fall below a minimum continuous power value admitted by the inductor.

This permissible minimum continuous power depends in particular on the inverter, and in particular on the operation of the IGBT switch, that is to say on its switching possibilities.

If the user-specified desired power is less than this minimum continuous power, an instantaneous power equal to the minimum continuous power is applied over a part of the program period to respect the average setpoint power value over that program period. .

By adjusting the duration of the program period taking into account the instantaneous power variation over this program period, it is possible to improve the regularity of the power delivered to the inductor over time.

According to a second aspect, the present invention relates to an electric cooking apparatus comprising means for cyclically feeding at least one electrical element over a program period to at least one instantaneous power supply, and comprising means for determining the power supply. a program period duration as a function of the instantaneous power variation supplying said at least one electrical element during the cyclic supply.

In a practical embodiment of the invention, the electric cooking apparatus is in particular an induction hob comprising two inductors connected in parallel on the same power phase of a power supply and powered respectively by two inverters controlled by a same frequency generator, comprising a processing unit adapted to implement the power supply method according to the invention.

This electric cooking appliance has characteristics and advantages similar to those described above in connection with the power supply method.

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 ;
• la figure 4 est une courbe illustrant un nombre de variations de tension par minute autorisée en fonction de la valeur de la variation de tension ;
• la figure 5 est une courbe illustrant une relation préétablie entre une durée minimale d'une période programme et un écart donné de puissance instantanée ; et
• la figure 6 est un schéma illustrant la puissance consommée sur un réseau d'alimentation électrique pendant une phase d'alimentation mixte de deux inducteurs d'un appareil de cuisson conforme à un mode de réalisation de l'invention.

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 figure 4 is a curve illustrating a number of voltage variations per minute allowed as a function of the value of the voltage variation;
• the figure 5 is a curve illustrating a pre-established relationship between a minimum duration of a program period and a given instantaneous power deviation; and
• the figure 6 is a diagram illustrating the power consumed on a power supply network during a mixed feed phase of two inductors of a cooking appliance according to an embodiment of the invention.

The present invention will be described for an electric cooking appliance consisting of an induction hob as illustrated in FIG. Figures 1 and 2 .

Of course, the present invention is not limited to an application to an induction hob but can be applied to any type of electric cooking appliance in which an electric element is supplied with power over a program period in accordance with a cyclic power supply.

Such an electric cooking appliance may be in particular a hob with radiant heating elements, or a cooking oven having one or more electric heating resistors.

In the example shown in figure 1 , the electric cooking apparatus is an induction hob 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 F1, F2, F3, F4 cooking hobs can also be identified by a 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 focus F1, F2, F3, F4, F5 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 F _T1 , F _T2 at which the transistors of the inverters 31, 32 are conductive or lock.

For this purpose, the processing unit 33 controls a frequency generator 34 adapted to control the working frequency of the inverters 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 .

The processing unit 33 is adapted to implement the power supply method which will be described below.

The processing unit 33 and the frequency generator 34 controlled by the processing unit 33 constitute cyclic feed means of the inductors I1, I2 at an instantaneous power supply.

This cyclic power supply is implemented over a program period Tprog so that the power restored by each inductor I1, I2 over the program period Tprog is substantially equal to the set power value P1d, P2d requested on each inductor I1, I2 .

According to the invention, the processing unit 33 incorporates means 33 for determining the duration of the program period Tprog, the latter depending on the variation of the instantaneous power, denoted in the following ΔP, supplying each inductor I1 , I2 during cyclic feeding.

Indeed, the Flicker standard mentioned above sets a maximum number of voltage variations per minute on a power supply network as a function of the value of this voltage variation.

We illustrated at the figure 4 a curve illustrating the permissible voltage distortion as a function of the number of voltage variations per minute.

This standard is intended to limit current calls responsible for a drop in the mains voltage when an electrical element, and here an inductor, is supplied with electrical power.

When the instantaneous power supplying an inductor I1, I2 during the program period Tprog varies, each variation ΔP corresponds to a voltage distortion.

Thus, it is possible to determine the minimum duration of the program period Tprog for a given deviation ΔP of instantaneous power from the curve illustrated in FIG. figure 5 .

In practice, for a power consumption value P on the power supply network, an effective current i is called on the power line.

où U est la valeur de la tension du réseau électrique, typiquement égale à 230 V.This current is equal to $\mathrm{i}=\frac{P}{U}$

where U is the value of the voltage of the electrical network, typically equal to 230 V.

Knowing the impedance of the electric line Z, set by the Flicker standard at 0.4 Ω, it is possible to deduce the voltage variation ΔU = Z * i.

The value of the voltage distortion ΔU / U makes it possible to know the number N of voltage distortions allowed per minute, directly deduced from the Flicker standard illustrated on the curve of the figure 4 .

By reducing the number N of voltage distortions per minute to a number n of voltage distortions per second, the minimum duration of the program period can be calculated according to the following formula: $$\mathrm{tprog}=\frac{1}{\left(2*\mathrm{not}\right)}$$

We have thus illustrated figure 5 the pre-established curve from the values of the standard illustrated in figure 4 , connecting the minimum duration of a Tprog program period (in seconds) to a given instantaneous power deviation ΔP (in watt).

Thus, for example, for a power deviation ΔP of the order of 1800 W, the duration of the program period must be at least equal to 15 seconds.

On the other hand, when the power deviation ΔP is relatively small, of the order of 500 to 600 W, a minimum program period equal to 1.2 seconds is sufficient.

Thanks to this pre-established relationship between the program period Tprog and the power deviation ΔP, the power supply method implemented in the processing unit 33 makes it possible to determine in advance a program period duration Tprog as a function of the instantaneous power variation ΔP supplying inductors I1, I2 during the cyclic supply step.

In particular, when only one of the two inductors I1, I2, and for example the inductor I1, is put into operation, if the instantaneous power P1 is greater than a desired power value P1d, the operating time of the inductor I1 during the period Tprog must be such that the average power restored P1m by the inductor I1 during the program period Tprog is substantially equal to the set power value P1d.

Indeed, for each inductor I1, I2, and more precisely for each inductor system associated with a container, a minimum continuous power admitted PminCont1, PminCont2 exists, depending in particular on the inverter 31, 32 supplying this inductor I1, I2.

The inverter 31, 32 particularly implements in operation an IGBT switch, having variable switching possibilities, thus limiting its working frequency F _T1 , F _T2 and thus the permissible power PminCont1, PminCont2 admitted by the system.

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.

A standard value can be set at 1400W.

Alternatively, the value of the permissible minimum continuous power PminCont1, PminCont2 can be determined for each inductor-receiver system as described below.

Returning to the example described above for the first inductor I1, if the setpoint power P1d is lower than the value of the minimum continuous power admitted Pmincont1 for the inductor I1, the The desired setpoint power P1d can only be satisfied by supplying the inductor I1 with an instantaneous power P1 substantially equal to the value of the minimum continuous power admitted Pmincont1 during a limited period of the program period Tprog.

In such a case, since the permissible minimum continuous power Pmincont1 is determined for inductor I1, it is possible, considering this value, to know from the pre-established relationship illustrated in FIG. figure 5 the minimum duration of the associated Tprog program period.

In practice, in order to determine the permissible minimum continuous power Pmincont1 by the inductor I1, it is possible to carry out a preliminary analysis phase during which a reference power applied to the inductor I1 is progressively reduced in order to determine the minimum value of this reference power, below which an Icom1 switching current is no longer present at the level of the inverter 31 supplying the inductor I1.

Of course, the same method can be implemented if only the second inductor I2 is operated at an instantaneous power P2, greater than the desired power P2d requested by the user.

When the two inductors I1, I2 are energized during a cyclic supply step, the duration of the program period Tprog must be determined as a function of the variations ΔP of instantaneous power P1, P2 supplying these two inductors I1, I2.

In certain types of cyclic power supply, the inductors I1, I2 can be powered alternately at an instantaneous power P1, P2 identical, equal to an alternating power value Palt.

When the two inductors I1, I2 are alternately energized at an identical instantaneous power Palt, permanently over the program period Tprog, the power consumption seen from the electrical network is constant in time so that the length of the program period Tprog is not important.

It is possible to determine a program period Tprog of minimum duration, fixed for example at 1.2 seconds.

We also illustrated at the figure 6 another type of cyclic supply of the two inductors I1, I2 comprising, on each program period Tprog, a fixed supply phase composed of a phase of supply in parallel of the two inductors I1, I2 and a phase of alternating power supply of the two inductors I1, I2.

In the parallel supply phase, the two inductors I1, I2 are powered respectively by the two inverters 31, 32 controlled at the same working frequency F _T.

This type of operation has the advantage of avoiding the generation of noise interference between the inductors and annoying noise for the user.

Although controlled at the same working frequency F _T , the instantaneous power P1, P2 on each inductor I1, I2 during the parallel supply phase, noted respectively P1 p, P2p, is not necessarily identical, depending in particular on the system constituted by the inductor and the container placed vis-à-vis.

However, the sum of the instantaneous power supply powers P1 p, P2p of the two inductors I1, I2 during the parallel supply phase is equal to the maximum power PmaxPhase delivered by the power phase of the power supply, and here equal at 3600 W.

During the alternating power supply phase, the two inductors I1, I2 are powered at the same power supply power Palt.

As well illustrated at the figure 6 , the duration of the program period Tprog is determined from the difference ΔP between the sum of the instantaneous powers P1p + P2p of the two inductors I1, I2 during the phase of parallel supply and the instantaneous power supply Palt of the two inductors I1, I2 during the alternating power phase.

The knowledge of this difference ΔP makes it possible from the pre-established relationship illustrated in FIG. figure 5 to determine the minimum duration of the Tprog program period that can be implemented during the cyclic power supply step with a mixed feed phase of the two inductors I1, I2.

Here, the variation of instantaneous power ΔP over the program period Tprog is equal to the difference between the maximum power PmaxPhase delivered by the power phase of the power supply and the instantaneous power supply power Palt of the two inductors I1, I2 during the alternating power phase: $$\mathrm{.DELTA.P}=\mathrm{PmaxPhase}-\mathrm{Palt}$$

It is thus possible to limit the length of the program period Tprog to a minimum duration sufficient to allow the variation of instantaneous power ΔP during the cyclic supply of the inductors I1, I2, without contravening the Flicker standard.

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

In particular, any type of cyclic supply of one or more inductors can be implemented, the duration of the program period Tprog being determined from the instantaneous power deviation existing during this cyclic supply.

Claims (9)

Power supply method at a target power value (P1d, P2d) of at least one electrical element (I1, I2), comprising a cyclic supply step over a program period (Tprog) of said at least one element electrical (I1, I2) to at least one instantaneous power supply (P1, P2, P1p, P2p, Palt) characterized in that it comprises a preliminary step of determining a program period duration (Tprog) according to the instantaneous power variation (ΔP) supplying said at least one electrical element (I1, I2) during said cyclic supply step. Power supply method according to claim 1, characterized in that said preliminary determination step is implemented from a predetermined relationship connecting the minimum duration of a program period (Tprog) to a given instantaneous power deviation ΔP ). Feeding method according to claim 2, characterized in that said predetermined relationship is determined from a standard setting a number of permissible voltage variations per minute on an electrical supply network of said at least one electrical element (I1 , I2), depending on the value of the voltage variation. Power supply method according to one of claims 1 to 3, characterized in that said at least one electrical element is an inductor (I1, I2) powered by an inverter (31, 32) controlled by a frequency generator (34). Feeding method according to claim 4, adapted to feed two inductors (I1, I2) connected in parallel on the same power phase of a power supply, characterized in that it comprises a preliminary step of determining a program period duration (Tprog) as a function of the variations (ΔP) of instantaneous power (P1p, P2p, Palt) supplying said two inductors (I1, I2) during a cyclic power supply step. Power supply method according to claim 5, characterized in that said cyclic power supply step comprises on each program period (Tprog) a mixed power supply phase composed of a parallel supply phase of said two inductors (I1, I2), wherein said two inductors (I1, I2) are respectively powered by two inverters (31, 32) controlled at the same working frequency (F _T ), and an alternating supply phase of said two inductors ( I1, I2), the duration of said program period (Tprog) being determined as a function of the difference (ΔP) between the sum of the instantaneous powers of supply (P1p, P2p) of said two inductors (I1, I2) during said phase parallel supply and the instantaneous power supply (Palt) of said two inductors (I1, I2) during said alternating power phase. Power supply method according to claim 6, characterized in that the instantaneous power variation (ΔP) is equal to the difference between the maximum power (PmaxPhase) delivered by said power phase of the power supply and the instantaneous power of supplying (Palt) said two inductors (I1, I2) during said alternating power supply phase. Electric cooking apparatus comprising means for cyclically feeding (33, 34) at least one electrical element (I1, I2) over a program period (Tprog) to at least one instantaneous power supply (P1, P2, P1 p, P2p, Palt), characterized in that it comprises means for preliminary determination (33) of a program period duration (Tprog) as a function of the instantaneous power variation (ΔP) supplying the said at least one electrical element (I1, I2) during cyclic feeding. Electric cooking appliance according to claim 8, and in particular induction hob (10), comprising 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 processing unit (33) adapted to implement the feeding method according to one of claims 1 to 7.

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