EP2200399A1 - Method for supplying power to at least one induction unit and cooking device implementing said method - Google Patents

Abstract

The method involves analyzing an inductor associated with a container to be heated to determine a function between the instantaneous power supplied to the inductor and a cutting period of a signal generated by a frequency generator controlling an inverter. The inductor analysis is carried out by measurements implemented for a sample of setpoint power values assigned to the inductor, where the sample of setpoint power values includes minimum setpoint power value and a maximum setpoint power value. 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 at least one inductor.

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

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, this type of regulation requires access to the value of the average current flowing in the resonant circuit comprising the inductor and the container.

The object of the present invention is to solve the aforementioned drawbacks and to propose a power supply method of at least one inductor making it possible to know the value of the power restored by this inductor without the measurement of a mean electric current flowing in this inductor.

The present invention thus aims in a first aspect a power supply method of at least one inductor associated with a container to be heated and powered by an inverter controlled by a frequency generator.

According to the invention, the feed method comprises a step of analyzing at least one inductor associated with the container to be heated, the analysis step being adapted to determine a function between the instantaneous power supplying the at least one inductor and the period of the chopper signal generated by the frequency generator controlling said at least one inverter, said analyzing step comprising measurements implemented for a sample of target power values allocated to said at least one inductor.

Thus, thanks to an analysis of the behavior of the resonant system formed by the inductor associated with a container to be heated, it is possible to predict the behavior of the system, that is to say the instantaneous power at each inductor according to the working frequency applied to each inverter.

Preferably, said analysis phase is implemented before a power supply step of said at least one inductor to a selected target power value.

According to a preferred characteristic of the invention, the analysis step is carried out regularly during power supply of said at least one inductor to a selected target power value.

By renewing the analysis step regularly during the power supply of an inductor, it is possible to take into account the modification of the behavior of the resonant circuit, and in particular of the temperature drift of the inductive load in the system constituted by by the inductor and the container to be heated, or the position of the container relative to the inductor.

In practice, the sample of target power values comprises at least a minimum reference power value corresponding to a minimum continuous power value admitted by the inductor and a maximum target power value corresponding to a maximum power value. continuous admitted by the inductor.

It is thus possible to know the behavior of the inductor-container system and the limits of the operating range.

Advantageously, the sample further comprises at least one intermediate setpoint power value between the minimum setpoint power value and the maximum setpoint power value.

In practice, the measurements implemented for a sample of target power values are adapted to define an affine function connecting the instantaneous power supplying said at least one inductor and the switching period generated by the frequency generator controlling said at least one inverter.

It is possible to determine the affine function connecting the instantaneous power supplying the inductor and the period of the switching signal of the associated inverter, for example by a conventional calculation method for approximating a line from a sampling of values.

In a practical embodiment of the invention, for powering two inductors connected in parallel on the same power phase of a power supply and powered respectively by two Inverters controlled by the same frequency generator, the supply method comprises the analysis step implemented on the inductors associated respectively with containers to be heated, and comprises a phase of supply in parallel of the two inductors, in which the two inductors are fed respectively by the two inverters controlled at the same working frequency, the working frequency being determined from the functions determined during the analysis step, between the switching period generated by the frequency generator commander the two inverters and the instantaneous power supplying each inductor, the sum of the instantaneous powers supplying each inductor during the parallel supply phase being equal to the maximum power supplied by the power phase of the power supply.

By mounting the inductors in parallel on the same power phase of a power supply and by supplying these inductors with inverters controlled at the same working frequency by means of a single frequency generator, the generation of interference between neighboring inductors, which can create audible and annoying noises for the user.

Thanks to the analysis step, when the two inductors operate simultaneously, it is possible to provide the power distribution between these two inductors connected in parallel on the same power phase.

It is thus possible to optimize the power distribution as a function of the working frequency on each inductor fed simultaneously from the same power phase of the power supply.

In practice, at the analysis step, if for at least one of the two inductors, the instantaneous power supplied to the inductor measured for a minimum reference power value and the instantaneous power supplied to the inductor measured for a power value. maximum setpoint are close to each other, the power supply method comprises only a phase of alternating power supply of the two inductors.

According to a second aspect, the present invention relates to an electric cooking appliance, and in particular an induction hob, comprising at least two cooking hobs respectively comprising two inductors connected in parallel on the same power phase of a power supply and fed respectively by two inverters.

According to the invention, the electric cooking appliance comprises a processing unit adapted to control the inverters at the same operating frequency and to implement the power supply method of the two inductors according to the present invention.

This electric 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 ;
• la figure 4 est un algorithme illustrant un procédé d'alimentation en puissance ;
• la figure 5 est un algorithme illustrant une étape d'analyse du procédé d'alimentation en puissance de la figure 4 ; et
• la figure 6 illustre des courbes montrant la variation de la puissance en fonction de la période associée à la fréquence de travail.

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 an algorithm illustrating a power supply process;
• the figure 5 is an algorithm illustrating a step of analysis of the power supply process of the figure 4 ; and
• the figure 6 illustrates curves showing the variation of the power as a function of the period associated with the working frequency.

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 control is managed by a processing unit 33. This processing unit 33 is adapted to control a frequency generator 34.

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.

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 4 to 6 the power supply method of an inductor according to the invention.

This algorithm will be described for an inductor I, this inductor I being able to be one or the other of the inductors I1, I2 described previously with reference to FIG. figure 3 .

In general, the power supply method of the inductor I is used to heat a container placed on this inductor I to a desired power Pd requested by the user.

After an acquisition step E40 of a reference power Pd, the power supply method comprises a step E41 of container detection placed vis-à-vis the inductor I.

The means used in an induction table to detect the presence of a container vis-à-vis an inductor are well known and do not need to be described in detail here.

In particular, this container detection can be implemented from the analysis by the processing unit 33 of a current flowing in the inductor I.

A test step E42 makes it possible to determine the presence or absence of a container.

If not, an incrementing step E43 of a counter and comparing E44 of the value of the counter with a limit value VI makes it possible, in a conventional manner, to repeat the steps of detecting the container E41 and the test E42 after the flow. a predetermined period of time.

If at the end of the test step E42, a container is detected, the power supply method comprises a step of analyzing the inductor I associated with the container to be heated to determine a function connecting the instantaneous power. P supplying the inductor I and the period of the switching signal T generated by the frequency generator 34 controlling the inverters 31, 32.

This analysis step E45 is carried out before a power supply step E46 of the inductor I to the selected set power value Pd.

Thanks to the function determined during the analysis step E45, the power supply of the inductor I to a reference power Pd is implemented by determining the period of the switching signal T generated by the frequency generator 34 from the function connecting this period of the switching signal T to the instantaneous power P supplying the inductor I.

Preferably, the analysis step E45 is carried out regularly during the power supply of the inductor I to the selected set power value Pd.

This periodic implementation of the analysis step E45 can be conveniently managed by a counter.

After a first analysis step E45 implemented before the supply step E46, an incrementation step E47 of a counter is implemented.

A test step E48 makes it possible to check whether the value of this counter has reached a second limit value VI 'or not.

If not, the incrementing step E47 is repeated.

By way of non-limiting example, the power supply method is adapted to implement an analysis step E45 every two minutes of operation of the inductor-container system.

It will be noted in particular that when the inductor I is powered alternately over a period of time, the analysis step E45 is carried out periodically as a function of the cumulative operating time of the inductor-container system.

Thus, by way of example, if the inductor I operates alternately 50% of the real time, the analysis step E45 in the preceding example will be carried out periodically every 4 minutes.

When at the end of the test step E48, the value of the counter has reached the second limit value VI ', the analysis step E45 is repeated.

The analysis step E45 will now be described in more detail, in particular with reference to the figures 5 and 6 .

The analysis step E45 first comprises a preliminary phase E45a in which the switching period T generated by the generator of frequency 34 controlling one of the inverters 31, 32 to supply the inductor I is gradually increased until the appearance of a switching current Icom across the inverter 31, 32.

This preliminary phase E45a aims to know the relationship between the value of the instantaneous power P supplying the inductor I and a measurement of the peak current Imax.

This solution has the advantage of allowing thereafter, by a measurement of the peak current Imax flowing in each inverter 31, 32, to deduce the instantaneous power P supplying the inductor I.

Of course, this preliminary phase E45a could be eliminated as soon as the processing unit 33 is adapted to know the value of the instantaneous power P supplying the inductor I from any other type of conventional measuring means.

Returning to the preliminary phase E45a, it is recalled that the behavior of the inverter 31, 32 depends on the type of container used, so that the value of the communication current Icom and the value of the peak current Imax depend in particular on the type of container used.

The containers that can be used vary in terms of materials (aluminum, enamelled sheet, variable type stainless steel, cast iron, aluminum combined with stainless steel sheet).

Moreover, the dimensions of the usable containers may also be variable, and for example for cylindrical containers, be between 12 and 24 cm in diameter.

Thus analyzing for various types and dimensions of containers the appearance of the Icom switching current and the value of the peak current Imax and the relation existing between the instantaneous power P and the value of the peak current Imax flowing in the inductor I, it is possible to experimentally determine coefficients that uniquely link these values. These coefficients are determined in the factory and stored in the processing unit 33.

During the preliminary phase E45a, by measuring the switching current Icom and the peak current Imax flowing in the inductor I, it is possible to find unambiguously the instantaneous power P feeding the inductor-container system from the stored coefficients.

Once the preliminary phase E45a has been performed, the analysis step E45 comprises an analysis phase E45b adapted to determine a function between the instantaneous power P supplying the inductor I and the switching period T generated by the frequency generator 34. .

It will be noted that in this analysis phase E45b, the value of the instantaneous power P supplying the inductor I can be deduced directly from the measurement of the peak current Imax flowing in the inductor I by virtue of the relationship connecting these two values identified during of the preliminary phase E45a of the analysis step E45.

The analysis phase E45b for determining the curve connecting the instantaneous power P supplying the inductor-container system to the switching period T makes it possible to anticipate the behavior of this inductor-container system as a function of the switching period T applied to the inverters. 31, 32.

The supply method firstly comprises an analysis phase of the inductor-container system for nominal power values comprising at least a minimum reference power value Pmin corresponding to a minimum continuous power value PminCont accepted by the controller. inductor I and a maximum target power value Pmax corresponding to a maximum continuous power value PmaxCont accepted by the inductor I.

The minimum continuous power allowed PminCont on each inductor I depends in particular on the inverter 31, 32 supplying this inductor I, and in particular the operation of the IGBT switch, that is to say, its switching possibilities.

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

Thus, in a first sampling step E51, the value of the minimum reference power Pmin is set to a standard minimum continuous power value admitted PminCont, here equal to 1400 W.

A test step E52 is adapted to check if the minimum reference power Pmin is reached.

If not, a delay step E53 is implemented to wait for a new sector period to achieve the servocontrol by the processing unit 33 at the working frequency F _T1 , F _T2 controlling the inverter 31, 32 supplying the inductor I.

The mains period corresponds to the periodicity of the alternating current supplying the electric cooking apparatus.

In the test step E52, the value of the instantaneous power P supplying the inductor-container system is measured by virtue of the value of the peak current Imax flowing in the inductor I.

When the value of the instantaneous power P reaches the minimum target power value Pmin, a test step E54 is adapted to check whether the switching current Icom is still present at the inverter 31, supplying the inductor I .

If so, a setting step E55 is adapted to decrease the minimum setpoint power value Pmin and steps E52 to E54 are repeated.

At the end of the test step E54, if the switching current Icom is no longer present, that is to say that the diode of the inverter 31, 32 no longer drives, it is considered that the value minimum setpoint power Pmin is equal to the minimum allowable continuous power value PminCont below which the inductor-container system can not operate.

A storage step E56 is then adapted to store the torque of the minimum reference power Pmin associated with the period of the switching signal Tmin.

A second sampling step E57 is carried out for a maximum target power value Pmax corresponding to the maximum continuous power value admitted PmaxCont by the inductor I.

This permissible maximum continuous power PmaxCont also depends on the components of the inverters 31, 32, and in particular the IGBT switch.

For example, this maximum continuous power admitted PmaxCont may be of the order of 2300 W.

A delay step E58 is implemented to wait for a new mains period to implement the servocontrol at the level of the processing unit 33 at the maximum setpoint power Pmax.

A test step E59 is adapted to verify that the period of the switching signal T applied to the inverter 31, 32 is well below a maximum value Tdmax.

In particular, the period of the switching signal T must be in a range of predetermined periods, between Tdmin and Tdmax.

By way of nonlimiting example, the minimum period Tdmin may be substantially equal to 1/38 kHz and the maximum period Tdmax may be substantially equal to 1/28 kHz.

If not, a safety step E60 is implemented, in particular to verify that the maximum permissible values on the peak current Imax are not reached.

Similarly, in the negative, it is verified in a test step E61 by measuring the peak current Imax flowing in the inductor I, and deduction of the instantaneous power P feeding the system, if the maximum setpoint value Pmax is reached.

If not, the delay step E58 is repeated, as are the steps E59 to E61.

If the value of the maximum period Tdmax is reached at the end of the test step E59, or if a safety limit is reached at the security step E60, or if the maximum target power Pmax is reached at the result of the test step E61, a storage step E62 is adapted to store the maximum setpoint power Pmax and the period of the associated switching signal Tmax.

These steps E51 to E62 of the analysis step E45 make it possible to determine the operating limits of the inductor-container system, and in particular to know the power range P that can supply this system.

At the end of the storage step E62, a comparison step E63 makes it possible to check whether the maximum power value Pmax and the minimum power value Pmin determined previously are close to each other.

In practice, the difference Pmax-Pmin is compared with a threshold value X, for example equal to 200 W.

If so, the container associated with the inductor I has a low instantaneous power dynamic P and the analysis step E45b is complete.

This characterization of the inductor-container system has repercussions on the possible type of power supply of this system as will be described later.

As well illustrated at the figure 6 , the function connecting the instantaneous power P supplying the inductor I and the period of the clipping signal T generated by the frequency generator 34 controlling the inverter 31, 32 is here, by way of nonlimiting example, an affine function, represented by a straight line.

The determination of the pairs Pmin, Tmin and Pmax, Tmax in principle makes it possible to determine such an affine function connecting the instantaneous power P and the period of the switching signal T.

However, in the negative at the end of the comparison step E63, in order to obtain a better reliability of this analysis step E45, it further comprises measurements implemented for a sample of nominal power values. comprising, in addition to the minimum setpoint power value Pmin and the maximum target power value Pmax, at least one intermediate setpoint power value between the minimum setpoint power value Pmin and the maximum setpoint power value Pmax.

In this embodiment, a calculation step E65 makes it possible to determine two intermediate setpoint power values Pi1, Pi2.

et $\mathrm{Pi}2=P\min +2\times \frac{P\max -P\min }{3}$

For example : $\mathrm{pi}1=P\min +\frac{P\max -P\min }{3}$

and $\mathrm{pi}2=P\min +2\times \frac{P\max -P\min }{3}$

Knowledge of the measurements of the instantaneous power P and the period of the switching signal T for a sample of four values makes it possible to reliably determine the variation line between the instantaneous power P and the period of the switching signal T.

Any method of determining such a straight line, and for example linear regression, can be applied.

In practice, a sampling step E66 makes it possible to set the target power value to a first intermediate command power value Pi1.

A timing step E67 is adapted to wait for a new mains period to implement the servocontrol at the level of the control of the inverter 31, 32.

A test step E68 is adapted as previously to check if the intermediate setpoint power value Pi1 is reached.

If not, the timing steps E67 and E68 are repeated.

If at the end of the test step E68, the power P measured using the value of the peak current Imax flowing in the inductor I, is equal to the intermediate reference power Pi1, a storage step E69 is adapted to memorize the instantaneous power pair Pi1 and the period of the associated switching signal Ti1.

A sampling period E70 then makes it possible to set the value of the reference power to the second intermediate control power value Pi2, analogous timing steps E71 and of test E72 being implemented in a similar manner to the timer steps E67. and E68 test.

If at the end of the test step E72, the value of the instantaneous power P reaches the value of the second intermediate command power Pi2, a storage step E73 is adapted to memorize the power pair Pi2 and the period of the associated clipping signal Ti2.

A calculation step E74 makes it possible to determine the parameters A and B of the affine function connecting the instantaneous power P to the period of the switching signal T according to the formula: $$\mathrm{P}\mathrm{=}\mathrm{AT}\mathrm{\times }\mathrm{T}\mathrm{+}\mathrm{B}$$

We illustrated at the figure 6 examples of affine functions connecting the instantaneous power supplying each inductor-container system and the period of the switching signal T, as a function of the type of containers R1 to R6.

The analysis phase E45b is then completed for this inductor-container system when the affine function is thus determined.

Of course, the analysis step E45 is carried out independently on the different inductor-container systems when a container is detected vis-à-vis an inductor I of the electric cooking apparatus.

Although the curves have been illustrated over large power ranges, in operation, the instantaneous power P admitted on each inductor I must remain between the values of minimum continuous power PminCont and maximum continuous power PmaxCont determined as indicated above.

The feed method described above can be adapted to power two power P1d, P2d two inductors I1, I2 connected in parallel on the same power phase and powered by the two inverters 31, 32 controlled by the generator of frequency 34. An analysis step E45 is then carried out on the two inductor systems I1, I2 associated respectively with containers to be heated.

This power supply method can then comprise a phase of supply in parallel of the two inductors I1, I2 in which the two inductors I1, I2 are powered respectively by the two inverters 31, 32 controlled at the same working frequency F _T = F _T1 = F _T2 .

As well illustrated at the figure 6 , the analysis step E45 makes it possible to determine whether two inductor-receptacle systems admit operation in parallel, that is to say if it is possible to control at the same working frequency F _T , and therefore to a same period of the switching signal T equal to T _p , two inverters 31, 32 so as to obtain in parallel two instantaneous powers P1 p, P2p included in the operating range of each inductor-container system.

In particular, if at the end of the step E63 of the analysis step E45, the maximum power values Pmax and minimum Pmin are very close to each other, that is to say that the curve shown in 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 receptacles, the working frequency F _T is determined from the functions determined during the analysis step E45 described above, connecting the period of the switching signal T _p generated by the frequency generator 34 controlling the two inverters 31, 32 and the instantaneous power P1p, P2p supplying each inductor I1, I2, the sum of the instantaneous powers P1p, P2p supplying each inductor I1, I2 during the parallel being equal to the maximum power provided by the power phase of the power supply.

Thus, 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.

When the two inductors I1, I2 are supplied in parallel, that is to say simultaneously, the sum of the instantaneous powers P1 p, P2p distributed on each inductor I1, I2 corresponds to the power absorbed on the network: $$\mathrm{P}1\mathrm{p}+\mathrm{P}2\mathrm{p}=3600\mathrm{W}\mathrm{.}$$

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 a period of the switching signal T _p , is identical.

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

With the analysis step E45 described above, the linear relationship connecting the instantaneous power P1p, P2p for each inductor I1, I2 to the period of the chopping signal T _{p is known} according to the following equations: $$\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{=}\mathrm{AT}\mathrm{1}\times {\mathrm{T}}_{\mathrm{p}}\mathrm{+}\mathrm{B}\mathrm{1}$$

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

It is thus possible to calculate the value of the period of the switching signal T _p by knowing the coefficients A1, B1, A2, B2 determined during the analysis step E45 of the containers.

The period of the switching signal T _{p is} then compared during parallel operation to the minimum value Tmin allowed for the period of the switching signal T and to the maximum value T max allowed for the period of the switching signal T.

If the period of the switching signal T _p in parallel is not greater than the minimum permitted value Tmin and less than the maximum allowed value Tmax, the parallel mode can not be implemented and, alternately, a power supply phase. of the two inductors I1, I2 is implemented.

However, this alternating power supply will not achieve the desired power P1d, P2d on each inductor I1, I2.

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

On the other hand, if the period of the switching signal T _p in parallel is between the minimum value Tmin and the maximum value Tmax allowed for the period of the switching signal T, the instantaneous power P1p is determined for the two inductors I1, I2. P2p on this inductor I1, I2 as a function of the characterization of the container described above: $$\mathrm{P}\mathrm{1}\mathrm{p}\mathrm{=}\mathrm{AT}\mathrm{1}\times {\mathrm{T}}_{\mathrm{p}}\mathrm{+}\mathrm{B}\mathrm{1.}$$

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

The knowledge of the instantaneous powers P1p, P2p supplying each inductor I1, I2 operating in parallel from the same period the switching signal T _p makes it possible to manage, over a program period Tprog, the average power restored P1m, P2m at each container.

The program period Tprog is a succession of sector periods.

The electrical standard EN-61000-3-3 (Flicker standard) fixes for the power supply network a maximum number of variations of the voltage per minute according to the amplitude of this variation.

According to this electrical standard, the number of sector periods that make up the Tprog program period is determined according to the power difference existing over the Tprog program period, which must remain in compliance with the Flicker standard.

We can consider a Tprog program period long enough, for example equal to fifteen seconds, likely to be suitable for a large power deviation of the order of 1800 Watts.

The average power P1 m, P2m restored during the program period Tprog by the inductors I1, I2 associated respectively with containers to be heated is determined by multiplying the duration Np of the parallel supply phase by the value of the instantaneous powers P1p, P2p .

The duration Np of the parallel supply phase is determined so that the average powers P1m, P2m delivered by the inductors I1, I2 are close to the values of reference powers P1d, P2d respectively associated with the two inductors I1, I2 and requested. by the user.

Returning to 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 T _p , at least one of the instantaneous powers P1p, P2p may 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.

The present invention thus makes it possible to characterize an inductor-container system and to know the instantaneous power P supplying this system as a function of the period of the switching signal controlling the associated inverter.

Although the foregoing description has been illustrated for a control structure comprising a single IGBT switch, it can also be implemented on a half-bridge feed structure or a complete bridge assembly of the inductors.

Thanks to this characterization, it is possible to know the power behavior of two inductors I1, I2 operating in parallel and controlled by the same period of the switching signal T _p .

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

In particular, the function connecting the instantaneous power P and the period of the switching signal T may be arbitrary, the invention not being limited to an affine function.

Claims (10)

Power supply method of at least one inductor (I, I1, I2) associated with a heating vessel (R1-R6) and supplied by an inverter (31, 32) controlled by a frequency generator (34), characterized in that it comprises an analysis step (E45) of said at least one inductor (I1, I2) associated with said container to be heated (R1-R6), said analyzing step (E45) being adapted to determine a function between the instantaneous power (P) feeding said at least one inductor (I) and the period of the chopper signal (T) generated by said frequency generator (34) controlling said inverter (31, 32), said analyzing step ( E45) comprising measurements implemented for a sample of nominal power values (Pmin, Pmax, Pi1, Pi2) allocated to said at least one inductor (I, I1, I2). Feeding method according to claim 1, characterized in that said analyzing step (E45) is carried out before a step of power supply (E46) of said at least one inductor (I, I1, I2) to a selected target power value (Pd, P1d, P2d). Feeding method according to one of claims 1 or 2, characterized in that said analyzing step (E45) is carried out regularly during power supply of said at least one inductor (I, I1, I2) to a selected setpoint power value (Pd, P1d, P2d). Power supply method according to one of Claims 1 to 3, characterized in that the sample of target power values comprises at least one minimum reference power value (Pmin) corresponding to a minimum continuous power value admitted. (PminCont) by said inductor (I, I1, I2) and a maximum target power value (Pmax) corresponding to a permissible maximum continuous power value (PmaxCont) by said inductor (I, I1, I2). Feeding method according to claim 4, characterized in that the sample further comprises at least one intermediate target power value (Pi1, Pi2) lying between said power value of minimum setpoint (Pmin) and said maximum setpoint power value (Pmax). Power supply method according to one of claims 1 to 5, characterized in that said measurements implemented for a sample of desired power values (Pmin, Pmax, Pi1, Pi2) are adapted to define an affine function connecting the instantaneous power (P) supplying said at least one inductor (I, I1, I2) and the period of the chopper signal (T) generated by the frequency generator (34) controlling said at least one inverter (31, 32). Feeding method according to one of claims 1 to 6, characterized in that the analyzing step (E45) further comprises a preliminary phase (E45a) in which the period of the cutting signal (T) generated by the frequency generator (34) controlling said at least one inverter (31, 32) is progressively increased until a switching current (Icom) appears at the terminals of said at least one inverter (31, 32). Power supply method according to one of Claims 1 to 7, for supplying power to two inductors (I1, I2) connected in parallel on the same power phase of a power supply and supplied respectively by two inverters (31, 32). ) controlled by the same frequency generator (34), characterized in that it comprises said analysis step (E45) carried out on said inductors (I1, I2) respectively associated with containers to be heated (R1-R6) , and in that it comprises a phase of supply in parallel of said two inductors (I1, I2), in which said two inductors (I1, I2) are respectively fed by said two inverters (31, 32) controlled at the same working frequency (F _T ), said working frequency (F _T ) being determined from said functions determined during said analyzing step (E45) between the period of the switching signal (T) generated by the frequency generator ( 34) c ommandant said two inverters (31, 32) and the instantaneous power (P) supplying each inductor (I1, I2), the sum of the instantaneous powers (P1p, P2p) supplying each inductor (I1, I2) during the power supply phase. parallel being equal to the maximum power supplied by said power phase of the power supply. Power supply method according to claim 8, characterized in that in said analyzing step (E45), if for at least one of said two inductors (I1, I2), a minimum desired power value (Pmin) and a maximum power of reference value (Pmax) are close to each other, the power supply method comprises only a phase of alternating supply of said two inductors (I1, I2). 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 powered respectively by two inverters (31, 32), characterized in that it comprises a processing unit (33) adapted to control at a same working frequency (F _T ) said inverters (31 , 32) and to implement the power supply method of the two inductors (I1, I2) according to one of claims 1 to 9.

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