EP2445308A1 - Method for testing periodic control signals, in particular for an induction cooktop - Google Patents

Abstract

The method involves periodically implementing a synchronization step at a predetermined instant (t3) of predefined periodic timing signal (Sc). Periodic control signals (S1-S3) are stopped or started during the synchronization step, where the control signals have different frequencies. One of the control signals is stopped and started during the synchronization step implemented at the predetermined instant of following period (T3) succeeding to given periods (T1, T2) of the timing signal when the control signal is activated during one of the given periods of the timing signal. An independent claim is also included for an induction cook top, comprising inductors distributed under a cooking surface according a bi-dimensional frame.

Description

The present invention relates to a method for controlling periodic control signals implemented for the control in operation of inductors of an induction hob.

It also relates to an induction hob adapted to implement the control method.

In general, the present invention applies to the field of induction cooking, and more specifically to a hob comprising several heating elements formed by inductors.

It finds particular application, but not limited to, in an induction hob comprising a large number of inductors distributed under a cooking plane in a two-dimensional grid.

Such a hob is particularly described in the document FR 2 863 039 and allows the heating of one or more containers placed on the hob without a predefined zone for the cooking hobs.

In order to ensure the independent supply of each inductor in such a hob, the inductors are fed respectively by control blocks, themselves controlled respectively by periodic control signals.

These periodic control signals are particularly adapted to control electronic power switches associated with each inductor. By varying the frequency of these periodic control signals and / or alternating the periods of activity and the rest periods of the electronic power switches, the power delivered by each inductor to a container can be set to a set value.

In traditional hobs, a control unit is used to control the periodic control signals addressed respectively to the control units of inductors of the hob, in particular to adjust the power delivered to the containers.

In particular, this control unit performs certain synchronized operations taking into account the periodic signal from the AC voltage signal of the electrical supply network of the hob.

Referring to the figure 1 the sinusoidal AC voltage signal of the supply network Ss and a periodic timing signal Sc are illustrated on the time axis.

Here, this periodic timing signal Sc is a 0/1 "square" signal, each edge of which corresponds to a 0 volt change in the AC voltage signal Ss.

In the state of the art, the control unit of the periodic control signals is adapted to make modifications to these periodic control signals S1, S2.

As illustrated in figure 1 the periodic control signals can in particular be stopped or started at a predetermined time of the periodic timing signal Sc.

For this, the control unit controls the periodic control signals S1, S2 independently, by looping on the various periodic control signals to be controlled.

Thus, the periodic control signals S1, S2 are started, stopped, modified or maintained without modification, without taking into account the operations performed on the other periodic control signals.

So, in the example shown in the figure 1 a first periodic control signal S1 is stopped at the beginning of a second period T2 and then started at the beginning of a third period T3 while a second periodic control signal S2 is kept permanently active on the different periods T1 , T2, T3 successive periodic timing signal Sc.

However, this type of control of the prior art has the disadvantage of introducing a variable phase difference between the periodic control, from one period to another of the periodic timing signal Sc.

This variable phase difference, symbolized by the interval Δ separating the respective rising edges of two periodic control signals S1, S2, is visible for example in FIG. figure 1 between the first period T1 and the third period T3 of the periodic timing signal.

However, this variation in the phase shift of the periodic control signals intended to control the operation of inductors located close to each other in a hob induces a difference in the coupling result between these inductors, leading to different power consumption on each period T1, T2, T3 of the periodic timing signal Sc.

Similarly, as illustrated in figure 2 when the parameters of the periodic control signals S1, S2 remain identical from a first period T1 of a periodic timing signal Sc to a second period T2 of the periodic timing signal Sc, and when these periodic control signals S1, S2 have a difference in their operating parameters, and for example in their frequency, there is a relative phase shift d between these periodic control signals S1, S2, not constant from one period to another of the periodic timing signal Sc.

This variation of the relative phase shift d also corresponds to a modification of the phase between the periodic control signals S1, S2 over each period of the periodic timing signal Sc.

As previously, the variation of the phase shift between the periodic control signals S1, S2 leads to a difference in the coupling result between adjacent inductors whose operation is controlled from these periodic control signals S1, S2.

As before, the power consumed by each inductor is different at each period of the periodic timing signal Sc.

These power fluctuations consumed over time cause instability of the system.

They can be particularly poorly perceived by the user who finds a variable intensity of the boiling water contained in one or more containers placed on the hob.

There is known a control circuit of a cooking device described in the document EP 2 034 800 , comprising several heating units and a fireplace forming unit provided to form a home grouping several heating units according to the position of a dish.

This cooking device comprises a synchronization unit provided for synchronizing together at least two cooking hobs.

The object of the present invention is to propose a method for controlling periodic control signals making it possible to obtain a better stability in the power delivered by inductors of a hob.

To this end, the present invention relates, in a first aspect, to a method for controlling periodic control signals addressed respectively to control units of inductors of a hob.

According to the invention, this control method comprises a synchronization step periodically implemented at a predetermined time of a predefined periodic timing signal, the periodic control signals being stopped and / or started during the synchronization step, and the periodic control signals having a different frequency.

Thus, all the periodic control signals are stopped and / or started synchronously, to generate a complete control cycle on each period.

This gives a repetition of the pattern of each periodic control signal on each period of the periodic timing signal.

Thus, the phase of the periodic control signals is controlled so that the phase difference between the periodic control signals is identical from one period to another of the predefined periodic timing signal.

The periodic control signals can thus be controlled independently and have a different frequency, the synchronization step for controlling the phase difference between the different periodic control signals.

This mastering of the phase of all the periodic control signals makes it possible to ensure a stability of the power consumed by each inductor whose operation is controlled from these periodic control signals.

In practice, the periodic control signals are reset during each synchronization step.

In particular, when one of the periodic control signals is activated during a given period of the predefined periodic timing signal, the periodic control signal is stopped and restarted during the synchronization step implemented at said predetermined instant of a next period succeeding the given period of the predefined periodic timing signal.

By stopping and then restarting at the predetermined time, during each synchronization step, all the periodic control signals, the periodic control signals execute a complete cycle on each period of the predefined periodic timing signal.

In a practical embodiment of the invention, the predefined periodic timing signal corresponds to the AC voltage signal of the electrical supply network of the hob.

The present invention also relates, according to a second aspect, to an induction hob comprising a plurality of inductors distributed under a cooking plane in a two-dimensional grid, the inductors being fed respectively by control blocks controlled respectively by periodic control signals.

This induction hob includes a control unit adapted to implement the control method described above.

In particular, the periodic control signals are adapted to control power switches integrated in the control units of the inductors.

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

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

• la figure 1 est un schéma illustrant le contrôle de signaux de commande périodiques selon un premier mode de réalisation de l'art antérieur ;
• la figure 2 est un schéma illustrant le contrôle de signaux de commande périodiques selon un second mode de réalisation de l'art antérieur ;
• la figure 3 est un schéma bloc illustrant une table de cuisson à induction conforme à un mode de réalisation de l'invention ;
• la figure 4 est un schéma illustrant un procédé de contrôle de signaux de commande périodiques utile à la compréhension de l'invention ; et
• la figure 5 est un schéma illustrant le procédé de contrôle de signaux de commande périodiques conformément à un mode de réalisation de l'invention.

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

• the figure 1 is a diagram illustrating the control of periodic control signals according to a first embodiment of the prior art;
• the figure 2 is a diagram illustrating the control of periodic control signals according to a second embodiment of the prior art;
• the figure 3 is a block diagram illustrating an induction hob according to an embodiment of the invention;
• the figure 4 is a diagram illustrating a method of controlling periodic control signals useful for understanding the invention; and
• the figure 5 is a diagram illustrating the method of controlling periodic control signals according to an embodiment of the invention.

We will now describe with reference to the figure 3 an embodiment of a hob according to the invention.

This hob includes several inductors I1, I2, ... In placed under a hob, to allow induction heating in a conventional manner of a container placed on the hob.

In this embodiment, a large number of inductors 11, I2, ... In are arranged under the cooking plane, and distributed in a two-dimensional grid to cover a large area of the hob. A typical number of inductors can thus be between 30 and 40.

In such a table, the inductors 11, 12, ... ln are generally of low power and distributed for example in a matrix arrangement or in lines arranged staggered with respect to each other.

Of course, the invention is not limited to this type of hob, also called matrix induction hob, and can be applied to hobs having predetermined foci, each hearth being itself constituted one or more adjacent inductors.

Each inductor 11, 12, ... In is fed respectively by control blocks B1, B2, ... Bn.

These control blocks B1, B2,... Bn do not need to be described in detail here and are conventionally constituted by electronic power switches, for example switches of the IGBT type (acronym for the English term). Saxon Insulated Gate Bipolar Transistor).

The structure of these control blocks associated with the inductors may be a half-bridge structure or a quasi-resonant architecture.

Whatever the structure, these control blocks B1, B2,... Bn, and more particularly the electronic power switches, are respectively controlled by periodic control signals S1, S2,... Sn.

Each inductor 11, 12, ... In can thus be controlled independently of the others thanks to the control blocks B1, B2 ... Bn.

The periodic control signals S1, S2,... Sn are signals which can be adjusted in frequency or in pulse width (PWM signals, acronym for the English term Pulse With Modulation or PWM signals, acronym in French of term Pulse Width Modulation), in order to modify the current flowing in the inductors 11, 12, ... In and thus vary the power delivered by these inductors 11, 12, ... In to the containers covering them.

In order to control these periodic control signals S1, S2,... Sn, the hob 10 also comprises a control unit C making it possible to manage, in particular, the start, stop, and frequency of the periodic control signals S1, S2, ... Sn.

In order to ensure this control synchronously, a predefined periodic timing signal Sc is inputted to this control unit C.

In this embodiment and in a nonlimiting manner, the periodic timing signal Sc corresponds, in terms of periodicity, to the AC voltage signal Ss of the electrical supply network 12 of the hob 10.

For this purpose, the hob 10 comprises a synchronization circuit H adapted to generate a periodic square signal 0/1 from the sinusoidal AC voltage signal Ss of the power supply network 12.

Thus, the control unit C can operate using this predefined periodic timing signal Sc, which consists of a periodic square signal that can take two binary values 1 or 0.

As an example, we have illustrated figure 4 the sinusoidal AC voltage signal Ss of the power supply network 12 as well as the periodic timing signal Sc as generated by the synchronization circuit H.

We will now describe with reference to this figure 4 a control method implemented in the control unit C of the hob 10 described in FIG. figure 3 .

This method of controlling the periodic control signals S1, S2,... Sn is adapted to control in particular the starting, stopping, or modification of the periodic control signals S1, S2,... Sn.

Typically, the frequency of the periodic control signals S1, S2,... Sn is between 10 kHz and 100 kHz and is adapted to control the operation of electronic power switches of the IGBT type.

In comparison, the predefined periodic timing signal Sc may have a frequency of between 20 and 100 Hz.

It can typically be equal to 50 Hz or 60 Hz, corresponding to the frequency of the sinusoidal signal Ss of AC voltage of a current power supply network.

Note that we have illustrated on Figures 4 and 5 the periodic timing signal Sc as well as periodic control signals S1, S2, S3, S4, S5.

Given the frequencies (for example 50 Hz for the periodic timing signal Sc and 40 kHz for the periodic control signals S1, S2, ... Sn), the periodic control signals S1, S2, S3, S4, S5 have a period about 400 to 1600 times shorter than the period of the periodic timing signal Sc.

In order to facilitate understanding of the figures, the scale between the periods of the periodic timing signal Sc and the periodic control signals S1, S2, S3, S4, S5 has not been respected.

This control method further comprises a synchronization step periodically implemented at a predetermined time of the periodic timing signal Sc.

In the exemplary embodiment described in figure 4 this predetermined instant t1, t2, t3, t4 occurs periodically, at each period T1, T2, T3, T4 of the periodic timing signal Sc.

In this embodiment, where the periodic timing signal Sc corresponds to the sinusoidal signal Ss of AC voltage of the power supply network 12, this predetermined instant t1, t2, t3, t4 corresponds to the passage through 0 in the increasing direction of this sinusoidal signal Ss, which also corresponds to a rising edge, that is to say from the value 0 to the value 1, of the periodic clock signal Sc of square form.

Of course, in another embodiment, the predetermined instant t1, t2, t3, t4 could correspond to the passage by 0 in the decreasing direction of the sinusoidal signal Ss of alternating voltage, corresponding then to a falling edge, that is, that is, from the value 1 to the value 0, of the periodic clocking signal Sc of square form.

Thus, at each predetermined instant t1, t2, t3, t4 of the periodic timing signal Sc, all the periodic control signals, and here at the figure 4 the periodic control signals S1, S2, S3 are stopped and / or started during the synchronization step.

Thus, for example, the second periodic control signal S2 is not active during the first two periods T1, T2 of the periodic timing signal Sc.

On the other hand, when it is started, the start of this second periodic control signal S2 is carried out during the synchronization step, at the predetermined time t3, corresponding to the beginning of the third period T3 of the periodic timing signal Sc .

Thus, this start ensures the execution of a complete cycle of this second periodic control signal S2 on this third period T3.

The start of this second periodic control signal S2 thus makes it possible to activate an additional inductor 12.

The activation of an additional inductor may be due either to the operation of an additional cooking zone, or during the power control of a cooking hearth already in operation, which causes periodic stops of operation of one or more inductors associated with this cooking hearth.

The activation of an additional inductor may also be due to the displacement of a container on the cooktop, thus displacing the cooking chamber during operation and thus modifying the activated inductors.

Moreover, when a periodic control signal, such as, for example, the first periodic control signal S1, is activated during a given period, and for example the second period T2 of the periodic timing signal Sc, this first periodic control signal S1 is stopped and restarted during the synchronization step implemented at the predetermined time t3 of the next period T3, succeeding the second period T2 of the periodic timing signal Sc.

It is the same for each synchronization step implemented at each predetermined time t2, t3, t4 when a signal is maintained in operation on the different periods T1, T2, T3, T4 of the periodic timing signal Sc.

The periodic control signals S1, S2, S3 are thus reset at each predetermined instant t2, t3, t4 of each period T2, T3, T4 of the periodic timing signal Sc.

This stop, then restart at a predetermined time t2, t3, t4 during each synchronization phase is thus achieved in a short time, and the execution of a complete cycle of the periodic control signals S1, S2, S3 is provided on each period T1, T2, T3, T4 of the periodic timing signal Sc.

By way of non-limiting example, this brief delay can have a duration of approximately 100 μs.

The duration of this brief delay depends in particular on the speed of the control unit C as well as the number of inductors 11, 12 ... In which are controlled.

Thus, all the periodic control signals S1, S2, S3 active at a given period or to be started at the next period are stopped briefly at a predetermined time t2, t3, t4 corresponding here to the rising edge of the periodic timing signal Sc, then restarted to perform a complete cycle during each period T2, T3, T4.

Thus, the pattern of each periodic control signal S1, S2, S3 is repeated identically on each period T1, T2, T3, T4 of the periodic timing signal Sc.

Finally, it will be noted that the stopping of a periodic control signal is also implemented during the synchronization step.

Thus, the periodic control signals S2, S3 as illustrated in the example of the figure 4 are stopped at the predetermined time t4, corresponding to the beginning of the fourth period T4 of the periodic timing signal Sc, during the synchronization step implemented at this time t4.

In the example shown in figure 4 the periodic control signals S1, S2, S3 also have the particularity of having an identical frequency.

Thanks to the synchronization step described above, the periodic control signals S1, S2, S3 are synchronous at all times during the control of the corresponding inductors 11, 12, 13 of the hob 10.

We also illustrated at the figure 5 an embodiment of the invention wherein the periodic control signals S4, S5 are controlled at different frequencies.

As before, the periodic control signals S4, S5 are reset, that is to say are stopped and restarted at each predetermined time t2, t3, t4 of each period T2, T3, T4 of the periodic timing signal Sc.

When the periodic control signals S4, S5 have a different frequency, the value of the phase shift d changes during the same period T1, T2, T3, T4 of the periodic timing signal Sc.

However, the phase shift d between the periodic control signals S4, S5, taken at the same predetermined time of each period T1, T2, T3, T4 of the periodic timing signal Sc, remains constant from one period to the other of the signal periodic timing Sc.

Thus, the phase of the periodic control signals S4, S5 is controlled throughout the control of the corresponding inductors 14, 15.

The pattern of each periodic control signal S4, S5 is thus repeated identically from one period to another of the periodic timing signal Sc.

This control of the phase (maintenance of the synchronous signals or of an identical phase shift at a given instant of each period of the periodic timing signal Sc) makes it possible to ensure the stability of the power consumed by the inductors 11, 12, ... In, by limiting the impact of the coupling between inductors on the fluctuations of the power consumed by each inductor.

This control method thus makes it possible to have a better management of the power delivered to each container and thus a better overall control of the delivered power which must be enslaved to a desired power demanded by the user.

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

In particular, the predefined periodic timing signal Sc may be arbitrary and not deduced from the sinusoidal signal Ss of alternating voltage of the power supply network 12.

Claims (9)

A method of controlling periodic control signals (S1, S2, ... Sn) addressed respectively to control blocks (B1, B2, ... Bn) of the inductors (11, 12, ... In) of a hob (10), characterized in that it comprises a synchronization step periodically implemented at a predetermined time (t1, t2, t3, t4) of a predefined periodic timing signal (Sc), said periodic control (S1, S2, ... Sn) being stopped and / or started during the synchronization step and said periodic control signals (S4, S5) having a different frequency. Control method according to claim 1, characterized in that in the synchronization step the periodic control signals (S1, S2, ... Sn) are reset. A control method according to one of claims 1 or 2, characterized in that , when one of said periodic control signals (S4, S5) is activated for a given period (T2) of said predefined periodic timing signal (Sc ), said periodic control signal (S4, S5) is stopped and restarted during the synchronization step implemented at said predetermined time (t3) of a following period (T3) succeeding said given period (T2) of said signal periodic predefined timing (Sc). Control method according to one of claims 1 to 3, characterized in that said predefined periodic timing signal (Sc) corresponds to the AC voltage signal (Ss) of the electrical supply network (12) of the hob. (10). Control method according to claim 4, characterized in that said predetermined instant (t1, t2, t3, t4) corresponds to the passage by 0 in the increasing or decreasing direction of the sinusoidal signal of alternating voltage (Ss) of the supply network electric (12). Control method according to one of claims 1 to 5, characterized in that said predefined periodic timing signal (Sc) has a frequency substantially equal to 50 Hz or 60 Hz. Control method according to one of claims 1 to 6, characterized in that said periodic control signals (S1, S2, ... Sn) have a frequency between 10 kHz and 100 kHz. Induction hob comprising a plurality of inductors (11, 12, ... In) distributed under a cooking plane in a two-dimensional grid, said inductors (11, 12, ... In) being fed respectively by control blocks ( B1, B2, ... Bn) controlled respectively by periodic control signals (S1, S2, ... Sn), characterized in that it comprises a control unit (C) adapted to implement the method according to in one of claims 1 to 7. Induction hob according to claim 8, characterized in that said periodic control signals (S1, S2, ... Sn) are adapted to control power switches integrated with said control blocks (B1, B2, .. Bn) of said inductors (11, 12, ... In).

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