ES2362607A1 - Method for multiplexing two induction heating loads of circuit of household heating device by electronic switching device, involves deactivating two induction heating loads for prespecified time interval - Google Patents

Abstract

The method involves deactivating the two induction heating loads for a prespecified time interval as the respective electronic switching devices are switched off. The prespecified time interval is arranged in a blanking gap in relation to the multiplexing. A converter, which controls the two induction heating loads, is partially switched off during the prespecified time interval. An independent claim is also included for a circuit with a control unit.

Description

Multiplexing of heating loads by induction.

The invention relates to a method for multiplex induction heating loads, to a circuit according to a domestic heating device comprising such circuit.

You can get multiplex temporarily domestic induction heating charges being used bidirectional unipolar switches, or using switches bi-directional bipolar. For example, any type can be used transistor with an intrinsic diode or with an antiparallel diode external. In addition, electronic devices or electromechanical for connection purposes. For example, you can use a triac (triode for alternating current), in which Triacs are used at low switching frequencies (up to 1 kHz), for example, for motor control or for reduction purposes bright.

Figure 1 shows an exemplary group of composite switches, for example, IGBT (bipolar transistor of insulated door), which provide switching frequencies of Up to tens of kHz. An arrangement 101 shows an approach conventional comprising two IGBT and two diodes, an implementation 102 represents two reverse blocking IGBT, and an example 103 shows four diodes and a single IGBT implementation.

In addition, the connection can be carried out through electromagnetic relays, which can be incorporated in single-pole unipolar configurations (SPST, or Single Pole Single Throw ) or unipolar double throw (SPDT, or Single Pole Double Throw ). The SPDT configuration allows two multiplexes to be directly multiplexed as shown, for example, in EP 0 971 562.

Figure 2 shows an implementation of SPST and SPDT configurations that use triacs and relays. A column 201 shows schematic symbols, a column 202 shows a relay implementation, and a column 203 shows a triac implementation of SPST and SPDT configurations.

It should be noted that any functionality of multiplexing or any complexity routing matrix Increased can be implemented using SPST devices. The Figure 3 shows a symbol 301 of a multiplexer (one input and N outputs) and a corresponding 302 implementation that uses triacs

Temporary multiplexing requires that loads and inverters are arranged using a matrix of routing that is configured for low frequency values (below 1 kHz) for a bipolar device as said Triac work properly. The bipolar device, however, When connecting at low frequencies, you need to allow currents of high frequency (in the order of tens of kHz) are passed to through said device. In addition, a tension through the triac may vary rapidly (in the order of tens of kHz) during the triac blocking state; in that case, the triac needs to block oscillating voltages without any significant leakage.

Figure 4A shows a low frequency application of a triac 401, which is arranged in series with an inductive load comprising an inductor 402 and a resistor 403. The inductive load is connected to a switching frequency AC voltage of 50/60 Hz through said triac 401, where the triac 401 performs a phase control. The frequency of the current flowing through the triac and the switching frequency of the device are the
same.

Figure 4B shows a behavior of circuit of figure 4A in case of a load mainly resistive (R >> \ omegaL). An operation of the triac 401 is delayed based on a delay? Delta? introduced in gate control waveform with respect to zero crossing of the current. A disconnection of the triac 401 takes place in the next zero step of the current after the signal of gate v_ {G} of the triac has been deactivated. The triac remains disconnected until said gate signal v_ {G} is activated from new.

Figure 4C shows a behavior of circuit of figure 4A in case of a load mainly inductive (R << \ omegaL). Here, there is a gap between the voltage across the inductor v_ {L} and the current i_ {L}, and a transient voltage oscillation dv_ {L} / dt significant it may be evident at the moment when the current is withdrawn of the circuit Such transient voltage oscillation dv_ {L} / dt may lead to poor activation of triac 401. To avoid this problem, an RC shock absorber circuit is arranged in parallel with the triac to reduce any such oscillations Temporary voltage. In addition, manufacturers introduced triacs without shock absorber that face dv / dt values high.

The problem to be solved is to overcome the disadvantages mentioned above and, in particular, to provide an effective approach to control connection devices, in particular triacs, when used for temporary multiplexing of domestic induction heating loads.

This problem is solved in accordance with the characteristics of the independent claims. Other forms of embodiment result from the dependent claims.

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In order to overcome this problem, a method to multiplex at least two heating loads by induction through an electronic connection device used for each load,

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where the at least two induction heating charges are inactive for a predetermined time interval disconnecting the electronic connection devices respective,

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being arranged said predetermined time interval in an interval of suppression with respect to said multiplexing.

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Therefore, the suppression interval is provided between the induction heating loads that are active (for example, alternately). For example, if a Induction heating load is disabled, and another load induction heating is activated using said multiplexing, said suppression interval does not determine a duration for any of the induction heating loads that are activated. Electronic connection devices can be deactivated during the entire period of time of this suppression interval or during a part thereof.

This avoids or advantageously reduces any transient oscillation that may lead to erroneous activation of the electronic connection device, and reduces or eliminates effective way the heating load current by induction.

Said multiplexing can provide a alternating activation of one or more heating loads by induction. In particular, if at least one heating load per induction is active, at least another heating load by induction may be inactive (for example, all loads of Induction heating remaining may be inactive). TO in this regard, "inactive" means that there is no activation to through the electronic connection device arranged for this respective induction heating load. Therefore, "active" means that the connection device activates its associated induction heating load.

As indicated, a electronic connection device for each heating load inductively. Thus, this electronic connection device can enable / disable your induction heating load and thus allow multiplexing between several heating loads by induction. Multiplexing can be controlled by a unit of central control that activates and / or deactivates the devices connection electronics accordingly.

It is also an option that more than one load of induction heating is associated with a device electronic connection

In one embodiment, a converter that power the at least two induction heating loads is disconnected at least partially during the time interval predetermined.

Said converter can control the load of induction heating and electronic device connection, where the electronic connection device and charging induction heating are connected in series. He converter can control several such heating loads by induction with its electronic connection devices Associates Said induction heating load and the electronic connection device can be understood as a unit, where several such units are connected in parallel with each other, and be driven by said converter. He converter can comprise at least one electronic switch that be controlled by a central control function.

Advantageously, said converter is disconnected during said predetermined time interval, in particular, during said suppression interval.

In another embodiment, said converter is disconnected for the duration of the suppression interval.

Therefore, said converter is disconnected in the case that no load is being connected to it. This effectively allows any current stored in a capacitor at the input of said converter is discharged. Such capacitor can, in particular, be a filter capacitor arranged after a rectifier before said converter. For the therefore, a supply address of the at least one load of induction heating can be perceived from a source of power (for example, an AC voltage supply) through a filter and a rectifier through said capacitor to the converter, and continuing to induction heating load which is driven by said converter. As described above, each induction heating load comprises a electronic connection device (connected in series with said induction heating load), which is used to multiplex several of such heating charges by induction.

In another embodiment, said converter is a resonant semipuente inverter or a resonant inverter of full bridge where induction heating loads they are, in particular, connected to the output of said converter.

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Advantageously, the resonant inverter allows a efficient operation of said various heating loads by induction. When an induction heating load particular is active (multiplexed), the converter can supply various modulation parameters depending on the actual load connected, and the target requirement or value set, by for example, by a user of a home device of heating. Therefore, the parameters can be different for each active multiplexing cycle, that is, for each period of time that is associated with a load of particular induction heating.

In a following embodiment, the al less an induction heating load is connected to a central socket between switches of said converter.

It is also an embodiment that said electronic connection device comprises at least one of the following components:

- a triac;

- a triac without shock absorber;

- a transistor;

- a MOSFET (field effect transistor semiconductor metal oxide);

- an IGBT (bipolar gate transistor isolated).

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Such connection devices are used in particular to temporarily multiplex multiple loads of induction heating, in which each such load of induction heating is activated and deactivated through its electronic connection device. It should be noted that the electronic connection device can activate the charging of respective induction heating, and the output signal provided by the converter can be used to control modulation parameters depending on the heating load by real induction. It should be noted, in particular, that, through said multiplexing, during a given time interval can only an induction heating load is activated while the other induction heating loads are deactivated by said electronic connection devices. Also, several induction heating loads can be activated during said given time interval.

In relation to another embodiment, the predetermined time interval is sized such that a capacitor that is arranged at the input of the inverter can be substantially discharged during said time interval predetermined.

Therefore, it can be reduced and / or eliminated any transient oscillation that may come from the burden of This capacitor In particular, any charge accumulating effect that may result in a significant transient oscillation is effectively avoided by means of said time interval default disconnecting electronic devices from connection (and the converter).

The problem described above is further resolved. through a circuit that includes

- at least two heating loads per induction that are controlled by an electronic device of connection, where said at least two heating charges by induction are being multiplexed;

- a control unit for operating said electronic connection devices in such a way that at least two heating loads are inactive for an interval of default time disconnecting electronic devices respective connection, where said time interval default be arranged in a suppression interval with regarding said multiplexing.

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According to one embodiment, a converter to drive the at least two heating loads by induction, where the converter is disconnected at least partially during the predetermined time interval, in in particular, for the duration of the suppression interval.

According to another embodiment, the converter is a full bridge resonant inverter or a resonant inverter of semipuente.

The problem stated above is also solved. by means of a domestic heating device that comprises the circuit as described here.

The following figures show and illustrate schematically embodiments of the invention:

Fig. 5 shows a triac driver circuit example, where a generator produces a square wave that is supplied to an optical coupler to control said triac;

Fig. 6 shows another example of a circuit triac exciter, where a generator is connected to one side primary of a transformer, whose secondary side is connected to the door of said triac;

Fig. 7 shows a circuit diagram that uses triacs as load multiplexing devices, where a series resonant inverter powered by semipuente voltage provides multiple outputs that are multiplexed by said triacs;

Fig. 8 shows a circuit diagram equivalent for the inverter topology illustrated in Figure 7, where a pulsing DC voltage is supplied to a modulator, which is also fed by a signal from a generator to provide a modulated output signal to drive various load branches of induction heating;

Fig. 9 shows timing charts that represent waveforms of currents and voltages represented in figure 8;

Fig. 10 shows timing charts that illustrate current and voltage waveforms illustrated in the Figure 8, associated with a triac behavior in a state driver;

Fig. 11 shows timing charts based on the circuits illustrated in Figure 7 and Figure 8, where a T0ff disconnection period is planned between multiplexing segments to avoid transient oscillation of the current.

Figure 5 shows an exciter circuit of exemplary triac with a triac 501 (comprising terminals T1, T2, and a gate G), where a generator 506 produces a wave square which is supplied to an optical coupler 505 comprising a photodiode 504 and an optotriac 503. The generator 506 is connected to photodiode 504 of optical coupler 505, and optotriac 503 is connected to the door of triac 501 and, through a resistor 502, to terminal T2 of triac 501.

The triac 501 is driven by said generator 506 through the optical coupler 505. A main stream i_ {2} is used to enter the gate current i_ {G} required to drive the triac 501, where said current of gate i_ {G} is limited by resistor 502. When triac 501 is connected, the current i_ {2} 'through triac 501 amounts to i_ {2}, where the current i_ {G} amounts to 0 due to the lowest impedance presented on this path.

The signal from generator 506 can be a form two-level wave that indicates the duration of the state of driving. At the moment i_ {2} '= 0, if the voltage v_ {G} in the triac 501 door is in an elevated state, the current i_ {2} It can flow back to the door of the triac 501.

It should be noted that the optotriac 503 is connected between the door and terminal T2 of triac 501. This optotriac 503 can be perceived as an activating circuit in this example.

Figure 6 shows another example of a circuit triac exciter with a triac 601 (comprising the terminals T1, T2, and a gate G). A generator 604 is connected to one side primary 603 of a transformer, whose secondary side 602 is connected through gate G and terminal T1 of said triac 601

The transformer is used as a circuit activator. A short pulse provided by generator 604 is used to introduce a required current into gate G of the triac 601. Preferably, small transformers (dv / dt can be used small available) to transport short pulses to the side secondary; the activation pulse can be repeated so continues during a triac 601 connection interval, in particular, essentially in the zero crossing of the current i_ {2} '.

Figure 7 shows a circuit diagram that uses triacs as load multiplexing devices, where a series resonant inverter powered by semipuente voltage provides multiple outputs that are multiplexed by said triacs

A 701 power supply provides a voltage AC that is supplied to a filter 702 and a rectifier 703 resulting in a pulsing DC voltage that is filtered by a capacitor 704. The filtered DC voltage is connected to a semipuente comprising two switches 706 and 707, where each switch 706, 707 has a damping capacitor connected in parallel (C_ {snb1}, C_ {snb2}). A triac 708 is connected in series with a load 711, a triac 709 is connected in series with a load 712, and a triac 710 is connected in series with a 713 load. Each one such load comprises a series connection of an inductor and a resistor (for example, inductive heating element). The serial connections comprising triac 708, load 711, triac 709, load 712, and triac 710, load 713 are connected in parallel ones with others, and are connected through a central socket between said switches 706, 707, and a central outlet between two 714 and 715 capacitors, which are connected in series and are connected to the pulsating DC voltage. Capacitors 714 and 715 they can be resonant capacitors, for example, that amount to C_ {res} / 2 each.

Switches 706, 707 are operated by a control unit and exciter 705 by means of signals Q_ {1} (for switch 706) and Q_ {(for switch 707).

The inverter topology of Figure 7 comprises said voltage-fed series resonant inverter of semipuente that delivers power to N domestic loads of induction heating 711 to 713. Each load 711 to 713 is activated at particular (different) intervals by your triac 708 a 710 respective.

The example in figure 7 shows a capacitor 714, 715 common resonant for all charges 711 to 713, although may have particular resonant capacitors for each load 711 to 713.

A similar scheme can be applied for a full bridge topology using a series resonant capacitor individual, which amounts to C_ {res}, instead of two 714 and 715 separate capacitors.

When one of the loads 711 to 713 is connected to the inverter, an equivalent circuit can be represented according to the figure 8.

Figure 8 shows a pulsing DC voltage 801 which is supplied to a modulator 803. Also, a signal from a generator 802 is supplied to said modulator 804. The signal of output of modulator 804 is supplied to a branch A comprising a serial connection of a triac 804, a load 806 and a capacitor resonant 808. A ground is connected to the DC voltage 801, to the 802 generator, to the 803 modulator and to the remaining plug of the capacitor 808.

Also, a branch B is indicated comprising a serial connection of a triac 805 and a load 807 that is connected through the resonant capacitor 808 to ground.

Each load 806, 807 comprises a connection in series of an inductor and a resistor (heating element inductive).

The 802 generator can provide a signal from square wave to modulator 803. Modulator 803 can provide a amplitude modulated signal.

The modulator 803 modulates, in particular, the signal of the pulsing DC voltage at a frequency that can be twice (greater than) the main frequency. As a carrier frequency, it you can use a square wave [unipolar or bipolar depending on the circuit topology, that is, semipuente (unipolar) topology or full bridge (bipolar)]. This carrier frequency is corresponds to the input signal of the inverter according to the figure 7.

The amplitude modulated signal is connected to a resonant load in series 806 (or 807), which comprises the load of induction heating, and the common resonant capacitor.

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The behavior of the triac 708 to 710 or 804, 805 It can be illustrated as follows:

Triac in locked state :

If the triac 804 is in a CONNECTED state, the parallel triac 805 is in a DISCONNECTED state, blocking from that mode a load voltage v_ {L} in case of a resonant capacitor 808 commonly shared (or blocking an output voltage v_ {O} in case of an individual resonant capacitor, not shown in Figure 8).

Figure 9 shows waveforms of the exemplary voltage across the triac for the blocking state, based on the circuit in figure 8.

In order to maintain the blocking state of the triac 805, a maximum dv / dt value should not be exceeded through terminals T2 and T1 of the triac 805. Otherwise, the triac 805 It can be connected by mistake due to a wrong activation. A voltage v_ {L} through load 807 and an output voltage v_ {O} of modulator 803 can produce contours with spikes based on the connection speed of the inverter and based on the buffer capacitors C_ {SNB1}, C_ {SNB2}. Therefore the inverter can be adapted to avoid reaching or exceeding such value dv / dt maximum.

Preferably, the inverter can operate in a ZVS mode ( zero voltage switching , or zero voltage switching ), that is, the buffer capacitors C_ {SNB1}, C_ {SNB2} can be sized sufficiently large. Also, a cut-off switch current value may be limited under expected operating conditions.

In addition, a high dv / dt value can be produced in case the triac 805 is in the OFF state, and all The loads are disconnected from the inverter. Therefore, the buffer capacitors C_ {SNB1}, C_ {SNB2} are being loaded and unloaded continuously. The effective load of the inverter results in a high impedance resistive load. How As a result, all triac blocks the output voltage v_ {O}, the what is a square waveform with peaks with a dv / dt value high. Preferably, this situation can be avoided by avoiding any mode of operation such that the inverter does not Experience any real load. Therefore, if it is not connected no load to the inverter, inverter modulation It can be disconnected.

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Also, in case of discontinuous operation of the inverter, capacitor 704 cannot be completely discharged at the beginning of a subsequent active time interval. For the therefore, during several cycles of the inverter being active repeatedly, transient oscillations of the voltage at the output of the inverter. The higher the capacitor voltage 704, the greater the risk with respect to potential transient oscillations (dv / dt values). Such Transient oscillation generation (dv / dt) can be reduced at least partially (in particular, avoided) by downloading (at least partially) capacitor 704 before a subsequent cycle, or in if the remaining voltage of capacitor 704 is small enough

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Triac in driving state :

Figure 10 shows waveforms that illustrate a triac behavior during a CONNECTED state, that is, in the event that a load is being connected. After every cycle (with an adjustable delay), the load is connected to the investor.

Figure 10 illustrates a charging current i_ {L}, which is also the current that flows through the triac 804. It should be noted that a high frequency current generated by the inverter is visible on the triac 804. For values of high di / dt, the triac 804 can react differently in comparison with low frequency applications.

To DISCONNECT the triac 804, the envelope of the current i_ {L} needs to approach zero to ensure i_ {L} = 0 and di_ {L} / dt = 0. Thus, for current frequencies high, disconnecting the triac 804 depends more on the envelope of low frequency of the current than of the value of the current instant.

To ensure effective triac disconnection 804, the current envelope needs to reach almost zero, as shown in the lower part of figure 10. Since the current i_ {L} depends on the voltage v_ {bus} across the capacitor 704 (see figure 4), v_ {bus} needs to reach zero too. This requirement can be met if capacitor 704 is downloaded (essentially) completely with the end of each cycle without any (considerable) amount of tension remaining in this capacitor 704.

The value of capacitor 704 affects the high frequency currents and for any purpose of decoupling between rectifier 703 and inverter. For the Therefore, the capacitor value cannot be arbitrarily reduced. The approach provided here suggests in particular to ensure that the triac 804 is OFF to disconnect the modulator, and to ensure i_ {L} = 0, as well as di_ {L} / dt = 0.

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Control scheme :

To effectively control the triac in a Multiplexing application, the following scheme can be applied of control. This prevents any erroneous activation of the triac based in high transient dv / dt oscillations. In particular, the approach suggests effectively reduce oscillations transient di / dt.

Figure 11 shows timing charts based on the circuits illustrated in Figure 7 and Figure 8. The signal Q_ {1} shows the control of switch 706, the signal Q_ {2} shows switch 707 control, signal 1101 shows the control signal for triac 708, signal 1102 shows the control signal for triac 709, signal 1103 shows the control signal for triac 710, v_ {bus} is the voltage across of capacitor 704, i_ {L1} is the charging current for charging 711, i_ {L2} is the charging current for load 712, and i_ {LN} is the charging current for load 713.

The signals Q_ {1} and Q_ {2} represent the control waveform applied to inverter switches 706, 707. Those may be based on a modulation scheme arbitrary. Signals 1101 to 1103 represent signals from activation for each of the triac multiplexers 708 to 710. The voltage v_ {bus} corresponds to the voltage waveform rectified at a frequency that can amount, in particular, to 100/120 Hz. The signals i_ {L1} to i_ {LN} represent the shapes of load current wave.

Each load 711 to 713 is connected to the inverter a arbitrary number of half cycles periodically. The investor is controlled by different modulation parameters (T_ {S, \ N}, T_ {ON, \ N}, t_ {m, N}), depending on the respective load connected to it.

To avoid any faulty activation of Any triac, it can be advantageous to DISCONNECT the triac and ensure the inverter modulation signal Q_ {i} be disconnected for a period of time T_ {OFF} around the voltage v_ {bus} that passes through 0 volts. This allows to obtain i_ {L} = 0 and di_ {L} / dt = 0 in return.

The interval T_ {OFF} can be sized extensive enough to allow the triac to disconnect

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Other advantages :

The solution proposed here uses triacs in high frequency applications such as household devices of induction heating. Otherwise, the use would not be feasible. of such triacs as multiplexer elements.

The approach that triacs uses allows for switching frequency sufficiently high, as required by application (about 1 kHz).

Another advantage is that, due to the disposition of triacs, no acoustic noise is produced during connection.

Claims (11)

1. Method to multiplex at least two charges Induction heating through a device electronic connection used for each load;

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where the at least two induction heating charges are inactive for a predetermined time interval disconnecting the electronic connection devices respective,

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being arranged said predetermined time interval in an interval of suppression with respect to said multiplexing.

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2. Method according to claim 1, wherein a converter that drives the at least two heating loads by induction is disconnected at least partially during the interval Default time. 3. Method according to claim 2, wherein said converter is disconnected for the duration of the interval of suppression. 4. Method according to any of the claims 2 or 3, wherein said converter is an inverter semi-bridge resonant or a full bridge resonant inverter, where induction heating charges are, in particular, connected to the output of said converter. 5. Method according to claim 4, wherein the al less an induction heating load is connected to a central socket between switches of said converter. 6. Method according to any of the claims set forth above, wherein said device electronic connection comprises at least one of the following components:

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a triac (triode for alternating current);

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a triac without shock absorber;

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a transistor;

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a MOSFET (metal-oxide field effect transistor semiconductor);

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a IGBT (insulated gate bipolar transistor).

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7. Method according to any of the claims set forth above, where the range of predetermined time is sized such that a capacitor which is arranged at the input of the inverter can be downloaded substantially during said time interval predetermined. 8. Circuit comprising

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to the minus two induction heating charges that are controlled by an electronic connection device, where said at least two induction heating charges are being multiplexed;

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a control unit for operating said electronic devices of connection such that the at least two heating loads are inactive for a predetermined time interval disconnecting the electronic connection devices respective, where said predetermined time interval is arranged in a suppression interval with respect to said multiplexing

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9. Circuit according to claim 8, which it comprises a converter to drive the at least two loads of induction heating, where the converter is disconnected at less partially during the predetermined time interval, in in particular, for the duration of the suppression interval. 10. Circuit according to any of the claims 8 or 9, wherein said converter is an inverter full bridge resonant or a resonant inverter of semipuente. 11. Domestic heating device that comprises the circuit according to any of claims 8 to 10.