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WO2018184893A1 - Procédé et système de chauffe par induction - Google Patents

Procédé et système de chauffe par induction Download PDF

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Publication number
WO2018184893A1
WO2018184893A1 PCT/EP2018/057648 EP2018057648W WO2018184893A1 WO 2018184893 A1 WO2018184893 A1 WO 2018184893A1 EP 2018057648 W EP2018057648 W EP 2018057648W WO 2018184893 A1 WO2018184893 A1 WO 2018184893A1
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WIPO (PCT)
Prior art keywords
actuation
current
value
freguency
frequency
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PCT/EP2018/057648
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English (en)
Inventor
Andrea De Angelis
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Electrolux Appliances AB
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Electrolux Appliances AB
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Publication of WO2018184893A1 publication Critical patent/WO2018184893A1/fr
Anticipated expiration legal-status Critical
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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/06—Control, e.g. of temperature, of power
    • H05B6/062—Control, e.g. of temperature, of power for cooking plates or the like
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2213/00—Aspects relating both to resistive heating and to induction heating, covered by H05B3/00 and H05B6/00
    • H05B2213/04—Heating plates with overheat protection means

Definitions

  • the present invention generally relates to the field of induction heating. More specifically, the present invention relates to monitoring heating during induction heating.
  • Induction heating is a well-known method for heating an electrically conducting load by inducing eddy currents in the load through a time-varying magnetic field generated by an alternating current (hereinafter, simply AC current) flowing in an induction heating coil.
  • the internal resistance of the load causes the induced eddy currents to generate heat in the load itself.
  • Induction heating is used in the field of induction cooking, particularly in induction ovens, induction cooktops and induction hobs.
  • induction hob induction heating coils are located under a cooking hob surface for heating cooking pans made (or including portions) of electrically ferromagnetic material placed on the cooking hob surface.
  • the amount of heat generated in the load depends on the electric power delivered to the load through the induction heating coil, which in turn depends on the freguency of the AC current flowing through the latter, the coupling between the load and the induction heating coil, and the time spent by the load at the induction heating coil.
  • the AC current used to generate the time-varying magnetic field is generated by means of an inverter circuit, such as a half bridge inverter, a full bridge inverter, or a quasi-resonant inverter, comprising a switching section including power switching elements, such as for example Insulated-Gate Bipolar Transistors (IGBT), and a resonant section comprising inductor (s) and capacitor ( s ) , with the induction heating coil that is an inductor of the latter section.
  • IGBT Insulated-Gate Bipolar Transistors
  • the inverter circuit is configured to receive an input alternating voltage (hereinafter, simply AC voltage), such as the mains voltage taken from the power grid, and to accordingly generate an AC current (flowing through the induction heating coil) oscillating at a frequency corresponding to actuation frequency of the power switching elements (i.e., the frequency with which they are switched between the on and the off state) and having an envelope following the input AC voltage, with the amplitude of the envelope that depends in turn on the actuation frequency itself (the lower the actuation frequency, the higher the amplitude thereof) .
  • the current flowing through the induction heating coil is sourced/drained by the power switching elements of the switching section.
  • the electric power delivered to the load through the induction heating coil depends on the frequency of the AC current flowing through the latter.
  • the electric power provided to the load is at its maximum when the current flowing through the induction heating coil oscillates at the resonance frequency of the resonant section, i.e., when the actuation frequency is equal to the resonance frequency.
  • the electric power delivered to the load strongly depends on the coupling between the induction heating coil and the load, i.e., it depends from a series of unpredictable features such as the type of load, the distance between load and induction heating coil, the geometry of the load and of the induction heating coil.
  • unpredictable features such as the type of load, the distance between load and induction heating coil, the geometry of the load and of the induction heating coil.
  • the resonance frequency strongly depends on the coupling between the induction heating coil and the load, i.e., it depends from a series of unpredictable features such as the type of load, the distance between load and induction heating coil, the geometry of the load and of the induction heating coil .
  • Devices which exploit induction heating should be provided with a control unit specifically designed to carry out dynamic measurements so as to obtain an indication about how the actuation frequency and the electric power delivered to the load are related to each other.
  • control unit When a user of a device of this kind is requesting a specific electric power (e.g., corresponding to a specific temperature to be reached by a cooking pan), such control unit has to carry out measurements to assess the actuation frequency/electric power relation corresponding to the actual condition (e.g., corresponding to the actual coupling between the induction heating coil and the load) ; then, the control unit is configured to dispense the requested electric power by setting the actuation frequency according to the assessed actuation frequency/electric power relation.
  • actuation frequency/electric power relation corresponding to the actual condition (e.g., corresponding to the actual coupling between the induction heating coil and the load)
  • control unit may be configured to set the electric power to a safe level different from the reguested one.
  • the envelope of the AC current flowing through the induction heating coil has an amplitude that depends on the actuation freguency (the lower the actuation freguency, the higher the amplitude thereof), it is not possible to known a priori whether a selected actuation freguency corresponds to a current flowing through the induction heating coil that is lower than the maximum current or not .
  • EP 1734789 Al discloses a method involving providing an alternating supply voltage and a freguency converter with an adjustable switching unit.
  • the operating freguency of the switching unit and/or the freguency converter is increased from a freguency base in the course of half cycle of the voltage.
  • the freguency is then decreased to the base, so that the freguency amounts to the base, at the zero crossing of the supply voltage.
  • WO 2016/041684 Al there is disclosed an induction hob having a vibrational sensor for detecting audible sound generated when substances are boiling on the heating zones of the induction hob.
  • the controller of the induction hob may control the cooking process, such as by lowering the power supplied to the respective heating zone, so as to avoid overboiling or to provide for simmering of the food articles being cooked at a constant cooking temperature.
  • EP 1732357 A2 discloses a method for monitoring the cooking temperature in an induction hob, in which method the frequency of alternating current flowing through the inductor is set to a fixed value, and an electrical parameter of the hob is monitored, which is correlated to the power of the inductor, such as coil current.
  • the method described in EP 1732357 A2 has several disadvantages, such as that during the measuring process the power supply has to be set to a predetermined power level which may substantially differ from the power level that corresponds to the temperature selected by the use.
  • Applicant has observed that it would be advantageous to provide an induction heating system with a control unit which has the capability of rapidly obtaining an indication about how the actuation frequency and the electric power delivered to the load are related to each other in the actual condition (e.g., corresponding to the actual coupling between the induction heating coil and the load) , wherein by evaluating the amount of electric power delivered to the load the temperature variation of the load can be determined.
  • the present invention in a first aspect, is a method for managing an induction heating system as it is defined in claim 1.
  • the induction heating system comprises an electrically conducting load and an inverter circuit comprising a switching section and a resonant section.
  • the switching section comprises switching devices adapted to generate an AC current from an AC input voltage comprising a plurality of half-waves.
  • the resonant section comprises an induction heating coil adapted to receive the AC current for generating a corresponding time-varying magnetic field in order to generate heat in the electrically conducting load by inductive coupling.
  • the AC current oscillates at an actuation freguency of the switching devices and has an envelope comprising a plurality of half-waves corresponding to the half-waves of the AC input voltage.
  • the amount of heat generated in the load depends on the freguency of the AC current.
  • the method comprises performing at least once a seguence of steps in which:
  • the actuation freguency is varied according to a seguence of actuation freguency values, each actuation freguency value of the seguence being set for a corresponding time interval corresponding to a fraction of the duration of the half-wave of the envelope;
  • a corresponding current peak value is calculated based on a corresponding set of at least one absolute value peak assumed by the AC current during the corresponding time interval, so as to generate a corresponding current peak/actuation freguency relation;
  • the above procedure preferably is carried out either continuously for a predetermined duration, during which a number of consecutive measurements is made, or is repeated at a certain freguency, such as every 3 seconds until boiling is detected.
  • the method suggested herein can be performed any time during operation of the induction heating system, such as during heating up the heating element by providing electric power to the heating element, or at a point in time when the power delivery is turned off.
  • the procedure of varying the actuation freguency is effected within a single half-wave of the envelope, and hence only a very short time is reguired to carry out these procedures, such freguency scan provides for minimal interference with the power delivery to the heating element. Therefore, the method suggested herein when carried out during heating up the heating element does noticeably prolongate the heating procedure, because the power delivery at the optimum activation freguency is interrupted only for a very short time.
  • the method also may be carried out when the power delivery is turned off, such as when the heating element has been heated to a selected temperature and thus the power delivery is interrupted until the temperature of the heating element has fallen below a predetermined margin.
  • the power delivered during the freguency scan is so small that it does not provide for noticeable heating.
  • the present invention is an induction heating system for heating an electrically conducting load as it is defined in claim 12.
  • a boiling condition is determined when variations in the current peak/actuation frequency relations are less than a predetermined minimum value. While in the "ideal" case boiling is detected when there is no variation and thus the incline of the relation of current peak to actuation frequency has decreased to zero, in order to allow for measuring inaccuracies a boiling condition can be assumed when the variations in the current peak/actuation frequency relations fall within a certain minimum range.
  • the method further comprises averaging variations in the current peak/actuation frequency relations generated for plural actuation frequencies, and determining a boiling condition when a thus obtained average variation in the current peak/actuation frequency relations is less than a predetermined minimum value .
  • a boiling condition is determined when said variation or said average variation is less than a predetermined minimum value in a predetermined number of subsequent time increments, in each of which the sequence of steps (a) to (c) is performed.
  • the method may comprise considering a subset of the overall current peak/actuation frequency relations generated for plural actuation frequencies, and determining a boiling condition when at least one variation in the said subset is less than a predetermined minimum value.
  • a boiling condition can be determined when the variation in any selected number of these relations is less than a predetermined minimum value. That is, assuming that for example 10 freguencies are evaluated, a boiling condition can be assumed when for example a minimum of for example 4 of the 10 current peak/actuation freguency curves exhibit a plateau in which the variations, i.e. the slope of the curves, falls below a predetermined minimum value.
  • a mean value can be determined from all or selected of the relations that are determined.
  • a further option to avoid or minimize the effects of noise in the determined relations is to determine the variations in the individual relations and provide for weighing the variations. Thus, for example by introducing a weight that is inversely proportional to the noise, those relations can be neglected that exhibit the largest variations.
  • said seguence of actuation freguency values comprises a first seguence portion starting from a first actuation freguency value and then proceeding with lower actuation freguency values at every time interval corresponding to a fraction of the duration of the half-wave of the envelope.
  • said seguence of actuation freguency values preferably comprises a second seguence portion starting from the last actuation freguency value of the first seguence portion and then proceeding with higher actuation freguency values at every time interval corresponding to a fraction of the duration of the half-wave of the envelope.
  • said sequence of actuation frequency values comprises a first sequence portion startinq from a first actuation frequency value and then proceedinq with hiqher actuation frequency values at every time interval correspondinq to a fraction of the duration of the half-wave of the envelope.
  • said sequence of actuation frequency values preferably comprises a second sequence portion startinq from the last actuation frequency value of the first sequence portion and then proceedinq with lower actuation frequency values at every time interval correspondinq to a fraction of the duration of the half-wave of the envelope.
  • said step of varyinq, within a same half-wave of the envelope, the actuation frequency comprises settinq each new actuation frequency value of the sequence except the first one based on the distance of the previous actuation frequency value in the sequence with respect to the actual resonance frequency.
  • the correspondinq current peak value can comprise normalizinq each one of the absolute value peaks of the correspondinq set of at least one absolute value peak accordinq to the position of the correspondinq time interval with respect to said half- wave to obtain a correspondinq set of at least one normalised current peak value, and then calculatinq the peak value based on the normalised current peak values of the set.
  • the step of calculatinq the peak value based on the normalised current peak values of the set can comprise calculating an average value of said at least two absolute value peaks .
  • said inverter circuit can be selected one among:
  • the induction heating system of the present invention may be part of any inducting heating system that is designed to heat a food item, such as an induction oven, wherein said electrically conducting load is an induction shelf and said induction heating coil is mounted along a bottom, top or sidewall of said induction oven, or a cooking hob, in which said induction heating coil is mounted below a cooking plate or zone and said electrically conducting load is a portion of a cooking pan or pot, or a water heater, wherein said electrically conducting load is a water tank and said induction heating coil is mounted below the tank.
  • a food item such as an induction oven
  • said electrically conducting load is an induction shelf and said induction heating coil is mounted along a bottom, top or sidewall of said induction oven, or a cooking hob, in which said induction heating coil is mounted below a cooking plate or zone and said electrically conducting load is a portion of a cooking pan or pot, or a water heater, wherein said electrically conducting load is a water tank and said induction heating coil
  • Figure 1 illustrates an exemplary cooking hob system
  • Figure 2A is an exemplary circuit diagram of an inverter circuit for feeding AC current to an induction coil of the cooking hob system of Figure 1;
  • Figure 2B is an exemplary circuit of another inverter circuit for feeding AC current to an induction coil of the cooking hob system of Figure 1;
  • Figure 3 illustrates a time trend of the induction heating coil current of the inverter circuit of Figure 2A, as well as the envelope of such current;
  • Figures 4A and 4B illustrate the evolution in time of the actuation frequency of control signals of the inverter circuit of Figure 2A during a procedure of varying the actuation frequency within a same half-wave according to embodiments of the invention following two exemplary different predefined sequences of actuation frequency values;
  • Figure 4C illustrates the evolution in time of the actuation frequency of control signals of the inverter circuit of Figure 2A during a procedure of varying the actuation frequency within a same half-wave according to an embodiment of the invention following an exemplary dynamically calculated sequence of actuation frequency values;
  • Figure 5 illustrates an example of a frequency profile obtained in the method suggested herein
  • Figure 6 illustrates an example of coil current peak curve obtained in the method suggested herein
  • Figure 7 illustrates a relation of current peak, positive and negative, vs. actuation frequency calculated from the frequency profile of Figure 5 and the coil current peak curve of Figure 6;
  • Figure 8 illustrates positive and negative current peaks measurements vs. actuation which were determined at different times ;
  • Figure 9 illustrates current, positive and negative, vs. frequency curves which were determined at different times;
  • Figure 10 shows curves indicating positive normalized peak current vs . freguency which were determined at different times ;
  • Figure 11 illustrates current curves over time obtained for various freguencies
  • Figure 12 illustrates a current curve over time obtained by averaging the plural current curves illustrated in Figure 11;
  • Figure 13 shows an example of providing for power delivery phases for temperature control based on the method of boiling detection suggested herein.
  • Figure 1 illustrates an exemplary induction cooking system 100 wherein the concepts of the solution according to embodiments of the invention can be applied.
  • the induction cooking system 100 comprises a (e.g., glass-ceramic) cooking surface 165.
  • a number of induction coils 135 are placed underneath the cooking surface 165.
  • the induction coils 135 are selectively operable for defining one or more cooking zones 170, wherein plural individual cooking zones 170 also may be combined into a combined cooking zone 190.
  • each induction coil 135 is selectively operable to be fed with AC current provided by a respective inverter circuit 140.
  • the inverter circuit (s) 140 causes an AC current to flow through the (one or more) respective induction coil(s) 135.
  • This current flow generates a time-varying magnetic field 145, which is capable of inducing eddy currents in the cooking pan 180 (or in the portions thereof made of ferromagnetic material) .
  • the induced eddy currents cause the cooking pan 180 (or the portions thereof made of ferromagnetic material) to rapidly heat up to a desired working temperature.
  • the thermal energy lost by contact with the (non-illustrated) food contained in the cooking pan 180 is replaced continuously by the current provided by the inverter circuit 140.
  • the induction cooking system 100 comprises a control unit 160 configured to control the inverter circuits 140 in order to regulate the freguency of the AC current flowing in the induction coils 135 in such a way to regulate the electric power transferred from the generic inverter circuit 140 to the corresponding cooking pan 180, and therefore, the temperature of the latter.
  • Figure 2A is an exemplary circuit diagram of an inverter circuit 140 for feeding AC current to an induction coil 135 of the induction cooking system 100 wherein the concepts of the solution according to embodiments of the invention can be applied.
  • the inverter circuit 140 is a half-bridge inverter circuit, however similar considerations apply in case different types of inverter circuits arrangements are used, such as a full-bridge inverter circuit or a guasi-resonant inverter circuit .
  • the inverter circuit 140 comprises two main sections: a switching section 205 and a resonant section 210.
  • the switching section 205 comprises two insulated-gate bipolar transistors (IGBT) 212h, 2121 connected in series between the line terminal 215 and the neutral terminal 220 of the power grid.
  • An input AC voltage Vin (the mains voltage) develops between the line terminal 215 and the neutral terminal 220, oscillating at a mains freguency Fm, such as 50 Hz.
  • the IGBT 212h has a collector terminal connected to the line terminal 215, a gate terminal for receiving a control signal Al, and an emitter terminal connected to the collector terminal of the IGBT 2121, defining a circuit node 222 therewith.
  • the IGBT 2121 has an emitter terminal connected to neutral terminal 220 and a gate terminal for receiving a control signal A2.
  • the control signals Al and A2 are digital periodic signals oscillating at a same freguency, hereinafter referred to as actuation freguency Fa, between a high value and a low value, with a mutual phase difference of 180°, so that when the IGBT 212h is turned on, the IGBT 2121 is turned off, and vice versa. Similar considerations apply if different types of electronic switching devices are employed in place of IGBTs.
  • the resonant section 210 comprises the induction coil 135 and two resonance capacitors 225, 230.
  • the resonance capacitor 225 has a first terminal connected to the collector terminal of the IGBT 212h and a second terminal connected to a first terminal of the resonance capacitor 230, defining a circuit node 223 therewith.
  • the resonance capacitor 230 has a second terminal connected to the emitter terminal of the IGBT 2121.
  • the induction heating coil 135 is connected between circuit nodes 222 and 223.
  • the current Ic flowing through the induction heating coil 135 is alternatively sourced by the IGBT 212h (when the IGBT 212h is on and the IGBT 2121 is off) and drained by the IGBT 2121 (when the IGBT 212h is off and the IGBT 2121 is on) .
  • the induction heating coil current Ic oscillates at the actuation frequency Fa, and has an envelope 300 that follows the input AC voltage Vin, i.e., it comprises a plurality of half waves 310 (i), each one corresponding to a respective half wave of the input AC voltage Vin and therefore having a duration equal to the semiperiod of the input AC voltage Vin (i.e., 1/ (2*Fm)) .
  • the induction heating coil current Ic returns to zero (if an actuation with a suitable load is performed) .
  • the envelope 300 has an amplitude that depends on the actuation frequency Fa: the lower the actuation frequency Fa, the higher the amplitude.
  • the portion of the envelope 300 of the induction heating coil current Ic illustrated in Figure 3 has three half waves 310(1), 310(2), 310(3), each one having a corresponding amplitude E(l), E(2), E(3) .
  • the first two half waves 310(1), 310(2) of the envelope 300 correspond to an actuation frequency Fa higher than the one corresponding to the third half wave 310(3) . Therefore, the amplitude E(3) of the third half wave 310(3) is higher than the one of the first two half waves 310 (1) , 310 (2) .
  • an inverter circuit 140 of the quasi-resonant type such as the one illustrated in Figure 2B, comprising a rectifier 250 (for example, a bridge rectifier) adapted to rectify the input AC voltage Vin, a quasi-resonant circuit 260 (for example comprising an inductor in parallel to a capacitor) corresponding to the resonant section 210 of the half-bridge inverter circuit 140 of Figure 2A, and a switching circuit 270 (for example comprising a single transistor) corresponding to the switching section 205 of the half-bridge inverter circuit 140 of Figure 2A.
  • a rectifier 250 for example, a bridge rectifier
  • quasi-resonant circuit 260 for example comprising an inductor in parallel to a capacitor
  • switching circuit 270 for example comprising a single transistor
  • the actuation frequency Fa should be set higher than the resonance frequency Fr.
  • the actuation frequency Fa should be set higher than the current limit frequency Fc, as will be explained in further detail below.
  • the control unit 160 when the temperature setting provided by the user of the cooking system 100 involves the request of a specific amount of electric power to be delivered, the control unit 160 is configured to check whether such electric power request corresponds to an actuation frequency Fa which falls within a safe frequency range .
  • control unit 160 advantageously is configured to dynamically (i.e., during the operation of the cooking system 100) determine, or at least assess, the resonance frequency Fr as well as the current limit frequency Fc, or checking whether a certain actuation frequency range is a safe range (in the sense that the above- mentioned frequency limits are respected) . In this way, account is taken of the fact that both the resonance frequency Fr and the current limit frequency Fc strongly depend on the actual coupling between the cooking pan 180 and the induction heating coil 135.
  • a preliminary inspection phase can be carried out (i.e., before the actual power delivery phase) in which the actuation frequency Fa is varied step by step according to a sequence of predetermined actuation frequency values, with each actuation frequency value of the sequence that is maintained for a respective half wave (or also more than one consecutive half waves) of the envelope of the AC voltage Vin.
  • actuation frequency Fa is varied step by step according to a sequence of predetermined actuation frequency values, with each actuation frequency value of the sequence that is maintained for a respective half wave (or also more than one consecutive half waves) of the envelope of the AC voltage Vin.
  • known resonance identification procedures such as by measuring the distance between the zero crossing time of the induction heating coil current Ic and the zero crossing time of the induction heating coil voltage, a check is made during each half wave of the envelope of the AC voltage Vin to evaluate the closeness of the corresponding actuation frequency value to the resonance frequency Fr.
  • a corresponding power measurement is carried out for each actuation frequency value.
  • a power characteristic curve is then construed from such measurements, expressing how the power deliverable to the load varies in function of the actuation frequency.
  • the relationships of peak current versus actuation frequency could be obtained by varying the actuation frequency of the respective induction coil over plural periods of the envelope wave, such approach would be time consuming and hence interfere with the temperature control of the respective cooking site. Therefore, in accordance with the method suggested herein, the actuation frequency is varied within a single half-wave.
  • the power delivery phase may be immediately initiated by setting the actuation frequency Fa step by step, with each actuation frequency value of the sequence that is maintained for a respective half wave of the envelope of the AC voltage Vin, starting from a safe (e.g., high) actuation frequency value, and continuing until the desired power value is reached or until a frequency close to the resonance frequency Fr is reached (if the latter actuation frequency occurs prior the one corresponding to desired power value) .
  • a safe e.g., high
  • a possible method may provide for varying the actuation frequency step by step according to a sequence of (decreasing) predetermined actuation frequency values, with each actuation frequency value of the sequence that is maintained for a respective half wave of the envelope of the AC voltage Vin, until the limit is reached. Then, the value taken by the actuation frequency during the half wave of the envelope of the AC voltage Vin in which the maximum current is approached is identified as the current limit frequency Fc, i.e. the minimum actuation frequency value for which the AC current Ic flowing through the induction heating coil is lower than the maximum current that can be sustained (for a relatively prolonged) by the power switching elements.
  • the maximum peak current value is advantageously measured within the corresponding half wave of the envelope of the AC voltage Vin, so as to be able to construct an induction heating coil current characteristic curve, expressing how the maximum peak current varies in function of the actuation frequency.
  • the coupling between the load (i.e., the cooking pan 180) and the induction heating coil 135 may change in a very fast way (e.g., within 0.1-0.5 sec), which is not compatible with the time reguired by the inspection methods mentioned above.
  • the load-coil coupling may change every time the position of the cooking pan 180 changes with respect to the position of the induction heating coil 135. Therefore, the inspection methods mentioned above may not be efficient from the power delivery point of view.
  • the induction heating system employed in the present invention preferably is designed such that when the temperature setting provided by the user of the cooking system 100 involves the reguest of a specific amount of electric power Pt to be delivered, the control unit 160 is configured to dynamically carry out an actuation freguency selection procedure adapted to asses a value Fa* of the actuation freguency Fa that corresponds to the reguested electric power Pt .
  • control unit 160 is configured to actually set the freguency of the AC current flowing in the induction coils 135 (i.e., the actuation freguency Fa) taking into consideration the assessed value Fa*, in such a way to regulate the delivered electric power according to the reguest of the user.
  • a preferred actuation frequency selection procedure comprises a first phase in which the control unit 160 varies step by step the actuation frequency Fa of the control signals Al, A2 according to a sequence of actuation frequency values TFa(j) within a same half wave 310 (i) of the envelope 300 of the current Ic, for measuring corresponding peak values of the induction heating coil current Ic to generate a corresponding actuation frequency/current peak relation.
  • the first phase is initiated by the control unit 160 by setting the actuation frequency Fa to the first actuation frequency value TFa(l) of the sequence as soon as a half-wave 310 (i) of the envelope 300 of the induction heating coil current Ic is initiated.
  • This can be detected by assessing the zero crossing time of the input AC voltage Vin (which identifies the beginning of a half-wave 310 (i) of the envelope 300) through a proper zero voltage crossing circuit (not illustrated) .
  • the following actuation frequency values TFa(j) of the sequence are then set step by step by the control unit 160 within the same half-wave 310 (i) of the envelope 300.
  • the control unit 160 measures corresponding peak values of the induction heating coil current Ic.
  • the sequence of actuation frequency values TFa (j) is a predefined sequence, for example stored in the control unit itself 160 in form of tables or defined by means of a mathematic relationship, such as for example "decreasing by an amount X multiplied by a factor related to the distance from the resonance frequency Fr" .
  • control unit 160 is configured to assess whether the frequency range spanned by the sequence of actuation frequency values TFa(j) is a safe actuation frequency range for the operation of the system by taking into consideration the closeness of each actuation frequency value TFa(j) of the sequence to the resonance frequency Fr (e.g., by calculating for each actuation frequency value TFa (j) the distance between the zero crossing time of the induction heating coil voltage and the zero crossing time of the induction heating coil current Ic) .
  • the control unit 160 is aware of the possibility to set (for power delivery) the actuation frequency Fa to any value comprised in said actuation frequency range without incurring in the risk of reaching and going below the resonance frequency Fr.
  • the control unit 160 cannot freely set the actuation frequency Fa to any value comprised in said actuation frequency ranqe, because at least a portion of such actuation frequency ranqe comprises frequencies which are lower than the resonance frequency Fr.
  • control unit 160 may select a safe actuation frequency subranqe from the spanned frequency ranqe based on the closeness of the actuation frequency values TFa (j) of the sequence to the resonance frequency Fr, such as for example by settinq a lower boundary for such subranqe equal to or hiqher than the actuation frequency value TFa (j) which has been assessed to be the closest one to the resonance frequency Fr.
  • Fiqures 4A and 4B illustrate the evolution in time of the actuation frequency Fa of the control siqnals Al, A2 set by the control unit 160 durinq a procedure as may be used in the method suqqested herein followinq two exemplary different predefined sequences of actuation frequency values TFa (j) .
  • the predefined sequence of actuation frequency values TFa (j) provides for startinq from a first actuation frequency value TFa(l), then proceedinq with lower and lower actuation frequency values TFa (j) every time interval tj equal to a fraction of the semiperiod of the input AC voltaqe Vin (and therefore equal to a fraction of the duration of the half wave 310 (i) of the envelope 300), until substantially reachinq the centre of the half wave 310 (i); then, the predefined sequence of actuation frequency values TFa (j) provides for proceedinq with hiqher and hiqher actuation frequency values TFa (j) every time interval tj until reachinq the end of the half wave 310 (i) .
  • tj may be equal to 0,3 msec.
  • the evolution in time of the actuation frequency Fa comprises a decreasing ramp followed by an increasing ramp.
  • the predefined seguence of actuation freguency values TFa (j) provides for starting from a first actuation freguency value TFa(l), then proceeding with higher and higher actuation freguency values TFa (j) every time interval tj egual to a fraction of the semiperiod of the input AC voltage Vin (and therefore egual to a fraction of the duration of the half wave 310 (i) of the envelope 300), until substantially reaching the centre of the half wave 310 (i); then, the predefined seguence of actuation freguency values TFa(j) provides for proceeding with lower and lower actuation freguency values TFa (j) every time interval tj until reaching the end of the half wave 310 (i) .
  • the evolution in time of the actuation freguency Fa comprises an increasing ramp followed by a decreasing ramp.
  • the higher actuation freguency value TFa(j) of the seguence i.e., the one corresponding to substantially the centre of the half wave 310 (i)
  • the procedure can be configured such that as soon as the control unit 160 assesses that an actuation frequency value TFa (j) results to be very close to the resonance frequency Fr (e.g., when the distance between the zero crossing time of the induction heating coil voltage and the zero crossing time of the induction heating coil current Ic is lower than a safe threshold) , the actuation frequency Fa is clamped to said actuation frequency value TFa(j) (or also to a higher value) for the rest of the half- wave 310 (i), or for more than one subsequent half-waves for allowing a fast high power delivery, or even for the rest of the half-wave in which the user has requested a power corresponding to a lower actuation frequency.
  • each new actuation frequency value TFa (j) in the sequence also can be dynamically calculated by the control unit 160 based, for instance, on the distance of the previous actuation frequency value TFa (j) in the sequence with respect to the actual resonance frequency Fr (wherein said distance may be evaluated according to one of the previously mentioned methods) . In this way, it is possible to refine the resonance frequency Fr search when in the proximity of the resonance frequency Fr itself.
  • An example of a sequence of actuation frequency values TFa(j) calculated in a dynamic way is illustrated in Figure 4C.
  • the actuation frequency can be dynamically adjusted to provide for a temperature control which precisely reflects a temperature setting selected by the user of the induction cooking system 100, in the following the procedure for boiling detection in accordance with the present invention will be explained in detail .
  • Figure 5 there is illustrated an example of an actuation frequency profile as may be employed in the method suggested herein, wherein the profile shown in Figure 5 is symmetric about a minimum frequency similar as that shown in Figure 4A, but wherein the frequency is varied from step to step not in a constant fashion as in Figure 4A, but is dynamically varied similarly as the in the profile shown Figure 4C.
  • the distance among the actuation frequency values TFa (j) of the sequence with respect to the actual resonance frequency Fr can be evaluated by calculating the power factor costp corresponding to the induction coil 135 (the closer the power factor costp to 1, the closer the actuation frequency value TFa (j) to the resonance frequency Fr) .
  • the inverter circuit 140 may be provided with a clamping circuit (not illustrated) configured to clamp the induction heating coil current Ic when it reaches the maximum current that can be sustained by the IGBTs 212h, 2121.
  • a software protection may be provided, configured to clamp the actuation freguency Fa of the control signals Al, A2 before the induction heating coil current Ic reaches the maximum current that can be sustained by the IGBTs 212h, 2121.
  • the procedure for assessing the safe actuation freguency range having regard to current limit freguency Fc can be carried out by the control unit 160 by varying step by step the actuation freguency Fa of the control signals Al, A2 in the same way as for the procedure for assessing the safe actuation freguency range having regard to resonance freguency, i.e., according to a seguence of actuation freguency values TFa(j) within a same half wave 310 (i) of the envelope 300 of the current Ic, until a condition of maximum allowable current is approached, reguiring to clamp the actuation freguency Fa to an actuation freguency value TFa (j) corresponding to an induction heating coil current Ic value close to the maximum current that can be sustained by the IGBTs 212h, 2121, or until a suitable range of actuation freguencies TFa(j) is explored.
  • Figure 6 illustrates, as a result of a test performed by the Applicant, a current peak/actuation (i.e. time) relation of the positive peaks Pk + and the negative peaks Pk ⁇ measured by the control unit 160 with respect to time during an actuation frequency Fa step by step variation within an half wave 310 (i) of the envelope 300.
  • the measures are carried out by varying the actuation frequency Fa within a same half wave 310 (i) of the envelope 300, and the values of the positive and negative peaks Pk + , Pk ⁇ also depend on the position of the respective time interval tj with respect to the half wave 310 (i) (for the same frequency, the more the time interval tj is close to the centre of the half wave 310 (i), the higher the positive and negative peaks Pk + , Pk ⁇ (in absolute value)) .
  • the normalised positive and negative peaks Pk + , Pk ⁇ can be obtained by modifying each corresponding positive and negative peak Pk + , Pk ⁇ according to the position of the time interval tj of the measure with respect to the half wave 310 (i) .
  • the normalised positive and negative peaks Pk + conp r Pk ' conp are obtained by modifying each corresponding positive and negative peak Pk + , Pk ⁇ through (e.g., by multiplying them by) an expansion coefficient ec(j) whose value depends on the position of the time interval tj of the measure with respect to the half wave 310 (i) .
  • such expansion coefficient can be selected such that the more the time interval tj is far from the centre of the half wave 310 (i), the higher the expansion coefficient ec(j).
  • the position of the time interval tj with respect to the half wave 310 (i) can be determined by measuring the value of the input AC voltage Vin during the time interval tj.
  • An estimation of the current limit frequency Fc can be calculated by taking into account the actuation frequency value TFa (j) which is the one whose corresponding normalised positive or negative peak Pk + oMP, Pk ⁇ C oMP is the closest one to the maximum current that can be sustained by the IGBTs 212h, 2121.
  • Figure 10 is an illustration similar of determined current peak vs freguency curves similar as those shown in Figure 9, wherein Figure 10 shows the positive current peak curves in further detail .
  • the present method provides a current over time curve for each actuation freguency that has been set during the freguency sweep, so that there are obtained a plurality of measuring curves virtually simultaneously, i.e. within a single half-wave.
  • the reliability of the boiling detection can be substantially improved .
  • the thus obtained measuring data allows to select a set of freguency curves in which the variation is maximum, so to provide for a better resolution which is independent from the type of load. That is, while the curves obtained are dependent on the specific cooking pan or pot used as well as on the load which is heated therein, the method for boiling detection suggested herein can easily be adapted to the specific circumstances of the cooking situation encountered.
  • the procedures described herein are particularly beneficial because they provide for an indirect measurement of physical parameters (temperature of the load) which is effected by monitoring electrical parameters, such as the coil current. Given that due to the short time needed to carry out these procedures, and which thus provide for minimal interference with the power delivery phases, the measures useful for the sensing procedure can be performed in any moment of the cooking process.
  • the measurements described herein can be performed also at a time when the power delivery is turned off, such as when the boiling condition is reached and hence less power is required as compared with the phase of heating- up the cooking site.
  • the induction coils can be operated intermittently so as to maintain a boiling condition, wherein the above measurements can be effected at a chosen repetition rate, such as every 30s, so as to provide for a continuous monitoring of the pot.
  • a power delivery cycle upon reaching the boiling condition is illustrated in Figure 13.
  • the induction coils can be operated intermittently, i.e. can be turned off until it is determined that the temperature has fallen below a chosen temperature threshold, at which time the power delivery is reactivated automatically so as to assure that the temperature swing of the pot is kept within a certain temperature range .
  • the thermal status of the pot thus can be evaluated by an indirect measurement of electrical parameters, such as the current provided to the induction coil that is heating the pot.
  • electrical parameters such as the current provided to the induction coil that is heating the pot.
  • the measurements by a freguency sweep within a single half-wave should be repeated more often when approaching the boiling condition.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Induction Heating (AREA)
  • Induction Heating Cooking Devices (AREA)

Abstract

L'invention concerne un procédé de détection d'ébullition dans un système de chauffe par induction, dans lequel le système de chauffe par induction comprend une charge électroconductrice et un circuit inverseur comprenant une section de commutation et une section résonante, la section de commutation comprenant des dispositifs de commutation conçus pour générer un courant alternatif à partir d'une tension alternative d'entrée comprenant une pluralité de demi-ondes, et la section résonante comprenant une bobine de chauffe par induction conçue pour recevoir le courant alternatif pour générer un champ magnétique variant dans le temps correspondant afin de générer de la chaleur dans la charge électroconductrice par un couplage inductif, le courant alternatif oscillant à une fréquence d'activation des dispositifs de commutation et ayant une enveloppe comprenant une pluralité de demi-ondes correspondant aux demi-ondes de la tension alternative d'entrée, et la quantité de chaleur générée dans la charge dépendant de la fréquence du courant alternatif. Le procédé consiste à exécuter au moins une fois la séquence suivante d'étapes consistant à : (a) faire varier, à l'intérieur d'une même demi-onde de l'enveloppe, la fréquence d'activation conformément à une séquence de valeurs de fréquence d'activation, chaque valeur de fréquence d'activation de la séquence étant définie pour un intervalle de temps correspondant correspondant à une fraction de la durée de la demi-onde de l'enveloppe ; (b) pour chaque valeur de fréquence d'activation de la séquence, calculer une valeur de pointe de courant correspondante sur la base d'un ensemble correspondant d'au moins un pic de valeur absolue pris par le courant alternatif pendant l'intervalle de temps correspondant, de façon à générer une relation de pointe de courant/fréquence d'activation correspondante ; et (c) sur la base de l'évaluation de variations des relations de pointe de courant/fréquence d'activation générées pour plusieurs fréquences d'activation, déterminer un état d'ébullition.
PCT/EP2018/057648 2017-04-04 2018-03-26 Procédé et système de chauffe par induction Ceased WO2018184893A1 (fr)

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ES2713379A1 (es) * 2017-11-20 2019-05-21 Bsh Electrodomesticos Espana Sa Procedimiento para el montaje de un sistema de coccion
FR3092464B1 (fr) * 2019-02-06 2023-04-28 Groupe Brandt Procédé de détermination d’une puissance minimale continue induite dans un récipient.
DE102023119708A1 (de) 2023-07-25 2025-01-30 Haimer Gmbh Induktionsspulen-Baueinheit und Verfahren zur Steuerung eines induktiven Erwärmungsvorgangs für eine Induktionsspulen-Baueinheit

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EP1420613A2 (fr) * 2002-11-15 2004-05-19 Electrolux Home Products Corporation N.V. Procédé et dispositif de surveillance thermique d'un ustensile de cuisson chauffable inductivement
EP2533605A2 (fr) * 2011-06-06 2012-12-12 General Electric Company Détection de poêle de cuisson à induction
WO2013064332A1 (fr) * 2011-11-03 2013-05-10 Arcelik Anonim Sirketi Cuiseur à induction

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ES2292299B1 (es) 2005-06-08 2008-10-16 Bsh Electrodomesticos España, S.A. Dispositivo de calentamiento para una cocina de induccion.
DE102005028829A1 (de) 2005-06-14 2007-01-11 E.G.O. Elektro-Gerätebau GmbH Verfahren und Anordnung zur Leistungsversorgung einer Induktionsheizeinrichtung
EP2999301B1 (fr) 2014-09-18 2019-03-06 Electrolux Appliances Aktiebolag Plaque de cuisson à induction avec détection d'ébullition et commande de l'énergie par induction, procédé pour chauffer des aliments avec une plaque de cuisson à induction et programme informatique

Patent Citations (3)

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Publication number Priority date Publication date Assignee Title
EP1420613A2 (fr) * 2002-11-15 2004-05-19 Electrolux Home Products Corporation N.V. Procédé et dispositif de surveillance thermique d'un ustensile de cuisson chauffable inductivement
EP2533605A2 (fr) * 2011-06-06 2012-12-12 General Electric Company Détection de poêle de cuisson à induction
WO2013064332A1 (fr) * 2011-11-03 2013-05-10 Arcelik Anonim Sirketi Cuiseur à induction

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