CN109511188B - Electromagnetic heating device, electromagnetic heating system and control method thereof - Google Patents
Electromagnetic heating device, electromagnetic heating system and control method thereof Download PDFInfo
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- CN109511188B CN109511188B CN201710828930.XA CN201710828930A CN109511188B CN 109511188 B CN109511188 B CN 109511188B CN 201710828930 A CN201710828930 A CN 201710828930A CN 109511188 B CN109511188 B CN 109511188B
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- 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
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- 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
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Abstract
The invention discloses an electromagnetic heating system and a control method thereof, wherein the electromagnetic heating system comprises a resonance heating circuit, a synchronous circuit, a power switch tube and a driving circuit, and the method comprises the following steps: controlling the electromagnetic heating system to enter a current heating period, wherein the current heating period comprises a discharging stage, a heating stage and a stopping stage, and the driving circuit is controlled to output a plurality of first pulse signals to the power switch tube in the discharging stage; recording the number of pulses which do not meet preset conditions in the plurality of first pulse signals through a counter to obtain a current count value; the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period are/is adjusted according to the current count value, so that the driving pulse width and/or pulse width increment of the driving circuit can be automatically adjusted, and the pulse current is effectively inhibited. The invention also discloses an electromagnetic heating device.
Description
Technical Field
The invention relates to the technical field of household appliances, in particular to a control method of an electromagnetic heating system, the electromagnetic heating system and an electromagnetic heating device.
Background
The related electromagnetic heating system, such as an induction cooker, generally drives the IGBT tube through a driving circuit, that is, the driving circuit may provide a driving signal to the IGBT tube to control the IGBT tube to turn on or off. A low-power heating electromagnetic oven adopts a wave-losing mode to realize low-power heating, adopts a driving voltage smaller than a normal driving voltage to perform discharge treatment in a low-power stage, and requires a small pulse width. The heating stage is driven with a normal voltage of normal width. However, the response degree of different models of IGBT tubes or peripheral driving circuit parameters to the PPG width is different, and in the low-power discharge stage, due to the small pulse width, some models of IGBTs are not sufficiently conducted, so that the discharge is incomplete, and the IGBTs are too large in loss and easily generate heat. And in the stage of switching to normal heating, the voltage of the C electrode of the IGBT is too high, so that the IGBT is easily burnt due to too large current.
Accordingly, there is a need for improvement in the related art.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, a first object of the present invention is to provide a control method for an electromagnetic heating system, which can automatically adjust the driving pulse width of a driving circuit and effectively suppress a pulse current.
A second object of the present invention is to provide an electromagnetic heating system, and a third object of the present invention is to provide an electromagnetic heating apparatus.
In order to achieve the above object, a first embodiment of the present invention provides a method for controlling an electromagnetic heating system, where the electromagnetic heating system includes a resonant heating circuit, a synchronous circuit, a power switch and a driving circuit, and the method includes the following steps: controlling the electromagnetic heating system to enter a current heating period, wherein the current heating period comprises a discharging stage, a heating stage and a stopping stage, and the driving circuit is controlled to output a plurality of first pulse signals to the power switch tube in the discharging stage; recording the number of pulses which do not meet preset conditions in the plurality of first pulse signals through a counter to obtain a current count value; and adjusting the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period according to the current counting value.
According to the control method of the electromagnetic heating system provided by the embodiment of the invention, firstly, the electromagnetic heating system is controlled to enter the current heating period, and controls the driving circuit to output a plurality of first pulse signals to the power switch tube at the discharging stage of the current heating period, then, the number of pulses in the plurality of first pulse signals which do not meet the preset condition is recorded through a counter to obtain a current count value, further adjusting the initial pulse width and/or pulse width increment of a plurality of first pulse signals in the next heating period according to the current counting value, so that the drive pulse width and/or pulse width increment of the drive circuit can be automatically adjusted, the power switch tube circuit can be matched with power switch tubes of different models or different peripheral circuits, effectively inhibit pulse current of the power switch tubes, prevent the power switch tubes from being burnt due to heating, reduce loss of the power switch tubes and improve reliability of the power switch tubes.
In addition, the control method of the electromagnetic heating system proposed according to the above embodiment of the present invention may further have the following additional technical features:
according to an embodiment of the present invention, adjusting the initial pulse width and/or the pulse width increment of the plurality of first pulse signals in the next heating period according to the current count value includes: if the current count value is smaller than a first preset threshold value, reducing the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period; and if the current counting value is larger than a second preset threshold value, increasing the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period, wherein the second preset threshold value is larger than or equal to the first preset threshold value.
According to an embodiment of the invention, the first preset threshold is 2-4 and the second preset threshold is 9-11.
According to an embodiment of the present invention, the synchronous circuit is turned over when the state of the resonant heating circuit satisfies a preset on condition, and the controlling the driving circuit to output a plurality of first pulse signals to the power switch tube includes: controlling the driving circuit to output an ith first pulse signal to the power switch tube; judging whether the turn-off time of the power switch tube reaches the preset turn-off time or whether the synchronous circuit is turned over after the ith first pulse signal is output; if the turn-off time of the power switch tube reaches the preset turn-off time, controlling the driving circuit to output an (i +1) th first pulse signal to the power switch tube and controlling the count value of the counter to increase; and if the synchronous circuit is turned over, controlling the driving circuit to output an (i +1) th first pulse signal to the power switch tube and controlling the count value of the counter to be kept unchanged, wherein i is a positive integer.
According to one embodiment of the present invention, the initial pulse width ranges from 0.1us or more to 2us or less, and the pulse width increment ranges from 0.05us or more to 2us or less.
In order to achieve the above object, a second embodiment of the present invention provides an electromagnetic heating system, including: a resonant heating circuit; a power switch tube; the synchronous circuit is connected with the resonant heating circuit and is used for overturning when the state of the resonant heating circuit meets a preset switching-on condition; the driving circuit is connected with the power switch tube and is used for driving the power switch tube to be switched on or switched off; the control unit is respectively connected with the synchronization circuit and the driving circuit, and is used for controlling the electromagnetic heating system to enter a current heating cycle, wherein the current heating cycle comprises a discharging stage, a heating stage and a stopping stage, the driving circuit is controlled to output a plurality of first pulse signals to the power switch tube in the discharging stage, the number of pulses in the plurality of first pulse signals, which do not meet preset conditions, is recorded through a counter so as to obtain a current count value, and the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating cycle is adjusted according to the current count value.
According to the electromagnetic heating system provided by the embodiment of the invention, firstly, the electromagnetic heating system is controlled to enter the current heating period, and controls the driving circuit to output a plurality of first pulse signals to the power switch tube at the discharging stage of the current heating period, then, the number of pulses in the plurality of first pulse signals which do not meet the preset condition is recorded through a counter to obtain a current count value, further adjusting the initial pulse width and/or pulse width increment of a plurality of first pulse signals in the next heating period according to the current counting value, so that the drive pulse width and/or pulse width increment of the drive circuit can be automatically adjusted, the power switch tube circuit can be matched with power switch tubes of different models or different peripheral circuits, effectively inhibit pulse current of the power switch tubes, prevent the power switch tubes from being burnt due to heating, reduce loss of the power switch tubes and improve reliability of the power switch tubes.
In addition, the electromagnetic heating system proposed according to the above embodiment of the present invention may further have the following additional technical features:
according to an embodiment of the present invention, if the current count value is smaller than a first preset threshold, the control unit decreases the initial pulse width and/or the pulse width increment of the plurality of first pulse signals in the next heating cycle; and if the current count value is larger than a second preset threshold value, the control unit increases the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period, wherein the second preset threshold value is larger than or equal to the first preset threshold value.
According to an embodiment of the invention, the first preset threshold is 2-4 and the second preset threshold is 9-11.
According to an embodiment of the present invention, the synchronous circuit is turned over when the state of the resonant heating circuit satisfies a preset on condition, and the control unit is further configured to: controlling the driving circuit to output an ith first pulse signal to the power switching tube, judging whether the turn-off time of the power switching tube reaches a preset turn-off time or whether the synchronous circuit overturns after the ith first pulse signal is output, if the turn-off time of the power switching tube reaches the preset turn-off time, controlling the driving circuit to output an (i +1) th first pulse signal to the power switching tube, controlling the count value of the counter to increase, and if the synchronous circuit overturns, controlling the driving circuit to output an (i +1) th first pulse signal to the power switching tube, and controlling the count value of the counter to keep unchanged, wherein i is a positive integer.
According to one embodiment of the present invention, the initial pulse width ranges from 0.1us or more to 2us or less, and the pulse width increment ranges from 0.05us or more to 2us or less. In order to achieve the above object, a third embodiment of the present invention provides an electromagnetic heating apparatus, which includes the electromagnetic heating system.
According to the electromagnetic heating device provided by the embodiment of the invention, the driving pulse width and/or pulse width increment of the driving circuit can be automatically adjusted to match with power switching tubes of different models or different peripheral circuits, so that the pulse current of the power switching tubes is effectively inhibited, the power switching tubes are prevented from being heated and burnt, the loss of the power switching tubes is reduced, and the reliability of the power switching tubes is improved.
According to an embodiment of the present invention, the electromagnetic heating device may be an induction cooker, an electromagnetic rice cooker, or the like.
Drawings
Fig. 1 is a flowchart of a control method of an electromagnetic heating system according to an embodiment of the present invention;
fig. 2 is a waveform diagram illustrating a control method of an electromagnetic heating system according to an embodiment of the present invention;
FIG. 3 is an enlarged view of the driving waveforms of the discharge phase, the heating phase and the stop phase of FIG. 2;
fig. 4 is a schematic diagram illustrating an output principle of a PPG pulse signal in a control method of an electromagnetic heating system according to an embodiment of the present invention;
fig. 5 is a control schematic diagram of a control method of an electromagnetic heating system according to an embodiment of the present invention;
FIG. 6 is a driving waveform diagram for the discharge phase of FIG. 2;
FIG. 7 is a block schematic diagram of an electromagnetic heating system according to an embodiment of the present invention;
FIG. 8 is a schematic circuit diagram of an electromagnetic heating system in accordance with a specific embodiment of the present invention; and
fig. 9 is a block schematic diagram of an electromagnetic heating apparatus according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
A control method of an electromagnetic heating system according to an embodiment of the first aspect of the present invention is described below with reference to the drawings.
Fig. 1 is a flowchart of a control method of an electromagnetic heating system according to an embodiment of the present invention. The electromagnetic heating system comprises a resonant heating circuit, a synchronous circuit, a power switch tube and a driving circuit.
As shown in fig. 1, a control method of an electromagnetic heating system according to an embodiment of the present invention includes the steps of:
s101: and controlling the electromagnetic heating system to enter a current heating period, wherein the current heating period comprises a discharging phase D1, a heating phase D2 and a stopping phase D3, and the driving circuit is controlled to output a plurality of first pulse signals to the power switch tube in the discharging phase D1.
In an embodiment of the present invention, the electromagnetic heating system may implement low-power heating by using step voltage driving, that is, when the target heating power W1 is less than the preset power W2, the electromagnetic heating system is controlled to sequentially enter a discharging phase D1, a heating phase D2 and a stopping phase D3 in each heating cycle, wherein a plurality of first pulse signals are output to the power switch tube in the discharging phase D1 to make the power switch tube operate in an amplifying state, wherein the amplitude of the first pulse signals is the first driving voltage V1, that is, the power switch tube is driven to turn on by the first driving voltage V1 in the discharging phase; outputting a plurality of second pulse signals to the power switch tube in a heating stage D2 to enable the power switch tube to operate in a saturation state, wherein the amplitude of the second pulse signals is a second driving voltage V2, that is, the power switch tube is driven to be turned on by the second driving voltage V2 in the heating stage; in the stop phase D3, the power switch is driven to turn off by the third driving voltage V3, for example, 0V. Therefore, before the heating phase D2, the discharging phase D1 is entered, so as to effectively suppress the pulse current of the power switch tube, and release the electric energy stored in the filter capacitor (i.e. C1 of fig. 8) during the previous stop phase D3, so that the collector voltage of the power switch tube is substantially 0V when the heating phase D2 is entered.
According to an embodiment of the present invention, the first driving voltage V1 is equal to or greater than 5V and equal to or less than 14.5V, for example, may be preferably 9V, and the second driving voltage V2 is equal to or greater than 15V, for example, may be preferably 18V.
Further, as shown in fig. 2, during each heating cycle, a zero-crossing point of the alternating current supplied to the electromagnetic heating system is also detected, and the electromagnetic heating system is controlled to enter the heating phase D2 and the stop phase D3 according to the zero-crossing point.
For example, as shown in fig. 2-3, the heating is performed by using 2/4 duty cycle, taking four half-waves of the mains supply as an example of a control cycle, and the discharge phase D1 is entered before the first zero-crossing point, for example, the first zero-crossing point may be estimated, and then the starting time of the discharge phase D1 may be obtained according to the estimated first zero-crossing point and the duration of the discharge phase D1, at which the electromagnetic heating system is controlled to enter the discharge phase D1. Therefore, after the discharging phase D1 is entered, a first pulse signal with the amplitude of the first driving voltage V1 is output to the control electrode (for example, the G electrode of the IGBT) of the power switch tube, so that the power switch tube operates in an amplifying state. When the first zero-crossing point is detected, the electromagnetic heating system is controlled to enter the heating stage D2, namely the starting moment of the heating stage D2 is near the first zero-crossing point, and after the first zero-crossing point, a second pulse signal with the amplitude of the second driving voltage V2 is output to the control electrode of the power switch tube, so that the power switch tube works in a saturated conducting state. The duration of the heating phase D2 may be two half-wave periods, in which case, when the third zero-crossing point is detected, the electromagnetic heating system is controlled to enter the stop phase D3, and a third driving voltage, for example, 0V, is output to the control electrode of the power switch tube, so that the power switch tube operates in the off state, and the stop phase D3 lasts two half-wave periods.
Therefore, in each heating cycle, the discharging stage D1 is entered, that is, the power switch tube is driven by a plurality of first pulse signals, for example, 9V driving voltage to perform discharging process (wherein, the 9V driving voltage makes the power switch tube work in an amplifying state, and the current is constant), wherein the initial pulse width of the plurality of first pulse signals can be set to be relatively small, so as to effectively suppress noise, and the pulse width of the plurality of first pulse signals can be gradually increased. Then, near the zero crossing point, the heating phase D2 is entered, that is, the power switch is driven by a plurality of second pulse signals, for example, an 18V driving voltage, so that the power switch operates in a saturated conducting state.
It should be understood that, as shown in fig. 3, the pulse widths of the plurality of first pulse signals may gradually increase, that is, during the discharging phase D1, the power switch tubes are driven to turn on and off by the plurality of first pulse signals to release the electric energy stored in the filter capacitor (e.g., C1 shown in fig. 8) during the stop phase D3, where the plurality of first pulse signals may be M, and the pulse widths of the M first pulse signals may be YM, YM-1, YM-2, …, Y2, Y1, and the pulse widths of the M first pulse signals may gradually increase.
According to an embodiment of the present invention, the pulse widths of the M first pulse signals may be increased by a pulse width increment Δ Y, i.e., Y2 ═ Y1 +/Δ Y, Y3 ═ Y2 +/Δ Y, …, and YM ═ YM-1 +/Δ Y. Wherein, Δ Y is the pulse width increment, Y1 is the initial pulse width, Y1 can be greater than or equal to 0.1us and less than or equal to 2us, and Δ Y can be greater than or equal to 0.05us and less than or equal to 2 us. Wherein, when the main frequency of the chip is 16MHz, the width of a single PPG is 0.0625us, namely 1/16 us. Namely, the value range of the delta Y is 1-32 PPG widths.
S102: and recording the number of pulses which do not meet the preset condition in the plurality of first pulse signals through a counter to obtain a current count value n.
According to an embodiment of the present invention, the step of the synchronous circuit inverting when the state of the resonant heating circuit satisfies a preset on condition, and the step of controlling the driving circuit to output a plurality of first pulse signals to the power switch tube includes: controlling the driving circuit to output the ith first pulse signal to the power switch tube; judging whether the turn-off time of the power switch tube reaches the preset turn-off time or whether the synchronous circuit is turned over after the ith first pulse signal is output; if the turn-off time of the power switch tube reaches the preset turn-off time, controlling the driving circuit to output an (i +1) th first pulse signal to the power switch tube and controlling the count value of the counter to increase; and if the synchronous circuit is turned over, controlling the driving circuit to output an (i +1) th first pulse signal to the power switch tube, and controlling the count value of the counter to be kept unchanged, wherein i is a positive integer.
It should be noted that, as shown in fig. 4, the pulse signal output control authority of the driving circuit has 3, and one is the program start pulse signal output, that is, the first pulse of start is controlled by the program; secondly, in the subsequent pulse signal, the voltages Va and Vb at two ends of a resonant capacitor (such as C2 in fig. 8) are used for comparison, inversion and follow-up output (namely synchronous comparison output); and thirdly, forcibly outputting the subsequent pulse signals after the maximum turn-off time is up, namely forcibly outputting the pulse signals when the turn-off time reaches the preset turn-off time. For example, in some special cases, the pulse width is too small or the voltage is too low in the voltage zero-crossing stage, which causes insufficient turn-on energy, Va and Vb are not inverted, and then the pulse signal is output forcibly after the turn-off time reaches the preset maximum turn-off time.
That is, the preset condition may be that the pulse signal is output when the synchronization circuit is inverted. In other words, the number of the first pulse signals which are forcibly output to the preset off time in the plurality of first pulse signals is recorded by the counter.
Specifically, the driving circuit is controlled to output a plurality of first pulse signals, for example, 9V to the power switching tube in the discharging phase D1 of the first heating cycle, after the driving circuit outputs the ith first pulse signal to the power switching tube, when the ith pulse signal is completely output, that is, the ith pulse signal is changed from the high level to the low level, the turn-off time of the power switching tube is started to be timed, if the inversion of the synchronous circuit is not detected within the preset turn-off time, the (i +1) th first pulse signal is forcibly output, and the count value of the counter is controlled to be increased by 1, so as to count the number of the first pulse signals forcibly output until the preset turn-off time; and (3) outputting the (i +1) th first pulse signal along with the overturning signal until the synchronous circuit is detected to overturn within the preset turn-off time, controlling the counter to stop counting, and recording the counting value at the moment, namely recording the counting value as n.
Wherein, the synchronous circuit may include a detection unit and a comparator, the detection unit is configured to detect a voltage across a resonant capacitor (e.g., C2 in fig. 8), for example, the detection unit may detect a voltage at a left end of the resonant capacitor to output a first detection voltage Va through a first output terminal, and may detect a voltage at a right end of the resonant capacitor to output a second detection voltage Vb through a second output terminal, the first output terminal and the second output terminal of the detection unit are respectively connected to a negative input terminal and a positive input terminal of the comparator, and the comparator may compare the first detection voltage Va and the second detection voltage Vb, and output a synchronous signal according to a comparison result. Wherein the comparator is integrated with the control unit.
As shown in fig. 5 and 6, in the discharging phase D1, the initial pulse width of the first pulse signal is sufficiently small, for example, 0.1us or more and 2us or less, and the pulse increase amplitude Δ Y between two adjacent pulse signals is also relatively small, so that the pulse current can be reduced and the current can smoothly rise. However, the smaller pulse width will cause the insufficient on-energy of the power switch tube, and the oscillation condition of the resonant heating circuit cannot be reached, and at this time, the forced output is performed after the maximum off-time is reached, that is, the interval D11 in fig. 5-6, and the pulse number of the forced output at this time is recorded. With the increase of the pulse width, in the interval D12, the pulse width is larger to provide enough energy to reach the oscillation condition of the resonant heating circuit, and at this time, the synchronous comparison output is adopted, and the pulse signal is compared and inverted by the synchronous circuit.
As shown in fig. 5 and 6, the discharging phase D1 can be divided into two intervals, i.e., a first interval D11 and a second interval D12. In a first interval D11, the pulse width is relatively small, the turn-on energy of the power switching tube is insufficient, the resonant heating circuit does not reach the oscillation condition, the synchronous circuit does not turn over, and after the preset turn-off time is reached, the pulse signal is forcibly output, that is, the pulse signal output by the synchronous circuit cannot be detected to be turned over within the preset turn-off time, and the pulse signal is forcibly output; in a second interval D12, the pulse width is increased, the turn-on energy of the power switch tube is sufficient, the resonant heating circuit reaches the oscillation condition, the synchronous circuit is turned over, and a pulse signal is output during turning over. That is, it can be detected that the synchronization signal output from the synchronization circuit is inverted during a preset off time, and a pulse signal is output during the inversion. In the discharging phase D1 of the first heating period, the number of pulses n that do not satisfy the preset condition, that is, only the number of pulses that do not allow the resonant heating circuit to reach the resonant condition, is recorded by the counter.
S103: and adjusting the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period according to the current counting value.
It should be noted that the power switching tubes of different models or peripheral driving circuit parameters cause different response degrees to the PPG pulse width, so that the energy released by the power switching tubes is different, for example, if the power switching tubes are not sensitive to the pulse width response, when a heating stage is started near a zero crossing point, the C-pole voltage of the power switching tubes cannot be released to 0V, and at this time, the power switching tubes work in an amplification state, are too large in loss, and are easily burned out; for another example, if the power switch is too sensitive to the pulse width response, the starting current is large or the current rises fast in the discharging stage, and the noise is large.
In the embodiment of the invention, according to the current heating period, the pulse number of the first pulse signals which does not meet the preset condition is used for adjusting the initial pulse width and/or the pulse width increment of the first pulse signals in the next heating period, so that the parameters of power switch tubes or peripheral driving circuits of different models can be matched, the pulse current of the power switch tubes is effectively inhibited, the power switch tubes are prevented from being heated and burnt, the loss of the power switch tubes is reduced, and the reliability of the power switch tubes is improved.
According to one embodiment of the present invention, if the current count value n is less than the first preset threshold value a, the initial pulse width and/or the pulse width increment of the plurality of first pulse signals in the next heating period is decreased; and if the current counting value n is larger than a second preset threshold value B, increasing the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period, wherein the second preset threshold value B is larger than or equal to the first preset threshold value A.
Wherein the first preset threshold value a and the second preset threshold value B are stored in the control unit in advance. In a specific example of the present invention, the first preset threshold a may take a value greater than 2 and less than 4, and the second preset threshold B may take a value greater than 9 and less than 11.
Specifically, the first preset threshold a may be preferably 3, the second preset threshold B may be preferably 10, the default initial pulse width may be 1us, and the default pulse width increment may take 3 PPG widths.
If the current count value n is less than the first preset threshold value a, for example, 3, the initial pulse widths and/or pulse width increments of the plurality of first pulse signals are reduced in the next heating cycle, that is, only the initial pulse widths of the plurality of first pulse signals are reduced or only the pulse width increments of the plurality of first pulse signals are reduced or both the initial widths and the pulse width increments of the plurality of first pulse signals are reduced in the next heating cycle, so that the count value of the next heating cycle is increased to reach a reasonable range, for example, between 3 and 10, thereby being capable of adapting to IGBT tubes sensitive to driving pulse width response and reducing noise.
Similarly, if the current count value n is greater than the second preset threshold value B, for example, 10, the initial pulse widths and/or pulse width increments of the plurality of first pulse signals are increased in the next heating cycle, that is, the initial pulse widths and pulse width increments of the plurality of first pulse signals are increased only or the pulse width increments of the plurality of first pulse signals are increased only or both the initial widths and pulse width increments of the plurality of first pulse signals are increased simultaneously in the next heating cycle, so that the count value of the next heating cycle is decreased to a reasonable range, for example, between 3 and 10, thereby being capable of adapting to the IGBT tube insensitive to the driving pulse width response, and enabling the IGBT tube to be completely discharged in the discharging phase D1.
Therefore, the initial pulse width and/or pulse width increment of the plurality of first pulse signals of the next heating period can be increased or decreased according to the pulse number which does not meet the preset condition in the plurality of first pulse signals of the current heating period, so that the number of pulses which do not meet the preset condition in the discharging stage is within the range of 3 to 10, the power switching tube can be adapted to different response degrees of the power switching tubes of different models to the driving pulse width of the driving circuit, the power switching tube is prevented from being heated and burnt, the loss of the power switching tube is reduced, and the reliability of the power switching tube is improved.
Specifically, as shown in fig. 4 and 5, the control unit of the electromagnetic heating system may control the driving voltage output by the driving circuit by the enable signal EN, for example, the driving circuit outputs the first driving voltage V1 when the enable signal EN is at a high level, and the driving circuit outputs the second driving voltage V2 when the enable signal EN is at a low level.
Therefore, in the embodiment of the present invention, the power switch tube is first driven by the plurality of first pulse signals in the discharging phase D1 of the current heating cycle, where the amplitude of the first pulse signals may be 9V and the pulse width gradually increases, the power switch tube operates in the amplifying state, the current flowing through the power switch tube is constant, at this time, the number of pulses in the plurality of first pulse signals that do not satisfy the preset condition is recorded by the counter to obtain the current count value, and the initial pulse width and/or the pulse width increment of the plurality of first pulse signals in the next heating cycle are obtained according to the current count value. In the heating stage D2, the power switch tube is driven by a pulse signal with an amplitude of 18V, and the pulse width adopts a normal width value, and the power switch tube operates in a saturated conducting state, at which the power switch tube acts like a conducting switch, and then in the stopping stage D3, a driving voltage of 0V is used, so that the power switch tube is in an off state.
In summary, according to the control method of the electromagnetic heating system provided by the embodiment of the invention, firstly, the electromagnetic heating system is controlled to enter the current heating cycle, and the driving circuit is controlled to output a plurality of first pulse signals to the power switch tube in the discharging stage of the current heating cycle, then the counter records the number of pulses in the plurality of first pulse signals which do not meet the preset condition to obtain the current count value, and further the initial pulse width and/or the pulse width increment of the plurality of first pulse signals in the next heating cycle are adjusted according to the current count value, so that the driving pulse width and/or the pulse width increment of the driving circuit can be automatically adjusted to match the parameters of the power switch tubes of different models or different peripheral driving circuits, the pulse current of the power switch tubes is effectively inhibited, the power switch tubes are prevented from being heated and burned, and the loss of the power switch tubes is reduced, the reliability of the power switch tube is improved.
An electromagnetic heating system according to an embodiment of the second aspect of the present invention is described below with reference to fig. 7 and 8.
Fig. 7 is a block schematic diagram of an electromagnetic heating system according to an embodiment of the present invention. As shown in fig. 7, the electromagnetic heating system 100 includes: the resonant heating circuit 10, the power switch tube 20, the synchronization circuit 30, the driving circuit 40 and the control unit 50.
The synchronous circuit 30 is connected with the resonant heating circuit 10, and the synchronous circuit 30 is used for turning over when the state of the resonant heating circuit 10 meets a preset turn-on condition; the driving circuit 40 is connected with the power switch tube 20, and the driving circuit 40 is used for driving the power switch tube 20 to be switched on or switched off; the control unit 50 is respectively connected with the synchronization circuit 30 and the driving circuit 40, the control unit 50 is configured to control the electromagnetic heating system to enter a current heating cycle, the current heating cycle includes a discharging phase D1, a heating phase D2 and a stopping phase D3, wherein in the discharging phase D1, the driving circuit 40 is controlled to output a plurality of first pulse signals to the power switch tube 20, and record the number of pulses of the plurality of first pulse signals, which do not meet a preset condition, through a counter to obtain a current count value, and adjust the initial pulse width and/or pulse width increment of the plurality of first pulse signals in a next heating cycle according to the current count value.
In each heating cycle, the discharging stage D1 is entered, that is, the power switch is driven by a plurality of first pulse signals, for example, a 9V driving voltage, to perform discharging process (wherein, the 9V driving voltage makes the power switch operate in an amplifying state, and the current is constant), wherein the initial pulse widths of the plurality of first pulse signals can be set to be relatively small, so as to effectively suppress noise, and the pulse widths of the plurality of first pulse signals can be gradually increased. Then, near the zero crossing point, the heating phase D2 is entered, that is, the power switch is driven by a plurality of second pulse signals, for example, an 18V driving voltage, so that the power switch operates in a saturated conducting state.
It should be understood that, as shown in fig. 3, the pulse widths of the plurality of first pulse signals may gradually increase, that is, during the discharging phase D1, the power switch 20 is driven to turn on and off by the plurality of first pulse signals to release the electric energy stored in the filter capacitor (e.g., C1 shown in fig. 8) during the stop phase D3, where the plurality of first pulse signals may be M, and the pulse widths of the M first pulse signals may be YM, YM-1, YM-2, …, Y2, Y1, and the pulse widths of the M first pulse signals may gradually increase.
According to an embodiment of the present invention, the pulse widths of the M first pulse signals may be increased by a pulse width increment Δ Y, i.e., Y2 ═ Y1 +/Δ Y, Y3 ═ Y2 +/Δ Y, …, and YM ═ YM-1 +/Δ Y. Wherein, Δ Y is a pulse width increment, Y1 is an initial pulse width, Y1 can be greater than or equal to 0.1us and less than or equal to 2us, Δ Y can be greater than or equal to 0.05us and less than or equal to 2us, and when the main frequency of the chip is 16MHz, the single PPG width is 0.0625us, i.e. 1/16 us.
According to an embodiment of the invention, the control unit 50 is further configured to: the control driving circuit 40 outputs an ith first pulse signal to the power switching tube 20, and after the output of the ith first pulse signal is completed, whether the turn-off time of the power switching tube 20 reaches a preset turn-off time or whether the synchronous circuit 30 is turned over is judged, if the turn-off time of the power switching tube 20 reaches the preset turn-off time, the control driving circuit 40 outputs an (i +1) th first pulse signal to the power switching tube 20, the count value of the counter is increased, if the synchronous circuit 30 is turned over, the control driving circuit 40 outputs an (i +1) th first pulse signal to the power switching tube 20, and the count value of the counter is kept unchanged.
It should be noted that, as shown in fig. 4, the pulse signal output control authority of the driving circuit 40 has 3, and one is the program start pulse signal output, that is, the first pulse to start is controlled by the program; secondly, in the subsequent pulse signal, the voltages Va and Vb at two ends of a resonant capacitor (such as C2 in fig. 8) are used for comparison, inversion and follow-up output (namely synchronous comparison output); and thirdly, forcibly outputting the subsequent pulse signals after the maximum turn-off time is up, namely forcibly outputting the pulse signals when the turn-off time reaches the preset turn-off time. For example, in some special cases, the pulse width is too small or the voltage is too low in the voltage zero-crossing stage, which causes insufficient turn-on energy, Va and Vb are not inverted, and at this time, the pulse signal is output forcibly after the turn-off time reaches the preset maximum turn-off time.
That is, the preset condition may be that the pulse signal is output when the synchronization circuit 30 is flipped. In other words, the number of the first pulse signals which are forcibly output to the preset off time in the plurality of first pulse signals is recorded by the counter.
Specifically, the driving circuit 40 is controlled to output a plurality of first pulse signals, for example, 9V to the power switch tube 20 in the discharging phase D1 of the first heating cycle, after the driving circuit 40 outputs the ith first pulse signal to the power switch tube 20, when the ith pulse signal is completely output, that is, the ith pulse signal is changed from the high level to the low level, the turn-off time of the power switch tube 20 is started to be timed, if the inversion of the synchronization circuit 30 is not detected within the preset turn-off time, the (i +1) th first pulse signal is forcibly output, and the count value of the counter is controlled to be increased by 1, so as to count the number of the first pulse signals forcibly output until the preset turn-off time is reached; until the synchronous circuit 30 is detected to be turned over within the preset turn-off time, the (i +1) th first pulse signal is output along with the turning signal, the counter is controlled to stop counting, and the counting value at the moment is recorded, namely, the counting value is recorded as n.
Wherein, the synchronous circuit 30 may include a detecting unit 70 and a comparator 60, the detecting unit 70 is configured to detect a voltage across a resonant capacitor (e.g., C2 in fig. 8), for example, detect a voltage at a left end of the resonant capacitor to output a first detected voltage Va through a first output terminal, and detect a voltage at a right end of the resonant capacitor to output a second detected voltage Vb through a second output terminal, the first output terminal and the second output terminal of the detecting unit 70 are respectively connected to a negative input terminal and a positive input terminal of the comparator 60, and the comparator 60 may compare the first detected voltage Va and the second detected voltage Vb, and output a synchronous signal according to a comparison result. Wherein the comparator 60 is provided integrally with the control unit 50.
As shown in fig. 5 and 6, in the discharging phase D1, the initial pulse width of the first pulse signal is sufficiently small, for example, 0.1us or more and 2us or less, and the pulse increase amplitude Δ Y between two adjacent pulse signals is also relatively small, so that the pulse current can be reduced and the current can smoothly rise. However, the smaller pulse width will cause the on energy of the power switch 20 to be insufficient, and the oscillation condition of the resonant heating circuit 10 cannot be achieved, and at this time, the pulse number of the forced output is recorded by adopting the forced output after the maximum off time is reached, i.e., the interval D11 in fig. 5-6. With the increase of the pulse width, the larger pulse width provides enough energy to reach the oscillation condition of the resonant heating circuit 10 in the interval D12, and the pulse signal follows the comparison and inversion output of the synchronization circuit 30.
As shown in fig. 5 and 6, the discharging phase D1 can be divided into two intervals, i.e., a first interval D11 and a second interval D12. In a first interval D11, the pulse width is relatively small, the turn-on energy of the power switch tube 20 is insufficient, the resonant heating circuit 10 does not reach the oscillation condition, the synchronous circuit 30 does not turn over, and after the preset turn-off time is reached, the pulse signal is forcibly output, that is, the pulse signal output by the synchronous circuit 30 cannot be detected to be turned over within the preset turn-off time, and the pulse signal is forcibly output; in the second interval D12, the pulse width increases, the turn-on energy of the power switch 20 is sufficient, the resonant heating circuit 10 reaches the oscillation condition, the synchronization circuit 30 inverts, and a pulse signal is output during the inversion. That is, it is possible to detect that the synchronization signal output from the synchronization circuit 30 is inverted during a preset off time, and output a pulse signal at the time of inversion. In the discharging phase D1 of the first heating cycle, the number of pulses n that do not satisfy the preset condition among the plurality of first pulse signals, that is, only the number of pulses that do not allow the resonant heating circuit 10 to reach the resonant condition, is recorded by the counter.
It should be noted that, the power switch tube 20 of different models or parameters of the peripheral driving circuit cause different response degrees to the PPG pulse width, so that the energy released by the power switch tube 20 is different, for example, if the power switch tube 20 is not sensitive to the pulse width response, when the heating stage is started near the zero crossing point, the C-pole voltage of the power switch tube 20 cannot be released to 0V, and at this time, the power switch tube 20 works in an amplification state, the loss is too large, and the heating burn out is easy to occur; for another example, if the power switch tube 20 is too sensitive to the pulse width response, the voltage of the C-pole of the power switch tube 20 is released to 0V in advance before the heating stage is started near the zero crossing point, and at this time, the pulse current of the power switch tube is large and the noise is large.
In the embodiment of the invention, according to the current heating period, the pulse number of the first pulse signals which does not meet the preset condition is used for adjusting the initial pulse width and/or the pulse width increment of the first pulse signals in the next heating period, so that the power switching tubes of different models or different peripheral circuits can be matched, the pulse current of the power switching tubes is effectively inhibited, the power switching tubes are prevented from being heated and burnt, the loss of the power switching tubes is reduced, and the reliability of the power switching tubes is improved.
According to one embodiment of the present invention, if the current count value n is less than the first preset threshold value a, the initial pulse width and/or the pulse width increment of the plurality of first pulse signals in the next heating period is decreased; and if the current counting value n is larger than a second preset threshold value B, increasing the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period, wherein the second preset threshold value B is larger than or equal to the first preset threshold value A.
Wherein a first preset threshold a and a second preset threshold B are stored in advance in the control unit 50. In a specific example of the present invention, the first preset threshold a may take a value greater than 2 and less than 4, and the second preset threshold B may take a value greater than 9 and less than 11.
Specifically, the first preset threshold a may be preferably 3, the second preset threshold B may be preferably 10, the default initial pulse width may be 1us, and the default pulse width increment may take 3 PPG widths.
If the current count value n is less than the first preset threshold value a, for example, 3, the initial pulse widths and/or pulse width increments of the plurality of first pulse signals are reduced in the next heating cycle, that is, only the initial pulse widths of the plurality of first pulse signals are reduced or only the pulse width increments of the plurality of first pulse signals are reduced or both the initial widths and the pulse width increments of the plurality of first pulse signals are reduced in the next heating cycle, so that the count value of the next heating cycle is increased to reach a reasonable range, for example, between 3 and 10, thereby being capable of adapting to IGBT tubes sensitive to driving pulse width response and reducing noise.
Similarly, if the current count value n is greater than the second preset threshold value B, for example, 10, the initial pulse widths and/or pulse width increments of the plurality of first pulse signals are increased in the next heating cycle, that is, the initial pulse widths and pulse width increments of the plurality of first pulse signals are increased only or the pulse width increments of the plurality of first pulse signals are increased only or both the initial widths and pulse width increments of the plurality of first pulse signals are increased simultaneously in the next heating cycle, so that the count value of the next heating cycle is decreased to a reasonable range, for example, between 3 and 10, thereby being capable of adapting to the IGBT tube insensitive to the driving pulse width response, and enabling the IGBT tube to be completely discharged in the discharging phase D1.
Therefore, the initial pulse width and/or pulse width increment of the plurality of first pulse signals of the next heating period can be increased or decreased according to the pulse number which does not meet the preset condition in the plurality of first pulse signals of the current heating period, so that the number of pulses in the heating period is within the range of 3 to 10, the different response degrees of the power switching tubes 20 of different models to the driving pulse width of the driving circuit 40 are adapted, the power switching tubes are prevented from being heated and burnt, the loss of the power switching tubes is reduced, and the reliability of the power switching tubes is improved.
Specifically, as shown in fig. 4 and 5, the control unit 50 of the electromagnetic heating system may control the driving voltage output by the driving circuit 40 by the enable signal EN, for example, when the enable signal EN is at a high level, the driving circuit 40 outputs the first driving voltage V1, and when the enable signal EN is at a low level, the driving circuit 40 outputs the second driving voltage V2.
Therefore, in the embodiment of the present invention, the power switch tube 20 is first driven by the first pulse signals in the discharging phase D1 of the current heating cycle, where the amplitude of the first pulse signals may be 9V and the pulse width gradually increases, the power switch tube 20 operates in the amplifying state, the current flowing through the power switch tube 20 is constant, the number of pulses in the first pulse signals that do not satisfy the preset condition is recorded by the counter to obtain the current count value, and the initial pulse width and/or the pulse width increment of the first pulse signals in the next heating cycle are obtained according to the current count value. Then, in the heating stage D2, the power switching tube 20 is driven by a pulse signal with an amplitude of 18V, and the pulse width adopts a normal width value, the power switching tube 20 operates in a saturated on state, at this time, the power switching tube 20 acts like an on switch, and then, in the stopping stage D3, a driving voltage of 0V is used, so that the power switching tube 20 is in an off state.
In summary, according to the electromagnetic heating system provided by the embodiment of the invention, the electromagnetic heating system is firstly controlled to enter the current heating cycle, and controls the driving circuit to output a plurality of first pulse signals to the power switch tube at the discharging stage of the current heating period, then, the number of pulses in the plurality of first pulse signals which do not meet the preset condition is recorded through a counter to obtain a current count value, further adjusting the initial pulse width and/or pulse width increment of a plurality of first pulse signals in the next heating period according to the current counting value, so that the drive pulse width and/or pulse width increment of the drive circuit can be automatically adjusted, the power switch tube circuit can be matched with power switch tubes of different models or different peripheral circuits, effectively inhibit pulse current of the power switch tubes, prevent the power switch tubes from being burnt due to heating, reduce loss of the power switch tubes and improve reliability of the power switch tubes.
An electromagnetic heating apparatus according to a third embodiment of the present invention will be described with reference to fig. 9.
Fig. 9 is a block schematic diagram of an electromagnetic heating apparatus according to an embodiment of the present invention. As shown in fig. 9, the electromagnetic heating apparatus 200 includes the electromagnetic heating system 100 described above.
According to an embodiment of the present invention, the electromagnetic heating device 200 may be an induction cooker, an electromagnetic rice cooker, or the like.
In summary, according to the electromagnetic heating apparatus provided in the embodiment of the present invention, the driving pulse width and/or the pulse width increment of the driving circuit can be automatically adjusted according to different response degrees of different types of power switching tubes to the driving pulse width of the driving circuit, so as to match different types of power switching tubes or different peripheral circuits, effectively suppress the pulse current of the power switching tubes, prevent the power switching tubes from being heated and burned, reduce the loss of the power switching tubes, and improve the reliability of the power switching tubes.
In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "M, N" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or M, N of the embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (12)
1. A method of controlling an electromagnetic heating system, the electromagnetic heating system comprising a resonant heating circuit, a synchronization circuit, a power switching tube and a drive circuit, the method comprising the steps of:
controlling the electromagnetic heating system to enter a current heating period, wherein the current heating period comprises a discharging stage, a heating stage and a stopping stage, and the driving circuit is controlled to output a plurality of first pulse signals to the power switch tube in the discharging stage;
recording the number of pulses which do not meet preset conditions in the plurality of first pulse signals through a counter to obtain a current count value;
and adjusting the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period according to the current counting value.
2. The method of controlling an electromagnetic heating system according to claim 1, wherein adjusting an initial pulse width and/or a pulse width increment of the plurality of first pulse signals in a next heating period according to the current count value comprises:
if the current count value is smaller than a first preset threshold value, reducing the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period;
and if the current counting value is larger than a second preset threshold value, increasing the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period, wherein the second preset threshold value is larger than or equal to the first preset threshold value.
3. A control method of an electromagnetic heating system according to claim 2, characterized in that the first preset threshold value is 2-4 and the second preset threshold value is 9-11.
4. The method of claim 1, wherein the synchronous circuit is turned over when the state of the resonant heating circuit satisfies a preset turn-on condition, and the controlling the driving circuit to output a plurality of first pulse signals to the power switch tube comprises:
controlling the driving circuit to output an ith first pulse signal to the power switch tube;
judging whether the turn-off time of the power switch tube reaches the preset turn-off time or whether the synchronous circuit is turned over after the ith first pulse signal is output;
if the turn-off time of the power switch tube reaches the preset turn-off time, controlling the driving circuit to output an (i +1) th first pulse signal to the power switch tube and controlling the count value of the counter to increase;
and if the synchronous circuit is turned over, controlling the driving circuit to output an (i +1) th first pulse signal to the power switch tube and controlling the count value of the counter to be kept unchanged, wherein i is a positive integer.
5. The control method of an electromagnetic heating system according to claim 1, wherein the initial pulse width ranges from 0.1us or more to 2us or less, and the pulse width increment ranges from 0.05us or more to 2us or less.
6. An electromagnetic heating system, comprising:
a resonant heating circuit;
a power switch tube;
the synchronous circuit is connected with the resonant heating circuit and is used for overturning when the state of the resonant heating circuit meets a preset switching-on condition;
the driving circuit is connected with the power switch tube and is used for driving the power switch tube to be switched on or switched off;
the control unit is respectively connected with the synchronous circuit and the driving circuit, and is used for controlling the electromagnetic heating system to enter a current heating period, wherein the current heating period comprises a discharging stage, a heating stage and a stopping stage, the driving circuit is controlled to output a plurality of first pulse signals to the power switch tube in the discharging stage, the number of pulses in the plurality of first pulse signals, which do not meet preset conditions, is recorded through a counter so as to obtain a current count value, and the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period are/is adjusted according to the current count value.
7. Electromagnetic heating system according to claim 6,
if the current count value is smaller than a first preset threshold value, the control unit reduces the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period;
and if the current count value is larger than a second preset threshold value, the control unit increases the initial pulse width and/or pulse width increment of the plurality of first pulse signals in the next heating period, wherein the second preset threshold value is larger than or equal to the first preset threshold value.
8. Electromagnetic heating system according to claim 7, characterized in that said first preset threshold value is 2-4 and said second preset threshold value is 9-11.
9. The electromagnetic heating system of claim 6, wherein the synchronous circuit is turned over when the state of the resonant heating circuit satisfies a preset on condition, the control unit is further configured to control the driving circuit to output an ith first pulse signal to the power switch tube, and determine whether the off time of the power switch tube reaches a preset off time or whether the synchronous circuit is turned over after the ith first pulse signal is completely output, if the off time of the power switch tube reaches the preset off time, control the driving circuit to output an (i +1) th first pulse signal to the power switch tube, and control the counter value of the counter to increase, and if the synchronous circuit is turned over, control the driving circuit to output an (i +1) th first pulse signal to the power switch tube, and controlling the count value of the counter to be kept unchanged, wherein i is a positive integer.
10. The electromagnetic heating system according to claim 6, wherein the initial pulse width ranges from 0.1us or more to 2us or less, and the pulse width increment ranges from 0.05us or more to 2us or less.
11. Electromagnetic heating device, characterized in that it comprises an electromagnetic heating system according to any one of claims 6-10.
12. The electromagnetic heating device according to claim 11, wherein the electromagnetic heating device is an induction cooker, an induction cooker or an electromagnetic rice cooker.
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