JP2004103523A - Induction heating cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To minimize increase of cost by making changes of circuit in a small scale while doubling the resolution of conventional power control and suppressing effect of noises. <P>SOLUTION: This induction heating cooker comprises a first and a second switching elements 3, 4 that make high frequency current flow by being driven alternately, and a control means 11 that controls the whole circuit. The control means 11 performs control by selecting one of the states out of a state in which the ON time of both switching elements 3, 4 is made nearly equal by driving the first and the second switching elements 3, 4 by a count value outputted by a gate count setting means 14, and a state in which one of the ON time duration is made longer than ON time duration of another side by driving one of the first or the second switching elements 3, 4 by a count, in which the count outputted by a minimum count setting means 15 is added to the count outputted by the gate count setting means 14, and by driving the other by the count outputted by the gate count setting means 14. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power control method for an induction heating cooker.
[0002]
[Prior art]
A conventional induction heating cooker has been recognized as a heat source that replaces a tabletop gas table or the like because it does not generate an open flame, can control the temperature of a load, and has high safety. In addition, as an electric cooker to be incorporated in a system kitchen or the like, a conventional heater using a resistor such as a sheathed heater, a plate heater, or a halogen heater as a heat source, replacing one of the heaters with induction heating, or inducing two or more heaters. It is replacing the cooker.
[0003]
The induction heating cooker converts an AC power supply into a DC power supply, and then turns it on and off with a switching element to convert it into a high-frequency current. The high-frequency current flows through the heating coil, and is arranged in the vicinity by electromagnetic induction caused by the generated magnetic flux. An eddy current is generated in the metal load, and the eddy current heats the load by generating heat.
[0004]
As a control method of an induction heating cooker, a method of using two switching elements and alternately driving them to flow a high-frequency current is one of the typical methods, and a control means generally formed by a microcomputer or the like. The ON time of the two switching elements is varied according to the above command to control the power supplied to the heating coil.
[0005]
Such a conventional example will be described with reference to the drawings. FIG. 6 is a circuit block diagram of a conventional example, FIG. 7 is a diagram showing a first example of a waveform of a main portion of the conventional example, and FIG. 8 is a diagram showing a second example of a waveform of a main portion of the conventional example.
[0006]
In FIG. 6, the input terminal of the rectifier 2 is connected to the AC power supply 1, the first switching element 3 and the second switching element 4 are connected in series, and the collector terminal of the first switching element 3 is connected to the rectifier 2 And the emitter terminal of the second switching element is connected to the low-voltage output terminal of the rectifier 2. One end of a resonance circuit 7 composed of the heating coil 5 and the resonance capacitor 6 is connected to a low-voltage output terminal of the rectifier 2, and the other end is connected to a series connection point of the first and second switching elements 3 and 4. . The above configuration is the main circuit section. Reference numeral 8 denotes a load near the heating coil 5.
[0007]
The control unit includes drive means 9 and 10 for driving the first and second switching elements 3 and 4 respectively, control means 11 formed of a microcomputer or the like, a digital / analog conversion circuit for converting digital to analog (hereinafter referred to as a DA circuit). 22, an oscillating means 23 for generating on / off times of the first and second switching elements 3 and 4, and a blank time so that the first and second switching elements 3 and 4 do not overlap each other. It comprises a blanking time setting means 17, an oscillating means 23 and a separating means 20 for separating the output of the blanking time setting means 17 into first or second switching elements 3 and 4 and outputting the separated switching elements.
[0008]
The operation of the above configuration will be described.
The rectifying means 2 rectifies the AC power supply 1 and converts it to DC. The DC power supply is supplied to a resonance circuit 7 including first and second switching elements 3 and 4, a heating coil 5 and a resonance capacitor 6, When the second switching elements 3 and 4 are alternately driven, a high-frequency current flows through the resonance circuit 7, that is, the heating coil 5. The load 8 is self-heated and heated by the eddy current.
[0009]
The control unit 11 outputs a digital / analog signal corresponding to the set power to the DA circuit 22, and the DA circuit 22 converts the digital / analog signal into a signal and outputs the signal to the oscillation unit 23. The oscillating means 23 outputs a signal of the on / off time of the first and second switching elements 3 and 4 to the separating means 20 in accordance with the output signal of the DA circuit 22, and further outputs a signal to the blank time setting means 17. The blank time setting means 17 sets a blank time in synchronization with the signal of the oscillation means 23 and outputs the same to the separation means 20. The separating means 20 separates the on / off time signal from the oscillating means 23 and the signal of the blank time setting means 17 into a signal for the first switching element 3 or the second switching element 4 in accordance with a command from the control means 11, and 9 or drive means 10.
[0010]
Next, a detailed operation of the main part will be described with reference to signal waveforms.
7 and 8, the signals of SEP1 and SEP2 are the waveforms of the output signals to the drive means 9 and 10 of the separation means 20, respectively, and correspond to the first and second switching elements 3 and 4. IL is a waveform of a current flowing through the heating coil 5. The sections are shown for temporally dividing each signal, and there are four sections A, B, C, and D. The horizontal axis of each signal is time. Hereinafter, these are the same in the drawings showing the signals unless otherwise specified.
[0011]
FIG. 7 is a diagram showing a first example of the waveform of the main part of the conventional example, in which the ON times of the first and second switching elements 3 and 4 are both tN.
[0012]
In FIG. 7, the control means 11 outputs a digital / analog signal based on a digital value N corresponding to the set power to the DA circuit 22, and in response to this, the first switching element 3 periodically causes tN The second switching element 4 is similarly turned on for a period of time tN (section C in the figure) so that the ON does not overlap with the first switching element 3 (section C in the figure). The current of the peak value ILPN flows in the upper and lower directions indicated by. The power at this time is defined as PN.
[0013]
The oscillating means 23 determines the ON time tN of the first and second switching elements 3 and 4, and determines the ON time of the first switching element 3 and the ON time of the second switching element 4. The blanking period (sections B and D in the figure) is a blank time and is always constant. The blank time setting means 17 determines the blank time.
[0014]
When the set power changes by one step, for example, by one step, the control means 11 changes the digital value that is the source of the digital / analog signal output to the DA circuit 22 from N to N + 1, whereby the first and second powers are changed. The ON time of the two switching elements 3 and 4 becomes longer from tN to tN + 1. FIG. 8 shows this pattern.
[0015]
In FIG. 8, since the ON time of the first and second switching elements 3 and 4 is tN + 1, the current flowing through the heating coil 5 has a peak value ILPN + ΔILP3 on both the upper and lower sides. It becomes a large current. Therefore, the power at this time is PN + ΔP2, which is higher by ΔP2 than in the case of the ON time tN.
[0016]
When the set power increases by two steps, the digital value serving as the source of the digital / analog signal output from the control means 11 becomes N + 2, and the ON time of the first and second switching elements 3 and 4 becomes tN + 2. When the set power decreases by one step, the digital value serving as the source of the digital / analog signal output from the control means 11 becomes N-1, and the ON time of the first and second switching elements 3, 4 becomes tN-1. It becomes. That is, the ON times of the first and second switching elements 3 and 4 change stepwise according to the set power.
[0017]
As a similar example of the above-mentioned method, there is an example of Patent Document 1 which shows a method of controlling power by alternately driving two switching elements and changing an on-time.
[0018]
[Patent Document 1] Japanese Patent Application Laid-Open No. 7-192861.
[0019]
[Problems to be solved by the invention]
As described above, the conventional induction heating cooker uses a microcomputer as the control means 11 because it has a small number of parts and is inexpensive. The output of the microcomputer has a resolution of only about 8 bits. The resolution (the number of steps) of the power control depends on the number of bits of the output of the microcomputer. Therefore, the conventional method cannot simply and inexpensively increase the resolution of power control.
[0020]
Further, since the DA circuit 22 and the oscillation circuit 23 for converting the output signal of the control means 11, that is, the microcomputer into the on / off signals of the two switching elements 3 and 4, are circuits utilizing the charging and discharging operation of the resistor and the capacitor. Fluctuations in frequency and pulse width were caused by fluctuations in the ambient temperature and self-temperature rise. Such a fluctuation has an element that makes its control unstable as a power fluctuation. Accordingly, the input power is stabilized, and the power control value by the load 8 shifts with time, which may deviate from the control range, and may cause equipment failure.
[0021]
Therefore, in order to avoid the above-mentioned problem, a high-frequency reference oscillating means using a crystal oscillator or a ceramic oscillator is provided, and its output pulse is counted, and a predetermined frequency of the first and second switching elements 3 and 4 is determined. A method of obtaining the driving pulse width, that is, the ON time, is considered.
[0022]
However, since the drive pulse widths of the first and second switching elements 3 and 4, that is, the on-time, must be set to be substantially equal, when the modulation degree is changed by one step, the first and second switching elements 3 and 4 are changed. Since the driving pulse width, that is, the ON time, is changed, there arises a problem that the resolution between the minimum setting and the maximum setting of the power is insufficient.
[0023]
Therefore, in order to secure the resolution of power control, a method of providing high-frequency oscillation means and increasing the number of stages of the counting means can be considered. However, this method also has a problem that high-frequency noise is generated from high-frequency oscillating means, which causes malfunction of other circuit parts, and increases the number of stages of the counting means, thereby increasing the circuit scale and increasing the cost. , Was difficult to implement.
[0024]
The present invention has been made to solve the above-described problems, and has an object to double the resolution of conventional power control, suppress the influence of noise, minimize circuit changes, and minimize cost increases. I do.
[0025]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides first and second switching elements that are alternately driven to supply a high-frequency current, and that the high-frequency current flows to generate an eddy current in a nearby load, thereby causing the load to be self-contained. A heating coil for generating heat, and control means for controlling the entire circuit, wherein an induction time for controlling the power supplied to the heating coil by varying the on time of the first and second switching elements according to a command from the control means. In the heating cooker, reference oscillation means for generating a pulse serving as a reference for the on / off time of the first and second switching elements, and a gate for setting and outputting the on time of the first and second switching elements as a count value Count setting means, and a minimum count setting means for setting and outputting a minimum count value of the ON time of the first and second switching elements, wherein the control means is A state in which the first and second switching elements are driven by the count value output by the gate count setting means to make the on-time of both switching elements substantially equal, and one of the first and second switching elements is The count value output from the gate count setting means is added to the count value output from the minimum count setting means, and the other is driven by the count value output from the gate count setting means. Is selected and controlled to be longer than the other ON time.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, the present invention provides a first and a second switching element that are alternately driven to flow a high-frequency current, and a heating coil that generates an eddy current in a nearby load when the high-frequency current flows and self-heats the load. And control means for controlling the entire circuit, wherein the induction heating cooker controls the power supplied to the heating coil by varying the ON time of the first and second switching elements according to a command from the control means. Reference oscillation means for generating a pulse serving as a reference for the on / off time of the first and second switching elements, and gate count setting means for setting and outputting the on time of the first and second switching elements with a count value Minimum count setting means for setting and outputting the minimum count value of the on-time of the first and second switching elements, wherein the control means comprises the first and second switching elements. A state in which the switching elements are driven by the count value output from the gate count setting means to make the on-time of both switching elements substantially equal, and one of the first and second switching elements is changed by the gate count setting means. The count value output by the count value output from the minimum count setting means is added to the count value, and the other is driven by the count value output from the gate count setting means to set one of the ON times to the other ON time. One of the states to be longer is selected and controlled.
[0027]
As a result, the resolution of the conventional power control can be doubled, the influence of noise can be suppressed, and the cost of the circuit can be reduced by miniaturizing the circuit.
[0028]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0029]
FIG. 1 is a circuit block diagram of one embodiment of the present invention, FIG. 2 is a diagram showing a first example of a waveform of a main part in one embodiment of the present invention, and FIG. 3 is a diagram of a main part in one embodiment of the present invention. FIG. 4 is a diagram showing a second example of a waveform, FIG. 4 is a diagram showing a third example of a waveform of a main part in one embodiment of the present invention, and FIG. 5 is an on-time and power of a switching element in one embodiment of the present invention. FIG.
[0030]
Referring to FIG. 1, the overall configuration of an embodiment of the present invention will be described.
[0031]
In the figure, reference numeral 1 denotes an AC power supply. Reference numeral 2 denotes a rectifier, which is composed of a plurality of rectifiers, and whose input terminals (-terminals in the figure) are connected to the AC power supply 1, rectifies the AC power supply 1, converts it into a DC power supply, and outputs the output terminals (+ terminal and-in the figure). Terminal).
[0032]
Reference numerals 3 and 4 denote first and second switching elements, which are connected in series, one end of which is connected to the high-voltage output terminal (+ terminal in the figure) of the rectifying means 2 and the other end of which is connected to the rectifying means 2. It is connected to a low-voltage output terminal (-terminal in the figure) and is driven alternately to supply a high-frequency current to the heating coil 5 described later.
[0033]
A heating coil 5 has one end connected to a series connection point of the first switching element 3 and the second switching element 4 and the other end connected to one end of a resonance capacitor 6 to be described later. An eddy current is generated in the load 8, which will be described later, so that the load 8 generates heat.
[0034]
Reference numeral 6 denotes a resonance capacitor, one end of which is connected to the heating coil 5, and the other end of which is connected to the low-voltage output terminal of the rectifier 2 (the negative terminal in the figure). Reference numeral 7 denotes a resonance circuit, which includes a heating coil 5 and a resonance capacitor 6. Reference numeral 8 denotes a load, such as a metal pot.
[0035]
Reference numerals 9 and 10 denote drive means connected to the gate terminals of the first and second switching elements 3 and 4, respectively, and convert the input signal to an appropriate voltage level and the like to switch the first and second switching elements 3 and 4 to each other. Drive.
[0036]
Numeral 11 denotes a control means which is formed by a microcomputer or the like and controls the entire circuit by issuing an appropriate command. The power supplied to the heating coil 5 is controlled by varying the on-time and off-time of the first and second switching elements 3 and 4 according to a command from the control means 11. Further, the control means 11 drives the first and second switching elements 3 and 4 with the count value output by the gate count setting means 14 described later to make the on-time of both switching elements 3 and 4 substantially equal. One of the first and second switching elements 3 and 4 is driven by a count value obtained by adding the count value output by the later-described minimum count setting means 15 to the count value output by the later-described gate count setting means 14, and the other is written by the following. Driving is performed with the count value output from the gate count setting means 14 to select and control one of the states in which one of the ON times is longer than the other ON time.
[0037]
Reference numeral 12 denotes a reference oscillating means for generating a pulse which is a reference for the on / off time of the first and second switching elements 3 and 4. 13 is a counting means for counting the pulses output from the reference oscillating means 12.
[0038]
A gate count setting means 14 sets and outputs the ON time of the first and second switching elements 3 and 4 as a count value based on a command from the control means 11. Reference numeral 15 denotes a minimum count setting means for setting and outputting the minimum count value of the ON time of the first and second switching elements 3 and 4.
[0039]
Reference numeral 16 denotes an adder which adds the output signal of the gate count setting means 14 and the output signal of the minimum count setting means 15 and outputs the result. A blank time setting means 17 creates and outputs a blank time so that the ON states of the first and second switching elements 3 and 4 do not overlap each other.
[0040]
A selecting means 18 selects and outputs one of the outputs of the gate count setting means 14, the adding means 16 and the blank time setting means 17. Reference numeral 19 denotes a comparing means which compares the output of the counting means 13 with the output of the selecting means 18 and outputs a reset signal to the counting means 13 when the two outputs coincide with each other. Clear
[0041]
Reference numeral 20 denotes a separating unit that separates the output signal of the counting unit 13 into the driving unit 9 for the first switching element 3 or the driving unit 10 for the second switching element 4 based on the output signal of the state setting unit 21 described later. Sort and output. Reference numeral 21 denotes state setting means for transmitting a command from the control means 11 to the selection means 18 and the separation means 20 to set respective states.
[0042]
The operation of the above configuration will be described.
When a user (not shown) turns on a power switch (not shown), the rectifying means 2 rectifies the AC power supply 1 and converts it to DC to form a DC power supply. , 4, a resonance circuit 7 comprising a heating coil 5 and a resonance capacitor 6.
[0043]
Here, when the user (not shown) sets the power and starts heating, the control means 11 recognizes this fact and responds to the power set in the gate count setting means 14 and the state setting means 21 and respectively. The command corresponding to the means is output.
[0044]
The reference oscillating means 12 generates a pulse which is a reference for the on / off time of the first and second switching elements 3 and 4, and the counting means 13 counts and outputs this pulse.
[0045]
The gate count setting means 14 sets and outputs the ON time of the first and second switching elements corresponding to the power set by the command of the control means 11 by a count value. The minimum count setting means 15 sets and outputs the minimum count value of the ON time of the first and second switching elements 3 and 4.
[0046]
The adding means 16 adds the output signal of the gate count setting means 14 and the output signal of the minimum count setting means 15 and outputs the result. The blank time setting means 17 creates and outputs a blank time so that the ON states of the first and second switching elements 3 and 4 do not overlap each other.
[0047]
The selecting means 18 selects one of the outputs of the gate count setting means 14, the adding means 16 and the blank time setting means 17 in accordance with a command from the control means 11 and outputs the selected output to the comparing means 19.
[0048]
The comparing means 19 compares the output of the selecting means 18 with the output of the counting means 13 and outputs a reset signal to the counting means 13 when the two outputs coincide with each other. clear. That is, the counting means 13 outputs a periodic signal to the comparing means 19 and the separating means 20.
[0049]
The separating means 20 converts the output signal of the counting means 13 into the driving means 9 for the first switching element 3 or the driving means for the second switching element 4 according to the output signal of the state setting means 21 which transmits the command of the control means 11. It is separated into 10 and distributed and output. The drive means 9 and 10 convert the output signal of the separation means 20 into an appropriate voltage level or the like, and drive the first and second switching elements 3 and 4, respectively.
[0050]
The first and second switching elements 3 and 4 are alternately driven to supply a high-frequency current to the resonance circuit 7, that is, the heating coil 5, generate an eddy current in the load 8 near the heating coil 5, and cause the load 8 to generate heat. .
[0051]
Next, a detailed operation of the main part will be described with reference to signal waveforms.
First, a case where the ON times of the first and second switching elements 3 and 4 are the same tN time will be described with reference to FIG. FIG. 2 is a diagram showing a first example of a waveform of a main part in one embodiment of the present invention, in which the ON times of the first and second switching elements 3 and 4 are both tN times.
[0052]
In FIG. 2, the OSC signal has a pulse waveform generated by the reference oscillation means 12. The COUNT signal is the output waveform of the counting means 13. The SEL signal is the output waveform of the selection means 18. For "S1" and the like shown in the waveform, "S1" indicates that the gate count selection means 14 is selected, and "S2" indicates that the minimum count setting means 15 is selected. If selected, "S3" means a case where blank time setting means 17 is selected. The signal of CMP is the output waveform of the comparing means 19. The signals of SEP1 and SEP2 are output waveforms to the driving means 9 and 10 of the separating means 20, respectively, and correspond to the first and second switching elements 3 and 4. IL is a waveform of a current flowing through the heating coil 5. The sections are shown for temporally dividing each signal, and there are four sections A, B, C, and D. These are the same in FIGS. 3 and 4.
[0053]
In the section A, the first switching element 3 is on (time tN), in the section B, both the first and second switching elements 3 and 4 are off (blank time), and in the section C, the second switching element 4 Is on (time tN), and in the section D, both the first and second switching elements 3 and 4 are off (blank time). After the section D, the state returns to the same state as the section A. That is, each state of the section A, the section B, the section C, and the section D is periodically repeated. In the sections A and C, the number of pulses generated by the reference oscillation means 12 is N. N is a positive integer.
[0054]
As shown in FIG. 2, when the ON times of the first and second switching elements 3 and 4 are both set to tN, the following operation is performed.
[0055]
The control means 11 instructs the gate count setting means 14 to output a count value corresponding to the time tN at the timing when the first switching element 3 is turned on, and at the same time, sets the ON time of the first switching element 3 to tN. To the selecting means 18 and the separating means 20 via the state setting means 21.
[0056]
The selecting means 18 selects the gate count setting means 14 from the gate count setting means 14, the adding means 16 and the blank time setting means 17 based on the command of the control means 11 sent via the state setting means 21. The output of the gate count setting means 14 is output to the comparing means 19. The separating means 20 outputs an output signal of the counting means 13 to the driving means 9 based on the command of the control means 11 sent via the state setting means 21. Thereby, the ON time of the first switching element 3 becomes tN.
[0057]
Next, the control means 11 commands the state setting means 21 to turn off both the first and second switching elements 3 and 4. The state setting means 21 receives this command and transmits it to the selecting means 18 and the separating means 20. The selecting means 18 selects and outputs the blank time setting means 17 according to this command. The separation unit 20 outputs an OFF signal to both the drive units 9 and 10 according to this command. As a result, the first and second switching elements 3 and 4 are both turned off for the blank time.
[0058]
Next, the operation of setting the ON time of the second switching element 4 to tN is the same as that of the first switching element 3 except for the timing.
[0059]
Next, the operation of turning off both the first and second switching elements 3 and 4 for the blank time is the same as described above. The above operation is one cycle, and these operations are repeated.
[0060]
In this case, the current flowing through the heating coil 5 indicated by IL has a substantially vertically symmetric current waveform centering on 0 A, and the peak value is ILPN. The power at this time is defined as PN.
[0061]
Meanwhile, the peak value ILPN of the current flowing through the heating coil 5 has a positive correlation with the on-time tN of the first and second switching elements 3 and 4, and also has a positive correlation with the power PN. The ON time tN of the first and second switching elements 3 and 4 is directly proportional to the number N of pulses generated by the reference oscillation means 12. That is, this relationship can be expressed by the following equation. The period of the pulse output from the reference oscillating means 12 is defined as Tosc.
tN = Tosc × N.
[0062]
Therefore, for example, when the power is changed to a higher value, the ON time tN of the first and second switching elements 3 and 4 may be increased. The time obtained by extending the ON time tN by one step is tN + 1 = Tosc × (N + 1).
[0063]
FIG. 3 shows each signal waveform when the ON time of both the first and second switching elements 3 and 4 is set to tN + 1, and the ON time of the first switching element 3 is set to tN + 1 and the second switching is performed. FIG. 4 shows each signal waveform when the ON time of the element 4 is tN.
[0064]
As shown in FIG. 3, when the ON time of both the first and second switching elements 3 and 4 is set to tN + 1, the ON time of both the first and second switching elements 3 and 4 is set to tN + 1. Since the time tN may be replaced with tN + 1 in the operation in the case of, the description is omitted.
[0065]
In this case, the current flowing through the heating coil 5 has a peak value ILPN + ΔILP3 on both the upper and lower sides, and the current whose peak value is larger by ΔILP3 on both the upper and lower sides than when the ON times of the first and second switching elements 3 and 4 are both tN. It becomes. Therefore, the power at this time is PN + ΔP2, which is higher by ΔP2 than when the ON times of the first and second switching elements 3 and 4 are both tN.
[0066]
As shown in FIG. 4, when the ON time of the first switching element 3 is tN + 1 and the ON time of the second switching element 4 is tN, the following operation is performed. The blank time, that is, the operation in the section B and the section D is the same as that described above, and thus will not be described.
[0067]
The control means 11 instructs the gate count setting means 14 to output a count value corresponding to the time tN + 1 at the timing when the first switching element 3 is turned on, and simultaneously sets the ON time of the first switching element 3 to tN + 1. To the selecting means 18 and the separating means 20 via the state setting means 21.
[0068]
The selecting means 18 selects the adding means 16 from the gate count setting means 14, the adding means 16 and the blank time setting means 17 based on the command from the control means 11 sent via the state setting means 21 and The output of 16 is output to the comparison means 19. The separating means 20 outputs an output signal of the counting means 13 to the driving means 9 based on the command of the control means 11 sent via the state setting means 21. Thus, the ON time of the first switching element 3 becomes tN + 1.
[0069]
Then, at the timing when the second switching element 4 is turned on, the control means 11 instructs the gate count setting means 14 to output a count value corresponding to the time tN, and at the same time, sets the ON time of the second switching element 4 to tN. Is instructed to the selecting means 18 and the separating means 20 via the state setting means 21.
[0070]
The selecting means 18 selects the gate count setting means 14 from the gate count setting means 14, the adding means 16 and the blank time setting means 17 based on the command of the control means 11 sent via the state setting means 21. The output of the gate count setting means 14 is output to the comparing means 19. The separating unit 20 outputs an output signal of the counting unit 13 to the driving unit 10 based on a command from the control unit 11 sent via the state setting unit 21. Thereby, the ON time of the second switching element 4 becomes tN.
[0071]
In this case, the current of the heating coil 5 becomes the upper peak value ILPN + ΔILP1, becomes the lower peak value ILPN + ΔILP2, and the on-time of the first and second switching elements 3 and 4 is lower than that of the case where both of the on-times tN. ΔILP1, the current whose lower side peak value is larger by ΔILP2. Therefore, the electric power at this time is PN + ΔP1, and the electric power is higher by ΔP1 than when the ON times of the first and second switching elements 3 and 4 are both the ON time tN.
[0072]
The magnitude relationship between the three increases in the peak value of the current of the heating coil 5 is “ΔILP3>ΔILP1> ΔILP2”. Note that there is no significant difference between ΔILP2 and ΔILP1.
[0073]
Therefore, the magnitude relationship between the power PN when the ON times of the first and second switching elements 3 and 4 are both tN, the power PN + ΔP2 when both are tN + 1, and the power PN + ΔP1 when one is tN + 1 and the other is tN. Becomes “PN <[PN + ΔP1] <[PN + ΔP2]”.
[0074]
The above-described case where the ON time of the first and second switching elements 3 and 4 is both tN and the case where both of them are tN + 1 are the conventionally realized states. However, when one is tN + 1 and the other is tN, the conventional state is realized. It is a state that could not be realized. Conventionally, the power on one stage of the power PN is PN + ΔP2, but with this configuration, the power PN + ΔP1 can be provided between the power PN and the power PN + ΔP2.
[0075]
FIG. 5 shows this pattern. FIG. 5 is a diagram showing the relationship between the on-time of the first and second switching elements 3 and 4 and the power, and ton1 and ton2 are the on-time of the first and second switching elements 3 and 4, respectively. Means
[0076]
In FIG. 5, the ON time has a magnitude relationship of “tN <[tN + 1] <[tN + 2]”, and the power is “PN <[PN + ΔP1] <[PN + ΔP2] <[PN + ΔP3] <[PN + ΔP4] <[PN + ΔP5] Is a magnitude relationship.
[0077]
In the case of the conventional method in which the ON times of the first and second switching elements 3 and 4 are both changed at the same time, the power on the next level of the power PN is PN + ΔP2, and the power on the next level is PN + ΔP4, ...
[0078]
That is, with such a configuration, the resolution of the conventional power control can be doubled even if a microcomputer having the same bit configuration as the conventional one is used for the control means 11. Further, since it is not necessary to increase the oscillation frequency of the reference oscillation means 12, the influence of noise can be suppressed. Further, the circuit need only be changed on a small-scale basis such as the minimum counting means 15 and the adding means 16 and the like, and the increase in cost can be minimized.
[0079]
In addition, since it is possible to use a crystal oscillator or a ceramic oscillator having high stability as the reference oscillating means 12, fluctuations in the drive time of the first and second switching elements 3, 4 due to frequency fluctuations can be reduced. Power control with higher stability can be realized.
[0080]
In the above example, the minimum count setting means 15, the state setting means 21 and the like are provided outside the control means 11, but they may be provided inside the control means 11 or realized by another circuit configuration. . Further, although one resonance capacitor 6 as a component of the resonance circuit 7 is used, a configuration using two resonance capacitors may be considered.
[0081]
【The invention's effect】
As described above, according to the induction heating cooker of the present invention, the first and second switching elements that are alternately driven to flow a high-frequency current, and the high-frequency current flows to generate an eddy current in a nearby load. A heating coil for self-heating the load, and control means for controlling the entire circuit, and varying the on-time of the first and second switching elements according to a command from the control means to supply electric power to the heating coil. In the induction heating cooker to be controlled, reference oscillation means for generating a pulse which is a reference for the on / off time of the first and second switching elements, and the on time of the first and second switching elements are set by a count value. A gate count setting means for outputting, and a minimum count setting means for setting and outputting a minimum count value of the ON time of the first and second switching elements, The stage drives the first and second switching elements with the count value output from the gate count setting means to make the on-time of both switching elements substantially equal, and any one of the first and second switching elements. Either one is driven by the count value obtained by adding the count value output by the minimum count setting means to the count value output by the gate count setting means, and the other is driven by the count value output by the gate count setting means. One of the states in which one ON time is longer than the other ON time is selected and controlled.
[0082]
As a result, it is possible to double the resolution of the conventional power control, suppress the influence of noise, and minimize the increase in cost by making small-scale circuit changes.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram of one embodiment of the present invention.
FIG. 2 is a diagram showing a first example of a waveform of a main part in one embodiment of the present invention.
FIG. 3 is a diagram showing a second example of a waveform of a main part in one embodiment of the present invention.
FIG. 4 is a diagram showing a third example of a waveform of a main part in one embodiment of the present invention.
FIG. 5 is a diagram showing a relationship between an on-time of a switching element and power in one embodiment of the present invention.
FIG. 6 is a circuit block diagram of a conventional example.
FIG. 7 is a diagram showing a first example of a waveform of a main part of a conventional example.
FIG. 8 is a diagram showing a second example of the waveform of the main part of the conventional example.
[Explanation of symbols]
3 First switching element
4 Second switching element
5 heating coil
8 Load
11 control means
12 Reference oscillation means
14 Gate count setting means
15 Minimum count setting means

Claims (1)

First and second switching elements (3) and (4), which are alternately driven to flow a high-frequency current, and generate an eddy current in a nearby load (8) by the flow of the high-frequency current, thereby allowing the load (8) to self-load A heating coil (5) for generating heat and control means (11) for controlling the entire circuit are provided, and the first and second switching elements (3) and (4) are turned on by a command from the control means (11). In an induction heating cooker for varying the time to control the power supplied to the heating coil (5),
Reference oscillating means (12) for generating a pulse serving as a reference for the on / off time of the first and second switching elements (3) and (4); and the first and second switching elements (3) and (4). ), A gate count setting means (14) for setting and outputting the ON time as a count value, and a minimum count for setting and outputting the minimum count value of the ON time of the first and second switching elements (3), (4). Setting means (15), wherein the control means (11) drives the first and second switching elements (3), (4) with the count value output from the gate count setting means (14). A state in which the ON times of the two switching elements (3) and (4) are made substantially equal, and one of the first and second switching elements (3) and (4) is set by the gate count setting means (14). Output The count value is added to the count value output from the minimum count setting means (15), and the other is driven by the count value output from the gate count setting means (14), and the other is driven by the count value. An induction heating cooker characterized by selecting and controlling one of the states that is longer than the other ON time.

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