JP2002151241A - Keep-warm cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a keep-warm cooker with improved reliability which can stably control current supplied to a plurality of induction heating coils and improve controlling stability. SOLUTION: Resonant capacitors are connected in series to two induction heating coils for heating a cooker to form a resonant circuit having different resonant frequencies is formed and connected in parallel. To this resonant circuit, current is supplied from an inverter main circuit ad a driving frequency f. Δf set at around 1/100 of the frequency between the resonant frequencies of the resonant circuit, when the drive frequency f set at the start of heating is changed to (f+Δf), a current level of each resonant circuit is detected, drive frequency f is adjusted so that minimal change of the detected voltage ΔE1 be a positive value and ΔE2 a negative value, and, at same time, sum of the detected value E1(f)+E2(f) will not exceed the upper limit level Emax, and, therefore, input power ratio is controlled to be at a given condition by making the difference between the both be a given value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulated kettle having a configuration in which a high-frequency current is supplied from an inverter main circuit to an induction heating coil arranged to face an iron kettle.

[0002]

2. Description of the Related Art This type of heat-insulating kettle is configured such that an induction heating coil is arranged to face a steel kettle, and a high-frequency current is supplied to the induction heating coil from an inverter main circuit. As a result, an induction current flows in a portion of the kettle facing the induction heating coil, which generates eddy current loss and generates heat, thereby directly heating the kettle.

[0003] Generally, as a condition for cooking delicious rice, heating is performed so that the temperature in the pot during cooking is uniform. For this reason, conventionally, the convection effect in the kettle is actively used to control the temperature of the entire kettle to be uniform. For example, strong heating is performed at the outer peripheral portion of the bottom surface of the kettle to generate convection from the outer peripheral portion to the upper portion.

[0004]

However, in the above-described conventional structure, uneven heating may occur in the following points, and it may be difficult to satisfy the uniform temperature condition in the kettle. Was. That is, when convection occurs as described above, the heated rice and water are raised at the outer peripheral portion and cause convection so as to descend from the upper center in the kettle. Since the temperature at the center of the bottom surface is lower than the temperature at the time of rising, the temperature near the center portion of the bottom surface of the pot tends to be slightly lower as a whole, causing uneven heating.

[0005] In order to suppress such uneven heating,
It is conceivable to increase the input power by the induction heating coil so that the entire inside of the kettle is heated at once, but if the use in home appliances is assumed, the input power can also be increased. There is a limitation that it cannot be easily adopted because it goes against the trend of energy saving.

Therefore, as a method of reducing uneven heating without increasing the input power, for example, an induction heating coil is provided concentrically on the bottom portion of the pot in correspondence with the inside and outside, and each of them is provided with a corresponding coil. To provide an inverter main circuit,
When it is necessary to heat the central part of the shuttle, it is conceivable to heat the inner induction heating coil by energizing the coil by the inverter main circuit.

However, providing an inverter main circuit for supplying a current to each of the plurality of induction heating coils as described above leads to an increase in cost and a complicated control for switching the conduction to each induction heating coil. Are difficult to adopt.

On the other hand, a plurality of induction heating coils installed so as to face the lower surface and side surfaces of the iron kettle,
A change in inductance is caused by a change in the position of the hook and the temperature. Therefore, in the inverter main circuit, it is difficult to control the plurality of induction heating coils at a desired input power ratio because the constant of the circuit formed by the induction heating coils changes for the above-described reason. There are circumstances.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a plurality of induction heating coils, and to provide an inverter main circuit or a changeover switch for each of them. It is possible to stably adjust the current supplied to the multiple induction heating coils by adding a low-cost configuration to drive the multiple induction heating coils at a desired input power ratio. An insulated pot with improved stability and improved reliability by being able to detect that the total input power supplied to the induction heating coil exceeds the normal operating range and detecting any failure state Is to provide.

[0010]

According to a first aspect of the present invention, there is provided an insulated pot having a power supply circuit for converting an AC input into a DC output and a plurality of induction heating units for heating an iron pot. A resonance circuit formed by connecting a resonance capacitor in series to each of the coils, and a resonance circuit in which a plurality of these resonance circuits are set in parallel so that their resonance frequencies are different from each other, and the DC output of the power supply circuit is An inverter main circuit that converts the signal into an AC output having a set driving frequency and outputs the AC output to the resonance circuit unit, a signal detection unit that detects signals obtained from the plurality of resonance circuits, The drive frequency of the inverter main circuit is set based on the level of the signal detected by the signal detection means so that the heating coil performs the heating operation at the given input power ratio set value. Characterized in was configured to include a that control means.

According to such a configuration, the following operation is provided. That is, since the resonance frequencies of the plurality of resonance circuits are set to be different from each other, the frequency admittance characteristics of the resonance circuits are different from each other. Therefore, when the inverter main circuit is driven at a specific frequency,
An admittance current corresponding to the frequency is supplied to the induction heating coil of each resonance circuit. The control means sets the drive frequency based on the input power ratio set value given to the plurality of induction heating coils, so that a different current is supplied to each of the plurality of induction heating coils. At this time, the signal detecting means has detected signals based on different currents input to the plurality of induction heating coils, and the control means has determined that the input to the plurality of induction heating coils has been given based on the level of this signal. It is determined whether or not the heating operation is being performed based on the set value of the power ratio, and if it is deviated from the set value, the drive frequency is set so as to be the set value.
Thereby, a plurality of induction heating coils are controlled at a desired input power ratio by one inverter main circuit without providing an inverter main circuit corresponding to each of the plurality of induction heating coils or providing a changeover switch or the like. be able to. Further, the inverter main circuit can be controlled while detecting the output actually supplied to each resonance circuit so that the current supplied to the plurality of induction heating coils can be stably adjusted. That is, control stability can be improved.

2. The invention according to claim 1, wherein said control means controls the output level of said inverter main circuit when a sum of signal levels detected by said signal detection means exceeds a preset upper limit level. It is preferable to perform a first determination operation for determining that the value is out of the normal operation range (claim 2).

According to such a configuration, the following operation is provided. That is, the signal detection means detects signals obtained from the plurality of resonance circuits and outputs the signals to the control means. The control means calculates the sum of the signal levels of the signal detection means, and when the sum exceeds a preset upper limit level,
The first determination operation determines that the output level of the inverter main circuit is out of the normal operation range. This makes it possible to detect a state where the total input power supplied to the induction heating coil exceeds the normal operation range for some reason.

The invention according to claim 1 or 2, wherein the resonance circuit section is provided with two resonance circuits.
When the control means changes the level of the signal of the signal detection means when the drive frequency of the inverter main circuit is changed by a first change, or when both of the control means change the drive frequency of the inverter main circuit, the drive frequency of the inverter main circuit is changed. Is desirably configured to perform a second determination operation for determining that the value is out of the normal operation range (claim 3).

According to such a configuration, the following operation is provided. The control means sets the drive frequency of the inverter main circuit such that the drive frequency is changed by a first change that is set to be smaller than the difference between the resonance frequencies of the respective resonance circuits. The signal detecting means detects a change in the level of the signal accompanying a change in the driving frequency. Since the resonance frequencies of the two resonance circuits are set to different values, if the changes in the levels of the detected signals both increase or decrease, the driving frequency at that time is in the frequency range of the two resonance frequencies. That is, it is out of the normal operation range. The control unit determines which frequency range in which the drive frequency of the inverter main circuit is divided by the resonance frequency of each resonance circuit in accordance with the increase / decrease direction that changes at the maximum value of the admittance characteristic of each resonance circuit. Can be determined, and it can be determined by the second determination operation whether or not it is out of the normal operation range.

Further, in the invention according to claim 3,
When the control means determines that the output level or the drive frequency of the inverter main circuit is out of the normal operation range, the control means sets the drive frequency of the inverter main circuit to the second change which is set to be larger than the first change. It is preferable that the first or second determination operation is performed after the change is made by an amount (claim 4).

According to such a configuration, the following operation is provided. The control means determines that the output level of the inverter main circuit is out of the normal operation range by the first determination operation, or that the drive frequency of the inverter main circuit is out of the normal operation range by the second determination operation. When it is determined that it is deviated, the drive frequency of the inverter main circuit is changed by the second change. At this time, the second change is set to be larger than the first change, and the state largely changes from a state where the output level of the inverter main circuit is out of the normal operation range. afterwards,
The control unit performs the first or second determination operation again to determine that the output level or the drive frequency of the inverter main circuit is out of the normal operation range.
Thereby, the reliability can be improved.

In the invention according to claim 3 or 4, when the input power ratio set value is set for the two resonance circuits, when the heating operation is performed at the input power ratio set value. The level difference between the two signals to be detected by the signal detecting means is determined as a set signal level difference, and the control means determines the level difference between the two signals detected by the signal detecting means and the set signal level difference. It is preferable that the driving frequency of the inverter main circuit is set so that the driving frequency is substantially equal (claim 5).

According to such a configuration, the operation is as follows. When the input power ratio setting value is set for the two resonance circuits, the control unit obtains a level difference between the two signals that must be detected by the signal detection unit as a set signal level difference. The signal detecting means detects the two signals and outputs them to the control means. The control means sets the drive frequency of the inverter main circuit to increase or decrease so that the set signal level difference and the level difference between the two signals become substantially equal. Thus, when the input power ratio setting value is set, the two induction heating coils can be controlled at the set input power ratio while detecting the actual output.
It is possible to stably adjust the current supplied to each of the induction heating coils, thereby improving the control stability.

In the invention according to claim 3 or 4, when the input power ratio set value is set for the two resonance circuits, the control means performs a heating operation at the input power ratio set value. To be detected by the signal detecting means.
The level difference between the two signals is determined as the set signal level difference so that the absolute value of the level difference between the two signals detected by the signal detecting means is substantially equal to the absolute value of the set signal level difference. When the drive frequency of the inverter main circuit is set, when the levels of the two signals are in an inverse relationship with respect to the input power ratio set values of the two resonance circuits, the set drive frequency is used as a basis. It is preferable that the control means be configured so as to set the original drive frequency of the inverter main circuit.

According to such a configuration, the operation is as follows. When the input power ratio setting value is set for the two resonance circuits, the control unit obtains a level difference between the two signals that must be detected by the signal detection unit as a set signal level difference. The signal detecting means detects the two signals and outputs them to the control means. Then, the control means sets the drive frequency of the inverter main circuit such that the absolute value of the set signal level difference and the absolute value of the level difference between the two signals detected by the signal detection means are substantially equal. The control means is set when the levels of the two signals are in an inverse relationship with respect to the input power ratio setting values of the two resonance circuits, that is, when the absolute values are substantially equal but the sign of the difference is different. The original drive frequency of the inverter main circuit is set based on the drive frequency. Thereby, when the input power ratio set value is set, 2
It is possible to quickly control the two induction heating coils at a desired input power ratio, and it is possible to stably adjust the current supplied to the two induction heating coils,
Control stability can be improved.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. FIG. 2 is a vertical sectional side view showing the positional relationship between the shuttle 1 and the induction heating coils 2a and 2b for heating the same. Note that, here, the description of other parts constituting the heat retaining pot is omitted, but it is assumed that a well-known configuration is employed. Two circularly wound induction heating coils 2a and 2b are concentrically arranged on the lower surface and the side surface of the iron-made iron pot 1 having a bottom and a cylindrical shape. The two induction heating coils 2a and 2b are configured to supply a high-frequency current as described later. Thus, the induction heating coils 2a, 2
An induced current flows in a portion facing b, which generates eddy current loss and generates heat, thereby directly heating the pot 1 to perform a rice cooking operation.

FIG. 1 schematically shows the electrical configuration.
Both terminals of the commercial AC power supply 3 are connected to an AC input terminal of a rectifier bridge 5 via a choke coil 4, and DC output terminals of the rectifier bridge 5 are connected to DC buses 6 and 7. A smoothing capacitor 8 is connected between the DC buses 6 and 7. The choke coil 4, the rectifying bridge 5, the DC buses 6 and 7, and the smoothing capacitor 8 constitute a power supply circuit. The DC bus 7 is connected to GND.

Between the DC buses 6 and 7, the NP on the upper arm side
A half-bridge type inverter main circuit 11 including an N-type transistor 9 and an NPN-type transistor 10 on the lower arm side is connected. Flywheel diodes 12 and 13 are connected between the collector and the emitter of the transistors 9 and 10, respectively, with the polarity shown in the figure. Between the output terminal of the inverter main circuit 11 and the DC bus 7, there is provided a resonance circuit 15a, an induction heating coil 2b and a resonance capacitor 14b which are configured by connecting the induction heating coil 2a and the resonance capacitor 14a in series. Resonant circuits 15b connected in series are connected in parallel. A resonance circuit section 16 is configured by the resonance circuits 15a and 15b.

FIG. 3 shows the admittance-frequency characteristics of each of the resonance circuit 15a and the resonance circuit 15b. Here, the resonance frequency f1 of the resonance circuit 15a is set to, for example, about 25 kHz. Also, the resonance circuit 1
The resonance frequency f2 of 5b is set to, for example, about 45 kHz.

The current transformers 17a and 17b are provided to detect respective currents of the resonance circuits 15a and 15b. In this case, both output terminals of the current transformer 17a are connected to both terminals of the capacitor 18a and to the AC input terminal of the rectifier bridge 19a. The DC output terminal of the rectifying bridge 19a is connected to a resistor 20a.
Are connected between both terminals. The rectifying bridge 19
a terminal of the DC output is connected to the resistor 21a and the resistor 2a.
2a is connected to a first analog input terminal of a control circuit 23 as a control means, and the other DC output terminal is
D. Further, the capacitor 24a is connected between the common connection terminal of the resistors 21a and 22a and GND. That is, the current transformer 17a
An alternating current flowing through the induction heating coil 2a is detected, and the rectifying bridge 19a, the resistors 20a to 22a and the capacitors 18a and 24a convert the alternating current to a direct current voltage and output the converted direct current voltage to a first analog input terminal of the control circuit 23. It is supposed to.

Similarly, both output terminals of the current transformer 17b are connected to both terminals of the capacitor 18b and to the AC input terminal of the rectifier bridge 19b. The DC output terminal of the rectifying bridge 19b is connected to a resistor 20b.
Are connected between both terminals. The rectifying bridge 19
b is connected to a resistor 21b and a resistor 22b.
b, it is connected to the second analog input terminal of the control circuit 23, and the other DC output terminal is connected to GND. Further, the capacitor 24b is connected between the common connection terminal of the resistors 21b and 22b and GND. That is, the current transformer 17b detects the AC current flowing through the induction heating coil 2b, and
b, resistors 20b to 22b and capacitors 18b, 24
At b, the AC current is converted to a DC voltage and output to the second analog input terminal of the control circuit 23.

The current transformers 17a and 17b, the resistors 20a to 22a, the resistors 20b to 22b, and the capacitor 18
a, 18b, 24a, 24b and rectifying bridge 19
a, 19b constitute a signal detection circuit 25 as signal detection means in the present invention.

The control circuit 23 is mainly composed of a microcomputer, a ROM, and a RAM (not shown), and supplies a signal for designating a drive frequency to the drive circuit 26. The drive circuit 26 is connected so as to provide a control output to a base of the inverter main circuit 11 so as to turn on and off the transistors 9 and 10 at a designated drive frequency. A desired input power ratio to be input to each of the induction heating coils 2a and 2b is set in the RAM in the control circuit 23 by a rice cooking operation program. A program is stored in the ROM in advance so as to control the entire process of cooking rice in accordance with the operation of a key (not shown) by the user. That is, the control circuit 23 sets the input power ratio of the induction heating coils 2a and 2b to the drive circuit 26 in correspondence with the entire process of the rice cooking operation, as will be described later.

The operation of this embodiment will be described with reference to FIGS.
1 will be described. In addition, in each operation of rice cooking and heat retention, the input power ratio given to each of the inner induction heating coil 2a and the outer induction heating coil 2b as a heating pattern is set in the RAM in the control circuit 23 in advance. According to the input power ratio, the coil designation flag flg indicating whether the input power of the induction heating coil 2b on the outer side needs to be larger than that of the induction heating coil 2a on the inner side is set in the RAM in the control circuit 23. Is stored. In this case, the inner induction heating coil 2a
Is set to an input power ratio that is greater than or equal to the input power of the outer induction heating coil 2b, flg = 0, and the input power of the induction heating coil 2b outside the inner induction heating coil 2a is increased. When setting, flg = 1 is set.

When the control circuit 23 starts the rice cooking operation,
The inverter main circuit 11 is driven as follows according to a rice cooking program (not shown). At this time, when the heating pattern is set, the drive frequency f is set according to the flowchart shown in FIG. First, the drive frequency f is specified for the drive circuit 26. At this time, the control circuit 23 outputs an appropriate drive frequency f to the drive circuit 26, which is considered to be a frequency between the respective resonance frequencies and is considered to be set to a desired input power ratio. The drive circuit 26 uses the drive frequency f to drive the inverter main circuit 1
1 is started (step S1). The inverter main circuit 11 uses the admittance (1 / | Z) of each of the resonance circuits 15a and 15b shown in the admittance-frequency characteristics of FIG.
A current proportional to |) is supplied to each resonance circuit. The current transformers 17a and 17b detect currents flowing through the respective resonance circuits 15a and 15b when driven at the frequency f, and output currents from the capacitors 18a and 18b to the rectifier bridge 19, respectively.
The DC voltages rectified by a, 19b and capacitors 20a, 20b are output to the first and second input terminals of the control circuit 23 as detection voltages E1 (f) and E2 (f), respectively. (The detection voltages E1 (f) and E2 (f) indicate the detection voltages E1 and E2 corresponding to the current levels of the resonance circuits 15a and 15b at the drive frequency f.) The control circuit 23 detects the detection voltage E1 (f). And E2 (f) are stored in the RAM in the control circuit 23 (step S2), for example, the resonance circuits 15a and 15b
The drive frequency is increased, for example, by Δf (= (f2−f1) ÷ 100) which is 1/100 of the frequency of the difference between the resonance frequencies f1 and f2 (step S3). That is, the control circuit 23 outputs a drive frequency of (f + Δf) to the drive circuit 26, and the drive circuit 26
At a frequency of (f + Δf). Current transformer 1
7a and 17b detect the current flowing through each of the resonance circuits 15a and 15b, respectively, and apply the detection voltage E1 to the first and second input terminals of the control circuit 23 from the same operation as described above.
(f + Δf) and E2 (f + Δf) are output.

The control circuit 23 stores the detected voltages E1 (f + Δf) and E2 (f + Δf) in the RAM in the control circuit 23 (step S4), and stores E1 (f) and E2 (f ) Is calculated from the following equation: ΔE1 ← E1 (f + Δf) −E1 (f) (1) ΔE2 ← E2 (f + Δf) −E2 (f) (2) These are calculated from the drive frequency f by (f + Δ
At the time of changing to f), it is obtained as minute changes ΔE1 and ΔE2 of the detected voltage (step S5).

The control circuit 23 detects a minute change Δ in the detected voltage.
It is determined whether E1 and ΔE2 are larger than 0 (step S6). Minute change ΔE1 and ΔE2 of detection voltage
Are larger than 0, that is, the driving circuit 2
In the case where the respective detection voltages increase when the drive frequency given to f 6 is changed from f to (f + Δf), as shown in FIG. 6, driving is performed at a frequency lower than the resonance frequency f 1 of the resonance circuit 15 a. Is assumed. For this reason, the control circuit 23 sets the drive frequency f to fstep which is set to be larger than Δf, for example, about 1/10 of the frequency of the difference between the resonance frequencies f1 and f2 of the resonance circuits 15a and 15b.
It is increased by (= (f2−f1) ÷ 10) (step S7). The control circuit 23 determines whether or not fstep has been added a predetermined number of times defined as, for example, 10 times. If the predetermined number of times has been added, it is determined that there is an abnormality (step S
9).

If it is determined in step S9 that there is an abnormality, the control circuit 23 assumes that some failure of other parts constituting the heating oven cannot be dealt with only by a change in the driving frequency for driving the inverter main circuit 11. Then, another processing routine (not shown), for example, temporarily stopping, and performing processing such as failure display and notification is performed.
If it is determined in step S8 that the drive frequency has not been added the predetermined number of times, the process returns to step S1 to start driving at a frequency obtained by adding fstep to the previous drive frequency f.

If the control circuit 23 determines NO in step S6, that is, if it determines that one or both of the minute changes ΔE1 and ΔE2 of the detected voltage is not a value larger than 0, the control circuit 23 proceeds to the next step. Next, it is determined whether the minute changes ΔE1 and ΔE2 of the detection voltage are both smaller than 0 (step S10). The control circuit 23
When it is determined that the minute changes ΔE1 and ΔE2 in the detection voltage are both smaller than 0, that is, when the drive frequency f is changed to (f + Δf), the respective detection voltages E
If it is determined that 1, E2 decreases, it is assumed that the driving is performed at a frequency higher than the resonance frequency f2 of the resonance circuit 15a, as shown in FIG. Therefore, the control circuit 2
No. 3 greatly reduces the driving frequency f by fstep (step S11).

The control circuit 23 determines whether or not fstep has been reduced by a predetermined number of times defined as, for example, 10 times. If the number of times has been reduced by the predetermined number of times, it is determined in step S9 that there is an abnormality. At this time, similarly to the above, the control circuit 23 determines that some failure of other portions constituting the heat retaining pot, which cannot be dealt with only by the change of the driving frequency for driving the inverter main circuit 11, is assumed, and is not illustrated. Another processing routine, for example, temporarily stopping and performing processing such as failure display and notification is performed.

If it has not been reduced by the predetermined number in step S12, the process returns to step S1 to start driving at a frequency obtained by adding fstep to the previous driving frequency f.

Further, the control circuit 23 determines in step S10
When the determination is NO, that is, when the minute changes ΔE1 and ΔE2 of the detection voltage do not show an increasing tendency or a decreasing tendency, the sum of the signal levels calculated by E1 (f) + E2 (f) is obtained. Is the upper limit level Emax set as the maximum output level.
It is determined whether or not the above is the case (step S13). If the level is equal to or higher than the upper limit level Emax, the “processing when the sum of the DC voltages exceeds the upper limit level” described later is performed (step S14). In step S13, when the sum of the detected voltage values is not equal to or higher than the upper limit level Emax, it is determined that it is normal (step S15), and a "drive frequency adjustment process" described later is performed (step S16). As shown in FIG. 5, when it is determined in step S15 that the operation is normal, the drive frequency and the output level of the inverter main circuit 11 are determined to be in a normal operation range (f3 <f <f4 in the figure). It is shown that. 7 (a) and 7 (b)
When the driving frequency increases (Δf), the change in the detection voltage becomes Δ
The drive frequency f when E1 decreases and ΔE2 increases, that is, when NO is determined in step S10.
Is shown in principle.

FIG. 9 is a flow chart showing the "processing when the sum of the DC voltages exceeds the upper limit level" in step S14 described above. The control circuit 23 determines that E1 (f) is E2 (f) from the input detection voltage E1 (f) of the inner induction heating coil 2a and the detection voltage E2 (f) of the outer induction heating coil 2b.
It is determined whether or not E1 (f) exceeds E2 (f), that is, whether or not E1 (f)> E2 (f) (step T1).
Is exceeded, that is, if it is determined to be YES, the drive frequency f is set to be increased by fstep (step T2). Further, the control circuit 23 sets fstep
It is determined whether or not the process of increasing the number has been performed a predetermined number of times (step T3), and if YES, it is determined that there is an abnormality (step T4). If it is determined in step T4 that there is an abnormality, the control circuit 23
It is determined that some failure of the other parts constituting the insulated kettle, which cannot be dealt with only by adjusting the driving frequency f of 1, is assumed, and another processing routine not shown, for example, processing such as temporarily stopping and displaying a failure or notifying is performed. Perform

If NO is determined in step T3, the process returns to step S1 (see FIG. 4), and the drive of the inverter main circuit 11 is started again at the drive frequency f increased by fstep in step T2.

Further, when the determination is NO in step T1, that is, when E2 (f) is equal to or more than E1 (f), the control circuit 23 reduces the drive frequency f by fstep (step T5). ). Further, the control circuit 23
Determines whether or not the process of decreasing fstep has been performed a predetermined number of times (step T6).
In step T4, it is determined that there is an abnormality. At this time, if it is determined that the abnormality is the same as described above, the control circuit 23
It is determined that some failure of the other parts of the heating pot, which cannot be dealt with only by the change of the drive frequency of the inverter main circuit 11, is assumed, and another processing routine (not shown), for example, temporarily stopping and displaying a failure or notification, etc. Is performed.

If NO is determined in step T6, the process proceeds to step S1 and f
The drive of the inverter main circuit is restarted at the drive frequency f reduced by step.

By repeating this operation, if no failure or the like has occurred, f3 shown in FIG.
The inverter main circuit 11 is driven in a state where the drive frequency f is set in the normal operation range, which is a frequency range from f4 to f4.

When the inverter main circuit 11 is driven at the drive frequency f in the normal operation range, the control circuit 23 sets the input power to the two induction heating coils 2a and 2b first. Is controlled so as to achieve the desired input power ratio. That is, the operation of the “driving frequency adjustment processing” described above will be described with reference to FIGS. 10 and 11. The control circuit 23 gives the drive circuit 26 a drive frequency f within the normal operating range, and causes the drive circuit 26 to drive the inverter main circuit 11 at the drive frequency f (step U).
1). Next, the control circuit 23 substitutes ΔE ← ABS {E1 (f) −E2 (f)} (3) for a variable ΔE used in a calculation process described later. Further, the control circuit 23 controls the variable FLG
The sign is detected and substituted as FLG ← SGN {E1 (f) −E2 (f)} (4) (step U2). still,
In the expression (3), “ABS” indicates a function for outputting the absolute value of the value of the expression in curly braces. In equation (4), “SGN” indicates a function that outputs the sign of the value of the expression in curly braces, and “0” if the result is positive or zero.
Is output, and when the result is negative, "1" is output.

The control circuit 23 defines a difference between two detection voltages to be detected by the signal detection circuit 25 when a heating operation is performed at a given input power ratio set value as a set signal level difference, and determines the corresponding input potential difference. Set. Control circuit 23
Subtracts the absolute value ΔE of the detection voltage calculated by the equation (3) from the absolute value ΔE0 of the corresponding input potential difference, that is, calculates (ΔE0−ΔE), and this value is set to a predetermined value set as an allowable error. It is determined whether the value is equal to or less than the value (step U3). That is, the control circuit 23 determines whether or not ΔE0 and ΔE are substantially equal. If the determination is YES, the coil designation flag flg and the detected code FL are determined.
G (step U4), and if the values are the same, the sign and absolute value of the set input potential difference and the detected input potential difference match, so that a predetermined input power ratio , And the drive frequency adjustment processing ends.

Control circuit 23 determines in step U4 that N
When it is determined as O, that is, when it is determined that the coil designation flag flg and the detected code FLG do not match, it is determined whether or not the absolute value ΔE0 of the corresponding input potential difference exceeds the absolute value ΔE of the detected voltage ( Step U5). When the control circuit 23 determines YES, that is, when ΔE
If 0 exceeds ΔE, the coil designation flag f
It is determined whether or not lg is 0 (step U6). When the coil designation flag flg is 0, the control circuit 23 reduces the driving frequency f by a minute frequency fmin of, for example, about 100 Hz (step U7). Thereafter, returning to step U1, the control circuit 23 outputs the substituted drive frequency f to the drive circuit 26, and causes the drive circuit 26 to drive the inverter main circuit 11 at the drive frequency f. Thereafter, the drive frequency adjustment processing is repeated until the control circuit 23 determines in step U4 that the coil designation flag flg matches the detected code FLG.

In step U6, the control circuit 2
In step 3, if the coil designation flag flg is not 0, the drive frequency f is increased by the minute frequency fmin (step U8). Thereafter, the process returns to step U1, where the drive frequency f is again supplied to the drive circuit 26, and the drive circuit 26 drives the inverter main circuit 11.

Further, in step U5, if the determination is NO, that is, if ΔE is equal to or greater than ΔE0, the control circuit 23 determines whether the detected code FLG is 0 (step U9). . The control circuit 23 determines that the detected code FLG is 0 (see FIG. 11).
), A small frequency fmin with respect to the driving frequency f
(Step U10). After that, the process returns to step U1 in the same manner as described above, and the drive frequency f is again supplied to the drive circuit 26, and the drive circuit 26 drives the inverter main circuit 11.

If it is determined in step U9 that the detected code FLG is not 0, the drive frequency f is reduced by the minute frequency fmin (step U1).
1). Thereafter, the process returns to step U1 in the same manner as described above, and provides the drive frequency f to the drive circuit 26 again.
The inverter main circuit 11 is driven.

Finally, the difference ΔE between the two detection voltages detected by the signal detection circuit 25 and the corresponding input potential difference which is the difference between the two detection voltages to be detected by the signal detection circuit 25 The above operation will be repeated until they are substantially equal.

According to the first embodiment, the resonance circuit 15a and the resonance circuit 15b constituted by the induction heating coils 2a and 2b are set so that the resonance frequencies f1 and f2 are different from each other. The resonance circuit section 16 is connected in parallel, and the control circuit 23 drives the inverter main circuit 11 at a drive frequency f corresponding to the input power ratio. Therefore, the induction heating coils 2a and 2b
Inverter main circuits can be provided individually for
A desired input power ratio set by one inverter main circuit 11 can be set to be supplied to the induction heating coils 2a and 2b without providing a changeover switch or the like.

The signal detection circuit 15 detects the current supplied to the induction heating coils 2a and 2b, and
3 and the control circuit 23 calculates the sum of the rectified DC voltages corresponding to those currents, and outputs the detected voltages E1 (f),
When the sum of E2 (f) exceeds the upper limit level Emax, it is determined that the output level of the inverter main circuit 11 is out of the normal operation range.
It is possible to detect an abnormality in the driving frequency f or the output level for driving the driving device 1. Further, at this time, the control circuit 23 changes the drive frequency of the inverter main circuit 11 by fstep set to be larger than Δf, and then changes the drive frequency of the inverter main circuit 11.
Since it is determined that the output level 1 is out of the normal operation range, the reliability can be improved.

The inverter main circuit is used in a relatively low frequency range of 25 kHz to 45 kHz in which an eddy current can be efficiently generated by the induction heating coils 2a and 2b by using the iron pot 1 in particular. Drive 11,
The current supplied to the induction heating coils 2a and 2b can be adjusted stably.

(Second Embodiment) FIGS. 12 and 13
Shows a second embodiment of the present invention. Hereinafter, only portions different from the first embodiment will be described. FIG. 12 is a flowchart corresponding to FIG. 10 in the first embodiment. In step U3, when the control circuit 23 determines that ΔE0−ΔE is equal to or less than a predetermined value, the control circuit 23 determines that the coil designation flag flg and the detected code F
It is determined whether LG has the same value (step U1).
2). When the control circuit 23 determines that the coil designation flag flg and the detected code FLG have the same value, the control circuit 23 calculates the value of the set input potential difference and the detected input potential difference.
Since the sign and the absolute value match, the input power ratio is set to a predetermined input power ratio, and the drive frequency f
Finish the setting of. When determining NO in step U12, that is, when determining that the coil designation flag flg does not match the detected code FLG, the control circuit 23 substitutes (f1 + f2-f) for the drive frequency f. Then, the inverter main circuit 11 is driven again at the drive frequency f. The processing in step U13 is (f1 + f
2) An operation of changing the drive frequency so as to be inverted with respect to fmid calculated in ÷ 2 (in FIG. 13, a value obtained by roughly calculating the frequency at which the detected voltage characteristics cross each other) (｛fmi
d + (fmid-f)} or {fmid- (f-fmi
d) ②) is shown. FIG. 13 shows this principle in principle.

Finally, the difference ΔE between the two detection voltages detected by the signal detection circuit 25 and the corresponding input potential difference, which is the value of the difference between the two detection voltages to be detected by the signal detection circuit 25, are substantially equal. The above operation will be repeated until it is.

According to the second embodiment, the detected code FLG is set to the set coil designation flag f
lg, when the inverter main circuit 11 is driven within the frequency range of the normal operation range, the control circuit 23 operates within one frequency range that should not be driven. That is, the inverter main circuit 11 is driven at a certain frequency. Then, the control circuit 2
No. 3 substitutes (f1 + f2-f) for the driving frequency f and outputs the driving frequency to the driving circuit 26, so that the frequency shifts to a certain frequency in the other frequency region which needs to be driven in the normal operating range. it can. Thereby, the first
The inverter main circuit 11 can be quickly driven at a drive frequency capable of supplying a desired input power ratio to the induction heating coils 2a and 2b without deteriorating the effects of the embodiment.
Can be driven.

[0057]

As is clear from the above description, the present invention has the following excellent effects. That is, according to the insulated pot of claim 1, the signal detecting means detects a signal based on different currents input to the plurality of induction heating coils and outputs the signal to the control means. Is set based on the driving frequency. Thereby, a plurality of induction heating coils are controlled at a desired input power ratio by one inverter main circuit without providing an inverter main circuit corresponding to each of the plurality of induction heating coils or providing a changeover switch or the like. be able to. Further, the inverter main circuit can be controlled so that the current supplied to the plurality of induction heating coils can be stably adjusted. That is, control stability can be improved.

According to the second aspect of the present invention, the signal detecting means detects signals obtained from the plurality of resonance circuits and outputs the signals to the control means, and the control means detects the level of the signal of the signal detecting means. When the sum is calculated and exceeds an upper limit level set in advance, the first determination operation determines that the output level of the inverter main circuit is out of the normal operation range. It is possible to detect a state due to a setting deviation.

According to the third aspect of the present invention, the signal detecting means detects a change in the signal level accompanying a change in the driving frequency in accordance with the gradient of the change in the admittance characteristic of each resonance circuit, and controls the signal. The means can determine that the signal level is out of the normal operation range as the second determination operation when both the increasing and decreasing directions in which the signal levels of the respective resonance circuits change increase or decrease. This makes it possible to detect an abnormality in the input power ratio supplied to the induction heating coil.

According to the fourth aspect of the present invention, the control means determines that the output level of the inverter main circuit is out of the normal operation range by the first determination operation, or When it is determined by the determination operation that the drive frequency of the inverter main circuit is out of the normal operation range, the drive frequency of the inverter main circuit is changed by the second change. At this time, the second change is set to be larger than the first change, and the state largely changes from a state where the output level of the inverter main circuit is out of the normal operation range. Thereafter, the control unit performs the first or second determination operation again to determine that the output level or the drive frequency of the inverter main circuit is out of the normal operation range, so that the reliability can be improved. it can.

According to the fifth aspect of the present invention, when the input power ratio set value is set for the two resonance circuits, the control means detects the input power ratio set value by the signal detection means. The level difference between the two signals to be performed is determined as a set signal level difference. The signal detection means detects the two signals and outputs the two signals to the control means. The control means sets the drive frequency of the inverter main circuit so that the set signal level difference and the level difference between the two signals become substantially equal. Coil can be controlled at a desired input power ratio,
It is possible to stably adjust the current supplied to each of the induction heating coils, thereby improving the control stability.

According to the invention, when the input power ratio set value is set for the two resonance circuits, the control means detects the input power ratio set value by the signal detection means. The level difference between the two signals to be performed is determined as a set signal level difference. The signal detecting means detects the two signals and outputs them to the control means. Then, the control means sets the drive frequency of the inverter main circuit such that the absolute value of the set signal level difference and the absolute value of the level difference between the two signals detected by the signal detection means are substantially equal. The control means sets the original drive frequency of the inverter main circuit based on the set drive frequency when the input power ratio set values of the two resonance circuits are in a relationship opposite to the level difference between the two signals. I do. Thus, when the input power ratio set value is set, the two induction heating coils can be quickly controlled at a desired input power ratio, and the current supplied to the two induction heating coils is stabilized. Adjustment can be performed, and the stability of control can be improved.

[Brief description of the drawings]

FIG. 1 is an electrical configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional side view showing an arrangement relationship between an iron pot and an induction heating coil.

FIG. 3 is an admittance-frequency characteristic diagram of a resonance circuit.

FIG. 4 is a flowchart showing a flow of setting a driving frequency (part 1);

FIG. 5 is a view for explaining the principle of setting a driving frequency in a detection voltage-frequency characteristic (part 1);

FIG. 6 is a view for explaining the principle of setting the drive frequency in the detection voltage-frequency characteristic (part 2).

FIG. 7 is a view for explaining the principle of setting the driving frequency in the detection voltage-frequency characteristic (part 3).

FIG. 8 is a view for explaining the principle of setting the driving frequency in the detection voltage-frequency characteristic (part 4).

FIG. 9 is a flowchart showing a flow of setting a driving frequency (part 2);

FIG. 10 is a flowchart illustrating a flow of setting a driving frequency (part 3);

FIG. 11 is a view for explaining the principle of setting the driving frequency in the detection voltage-frequency characteristic (part 5).

FIG. 12 is a view corresponding to FIG. 10, showing a second embodiment of the present invention;

FIG. 13 is a diagram corresponding to FIG. 11;

[Explanation of symbols]

1 is a pot, 2a and 2b are induction heating coils, 11 is an inverter main circuit, 15a and 15b are resonance circuits, 16 is a resonance circuit section, 17a and 17b are current transformers, 23 is a control circuit (control means), and 25 is It is a signal detection circuit (signal detection means).

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K051 AA02 AA08 AB05 AC07 AC12 CD02 4B055 AA02 BA28 BA63 DB14 GC17 GD01 GD02

Claims (6)

[Claims] 1. A power supply circuit for converting an AC input into a DC output, and a resonance circuit formed by connecting a resonance capacitor in series to each of a plurality of induction heating coils for heating an iron pot. A resonance circuit section in which resonance circuits in which resonance frequencies are set to be different from each other are connected in parallel, and when a DC output of the power supply circuit is given, this is converted to an AC output of a set drive frequency to convert the resonance circuit section to an AC output. An inverter main circuit that outputs a signal obtained from the plurality of resonance circuits, and the inverter so that the plurality of induction heating coils perform a heating operation at a given input power ratio set value. Control means for setting a drive frequency of the main circuit based on a level of a signal detected by the signal detection means. 2. The control means according to claim 1, wherein said output level of said inverter main circuit is out of a normal operation range when a sum of signal levels detected by said signal detection means exceeds a preset upper limit level. The heat retaining kettle according to claim 1, wherein a first determining operation for determining that the operation is performed is performed. 3. The resonance circuit section is provided with two resonance circuits, and the control means controls the signal detection means when the drive frequency of the inverter main circuit is changed by a first change. When the change in the signal level both increases or decreases together, the second to determine that the drive frequency of the inverter main circuit is out of the normal operation range.
The heat insulation pot according to claim 1 or 2, wherein the determination operation is performed. 4. When the control means determines that the output level or the drive frequency of the inverter main circuit is out of the normal operation range, the control means sets the drive frequency of the inverter main circuit higher than the first change. 4. The heat insulation pot according to claim 3, wherein the first or second determination operation is performed after the change is made by the second change amount. 5. 5. The control means, when the input power ratio set value is set for the two resonance circuits, is detected by the signal detection means when a heating operation is performed at the input power ratio set value. A level difference between two signals to be obtained is determined as a set signal level difference, and the drive frequency of the inverter main circuit is set so that the level difference between the two signals detected by the signal detecting means is substantially equal to the set signal level difference. The heat insulation kettle according to claim 3 or 4, wherein the temperature is set. 6. The control means, when the input power ratio setting value is set for the two resonance circuits, is detected by the signal detection means when a heating operation is performed at the input power ratio setting value. A level difference between two signals to be obtained is obtained as a set signal level difference, and the absolute value of the level difference between the two signals detected by the signal detecting means is substantially equal to the absolute value of the set signal level difference. When the drive frequency of the inverter main circuit is set, when the levels of the two signals are in an inverse relationship with respect to the input power ratio set values of the two resonance circuits, based on the set drive frequency, 5. The heat retaining pot according to claim 3, wherein a driving frequency of the inverter main circuit is set.