JP2000012202A - Induction heating cooking device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress application of overvoltage to a switching element caused by increase in power source voltage to prevent failure of the switching element by setting an applying electric power by weighting addition of signal levels of a DC voltage generating means and an input voltage detecting means. SOLUTION: Outputs of a DA conversion circuit 12 and a power source voltage detecting circuit 13 are inputted into a weighting adding circuit 14, two input voltage values are weighted, then converted into voltage suitable for a comparing circuit 15. Resonance voltage generated in a switching element 7 is detected, and a trigger pulse is outputted from a trigger circuit 10. A self oscillator 11 is an oscillator for outputting almost a chopping wave capable of triggering, and synchronizes with a resonance state after starting of operation of an inverter. The comparing circuit 15 compares voltage of the self oscillator 11 with that of the weighting adding circuit 14, and outputs the on/off pulse of the switching element 7 according to the large or small relation. A driving circuit 16 converts the pulse into driving output suitable for the driving of the switching element 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an induction heating cooker.

[0002]

2. Description of the Related Art In an inverter control of an induction heating cooker, an output of a free-running oscillator synchronized with a resonance state is compared with a DC conversion output of a power setting signal output from a control microcomputer by a comparator. Is often used as the drive signal of the inverter switching element.

The level setting of the power setting signal is performed by software processing based on the level set by the microcomputer according to the state of the power supply and the state of the load input to the device, and the level is changed.

[0004]

Since a resonance voltage proportional to the commercial power supply voltage is applied to the switching element for switching, a stress exceeding the rating of the switching element is applied by noise such as an external surge, and the destruction of the element and the surrounding area are caused. The circuit may be damaged.

Conventionally, in order to prevent such a failure of the switching element, a countermeasure by software processing as described above is provided.

[0006] However, the abnormal voltage generated in the commercial power supply varies in voltage and generation time, and it cannot be said that all of it can be covered by dealing only with software. Cannot be dealt with, which may lead to element destruction.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and comprises a rectifier circuit for converting an AC power supply to a DC power supply, a smoothing circuit for smoothing the DC power supply, and an output of the smoothing circuit. In an induction heating cooker comprising: an inverter for converting a high-frequency current by a switching element, supplying the current to a resonance circuit including a heating coil, a capacitor, and a load to heat the load, and a control unit for controlling the inverter; The unit is a free-running oscillator that generates a substantially triangular wave in synchronization with the resonance voltage of the inverter unit, DC voltage generating means whose level changes according to the setting of the energizing power, the self-running oscillator output and the energizing power setting output. Comparing means for outputting a result of the comparison, driving means for driving a switching element of the inverter unit by an output of the comparing means, and detecting an input voltage of the inverter unit. Input voltage detection means, the output of the input voltage detection means and the output of the DC voltage generation means are both in a direction in which the relationship between the voltage change and the power change is in the same direction, and the energized power setting output is the DC voltage generation means and the input Each signal level of the voltage detecting means is weighted and added.

[0008]

With such a configuration, the pulse width of the switching element automatically changes by changing the voltage for setting the power in accordance with the voltage fluctuation of the commercial power supply. Therefore, even when high voltage noise is applied to the commercial power supply, the control for shortening the pulse width of the switching element is performed, so that it is possible to prevent generation of a resonance voltage that may cause element destruction.

[0009]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a main block diagram showing an embodiment of the present invention.

A commercial power supply 1 is converted to a direct current by a rectifying element 2 and smoothed by a choke coil 3 and a capacitor 4. This DC power supply was switched at high speed by a diode 8 connected in anti-parallel with a switching element 7 and a resonance circuit composed of a heating coil 5 and a capacitor 6, and a high-frequency current was continuously supplied to the heating coil 5 and arranged near the coil. Heat the load.

The setting of the power supplied to the inverter is performed by a power setting signal of the microcomputer 9 and its output is provided by a digital / analog conversion circuit 12 which is a DC voltage generating means.
(Hereinafter referred to as a DA conversion circuit 12) to convert the analog voltage. A power supply voltage detection circuit 13 serving as input voltage detection means detects a DC voltage after rectification of commercial power supply.

The outputs of the DA conversion circuit 12 and the power supply voltage detection circuit 13 are input to a weighting addition circuit 14. The weighted addition circuit 14 weights each of the two input voltages and then adds them to convert the input voltage into a voltage suitable for the comparison circuit 15 at the subsequent stage.

On the other hand, in order to operate the inverter circuit continuously, a resonance voltage generated in the switching element 7 is detected, and a trigger pulse is output from the trigger circuit 10.

The free-running oscillator 11 is an oscillator that outputs a triangular wave that can be triggered. After the inverter starts operating, the operation timing is determined by the trigger of the trigger circuit 10 and is synchronized with the resonance state.

The comparison circuit 15 compares the voltages of the free-running oscillator 11 and the weighted addition circuit 14, and outputs an on / off pulse of the switching element 7 according to the magnitude relationship. The drive circuit 16 is suitable for driving the switching element. Is converted into a driving voltage.

FIG. 2 shows input / output signal waveforms of the comparison circuit 15.

FIG. 2A shows a comparison output waveform in the case of a low power setting (L setting) and a high power setting (H setting) for a substantially triangular wave of a free-running oscillation waveform. The voltage of the L setting is higher than the voltage of the H setting, and the comparison output has a shorter L setting and a longer H setting. Therefore, the relationship between the set voltage and the set power is represented as shown in FIG.

FIG. 3 shows an example of the output of the DA conversion circuit 12, the output of the power supply voltage detection circuit 13, and the output of the weighting addition circuit 14.

In this embodiment, the output voltage of the DA converter circuit is added by reducing the weight of the power supply voltage detection circuit voltage. Therefore, the power setting output from the microcomputer 9 is used as a center value, and the power supply voltage is corrected. In addition, since the weighted addition output is also corrected and output with respect to the noise voltage in the figure, the duty ratio of the switching element is reduced and the inverter resonance voltage is reduced.

FIG. 4 shows an example of the power supply voltage detection circuit 13.

The DC voltage after rectification of the commercial power is divided by resistors 131 and 132 and output.

FIG. 5 shows an example of the weighting and adding circuit 14.

The outputs of the DA conversion circuit 12 and the power supply voltage detection circuit 13 are connected via resistors 141 and 142, respectively, and output to the comparison circuit 15, whereby the resistances 141 and 1 are output.
According to the ratio of 42, the amount of the duty ratio correction for the fluctuation of the commercial power supply voltage is determined.

In this embodiment, the power supply voltage detecting circuit 13 and the DA
Since the output voltage of the conversion circuit 12 tends to decrease the duty ratio of the switching element as both increase,
It can be realized with a simple circuit configuration. When one of these signals is reversed, it is necessary to invert it, but the subsequent circuit processing has a similar circuit configuration.

[0026]

According to the present invention, in an induction heating cooker, application of an overvoltage to a switching element due to an increase in power supply voltage can be suppressed, and failure of the switching element can be prevented. Further, there is an advantage that the voltage can be corrected much faster than the software processing speed of the control microcomputer. further,
The elements required to configure the present invention are only required to add several resistance elements to the conventional circuit configuration, and can suppress an increase in cost.

[Brief description of the drawings]

FIG. 1 is a main part block diagram of an induction cooking device showing one embodiment of the present invention.

FIG. 2 is an input / output signal waveform diagram of a comparison circuit.

FIG. 3 is a diagram illustrating an operation example of a weighted addition circuit.

FIG. 4 is a diagram illustrating an example of a power supply voltage detection circuit.

FIG. 5 is a diagram illustrating an example of a weighted addition circuit.

[Explanation of symbols]

7 switching element, 9 microcomputer, 11
Free-running oscillator, 12 DA conversion circuit, 13 power supply voltage detection circuit, 14 weighted addition circuit, 15 comparison circuit

Claims (1)

[Claims] 1. A rectifier circuit for converting an AC power supply to a DC power supply, a smoothing circuit for smoothing the DC power supply, and an output of the smoothing circuit converted to a high-frequency current by a switching element, and a resonance comprising a heating coil, a capacitor, and a load. In an induction heating cooker comprising an inverter unit for supplying a circuit and heating a load, and a control unit for controlling the inverter unit,
The control unit includes a free-running oscillator (11) that generates a substantially triangular wave in synchronization with a resonance voltage of the inverter unit, and a DC voltage generation unit (12) whose level changes according to the setting of energized power.
A comparing means (15) for outputting a comparison result between the free-running oscillator output and the energized power setting output; and a driving means (16) for driving a switching element (7) of the inverter unit by an output of the comparing means. An input voltage detecting means (13) for detecting an input voltage of the inverter unit, wherein both the output of the input voltage detecting means and the output of the DC voltage generating means have the same relationship between the voltage change and the power change; Is
An induction heating cooker characterized in that each signal level of the DC voltage generating means and the input voltage detecting means is weighted and added.