JP3799161B2 - Induction heating cooker - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling an induction heating cooker.
[0002]
[Prior art]
The inverter control of the induction heating cooker compares the output of the self-running oscillation means synchronized with the resonance state with the DC conversion output of the power setting signal output from the control microcomputer, and the result is the inverter switching element. The drive signal is often used.
[0003]
Further, the level setting of the power setting signal is changed by software processing according to the state of the power source input to the device and the state of the load based on the level set by the microcomputer.
[0004]
[Problems to be solved by the invention]
Since a resonant voltage proportional to the commercial power supply voltage is applied to the switching element that performs switching, a stress exceeding the switching element rating is applied by noise such as an external surge, and the element is destroyed and the peripheral circuit is accordingly damaged.
[0005]
Conventionally, in order to prevent such a failure of the switching element, a correction means by software processing as described above is provided and dealt with.
[0006]
However, the abnormal voltage generated in the commercial power supply varies in voltage and generation time, and it cannot be said that it can be covered by software alone, and it can cope with abnormal voltage shorter than the software processing time. In some cases, the device may be destroyed.
[0007]
[Means for Solving the Problems]
The present invention solves the above problems, a rectifier circuit that converts an AC power source into a DC power source, a smoothing circuit that smoothes the DC power source, and an output of the smoothing circuit is converted into a high-frequency current by a switching element, In an induction heating cooker including an inverter unit that supplies a resonance circuit including a heating coil, a capacitor, and a load, and heats the load, and a control unit that controls the inverter unit, the control unit sets the resonance voltage of the inverter unit to A self-running oscillator that generates a substantially triangular wave in synchronism, a DC voltage generating means whose level changes according to the setting of the energization power, and a comparison means that outputs a comparison result between the self-running oscillator output and the energization power setting output; having drive means for driving the switching elements of the inverter section by the output of said comparing means and an input voltage detecting means for detecting an input voltage of the inverter section, The input voltage detecting means as input voltage after the AC power supply rectified to output DC voltage generating means and an input voltage detecting means both a relationship change between the current power and its voltage changes in the same direction, the energization power setting The output is corrected by weighting and adding each signal level of the output of the DC voltage generating means and the output of the input voltage detecting means so that the current-carrying rate of the switching element is lowered when the output of the input voltage detecting means increases. it is one in which was to so that.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
By adopting such a configuration, the pulse width of the switching element is automatically changed by changing the voltage for setting the power with the voltage fluctuation of the commercial power supply. Therefore, even when high voltage noise is applied to the commercial power supply, the control is performed to shorten the pulse width of the switching element, so that it is possible to prevent the generation of a resonance voltage that causes element destruction.
[0009]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0010]
FIG. 1 is a principal block diagram showing an embodiment of the present invention.
[0011]
The commercial power source 1 is converted into a direct current by the rectifying element 2 and smoothed by the choke coil 3 and the capacitor 4. This DC power supply is switched at high speed by a diode 8 connected in reverse parallel to the resonance circuit composed of the heating coil 5 and the capacitor 6 and the switching element 7, and a high-frequency current is continuously passed through the heating coil 5 and is arranged in the vicinity of the coil. Heat the load.
[0012]
The inverter energization power is set by a power setting signal of the microcomputer 9, and the output is converted into an analog voltage by a digital / analog conversion circuit 12 (hereinafter referred to as a DA conversion circuit 12) which is a DC voltage generating means. A power supply voltage detection circuit 13 as input voltage detection means detects a DC voltage after commercial power supply rectification.
[0013]
The outputs of the DA conversion circuit 12 and the power supply voltage detection circuit 13 are input to the weighting addition circuit 14. The weighted addition circuit 14 weights the two input voltages, adds them, and converts them to a voltage suitable for the comparison circuit 15 at the subsequent stage.
[0014]
On the other hand, in order to continuously operate the inverter circuit, a resonance voltage generated in the switching element 7 is detected, and a trigger pulse is output from the trigger circuit 10.
[0015]
The free-running oscillator 11 is an oscillator that outputs a substantially triangular wave that can be triggered. After the start of the inverter operation, the operation timing is determined by the trigger of the trigger circuit 10 and is synchronized with the resonance state.
[0016]
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 a drive voltage suitable for driving the switching element. It is to convert to.
[0017]
FIG. 2 shows input / output signal waveforms of the comparison circuit 15.
[0018]
FIG. 2A shows a comparative output waveform in the case of low power setting (L setting) and high power setting (H setting) with respect to the substantially triangular wave of the free-running oscillation waveform. The L setting voltage is higher than the H setting voltage, and the comparison output has a short L setting and a long H setting. Therefore, the relationship between the set voltage and the set power is expressed as shown in FIG.
[0019]
FIG. 3 shows an example of the DA conversion circuit 12 output, the power supply voltage detection circuit 13 output, and the weighted addition circuit 14 output.
[0020]
In this example, the power supply voltage detection circuit voltage is weighted and added to the DA converter circuit output voltage. Therefore, the power supply voltage output from the microcomputer 9 is set as a central value, and the power supply voltage is corrected. In addition, since the weighted addition output is output with correction applied to the noise voltage in the figure, it works in the direction of lowering the energization rate of the switching element and keeping the inverter resonance voltage low.
[0021]
FIG. 4 shows an example of the power supply voltage detection circuit 13.
[0022]
The DC voltage after commercial power supply rectification is divided by resistors 131 and 132 to be output.
[0023]
FIG. 5 shows an example of the weighted addition circuit 14.
[0024]
By connecting the outputs of the DA converter circuit 12 and the power supply voltage detection circuit 13 via the resistors 141 and 142 and outputting them to the comparison circuit 15, respectively, the current supply rate correction for the fluctuation of the commercial power supply voltage is made according to the ratio of the resistors 141 and 142. The amount is determined.
[0025]
In this example, since the output voltages of the power supply voltage detection circuit 13 and the DA conversion circuit 12 both tend to decrease the energization rate of the switching element as they become higher, this can be realized with a simple circuit configuration. When one of these signals is reversed, it is necessary to invert it, but the circuit configuration is the same for the subsequent circuit processing.
[0026]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, in the induction heating cooking appliance, the overvoltage application of the switching element by the raise of a power supply voltage can be suppressed, and failure of a switching element can be prevented. Further, there is an advantage that the correction for the voltage can be applied much faster than the software processing speed of the control microcomputer. Furthermore, the elements necessary for configuring the present invention are the extent that several resistance elements are added to the conventional circuit configuration, and an increase in cost can be suppressed.
[Brief description of the drawings]
FIG. 1 is a block diagram of a main part of an induction heating cooker showing an embodiment of the present invention.
FIG. 2 is a waveform diagram of input / output signals 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)

A rectifier circuit that converts an AC power source into a DC power source, a smoothing circuit that smoothes the DC power source, an output of the smoothing circuit is converted into a high-frequency current by a switching element, and is supplied to a resonance circuit including a heating coil, a capacitor, and a load. an inverter section for heating the load, in the induction heating cooker comprising a control unit for controlling the inverter unit, wherein the control unit includes a free-running oscillator for generating a substantially triangular wave in synchronization with the resonance voltage of the inverter section, a DC voltage generator hand stages, the level of which changes according to the setting of the energization power, and comparing means to output a comparison result between the free-running oscillator output energized power setting output, the switching of the inverter section by the output of the comparing means a driving means to drive the element, and an input voltage detecting means to detect the input voltage of the inverter unit, the input voltage detecting means voltage after the AC power supply rectified As input, and in the same direction the relationship of the change in the input voltage detecting means output of the DC voltage generating means along with its voltage variation and the energizing power, the energization power setting output when the output of the input voltage detection means is increased Induction heating cooking characterized in that each signal level of the output of the DC voltage generating means and the output of the input voltage detecting means is corrected by weighted addition so as to reduce the energization rate of the switching element. vessel.

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