JP2002299027A - Induction heating cooker - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent an increase in switching loss of a switching element or to prevent the influence of high-voltage noise according to a situation. A control unit includes: a free-running oscillator that generates a substantially triangular wave in synchronization with a resonance voltage of an inverter unit;
DC voltage generating means 16 whose level changes in accordance with the setting of energized power, power supply voltage detecting means 17 for detecting the DC power supply voltage, and the output level of DC voltage generating means 16 and the output level of power supply voltage detecting means 17 Weighting and adding means 19 for weighting and adding, comparing means 20 for outputting a result of comparison between the output of the free-running oscillator 14 and the output of the weighting and adding means 19, and using the output of the comparing means 20 for driving the switching element 9. It has a driving unit 21 that converts the output to a suitable driving voltage and outputs the same, and an addition switching unit 18. The addition switching unit 18 switches connection or disconnection of the output of the power supply voltage detection unit 17 to or from the weighting addition unit 19. .

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 Conventional inverter control of an induction heating cooker involves an output signal of a free-running oscillator synchronized with a resonance state and an electric power setting output from a control microcomputer and converted into digital / analog by DC voltage means. In many cases, the signals are compared by a comparator, and the result is level-converted and used as a drive signal for the inverter switching element.

[0003] The level setting of the power setting signal is performed by software correction based on the state of the power supply or the load input to the device based on the level set by the microcomputer, and the level is changed.

At this time, since a resonance voltage proportional to a commercial power supply voltage is applied to the switching element for switching, a stress exceeding the rating of the switching element is applied due to noise such as an external surge, and the switching element is destroyed and the peripheral circuit associated therewith is destroyed. Will be damaged.

Conventionally, in order to prevent such destruction of the switching element, it is common practice to provide correction means by software processing as described above.

However, the abnormal voltage generated in a 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, and the abnormal voltage is shorter than the software processing time. And the like, and the switching element may be destroyed.

[0007] To solve the above problems, Japanese Patent Laid-Open Publication No.
000-12202. This conventional example will be described with reference to FIG. FIG. 3 is a circuit block diagram showing a conventional example.

[0008] A rectifier circuit 2 for converting the AC power supply 1 to a DC power supply, a smoothing circuit 5 for smoothing the DC power supply, and an output of the smoothing circuit 5 converted to a high-frequency current by a switching element 9, a heating coil 6 and a capacitor 7. And an inverter unit 11 for supplying heat to a resonance circuit 8 including a load and heating the load.
In the induction heating cooker including the control unit 12 for controlling the inverter unit 11, the control unit 12 includes a free-running oscillator 14 that generates a substantially triangular wave in synchronization with a resonance voltage of the inverter unit 11, and a setting of energizing power. DC voltage generating means 16 whose level changes in accordance with the following, and comparing means 20 which outputs a result of comparison between the output of the free-running oscillator 14 and the output setting of energized power.
A driving unit 21 for driving the switching element 9 of the inverter unit 11 by an output of the comparing unit 20; and a power supply voltage detecting unit 17 for detecting an input voltage of the inverter unit 11.
Power supply voltage detecting means 17 and DC voltage generating means 1
6 is the same direction as the relationship between the voltage change and the power change, and the energized power setting output is such that the signal levels of the DC voltage generation means 16 and the power supply voltage detection means 17 are weighted and added. It is.

With such a configuration, the pulse width of the switching element 9 is automatically changed by changing the voltage for setting the power in accordance with the voltage fluctuation of the commercial AC power supply 1. Therefore, even when high voltage noise is applied to the commercial AC power supply 1, the control for shortening the pulse width of the switching element 9 is performed, so that it is possible to prevent the generation of a resonance voltage that may cause the destruction of the switching element 9 and the like. You can do it.

[0010]

SUMMARY OF THE INVENTION As described above, the induction heating cooker described in Japanese Patent Application Laid-Open No. 2000-12202,
By suppressing the resonance voltage, it is possible to prevent the occurrence of a resonance voltage that may cause the switching element 9 to be destroyed by high-voltage noise. However, when outputting low power, the resonance voltage falls below the voltage of the AC power supply 1 and the switching is performed. Element 9
Switching loss may be greatly increased.

The present invention solves the above-mentioned problems, and realizes prevention of an increase in switching loss of a switching element or prevention of the influence of high-voltage noise according to the situation.

It is another object of the present invention to reduce the switching loss of the switching element at the time of low power and to prevent the switching element and the like from being damaged by high voltage noise.

[0013]

According to the present invention, there is provided a rectifying circuit for converting an AC power supply to a DC power supply, a choke coil and a smoothing capacitor, and a smoothing circuit for smoothing the DC power supply. And an inverter for converting the output of the smoothing circuit into a high-frequency current by a diode connected in anti-parallel to the switching element, supplying the current to a resonance circuit including a heating coil, a capacitor and a load, and heating the load. And a control unit for controlling the induction heating cooker, wherein the control unit includes a free-running oscillator that generates a substantially triangular wave in synchronization with a resonance voltage of the inverter unit, and a DC voltage whose level changes according to the setting of the energizing power. Generating means, a power supply voltage detecting means for detecting the DC power supply voltage, and an output level of the DC voltage generating means and an output level of the power supply voltage detecting means. Weighting and adding means for adding and outputting, a comparing means for outputting a comparison result between the output of the free-running oscillator and the output of the weighting and adding means, and an output of the comparing means to a drive voltage suitable for driving the switching element. It has a driving means for converting and outputting, and an addition switching means, and the addition switching means switches connection or disconnection of the output of the power supply voltage detecting means to or from the weighting addition means.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention relates to a rectifier circuit for converting an AC power supply to a DC power supply, a smoothing circuit for smoothing the DC power supply, an inverter for heating a load, and an inverter. And a control unit for controlling the induction heating cooker, wherein the control unit is a self-running oscillator that generates a substantially triangular wave in synchronization with the resonance voltage of the inverter unit, and a DC voltage whose level changes according to the setting of the energizing power. Generating means;
Power supply voltage detection means for detecting the DC power supply voltage, weighted addition means for weighting and adding the output level of the DC voltage generation means and the output level of the power supply voltage detection means, and output of the free-running oscillator and weighted addition means. A comparing unit that outputs a result of comparison with the output, a driving unit that converts the output of the comparing unit into a driving voltage suitable for driving the switching element and outputs the driving voltage, and an addition switching unit. The output of the voltage detecting means is switched between connection and non-connection to the weighting addition means.

According to this, it is possible to select connection or non-connection by the addition switching means according to the situation, thereby preventing an increase in switching loss of the switching element or an effect of high voltage noise.

Further, the switching by the addition switching means is such that the output of the power supply voltage detecting means is connected to the weighting addition means in the case of high power, and is not connected in the case of low power, so that the switching element in the low power state is connected. The switching loss can be reduced, and the destruction of a switching element or the like due to high voltage noise can be prevented regardless of whether the power is low or high.

[0017]

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

FIG. 1 is a circuit block diagram showing one embodiment of the present invention, and FIG. 2 is a diagram showing the output of the weighting and adding means and the waveform of the resonance voltage in one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a commercial AC power supply. Reference numeral 2 denotes a rectifier circuit, which is connected to two input sections (〜 in the drawing) at both ends of the AC power supply 1 and has a negative (−) output terminal grounded, thereby converting the AC power supply 1 into a DC power supply.

A choke coil 3 has a first terminal connected to a positive (+) output terminal of the rectifier circuit 2. A smoothing capacitor 4 has a first terminal connected to the second terminal of the choke coil 3, and a second terminal grounded. The choke coil 3 and the smoothing capacitor 4 constitute a smoothing circuit 5 for smoothing the DC power supply.

6, 7 are heating coils and condensers,
The first connection point is connected in parallel with the choke coil 3
And a connection point of the smoothing capacitor 4, and a resonance circuit 8 is configured by these and a load (not shown).

Reference numerals 9 and 10 denote a switching element and a diode connected in anti-parallel to the switching element, for converting the output of the smoothing circuit 5 into a high-frequency current, and connecting the collector terminal of the switching element 9 to the cathode terminal of the diode 10. The point is connected to a second connection point between the heating coil 6 and the condenser 7. Emitter terminal of switching element 9 and diode 1
The connection point of the 0 anode terminal is grounded.

The heating coil 6, the capacitor 7, the switching element 9 and the diode 10 constitute an inverter unit 11. The inverter unit 11 includes a diode 10 connected in anti-parallel with the switching element 9,
The output of the smoothing circuit 5 is converted into a high-frequency current by high-speed switching, supplied to the resonance circuit 8, and heats a load (not shown) arranged near the heating coil 6.

Reference numeral 12 denotes a control unit which includes the following elements and controls the inverter unit 11.

Reference numeral 13 denotes a trigger circuit which detects a resonance voltage (voltage a in FIG. 3) generated in the switching element 9 and outputs a trigger pulse in order to operate the inverter section 11 continuously. Reference numeral 14 denotes a free-running oscillator, which generates a substantially triangular wave in synchronization with the resonance voltage (voltage a in FIG. 3) of the inverter unit 11, and operates by a trigger pulse output from the trigger circuit 13 after the start of the inverter operation. The timing is fixed and synchronized with the resonance state.

Reference numeral 15 denotes a microcomputer which sets the power to be supplied to the inverter and outputs a digital power setting signal. Reference numeral 16 denotes a DC voltage generating means for converting a digital power setting signal output from the microcomputer 15 into an analog signal to generate and output a DC voltage, the level of which varies according to the setting of the energized power.

Reference numeral 17 denotes power supply voltage detecting means for detecting the rectified DC power supply voltage of the AC power supply 1, that is, the voltage of the plus (+) terminal of the rectifier circuit 2, converting the level, and outputting the result.

Numeral 18 denotes an addition switching means for switching connection or disconnection of the output (b in the figure) of the power supply voltage detection means 17 to the weighting addition means 19 described later. ) Is a level obtained by weighting and adding the output (c in the figure) of the DC voltage generating means 16 and the output (b in the figure) of the power supply voltage detecting means 17 when connection is selected. Is selected, the output (c in the figure) level of the DC voltage generating means 16 remains unchanged.

Numeral 19 denotes a weighting and adding means having two inputs, one of which is connected to the output of the DC voltage generating means 16,
The output of the addition switching means 18 is connected to the other, and these two output levels are weighted and added and output (d in the figure).

A comparing means 20 compares the output of the free-running oscillator 14 with the output (d in the figure) of the weighting and adding means 19, and outputs an on / off pulse of the switching element 9 according to the magnitude relation therebetween. Reference numeral 21 denotes a driving unit,
The output of 0 is converted into a drive voltage suitable for driving the switching element 9 and output.

These trigger circuit 13, free-running oscillator 14,
The control unit 12 includes the microcomputer 15, the DC voltage generation unit 16, the power supply voltage detection unit 17, the addition switching unit 18, the weight addition unit 19, the comparison unit 20, and the driving unit 21.

The overall operation of the above configuration will be described. The switching of the addition switching means 18 is performed by the power supply voltage detecting means 17.
Is connected to the weighting and adding means 19.

The AC power supply 1 is converted into a DC power supply by the rectifier circuit 2, smoothed by the smoothing circuit 5 including the choke coil 3 and the smoothing capacitor 4, and supplied to the resonance circuit 8 including the heating coil 6, the capacitor 7 and the load. Is done.

The trigger circuit 13 detects the voltage (a in the figure) of the collector terminal of the switching element 9 and outputs a trigger pulse. The free-running oscillator 14 generates a substantially triangular wave in synchronization with the trigger pulse, that is, the resonance voltage. Occurs and the comparing means 20
To enter.

On the other hand, the microcomputer 15 sets the power to be supplied to the inverter, outputs a digital power setting signal, and the DC voltage generating means 16 converts this signal into an analog signal to generate a DC voltage, and weights the signal. Input to the adding means 19.

The power supply voltage detecting means 17 detects the voltage at the plus (+) terminal of the rectifier circuit 2, converts the level, and outputs the converted voltage. The addition switching means 18 inputs this to the weighted adding means 19.

The weighting and adding means 19 weights and adds the output level of the DC voltage generating means 16 and the output level of the addition switching means 18 and outputs the result.

The comparing means 20 compares the output of the free-running oscillator 14 with the output of the weighting and adding means 19, and outputs an on / off pulse of the switching element 9 according to the magnitude relation between them. The drive unit 21 converts this signal into a drive voltage suitable for driving the switching element 9 and inputs the signal to the switching element 9.

The switching element 9, together with the diode 10 connected in anti-parallel, is switched at a high speed by the output signal of the driving means 21, converts the output of the smoothing circuit 5 into a high-frequency current, and supplies the high-frequency current to the resonance circuit 8, so that the heating coil Heat the load placed in the vicinity of 6.

Next, with reference to FIG. 2, a description will be given of what difference occurs in the resonance voltage generated in the switching element 9 due to the switching of the addition switching means 18.

FIG. 2 shows an output waveform (d) of the weighting and adding means 19 and a resonance voltage waveform (a) generated in the switching element 9. FIG. 2A shows a case where the output of the power supply voltage detecting means 17 is not connected to the weighting and adding means 19 by the addition switching means 18, and FIG.

In the case of the connection (A), the resonance voltage (a) generated in the switching element 9 has a mountain-like shape connecting the vertices of each pulse. In the connection (B), the resonance voltage (a) changes the peak of each pulse. The shape of the connection is a plateau that is almost flat at the peak.

In the case of the connection (A), the peak of the resonance voltage (a) cannot be suppressed, but there is an advantage that the switching loss of the switching element 9 is small. In the case of the connection (B), the influence of high voltage noise can be prevented by suppressing the peak portion of the resonance voltage (a), but the switching loss of the switching element 9 may increase significantly.

Taking advantage of these respective advantages and selecting connection or non-connection by the addition switching means 18 depending on the case, it is possible to prevent an increase in switching loss of the switching element 9 or an effect of high voltage noise.

In particular, the switching by the addition switching means 18 has the following effects by connecting the output of the power supply voltage detecting means 17 to the weighting and adding means 19 in the case of high power and not connecting it in the case of low power. can get.

When the power supply of the inverter is set to high power, the output of the power supply voltage detecting means 17 is connected to the weighting and adding means 19 to suppress the peak of the resonance voltage because the influence of high voltage noise is large. The effect of high voltage noise can be prevented.

In the case of low power, since the effect of high voltage noise is small and the effect of increase in switching loss of the switching element 9 is large, the output of the power supply voltage detecting means 17 is disconnected from the weighting and adding means 19 and switching is performed. The switching loss of the element 9 can be suppressed.

[0048]

As described above, according to the induction heating cooker of the present invention, the control unit controls the free-running oscillator that generates a substantially triangular wave in synchronization with the resonance voltage of the inverter unit and the setting of the power supply. DC voltage generating means for changing the level, power supply voltage detecting means for detecting a DC power supply voltage, weighting adding means for weighting and adding the output level of the DC voltage generating means and the output level of the power supply voltage detecting means, Comparison means for outputting a result of comparison between the output of the free-running oscillator and the output of the weighting addition means; drive means for converting the output of the comparison means into a drive voltage suitable for driving the switching element and outputting the output; Since the addition switching means switches connection or disconnection of the output of the power supply voltage detection means to the weighting addition means, connection or disconnection by the addition switching means is performed according to the situation. Select connection may prevent the effect of increasing the prevention or high voltage noise at the switching loss of the switching element.

In particular, the switching by the addition switching means is achieved by connecting the output of the power supply voltage detection means to the weighting addition means in the case of high power, and by not connecting the output in the case of low power, thereby obtaining the following effects. It is highly likely.

When the power supply of the inverter is set to high power, the output of the power supply voltage detecting means is connected to the weighting and adding means to suppress the peak of the resonance voltage, The effect of noise can be prevented.

In the case of low power, since the effect of high voltage noise is small and the effect of increase in switching loss of the switching element is large, the output of the power supply voltage detecting means is not connected to the weighting and adding means, and the switching of the switching element is performed. Loss can be reduced.

That is, irrespective of low power or high power,
It is possible to reduce the switching loss of the switching element, prevent the switching element and the like from being damaged by high voltage noise, and improve the reliability.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing an output of a weighting and adding means and a waveform of a resonance voltage according to an embodiment of the present invention.

FIG. 3 is a circuit block diagram showing a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 AC power supply 2 Rectifier circuit 5 Smoothing circuit 6 Heating coil 8 Resonant circuit 9 Switching element 11 Inverter unit 12 Control unit 13 Trigger circuit 14 Free-running oscillator 15 Microcomputer 16 DC voltage generating means 17 Power supply voltage detecting means 18 Addition switching means 19 Weighting Adding means 20 comparing means 21 driving means

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yasuo Onuki 3-1, Shinjuyoichi, Kashiwa-shi, Chiba Pref. Within Nichi Home Tech Co., Ltd. 3K051 AA03 AC03 AD13 AD14 AD18 AD25 BD01 BD24 CD14 5H007 BB04 CA01 CB07 CB09 DA04 DB01 DB12 DC05 EA03

Claims (2)

[Claims] 1. A rectifier circuit (2) for converting an AC power supply (1) to a DC power supply, and a smoothing circuit (5) comprising a choke coil (3) and a smoothing capacitor (4) for smoothing the DC power supply. The output of the smoothing circuit (5) is converted into a high-frequency current by a diode (10) connected in anti-parallel with the switching element (9), and the resonance circuit (8) including a heating coil (6), a capacitor (7) and a load is provided. ), The induction heating cooker comprising an inverter section (11) for heating the load and a control section (12) for controlling the inverter section (11). A free-running oscillator (14) for generating a substantially triangular wave in synchronization with the resonance voltage of (11), a DC voltage generating means (16) whose level changes according to the setting of energized power, and a power supply for detecting the DC power supply voltage Voltage Detecting means (17), output level of DC voltage generating means (16) and power supply voltage detecting means (17)
Weighting and adding means (19) for weighting and adding the output level of the signal; and comparing means (20) for outputting a comparison result between the output of the free-running oscillator (14) and the output of the weighting and adding means (19). A driving means (21) for converting an output of the means (20) into a driving voltage suitable for driving the switching element (9) and outputting the driving voltage; and an addition switching means (18), wherein the addition switching means (18) Is power supply voltage detecting means (17)
Switching between connection and disconnection of the output of (1) to the weighting and adding means (19). The switching by the addition switching means (18) is such that the output of the power supply voltage detection means (17) is connected to the weighting addition means (19) in the case of high power, and is not connected in the case of low power. The induction heating cooker according to claim 1, wherein: