KR100253984B1 - High frequency induction heating cooker - Google Patents

Abstract

PURPOSE: A high frequency induction heating cooking device is provided to form an output end portion of a high frequency induction heating cooking device by using only one resonant capacitor. CONSTITUTION: An induction heating coil(8) heats an object. A resonant capacitor(29) is connected directly to the induction heating coil(8). A couple of IGBT(Isolated-Gate Bipolar Transistor)(9,11) switch an electric energy to the resonant capacitor(29). A rectification and constant voltage generator(7) provides a driving voltage to the induction heating coil(8). A self-starting oscillation and IGBT driver(26) generates an alternative pulse for driving the IGBT(9,11). A voltage/capacitance converter(32) controls an oscillation frequency of the self-starting oscillation and IGBT driver(26). A microprocessor(17) controls the voltage/capacitance converter(32).

Description

High frequency induction heating cooker

The present invention relates to a high frequency induction heating cooking apparatus, and particularly in a high frequency induction heating cooking apparatus using a commercial AC voltage of 200 volts or more, using a self-contained isolated-gate bapolar transistor (IGBT) driver element to simplify the configuration circuit The present invention relates to a high frequency induction heating cooking apparatus using one resonant capacitor, unlike a conventional technique in which two resonant capacitors are used in series with a resonant circuit of an output terminal.

Looking at the prior art as follows. 1 is a block diagram of a conventional high frequency induction heating cooking apparatus, and FIG. 2 is a waveform diagram of the main part of FIG.

In general, the high frequency induction heating cooker switches on a commercial DC voltage applied to an induction heating coil, and the counter electromotive force generated when the commercial DC voltage is turned off forms a strong magnetic field on the induction heating coil, thereby placing it on the induction heating coil. It is a device which heats a magnetic container and cooks food. Referring to FIG. 1, a current detection transformer 1 for receiving a commercial AC voltage for home use, a bridge diode 2 for converting a commercial AC voltage into a commercial DC voltage, and a smoothing capacitor 3 And the choke coil (4), the noise filtering capacitor (5), the voltage drop power supply transformer (6), and the rectification and constant voltage generator (7).

In addition, the upper IGBT (9) and the upper freewheeling diode (10) and the lower IGBT (11) and the lower freewheeling diode (12) and the upper bridge capacitor (13) around the induction heating coil (8) for heating the object. The upper bridge resistor 14, the lower bridge capacitor 15, and the lower bridge resistor 16 are configured in a full bridge form.

In the above, when the microprocessor 17 initially applies an initial driving command to the voltage / frequency converter 18, the voltage / frequency converter 18 receives a DC voltage from the voltage / voltage buffer 19. Convert to a frequency proportional to the voltage magnitude. That is, when the voltage supplied from the voltage / voltage buffer unit 19 is high, it is converted to a high frequency. When the voltage supplied from the voltage / voltage buffer unit 19 is low, it is oscillated at a low frequency and output to the timing distribution unit 20. do.

As described above, the reason why the oscillation frequency is changed according to the magnitude of the input voltage of the voltage / frequency converter 18 is that, in the characteristic of the induction heating coil 8, when the frequency is increased, the current consumption decreases. This is to maintain a constant current flowing in the induction heating coil 8 through the increasing principle.

As a result, when the current of the induction heating coil 8 increases, the detection voltage of the current detection transformer 1 also increases in proportion to the current, and the increased detection voltage is increased again through the voltage / voltage buffer 19. By returning to (18) to raise the frequency, the constant current always operates to balance.

The rectifier diode 21 rectifies and converts the AC voltage waveform detected by the current detection transformer 1 into DC. In addition, the timing distributor 20 may use one continuous oscillation signal (CK in FIG. 2) transmitted from the voltage / frequency converter 18 to perform two operations required for the operation of the upper IGBT 9 and the lower IGBT 11. It is converted into an independent alternating pulse train (Y1, Y2 in FIG. 2) and applied to the upper pulse driver 22 and the lower pulse driver 23, respectively, and the signal is upper side in the upper pulse driver 22 and the lower pulse driver 23. Amplified with sufficient power to drive the IGBT 9 and the lower IGBT 11 and applied to the upper IGBT driver 26 and the lower IGBT driver 27 through the respective upper pulse transformer 24 and the lower transformer 25. The upper pulse transformer 24 and the lower pulse transformer 25 have a weak voltage part that operates with the driving voltage Vcc supplied from the secondary side of the power supply (rectification and constant voltage generator 7) in addition to the signal transmission function between the front and rear ends. ) And power supply primary side (using commercial AC and commercial DC) It also plays an important role in separating (insulating) the strong voltage section).

The upper IGBT driver 26 and the lower IGBT driver 27 are arranged in a waveform form suitable for each IGBT (9, 11) to operate based on the pulse signal supplied from the front end without the need for a separate power supply. And output to the upper IGBT 9 and the lower IGBT 11, respectively.

As shown in FIG. 2, the upper IGBT 9 is turned on by the Y1 signal, the lower IGBT 11 is turned on by the Y2 signal, and the midpoint Y3 of the IGBTs 9 and 11 is Y1. The electric energy is supplied to the induction heating coil 8 only in the 'high' state from the time of rise to the time of rise of Y2.

Thereafter, when the upper IGBT 9 is tone-on and current starts to flow in the induction heating coil 8, the midpoint Y4 of the bridge capacitors 13 and 15 is initially shown with a downward curve toward the minus side, as shown in FIG. It then rises slowly with increasing current, reaching a voltage level of about 400 volts. At this time, the upper bridge capacitor 13 is in a discharge state, the lower bridge capacitor 15 is in a charged state.

Then, when the upper IGBT 9 is turned on and the lower IGBT 11 is turned on, Y4 initially draws an ascending curve and begins to descend so as to be opposite to the above-described process, and then falls to a voltage level of 0 volts. In this case, the upper bridge capacitor 13 is in a charged state, the lower bridge capacitor 15 is in a discharge state.

As described above, the induction heating coil 8 flows the charge / discharge induction current of the upper bridge capacitor 13 and the lower bridge capacitor 15 according to the mutual operation of the upper IGBT 9 and the lower IGBT 11. As the strong induction magnetic field is converted into eddy current at the bottom of the object, heat is generated, where the upper freewheeling diode 10 and the lower freewheeling diode 12 are counter-electromotive voltages generated by the induction heating coil 8. The upper bridge resistor 14 and the lower bridge resistor 16 discharge the electric charge of each of the upper ridge capacitor 13 and the bridge capacitor 15 during the rest period, so that the shock during the next initial operation is reduced. It acts to prevent it.

The high frequency induction heating cooking apparatus according to the prior art as described above has a problem in that the circuit is complicated and the parts cost and manufacturing cost are high by using two resonant capacitors at the output terminals.

The present invention has been made to solve the problems of the prior art as described above, and an object of the present invention is to provide a high frequency induction heating cooking apparatus configured to configure the output terminal of the high frequency induction heating cooking apparatus with one resonant capacitor.

1 is a block diagram of a conventional high frequency induction heating cooking apparatus.

FIG. 2 is a waveform diagram of the main part of FIG. 1.

3 is a block diagram of a high frequency induction heating cooking apparatus according to the present invention.

4 is a waveform diagram of the main part of FIG.

<Description of the code | symbol about the principal part of drawing>

1: current detection transformer 20: timing divider

2: bridge diode 21: rectifier diode

3: smoothing capacitor 22, 24: pulse driving unit

4: choke coil 23, 25: pulse transformer

5: noise filtering capacitor 26, 27: IGBT driver

6: power transformer 28: self-contained IGBT driver element

7: rectification and constant voltage generator 29: resonant capacitor

8: induction heating coil 30: oscillation resistance

9, 11: IGBT 31: oscillating capacitor

10, 12: freewheeling diode 32: voltage / capacitance conversion unit

13, 15: bridge capacitor 33: noise filtering capacitor

14, 16: bridge resistance 34: conduction resistance

17 microprocessor 35 varistor diode

18: voltage / frequency converter 36: capacitive conducting capacitor

19: voltage / voltage buffer

One preferred embodiment of the high frequency induction heating cooking apparatus according to the present invention for achieving the above object,

An induction heating coil unit for heating an object;

A resonant capacitor unit connected in series with the induction heating coil;

A pair of IGBT units for switching electrical energy to the resonant capacitor;

A rectifier and a constant voltage generator configured to receive a commercial DC voltage and supply a driving voltage of the induction heating coil;

A self oscillation and IGBT driver for generating alternating pulses for driving the IGBT;

A voltage / capacitance converter for controlling the oscillation frequency of the self-oscillating oscillation and the IGBT driver; And

And a microprocessor controlling the voltage / capacitance converter.

In the present invention, it is preferable that the induction heating coil and the resonant capacitor constitute a series resonant circuit.

Preferably, the voltage / capacitance converter includes a conductive resistor and a noise filtering capacitor and a varactor diode connected in parallel to the conductive resistor, respectively, and one end of the noise filtering capacitor and the varactor diode is grounded.

It is preferable to further include a capacitive conductive capacitor between the voltage / capacitance converter and the oscillation and IGBT driver.

An oscillation resistor and an oscillation capacitor are connected in parallel with the capacitive conducting capacitor, one end of the oscillation capacitor is grounded, and one end of the oscillation resistor is connected to the oscillation and IGBT driving unit.

Preferably, a freewheeling diode is connected to the IGBT unit in parallel.

It is preferable that a voltage drop power transformer is installed at the output terminal of the rectification and constant voltage generator.

A bridge diode for converting a commercial AC voltage into a commercial DC voltage in parallel to the voltage drop power transformer is preferably connected.

It is preferable to provide a current detecting transformer for detecting a drive current of the device itself at one end of an input side of the bridge diode,

Preferably, the output signal of the current detection transformer is input to the microprocessor via a rectifying diode,

It is preferable that one end of one IGBT is grounded among the pair of IGBTs.

It is preferable to use only one resonant capacitor to form an output end of the high frequency induction heating cooker,

Preferably, the varistor diode has a characteristic that the charging capacity is decreased when the level of the control voltage applied from the microprocessor is high, and the charging capacity is increased when the level of the applied control voltage is low.

Preferably, the noise filtering capacitor filters noise components included in a signal applied from the microprocessor.

It is preferable that the charge / discharge induction current of the resonant capacitor according to the interaction of the pair of IGBTs flows to the induction heating coil, so that heat is generated by converting into an eddy current at the bottom of the object due to the induction magnetic field generated.

The freewheeling diode is preferably a path of the counter electromotive voltage generated in the induction heating coil,

Preferably, the current control flowing through the induction heating coil is performed by controlling the oscillation frequency through a change in capacitance of the oscillation capacitor.

The capacitive conducting capacitor preferably attenuates the capacitance of the varactor diode by a predetermined amount and applies it to the oscillation part of the self-supporting IGBT driver.

Hereinafter, a detailed operation principle of the present invention will be described with reference to the drawings.

3 is a block diagram of a high frequency induction heating cooking apparatus according to the present invention, Figure 4 is a waveform diagram of the main part of FIG.

As shown in FIG. 3, the self-supporting IGBT driver element 28 is one active element in which a self oscillation function and an IGBT driver part are incorporated together in one device.

When power is applied to the self-contained IGBT driver element 28 as described above, the self-contained IGBT driver element 28 transmits an alternating signal such as Y1 and Y2 to the upper IGBT 9 and the lower IGBT 11 as shown in FIG. 4. ), And the upper IGBT 9 is turned on by the Y1 signal, and the lower IGBT 11 is turned on by the Y2 signal.

Once the upper IGBT 9 is turned on, the midpoint Y3 of each IGBT 9, 11 is in a logic 'high' state, as shown in FIG. 4, through the resonant capacitor 29 through the induction heating coil 8. To supply electrical energy.

In addition, while Y3 is in the logic 'high' state, the resonant capacitor 29 initially goes to a charged state, and by the counter electromotive voltage of the induction heating coil 8, Y4 discharges to minus hundreds of volts as shown in FIG. do.

After that, when the upper IGBT 9 is turned off and the lower IGBT 11 is turned on, the resonant capacitor 29 is initially switched to a discharge state so as to be opposite to the above-described process, and then the induction heating coil 8 By the counter electromotive voltage, Y4 is charged up to a few hundred volts as shown in FIG.

As described above, the charging / discharging induction current of the resonant capacitor 29 according to the interaction of the upper IGBT 9 and the lower IGBT 11 flows to the induction heating coil 8 so that a strong induction magnetic field generated at this time is an eddy current at the bottom of the object. Is converted into heat.

In the above, the upper freewheeling diode 10 and the lower freewheeling diode 12 serve as a path of the counter electromotive voltage generated in the induction heating coil 8.

In addition, the conventional induction heating cooking apparatus takes two resonant capacitors in the form of a bridge, whereas in the present invention, only one is used to play the role.

In addition, the current flowing in the induction heating coil 8 decreases when the oscillation frequency is increased as described above, and increases when the oscillation frequency is decreased, and the oscillation frequency of the self-contained IGBT driver element 28 is changed by the oscillation resistance 30 value. Or, since the method of controlling the oscillation frequency by changing the capacitance of the oscillation capacitor 31 is simple, the method was chosen.

The oscillation frequency f of the self-supporting IGBT driver element 28 is as follows.

When the digital / analog conversion signal is applied to the voltage / capacitance conversion section 32 in the microprocessor 17, the current resistance included in the analog conversion signal is removed from the noise filtering capacitor 33, and then the conduction resistor 34 is removed. Is applied to the varistor diode 35.

The varistor diode 35 has a characteristic that the capacitance decreases when the applied voltage is increased, whereas the capacitance increases when the applied voltage is decreased, so that the oscillation frequency of the self-contained IGBT driver element 28 is controlled by using this.

That is, after the amount of current detected from the current detection transformer 1 is applied to the microprocessor 17 and read, the digital / analog conversion value is adjusted and output in accordance with the determination of the microprocessor 17 to convert the voltage / capacitance conversion unit 32. By applying to, very fine current control is performed.

The capacitive conducting capacitor 36 attenuates the capacitance of the varactor diode 35 by a certain amount so that the total capacitance Ct of the capacitor belonging to the oscillation part of the IGBT driver element 28 is as follows.

Unlike the conventional method using two resonant capacitors, the present invention configured as described above is operated by one resonant capacitor by configuring a series resonant circuit in which the induction heating coil and the resonant capacitor of the output terminal are connected in series. It is possible to drastically reduce manufacturing costs.

Claims (18)

An induction heating coil unit for heating an object; A resonant capacitor unit connected in series with the induction heating coil; A pair of IGBT units for switching electrical energy to the resonant capacitor; A rectifier and a constant voltage generator configured to receive a commercial DC voltage and supply a driving voltage of the induction heating coil; A self oscillation and IGBT driver for generating alternating pulses for driving the IGBT; A voltage / capacitance converter for controlling the oscillation frequency of the self-oscillating oscillation and the IGBT driver; And And a microprocessor for controlling the voltage / capacitance converter. The high frequency induction heating cooker according to claim 1, wherein the induction heating coil and the resonant capacitor constitute a series resonant circuit. The method of claim 1, wherein the voltage / capacitance converter comprises a conductive resistance, a noise filtering capacity and a varistor diode connected in parallel to the conductive resistance, respectively, and one end of the noise filtering capacity and the varactor diode is grounded. High frequency induction heating cooker. 4. The high frequency induction heating cooker according to claim 1 or 3, further comprising a capacitive conductive capacitor between the voltage / capacitance converter and the oscillation and IGBT driver. The induction heating cooking apparatus of claim 4, wherein an oscillation resistor and an oscillation capacitor are connected in parallel with the capacitive conducting capacitor, one end of the oscillation capacitor is grounded, and one end of the oscillation resistance is connected to the oscillation and IGBT driving unit. The high frequency induction heating cooking apparatus of claim 1, wherein a freewheeling diode is connected to the IGBT unit in parallel. The high frequency induction heating cooking device according to claim 1, wherein a voltage drop power transformer is installed at an output terminal of the rectification and constant voltage generator. 8. The high frequency induction heating cooking device according to claim 7, wherein a bridge diode for converting a commercial AC voltage into a commercial DC voltage is connected to the voltage drop power transformer in parallel. The high frequency induction heating cooking device according to claim 8, wherein a current detection transformer for detecting a drive current of the device itself is provided at one end of the bridge diode. 10. The high frequency induction heating cooker according to claim 9, wherein an output signal of the current detection transformer is input to the microprocessor via a rectifying diode. The high frequency induction heating cooker according to claim 1, wherein one end of one IGBT is grounded among the pair of IGBTs. 2. The high frequency induction heating cooker of claim 1, wherein only one resonant capacitor is used to form an output end of the high frequency induction heating cooker. 4. The high frequency induction heating of claim 3, wherein the varactor diode has a characteristic in that the charge capacity is decreased when the level of the control voltage applied from the microprocessor is high, and the charge capacity is increased when the level of the applied control voltage is low. Cooking device. The high frequency induction heating cooker of claim 3, wherein the noise filtering capacitor filters noise components included in a signal applied from the microprocessor. The charging / discharging induction current of the resonant capacitor according to the interaction of the pair of IGBTs flows to the induction heating coil to convert the eddy current into the eddy current at the bottom of the object due to the induction magnetic field. , High frequency induction heating cooker. 7. The high frequency induction heating cooking apparatus according to claim 6, wherein the freewheeling diode is a path of a counter electromotive voltage generated in the induction heating coil. 6. The high frequency induction heating cooking apparatus according to claim 5, wherein the current control flowing in the induction heating coil is performed by controlling the oscillation frequency through a change in capacity of the oscillation capacitor. 5. The high frequency induction heating cooking apparatus according to claim 4, wherein the capacitive conductive capacitor attenuates the capacitance of the varactor diode by a predetermined amount and applies it to the oscillation unit of the self-supporting IGBT driving unit.

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