KR0158503B1 - Serial resonance converter system for induction heating cooker - Google Patents

Abstract

The present invention relates to a converter system for an induction heating cooker, comprising: an oscillation circuit (400) for generating an oscillation signal having a frequency corresponding to the magnitude of an input voltage and providing the oscillation signal to the driving circuit (300) of the inverter circuit (200). The amount of input current is controlled by detecting the amount of input current flowing from the power source 1 to the DC power source 100 and controlling the magnitude of the input voltage of the oscillation circuit 400 according to the amount of the input current. Resonance to reduce the amount of resonant current by detecting the amount of resonant current flowing through the input current control circuit 500 and the inductor 250 and if the amount is greater than or equal to a predetermined amount When the current limiting circuit 600 and the input current from the AC power source 1 are present, the oscillation signal from the oscillation circuit 400 is provided to the driving circuit and the oscillation when the input current is not present. And a load presence or absence discrimination means for the oscillation signal from the furnace no longer available in the driver circuit 900.

Description

Series resonant converter system for induction cooker

1 is a view schematically showing the configuration of a conventional converter system for induction heating cooker.

2 is a preferred embodiment of the present invention.

3 is a waveform diagram for explaining an operation state of the phase difference correction circuit.

4 is a waveform diagram for explaining a non-operational state of a phase difference correction circuit.

* Explanation of symbols for main parts of the drawings

1: AC power source 100: DC power source

200: inverter circuit 300: drive circuit

400: voltage controlled oscillator 500: input current control circuit

600: resonance current limiting circuit 700: dead time generating circuit

800: phase difference correction circuit 900: load presence discrimination circuit

Vcc: DC voltage source

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter system of an induction heating cooker that heats a load using a high frequency magnetic field induced in an inductor by resonance, and more particularly, to a series resonant converter system. will be.

1 shows a series resonant converter system of a conventional induction cooker. In FIG. 1, reference numeral 1 denotes an AC power source for supplying AC power, and numeral 3 denotes a DC power source for converting AC power into DC power and supplying the system. Denotes inverter circuits which are induction heating means, respectively. As shown in the figure, the inverter circuit 9 is composed of resonance inductors 19 and capacitors 21 connected in series with each other, and switching circuits 11, 13, 15, and 17 for their resonance. . The switching circuit for resonance of the inductor 19 and the capacitor 21 includes an insulated gate bipolar transistor (IGBT) 11 and 13 and a fast recovery diode 15 and 17. Again, in FIG. 1, reference numeral 20 denotes an inverter voltage phase detection circuit for detecting the phase of the voltage V _IN applied to the inductor 19 in the inverter circuit 9, and 22 denotes a capacitor voltage V _C1 . The capacitor voltage phase detection circuit 23 for detecting a phase of denotes a phase comparison circuit for comparing the phase of the inductor voltage V _{IN with} the phase of the capacitor voltage V _C1 , respectively. Reference numeral 25 denotes a low pass filter, 27 is a phase difference setting circuit, 29 is a voltage controlled oscillator, 31 is a driving circuit for driving the inverter circuit 9, 33 is used for cooking. Material detection circuit for detecting resonant current (Iin) flowing through inductor 19 and converting it into voltage according to the material of the container (iron, magnetic stainless steel, non-magnetic stainless steel, etc.) and no load condition, 35 and 37 and 39 denotes comparators for comparing the voltage corresponding to the amount of resonant current which varies with the type of vessel and the no-load state and the reference voltages set according to the type, and CT1 denotes the current transformer.

In the conventional technique as described above, the resonance current Iin measured by the current transformer CT1 of the inverter circuit 9 is converted into a voltage level by the material detection circuit 33, and the voltage level is converted into a comparator 39. The presence or absence of the load is determined by comparing the no-load voltage level between the resistors 15 and 16. Details of this technology are disclosed in US Pat. No. 5,248,866.

However, according to this technique, by using the resonant current to determine whether there is a load and the type of load, sufficient control according to various kinds of loads (for example, stainless steel container, aluminum container, copper container, etc.) and the determination of the load presence At least three or more comparators 35, 37, and 39 are required for this purpose.

An object of the present invention is to provide a converter system capable of controlling according to the type of container and the presence or absence of a load by using only one comparator.

The system of the present invention for achieving the above object is an AC power source; A DC power source which obtains DC power from the AC power source; A switching means composed of an inverter circuit having a first IGBT and a first diode and a second IGBT and a second diode, wherein each of the first and second IGBTs is turned on / off by a switching frequency signal; An induction heating means composed of an inductor and a first capacitor sequentially connected to the switching means, the induction heating means for heating a load by using a high frequency magnetic field generated in the inductor due to resonance of the inductor and the first capacitor; Driving means for driving the first IGBT and the second IGBT corresponding to a frequency of an input signal; Oscillating means for generating an oscillating signal having a frequency corresponding to the magnitude of the input voltage; Input current control for controlling the amount of the input current by detecting the amount of input current flowing from the AC power source to the DC power source and controlling the magnitude of the input voltage of the oscillation means in accordance with the amount of the input current. Means; Resonance current limiting means for detecting an amount of the resonance current flowing through the inductor and reducing the amount of the resonance current by reducing the magnitude of the input voltage of the oscillation means if the amount of the resonance current is equal to or greater than a predetermined amount; Dead time generating means for providing the driving means with a dead time for preventing the first IGBT and the second IGBT from being turned on at the same time; The oscillation signal from the oscillating means is provided to the driving means when the input current from the AC power source is present, and the oscillating signal from the oscillating means is the driving means when the input current is not present. It is characterized by including a load-free judging means that is not provided by.

As another feature of the present invention, the system is a phase difference correction means for controlling the phase of the switching frequency signal by controlling the frequency of the oscillation signal by comparing the phase of the output signal of the dead time generating means with a predetermined reference phase. It is to include additionally.

The present invention will now be described in detail with reference to the attached FIGS. 2 to 4.

FIG. 2 shows a preferred embodiment of the present invention. FIG. 3 is a waveform diagram for explaining an operation state of the phase difference correction circuit, and FIG. 4 is a waveform diagram for explaining a non-operation state of the phase difference correction circuit.

First, referring to FIG. 2, a series resonant converter system for an induction heating cooker according to the present invention includes an AC power source 1, a DC power source 100, an inverter circuit 200 which is an induction heating means, a driving circuit ( 300, a voltage controlled oscillation circuit 400, an input current control circuit 500, a resonant current limiting circuit 600, a phase difference correction circuit 800, a load presence discrimination circuit 900.

The DC power source 100, which is the main power source of the present system, includes a rectifier 110, resistors 111 and 112, a smoothing capacitor 113, and the like, and obtains DC power from the AC power source 1.

Inverter circuit 200, which is an induction heating means, is connected to two Insulated Gate Bipolar Transistors (IGBTs) 210 and 230 and two fast recovery diodes 220 and 240, which are connected to each other in half-bridges, and serially connected thereto. Consisting of an inductor 250 and a capacitor 260. Each of the two IGBTs (hereinafter, referred to as 'first and second transistors') 210 and 230 may be turned on or off by a switching frequency signal through the driving circuit 300 to generate a high frequency DC power from the DC power source 100. Convert to power. As a result, a high frequency magnetic field is generated around the inductor 250 due to the resonance of the inductor 250 and the capacitor 260, and the load (cooking vessel) is heated by the high frequency magnetic field.

The driving circuit 300 is composed of two electrically insulated gate drives (EIGDs) 310 and 320 connected to the gates of the first and second transistors 210 and 230, respectively. Each EIGD corresponds to the frequency of an input pulse signal. The first transistor and the second transistor are turned on / off.

The voltage controlled oscillator circuit (hereinafter, referred to as an "oscillator circuit") 400 generates an oscillation signal having a frequency corresponding to the magnitude of the input voltage V11 and provides it to the dead time generation circuit 700 which will be described later. .

The input current control circuit 500 includes a current transformer 10 connected to an AC power source 1 to convert an input current, rectifier circuits 510, 511 and 512 connected to the current transformer to convert AC into direct current, and A capacitor 513 connected to the output terminal to smooth its output, a reference voltage generation circuit (Vcc, 515, 516) connected to the negative terminal of the capacitor to generate a predetermined reference voltage (V1), An inverting input terminal is connected to the positive terminal of the capacitor 513 through the resistor 514, a non-inverting input terminal is connected to the soft-start circuit 530, and the output terminal is the oscillation through the resistor 541. Amplification circuits 520, 521, and 522 which are connected to the input terminal of the circuit 400 and which amplify the line pressures of the two input voltages, and which are connected to the non-inverting input terminals of the amplification circuit to prevent a sudden increase in the resonance current during initial operation. Composed of a start circuit 530 All. The soft-start circuit 530 is connected to the non-inverting terminals of the amplifying circuits 520, 521, and 522 to generate a predetermined reference voltage V2, and the reference voltage generating circuits Vcc, 531, 532 and the amplification circuits 520, 521, and 522. A capacitor 533 and a normally-on switch 534 are connected between the non-inverting input terminal and ground, respectively, and are connected in parallel with the reference voltage generating circuits Vcc, 531 and 532, respectively. The input current control circuit 500 detects the amount of input current flowing from the AC power source 1 to the DC power source 100 and controls the magnitude of the input voltage of the oscillation circuit 400 according to the amount of the input current. This controls the amount of input current. More specifically, first, when the amount of input current decreases, the voltage V13 smoothed on the capacitor 513 becomes lower than the reference voltage V2 provided by the soft-start circuit 530. The output voltages V3 of 520, 521, and 522 increase. As a result, the oscillation circuit 400 outputs a low frequency signal, which results in an increase in the amount of resonance current, so that the resonance current in a steady state flows through the inductor 250. On the other hand, when the voltage V13 smoothed on the capacitor 513 becomes higher than the reference voltage V2 provided by the soft-start circuit 530 as the amount of input current increases, the output voltages of the amplifying circuits 520, 521, and 522 are increased. V3) is lowered. As a result, the oscillation circuit 400 outputs a high frequency signal, which results in a decrease in the amount of resonance current, so that the resonance current in a steady state flows through the inductor 250.

Resonant current limiting circuit 600 is connected between the resonant inductor 250 and the resonant capacitor 260 current transformer 270 for converting the resonant current (Ir), and connected to the current transformer for converting AC into direct current A rectifier circuit 610, 611, 612, a capacitor 613 connected to the output terminal of the rectifier circuit for smoothing its output, and an inverting input terminal connected to the positive terminal of the capacitor to amplify the differential voltage of the two input voltages. Amplification circuits 620, 613 and 614, reference voltage generation circuits 621 and 622 connected to the non-inverting input terminals of the amplification circuit and generating a predetermined reference voltage V4, and cathodes connected to the output terminals of the amplification circuits 620, 613 and 614. A diode 38 is connected to the anode of the oscillation circuit 400. The resonant current limiting circuit 600 detects the amount of resonant current Ir flowing through the inductor 250 and reduces the magnitude of the input voltage of the oscillation circuit 400 if the amount of the resonant current is equal to or greater than a predetermined amount. This reduces the amount of resonance current Ir. More specifically, first, when the voltage smoothed on the capacitor 613 becomes higher than the predetermined reference voltage V4 as the amount of the resonance current increases, the output voltages of the amplifying circuits 620, 613, 614 become low level. . As a result, since the diode 630 is forward biased and conducted, the input voltage V11 of the oscillation circuit 400 is lowered. As a result, the oscillation circuit 400 outputs a high frequency signal, which results in a decrease in the amount of resonance current, so that the resonance current in a steady state flows through the inductor 250. On the other hand, when the amount of the resonance current decreases, when the voltage smoothed on the capacitor 613 becomes lower than the predetermined reference voltage V4, the output voltages of the amplifying circuits 620, 613, and 614 become high levels. As a result, since the diode 630 is reverse biased and not conducting, the resonance current limiting circuit 600 does not operate.

On the other hand, when the switching frequency is less than the resonant frequency, the reverse recovery of the first and second fast recovery diodes 220 and 240 connected in reverse parallel to the first and second transistors 210 and 230 in the inverter circuit 200, respectively. Due to its characteristics, a short-through phenomenon occurs. This phenomenon causes a large loss of power.

The dead time generating circuit 700 is composed of a D-flip flop 710, two end gates 720 and 730, resistors 721 and 731, and capacitors 722 and 732, and a first transistor 210 and a first transistor 210. In order to prevent the two transistors 230 from being turned on at the same time, a dead time is provided to the driving circuit 300. As a result, a short-through phenomenon between the first transistor 210 and the second transistor 230, which causes a large loss of power, is prevented.

The phase difference correction circuit 800 described below is for preventing a short-through phenomenon that occurs when the switching frequency becomes less than the resonance frequency. The phase difference correction circuit 800 is connected to the reference voltage generating circuits Vcc, 811 and 812 for generating a predetermined reference voltage V5, the current transformer 270, and a non-inverting input connected between the ground through a resistor 813. A comparison circuit 810 having a terminal and an inverting input terminal connected to the reference voltage generating circuits Vcc, 811 and 812 and comparing the reference voltage of the reference voltage generating circuits Vcc, 811 and 812 with an input voltage from the AC power source 1. ), A phase comparison circuit 820 for comparing the phase of the output signal V6 of the comparison circuit with the phase of the output signal V7 of the dead time generating circuit 700, and a predetermined reference for limiting the phase difference. A phase difference limiting circuit 830 for generating a phase difference signal;

Amplifying circuits 840, 841, 842 having an inverting input terminal connected to the output terminal of the phase comparator 820 through a resistor 821 and a non-inverting input terminal connected to the phase difference limiting means, and amplifying a difference voltage between two input voltages; And a diode 850 having a cathode connected to the output terminal of the amplifier circuit and an anode connected to the input terminal of the oscillation circuit 400. The phase difference correction circuit 800 is switched by comparing the output phase of the phase comparator 820 with a predetermined reference phase which is the output of the phase difference limiting circuit 830 to control the frequency of the oscillation signal of the oscillation circuit 400. Control the phase of the frequency signal. More specifically, first, the phase of the output voltage V7 of the dead time generation circuit 700 is compared with the phase of the output voltage V6 of the comparison circuit 810 by the phase inversion circuit 820. Referring to FIG. 3, when the output voltage V8 of the phase comparison circuit 820 is higher than the predetermined reference voltage V10 of the phase difference limiting circuit 830, the output voltages V9 of the amplifying circuits 840, 841, 842. The diode 850 is forward biased so that the input voltage V11 of the oscillation circuit 400 drops so that the oscillation circuit 400 outputs a high frequency signal. As a result, the phase of the switching frequency signal is delayed more than the phase of the resonance frequency signal. As described above, the phase difference correction circuit 800 is operated when the phase difference between the switching frequency signal and the resonance frequency signal is less than or equal to a predetermined reference phase set in the phase difference limiting circuit 830. However, referring to FIG. 4, when the phase difference between the switching frequency signal and the resonant frequency signal is higher than or equal to a predetermined reference phase set in the phase difference limiting circuit 830, the output voltages V9 of the amplifying circuits 840, 841, 842 are brought to a high level. The diode 850 is reverse biased. As a result, the phase difference correction circuit 800 does not operate.

In the load discrimination circuit 900, a non-inverting input terminal is connected to the positive terminal of the capacitor 513 and an inverting input terminal is connected to the output terminal of the input current control circuit 500 to compare the two inputs. And a protection circuit 920 which stops the operation of the driving circuit 300 when the output signal V12 of this comparison circuit is at a predetermined level to indicate a no-load operation state. The load presence / absence discrimination circuit 900 causes the oscillation signal from the oscillation circuit 400 to be provided to the drive circuit 300 when there is an input current from the AC power source 1 and the input current does not exist. In this case, the oscillation signal from the oscillation circuit 400 is not provided to the driving circuit 300. More specifically, first, the load operation state, the input current detected by the current transformer 10 during the initial operation of the system gradually increases, the smoothing voltage (V13) also gradually increases with it, the oscillation circuit The input front V11 of 400 is also gradually increased and then stabilized. In this load operation state, since the smoothing voltage Vl3 is always higher than the input voltage V11 of the oscillation circuit 400, the output voltage V12 of the comparison circuit 910 becomes high level, so that the present system operates normally. However, in the no-load operation state, since the input current hardly flows during the initial operation of the system, the smoothing voltage V13 becomes almost equal to the reference voltage V1, so that the smoothing voltage V13 becomes the input voltage of the oscillation circuit 400. Lower than V11). As a result, the protection circuit 920 is operated by the output voltage V12 of the comparison circuit 910 becoming low. At this time, the protection circuit 920 prevents the system from operating by blocking its input signal from being provided to the driving circuit 300.

Claims (7)

An AC power source 1; A DC power source (100) which obtains DC power from the AC power source; The first transistor 210 and the first diode 220 and the second transistor 230 and the second diode 240 are provided, each of the first and second transistors are turned on / off by a switching frequency signal, switching Means 210,220,230.240, and an inductor 250 and a first capacitor 260 sequentially connected to the switching means, and a high frequency magnetic field generated in the inductor due to resonance of the inductor and the first capacitor. Induction heating means 200 for heating the load using; An oscillating means 400 for generating an oscillating signal having a frequency corresponding to the magnitude of the voltage input for driving the switching means; Driving means (300) for turning on / off the first transistor and the second transistor corresponding to a frequency of an input signal; The input by detecting the amount of input current flowing from the AC power source 1 to the DC power source 100 and controlling the magnitude of the input voltage of the oscillation means 400 in accordance with the amount of the input current. An input current control means 500 for controlling the amount of current; The resonance current Ir is detected by detecting the amount of the resonance current Ir flowing through the inductor 250 and reducing the magnitude of the input voltage of the oscillation means 400 when the amount of the resonance current is equal to or greater than a predetermined amount. Resonance current limiting means (600) for reducing the amount of; Dead time generating means (700) for providing the driving means with a dead time for preventing the first transistor and the second transistor from being turned on at the same time when the oscillating signal is provided from the oscillating means to the driving means; The oscillation signal from the oscillation means 400 is provided to the driving means when the input current from the AC power source 1 is present, and the oscillation means from the oscillation means when the input current is not present. A series resonant converter system for an induction heating cooker comprising a load presence / absorption means (900) for preventing an oscillation signal from being provided to the driving means. The method of claim 1, wherein the input current control means 500 is connected to the AC power source (1) and the first current flow means (10) for converting the input current, and the first current flow means connected to the first current flow means First rectifying means (510, 511, 512) for converting to direct current, a second capacitor (513) connected to an output terminal of the first rectifying means to smooth its output, and a negative terminal of the second capacitor, First reference voltage generating means (Vcc, 515, 516) for generating a first reference voltage (V1) and an inverting input terminal are connected to the positive terminal of the second capacitor (513) through a resistor (514) and output terminal First amplification means 520, 521, and 522 connected to an input terminal of the oscillation means 400 to amplify a differential voltage between two input voltages through a magnetic resistor 541, and a non-inverting input terminal of the first amplification means. Soft-start means 530 for preventing a sharp increase in resonance current Series resonant converter system for induction heating cooker comprising a). 3. The second reference voltage generating means (Vcc, 531, 532) according to claim 2, wherein the soft-start means (530) is connected to the non-inverting terminal of the first amplifying means to generate a predetermined second reference voltage (V2). And a third capacitor 533 and a normally-on switch 534 connected between the non-inverting input terminal of the first amplifying means and ground, respectively, and connected in parallel with the second reference voltage generating means. Series resonant converter system for induction heating cooker. The method of claim 3, wherein the resonant current limiting means 600 is connected between the inductor 250 and the first capacitor 260, the second current flow means 270 for converting the resonant current, and the second Second rectifying means (610, 611, 612) connected to the current transformer for converting alternating current into direct current, a third capacitor (613) connected to the output terminal of the second rectifying means for smoothing its output, and a third capacitor Inverting input terminal is connected to the positive terminal to the second amplifying means (620, 613, 614) for amplifying the difference voltage of the two input voltage, and the predetermined third reference voltage (V4) connected to the non-inverting input terminal of the second amplifying means Third reference voltage generating means (621,622) for generating a; and a third diode (38) having a cathode connected to the output terminal of the second amplifying means and an anode connected to the input terminal of the oscillation means (400). Series resonant converter system for induction heating cooker. The phase of the switching frequency signal according to any one of claims 1 to 4, wherein the frequency of the oscillation signal is controlled by comparing the phase of the output signal of the dead time generating means 700 with a predetermined reference phase. Induction heating cooker series resonant converter system further comprising a phase difference correction means for controlling the (800). The method of claim 5, wherein the phase difference correcting means (800) is a fourth reference voltage generating means (Vcc, 811, 812) for generating a predetermined fourth reference voltage (V5), and one end of the second current flow means (270) A first comparison having a non-inverting input terminal connected to ground through a resistor 813 and an inverting input terminal connected to the fourth reference voltage generating means, and comparing the fourth reference voltage and the input voltage; Means 810, phase comparison means 820 for comparing the phase of the output signal V6 of the first comparing means and the phase of the output signal V7 of the dead time generating means 700, and the limitation of the phase difference A phase difference limiting means 830 for generating a predetermined reference phase difference signal for the non-inverting input connected to an output terminal of the phase comparing means 820 through a resistor 821 and a non-inverting input connected to the phase difference limiting means. A third amplifier with terminals and amplifying the difference between the two input voltages Means 840, 841, 842, and a fourth diode 850 having a cathode connected to an output end of the third amplification means and an anode connected to an input end of the oscillation means 400. system. The non-inverting input terminal is connected to the positive terminal of the second capacitor 513, and the inverting input terminal is connected to the output terminal of the input current control means 500. The second comparing means 910 for comparing the two inputs and the output signal V12 of the second comparing means become a predetermined level so that the operation of the driving means 300 is indicated when the no-load driving state is indicated. A series resonant converter system for an induction heating cooker comprising a stopping means (920).