KR100764897B1 - An induction heating cooker using Phase Adaptive Modulation control method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker using a phase adaptive modulation (PAM) control method. The rectifier 2 receives power from a commercial power supply 1 and delivers the power to a work coil 5, the work. Absorption of the counter electromotive force generated by the coil 5 and returning again is repeated to compare the phases of both ends of the resonant capacitor 4 and the work coil 5 to generate a high frequency magnetic field in the work coil 5. Trigger generator 30 for generating an output signal when the resonant stage voltage is the lowest, the oscillator 40 for receiving the output signal of the trigger generator outputs a pulse for driving the gate of the IGBT (7), the gate resistor 12 10), the microprocessor 50 for setting the oscillation frequency of the oscillation unit 40 by adjusting the size of the voltage sent out, and the resonance envelope of a phase equal to the angular velocity of the AC input voltage. In the conventional induction heating cooker comprising a phase-adaptive modulation control unit 60 for selectively varying the oscillation frequency by superimposing the output control voltage (VC) output from the parser 50, and comprises an expensive high voltage class IGBT By adding a Phase Adaptive Modulation (PAM) control technique, it is possible to heat a specific material load (bowl) even with a medium voltage class IGBT, thereby greatly reducing the member price of the induction cooker.

 Induction Heating, Induction, Phase Adaptive Modulation, Phase Adaptive Modulation (PAM)

Description

Induction heating cooker using Phase Adaptive Modulation control method

1 is a block diagram of an induction heating cooker including a PAM (Phase Adaptive Modulation) control unit according to the present invention.

2A to 2C are graphs showing the operating waveforms of FIG.

3 is a block diagram of a conventional induction heating cooker.

4A to 4C are graphs showing the operation waveforms of FIG. 3.

<Explanation of symbols for main parts of the drawings>

1: Commercial AC power supply 2: Power rectifier (bridge diode)

3: smoothing capacitor 4: resonant capacitor

5: WORK COIL 6: Load (Bowl)

7: IGBT (Power Device) 8: FET (Field Effect Transistor)

9: oscillation capacitor 10, 12: gate resistance

11: filter capacitor 30: trigger generator

40: oscillation unit 50: microprocessor

60: PAM (Phase Adaptive Modulation) unit

61, 62: voltage divider 63: zener diode

The present invention relates to an induction heating cooker, which is a kind of home cooking appliance, and more particularly, to an induction heating cooker using a phase adaptive modulation (PAM) control method.

Induction heating cooker is a principle that heats the bowl by using high frequency magnetic field that flows high voltage high current to WORK COIL, and more specifically, high frequency magnetic field is iron metal When it comes in contact with the vessel, an eddy current (EDDY CURRENT) is generated on the surface of the vessel, the eddy current is converted into thermal energy.

In order to pass a high frequency current through the work coil, it is generally through an IGBT, which is called a high-power semiconductor. When the IGBT operates, the collector voltage (= resonant voltage) is considerably high from about 1,000 V to 1,500 V. Is about 40Khz to 20Khz.

Since IGBTs are high-power semiconductors, they are expensive, making up a large portion of the induction cookers. In particular, the price difference is large depending on the collector withstand voltage class. For example, the high voltage class IGBT having the withstand voltage characteristic of about 1,500V is about twice the price of the medium voltage class IGBT having the withstanding voltage of about 1,200V. Therefore, in order to reduce the cost of induction cookers, it is preferable to use IGBTs of low voltage class, but the collector voltage, that is, the resonance voltage is determined by the material of the load (bowl), and therefore, especially copper or nickel Alternatively, in the case of 'special materials' plated with non-ferrous metals such as gold, the resonance voltage is the highest, and high-voltage IGBTs must be used.

As described above, the conventional induction heating cooker adopts a high voltage class IGBT in case of using a specific material load (bowl), which causes a problem in that component cost increases.

The output control of the induction heating cooker is achieved by varying the oscillation frequency.In other words, if the oscillation frequency is increased to around 40Khz, the output is reduced while the resonance voltage is extremely low. This increases. Here, the resonant voltage is not a constant linear value over the entire band, but repeats the peak and valley as shown in Figure 4a according to the phase angle of the pulse flow supplied from the rectifier. That is, at 90 'and 270', which are the top dead centers of the AC phase, the resonance voltage becomes the highest value, and at 0 'and 180', which is the zero crossing, the resonance voltage becomes the lowest value and approaches 0V.

Here, the section where the internal voltage of the IGBT is actually a problem is only near the top dead center of the AC phase, and since the resonance voltage is lower than 80% of the left and right of the top dead center, the withstand voltage does not matter at all. Accordingly, in the present invention, the oscillation frequency is lowered by increasing the oscillation frequency in the vicinity of the top dead center where the withstand voltage problem is considered due to the high resonance voltage, and the output is boosted by lowering the oscillation frequency in the lower voltage section of 80% or less at the top and left of the top dead center. Through the so-called Phase Adaptive Modulation (PAM) technique, which is designed to achieve a BOOST, the present invention proposes a configuration and a method for driving a conventional special material load (bowl) even with a medium voltage class IGBT.

The reason for boosting the output by lowering the oscillation frequency in the low voltage section is to compensate for the reduced output at the top dead center. A phase is added before Adaptive Modulation, which means adaptive frequency modulation, which means that an envelope of a resonant waveform having the same angular velocity as the power phase is used as a source of modulation, as described below. .

Induction heating cooker according to the present invention for achieving the above object,

Rectifier (2) for receiving power from the commercial power source (1) and delivering it to the work coil (5),

A resonant capacitor (4) for absorbing back electromotive force generated in the work coil (5) and returning it back to generate a high frequency magnetic field in the work coil (5);

A trigger generator 30 for generating an output signal when the resonator voltage is the lowest by comparing the phases of both ends of the work coil 5,

An oscillator 40 which receives an output signal of the trigger generator and outputs a pulse for driving a gate of the IGBT 7;

A microprocessor 50 for setting the oscillation frequency of the oscillator 40 by adjusting the voltage magnitude sent out to the gate resistors 12 and 10, and

A phase adaptive modulation controller 60 for selectively varying the oscillation frequency by superimposing a resonance envelope of a phase equal to the angular velocity of an AC input voltage to the output control voltage VC output from the microprocessor 50; It is composed.

In the present invention, the resonant envelope is preferably generated by integrating the resonant end voltage after dividing the voltage. The phase-adaptive modulation control unit 60 increases the oscillation frequency at the top dead center to selectively change the oscillation frequency, and zero. In the crossing portion, it is preferable to be configured to lower the oscillation frequency.

Hereinafter, the configuration and operation of the induction heating cooker according to the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram of a conventional induction heating cooker, Figure 1 is a block diagram of an induction heating cooker including a PAM (60) configured according to the present invention. First of all, the common parts of these two components will be described first.

When commercial power (1) is applied to the rectifier (2), the rectifier (2) output is applied to the work coil (5) in a pulsating state, even though there is a smoothing capacitor (3), the rectifier (2) output is not a direct current The reason for this is that the capacity of the smoothing capacitor 3 is very small compared to the amount of current consumed by the work coil 5, where the actual role of the smoothing capacitor 3 is a switching that occurs when the IGBT switches rather than the smoothing action. Do more to absorb noise.

The resonant capacitor 4 is connected in parallel with the work coil 5 so as to absorb (charge) back electromotive force generated in the work coil 5 and return (discharge) the work coil 5 back to the work coil 5 every cycle. Repeated at high speed (20Khz ~ 40Khz), the high frequency magnetic field is generated in the work coil (5).

The trigger generator 30 compares the phases of both ends of the work coil 5, and outputs an output signal to the oscillator 40 when the resonance stage (collector of IGBT) voltage is the lowest. The oscillator 40 outputs a pulse output for driving the gate of the IGBT 7, and outputs one pulse only when a trigger signal is received from the trigger generator 30.

As described above, when the oscillation frequency of the oscillator 40 is changed, the output fluctuates. The method of changing the oscillation frequency of the oscillator 40 uses the drain-source resistance change of the field effect transistor 8, that is, the Rds characteristic. . Increasing the gate voltage of the field effect transistor 8 decreases the Rds value, and decreasing the gate voltage increases the Rds value. More briefly, the field effect transistor 8 may be equivalently viewed as a potentiometer (volume), but may be referred to as an electronic volume in which the resistance value changes according to the gate voltage value.

Although the role of the microprocessor 50 varies widely, it can be regarded simply as a variable voltage device in the limited part of the present invention. That is, the Rds value of the field effect transistor 8 is changed in accordance with the voltage magnitude that the microprocessor 50 sends to the gate resistors 12 and 10, and then the oscillation frequency is changed to set the desired arbitrary output.

Figure 4a is a resonant waveform of a conventional induction heating cooker, Figure 4b is an enlarged portion of the zero crossing portion of Figure 4a, Figure 4c is an enlarged top dead center portion of Figure 4a, it should be noted here The top dead center or resonant frequency is about 23.5Khz ~ 23.1Khz, which is almost the same. In this case, the resonant voltage at the top dead center portion is high, and as described above, there is a difficulty in using a high voltage class IGBT.

On the other hand, Figure 2a is a resonant waveform reflecting the effect of the present invention, it can be seen that the voltage of the top dead center is significantly lower than that of Figure 4a. FIG. 2B is an enlargement of the zero crossing portion of FIG. 2A, and FIG. 2C is an enlargement of the top dead center portion of FIG. 2A, where it should be noted that the resonant frequency of the zero crossing portion is 22.0 Khz, and the resonant frequency of the top dead center portion is You can see that it works differently with 25.8Khz. As such, in order to selectively change the resonance frequency only near the top dead center, the output control voltage VC must be selectively changed.

As shown in FIG. 4A, since the output control voltage VC is almost straight, the resonance (= oscillation) frequency is constant over the entire band, whereas the output control voltage VC in FIG. It can be seen that the oscillation frequency near the point is increased.

In Fig. 1 constructed by the present invention, the AC power source source SOURCE loaded on the output control voltage VC is a divided resonant voltage. That is, the resonance voltage is appropriately lowered through the voltage divider resistors 61 and 62 and then applied to the filter capacitor 11 through the zener diode 63 and the forward diode 65 to be supplied from the microprocessor 50. Superimposed on voltage VC. Here, the zener diode 63 passes only the top dead center portion of the resonant voltage, thereby preventing excessive distortion of the resonant waveform, and the zener leakage current path resistance 64 passes the leakage current of the zener diode 63 to pass the zener diode 63. The operation characteristic of 63 is improved, and unnecessary voltage is applied to the VC stage. The filter capacitor 11 integrates the resonance (AC) waveform of several tens of kilohertz included in the overlapping voltage applied from the resonance stage, and refines it into a series of envelope waveforms.

As described above, the resonant envelope of a phase equal to the angular velocity of the AC input voltage is superimposed on the output control voltage VC to selectively change the oscillation frequency, referred to as 'Phase Adaptive Modulation'. Modulation).

As described in detail above, the effect obtained by the present invention requires a high voltage class IGBT in order to heat a load of a specific material in the prior art, but in the present invention, a medium voltage class IGBT is required through a PAM (Phase Adaptive Modulation) control technique. By making it possible, the member price of the induction cooker can be greatly reduced.

Claims (3)

delete A rectifier 2 receiving power from the commercial power source 1 and transferring the power to the work coil 5; A resonant capacitor (4) for absorbing back electromotive force generated in the work coil (5) and returning it back to generate a high frequency magnetic field in the work coil (5); A trigger generator 30 for generating an output signal when the resonator voltage is lowest when comparing the phases of both ends of the work coil 5; An oscillator 40 receiving the output signal of the trigger generator and outputting a pulse for driving a gate of the IGBT 7; A microprocessor (50) for setting the oscillation frequency of the oscillator (40) by adjusting the voltage magnitude sent to the gate resistors (12, 10); And And a phase adaptive modulation controller 60 for selectively varying the oscillation frequency by superimposing a resonant envelope of a phase equal to the angular velocity of an AC input voltage to the output control voltage VC output from the microprocessor 50. In induction cooker, The resonance envelope is generated by integrating after the resonant stage voltage, induction heating cooker, characterized in that it is generated. A rectifier 2 receiving power from the commercial power source 1 and transferring the power to the work coil 5; A resonant capacitor (4) for absorbing back electromotive force generated in the work coil (5) and returning it back to generate a high frequency magnetic field in the work coil (5); A trigger generator 30 for generating an output signal when the resonator voltage is lowest when comparing the phases of both ends of the work coil 5; An oscillator 40 receiving the output signal of the trigger generator and outputting a pulse for driving a gate of the IGBT 7; A microprocessor (50) for setting the oscillation frequency of the oscillator (40) by adjusting the voltage magnitude sent to the gate resistors (12, 10); And And a phase adaptive modulation controller 60 for selectively varying the oscillation frequency by superimposing a resonant envelope of a phase equal to the angular velocity of an AC input voltage to the output control voltage VC output from the microprocessor 50. In induction cooker, The phase-adaptive modulation control unit 60 is configured to increase the oscillation frequency at the top dead center portion and lower the oscillation frequency at the zero crossing portion to selectively vary the oscillation frequency.

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