JP2005209563A - Electromagnetic induction heating cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the power consumed in a pan can not be accurately controlled in performing constant input power control of a conventional technique since loss values of an inverter circuit and a controlling circuit are contained in input power. <P>SOLUTION: In this electromagnetic induction heating cooker controlling an output power frequency of the inverter circuit according to a value of comparison operation of an induction heating coil forming a series resonant circuit with a resonant capacitor, the inverter circuit supplying a high frequency current to the induction heating coil, an input power operation circuit calculating the input power of the inverter circuit, and a power-control differential amplification circuit performing a comparison operation of the input power and a power set value, an output power operation circuit calculating the output power of the inverter circuit with the phase difference generated between voltage generated at ends of the induction heating coil, the output current of the inverter circuit, the output voltage of the inverter circuit and the output currents is replaced with the input power operation circuit, and the output power frequency of the inverter circuit is controlled according to the value obtained by the comparison operation of the output power and the power set value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electromagnetic induction heating cooker that uses an inverter circuit to supply a high-frequency current to an induction heating coil to heat a cooking pan by electromagnetic induction, and particularly relates to a power control technique.

  In the electromagnetic induction heating cooker of the prior art shown in FIG. 8, the voltage of the smoothing capacitor C1 (inverter input voltage) is detected by the input voltage detection circuit PT3, and the detected input voltage is output as the input voltage detection signal Pt3. The input current of the inverter circuit is detected by an input current detection circuit CT1, the detected input current is output as an input current detection signal Ct1, and the detected input voltage detection signal Pt3 and input current detection signal Ct1 are input power calculation circuit. The input power calculation circuit PI calculates an input power value and outputs it as an input power calculation signal Pi.

  The power control differential amplifier circuit compares the input power calculation signal from the input power calculation circuit with a power setting signal having a predetermined value and outputs the result as a power control differential amplification signal. The V / F converter circuit VF outputs a V / F converter signal Vf for controlling the output frequency of the inverter circuit in accordance with the power control differential amplification signal. As a prior document disclosing the technique for performing the above-described constant input power control, for example, there is Patent Document 1.

Japanese Patent Application No. 2002-231662

  In the prior art described above, when the input power value is calculated by the input voltage and the input current and the input power constant control is performed so that the calculated input power value becomes a predetermined power setting value, each of the inverter circuits Since the loss value of the switching element and the loss value of each control circuit are included in the calculation result of the input power value, the power consumed in the pan cannot be accurately controlled.

  In order to solve the above-described problems, the first invention is an induction heating coil that forms a series resonance circuit with a resonance capacitor, a rectification circuit that rectifies a commercial AC power source and converts it into a DC voltage, and a start signal is input. Then, an inverter circuit that supplies a high frequency current to the induction heating coil using the DC voltage of the rectifier circuit as an input, an input power calculation circuit that calculates the input power of the inverter circuit, and an input power calculation of the input power calculation circuit A power control differential amplifier circuit for comparing and calculating a signal and a power setting signal having a predetermined value and outputting the power control signal as a power control differential amplification signal, and in response to the power control differential amplification signal, In an electromagnetic induction heating cooker that controls an output frequency, an output current detection circuit that detects an output current of the inverter circuit and outputs it as an output current detection signal; A phase difference detection circuit that detects a phase difference between the second switching element drive signal of the barter circuit and the output current detection signal of the inverter circuit and outputs the phase difference detection signal; and a voltage generated at both ends of the induction heating coil. The output power of the inverter circuit is calculated based on the detected heating coil voltage signal, the detected heating coil voltage signal, the detected output current detection signal, and the detected phase difference detection signal. The output power calculation circuit that outputs the output power calculation signal is replaced with the input power calculation circuit, and the output power calculation signal and the power setting signal are compared and output as a differential amplification signal for power control. The electromagnetic induction heating cooker controls the output frequency of the inverter circuit in accordance with the differential amplification signal for power control.

  A second invention includes an output voltage detection circuit that detects an output voltage from an input voltage of the inverter circuit and outputs an output voltage detection signal, and replaces the output power calculation circuit with a second output power calculation circuit. The second output power calculation circuit that calculates the output power of the inverter circuit based on the detected output voltage detection signal, the detected output current detection signal, and the detected phase difference detection signal. The electromagnetic induction heating cooker according to 1.

  According to the first aspect of the invention, the output power is determined by the voltage of the heating coil that is generated at both ends of the induction heating coil, and the phase difference between the output current of the inverter circuit and the output voltage and output current of the inverter circuit. , The power consumed by the resonant capacitor C2 and the resonant capacitor C3 of the series resonant circuit can be removed, and only the power consumed by the induction heating coil including the heated object such as a pan can be calculated. High-accuracy power control is possible by the power consumption of the heating coil.

  According to the second aspect of the invention, when the output power is calculated from the output voltage, output current and phase difference of the inverter circuit, the loss value of each control circuit for controlling the inverter circuit can be removed. The power consumption of the induction heating coil of the series resonance circuit including the heated object, the resonance capacitor C2, and the resonance capacitor C3 can be calculated. The power control of the series resonance circuit calculated above is inferior to that of the first invention but with high accuracy. Is possible.

[Embodiment 1]
FIG. 1 is an electrical connection diagram of an electromagnetic induction heating cooker according to the present invention. In FIG. 1, the primary rectifier circuit DR1 rectifies the output of the three-phase AC commercial power supply AC and converts it into a DC voltage, and the smoothing capacitor C1 smoothes the voltage converted into DC by the primary rectifier circuit DR1.

  The first switching element TR1 and the second switching element TR2 are switching elements that form a half-bridge type inverter circuit, and for example, MOSFETs or IGBTs are used. The induction heating coil L forms a series resonance circuit with the resonance capacitor C2 and the resonance capacitor C3, and a pan (not shown) is placed on the induction heating coil L and heated by electromagnetic induction.

  As shown in FIG. 3, the output power calculation circuit PO includes an effective value conversion circuit RMS, a first AD conversion circuit A / D1, a second effective value conversion circuit RMS2, a second AD conversion circuit A / D2, a third The AD conversion circuit A / D3, the arithmetic circuit CC, and the DA conversion circuit D / A. The output power calculation circuit PO detects the voltage generated at both ends of the induction heating coil L by the heating coil voltage detection circuit PT2, inputs the detected voltage as the heating coil voltage detection signal Pt2, and outputs the inverter circuit. The current is detected by the output current detection circuit CT2, the detected current is input as the output current detection signal Ct2, and the phase difference detection signal Pf detected by the phase difference detection circuit PF shown below is input.

The heating coil voltage detection signal Pt2 is converted into an effective value by a second effective value conversion circuit RMS2 shown in FIG. 3, and the converted voltage is A / D converted by a second AD conversion circuit A / D2. To the arithmetic circuit CC. The output current detection signal Ct2 is converted into an effective value by the effective value conversion circuit RMS, and the current subjected to the effective value conversion is AD converted by the first AD conversion circuit A / D1 and input to the arithmetic circuit CC. Further, the third AD conversion circuit A / D3 AD-converts the value of the phase difference θ detected by the phase difference detection circuit PF described below and inputs the value to the arithmetic circuit CC. The arithmetic circuit CC converts the input value after AD conversion into
An output power value is obtained from an arithmetic expression of V × I × cos θ. The DA conversion circuit D / A converts the obtained output power value by D / A conversion and outputs it as an output power calculation signal Po.

  The power control differential amplifier DA1 shown in FIG. 1 obtains the difference between the output power calculation signal Po and the power setting signal Wa, amplifies the obtained difference value to a predetermined value, and performs positive power control. Output as a differential amplification signal Da1.

  The phase difference detection circuit PF is formed by a pulse circuit PK and a phase difference / voltage conversion circuit PE shown in FIG. 2, and the pulse circuit PK outputs an output current detection signal Ct2 shown in FIG. Is converted into a pulse signal Pk shown in FIG. The phase difference / voltage conversion circuit PE detects the phase difference θ between the pulse signal Pk and the second switching element drive signal Tr2 shown in FIG. 4B, and converts the phase difference θ into a voltage to detect the phase difference. Output as signal Pf. When the value of the phase difference θ is large, the output voltage becomes high. Conversely, when the value of the phase difference θ is small, the output voltage becomes small.

  As shown in FIG. 1, the input end of the V / F converter VF is grounded via a resistor (not shown). Therefore, unless the power control differential amplification signal Da1 of the power control differential amplifier circuit DA1 becomes a positive value, the voltage at the input terminal of the V / F converter VF is maintained at zero potential, and the V / F converter VF When the input potential is zero, a frequency signal for controlling the inverter circuit at the lowest frequency is output.

  The operation command circuit SC operates the drive circuit DC by outputting an operation command signal Sc. The drive circuit DC performs PFM control for modulating the pulse frequency with a constant pulse width ratio according to the value of the output signal Vf from the V / F converter VF shown below, and performs the first switching element TR1 and the first switching element TR1. The first switching element drive signal Tr1 and the second switching element drive signal Tr2 that alternately drive the two switching elements TR2 are output.

  FIG. 4 is a waveform diagram for explaining the operation of the phase difference detection circuit shown in FIG. 4A shows the first switching element drive signal Tr1, FIG. 4B shows the second switching element drive signal Tr2, FIG. 4C shows the output voltage detection signal Pt1, FIG. 4D shows the output current detection signal Ct2, and FIG. 4E shows the pulse signal Pk.

  FIG. 5 is a waveform diagram for explaining the operation of the present invention. 5A shows the power setting signal Wa, FIG. 5B shows the output power calculation signal Po, and FIG. 5C shows the power control differential amplification signal Da1. .

The operation of the present invention will be described with reference to the waveform diagrams shown in FIGS. When the power setting signal Wa is increased by the power setting circuit WA at time t = t0 shown in FIG. 5, the phase difference detection circuit PF causes the second switching element drive signal Tr2 shown in FIG. ) Is detected, and the phase difference θ is converted into a voltage and output as a phase difference detection signal Pf. At this time, the value of the phase difference θ decreases. Then, the output power calculation circuit PO calculates the effective value of the output current of the inverter circuit, the effective value of the voltage generated at both ends of the induction heating coil L, and the value of the phase difference θ.
The power calculation formula V × I × cos θ is used to output an output power calculation signal Po shown in FIG.

  When the power setting signal Wa increases at time t = t0 to t2, the power control differential amplification signal Da1 shown in FIG. 5C continues to decrease, and the V / F converter VF performs the power control differential amplification. In response to the decrease of the signal Da1, the output frequency of the inverter circuit is decreased to increase the current flowing through the induction heating coil L.

  When the increase of the power setting signal Wa is finished at time t = t1, the decrease of the power control differential amplification signal Da1 shown in FIG. 5C is stopped, and the decrease in the output frequency of the inverter circuit is stopped and the induction heating coil L Is limited to a predetermined value.

  After time t = t2, the power setting signal Wa shown in FIG. 5A and the output power calculation signal Po shown in FIG. 5B are close to each other, and the output power is controlled to be constant. From the above, since the output power is obtained using the voltage across the induction heating coil L, the power consumed by the resonant capacitor C2 and the resonant capacitor C3 is eliminated, so the power consumed in the pan can be calculated more accurately. .

[Embodiment 2]
FIG. 6 is an electrical connection diagram of the electromagnetic induction heating device according to the second embodiment. In the figure, the same reference numerals as those in the electrical connection diagram of the electromagnetic induction heating cooker of the present invention shown in FIG.

  The output voltage detection circuit PT1 has a first input terminal connected to the drain side of the first switching element TR1 forming the inverter circuit shown in FIG. 6, and a second input terminal connected to the source side of the second switching element TR2. Then, the output voltage of the inverter circuit is detected and output as an output voltage detection signal Pt1.

  The first switching element TR1 and the second switching element TR2 are repeatedly turned on and off alternately with a duty of 50%, and the output voltage of the inverter circuit is output by the output voltage detection circuit PT1 as shown in FIG. The detection signal Pt1 is output as an AC square wave. The peak value of the square wave of the output voltage of the inverter circuit becomes the effective value as it is.

  The second output power calculation circuit PO2 includes an RMS conversion circuit RMS, a first AD conversion circuit A / D1, a second AD conversion circuit A / D2, a third AD conversion circuit A / D3, an operation circuit CC, and It is formed by a DA conversion circuit D / A. The second output power calculation circuit PO2 inputs the output voltage of the inverter circuit detected by the output voltage detection circuit PT1 as the output voltage detection signal Pt1, and uses the inverter circuit output current detected by the output current detection circuit CT2. The output current detection signal Ct2 is input, and the phase difference detection signal Pf detected by the phase difference detection circuit PF is input.

The input output voltage detection signal Pt1 is A / D converted by the second AD conversion circuit A / D2 and input to the arithmetic circuit CC. Further, the output current detection signal Ct2 is converted into an effective value by the effective value conversion circuit RMS, and the current converted into the effective value is AD converted by the first AD conversion circuit A / D1 and input to the arithmetic circuit CC. Further, the third AD conversion circuit A / D3 AD-converts the value of the phase difference θ detected by the phase difference detection circuit PF and inputs it to the arithmetic circuit CC. Then, the arithmetic circuit CC converts the input value after AD conversion,
An output power value is obtained by calculation using an equation of V × I × cos θ.
The DA conversion circuit D / A converts the obtained output power value by D / A conversion, and outputs it as the second output power calculation signal Po2.

  From the above, it is possible to calculate the power consumption of only the induction heating coil L, the resonance capacitor C2, and the resonance capacitor C3 of the series resonance circuit excluding the power consumed by each control circuit that controls the inverter circuit.

It is an electrical connection figure of the electromagnetic induction heating cooking appliance of this invention. FIG. 2 is a detailed electrical connection diagram of the phase difference detection circuit shown in FIG. 1. It is a detailed electrical connection diagram of the output power calculation circuit shown in FIG. FIG. 3 is a waveform diagram for explaining the operation of the phase difference detection circuit shown in FIG. 2. It is a wave form diagram explaining operation | movement of this invention. 6 is an electrical connection diagram of the electromagnetic induction heating device of Embodiment 2. FIG. FIG. 8 is a detailed electrical connection diagram of the second output power calculation circuit according to the second embodiment illustrated in FIG. 7. It is an electrical connection figure of the electromagnetic induction heating cooking appliance of a prior art.

Explanation of symbols

A / D1 First AD conversion circuit A / D2 Second AD conversion circuit A / D3 Third AD conversion circuit CC arithmetic circuit C1 smoothing capacitor C2 resonance capacitor C3 resonance capacitor CT1 input current detection circuit CT2 output current detection circuit D / A DA converter circuit DC drive circuit DA1 differential amplifier circuit for power calculation DR1 rectifier circuit L induction heating coil PE phase difference / voltage conversion circuit PF phase difference detection circuit PI input power calculation circuit PK pulsing circuit PO output power calculation circuit PO2 Second output power calculation circuit PT1 Output voltage detection circuit PT2 Heating coil voltage detection circuit PT3 Input voltage detection circuit RMS RMS conversion circuit RMS2 Second RMS conversion circuit SC operation command circuit TR1 first switching element TR2 second switching element VF V / F converter WA Power setting circuit t1 input current detection signal Ct2 output current detection signal Da1 power control differential amplification signal Pk pulse signal Po output power calculation signal Pf phase difference detection signal Pt1 output voltage detection signal Pt2 heating coil voltage detection signal Pt3 input voltage detection signal Sc operation command Signal Tr1 First switching element drive signal Tr2 Second switching element drive signal Vf V / F converter signal Wa Power setting signal

Claims (2)

  An induction heating coil that forms a series resonance circuit with a resonance capacitor, a rectification circuit that rectifies a commercial AC power supply and converts it into a DC voltage, and the induction heating using the DC voltage of the rectification circuit as an input when a start signal is input An inverter circuit that supplies a high frequency current to the coil, an input power calculation circuit that calculates the input power of the inverter circuit, and an input power calculation signal of the input power calculation circuit and a power setting signal of a predetermined value are compared and calculated. A power control differential amplifier circuit that outputs a power control differential amplification signal, and an electromagnetic induction heating cooker that controls an output frequency of the inverter circuit in accordance with the power control differential amplification signal. An output current detection circuit for detecting the output current of the inverter circuit and outputting it as an output current detection signal; and a second switching element drive signal for the inverter circuit; A phase difference detection circuit that detects a phase difference from the output current detection signal of the inverter circuit and outputs it as a phase difference detection signal, and detects a voltage generated at both ends of the induction heating coil and outputs it as a heating coil voltage signal An output for calculating the output power of the inverter circuit by the heating coil voltage detection circuit, the detected heating coil voltage signal, the detected output current detection signal, and the detected phase difference detection signal, and outputting it as an output power calculation signal Replacing the power calculation circuit with the input power calculation circuit, comparing and calculating the output power calculation signal and the power setting signal and outputting as a power control differential amplification signal, and according to the power control differential amplification signal An electromagnetic induction heating cooker that controls the output frequency of the inverter circuit. An output voltage detection circuit that detects an output voltage of the inverter circuit and outputs an output voltage detection signal is provided, the output power calculation circuit is replaced with a second output power calculation circuit, and the detected output voltage detection signal 2. The electromagnetic induction heating cooker according to claim 1, wherein the electromagnetic induction heating cooker is a second output power calculation circuit that calculates the output power of the inverter circuit based on the detected output current detection signal and the detected phase difference detection signal.

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