JP5431899B2 - Electromagnetic induction heating cooker - Google Patents

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 pan by electromagnetic induction, and more particularly to a current limiting technique.

  FIG. 7 is an electrical connection diagram of a conventional electromagnetic induction heating apparatus. In the figure, DR1 is a rectifier circuit that rectifies the output of the commercial AC power source and converts it into a DC voltage, C1 is a smoothing capacitor that smoothes the voltage converted into DC by the rectifier circuit DR1, and TR1 and TR2 are half bridges For example, a MOSFET or an IGBT is used as a switching element forming an inverter circuit. L is an induction heating coil that forms a series resonance circuit with the resonance capacitors C2 and C3. A cooking pot is placed on the induction heating coil and heated by electromagnetic induction.

  PO inputs the signal from the voltage detector PT1 for detecting the voltage of the smoothing capacitor C1 (input voltage of the inverter) and the signal from the primary current detector CT1 for detecting the current at the input terminal of the inverter to input the inverter. A power calculation circuit that calculates power, and DC is a drive circuit that drives the switching elements TR1 and TR2.

  FIG. 8 is a detailed diagram of the power control differential amplifier DA1 shown in FIG. 7, in which the input signal Po from the power calculation circuit PO is set to the non-inverting input terminal and the power setting signal set to the inverting input terminal by the power setting circuit WA. Each Wa is input. When the power calculation signal Po is smaller than the power setting signal Wa, the power control differential amplifier circuit DA1 outputs a negative power control differential amplification signal Da1 obtained by amplifying the knitting difference between the two, and the power calculation signal Po. Is greater than the power setting signal Wa, a positive power control differential amplification signal Da1 obtained by amplifying the difference between the two is output.

  The operation command circuit SC controls the operation of the drive circuit DC according to the signals of the start switch SW and the overcurrent detection circuit CP. The overcurrent detection circuit CP compares the predetermined overcurrent setting signal Io set by the overcurrent setting circuit IO with the output current detection signal Ct2, and when the output current detection signal Ct2 becomes larger than the overcurrent setting signal Io, The current detection signal Cp is output, and the operation command circuit SC stops the operation of the drive circuit DC when the overcurrent detection signal Cp is input, and stops supplying the current flowing through the induction heating coil.

  FIG. 8 is a detailed diagram of the current control differential amplifier circuit Da2 shown in FIG. 7. The output current detection signal Ct2 from the output current detector CT2 is supplied to the non-inverting input terminal and the current limiting circuit IC is supplied to the inverting input terminal. Each of the signals Ic is input. When the output current detection signal Ct2 is smaller than the current limit signal Ic, the current control differential amplifier circuit DA2 outputs a negative current control differential amplification signal Da2 obtained by amplifying the knitting difference between the two to detect the output current. When the signal Ct2 is larger than the current limit signal Ic, a positive current control differential amplification signal Da2 obtained by amplifying the knitting difference between the two is output.

  The current limit control circuit is formed by a diode DR2, a diode DR3, a resistor R1, and a V / F converter VF shown in FIG. Then, the current limit control circuit is connected to the power control differential amplifier circuit DA1 via the diode DR2 and the current control differential amplifier circuit DA2 via the diode DR3 to form an OR logic, and to control the power control difference. The maximum value of the dynamic amplification signal Da1 and the current control differential amplification signal Da2 is selected and output as Vi. The V / F converter VF outputs a frequency command signal Vf according to the value of Vi, and performs level conversion by the drive circuit DC to control the output frequency of the inverter circuit.

For example, when a cooker replaces a stainless steel pan with a non-standard aluminum or copper pan and cooks boiled food, the power setting value Wa is set as shown in FIG. When the point c is set, a large difference occurs in the output current of the inverter circuit. At this time, a large eddy current is generated inside the metal in the aluminum or copper pan, but since the surface resistance value is small, the eddy current loss is small and it is not possible to sufficiently heat compared with the stainless steel pan.
(For example, Patent Document 1)

JP 2004-253313 A

When a non-standard aluminum or copper pan is used in an electromagnetic induction heating cooker, the output current of the inverter circuit increases rapidly, but a current limit is provided so that the output current does not exceed the specified value. Each of the switching elements forming the circuit is protected.
The current limit set value is set to a value slightly exceeding the current at which the maximum power can be supplied to the stainless steel pan. At this time, if the stainless steel pan is replaced with an aluminum or copper pan, the output current of the inverter circuit increases rapidly. However, compared to this increase in output current, the pan's power supply is low and the pan is heated sufficiently. Before the operation, the output current of the inverter circuit is limited by the current limit setting value, and the pan cannot be heated sufficiently.
If this pan cannot be heated sufficiently for a long time, the output current of each switching element that forms the inverter circuit is output near the maximum rating, and the deterioration of parts is induced by the heat loss that occurs during switching, thus prolonging the life of the product. shorten.

  Accordingly, the present invention has been made to solve the above-described problems, and its purpose is to provide electromagnetic induction that can suppress deterioration of parts even when used by replacing a stainless steel pan with an aluminum or copper pan. An object is to provide a cooking device.

In order to solve the above-described problems, a first invention includes a resonance capacitor, an induction heating coil that forms a series resonance circuit together with the resonance capacitor, an inverter circuit that supplies a high-frequency current to the induction heating coil, and the inverter A power calculation circuit that calculates input power based on an input current and an input voltage of the circuit, and an overcurrent detection that detects an output current value of the inverter circuit and stops the inverter circuit when a predetermined overcurrent set value is exceeded. A circuit, a power control differential amplification circuit that differentially amplifies the power calculation value and a predetermined power setting value to output a power control differential amplification value, and outputs a predetermined current limit setting value A current limit setting circuit; a current control differential amplification circuit that differentially amplifies the output current value and a predetermined current limit setting value to output a current control differential amplification value; and A current limiting control circuit that inputs a differential amplification value for force control and a differential amplification value for current control and outputs the larger value to a frequency conversion circuit that controls the inverter circuit; and electromagnetic induction heating cooking In the vessel
The current limit setting circuit is characterized in that the current limit set value changes according to the power set value and the maximum value of the current limit set value is less than the overcurrent set value. It is a cooker.

  According to a second aspect of the invention, the current limit set value changes linearly or parabolically according to the power set value, and when the power set value exceeds a predetermined power set reference value, the change ends and the final change The electromagnetic induction heating cooker according to claim 1, wherein the value is maintained.

  According to a third aspect of the invention, the current limit set value changes trapezoidally according to the power set value, and when the power set value exceeds a predetermined power set reference value, the change ends and the final change value is maintained. The electromagnetic induction heating cooker according to claim 1, wherein:

In the first invention, the current limit set value changes according to the power set value. At this time, for example, when the power setting value is set from the maximum to the middle, the current limit setting value decreases as the power setting value decreases. Stainless steel pans can be heated sufficiently even if the power setting is set to the middle. However, if it is replaced with an aluminum or copper pan in this state, the output current of the inverter circuit will increase rapidly. Loss is small and heating is not possible. And only the heat loss of each switching element which forms an inverter circuit becomes large.
However, in the present invention, since the current limit set value is reduced in accordance with the decrease in the power set value, the heat loss is limited by the small current limit set value when the non-standard aluminum or copper pan is heated. The heat loss of the switching element can be suppressed, and the deterioration of the parts due to the heat loss can be prevented.

In addition to the effects described above, in the present invention, the difference between the overcurrent set value and the current limit set value increases as the power set value decreases.
For example, if the power setting value is changed from the maximum to the middle, the difference between the overcurrent setting value and the current limit setting value becomes large. If the stainless steel pot is replaced with an aluminum or copper pot in this state, the output of the inverter circuit Although the current increases rapidly, the output current of the inverter circuit is also limited to a small value because the current limit set value is set small. At this time, an overshoot occurs when the output current is limited due to a delay in the response of the output control. However, since the difference between the overcurrent set value and the current limit set value is large, the output current is limited by the current limit set value before reaching the overcurrent set value. Therefore, when the stainless steel pan is replaced with an aluminum or copper pan, the operation of the inverter circuit is not stopped by the overcurrent protection operation, and the heating felt when the cooker replaces the nonstandard pan You can remove the sense of incongruity of being cut.

  In the second and third inventions, the current limit set value changes with high accuracy according to the power set value. Therefore, when the stainless steel pan is replaced with a non-standard aluminum or copper pan, Protection coordination is further improved.

It is an electrical connection diagram of the electromagnetic induction heating cooking device of Embodiment 1 of the present invention. FIG. 2 is a detailed connection diagram of the current limit control circuit shown in FIG. 1. It is a waveform timing diagram explaining the operation. It is a 2nd waveform timing diagram explaining operation | movement. It is a relationship diagram between a power setting value and an output current. It is a relationship diagram between a power setting value and an output current. It is an electrical connection figure of the electromagnetic induction heating cooking appliance of a prior art. FIG. 8 is a detailed view of the current control differential amplifier circuit and the power control differential amplifier circuit shown in FIG. 7.

  Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is an electrical connection diagram of the electromagnetic induction heating apparatus of the present invention. FIG. 2 is a detailed connection diagram of the current limit setting circuit shown in FIG. In FIG. 1, the same reference numerals as those of the conventional electrical connection diagram shown in FIG.

  FIG. 2 is a detailed diagram of the current limit setting circuit IC2, which is formed by an adder circuit and a limiter circuit composed of operational amplifiers. The adder circuit generates a power setting signal Wa from the power setting circuit WA and a predetermined reference signal Va. Add, invert and amplify to output a negative signal. The limiter circuit inverts the negative signal to a positive signal, and changes the current limit setting value Ic2 according to the value of the power setting signal Wa when it is less than a predetermined power setting reference value (the Zener diode reference voltage). When the power setting reference value is exceeded, a predetermined current limit setting value Ic2 smaller than the overcurrent setting value Io is output. At this time, even if the value of the power setting signal Wa is zero, the value of the current limit setting value Ic2 is output as a predetermined value by the adding circuit.

  As shown in FIG. 1, the input end of the V / F converter VF is grounded via a resistor R1. Therefore, the voltage at the input terminal of the V / F converter VF is kept at zero potential unless the output signal Da1 of the power control differential amplifier DA1 and the output signal Da2 of the current control differential amplifier DA2 become positive values. The V / F converter VF outputs a frequency signal for controlling the inverter at the lowest frequency when its input potential is zero. Here, the minimum frequency of the inverter circuit is set to a value slightly higher than the resonance frequency of the series resonance circuit including the heating coil L including the cooking pot to be placed and the resonance capacitors C2 and C3.

  FIG. 3 shows a timing when an aluminum or copper pan is used for the electromagnetic induction heating cooker according to the first embodiment of the present invention, and the value of the current limit set value Ic2 is increased in accordance with the increase of the power set value Wa. FIG. In the same figure, (A) shows the output current detection signal Ct2, (B) shows the power setting signal Wa, (C) shows the power calculation signal Po, D) shows the differential amplification signal Da2 for current control, (E) shows the differential amplification signal Da1 for power control, and (F) shows the input signal Vi of the V / F converter VF. FIG. 5G shows the current limit set value Ic2. Hereinafter, the operation will be described with reference to FIG.

  An aluminum or copper pan is placed on the induction heating coil, and at time t = t0 shown in FIG. 3, the power setting circuit WA shown in FIG. When the value is increased, the value of the power calculation signal Po shown in FIG. 3C increases as the value of the power setting signal Wa increases. However, the output current detection signal shown in FIG. The increase in the value of Ct2 is remarkable.

  Further, when the value of the power setting signal Wa increases at time t = t0, the value of the power control differential amplification signal Da1 shown in FIG. 3E decreases, and conversely, the current shown in FIG. The value of the control differential amplification signal Da2 increases. The input signal Vi of the V / F converter VF shown in FIG. 5F is supplied to the power control differential amplification signal Da1 or the current control difference by the diodes DR2 and DR3 and the resistor R1 at the input end of the V / F converter VF. The signal that is larger of the positive voltage of the dynamic amplification signal Da2 becomes the input signal Vi. The V / F converter VF decreases the output frequency of the inverter and increases the current flowing through the induction heating coil in accordance with the decrease of the input voltage Vi shown in FIG.

  When the value of the power setting signal Wa shown in FIG. 5 increases from the point a to the point b at time t = t1, the value of the output current detection signal Ct2 becomes larger than the value of the current limit setting signal Ic2, and FIG. The current control differential amplification signal Da2 shown is output as a positive potential. At this time, the value is larger than the value of the power control differential amplification signal Da1 shown in FIG. 3E, and the current control differential amplification signal Da2 is selected by the diode DR2 and the diode DR3 and input to the V / F converter VF. .

  After time t = t2, the output frequency of the inverter circuit is controlled in accordance with the current control differential amplification signal Da2, and the value of the output current detection signal Ct2 is limited by the current limit setting value at point b shown in FIG. The

  From the above, when the stainless steel pan is replaced with a non-standard aluminum or copper pan, the current flowing through the induction heating coil increases rapidly, but the current limit setting value is set to a value corresponding to the stainless steel pan. Therefore, the output current of the inverter circuit is limited by the current limit setting value. Thereby, even if it uses a nonstandard pan, the heat loss of each switching element which forms an inverter circuit can be controlled, and degradation of parts can be prevented. Moreover, since the current limit set value is smaller as the power set value is smaller, the suppression of heat loss of each switching element is further increased.

  FIG. 4 is a timing diagram when the stainless steel pan is replaced with an aluminum or copper pan during heating by the electromagnetic induction heating cooker. In the same figure, (A) shows the output current detection signal Ct2, (B) shows the power calculation signal Po, and (C) shows the current control differential amplification signal Da2. FIG. 4D shows the power control differential amplification signal Da1, and FIG. 4E shows the input signal Vi of the V / F converter VF. Hereinafter, the operation will be described with reference to FIG.

  When the value of the power setting signal Wa shown in FIG. 5 is set to point b and the stainless steel pan is replaced with an aluminum or copper pan in this state, a sudden load fluctuation occurs at time t = t3 shown in FIG. As a result, the value of the output current detection signal Ct2 increases.

  Since there is a response delay in the current control differential amplifier circuit DA2, the output current detection signal Ct2 excessively overshoots when the output current is limited at t = t4 shown in FIG. Exceeds the current limit setting signal Ic2. At this time, the value of the power setting signal Wa is set at the position of point b shown in FIG. 5, and the difference between the value of the overcurrent setting signal Io and the value of the current limit setting signal Ic2 is large.

  At time t = t4 shown in FIG. 4, the current control differential amplification signal Da2 becomes larger than the power control differential amplification circuit Da1, and the control of the inverter circuit is controlled from the power control differential amplification circuit Da1. Switching to the dynamic amplification signal Da2. At this time, the potential of the input signal Vi shown in FIG. 4E of the V / F converter VF rises, the output frequency of the inverter is increased to suppress the current supplied to the induction heating coil, and the output current is set to be current limited. Since the value is substantially the same as the value of the signal Ic2, the value of the output current detection signal Ct2 does not reach the overcurrent setting signal Io.

  At time t = t4 to t5, the value of the output current detection signal Ct2 does not reach the value of the overcurrent setting signal Io. Therefore, even if the stainless steel pot is replaced with an aluminum or copper pot, the overcurrent protection operates and the inverter The circuit is not stopped, and it is possible to remove the uncomfortable feeling that the heating that the cook feels when the pan is changed is cut off.

  From the above, the difference between the overcurrent set value Io and the current limit set value Ic2 is, for example, as shown in FIG. 5, when the power set value Wa is compared between the c point and the b point, the difference decreases as the power set value decreases. growing. For example, if the power setting value is set to point b shown in FIG. 5 and the pan is replaced in this state, the difference between the overcurrent setting value Io and the current limit setting value Ic2 is large. If it is replaced with a steel or copper pan, the current flowing in the induction heating coil increases rapidly, but the current limit setting value is set small, so the maximum overshoot that occurs when the output current is limited The overcurrent set value is not reached. Therefore, the protection coordination of overcurrent protection is improved as the power setting value is decreased.

[Embodiment 2]
FIG. 6 is a relationship diagram between the power setting value and the output current in the second embodiment.
In the first embodiment, as shown in FIG. 5, the current limit set value Ic2 is linearly increased in accordance with the increase in the power set value Wa, but the current limit set value Ic2 is increased in accordance with the increase in the power set value Wa. As shown in FIG. 6, when the power setting value Wa exceeds a point c (for example, a predetermined power setting reference value), it is maintained at a predetermined value of the current limit setting value Ic2 shown in FIG. You may do it.

  As shown in FIG. 6, by increasing the current limit set value Ic2 in a parabolic or trapezoidal manner according to the increase in the power set value Wa, a more accurate current limit set value Ic2 that can be increased linearly can be set. The protection coordination of the overcurrent protection is further improved when using an outer aluminum or copper pan.

CP overcurrent detection circuit C1 smoothing capacitor C2 resonance capacitor C3 resonance capacitor CT1 input current detector CT2 output current detector DC drive circuit DA1 power control differential amplifier DA2 current control differential amplifier DR1 rectifier circuit DR2 diode DR3 diode IC2 Current limit setting circuit IO Overcurrent setting circuit L Induction heating coil PO Power calculation circuit PT1 Voltage detector R1 Resistor R2 Resistor R3 Resistor R4 Resistor R5 Resistor SC Operation command circuit SW Start switch TR1 Switching element TR2 Switching element VF V / F converter WA Power setting circuit Cp Overcurrent detection signal Ct1 Input current detection signal Ct2 Output current detection signal Da1 Power control differential amplification signal Da2 Current control differential amplification signal Ic2 Current limit setting signal Io Current setting signal Po power calculating signal Pt1 voltage detection signal Sc operation command signal Sw activation signal Vf V / F converter signal Wa power setting signal

Claims (3)

Calculation of input power based on a resonance capacitor, an induction heating coil that forms a series resonance circuit with the resonance capacitor, an inverter circuit that supplies a high-frequency current to the induction heating coil, and an input current and an input voltage of the inverter circuit A power calculation circuit that detects an output current value of the inverter circuit and stops the inverter circuit when a predetermined overcurrent set value is exceeded, the power calculation value and a predetermined power set value, Differential amplification circuit for power control that outputs a differential amplification value for power control, a current limit setting circuit that outputs a predetermined current limit setting value, and the output current value and a predetermined current A differential amplification circuit for current control that differentially amplifies the limit set value and outputs a differential amplification value for current control, and the differential amplification value for power control and the differential increase for current control In the electromagnetic induction heating cooker, comprising: a current limit control circuit configured to enter a value larger values of the frequency converting circuit for controlling said inverter circuit, and
The current limit setting circuit is characterized in that the current limit set value changes in accordance with the power set value and the maximum value of the current limit set value is less than the overcurrent set value. It is a vessel.   The current limit set value changes linearly or parabolically according to the power set value, and when the power set value exceeds a predetermined power set reference value, the change ends and the final change value is maintained. The electromagnetic induction heating cooker according to claim 1, wherein:   The current limit set value changes in a trapezoidal manner according to the power set value, and when the power set value exceeds a predetermined power set reference value, the change ends and the final change value is maintained. The electromagnetic induction heating cooker according to claim 1.

Images