JP7107746B2 - electromagnetic induction cooker - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electromagnetic induction cooking device that heats a pot using a plurality of heating coils, that is, a so-called IH (Induction Heating) cooking heater.

2. Description of the Related Art In recent years, so-called IH cooking heaters, i.e., inverter-type electromagnetic induction cookers that heat an object to be heated such as a pot without using fire, have been widely used. An IH cooking heater sends a high-frequency current through a heating coil to generate an eddy current in a pan made of iron, stainless steel, or other material that is placed close to the heating coil, generating heat from the electrical resistance of the pan itself. be. In this way, IH cooking heaters are rapidly gaining popularity in place of gas ranges because they can cook without using fire and are highly safe and provide a comfortable cooking environment.

In a conventional IH cooking heater, a heating coil is arranged under a glass top plate, and an inverter for supplying a high-frequency current is connected to the heating coil. A pan placed on the top plate is heated using one heating coil.
However, in the method of heating the pot using one heating coil, there is a problem that only a part of the bottom of the pot is heated depending on the size and arrangement of the pot, causing uneven heating. Therefore, an induction heating apparatus has been proposed that uses a plurality of heating coils to appropriately heat pots of various sizes and arrangements.

For example, in claim 1 of Patent Document 1, "an inverter circuit that generates and outputs high-frequency power of a predetermined frequency, and the high-frequency power supplied from the inverter circuit generates a magnetic field of a predetermined frequency, a heating coil for inductively heating an object; and a self-resonant coil disposed between the object to be heated and the heating coil, wherein the self-resonant coil comprises a resonance coil and a resonance capacitor, and a magnetic field generated by the heating coil. An induction heating device that self-resonates at a frequency of .

JP 2011-60631 A

However, in Patent Document 1, a self-resonant coil is arranged between the object to be heated and the heating coil. can't In addition, since the heating coil and the self-resonant coil are vertically overlapped, the object to be heated and the heating coil are separated from each other, and the heating efficiency is deteriorated due to a decrease in magnetic coupling.
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an electromagnetic induction heating cooker capable of efficiently heating a pan even when the placement position of the pan is changed.

In order to solve the above-described problems, the electromagnetic induction heating cooker of the present invention provides a heating coil that is connected to a first resonance capacitor to form a first resonance circuit, and is magnetically coupled to the heating coil via a magnetic material, A plurality of resonant heating coils each having a second resonant capacitor connected in series to form a second resonant circuit; and a control circuit for controlling the inverter circuit. It is characterized in that the current flowing through the coil increases or decreases .
The electromagnetic induction heating cooker of the present invention includes a heating coil that is connected to a first resonance capacitor to form a first resonance circuit, and a second resonance capacitor that is magnetically coupled to the heating coil via a magnetic material and that is connected in series. a plurality of resonant heating coils configured to form a second resonant circuit; an inverter circuit for applying voltage to the first resonance circuit; and a control circuit for controlling the inverter circuit, wherein the magnetic material is arranged immediately below the heating coil and the plurality of resonance heating coils, and Directly below the heating coil, a first magnetic material is radially arranged. Directly below the plurality of resonant heating coils, a second magnetic material is radially arranged, and part of the first magnetic material is It straddles the resonance heating coil concerned.
Other means are described in the detailed description.

ADVANTAGE OF THE INVENTION According to this invention, in an electromagnetic induction heating cooker, even when the mounting position of a pot changes, it can heat a pot efficiently.

1 is a block diagram of an electromagnetic induction heating cooker according to a first embodiment; FIG. Fig. 2 is a perspective view showing the arrangement of heating coils and ferrites of the electromagnetic induction heating cooker; FIG. 3 is a top view showing the arrangement of heating coils and ferrites of the electromagnetic induction heating cooker; FIG. 4 is a cross-sectional view showing the arrangement of the heating coil and ferrite of the electromagnetic induction heating cooker; It is a top view which shows the pot deviation state of an electromagnetic induction heating cooker. 4 is a graph showing frequency characteristics of impedance of a resonant circuit; It is a perspective view which shows the arrangement|positioning of a heating coil and a ferrite in the 1st modification of 1st Embodiment. It is a sectional view showing arrangement of a heating coil and ferrite in the 1st modification of a 1st embodiment. It is a perspective view which shows arrangement|positioning of a heating coil and a ferrite in the 2nd modification of 1st Embodiment. It is a sectional view showing arrangement of a heating coil and ferrite in the 2nd modification of a 1st embodiment. FIG. 4 is a circuit configuration diagram of an electromagnetic induction heating cooker according to a second embodiment; It is a figure which shows the resistance value of each to-be-heated material, and the inductance ratio with respect to iron. It is an operation waveform of an inverter. It is the frequency characteristic of the input electric power of an electromagnetic induction heating cooker. It is the duty characteristic of the input electric power of an electromagnetic induction heating cooker. FIG. 10 is a circuit configuration diagram of an electromagnetic induction heating cooker according to a third embodiment; It is an operation waveform of an electromagnetic induction heating cooker. It is the frequency characteristic of the input electric power of an electromagnetic induction heating cooker.

EMBODIMENT OF THE INVENTION Henceforth, the form for implementing this invention is demonstrated in detail with reference to each figure.
<<1st Embodiment>>
First, an electromagnetic induction heating cooker 1 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG.

FIG. 1 is a block diagram of an electromagnetic induction heating cooker according to the first embodiment.
The electromagnetic induction heating cooker 1 of the first embodiment includes a power supply circuit 2 functioning as a DC power supply, inverters 3a to 3c, resonance circuits 4a to 4c, a drive circuit 51, a resonance current detection circuit 52, a control circuit 53, an input power A setting unit 54 is provided. The electromagnetic induction heating cooker 1 can heat an object to be heated such as a pot placed on a top plate (not shown) by a plurality of heating coils 33 corresponding to each inverter 3 . Since each inverter 3 has the same configuration, the inverter 3a will be described below as a representative.

The inverter 3 a includes a switching circuit 31 , a resonance circuit 32 and a current detector 37 . The switching circuit 31 is connected between the positive electrode p and the negative electrode o of the power supply circuit 2 , converts the DC voltage applied by the power supply circuit 2 into a high-frequency AC voltage, and applies it to the resonance circuit 32 . . The resonance circuit 32 is a first resonance circuit, and is a circuit in which the heating coil 33 and the resonance capacitor C0 are connected. High-frequency power is supplied to the heating coil 33 from the switching circuit 31 . A current detector 37 detects the current flowing through the resonance circuit 32 .

The resonance circuit 4a is a second resonance circuit, and is magnetically coupled to the heating coil 33 of the resonance circuit 32 via ferrite (an example of a magnetic material). The resonance circuit 4a includes a series circuit of the resonance heating coil 41 and the resonance capacitor C1, a series circuit of the resonance heating coil 42 and the resonance capacitor C2, a series circuit of the resonance heating coil 43 and the resonance capacitor C3, and a resonance heating coil 44. It is constructed as a series circuit of a capacitor C4.

Inverter 3 a is controlled by control circuit 53 , resonance current detection circuit 52 , input power setting section 54 and drive circuit 51 . The output value of the current detector 37 of the inverter 3 a is calculated by the resonance current detection circuit 52 and the calculation result is output to the control circuit 53 . The input power setting unit 54 is an interface for setting the input power (thermal power) by the user, and outputs a signal corresponding to the set thermal power to the control circuit 53 . The control circuit 53 generates a drive signal according to the calculation result output from the resonance current detection circuit 52 and the signal output from the input power setting section 54 .
The drive circuit 51 generates a drive signal waveform for controlling the switching circuit 31 of the inverter 3a based on the drive signal.

Next, the operation of inverter 3a will be described. An IH cooking heater generally uses a resonant inverter. In the resonance type inverter 3a, the drive frequency fs of the switching circuit 31 is set to be higher than the resonance frequency fr of the resonance circuit 32 when the pot is placed on the heating coil 33, so that the characteristics of the resonance load are adjusted. Make it inductive. As a result, the resonance current IL flowing through the resonance circuit 32 has a delayed phase with respect to the output voltage of the switching circuit 31, so an increase in loss in the switching circuit 31 can be suppressed.

In other words, the loss of the switching circuit 31 can be suppressed by controlling the resonance current IL flowing through the resonance circuit 32 so that it lags behind the voltage of the output terminal t, which is the connection point between the switching circuit 31 and the resonance circuit 32. .
Further, when a pot is placed on the resonance heating coils 41 to 44, the heating coil 33 and the resonance heating coils 41 to 44 are magnetically coupled, and the resonance frequencies of the resonance circuits 32 and 4 become substantially the same. As a result, current flows through the resonance circuit 32 to heat the pan placed on the heating coil 33, and current also flows through the resonance circuit 4 to heat the pan placed on the resonance heating coils 41 to 44. do.

However, if the power control is performed by changing the conduction period of the switching circuit 31 while the drive frequency fs is fixed, the polarity of the resonance current IL is reversed during the conduction period of the switching circuit 31, and the resonance current IL is changed to the switching circuit 31. In some cases, the mode shifts to a phase-advance mode in which the phase leads the output voltage. The phase-advance mode causes an increase in loss in the switching circuit 31, so it must be avoided in the resonant inverter.

Next, the arrangement of the plurality of heating coils 33 and the resonance heating coils 41 to 44 in the electromagnetic induction heating cooker 1 of the first embodiment will be described with reference to FIGS. 2 and 3. FIG. Generally, in the electromagnetic induction heating cooker 1, a heating coil 33 and resonance heating coils 41 to 44 are arranged under a glass top plate (not shown). Here, the electromagnetic induction heating cooker 1 that heats one pot by using the heating coil 33 and the resonance heating coils 41 to 44 built in one inverter 3 will be described as an example.

FIG. 2 is a perspective view showing the arrangement of the heating coil 33, the resonance heating coils 41 to 44, and the ferrites 34, 45 of the electromagnetic induction heating cooker 1. FIG.
In the electromagnetic induction heating cooker 1 shown in FIG. 2, resonance heating coils 41 to 44 are arranged on the front, rear, left, and right of the heating coil 33 when viewed from above. A glass top plate (not shown) is arranged above the heating coil 33 and the resonance heating coils 41 to 44, and the pan 6 is placed thereon. Here, the pan 6 is indicated by a dashed line.

The inverter 3 is connected to the heating coil 33 . Each resonance capacitor C1-C4 is connected to each resonance heating coil 41-44. Below the heating coil 33, magnetic ferrite 34 is radially arranged. Below the resonance heating coils 41 to 44, ferrite 45 made of a magnetic material is radially arranged. These ferrites 34 and 45 effectively induce the magnetic flux to the pot 6 and improve the magnetic coupling between the heating coil 33 and the resonance heating coils 41-44.

By making a part of the ferrite 34 radially arranged directly under the heating coil 33 close to the ferrite 45 of the resonance heating coils 41 to 44, the magnetic coupling with the heating coil 33 is further increased, and the leakage magnetic flux is reduced. can be reduced and the heating efficiency can be improved.

FIG. 4 is a sectional view showing the arrangement of the heating coil 33 and the resonance heating coils 41 to 44 and the ferrites 34 and 45 of the electromagnetic induction heating cooker 1. As shown in FIG.
The heating coil 33 and the resonance heating coils 41 to 44 are arranged substantially on the same plane. A distance L between the heating coil 33 and the resonance heating coils 41 to 44 is narrower than a distance D between the heating coil 33 and the resonance heating coils 41 to 44 and the pot 6 . As a result, the degree of magnetic coupling between the heating coil 33 and the resonance heating coils 41 to 44 is enhanced, the power transmission efficiency from the heating coil 33 to the resonance heating coils 41 to 44 is improved, and the pan 6 can be heated over a wide range.
Furthermore, the spacing F between the heating coil 33 and the ferrite 34 is smaller than the spacing D between the heating coil 33 and the pot 6 and smaller than the spacing L between the heating coil 33 and the resonance heating coils 41-44.
Further, the spacing F between the resonance heating coils 41-44 and the ferrite 45 is narrower than the spacing D between the heating coil 33 and the pan 6, and narrower than the spacing L between the heating coil 33 and the resonance heating coils 41-44.

FIG. 5 is a top view showing a case where the pot 6 is shifted and placed only on the resonance heating coil 43. FIG.
In FIG. 5 the pot 6 is placed only on the resonant heating coil 43 . In this case, the resonant circuit 32 composed of the heating coil 33 and the resonant capacitor C0 and the resonant circuit composed of the resonant heating coil 43 magnetically coupled to the heating coil 33 and the resonant capacitor C3 have substantially the same resonant frequency. . Control circuit 53 drives inverter 3a at a frequency slightly higher than its resonance frequency. As a result, a high-frequency current flows from the inverter 3a to the resonance heating coil 43 via the heating coil 33, so that the pan 6 can be induction-heated. On the other hand, in the resonance heating coils 41, 42, and 44 on which the pan 6 is not placed, the inverter drive frequency and the resonance frequency do not match, and current does not flow. This phenomenon will be described with reference to FIG.

FIG. 6 is a graph showing the relationship between the inverter driving frequency and the impedance characteristics of the resonance circuit. The vertical axis of the graph indicates the impedance of the resonant circuit, and the horizontal axis indicates the driving frequency of the inverter.
A characteristic 1 indicated by a dashed line is the impedance characteristic of the resonance circuit 4 composed of the resonance heating coil 43 on which the pan 6 is placed and the resonance capacitor C3, and the impedance characteristic of the resonance circuit 4 composed of the heating coil 33 and the resonance capacitor C0. 32 shows impedance characteristics.
A characteristic 2 indicated by a solid line is an impedance characteristic of a resonance circuit composed of the resonance heating coil 41 on which the pot 6 is not placed and the resonance capacitor C1.

Although not shown, the impedance characteristics of the resonance circuit composed of the resonance heating coil 42 and the resonance capacitor C2 and the impedance characteristics of the resonance circuit composed of the resonance heating coil 44 and the resonance capacitor C4 are substantially the same as the characteristic 2. FIG.

When the inverter 3a of characteristic 1 is driven at a frequency f1 slightly higher than the resonance frequency fr1, the impedance of the resonance circuit becomes Z1 close to the minimum value Z0. Therefore, a large current can be passed through the resonance heating coil 43 . As a result, magnetic flux is generated from the resonant heating coil 43, and the magnetic flux interlinks the pan 6, causing an eddy current to flow through the pan 6 and the pan 6 itself to generate heat.

On the other hand, in the resonance circuit of the resonance heating coils 41, 42, and 44 on which the pot 6 is not placed, the impedance at the frequency f1 is Z2 because the characteristic 2 is obtained. The impedance Z2 of the resonance heating coils 41, 42, and 44 is much larger than the impedance Z1 of the resonance heating coil 43. FIG. Therefore, almost no current flows through the resonance heating coils 41, 42, 44, and the pot 6 cannot be induction-heated. Further, since almost no current flows through the resonance heating coils 41, 42, 44, unnecessary radiation magnetic fields can be suppressed.
That is, since a large current can be applied only to the heating coil 33 and the resonance heating coil 43 on which the pan 6 is mounted, the pan 6 on the coil can be heated without being detected by a sensor or the like.
In addition, this is not limited to the case where the pan 6 is shifted. For example, consider the case where a large pot covering the resonance heating coils 41 to 44 is placed in the center of the heating coil 33 . The resonance circuits of the resonance heating coils 41 to 44 all have the characteristic 1, and can efficiently heat the large pot. Also, when a small pot having a diameter smaller than that of the heating coil 33 is placed in the center of the heating coil 33, the resonance circuits of the resonance heating coils 41 to 44 all have the characteristic 2. FIG. Therefore, almost no current flows through these resonance heating coils 41 to 44, so that unnecessary radiation magnetic fields can be suppressed.

As described above, according to the electromagnetic induction heating cooker 1 of the present embodiment, when the pot 6 is placed on the resonance heating coils 41 to 44, the power supplied by the inverter 3a is applied to the heating coil 33 and the ferrite. 34 to the resonant heating coils 41-44. As a result, a large high-frequency current can flow through the resonance heating coils 41 to 44 , and the pot 6 can be induction-heated together with the heating coil 33 .
Further, when the pot 6 is not placed on the resonance heating coils 41-44, the impedance of the resonance circuit increases, so that almost no current flows through the resonance heating coils 41-44. This makes it possible to suppress unnecessary radiation magnetic fields.

<<First Modification>>
FIG. 7 is a perspective view showing the arrangement of the heating coil 33, resonance heating coils 41 to 44, and ferrites 34 and 45 in the first modification of the first embodiment.
In the electromagnetic induction heating cooker 1 shown in FIG. 7, resonance heating coils 41 to 44 are arranged on the front, back, left, and right of the heating coil 33 when viewed from above. A glass top plate (not shown) is arranged above the heating coil 33 and the resonance heating coils 41 to 44, and the pan 6 is placed thereon. Here, the pan 6 is indicated by a dashed line.

The inverter 3 is connected to the heating coil 33 . Each resonance capacitor C1-C4 is connected to each resonance heating coil 41-44. A ferrite 35 made of a magnetic material is radially arranged below the heating coil 33 and straddles the lower portions of the resonance heating coils 41 to 44 . A ferrite 35 and a ferrite 45 are radially arranged below the resonance heating coils 41 to 44 . These ferrites 34 and 45 effectively induce the magnetic flux to the pot 6 and improve the magnetic coupling between the heating coil 33 and the resonance heating coils 41-44.
A portion of the ferrite 35 radially arranged directly under the heating coil 33 is straddled over the lower portions of the resonance heating coils 41 to 44, thereby further increasing the magnetic coupling with the heating coil 33 and reducing the leakage magnetic field. can be reduced and the heating efficiency can be improved.

FIG. 8 is a cross-sectional view showing the arrangement of the heating coil 33, resonance heating coils 41 to 44, and ferrites 35, 45 in the first modification of the first embodiment.
The heating coil 33 and the resonance heating coils 41 to 44 are arranged substantially on the same plane. A distance L between the heating coil 33 and the resonance heating coils 41 to 44 is narrower than a distance D between the heating coil 33 and the resonance heating coils 41 to 44 and the pot 6 . As a result, the degree of magnetic coupling between the heating coil 33 and the resonance heating coils 41 to 44 is enhanced, the power transmission efficiency from the heating coil 33 to the resonance heating coils 41 to 44 is improved, and the pan 6 can be heated over a wide range.

Furthermore, the spacing F between the heating coil 33 and the ferrite 35 is narrower than the spacing D between the heating coil 33 and the pan 6, and narrower than the spacing L between the heating coil 33 and the resonance heating coils 41-44.
Further, the spacing F between the resonance heating coils 41-44 and the ferrite 45 is narrower than the spacing D between the heating coil 33 and the pan 6, and narrower than the spacing L between the heating coil 33 and the resonance heating coils 41-44.

<<Second modification>>
FIG. 9 is a perspective view showing the arrangement of the heating coil 33, resonance heating coils 41-44, and ferrite 35 in the second modification of the first embodiment.
In the electromagnetic induction heating cooker 1 shown in FIG. 7, resonance heating coils 41 to 44 are arranged on the front, back, left, and right of the heating coil 33 when viewed from above. A glass top plate (not shown) is arranged above the heating coil 33 and the resonance heating coils 41 to 44, and the pan 6 is placed thereon. Here, the pan 6 is indicated by a dashed line.

The inverter 3 is connected to the heating coil 33 . Each resonance capacitor C1-C4 is connected to each resonance heating coil 41-44. A magnetic ferrite 36 is arranged under the heating coil 33 and straddles the bottoms of the resonance heating coils 41 to 44 . A ferrite 36 is arranged below the resonance heating coils 41 to 44 . The ferrite 36 effectively induces the magnetic flux to the pot 6 and improves the magnetic coupling between the heating coil 33 and the resonant heating coils 41-44.

The structure in which the ferrite 36 radially arranged directly under the heating coil 33 straddles the lower portions of the resonance heating coils 41 to 44 further increases the magnetic coupling with the heating coil 33, reduces the leakage magnetic field, Heating efficiency can be improved.

FIG. 10 is a cross-sectional view showing the heating coil 33, resonance heating coils 41-44, and ferrite 36 in the second modification of the first embodiment.
The heating coil 33 and the resonance heating coils 41 to 44 are arranged substantially on the same plane. A distance L between the heating coil 33 and the resonance heating coils 41 to 44 is narrower than a distance D between the heating coil 33 and the resonance heating coils 41 to 44 and the pot 6 . As a result, the degree of magnetic coupling between the heating coil 33 and the resonance heating coils 41 to 44 is enhanced, the power transmission efficiency from the heating coil 33 to the resonance heating coils 41 to 44 is improved, and the pan 6 can be heated over a wide range.

Furthermore, the space F between the heating coil 33 and the ferrite 36 is narrower than the space D between the heating coil 33 and the pot 6 and narrower than the space L between the heating coil 33 and the resonance heating coils 41-44.
Further, the spacing F between the resonance heating coils 41-44 and the ferrite 36 is narrower than the spacing D between the heating coil 33 and the pan 6, and narrower than the spacing L between the heating coil 33 and the resonance heating coils 41-44.

<<Second embodiment>>
Next, an electromagnetic induction heating cooker 1 according to a second embodiment of the present invention, which employs a herb bridge circuit configuration for the switching circuit 31, will be described with reference to FIGS. 11 to 15. FIG. Duplicate descriptions of the points in common with the first embodiment will be omitted.

FIG. 11 shows the circuit configuration of the electromagnetic induction heating cooker 1 according to the second embodiment. The electromagnetic induction heating cooker 1 of the present embodiment also includes three inverters 3a to 3c as in the first embodiment.

In FIG. 11, a power supply circuit 2 converts an AC voltage from a commercial power supply 7 into a DC voltage and applies the converted DC voltage to an inverter 3a. It consists of a smoothing circuit composed of a capacitor C5. The switching circuit 31 of the inverter 3a is connected between the positive electrode p and the negative electrode o of the filter capacitor C5.

The switching circuit 31 of the inverter 3a is configured by connecting in series IGBTs 38 and 39, which are power semiconductor switching elements. Diodes D1 and D2 are connected in parallel to the IGBTs 38 and 39, respectively. The collector terminal of the IGBT 38 is connected to the cathode terminal of the diode D1, and the emitter terminal of the IGBT 38 is connected to the anode terminal of the diode D1. The collector terminal of the IGBT 39 is connected to the cathode terminal of the diode D2, and the emitter terminal of the IGBT 39 is connected to the anode terminal of the diode D2.

Hereinafter, the circuit composed of the IGBT 38 and the diode D1 will be referred to as the upper arm, and the circuit composed of the IGBT 39 and the diode D2 will be referred to as the lower arm. Snubber capacitors C6 and C7 are connected in parallel to the IGBTs 38 and 39, respectively. The snubber capacitors C6 and C7 are charged or discharged by the cutoff current when the IGBT 38 or IGBT 39 is turned off. Since the capacitance of snubber capacitors C6 and C7 is sufficiently larger than the output capacitance between the collectors and emitters of IGBTs 38 and 39, the change in voltage applied to IGBTs 38 and 39 during turn-off is reduced, suppressing turn-off loss.

A resonance circuit 32 is connected to the output terminal t, which is a connection point of the IGBTs 38 and 39, and the positive electrode p and the negative electrode o of the power supply circuit 2. FIG. A resonance circuit 32 of the second embodiment is composed of a heating coil 33 and resonance capacitors C0 and C8. Here, the direction of flow from the output terminal t toward the heating coil 33 is defined as the positive direction of the resonance current IL.

A current detector 37 detects the current flowing through the resonance circuit 32 . The resonance current detection circuit 52 converts the output signal level of the current detector 37 of each inverter 3 into a signal suitable for the input level of the control circuit 53 . Current detector 22 detects current input from commercial power supply 7 . Input current detection circuit 55 converts the output signal level of current detector 37 into a signal suitable for the input level of control circuit 53 .

The control circuit 53 determines the material and state of the object to be heated from the relationship between the input current detected by the input current detection circuit 55 and the resonance current detected by the resonance current detection circuit 52, and starts or stops the heating operation. Objects to be heated are distinguished into magnetic substances and non-magnetic substances. As a method for distinguishing between them, low power (approximately 300 W) is applied before heating. The resonance current IL or the current values of the IGBTs 38 and 39 at that time are detected, and the material of the object to be heated is determined based on the current values. If the current value is small, the object to be heated is determined to be a magnetic object such as iron.

FIG. 12 shows the resistance value of each object to be heated at a frequency of 20 kHz.
Non-magnetic stainless steel has a resistance value about 1/3 that of iron. Aluminum has a resistance value about 1/20 that of iron. Copper has a resistance value about 1/25 that of iron.

The control circuit 53 also controls the input power by setting the conduction period of the IGBTs 38 and 39 of the switching circuit 31 via the drive circuit 51 according to the signal from the input power setting unit 54 . Material detection needs to be performed at low power and in a short time to prevent overcurrent and overvoltage.
Also, as shown in FIG. 11, the current Ic1 is the current that flows through the upper arm of the switching circuit 31 . A current Ic2 is a current flowing through the lower arm of the switching circuit 31 . A resonance current IL is a current flowing through the heating coil 33 . A resonance current ILr is a current that flows through the resonance heating coil 41 . A voltage Vc1 is a voltage between the collector terminal and the emitter terminal of the IGBT 38 of the upper arm. A voltage Vc2 is a voltage between the collector terminal and the emitter terminal of the IGBT 39 of the lower arm. A voltage Vc3 is a resonance voltage of the resonance capacitor C0. Let the resonance voltage of the resonance capacitor C0 be voltage Vcr. Let the power supply voltage of the inverter 3 be voltage Vp.

Next, operation of the second embodiment will be described.
FIG. 13 is a time chart showing operation waveforms from mode 1 to mode 4 of the inverter 3 in the second embodiment.
The first time chart shows the drive signal for the high-side IGBT 38 . The second time chart shows the drive signal for the IGBT 39 on the low side.
The third time chart shows the current Ic1 flowing through the collector of the IGBT 38 on the high side. The fourth time chart shows the collector-emitter voltage Vc1 of the high-side IGBT 38 .

The fifth time chart shows the current Ic2 flowing through the collector of the IGBT 39 on the low side. The sixth time chart shows the collector-emitter voltage Vc2 of the IGBT 39 on the low side. The seventh time chart shows the voltage Vcr applied across the resonance capacitor C0.
The eighth time chart shows the voltage ILc applied across the resonant capacitor C1. The ninth time chart shows the voltage ILr applied across the resonant heating coil 41 .

In either mode, the drive signal for the IGBTs 38 and 39 is provided with a dead time period, and the IGBTs 38 and 39 are driven complementarily.
Detailed operations in modes 1 to 4 will be described below.

《Mode 1》
Mode 1 starts at the timing when the current Ic1 of the IGBT 38 becomes 0A. No current flows through the IGBT 38 at the start of mode 1, but since the IGBT 38 is already turned on, the current Ic1 begins to flow through the IGBT 38 immediately after the start of mode 1. At this time, since the voltage across the IGBT 38 (the voltage Vc1 between the collector terminal and the emitter terminal) is 0V, the IGBT 38 is turned on by ZVZCS (Zero Voltage Zero Current Switching) with no loss.

《Mode 2》
When the control circuit 53 cuts off the IGBT 38, the mode transitions to mode 2. In mode 2, the resonance current IL follows a path of power supply circuit 2→snubber capacitor C6→heating coil 33→resonance capacitor C0, a path of heating coil 33→resonance capacitor C0→snubber capacitor C7, and a path of heating coil 33→resonance capacitor C0→ It flows through the snubber capacitor C6. At this time, the snubber capacitor C6 is charged and the snubber capacitor C7 is discharged. As a result, the voltage across the IGBT 38 gently rises, ZVS (Zero Voltage Switching) turns off, and switching loss can be reduced.

When the voltage Vc1 of the snubber capacitor C6 becomes equal to or higher than the power supply voltage (voltage between p and o), the voltage Vc2 of the snubber capacitor C7 becomes 0 V, the diode D2 is turned on, and the resonance current IL continues to flow. The control circuit 53 inputs an ON signal to the IGBT 39 while current is flowing through the diode D2.

《Mode 3》
Mode 3 starts at the timing when the current Ic2 of the IGBT 39 becomes 0A. At the start of mode 3, no current flows through the IGBT 39, but since the IGBT 39 is already turned on, the current Ic2 begins to flow through the IGBT 39 immediately after the start of mode 3. At this time, since the voltage across the IGBT 39 (the voltage Vc2 between the collector terminal and the emitter terminal) is 0V, the IGBT 39 is turned on in a ZVZCS manner with no loss.

《Mode 4》
When the control circuit 53 cuts off the IGBT 39, a transition to mode 4 is made. In mode 4, the resonance current IL follows a path of heating coil 33→snubber capacitor C7→power supply circuit 2→resonance capacitor C0, a path of heating coil 33→snubber capacitor C7→resonance capacitor C0, and a path of heating coil 33→snubber capacitor C6→ It flows through the path of the resonance capacitor C0. At this time, the snubber capacitor C7 is charged and the snubber capacitor C6 is discharged. As a result, the voltage across the IGBT 39 gently rises, ZVS turns off, and the switching loss can be reduced.

By repeating the above operations from mode 1 to mode 4, a high frequency current flows through the resonance circuit 4 including the resonance heating coil 41 magnetically coupled to the heating coil 33, and this high frequency current flows through the heating coil 33 and the resonance heating coil 41. Generate magnetic flux. This magnetic flux causes an eddy current to flow through the pot 6 placed on the heating coil 33 and the resonance heating coil 41, and the pot 6 itself generates heat by induction heating.

Next, the power control method will be explained. FIG. 14 is a graph showing the relationship between frequency and input power. The vertical axis of the graph indicates input power, and the horizontal axis indicates frequency.
The IH cooking heater uses a resonance phenomenon to apply a large high-frequency current to the heating coil 33 . Therefore, the frequency characteristics of the input power show resonance characteristics. As shown in FIG. 12, since the resistance of iron is large, the resonance Q becomes small and exhibits gentle resonance characteristics. On the other hand, materials with low resistance, such as aluminum and copper, exhibit a steep resonance characteristic because the resonance Q is large. For an iron pan with a small resonance Q, power can be controlled by frequency using the gentle resonance characteristics.
Also, FIG. 15 is a graph showing the relationship between the duty of the IGBT 38 and the input power. The vertical axis of the graph indicates input power, and the horizontal axis indicates duty.
As shown in the graph of FIG. 14, power control by Duty is also possible for an iron pan with a small resonance Q or the like. On the other hand, in the case of steep resonance characteristics such as aluminum, frequency control and duty control are difficult, and power can be controlled by controlling the output voltage of the power supply circuit 2 .

According to the electromagnetic induction heating cooker 1 of the second embodiment described above, even when the herb bridge circuit configuration is adopted, by supplying high-frequency power to the heating coil 33 from the inverter 3, the heating coil A similar current flows through the resonant heating coils 41 to 44 magnetically coupled to 33, so that the pot 6 can be heated.

<<Third embodiment>>
Next, an electromagnetic induction heating cooker 1 according to a third embodiment of the present invention will be described with reference to FIG. Duplicate descriptions of the points in common with the above-described embodiment will be omitted.

FIG. 16 shows the circuit configuration of the electromagnetic induction heating cooker 1 according to the third embodiment.
A switching circuit 31A (voltage resonance inverter) of the present embodiment is configured by connecting a resonance circuit 32 and an IGBT 39 in series. The resonance circuit 32 is configured by connecting a heating coil 33 and a resonance capacitor C0 in parallel. A diode D2 is connected in anti-parallel to the IGBT39.

Next, a normal heating operation will be described using the time chart of FIG. Here, as for the direction of the electric current of the heating coil 33, the direction of the arrow in FIG. 16 is assumed to be positive.
The first time chart shows the current Ic1 flowing through the collector of the IGBT 39 . The second time chart shows the collector-emitter voltage Vc1 of the IGBT 39 . The third time chart shows the current IL flowing through the heating coil 33 .

《Mode 1》
Mode 1 is the period from when the IGBT 39 is turned off until the collector voltage of the IGBT 39 reaches its peak. In mode 1, when the control circuit 50 turns off the IGBT 39, the current flowing through the IGBT 39 is interrupted, and the energy stored in the heating coil 33 causes current to flow through the path between the heating coil 33 and the resonance capacitor C0. At this time, the collector voltage of the IGBT 39 rises sinusoidally, resulting in zero voltage switching (ZVS) turn-on.

《Mode 2》
Mode 2 is the period from the peak of the collector voltage of the IGBT 39 to 0V. In mode 2, when the collector voltage of the IGBT 39 reaches its peak, the current in the heating coil 33 switches from positive to negative and the direction of current is reversed, and the current flows through the path of the resonant capacitor C0 and the heating coil 33 .

《Mode 3》
Mode 3 is the conducting period of the diode D2. In mode 3, when the resonant capacitor C0 is discharged and the collector voltage of the IGBT 39 becomes 0 V, the diode D2 is turned on and current flows through the path of the heating coil 33→filter capacitor C5→diode D2. The gate of the IGBT 39 is turned on during the conduction period of the diode D2.

《Mode 4》
Mode 4 is the energization period of the IGBT 39 . In mode 4, when the heating coil 33 loses energy, the resonant current IL switches from negative to positive. At this time, the gate of the IGBT 39 is already turned on, so current begins to flow. At this time, a ZVS turn-on occurs without switching loss. Current flows through the path of the filter capacitor C5, the heating coil 33, and the IGBT 39 and the path of the commercial power supply 7, the rectifier circuit 21, the inductor L1, the heating coil 33, the IGBT 39, and the rectifier circuit 21.

By repeating the above operations from mode 1 to mode 4, a high frequency current flows through the resonance circuit 4 including the resonance heating coil 41 magnetically coupled to the heating coil 33, and magnetic flux is generated from the heating coil 33 and the resonance heating coil 41. . This magnetic flux causes an eddy current to flow through the pot 6 placed on the heating coil 33 and the resonance heating coil 41, and the pot 6 itself generates heat by induction heating.

FIG. 18 is a graph showing the relationship between frequency and input power. The vertical axis of the graph indicates input power, and the horizontal axis indicates frequency.
This embodiment forms a parallel resonance circuit in which the heating coil 33 and the resonance capacitor C0 are connected in parallel. Therefore, the frequency characteristics shown in FIG. 18 show downwardly convex characteristics. In parallel resonance, the power at the resonance point is the lowest power, and the power can be controlled by lowering the frequency.

According to the electromagnetic induction heating cooker of the first to third embodiments described above, even if the voltage resonance circuit configuration is adopted, by supplying high-frequency power from the inverter 3 to the heating coil 33, A similar current flows through the resonance heating coils 41 to 44 magnetically coupled to the heating coil 33, so that the pot 6 can be heated.

(Modification)
The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Moreover, it is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

Some or all of the above configurations, functions, processing units, processing means, etc. may be realized by hardware such as integrated circuits. Each of the above configurations, functions, etc. may be realized by software by a processor interpreting and executing a program for realizing each function. Information such as programs, tables, and files that implement each function can be stored in recording devices such as memory, hard disks, SSDs (Solid State Drives), or recording media such as flash memory cards and DVDs (Digital Versatile Disks). can.

In each embodiment, the control lines and information lines indicate what is considered necessary for explanation, and not all control lines and information lines are necessarily indicated on the product. In fact, it may be considered that almost all configurations are interconnected.
Modifications of the present invention include, for example, the following (a) to (e).

(a) The magnetic material placed under the heating coil and the resonance heating coil is not limited to ferrite and may be any material.
(b) The magnetic materials placed under the heating coils and the resonance heating coils are not limited to being radially arranged in four directions, front, back, left and right, but may be arranged radially in three, five, or six directions.
(c) The arrangement of the resonance heating coils with respect to the heating coils is not limited to four on the front, back, left, and right when viewed from above. For example, three resonant heating coils may be arranged in a triangular shape centered on the heating coil, five resonant heating coils may be arranged in a pentagonal shape, or six resonant heating coils may be arranged in a hexagonal shape. .
(d) The configuration of the drive circuit connected to the heating coil is not limited to the half-bridge circuit configuration, and may be a full-bridge circuit configuration.
(e) The resonant capacitors connected to the resonant heating coil may have different capacitance values, and the frequency may be selected by the inverter.

1 electromagnetic induction heating cooker 2 power supply circuit (DC power supply)
21 rectifier circuit 22 current detectors 3, 3a to 3c inverter 31 switching circuit 32 resonance circuit (first resonance circuit)
33 Heating coil 34-36 Ferrite (magnetic material)
37 current detector 38, 39 IGBT
4, 4a to 4c resonant circuit (second resonant circuit)
41 to 44 Resonant heating coils 45, 46 Ferrite (magnetic material)
47 Current detector 51 Drive circuit 52 Resonance current detection circuit 53 Control circuit 54 Input power setting unit 55 Input current detection circuit 6 Pot (object to be heated)
7 Commercial power supply L1 Inductors C0, C8 Resonance capacitor (first resonance capacitor)
C1 to C4 Resonant capacitor (Second resonant capacitor)
C5 filter capacitor C6, C7 snubber capacitor

Claims (10)

a heating coil connected to the first resonance capacitor to form a first resonance circuit;
a plurality of resonant heating coils that are magnetically coupled to the heating coil via a magnetic material and that are each connected in series with a second resonant capacitor to form a second resonant circuit;
a DC power supply;
an inverter circuit that is connected to both terminals of the DC power supply, converts a DC voltage applied by the DC power supply into a high-frequency AC voltage, and applies the AC voltage to the first resonance circuit;
a control circuit for controlling the inverter circuit;
and
The presence or absence of an object to be heated on the resonance heating coil increases or decreases the current flowing through the resonance heating coil.
An electromagnetic induction heating cooker characterized by: The heating coil and the resonant heating coil are arranged on the same plane,
The electromagnetic induction heating cooker according to claim 1, characterized in that: The distance between the heating coil and each of the resonant heating coils is narrower than the distance between the heating coil and each of the resonant heating coils and the object to be heated.
The electromagnetic induction heating cooker according to claim 1 or 2 , characterized in that: the magnetic material is disposed immediately below the heating coil and the plurality of resonant heating coils;
The electromagnetic induction heating cooker according to any one of claims 1 to 3 , characterized in that: the spacing between the magnetic material and the heating coil and each of the plurality of resonant heating coils is smaller than the spacing between the heating coil and each of the resonant heating coils;
The electromagnetic induction heating cooker according to claim 4 , characterized in that: a heating coil connected to the first resonance capacitor to form a first resonance circuit;
a plurality of resonant heating coils that are magnetically coupled to the heating coil via a magnetic material and that are each connected in series with a second resonant capacitor to form a second resonant circuit;
a DC power supply;
an inverter circuit that is connected to both terminals of the DC power supply, converts a DC voltage applied by the DC power supply into a high-frequency AC voltage, and applies the AC voltage to the first resonance circuit;
a control circuit for controlling the inverter circuit;
and
The magnetic material is disposed immediately below the heating coil and the plurality of resonant heating coils,
A first magnetic material is radially arranged immediately below the heating coil,
A second magnetic material is radially arranged immediately below the plurality of resonant heating coils, and a portion of the first magnetic material straddles the resonant heating coils.
An electromagnetic induction heating cooker characterized by: A first magnetic material is radially arranged immediately below the heating coil,
A second magnetic material is radially arranged immediately below the plurality of resonant heating coils, and any one of the first magnetic materials is arranged in proximity to the second magnetic material.
The electromagnetic induction heating cooker according to claim 4 , characterized in that: A magnetic material is arranged in a plane directly below the heating coil and directly below the plurality of resonant heating coils.
The electromagnetic induction heating cooker according to claim 4 , characterized in that: The inverter circuit is
a switching circuit in which the upper arm and the lower arm are connected in series;
the first resonant capacitor composed of two capacitors connected in series to both terminals of the DC power supply;
the heating coil;
The electromagnetic induction heating cooker according to any one of claims 1 to 8 , characterized by comprising: The inverter circuit is
the first resonant circuit;
a switching circuit connected to the first resonant circuit;
The electromagnetic induction heating cooker according to any one of claims 1 to 8 , characterized by comprising:

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