JP2019204733A - Electromagnetic induction heating cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently heat a pan in an electromagnetic induction heating cooker even when the mounting position of the pan changes. SOLUTION: An electromagnetic induction heating cooker 1 is magnetically coupled to a heating coil 33 which is connected in series with a resonance capacitor C0 to form a resonance circuit, and is magnetically coupled to the heating coil 33, and resonance capacitors C1 to C4 are respectively connected in series to cause resonance. A plurality of resonance heating coils 41 to 44 forming a circuit, a power supply circuit 2, and a heating coil connected to both terminals of the power supply circuit 2 to convert a DC voltage applied by the power supply circuit 2 into a high-frequency AC voltage. The inverter 3 applied to the inverter 33 and the control circuit 53 for controlling the inverter 3 are provided. [Selection diagram] Figure 1

Description

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

  In recent years, an inverter type electromagnetic induction heating cooker that heats an object to be heated such as a pot without using a fire, that is, a so-called IH cooking heater has been widely used. An IH cooking heater is a device that allows high-frequency current to flow through a heating coil, generates eddy current in a pan made of a material such as iron or stainless steel, which is placed close to the heating coil, and generates heat by the electrical resistance of the pan itself. is there. As described above, the IH cooking heater can be cooked without using fire, and has high safety and comfort in the cooking environment.

In the conventional IH cooking heater, a heating coil is disposed below the glass top plate, and an inverter for supplying a high-frequency current is connected to the heating coil. The pan placed on the top plate is heated using one heating coil.
However, in the method of heating a pan using a single heating coil, only a part of the pan bottom is heated depending on the size and arrangement of the pan, and there is a problem that uneven heating occurs. Then, the induction heating apparatus which heats the pot of various magnitude | sizes and arrangement | positioning appropriately by using a some heating coil is proposed.

  For example, in claim 1 of Patent Document 1, “an inverter circuit that generates and outputs high-frequency power of a predetermined frequency and a magnetic field of a predetermined frequency is generated by the high-frequency power supplied from the inverter circuit, A heating coil for inductively heating an object, and a self-resonant coil installed between the object to be heated and the heating coil, the self-resonant coil comprising a resonance coil and a resonance capacitor, and a magnetic field generated by the heating coil 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, and when the object to be heated is placed at a position deviated from the self-resonant coil, heating is efficiently performed. I can't. Moreover, since the heating coil and the self-resonant coil overlap each other, the distance between the object to be heated and the heating coil is increased, and the heating efficiency is deteriorated due to a decrease in magnetic coupling.
Then, this invention makes it a subject to enable a pot to be heated efficiently, even when the mounting position of a pan changes in an electromagnetic induction heating cooking appliance.

In order to solve the above-described problem, an electromagnetic induction heating cooker according to the present invention is connected to a first resonance capacitor to form a first resonance circuit, and is magnetically coupled via the heating coil and a magnetic material. A plurality of resonant heating coils, each of which is connected in series with a second resonant capacitor, are connected to both terminals of the DC power source and the DC power source, and a DC voltage applied by the DC power source is high frequency. An inverter circuit that converts the AC voltage into the first resonant circuit and a control circuit that controls the inverter circuit.
Other means will be described in the embodiment for carrying out the invention.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where the mounting position of a pan changes in an electromagnetic induction heating cooking appliance, a pan can be efficiently heated.

It is a block diagram of the electromagnetic induction heating cooking appliance in 1st Embodiment. It is a perspective view which shows arrangement | positioning of the heating coil and ferrite of an electromagnetic induction heating cooking appliance. It is a top view which shows arrangement | positioning of the heating coil and ferrite of an electromagnetic induction heating cooking appliance. It is sectional drawing which shows arrangement | positioning of the heating coil and ferrite of an electromagnetic induction heating cooking appliance It is a top view which shows the pan shift state of an electromagnetic induction heating cooking device. It is a graph which shows the frequency characteristic of the impedance of a resonance circuit. It is a perspective view which shows arrangement | positioning of the heating coil and ferrite in the 1st modification of 1st Embodiment. It is sectional drawing which shows arrangement | positioning of the heating coil and ferrite in the 1st modification of 1st Embodiment. It is a perspective view which shows arrangement | positioning of the heating coil and ferrite in the 2nd modification of 1st Embodiment. It is sectional drawing which shows arrangement | positioning of the heating coil and ferrite in the 2nd modification of 1st Embodiment. It is a circuit block diagram of the electromagnetic induction heating cooking appliance in 2nd Embodiment. It is a figure which shows the resistance value of each to-be-heated object, and the inductance ratio with respect to iron. It is an operation | movement waveform of an inverter. It is a frequency characteristic of the input power of an electromagnetic induction heating cooking device. It is a duty characteristic of input electric power of an electromagnetic induction heating cooking device. It is a circuit block diagram of the electromagnetic induction heating cooking appliance in 3rd Embodiment. It is an operation | movement waveform of an electromagnetic induction heating cooking appliance. It is a frequency characteristic of the input power of an electromagnetic induction heating cooking device.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
<< First Embodiment >>
First, the electromagnetic induction heating cooking appliance 1 in the 1st Embodiment of this invention is demonstrated using FIGS.

FIG. 1 is a block diagram of an electromagnetic induction heating cooker according to the first embodiment.
The electromagnetic induction heating cooker 1 according to the first embodiment includes a power supply circuit 2 that functions 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, and input power. A setting unit 54 is provided. The electromagnetic induction heating cooker 1 can heat an object to be heated such as a pan placed on a top plate (not shown) by a plurality of heating coils 33 corresponding to each inverter 3. In addition, since the structure of each inverter 3 is equivalent, below, it demonstrates on behalf of the inverter 3a.

  The inverter 3a 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. The current detector 37 detects a 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 a 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 circuit of the resonance heating coil 44. It is configured as a series circuit of a capacitor C4.

The inverter 3 a is controlled by the control circuit 53, the resonance current detection circuit 52, the input power setting unit 54, and the 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 the user to set input power (thermal power), and outputs a signal corresponding to the set thermal power to the control circuit 53. The control circuit 53 generates a drive signal corresponding to the calculation result output from the resonance current detection circuit 52 and the signal output from the input power setting unit 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 the inverter 3a will be described. In the IH cooking heater, a resonance type inverter is generally used. 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 pan is placed on the heating coil 33, and the characteristic of the resonance load is set. Make it inductive. As a result, the resonance current IL flowing through the resonance circuit 32 is delayed in phase with respect to the output voltage of the switching circuit 31, so that an increase in loss in the switching circuit 31 can be suppressed.

That is, the loss of the switching circuit 31 can be suppressed by controlling the resonance current IL flowing through the resonance circuit 32 so as to be in a lagging phase with respect to the voltage at the output terminal t that is the connection point between the switching circuit 31 and the resonance circuit 32. .
When the pan 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 circuit 32 and the resonance circuit 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. To do.

  However, if power control is performed by changing the conduction period of the switching circuit 31 with the driving frequency fs 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 In some cases, the phase shifts to a phase advance mode in which the phase advances from the output voltage. The phase advance mode causes an increase in the loss of the switching circuit 31 and must be avoided in the resonance type inverter.

  Next, the arrangement | sequence of the some heating coil 33 and the resonance heating coils 41-44 in the electromagnetic induction heating cooking appliance 1 of 1st Embodiment is demonstrated using FIG. 2, FIG. Generally, in the electromagnetic induction heating cooker 1, a heating coil 33 and resonant heating coils 41 to 44 are disposed under a glass top plate (not shown). Here, description will be given by taking as an example the electromagnetic induction heating cooker 1 that heats one pot using the heating coil 33 and the resonance heating coils 41 to 44 built in one inverter 3.

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 and 45 of the electromagnetic induction heating cooker 1.
In the electromagnetic induction heating cooker 1 shown in FIG. 2, resonant heating coils 41 to 44 are arranged on the front, rear, left and right of the heating coil 33 as viewed from above. A glass top plate (not shown) is disposed 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 one-dot chain line.

  The inverter 3 is connected to the heating coil 33. Resonance capacitors C1 to C4 are connected to the resonance heating coils 41 to 44, respectively. Below the heating coil 33, magnetic material ferrite 34 is radially arranged. Below the resonance heating coils 41 to 44, ferrites 45 of magnetic material are arranged radially. These ferrites 34 and 45 effectively induce magnetic flux to the pan 6 and improve the magnetic coupling between the heating coil 33 and the resonance heating coils 41 to 44.

  By adopting a structure in which a portion of the ferrite 34 that is radially disposed immediately below the heating coil 33 is brought 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. The heating efficiency can be improved.

FIG. 4 is a cross-sectional view showing the arrangement of the heating coils 33 and the resonance heating coils 41 to 44 and the ferrites 34 and 45 of the electromagnetic induction heating cooker 1.
The heating coil 33 and the resonance heating coils 41 to 44 are arranged on substantially the same plane. An interval L between the heating coil 33 and the resonance heating coils 41 to 44 is narrower than an interval D between the heating coil 33 and the resonance heating coils 41 to 44 and the pan 6. Thereby, the magnetic coupling degree of the heating coil 33 and the resonance heating coils 41-44 is raised, the electric power transmission efficiency of the resonance heating coils 41-44 from the heating coil 33 improves, and the pan 6 can be heated to a high range.
Further, the distance F between the heating coil 33 and the ferrite 34 is smaller than the distance D between the heating coil 33 and the pan 6 and smaller than the distance L between the heating coil 33 and the resonance heating coils 41 to 44.
Further, the interval F between the resonance heating coils 41 to 44 and the ferrite 45 is narrower than the interval D between the heating coil 33 and the pan 6 and is smaller than the interval L between the heating coil 33 and the resonance heating coils 41 to 44.

FIG. 5 is a top view showing a case where the pan 6 is displaced and placed only on the resonance heating coil 43.
In FIG. 5, the pan 6 is placed only on the resonance heating coil 43. In this case, the resonance frequency of the resonance circuit 32 composed of the heating coil 33 and the resonance capacitor C0 and the resonance circuit composed of the resonance heating coil 43 magnetically coupled to the heating coil 33 and the resonance capacitor C3 are substantially the same frequency. . The control circuit 53 drives the inverter 3a at a frequency slightly higher than the resonance frequency. Thereby, the high frequency current flows from the inverter 3a to the resonance heating coil 43 via the heating coil 33, and the pot 6 can be induction-heated. On the other hand, in the resonance heating coils 41, 42, and 44 where the pan 6 is not placed, the inverter drive frequency and the resonance frequency do not match and no current flows. This phenomenon will be described with reference to FIG.

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

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

  When the inverter 3a having the 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. Thereby, a magnetic flux is generated from the resonance heating coil 43, and the magnetic flux links the pan 6 so that an eddy current flows through the pan 6 and the pan 6 itself generates heat.

On the other hand, since the resonance circuit of the resonance heating coils 41, 42, and 44 where the pan 6 is not placed has the characteristic 2, the impedance at the frequency f1 is Z2. The impedance Z2 of the resonance heating coils 41, 42, and 44 is significantly larger than the impedance Z1 of the resonance heating coil 43. For this reason, almost no current flows through the resonant heating coils 41, 42, 44, and the pot 6 cannot be induction-heated. In addition, since almost no current flows through the resonance heating coils 41, 42, 44, an unnecessary radiation magnetic field can be suppressed.
That is, since a large current can be passed only to the resonance heating coil 43 on which the heating coil 33 and the pan 6 are placed, 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 and placed. For example, consider a case where a large pan that covers the resonance heating coils 41 to 44 is placed at 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. Further, when a small pan having a diameter less than that of the heating coil 33 is placed at the center of the heating coil 33, the resonance circuits of the resonance heating coils 41 to 44 all have the characteristic 2. Therefore, since an electric current hardly flows through these resonance heating coils 41 to 44, an unnecessary radiation magnetic field can be suppressed.

As explained above, according to the electromagnetic induction heating cooker 1 of the present embodiment, when the pan 6 is placed on the resonance heating coils 41 to 44, the power supplied from the inverter 3a is supplied to the heating coil 33 and the ferrite. 34 to the resonance heating coils 41 to 44. Thereby, a high-frequency large current can be passed through the resonance heating coils 41 to 44, and the pot 6 can be induction-heated together with the heating coil 33.
In addition, when the pan 6 is not placed on the resonance heating coils 41 to 44, since the impedance of the resonance circuit increases, almost no current flows through the resonance heating coils 41 to 44. Thereby, an unnecessary radiation magnetic field can be suppressed.

<< First Modification >>
FIG. 7 is a perspective view showing the arrangement of the heating coil 33, the resonance heating coils 41 to 44, and the 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, rear, left and right of the heating coil 33 as viewed from above. A glass top plate (not shown) is disposed 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 one-dot chain line.

The inverter 3 is connected to the heating coil 33. Resonance capacitors C1 to C4 are connected to the resonance heating coils 41 to 44, respectively. Under the heating coil 33, magnetic material ferrite 35 is radially disposed, and straddles the lower portions of the resonance heating coils 41 to 44. Below the resonance heating coils 41 to 44, ferrites 45 are arranged radially together with the ferrites 35. These ferrites 34 and 45 effectively induce magnetic flux to the pan 6 and improve the magnetic coupling between the heating coil 33 and the resonance heating coils 41 to 44.
By adopting a structure in which a part of the ferrite 35 that is radially arranged immediately below the heating coil 33 is straddled under the resonance heating coils 41 to 44, the magnetic coupling with the heating coil 33 is further increased, and the leakage magnetic field is reduced. The heating efficiency can be improved.

FIG. 8 is a cross-sectional view showing the arrangement of the heating coil 33, the resonance heating coils 41 to 44, and the ferrites 35 and 45 in the first modification of the first embodiment.
The heating coil 33 and the resonance heating coils 41 to 44 are arranged on substantially the same plane. An interval L between the heating coil 33 and the resonance heating coils 41 to 44 is narrower than an interval D between the heating coil 33 and the resonance heating coils 41 to 44 and the pan 6. Thereby, the magnetic coupling degree of the heating coil 33 and the resonance heating coils 41-44 is raised, the electric power transmission efficiency of the resonance heating coils 41-44 from the heating coil 33 improves, and the pan 6 can be heated to a high range.

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

<< Second Modification >>
FIG. 9 is a perspective view showing an arrangement of the heating coil 33, the resonance heating coils 41 to 44, and the 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, rear, left and right of the heating coil 33 as viewed from above. A glass top plate (not shown) is disposed 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 one-dot chain line.

  The inverter 3 is connected to the heating coil 33. Resonance capacitors C1 to C4 are connected to the resonance heating coils 41 to 44, respectively. A ferrite 36 made of a magnetic material is disposed below the heating coil 33 and straddles the lower portions of the resonance heating coils 41 to 44. A ferrite 36 is disposed below the resonance heating coils 41 to 44. The ferrite 36 effectively induces the magnetic flux to the pan 6 and improves the magnetic coupling between the heating coil 33 and the resonance heating coils 41 to 44.

  By adopting a structure in which the ferrite 36 arranged radially immediately below the heating coil 33 is straddled across the lower portions of the resonance heating coils 41 to 44, the magnetic coupling with the heating coil 33 is further increased, the leakage magnetic field is reduced, Heating efficiency can be improved.

FIG. 10 is a cross-sectional view showing the heating coil 33, the resonance heating coils 41 to 44, and the ferrite 36 in the second modification of the first embodiment.
The heating coil 33 and the resonance heating coils 41 to 44 are arranged on substantially the same plane. An interval L between the heating coil 33 and the resonance heating coils 41 to 44 is narrower than an interval D between the heating coil 33 and the resonance heating coils 41 to 44 and the pan 6. Thereby, the magnetic coupling degree of the heating coil 33 and the resonance heating coils 41-44 is raised, the electric power transmission efficiency of the resonance heating coils 41-44 from the heating coil 33 improves, and the pan 6 can be heated to a high range.

Further, the interval F between the heating coil 33 and the ferrite 36 is narrower than the interval D between the heating coil 33 and the pan 6 and is smaller than the interval L between the heating coil 33 and the resonance heating coils 41 to 44.
Further, the interval F between the resonance heating coils 41 to 44 and the ferrite 36 is narrower than the interval D between the heating coil 33 and the pan 6 and is smaller than the interval L between the heating coil 33 and the resonance heating coils 41 to 44.

<< Second Embodiment >>
Next, the electromagnetic induction heating cooker 1 in the 2nd Embodiment of this invention which employ | adopted the herb bridge circuit structure for the switching circuit 31 is demonstrated using FIGS. 11-15. In addition, duplication description is abbreviate | omitted in common with 1st Embodiment.

  FIG. 11 is a circuit configuration of the electromagnetic induction heating cooker 1 in the second embodiment. Similarly to the first embodiment, the electromagnetic induction heating cooker 1 of this embodiment includes three inverters 3a to 3c, but the illustration of the inverters 3b and 3c is omitted.

  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. A rectifier circuit 21 for rectifying the AC voltage, an inductor L1, and a filter 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 IGBTs 38 and IGBTs 39, which are power semiconductor switching elements, in series. Diodes D1 and D2 are respectively connected in parallel to the IGBTs 38 and 39 in the reverse direction. The cathode terminal of the diode D1 is connected to the collector terminal of the IGBT 38, and the anode terminal of the diode D1 is connected to the emitter terminal of the IGBT 38. The cathode terminal of the diode D2 is connected to the collector terminal of the IGBT 39, and the anode terminal of the diode D2 is connected to the emitter terminal of the IGBT 39.

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

  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. The resonance circuit 32 of the second embodiment includes a heating coil 33 and resonance capacitors C0 and C8. Here, the direction flowing from the output terminal t toward the heating coil 33 is the positive direction of the resonance current IL.

  The current detector 37 detects a 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. The current detector 22 detects a current input from the commercial power supply 7. The input current detection circuit 55 converts the output signal level of the current detector 37 into a signal suitable for the input level of the 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. The object to be heated is distinguished from a magnetic material and a non-magnetic material. As a method of distinguishing, energization is performed with low power (about 300 W) before heating. The current value of the resonance current IL or IGBT 38, 39 at that time is detected, and the material of the object to be heated is determined based on the current value. When the current value is small, it is determined that the object is a magnetic material such as iron, and when the current value is large, it is determined as a non-magnetic material such as nonmagnetic stainless steel, aluminum, or copper.

FIG. 12 shows the resistance value of each object to be heated at a frequency of 20 kHz.
Nonmagnetic stainless steel has a resistance of about 1/3 that of iron. In aluminum, the resistance value is about 1/20 that of iron. Copper has a resistance value of about 1/25 that of iron.

In addition, the control circuit 53 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 in accordance with the signal from the input power setting unit 54. The material detection needs to be performed in a short time with low power to prevent the occurrence of overcurrent and overvoltage.
Also, as shown in FIG. 11, the current Ic1 is a current that flows through the upper arm of the switching circuit 31. The current Ic2 is a current flowing through the lower arm of the switching circuit 31. The resonance current IL is a current that flows through the heating coil 33. The resonance current ILr is a current that flows through the resonance heating coil 41. The voltage Vc1 is a voltage between the collector terminal and the emitter terminal of the IGBT 38 of the upper arm. The voltage Vc2 is a voltage between the collector terminal and the emitter terminal of the IGBT 39 of the lower arm. The voltage Vc3 is a resonance voltage of the resonance capacitor C0. The resonant voltage of the resonant capacitor C0 is assumed to be a voltage Vcr. The power supply voltage of the inverter 3 is set to voltage Vp.

Next, the 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 part of the time chart shows a drive signal for the high-side IGBT 38. The second part of the time chart shows a drive signal for the low-side IGBT 39.
The third part of the time chart shows the current Ic1 flowing through the collector of the high-side IGBT 38. The fourth part of the time chart shows the collector-emitter voltage Vc1 of the high-side IGBT 38.

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

In any mode, the drive signals of the IGBTs 38 and 39 are provided with a dead time period, and the IGBTs 38 and 39 are driven in a complementary manner.
Hereinafter, detailed operations in modes 1 to 4 will be described.

<Mode 1>
Mode 1 starts at the timing when the current Ic1 of the IGBT 38 becomes 0A. Although no current flows through the IGBT 38 at the start of mode 1, the IGBT 38 is already turned on, so that 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 0 V, ZVZCS (Zero Voltage Zero Current Switching) in which no loss occurs in the IGBT 38 is turned on.

<Mode 2>
When the control circuit 53 shuts off the IGBT 38, the mode 2 is entered. In mode 2, the resonance current IL is changed from the power supply circuit 2 → the snubber capacitor C6 → the heating coil 33 → the resonance capacitor C0, the heating coil 33 → the resonance capacitor C0 → the path of the snubber capacitor C7, and the heating coil 33 → the resonance capacitor C0 → It flows in the path of 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 between both ends of the IGBT 38 gradually rises, ZVS (Zero Voltage Switching) is turned off, and the 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 po), the voltage Vc2 of the snubber capacitor C7 becomes 0V, 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 during a period in which a current flows through the diode D2.

<Mode 3>
Mode 3 starts from 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 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 0 V, the IGBT 39 is turned on so that no loss occurs.

<Mode 4>
When the control circuit 53 shuts off the IGBT 39, the mode 4 is entered. In mode 4, the resonance current IL is changed from the heating coil 33 → the snubber capacitor C7 → the power supply circuit 2 → the resonance capacitor C0, the heating coil 33 → the snubber capacitor C7 → the resonance capacitor C0, and the heating coil 33 → the snubber capacitor C6 → It flows in the path of the resonant 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 rises gently, ZVS turn-off occurs, and switching loss can be reduced.

  By repeating the operations from mode 1 to mode 4 described above, 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 into the heating coil 33 and the resonance heating coil 41. Generate magnetic flux. This magnetic flux causes an eddy current to flow through the pan 6 disposed on the heating coil 33 and the resonance heating coil 41, and the pan 6 itself generates heat by induction heating.

Next, the power control method will be described. FIG. 14 is a graph showing the relationship between frequency and input power. The vertical axis of the graph represents input power, and the horizontal axis represents frequency.
The IH cooking heater applies a high-frequency large current to the heating coil 33 using a resonance phenomenon. For this reason, the frequency characteristic of input power shows a resonance characteristic. As shown in FIG. 12, since the resistance of iron is large, the resonance Q is small, and a gentle resonance characteristic is exhibited. On the other hand, a low-resistance material such as aluminum or copper exhibits a sharp resonance characteristic because the resonance Q is large. An iron pan or the like having a small resonance Q can control power by frequency using a gentle resonance characteristic.
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 represents input power, and the horizontal axis represents Duty.
As shown in the graph of FIG. 14, in an iron pan or the like having a small resonance Q, power control by duty is also possible. On the other hand, in the case of steep resonance characteristics such as aluminum, it is difficult to perform frequency control or duty control, 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, the heating coil can be obtained by supplying high frequency power from the inverter 3 to the heating coil 33. Since the same electric current flows also in the resonance heating coils 41 to 44 magnetically coupled to 33, the pan 6 can be heated.

<< Third Embodiment >>
Next, the electromagnetic induction heating cooking appliance 1 in the 3rd Embodiment of this invention is demonstrated using FIG. In addition, duplication description is abbreviate | omitted in common with the Example mentioned above.

FIG. 16 is a circuit configuration of the electromagnetic induction heating cooker 1 in the third embodiment.
The 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. Further, a diode D2 is connected to the IGBT 39 in antiparallel.

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

<Mode 1>
Mode 1 is a period from when the IGBT 39 is turned off until the collector voltage of the IGBT 39 reaches a peak. In mode 1, when the control circuit 50 turns off the IGBT 39, the current flowing in the IGBT 39 is interrupted, and the current flows in the path between the heating coil 33 and the resonance capacitor C0 by the energy stored in the heating coil 33. At this time, the collector voltage of the IGBT 39 rises in a sine wave shape, and zero voltage switching (hereinafter referred to as ZVS) is turned on.

<Mode 2>
Mode 2 is a 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 a peak, the current of the heating coil 33 is switched from positive to negative, the direction of the current is reversed, and the current flows through the path of the resonance capacitor C0 and the heating coil 33.

<Mode 3>
Mode 3 is an energization period of the diode D2. In mode 3, when the resonant capacitor C0 is discharged and the collector voltage of the IGBT 39 becomes 0V, the diode D2 is turned on, and a 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 energization period of the diode D2.

<Mode 4>
Mode 4 is an energization period of the IGBT 39. In mode 4, when the energy of the heating coil 33 runs out, the resonance current IL switches from negative to positive. At this time, the current starts to flow in the IGBT 39 because the gate is already turned on. At this time, the ZVS turn-on with no switching loss occurs. The 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 source 7, the rectifier circuit 21, the inductor L1, the heating coil 33, the IGBT 39, and the rectifier circuit 21.

  By repeating the operations from mode 1 to mode 4 described above, 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 pan 6 disposed on the heating coil 33 and the resonance heating coil 41, and the pan 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 represents input power, and the horizontal axis represents frequency.
The present embodiment is a parallel resonance circuit in which the heating coil 33 and the resonance capacitor C0 are connected in parallel. Therefore, the frequency characteristic shown in FIG. 18 shows a characteristic that protrudes downward. 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 when the voltage resonance circuit configuration is adopted, by supplying high frequency power from the inverter 3 to the heating coil 33, Since the same current flows also in the resonance heating coils 41 to 44 magnetically coupled to the heating coil 33, the pan 6 can be heated.

(Modification)
The present invention is not limited to the embodiments described above, and includes various modifications. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  A part or all of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware such as an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by a processor interpreting and executing a program that realizes each function. Information such as programs, tables, and files for realizing each function may be stored in a recording device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as a flash memory card or a DVD (Digital Versatile Disk). it can.

In each embodiment, the control lines and information lines indicate what is considered necessary for the explanation, and not all control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.
Examples of modifications of the present invention include the following (a) to (e).

(A) The magnetic material disposed under the heating coil or the resonance heating coil is not limited to ferrite, and may be any material.
(B) The magnetic material disposed under the heating coil or the resonance heating coil is not limited to the radial direction in the front, rear, left, and right directions, and may be disposed radially in three directions, five directions, six directions, or the like.
(C) The arrangement of the resonance heating coil with respect to the heating coil is not limited to four on the front, rear, left and right as viewed from above. For example, three resonance heating coils may be arranged in a triangular shape centering on the heating coil, five resonance heating coils may be arranged in a pentagon shape, or six resonance 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 frequency of the resonance capacitor connected to the resonance heating coil may be set to a different value, and the frequency may be selectively set by an inverter.

1 Electromagnetic induction cooking device 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 coils 34 to 36 Ferrite (magnetic material)
37 Current detector 38, 39 IGBT
4, 4a to 4c resonance circuit (second resonance circuit)
41 to 44 Resonant heating coils 45, 46 Ferrite (magnetic material)
47 Current detector 51 Drive circuit 52 Resonant current detection circuit 53 Control circuit 54 Input power setting unit 55 Input current detection circuit 6 Pan (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 (11)

A heating coil connected to the first resonant capacitor to form a first resonant circuit;
A plurality of resonant heating coils that are magnetically coupled to the heating coil via a magnetic material, each of which has a second resonant capacitor connected in series to form a second resonant circuit;
DC power supply,
An inverter circuit connected to both terminals of the DC power source, converting a DC voltage applied by the DC power source into a high frequency AC voltage, and applying the high frequency AC voltage to the first resonance circuit;
A control circuit for controlling the inverter circuit;
An electromagnetic induction heating cooker comprising: The heating coil and the resonance heating coil are arranged on the same plane.
The electromagnetic induction heating cooker according to claim 1. Depending on the presence or absence of the object to be heated on the resonance heating coil, the current flowing through the resonance heating coil increases or decreases
The electromagnetic induction heating cooker according to claim 1 or 2, characterized in that. An interval between the heating coil and each resonance heating coil is narrower than an interval between the heating coil and each resonance heating coil and an object to be heated.
The electromagnetic induction heating cooker according to any one of claims 1 to 3, wherein 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 4, wherein the cooking device is an electromagnetic induction heating cooker. An interval between the magnetic material and the heating coil and each of the plurality of resonance heating coils is narrower than an interval between the heating coil and each of the resonance heating coils.
The electromagnetic induction heating cooker according to claim 5. Directly below the heating coil, the first magnetic material is arranged radially,
Immediately below the plurality of resonance heating coils, the second magnetic material is arranged radially, and a part of the first magnetic material straddles the resonance heating coil.
The electromagnetic induction heating cooker according to claim 5. Directly below the heating coil, the first magnetic material is arranged radially,
The second magnetic material is arranged radially immediately below the plurality of resonance heating coils, and any one of the first magnetic materials is arranged close to the second magnetic material.
The electromagnetic induction heating cooker according to claim 5. A magnetic material is arranged in a planar shape directly below the heating coil and directly below the plurality of resonant heating coils.
The electromagnetic induction heating cooker according to claim 5. 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;
An electromagnetic induction heating cooker according to any one of claims 1 to 9, characterized by comprising: The inverter circuit is
The first resonant circuit;
A switching circuit connected to the first resonant circuit;
An electromagnetic induction heating cooker according to any one of claims 1 to 9, characterized by comprising:

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