JP6913048B2 - Electromagnetic induction heating device - Google Patents

Description

The present invention relates to an inverter type electromagnetic induction heating device that supplies desired electric power to an object to be heated to perform induction heating.

In recent years, an inverter type electromagnetic induction heating device that induces and heats a metal pot without using fire has been widely used. In the electromagnetic induction heating device, a high-frequency current is passed through a heating coil, an eddy current is generated in a pot bottom of a metal pot arranged close to the heating coil, and heat is generated by the electric resistance of the pot bottom itself. As a conventional example of an electromagnetic induction heating device, there is an induction heating cooker as disclosed in Patent Document 1.

In the method of Patent Document 1, as shown in FIG. 1 and the like of the same document, a high-frequency current is passed through a series resonance circuit of a heating coil and a resonance capacitor by a half-bridge type inverter that turns on and off two switching elements, and a metal pot is used. Is induced and heated.

Japanese Unexamined Patent Publication No. 2001-126853

In Patent Document 1, as will be described later with reference to FIG. 2B, a current having the same value as that of the heating coil flows through the conducting switching element. Therefore, for example, when a large thermal power is to be used, or when a large current is passed through the heating coil to heat a metal pot having a low resistance, the same large current also flows through the switching element, so that the switching element is conductive. There was a problem that it caused an increase in loss and turn-off loss.

An object of the present invention is to address the above problems, and in particular, to provide an inverter type electromagnetic induction heating device capable of efficiently supplying desired electric power by reducing the current flowing through the switching element regardless of the material of the metal pot. It is to be.

In order to achieve the above object, the electromagnetic induction heating device of the present invention has a DC power supply that supplies a DC voltage, an upper and lower arms connected between the positive and negative electrodes of the DC power supply, and a heating coil that induces and heats an object to be heated. A high-frequency current is supplied to the resonance load circuit including the heating coil by the inverter using the upper and lower arms, and the resonance load circuit can form the first to third resonance load circuits. The resonance load circuit of is a series of a first heating coil and a first resonance capacitor, and a second resonance capacitor connected to the series, and the second resonance load circuit is a second. of the heating coil second resonance capacitors has been connected in series, the third resonance load circuit state, and are not the second heating coil and the series body and connected in series, further A third resonance capacitor is provided in parallel with the first resonance capacitor, and a relay for disconnecting the third resonance capacitor from the first resonance capacitor. The relay is used when the object to be heated is a non-magnetic material. the turned off state, the object to be heated is ing the on state when the magnetic body.

According to the present invention, a desired large current can be passed through the heating coil while reducing the current flowing through the switching element and significantly reducing the conduction loss and turn-off loss at the switching element, so that the inverter circuit can be miniaturized. It is possible to efficiently supply the desired electric power to the metal pot.

The circuit block diagram of the electromagnetic induction heating apparatus of Example 1. FIG. The operating waveform of the electromagnetic induction heating device of FIG. Operating waveform of a conventional electromagnetic induction heating device. The explanatory view of the current path flowing through the resonance load circuit of FIG. The explanatory view of the current path flowing through the resonance load circuit of FIG. The explanatory view of the current path flowing through the resonance load circuit of FIG. The explanatory view of the current path flowing through the resonance load circuit of FIG. The circuit block diagram of the electromagnetic induction heating apparatus of Example 2. FIG. The operating waveform of the electromagnetic induction heating device of FIG. The circuit block diagram of the electromagnetic induction heating apparatus of Example 3. FIG. The circuit block diagram of the electromagnetic induction heating apparatus of Example 4. FIG. The circuit block diagram of the electromagnetic induction heating apparatus of Example 5. The operating waveform of the electromagnetic induction heating device of FIG. The operating waveform of the electromagnetic induction heating device of FIG. The heating coil plan view and the cross-sectional oblique view of the electromagnetic induction heating apparatus of Example 6. The heating coil plan view and the cross-sectional oblique view of the electromagnetic induction heating device of Example 7. The heating coil plan view and the cross-sectional oblique view of the electromagnetic induction heating apparatus of Example 8.

Hereinafter, examples of the present invention will be described with reference to the drawings. In each figure, those having the same reference number indicate the same constituent requirements or constituent requirements having similar functions, and duplicate explanations are omitted as appropriate.

FIG. 1 is a circuit configuration diagram of the electromagnetic induction heating device of the first embodiment. In FIG. 1, the DC power supply 1 is a power supply that rectifies an AC voltage supplied from a commercial AC power supply (not shown) and outputs a DC voltage. An upper and lower arm 3 in which power semiconductor switching elements (hereinafter, simply referred to as "switching elements") 5a and 5b are connected in series is connected between the positive electrode and the negative electrode of the DC power supply 1.

Diodes 6a and 6b are connected in parallel to the switching elements 5a and 5b, respectively, and snubber capacitors 7a and 7b are connected in parallel to the switching elements 5a and 5b, respectively. The snubber capacitors 7a and 7b are charged or discharged by the breaking current at the time of turn-off of the switching element 5a or 5b, and the change in the voltage applied to both switching elements is reduced to suppress the turn-off loss.

The first resonance in which the second resonance capacitor 22 is connected in parallel to the series of the first heating coil 11 and the first resonance capacitor 12 between the output terminal of the upper and lower arms 3 and the negative electrode of the DC power supply 1. A series circuit of the load circuit 70 and the second heating coil 21 is connected. Here, the second heating coil 21 and the second resonance capacitor 22 constitute the second resonance load circuit 80, and the second heating coil 21, the first heating coil 11, and the first resonance capacitor 12 are the first. It constitutes three resonance load circuits 90.

The difference from Patent Document 1 is that in the present embodiment, the second heating coil 21 and the second resonance capacitor 22 are added, and the second heating coil 21 has a plurality of roles as well as the role of the heating coil. It is a component of the resonant load circuit. That is, a major feature of this embodiment is that the heating coil 21 also serves as a heating coil and a composite resonance inductor. The heating coil 11 and the first resonance capacitor 12 may be replaced with each other, or the first resonance load circuit 70 and the second heating coil 21 may be replaced with each other. Further, the first resonance load circuit 70 and the second heating coil 21 may be connected between the output terminals of the upper and lower arms 3 and the positive electrodes of the DC power supply 1.

FIG. 2A is an operation waveform for one cycle of the switching frequency in this embodiment. Further, FIG. 2B shows the operation waveform of the electromagnetic induction heating device of Patent Document 1 which does not have the second heating coil 21 and the second resonance capacitor 22 as a comparative example for explaining the effect of this embodiment. .. The waveforms in the figure are, from the top, the gate signals v (5a) and v (5b) of the switching element, the upper and lower arm output voltages v (AB), the currents i (11) and i (21) of the heating coil, and the elements. The currents ic (5a), ic (5b), id (6a), id (6b), and the voltage v (22) of the resonance capacitor.

In the circuit configuration of Patent Document 1 in which the switching element and the heating coil are directly connected (see FIG. 1 of Patent Document 1), the coil current i (11) of FIG. 2B is compared with the element currents ic (5a) and ic (5b). As can be seen from the above, since the current of the switching element in the ON state flows to the heating coil as it is, the current amplitudes of the switching element and the heating coil have the same value.

On the other hand, as shown in FIG. 2A, when the circuit configuration of this embodiment is applied, the amplitudes of the currents ic (5a) and ic (5b) flowing in the switching element are the currents i (11) flowing in the heating coil 11. It is smaller than that of FIG. 2B to which the first embodiment is not applied. As described above, in the first embodiment, the second resonance load circuit 80 including the second heating coil 21 and the second resonance capacitor 22 is provided, so that the second resonance capacitor 22 is v. By generating the resonance voltage as in (22) and using this resonance voltage, it is possible to pass a large current through the first resonance load circuit 70.

3A to 3D show an example of the current path flowing through the first heating coil 11 and the second heating coil 21 in this embodiment. By alternately turning on and off the switching elements 5a and 5b, the current path is as shown in FIGS. 3A and 3B when a current in the right direction is flowing through the second heating coil 21, and when a current is flowing in the left direction. The current path is as shown in FIGS. 3C and 3D. The current flowing through the resonance load circuit is the equivalent inductance due to the coupling between the heating coil 21 and the metal pot and the resonance current of the resonance capacitor 22, and the equivalent inductance due to the coupling between the heating coil 11 and the metal pot and the resonance capacitors 12, 22. There is a resonance current of the above, an equivalent inductance due to the coupling of the heating coils 11 and 12 and the metal pot, and a resonance current of the resonance capacitor 12. In this embodiment, the resonance constants of each resonant load circuit are set so that the current of the heating coil 11 has a delayed phase from the output voltage of the upper and lower arms. As a result, when each switching element turns on, switching can be performed while the voltage of the switching element is zero volt, and no turn-on loss occurs. The output power can be adjusted by varying the switching frequency of the upper and lower arms 3 or the DC voltage of the DC power supply 1.

According to the electromagnetic induction heating device of the present embodiment described above, the current flowing through the switching element can be reduced by the effect of the second heating coil 21 and the second resonance capacitor 22, and the conduction loss and the turn-off loss can be significantly reduced. Since it can be reduced, the inverter circuit can be miniaturized, and the desired electric power can be efficiently supplied to the metal pot.

FIG. 4 is a circuit configuration diagram of the electromagnetic induction heating device of the second embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the series circuit of the third resonance capacitor 13 and the relay 20 is connected in parallel with the first resonance capacitor 12.

Here, since the heating coils 11 and 21 and the metal pot (not shown) which is the object to be heated are magnetically coupled, when the metal pot is converted into an equivalent circuit viewed from the heating coils 11 and 21 side, it is made of metal. The equivalent resistance of the pot and the equivalent inductance are connected in series. The equivalent resistance and equivalent inductance differ depending on the material of the metal pot. In the case of non-magnetic materials such as low-resistance copper and aluminum, both the equivalent resistance and equivalent inductance become smaller, and in the case of high-resistance iron and other magnetic materials, whichever Also grows.

Here, since the low-resistance non-magnetic material has a small equivalent resistance, it is necessary to pass a large current in order to obtain a desired output. The skin resistance of the object to be heated has a characteristic of being proportional to the square root of the frequency, and it is effective to increase the frequency when heating the object to be heated with low resistance. Therefore, the capacitance of the first resonant capacitor 12 is set so that the inverter can be driven at a frequency of, for example, about 90 kHz.

On the other hand, when the object to be heated heats a magnetic material having high resistance such as an iron pan, it is difficult for current to flow through the heating coils 11 and 21 because the equivalent resistance is large. Further, in the case of copper and aluminum mentioned above, since the resistance is small, the frequency of the inverter is increased to about 90 kHz to increase the skin resistance, but in the case of iron, the resistance is originally large, so the frequency is rather lowered, for example, the frequency of about 40 kHz. It is desirable to drive with. Therefore, in this embodiment, when the object to be heated heats a high-resistance magnetic material such as an iron pan, the relay 20 is turned on and the third resonance capacitor 13 is connected in parallel to the first resonance capacitor 12. This makes it possible to lower the resonance frequencies of the resonance load circuits 70 and 90.

FIG. 5 is an operation waveform for one cycle of the switching frequency when the relay 20 is turned on. The waveforms in the figure are, from the top, the gate signals v (5a) and v (5b) of the switching element, the upper and lower arm output voltages v (AB), the currents i (11) and i (21) of the heating coil, and the elements. Currents ic (5a), ic (5b), id (6a), id (6b), voltage v (22) of the resonance capacitor, and drive signal v (20) of the relay.

As shown in FIG. 5, even when the resonance frequencies of the resonance load circuits 70 and 90 are lowered with the relay 20 turned on and the frequency of the inverter is lowered, the currents ic (5a) and ic (5b) flowing through the switching element The amplitude is smaller than the current i (11) flowing through the heating coil 11.

Similar to FIG. 1 of the above-described first embodiment, in this embodiment as well, by providing the second resonance load circuit 80 composed of the second heating coil 21 and the second resonance capacitor 22, the second resonance capacitor is provided. By generating a resonance voltage such as v (22) in 22 and utilizing this resonance voltage, it is possible to pass a large current through the first resonance load circuit 70.

As described above, in this embodiment, the same effect as that of the first embodiment can be obtained, and the capacitance of the resonance capacitors of the resonance load circuits 70 and 90 can be switched by switching the relay 20. Therefore, the setting range of the drive frequency of the inverter can be widened, and heating can be performed at an optimum frequency according to the material of the object to be heated.

FIG. 6 is a circuit configuration diagram of the electromagnetic induction heating device of the third embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, in addition to the first resonance capacitor 12 and the second resonance capacitor 22 of the first embodiment, a fourth resonance capacitor 14 and a fifth resonance between their connection points and the positive electrode of the DC power supply 1 The capacitor 24 is connected.

As described above, by further providing the fourth resonance capacitor 14 and the fifth resonance capacitor 24, the ripple current due to the switching frequency flowing through the DC power supply 1 can be reduced as compared with the configuration of the first embodiment.

FIG. 7 is a circuit configuration diagram of the electromagnetic induction heating device of the fourth embodiment. The same parts as those in FIG. 6 are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the series circuit of the third resonance capacitor 13 and the relay 20 is connected in parallel with the first resonance capacitor 12.

According to the configuration of the present embodiment, in addition to the effect obtained by the configuration of the third embodiment, the effect obtained by the configuration of the second embodiment is added, and the setting range of the drive frequency of the inverter can be expanded, and the material of the object to be heated can be expanded. It can be heated at the optimum frequency according to the above.

FIG. 8 is a circuit configuration diagram of the electromagnetic induction heating device of the fifth embodiment. The same parts as those in FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the second upper and lower arms 4 to which the switching elements 5c and 5d are connected in series are connected between the positive electrode and the negative electrode of the DC power supply 1, and the output terminals of the first upper and lower arms 3 are connected. And the resonance load circuits 70, 80, 90 are connected between the output terminals of the second upper and lower arms 4.

Diodes 6c and 6d are connected in parallel to the switching elements 5c and 5d, respectively, and snubber capacitors 7c and 7d are connected in parallel to the switching elements 5c and 5d, respectively. The snubber capacitors 7c and 7d play the same role as the snubber capacitors 7a and 7b described above, and are charged or discharged by the breaking current at the time of turn-off of the switching element 5c or 5d, and the change in the voltage applied to both switching elements is changed. The turn-off loss is suppressed by reducing the amount. In the following, using the operation waveforms of the switching frequency of one cycle shown in FIGS. 9 and 10, the half-bridge circuit method (FIG. 9) used when heating a non-magnetic material such as an aluminum pan and the operation waveform when heating a magnetic material such as an iron pan are used. The difference between the full bridge circuit system (FIG. 10) will be described.

When the object to be heated is a non-magnetic material such as a copper pot or an aluminum pot, the metal pot is induced and heated using a half-bridge circuit type inverter. Specifically, as shown in FIG. 9, the relay 20 is turned off, the switching elements 5a and 5b of the first upper and lower arms 3 are alternately turned on and off, and the switching elements 5c of the second upper and lower arms 4 are always off. performing heating in inverter SEPP (S ingle E nded P ush- P ull) scheme that regularly on the switching element 5d. The difference from the operating waveform shown in FIG. 2A is that the positive current of the heating coil 21 flows through the switching element 5d and the negative current flows through the diode 6d. The switching element 5c of the second upper and lower arms 4 may be always on, and the switching element 5d may be always off. In that case, the positive current of the heating coil 21 flows through the diode 6c, and the negative current flows through the switching element 5c.

As described above, since the low resistance non-magnetic material has a small equivalent resistance, it is necessary to pass a large current in order to obtain a desired output. The skin resistance of the object to be heated has a characteristic of being proportional to the square root of the frequency, and when heating a low-resistance object to be heated such as copper or aluminum, it is effective to increase the frequency. Therefore, the capacitance of the first resonance capacitor 12 is set so that the first upper and lower arms 3 can be driven at a frequency of, for example, about 90 kHz.

On the other hand, when the object to be heated is a magnetic material such as an iron pan, the metal pan is induced and heated by using a full bridge circuit type inverter. Specifically, as shown in FIG. 10, the relay 20 is turned on, the switching elements 5a and 5b of the first upper and lower arms 3 are alternately turned on and off, and the switching elements 5c and 5d of the second upper and lower arms 4 are alternately turned on and off. It is turned on and off and heated by a full bridge type inverter.

As described above, since the high resistance magnetic material has a large equivalent resistance, it is difficult for current to flow through the heating coils 11 and 21. Therefore, by switching to the full bridge circuit method, the output voltage of the inverter, that is, the output voltage of the two upper and lower arms is doubled as shown in v (AB) of FIG. 13 to obtain the desired output. be able to. In the case of copper and aluminum mentioned above, the frequency of the inverter was increased to about 90 kHz to increase the skin resistance because the resistance was small, but in the case of iron, the resistance was originally large, so for example, the first upper and lower arms 3 at a frequency of about 40 kHz, It is desirable to drive the second upper and lower arm 4. Therefore, the capacitance of the third resonant capacitor 13 is set so that the combined capacitance of the first resonant capacitor 12 and the third resonant capacitor 13 has a driving frequency of about 40 kHz.

The output power can be adjusted by varying the switching frequencies of the upper and lower arms 3 and 4 or the DC voltage of the DC power supply 1. Further, in the present embodiment, the output power can be adjusted by the phase difference control between the upper and lower arms 3 and the upper and lower arms 4, so that the controllability of the power adjustment is improved.

As described above, in this embodiment, the full bridge circuit system and the half bridge circuit system can be switched by switching the drive conditions of the upper and lower arms 3 and 4, and the resonance capacitors of the resonance load circuits 70 and 90 can be switched by switching the relay 20. Capacity can be switched. Therefore, the output voltage range of the inverter and the setting range of the drive frequency can be widened, and heating can be performed at the optimum inverter voltage and frequency according to the material of the object to be heated.

FIG. 11 is a plan view of the heating coil of the electromagnetic induction heating device of the sixth embodiment and a cross-sectional oblique view between the abs shown on the plan view. It should be noted that the common points with the above-described embodiment are omitted from the duplicate description.

In FIG. 11, the first and second heating coils 11 and 21 are arranged so as to be concentric circles on the inner side and the outer side on substantially the same plane, respectively. The heating coils 11 and 21 have a structure in which litz wires having low high-frequency resistance are wound concentrically, and are represented as a half-moon-shaped mass in the cross-sectional oblique view. U-shaped magnetic materials arranged radially at the same angle from the center of the coil are provided on the lower surfaces of the heating coils 11 and 21. Here, 12 magnetic materials 51a to 51l are arranged every 30 degrees. These magnetic materials suppress the leakage magnetic flux with respect to the lower surface and the side surface direction of the heating coils 11 and 21, and induce the magnetic flux toward the upper surface direction of the heating coils 11 and 21, that is, to the pan which is the object to be heated.

In FIG. 11, the first heating coil 11 through which a large current flows is arranged inside, and the second heating coil 21 through which a small current flows is arranged outside, but it is also possible to arrange them in reverse. However, by arranging the first heating coil 11 through which a large current flows as in this embodiment, it is possible to efficiently heat a metal pot having a small outer diameter. Further, as shown in FIG. 2A, by arranging the second heating coil 21 through which a small current flows on the outside, the effect of reducing the magnetic field leaking to other than the pan can be obtained.

In FIG. 11 of Example 6, although the current values flowing through the heating coil 11 and the heating coil 21 are significantly different as shown in FIG. 2A, since there is a phase difference between the currents, the heating coil 11 is placed on the magnetic bodies 51a to 51l. When there are 21 and 21, there arises a problem that the magnetic fields created by the heating coils 11 and 21 act in a direction of canceling each other out. Therefore, the heating coil of this embodiment for solving this problem will be described. It should be noted that the common points with the above-described embodiment are omitted from the duplicate description.

FIG. 12 is a plan view of the heating coil of the electromagnetic induction heating device of the seventh embodiment and a cross-sectional oblique view between the abs shown on the plan view. The difference from FIG. 11 of Example 6 is that the heating coils 11 and 21 are provided with separate and independent magnetic bodies 51a to 51l and 71a to 71l in order to suppress magnetic coupling. ..

The gap between the two coils should be wide to suppress the magnetic coupling between the coils, but to increase the number of turns of each heating coil and reduce the current with a limited outer diameter dimension, narrow the gap between the coils. There is a need. Therefore, in this embodiment, the inner magnetic bodies 51a to 51l are arranged at every 30 degree angle, and the outer magnetic bodies 71a to 71l are arranged so as to be offset by 15 degrees with respect to the inner magnetic bodies 51a to 51l.

As a result, the outer rising portion of the magnetic bodies 51a to 51l and the inner rising portion of the magnetic bodies 71a to 71l are located at approximately the same distance r from the center of the coil, and the gap between the heating coil 11 and the heating coil 21 is narrowed, which is limited. A larger number of turns can be secured in the space.

In Examples 6 and 7, since the first heating coil 11 through which a large current flows is arranged inside, when heating a pot having a large outer diameter, the magnetic field inside is strong and uneven heating occurs. There is. Therefore, a heating coil for solving this problem will be described. It should be noted that the common points with the above-described embodiment are omitted from the duplicate description.

FIG. 13 is a plan view of the heating coil of the electromagnetic induction heating device of the eighth embodiment and a cross-sectional oblique view between the abs shown on the plan view. The difference from the above-described Examples 6 and 7 (FIGS. 11 and 12) is that the heating coils are concentrically divided inside, inside, and outside, and the first heating coil 11 is divided and arranged inside and outside. The point is that it has a triple-wound structure so as to sandwich the second heating coil 21. As a result, the above-mentioned uneven heating can be prevented by inducing heating by passing a large current through the first heating coils 11 arranged inside and outside.

1 DC power supply,
3, 4 upper and lower arms,
5a-5d switching element,
6a-6d diodes,
7a-7d snubber capacitors,
12-14, 22, 24 resonant capacitors,
11, 21 heating coil,
20 relays,
51a-51l, 71a-71l magnetic material,
70 First resonant load circuit,
80 Second resonant load circuit,
90 Third resonant load circuit

Claims (6)

A DC power supply that supplies DC voltage and
The upper and lower arms connected between the positive and negative electrodes of the DC power supply,
It is equipped with a heating coil that induces and heats the object to be heated.
An electromagnetic induction heating device that supplies a high-frequency current to a resonant load circuit including the heating coil with an inverter using the upper and lower arms.
The resonance load circuit can form the first to third resonance load circuits.
In the first resonance load circuit, a first series body in which a first heating coil and a first resonance capacitor are connected in series and a second resonance capacitor are connected in parallel to the first series body. And
In the second resonant load circuit, the second heating coil and the second resonant capacitor are connected in series.
The third resonance load circuit state, and are not the first series body and the second heating coils are connected in series, and further,
In parallel with the first resonant capacitor, a third resonant capacitor,
A relay for disconnecting the third resonant capacitor from the first resonant capacitor is provided.
The relay is turned off when the object to be heated is a non-magnetic material.
The electromagnetic induction heating device the heated object, characterized in Rukoto such an ON state when the magnetic body. In the electromagnetic induction heating device according to claim 1,
One end of the first resonant capacitor and one end of the second resonant capacitor are connected to a negative electrode.
The first resonant load circuit further includes a second series in which the first heating coil and the fourth resonant capacitor are connected in series, and a fifth in parallel with the second series. Has a resonant capacitor of
In the second resonance load circuit, the fifth resonance capacitor is connected between the connection point of the second heating coil and the second resonance capacitor and the positive electrode.
The third resonance load circuit is electromagnetic induction characterized in that the fourth resonance capacitor is connected between the connection point of the first heating coil and the first resonance capacitor and the positive electrode. Heating device. In the electromagnetic induction heating device according to claim 1,
The upper and lower arms include a first upper and lower arm and a second upper and lower arm.
An electromagnetic induction heating device, wherein the first to third resonance load circuits are connected between the output terminals of the first upper and lower arms and the output terminals of the second upper and lower arms. In the electromagnetic induction heating device according to any one of claims 1 to 3.
The first and second heating coils are arranged on substantially the same plane, and the first and second heating coils are arranged on substantially the same plane.
It is provided with a magnetic material that suppresses the magnetic flux generated by the first and second heating coils from leaking toward the lower surface and the side surface.
An electromagnetic induction heating device characterized in that the magnetic material is radially arranged at substantially uniform angles on the lower surfaces of the first and second heating coils. In the electromagnetic induction heating device according to claim 4,
The first and second heating coils are concentrically arranged, and the magnetic material is a U-shaped magnetic material radially arranged at substantially equal angles on the lower surfaces of the first and second heating coils. ,
The magnetic material arranged on the lower surface of the inner heating coil and the magnetic material arranged on the lower surface of the outer heating coil are staggered and arranged at substantially uniform angles.
An electromagnetic induction heating device is characterized in that the outer rising portion of the inner magnetic material and the inner rising portion of the outer magnetic material are located at substantially the same distance from the center of the coil. In the electromagnetic induction heating device according to claim 4,
The first heating coil is divided into concentric inner and outer parts.
The electromagnetic induction heating device, wherein the second heating coil is arranged between the first heating coil and the first heating coil separately arranged on the inner side and the outer side.

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