Electromagnetic induction heating device

Abstract

To increase magnetomotive force when a non-magnetic pot having low resistance is heated.SOLUTION: An electromagnetic induction heating device is composed of a first inverter performing half-bridge operation, a second inverter performing half-bridge operation, and a third inverter performing full-bridge operation, wherein a series body to a first heating coil, a first resonance capacitor and a second heating coil is connected between the first inverter terminal and a negative electrode, a series body to the first heating coil, the first resonance capacitor and a third heating coil is connected between the first inverter terminal and a positive electrode, a series body to a fourth heating coil, a second resonance capacitor and a fifth heating coil is connected between a second inverter terminal and the negative electrode, a series body to the fourth heating coil, the second resonance capacitor and a sixth heating coil is connected between the second inverter terminal and the positive electrode, a series body to the first heating coil, a third resonance capacitor and the fourth heating coil is connected between the third inverter terminals, and the first and second resonance capacitors have capacitances smaller than that of the third resonance capacitor.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an inverter type electromagnetic induction heating device that supplies a desired amount of power to objects to be heated that are made of different materials, thereby performing induction heating. [Background technology]

[0002] In recent years, inverter-type electromagnetic induction heating devices that heat objects such as pots without using fire have become widely used. An electromagnetic induction heating device applies high-frequency current to a heating coil, generates eddy currents in a metal object to be heated that is placed close to the heating coil, and generates heat due to the electrical resistance of the object to be heated. In general, objects to be heated that are magnetic, such as iron, with a high specific resistance, are easy to heat, whereas objects to be heated that are non-magnetic, such as copper or aluminum, with a low specific resistance, are difficult to heat.

[0003] An example of a conventional device that can appropriately heat objects to be heated, whether they are magnetic or non-magnetic, is the electromagnetic induction heating device disclosed in Patent Document 1. The electromagnetic induction heating device in this patent document determines whether a cooking pot is a magnetic or non-magnetic pot, and depending on the determination result, changes the circuit type of the high-frequency inverter to a half-bridge type when heating a non-magnetic pot, and to a full-bridge type when heating a magnetic pot, while simultaneously switching the capacity of the resonant capacitor, thereby inductively heating objects to be heated that are made of different materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7222806 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, when a high-resistance magnetic pot is heated, the high-frequency inverter is switched to a full-bridge circuit method, and the magnetic pot is inductively heated using a first heating coil (Figure 1 of Document 1, symbol 11), a second heating coil (same document, symbol 14), and mainly a third resonant capacitor with a large capacity (same document, symbol 13).

[0006] On the other hand, when heating a low-resistance non-magnetic pot, the high-frequency inverter is switched to a half-bridge circuit type, and the first heating coil (same document, reference number 11), the second heating coil (same document, reference number 14), and mainly the first resonant capacitor (Figure 1 in the same document, reference number 12) and the second resonant capacitor (same document, reference number 15), which have small capacitance, are used to increase the frequency and inductively heat the non-magnetic pot.

[0007] In this way, when heating a low-resistance non-magnetic pot, the frequency is increased and the increase in the surface resistance of the heated object is utilized; however, the Radio Law places a limit on the frequency that can be used at 100 kHz, so there is a limit to how high the frequency can be.

[0008] The object of the present invention is to address the above-mentioned problems, in particular, to provide an inverter-type electromagnetic induction heating device that can increase the magnetomotive force when heating low-resistance non-magnetic pots and efficiently supply the desired power to heated objects made of different materials. [Means for solving the problem]

[0009] In order to achieve the above object, the electromagnetic induction heating device of the present invention includes a heating coil for induction heating an object to be heated, first upper and lower arms which are a series body of two switching elements, second upper and lower arms which are a series body of two switching elements, and an inverter circuit which converts a DC voltage into an AC voltage and supplies the AC voltage to the heating coil, the inverter circuit being composed of a first inverter circuit which operates as a half-bridge type inverter by driving the switching elements of the first upper and lower arms, a second inverter circuit which operates as a half-bridge type inverter by driving the switching elements of the second upper and lower arms, and a third inverter circuit which operates as a full-bridge type inverter by driving the switching elements of the first and second upper and lower arms, and an output terminal of the first inverter circuit is connected to a load of a DC power supply. A series connection of a first heating coil, a first resonant capacitor and a second heating coil is connected between the electrodes, a series connection of the first heating coil, a first resonant capacitor and a third heating coil is connected between the output terminal of the first inverter circuit and the positive electrode of a DC power supply, a series connection of a fourth heating coil, a second resonant capacitor and a fifth heating coil is connected between the output terminal of the second inverter circuit and the negative electrode of a DC power supply, a series connection of the fourth heating coil, a second resonant capacitor and a sixth heating coil is connected between the output terminal of the second inverter circuit and the positive electrode of a DC power supply, and a series connection of the first heating coil, a third resonant capacitor and the fourth heating coil is connected between the output terminals of the third inverter circuit, and the first resonant capacitor and the second resonant capacitor have a smaller capacity than the third resonant capacitor. Effect of the Invention

[0010] According to the present invention, by switching the inverter system, the resonant capacitor, or the number of turns of the heating coil, it is possible to efficiently supply desired power to objects to be heated that are made of different materials. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1 is a circuit diagram of an electromagnetic induction heating device according to a first embodiment. [Diagram 2] 4 is an operational waveform when a magnetic material is heated in the first embodiment. [Diagram 3] 4 is an operational waveform when a non-magnetic material is heated in the first embodiment. [Figure 4] 4 is an operational waveform when a non-magnetic material is heated in the first embodiment. [Diagram 5] FIG. 2 is an explanatory diagram of the arrangement of the heating coils in the first embodiment and the electric current when the magnetic material is heated. [Figure 6] FIG. 2 is an explanatory diagram of the arrangement of the heating coils in the first embodiment and the current when a non-magnetic material is heated. [Figure 7] FIG. 11 is an explanatory diagram of the arrangement of the heating coils in the second embodiment and the electric current when the magnetic material is heated. [Figure 8] FIG. 11 is an explanatory diagram of the arrangement of the heating coils in the second embodiment and the current when a non-magnetic material is heated. [Figure 9] FIG. 11 is a circuit diagram of an electromagnetic induction heating device according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same reference numerals indicate the same components or components having similar functions, and duplicated explanations will be omitted as appropriate. EXAMPLES

[0013] Fig. 1 is a circuit diagram of an electromagnetic induction heating device of Example 1. The electromagnetic induction heating device of this example has a top plate made of heat-resistant glass placed on top of a metal housing, and a high-frequency current is supplied to a heating coil placed below the top plate to induction heat a metal object to be heated placed at a predetermined position on the top surface of the top plate, but a description of such a well-known configuration will be omitted below.

[0014] 1, a 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. A first upper and lower arm 3 having power semiconductor switching elements (hereinafter simply referred to as "switching elements") 5a and 5b connected in series, and a second upper and lower arm 4 having switching elements 5c and 5d connected in series are connected between a positive electrode P and a negative electrode N of the DC power supply 1.

[0015] Diodes 6a to 6d are connected in parallel in the opposite direction to the switching elements 5a to 5d, respectively, and snubber capacitors 7a to 7d are connected in parallel to the switching elements 5a to 5d, respectively. The snubber capacitors 7a to 7d are charged or discharged by the interruption current when the switching elements 5a to 5d are turned off, and the change in voltage applied to each switching element is reduced, thereby suppressing turn-off loss.

[0016] One end of the first heating coil 11 is connected to the output terminal A of the first upper and lower arms 3, one end of the first resonant capacitor 21b is connected to the other end B of the first heating coil 11, one end F of the second heating coil 12 is connected to the other end of the first resonant capacitor 21b, and the other end of the second heating coil 12 is connected to the negative electrode N of the DC power supply 1. In addition, one end of the first resonant capacitor 21a is connected to the other end B of the first heating coil 11, one end E of the third heating coil 13 is connected to the other end of the first resonant capacitor 21a, and the other end of the third heating coil 13 is connected to the positive electrode P of the DC power supply 1.

[0017] Similarly, one end of the fourth heating coil 14 is connected to the output terminal C of the second upper and lower arms 4, one end of the second resonant capacitor 22b is connected to the other end D of the fourth heating coil 14, and the other end of the second resonant capacitor 22b is connected to one end F of the second heating coil 12. In addition, one end of the second resonant capacitor 22a is connected to the other end D of the fourth heating coil 14, and the other end of the second resonant capacitor 22a is connected to one end E of the third heating coil 13.

[0018] A third resonant capacitor 23 is connected between the other end B of the first heating coil 11 and the other end D of the fourth heating coil 14.

[0019] Here, heating coils 11-14 and a metal pan (not shown) that is the object to be heated are magnetically coupled, so when the metal pan is converted into an equivalent circuit seen from the heating coils 11-14 side, the equivalent resistance and equivalent inductance of the metal pan are connected in series. The equivalent resistance and equivalent inductance differ depending on the material of the metal pan; in the case of a low-resistance non-magnetic material, both the equivalent resistance and the equivalent inductance are small, and in the case of a high-resistance magnetic material, both are large.

[0020] In the electromagnetic induction heating device of this embodiment, the object is heated by changing the driving method of the first upper and lower arms 3 and the second upper and lower arms 4 according to the material of the object and the set heating power. Below, the difference in control when heating a magnetic material such as iron and when heating a non-magnetic material such as aluminum will be explained.

[0021] <Control when heating magnetic material> First, the control during heating of the magnetic material will be described with reference to FIG.

[0022] Fig. 2 shows the operating waveforms when the object to be heated is a magnetic body such as an iron pan. The waveforms are the gate drive signals vg(5a)-vg(5d) of the switching elements 5a-5d, the currents i11-i14 of the heating coils 11-14, and the currents i5a-i5d and i6a-i6d of the elements of the upper and lower arms 3 and 4. The direction of the currents i11-i14 flowing through the heating coils 11-14 is positive in the direction of the dashed arrow in Fig. 1.

[0023] In this embodiment, when the object to be heated is a magnetic body such as an iron pan, a full-bridge inverter circuit is used to induction heat the metal pan. Specifically, as shown in FIG. 2, the switching element 5a of the upper arm of the first upper and lower arm 3 and the switching element 5d of the lower arm of the second upper and lower arm 4 are turned on and off almost simultaneously, and the switching element 5b of the lower arm of the first upper and lower arm 3 and the switching element 5c of the upper arm of the second upper and lower arm 4 are turned on and off almost simultaneously. This functions as a full-bridge inverter circuit composed of a resonant load circuit 53 consisting of the first heating coil 11, the third resonant capacitor 23, and the fourth heating coil 14, the first upper and lower arm 3, and the second upper and lower arm 4. The phases of the current i11 of the first heating coil 11 and the current i14 of the fourth heating coil 14 are inverted, but this is because the direction of the dashed arrow in FIG. 1 is the positive direction. When a full-bridge inverter circuit is used, no current flows through the second heating coil 12 and the third heating coil 13. The switching elements 5a to 5d can be turned on during the period when current flows through the diodes 6a to 6d, enabling a soft switching operation with little switching loss.

[0024] As mentioned above, a high-resistance magnetic material has a large equivalent resistance, so it is difficult for a current to flow through the resonant load circuit. Therefore, by changing to a full-bridge circuit, the output voltage of the inverter circuit can be increased to twice that of the half-bridge circuit, and the desired output can be obtained. When the object to be heated is iron, the resistance is originally large, so the first upper and lower arms 3 and the second upper and lower arms 4 are driven at a frequency of about 20 kHz. For this reason, the capacitance of the third resonant capacitor 23 is set to match the drive frequency of about 20 kHz.

[0025] <Control when heating non-magnetic materials> Next, the control during heating of the non-magnetic material will be described with reference to FIG. 3 and FIG.

[0026] Figure 3 shows the operating waveforms when the object to be heated is a non-magnetic material such as an aluminum pan. Note that the meanings of vg(5a) and other symbols in Figure 3 are the same as those in Figure 2.

[0027] In this embodiment, when the object to be heated is a non-magnetic material such as a copper pan or an aluminum pan, a metal pan is induction heated mainly using an inverter circuit of a half-bridge circuit type. Specifically, a period in which the upper arms (switching elements 5a, 5c) of the first upper and lower arms 3 and the second upper and lower arms are turned on and a period in which the lower arms (switching elements 5b, 5d) are turned on are provided. This functions as a half-bridge inverter circuit composed of a resonant load circuit 51 consisting of the first heating coil 11 to the third heating coil 13 and the first resonant capacitors 21a and 21b, and the first upper and lower arms 3, and a half-bridge inverter circuit composed of a resonant load circuit 52 consisting of the second heating coil 12 to the fourth heating coil 14 and the second resonant capacitors 22a and 22b, and the second upper and lower arms 4. The currents i11 to i14 of the first heating coil 11 to the fourth heating coil 14 are in phase. When an inverter circuit of a half-bridge circuit type is used, a current flows through all of the heating coils of the first heating coil 11 to the fourth heating coil 14.

[0028] As mentioned above, since the equivalent resistance of a low-resistance non-magnetic material is small, it is necessary to increase the magnetomotive force to obtain a desired output. In this embodiment, the number of turns is increased by adding the second heating coil 12 and the third heating coil 13, thereby increasing the magnetomotive force. Here, the skin resistance of the heated object is proportional to the square root of the frequency, and it is effective to increase the frequency when heating a low-resistance heated object such as copper or aluminum. Therefore, the capacitances of the first resonant capacitors 21a, 21b and the second resonant capacitors 22a, 22b are set so that the upper and lower arms 3, 4 can be driven at a frequency of, for example, about 90 kHz, and the capacitance is sufficiently smaller than the capacitance of the third resonant capacitor 23.

[0029] For example, the combination of the capacitances of the first resonant capacitors 21a, 21b and the second resonant capacitors 22a, 22b has a capacitance of 20 to 25 nF, and the third resonant capacitor 23 has a capacitance of 250 to 500 nF. In this way, if the former has a capacitance one order of magnitude smaller than the latter, the above-mentioned effect can be obtained.

[0030] FIG. 4 shows an example of an operating waveform when a high-frequency current suitable for heating non-magnetic materials is passed through each heating coil, as in FIG. 3, while the switching period of each switching element is lengthened to suppress loss in each switching element.

[0031] This example shows the operating waveforms when the switching frequency is about 1 / 3 of that in FIG. 3 (about 90 kHz in FIG. 3, and about 30 kHz in FIG. 4), and the polarity of the currents i11 to i14 in the first to fourth heating coils 11 to 14 switches during a half cycle of the switching frequency. In this case, as shown by the waveforms in FIG. 4, the frequency of the currents in the switching elements 5a to 5d and the coil currents in the heating coils 11 to 14 increases. Therefore, without increasing the switching frequency of the switching elements 5a to 5d as much as in FIG. 3, the frequency of the current flowing through the heating coils can be increased to a high frequency suitable for heating non-magnetic materials, and the turn-off loss of the switching elements 5a to 5d can be significantly reduced compared to FIG. 3.

[0032] <Arrangement of the first to fourth heating coils in the electromagnetic induction heating device> By using the above-described control depending on the type of object to be heated, the electromagnetic induction heating device can supply the desired power required to achieve the set heating power to the object to be heated, whether it is heating a magnetic material or a non-magnetic material. On the other hand, in order to save power, it is also necessary to secure a larger number of turns for each heating coil and reduce the heating coil current when achieving the desired heating power. However, in an electromagnetic induction heating device that uses two or more heating coils to heat one object to be heated, a high resonant voltage may occur between the two heating coils, so it is necessary to secure a sufficient insulation distance between the heating coils.

[0033] For this reason, in a conventional electromagnetic induction heating device that uses two or more heating coils to heat one heated object, if priority is given to housing all the heating coils in a metal casing whose dimensions are determined by the system kitchen standards, a small heating coil with fewer turns must be used, making it difficult to achieve power saving. On the other hand, if priority is given to power saving, a larger metal casing must be used to house multiple large heating coils with many turns, making it difficult to keep the dimensions of the metal casing below the standard size. Therefore, below, a heating coil arrangement that can increase the number of turns of each heating coil while suppressing the dimensions of the metal casing is explained using Figures 5 and 6.

[0034] Fig. 5 is a configuration diagram showing a specific arrangement of the first to fourth heating coils 11 to 14 shown in Fig. 1. In Fig. 5 to Fig. 8, the first and fourth heating coils 11 and 14 are indicated by dashed lines, and the second and third heating coils 12 and 13 are indicated by solid lines.

[0035] In this embodiment, the first to fourth heating coils are wound in a substantially D-shape, with the first heating coil 11 and the third heating coil 13 arranged on the upper side in the figure, the second heating coil 12 and the fourth heating coil 14 arranged on the lower side in the figure, the third heating coil 13 arranged on the outside of the first heating coil 11, and the second heating coil 12 arranged on the outside of the fourth heating coil 14. When the heating coils are arranged so that their straight portions face each other as in this embodiment, if the gap (insulation distance) between the outermost periphery of the straight portion of the second heating coil 12 and the outermost periphery of the straight portion of the third heating coil 13 can be narrowed, it is possible to secure a larger number of turns for each heating coil.

[0036] Therefore, in this embodiment, the positive electrode P of the DC power supply 1 is connected to the outer periphery of the third heating coil 13, and the negative electrode N of the DC power supply 1 is connected to the outer periphery of the second heating coil 12. As a result, only the voltage of the DC power supply 1 is applied between the positive electrode P and the negative electrode N of the DC power supply 1 at most, so that it is possible to narrow the gap between the outermost periphery of the straight portion of the second heating coil 12 and the outermost periphery of the straight portion of the third heating coil 13.

[0037] If the first heating coil 11 is wound counterclockwise from the inner circumference to the outer circumference and the fourth heating coil 14 is wound clockwise from the inner circumference to the outer circumference as shown in Figure 5, when a magnetic material is heated using a full-bridge circuit method, the current i11 of the first heating coil 11 and the current i14 of the fourth heating coil 14 will be in opposite phase in the straight sections of each heating coil, as shown by the dotted arrows in Figure 5, which may cause concerns about cancellation of magnetic flux; however, when heating a magnetic material, the magnetic flux generated by each heating coil interlinks with the pot, so there is no significant effect on the generation of eddy currents.

[0038] On the other hand, when a non-magnetic material is heated using a half-bridge circuit, the currents i11-i14 in the straight sections of the first to fourth heating coils 11-14 are in phase and there is no cancellation of magnetic flux, as shown by the dashed-dotted arrows in Figure 6. Therefore, when heating a non-magnetic material, the magnetic flux created by the four heating coils causes large eddy currents to flow in the pot in a direction that cancels out the magnetic flux, allowing the desired amount of heat to be obtained. EXAMPLES

[0039] Next, an electromagnetic induction heating device according to a second embodiment of the present invention will be described with reference to Figures 7 and 8. Note that a duplicated description of the points common to the first embodiment will be omitted.

[0040] FIG. 7 is a configuration diagram showing a specific arrangement of the first to fourth heating coils 11 to 14 shown in FIG.

[0041] In this embodiment, the first to fourth heating coils are wound in a substantially D-shape, with the first heating coil 11 and the third heating coil arranged on the upper side of the figure, the second heating coil 12 and the fourth heating coil 14 arranged on the lower side of the figure, the third heating coil 13 arranged inside the first heating coil 11, and the second heating coil 12 arranged inside the fourth heating coil 14. Even when the heating coils are arranged such that the straight portions of the outer first heating coil 11 and the fourth heating coil 14 face each other as in this embodiment, if the gap (insulation distance) between the outermost periphery of the straight portion of the first heating coil 11 and the outermost periphery of the straight portion of the fourth heating coil 14 can be narrowed, it is possible to secure a larger number of turns for each heating coil.

[0042] Therefore, in this embodiment, output terminal A of upper and lower arms 3 is connected to the outer periphery of the first heating coil 11, and output terminal C of upper and lower arms 4 is connected to the outer periphery of the fourth heating coil 14. As a result, only the voltage of the DC power supply 1 is applied at most between output terminal A of upper and lower arms 3 and output terminal C of upper and lower arms 4, so that it is possible to narrow the gap between the outermost periphery of the straight portion of the first heating coil 11 and the outermost periphery of the straight portion of the fourth heating coil 14.

[0043] If the first heating coil 11 is wound clockwise from the outer circumference to the inner circumference and the fourth heating coil 14 is wound counterclockwise from the outer circumference to the inner circumference as shown in Figure 7, when a magnetic material is heated using a full-bridge circuit method, the current i11 of the first heating coil 11 and the current i14 of the fourth heating coil 14 will be in opposite phase in the straight sections of each heating coil, as shown by the dotted arrows in Figure 7, which may cause concerns about cancellation of magnetic flux; however, when heating a magnetic material, the magnetic flux generated by each heating coil interlinks with the pot, so there is no significant effect on the generation of eddy currents.

[0044] On the other hand, when a non-magnetic material is heated using a half-bridge circuit, as shown by the dashed arrows in Figure 8, the currents i11-i14 in the first to fourth heating coils 11-14 in the straight sections of each heating coil are in phase, and there is no cancellation of magnetic flux. Therefore, when heating a non-magnetic material, the magnetic flux created by the four heating coils causes a large eddy current to flow in the pot in a direction that cancels the magnetic flux, and the desired amount of heat can be obtained. When heating a non-magnetic material, the voltages of the output terminal A of the first upper and lower arms 3 and the output terminal C of the second upper and lower arms 4 are at the same potential, so the gap between the first heating coil 11 and the fourth heating coil 14 should be an insulation distance that takes into account the voltage of the DC power source 1, which is the potential difference in the full-bridge circuit. EXAMPLES

[0045] Fig. 9 is a circuit diagram of an electromagnetic induction heating device according to Example 3. The same parts as those in Fig. 1 are given the same reference numerals and repeated explanations will be omitted.

[0046] In this embodiment, one end of the fourth heating coil 14 is connected to the output terminal C of the second upper and lower arms 4, one end of the second resonant capacitor 22b is connected to the other end D of the fourth heating coil 14, the other end of the second resonant capacitor 22b is connected to one end of the fifth heating coil 15, and the other end of the fifth heating coil 15 is connected to the negative electrode N of the DC power supply 1. In addition, one end of the second resonant capacitor 22a is connected to the other end D of the fourth heating coil 14, the other end of the second resonant capacitor 22a is connected to one end of the sixth heating coil 16, and the other end of the sixth heating coil 16 is connected to the positive electrode P of the DC power supply 1.

[0047] In the first embodiment, the second heating coil 12 and the third heating coil 13 are used as components of the resonant load circuits 51 and 52, but in the present embodiment, the second heating coil 12 and the third heating coil 13 are components of the resonant load circuit 51, and the fifth heating coil 15 and the sixth heating coil 16 are components of the resonant load circuit 52. As a result, when a non-magnetic material is heated by the half-bridge circuit method, it is possible to drive only the first upper and lower arms 3 to pass a current only through the first to third heating coils 11 to 13 for heating, or drive only the second upper and lower arms 4 to pass a current only through the fourth to sixth heating coils 14 to 16 for heating. [Explanation of symbols]

[0048] 1 DC power supply, 3 First upper and lower arms, 4 second upper and lower arms, 5a to 5d switching elements, 6a to 6d Diodes, 7a~7d snubber capacitors, 11~16 heating coil, 21a, 21b First resonant capacitor 22a, 22b Second resonant capacitor 23 Third resonant capacitor 51, 52, 53 Resonant load circuit

Claims

1. A heating coil for induction heating an object to be heated; A first upper and lower arm 3 which is a series body of two switching elements 5a and 5b; A second upper and lower arm 4 which is a series body of two switching elements 5c and 5d; an inverter circuit that converts a DC voltage into an AC voltage and supplies the AC voltage to the heating coil; An electromagnetic induction heating device comprising: The inverter circuit includes: a first inverter circuit that operates as a half-bridge inverter by driving the switching elements 5 a, 5 b of the first upper and lower arms 3; a second inverter circuit that operates as a half-bridge inverter by driving the switching elements 5c and 5d of the second upper and lower arms 4; a third inverter circuit that operates as a full-bridge inverter by driving the switching elements 5a to 5d of the first and second upper and lower arms 3 and 4; It is composed of A series circuit of a first heating coil 11, a first resonant capacitor 21b, and a second heating coil 12 is connected between an output terminal A of the first inverter circuit and a negative electrode N of a DC power source 1, A series circuit of the first heating coil 11, the first resonant capacitor 21a, and the third heating coil 13 is connected between the output terminal A of the first inverter circuit and the positive electrode P of the DC power supply 1, A series circuit of a fourth heating coil 14, a second resonant capacitor 22b, and a fifth heating coil 15 is connected between the output terminal C of the second inverter circuit and the negative electrode N of the DC power supply 1. A series circuit of the fourth heating coil 14, the second resonant capacitor 22a, and the sixth heating coil 16 is connected between the output terminal C of the second inverter circuit and the positive electrode P of the DC power source 1, A series circuit of the first heating coil 11, the third resonant capacitor 23, and the fourth heating coil 14 is connected between output terminals A and C of the third inverter circuit, The electromagnetic induction heating device, wherein the first resonant capacitors 21a, 21b and the second resonant capacitors 22a, 22b have a smaller capacity than the third resonant capacitor 23.

2. 2. The electromagnetic induction heating device according to claim 1, The second heating coil 12 also serves as the fifth heating coil 15, The electromagnetic induction heating device is characterized in that the third heating coil (13) also serves as the sixth heating coil (16).

3. 3. The electromagnetic induction heating device according to claim 2, The first to fourth heating coils are heating coils wound in a substantially D-shape, The third heating coil 13 is disposed outside the first heating coil 11, The second heating coil 12 is disposed outside the fourth heating coil 14, The second heating coil 12 and the third heating coil 13 are arranged so that their straight portions face each other, The positive electrode P of the DC power source 1 is connected to the outer periphery of the third heating coil 13, and the negative electrode N of the DC power source 1 is connected to the outer periphery of the second heating coil 12, An electromagnetic induction heating device, characterized in that a potential difference between the second heating coil 12 and the third heating coil 13 in their adjacent portions is equal to or lower than the DC voltage.

4. 3. The electromagnetic induction heating device according to claim 2, The first to fourth heating coils are heating coils wound in a substantially D-shape, The third heating coil 13 is disposed inside the first heating coil 11, The second heating coil 12 is disposed inside the fourth heating coil 14, The first heating coil 11 and the fourth heating coil 14 are arranged such that their straight portions face each other, The output terminal A of the first upper and lower arms is connected to the outer circumferential side of the first heating coil 11, and the output terminal C of the second upper and lower arms is connected to the outer circumferential side of the fourth heating coil 14, An electromagnetic induction heating device, characterized in that a potential difference between the first heating coil (11) and the fourth heating coil (14) in their adjacent portions is equal to or lower than the DC voltage.

5. The electromagnetic induction heating device according to any one of claims 1 to 4, When the object to be heated is a magnetic material, the third inverter circuit supplies high-frequency current to the first heating coil 11 and the fourth heating coil 14 to heat the object to be heated.

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