Electromagnetic induction heating device

Abstract

To reduce a voltage of a heating coil when a non-magnetic pot having low resistance is heated.SOLUTION: A series body of a first capacitor, a first heating coil and a second capacitor is connected between a terminal of a first inverter terminal performing half-bridge operation and a negative electrode, a series body of the first capacitor, a second heating coil and the second capacitor is connected between the first inverter terminal and a positive electrode, a series body of a third capacitor, a third heating coil and the second capacitor is connected between a second inverter terminal performing half-bridge operation and the negative electrode, a series body of the third capacitor, a fourth heating coil and the second capacitor is connected between the second inverter terminal and the positive electrode, a series body of the first capacitor, the second heating coil, the fourth heating coil and the third capacitor and a series body of the first capacitor, the first heating coil, the third heating coil and the third capacitor are connected between third inverters performing full-bridge operation, and the second capacitor has capacitance smaller than those of the first and third capacitors.SELECTED DRAWING: Figure 1

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 source, reference number 11), the second heating coil (same source, reference number 14), and mainly the first resonant capacitor (Figure 1 in the same document, reference number 12) and the second resonant capacitor (same source, 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 higher frequency causes the voltage of the heating coil to increase, making it difficult to increase the heating output.

[0008] The object of the present invention is to address the above-mentioned problems, and in particular to provide an inverter-type electromagnetic induction heating device that uses multiple heating coils to reduce the voltage of the heating coil when heating a low-resistance non-magnetic pot, and can 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 each being a series body of two switching elements, second upper and lower arms each being a series body of two switching elements, and an inverter circuit for converting a DC voltage into an AC voltage and supplying 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 a first resonant capacitor, a first heating coil, and a second resonant capacitor are connected between an output terminal of the first inverter circuit and a negative electrode of a DC power source. a series connection of the first resonant capacitor, the second heating coil and the second resonant capacitor 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 third resonant capacitor, the third heating coil and the second resonant capacitor 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 third resonant capacitor, a fourth heating coil and the second resonant capacitor 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 resonant capacitor, the second heating coil, the fourth heating coil and the third resonant capacitor and a series connection of the first resonant capacitor, the first heating coil, the third heating coil and the third resonant capacitor are connected between the output terminals of the third inverter circuit, and the second resonant capacitor has a smaller capacity than the first and third resonant capacitors. Effect of the Invention

[0010] According to the present invention, a plurality of heating coils are used, and the voltage of each heating coil can be reduced while efficiently supplying 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 a circuit diagram of an electromagnetic induction heating device according to a second embodiment. [Figure 8] 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 a first resonant capacitor 21 is connected to an output terminal A of the first upper and lower arms 3, the other end of the first resonant capacitor 21 is connected to one end of a first heating coil 11, the other end of the first heating coil 11 is connected to one end of a second resonant capacitor 22b, and the other end of the second resonant capacitor 22b is connected to a negative electrode N of the DC power supply 1. One end of a second heating coil 12 is connected to the other end of the first resonant capacitor 21, one end of a second resonant capacitor 22a is connected to the other end of the second heating coil 12, and the other end of the second resonant capacitor 22a is connected to a positive electrode P of the DC power supply 1. A connection point between the first heating coil 11 and the second heating coil 12 is a terminal B.

[0017] Similarly, one end of a third resonant capacitor 23 is connected to the output terminal C of the second upper and lower arms 4, the other end of the third resonant capacitor 23 is connected to one end of the third heating coil 13, and the other end of the third heating coil 13 is connected to the other end of the first heating coil 11. One end of a fourth heating coil 14 is connected to the other end of the third resonant capacitor 23, and the other end of the fourth heating coil 14 is connected to the other end of the second heating coil 12. The connection point between the third heating coil 13 and the fourth heating coil 14 is terminal D. The connection point between the second heating coil 12 and the fourth heating coil is terminal E, and the connection point between the first heating coil 11 and the third heating coil is terminal F.

[0018] Here, heating coils 11, 12, 13, and 14 are magnetically coupled to a metal pan (not shown) that is the object to be heated, so when the metal pan is converted into an equivalent circuit seen from the heating coil 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 equivalent inductance are small, and in the case of a high-resistance magnetic material, both are large.

[0019] 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. <Control when heating magnetic material> First, the control during heating of the magnetic material will be described with reference to FIG.

[0020] 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) to vg(5d) of the switching elements 5a to 5d, the currents i11, i12, i13, and i14 of the heating coils 11, 12, 13, and 14, and the currents i5a to i5d and i6a to i6d of the elements of the upper and lower arms 3 and 4. The direction of the currents i11 to i14 flowing through the heating coils 11 to 14 is positive in the direction of the dashed arrow in Fig. 1.

[0021] 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 an inverter circuit of a full-bridge circuit type consisting of a resonant load circuit 53 consisting of a first resonant capacitor 21, a first heating coil 11, a second heating coil 12, a third heating coil 13, a fourth heating coil 14, and a third resonant capacitor 23, the first upper and lower arm 3, and the second upper and lower arm 4. The current i13 of the third heating coil 13 and the current i14 of the fourth heating coil 14 are in phase with respect to the current i11 of the first heating coil 11 and the current i12 of the second heating coil 12, but the direction of the dashed arrow in Fig. 1 is set as the positive direction. The switching elements 5a to 5d can be turned on during the period when current flows through the diodes 6a to 6d, enabling soft switching operation with little switching loss.

[0022] 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 capacitances of the first resonant capacitor 21 and the third resonant capacitor 23 are set to match the drive frequency of about 20 kHz. <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.

[0023] 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.

[0024] 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 allows the inverter circuit to function as a half-bridge type inverter circuit composed of the first upper and lower arms 3 and the resonant load circuit 51 composed of the first heating coil 11 and the second heating coil 12, the first resonant capacitor 21 and the second resonant capacitor 22a, 22b, and the first upper and lower arms, and as a half-bridge type inverter circuit composed of the third heating coil 13 and the fourth heating coil 14, the third resonant capacitor 23 and the second resonant capacitor 22a, 22b, and the second upper and lower arms 4. The currents i11 through i14 of the first heating coil 11 through the fourth heating coil 14 are in phase with each other.

[0025] Here, the skin resistance of the object to be heated is proportional to the square root of the frequency, and it is effective to increase the frequency when heating an object with low resistance such as copper or aluminum. Therefore, it is necessary to design the combined capacitance of the first resonant capacitor 21, the second resonant capacitors 22a and 22b, and the third resonant capacitor 23 so that the upper and lower arms 3 and 4 can be driven at a frequency of, for example, about 90 kHz, and the capacitance of the second resonant capacitors 22a and 22b is set to a value sufficiently smaller than the capacitance of the first resonant capacitor 21 and the third resonant capacitor 23. In this case, the voltage of the heating coil increases due to the high frequency, but in this embodiment, the voltage of each heating coil can be reduced by using four heating coils, and the coil current can be increased to increase the magnetomotive force.

[0026] The combination of the capacitances of the capacitors is, for example, 20 to 25 nF for the second resonant capacitors 22a and 22b, and 250 to 500 nF for the first and third resonant capacitors 21 and 23. In this way, if the former has a capacitance one order of magnitude smaller than the latter, the above-mentioned effect can be obtained.

[0027] 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.

[0028] 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. <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.

[0029] 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.

[0030] FIG. 5 is a configuration diagram showing a specific arrangement of the first to fourth heating coils 11 to 14 shown in FIG.

[0031] In this embodiment, the first to fourth heating coils are wound in a substantially fan-like shape with an interior angle of approximately 90°, and the first heating coil 11 is disposed at the lower left in the figure, the second heating coil 12 at the upper left in the figure, the third heating coil 13 at the lower right in the figure, and the fourth heating coil 14 at the upper right in the figure. When the heating coils are disposed so that their straight portions face each other as in this embodiment, if the gap (insulation distance) at the outermost periphery of the straight portions of each heating coil can be narrowed, it becomes possible to secure a larger number of turns for each heating coil.

[0032] Therefore, in this embodiment, terminal B, which is a connection point between one end of the first heating coil 11 and one end of the second heating coil 12, is connected to the outer periphery of the heating coil, and terminal D, which is a connection point between one end of the third heating coil 13 and the fourth heating coil 14, is connected to the outer periphery of the heating coil. As a result, only the voltage between terminals BD is applied at most between the outermost periphery of the straight portion of the first heating coil 11 and the third heating coil 13, and between the outermost periphery of the straight portion of the second heating coil 12 and the fourth heating coil 14. When a non-magnetic material is heated in the half-bridge circuit system, the voltages of terminals B and D are almost at the same potential, so it is only necessary to ensure the insulation distance by considering the voltage between terminals BD when a magnetic material is heated in the full-bridge circuit system, that is, the voltages of the first to fourth heating coils. When a magnetic material is heated, the frequency is low, so the voltage of the heating coil is lower than when a non-magnetic material is heated. When heating a non-magnetic material, if the inductances of the first to fourth heating coils are the same, the potential difference between the terminals EF is small, but if the inductances are different, the heating coil voltage will be higher as the frequency increases, and it is expected that a large potential difference will occur between the terminals EF. Therefore, it is easier to arrange the heating coils taking into account the voltage between the terminals BD than to arrange the heating coils taking into account the voltage between the terminals EF.

[0033] In addition, if the first heating coil 11 and the fourth heating coil 14 are wound clockwise from the outer circumference to the inner circumference, and the second heating coil 12 and the third heating coil 13 are wound counterclockwise from the outer circumference to the inner circumference as shown in Figure 5, when heating a magnetic material using a full-bridge circuit method, as shown by the dotted arrows in Figure 5, the currents i11 and i13 in the vertical straight sections of the first heating coil 11 and the third heating coil 13 will be in opposite phase, and the currents i12 and i14 in the vertical straight sections of the second heating coil 12 and the fourth heating coil 14 will be in opposite phase, which may raise concerns about cancellation of magnetic flux; however, in 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.

[0034] On the other hand, when heating a non-magnetic material using the half-bridge circuit method, the currents i11, i12, i13, and i14 in the straight sections of the first to fourth heating coils 11, 12, 13, and 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 generated by all of the heating coils causes large eddy currents to flow in the pot in a direction that cancels out the magnetic flux, and the desired amount of heat can be obtained. EXAMPLES

[0035] Fig. 7 is a circuit diagram of an electromagnetic induction heating device of Example 2. The same parts as in Fig. 1 are given the same reference numerals and repeated explanations will be omitted.

[0036] In this embodiment, a current balancing capacitor 24 is provided between terminals E and F. In the first embodiment, if the inductances of the first heating coil 11 to the fourth heating coil 14 differ greatly during heating of a non-magnetic material, the balance of the currents flowing through each heating coil may be lost. In this embodiment, the current balancing capacitor 24 is connected in parallel to the series body of the first heating coil 12 and the second heating coil 12 and the series body of the third heating coil 13 and the fourth heating coil 14, so that the currents flowing through the first heating coil 12 and the second heating coil 12 are made equal, and similarly, the currents flowing through the third heating coil 13 and the fourth heating coil 14 are made equal. The current balancing capacitor 24 is included in the resonant load circuit 53 during heating of a magnetic material, but since its capacitance is sufficiently smaller than that of the first resonant capacitor 21 and the third resonant capacitor 23, it does not have a significant effect on operation. EXAMPLES

[0037] Fig. 8 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 will not be described again.

[0038] In this embodiment, a series circuit of a first resonant capacitor 21 and a fifth heating coil 15 is connected between output terminals A and B of the upper and lower arms 3, and a series circuit of a third resonant capacitor 23 and a sixth heating coil 16 is connected between output terminals C and D of the upper and lower arms 4. This makes it possible to lower the coil voltage per heating coil by adding a heating coil, and the constraints on the distance between the heating coils are relaxed, allowing the coils to be arranged as close as about 1 mm to each other, for example. Furthermore, since the metal pot can be heated with multiple heating coils, the heating can be more uniformly heated. [Explanation of symbols]

[0039] 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, 21 First resonant capacitor 22a, 22b Second resonant capacitor 23 Third resonant capacitor 24 Current balancing 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 resonant capacitor 21, a first heating coil 11, and a second resonant capacitor 22b is connected between the output terminal A of the first inverter circuit and the negative electrode N of the DC power source 1. A series circuit of the first resonant capacitor 21, the second heating coil 12, and the second resonant capacitor 22a is connected between the output terminal A of the first inverter circuit and the positive electrode P of the DC power source 1, A series circuit of a third resonant capacitor 23, a third heating coil 13, and the second resonant capacitor 22b is connected between an output terminal C of the second inverter circuit and a negative electrode N of a DC power source 1. A series circuit of the third resonant capacitor 23, the fourth heating coil 14, and the second resonant capacitor 22a 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 connection of the first resonant capacitor 21, the second heating coil 12, the fourth heating coil 14, and the third resonant capacitor 23, and a series connection of the first resonant capacitor 21, the first heating coil 11, the third heating coil 13, and the third resonant capacitor 23 are connected between output terminals A and C of the third inverter circuit, The electromagnetic induction heating device is characterized in that the second resonant capacitors 22a, 22b have smaller capacitances than the first and third resonant capacitors 21, 23.

2. 2. The electromagnetic induction heating device according to claim 1, An electromagnetic induction heating device characterized by comprising a current balancing capacitor 24 in parallel with the series body of the first heating coil 11 and the second heating coil 12 and the series body of the third heating coil 13 and the fourth heating coil 14.

3. 3. The electromagnetic induction heating device according to claim 1, A fifth heating coil 15 is connected in series with the first resonant capacitor 21, An electromagnetic induction heating device, characterized in that a sixth heating coil (16) is connected in series with the third resonant capacitor (23).

4. 3. The electromagnetic induction heating device according to claim 1, The first to fourth heating coils 11 to 14 are all heating coils wound in a substantially fan-like shape, An electromagnetic induction heating device, characterized in that the straight portions of the first to fourth heating coils (11 to 14) are arranged so as to face each other.

5. 5. The electromagnetic induction heating device according to claim 4, The electromagnetic induction heating device is characterized in that the inverter circuit passes currents of opposite phases through parts of the straight portions of the first to fourth heating coils (11 to 14).

6. 5. The electromagnetic induction heating device according to claim 4, The electromagnetic induction heating device is characterized in that the inverter circuit supplies currents of the same phase to the straight portions of the first to fourth heating coils (11 to 14).

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