WO2024214403A1

WO2024214403A1 - Induction heating device

Info

Publication number: WO2024214403A1
Application number: PCT/JP2024/006609
Authority: WO
Inventors: 昇平米田; 駿汰稲見
Original assignee: 国立大学法人東京海洋大学
Priority date: 2023-04-14
Filing date: 2024-02-22
Publication date: 2024-10-17

Abstract

Provided is an induction heating device capable of controlling the heating distribution of a coil while suppressing distortion of a power supply current. The heating device according to one embodiment comprises: three converters (11, 12, 13) that directly convert three power supply currents of a three-phase AC power supply (30) to three high-frequency AC currents having a frequency higher than the frequency of the power supply currents; and three coils (21, 22, 23) that heat an object (50) to be heated by means of harmonic alternating currents supplied individually from the three converters (11, 12, 13). The three coils (21, 22, 23) are disposed so that the distance between the centers thereof is not more than the diameter of the coils.

Description

Induction Heating Equipment

The present invention relates to an induction heating device that can control the heating distribution of a coil.

Induction heating devices that use the principles of induction heating to heat objects are proposed, for example, in Patent Documents 1 and 2.

Patent Document 1 discloses an induction heating cooker that uses a single-phase inverter. In the induction heating cooker, three inverters with approximately the same capacity are connected in parallel to a three-phase power source, and each single-phase inverter is connected to three coils arranged concentrically. This combination of three single-phase inverters is said to reduce harmonics and suppress interference noise.

Patent Document 2 discloses a dielectric heating cooker that switches the phase difference between the currents flowing through two coils connected to each other in a range of 0 to π. In this dielectric heating cooker, the currents are synchronized between the coils, allowing the heated object to be heated evenly.

JP 2012-3846 A JP 2010-153060 A

In the device proposed in Patent Document 1, the power supply current of a three-phase AC power supply is converted to DC by a diode rectifier and then input to an inverter. This can result in significant distortion of the power supply current.

In addition, the device proposed in Patent Document 2 aims to heat the pan, which is the object to be heated, evenly, so the heating distribution of the coil is inevitably limited to a uniform distribution.

The present invention aims to provide an induction heating device that can control the heating distribution of the coil while suppressing distortion of the power supply current.

An induction heating device according to an embodiment of the present invention includes three converters that directly convert three-phase power supply currents of a three-phase AC power supply into three high-frequency AC currents having frequencies higher than the frequency of the power supply currents;
and three coils for heating an object to be heated with harmonic alternating current supplied individually from the three converters;
The three coils are arranged so that their centers are spaced within a coil diameter.

In addition, in the induction heating device,
The three coils may be arranged in a triangular shape.

In addition, in the induction heating device,
each of the three converters is a harmonic cycloconverter;
The harmonic cycloconverter may include a first semiconductor switch and a second semiconductor switch connected in series to each other, and a third semiconductor switch and a fourth semiconductor switch connected in series to each other in the opposite direction to the first semiconductor switch and the second semiconductor switch.

In addition, in the induction heating device,
The first to fourth semiconductor switches are switched to an on state or an off state according to a level of a gate signal input to each gate,
When the first semiconductor switch is in an on state, the second semiconductor switch is in an off state, the third semiconductor switch is in an on state, and the fourth semiconductor switch is in an off state;
When the first semiconductor switch is in an off state, the second semiconductor switch may be in an on state, the third semiconductor switch may be in an off state, and the fourth semiconductor switch may be in an on state.

In addition, in the induction heating device,
The phase difference of the coil currents among the three converters may be 120 degrees.

In addition, in the induction heating device,
The centres of the three coils may be located at the vertices of an equilateral triangle.

In addition, in the induction heating device,
The three coils may partially overlap each other.

In addition, in the induction heating device,
The three coils may be arranged in a row.

In addition, in the induction heating device,
The three coils may be arranged in an L-shape.

In addition, in the induction heating device,
The phase of the coil current may be the same among the three coils.

In addition, in the induction heating device,
Of the three coils, a phase difference between coil currents of two adjacent coils may be 0 degrees or 180 degrees.

The present invention provides an induction heating device that can control the heat distribution of the coil while suppressing distortion of the power supply current.

1 is a block diagram showing a schematic configuration of an induction heating device according to a first embodiment. FIG. 13 is a schematic diagram showing another example of a coil arrangement. FIG. 2 is a diagram showing an equivalent circuit of the induction heating device according to the first embodiment. 4 is a timing chart of a gate signal of the semiconductor switch according to the first embodiment. FIG. 4 is a diagram showing an example of a waveform of a power supply current in the first embodiment. 5A to 5C are diagrams illustrating the amplitude waveform and direction of an output current of the converter in the first embodiment. 5A to 5C are diagrams illustrating an example of a heating pattern of a coil in the first embodiment. 10 is a timing chart of a gate signal of a semiconductor switch according to a second embodiment. FIG. 11 is a diagram showing an example of a waveform of a power supply current in the second embodiment. 13A to 13C are diagrams showing the amplitude waveform and direction of the output current of the converter in the second embodiment. 13A and 13B are diagrams illustrating an example of a heating pattern of a coil in the second embodiment. FIG. 13 is a diagram showing experimental results of heating distribution of a coil. FIG. 13 is a schematic diagram showing a coil arrangement in a third embodiment. FIG. 13 is a diagram showing an example of a heating pattern when the directions of coil currents are all positive in the third embodiment. FIG. 13 is a diagram showing an example of a heating pattern when the directions of coil currents are all negative in the third embodiment. FIG. 13 is a diagram showing an example of a waveform of a power supply current in a synchronous mode. 13 is a diagram showing an example of a heating pattern when the phase of the U-phase coil current is shifted 180 degrees from the phases of the V-phase and W-phase coil currents. FIG. FIG. 11 is a diagram showing another example of a heating pattern when the phase of the U-phase coil current is shifted by 180 degrees from the phases of the V-phase and W-phase coil currents. 13 is a diagram showing an example of a heating pattern when the phase of the V-phase coil current is shifted 180 degrees from the phases of the U-phase and W-phase coil currents. FIG. FIG. 13 is a diagram showing another example of a heating pattern when the phase of the V-phase coil current is shifted by 180 degrees from the phases of the U-phase and W-phase coil currents. 13 is a diagram showing an example of a heating pattern when the phase of the W-phase coil current is shifted 180 degrees from the phases of the U-phase and V-phase coil currents. FIG. FIG. 13 is a diagram showing another example of a heating pattern when the phase of the W-phase coil current is shifted by 180 degrees from the phases of the U-phase and V-phase coil currents. FIG. 13 is a diagram showing an example of a waveform of a power supply current in a 180-degree mode. FIG. 13 is a schematic diagram showing a coil arrangement in a modified example of the third embodiment.

Below, an embodiment of the present invention will be described with reference to the drawings. In each drawing, components having equivalent functions are given the same reference numerals.

First Embodiment
Fig. 1 is a block diagram showing a schematic configuration of an induction heating device according to a first embodiment. The induction heating device 1 shown in Fig. 1 includes three converters 11, 12, and 13, and three coils 21, 22, and 23.

The three converters 11, 12, and 13 directly convert the three-phase power supply current of the three-phase AC power supply 30 into three high-frequency AC currents having frequencies higher than the frequency of the power supply currents. Specifically, the converter 11 directly converts the U-phase power supply current _IU into a high-frequency AC current, the converter 12 directly converts the V-phase power supply current _IV into a high-frequency AC current, and the converter 13 directly converts the W-phase power supply current _IW into a high-frequency AC current. The frequency of the power supply current is, for example, 50 Hz or 60 Hz. On the other hand, the frequency of the high-frequency AC current is, for example, 20 kHz.

The three coils 21, 22, and 23 heat the object to be heated 50 with harmonic alternating current supplied individually from the three converters 11, 12, and 13. The object to be heated 50 is, for example, a metal plate. In this embodiment, the coil 21 is connected to the converter 11 via a resonant capacitor 41. The coil 22 is connected to the converter 12 via a resonant capacitor 42. The coil 23 is connected to the converter 13 via a resonant capacitor 43. The three coils 21, 22, and 23 have the same number of turns and winding direction. The capacitance values of the resonant capacitors 41, 42, and 43 are also the same.

In this embodiment, the three coils 21, 22, and 23 are arranged in a triangular shape as shown in Fig. 1. Specifically, the centers _O1 , _O2 , and _O3 of the coils are arranged at the vertices of an equilateral triangle. Note that in this embodiment, the three coils 21, 22, and 23 are arranged so that the outermost windings of the coils are in contact with each other so that the distance D between the centers is within the diameter d of each coil, but the present invention is not limited to this arrangement.

FIG. 2 is a schematic diagram showing another example of coil arrangement. In FIG. 2, three coils 21, 22, 23 are arranged so that each coil partially overlaps with the other. When the three coils 21, 22, 23 are arranged as shown in FIG. 2, the coupling coefficient (cross-coupling) between each coil may be minimized. In this case, it is possible to reduce distortion of the power supply current. Note that in order to minimize this coupling coefficient, it is desirable to reduce the spatial distance between the heated object 50 and the coils 21, 22, and 23.

FIG. 3 is a diagram showing an equivalent circuit of the induction heating device 1 according to the first embodiment. In this embodiment, the converters 11, 12, and 13 are composed of high-frequency cycloconverters.

Specifically, the converter 11 has a first semiconductor switch S _U1 to a fourth semiconductor switch S _U4 , a first diode D _U1 to a fourth diode D _U4 , and a first capacitor C _U1 to a sixth capacitor C _U6 . Similarly to the converter 11, the converter 12 also has a first semiconductor switch S _V1 to a fourth semiconductor switch S _V4 , a first diode D _V1 to a fourth diode D _V4 , and a first capacitor C _V1 to a sixth capacitor C _V6 . Similarly to the converter 11, the converter 13 also has a first semiconductor switch S _W1 to a fourth semiconductor switch S _W4 , a first diode D _W1 to a fourth diode D _W4 , and a first capacitor C _W1 to a sixth capacitor C _W6 .

As shown in FIG. 3, the circuit configurations of converters 11, 12, and 13 are all the same. Therefore, only the circuit configuration of converter 11 will be described here, and the description of the circuit configurations of converters 12 and 13 will be omitted.

In this embodiment, the first semiconductor switch S _U 1 to the fourth semiconductor switch S _U 4 are N-channel type Metal Oxide Semiconductor Field Effect Transistors (MOSFETs). However, each semiconductor switch is not limited to a MOSFET and may be another semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor).

The first semiconductor switch S _U1 and the second semiconductor switch S _U2 are connected in series. Specifically, the drain of the first semiconductor switch S _U1 is connected to the three-phase AC power supply 30, and the source of the first semiconductor switch S _U1 is connected to the drain of the second semiconductor switch S _U2 . The source of the second semiconductor switch S _U2 is connected to the source of the third semiconductor switch S _U3 .

The third semiconductor switch S _U3 and the fourth semiconductor switch S _U4 are connected in series in the opposite direction to the first semiconductor switch S _U1 and the second semiconductor switch S _U2 . Specifically, the drain of the third semiconductor switch S _U3 is connected to the source of the fourth semiconductor switch S _U4 . The drain of the fourth semiconductor switch S _U4 is connected to the drains of the fourth semiconductor switch S _V4 and the fourth semiconductor switch S _W4 .

A resonant capacitor 41, a coil 21, and a resistive element R are connected in series between the connection point of the source of the first semiconductor switch S _U1 and the drain of the second semiconductor switch S _U2 and the connection point of the drain of the third semiconductor switch S _U3 and the source of the fourth semiconductor switch S _U4 . The resistive element R corresponds to the electrical resistance of the object 50 to be heated by the coils 21 to 23. The resonant capacitor 41, the coil 21, and the resistive element R correspond to the load circuit of the converter 11.

The first diode D _U1 to the fourth diode D _U4 are connected in anti-parallel between the drain-source of the first semiconductor switch S _U1 to the fourth semiconductor switch S _U4 , respectively. The first diode D _U1 to the fourth diode D _U4 are return diodes that return the energy stored in the coil 21 to the three-phase AC power supply 30 when each semiconductor switch is in the off state.

One end of the first capacitor C _U1 to the fourth capacitor C _U4 is connected to the anodes of the first diode D _U1 to the fourth diode D _U4 , respectively, and the other end is connected to the cathodes of the first diode D _U1 to the fourth diode D _U4 , respectively. Furthermore, one end of the fifth capacitor C _U5 is connected to the drain of the first semiconductor switch S _U1 , and the other end is connected to the sources of the second semiconductor switch S _U2 and the third semiconductor switch S _U3 . Furthermore, one end of the sixth capacitor C _U6 is connected to the other end of the fifth capacitor C _U5 and to the sources of the second semiconductor switch S _U2 and the third semiconductor switch S _U3 . The other end of the sixth capacitor C _U6 is connected to the drain of the fourth semiconductor switch S _U4 .

The first semiconductor switch S _U1 to the fourth semiconductor switch S _U4 of the converter 11, the first semiconductor switch S _V1 to the fourth semiconductor switch S _V4 of the converter 12, and the first semiconductor switch S _W1 to the fourth semiconductor switch S _W4 of the converter 13 are switched to an on state or an off state depending on the level of a gate signal input to each gate.

4 is a timing chart of gate signals of the semiconductor switches according to the first embodiment. In this embodiment, as shown in FIG. 4, in order to make the phase of the coil currents the same among the three coils 21, 22, and 23, the gate signals are in phase among the three converters 11, 12, and 13. For example, the timing of the signal levels of the on state (high level) and off state (low level) of the first semiconductor switch S _U 1 of the converter 11 is the same as those of the first semiconductor switch S _V 1 of the converter 12 and the first semiconductor switch S _W 1 of the converter 13, respectively. The same is true for the second semiconductor switch S _U 2 to the fourth semiconductor switch S _U 4.

4, when the first semiconductor switches S _U1 , S _V1 , and S _W1 are on, the second semiconductor switches S U2, S V2, and S W2 are off, the third semiconductor switches S _U3 , S _V3 , and S _W3 are on, and the fourth semiconductor switches S _U4 , S _V4 , and S _W4 are off. Conversely, when the first semiconductor switches S _U1 , S _V1 , and S _W1 are off, the second semiconductor switches _S _U2 , S _V2 , and S _W2 are on, the third semiconductor switches S _U3 , S _V3 , and _S _W3 are off, and the fourth semiconductor switches S _U4 , S _V4 , and S _W4 are on _.

Fig. 5 is a diagram showing an example of the waveforms of the power supply currents in the first embodiment. Fig. 5 shows the U-phase power supply current _IU , the V-phase power supply current _IV , and the W-phase power supply current _IW . The power supply current _IU is the input current of the converter 11. The power supply current _IV is the input current of the converter 12. The power supply current _IW is the input current of the converter 13.

In this embodiment, each converter directly converts the power supply currents _IU , _IV , and _IW into high-frequency AC without converting them into DC, so that the distortion of each power supply current is extremely small, as shown in FIG.

When the power supply currents _IU , _IV , and _IW are input to the converters 11, 12, and 13, the semiconductor switches of the converters 11, 12, and 13 are switched on and off based on the gate signals shown in Fig. 4. As a result, output currents _IUOUT , _IVOUT , and _IWOUT are output from the converters 11, 12, and 13, respectively, as high-frequency AC currents.

6 is a diagram showing the amplitude waveforms and directions of the output currents I _UOUT , I _VOUT , and I _WOUT of the converters 11, 12, and 13 in the first embodiment. In this embodiment, the gate signals of the first semiconductor switches S _U1 , S _V1 , and S _W1 to the fourth semiconductor switches S _U4 , S _V4 , and S _W4 are in phase among the three converters 11, 12, and 13. Therefore, as shown in FIG. 6, the phases of the output currents I _UOUT , I _VOUT , and I _WOUT are also the same. The output currents I _UOUT , I _VOUT , and I _WOUT are supplied individually to the three coils 21, 22, and 23. As a result, there are two patterns for the direction of the coil current flowing through each coil: a pattern in which all three are positive, and a pattern in which all three are negative.

The three coils 21, 22, and 23 heat the object to be heated 50 (specifically, the resistive element R) with coil current. As described above, there are two different directions of the coil current in one period. As a result, there are also two different heating patterns using the three coils 21, 22, and 23. Here, the heating patterns using the three coils 21, 22, and 23 will be explained with reference to Figures 7(a) and 7(b).

FIG. 7(a) is a diagram showing an example of a heating pattern when all coil currents flow in the positive direction. When all coil currents flow in the positive direction, the coil currents flow in the opposite directions in the inner regions of each coil, i.e., the region where coil 21 faces coil 22, the region where coil 22 faces coil 23, and the region where coil 23 faces coil 21. In this case, the magnetic fields cancel each other out, making it difficult for induction heating to occur in the object to be heated 50. On the other hand, in the outer regions of each coil, the magnetic fields do not cancel each other out, so induction heating occurs in the object to be heated 50. Therefore, when all coil currents flow in the positive direction, a heating pattern is obtained in which the outer regions of each coil are heated, as shown in FIG. 7(a).

Figure 7(b) is a diagram showing an example of a heating pattern when the coil currents are all negative. Even when all coil currents flow in the negative direction, the coil currents flow in the opposite directions in the inner regions of each coil. This causes the magnetic fields to cancel each other out, making it difficult for induction heating to occur in the object to be heated 50. Furthermore, in the outer regions of each coil, the magnetic fields do not cancel each other out, so induction heating occurs in the object to be heated 50. Therefore, even when all coil currents flow in the negative direction, a heating pattern is obtained in which the outer regions of each coil are heated, as shown in Figure 7(b).

In the first embodiment, the heating pattern shown in FIG. 7(a) and the heating pattern shown in FIG. 7(b) are periodically repeated alternately. As a result, a heating distribution is obtained in which the outer region of the coil is hotter than the inner region of the coil.

According to the present embodiment described above, when the converters 11 to 13 convert the power supply currents _IU to _IW into the output currents _IUOUT to _IWOUT , the output currents _IUOUT to _IWOUT are directly converted into harmonic AC without passing through DC. This makes it possible to suppress distortion of the power supply currents _IU to _IW . In particular, in this embodiment, the converters 11 to 13 have a circuit configuration that does not require a diode rectifier or a smoothing capacitor that converts the power supply current of the three-phase AC power supply 30 into DC. This makes it possible to miniaturize the converters 11 to 13.

In addition, in this embodiment, the three coils 21, 22, and 23 are arranged in a triangular shape. The currents flowing through each coil are set to be in phase. This makes it possible to control the heating distribution of the coils 21 to 23 so that the outer regions of each coil are hotter than the inner regions of each coil.

Second Embodiment
A second embodiment of the present invention will be described. The induction heating device according to this embodiment includes three converters 11, 12, and 13 and three coils 21, 22, and 23, similar to the induction heating device 1 according to the first embodiment. The converters 11, 12, and 13 are configured with high-frequency cycloconverters, as shown in FIG. 3. Meanwhile, in this embodiment, in order to set the phase difference of the coil currents among the three coils 21, 22, and 23 to 120 degrees, the phase difference of the gate signals of the semiconductor switches among the three converters 11, 12, and 13 is 120 degrees. Here, the gate signals of the semiconductor switches according to the second embodiment will be described with reference to FIG. 8.

8 is a timing chart of the gate signals of the semiconductor switches according to the second embodiment. In this embodiment, as shown in FIG. 4, the phase difference between the gate signals of the first semiconductor switch S _U 1 to the fourth semiconductor switch S _U 4 of the converter 11 and the gate signals of the first semiconductor switch S _V 1 to the fourth semiconductor switch S _V 4 of the converter 12 is 120 degrees. Also, the phase difference between the gate signals of the first semiconductor switch S _U 1 to the fourth semiconductor switch S _U 4 of the converter 11 and the gate signals of the first semiconductor switch S _W 1 to the fourth semiconductor switch S _W 4 of the converter 13 is 240 degrees. In other words, the phase difference between the gate signals of the first semiconductor switch S _V 1 to the fourth semiconductor switch S _V 4 of the converter 12 and the gate signals of the first semiconductor switch S _W 1 to the fourth semiconductor switch S _W 4 of the converter 13 is 120 degrees.

In the converter 11, when the first semiconductor switch S _U 1 is on, the second semiconductor switch S _U 2 is off, the third semiconductor switch S _U 3 is on, and the fourth semiconductor switch S _U 4 is off based on the gate signals shown in Fig. 8. Conversely, when the first semiconductor switch S _U 1 is off, the second semiconductor switch S _U 2 is on, the third semiconductor switch S _U 3 is off, and the fourth semiconductor switch S _U 4 is on. In the converters 12 and 13, the semiconductor switches are switched on or off based on the gate signals shown in Fig. 8 in the same manner as in the converter 11.

Fig. 9 is a diagram showing an example of the waveform of the power supply current in the second embodiment. In this embodiment, as in the first embodiment, each converter is configured with a high-frequency cycloconverter as shown in Fig. 3. Therefore, each converter directly converts the power supply currents _IU , _IV , _IW into high-frequency AC without converting them into DC. Therefore, in this embodiment as well, the distortion of each power supply current is very small as shown in Fig. 9.

When the power supply currents _IU , _IV , and _IW are input to the converters 11, 12, and 13, the semiconductor switches of the converters 11, 12, and 13 are switched on and off based on the gate signals shown in Fig. 8. As a result, output currents _IUOUT , _IVOUT , and _IWOUT are output from the converters 11, 12, and 13, respectively, as high-frequency AC currents.

10 is a diagram showing the amplitude waveforms and directions of the output currents I _UOUT , I _VOUT , and I _WOUT of the converters 11, 12, and 13 in the second embodiment. In this embodiment, the phase of the gate signals of the first semiconductor switches S _U1 , S _V1 , and S _W1 to the fourth semiconductor switches S _U4 , S _V4 , and S _W4 is 120 degrees among the three converters 11, 12, and 13. Therefore, as shown in FIG. 10, the phase difference of the output currents I _UOUT , I _VOUT , and I _WOUT is also 120 degrees. As a result, there are six possible directions of the coil currents flowing through each coil, including three patterns in which two of the three coil currents are positive and three patterns in which two of the three coil currents are negative, as shown in FIG. 10.

The three coils 21, 22, and 23 heat the object to be heated 50 (specifically, the resistive element R) with coil current. As described above, there are six possible directions of the coil current. As a result, there are six possible heating patterns using the three coils 21, 22, and 23. Here, the heating patterns using the three coils 21, 22, and 23 will be explained with reference to Figures 11(a) to 11(f).

FIG. 11(a) shows an example of a heating pattern when the direction of the current flowing through coils 21 and 23 is positive and the direction of the current flowing through coil 22 is negative. In this case, the outer regions of coil 21 and coil 23 are heated. Furthermore, the direction of the coil current is the same in the region where coils 21 and 22 face each other and the region where coils 22 and 23 face each other. Therefore, these regions are also heated. On the other hand, in the region where coils 21 and 23 face each other, the directions of the coil current are opposite to each other. Therefore, in this region, the magnetic fields cancel each other out, making it difficult for induction heating to occur in the heated object 50.

Figure 11 (b) shows an example of a heating pattern when the direction of the current flowing through coil 21 is positive and the direction of the current flowing through coils 22 and 23 is negative. In this case, the outer regions of coil 22 and coil 23 are heated. Furthermore, in the regions where coil 21 faces coils 22 and 23, the coil current flows in the same direction, so these regions are also heated. On the other hand, in the region where coils 22 and 23 face each other, the coil current flows in opposite directions, so induction heating is less likely to occur in object to be heated 50.

Figure 11 (c) shows an example of a heating pattern when the direction of the current flowing through coils 21 and 22 is positive and the direction of the current flowing through coil 23 is negative. In this case, the outer regions of coil 21 and coil 22 are heated. Furthermore, in the regions where coil 23 faces coils 21 and 22, the coil current flows in the same direction, so these regions are also heated. On the other hand, in the region where coils 21 and 22 face each other, the coil current flows in opposite directions, so induction heating is less likely to occur in object to be heated 50.

Figure 11(d) is a diagram showing an example of a heating pattern when the direction of the current flowing through coil 22 is positive and the direction of the current flowing through coils 21 and 23 is negative. In this case, the outer regions of coil 21 and coil 23 are heated. Furthermore, in the regions where coil 22 faces coils 21 and 23, the coil current flows in the same direction, so these regions are also heated. On the other hand, in the region where coils 21 and 23 face each other, the coil current flows in opposite directions, so induction heating is less likely to occur in object to be heated 50.

Figure 11(e) is a diagram showing an example of a heating pattern when the direction of the current flowing through coils 22 and 23 is positive and the direction of the current flowing through coil 21 is negative. In this case, the outer regions of coil 22 and coil 23 are heated. Furthermore, in the regions where coil 21 faces coils 22 and 23, the coil current flows in the same direction, so these regions are also heated. On the other hand, in the region where coils 22 and 23 face each other, the coil current flows in opposite directions, so induction heating is less likely to occur in object to be heated 50.

Figure 11(f) shows an example of a heating pattern when the direction of the current flowing through coil 23 is positive and the direction of the current flowing through coils 21 and 22 is negative. In this case, the outer regions of coil 21 and coil 22 are heated. Furthermore, in the regions where coil 23 faces coils 21 and 22, the coil current flows in the same direction, so these regions are also heated. On the other hand, in the region where coils 21 and 22 face each other, the coil current flows in opposite directions, so induction heating is less likely to occur in object to be heated 50.

Here, we will explain the experimental results of actually heating coils 21, 22, and 23 using the heating pattern of the first embodiment and the heating pattern of the second embodiment.

FIG. 12(a) shows the heating distribution when coils 21, 22, and 23 are actually heated with the heating pattern of the first embodiment. Also, FIG. 12(b) shows the heating distribution when coils 21, 22, and 23 are actually heated with the heating pattern of the second embodiment. The heating distributions shown in FIG. 12(a) and FIG. 12(b) can be measured using a thermoviewer.

In the first embodiment described above, the heating patterns shown in Fig. 7(a) and Fig. 7(b) are repeated periodically. Therefore, as shown in Fig. 12(a), the temperature of the outer region of the coil becomes higher than the temperature of the inner region of the coil.

In contrast, in the second embodiment, the heating patterns shown in Figures 11(a) to 11(f) are repeated periodically. As a result, both the outer and inner regions of the coil are heated, resulting in a heating distribution in which the temperature difference between the inner and outer regions is smaller than in the first embodiment, as shown in Figure 12(b). At this time, because the heat source is concentrated in the inner region, it is possible to control the heating distribution so that the inner region is hotter than the outer region.

In the present embodiment described above, similarly to the first embodiment, when the converters 11 to 13 convert the power supply currents _IU to _IW into the output currents _IUOUT to _IWOUT , the output currents _IUOUT to _IWOUT are directly converted into harmonic AC without passing through DC. This makes it possible to suppress distortion of the power supply currents _IU to _IW . Also, in this embodiment, the converters 11 to 13 have a circuit configuration that does not require a diode rectifier or a smoothing capacitor that converts the power supply current of the three-phase AC power supply 30 into DC. This makes it possible to miniaturize the converters 11 to 13.

Furthermore, as in the first embodiment, the three coils 21, 22, and 23 are arranged in a triangular shape. On the other hand, in this embodiment, the phase difference of the current flowing through each coil is set to 120 degrees. This makes it possible to control the heating distribution of the coils 21 to 23 so that not only the outer region of each coil but also the inner region of each coil is heated.

Third Embodiment
A third embodiment of the present invention will now be described. The induction heating device according to this embodiment includes three converters 11, 12, and 13 and three coils 21, 22, and 23, similar to the induction heating device 1 according to the first embodiment. The converters 11, 12, and 13 are configured with high-frequency cycloconverters as shown in Fig. 3. However, in this embodiment, the arrangement of the three coils 21, 22, and 23 is different from that of the first embodiment.

FIG. 13 is a schematic diagram showing the coil arrangement in the third embodiment. In this embodiment, three coils 21, 22, and 23 are arranged in a row. In this case, as in the first embodiment, the distance D between the centers of adjacent coils is within the diameter d of each coil. Note that in FIG. 13, the distance D is shown as being longer than the diameter d in order to make it easier to understand the direction of the current flowing through each coil.

In this embodiment, when the gate signals of the first semiconductor switches S _U1 , S _V1 , S _W1 to the fourth semiconductor switches S _U4 , S _V4 , S _W4 are in phase among the three converters 11, 12, 13, the three converters 11, 12, 13 are driven in a synchronous mode in which the phases of the output currents I _UOUT , I _VOUT , and I _WOUT are in the same phase, as in the first embodiment (see FIG. 6). In the synchronous mode, there are two patterns for the direction of the coil current flowing through each coil: a pattern in which all three are positive, and a pattern in which all three are negative. FIG. 13 shows a pattern in which all the coil currents are positive. Here, the heating pattern by the three coils 21, 22, 23 will be described with reference to FIG. 14.

FIG. 14 is a diagram showing an example of a heating pattern when the coil currents are all positive in the third embodiment. When the coil currents all flow in the positive direction, the directions of the coil currents are opposite to each other in the inner regions of each coil, i.e., the region where coil 21 faces coil 22, and the region where coil 22 faces coil 23. In this case, the magnetic fields cancel each other out, making it difficult for induction heating to occur in the heated object 50.

On the other hand, in the outer regions of each coil, the phenomenon of magnetic fields canceling each other out does not occur, and induction heating occurs in the heated object 50. Therefore, when the directions of the coil currents are all positive, the heating pattern heats the outer regions of each coil, as shown in FIG. 14.

FIG. 15 is a diagram showing an example of a heating pattern when the coil currents are all negative in the third embodiment. Even when the coil currents all flow in the negative direction, the coil currents flow in opposite directions in the inner regions of each coil, i.e., the region where coil 21 faces coil 22, and the region where coil 22 faces coil 23. Therefore, the heating pattern heats the outer regions of each coil, just like when the coil currents are all positive.

Fig. 16 is a diagram showing an example of the waveforms of the power supply currents in the synchronous mode, which respectively show the power supply current _IU of the converter 11 (U phase), the power supply current _IV of the converter 12 (V phase), and the power supply current IW of the converter 13 (W phase) when the converters 11, 12, and ₁₃ are driven in the synchronous mode.

In this embodiment, similarly to the first embodiment, each converter directly converts the power supply currents _IU , _IV , and _IW into high-frequency AC without converting them into DC, so that the distortion of each power supply current is extremely small, as shown in FIG.

In the present invention, the driving mode of the three converters 11, 12, and 13 is not limited to the above-mentioned synchronous mode, and may be, for example, a 180-degree mode. In the 180-degree mode, the phase difference of the gate signals of the first semiconductor switches S _U 1, S V 1, and S _W 1 to the fourth semiconductor switches S _U 4, S _V 4, and S _W 4 for driving each converter between two converters that supply harmonic AC to two adjacent coils among the three converters 11, ₁₂ , and 13 is 0 degrees or 180 degrees. In other words, in the 180-degree mode, the phase of one coil current among the three coils 21, 22, and 23 is shifted by 180 degrees with respect to the phases of the other two coil currents. Here, the heating pattern by the coils 21, 22, and 23 in the 180-degree mode will be described.

FIG. 17 is a diagram showing an example of a heating pattern when the phase of the U-phase coil current is shifted 180 degrees from the phase of the V-phase and W-phase coil currents. In FIG. 17, current flows in a positive direction in U-phase coil 21, while current flows in a negative direction in V-phase coil 22 and W-phase coil 23.

As shown in FIG. 17, in the region between coils 21 and 22, the current flows in the same direction, so the magnetic fields do not cancel each other out. This results in a heating pattern in which the inner region is heated. On the other hand, in the region between coils 22 and 23, the current flows in the opposite direction, so the magnetic fields cancel each other out. This results in a heating pattern in which the outer region is heated.

FIG. 18 shows another example of a heating pattern when the phase of the U-phase coil current is shifted 180 degrees from the phases of the V-phase and W-phase coil currents. In FIG. 18, current flows in the negative direction in coil 21, while current flows in the positive direction in coils 22 and 23.

As shown in FIG. 18, the direction of the current is the same in the region between coils 21 and 22, while the direction of the current is opposite in the region between coils 22 and 23. Therefore, in the heating pattern shown in FIG. 18, like the heating pattern shown in FIG. 17, the inner region between coils 21 and 22 is heated, and the outer region between coils 22 and 23 is heated.

Figure 19 shows an example of a heating pattern when the phase of the V-phase coil current is shifted 180 degrees from the phase of the U-phase and W-phase coil currents. In Figure 19, current flows in a positive direction in V-phase coil 22, while current flows in a negative direction in U-phase coil 21 and W-phase coil 23.

As shown in FIG. 19, the direction of the current is the same in the region between coils 21 and 22, resulting in a heating pattern in which the inner region is heated. Also, the direction of the current is the same in the region between coils 22 and 23, resulting in a heating pattern in which the inner region is heated.

FIG. 20 shows another example of a heating pattern when the phase of the V-phase coil current is shifted 180 degrees from the phase of the U-phase and W-phase coil currents. In FIG. 20, current flows in the negative direction in coil 22, while current flows in the positive direction in coils 21 and 23.

As shown in FIG. 20, the direction of the current is the same in the region between coils 21 and 22, and also in the region between coils 22 and 23. Therefore, the heating pattern shown in FIG. 20 heats the inner region between the coils, similar to the heating pattern shown in FIG. 19.

FIG. 21 shows an example of a heating pattern when the phase of the W-phase coil current is shifted 180 degrees from the phase of the U-phase and V-phase coil currents. In FIG. 21, current flows in a positive direction in the W-phase coil 23, while current flows in a negative direction in the U-phase coil 21 and the V-phase coil 22.

As shown in FIG. 21, in the region between coils 21 and 22, the current flows in the opposite direction, resulting in a heating pattern in which the outer region is heated. On the other hand, in the region between coils 22 and 23, the current flows in the same direction, resulting in a heating pattern in which the inner region is heated.

FIG. 22 shows another example of a heating pattern when the phase of the W-phase coil current is shifted 180 degrees from the phase of the U-phase and V-phase coil currents. In FIG. 22, current flows in the negative direction in coil 23, while current flows in the positive direction in coils 21 and 22.

As shown in FIG. 22, the direction of the current is opposite in the region between coils 21 and 22, while the direction of the current is the same in the region between coils 22 and 23. Therefore, in the heating pattern shown in FIG. 22, like the heating pattern shown in FIG. 21, the outer region is heated between coils 21 and 22, and the inner region is heated between coils 22 and 23.

FIG. 23 is a diagram showing an example of a power supply current waveform in 180-degree mode. FIG. 23 shows an example of a power supply current waveform in which the U-phase coil current is shifted 180 degrees relative to the V-phase and W-phase coil currents.

Even when each converter is driven in the 180 degree mode, as in the synchronous mode, each converter directly converts the power supply currents _IU , _IV , and _IW into high-frequency AC without converting them into DC. Therefore, the distortion of each power supply current is very small, as shown in Fig. 23. Note that, even when the V-phase coil current and the W-phase coil current are shifted by 180 degrees, the distortion of the power supply currents _IU , _IV , and _IW is also very small.

FIG. 24 is a schematic diagram showing the coil arrangement in a modified example of the third embodiment. In this modified example, three coils 21, 22, and 23 are arranged in an L-shape. In this case, as in the third embodiment, the distance D between the centers of adjacent coils is within the diameter d of each coil.

In this modified example, the three converters 11, 12, and 13 can be driven in the synchronous mode or 180-degree mode described above. In this case, if the direction of the coil current is the same between two adjacent coils, the inner region is heated. Conversely, if the direction of the coil current is opposite, the outer region is heated.

In this modification, the three converters 11, 12, and 13 directly convert the power supply currents _IU , _IV , and _IW into high-frequency AC without converting them into DC. Therefore, in this modification as well, the distortion of each power supply current is extremely small.

According to the present embodiment described above, similarly to the first embodiment, when the converters 11 to 13 convert the power supply currents _IU to _IW into the output currents _IUOUT to _IWOUT , the output currents _IUOUT to _IWOUT are directly converted into harmonic AC without passing through DC, thereby making it possible to suppress distortion of the power supply currents _IU to _IW .

Also, in this embodiment, the converters 11 to 13 have a circuit configuration that does not require a diode rectifier or smoothing capacitor to convert the power supply current of the three-phase AC power supply 30 to DC. This makes it possible to miniaturize the converters 11 to 13.

Furthermore, in this embodiment, the three coils 21, 22, and 23 are arranged in a line or in an L-shape. By heating the coils 21 to 23 arranged in this manner with each converter driven in synchronous mode or 180-degree mode, it becomes possible to control the heating of the outer region of each coil and the inner region of each coil.

In the first and second embodiments described above, the converters 11 to 13 are configured with high-frequency cycloconverters, but in the present invention, the circuit configuration of each converter is not limited to that shown in Fig. 3. For example, each converter may be a matrix converter configured with bidirectional switches connected to each phase of the three-phase AC power supply 30. This bidirectional switch is configured with two semiconductor switches connected in series in the opposite directions, such as the second semiconductor switch S _U 2 and the third semiconductor switch S _U 3 shown in Fig. 3. Furthermore, each converter may be a converter in which this bidirectional switch is provided in a chopper circuit.

Furthermore, in the present invention, the circuit configuration of each converter may be any circuit configuration that converts the power supply current of the three-phase AC power supply 30 into harmonic AC without converting it into DC. Therefore, each converter may have a circuit configuration including an inverter circuit and an AC/DC converter. The inverter circuit includes two arms connected in series, such as the first semiconductor switch S _U 1 and the second semiconductor switch S _U 2 shown in FIG. 3. The AC/DC converter is, for example, a diode rectifier. In this case, the capacity of the capacitor connected between the inverter circuit and the AC/DC converter is reduced so as not to smooth the power supply current, thereby making it possible to directly convert the power supply current into high-frequency AC while leaving the AC component of the power supply current.

Based on the above description, a person skilled in the art may be able to conceive of additional effects and various modifications of the present invention, but the aspects of the present invention are not limited to the above-described embodiments. Various additions, modifications, and partial deletions are possible within the scope that does not deviate from the conceptual idea and intent of the present invention derived from the contents defined in the claims and their equivalents.

1: induction heating device 11-13: converter 21-23: coil 30: three-phase AC power supply 50: object to be heated S _U 1, S _V 1, S _W 1: first semiconductor switch S _U 2, S _V 2, S _W 2: second semiconductor switch S _U 3, S _V 3, S _W 3: third semiconductor switch S _U 4, S _V 4, S _W 4: fourth semiconductor switch

Claims

Three converters for directly converting three-phase power supply currents of a three-phase AC power supply into three high-frequency AC currents having frequencies higher than the frequency of the power supply currents;
and three coils for heating an object to be heated with harmonic alternating current supplied individually from the three converters;
The three coils are arranged such that the center-to-center distance is within a coil diameter.
The induction heating device of claim 1, wherein the three coils are arranged in a triangular shape.
each of the three converters is a harmonic cycloconverter;
2. The induction heating device according to claim 1, wherein the harmonic cycloconverter includes a first semiconductor switch and a second semiconductor switch connected in series with each other, and a third semiconductor switch and a fourth semiconductor switch connected in series with each other in a direction opposite to that of the first semiconductor switch and the second semiconductor switch.
The first to fourth semiconductor switches are switched to an on state or an off state according to a level of a gate signal input to each gate,
When the first semiconductor switch is in an on state, the second semiconductor switch is in an off state, the third semiconductor switch is in an on state, and the fourth semiconductor switch is in an off state;
4. The induction heating device according to claim 3, wherein when the first semiconductor switch is in an off state, the second semiconductor switch is in an on state, the third semiconductor switch is in an off state, and the fourth semiconductor switch is in an on state.
The induction heating device of claim 2, wherein the phase difference of the coil currents between the three coils is 120 degrees.
The induction heating device of claim 2, wherein the centers of the three coils are located at the vertices of an equilateral triangle.
An induction heating device as described in any one of claims 1 to 6, in which the three coils partially overlap each other.
The induction heating device of claim 1, wherein the three coils are arranged in a row.
The induction heating device of claim 1, wherein the three coils are arranged in an L-shape.
An induction heating device as described in claim 2, 8, or 9, in which the phase of the coil current is the same among the three coils.
An induction heating device as described in claim 2, 8, or 9, in which the phase difference of the coil current between two adjacent coils among the three coils is 0 degrees or 180 degrees.