JP7657095B2 - Electromagnetic induction heating device - Google Patents

Description

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

In recent years, inverter-type electromagnetic induction heating devices that heat objects such as pots without using fire have come into widespread use. An electromagnetic induction heating device passes a high-frequency current through a heating coil, generating eddy currents in a metal object to be heated (such as a pot) placed close to the heating coil, causing the object to generate heat through its own electrical resistance.

An electromagnetic induction heating device disclosed in Patent Document 1 is a conventional example that can heat when two heating coils are provided. This electromagnetic induction heating device has three semiconductor switches (Q1a, Q1b, and Q1c, Figure 1 of the same document) connected in series to a DC power source. When it is desired to heat by passing currents of the same phase through the two heating coils (6 and 7, Figure 1 of the same document), Q1b is always on and Q1a and Q1c are alternately turned on and off (Figure 3 of the same document) for induction heating. When it is desired to heat by passing currents of opposite phases through the two heating coils, Q1b is exclusively turned on and off (Figure 24 of the same document) for induction heating, while Q1a and Q1c are turned on and off synchronously.

International Publication No. 2014/064932

In Patent Document 1, when the equivalent impedance including the resistance of the heating coil and the object to be heated differs depending on the magnetic coupling state between the heating coil and the object to be heated (for example, when the material or position of the object to be heated differs), the magnitude of the current flowing through the two heating coils is determined by their respective equivalent impedances, so the coil currents are not uniform and the heating efficiency decreases.

The object of the present invention is to address the above-mentioned problems and to provide an inverter-type electromagnetic induction heating device that can equalize the current flowing through multiple heating coils and efficiently supply the desired power to the heated object, even when the equivalent impedance, including the resistance of the heating coils and the heated object, is different.

In order to achieve the above object, the electromagnetic induction heating device of the present invention is an electromagnetic induction heating device including a DC power source that outputs a DC voltage, an inverter circuit that converts the DC voltage into an AC voltage, and a heating coil that uses the AC voltage to inductively heat an object to be heated. The inverter circuit includes a switching element series body in which three or more switching elements are connected in series, which is provided between the positive electrode and the negative electrode of the DC power source. The negative electrode is connected to a first series body in which a first switching element, a first heating coil, and a first resonant capacitor are connected in series, and a second series body in which the first switching element, a second switching element, a first power supply capacitor, a second heating coil, and a second resonant capacitor are connected in series. The first switching element and the second switching element are included in the switching element series body.

The electromagnetic induction heating device of the present invention can equalize the currents in multiple heating coils and efficiently supply the desired power to the heated object even when the equivalent impedances, including the resistances of the heating coils and the heated object, are different.

FIG. 2 is a circuit diagram of the electromagnetic induction heating device according to the first embodiment. 4 shows operational waveforms of the electromagnetic induction heating device of the first embodiment. 4 shows a current path in mode a in the first embodiment. 4 shows a current path in mode b in the first embodiment. 4 shows a current path in mode c in the first embodiment. 4 shows a current path in mode d in the first embodiment. FIG. 11 is a circuit diagram of an electromagnetic induction heating device according to a second embodiment. 11 is an operational waveform of the electromagnetic induction heating device of the second embodiment. 11 is an operational waveform of the electromagnetic induction heating device of the second embodiment. FIG. 11 is a circuit diagram of an electromagnetic induction heating device according to a third embodiment. FIG. 11 is a circuit diagram of an electromagnetic induction heating device according to a third embodiment.

The following describes an embodiment of the present invention with reference to the drawings. Note that in each drawing, the same reference numerals indicate the same components or components with similar functions, and redundant explanations are omitted where appropriate.

First, an electromagnetic induction heating device according to a first embodiment of the present invention will be described with reference to Figures 1 to 3D. The electromagnetic induction heating device of this embodiment has a heat-resistant glass top plate placed on top of a metal housing, and a high-frequency current is supplied to a heating coil placed below the top plate to inductively heat a metal object to be heated placed at a predetermined position on the top surface of the top plate; however, a description of this well-known configuration will be omitted below.

Figure 1 is a circuit diagram of an electromagnetic induction heating device of Example 1. In Figure 1, a DC power supply 1 is a power supply that rectifies an AC voltage supplied from a commercial AC power supply of 200V or 100V and outputs a DC voltage. Four power semiconductor switching elements (hereinafter simply referred to as "switching elements") 5a, 5c, 5e, and 5f are connected in series between the positive electrode P and the negative electrode N of this DC power supply 1. In addition, diodes 6a, 6c, 6e, and 6f are connected in parallel in the opposite direction to the switching elements 5a, 5c, 5e, and 5f, respectively. Note that, although Figure 1 illustrates a configuration in which four switching elements are connected in series, the present invention can be applied to any electromagnetic induction heating device in which a series body of three or more switching elements is arranged between the positive electrode P and the negative electrode N.

Here, the connection point of switching elements 5a and 5c is referred to as output terminal A, the connection point of switching elements 5c and 5e is referred to as output terminal C, and the connection point of switching elements 5e and 5f is referred to as output terminal E.

As shown in FIG. 1, one end of the power supply capacitor 31 is connected to the output terminal A, and a series circuit of the heating coil 11 and resonant capacitor 21 is connected between the other end of the power supply capacitor 31 and the negative electrode N of the DC power supply 1. This configuration can also be considered as a series circuit of the switching elements 5f, 5e, 5c, the power supply capacitor 31, the heating coil 11, and the resonant capacitor 21 being connected to the negative electrode N. Note that there is no problem if the connection order of the heating coil 11 and the resonant capacitor 21 is reversed.

In addition, one end of the power supply capacitor 32 is connected to the output terminal C, and a series circuit of the heating coil 12 and resonant capacitor 22 is connected between the other end of the power supply capacitor 32 and the negative electrode N of the DC power supply 1. This configuration can also be considered as a series circuit of the switching elements 5f, 5e, power supply capacitor 32, heating coil 12, and resonant capacitor 22 being connected to the negative electrode N. Note that there is no problem if the connection order of the heating coil 12 and resonant capacitor 22 is reversed.

Furthermore, a series circuit of the heating coil 13 and the resonant capacitor 23 is connected between the output terminal E and the negative electrode N of the DC power supply 1. This configuration can also be regarded as a series circuit of the switching element 5f, the heating coil 13, and the resonant capacitor 23 being connected to the negative electrode N. Note that there is no problem if the connection order of the heating coil 13 and the resonant capacitor 23 is reversed.

In an electromagnetic induction heating device with the circuit configuration described above, by appropriately turning on and off the switching elements 5a, 5c, 5e, and 5f, a current resonant inverter that flows current evenly through the heating coils 11 to 13 can be realized.

Next, a specific method for controlling each switching element provided in the electromagnetic induction heating device of this embodiment will be described with reference to Fig. 2 and Fig. 3A to Fig. 3D. Note that the direction of currents _i11 , i12, and i13 flowing through heating coils 11, ₁₂ , and ₁₃ is defined as the positive direction in the dashed-dotted arrow direction shown in Fig. 1.

Figure 2 shows the operating waveforms of each part, from top to bottom: (a) gate drive signals _vg5a to _vg5f of each switching element, (b) currents _i11 , _i12 , and _i13 of each heating coil, and (c) currents _i5a to _i5f , and _i6a to _i6f of each switching element and diode.

In the lower part of Figure 2, a to d indicate four operating modes defined by the on/off state of switching elements 5a to 5f. The current paths in each operating mode are explained below with reference to Figures 3A to 3D.

<Mode a>
3A, during a period in which switching elements 5a and 5e are on and switching elements 5c and 5f are off, a current flows from DC power supply 1 through switching element 5a, power supply capacitor 31, heating coil 11, and resonant capacitor 21. This current causes charge to accumulate in power supply capacitor 31. Note that power supply capacitor 31 has a capacity equal to or greater than resonant capacitor 21 and can accumulate a charge equal to or greater than that of resonant capacitor 21. Also, with power supply capacitor 32 charged in mode c, which will be described later, as a voltage source, a current flows through the path of switching element 5e, heating coil 13, resonant capacitor 23, resonant capacitor 22, and heating coil 12.

<Mode b>
Next, when switching elements 5a and 5e are turned off and switching elements 5c and 5f are turned on, as shown in Fig. 3B, the stored energy in heating coils 11 and 12 causes a current to circulate through the path of heating coil 11, resonant capacitor 21, resonant capacitor 22, heating coil 12, power supply capacitor 32, diode 6c, and power supply capacitor 31. Also, the stored energy in heating coil 13 causes a current to circulate through the path of heating coil 13, resonant capacitor 23, and diode 6f.

Here, by turning on switching elements 5c and 5f while current is flowing through diodes 6c and 6f, zero-voltage switching operation is performed, enabling soft switching operation with little switching loss.

<Mode c>
When the stored energy in heating coils 11 and 12 becomes zero, as shown in Fig. 3C, current flows through a path of switching element 5c, power supply capacitor 32, heating coil 12, resonant capacitor 22, resonant capacitor 21, and heating coil 11, with power supply capacitor 31 as a voltage source, and the current in heating coils 11 and 12 switches to the negative direction. This mode c causes the charge in power supply capacitor 31 to move to power supply capacitor 32. Note that power supply capacitor 32 has a capacity equal to or greater than that of resonant capacitor 22, and can store a charge equal to or greater than that of resonant capacitor 22. Furthermore, when the stored energy in heating coil 13 becomes zero, current flows through a path from resonant capacitor 23 to heating coil 13 and switching element 5f, and the current in heating coil 13 also switches to the negative direction.

<Mode d>
3D, the stored energy in heating coil 11 causes a current to circulate through the path of heating coil 11, power supply capacitor 31, diode 6a, and DC power supply 1. The stored energy in heating coils 12 and 13 also causes a current to circulate through the path of heating coil 12, resonant capacitor 22, resonant capacitor 23, heating coil 13, diode 6e, and power supply capacitor 32.

Here, by turning on the switching elements 5a and 5e while current is flowing through the diodes 6a and 6e, zero-voltage switching operation is performed, enabling soft switching operation with little switching loss.

When the stored energy in heating coils 11 to 13 becomes zero, the mode changes to mode a and the current in heating coils 11 to 13 switches to the positive direction.

By repeating the above modes a to d, in mode a, the current flowing through the heating coil 11 charges the resonant capacitor 21 and the power supply capacitor 31, in mode c, the current flowing through the heating coil 12 using the power supply capacitor 31 as the power supply charges the resonant capacitor 22 and the power supply capacitor 32, and in mode a, the current flowing through the heating coil 13 using the power supply capacitor 32 as the power supply charges the resonant capacitor 23. In this way, by using the power supply capacitor 31 and the power supply capacitor 32, current flows through the heating coils 11 to 13 while the charge amount of the power supply capacitor 31 and the power supply capacitor 32 is preserved. As a result, even if the equivalent impedance including the resistance of the heating coil and the heated object is different, the current of the heating coils 11 to 13 is naturally balanced without applying special control. Note that the current of the heating coils 11 to 13 can be balanced even in a configuration in which the resonant capacitor 21 and the resonant capacitor 22 are omitted, but the withstand voltage can be improved by providing the resonant capacitor and the power supply capacitor separately and connecting them in series.

As described above, the electromagnetic induction heating device of this embodiment can equalize the currents in multiple heating coils and efficiently supply the desired power to the heated object even when the equivalent impedances, including the resistances of the heating coils and the heated object, are different.

Next, an electromagnetic induction heating device according to a second embodiment of the present invention will be described with reference to Figures 4 to 6. Note that a duplicated description of the points common to the first embodiment will be omitted.

The circuit configuration of this embodiment shown in FIG. 4 is roughly the same as that of the embodiment 1 shown in FIG. 1, with two parallel switching elements (switching elements 5b, 5d) added. In FIG. 4, if the connection point between the power supply capacitor 31 and the heating coil 11 is called output terminal B, switching element 5b is connected between output terminal B and the negative electrode N of the DC power supply 1. If the connection point between the power supply capacitor 32 and the heating coil 12 is called output terminal D, switching element 5d is connected between output terminal D and the negative electrode N of the DC power supply 1. Diodes 6b, 6d are connected in parallel in the opposite direction to switching elements 5b, 5d, respectively.

In this embodiment, the added switching element 5b turns on and off in a complementary manner with the switching element 5a, and the added switching element 5d turns on and off in a complementary manner with the switching element 5c. As a result, the switching elements 5a and 5b, the power supply capacitor 31, the heating coil 11, and the resonant capacitor 21 form a first-stage inverter, the switching elements 5c and 5d, the power supply capacitor 32, the heating coil 12, and the resonant capacitor 22 form a second-stage inverter, and the switching elements 5e and 5f, the heating coil 13, and the resonant capacitor 23 form a third-stage inverter. Below, the characteristic current paths of modes a and c are explained as an example of how to use each inverter.

In mode a of embodiment 1, as shown in FIG. 3A, current flows through the path of switching element 5e, heating coil 13, resonant capacitor 23, resonant capacitor 22, and heating coil 12, with power supply capacitor 32 as the voltage source. However, in mode a of this embodiment, switching element 5d, which turns on and off complementarily to switching element 5c, is turned on, so current flows through the path of switching element 5e, heating coil 13, resonant capacitor 23, and switching element 5d, with power supply capacitor 32 as the voltage source, that is, a path that avoids heating coil 12. In this way, a current path can be formed that does not supply power from power supply capacitor 32 to heating coil 12.

In addition, in mode c of Example 1, as shown in FIG. 3C, current flows through the path of switching element 5c, power supply capacitor 32, heating coil 12, resonant capacitor 22, resonant capacitor 21, and heating coil 11, with power supply capacitor 31 as the voltage source. However, in mode c of this embodiment, switching element 5b, which turns on and off complementarily to switching element 5a, is turned on, so current flows through the path of switching element 5c, power supply capacitor 32, heating coil 12, and resonant capacitor 22, with power supply capacitor 31 as the voltage source, that is, a path that avoids heating coil 11. In this way, a current path that does not supply power from power supply capacitor 31 to heating coil 11 can be formed.

Figure 5 shows the operating waveforms of each part, from top to bottom: (a) gate drive signals _vg5a to _vg5f of each switching element, (b) currents _i11 , _i12 , and _i13 of each heating coil, and (c) currents _i5a to _i5f , and _i6a to _i6f of each switching element and diode.

In FIG. 5, by shifting the timing at which switching elements 5a, 5c, and 5e are turned on by 120 degrees each within a switching period, it is possible to balance the current while shifting the current phase of heating coils 11 to 13 by 120 degrees each.

If the number of inverter stages is increased from three to four, it is possible to similarly shift the phase of the heating coil current by shifting it by 90 degrees at a time. In this way, it is possible to balance the current while shifting the current phase of multiple heating coils, thereby heating the object to be heated evenly.

In the electromagnetic induction heating device of Example 2, if the currents in heating coils 11 to 13 are to flow in the same phase without shifting the phase of the heating coil current, it is sufficient to synchronize the timing at which switching elements 5a, 5d, and 5e are turned on, as shown in Figure 6.

Figures 7 and 8 are circuit diagrams of the electromagnetic induction heating device of Example 3. A duplicated explanation of points common to Examples 1 and 2 will be omitted.

The electromagnetic induction heating device shown in Figure 7 is, in general, a device in which the heating coil and resonant capacitor of Example 1 shown in Figure 1 have been moved to the positive electrode P side of the DC power supply 1, and the current phase of each heating coil is controlled by driving switching elements 5a, 5c, 5e, and 5f in the same manner as in Example 1.

Similarly, the electromagnetic induction heating device shown in FIG. 8 is roughly the same as that shown in FIG. 4, except that the heating coil and resonant capacitor of the second embodiment are moved to the positive electrode P side of the DC power supply 1, and the current phase of each heating coil is controlled by driving the switching elements 5a to 5f in the same manner as in the second embodiment.

Even if the electromagnetic induction heating device is configured as shown in Figures 7 and 8, the same effects as in Examples 1 and 2 can be obtained.

1 DC power source,
2 inverters,
5 switching element,
6 diodes,
11 to 13 heating coil,
21 to 23 resonant capacitor,
31, 32 Power supply capacitor

Claims (8)

A DC power supply that outputs a DC voltage;
an inverter circuit that converts the DC voltage into an AC voltage;
A heating coil that uses the AC voltage to inductively heat an object to be heated;
An electromagnetic induction heating device comprising:
the inverter circuit includes a switching element series body having three or more switching elements connected in series, the switching element series body being provided between a positive electrode and a negative electrode of the DC power supply,
The negative electrode has
a first circuit in which a first switching element, a first heating coil, and a first resonant capacitor are connected in a ring ;
a second circuit in which the first switching element, the second switching element, a first power supply capacitor, a second heating coil, and a second resonant capacitor are connected in a ring ;
is connected,
The electromagnetic induction heating device, wherein the first switching element and the second switching element are included in the switching element series body. A DC power supply that outputs a DC voltage;
an inverter circuit that converts the DC voltage into an AC voltage;
A heating coil that uses the AC voltage to inductively heat an object to be heated;
An electromagnetic induction heating device comprising:
the inverter circuit includes a switching element series body having three or more switching elements connected in series, the switching element series body being provided between a positive electrode and a negative electrode of the DC power supply,
The positive electrode includes:
a first circuit in which a first switching element, a first heating coil, and a first resonant capacitor are connected in a ring ;
a second circuit in which the first switching element, the second switching element, a first power supply capacitor, a second heating coil, and a second resonant capacitor are connected in a ring ;
is connected,
The electromagnetic induction heating device, wherein the first switching element and the second switching element are included in the switching element series body. 3. The electromagnetic induction heating device according to claim 1,
An electromagnetic induction heating device characterized in that, during a period in which the first switching element is turned off and the second switching element is turned on, a current flows through a path of the second switching element, the first heating coil, the first resonant capacitor, the second resonant capacitor, and the second heating coil, with the first power supply capacitor as a voltage source. 3. The electromagnetic induction heating device according to claim 1,
An electromagnetic induction heating device, characterized in that a first parallel switching element is connected in parallel to the second heating coil and the second resonant capacitor. 2. The electromagnetic induction heating device according to claim 1,
An electromagnetic induction heating device characterized in that a third circuit in which the first switching element, the second switching element, the third switching element, a second power supply capacitor, a third heating coil, and a third resonant capacitor are connected in a ring shape to the negative electrode, and the third switching element is included in the switching element series. 3. The electromagnetic induction heating device according to claim 2,
An electromagnetic induction heating device characterized in that a third circuit in which the first switching element, the second switching element, the third switching element, a second power supply capacitor, a third heating coil, and a third resonant capacitor are connected in a ring shape to the positive electrode, and the third switching element is included in the switching element series. 7. The electromagnetic induction heating device according to claim 5,
an electromagnetic induction heating device characterized in that, during a period in which the second switching element is turned off and the third switching element is turned on, a current flows through a path of the third switching element, the first power supply capacitor, the second heating coil, the second resonant capacitor, the third resonant capacitor, and the third heating coil, with the second power supply capacitor as a voltage source. 7. The electromagnetic induction heating device according to claim 5,
An electromagnetic induction heating device, characterized in that a second parallel switching element is connected in parallel to the third heating coil and the third resonant capacitor.

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