JP7222806B2 - Electromagnetic induction heating device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inverter-type electromagnetic induction heating apparatus that performs induction heating by supplying desired power to objects of different materials to be heated.

2. Description of the Related Art In recent years, an inverter-type electromagnetic induction heating apparatus that heats an object to be heated such as a pot without using fire has been widely used. An electromagnetic induction heating device applies a high-frequency current to a heating coil to generate an eddy current in a metal object to be heated which is placed in the vicinity of the heating coil, thereby generating heat from the electrical resistance of the object to be heated. In general, when an object to be heated is a magnetic material such as iron with high specific resistance, it is easy to heat, and when it is a non-magnetic material such as copper or aluminum with low specific resistance, it is difficult to heat.

As a conventional example that can appropriately heat an object to be heated whether it is a magnetic material or a non-magnetic material, there is an electromagnetic induction heating apparatus disclosed in Patent Document 1. The electromagnetic induction heating device of this patent document determines whether the cooking pot is a magnetic pot or a non-magnetic pot, and switches a relay (reference numeral 20 in FIG. 1 of the same document) according to the determination result, so that the high-frequency inverter circuit The method is changed to a half-bridge method when heating a non-magnetic pot and to a full-bridge method when heating a magnetic pot, and at the same time, the capacitance of the resonance capacitor is switched to induction-heat objects made of different materials.

Japanese Patent No. 4909968

In Patent Document 1, when heating a high-resistance magnetic pot, a switch (relay) that switches between the circuit system of the high-frequency inverter and the capacity of the resonance capacitor is turned on, and the inverter is switched to the full-bridge circuit system. A magnetic pot is induction-heated using a resonance capacitor (reference numeral 12 in FIG. 1 of the same document), a second resonance capacitor (identification reference numeral 15) and a third resonance capacitor (identification reference numeral 13).

On the other hand, when heating a low-resistance non-magnetic pot, the switch (relay) is turned off, the inverter is switched to a half-bridge circuit, and the large-capacity third resonant capacitor is completely disconnected, and the small-capacity A non-magnetic pot is heated by induction using the first resonant capacitor and the second resonant capacitor.

Thus, a switch (relay) is required to switch between the circuit system of the high-frequency inverter and the capacity of the resonance capacitor, which hinders miniaturization.

SUMMARY OF THE INVENTION An object of the present invention is to address the above problems, and in particular, to efficiently supply desired power to objects to be heated of different materials without using an inverter system or a switch (relay) for switching a resonance capacitor. An object of the present invention is to provide an inverter-type electromagnetic induction heating device that can be supplied well.

In order to achieve the above object, the electromagnetic induction heating apparatus of the present invention includes a heating coil for induction heating of an object to be heated, a first upper and lower arm that is a series body of two switching elements, and two switching elements. and an inverter circuit that converts a DC voltage into an AC voltage and supplies it to the heating coil, wherein the inverter circuit is connected to the first upper and lower arms A first inverter circuit that operates as a half-bridge inverter by driving the switching elements of the second inverter circuit, and a second inverter circuit that operates as a half-bridge inverter by driving the switching elements of the second upper and lower arms. and a third inverter circuit that operates as a full-bridge inverter by driving the switching elements of the first and second upper and lower arms, and the output terminal of the first inverter circuit and A series body of a first heating coil and a first resonance capacitor , the first heating coil, a third resonance capacitor, and a second resonance capacitor are provided between the positive electrode or the negative electrode or the positive and negative electrodes of the DC power supply. is connected , and between the output terminal of the second inverter circuit and the positive electrode or the negative electrode or the positive and negative electrodes of the DC power supply, a series body of the second heating coil and the second resonance capacitor ; A series body of the second heating coil, the third resonance capacitor, and the first resonance capacitor is connected, and the first heating coil and the third heating coil are connected between the output terminals of the third inverter circuit. A series body of the resonance capacitor and the second heating coil is connected, and the potential difference in the vicinity of the first heating coil and the second heating coil is less than or equal to the DC voltage , and The first resonance capacitor and the second resonance capacitor are smaller in capacity than the third resonance capacitor .

According to the present invention, desired electric power can be efficiently supplied to objects to be heated made of different materials without using an inverter system or a switch (relay) for switching resonance capacitors.

FIG. 2 is a circuit configuration diagram of the electromagnetic induction heating device of Example 1. FIG. FIG. 10 is an operation waveform during heating of the magnetic body in Example 1; FIG. 4 is a relational diagram between a switching frequency and a coil current during heating of a magnetic body in Example 1. FIG. FIG. 10 is an operation waveform during heating of a non-magnetic material in Example 1. FIG. FIG. 2 is a relational diagram between the ON time of the switching element and the coil current during heating of the non-magnetic material in Example 1; FIG. 4 is a connection diagram of the heating coil and the upper and lower arms when the magnetic material is heated in Example 1; FIG. 4 is a connection diagram of a heating coil and upper and lower arms when heating a non-magnetic material in Example 1; FIG. 10 is a connection diagram of the heating coil and the upper and lower arms when the magnetic material is heated in Example 2; FIG. 10 is a connection diagram of a heating coil and upper and lower arms when heating a non-magnetic material in Example 2; The circuit block diagram of the electromagnetic induction heating apparatus of Example 3. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each figure, the same reference numerals denote the same components or components having similar functions, and overlapping descriptions are omitted as appropriate.

FIG. 1 is a circuit configuration diagram of an electromagnetic induction heating device of Example 1. FIG. In the electromagnetic induction heating apparatus of this embodiment, a top plate made of heat-resistant glass is installed on the upper part of the metal housing, and a high-frequency current is supplied to the heating coil arranged below the top plate, so that the top surface of the top plate is heated. A metal object to be heated placed at a predetermined position is induction-heated, but a description of such a well-known configuration will be omitted below.

In FIG. 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. Between the positive electrode and the negative electrode of this DC power supply 1 are a first upper and lower arm 3 in which power semiconductor switching elements (hereinafter simply referred to as "switching elements") 5a and 5b are connected in series, and a switching element 5c. 5d is connected in series with the second upper and lower arms 4. As shown in FIG.

Diodes 6a-6d are connected in parallel to switching elements 5a-5d, respectively, and snubber capacitors 7a-7d are connected in parallel to switching elements 5a-5d, respectively. The snubber capacitors 7a-7d are charged or discharged by the cut-off current when the switching elements 5a-5d are turned off, and suppress turn-off loss by reducing changes in the voltage applied to each switching element.

One end of a first heating coil 11 is connected to the output terminal A of the first vertical arm 3 , and a first heating coil 11 is connected between the other end B of the first heating coil 11 and the negative electrode of the DC power supply 1 . A resonance capacitor 12 is connected.

Similarly, one end of the second heating coil 14 is connected to the output terminal C of the second vertical arm 4, and between the other end D of the second heating coil 14 and the negative electrode of the DC power supply 1, A second resonant capacitor 15 is connected.

A third resonance capacitor 13 is connected between the other end B of the first heating coil 11 and the other end D of the second heating coil 14 .

Here, since the heating coils 11 and 14 and the metal pot (not shown) which is the object to be heated are magnetically coupled, if the metal pot is converted into an equivalent circuit viewed from the heating coils 11 and 14 side, the metal pot The pot's equivalent resistance and equivalent inductance are connected in series. Equivalent resistance and equivalent inductance differ depending on the material of the metal pot. A low-resistance non-magnetic material reduces both the equivalent resistance and equivalent inductance, and a high-resistance magnetic material increases both.

In the electromagnetic induction heating apparatus of this embodiment, the object to be heated is heated by changing the driving method of the first vertical arm 3 and the second vertical arm 4 according to the material of the object to be heated and the set heating power. The difference in control when heating a magnetic material typified by iron and when heating a non-magnetic material typified by aluminum will be described below.
<Control during heating of magnetic material>
First, the control during heating of the magnetic material will be described with reference to FIGS. 2 and 3. FIG.

FIG. 2 shows operation waveforms when the object to be heated is a magnetic material such as an iron pot. The waveforms are gate drive signals vg(5a) to vg(5d) of switching elements 5a to 5d, currents i(11) and i(14) of heating coils 11 and 14, current i(12) of resonance capacitors 12 and 15, voltage v(13) of resonance capacitor 13; The directions of the currents i(11) and i(14) flowing through the heating coils 11 and 14 are positive in the direction of the dashed-dotted arrows shown in FIG.

In this embodiment, when the object to be heated is a magnetic material such as an iron pot, the metal pot is induction-heated using a full-bridge inverter circuit. Specifically, as shown in FIG. 2, the upper arm 5a of the first vertical arm 3 and the lower arm 5d of the second vertical arm 4 are turned on and off almost simultaneously, and the lower arm 5b of the first vertical arm 3 and the second vertical arm 5b are turned on and off at the same time. The upper arm 5c of the two upper and lower arms 4 is turned on and off almost simultaneously. Thereby, it functions as a full-bridge circuit type inverter circuit composed of a series resonance load circuit of the upper and lower arms 3, 4, the first heating coil 11, the third resonance capacitor 13, and the second heating coil 14. . The switching elements 5a to 5d can be turned on during the period in which the current flows through the diodes 6a to 6d, enabling soft switching operation with little switching loss.

As described above, since the high-resistance magnetic material has a large equivalent resistance, it is difficult for current to flow through the resonance load circuit. Therefore, by changing to the full-bridge circuit system, the output voltage of the inverter circuit can be increased to twice that of the half-bridge circuit system, and a desired output can be obtained. When the object to be heated is iron, the resistance is originally large, so the first vertical arm 3 and the second vertical arm 4 are driven at a frequency of about 20 kHz. Therefore, the capacitance of the third resonance capacitor 13 is set according to the drive frequency of about 20 kHz. As shown in FIG. 2, a small amount of current i (12, 15) also flows through the first resonance capacitor 12 and the second resonance capacitor 15. This is because it is set to a value sufficiently smaller than the capacitance of the resonance capacitor 13 . Details will be described later.

FIG. 3 shows the relationship between the switching frequency and the currents i(11) and i(14) of the heating coils 11 and 14 when the magnetic material is heated. As described above, since the high-resistance magnetic material has a large equivalent resistance, the rate of current change with respect to the change in switching frequency is small, and the heating coil current can be easily controlled by frequency control of the inverter circuit.
<Control during heating of non-magnetic material>
Next, the control during heating of the non-magnetic material will be described with reference to FIGS. 4 and 5. FIG.

FIG. 4 shows operating waveforms when the object to be heated is a non-magnetic material such as an aluminum pot. Note that the meanings of vg(5a) and the like in FIG. 4 are the same as those in FIG.

In this embodiment, when the object to be heated is a non-magnetic material such as a copper pot or an aluminum pot, the metal pot is induction-heated mainly using a half-bridge inverter circuit. Specifically, the period in which the upper arms (switching elements 5a and 5c) of the first upper and lower arms 3 and the second upper and lower arms are on and the lower arms (switching elements 5b and 5d) are on. Set a period. As a result, a deformed half-bridge SEPP (Single Ended Push Push Capacitor) composed of the combined capacitance of the first upper and lower arm 3, the first heating coil 11, and the first resonance capacitor 12 to the third resonance capacitor 13 is formed. -Pull ) method inverter circuit, second upper and lower arm 4, SEPP (Single Ended) composed of combined capacitance of second heating coil 14 and first resonance capacitor 12 to third resonance capacitor 13 Push - Pull ) type inverter circuit.

Further, in this embodiment, as shown in FIG. 4, the period during which the upper arm (switching element 5a) of the first vertical arm 3 and the lower arm (switching element 5d) of the second vertical arm 4 are simultaneously turned on. However, since the switching elements 5a to 5d are turned on during the period when the current flows through the diodes 6a to 6d to realize the soft switching operation, there is no problem in operation. Therefore, in this embodiment, the proportion of the ON time of the switching element 5a in one cycle of switching control (hereinafter referred to as ON time duty) can be made different from the ON time duty of the switching element 5c.

As described above, a low-resistance non-magnetic material has a small equivalent resistance, so a large current must flow to obtain a desired output. The skin resistance of an 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 to be heated having a low resistance such as copper or aluminum. Therefore, the capacitances of the first and second resonance capacitors 12 and 15 are set so that the upper and lower arms 3 and 4 can be driven at a frequency of, for example, about 90 kHz. becomes a small value. Therefore, the voltages of the first resonance capacitor 12 and the voltage of the second resonance capacitor 15 are approximately the same as shown in FIG. The reason why the currents i(12) and i(15) slightly flowed through the first resonance capacitor 12 and the second resonance capacitor 15 during the heating of the magnetic material is that the capacity of the third resonance capacitor 13 is larger than that of the third resonance capacitor 13. because they are different.

FIG. 5 shows the relationship between the ON time duty of the switching elements 5a and 5c and the currents i(11) and i(14) of the heating coils 11 and 14 during heating of the non-magnetic material. Here, an example is shown in which the switching elements 5a and 5c are turned on at the same time and operated with the same on-time duty. As described above, since a low-resistance nonmagnetic material has a small equivalent resistance, the rate of current change with respect to frequency change is large, making it difficult to control. Therefore, in the case of non-magnetic material heating, the heating coil current is controlled by varying the on-time duty.
<Arrangement of the first and second heating coils in the electromagnetic induction heating device>
By selectively using the control described above according to the type of object to be heated, the electromagnetic induction heating device can provide the desired power required to achieve the set thermal power for both magnetic and non-magnetic heating. can be supplied to On the other hand, in order to save power, it is also required to secure a larger number of turns of each heating coil and to reduce the heating coil current when realizing the desired heating power. However, in an electromagnetic induction heating device that uses two or more heating coils to heat a single object to be heated, a high resonance voltage may occur between the two heating coils. had to be ensured.

For this reason, in conventional electromagnetic induction heating devices that use two or more heating coils to heat one object to be heated, if priority is given to housing all the heating coils in a metal housing of dimensions determined by standards, the number of turns is small. A small heating coil had to be used, making it difficult to achieve power saving. On the other hand, if priority is given to power saving, a large metal housing must be used to accommodate multiple large heating coils with many turns, and it is difficult to keep the dimensions of the metal housing below the standard size. rice field. Therefore, hereinafter, a heating coil arrangement that can reduce the size of the metal housing while increasing the number of turns of each heating coil will be described with reference to FIGS. 6 and 7. FIG.

FIG. 6 shows the connection between the first and second heating coils 11 and 14 and the first and second upper and lower arms 3 and 4 shown in FIG. FIG. 2 is a configuration diagram shown together with an arrangement; As shown here, the first heating coil 11 and the second heating coil 14 are concentrically wound with the first heating coil 11 on the inside and the second heating coil 14 on the outside. . When the heating coils are arranged in this way, it is necessary to secure the insulation distance described above between the outer peripheral portion of the first heating coil 11 and the inner peripheral portion of the second heating coil 14. If the gap between them can be narrowed, it becomes possible to ensure a larger number of turns of each heating coil.

Therefore, as shown in FIG. 6, the output terminal A of the vertical arm 3 is connected to the outer peripheral portion of the first heating coil 11, and the output terminal C of the vertical arm 4 is connected to the inner peripheral portion of the second heating coil 14. bottom. As a result, only a relatively low voltage, which is the voltage of the DC power supply 1 at maximum, is applied between the output terminal A of the upper and lower arms 3 and the output terminal C of the upper and lower arms 4 when the magnetic material is heated. At any position where the coil 11 and the second heating coil face each other, the potential difference in the adjacent portion is equal to or lower than the voltage of the DC power supply 1, and even if the gap between the two heating coils is narrowed, a sufficient insulation distance can be secured. It is possible.

In addition, as shown in FIG. 6, when the first heating coil 11 is wound from the outer circumference to the inner circumference to the right, and the second heating coil 14 is wound from the inner circumference to the outer circumference to the right, the magnetism When the body is heated by the full bridge circuit method, the current i (11) of the first heating coil 11 and the current i (14) of the second heating coil 14 are in opposite phase, and the magnetic flux is generated between both heating coils. There is a concern about cancellation, but in magnetic heating, the magnetic flux generated by each heating coil interlinks with the pot, so there is no significant effect on the generation of eddy currents.

On the other hand, when heating a non-magnetic material by a half-bridge circuit method, as indicated by the dashed-dotted arrows in FIG. (14) has the same phase and there is no magnetic flux cancellation. Therefore, when the non-magnetic material is heated, the magnetic flux generated by the two heating coils causes a large eddy current to flow in the pan in the direction of canceling the magnetic flux, and a desired amount of heat can be obtained. During heating of the non-magnetic material, the voltages of the output terminal A of the first vertical arm 3 and the voltage of the output terminal C of the second vertical arm 4 become the same potential, so that the first heating coil 11 and the second heating coil , the insulation distance should be secured in consideration of the potential difference in the full-bridge circuit system. It should be noted that even if the winding directions of the heating coils are reversed, the same operation is performed.

As described above, according to the electromagnetic induction heating device of the present embodiment, the circuit configuration is such that the potential difference between the first heating coil and the second heating coil is equal to or lower than the DC voltage. Therefore, the insulation distance between both heating coils can be narrowed, and the number of turns of each heating coil can be increased by the amount of the narrowed insulation distance. In addition, a plurality of inverter circuits prepared for heating pairs of objects to be heated made of different materials can be switched without using switches (relays), and desired electric power can be efficiently supplied to objects to be heated of any material. can supply.

Next, an electromagnetic induction heating apparatus according to Embodiment 2 of the present invention will be described with reference to FIGS. 8 and 9. FIG. Duplicate descriptions of common points with the first embodiment will be omitted.

FIG. 8 is a connection configuration diagram of the first and second heating coils 11 and 14 and the first and second upper and lower arms 3 and 4 of the second embodiment. Here, a method of connecting the first heating coil 11 wound in a crescent shape, the second heating coil 14, and the upper and lower arms is shown.

In this embodiment, the first heating coil 11 is arranged on the right side and the second heating coil 14 is arranged on the left side. Even when the heating coils are arranged as in this embodiment, if the gap (insulation distance) between the outermost circumference of the straight portion of the first heating coil 11 and the outermost circumference of the straight portion of the second heating coil 14 can be narrowed, Accordingly, it becomes possible to secure a larger number of turns of each heating coil.

Therefore, in this embodiment, the output terminal A of the vertical arm 3 is connected to the outer peripheral portion of the first heating coil 11 and the output terminal C of the vertical arm 4 is connected to the outer peripheral portion of the second heating coil 14 . As a result, only the voltage of the DC power supply 1 is applied between the output terminal A of the vertical arm 3 and the output terminal C of the vertical arm 4 at the maximum. It is possible to narrow the gap between the linear portion of the heating coil and the outermost circumference.

As shown in FIG. 8, when the first heating coil 11 is wound from the outer circumference to the inner circumference to the left, and the second heating coil 14 is wound from the outer circumference to the inner circumference to the right, the magnetism When heating the body by the full-bridge circuit method, as shown by the dashed-dotted arrow in FIG. The current i(14) has an opposite phase, and there is concern about magnetic flux cancellation.

On the other hand, when heating a non-magnetic material by a half-bridge circuit method, as shown by the dashed-dotted arrow in FIG. , the current i (14) of the heating coil 14 is in phase and there is no magnetic flux cancellation. Therefore, when the non-magnetic material is heated, the magnetic flux generated by the two heating coils causes a large eddy current to flow in the pan in the direction of canceling the magnetic flux, and a desired amount of heat can be obtained. During heating of the non-magnetic material, the voltages of the output terminal A of the first vertical arm 3 and the voltage of the output terminal C of the second vertical arm 4 become the same potential, so that the first heating coil 11 and the second heating coil , the insulation distance should be secured in consideration of the potential difference in the full-bridge circuit system.

FIG. 10 is a circuit configuration diagram of an electromagnetic induction heating device of Example 3. FIG. The same parts as those in FIG. 1 are denoted by the same reference numerals, and repeated explanations are omitted.

In this embodiment, first resonance capacitors 12 a and 12 b are connected between the other end B of the first heating coil 11 and the positive and negative electrodes of the DC power supply 1 . Similarly, second resonance capacitors 15 a and 15 b are connected between the other end D of the second heating coil 14 and the positive and negative electrodes of the DC power supply 1 .

In this embodiment having such a circuit configuration, when the object to be heated is a non-magnetic material such as an aluminum pot, the first upper and lower arm 3, the first heating coil 11, the first resonance capacitors 12a and 12b, the second A half-bridge inverter circuit composed of a combined capacitance of two resonant capacitors 15a and 15b and a third resonant capacitor 13, a second upper and lower arm 4, a second heating coil 14, and a first resonant capacitor 12a. , 12b, the second resonance capacitors 15a and 15b, and the third resonance capacitor 13 function as a half-bridge inverter circuit.

In the first embodiment, the current flows from the DC power supply 1 only when the upper arm is turned on. However, in this embodiment, the current flows from the DC power supply 1 even when the lower arm is turned on. can be reduced. When the converter is connected to the front stage of the inverter circuit, an electrolytic capacitor or a film capacitor is connected between the inverter circuit and the converter, so that the ripple current is reduced and the size of the capacitor can be reduced. Moreover, since the amount of heat generated by the internal resistance of the capacitor can be reduced, the reliability can be improved.

1 DC power supply,
3 first upper and lower arms,
4 second upper and lower arms,
5a to 5d switching elements,
6a-6d diodes,
7a-7d snubber capacitors,
11 first heating coil,
14 second heating coil,
12, 12a, 12b first resonant capacitor;
15, 15a, 15b second resonant capacitor,
13 third resonant capacitor

Claims (5)

a heating coil that induction-heats an object to be heated;
a first upper and lower arm that is a series body of two switching elements;
a second upper and lower arm that is a series body of two switching elements;
an inverter circuit that converts a DC voltage into an AC voltage and supplies it to the heating coil;
An electromagnetic induction heating device comprising
The inverter circuit is
a first inverter circuit that operates as a half-bridge inverter by driving the switching elements of the first upper and lower arms;
a second inverter circuit that operates as a half-bridge inverter by driving the switching elements of the second upper and lower arms;
a third inverter circuit that operates as a full-bridge inverter by driving the switching elements of the first and second upper and lower arms;
is composed of
Between the output terminal of the first inverter circuit and the positive electrode or the negative electrode or the positive and negative electrodes of the DC power supply, a series body of the first heating coil and the first resonance capacitor , the first heating coil and the second A series body of three resonant capacitors and a second resonant capacitor is connected,
Between the output terminal of the second inverter circuit and the positive electrode or the negative electrode or the positive and negative electrodes of the DC power supply, a series body of the second heating coil and the second resonance capacitor , and the second heating coil A series body of the third resonant capacitor and the first resonant capacitor is connected,
A series body of the first heating coil, the third resonance capacitor, and the second heating coil is connected between the output terminals of the third inverter circuit,
A potential difference in the vicinity of the first heating coil and the second heating coil is equal to or less than the DC voltage,
The electromagnetic induction heating device , wherein the first resonance capacitor and the second resonance capacitor have smaller capacitances than the third resonance capacitor . In the electromagnetic induction heating device according to claim 1,
Both heating coils are arranged concentrically such that the first heating coil is on the inside and the second heating coil is on the outside,
The output terminal of the first vertical arm is connected to the outer peripheral side of the first heating coil, and the output terminal of the second vertical arm is connected to the inner peripheral side of the second heating coil. An electromagnetic induction heating device characterized by: In the electromagnetic induction heating device according to claim 1,
Both heating coils are installed adjacent to each other such that the first heating coil is on the right side and the second heating coil is on the left side,
The output terminal of the first vertical arm is connected to the outer peripheral side of the first heating coil, and the output terminal of the second vertical arm is connected to the outer peripheral side of the second heating coil. An electromagnetic induction heating device characterized by: In the electromagnetic induction heating device according to any one of claims 1 to 3,
When the object to be heated is a magnetic material, the third inverter circuit supplies high-frequency current to the first heating coil and the second heating coil to heat the object to be heated. and an electromagnetic induction heating device. In the electromagnetic induction heating device according to claim 4 ,
The electromagnetic induction heating device, wherein the third inverter circuit controls the magnitude of the high-frequency current by controlling switching frequencies of the first upper and lower arms and the second upper and lower arms.

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