TW201414359A - Electromagnetic induction heating device - Google Patents

Abstract

The subject of the present invention provides an electromagnetic inductive heating device capable of restraining the loss of switching elements and performing current conversion manners by inductive heating for objects of different material to-be-heated. An electromagnetic inductive heating device comprises a current converter in which the current converter includes: a first up/down branch connected with two switching elements in series; a second up/down branch connected with two switching elements in series; a serial circuit of a heating coil to inductively heating objects to-be-heated and a first resonant capacitor connected to a node between the output terminal of the first up/down branch and the electrode of a DC power; a serial circuit of the heating coil and a first switching means connected to a node between the output terminals of the first up/down branch and the second up/down branch; and a second switching means which is short-circuited between the output terminals of the first up/down branch and the second up/down branch, wherein the switching elements used in the second up/down branch operate at a speed higher than that in the first up/down branch.

Description

Electromagnetic induction heating device

The present invention relates to an electromagnetic induction heating device for a commutation method of an induction heating conditioner or the like.

In the electromagnetic induction heating device, a high-frequency current flows in a heating coil, and an eddy current is generated in a metal-made object placed near the coil, and heat is generated by the resistance of the object to be heated. Because it can control the temperature of the object to be heated and has high safety, it is widely recognized as a new heat source. Generally, the object to be heated is a magnetic body, and iron having a larger specific resistance is easily heated; non-magnetic material, low-resistance copper or aluminum or the like is difficult to heat.

As an example of the prior art for solving such a problem, there is an induction heating device disclosed in Japanese Patent No. 4,794,533. This device switches the full-bridge circuit structure and the half-bridge circuit structure in response to the state and type of the object to be heated, and alternately drives two half bridges while heating a non-magnetic material such as aluminum. A circuit supplies current to the heating coil.

[Previous Technical Literature] [Patent Document]

[Patent Document 1] Japanese Patent No. 4794533

In the prior art disclosed in Patent Document 1, since the two half bridge circuits are alternately driven, the switching loss can be reduced, but the total current of the heating coil is flown in one of the half bridge circuits during the suspension, and conduction is performed. It is hard to say that it is effective to use two half-bridge circuits.

The present invention provides a method of reducing conduction loss and switching loss when heating copper, aluminum or the like having a low resistance of a non-magnetic material, and reducing heating of iron or the like having high resistance to a magnetic material. An electromagnetic induction heating device that switches losses and suppresses heat generation of the switching element and has high heating efficiency.

In order to solve the above problems, an electromagnetic induction heating device according to the present invention includes: a DC power supply; and an inverter that converts a DC voltage from the DC power source into an AC voltage; and the inverter includes: a first upper and lower branch The circuit is connected in series with two switching elements; the second upper and lower branches are connected in series with two switching elements; the series circuit of the heating coil of the induction heating object and the first resonant capacitor is connected to the first upper and lower branches The output terminal is connected to the electrode of the DC power source; the heating coil and the second resonance a series circuit of the capacitor and the first switching means is connected between the first upper and lower branches and the output terminals of the second upper and lower branches; and the second switching means is short-circuited in the first upper and lower branches and the second upper and lower branches Between the output terminals of the road; in the second upper and lower branches, a switching element higher than the first upper and lower branches is used.

According to the present invention, it is possible to provide a reduction in conduction loss and switching loss when heating a low-resistance copper or aluminum of a non-magnetic material, and to reduce heating of iron or the like having high resistance to a magnetic material. The electromagnetic induction heating device with high heating efficiency is suppressed by switching loss and suppressing heat generation of the switching element.

1‧‧‧DC power supply

3‧‧‧First up and down branch

4‧‧‧Second upper and lower branches

5a~5f‧‧‧Semiconductor switching components

6a~6f‧‧‧ diode

7a~7d‧‧‧ snubber capacitor

8a, 8c‧‧‧Inductance

9a~9d‧‧‧ capacitor

11‧‧‧heating coil

12‧‧‧First Resonance Capacitor

13‧‧‧Second resonant capacitor

50‧‧‧First resonant load circuit

60‧‧‧Second resonant load circuit

Fig. 1 is a circuit configuration diagram of an electromagnetic induction heating device of the first embodiment.

Fig. 2 is an operation explanatory view of the electromagnetic induction heating device of the first embodiment.

Fig. 3 is an operation waveform of the electromagnetic induction heating device of the first embodiment.

Fig. 4 is an operation waveform of the electromagnetic induction heating device of the comparative example.

Fig. 5 is an operation explanatory view of the electromagnetic induction heating device of the first embodiment.

Fig. 6 is an operation waveform of the electromagnetic induction heating device of the first embodiment.

Fig. 7 is a circuit configuration diagram of an electromagnetic induction heating device of the second embodiment.

Fig. 8 is an operation explanatory view of the electromagnetic induction heating device of the second embodiment.

Fig. 9 is an operation waveform of the electromagnetic induction heating device of the second embodiment.

Fig. 10 is an operation explanatory view of the electromagnetic induction heating device of the second embodiment.

Fig. 11 is an operation waveform of the electromagnetic induction heating device of the second embodiment.

Fig. 12 is a circuit configuration diagram of an electromagnetic induction heating device of the third embodiment.

Fig. 13 is an operation explanatory view of the electromagnetic induction heating device of the third embodiment.

Fig. 14 is an operation explanatory view of the electromagnetic induction heating device of the third embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[Example 1]

Fig. 1 is a circuit configuration diagram of an electromagnetic induction heating device of a first embodiment, in which an object to be heated (for example, a conditioning pot) (not shown) is magnetically coupled to a heating coil 11 to supply electric power to an object to be heated (a conditioning pot). In FIG. 1, between the positive electrode and the negative electrode of the DC power source 1, the first upper and lower branches 3 of the power semiconductor switching elements 5a and 5b are connected in series, and the power semiconductor switching elements 5c and 5d are connected in series. The two upper and lower branches are connected to each other. The switching elements 5a and 5b of the first upper and lower branches 3 use an IGBT (Insulated Gate Type Bipolar Transistor) suitable for a large current. On the other hand, the switching elements 5c and 5d of the second upper and lower branches 4 use a power semiconductor switching element whose switching speed is faster than that of the switching elements 5a and 5b of the first upper and lower branches 3. In the present embodiment, an SJ (Super Junction)-MOSFET (MOS type field effect transistor) is used, and in recent years, an element which uses an existing MOSFET to make the impedance sharply smaller has been developed. Accordingly, it is also effective to reduce the switching loss due to the high frequency, and to reduce the conduction loss. The diodes 6a to 6d are connected in parallel in the reverse direction from the respective switching elements 5a to 5d. Further, a parasitic diode of a MOSFET can also be used for the diodes 6c and 6d. The snubber capacitors 7a to 7d are connected in parallel from the respective switching elements 5a to 5d.

One end of the heating coil 11 is connected to the output terminal of the first upper and lower branches 3, and the other resonant capacitor 12 is connected between the other end of the heating coil 11 and the negative electrode of the DC power supply 1 to constitute the first resonant load circuit 50. Further, a series circuit of the second resonance capacitor 13 and the relay 20 is connected between the other end of the heating coil 11 and the output terminal of the second upper and lower branches. Using the heating coil 11 and the first resonant capacitor 12 and the second resonant capacitor 13 constitutes the second resonance load circuit 60, and the first resonance load circuit 50 and the second resonance load circuit 60 can be switched by switching the relay 20 in accordance with the material of the object to be heated or the setting of the heating power. Further, in FIG. 1, the series circuit of the heating coil 11 and the first resonant capacitor 12 is provided between the output terminal of the first upper and lower branches 3 and the negative electrode of the DC power source 1, but may be provided in the first upper and lower branches. The output terminal of the path 3 is between the positive electrode of the DC power source 1.

A relay 21 is connected between the first upper and lower branches 3 and the output terminals of the second upper and lower branches 4. When the relay 20 is in the off state and the second upper and lower branches 4 are disconnected from the second resonant load circuit 60, the output terminals of the second upper and lower branches 4 are connected to the first upper and lower branches in such a manner that the relay 21 is switched to the open state. The output terminal of the path 3 is connected in parallel with the switching elements of the upper and lower branches of the first and second upper and lower branches.

Here, in FIG. 1, the heating coil 11 is magnetically coupled to the object to be heated (not shown), and when the object to be heated is converted into an equivalent circuit from the side of the heating coil 11, the connection is formed in series. The equivalent resistance of the heating object and the equivalent inductance. The equivalent resistance and the equivalent inductance differ depending on the material of the object to be heated. In the case of non-magnetic low-resistance copper or aluminum, the equivalent resistance and the equivalent inductance are small, and the high-resistance iron in the magnetic body The situation is all big.

Next, the operation of the case where the object to be heated is copper or aluminum will be described using the operation explanatory diagram of FIG. 2 and the operation waveforms of FIGS. 3 and 4. Fig. 2 shows the open and closed states of the respective elements of the embodiment. Fig. 3 shows the operation waveform of this embodiment. Fig. 4 is a view showing an operation waveform of a comparative example. In Figs. 3 and 4, it is shown that vg(5a) to vg(5d) are the respective gate voltages of the switching elements 5a to 5d, and i(5a) to i(5d) are the respective currents of the switching elements 5a to 5d, i(6a) to i(6d) are the respective currents of the diodes 6a to 6d, and vc(5a) to vc(5d) are the respective voltages of the switching elements 5a to 5d, and loss(5a) to loss(5d) are Loss of each switching element 5a to 5d. In Fig. 2, in the case where the object to be heated is copper or aluminum, the relay 20 is turned off, the relay 21 is turned on, and current flows to the heating coil in a state where the first upper and lower branches 3 and the second upper and lower branches 4 are connected in parallel. 11 and the first resonant capacitor 12. This configuration is a so-called current resonance type modified half-bridge type SEPP (Single Ended Push-Pull) type inverter. The skin resistance of the object to be heated has a characteristic that it is proportional to the square root of the frequency, and in the case of heating a low-resistance object such as copper or aluminum, it is effective to increase the frequency. Thereby, the capacity of the first resonance capacitor 12 is set such that the first upper and lower branches 3 can be driven at a frequency of, for example, about 90 kHz. As described above, the non-magnetic low-resistance heating target has a small equivalent resistance, and it is necessary to flow a large current in order to obtain a desired output.

In the present embodiment, as shown in FIGS. 2 and 3, the current of the heating coil 11 is shunted by synchronizing the switching elements 5a of the first upper and lower branches 3 and the switching elements 5c of the second upper and lower branches 4, respectively. (i (5a), i (5c)) and flows to the switching elements 5a and 5c. Similarly, by synchronizing the switching elements 5b of the first upper and lower branches 3 and the switching elements 5d of the second upper and lower branches 4, the current of the heating coil 11 is shunted (i(5b), i(5d)) and flows. To the switching elements 5b and 5d. Therefore, as shown in the comparative example of FIG. 4, it is heated only by the first upper and lower branches 3 In the case, the conduction loss that occurs can be reduced during the flow of current to the switching element.

Here, in the present embodiment, as described above, the IGBT is used for the switching elements 5a and 5b of the upper and lower branches 3, and the SJ-MOSFET is used for the switching elements 5c and 5d of the upper and lower branches 4. Generally, the IGBT is a flow-off current (i(5a), i(5b)) at the time of turnoff, as shown in the comparative example of FIG. 4, and the shutdown loss (loss (5a), loss (5b)) Become bigger. On the other hand, the MOSFET is faster than the IGBT, and the shutdown loss can be reduced. Here, in the present embodiment, as shown in FIGS. 2 and 3, the switching elements 5a and 5o (IGBT) of the upper and lower branches 3 are turned off at a time t1 earlier than the switching elements 5c and 5d (MOSFET). Accordingly, the voltages (vc(5a), vc(5d)) applied to the elements by the switching elements 5a, 5b (IGBT) are turned off in the state of zero volts, and the switching elements 5a, 5b are shown in FIG. The shutdown loss of the IGBT) can be zero, and only the conduction loss (loss (5a), loss (5b)) is lost. On the other hand, in the switching elements 5c and 5d (MOSFET) of the upper and lower branches 4, a current is increased during t1, and a large current is interrupted during shutdown, but the switching speed is fast, and the period of overlap of current and voltage is short. It is suppressed to be lower than the switching loss of the case where only the upper branch 3 (IGBT) is heated (Fig. 4: loss (5a)).

Thus, in the case where the object to be heated in the present embodiment is copper or aluminum, the conduction loss is reduced by synchronously driving the two upper and lower branches and diverting the large coil current flow to the respective upper and lower branches, and is shielded at a high frequency. The switching element of the off current can reduce the switching loss by using the MOSFET. Lost.

Next, an operation of the case where the object to be heated is iron will be described using the operation explanatory diagram of FIG. 5 and the operation waveform of FIG. 6. In FIG. 5, when the object to be heated is iron, the relay 20 is turned on, and the relay 21 is turned off to utilize the first upper and lower branches 3 and the second upper and lower branches 4, the heating coil 11, and the first and second resonance capacitors 12, 13 full-bridge converters of the structure are heated. As described above, the high-resistance object of the magnetic body has a large equivalent resistance, and it is difficult for the current in the resonance load circuit to flow. Thereby, the output voltage of the inverter is increased by 2 times by switching in a full bridge manner, and a desired output is obtained. In the case of copper or aluminum described above, the impedance of the converter is small, and the frequency of the inverter is set at about 90 kHz to increase the skin resistance. However, in the case of iron, the impedance is large, and the first upper and lower branches 3 are driven at a frequency of about 20 kHz. And the second upper and lower branches 4. As described above, the capacity of the first resonant capacitor 12 is set to match the driving frequency of about 90 kHz, but the capacity of the second resonant capacitor 13 is set to match the driving frequency of about 20 kHz. The drive frequency is greatly different, and the capacity of the second resonant capacitor 13 becomes sufficiently larger than the first resonant capacitor 12. Therefore, the resonance frequency of the full-bridge inverter is mainly set by the second resonance capacitor 13. In the present embodiment, by switching the relay 20, the capacity of the resonant capacitor can be switched at the same time, and the setting range of the driving frequency of the inverter can be opened in accordance with the material of the object to be heated, and heating can be performed at an optimum frequency.

In the present embodiment, the switching elements 5a and 5b of the upper and lower branches 3 use the IGBT, and the problem of switching loss remains. Here, in the present embodiment, as shown in FIGS. 5 and 6, the switching elements 5a, 5b are utilized. The upper and lower branches 3 formed by (IGBT) and the upper and lower branches 4 formed by the switching elements 5c and 5d (MOSFET) are provided with a phase difference φ, and the upper and lower branches 3 are driven later than the upper and lower branches 4. As a result, as shown in FIG. 6, the blocking current (ioff(5a)) of the switching element 5a (IGBT) can be set smaller than the blocking current (ioff(5d)) of the switching element 5d, and switching can be suppressed. Switching loss of component 5a (IGBT) (loss (5a)). Although not shown, the switching element 5b (IGBT) is also used, and the switching loss can be suppressed similarly.

As described above, in the present embodiment, when the object to be heated is iron, a phase difference is provided in the two upper and lower branches, and the switching loss can be reduced by using a MOSFET in a switching element that blocks a large current.

[Example 2]

Fig. 7 is a circuit configuration diagram of an electromagnetic induction heating device of the second embodiment. The same portions as those in Fig. 1 of the first embodiment are denoted by the same reference numerals, and their description is omitted.

7, the difference from FIG. 1 is that the upper branch of the upper and lower branches 3 is replaced by the switching element 5a as the inductance 8a, and the upper branch of the upper and lower branches 4 is replaced by the switching element 5c into the inductance 8c. Further, the capacitors 9b and 9d which are connected in parallel to the switching elements 5b and 5d are operated as voltage resonance capacitors. As a result, the second embodiment is configured as a voltage resonance type inverter, and the voltages of the switching elements 5b and 5d are different from those of the current resonance type inverter of the first embodiment.

Next, the operation description of FIG. 8 and the operation of FIG. 9 are used. The waveform indicates the action of the case where the object to be heated is copper or aluminum. Fig. 8 is a view showing the open and closed states of the respective elements of the embodiment. Fig. 9 shows the operation waveform of this embodiment. In Fig. 8, in the case where the object to be heated is copper or aluminum, the relay 20 is turned off, the relay 21 is turned on, and current flows to the heating coil in a state where the first upper and lower branches 3 and the second upper and lower branches 4 are connected in parallel. 11 and the first resonant capacitor 12. This structure is called a voltage resonance type half bridge type. In the present embodiment, as shown in FIGS. 8 and 9, the current of the heating coil 11 is shunted by synchronizing the switching elements 5b of the first upper and lower branches 3 and the switching elements 5d of the second upper and lower branches 4, respectively. It flows to the switching elements 5b and 5d (i(5b), i(5d)). Thereby, the conduction loss occurring can be reduced during the flow of current to the switching element than by heating only the first upper and lower branches 3.

Here, in the present embodiment, as described above, the IGBT is used for the switching element 5b of the upper and lower branches 3, and the SJ-MOSFET is used for the switching element 5d of the upper and lower branches 4. Similarly to the first embodiment, in the present embodiment, as shown in Figs. 8 and 9, the switching element 5b (IGBT) of the upper and lower branches 3 is set earlier than the switching element 5d (MOSFET) of the upper and lower branches 4 by t1. Shut down. Thereby, the voltage (vc(5b)) applied to the element by the switching element 5b (IGBT) is turned off in the state of zero volt, and the shutdown loss of the switching element 5b (IGBT) is zero as shown in FIG. As a loss, only conduction loss (loss (5b)). On the other hand, in the switching element 5d (MOSFET) of the upper and lower branches 4, a current is increased during t1, and a large current is blocked during shutdown. However, the switching speed is fast, and the period of overlap of current and voltage is short, and the reduction can be suppressed. Loss of shutdown.

Thus, in the case where the object to be heated in the present embodiment is copper or aluminum, the conduction loss is reduced by synchronously driving the two upper and lower branches and diverting the large coil current flow to the respective upper and lower branches, and is shielded at a high frequency. The switching element of the off current can reduce the switching loss by using a MOSFET.

Next, an operation of the case where the object to be heated is iron will be described using the operation explanatory diagram of FIG. 10 and the operation waveform of FIG. 11. In FIG. 10, in the case where the object to be heated is iron, the relay 20 is turned on, the relay 21 is turned off, and the current flows from the first upper and lower branches 3 and the second upper and lower branches 4 to the heating coil 11 and the first and second resonance capacitors. 12, 13. This structure is called a voltage resonance type full bridge type. In the present embodiment, by switching the relay 20, the capacity of the resonant capacitor can be switched at the same time, and the setting range of the driving frequency of the inverter can be opened in accordance with the material of the object to be heated, and heating can be performed at an optimum frequency.

In the present embodiment, the IGBT is used in the switching element 5b of the upper and lower branches 3, and the problem of switching loss remains. Here, in the present embodiment, as shown in FIGS. 10 and 11, the opening period of the switching element 5b (IGBT) for driving the upper and lower branches 3 is longer than the switching period of the switching element 5d (MOSFET) of the upper and lower branches 4. long. As a result, as shown in FIG. 11, the blocking current (ioff(5b)) of the switching element 5b (IGBT) can be set smaller than the blocking current (ioff(5d)) of the switching element 5d, and switching can be suppressed. Switching loss of component 5b (IGBT) (loss (5b)).

As described above, in the present embodiment, when the object to be heated is iron, there is a difference in the opening time of the two upper and lower branches, so that the switching loss can be reduced by using the MOSFET in the switching element that blocks the large current.

[Example 3]

Fig. 12 is a circuit configuration diagram of an electromagnetic induction heating device of the third embodiment. The same portions as those in Fig. 7 of the second embodiment are denoted by the same reference numerals, and their description is omitted.

In Fig. 12, in contrast to Fig. 7, a series circuit in which the auxiliary switching element 5e and the capacitor 9a are connected in parallel with the inductor 8a is connected in parallel with the inductor 8c, and a series circuit of the auxiliary switching element 5f and the capacitor 9c is connected. As a result, the third embodiment is configured as an active clamp voltage resonance type inverter, and it is possible to suppress the voltages of the main switching elements 5b and 5d from being lowered as compared with the voltage resonance type inverter of the second embodiment. Further, the diodes 6e and 6f are connected in parallel in the reverse direction to the respective auxiliary switching elements 5e and 5f.

Next, the operation of the case where the object to be heated is copper or aluminum will be described using the operation explanatory diagram of Fig. 13 . In Fig. 13, the open/close state of each element of the present embodiment is shown. When the object to be heated is copper or aluminum, the relay 20 is turned off, the relay 21 is turned on, and the first upper and lower branches 3 and 2 are connected in parallel. In the state of the upper and lower branches 4, a current flows to the heating coil 11 and the first resonance capacitor 12. This structure is called an active clamp voltage resonance type half bridge type. In the present embodiment, as shown in FIG. 13, the current of the heating coil 11 is shunted by synchronizing the auxiliary switching elements 5e of the first upper and lower branches 3 and the auxiliary switching elements 5f of the second upper and lower branches 4, respectively. It flows to the auxiliary switching elements 5e and 5f. Similarly, by synchronizing the main switching element 5b of the first upper and lower branches 3 and the main switching element 5d of the second upper and lower branches 4, the current of the heating coil 11 is shunted and flows to the main cut. Replace components 5b and 5d. Thereby, the conduction loss occurring can be reduced during the flow of current to the switching element as compared with the case where only the first upper and lower branches 3 are heated.

Here, in the present embodiment, the IGBT is used for the switching elements 5e and 5b of the upper and lower branches 3, and the SJ-MOSFET is used for the switching elements 5f and 5d of the upper and lower branches 4. Similarly to the first embodiment, in the present embodiment, as shown in FIG. 13, the switching elements 5e and 5b of the upper and lower branches 3 are immersed earlier than the switching elements 5f and 5d (MOSFET) of the upper and lower branches 4 (IGBT). ) Shut down. As a result, the voltage applied to the element by the switching elements 5e, 5b (IGBT) can be turned off in the state of zero volts, and the shutdown loss of the switching elements 5e, 5b (IGBT) can be zero, and only conduction loss as a loss. On the other hand, the switching elements 5f and 5d (MOSFET) in the upper and lower branches 4 increase the current during the period t1, and block the large current during the shutdown. However, the switching speed is fast, and the overlap period of the current and the voltage is short. It is suppressed to be lower than the switching loss of the case where only the upper branch 3 (IGBT) is heated.

Thus, in the case where the object to be heated in the present embodiment is copper or aluminum, the conduction loss is reduced by synchronously driving the two upper and lower branches and diverting the large coil current flow to the respective upper and lower branches, and is shielded at a high frequency. The switching element of the off current can reduce the switching loss by using a MOSFET.

Next, the operation of the case where the object to be heated is iron will be described using the operation explanatory diagram of Fig. 14 . In FIG. 14, in the case where the object to be heated is iron, the relay 20 is turned on, and the relay 21 is turned off to the first upper and lower branches 3 The current flows to the heating coil 11 and the first and second resonance capacitors 12 and 13 with the second upper and lower branches 4 . This structure is called an active clamp voltage resonance type full bridge type.

In the present embodiment, the switching elements 5e and 5b of the upper and lower branches 3 use the IGBT, and the problem of switching loss remains. Here, as in the second embodiment, in the present embodiment, as shown in FIG. 14, the opening period of the main switching element 5b (IGBT) that drives the upper and lower branches 3 is higher than that of the switching element 5d (MOSFET) of the upper and lower branches 4. It will be longer during the opening period. The auxiliary switching element 5e of the upper and lower branches 3 and the auxiliary switching element 5f of the upper and lower branches 4 are each driven in complementary with the main switching elements 5b and 5d. As a result, in the same manner as in the second embodiment, the blocking current of the main switching element 5b (IGBT) can be set smaller than the blocking current of the main switching element 5d, and the switching loss of the switching element 5b (IGBT) can be suppressed.

As described above, in the case where the object to be heated is iron, the opening time of the main switching elements of the two upper and lower branches is different, so that the switching loss can be reduced by using the MOSFET in the switching element that blocks the large current. .

1‧‧‧DC power supply

3‧‧‧First up and down branch

4‧‧‧Second upper and lower branches

5a~5d‧‧‧Semiconductor switching components

6a~6d‧‧‧dipole

7a~7d‧‧‧ snubber capacitor

11‧‧‧heating coil

12‧‧‧First Resonance Capacitor

13‧‧‧Second resonant capacitor

20, 21‧‧‧ relay

50‧‧‧First resonant load circuit

60‧‧‧Second resonant load circuit

Claims (7)

An electromagnetic induction heating device comprising: a DC power supply; and an inverter for converting a DC voltage from the DC power source into an AC voltage; wherein the inverter has: a first upper and lower branch, and a string Two switching elements are connected; the second upper and lower branches are connected in series with two switching elements; the series circuit of the heating coil of the induction heating object and the first resonant capacitor is connected to the output terminals of the first upper and lower branches and Between the electrodes of the DC power source; the series circuit of the heating coil and the second resonant capacitor and the first switching means is connected between the output terminals of the first upper and lower branches and the second upper and lower branches; and the second switching means The short circuit is between the first upper and lower branches and the output terminals of the second upper and lower branches; and the second upper and lower branches use a switching element higher than the first upper and lower branches. An electromagnetic induction heating device comprising: a DC power supply; and an inverter for converting a DC voltage from the DC power source into an AC voltage; wherein the inverter has: a first upper and lower branch, and a string Connecting the first inductor and the first switching element; The second upper and lower branches are connected in series with the second inductor and the second switching element; the series circuit of the heating coil of the induction heating object and the first resonance capacitor is connected to the output terminal of the first upper and lower branches and the DC Between the electrodes of the power source; the series circuit of the heating coil and the second resonant capacitor and the first switching means is connected between the first upper and lower branches and the output terminals of the second upper and lower branches; and the second switching means The short circuit is between the first upper and lower branches and the output terminals of the second upper and lower branches; and the second upper and lower branches use a switching element higher than the first upper and lower branches. The electromagnetic induction heating device of claim 2, wherein, in parallel with the first inductor, a series circuit of the first auxiliary switching element and the first capacitor is provided; and, in parallel with the second inductor, a second auxiliary switching element is provided. A series circuit with a second capacitor. The electromagnetic induction heating device according to any one of claims 1 to 3, wherein the heating coil and the first resonant capacitor constitute a first resonant load circuit, and the heating coil and the first resonant capacitor and the first The second resonant capacitor constitutes a second resonant load circuit; the first switching means switches: a half-bridge commutation state formed by the first and second upper and lower branches and the first resonant load circuit; and a full-bridge commutation state formed by the first and second upper and lower branches and the second resonant load circuit; and the second switching means is when the inverter is a half-bridge commutation state Next, the output terminals of the first and second upper and lower branches are short-circuited, and the upper and lower branches of the first and second upper and lower branches are connected in parallel. The electromagnetic induction heating device of claim 4, wherein, in the case where the inverter is a half-bridge commutation state branch, the shutdown timing of the second upper and lower branches is later than the shutdown timing of the first upper and lower branches . The electromagnetic induction heating device of claim 1, wherein the heating coil and the first resonant capacitor constitute a first resonant load circuit, and the heating coil and the first resonant capacitor and the second resonant capacitor form a second a resonant load circuit; wherein the first switching means switches: a half-bridge commutation state formed by the first and second upper and lower branches and the first resonant load circuit; and using the first and second upper and lower a full-bridge commutation state formed by the branch and the second resonant load circuit; and the second switching means short-circuiting the first and the second when the inverter is a half-bridge commutation state The output terminals of the two upper and lower branches are connected in parallel to the upper branches and the lower branches of the first and second upper and lower branches; in the case where the inverter is a full-bridge commutation state, The driving signals of the first and second upper and lower branches are provided with a phase difference, and the phase of the second upper and lower branches is further ahead of the first upper and lower branches. The electromagnetic induction heating device of claim 2, wherein the heating coil and the first resonant capacitor constitute a first resonant load circuit, and the heating coil and the first resonant capacitor and the second resonant capacitor form a second a resonant load circuit; wherein the first switching means switches: a half-bridge commutation state formed by the first and second upper and lower branches and the first resonant load circuit; and using the first and second upper and lower a full-bridge commutation state formed by the branch and the second resonant load circuit; and the second switching means short-circuiting the first and the second when the inverter is a half-bridge commutation state The output terminals of the two upper and lower branches are connected in parallel to the upper and lower branches of the first and second upper and lower branches; and when the inverter is in a full-bridge commutation state, the foregoing The conduction period of the two upper and lower branches is set to be shorter than the conduction period of the first upper and lower branches.