Electromagnetic induction heating device

Abstract

To provide an inverter type electromagnetic induction heating device for performing induction heating by supplying desired power to objects to be heated of different materials.SOLUTION: In the inverter circuit, the first upper and lower arms and the second upper and lower arms are connected in series between the positive and negative electrodes of the DC power supply, the capacitor is connected between the first upper and lower arms, one end of the first heating coil is connected to the first output terminal, the first resonant capacitor is connected between the other end of the first heating coil and the positive electrode or the negative electrode of the DC power supply, and the third upper and lower arms and the fourth upper and lower arms are connected in series between the positive and negative electrodes of the DC power supply; A capacitor is connected between the third upper and lower arms and the fourth upper and lower arms, one end of the second heating coil is connected to the second output terminal, a second resonant capacitor is connected between the other end of the second heating coil and the positive electrode or the negative electrode of the DC power supply, and a third resonant capacitor is connected between the other end of the first heating coil and the other end of the second heating coil.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an inverter-type electromagnetic induction heating device that supplies a desired amount of power to an object to be heated to perform induction heating. [Background technology]

[0002] In recent years, inverter-type electromagnetic induction heating devices that heat objects such as pots without using fire have become widely used. Electromagnetic induction heating devices pass a high-frequency current through a heating coil, generating eddy currents in a metal object (such as a pot) placed close to the heating coil, causing the object to generate heat due to its own electrical resistance.

[0003] An example of a conventional device that can appropriately heat both magnetic and non-magnetic objects is the electromagnetic induction heating device disclosed in Patent Document 1. The electromagnetic induction heating device in this patent document determines whether a cooking pot is magnetic or non-magnetic, and switches a relay (reference numeral 20 in Figure 1 of the document) depending on the result of this determination, thereby changing the circuit method of the high-frequency inverter and simultaneously switching the capacity of the resonant capacitor, thereby inductively heating objects made of different materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4909662 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, when a high-resistance magnetic pot is heated, a switch means (20) for switching the circuit type of the high-frequency inverter is turned on, and the inverter is switched to a full-bridge circuit type.

[0006] On the other hand, when a low-resistance non-magnetic pot is heated, the switch means is turned off, the inverter is switched to a half-bridge circuit configuration, and a step-down chopper circuit (40) is provided in the preceding stage of the inverter to reduce the DC voltage applied to the inverter.

[0007] In this way, when heating a non-magnetic pot, the inverter switches to a half-bridge circuit, so one of the two legs (leg 4) is inactive and not used effectively. Also, a step-down chopper circuit is required to limit the resonant current.

[0008] Furthermore, a switch (relay) was required to switch the circuit type of the high-frequency inverter and the capacitance of the resonant capacitor, which hindered miniaturization.

[0009] The object of the present invention is to address the above-mentioned problems by effectively utilizing all semiconductor switching elements used in the inverter, while lowering the withstand voltage of each semiconductor switching element while maintaining a high DC voltage applied to the inverter, and to provide an inverter-type electromagnetic induction heating device that can efficiently supply the desired power to objects made of different materials without using a switch (relay) for switching between inverter types or resonant capacitors. [Means for solving the problem]

[0010] In order to achieve the above object, the electromagnetic induction heating device of the present invention is an electromagnetic induction heating device comprising a plurality of heating coils for induction heating one object to be heated, and an inverter circuit for converting a DC voltage output from a DC power supply into an AC voltage and supplying the AC voltage to the heating coil, in which the inverter circuit has a first upper and lower arm which is a series circuit of a first upper arm switching element and a first lower arm switching element, and a second upper and lower arm which is a series circuit of a second upper arm switching element and a second lower arm switching element, connected in series between a positive electrode and a negative electrode of the DC power supply, and a capacitor connected between a junction of the first upper arm switching element and the first lower arm switching element constituting the first upper and lower arm and a junction of the second upper arm switching element and the second lower arm switching element, one end of the first heating coil is connected to a first output terminal which is the junction of the first upper and lower arm and the second upper and lower arm, and the other end of the first heating coil is connected to a positive electrode or a negative electrode of the DC power supply, or a first resonant capacitor is connected between the positive and negative electrodes of the third upper and lower arms, a third upper and lower arm which is a series connection of a third upper arm switching element and a third lower arm switching element, and a fourth upper and lower arm which is a series connection of a fourth upper arm switching element and a fourth lower arm switching element are connected in series between the positive and negative electrodes of the DC power supply, and a capacitor is connected between the connection point of the third upper arm switching element and the third lower arm switching element which constitute the third upper and lower arm (53) and the connection point of the fourth upper arm switching element and the fourth lower arm switching element which constitute the fourth upper and lower arm, one end of a second heating coil is connected to a second output terminal which is the connection point of the third upper and lower arm and the fourth upper and lower arm, a second resonant capacitor is connected between the other end of the second heating coil and the positive electrode, or the negative electrode, or the positive and negative electrode of the DC power supply, and a third resonant capacitor is connected between the other end of the first heating coil and the other end of the second heating coil. [Effects of the Invention]

[0011] According to the present invention, a low-voltage switching element with low on-resistance can be applied, and the DC voltage applied to the inverter can be kept high, so that the desired power can be efficiently supplied to heated objects made of different materials without using a switch (relay) to switch between inverter systems or resonant capacitors. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a circuit diagram of an electromagnetic induction heating device according to a first embodiment. [Figure 2] FIG. 2 is a circuit diagram of a DC power supply according to the first embodiment. [Figure 3] 10 shows the operating waveforms when the magnetic material is heated in Example 1. [Figure 4] 10 shows operational waveforms when a non-magnetic material is heated in Example 1. [Figure 5] FIG. 10 is a circuit diagram of an electromagnetic induction heating device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same reference numerals indicate the same components or components having similar functions, and redundant explanations will be omitted where appropriate. [Example]

[0014] 1 is a circuit diagram of an electromagnetic induction heating device according to Example 1 of the present invention. The electromagnetic induction heating device of this example has a top plate made of heat-resistant glass placed on top of a metal housing, and a high-frequency current is supplied to a heating coil placed below the top plate to induction heat a metal object to be heated placed at a predetermined position on the top surface of the top plate, but a description of this well-known configuration will be omitted below.

[0015] 1, DC power supply 1 is a power supply that rectifies AC voltage supplied from a 200V or 100V commercial AC power supply and outputs DC voltage. A first upper and lower arm 51, in which power semiconductor switching elements (hereinafter simply referred to as "switching elements") 51a and 51b are connected in series, and a second upper and lower arm 52, in which switching elements 52a and 52b are connected in series, are connected in series between a positive electrode P and a negative electrode N of DC power supply 1. Similarly, a third upper and lower arm 53, in which switching elements 53a and 53b are connected in series, and a fourth upper and lower arm 54, in which switching elements 54a and 54b are connected in series, are connected in series between the positive electrode P and the negative electrode N of DC power supply 1.

[0016] Diodes 61a-64a and 61b-64b are connected in parallel to the switching elements 51a-54a and 51b-54b, respectively, in the opposite direction. Capacitors 71a-74a and 71b-74b are connected in parallel to the switching elements 51a-54a and 51b-54b, respectively. These capacitors 71a-74a and 71b-74b are charged or discharged by the interruption current when the switching elements 51a-54a and 51b-54b are turned off, reducing the change in voltage applied to each switching element and suppressing turn-off loss. These capacitors also serve to balance the voltages applied to the off-state switching elements 51a-54a and 51b-54b. In other words, these capacitors are used as both snubber capacitors and voltage balancing capacitors.

[0017] Here, the connection point between the upper arm switching element 51a and the lower arm switching element 51b of the first upper and lower arm 51 is connected to a terminal O. 51a The connection point between the first upper and lower arms 51 and the second upper and lower arms 52 is connected to an output terminal O A The connection point between the upper arm switching element 52a and the lower arm switching element 52b of the second upper and lower arm 52 is connected to a terminal O. 52a The connection point between the upper arm switching element 53a and the lower arm switching element 53b of the third upper and lower arm 53 is connected to a terminal O. 53aThe connection point between the third upper and lower arms 53 and the fourth upper and lower arms 54 is connected to the output terminal O. B The connection point between the upper arm switching element 54a and the lower arm switching element 54b of the fourth upper and lower arm 54 is connected to a terminal O. 54a It will be called the "

[0018] As shown in Figure 1, the output terminal O A One end of the first heating coil 11 is connected to the output terminal O, a first resonant capacitor 21a is connected between the other end of the first heating coil 11 and the positive electrode P of the DC power supply 1, and a first resonant capacitor 21b is connected between the other end of the heating coil 11 and the negative electrode N of the DC power supply 1. There is no problem in terms of circuit operation even if only one of the first resonant capacitors 21a and 21b is connected, but it is better to provide both in order to reduce the ripple current of the DC power supply 1. Similarly, when the output terminal O B One end of the second heating coil 12 is connected to the positive electrode P of the DC power supply 1, a second resonant capacitor 22a is connected between the other end of the second heating coil 12 and the positive electrode P of the DC power supply 1, and a second resonant capacitor 22b is connected between the other end of the second heating coil 12 and the negative electrode N of the DC power supply 1. There is no problem in terms of circuit operation even if only one of the second resonant capacitors 22a and 22b is connected, but in terms of reducing the ripple current of the DC power supply 1, it is better to provide both.

[0019] Furthermore, a third resonant capacitor 23 is connected between the other end of the first heating coil 11 and the other end of the second heating coil 12 .

[0020] Terminal O of the first upper and lower arms 51 51a and the terminal O of the second upper and lower arms 52 52a A capacitor 41 is connected between the terminals O and 53, and maintains a value of approximately half the voltage of the DC power supply 1. 53a and the terminal O of the fourth upper and lower arms 54 54a A capacitor 42 is connected between the two terminals, and maintains a value that is approximately half the voltage of the DC power supply 1. Note that approximately half means, for example, 0.45 to 0.55.

[0021] Here, the DC power supply 1 is a power supply that rectifies AC voltage supplied from a commercial AC power supply 100 as shown in FIG. 2, for example, using diodes 101a to 101d, passes the rectified voltage through a normal filter made up of an inductor 102a and a capacitor 103a, and outputs a DC voltage using a boost chopper made up of a boost inductor 102b, a switching element 105, a diode 106a, and a smoothing capacitor 103b.

[0022] Because the heating coil 11 and the metal pan (not shown), which is the object to be heated, are magnetically coupled, when the metal pan is converted into an equivalent circuit viewed from the heating coil 11 side, the equivalent resistance and equivalent inductance of the metal pan are connected in series. The equivalent resistance and equivalent inductance differ depending on the material of the metal pan; if the metal pan is made of a low-resistance non-magnetic material, both the equivalent resistance and the equivalent inductance will be small, and if the metal pan is made of a high-resistance magnetic material, both will be large.

[0023] In the electromagnetic induction heating device of this embodiment, it is determined whether the object to be heated is a magnetic pot or a non-magnetic pot, and depending on the determination result, the driving method of the upper arm switching elements 51a to 54a and the lower arm switching elements 51b to 54b of the upper and lower arms 51 to 54 is changed. A and O B The object to be heated is heated by changing the output voltage amplitude of the power supply 1 to either voltage V1 or V1 / 2. Below, we will explain the difference in control when heating a magnetic pot and when heating a non-magnetic pot.

[0024] <Control when heating magnetic material> First, the control during heating of the magnetic material will be described with reference to FIG.

[0025] 3 shows the operating waveforms when the object to be heated is a magnetic body such as an iron pot. The waveforms shown here are, from top to bottom, (a) gate drive signals vgs of the switching elements 51a to 54a and 51b to 54b, 51a~54a , vgs 51b~54b , (b) Output terminal O A and O B Voltage between V OA-OB , the current i in the heating coils 11 and 12 11, i 12 (c) Voltages vds applied to the switching elements 51a, 51b, 54a, and 54b of the upper and lower arms 51 and 54 51a , vds 51b , vds 54a , vds 54b , the current i flowing through the switching elements 51a, 51b, 54a, and 54b of the upper and lower arms 51 and 54 51a , i 51b , i 54a , i 54b , the current i flowing through the diodes 61a, 61b, 64a, and 64b 61a , i 61b , i 64a , i 64b (d) Voltages vds applied to the switching elements 52a, 52b, 53a, and 53b of the upper and lower arms 52 and 53 52a , vds 52b , vds 53a , vds 53b , the current i flowing through the switching elements 52a, 52b, 53a, and 53b of the upper and lower arms 52 and 53 52a , i 52b , i 53a , i 53b , the current i flowing through the diodes 62a, 62b, 63a, and 63b 62a , i 62b , i 63a , i 63b The current i of the heating coil 11 is 11 and the current i of the heating coil 12 12 The direction shown in Figure 1 is positive.

[0026] 3A, when the magnetic material is heated in this embodiment, a period of mode M1 in which the upper arm switching elements 51a, 54a and the lower arm switching elements 51b, 54b of the upper and lower arms 51, 54 are turned on, and a period of mode M2 ​​in which the upper arm switching elements 52a, 53a and the lower arm switching elements 52b, 53b of the upper and lower arms 52, 53 are turned on are provided. This causes the inverter 2 to be a full-bridge circuit.

[0027] <Mode M1> In mode M1 in which the upper arm switching elements 51a, 54a and the lower arm switching elements 51b, 54b of the upper and lower arms 51, 54 are turned on, as shown in FIG. 3(b), A and O B The voltage V1 of DC power supply 1 is output between 11 The polarity of switches from negative to positive, and the coil current i 12 When the polarity switches from positive to negative, a current flows from the DC power supply 1 through the upper arm switching element 51a, the lower arm switching element 51b, the heating coil 11, the third resonant capacitor 23, the heating coil 12, the upper arm switching element 54a, and the lower arm switching element 54b.

[0028] At this time, the upper and lower arms 51 and 54 are in the ON state, so as shown in FIG. 3(c), the voltages vds of the upper arm switching elements 51a and 54a 51a , vds 54a and Vds of the lower arm switching elements 51b and 54b 51b , vds 54b On the other hand, the upper and lower arms 52 are in the OFF state, and the upper arm switching element 52a and the lower arm switching element 52b are connected in series to the DC power supply 1. Therefore, as shown in FIG. 3(d), a voltage of V1 / 2, which is approximately half the voltage V1 of the DC power supply 1, is applied to the upper arm switching element 52a and the lower arm switching element 52b. Therefore, the voltage at the terminal O of the first upper and lower arms 51 is 51a and the terminal O of the second upper and lower arms 52 52a The voltage V of the capacitor 41 connected between 41 is maintained at V1 / 2 as shown in Figure 3(b).

[0029] Similarly, the third upper and lower arms 53 are in an OFF state, and the upper arm switching element 53a and the lower arm switching element 53b are connected in series to the DC power supply 1. Therefore, as shown in FIG. 3(d), a voltage V1 / 2, which is approximately half the voltage V1 of the DC power supply 1, is applied to the upper arm switching element 53a and the lower arm switching element 53b. Therefore, the terminal O of the third upper and lower arms 5353a and the terminal O of the fourth upper and lower arms 54 54a The voltage V of the capacitor 42 connected between 42 is maintained at V1 / 2 as shown in Figure 3(b).

[0030] <Mode M2> In mode M2 ​​in which the upper arm switching elements 52a, 53a and the lower arm switching elements 52b, 53b of the upper and lower arms 52, 53 are turned on, as shown in FIG. 3(b), A and O B Between them is -V1 / 2 volts, and the coil current i 11 The polarity of switches from positive to negative, and the coil current i 12 When the polarity of the resonant capacitor 23 switches from negative to positive, a current flows from the DC power supply 1 through the upper arm switching element 53a, the lower arm switching element 53b, the heating coil 12, the third resonant capacitor 23, the heating coil 11, the upper arm switching element 52a, and the lower arm switching element 52b.

[0031] At this time, the upper and lower arms 52 and 53 are in the ON state, and therefore, as shown in FIG. 3(d), the voltages vds of the upper arm switching elements 52a and 53a 52a , vds 53a and Vds of the lower arm switching elements 52b and 53b 52b , vds 53b On the other hand, the first upper and lower arms 51 are in an OFF state, and the upper arm switching element 51a and the lower arm switching element 51b are connected in series to the DC power supply 1. Therefore, as shown in FIG. 3(c), a voltage of V1 / 2, which is approximately half the voltage V1 of the DC power supply 1, is applied to the upper arm switching element 51a and the lower arm switching element 51b. Therefore, the voltage at the terminal O of the first upper and lower arms 51 is 51a and the terminal O of the second upper and lower arms 52 52a The voltage V of the capacitor 41 connected between 41 is maintained at V1 / 2 as shown in Figure 3(b).

[0032] Similarly, the fourth upper and lower arms 54 are in the OFF state, and the upper arm switching element 54a and the lower arm switching element 54b are connected in series to the DC power supply 1. Therefore, as shown in FIG. 3(c), a voltage V1 / 2, which is approximately half the voltage V1 of the DC power supply 1, is applied to the upper arm switching element 54a and the lower arm switching element 54b. Therefore, the terminal O of the third upper and lower arms 53 53a and the terminal O of the fourth upper and lower arms 54 54a The voltage V of the capacitor 42 connected between 42 is maintained at V1 / 2 as shown in Figure 3(b).

[0033] As described above, when heating the magnetic material in this embodiment, the voltage applied to the switching elements 51a-54a and 51b-54b is approximately half the voltage V1 of the DC power supply 1, so the withstand voltage of the switching elements can be lowered and switching elements with low on-resistance can be used, which is effective in reducing loss. Furthermore, when MOSFETs are used for the switching elements 51a-54a and 51b-54b, the current flowing through the diodes 61a-64a and 61b-64b can be made to flow through the MOSFETs, and loss reduction due to synchronous rectification can also be expected.

[0034] High-resistivity magnetic materials have a high equivalent resistance, making it difficult for current to flow through the resonant load circuit. Therefore, in this embodiment, by changing to a full-bridge topology, the inverter output voltage is increased to twice that of a half-bridge topology, achieving the desired output. When the heated object is a magnetic pot, the resistance is inherently high, so the upper and lower arms 51-54 are driven at a frequency of approximately 25 kHz. Therefore, the capacitance of the third resonant capacitor 23 is set to match the drive frequency of approximately 25 kHz and is sufficiently larger than the capacitances of the first and second resonant capacitors 21a, 21b, 22a, and 22b. Therefore, most of the coil current flows through the third resonant capacitor 23.

[0035] As mentioned above, since a high-resistivity magnetic material has a large equivalent resistance, the ratio of current change to a change in switching frequency is small, and the heating coil current can be easily controlled by controlling the frequency of the inverter circuit.

[0036] <Control when heating non-magnetic materials> Next, the control when heating a non-magnetic material will be described with reference to FIG.

[0037] Figure 4 shows the operating waveform when the object to be heated is a non-magnetic material such as an aluminum pot. 51a The meanings of the above are the same as those in Figure 3.

[0038] When heating a non-magnetic material in this embodiment, as shown in FIG. 4(a), the upper arm switching elements 51a, 53a of the upper and lower arms 51, 53 and the lower arm switching elements 52b, 54b of the upper and lower arms 52, 54 are complementarily driven, the lower arm switching elements 51b, 53b of the upper and lower arms 51, 53 and the upper arm switching elements 52a, 54a of the upper and lower arms 52, 54 are complementarily driven, and the turn-on timing of the upper arm switching elements 51a, 53a of the upper and lower arms 51, 53 and the lower arm switching elements 51b, 53b are driven with a phase shift of 180 degrees, thereby providing the following modes M1 to M3.

[0039] <Mode M1> In mode M1 in which the upper arm switching elements 51a and 53a of the upper and lower arms 51 and 53 and the upper arm switching elements 52a and 54a of the upper and lower arms 52 and 54 are turned on, as shown in FIG. 4(b), A The voltage V1 / 2 obtained by subtracting the voltage V1 / 2 of the capacitor 41 from the voltage V1 of the DC power supply 1 is output to the output terminal O. B The voltage V1 / 2 obtained by subtracting the voltage V1 / 2 of the capacitor 42 from the voltage V1 of the DC power supply 1 is output to the 11 , i 12When the polarity of the input terminal changes from negative to positive, current flows through a path from the DC power supply 1 to the upper-arm switching element 51a, capacitor 41, diode 62a, heating coil 11, and first resonant capacitor 21b, and also through a path from the DC power supply 1 to the upper-arm switching element 53a, capacitor 42, diode 64a, heating coil 12, and second resonant capacitor 22b. Also, a coil current flows through a free-wheeling path from the first resonant capacitor 21a to the upper-arm switching element 51a, capacitor 41, diode 62a, and heating coil 11, and also through a free-wheeling path from the second resonant capacitor 22a to the upper-arm switching element 53a, capacitor 42, diode 64a, and heating coil 12.

[0040] Here, when the switching elements 52a and 54a are MOSFETs, synchronous rectification is possible, and therefore the currents in the diodes 62a and 64a flow from the sources to the drains of the switching elements 52a and 54a, respectively.

[0041] Since the upper arm switching elements 51a and 52a are in the on state, the voltage vds of the upper arm switching element 51a is 51a and the voltage vds of the upper arm switching element 52a 52a On the other hand, the lower arm switching elements 51b and 52b are in the OFF state and are connected in series to the DC power supply 1, so that a voltage of V1 / 2, which is about half the voltage V1 of the DC power supply 1, is applied to each of the lower arm switching elements 51b and 52b, as shown in FIGS. 4(c) and 4(d). Therefore, the voltage at the terminal O of the first upper and lower arms 51 is 51a and terminal O of upper and lower arms 52 52a The voltage V of the capacitor 41 connected between 41 is maintained at V1 / 2 as shown in Figure 4(b).

[0042] Similarly, since the upper arm switching elements 53a and 54a are in the on state, the voltage vds of the upper arm switching element 53a is 53aand the voltage vds of the upper arm switching element 54a 54a On the other hand, the lower arm switching elements 53b and 54b are in the OFF state and are connected in series to the DC power supply 1, so that a voltage of V1 / 2, which is approximately half the voltage V1 of the DC power supply 1, is applied to the lower arm switching elements 53b and 54b, as shown in FIGS. 4(c) and 4(d). Therefore, the voltage at the terminal O of the third upper and lower arms 53 is 53a and terminal O of upper and lower arms 54 54a The voltage V of the capacitor 42 connected between 42 is maintained at V1 / 2 as shown in Figure 4(b).

[0043] <Mode M2> In mode M2 ​​in which the upper arm switching elements 52a, 54a and the lower arm switching elements 52b, 54b of the upper and lower arms 52, 54 are turned on, as shown in FIG. 4(b), A and O B becomes zero volts, and the coil current i 11 , i 12 When the polarity of the resonant capacitor 21b switches from positive to negative, a current flows through a path from the DC power supply 1 to the capacitor 21a, the heating coil 11, the upper arm switching element 52a, and the lower arm switching element 52b, and also through a path from the DC power supply 1 to the capacitor 22a, the heating coil 12, the upper arm switching element 54a, and the lower arm switching element 54b. Also, a coil current flows through a free-wheeling path from the first resonant capacitor 21b to the heating coil 11, the upper arm switching element 52a, and the lower arm switching element 52b, and also through a free-wheeling path from the second resonant capacitor 22b to the heating coil 12, the upper arm switching element 54a, and the lower arm switching element 54b.

[0044] At this time, since the upper arm switching element 52a and the lower arm switching element 52b are in the ON state, as shown in FIG. 4(d), the voltage vds of the upper arm switching element 52a 52a and the voltage vds of the lower arm switching element 52b 52bOn the other hand, the upper arm switching element 51a and the lower arm switching element 51b are in the OFF state and are connected in series to the DC power supply 1, so that as shown in FIG. 4(c), a voltage of V1 / 2, which is about half the voltage V1 of the DC power supply 1, is applied to each of the upper arm switching element 51a and the lower arm switching element 51b. Therefore, the voltage at the terminal O of the first upper and lower arms 51 is 51a and the terminal O of the second upper and lower arms 52 52a The voltage V of the capacitor 41 connected between 41 is maintained at V1 / 2 as shown in Figure 4(b).

[0045] Similarly, since the upper arm switching element 54a and the lower arm switching element 54b are in the ON state, as shown in FIG. 4(d), the voltage vds of the upper arm switching element 54a 54a and the voltage vds of the lower arm switching element 54b 54b On the other hand, the upper arm switching element 53a and the lower arm switching element 53b are in the OFF state and are connected in series to the DC power supply 1, so that as shown in FIG. 4(c), a voltage of V1 / 2, which is about half the voltage V1 of the DC power supply 1, is applied to the upper arm switching element 53a and the lower arm switching element 53b. Therefore, the voltage at the terminal O of the third upper and lower arms 53 is 53a and terminal O of upper and lower arms 54 54a The voltage V of the capacitor 42 connected between 42 is maintained at V1 / 2 as shown in Figure 4(b).

[0046] <Mode M3> In mode M3 in which the lower arm switching elements 51b and 53b of the upper and lower arms 51 and 53 and the lower arm switching elements 52b and 54b of the upper and lower arms 52 and 54 are turned on, as shown in FIG. 4(b), A The voltage V1 / 2 of the capacitor 41 is output to the output terminal O B The voltage V1 / 2 of the capacitor 42 is output to the 11 , i 12When the polarity of the first resonant capacitor 21a switches from negative to positive, current flows through a path from capacitor 41 to lower-arm switching element 51b, heating coil 11, first resonant capacitor 21b, and diode 62b, and also through a path from capacitor 42 to lower-arm switching element 53b, heating coil 12, second resonant capacitor 22b, and diode 64b. Also, a coil current flows through a return path from first resonant capacitor 21a to DC power supply 1, diode 62b, capacitor 41, lower-arm switching element 51b, and heating coil 11, and also through a return path from second resonant capacitor 22a to DC power supply 1, diode 64b, capacitor 42, lower-arm switching element 53b, and heating coil 12. Here, if the lower-arm switching elements 52b and 54b are MOSFETs, synchronous rectification operation is possible, and so the currents in diodes 62b and 64b flow from the sources to the drains of switching elements 52b and 54b, respectively.

[0047] At this time, since the switching elements 51b and 52b are in the ON state, the voltage vds of the lower arm switching element 51b is 51b and the voltage vds of the lower arm switching element 52b 52b On the other hand, the upper arm switching elements 51a and 52a are in the OFF state and are connected in series to the DC power supply 1, so that a voltage of V1 / 2, which is about half the voltage V1 of the DC power supply 1, is applied to each of the upper arm switching elements 51a and 52a, as shown in FIGS. 4(c) and 4(d). Therefore, the voltage at the terminal O of the first upper and lower arms 51 is 51a and the terminal O of the second upper and lower arms 52 52a The voltage V of the capacitor 41 connected between 41 is maintained at V1 / 2 as shown in Figure 4(b).

[0048] Similarly, since the switching elements 53b and 54b are in the on state, the voltage vds of the lower arm switching element 53b is 53b and the voltage vds of the lower arm switching element 54b 54bOn the other hand, the upper arm switching elements 53a and 54a are in the OFF state and are connected in series to the DC power supply 1, so that a voltage of V1 / 2, which is approximately half the voltage V1 of the DC power supply 1, is applied to each of the upper arm switching elements 53a and 54a, as shown in FIGS. 4(c) and 4(d). Therefore, the voltage at the terminal O of the third upper and lower arm 53 is 53a and the terminal O of the fourth upper and lower arms 54 54a The voltage V of the capacitor 42 connected between 42 is maintained at V1 / 2 as shown in Figure 4(b).

[0049] In this way, when heating a non-magnetic material in this embodiment, the voltage applied to the switching elements 51a to 54a and 51b to 54b is approximately half the voltage V1 of the DC power supply 1, so that the withstand voltage of the switching elements can be reduced and switching elements with low on-resistance can be used, which is effective in reducing loss.

[0050] Also, for the switching period Ts, the heating coil current i 11 , i 12 Since the period is Ts / 2, for example, when heating at a frequency of approximately 90 kHz, it becomes possible to drive the switching frequency at approximately 45 kHz, which is also effective in reducing the switching loss of each switching element.

[0051] As mentioned above, low-resistivity non-magnetic materials have low equivalent resistance, so a large current is required to achieve the desired output. The skin resistance of the heated object is proportional to the square root of the frequency. Therefore, increasing the frequency is effective when heating low-resistivity objects such as copper or aluminum. Therefore, the capacitances of the first and second resonant capacitors 21a, 21b, 22a, and 22b are set so that the frequency of the heating coil current is approximately 90 kHz. If the currents in the heating coils 11 and 12 are the same, the voltages across the first and second resonant capacitors 21b and 22b will also be the same, and the voltage applied to the third resonant capacitor 23 will be nearly zero. Therefore, even when the third resonant capacitor 23 is connected, it does not affect the heating of non-magnetic materials.

[0052] Because low-resistivity non-magnetic materials have a small equivalent resistance, the ratio of current change to frequency change is large, and current flows easily. Therefore, it is desirable to control the voltage applied to the resonant load circuit consisting of the heating coil and resonant capacitor low. When heating the non-magnetic material in this embodiment, the heating coil current is controlled by varying the voltage of smoothing capacitor 103b using the boost chopper shown in Figure 2, i.e., the voltage of DC power supply 1 applied to inverter 2. By changing the driving method of upper arm switching elements 51a-54a and lower arm switching elements 51b-54b of upper and lower arms 51-54, inverter 2 can reduce the inverter output voltage to half the voltage V1 of DC power supply 1, thereby keeping the voltage applied to the resonant load circuit low. [Example]

[0053] 5 is a circuit diagram of an electromagnetic induction heating device according to a second embodiment of the present invention. In the following, commonalities with the first embodiment will be explained while omitting redundant explanations.

[0054] 5, in comparison with the circuit configuration of Example 1 shown in Fig. 1, third resonant capacitors 23a and 23b are connected in series to the heating coils 11 and 12, respectively. In this example, the circuit configuration does not include the third resonant capacitor 23 of Example 1, and the first resonant capacitors 21a and 21b serve as the resonant capacitors for both the first heating coil 11 and the second heating coil 12. This makes it possible to reduce the number of resonant capacitors by one. [Explanation of symbols]

[0055] 1 DC power supply, 2 inverters 51a to 54a, 51b to 54b, 105 switching element, 61a to 64a, 61b to 64b, 101a to 101d, 106a, 106b diodes, 71a to 74a, 71b to 74b, 41, 42, 103a, 103b capacitors, 11 first heating coil; 12 second heating coil, 21a, 21b first resonant capacitor; 22a, 22b second resonant capacitor; 23, 23a, 23b third resonant capacitor; 51, 52, 53, 54 Upper and lower arms, 100 Commercial AC power supply 102a, 102b inductors

Claims

1. A plurality of heating coils for induction heating one object to be heated; an inverter circuit (2) that converts a DC voltage output from a DC power source (1) into an AC voltage and supplies the AC voltage to the heating coil; An electromagnetic induction heating device comprising: The inverter circuit (2) A first upper and lower arm (51) which is a series circuit of a first upper arm switching element (51a) and a first lower arm switching element (51b) and a second upper and lower arm (52) which is a series circuit of a second upper arm switching element (52a) and a second lower arm switching element (52b) are connected in series between a positive electrode (P) and a negative electrode (N) of the DC power supply (1); The first upper arm switching element (51a) and the first lower arm switching element (51b) constituting the first upper and lower arms (51) are connected at a connection point (O ５１ａ ) and a connection point (O) between the second upper arm switching element (52a) and the second lower arm switching element (52b) constituting the second upper and lower arm (52). ５２ａ ) and a capacitor (41) is connected between the A first output terminal (O) is a connection point between the first upper and lower arms (51) and the second upper and lower arms (52). Ａ ), one end of a first heating coil (11) is connected to the positive electrode (P) or the negative electrode (N) or the positive and negative electrodes (P, N) of the DC power source (1), and first resonant capacitors (21a, 21b) are connected between the other end of the first heating coil (11) and the positive electrode (P) or the negative electrode (N) or the positive and negative electrodes (P, N) of the DC power source (1); a third upper and lower arm (53) which is a series body of a third upper arm switching element (53a) and a third lower arm switching element (53b) and a fourth upper and lower arm (54) which is a series body of a fourth upper arm switching element (54a) and a fourth lower arm switching element (54b) are connected in series between a positive electrode (P) and a negative electrode (N) of the DC power supply (1); The third upper arm switching element (53a) and the third lower arm switching element (53b) constituting the third upper and lower arm (53) are connected at a connection point (O ５３ａ ) and a connection point (O) between the fourth upper arm switching element (54a) and the fourth lower arm switching element (54b) constituting the fourth upper and lower arm (54). ５４ａ ) and a capacitor (42) is connected between the A second output terminal (O) which is a connection point between the third upper and lower arm (53) and the fourth upper and lower arm (54) Ｂ ), one end of a second heating coil (12) is connected to the positive electrode (P) or the negative electrode (N) or the positive and negative electrodes (P, N) of the DC power source (1), and second resonant capacitors (22a, 22b) are connected between the other end of the second heating coil (12) and the positive electrode (P) or the negative electrode (N) or the positive and negative electrodes (P, N) of the DC power source (1); An electromagnetic induction heating device characterized in that a third resonant capacitor (23) is connected between the other end of the first heating coil (11) and the other end of the second heating coil (12).

2. 2. The electromagnetic induction heating device according to claim 1, The electromagnetic induction heating device is characterized in that a capacitor for snubber use and a capacitor for voltage balancing are connected in parallel to the switching element.

3. 3. The electromagnetic induction heating device according to claim 1, When the object to be heated is a magnetic material, the inverter circuit a period during which the first and fourth upper arm switching elements (51 a, 54 a) and the first and fourth lower arm switching elements (51 b, 54 b) of the first and fourth upper and fourth arms (51, 54) are turned on; a period in which the second and third upper arm switching elements (52a, 53a) and the second and third lower arm switching elements (52b, 53b) of the second and third upper and lower arms (52, 53) are turned on; The first and second output terminals (O Ａ , O Ｂ ) as the voltage of the DC power supply (1), and a high-frequency current is passed through the first and second heating coils to heat the object to be heated.

4. 3. The electromagnetic induction heating device according to claim 1, When the object to be heated is a non-magnetic material, the inverter circuit driving the first and third upper arm switching elements (51 a, 53 a) of the first and third upper and lower arms (51, 53) and the second and fourth lower arm switching elements (52 b, 54 b) of the second and fourth upper and fourth arms (52, 54) in a complementarily manner; driving the first and third lower arm switching elements (51b, 53b) of the first and third upper and lower arms (51, 53) and the second and fourth upper arm switching elements (52a, 54a) of the second and fourth upper and fourth arms (52, 54) in a complementarily manner; driving the first and third upper arm switching elements (51a, 53a) and the first and third lower arm switching elements (51b, 53b) of the first and third upper and lower arms (51, 53) with a phase difference of 180 degrees between their turn-on timings; The first and second output terminals (O Ａ , O Ｂ ) is set to about half the voltage of the DC power supply (1), and a high-frequency current having twice the switching frequency of the inverter circuit is passed through the first and second heating coils to heat the object to be heated.

5. A plurality of heating coils for induction heating one object to be heated; an inverter circuit (2) that converts a DC voltage output from a DC power source (1) into an AC voltage and supplies the AC voltage to the heating coil; An electromagnetic induction heating device comprising: The inverter circuit (2) A first upper and lower arm (51) which is a series circuit of a first upper arm switching element (51a) and a first lower arm switching element (51b) and a second upper and lower arm (52) which is a series circuit of a second upper arm switching element (52a) and a second lower arm switching element (52b) are connected in series between a positive electrode (P) and a negative electrode (N) of the DC power supply (1); The first upper arm switching element (51a) and the first lower arm switching element (51b) constituting the first upper and lower arms (51) are connected at a connection point (O ５１ａ ) and a connection point (O) between the second upper arm switching element (52a) and the second lower arm switching element (52b) constituting the second upper and lower arm (52). ５２ａ ) and a capacitor (41) is connected between the A first output terminal (O) is a connection point between the first upper and lower arms (51) and the second upper and lower arms (52). Ａ ) is connected to one end of a third resonant capacitor (23a), and the other end of the third resonant capacitor (23b) is connected to one end of a first heating coil (11); a third upper and lower arm (53) which is a series body of a third upper arm switching element (53a) and a third lower arm switching element (53b) and a fourth upper and lower arm (54) which is a series body of a fourth upper arm switching element (54a) and a fourth lower arm switching element (54b) are connected in series between a positive electrode (P) and a negative electrode (N) of the DC power supply (1); The third upper arm switching element (53a) and the third lower arm switching element (53b) constituting the third upper and lower arm (53) are connected at a connection point (O ５３ａ ) and a connection point (O) between the fourth upper arm switching element (54a) and the fourth lower arm switching element (54b) constituting the fourth upper and lower arm (54). ５４ａ ) and a capacitor (42) is connected between the A second output terminal (O) which is a connection point between the third upper and lower arm (53) and the fourth upper and lower arm (54) Ｂ ) is connected to one end of a third resonant capacitor (23b), and the other end of the third resonant capacitor (23b) is connected to one end of a second heating coil (12); an electromagnetic induction heating device, characterized in that a first resonant capacitor (21a, 21b) is connected between a connection point of the other end of the first heating coil (11) and the other end of the second heating coil (12) and the positive electrode (P), or the negative electrode (N), or the positive and negative electrodes (P, N) of the DC power source (1).

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