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: The inverter circuit includes first upper and lower arms and second upper and lower arms connected in series between a positive electrode and a negative electrode of a DC power supply, and a capacitor connected between a connection point of a first upper arm switching element and a first lower arm switching element constituting the first upper and lower arms and a connection point of a second upper arm switching element and a second lower arm switching element constituting the second upper and lower arms. Wherein one end of a heating coil is connected to an output terminal of the inverter circuit, and a first resonant capacitor is connected between the other end of the heating coil and a positive electrode, a negative electrode, or positive and negative electrodes of the DC power supply.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, depending on the determination result, changes the circuit type of the high-frequency inverter to a half-bridge type when heating a non-magnetic pot, and to a full-bridge type when heating a magnetic pot, thereby induction 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 configuration, 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] The object of the present invention is to address the above-mentioned problems and to provide an inverter-type electromagnetic induction heating device that effectively utilizes all semiconductor switching elements used in the inverter, reduces the withstand voltage of each semiconductor switching element while maintaining a high DC voltage applied to the inverter, and can efficiently supply the desired power to the object to be heated. [Means for solving the problem]

[0009] In order to achieve the above object, the electromagnetic induction heating device of the present invention is an electromagnetic induction heating device including a heating coil for induction heating one object to be heated, and an inverter circuit for converting a DC voltage output by 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 connection 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 connection of a second upper arm switching element and a second lower arm switching element, connected in series between the positive and negative electrodes of the DC power supply, and a capacitor connected between the junction of the first upper arm switching element and the first lower arm switching element that constitute the first upper and lower arm and the junction of the second upper arm switching element and the second lower arm switching element that constitute the second upper and lower arm, one end of the heating coil is connected to an output terminal of the inverter circuit, and a first resonant capacitor is connected between the other end of the heating coil and the positive electrode, or the negative electrode, or the positive and negative electrodes of the DC power supply. [Effects of the Invention]

[0010] According to the present invention, a low-voltage switching element with low on-resistance can be applied, and desired power can be efficiently supplied to an object to be heated while keeping the DC voltage applied to the inverter high. [Brief explanation of the drawings]

[0011] [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

[0012] 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]

[0013] 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.

[0014] 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 this DC power supply 1.

[0015] Diodes 61a, 61b, 62a, and 62b are connected in reverse parallel to switching elements 51a, 51b, 52a, and 52b, respectively. Capacitors 71a, 71b, 72a, and 72b are connected in parallel to switching elements 51a, 51b, 52a, and 52b, respectively. These capacitors 71a, 71b, 72a, and 72b are charged or discharged by the interruption current when switching elements 51a, 51b, 52a, and 52b are turned off, thereby 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, 51b, 52a, and 52b. In other words, these capacitors are used as both snubber capacitors and voltage balancing capacitors.

[0016] 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 It will be called the "

[0017] As shown in Figure 1, the output terminal O AOne end of the heating coil 11 is connected to the positive electrode P of the DC power supply 1, a first resonant capacitor 21a is connected between the other end of the 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 or 21b is connected, but in terms of reducing the ripple current of the DC power supply 1, it is better to provide both.

[0018] Furthermore, one end of a relay 20 is connected to the other end of the heating coil 11, a second resonant capacitor 22a is connected between the other end of the relay 20 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 relay 20 and the negative electrode N of the DC power supply 1. Similarly, there is no problem in terms of circuit operation even if only one of the second resonant capacitors 22a, 22b is connected, but in terms of reducing the ripple current of the DC power supply 1, it is better to provide both.

[0019] 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 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.

[0020] 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.

[0021] 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.

[0022] 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, it switches relay 20 on or off, and then changes the driving method of upper arm switching element 51a and lower arm switching element 51b of first upper and lower arm 51 and upper arm switching element 52a and lower arm switching element 52b of second upper and lower arm 52. As a result, output terminal O A 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.

[0023] <Control when heating magnetic material> First, the control during heating of the magnetic material will be described with reference to FIG.

[0024] Figure 3 shows the operating waveforms when the object to be heated is a magnetic material such as an iron pot. The waveforms shown here are, from top to bottom, (a) gate drive signals Vgs of switching elements 51a, 51b, 52a, and 52b; 51a , vgs 51b、 vgs 52a、 vgs 52b , (b) Output terminal O A Voltage V OA , the current i of the heating coil 11 11 (c) Voltage vds applied to the switching elements 51a and 51b of the first upper and lower arms 51 51a , vds 51b , the current i flowing through the switching elements 51a and 51b of the first upper and lower arms 51 51a , i 51b , the current i flowing through the diodes 61a and 61b 61a , i61b (d) Voltage vds applied to the switching elements 52a and 52b of the second upper and lower arms 52 52a , vds 52b , the current i flowing through the switching elements 52a and 52b of the second upper and lower arms 52 52a , i 52b , the current i flowing through the diodes 62a and 62b 62a , i 62b The current i of the heating coil 11 11 The direction shown in Figure 1 is positive.

[0025] When heating a magnetic material in this embodiment, the relay 20 in Figure 1 is turned on, and the first resonant capacitors 21a, 21b and the second resonant capacitors 22a, 22b are connected in parallel, respectively. As shown in Figure 3(a), a period of mode M1 is provided in which the upper arm switching element 51a and the lower arm switching element 51b of the first upper and lower arm 51 are on, and a period of mode M2 ​​is provided in which the upper arm switching element 52a and the lower arm switching element 52b of the second upper and lower arm 52 are on.

[0026] <Mode M1> In mode M1 in which the upper arm switching element 51a and the lower arm switching element 51b of the first upper and lower arms 51 are turned on, as shown in FIG. 3(b), A The voltage V1 of DC power supply 1 is output to 11 When the polarity of the resistor 51a switches from negative to positive, 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 first resonant capacitor 21b, and the second resonant capacitor 22b. Also, a coil current flows from the first resonant capacitor 21a and the second resonant capacitor 22a through the return path of the upper-arm switching element 51a, the lower-arm switching element 51b, and the heating coil 11.

[0027] At this time, since the first upper and lower arms 51 are in the ON state, as shown in FIG. 3(c), the voltage vds of the upper arm switching element 51a 51a and Vds of the lower arm switching element 51b51b On the other hand, the second upper and lower arms 52 are in an 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).

[0028] <Mode M2> In mode M2 ​​in which the upper arm switching element 52a and the lower arm switching element 52b of the second upper and lower arms 52 are turned on, as shown in FIG. 3(b), A becomes zero volts, and the coil current i 11 When the polarity of the resonant capacitor 21b switches from positive to negative, a current flows from the DC power supply 1 through the first resonant capacitor 21a, the second resonant capacitor 22a, the heating coil 11, the upper arm switching element 52a, and the lower arm switching element 52b. Also, a coil current flows from the first resonant capacitor 21b and the second resonant capacitor 22b through the circulation path of the heating coil 11, the upper arm switching element 52a, and the lower arm switching element 52b.

[0029] At this time, since the second upper and lower arms 52 are in the ON state, as shown in FIG. 3(d), the voltage vds of the upper arm switching element 52a 52a and the voltage vds of the lower arm switching element 52b 52b 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 is51a 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).

[0030] As described above, when heating the magnetic material in this embodiment, the voltage applied to the switching elements 51a, 51b, 52a, and 52b 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, if MOSFETs are used for the switching elements 51a, 51b, 52a, and 52b, the current flowing through the diodes 61a, 61b, 62a, and 62b can be made to flow through the MOSFETs, and loss reduction due to synchronous rectification can also be expected.

[0031] Here, when the object to be heated is a magnetic pot, the resistance is inherently high, so the first upper and lower arms 51 and the second upper and lower arms 52 are driven at a frequency of approximately 25 kHz. Therefore, the capacitances of the second resonant capacitors 22a and 22b are set to match the drive frequency of approximately 25 kHz and to a value sufficiently larger than the capacitances of the first resonant capacitors 21a and 21b. Therefore, the first resonant capacitors 21a and 21b and the second resonant capacitors 22a and 22b are connected in parallel, but because the capacitances of the second resonant capacitors 22a and 22b are sufficiently larger than the capacitances of the first resonant capacitors 21a and 21b, most of the current flows through the second resonant capacitors 22a and 22b.

[0032] 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.

[0033] <Control when heating non-magnetic materials> Next, the control when heating a non-magnetic material will be described with reference to FIG.

[0034] Figure 4 shows the operating waveform when the object to be heated is a non-magnetic material such as an aluminum pot. 51aThe meanings of the above are the same as those in Figure 3.

[0035] When heating a non-magnetic material in this embodiment, the relay 20 in FIG. 1 is turned off, and only the first resonant capacitors 21a and 21b are used. As shown in FIG. 4(a), the upper arm switching element 51a of the first upper and lower arm 51 and the lower arm switching element 52b of the second upper and lower arm 52 are complementarily driven, and the lower arm switching element 51b of the first upper and lower arm 51 and the upper arm switching element 52a of the second upper and lower arm 52 are complementarily driven, and the upper arm switching element 51a and the lower arm switching element 51b of the first upper and lower arm 51 are driven with a phase difference of 180 degrees between the turn-on timings of the upper arm switching element 51a and the lower arm switching element 51b of the first upper and lower arm 51, thereby providing the following modes M1 to M3.

[0036] <Mode M1> In mode M1 in which the upper arm switching element 51a of the first upper and lower arm 51 and the upper arm switching element 52a of the second upper and lower arm 52 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 11 When the polarity of the first resonant capacitor 21a switches from negative to positive, a current flows from the DC power supply 1 through the upper-arm switching element 51a, capacitor 41, diode 62a, heating coil 11, and first resonant capacitor 21b. Also, a coil current flows from the first resonant capacitor 21a through the free-wheeling path of the upper-arm switching element 51a, capacitor 41, diode 62, and heating coil 11. Here, if the switching element 52a is a MOSFET, synchronous rectification operation is possible, and therefore the current in the diode 62a flows from the source to the drain of the switching element 52a.

[0037] At this time, the upper arm switching elements 51a and 52a are in the ON state, and therefore, as shown in FIGS. 4(c) and 4(d), the voltage vds of the upper arm switching element 51a 51a and the voltage vds of the upper arm switching element 52a 52aOn 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 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).

[0038] <Mode M2> In mode M2 ​​in which the upper arm switching element 52a and the lower arm switching element 52b of the second upper and lower arms 52 are turned on, as shown in FIG. 4(b), A becomes zero volts, and the coil current i 11 When the polarity of the resonant capacitor 21b switches from positive to negative, a current flows from the DC power supply 1 through the capacitor 21a, the heating coil 11, the upper arm switching element 52a, and the lower arm switching element 52b. Also, a coil current flows from the first resonant capacitor 21b through the circulation path of the heating coil 11, the upper arm switching element 52a, and the lower arm switching element 52b.

[0039] 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 52b On 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 between41 is maintained at V1 / 2 as shown in Figure 4(b).

[0040] <Mode M3> In mode M3 in which the lower arm switching element 51b of the first upper and lower arm 51 and the lower arm switching element 52b of the second upper and lower arm 52 are turned on, as shown in FIG. 4(b), A The voltage V1 / 2 of the capacitor 41 is output to the 11 When the polarity of the first resonant capacitor 21a switches from negative to positive, a current flows from the capacitor 41 through the lower-arm switching element 51b, heating coil 11, first resonant capacitor 21b, and diode 62b. Also, a coil current flows through the return path from the first resonant capacitor 21a to the DC power supply 1, diode 62b, capacitor 41, lower-arm switching element 51b, and heating coil 11. If the lower-arm switching element 52b is a MOSFET, synchronous rectification operation is possible, and therefore the current in the diode 62b flows from the source to the drain of the switching element 52b.

[0041] 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).

[0042] In this way, when heating a non-magnetic material in this embodiment, the voltage applied to the switching elements 51a, 51b, 52a, and 52b is approximately half the voltage V1 of the DC power supply 1, so that 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.

[0043] Also, for the switching period Ts, the heating coil current i 11 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.

[0044] As mentioned above, low-resistivity non-magnetic materials have low equivalent resistance, so a large current is required to obtain the desired output. The skin resistance of the heated object is proportional to the square root of the frequency, so increasing the frequency is effective when heating low-resistivity objects such as copper or aluminum. Therefore, the capacitances of the first resonant capacitors 21a and 21b are set so that the frequency of the heating coil current can be, for example, approximately 90 kHz.

[0045] 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 the upper-arm switching element 51a and lower-arm switching element 51b of the first upper and lower arms 51 and the upper-arm switching element 52a and lower-arm switching element 52b of the second upper and lower arms 52, the inverter output voltage can be reduced to half the voltage V1 of DC power supply 1, thereby reducing the voltage applied to the resonant load circuit. [Example]

[0046] 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.

[0047] In Figure 5, compared to the circuit configuration of Example 1 shown in Figure 1, three switching elements 55a to 55c are connected in series to form a first upper, middle, and lower arm 55, and similarly three switching elements 56a to 56c are connected in series to form a second upper, middle, and lower arm 56.

[0048] Diodes 65a to 65c and 66a to 66c are connected in parallel in the opposite direction to the switching elements 55a to 55c and 56a to 56c, respectively, and capacitors 75a to 75c and 76a to 76c are connected in parallel to the switching elements 55a to 55c and 56a to 56c, respectively.

[0049] The connection point between the upper arm switching element 55a and the middle arm switching element 55b of the upper, middle, and lower arm 55 is connected to a terminal O. 55a The connection point between the middle arm switching element 55b and the lower arm switching element 55c is connected to a terminal O 55b The connection point between the upper arm switching element 56a and the middle arm switching element 56b of the upper, middle, and lower arm 56 is connected to a terminal O 56a The connection point between the middle arm switching element 56b and the lower arm switching element 56c is connected to a terminal O 56b In this embodiment, the terminals O of the upper, middle and lower arms 55 are 55b and terminal O of upper, middle and lower arm 56 56a A capacitor 42 is connected between the terminals O of the upper, middle and lower arms 55. 55a and terminal O of upper, middle and lower arm 56 56b A capacitor 43 is connected between them. Capacitor 42 holds a value that is about 1 / 3 of the voltage of DC power supply 1, and capacitor 43 holds a value that is about 2 / 3 of the voltage of DC power supply 1. Note that about 1 / 3 means, for example, 0.28 to 0.38.

[0050] <Control when heating magnetic material> When heating a magnetic material in this embodiment, the relay 20 in FIG. 1 is turned on, and a period in which the upper, middle, and lower arms 55 (switching elements 55a, 55b, 55c) are on and a period in which the upper, middle, and lower arms 56 (switching elements 56a, 56b, 56c) are on are set.

[0051] In this embodiment, the voltage applied to the switching elements 55a, 55b, 55c, 56a, 56b, and 56c is approximately one-third of the voltage V1 of the DC power supply 1, so that the withstand voltage of the switching elements can be further reduced and switching elements with low on-resistance can be used, which is effective in reducing loss.

[0052] <Control when heating non-magnetic materials> When heating a non-magnetic material in this embodiment, relay 20 in FIG. 1 is turned off, the upper arm switching element 55a of upper, middle, and lower arm 55 and the lower arm switching element 56c of upper, middle, and lower arm 56 are complementarily driven, the middle arm switching element 55b of upper, middle, and lower arm 55 and the middle arm switching element 56b of upper, middle, and lower arm 56 are complementarily driven, the lower arm switching element 55c of upper, middle, and lower arm 55 and the upper arm switching element 56a of upper, middle, and lower arm 56 are complementarily driven, and the turn-on timing of switching elements 55a, 55b, and 55c of upper, middle, and lower arm 55 are driven with a phase shift of 120 degrees.

[0053] In this embodiment, the voltage applied to the switching elements 55a, 55b, 55c, 56a, 56b, and 56c is approximately one-third of the voltage V1 of the DC power supply 1, so that the withstand voltage of the switching elements can be further reduced and switching elements with low on-resistance can be used, which is effective in reducing loss.

[0054] Also, for the switching period Ts, the heating coil current i 11 Since the period is Ts / 3, for example, when heating at a frequency of approximately 90 kHz, it becomes possible to drive the switching frequency at approximately 30 kHz, which is also effective in reducing the switching loss of each switching element. [Explanation of symbols]

[0055] 1 DC power supply, 2 inverters 51a, 51b, 52a, 52b, 55a, 55c, 56a, 56c, 105 switching elements, 61a, 61b, 62a, 62b, 65a, 65c, 66a, 66c, 101a to 101d, 106a, 106b diodes, 71a, 71b, 72a, 72b, 75a, 75c, 76a, 76c, 41 to 43, 103a, 103b capacitors, 11 heating coil, 20 relays, 21a, 21b first resonant capacitor; 22a, 22b second resonant capacitor; 51, 52 Upper and lower arms, 55, 56 upper, middle and lower arms, 100 Commercial AC power supply 102a, 102b inductors

Claims

1. A heating coil (11) 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 The output terminal (O Ａ ) one end of the heating coil (11) is connected to a positive electrode (P) or a negative electrode (N) or a positive and negative electrode (P, N) of the DC power source (1), and a first resonant capacitor (21a, 21b) is connected between the other end of the 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).

2. 2. The electromagnetic induction heating device according to claim 1, An electromagnetic induction heating device characterized in that one end of a relay (20) is connected to the other end of the heating coil (11), and second resonant capacitors (22a, 22b) are connected between the other end of the relay (20) and the positive electrode (P), or the negative electrode (N), or the positive and negative electrodes (P, N) of the DC power source (1).

3. 3. 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.

4. 3. The electromagnetic induction heating device according to claim 1, The inverter circuit a period during which a first upper arm switching element (51a) and a first lower arm switching element (51b) of the first upper and lower arms (51) are turned on; a period in which the second upper arm switching element (52a) and the second lower arm switching element (52b) of the second upper and lower arm (52) are turned on is provided; An electromagnetic induction heating device characterized in that the amplitude of the output voltage of the inverter circuit is used as the voltage of the DC power supply (1), and a high-frequency current is passed through the heating coil to heat the object to be heated.

5. 3. The electromagnetic induction heating device according to claim 1, The inverter circuit a first upper arm switching element (51a) of the first upper and lower arm (51) and a second lower arm switching element (52b) of the second upper and lower arm (52) are complementarily driven; a first lower arm switching element (51b) of the first upper and lower arm (51) and a second upper arm switching element (52a) of the second upper and lower arm (52) are complementarily driven; The first upper arm switching element (51a) and the first lower arm switching element (51b) of the first upper and lower arm (51) are driven with a phase difference of 180 degrees between their turn-on timings, An electromagnetic induction heating device characterized in that the amplitude of the output voltage of the inverter circuit is set to approximately 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 heating coil to heat the object to be heated.

6. 3. The electromagnetic induction heating device according to claim 2, When the object to be heated is a magnetic material, the relay (20) is turned on. The inverter circuit a period during which a first upper arm switching element (51a) and a first lower arm switching element (51b) of the first upper and lower arms (51) are turned on; a period in which the second upper arm switching element (52a) and the second lower arm switching element (52b) of the second upper and lower arm (52) are turned on is provided; An electromagnetic induction heating device characterized in that the amplitude of the output voltage of the inverter circuit is used as the voltage of the DC power supply (1), and a high-frequency current is passed through the heating coil to heat the object to be heated.

7. 3. The electromagnetic induction heating device according to claim 2, If the object to be heated is a non-magnetic material, the relay (20) is turned off. The inverter circuit a first upper arm switching element (51a) of the first upper and lower arm (51) and a second lower arm switching element (52b) of the second upper and lower arm (52) are complementarily driven; a first lower arm switching element (51b) of the first upper and lower arm (51) and a second upper arm switching element (52a) of the second upper and lower arm (52) are complementarily driven; The first upper arm switching element (51a) and the first lower arm switching element (51b) of the first upper and lower arm (51) are driven with a phase difference of 180 degrees between their turn-on timings, An electromagnetic induction heating device characterized in that the amplitude of the output voltage of the inverter circuit is set to approximately 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 heating coil to heat the object to be heated.

8. A heating coil (11) 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-middle-lower arm (55) which is a series circuit of a first upper arm switching element (55a), a first middle arm switching element (55b), and a first lower arm switching element (55c) and a second upper-middle-lower arm (56) which is a series circuit of a second upper arm switching element (56a), a second middle arm switching element (56b), and a second lower arm switching element (56c) are connected in series between a positive electrode (P) and a negative electrode (N) of the DC power supply (1); The connection point (O) of the first middle arm switching element (55b) and the first lower arm switching element (55c) that constitute the first upper, middle, and lower arm (55) ５５ｂ ) and a connection point (O) of the second upper arm switching element (56a) and the second middle arm switching element (56b) constituting the second upper middle lower arm (56). ５６ａ A first capacitor (42) is connected between the The first upper arm switching element (55a) and the first middle arm switching element (55b) constituting the first upper middle lower arm (55) are connected at a connection point (O ５５ａ ) and a connection point (O) of the second middle arm switching element (56b) and the second lower arm switching element (56c) constituting the second upper middle lower arm (56). ５６ｂ ) and a second capacitor (43) is connected between the first capacitor and the second capacitor (43), The output terminal (O Ａ ) one end of the heating coil (11) is connected to a positive electrode (P) or a negative electrode (N) or a positive and negative electrode (P, N) of the DC power source (1), and a first resonant capacitor (21a, 21b) is connected between the other end of the 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).

9. 9. The electromagnetic induction heating device according to claim 8, An electromagnetic induction heating device characterized in that one end of a relay (20) is connected to the other end of the heating coil (11), and second resonant capacitors (22a, 22b) are connected between the other end of the relay (20) and the positive electrode (P), or the negative electrode (N), or the positive and negative electrodes (P, N) of the DC power source (1).

10. 10. The electromagnetic induction heating device according to claim 8 or 9, 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.

11. 10. The electromagnetic induction heating device according to claim 8 or 9, The inverter circuit a period during which the first upper arm switching element (55a), the first middle arm switching element (55b), and the first lower arm switching element (55c) of the first upper, middle, and lower arm (55) are turned on; a period in which the second upper arm switching element (56a), the second middle arm switching element (56b), and the second lower arm switching element (56c) of the second upper, middle, and lower arm (56) are turned on; An electromagnetic induction heating device characterized in that the amplitude of the output voltage of the inverter circuit is used as the voltage of the DC power supply (1), and a high-frequency current is passed through the heating coil to heat the object to be heated.

12. 10. The electromagnetic induction heating device according to claim 8 or 9, The inverter circuit a first upper arm switching element (55a) of the first upper, middle, and lower arm (55) and a second lower arm switching element (56c) of the second upper, middle, and lower arm (56) are complementarily driven; a first middle arm switching element (55b) of the first upper, middle, and lower arm (55) and a second middle arm switching element (56b) of the second upper, middle, and lower arm (56) are complementarily driven; a first lower arm switching element (55c) of the first upper, middle, and lower arm (55) and a second upper arm switching element (56a) of the second upper, middle, and lower arm (56) are complementarily driven; the first upper arm switching element (55a), the first middle arm switching element (55b), and the first lower arm switching element (55c) of the first upper, middle, and lower arm (55) are driven with a phase difference of 120 degrees between their turn-on timings; An electromagnetic induction heating device characterized in that the amplitude of the output voltage of the inverter circuit is set to approximately 1 / 3 of the voltage of the DC power supply (1), and a high-frequency current three times the switching frequency of the inverter circuit is passed through the heating coil to heat the object to be heated.

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