JP2024072970A - Electromagnetic induction heating device - Google Patents

Abstract

To provide an electromagnetic induction heating device that can efficiently supply the desired power to a heated object.SOLUTION: An electromagnetic induction heating device includes a heating coil, a DC power supply, a step-down chopper circuit, and an inverter. The step-down chopper circuit includes: a first upper and lower arms being a series body of two switching elements; a step-down choke coil with one end connected to the output terminal of the first upper and lower arms; and a smoothing capacitor connected between the other end of the step-down choke coil and one end of the DC power supply. The inverter includes: second upper and lower arms being a series body of two switching elements; a heating coil with one end connected to the output terminal of the second upper and lower arms; a first resonant capacitor connected between the other end of the heating coil and one end of the smoothing capacitor; and a series body of a relay connected between the output terminal of the first upper and lower arms and the other end of the heating coil and a second resonant capacitor. The first upper and lower arms, when not operating as a part of the inverter, operates as a part of the step-down chopper circuit.SELECTED DRAWING: Figure 1

Description

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

In recent years, inverter-type electromagnetic induction heating devices that heat objects such as metal pots without using fire have come into widespread use. An electromagnetic induction heating device passes a high-frequency current through a heating coil, generating eddy currents in a metal object to be heated (such as a pot) placed close to the heating coil, causing the object to generate heat due to the electrical resistance of the object itself. In general, objects to be heated that are magnetic and have a high specific resistance, such as iron, are easy to heat, while non-magnetic objects with low resistance such as copper and aluminum are difficult to heat.

As a conventional technique for solving such problems, there is an induction heating device disclosed in Patent Document 1. As shown in Figure 6 of the document, this device uses an inverter that converts the DC voltage output from a step-down circuit into AC voltage, and switches the inverter between a full-bridge circuit configuration and a half-bridge circuit configuration depending on the state and type of the object to be heated. When heating an object to be heated that is made of a non-magnetic material such as aluminum, one leg of the full-bridge circuit is disconnected from the circuit and a half-bridge circuit that uses only the other leg is driven to supply current to the heating coil.

Patent No. 4910004

In Patent Document 1, when a high-resistance magnetic pot is heated, a switch (relay) that switches between the high-frequency inverter circuit type and the capacity of the resonant capacitor is turned on, the inverter is switched to a full-bridge circuit type, and the first resonant capacitor (Figure 1 of the same document, reference number 12) and the second resonant capacitor (same document, reference number 13) are used to inductively heat the magnetic pot.

On the other hand, when heating a low-resistance non-magnetic pot, the switch (relay) is turned off, the inverter is switched to a half-bridge circuit type, the large-capacity second resonant capacitor is completely disconnected, and the small-capacity first resonant capacitor is used to inductively heat the non-magnetic pot. In this way, when heating a low-resistance non-magnetic pot, the inverter uses a half-bridge circuit type that uses only one of the upper and lower arms, so the other upper and lower arms are idle and not used effectively.

The object of the present invention is to address the above-mentioned problems, and in particular to provide an inverter-type electromagnetic induction heating device that effectively utilizes all upper and lower arms of the inverter and can efficiently supply the desired power to heated objects made of different materials.

In order to achieve the above object, the electromagnetic induction heating device of the present invention is an electromagnetic induction heating device that includes a heating coil for induction heating an object to be heated, a DC power source that outputs a DC voltage, a step-down chopper circuit that steps down the DC voltage output by the DC power source, and an inverter that converts the output voltage of the step-down chopper circuit into an AC voltage and supplies it to the heating coil, and the step-down chopper circuit includes a first upper and lower arms that are a series body of two switching elements, a step-down choke coil having one end connected to the output terminal of the first upper and lower arms, and an inverter between the other end of the step-down choke coil and one end of the DC power source. and a smoothing capacitor connected to the second upper and lower arms, the inverter having a second upper and lower arm which is a series body of two switching elements, the heating coil having one end connected to the output terminal of the second upper and lower arms, a first resonant capacitor connected between the other end of the heating coil and one end of the smoothing capacitor, and a series body of a relay and a second resonant capacitor connected between the output terminal of the first upper and lower arms and the other end of the heating coil, the first upper and lower arms being an electromagnetic induction heating device which operates as part of the step-down chopper circuit when not operating as part of the inverter.

The electromagnetic induction heating device of the present invention can set the optimal inverter voltage and drive frequency even under conditions of large load fluctuations, and can efficiently supply the desired power to the load, despite the small number of parts.

FIG. 2 is a circuit diagram of the electromagnetic induction heating device according to the first embodiment. FIG. 2 is an explanatory diagram of a half-bridge type circuit of the electromagnetic induction heating device according to the first embodiment. 3 is an operational waveform of the electromagnetic induction heating device of FIG. 2 . 3 is an operational waveform of the electromagnetic induction heating device of FIG. 2 . FIG. 3 is an operational characteristic diagram of the electromagnetic induction heating device of FIG. 2 . FIG. 3 is an operational characteristic diagram of the electromagnetic induction heating device of FIG. 2 . FIG. 2 is an explanatory diagram of a full-bridge type circuit of the electromagnetic induction heating device according to the first embodiment. 7 is an operational waveform of the electromagnetic induction heating device of FIG. 6 . FIG. 7 is an operational characteristic diagram of the electromagnetic induction heating device of FIG. 6 . 7 is an operational waveform of the electromagnetic induction heating device of FIG. 6 . FIG. 7 is an operational characteristic diagram of the electromagnetic induction heating device of FIG. 6 . FIG. 7 is an operational characteristic diagram of the electromagnetic induction heating device of FIG. 6 . 7 is an operational waveform of the electromagnetic induction heating device of FIG. 6 . FIG. 7 is an operational characteristic diagram of the electromagnetic induction heating device of FIG. 6 . FIG. 7 is an operational characteristic diagram of the electromagnetic induction heating device of FIG. 6 . FIG. 11 is a circuit diagram of an electromagnetic induction heating device according to a second embodiment. FIG. 11 is a circuit diagram of an electromagnetic induction heating device according to a third embodiment. FIG. 11 is a circuit diagram of an electromagnetic induction heating device according to a fourth embodiment. FIG. 13 is a circuit diagram of an electromagnetic induction heating device according to a fifth embodiment.

Below, an embodiment of the electromagnetic induction heating device of the present invention will be described with reference to the drawings. Note that in each drawing, the same reference numerals indicate the same components or components with similar functions, and duplicate explanations will be omitted as appropriate.

Figure 1 is a circuit diagram of an electromagnetic induction heating device according to a first embodiment of the present invention. The electromagnetic induction heating device of this embodiment has a heat-resistant glass top plate placed on top of a metal housing, and a high-frequency current is supplied to a heating coil placed below the top plate to inductively heat a metal object to be heated (such as a pot) placed at a specified position on the top surface of the top plate; however, a description of this well-known configuration will be omitted below.

In FIG. 1, a first upper and lower arm 3 in which power semiconductor switching elements (hereinafter simply referred to as "switching elements") 5a and 5b are connected in series is connected between the positive and negative electrodes of a DC power supply 35. The switching elements 5a and 5b of the first upper and lower arms 3 use IGBTs (insulated gate bipolar transistors) suitable for large currents. Diodes 6a and 6b are connected in parallel in the opposite direction to each of the switching elements 5a and 5b.

One end of the step-down choke coil 41 is connected to the connection point (output terminal) of the switching elements 5a, 5b of the first upper and lower arms 3, and a smoothing capacitor 44 is connected between the other end of the step-down choke coil 41 and the negative electrode of the DC power supply 35.

The second upper and lower arms 4, in which switching elements 5c and 5d are connected in series, are connected in parallel to the smoothing capacitor 44. The switching elements 5c and 5d of the second upper and lower arms 4 use IGBTs (insulated gate bipolar transistors) suitable for large currents. Diodes 6c and 6d are connected in parallel in the opposite direction to the switching elements 5c and 5d, respectively.

One end of the heating coil 11 is connected to the connection point (output terminal) of the switching elements 5c and 5d of the second upper and lower arms 4, and the first resonant capacitors 12a and 12b are connected between the other end of the heating coil 11 and the positive and negative electrodes of the smoothing capacitor 44, respectively.

In addition, a series circuit of a second resonant capacitor 13 and a relay 20 is connected between the output terminal of the first upper and lower arms 3 and the other end of the heating coil 11.

Here, the metal pan (not shown) placed on the top plate and the heating coil 11 are magnetically coupled, so 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 vary depending on the material of the metal pan. For non-magnetic materials such as low-resistance copper or aluminum, both the equivalent resistance and equivalent inductance are small, and for magnetic materials such as high-resistance iron, both are large. Below, we explain the difference between the circuit method used when heating non-magnetic materials (step-down chopper circuit + half-bridge inverter) and the circuit method used when heating magnetic materials (step-down full-bridge inverter).

<Heating method for non-magnetic materials>
When the object to be heated is a non-magnetic material such as a copper pan or an aluminum pan, the metal pan is induction heated using a step-down chopper circuit and a half-bridge inverter. Specifically, as shown in Fig. 2, heating is performed using a step-down chopper circuit 40 (composed of the upper arm switching element 5a and the lower arm diode 6b of the first upper and lower arms 3, the step-down choke coil 41, and the smoothing capacitor 44) that is formed when the relay 20 is turned off, and a half-bridge inverter 100 (composed of the second upper and lower arms 4, the heating coil 11, and the first resonant capacitors 12a and 12b).

As mentioned above, low-resistance non-magnetic materials have a small equivalent resistance, so a large current must be passed through them to obtain the desired output. The skin resistance of the heated object is proportional to the square root of the frequency, and it is effective to increase the frequency when heating a low-resistance heated object such as copper or aluminum. Therefore, the combined capacitance of the first resonant capacitors 12a and 12b is set so that the second upper and lower arms 4 can be driven at a frequency of, for example, about 90 kHz.

Figure 3 shows the operating waveforms of the circuit in Figure 2. In Figure 3, the gate signals of the switching elements 5a, 5c, and 5d are vg(5a), vg(5c), and vg(5d), respectively, the current flowing through the step-down choke coil 41 is i(41), the voltage of the smoothing capacitor 44 is v(44), the currents flowing through the switching elements 5a, 5c, and 5d are i(5a), i(5c), and i(5d), respectively, the currents flowing through the diodes 6b, 6c, and 6d are i(6b), i(6c), and i(6d), respectively, the output voltage of the inverter 100 is v(100), the current flowing through the heating coil 11 is i(11), and the direction from left to right in Figure 2 is defined as positive.

In FIG. 3, when the switching element 5a of the step-down chopper circuit 40 is in the ON state, a current i (41) flows from the DC power supply 35 through the switching element 5a, the step-down choke coil 41, and the smoothing capacitor 44. When the switching element 5a is in the OFF state, the stored energy in the step-down choke coil 41 causes the current i (41) to circulate through the smoothing capacitor 44 and the diode 6b, performing a step-down operation.

The inverter 100 applies a rectangular wave whose amplitude is the output voltage of the step-down chopper circuit 40, i.e., the voltage v (44) of the smoothing capacitor 44, to the heating coil 11 and the resonant load circuit including the first resonant capacitors 12a and 12b by turning on and off the switching elements 5c and 5d in a complementary manner. By driving the inverter 100 at a switching frequency higher than the resonant frequency, a current i (11) that is a lag phase with respect to the output voltage v (100) of the inverter 100 flows through the heating coil 11. The switching elements 5c and 5d of the upper and lower arms 4 can achieve zero voltage switching by turning on the gates during the conduction period of the diodes 6c and 6d, and no switching loss occurs when they are turned on. Figure 3A shows the case where the ON time Duty of the switching element 5a is 0.5, and Figure 3B shows the case where the ON time Duty of the switching element 5a is 0.25. Comparing the two figures, it can be seen that when the on-time duty of the switching element 5a is reduced, the voltage v (44) of the smoothing capacitor 44 decreases and the current i (11) of the heating coil 11 decreases.

The power control method of the circuit in FIG. 2 will be described with reference to FIG. 4 and FIG. 5. As described above, the step-down chopper circuit 40 can control the voltage of the smoothing capacitor 44 by changing the on-time duty of the switching element 5a. FIG. 4 shows the relationship between the on-time duty and the output voltage of the step-down chopper circuit 40. The output voltage is the voltage of the DC power supply 35 multiplied by the on-time duty, so it changes in proportion to the on-time duty. The output voltage of the step-down chopper circuit 40 becomes the input voltage of the inverter 100. FIG. 5 shows the relationship between the input voltage of the inverter 100 and the power. The inverter 100 is operated at a substantially constant frequency near the resonant frequency in order to reduce the interruption current and suppress switching loss. As a result, the impedance of the resonant load circuit including the heating coil 11 and the first resonant capacitors 12a and 12b is also substantially constant. Therefore, it is possible to arbitrarily control the power by adjusting the input voltage of the inverter 100. That is, the power can be controlled by pulse amplitude control.

<Magnetic material heating method>
When the object to be heated is a magnetic body such as an iron pan, a step-down full-bridge inverter is used to inductively heat the metal pan. Specifically, as shown in Fig. 6, heating is performed using a step-down chopper circuit 40 (composed of the upper arm switching element 5a and the lower arm diode 6b of the first upper and lower arms 3, the step-down choke coil 41, and the smoothing capacitor 44) formed when the relay 20 is turned on, and a step-down full-bridge inverter 200 (composed of the second upper and lower arms 4 to which the output voltage of the step-down chopper circuit 40 is applied, the first upper and lower arms 3 to which the voltage of the DC power supply 35 is applied, the heating coil 11, and the second resonant capacitor 13). Therefore, the switching elements and diodes of the first upper and lower arms 3 operate as the switching elements and diodes of the step-down chopper circuit 40 and the switching elements and diodes of the inverter 200.

As mentioned above, a high-resistance magnetic material has a large equivalent resistance, so that it is difficult for a current to flow through the heating coil 11. Therefore, by using the first upper and lower arms 3 as one of the upper and lower arms of the full bridge system, the output voltage of the inverter 200 is applied to the resonant load circuit including the heating coil 11 and the first and second resonant capacitors 12a, 12b, and 13, and a rectangular wave having an amplitude equal to the voltage of the DC power supply 35 and the output voltage of the step-down chopper circuit 40 is applied. In this way, the output voltage of the inverter 200 of the full bridge circuit system can be made higher than the output voltage of the inverter 100 of the half bridge circuit system, so that the desired output required for heating the magnetic material can be obtained.

In the case of copper and aluminum mentioned above, the resistance is low, so the inverter frequency is increased to about 90 kHz to increase the skin resistance, but in the case of iron, the resistance is originally high, so the first upper and lower arms 3 and the second upper and lower arms 4 are driven at a frequency of about 20 kHz. For this reason, the capacitance of the second resonant capacitor 13 is set to match the drive frequency of about 20 kHz. Since the drive frequencies are significantly different, the capacitance of the second resonant capacitor 13 is sufficiently larger than the first resonant capacitors 12a and 12b. Therefore, the resonant frequency of the full-bridge type inverter is mainly set by the second resonant capacitor 13.

Figure 7 shows the operating waveforms of the circuit in Figure 6. In Figure 7, the gate signals of switching elements 5a to 5d are vg(5a) to vg(5d), respectively, the current flowing through step-down choke coil 41 is i(41), the voltage of DC power supply 35 is v(35), the voltage of smoothing capacitor 44 is v(44), the currents flowing through switching elements 5a to 5d are i(5a) to i(5d), respectively, the currents flowing through diodes 6a to 6d are i(6a) to i(6d), respectively, the output voltage of inverter 200 is v(200), the current flowing through heating coil 11 is i(11), and the direction from left to right in Figure 6 is defined as positive.

In FIG. 7, during the period when the switching elements 5a and 5d are simultaneously on, the switching element 5a serves both as an element of the step-down chopper circuit 40 and the inverter 200, and a composite current of the current i (41) of the step-down choke coil 41 and the current i (11) of the heating coil 11 flows. Therefore, the current i (5a) of the switching element 5a is larger than the current i (5d) of the switching element 5d, and the conduction loss increases, but when turned on, the current i (11) of the heating coil 11 flows back via the diode 6b, so zero-voltage switching operation is possible and no turn-on loss occurs. That is, in the embodiment of the present invention, the upper and lower arms 3 are also used as elements of the step-down chopper circuit 40, but by combining it with the operation of the inverter, it is possible to realize zero-voltage switching operation and suppress the increase in switching loss.

Next, we will explain several possible power control methods for heating magnetic materials.

<<First control method>>
The first control method is to change the switching frequency of the inverter 200. Figure 8 shows the relationship between the switching frequency of the inverter 200 and the power. When the inverter 200 is driven at a switching frequency higher than the resonant frequency of the resonant load circuit, the resonant load circuit becomes inductive. Therefore, by increasing the switching frequency, the reactance increases, so the current in the heating coil decreases, and the power decreases as shown in Figure 8. In other words, the power can be easily controlled by pulse frequency modulation control.

<<Second control method>>
The second control method is a method of changing the ON time Duty of the upper arm switching element 5a of the upper and lower arms 3. The lower arm switching element 5b of the upper and lower arms 3 is provided with a dead time and operates complementarily with the switching element 5a. FIG. 9 shows the operating waveforms under the condition that the ON time Duty of the switching element 5a is 0.25. In FIG. 9, when the ON time Duty of the switching element 5a is reduced, the voltage v(44) of the smoothing capacitor 44 is lowered compared to FIG. 7. The output voltage v(44) of the step-down chopper circuit 40 is applied to the second upper and lower arms 4 of the inverter 200, and the voltage v(35) of the DC power supply 35 is applied to the first upper and lower arms 3 of the inverter 200, and the inverter 200 operates as a full-bridge inverter. As shown in FIG. 9, the output voltage vout(200) of the inverter 200 is turned off earlier than the switching element 5d, so that positive and negative voltages with different voltage amplitudes are applied to the resonant load circuit while there is a period in which the output voltage is 0V.

Figure 10 shows the relationship between the upper arm on-time duty and the output voltage of the step-down chopper circuit 40. As mentioned above, the output voltage of the step-down chopper circuit 40 is the voltage of the DC power supply 35 multiplied by the on-time duty, so it changes in proportion to the on-time duty. Figure 11 shows the relationship between the upper arm on-time duty and power. Since the voltage applied to the second upper and lower arms 4 changes, it is possible to control power by combining pulse amplitude control of the inverter input voltage and pulse width modulation control of the first upper and lower arms 3.

<<Third control method>>
The third control method is a method of changing the phase difference between the first upper and lower arms 3 and the second upper and lower arms 4 of the inverter 200. Fig. 12 shows operation waveforms under a condition in which the phase of the switching elements (5c, 5d) of the second upper and lower arms 4 is advanced relative to the switching elements (5a, 5b) of the first upper and lower arms 3. Note that the on-time of each arm is the same and only the phase difference is changed.

12, the on-time of the switching element 5a is the same as that of FIG. 7, so the voltage v(44) of the smoothing capacitor 44 is almost the same as that of FIG. 7. Since there is a phase difference between the upper and lower arms 3 and 4, during the period when the upper arms are both on, the output voltage vout(200) of the inverter 200 is the difference between the voltage v(35) of the DC power supply 35 and the voltage v(44) of the smoothing capacitor 44 of the step-down chopper circuit 40. Conversely, during the period when the lower arms are both on, the output voltage vout(200) of the inverter 200 is 0V. The switching elements 5a and 5b are superimposed with the current of the step-down choke coil 41, and can be turned off while ensuring the interruption current required for zero voltage switching, so no switching loss occurs when turning on.

Figure 13 shows the relationship between the phase difference between the first upper and lower arms 3 and the second upper and lower arms 4 and the power. As shown here, as the phase difference increases, the output voltage of the inverter 200 decreases and the power decreases. In this way, it is possible to control the power by phase shift control as well.

<<Fourth control method>>
The fourth control method is to change the voltage of the DC power supply 35. Fig. 14 shows the relationship between the voltage and power of the DC power supply 35. By increasing the voltage of the DC power supply 35, the output voltage of the step-down chopper circuit 40 also increases at the same time, so the output voltage of the inverter 200 increases and the power increases. That is, the power can be easily controlled by pulse amplitude control.

In this way, in this embodiment, by switching relay 20 on and off, it is possible to switch between a circuit configuration consisting of a step-down chopper circuit and a half-bridge inverter for heating non-magnetic materials, and a circuit configuration consisting of a step-down full-bridge inverter for heating magnetic materials. In either case, all upper and lower arms are effectively utilized to adjust the inverter output voltage, and heating can be performed at the optimal frequency according to the material of the object to be heated. Therefore, with the electromagnetic induction heating device of this embodiment, despite the small number of parts, the optimal inverter voltage and drive frequency can be set even under conditions of large load fluctuations, and the desired power can be efficiently supplied to the load.

Figure 15 is a circuit diagram of an electromagnetic induction heating device of Example 2. The same parts as in Figure 1 are designated by the same reference numerals, and duplicate explanations will be omitted.

In FIG. 15, one end of the step-down choke coil 41 is connected to the output terminal of the first upper and lower arms 3, and a smoothing capacitor 44 is connected between the other end of the step-down choke coil 41 and the positive electrode of the DC power supply 35. The difference from the first embodiment in FIG. 1 is that the smoothing capacitor 44 is connected to the high side (positive electrode side). In this case, the switching element of the step-down chopper circuit 40 becomes the lower arm switching element 5b of the upper and lower arms 3, and the free wheel diode becomes the upper arm diode 6a.

Figure 16 is a circuit diagram of an electromagnetic induction heating device according to Example 3. The same parts as in Figure 1 are designated by the same reference numerals, and duplicate explanations will be omitted.

In FIG. 16, the switching elements 5c and 5d of the second upper and lower arms 4 use power semiconductor switching elements with a faster switching speed than the switching elements 5a and 5b of the first upper and lower arms 3. As mentioned above, when heating a low-resistance heated object such as copper or aluminum, it is effective to increase the frequency, and the second upper and lower arms 4 are driven at a higher frequency than the first upper and lower arms 3. Therefore, by using SJ (super junction)-MOSFETs (MOS field effect transistors) for the switching elements 5c and 5d of the second upper and lower arms 4, it is possible to switch faster than existing MOSFETs, and it is effective in reducing switching losses due to high frequencies. In addition, since a low-resistance non-magnetic material has a small equivalent resistance, a large current needs to be passed to obtain the desired output. In the present invention, since it is possible to make the voltage applied to the second upper and lower arms 4 lower than the voltage applied to the first upper and lower arms 3, the switching elements 5c and 5d of the second upper and lower arms 4 can use power semiconductor switching elements with a lower withstand voltage than the switching elements 5a and 5b of the first upper and lower arms 3. The lower the breakdown voltage of a power semiconductor device, the smaller its on-resistance becomes, which is also effective in reducing conduction losses.

Figure 17 is a circuit diagram of an electromagnetic induction heating device according to Example 4. The same parts as those in Figure 1 are designated by the same reference numerals, and duplicate explanations will be omitted.

In FIG. 17, the AC voltage supplied from the commercial AC power supply 1 is rectified by diodes 2a to 2d, and the DC power smoothed by the boost chopper circuit 30 consisting of a boost choke coil 31, a switching element 32, a diode 33, and a smoothing capacitor 34 is applied to the step-down chopper circuit 40. In the first embodiment of FIG. 1, the voltage of the DC power supply 35 is applied to the step-down chopper circuit 40, but in this embodiment 4, the DC power smoothed by the boost chopper circuit 30 is applied to the step-down chopper circuit 40. The boost chopper circuit 30 has the function of controlling the input power factor of the commercial AC power supply 1 and controlling the voltage of the smoothing capacitor 34.

The inverter 300 is connected to the rear of the boost chopper circuit 30 via a normal filter consisting of an inductor 45 and a capacitor 46. The inverter 300 is a half-bridge inverter, and mainly heats a pot of magnetic material. The inverter 300 has upper and lower arms, in which switching elements 5e and 5f are connected in series, connected between the positive and negative electrodes of the capacitor 46. One end of the heating coil 11A is connected to the connection point (output terminal) of the switching elements 5e and 5f, and resonant capacitors 12c and 12d are connected between the other end of the heating coil 11A and the positive and negative electrodes of the capacitor 46, respectively. Diodes 6e and 6f are connected in parallel in the opposite directions to the switching elements 5e and 5f, respectively.

Furthermore, the inverter 400 is connected to the rear stage of the boost chopper circuit 30 via a normal filter consisting of an inductor 47 and a capacitor 48. Like the inverter 300, the inverter 400 is also a half-bridge type inverter, and mainly heats a pot made of magnetic material. The inverter 400 has upper and lower arms, in which switching elements 5g and 5h are connected in series, connected between the positive and negative electrodes of the capacitor 48, and one end of the heating coil 11B is connected to the connection point (output terminal) of the switching elements 5g and 5h, and resonant capacitors 12e and 12f are connected between the other end of the heating coil 11B and the positive and negative electrodes of the capacitor 48, respectively. Diodes 6g and 6h are connected in parallel in the opposite direction to the switching elements 5g and 5h, respectively.

Here, electromagnetic induction cooking appliances sold on the market have two to three heating parts, and for example, one of the heating parts can heat all metal pots, including non-magnetic pots such as aluminum and copper, and the remaining heating parts can heat only magnetic pots, making it a low-priced cooker. In such a low-priced cooker, when mainly heating magnetic pots, the AC voltage supplied from a commercial AC power source is rectified by a diode bridge, and the non-smooth power obtained through a normal filter consisting of an inductor and a capacitor is applied to the inverter. Therefore, the current flowing through the heating coil pulsates at twice the frequency of the commercial AC power source, and depending on the material of the pot, there is a problem that excitation noise is generated. However, in this embodiment, the DC power smoothed by the boost chopper circuit 30 is applied to the inverters 300, 400 through a normal filter, so the current pulsation of the heating coil is suppressed and the generation of excitation noise can be prevented.

Figure 18 is a circuit diagram of an electromagnetic induction heating device according to Example 5. The same parts as those in Figure 16 are designated by the same reference numerals, and duplicate explanations will be omitted.

In FIG. 18, inverter 300 is different from Example 4 in that it is connected to the rear stage of step-down chopper circuit 40. When inverter 100 or inverter 200 is stopped, inverter 300 is operated at a substantially constant frequency near the resonant frequency to reduce the cutoff current, and the output voltage of step-down chopper circuit 40 can be adjusted to control the power. When inverter 100 or inverter 200 is operating, step-down chopper circuit 40 is controlled by prioritizing the operation of inverter 100 or inverter 200, so the input voltage of inverter 300 fluctuates. However, this is not a problem because inverter 300 can control the power by pulse frequency modulation control.

1. Commercial AC power supply,
2a to 2d, 6a to 6h, 33 Diode,
3 first upper and lower arms,
4 second upper and lower arms,
5a to 5h, 32 switching elements,
11 heating coil,
12, 13 Resonant capacitor,
20 Relay,
30 boost chopper circuit,
31 boost choke coil,
34, 44 smoothing capacitor,
35 DC power source,
40 Step-down chopper circuit 41 Step-down choke coil,
45, 47 inductor,
46, 48 Capacitor,
100, 200, 300, 400 Inverter

Claims (12)

A heating coil for induction heating an object to be heated;
A DC power supply that outputs a DC voltage;
a step-down chopper circuit that steps down a DC voltage output by the DC power supply;
an inverter that converts the output voltage of the step-down chopper circuit into an AC voltage and supplies the AC voltage to the heating coil;
An electromagnetic induction heating device comprising:
The step-down chopper circuit includes:
a first upper and lower arms each being a series body of two switching elements;
a step-down choke coil having one end connected to the output terminal of the first upper and lower arms;
a smoothing capacitor connected between the other end of the step-down choke coil and one end of the DC power supply,
The inverter is
a second upper and lower arms each being a series circuit of two switching elements;
The heating coil, one end of which is connected to the output terminal of the second upper and lower arms;
a first resonant capacitor connected between the other end of the heating coil and one end of the smoothing capacitor;
a series circuit including a relay and a second resonant capacitor connected between the output terminals of the first upper and lower arms and the other end of the heating coil,
The electromagnetic induction heating device, wherein the first upper and lower arms operate as part of the step-down chopper circuit when they do not operate as part of the inverter. A heating coil for induction heating an object to be heated;
A DC power supply that outputs a DC voltage;
a step-down chopper circuit that steps down a DC voltage output by the DC power supply;
an inverter that converts the output voltage of the step-down chopper circuit into an AC voltage and supplies the AC voltage to the heating coil;
An electromagnetic induction heating device comprising:
The step-down chopper circuit includes:
a first upper and lower arm which is a series body of two switching elements connected in parallel to the DC power supply;
a step-down choke coil having one end connected to the output terminal of the first upper and lower arms;
a smoothing capacitor connected between the other end of the step-down choke coil and one end of the DC power supply,
The inverter is
a second upper and lower arms each including two switching elements connected in series to the smoothing capacitor;
The heating coil, one end of which is connected to the output terminal of the second upper and lower arms;
a first resonant capacitor connected between the other end of the heating coil and one end of the smoothing capacitor;
a series circuit including a relay and a second resonant capacitor connected between the output terminals of the first upper and lower arms and the other end of the heating coil,
A diode is connected in inverse parallel to each switching element.
The first upper and lower arms include
When the relay is off, it operates as a part of the step-down chopper circuit,
When the relay is turned on, the relay operates as a part of the step-down chopper circuit and also operates as a part of the inverter,
The electromagnetic induction heating device, wherein the second upper and lower arms operate as part of the inverter regardless of whether the relay is on or off. 3. The electromagnetic induction heating device according to claim 2,
An electromagnetic induction heating device, characterized in that the second upper and lower arms use faster switching elements than the first upper and lower arms. 3. The electromagnetic induction heating device according to claim 2,
An electromagnetic induction heating device characterized in that, when the object to be heated is a non-magnetic material, the relay is turned off, thereby causing the inverter to be of a half-bridge type. 5. The electromagnetic induction heating device according to claim 4,
The electromagnetic induction heating device, wherein the step-down chopper circuit adjusts the power of the inverter by controlling the amplitude of the voltage applied to the second upper and lower arms. 3. The electromagnetic induction heating device according to claim 2,
An electromagnetic induction heating device characterized in that, when the object to be heated is a magnetic body, the relay is turned on to cause the inverter to be a full-bridge type. 7. The electromagnetic induction heating device according to claim 6,
The electromagnetic induction heating device is characterized in that the inverter controls a switching frequency to adjust power. 7. The electromagnetic induction heating device according to claim 6,
the step-down chopper circuit controls a voltage amplitude applied to the second upper and lower arms,
The electromagnetic induction heating device is characterized in that the inverter adjusts power by controlling a pulse width of a voltage applied to the heating coil. 7. The electromagnetic induction heating device according to claim 6,
The electromagnetic induction heating device is characterized in that the inverter adjusts power by controlling a phase difference between a first upper and lower arm and a second upper and lower arm. 7. The electromagnetic induction heating device according to claim 6,
The electromagnetic induction heating device, characterized in that the inverter adjusts power by controlling the amplitude of a voltage applied to the first upper and lower arms. The electromagnetic induction heating device according to any one of claims 1 to 10,
The DC voltage output from the DC power supply is a voltage obtained by rectifying an AC voltage supplied from a commercial AC power supply and smoothing it by a boost chopper circuit,
4. An electromagnetic induction heating device, comprising: a boost chopper circuit connected to a downstream side of the boost chopper circuit; and an inverter different from the inverter. The electromagnetic induction heating device according to claim 11,
An electromagnetic induction heating device, characterized in that an inverter different from the inverter is connected to a stage subsequent to the step-down chopper circuit.

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