JP4929305B2 - Electromagnetic induction heating device - Google Patents

Description

  The present invention relates to an electromagnetic induction heating apparatus having a plurality of heating units.

  In recent years, an inverter type electromagnetic induction heating apparatus that heats an object to be heated such as a pot without using a fire has been widely used. The electromagnetic induction heating device applies a high-frequency current to the heating coil, generates an eddy current in a heated object made of a material such as iron or stainless steel, which is disposed in the vicinity of the coil, and the electric resistance of the heated object itself. Causes fever. It is recognized as a new heat source because it can control the temperature of the object to be heated and is highly safe.

  Conventionally, electric cookers built into system kitchens and the like have used resistors such as sheathed heaters, plate heaters, and halogen heaters as heat sources, but in recent years some of them have been replaced with induction heating cookers. It is being replaced by one that has been used as an induction heating cooker. As a method of controlling the temperature of the object to be heated by changing the input power of the electromagnetic induction heating device, a method of changing the drive frequency of the inverter is common. However, when a plurality of heating coils are provided to heat different objects to be heated, there is a problem that interference sound is generated from the objects to be heated due to the difference frequency between the inverters.

  As a conventional example for solving such a problem, there is an induction heating inverter as disclosed in Patent Document 1. In this inverter, a part of the resonant capacitor is bypassed by a switching element at a constant drive frequency, and the conduction period is changed to control the input power. As a result, even if a plurality of inverters are operated, the input power can be changed at the same drive frequency, so that the generation of interference sound can be prevented.

Japanese Patent Laid-Open No. 2002-8840

  As described above, in Patent Document 1, it is possible to prevent the generation of interference sound, but there is a problem that a large loss occurs due to a large resonance current flowing through the switching element for bypass.

  The subject of this invention is providing the electromagnetic induction heating apparatus which can prevent generation | occurrence | production of the interference sound at the time of driving a some inverter simultaneously, and suppressed the loss generation | occurrence | production of the switching element for bypass.

The above-described problem is an electromagnetic induction heating apparatus having a DC power source, an inverter circuit that converts a DC voltage supplied from the DC power source into a high-frequency AC voltage, and a control circuit, wherein the inverter circuit includes a switching circuit, A resonance circuit; and a resonance point variable circuit, wherein the switching circuit is formed by series connection of an upper arm power semiconductor switching element and a lower arm power semiconductor switching element connected to both terminals of the DC power supply, The resonance circuit formed by connecting a heating coil, a first resonance capacitor, and a second resonance capacitor in series has one end connected to a connection point between the upper arm and the lower arm of the switching circuit, and the other end The resonance point variable circuit connected to one of the terminals of the DC power source and connected in parallel to the second resonance capacitor includes a third A series connection of the resonant capacitor and the first switching element, is formed by a first diode connected in anti-parallel to said first switching element, by the control circuit, the conduction period of the first switching element By controlling the resonance frequency of the resonance circuit , the second resonance capacitor capacitance is greater than or equal to the first resonance capacitor capacitance, and the third resonance capacitor capacitance is less than or equal to the second resonance capacitor capacitance. This is solved by an electromagnetic induction heating device.

Also, an electromagnetic induction heating device for induction heating of an object to be heated, the power supply circuit supplying a DC voltage from the positive electrode and the negative electrode, connected between the positive electrode and the negative electrode of the power supply circuit, A switching circuit that converts to an alternating voltage and outputs it, and is connected between the output terminal of the switching circuit and the terminal of the power supply circuit, and includes a series connection of a heating coil, a first resonance capacitor, and a second resonance capacitor. And a resonance point variable circuit that is connected in parallel to the second resonance capacitor and varies a resonance point of the resonance circuit, the resonance point variable circuit switching with the third resonance capacitor A series connection of elements and a diode connected in anti-parallel to the switching element, the capacitance of the second resonance capacitor being greater than or equal to the capacitance of the first resonance capacitor, and the second Is solved the capacitance of the resonance capacitor by the electromagnetic induction heating device for more than the capacity of said third resonant capacitor.

  According to the present invention, the resonance capacitor is provided with the resonance point variable circuit, and the resonance frequency is varied, whereby the load characteristic of the resonance circuit can be maintained inductive, the input power can be controlled by the duty control, and the switching element Generation of loss can be suppressed. Even when a plurality of inverters are driven at the same time, the drive frequencies of all the inverters can be made the same, so that it is possible to provide an electromagnetic induction heating device that does not generate interference noise.

It is a block diagram of the electromagnetic induction heating apparatus of Example 1. 5 is a modification of the circuit of the electromagnetic induction heating device according to the first embodiment. 5 is a modification of the circuit of the electromagnetic induction heating device according to the first embodiment. 5 is a modification of the circuit of the electromagnetic induction heating device according to the first embodiment. It is a circuit block diagram of the electromagnetic induction heating apparatus of Example 2. FIG. 6 is an operation explanatory diagram of Embodiment 2. It is explanatory drawing of the control method of Example 2. FIG. It is explanatory drawing of the control method of Example 2. FIG. It is explanatory drawing of the control method of Example 2. FIG. It is a circuit block diagram of the electromagnetic induction heating apparatus of Example 3. It is a circuit block diagram of the electromagnetic induction heating apparatus of Example 4. 7 is a part of the circuit of the electromagnetic induction heating device of Example 5. 6 is a part of a circuit of an electromagnetic induction heating device of Example 6. It is a figure which shows the resistance value of each to-be-heated object, and the inductance ratio with respect to iron. It is a modification of operation | movement explanatory drawing of Example 2. FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  The electromagnetic induction heating apparatus according to the first embodiment includes an inverter circuit that converts a DC voltage into a high-frequency AC voltage. The inverter circuit includes a switching circuit and a resonance circuit. The resonance circuit is connected in series to the heating coil and the heating coil. The resonance circuit is connected between either one of both terminals (p / o) of the DC power supply and the output terminal (t) of the switching circuit, and one of the resonance capacitors It has a resonance point variable circuit connected in parallel. Below, the electromagnetic induction heating apparatus of Example 1 is demonstrated in detail using figures.

  FIG. 1 is a block diagram of the electromagnetic induction heating apparatus according to the first embodiment. As shown in FIG. 1, the electromagnetic induction heating apparatus according to the present embodiment includes a first inverter 100, a second inverter 200, and a third inverter 300. Since each inverter can heat an object to be heated, the electromagnetic induction heating apparatus of this embodiment can simultaneously heat a plurality of objects to be heated. In this embodiment, since the configuration of each inverter is the same, the first inverter 100 will be described as a representative.

  In FIG. 1, the first inverter 100 includes a switching circuit 20, a resonance circuit 60, and a resonance point variable circuit 30. The switching circuit 20 is connected between the positive electrode p point and the negative electrode o point of the power supply circuit 10, converts the DC voltage supplied from the power supply circuit 10 into a high-frequency AC voltage and applies it to the resonance circuit 60. To do. The resonance circuit 60 includes a heating coil 5 and resonance capacitors 6 and 7 connected in series, and high frequency power is supplied to the heating coil 5 from the switching circuit 20. The resonance point variable circuit 30 is connected in parallel to the resonance capacitor 7, and controls the resonance point of the resonance circuit 60 by bypassing the current flowing through the resonance capacitor 7.

  The switching circuit 20 is driven by a drive circuit 61, and the resonance point variable circuit 30 is driven by a drive circuit 62. The drive circuits 61 and 62 are controlled by the control circuit 70. The input power setting unit 75 is an interface for the user to set input power (thermal power), and sends a signal to the control circuit 70 according to the setting. The control circuit 70 controls the switching circuit 20 and the resonance point variable circuit 30 according to the signal from the input power setting unit 75.

  In general, in a resonance type inverter, the drive frequency fs of the switching circuit is set to be greater than the resonance frequency fr of the resonance circuit, and the characteristic of the resonance load is made inductive, so that the current flowing through the resonance circuit Control so that the phase is delayed. This suppresses an increase in loss in the switching circuit. That is, in FIG. 1, the current IL <b> 5 flowing through the resonance circuit 60 is controlled so as to be in a lagging phase with respect to the voltage at the output terminal t, which is a connection point between the switching circuit 20 and the resonance circuit 60. Loss can be suppressed.

  However, when the power control is performed by changing the conduction period of the switching circuit 20 with the driving frequency fs fixed, the polarity of the current IL5 is reversed during the conduction period of the switching circuit 20, and the current IL5 becomes the output voltage of the switching circuit 20. In some cases, the phase shifts to a phase advance mode where the phase is more advanced. The phase advance mode causes an increase in loss of the switching circuit 20, and is a mode that should be avoided in a resonance type inverter.

  In the present embodiment, the conduction period of the resonance point variable circuit 30 is changed according to the material, shape, thickness, size of the object to be heated, or the magnitude of the set input power (thermal power), and the resonance circuit 60 The resonance point is controlled and the load characteristic of the resonance circuit 60 is maintained inductive. In other words, by controlling the resonance frequency fr so that the drive frequency fs of the switching circuit 20> the resonance frequency fr of the resonance circuit 60 is always satisfied, the phase advance mode can be avoided and an increase in loss of the switching circuit 20 can be avoided. For example, when the object to be heated is a magnetic material such as iron, when the power is high, conduction of the resonance point variable circuit 30 is stopped and heating is performed. When controlling the power, the power is reduced by lengthening the conduction period of the resonance point variable circuit 30. FIG. 14 shows the resistance value of each object to be heated and the inductance ratio to iron. In a non-magnetic material such as non-magnetic stainless steel, the inductance value is reduced to about 2/3 compared to iron. That is, the resonance point becomes higher due to a decrease in inductance. Therefore, it becomes capacitive (the driving frequency fs of the switching circuit <the resonance frequency fr of the resonance circuit). Therefore, the load characteristic is maintained inductive by making the resonance point variable circuit 30 conductive even at high power. When controlling the power, the power can be reduced by increasing the conduction period of the resonance point variable circuit as in the case of iron.

  As a result, the first inverter 100 can avoid the increase in loss of the switching circuit 20 even if the input power is controlled by changing the conduction period of the switching circuit 20 with the drive frequency fs kept constant. As described above, the resonance point variable circuit 30 serves as an auxiliary switching circuit for realizing an operation at a constant drive frequency fs.

  Next, a modification of the embodiment of FIG. 1 will be described with reference to FIGS. 2 to 4, the configurations and operations of the resonance circuit 60 and the resonance point variable circuit 30 are the same as those described with reference to FIG. As described above, in FIG. 1, the point o of the resonance circuit 60 is connected to the negative electrode o point of the power supply circuit 10, and the point o of the resonance point variable circuit 30 is connected to the negative electrode o point of the power supply circuit 10. As shown in FIG. 2, the point o of the resonance circuit 60 is connected to the negative electrode o point of the power supply circuit 10, and the point o of the resonance point variable circuit 30 is connected to the positive electrode p point of the power supply circuit 10. The effect of can be obtained. As shown in FIG. 3, the same effect can be obtained by connecting the point o of the resonance circuit 60 and the resonance point variable circuit 30 to the positive electrode p point of the power supply circuit 10. Further, as shown in FIG. 4, the point o of the resonance circuit 60 is connected to the positive electrode p point of the power supply circuit 10, and the point o of the resonance point variable circuit 30 is connected to the negative electrode o point of the power supply circuit 10. The same effect can be obtained.

  Note that by making the capacitance of the resonance capacitor 6 smaller than the capacitance of the resonance capacitor 7, the resonance voltage generated in the resonance capacitor 7 can be reduced and the voltage applied to the resonance point variable circuit can be reduced. That is, loss generation in the resonance point variable circuit 30 can be reduced and the withstand voltage performance can be improved.

  Example 2 which made the structure and operation | movement of the electromagnetic induction heating apparatus of Example 1 more concrete using FIG. 5 is demonstrated. In addition, the structure demonstrated in Example 1 attaches | subjects the same code | symbol, and abbreviate | omits description.

  In FIG. 5, a power supply circuit 10 is composed of a rectifier circuit 2 for rectifying an AC voltage from a commercial power supply 1, a smoothing circuit composed of an inductor 3 and a capacitor 4, and converts the AC voltage into a DC voltage to convert it to a first inverter. 100 is powered.

  A switching circuit 20 is connected between the positive electrode p point and the negative electrode o point of the capacitor 4 in the power supply circuit 10. The switching circuit 20 is configured by connecting IGBT11 and IGBT12 which are power semiconductor switching elements in series. Diodes 21 and 22 are connected in parallel to the IGBTs 11 and 12 in opposite directions, respectively. Hereinafter, a circuit composed of the IGBT 11 and the diode 21 is referred to as an upper arm, and a circuit composed of the IGBT 12 and the diode 22 is referred to as a lower arm. Further, snubber capacitors 31 and 32 are connected in parallel to the IGBTs 11 and 12, respectively. The snubber capacitors 31 and 32 are charged or discharged by a cutoff current when the IGBT 11 or the IGBT 12 is turned off. Since the capacitances of the snubber capacitors 31 and 32 are sufficiently larger than the output capacitance between the collectors and emitters of the IGBTs 11 and 12, changes in the voltage applied to both IGBTs at the time of turn-off are reduced, and turn-off loss is suppressed.

  A resonance circuit 60 is connected between the output terminal t point, which is a connection point between the IGBTs 11 and 12, and the negative electrode o point of the power supply circuit 10. The resonance circuit 60 includes a heating coil 5 and resonance capacitors 6 and 7 connected in series.

  The resonance point variable circuit 30 connected in parallel to the resonance capacitor 7 in the resonance circuit 60 is configured by a series connection of the resonance capacitor 8 and the IGBT 13 and a diode 23 connected in reverse parallel to the IGBT 13. Here, the direction flowing from the output terminal t toward the heating coil 5 is the positive direction of the resonance current IL5.

  The current detection element 71 detects a current flowing through the resonance circuit 60. The resonance current detection circuit 72 converts the output signal level of the current detection element 71 into a signal suitable for the input level of the control circuit 70. The current detection element 73 detects a current input from the commercial power source 1. The input current detection circuit 74 converts the output signal level of the current detection element 73 into a signal suitable for the input level of the control circuit 70. The control circuit 70 determines the material and state of the object to be heated from the relationship between the input current detected by the input current detection circuit 74 and the resonance current detected by the resonance current detection circuit 72, and starts or stops the heating operation. The object to be heated is distinguished from a magnetic material and a non-magnetic material. As a method of distinguishing, energization is performed with low power (about 300 W) before heating. The current value of the resonance current IL5 or IGBT 11, 12 at that time is detected, and the material of the object to be heated is determined based on the current value. When the current value is small, the magnetic material such as iron is discriminated, and when the current value is large, it is discriminated as a non-magnetic material to be heated such as nonmagnetic stainless steel, aluminum or copper. FIG. 14 shows the resistance value of each object to be heated at a frequency of 20 kHz. As shown in FIG. 14, the nonmagnetic stainless steel has a resistance value of 1/3 of iron, 1/20 of aluminum, and about 1/25 of copper.

  In addition, the control circuit 70 sets the conduction periods of the IGBTs 11 and 12 and the IGBT 13 of the switching circuit 20 via the drive circuits 61 and 62 in accordance with a signal from the input power setting unit 75 and controls the input power. The material detection needs to be performed in a short time with low power to prevent the occurrence of overcurrent and overvoltage. In the present embodiment, at the initial stage of material detection, the resonance point variable circuit 30 is turned on to increase the impedance of the resonance circuit, thereby preventing the occurrence of overcurrent and overvoltage and the rapid increase of input power. it can.

  As shown in FIG. 5, the current flowing through the upper arm of the switching circuit 20 is Ic1, the current flowing through the lower arm is Ic2, the current flowing through the resonance point variable circuit 30 is Ic3, and the resonance current is IL5. The voltage between the collector and emitter of the IGBT 11 of the upper arm is Vc1, the voltage between the collector and emitter of the IGBT 12 of the lower arm is Vc2, the voltage between the collector and emitter of the IGBT 13 of the resonance point variable circuit 30 is Vc3, and the resonance of the resonance capacitor 7 The voltage is Vc4, the resonance voltage of the resonance capacitor 8 is Vc5, and the power supply voltage of the inverter is Vp.

  In the above configuration, the operation when the input power of a magnetic object to be heated such as iron is lowered, or when the nonmagnetic object to be heated such as an aluminum pan is heated and the input power is reduced will be described. First, when a current is passed through the resonance point variable circuit 30, the resonance capacitor 8 is connected in parallel to the resonance capacitor 7, so that the impedance of the resonance circuit 60 is increased and the resonance frequency fr is lowered to reduce the input power. . The calculation formula (Formula 1) of the resonance frequency is shown below. As shown in (Expression 1), it can be seen that the resonance frequency decreases as the size of C increases.

ｆｒ：共振周波数、Ｌ：被加熱物を搭載した時の加熱コイルのインダクタンス、
Ｃ：共振コンデンサ６，７と共振点可変回路３０の合成容量

fr: resonance frequency, L: inductance of the heating coil when an object to be heated is mounted,
C: Combined capacity of the resonance capacitors 6 and 7 and the resonance point variable circuit 30

  In order to further reduce the input power, the arm conduction period is shortened and the lower arm conduction period is lengthened. At this time, the direction in which the resonance current IL5 flows is easily reversed from negative to positive during the conduction period of the lower arm. However, as described above, the resonance frequency fr decreases, and thus the difference between the drive frequency of the switching circuit and the resonance frequency fr. Becomes larger. For this reason, it is possible to prevent the polarity of the resonance current IL5 from being reversed from negative.

  Next, the operation when the input power is lowered by the conduction period control of the resonance point variable circuit 30 will be described in more detail with reference to FIG. As shown in FIG. 6, one cycle (drive cycle) of the control of the IGBTs 11 to 13 is represented by ts, and the conduction periods of the IGBTs 11, 12, and 13 are represented by t1, t2, and t3, respectively. Further, one period of the resonance current IL5 is divided into modes 1 to 5.

(Mode 1)
As shown in FIG. 6, in mode 1, the drive signals of the IGBTs 11, 12, and 13 are on, off, and on, respectively, and the IGBTs 11 and 13 are conducting. When the stored energy of the heating coil 5 becomes zero, the polarity of the resonance current IL5 changes from negative to positive, and the resonance current IL5 changes the path of the IGBT 11, the heating coil 5, the resonance capacitors 6 and 7, the IGBT 11, the heating coil 5, and the resonance capacitor. 6, 8, flows in the path of the IGBT 13. That is, the resonance characteristics of mode 1 are determined by the IGBT 11, the heating coil 5, and the resonance capacitors 6, 7, and 8. In mode 1, resonance capacitors 6, 7, and 8 are discharged by resonance current IL5.

(Mode 2)
Next, mode 2 following mode 1 will be described. In mode 2, the drive signals of the IGBTs 11, 12, and 13 are turned on, off, and off, respectively, so that only the IGBT 11 is conducted. That is, in mode 2, since the IGBT 13 is not conducted, Ic3 is blocked. As shown in FIG. 6, in mode 2, the resonance current IL5 has a positive polarity, and this current flows through the path of the IGBT 11, the heating coil 5, and the resonance capacitors 6 and 7. That is, the resonance characteristics of mode 2 are determined by the IGBT 11, the heating coil 5, and the resonance capacitors 6 and 7.

(Mode 3)
Next, mode 3 following mode 2 will be described. In mode 3, first, all drive signals of the IGBTs 11, 12, and 13 are turned off, and all the IGBTs are not conducted. As shown in FIG. 6, in mode 3, the resonance current IL5 has a positive polarity, and the resonance current IL5 includes the path of the snubber capacitor 31, the heating coil 5, the resonance capacitors 6 and 7, the snubber capacitor 32, and the heating. The flow continues through the coil 5 and the resonant capacitors 6 and 7, and the upper arm snubber capacitor 31 is charged and the lower arm snubber capacitor 32 is discharged. Accordingly, the voltage Vc1 between the collector and emitter of the IGBT 11 gradually increases, and the voltage Vc2 between the collector and emitter of the IGBT 12, that is, the output voltage gradually decreases. The resonance characteristics at this time are determined by the snubber capacitors 31 and 32, the heating coil 5, and the resonance capacitors 6 and 7.

  After that, when the voltage of Vc1 reaches the power supply voltage Vp of the inverter and a forward voltage is applied to the diode 22 of the lower arm, the resonance current IL5 becomes a recirculation current as the heating coil 5, the resonance capacitors 6, 7, and the diode 22 It flows along the route. At this time, when the drive signals of the IGBTs 11, 12, and 13 are turned off, on, and off, respectively, and only the IGBT 12 is turned on, the resonance current IL5 continues to flow through the diode 22 as long as the polarity of the resonance current IL5 does not change.

(Mode 4)
Next, mode 4 following mode 3 will be described. In mode 4, the drive signals of the IGBTs 11, 12, and 13 are off, on, and off, respectively, and only the IGBT 12 is conducting. When the stored energy of the heating coil 5 becomes zero and the polarity of the resonance current IL5 changes from positive to negative, the resonance current IL5 flows through the path of the resonance capacitors 7, 6, the heating coil 5, and the IGBT 12. That is, the resonance characteristics of mode 4 are determined by the IGBT 12, the heating coil 5, and the resonance capacitors 6 and 7. As shown in FIG. 6, since a negative voltage is applied to Vc5, no current in the negative direction flows through the resonance point variable circuit 30. In mode 4, resonant capacitors 6 and 7 are discharged by IL5.

(Mode 5)
Next, mode 5 following mode 4 will be described. In mode 5, first, the drive signals of the IGBTs 11, 12, and 13 are all turned off, and all the IGBTs are not conducted. As shown in FIG. 6, in mode 5, the resonance current IL5 has a negative polarity, and the resonance current IL5 includes the heating coil 5, the snubber capacitor 32, the path of the resonance capacitors 7, 6 and the heating coil 5, snubber. It continues to flow through the path of the capacitor 31, the capacitor 4, and the resonant capacitors 7 and 6, the upper arm snubber capacitor 31 is discharged, and the lower arm snubber capacitor 32 is charged. Therefore, the collector-emitter voltage Vc1 of the IGBT 11 gradually decreases, and the collector-emitter voltage Vc2 of the IGBT 12, that is, the output voltage gradually increases. The resonance characteristics at this time are determined by the snubber capacitors 31 and 32, the heating coil 5, and the resonance capacitors 6 and 7.

  Thereafter, when the voltage of Vc2 reaches the power supply voltage Vp of the inverter and a forward voltage is applied to the diode 21 of the upper arm, the resonance current IL5 is converted into a recirculation current by the heating coil 5, diode 21, capacitor 4, resonance capacitor 7 , 6 flows. At this time, the resonance capacitor 8 is charged with a negative voltage. When the negative charge voltage of the resonance capacitor 7 exceeds the charge voltage of the resonance capacitor 8, a forward voltage is applied to the diode 23, and the resonance current IL5 is The current is shunted and flows to the path of the diode 23, the resonance capacitor 8, 6, the heating coil 5, the diode 21, the capacitor 4 and the path of the resonance capacitor 7, 6, the heating coil 5, the diode 21, and the capacitor 4.

  At this time, when the drive signals of the IGBTs 11, 12, and 13 are turned on, off, and on, respectively, and the IGBTs 11 and 13 are both conducted, the resonance current IL5 continues to flow through the diode 21 as long as the polarity of the resonance current IL5 does not change.

  As described above, the operations of modes 1 to 5 are performed during one period of the resonance current IL5, and thereafter this operation is repeated. As is clear from the description of the mode 2 and the mode 4, the IGBTs 11 and 12 are cut off while the currents Ic1 and Ic2 are supplied to the IGBTs 11 and 12. As a result, the phase difference between 0 V of the voltage Vc2 and 0 A of the resonance current IL5 always operates in a current delay phase. Thus, in this embodiment, the resonance point variable circuit 30 is provided in parallel with the resonance capacitor 7 and the resonance characteristic of the load is changed, so that the operation can always be performed in the current delay phase, and the phase advance mode can be avoided.

  Next, as a method for further reducing the input power, the conduction period of the IGBT 11 is shortened and the conduction period of the IGBT 12 is lengthened. The inverter operation at this time will be described in detail with reference to FIG. As shown in FIG. 15, one cycle (drive cycle) of the control of the IGBTs 11 to 13 is represented by ts, and the conduction periods of the IGBTs 11 and 12 are represented by t1 and t2, respectively. The IGBT 13 is always on. Further, one period of the resonance current IL5 is divided into modes 1 to 4.

(Mode 1)
As shown in FIG. 15, in mode 1, the drive signals of the IGBTs 11, 12, and 13 are on, off, and on, respectively, and the IGBTs 11 and 13 are conducting. When the stored energy of the heating coil 5 becomes zero, the polarity of the resonance current IL5 changes from negative to positive, and the resonance current IL5 changes the path of the IGBT 11, the heating coil 5, the resonance capacitors 6 and 7, the IGBT 11, the heating coil 5, and the resonance capacitor. 6, 8, flows in the path of the IGBT 13. That is, the resonance characteristics of mode 1 are determined by the IGBT 11, the heating coil 5, and the resonance capacitors 6, 7, and 8. In mode 1, resonance capacitors 6, 7, and 8 are discharged by resonance current IL5.

(Mode 2)
Next, mode 2 following mode 1 will be described. In mode 2, first, the drive signals of the IGBTs 11, 12, and 13 are turned off, off, and on, respectively, and only the IGBT 13 is conducted. As shown in FIG. 15, in mode 2, the resonance current IL5 has a positive polarity, and the resonance current IL5 includes the path of the snubber capacitor 31, the heating coil 5, the resonance capacitors 6 and 7, the snubber capacitor 31, and the heating. The coil 5, the resonance capacitor 8, and the IGBT 13 path, the snubber capacitor 32, the heating coil 5, the resonance capacitors 6 and 7, and the snubber capacitor 32, the heating coil 5, the resonance capacitor 8, and the IGBT 13 continue to flow, The snubber capacitor 31 is charged, and the lower arm snubber capacitor 32 is discharged. Accordingly, the voltage Vc1 between the collector and emitter of the IGBT 11 gradually increases, and the voltage Vc2 between the collector and emitter of the IGBT 12, that is, the output voltage gradually decreases. The resonance characteristics at this time are determined by the snubber capacitors 31 and 32, the heating coil 5, and the resonance capacitors 6, 7, and 8.

  After that, when the voltage of Vc1 reaches the power supply voltage Vp of the inverter and a forward voltage is applied to the diode 22 of the lower arm, the resonance current IL5 becomes a recirculation current as the heating coil 5, the resonance capacitors 6, 7, and the diode 22 It flows through the path and the path of the heating coil 5, the resonant capacitor 8, and the diode 22. At this time, even if the drive signals of the IGBTs 11, 12, and 13 are turned off, on, and on, respectively, and the IGBT 12 is turned on, the resonance current IL5 continues to flow through the diode 22 as long as the polarity of the resonance current IL5 does not change.

(Mode 3)
Next, mode 3 following mode 2 will be described. In mode 3, the drive signals of the IGBTs 11, 12, and 13 are off, on, and on, respectively, and the IGBTs 12 and 13 are conducting. When the stored energy of the heating coil 5 becomes zero and the polarity of the resonance current IL5 changes from positive to negative, the resonance current IL5 is supplied to the paths of the resonance capacitors 7, 6, heating coil 5, IGBT 12, and the resonance capacitors 8, 6, heating coil. 5, flows in the path of the IGBT 12 and the diode 23. That is, the resonance characteristics of mode 4 are determined by the IGBT 12, the heating coil 5, and the resonance capacitors 6, 7, and 8. In mode 4, resonant capacitors 6, 7, and 8 are discharged by IL5.

(Mode 4)
Next, mode 4 following mode 3 will be described. In mode 5, first, the drive signals of the IGBTs 11, 12, and 13 are turned off, off, and on, and only the IGBT 13 is conducting. As shown in FIG. 15, in mode 4, the resonance current IL5 has a negative polarity, and the resonance current IL5 includes the path of the heating coil 5, the snubber capacitor 32, the resonance capacitors 7 and 6, the heating coil 5, the snubber. The path of the capacitor 32, the diode 23, the resonant capacitors 8 and 6, the heating coil 5, the snubber capacitor 31, the path of the capacitor 4, the resonant capacitors 7 and 6, the heating coil 5, the snubber capacitor 31, the capacitor 4, the diode 23, and the resonance The upper arm snubber capacitor 31 is discharged and the lower arm snubber capacitor 32 is charged. Therefore, the collector-emitter voltage Vc1 of the IGBT 11 gradually decreases, and the collector-emitter voltage Vc2 of the IGBT 12, that is, the output voltage gradually increases. The resonance characteristics at this time are determined by the snubber capacitors 31 and 32, the heating coil 5, and the resonance capacitors 6, 7, and 8.

  Thereafter, when the voltage of Vc2 reaches the power supply voltage Vp of the inverter and a forward voltage is applied to the diode 21 of the upper arm, the resonance current IL5 is converted into a recirculation current by the heating coil 5, diode 21, capacitor 4, resonance capacitor 7 , 6 flows. At this time, the resonance capacitor 8 is charged with a negative voltage. When the negative charge voltage of the resonance capacitor 7 exceeds the charge voltage of the resonance capacitor 8, a forward voltage is applied to the diode 23, and the resonance current IL5 is The current is shunted and flows to the path of the diode 23, the resonance capacitor 8, 6, the heating coil 5, the diode 21, the capacitor 4 and the path of the resonance capacitor 7, 6, the heating coil 5, the diode 21, and the capacitor 4.

  At this time, when the drive signals of the IGBTs 11, 12, and 13 are turned on, off, and on, respectively, and the IGBTs 11 and 13 are both conducted, the resonance current IL5 continues to flow through the diode 21 as long as the polarity of the resonance current IL5 does not change.

  As described above, the operations of modes 1 to 4 are performed during one period of the resonance current IL5, and thereafter this operation is repeated. When the resonance point variable circuit 30 is always turned on, as is apparent from the description of the modes 1 and 4, even if the conduction period t2 of the IGBT 12 becomes long, the resonance current IL5 remains in the period in which the diode 21 or 22 is conducting. Changes from negative to positive. For this reason, the polarity of the resonance current IL5 does not reverse from negative to positive, the load characteristics can be kept inductive, and the phase advance mode can be avoided.

  As a result, the input power can be controlled by changing the conduction period of the switching circuit 20.

  Further, the current flowing through the resonance capacitor 8 is determined by the capacitance ratio of the resonance capacitor 7 and the resonance capacitor 8. In this embodiment, since the resonance capacitor 7 capacity ≧ resonance capacitor 8 capacity, the current flowing through the resonance capacitor 8 is less than or equal to the resonance capacitor 7. Thereby, loss generation | occurrence | production in IGBT13 can be reduced and the electric current resistance performance of IGBT13 can be improved.

  Further, the voltage (Vc4) generated in the resonance capacitor 7 is determined by the capacitance of the resonance capacitor 6 and the capacitance of the resonance capacitor 7. Therefore, in order to reduce the voltage generated in the resonance capacitor 7, the voltage generated in the resonance capacitor 7 is reduced to ½ or less by setting the resonance capacitor 7 capacity ≧ the resonance capacitor 6 capacity. As a result, loss generation in the IGBT 13 can be reduced, the withstand voltage performance of the IGBT 13 can be increased, and a wide resonance point variable range can be set.

  Next, the charging voltage of the resonant capacitor 8 will be described. The relational expression (Formula 2) of the voltage of the resonant capacitor 8 (Vc5) is shown.

Ｃ７：共振コンデンサ７の容量、Ｃ８：共振コンデンサ８の容量

C7: Resonance capacitor 7 capacitance, C8: Resonance capacitor 8 capacitance

  In this embodiment, since C8 <C7, the voltage of Vc5 is charged lower than C7. The total voltage of Vc4 and Vc5 is applied to the IGBT 13, but since the voltage charged to Vc5 is low, it does not affect the increase in the element breakdown voltage of the IGBT 13.

  Next, a method for controlling the input power will be described with reference to FIG. As described with reference to FIG. 6, the conduction periods of the IGBTs 11, 12, and 13 are represented by t1, t2, and t3, and the drive cycle is represented by ts. FIG. 7 shows an example of the control conditions in the case of heating an iron object to be heated and nonmagnetic stainless steel at a high output power with an inverter drive frequency of 21 kHz, and the horizontal axis represents the duty period of the IGBT 13 and the duty (t3 / ts) of the IGBT 13, The vertical axis represents the input power Pin. Here, a description will be given of a case where the input power Pin is controlled by changing t3 without changing t1 and t2.

  As shown in FIG. 7, in the case of an iron object to be heated, the maximum input power is obtained when the duty of the IGBT 13 is 0 (the IGBT 13 is always in an off state). As the duty increases, the input power Pin decreases, and the input power Pin becomes substantially constant when the duty is about 0.5 or more. On the other hand, in the case of nonmagnetic stainless steel, the maximum power becomes 3 kW when the duty of the IGBT 13 is 0.45, the input power decreases by further increasing the duty, and becomes almost constant when the duty is 0.7 or more. As is clear from this, the input power Pin can be reduced by increasing the duty of the IGBT 13.

  The reason why the input power can be controlled by controlling the duty of the IGBT 13 will be described. When the IGBT 13 is turned on, the resonance capacitor 7 and the resonance capacitor 8 are connected in parallel, so that the combined resonance capacitor capacity of the resonance capacitors 6, 7, and 8 increases, and the resonance frequency determined by the heating coil 5 and the combined resonance capacitor decreases. FIG. 8 shows a resonance characteristic graph in the case where the duty of the IGBT 13 is changed when an iron object to be heated is heated. As shown in FIG. 8, when t3 is lengthened and the duty of the IGBT 13 is increased, the resonance frequency is lowered. For this reason, for example, when the inverter drive frequency is fixed at 21 kHz, the input power is about 3 kW when Duty = 0, the input power is about 1.5 kW when Duty = 0.35, and the input power when Duty = 0.5. Is about 0.5 kW. In this way, the input power can be controlled by controlling the on-time of t3 (duty of IGBT 13).

  As described above, when the duty of the IGBT 13 becomes about 0.5 or more, the input power Pin becomes constant at about 0.5 kW. This is because the resonance current IL5 changes from positive to negative during the period t3 when the IGBT 13 is on, and the current flows through the diode 23, exceeding the variable range of the resonance point variable circuit 30 at the duty of the IGBT 13. The period during which the resonance current IL5 can actually be controlled by the resonance point variable circuit 30 is a period during which the resonance current IL5 is positive. Therefore, the resonance point cannot be controlled even if the duty of the IGBT 13 is controlled while the resonance current IL5 is negative. Accordingly, the lower limit value of the input power Pin that can be adjusted only by t3 without changing t1 and t2 in FIG. 7 is about 0.5 kW, and when it is set below this value, it is necessary to change t1 and t2.

  Next, a case where the duty of the IGBT 13 is set to about 0.5 or more and t1 and t2 are changed to control the input power Pin will be described. FIG. 9 shows the control conditions when the object to be heated is heated at a low output, and the horizontal axis is Duty (= t1 / ts) indicating the conduction ratio of the conduction period t1 of the upper arm IGBT 11 with respect to the driving cycle ts. At this time, the conduction ratio of the IGBT 12 is 1-Duty. The vertical axis represents the input power Pin. As shown in FIG. 9, the input power Pin can be further reduced by setting the duty of the IGBT 13 in the resonance point variable circuit 30 to about 0.5 or more and reducing the duty of the IGBT 11.

  On the other hand, as shown in FIG. 14, the nonmagnetic stainless steel has an inductance value 2/3 that of iron, and therefore, the resonance frequency with the series circuit of the resonance capacitors 6 and 7 is higher than the driving frequency of the switching circuit 20. As a result, the load characteristic becomes capacitive and the phase advance mode is set. Therefore, it is necessary to increase the conduction period of the resonance point variable circuit 30, lower the resonance point, and make the load characteristic inductive. About the control method of input electric power, it can control by the duty of IGBT13 and the duty of IGBT1 similarly to the to-be-heated object made from iron.

  FIG. 10 is a circuit configuration diagram of the electromagnetic induction heating device according to the third embodiment. Description of the configuration of the third embodiment that is the same as the configuration described in the previous embodiment is omitted.

  In FIG. 10, the resonance circuit 60 constituted by the heating coil 5 and the resonance capacitors 6 and 7 is connected between the output terminal t point and the o point of the first inverter 100. A resonance point variable circuit 30 is connected in parallel to the resonance capacitor 7. The resonance point variable circuit 30 is connected in parallel in the reverse direction to the resonance capacitor 8 connected in series, the diode 25 blocking the reverse current, the IGBT 13, and the IGBT 13. It is comprised by the diode 23 made. Here, if the resonance current IL5 flowing from the output terminal t point toward the resonance capacitor 6 is positive, the current Ic3 flowing through the resonance point variable circuit 30 is in one positive direction. In this embodiment, it is possible to prevent the resonance capacitor 8 from being charged with a negative voltage, so that the voltage applied to the IGBT 13 becomes the charging voltage of the resonance capacitor 7. Therefore, the element withstand voltage can be reduced without charging the resonant capacitor 8 with a negative voltage. In general, when the breakdown voltage of the IGBT is lowered, the conduction loss can be reduced. Thereby, the element loss can be reduced.

  FIG. 11 shows a part of the circuit of the electromagnetic induction heating apparatus according to the fourth embodiment. Description of the configuration of the fourth embodiment that is the same as the configuration described in the previous embodiment is omitted.

  In FIG. 11, the switching element of the resonance point variable circuit 30 is a reverse current blocking IGBT 14 having a reverse breakdown voltage (an IGBT with a reverse breakdown function), and the IGBT 13 of FIG. The configuration is replaced with one IGBT 14. In the resonance point variable circuit 30 of FIG. 10, a loss is generated in each of the IGBT 13 and the diode 25. However, in this embodiment, the loss is in the IGBT 14, so the circuit loss in the first inverter 100 is reduced and the conversion efficiency is improved. To do. The operation of this embodiment is the same as that of the third embodiment, and a description thereof will be omitted.

  FIG. 12 shows a part of the circuit of the electromagnetic induction heating device of Example 5. Description of the configuration of the fifth embodiment that is the same as the configuration described in the previous embodiment is omitted.

  In FIG. 12, the difference from the third embodiment is that the IGBT 15 is connected in parallel to the diode 25 of the resonance point variable circuit 30, so that positive and negative currents can be controlled in the resonance point variable circuit 30. In this embodiment, it is possible to control the current flowing through the positive and negative resonance point variable circuit 30 by driving the IGBTs 13 and 15, and the resonance frequency is set to the resonance current IL5 while maintaining the load characteristic of the resonance circuit 60 inductive. The input power is changed by controlling the IGBT 13 or 15 in the positive and negative directions. As for the control method, the IGBT 13 synchronizes the on-timing with the IGBT 11 and performs duty control of the IGBT 13 as in the second embodiment, and the IGBT 15 synchronizes the on-timing with the IGBT 12 and performs duty control of the IGBT 15. When the resonance current IL5 is a positive current, the IGBT 13 is controlled, and when the resonance current IL5 is a negative current, the IGBT 15 is controlled. Thereby, since the resonance point can be varied in the positive / negative period of the resonance current IL5, the power control range can be expanded.

  FIG. 13 shows a part of the circuit of the electromagnetic induction heating apparatus of Example 6. The description of the configuration of the sixth embodiment that is the same as the configuration described in the previous embodiment is omitted.

  In FIG. 13, the resonance point variable circuit 30 has a configuration in which reverse current blocking IGBTs 14 and IGBTs 16 having a reverse breakdown voltage are connected in parallel in the reverse direction. In the resonance point variable circuit 30 of FIG. 12, since a positive current flows through the diode 25 and the IGBT 13 and a negative current flows through the diode 23 and the IGBT 15, a loss occurs in each of the diode and the IGBT. In this embodiment, the loss of the IGBT 14 and the IGBT 16 is lost, so that the circuit loss in the first inverter 100 is reduced and the conversion efficiency is improved. The operation of this embodiment is the same as that of the fifth embodiment, and a description thereof will be omitted.

DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Rectifier circuit 3 Inductor 4 Capacitor 5 Heating coil 6, 7, 8 Resonance capacitor 10 Power supply circuit 11, 12, 13, 14, 15, 16 IGBT
20 switching circuit 21, 22, 23, 25 diode 30 resonance point variable circuit 31, 32 snubber capacitor 60 resonance circuit 61, 62, 63 drive circuit 70 control circuit 71, 73 current detection element 72 resonance current detection circuit 74 input current detection circuit 75 Input power setting unit 100 First inverter 200 Second inverter 300 Third inverter

Claims (9)

In an electromagnetic induction heating apparatus having a DC power supply, an inverter circuit that converts a DC voltage supplied from the DC power supply into a high-frequency AC voltage, and a control circuit,
The inverter circuit includes a switching circuit, a resonance circuit, and a resonance point variable circuit,
The switching circuit is formed by a series connection of an upper arm power semiconductor switching element and a lower arm power semiconductor switching element connected to both terminals of the DC power supply,
The resonance circuit formed by connecting a heating coil, a first resonance capacitor, and a second resonance capacitor in series has one end connected to a connection point between the upper arm and the lower arm of the switching circuit, and the other end Connected to one of the terminals of the DC power supply,
The resonance point variable circuit connected in parallel with said second resonant capacitor, a first connected in series connection of the third resonant capacitor and the first switching element, in anti-parallel to said first switching element Formed by a diode
By the control circuit, and the resonant frequency of the resonant circuit is variable by controlling the conduction period of the first switching element,
The electromagnetic induction heating device, wherein the second resonance capacitor capacitance is equal to or greater than the first resonance capacitor capacitance, and the third resonance capacitor capacitance is equal to or less than the second resonance capacitor capacitance . In the electromagnetic induction heating device according to claim 1,
The resonance point variable circuit includes a second diode connected in series with a first switching element, and the first switching element includes a first diode connected in antiparallel. Induction heating device. In the electromagnetic induction heating device according to claim 1,
It said first switching element to form a resonance point variable circuit, an electromagnetic induction heating apparatus which is a first reverse blocking function switching element. The electromagnetic induction heating device according to claim 2,
An electromagnetic induction heating apparatus comprising a second switching element in antiparallel with the second diode. In the electromagnetic induction heating device according to claim 1,
It said first switching element to form a resonance point variable circuit includes a first electromagnetic induction heating apparatus which is a second reverse blocking function switching device connected in anti-parallel. In the electromagnetic induction heating device according to claim 1,
The electromagnetic induction heating device, wherein the switching circuit includes a first snubber capacitor in parallel with at least one of the power semiconductor switching element of the upper arm and the power semiconductor switching element of the lower arm. An electromagnetic induction heating apparatus for induction heating an object to be heated,
A power supply circuit for supplying a DC voltage from the positive electrode and the negative electrode;
A switching circuit that is connected between the positive electrode and the negative electrode of the power supply circuit, converts a DC voltage into an AC voltage, and outputs the AC voltage;
A resonance circuit connected between an output terminal of the switching circuit and a terminal of the power supply circuit, and configured by a series connection of a heating coil, a first resonance capacitor, and a second resonance capacitor;
A resonance point variable circuit that is connected in parallel to the second resonance capacitor and varies a resonance point of the resonance circuit;
Equipped with,
The resonance point variable circuit includes a series connection of a third resonance capacitor and a switching element, and a diode connected in antiparallel to the switching element.
An electromagnetic induction heating apparatus characterized in that a capacity of the second resonance capacitor is set to be equal to or greater than that of the first resonance capacitor, and a capacity of the second resonance capacitor is set to be equal to or greater than a capacity of the third resonance capacitor . The electromagnetic induction heating device according to claim 7 ,
The electromagnetic induction heating cooker characterized in that the polarity of a resonance current flowing from the switching circuit toward the heating coil changes from negative to positive during a period in which the switching element in the resonance point variable circuit is conductive. The electromagnetic induction heating cooker according to claim 7 ,
An electromagnetic induction heating cooker that controls input power supplied from the resonance circuit to an object to be heated by controlling a duty of a switching element in the resonance point variable circuit.

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