CN101841945A - Electromagnetic induction heating device - Google Patents

Abstract

An object of the present invention is to provide an electromagnetic induction heating device capable of preventing the generation of interference noise when a plurality of inverters are driven simultaneously and controlling each input power. The electromagnetic induction heating device of the present invention has an inverter circuit for converting DC voltage into high-frequency AC voltage. The inverter circuit includes a switch circuit and a resonant circuit. a resonant capacitor having a resonant point variable circuit connected in parallel to one of the resonant capacitors.

Description

Electromagnetic induction heating device

technical field

The present invention relates to an electromagnetic induction heating device having a plurality of heating parts.

Background technique

In recent years, an inverter-type electromagnetic induction heating device that does not heat an object to be heated, such as a pan, has been widely used. In the electromagnetic induction heating device, a high-frequency current flows through the heating coil, so that eddy currents are generated in the heated object made of iron or stainless steel that is placed close to the coil, so that it generates heat through the resistance of the heated object itself. Because it can control the temperature of the object to be heated and has high safety, it has been regarded as a new heat source.

Conventionally, electric cookers incorporated into system kitchens have used appliances using resistances such as armored heaters, flat-panel heaters, and halogen heaters as heat sources, but in recent years, some of them have been replaced with Appliances for induction heating cookers, or appliances for making induction heating cookers with two or more stoves. As a method of changing the input voltage of the electromagnetic induction heating device to control the temperature of the object to be heated, a method of changing the drive frequency of the inverter is generally used. However, when a plurality of heating coils are provided and different objects to be heated are heated separately, there is a problem that interference noise is generated from the object to be heated due to the difference frequency of the inverter.

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

[Patent Document 1] JP-A-2002-8840

As described above, in Patent Document 1, the generation of interference noise can be prevented, but since a large resonance current flows through the bypass switching element, there is a problem that the generated loss becomes large.

Contents of the invention

An object of the present invention is to provide an electromagnetic induction heating device capable of preventing generation of interference noise when a plurality of inverters are simultaneously driven, and suppressing loss of bypass switching elements.

The above-mentioned problems are solved by an electromagnetic induction heating device having a DC power supply, an inverter circuit for converting a DC voltage supplied from the DC power supply into a high-frequency AC voltage, and a control circuit, Wherein, the inverter circuit has a switch circuit, a resonant circuit, and a variable resonance point circuit; The series connection of semiconductor switching elements is formed; the resonance circuit formed by connecting the heating coil and the first resonance capacitor and the second resonance capacitor in series, one end is connected to the connection point of the upper arm and the lower arm of the switching circuit, and the other end is connected to the On a certain terminal of the DC power supply; the resonance point variable circuit connected in parallel with the second resonant capacitor, connected in series with the first switch element through the third resonant capacitor, and antiparallel connected with the first switch element A first diode is formed; and the resonance frequency of the resonance circuit is variable by controlling the conduction period of the first switching element by the control circuit.

In addition, the above-mentioned problems are solved by an electromagnetic induction heating device for inductively heating an object to be heated, which has: a power supply circuit for supplying a DC voltage from a positive electrode and a negative electrode; Between the negative electrodes, a switching circuit that converts the DC voltage into an AC voltage and then outputs it; is connected between the output terminal of the switching circuit and the terminal of the power supply circuit, and uses a heating coil and a first resonant capacitor and a second resonant capacitor and a resonant point variable circuit connected in parallel with the second resonant capacitor to change the resonant point of the resonant circuit.

According to the present invention, by providing the resonant point variable circuit on the resonant capacitor, the resonant frequency can be varied, the load characteristic of the resonant circuit can be maintained as inductive, the input power can be controlled by duty control, and the loss of switching elements can be suppressed. Even when a plurality of inverters are driven at the same time, since all the inverters can be driven at the same frequency, it is possible to provide an electromagnetic induction heating device that does not generate interference noise.

Description of drawings

FIG. 1 is a block diagram of the electromagnetic induction heating device of the first embodiment.

Fig. 2 is a modified example of the electric circuit of the electromagnetic induction heating device of the first embodiment.

Fig. 3 is a modified example of the electric circuit of the electromagnetic induction heating device of the first embodiment.

Fig. 4 is a modified example of the electric circuit of the electromagnetic induction heating device of the first embodiment.

5 is a circuit configuration diagram of the electromagnetic induction heating device of the second embodiment.

FIG. 6 is an explanatory view of the operation of the second embodiment.

FIG. 7 is an explanatory diagram of a control method of the second embodiment.

FIG. 8 is an explanatory diagram of a control method of the second embodiment.

FIG. 9 is an explanatory diagram of a control method of the second embodiment.

Fig. 10 is a circuit configuration diagram of the electromagnetic induction heating device of the third embodiment.

Fig. 11 is a circuit configuration diagram of the electromagnetic induction heating device of the fourth embodiment.

Fig. 12 is a part of the circuit of the electromagnetic induction heating device of the fifth embodiment.

Fig. 13 is a part of the circuit of the electromagnetic induction heating device of the sixth embodiment.

Fig. 14 is a graph showing the resistance value of each object to be heated and the inductance ratio to iron.

Fig. 15 is a modified example of the operation explanatory diagram of the second embodiment.

〖Symbol Description〗

1 commercial power supply

2 rectifier circuit

3 inductors

4 capacitors

5 heating coils

6, 7, 8 resonance capacitors

10 power circuit

11, 12, 13, 14, 15, 16IGBTs

20 switch circuit

21, 22, 23, 25 diodes

30 resonance point variable circuit

31, 32 Damping capacitors

60 resonant circuit

61, 62, 63 driving circuit

70 control circuit

71, 73 current detection element

72 Resonant current detection circuit

74 input current detection circuit

75 input power setting section

100 first inverter

200 second inverter

300 third inverter

Detailed ways

Embodiments of the present invention will be described below using the drawings.

【Example 1】

The electromagnetic induction heating device of Embodiment 1 has an inverter circuit that converts DC voltage into high-frequency AC voltage. The inverter circuit includes a switching circuit and a resonant circuit. The resonant circuit includes a heating coil and two series connected to the heating coil. a resonant capacitor, the resonant circuit is connected between one of the two terminals (p/o) of the direct current power supply and the output terminal (t) of the switch circuit, and the electromagnetic induction heating device also has the resonant capacitor An upper-parallel resonance point variable circuit.

FIG. 1 shows a block diagram of the electromagnetic induction heating device of the first embodiment. As shown in FIG. 1 , the electromagnetic induction heating device of this embodiment has a first inverter 100 , a second inverter 200 , and a third inverter 300 . Since each inverter can heat objects to be heated, the electromagnetic induction heating device of this embodiment can simultaneously heat a plurality of objects to be heated. In this embodiment, since each inverter has the same structure, the first inverter 100 is used as a representative for description.

In FIG. 1 , a first inverter 100 is composed of a switching circuit 20 , a resonance circuit 60 , and a resonance point variable circuit 30 . The switch circuit 20 is connected between the positive electrode point p 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 resonant circuit 60 . The resonant circuit 60 is composed of resonant capacitors 6 and 7 connected in series to the heating coil 5 , and high-frequency power is supplied to the heating coil 5 by the switching circuit 20 . The resonance point variable circuit 30 is connected in parallel with 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 switch 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 , 62 are controlled by a control circuit 70 . The input power setting unit 75 is an interface for the user to set the input power (heating power), and sends a signal to the control circuit 70 according to the setting. The control circuit 70 controls the switch circuit 20 and the resonance point variable circuit 30 based on a signal from the input power setting unit 75 .

Generally, in a resonant type inverter, by setting the driving frequency fs of the switching circuit > the resonant frequency fr of the resonant circuit, the characteristic of the resonant load is made inductive, and the current flowing into the resonant circuit is controlled to the output voltage of the switching circuit. become a lagging phase. An increase in loss in the switching circuit is thereby suppressed. That is, in FIG. 1 , the loss of the switching circuit 20 can be suppressed by controlling the current IL5 flowing in the resonant circuit 60 to have a lagging phase with respect to the voltage at the output terminal point t, which is the connection point between the switching circuit 20 and the resonant circuit 60 .

However, when the power control is performed by changing the on-period of the switch circuit 20 with the drive frequency fs fixed, the polarity of the current IL5 may be reversed during the on-period of the switch circuit 20 to shift to the current IL5. It is a phase leading method in which the phase is advanced from the output voltage of the switching circuit 20 . Since the phase leading method increases the loss of the switching circuit 20, it must be avoided in the resonance type inverter.

In this embodiment, the conduction period of the resonant point variable circuit 30 is changed according to the material or shape, thickness, size of the object to be heated, or the set input power (heating power), and the resonant point of the resonant circuit 60 is controlled. , to maintain the load characteristic of the resonant circuit 60 as inductive. That is, by controlling the resonant frequency fr such that the driving frequency fs of the switching circuit 20>the resonant frequency fr of the resonant circuit 60 is always satisfied, it is possible to avoid the phase advance method and avoid an increase in the loss of the switching circuit 20 . For example, when the object to be heated is a magnetic material such as iron, when the power is large, the conduction of the resonance point variable circuit 30 is stopped to perform heating. In the case of controlling electric power, the electric power is reduced by extending the conduction period of the resonance point variable circuit 30 . FIG. 14 shows the ratio of the resistance value of each object to be heated to the inductance ratio of iron. In non-magnetic materials such as non-magnetic stainless steel, the inductance value is about 2/3 lower than that of iron. That is, the resonance point will increase due to the decrease in inductance. Therefore, it becomes capacitive (the driving frequency fs of the switching circuit<the resonance frequency fr of the resonance circuit). Therefore, even at the time of large power, by turning on the resonance point variable circuit 30, the load characteristic is maintained as inductive. When controlling electric power, similar to iron, by extending the conduction period of the vibration point variable circuit, electric power can be reduced.

Thus, the first inverter 100 keeps the driving frequency fs constant, changes the conduction period of the switching circuit 20 , and can avoid an increase in loss of the switching circuit 20 even if the input power is controlled. In this way, the resonance point variable circuit 30 functions as an auxiliary switch circuit for realizing operation at a constant drive frequency fs.

Next, a modified example of the embodiment shown in FIG. 1 will be described using FIGS. 2 to 4 . In the modified examples of FIGS. 2 to 4 , since the structures and operations of the resonant circuit 60 and the resonant point variable circuit 30 are the same as those described in FIG. 1 , detailed descriptions are omitted. As described above, in FIG. 1 , point o of the resonant circuit 60 is connected to point o of the negative electrode of the power supply circuit 10 , and point o of the resonance point variable circuit 30 is connected to point o of the negative electrode of the power supply circuit 10 . As shown in FIG. 2, even if point o of the resonant circuit 60 is connected to point o of the negative electrode of the power supply circuit 10, and point o of the resonance point variable circuit 30 is connected to point p of the positive electrode of the power supply circuit 10, the same can be obtained. Effect. Also, as shown in FIG. 3 , the same effect can be obtained even if the resonance circuit 60 and the point o of the resonance point variable circuit 30 are connected to the point p of the positive electrode of the power supply circuit 10 . In addition, as shown in FIG. 4, even if the point o of the resonant circuit 60 is connected to the point p of the positive electrode of the power supply circuit 10, and the point o of the resonance point variable circuit 30 is connected to the point o of the negative electrode of the power supply circuit 10, the to get the same effect.

Furthermore, by making the capacity of the resonant capacitor 6 smaller than that of the resonant capacitor 7, the resonant voltage generated in the resonant capacitor 7 can be reduced, and the voltage applied to the resonant point variable circuit can be reduced. That is, it is possible to reduce the occurrence of losses in the resonance point variable circuit 30 and improve the withstand voltage performance.

[Embodiment 2] Embodiment 2 in which the configuration and operation of the electromagnetic induction heating device of Embodiment 1 are more concrete will be described using FIG. 5 . In addition, the same code|symbol is attached|subjected to the structure already demonstrated in Example 1, and description is abbreviate|omitted.

In Fig. 5, the power supply circuit 10 is composed of a rectifier circuit 2 which rectifies the AC voltage from the commercial power supply 1 and a filter circuit composed of an inductor 3 and a capacitor 4, and converts the AC voltage into a DC voltage, which is supplied to the first inverter. 100 supply electricity.

A switch circuit 20 is connected between a positive electrode p point and a 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 in opposite directions to IGBT11 and IGBT12, respectively. Hereinafter, the circuit constituted by the IGBT11 and the diode 21 is referred to as an upper arm, and the circuit constituted by the IGBT12 and the diode 22 is referred to as a lower arm. In addition, damping capacitors 31 and 32 are connected in parallel to IGBT11 and IGBT12, respectively. Damping capacitors 31 , 32 are charged or discharged by an off current when IGBT 11 or IGBT 12 is turned off. The capacity of damping capacitors 31 and 32 is much larger than the output capacitance between the collector and emitter of IGBT11 and 12, so it can reduce the voltage change applied to the two IGBTs when they are turned off, and can suppress the turn-off loss. .

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

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

The current detection element 71 detects the current flowing in 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 the current input from the commercial power supply 1 . The input current detection circuit 74 converts the level of the output signal 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 or state of the object to be heated from the relationship between the input current detected by the current detection circuit 74 and the resonance current detected by the resonance current detection circuit 72, and starts or stops the heating operation. Discrimination of the object to be heated is divided into magnetic body and non-magnetic body. As a method of distinguishing, conduct electricity with low power (about 300W) before heating. The resonance current IL5 or the current value of the IGBTs 11 and 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, it is determined that the object to be heated is a magnetic material such as iron; when the current value is large, it is determined that the object to be heated is a nonmagnetic material such as nonmagnetic stainless steel or aluminum or copper. FIG. 14 shows the resistance value of each object to be heated at a frequency of 20 kHz. As shown in Figure 14, the resistance value of non-magnetic stainless steel is 1/3 of that of iron, that of aluminum is 1/20 of that of iron, and that of copper is about 1/25 of that of iron.

In addition, the control circuit 70 controls the input power by setting the conduction periods of the IGBTs 11 , 12 and the IGBT 13 of the switch circuit 20 through the drive circuits 61 and 62 based on a signal from the input power setting unit 75 . In order to prevent the occurrence of overcurrent or overvoltage, it is necessary to perform material detection with low power and short time. In the present embodiment, in the initial stage of material detection, by turning on the resonance point variable circuit 30, the inductance of the resonance circuit can be increased, and the occurrence of overcurrent or overvoltage and a sudden increase in input power can be prevented.

In addition, as shown in FIG. 5 , let the current flowing into the upper arm of the switch circuit 20 be Ic1, the current flowing into the lower arm be Ic2, the current flowing into the resonance point variable circuit 30 be Ic3, and the resonance current be IL5. Assuming that the voltage between the collector and emitter of the IGBT11 of the upper arm is Vc1, and the voltage between the collector and emitter of the IGBT12 of the lower arm is Vc2, the collector and emitter of the IGBT13 of the resonance point variable circuit 30 The voltage between them is Vc3, the resonance voltage of the resonance capacitor 7 is Vc4, the resonance voltage of the resonance capacitor 8 is Vc5, and the power supply voltage of the inverter is Vp.

With the above configuration, the operation when reducing the input power of a magnetic object to be heated such as iron, or when reducing the heating input power of a nonmagnetic object to be heated such as an aluminum pan will be described. First, when a current flows into the resonance point variable circuit 30 , since the resonance capacitor 8 is connected in parallel with the resonance capacitor 7 , the inductance of the resonance circuit 60 increases and the resonance frequency fr decreases, thereby reducing input power. The formula (Formula 1) for calculating the resonance frequency is shown below. As shown in (Equation 1), it can be seen that the resonance frequency decreases as the magnitude of C increases.

【Mathematical formula 1】

$\mathrm{<span\; class="notranslate">\; fr</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\sqrt{\mathrm{<span\; class="notranslate">\; LC</span>}}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

fr: resonance frequency, L: inductance of the heating coil when the object to be heated is mounted,

C: combined capacity of resonance capacitors 6, 7 and resonance point variable circuit 30

In order to further reduce the input power, the conduction period of the lower arm is extended while the conduction period of the upper arm is shortened. At this time, the flow direction of the resonance current IL5 is easily reversed from negative to positive during the conduction period of the lower arm. However, since the resonance frequency fr decreases as described above, the difference between the driving frequency of the switching circuit and the resonance frequency fr increases. Therefore, 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 reduced by controlling the on-period of the resonance point variable circuit 30 will be described in more detail with reference to FIG. 6 . In addition, as shown in FIG. 6 , one cycle (drive cycle) of control of the IGBTs 11 to 13 is represented by ts, and conduction periods of the IGBTs 11 , 12 , and 13 are represented by t1 , t2 , and t3 , respectively. In addition, it is divided into patterns 1 to 5 to represent one period of the resonance current IL5.

(mode 1)

As shown in FIG. 6 , in method 1, the drive signals of IGBT11, 12, and 13 are turned on, off, and turned on, respectively, and IGBT11, 13 is turned on. When the accumulated 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 flows through the path of the IGBT11, the heating coil 5, the resonant capacitor 6, 7 and the IGBT11, the heating coil 5, and the resonant capacitor 6 , 8, the path of IGBT13. That is, the resonance characteristic of the form 1 is determined by the IGBT 11 , the heating coil 5 , and the resonance capacitors 6 , 7 , and 8 . In addition, in the mode 1, the resonance capacitors 6, 7, and 8 are discharged by the resonance current IL5.

(method 2)

Next, method 2 following method 1 will be described. In the mode 2, the drive signals of IGBT11, 12, and 13 are turned on, off, and off, respectively, and only IGBT11 is turned on. That is, in mode 2, since IGBT13 is not turned on, Ic3 is cut off. As shown in FIG. 6 , the resonance current IL5 has a positive polarity in the mode 2, and this current flows through the paths of the IGBT 11 , the heating coil 5 , and the resonance capacitors 6 and 7 . That is, the resonance characteristics of the mode 2 are determined by the IGBT 11 , the heating coil 5 , and the resonance capacitors 6 and 7 .

(mode 3)

Next, method 3 following method 2 will be described. In mode 3, all the driving signals of IGBT11, 12, and 13 are first turned off, and all IGBTs are not turned on. As shown in Figure 6, the resonance current IL5 has a positive polarity in mode 3, and the resonance current IL5 continues to flow through the path of the damping capacitor 31, the heating coil 5, the resonance capacitors 6, 7 and the damping capacitor 32, the heating coil 5 , the paths of the resonant capacitors 6 and 7, the upper arm damping capacitor 31 is charged, and the lower arm damping capacitor 32 is discharged. Therefore, the voltage Vc1 between the collector and the emitter of the IGBT11 gradually increases, and the voltage Vc2 between the collector and the emitter of the IGBT12, that is, the output voltage gradually decreases. The resonance characteristics at this time are determined by the damping capacitors 31 , 32 , the heating coil 5 , and the resonance capacitors 6 , 7 .

Thereafter, 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 flows through the heating coil 5, the resonance capacitors 6 and 7, and the diode 22 as a circulating current. path. At this time, when the drive currents of IGBT11, 12, and 13 are respectively turned off, on, and off, and only IGBT12 is turned on, the resonance current IL5 continues to flow through the diode 22 as long as the polarity of the resonance current IL5 remains unchanged. .

(mode 4)

Next, method 4 following method 3 will be described. In mode 4, first, the drive signals of IGBT11, 12, and 13 are respectively turned off, on, and off, and only IGBT12 is turned on. When the accumulated energy of heating coil 5 becomes zero and the polarity of resonance current IL% changes from positive to negative, resonance current IL5 flows through the paths of resonance capacitors 6 and 7 , heating coil 5 , and IGBT 12 . That is, the resonance characteristics of the 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 , current in the negative direction does not flow in the resonance point variable circuit 30 . In addition, in mode 4, the resonant capacitors 6 and 7 are discharged through the IL5.

(mode 5)

Next, method 5 subsequent to method 4 will be described. In mode 5, first, all the drive signals of IGBT11, 12, and 13 are turned off, and all IGBTs are not turned on. As shown in Figure 6, the resonance current IL5 has a negative polarity in mode 5, and the resonance current IL5 continues to flow through the path of the heating coil 5, the damping capacitor 32, the resonance capacitors 6 and 7, and the heating coil 5 and the damping capacitor 31 , capacitor 4, and resonant capacitors 6 and 7, the upper arm damping capacitor 31 is discharged, and the lower arm damping capacitor 32 is charged. Therefore, the voltage Vc1 between the collector and the emitter of the IGBT11 gradually decreases, and the voltage Vc2 between the collector and the emitter of the IGBT12, that is, the output voltage gradually increases. The resonance characteristics at this time are determined by the damping capacitors 31 , 32 , the heating coil 5 , and the resonance capacitors 6 , 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 flows through the heating coil 5, the diode 21, the capacitor 4, and the resonance capacitor 6 as a circulating current. , 7 paths. At this time, a negative voltage is charged on the resonant capacitor 8. When the negative charging voltage of the resonant capacitor 7 exceeds the charging voltage of the resonant capacitor 8, a positive direction voltage is applied to the diode 23, and the resonance current IL5 is shunted and flows through the diode 23, Paths of resonance capacitors 8, 6, heating coil 5, diode 21, capacitor 4 and resonance capacitors 7, 6, heating coil 5, diode 21, capacitor 4.

At this time, when the driving signals of IGBT11, 12, and 13 are respectively turned on, off, and turned on, and IGBT11 and IGBT13 are turned on together, the resonance current IL5 will continue to flow as long as the polarity of the resonance current IL5 remains unchanged. Diode 21.

As described above, the operations of modes 1 to 5 are performed during one cycle of the resonance current IL5, and the operations are repeated thereafter. As can be seen from the description of the form 2 and the form 4, the IGBTs 11 and 12 are turned off while the currents Ic1 and Ic2 are energized to the IGBTs 11 and 12 . Therefore, the phase difference between the voltage of Vc2 of 0V and the resonance current of IL5 of 0A always operates in a current lagging phase. Thus, in this embodiment, the resonance point variable circuit 30 is provided in parallel with the resonance capacitor to change the resonance characteristics of the load, so that the load can always be operated in a current lagging phase, thereby avoiding the phase advance method.

Next, as a method of further reducing the input power, the on-period of IGBT11 is shortened, and the on-period of IGBT12 is extended. The operation of the inverter at this time will be described in detail using FIG. 15 . As shown in FIG. 15 , one cycle of the IGBTs 11 to 13 is represented by ts, and the on-periods of the IGBTs 11 and 12 are represented by t1 and t2, respectively. IGBT13 is in a normally-on state. In addition, one cycle of the resonance current IL5 is divided into patterns 1 to 4 and shown.

(mode 1)

As shown in FIG. 15 , in method 1, the drive signals of IGBT11, 12, and 13 are turned on, off, and turned on, respectively, and IGBT11, 13 is turned on. When the accumulated 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 flows through the path of the IGBT11, the heating coil 5, the resonant capacitor 6, 7 and the IGBT11, the heating coil 5, and the resonant capacitor 6 , 8, the path of IGBT13. That is, the resonance characteristic of the form 1 is determined by the IGBT 11 , the heating coil 5 , and the resonance capacitors 6 , 7 , and 8 . In addition, in the mode 1, the resonance capacitors 6, 7, and 8 are discharged by the resonance current IL5.

(method 2)

Next, method 2 following method 1 will be described. In the mode 2, the drive signals of IGBT11, 12, and 13 are turned off, off, and on, respectively, and only IGBT13 is turned on. As shown in Figure 15, the resonance current IL5 has a positive polarity in mode 2, and the resonance current IL5 continues to flow through the damping capacitor 31, the heating coil 5, the paths of the resonance capacitors 6 and 7, and the damping capacitor 31 and the heating coil 5. , the path of resonance capacitor 8, IGBT13 and damping capacitor 32, heating coil 5, the path of resonance capacitor 6, 7 and the path of damping capacitor 32, heating coil 5, resonance capacitor 8, IGBT13, the damping capacitor 31 of the upper arm is charged , the damping capacitor 32 of the lower arm is discharged. Therefore, the voltage Vc1 between the collector and the emitter of the IGBT11 gradually increases, and the voltage Vc2 between the collector and the emitter of the IGBT12, that is, the output voltage gradually decreases. The resonance characteristics at this time are determined by the damping capacitors 31 , 32 , the heating coil 5 , and the resonance capacitors 6 , 7 , and 8 .

Thereafter, 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 flows through the heating coil 5, the resonance capacitors 6 and 7, and the diode 22 as a circulating current. Path and path of heating coil 5, resonant capacitor 8, diode 22. At this time, even if the drive currents of IGBT11, 12, and 13 are respectively turned off, on, and turned on, and IGBT12 is turned on, resonance current IL5 continues to flow through diode 22 as long as the polarity of resonance current IL5 remains unchanged.

(mode 3)

Next, method 3 following method 2 will be described. In mode 3, the drive signals of IGBT11, 12, and 13 are respectively turned off, on, and turned on, and IGBT12, 13 is turned on. When the accumulated 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 paths of the resonance capacitors 7 and 6, the heating coil 5, and the IGBT12 and the paths of the resonance capacitors 8 and 6 and the heating coil. 5. The path of IGBT12 and diode 23. That is, the resonance characteristics of the mode 4 are determined by the IGBT 12 , the heating coil 5 , and the resonance capacitors 6 , 7 , and 8 . In addition, resonance capacitors 6, 7, 8 are discharged through IL5.

(mode 4)

Next, method 4 following method 3 will be described. In mode 5, first, the drive signals of IGBT11, 12, and 13 are turned off, off, and on, and only IGBT13 is turned on. As shown in Figure 15, the resonance current IL5 has a negative polarity in mode 4, and the resonance current IL5 continues to flow through the path of the heating coil 5, the damping capacitor 32, the resonance capacitors 7 and 6, and the heating coil 5 and the damping capacitor 32. , diode 23, path of resonance capacitor 8, 6 and heating coil 5, damping capacitor 31, capacitor 4, path of resonance capacitor 7, 6 and heating coil 5, damping capacitor 31, capacitor 4, diode 23, resonance capacitor 8 , 6, the upper arm damping capacitor 31 is discharged, and the lower arm damping capacitor 32 is charged. Therefore, the voltage Vc1 between the collector and the emitter of the IGBT11 gradually decreases, and the voltage Vc2 between the collector and the emitter of the IGBT12, that is, the output voltage gradually increases. The resonance characteristics at this time are determined by the damping capacitors 31 , 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 flows through the heating coil 5, the diode 21, the capacitor 4, and the resonance capacitor 7 as a circulating current. , 6 paths. At this time, a negative voltage is charged to the resonant capacitor 8. When the negative charging voltage of the resonant capacitor 7 exceeds the charging voltage of the resonant capacitor 8, a positive direction voltage is applied to the diode 23, and the resonance current IL5 shunts and flows through the diode 23 and the resonant capacitor. 8, 6, the path of heating coil 5, diode 21, capacitor 4 and the path of resonant capacitor 7, 6, heating coil 5, diode 21, capacitor 4.

At this time, when the driving signals of IGBT11, 12, and 13 are respectively turned on, off, and turned on, and IGBT11 and 13 are turned on together, the resonance current IL5 will continue to flow as long as the polarity of the resonance current IL5 remains unchanged. Diode 21.

As described above, the operations of modes 1 to 4 are performed during one cycle of the resonance current IL5, and the operations are repeated thereafter. In the normally-on state of the resonance point variable circuit 30, as can be seen from the description of methods 1 and 4, even if the conduction period t2 of the IGBT12 is prolonged, the resonance current IL5 changes from negative to negative during the conduction period of the diode 21 or 22. just. Therefore, the resonant current IL5 does not reverse the polarity from negative to positive, the load characteristic remains inductive, and the phase advance method can be avoided.

Thus, by changing the period of the switching circuit 20, it is possible to control the input electric power.

In addition, the current flowing into the resonant capacitor 8 is determined by the capacity ratio of the resonant capacitor 7 and the resonant capacitor 8 . In this embodiment, since the capacity of resonance capacitor 7 ≥ the capacity of resonance capacitor 8 , the current flowing into resonance capacitor 8 is equal to or less than resonance capacitor 7 . This reduces the occurrence of losses in IGBT 13 and improves the withstand current performance of IGBT 13 .

In addition, the voltage ( Vc4 ) generated in resonance capacitor 7 is determined by the capacity of resonance capacitor 6 and the capacity of resonance capacitor 8 . Therefore, in order to reduce the voltage generated in the resonant capacitor 7, the capacity of the resonant capacitor 7 ≥ the capacity of the resonant capacitor 6 is set so that the generated voltage of the resonant capacitor 7 becomes 1/2 or less. Accordingly, it is possible to reduce the occurrence of losses in the IGBT 13 and improve the withstand voltage performance of the IGBT 13 , and to set a wide range of variable resonance points.

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

【Mathematical formula 2】

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="5"\; label="Vc"\; filenames="HSA00000018828900031.png,HSA00000018828900032.png"\; state="\{\{state\}\}">Vc</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; \&infin;</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="5"\; label="IL"\; filenames="HSA00000018828900031.png,HSA00000018828900032.png"\; state="\{\{state\}\}">IL</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 8</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="7"\; label="C"\; filenames="HSA00000018828900011.png,HSA00000018828900022.png"\; state="\{\{state\}\}">C</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 7</span>}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

C7: capacity of resonance capacitor 7, C8: capacity of resonance capacitor 8

In this embodiment, since C8<C7, the voltage of Vc5 is charged to a voltage lower than that of C7. The total voltage of Vc4 and Vc5 is applied to IGBT13, but since the voltage charged to Vc5 is low, it has no influence on the increase of the element withstand voltage of IGBT13.

Next, a method of controlling input power will be described using FIG. 7 . As already described in FIG. 6 , the conduction periods of the IGBTs 11 , 12 , and 13 are represented by t1 , t2 , and t3 , and the drive period is represented by ts. Fig. 7 shows an example of the control conditions in the case of heating the object to be heated made of iron and non-magnetic stainless steel with an inverter drive frequency of 21kHz and high output. Indicates the input voltage Pin. Here, the case where t1 and t2 are kept constant and t3 is changed to control the input voltage Pin will be described.

As shown in FIG. 7 , in the case of an iron-made object to be heated, the maximum input power is obtained when the duty of IGBT13 is 0 (the IGBT13 is in a normally-off state). When Duty increases, the input power Pin decreases, and when Duty=about 0.5 or more, the input power Pin is substantially constant. On the other hand, in non-magnetic stainless steel, the maximum power is 3 kW at Duty=0.45 of IGBT13, and the input power decreases by further increasing Duty, and becomes almost constant at Duty=0.7 or more. From this, it can be seen that the input power Pin can be reduced by increasing the Duty of the IGBT 13 .

Next, the reason why the input electric power can be controlled by controlling the duty of the IGBT 13 will be described. When the IGBT 13 is turned on, since the resonance capacitor 7 and the resonance capacitor 8 are connected in parallel, 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 is a graph showing resonance characteristics when the Duty of the IGBT 13 is changed when an iron object is heated. As shown in FIG. 8 , when t3 is extended to increase the duty of IGBT 13 , the resonance frequency decreases. Therefore, for example, when the inverter drive frequency is fixed at 21kHz, the input power is about 3kW when Duty=0, about 1.5kW when Duty=0.35, and about 0.5kW when Duty=0.5. By controlling the conduction time of t3 (the duty of the IGBT13) in this way, it is possible to control the input power.

As mentioned above, when the Duty of IGBT13 becomes about 0.5 or more, input electric power Pin becomes constant at about 0.5 kW. This is because, during the t3 period when the IGBT13 is turned on, the resonance current IL5 changes from positive to negative, and the current flows into the diode 23, exceeding the variable range of the resonance point variable circuit 30 under the Duty of the IGBT13. Actually, the period in which the resonance current can be controlled by the resonance point variable circuit 30 is the period in which the resonance current IL5 is positive. Therefore, while the resonance current IL5 is negative, the resonance point cannot be controlled even if the duty of the IGBT 13 is controlled. Therefore, in FIG. 7 , the lower limit value of the input power Pin that can be adjusted only by t3 without changing t1 and t2 is about 0.5 kW. To set it below this value, t1 and t2 need to be changed.

Next, a case where the input power Pin is controlled by changing t1 and t2 while making the Duty of the IGBT 13 approximately 0.5 or more will be described. 9 shows the control conditions for heating the object to be heated with a low output. The horizontal axis shows the conduction ratio (=t1/ts) of the conduction period t1 of the upper arm IGBT11 with respect to the drive period ts. At this time, the conduction ratio of the IGBT12 It is 1-Duty. The vertical axis represents the input electric power Pin. As shown in FIG. 9 , by reducing the Duty of the IGBT 11 while making the Duty of the IGBT 13 in the resonance point variable circuit 30 approximately 0.5 or more, the input power Pin can be further reduced. .

On the other hand, in non-magnetic stainless steel, as shown in FIG. 14 , since the inductance value becomes 2/3 compared with iron, the resonance frequency of the series circuit with the resonant capacitors 6 and 7 rises and becomes higher than that of the switching circuit 20. The drive frequency is high, the load characteristic becomes capacitive, and the phase lead method becomes. Therefore, it is necessary to increase the conduction period of the resonance point variable circuit 30 to lower the resonance point and make the load characteristic inductive. As for the control method of the input power, it can be controlled by the Duty of IGBT13 and the Duty of IGBT11 like the iron to-be-heated object.

[Example 3]

Fig. 10 is a circuit configuration diagram of the electromagnetic induction heating device of the third embodiment. Among the configurations of the third embodiment, descriptions of the same configurations as those already described in the previous embodiments are omitted.

In FIG. 10 , a resonant circuit 60 constituted by the heating coil 5 and the resonant capacitors 6 and 7 is connected between the output terminals t and o of the first inverter 100 . The resonant point variable circuit 30 is connected in parallel to the resonant capacitor 7. The resonant point variable circuit 30 is composed of a resonant capacitor 8 connected in series, a diode 25 for preventing reverse current, an IGBT13, and a diode 23 connected in parallel with the IGBT13 in the opposite direction. Here, when the resonance current IL5 flowing from the output terminal t toward the resonance capacitor 6 is positive, the current Ic3 flowing into the resonance point variable circuit 30 is positive. In this embodiment, the voltage applied to IGBT 13 becomes the charging voltage of resonance capacitor 7 in order to prevent negative voltage from being charged to resonance capacitor 8 . Therefore, the resonant capacitor 8 is not charged with a negative voltage, and the withstand voltage can be reduced. In general, the conduction loss can be reduced when the withstand voltage of the IGBT is lowered. Thereby, element loss can be reduced.

【Example 4】

FIG. 11 is a part of the circuit of the electromagnetic induction heating device of the fourth embodiment. Among the configurations of the fourth embodiment, descriptions of the same configurations as those already described in the previous embodiments are omitted.

In FIG. 11, the switching element of the resonance point variable circuit 30 is a reverse current blocking type IGBT4 (IGBT with a reverse voltage function) with a reverse withstand voltage. The diode 25 is replaced by an IGBT14 structure. In the resonance point variable circuit 30 of FIG. 10 described above, losses occur in the IGBT 13 and the diode 25 respectively, but in this embodiment, since the loss amount is the IGBT 14, the circuit loss in the first inverter 100 is reduced. , which improves the conversion efficiency. The operation of this embodiment is the same as that of the third embodiment described above, and description thereof will be omitted.

【Example 5】

Fig. 12 is a part of the circuit of the electromagnetic induction heating device of the fifth embodiment. Among the configurations of the fifth embodiment, descriptions of the same configurations as those already described in the previous embodiments are omitted.

In FIG. 12 , the difference from Embodiment 3 is that since IGBT 15 is connected in parallel to diode 25 of resonance point variable circuit 30 , positive and negative currents can be controlled in resonance point variable circuit 30 . In this embodiment, by driving the IGBTs 13 and 15, the positive and negative currents flowing into the resonance point variable circuit 30 can be controlled, and the resonance frequency can be varied at the resonance point while maintaining the load characteristic of the resonance circuit 60 as inductive. The positive and negative directions of the current IL5 control the IGBT 13 or 15 to change the input power. Regarding the control method, IGBT 13 performs duty control of IGBT 13 by synchronizing its on timing with IGBT 11 as in the above-mentioned second embodiment, and IGBT 15 performs duty control of IGBT 15 by synchronizing its on timing with IGBT 12 . When the resonance current IL5 is a positive current, the IGBT13 is controlled, and when the resonance current IL5 is a negative current, the IGBT15 is controlled. Accordingly, since the resonance point can be changed between the positive and negative periods of the resonance current IL5, the power control range can be expanded.

[Example 6]

Fig. 13 is a part of the circuit of the electromagnetic induction heating device of the sixth embodiment. Among the configurations of the sixth embodiment, descriptions of the same configurations as those already described in the previous embodiments are omitted.

In FIG. 13 , a resonance point variable circuit 30 is connected in antiparallel with reverse current blocking type IGBT14 and IGBT16 having reverse withstand voltage. In the above-mentioned variable resonance point circuit 30 of FIG. 12 , since a forward current flows into the diode 25 and the IGBT 13 and a negative current flows into the diode 23 and the IGBT 15 , a loss occurs in each of the diode and the IGBT. In this embodiment, since the losses of IGBT14 and IGBT16 are used, 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 described above, and description thereof is omitted.

Claims (13)

1. electromagnetic induction heater, it has DC power supply, be the dc voltage conversion by this direct-current power supply the inverter circuit and the control circuit of high-frequency ac voltage, it is characterized in that,

Described inverter circuit has switching circuit, resonant circuit and resonance point adjusted circuit;

Described switching circuit, the formation that is connected in series of the power semiconductor switch element by power semiconductor switch element that connect, upper arm and underarm on the two-terminal of described DC power supply;

Series connection heater coil and first resonating capacitor and second resonating capacitor and the described resonant circuit that forms, an end are connected on the tie point of the upper arm of described switching circuit and underarm, and the other end is connected on some terminals of described DC power supply;

The described resonance point adjusted circuit in parallel with described second resonating capacitor, the series connection by the 3rd resonating capacitor and first switch element and form with first diode of the described first switch element reverse parallel connection;

Make the resonance frequency of described resonant circuit variable by the conduction period of controlling described first switch element by described control circuit.

2. electromagnetic induction heater according to claim 1 is characterized in that,

Described resonance point adjusted circuit has second diode that is connected in series with first switch element, and described first switch element has first diode with its reverse parallel connection.

3. electromagnetic induction heater according to claim 1 is characterized in that,

Described resonance point adjusted circuit has first switch element of subsidiary anti-back-pressure function.

4. electromagnetic induction heater according to claim 2 is characterized in that,

Have the second switch element in parallel with described second diode reverse.

5. electromagnetic induction heater according to claim 1 is characterized in that,

Described resonance point adjusted circuit has first, second switch element reverse, subsidiary anti-back-pressure function.

6. electromagnetic induction heater according to claim 1 is characterized in that,

Described switching circuit has at least one side vibration damping capacitor in parallel in the power semiconductor switch element with the power semiconductor switch element of described upper arm and described underarm.

7. electromagnetic induction heater according to claim 1 is characterized in that,

The capacity of described second resonating capacitor is more than the capacity of described first resonating capacitor, and the capacity of described the 3rd resonating capacitor is below the capacity of described second resonating capacitor.

8. electromagnetic induction heater, it is used for the induction heating heating object, it is characterized in that,

Have:

Power circuit from positive electrode and negative electrode supply direct voltage;

Be connected between the positive electrode of this power circuit and the negative electrode, be dc voltage conversion the switching circuit of exporting behind the alternating voltage;

Be connected between the terminal of the lead-out terminal of this switching circuit and described power circuit, with the resonant circuit that is connected in series and constitutes of heater coil and first resonating capacitor and second resonating capacitor; With

With the variable resonance point adjusted circuit of described second resonating capacitor resonance point in parallel, that make described resonant circuit.

9. electromagnetic induction heater according to claim 8 is characterized in that,

Described resonance point adjusted circuit, being connected in series and constituting with the 3rd resonating capacitor and switch element with the diode of the reverse parallel connection of this switch element.

10. electromagnetic induction heater according to claim 9 is characterized in that,

From the polarity of described switching circuit, the switch element conduction period in described resonance point adjusted circuit, just become from negative towards the mobile resonance current of described heater coil.

11. electromagnetic induction heater according to claim 9 is characterized in that,

By controlling the Duty of the switch element in the described resonance point adjusted circuit, the input electric power of heating object is supplied with in control from described control circuit.

12. electromagnetic induction heater according to claim 9 is characterized in that,

The capacity that makes described second resonating capacitor is more than the capacity of described first resonating capacitor.

13. electromagnetic induction heater according to claim 9 is characterized in that,

The capacity that makes described second resonating capacitor is more than the capacity of described the 3rd resonating capacitor.

Images