JP3831298B2 - Electromagnetic induction heating device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic induction heating apparatus having a plurality of heating units.
[0002]
[Prior art]
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.
[0003]
Conventionally, electric cookers incorporated in 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.
[0004]
As an example of a conventional technique for solving such a problem, there is an induction heating cooker as disclosed in Japanese Patent No. 2532565. This cooker controls input power by changing the conduction period of the switching element at a constant driving frequency.
[0005]
[Problems to be solved by the invention]
In the above conventional example, since the input power can be changed at the same drive frequency even when a plurality of inverters are operated, the generation of interference sound can be prevented. However, when driving with low power, there is a problem that the loss generated in one switching element increases.
[0006]
An object of the present invention is to provide an electromagnetic induction heating device that controls the input power by suppressing the occurrence of loss of switching elements and preventing the generation of interference sound when a plurality of inverters are driven simultaneously.
[0007]
[Means for Solving the Problems]
The electromagnetic induction heating device of the present invention includes an inverter circuit that converts a DC voltage into a high-frequency AC voltage, the inverter circuit including a switching circuit and a resonance circuit, and the resonance circuit is connected in series to the heating coil and the heating coil. The resonance circuit is connected between one of both terminals (p / o) of the DC power supply and the output terminal (t) of the switching circuit, and is connected in parallel to the resonance capacitor. It has a bypass circuit
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
FIG. 1 is a block diagram of an electromagnetic induction heating apparatus according to the first embodiment of the present invention. In FIG. 1, the inverter 100 includes a switching circuit 20, a heating coil 5, a resonance circuit 60 including a resonance capacitor 6, and a bypass circuit 30.
[0009]
The switching circuit 20 is connected between the positive electrode p point and the negative electrode o point of the power supply 10, converts the voltage supplied from the power supply 10 into a high frequency voltage, applies it to the resonance circuit 60, and applies it to the heating coil 5. Supply high frequency power. The bypass circuit 30 is connected in parallel to the resonance capacitor 6, and controls the load characteristic of the resonance circuit 60 by bypassing the current flowing through the resonance capacitor 6. In general, in a resonance type inverter, the drive frequency fs is set to be higher than the resonance frequency fr so that the characteristic of the resonance load is inductive, and the current flowing through the resonance circuit is delayed in phase with respect to the output voltage of the inverter. To control. In FIG. 1, control is performed so that the current IL <b> 5 flowing through the resonance circuit 60 has a delayed phase with respect to the voltage at the connection point t between the switching circuit 20 and the resonance circuit 60.
[0010]
However, when power control is performed by changing the conduction period of the switching element with the driving frequency fs constant, the polarity of the current is inverted during the conduction period of the switching circuit 20 and the phase shifts to the phase advance mode in which the current advances from the output voltage. If you do. This is a mode that must be avoided in a resonance type inverter because it increases the loss of the switching circuit 20. In the present invention, the load characteristic of the resonance circuit 60 is controlled by controlling the voltage of the resonance capacitor by changing the conduction state of the bypass circuit according to the material and state of the object to be heated and the magnitude of the set input power. It can be maintained inductive. That is, the resonance frequency of the resonance circuit 60 can always be lower than the drive frequency of the switching circuit 20.
[0011]
As a result, the inverter 100 can control the input power by changing the conduction period of the switching circuit 20 while keeping the drive frequency fs constant. Thus, the bypass circuit 30 serves as an auxiliary switching circuit for realizing an operation at a constant drive frequency fs. The switching circuit 20 and the bypass circuit 30 are driven by drive circuits 61 and 62, respectively, and the drive circuits 61 and 62 are controlled by a control circuit 70. The input power setting unit 75 is an interface for the user to set input power, and sends a signal to the control circuit 70 according to the set output. The control circuit 70 controls the switching circuit 20 and the bypass circuit 30 according to the signal from the input power setting unit 75.
[0012]
(Example 2)
FIG. 2 is a circuit configuration diagram of an electromagnetic induction heating device according to the second embodiment of the present invention. In FIG. 2, a power source 10 includes a rectifier circuit 2 that rectifies an AC voltage of a commercial power source 1, a smoothing circuit including an inductor 3 and a capacitor 4, converts the AC voltage into a DC voltage, and supplies power to the inverter 100. . Between the positive electrode p point and the negative electrode o point of the capacitor 4, IGBT 11 and IGBT 12, which are power semiconductor switching elements, are connected in series to constitute a switching circuit 20. Diodes 21 and 22 are connected in parallel to the IGBTs 11 and 12 in opposite directions, respectively.
[0013]
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. When a connection point of the IGBTs 11 and 12, that is, an output terminal is a t point, a resonance circuit 60 constituted by the heating coil 5 and the resonance capacitor 6 is connected between the t point and the o point.
[0014]
A bypass circuit 30 is connected in parallel to the resonant capacitor 6, and the bypass circuit 30 includes a diode 25 that blocks reverse current of the IGBT 13 and the IGBT 13 connected in series and a diode 23 connected in parallel to the IGBT 13 in the reverse direction. Has been. Here, if the resonance current IL5 flowing from the point t toward the resonance capacitor 6 is positive, the bypass current Ic3 flowing in the bypass circuit 30 is in one negative direction. In this embodiment, when the input power is reduced, the conduction period of the upper arm is reduced and the conduction period of the lower arm is extended, so that the polarity of the resonance current IL5 is easily reversed from negative to positive during the conduction period of the lower arm. Therefore, when the resonance current IL5 flows in the negative direction, the polarity of the resonance current IL5 can be prevented from being reversed from negative to positive by flowing the bypass current Ic3.
[0015]
The switching circuit 20 and the bypass circuit 30 are driven by drive circuits 61 and 62, respectively, and the drive circuits 61 and 62 are controlled by a control circuit 70. In the present embodiment, by connecting the resonant capacitor 6 to the t point side of the inverter 100, the IGBT 13 of the bypass circuit 30 can be driven based on the t point. Therefore, the power supply of the drive circuit 62 can be shared with the power supply of the drive circuit 61 that drives the IGBT 11.
[0016]
The current detection element 71 detects a current flowing through the resonance circuit, and 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 (current detection means) detects a current input from the commercial power supply 1, and the input current detection circuit 74 changes the output signal level of the current detection element 73 to a signal suitable for the input level of the control circuit 70. Convert. The control circuit 70 determines the material and state of the object to be heated from the relationship between the input current and the resonance current, and starts or stops the heating operation.
[0017]
Further, according to the signal from the input power setting unit 75, the conduction periods of the IGBTs 11 and 12 of the switching circuit 20 and the IGBT 13 of the bypass circuit 30 are set to control 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, in the initial stage of material detection, by setting the bypass circuit 30 to the conductive state, the impedance of the resonance circuit can be increased, and the occurrence of overcurrent and overvoltage and the sudden increase in input power can be prevented.
[0018]
Next, the operation of this embodiment will be described with reference to FIG. 2 and 3, 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 bypass 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 resonance voltage of the resonance capacitor 6 is Vc3, and the power supply voltage of the inverter is Vp.
[0019]
(Mode 1) In FIG. 3, when the drive signal of the IGBT 11 is turned on and the accumulated energy of the heating coil 5 becomes zero, the polarity of the resonance current IL5 changes from negative to positive, and the path of the IGBT 11, the resonance capacitor 6, and the heating coil 5 A resonance current IL5 flows. The resonant capacitor C6 is discharged by the resonant current IL5, and Vc3 decreases.
(Mode 2) Next, when the drive signal of the IGBT 11 is turned off, the resonance current IL5 has a positive polarity. This current is applied to the snubber capacitor 31, the resonance capacitor 6, the path of the heating coil 5, the snubber capacitor 32, and the resonance. It continues to flow through the path of the capacitor 6 and the heating coil 5, and the upper arm snubber capacitor 31 is charged and the lower arm snubber capacitor 32 is discharged.
[0020]
Therefore, 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. 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 as a circulating current through the path of the heating coil 5, the diode 22, and the resonance capacitor 6. to continue. During this period, the drive signals of the IGBTs 12 and 13 are turned on, but continue to flow through the diode 22 as long as the polarity of the current does not change.
[0021]
(Mode 3) Next, 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 IGBT 12 is already turned on, so that the resonance current IL5 is supplied to the heating coil 5, the resonance capacitor 6, The resonance capacitor 6 is charged by the IL 5 through the path of the IGBT 12.
[0022]
(Mode 4) When the voltage Vc3 increases and a forward voltage is applied to the diode 25 of the bypass circuit 30, since the IGBT 13 is already turned on, the resonance current IL5 is applied to the heating coil 5, the diode 25, the IGBT 13, and the IGBT 12. It flows through the path, and charging of the resonant capacitor 6 is temporarily stopped.
[0023]
(Mode 5) Next, when the drive signal of the IGBT 13 is turned off, the resonance current IL5 flows again through the path of the heating coil 5, the resonance capacitor 6, and the IGBT 12, and the resonance capacitor 6 starts to be charged by IL5.
[0024]
(Mode 6) Next, when the drive signal of the IGBT 12 is turned off, the resonance current IL5 has a negative polarity. This current is applied to the heating coil 5, the resonance capacitor 6, the path of the snubber capacitor 31, the heating coil 5, and the resonance. It continues to flow through the path of the capacitor 6 and the snubber capacitor 32, the upper arm snubber capacitor 31 is discharged, and the lower arm snubber capacitor 32 is charged. Therefore, the voltage Vc1 between the collector and emitter of the IGBT 11 gradually decreases, and the voltage Vc2 between the collector and emitter of the IGBT 12, that is, the output voltage gradually increases. After that, 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 as a circulating current through the path of the heating coil 5, the resonance capacitor 6, and the diode 21. to continue. During this period, the drive signal of the IGBT 11 is turned on, but continues to flow through the diode 21 as long as the polarity of the current does not change.
[0025]
As described above, the above operation is performed during one period of the resonance current IL5, and thereafter this operation is repeated. Thus, in this embodiment, the phase advance mode can be avoided by providing the bypass circuit 30 in parallel with the resonance capacitor 6 and maintaining the load characteristics inductive. As a result, the input power can be controlled by changing the conduction period of the switching circuit 20.
[0026]
Next, a method for controlling the input power will be described. In FIG. 3, the conduction periods of the IGBTs 11, 12, and 13 are represented by t1, t2, and t3, and one period of the resonance current, that is, the drive period is represented by ts. FIG. 4 shows the control conditions when a material to be heated, for example, made of iron, is heated at a high output. The horizontal axis represents the conduction period t3 of the IGBT 13, and the vertical axis represents the input power Pin. Here, a case where t1 and t2 are not changed and t3 is changed to control the input power Pin will be described. From FIG. 4, it is possible to reduce the input power Pin by increasing t3. This is because the voltage amplitude value Vcp of the resonance voltage Vc3 decreases as t3 increases from FIG. 3, and the voltage applied to the heating coil 5 decreases, so that the resonance current IL5 decreases. The input power Pin becomes constant at about 1.1 kW when t3 is about 25 μs or more. This is because the voltage Vc3 of the resonance capacitor 6 changes from negative to positive during the period when the resonance current actually flows through the bypass circuit 30 during the period t3 when the IGBT 13 is on, and the forward voltage is applied to the diode 25 of the bypass circuit 30. This is because it is limited to a period from when the voltage is applied until the polarity of the resonance current is reversed from negative to positive while the IGBT 13 is on.
[0027]
Therefore, the lower limit value of the input power Pin that can be adjusted only by t3 without changing t1 and t2 in FIG. 4 is about 1.1 kW, and when set below this value, t1 and t2 are changed.
[0028]
Next, a case where the input power Pin is controlled by changing t1 and t2 by setting t3 to about 25 μs or more will be described. FIG. 5 shows the control conditions when the object to be heated is heated at a low output. The horizontal axis is Duty (= t1 / ts) indicating the conduction ratio of the upper arm conduction period t1 with respect to the driving cycle ts, and the vertical axis is It represents the input power Pin. As shown in FIG. 5, the input power Pin can be changed by changing the duty by setting the bypass circuit 30 to the conductive state. In this embodiment, when the duty is reduced and the input power is reduced, the switching circuit 20 may generate a turn-on loss.
[0029]
Next, the conditions under which turn-on loss occurs will be described with reference to FIG. In FIG. 6, when the IGBT 12 is turned off at the time of toff, the snubber capacitors 31 and 32 are discharged and charged by the cutoff current Ioff, respectively.
[0030]
However, if Ioff is small, the voltage rise of the voltage of the snubber capacitor 32, that is, the voltage Vc2 of the IGBT 12, is delayed. When the IGBT 11 is turned on after the dead time td of the IGBTs 11 and 12 elapses, Vc2 is lower than the power supply voltage Vp of the inverter, so that the IGBT 11 has a large current for discharging and charging the snubber capacitors 31 and 32, respectively. Flow, turn-on loss occurs. Similarly, even when the cutoff current of the IGBT 11 is small, a large current for charging / discharging the snubber capacitors 31 and 32 flows when the IGBT 12 is turned on, and a turn-on loss occurs.
[0031]
Therefore, when the input power is made lower than the desired power, the minimum value of Duty is set, the inverter is driven for several seconds, and then the input power is controlled by switching to intermittent control for stopping the inverter for several seconds. However, in the intermittent control, power larger than desired power is input when the inverter is driven, and it becomes impossible to always heat the object to be heated at a constant temperature. In this embodiment, as shown in FIG. 2, since the snubber capacitors 31 and 32 are always connected to the switching circuit 20, a turn-on loss may occur when heating at a low output.
[0032]
Example 3
FIG. 7 is a circuit configuration diagram of an electromagnetic induction heating device according to the third embodiment of the present invention. The same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted. 7 is different from the second embodiment in that a snubber capacitor switching circuit 40 in which a snubber capacitor 33 and an IGBT 14 are connected in series is connected between a point t and an o point of the inverter 100, and the snubber capacitor is turned off by turning off the IGBT 14. The point 33 can be separated from the switching circuit 20. A diode 24 is connected to the IGBT 14 in parallel in the reverse direction, and is used when discharging the charge of the snubber capacitor 33. The IGBT 14 is driven by a drive circuit 63, and the drive circuit 63 is controlled by a control circuit 70.
[0033]
Next, the operation of this embodiment will be described with reference to FIG. In FIG. 8, when the IGBT 12 is turned off at the time of toff, the output capacitance (not shown) between the collectors and emitters of the IGBTs 11 and 12 is discharged and charged by the cutoff current Ioff, respectively. Here, even if Ioff is small, the output capacitance of the IGBTs 11 and 12 is small, so that the voltage rise of the voltage Vc2 of the IGBT 12 is fast, and the time tr required for Vc2 to reach the power supply voltage Vp of the inverter is shorter than the dead time td. Become. When a forward voltage is applied to the parallel diode 21 of the IGBT 11, a reflux current flows through the diode 21, and the IGBT 11 is turned on at the time of ton, which is a reflux period. Therefore, zero volt switching can be realized at turn-on, and turn-on loss can be eliminated even when the cutoff current is small.
[0034]
Therefore, even when the output is low, the inverter can be continuously driven without stopping the driving of the inverter as in the intermittent control, and the object to be heated can be always heated at a constant temperature.
[0035]
On the other hand, when heating is performed at a high output, the capacitor 33 is connected between the point t and the point o of the inverter 100 by turning on the IGBT 14, and the voltage applied to both IGBTs at the time of turn-off as in the second embodiment. Changes are reduced and turn-off losses are suppressed. In FIG. 7, even if the snubber capacitor 33, the IGBT 14, and the diode 24 are connected to the IGBT 11 of the upper arm, the above-described effects can be obtained.
[0036]
Example 4
FIG. 9 is a circuit configuration diagram of an electromagnetic induction heating device according to the fourth embodiment of the present invention. The power supply 10 and the switching circuit 20 are omitted, and only the bypass circuit 30 and the resonance circuit 60 are shown. Also, the same parts as those in FIG.
[0037]
In FIG. 9, the resonance circuit 60 constituted by the heating coil 5 and the resonance capacitor 6 is connected between the p point and the t point of the inverter 100. A bypass circuit 30 is connected in parallel to the resonant capacitor 6, and the bypass circuit 30 includes a diode 25 that blocks reverse current of the IGBT 13 and the IGBT 13 connected in series and a diode 23 connected in parallel to the IGBT 13 in the reverse direction. Has been. Here, when the resonance current IL5 flowing from the point p toward the resonance capacitor 6 is positive, the bypass current Ic3 flowing in the bypass circuit 30 is in one negative direction. In this embodiment, when lowering the input power, the conduction period of the lower arm is extended to extend the conduction period of the upper arm, and therefore the polarity of the resonance current IL5 is easily reversed from negative to positive during the conduction period of the upper arm.
[0038]
Therefore, when the resonance current IL5 flows in the negative direction, the polarity of the resonance current IL5 can be prevented from being reversed from negative to positive by flowing the bypass current Ic3. In this embodiment, the IGBT 13 of the bypass circuit 30 is driven based on the point p, and the drive circuit of the bypass circuit 30 needs to provide a new drive power supply separately from the drive circuit 61 of the switching circuit 20.
[0039]
The operation of this embodiment is the same as that of the second embodiment except that the control of the upper and lower arms in the second embodiment is reversed.
[0040]
(Example 5)
FIG. 10 is a part of a circuit of an electromagnetic induction heating apparatus according to the fifth embodiment of the present invention. The power supply 10 and the switching circuit 20 are omitted, and only the bypass circuit 30 and the resonance circuit 60 are shown. Also, the same parts as those in FIG. 10, the switching element of the bypass circuit 30 is a reverse current blocking IGBT 16 having a reverse breakdown voltage, and the IGBT 13 and the reverse current blocking diode 25 of FIG. 2 are replaced with one IGBT 16. Become. In the bypass circuit 30 of FIG. 2, losses occur in the IGBT 13 and the diode 25, respectively, but in this embodiment, the loss is in the IGBT 16, so that the circuit loss in the inverter 100 is reduced and the conversion efficiency is improved. The operation of this embodiment is the same as that of the second embodiment, and a description thereof will be omitted.
[0041]
(Example 6)
FIG. 11 is a part of a circuit of an electromagnetic induction heating apparatus according to the sixth embodiment of the present invention. The power supply 10 and the switching circuit 20 are omitted, and only the bypass circuit 30 and the resonance circuit 60 are shown. Also, the same parts as those in FIG. In FIG. 11, a bypass circuit 30 is connected in parallel to the resonant capacitor 6, and the bypass circuit 30 is configured by an IGBT 18 and a diode 28 connected in parallel to the IGBT 18 in the reverse direction. The difference from the second embodiment is that positive and negative bypass currents flow in the bypass circuit 30. In this embodiment, when the input power is reduced, the conduction period of the upper arm is reduced and the conduction period of the lower arm is extended, so that the polarity of the resonance current IL5 is easily reversed from negative to positive during the conduction period of the lower arm.
[0042]
Therefore, when the resonance current IL5 flows in the negative direction, the polarity of the resonance current IL5 can be prevented from being reversed from negative to positive by causing the bypass current Ic4 to flow through the diode 28.
[0043]
Next, the operation of this embodiment will be described with reference to FIG. In FIG. 12, 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 bypass circuit 30 is Ic4, 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 resonance voltage of the resonance capacitor 6 is Vc4, and the power supply voltage of the inverter is Vp.
[0044]
(Mode 1) In FIG. 12, when the drive signal of the IGBT 18 is turned off while the drive signal of the IGBT 11 is on, the resonance current IL5 flows through the path of the IGBT 11, the heating coil 5, and the resonance capacitor 6, and the resonance capacitor C6 is the resonance current. Charging is started by IL5, and Vc4 increases.
[0045]
(Mode 2) Next, when the drive signal of the IGBT 11 is turned off, the resonance current IL5 has a positive polarity. This current is applied to the snubber capacitor 31, the heating coil 5, the path of the resonance capacitor 6, the snubber capacitor 32, and the heating. It continues to flow along the path of the coil 5 and the resonant capacitor 6, and the upper arm snubber capacitor 31 is charged and the lower arm snubber capacitor 32 is discharged. Therefore, 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. 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 as a circulating current through the path of the heating coil 5, the resonance capacitor 6, and the diode 22. to continue. During this period, the drive signal of the IGBT 12 is turned on, but continues to flow through the diode 22 as long as the polarity of the current does not change.
[0046]
(Mode 3) Next, 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 IGBT 12 is already turned on, and therefore the resonance current IL5 applies the voltage Vc4 of the resonance capacitor 6 to the voltage. The flow Vc4 decreases in the path of the heating coil 5 and IGBT 12 as a source.
[0047]
(Mode 4) When Vc4 decreases and a forward voltage is applied to the diode 28 of the bypass circuit 30, the resonance current IL5 flows through the path of the heating coil 5, the IGBT 12, and the diode 28.
[0048]
(Mode 5) Next, when the drive signal of the IGBT 12 is turned off, the resonance current IL5 has a negative polarity. This current is connected to the diode 28, the heating coil 5, the path of the snubber capacitor 31, the diode 28, and the heating coil 5. The upper arm capacitor 31 is discharged and the lower arm capacitor 32 is charged. Therefore, the voltage Vc1 between the collector and emitter of the IGBT 11 gradually decreases, and the voltage Vc2 between the collector and emitter of the IGBT 12, that is, the output voltage gradually increases. 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 continues to flow through the path of the diode 28, the heating coil 5, and the diode 21 as a circulating current. . The drive signal of the IGBT 18 is turned on with the timing when the IGBT 12 is turned off as a trigger, but continues to flow through the diode 28 as long as the polarity of the resonance current does not change. Similarly, the drive signal of the IGBT 11 is turned on during this circulation period, but continues to flow through the diode 21 as long as the polarity of the resonance current does not change.
[0049]
(Mode 6) Next, when the accumulated energy of the heating coil 5 becomes zero and the polarity of the resonance current IL5 changes from negative to positive, the IGBTs 11 and 18 are already turned on, so that the resonance current IL5 is the IGBT 11, the heating coil 5, It flows along the path of the IGBT 18.
[0050]
As described above, the above operation is performed during one period of the resonance current IL5, and thereafter this operation is repeated. Thus, in this embodiment, the phase advance mode can be avoided by providing the bypass circuit 30 in parallel with the resonance capacitor 6 and maintaining the load characteristics inductive. As a result, the input power can be controlled by changing the conduction period of the switching circuit 20.
[0051]
Next, a method for controlling the input power will be described. In FIG. 12, the conduction periods of the IGBTs 11, 12, and 18 are represented by t1, t2, and t4, and one period of the resonance current, that is, the drive period is represented by ts. In FIG. 12, when t4 is controlled, the voltage amplitude value Vcp of the resonance voltage Vc4 changes. In the above-described mode 3, since the resonance current IL5 in the negative direction flows through the path of the heating coil 5 and the IGBT 12 using the voltage Vc4 of the resonance capacitor 6 as a voltage source, the resonance current IL5 changes according to the magnitude of Vc4. Therefore, the input power Pin can be controlled by changing t4. Further, similarly to the second embodiment, it is also possible to control the input power Pin by changing the conduction periods of t1 and t2, and the conduction period is controlled according to the set input power.
[0052]
(Example 7)
FIG. 13 is a part of a circuit of an electromagnetic induction heating apparatus according to the seventh embodiment of the present invention. The power supply 10 and the switching circuit 20 are omitted, and only the bypass circuit 30 and the resonance circuit 60 are shown. Also, the same parts as those in FIG. 13 is different from the second embodiment in that the IGBT 15 is connected in parallel to the diode 25 of the bypass circuit 30, so that a positive and negative bypass current can flow through the bypass circuit 30. In the sixth embodiment, positive and negative currents flow through the bypass circuit 30, but since the negative direction flows through the diode 28, the current that can be controlled by the IGBT 18 is only in the positive direction. In this embodiment, it is possible to control the positive and negative bypass currents by driving the IGBTs 13 and 15, and while controlling the resonance voltage and the duty of the switching circuit while maintaining the load characteristics of the resonance circuit 60 inductive, the input power change. As for the control method, the IGBT 13 is controlled in the same way as in the second embodiment, and the IGBT 15 is the same as the IGBT 18 in the previous embodiment 6, so that the description is omitted.
[0053]
(Example 8)
FIG. 14 is a part of a circuit of an electromagnetic induction heating apparatus according to the eighth embodiment of the present invention. The power supply 10 and the switching circuit 20 are omitted, and only the bypass circuit 30 and the resonance circuit 60 are shown. Also, the same parts as those in FIG. In FIG. 14, the bypass circuit 30 has a configuration in which reverse current blocking IGBTs 16 and IGBTs 17 having a reverse breakdown voltage are connected in parallel in the reverse direction. In the bypass circuit 30 of FIG. 13, since a positive current flows through the diode 23 and the IGBT 15 and a negative current flows through the diode 25 and the IGBT 13, a loss occurs in each of the diode and the IGBT. In this embodiment, the loss of the IGBT 16 and the IGBT 17 is lost, so that the circuit loss in the inverter 100 is reduced and the conversion efficiency is improved. The operation of this embodiment is the same as that of the seventh embodiment, and a description thereof will be omitted.
[0054]
Example 9
FIG. 15 is a part of a circuit of an electromagnetic induction heating apparatus according to the ninth embodiment of the present invention. The power supply 10 and the switching circuit 20 are omitted, and only the bypass circuit 30 and the resonance circuit 60 are shown. Also, the same parts as those in FIG. In FIG. 15, an IGBT 19 and an auxiliary resonance capacitor 7 connected in series are connected in parallel to the resonance capacitor 6, and a diode 29 is connected in parallel to the IGBT 19 in the reverse direction. The difference from the second embodiment is that the bypass circuit 30 can pass a bypass current via the auxiliary resonant capacitor 7 and the IGBT 19 or the diode 29.
[0055]
As a result, when the IGBT 19 is turned on, the resonant capacitor 6 and the auxiliary resonant capacitor 7 are connected in parallel. Therefore, the resonant frequency of the resonant circuit 60 is lowered, and the inductive load characteristic is easily maintained. In addition, even when an object to be heated made of a low resistance material such as nonmagnetic stainless steel or aluminum becomes a load and the equivalent inductance is reduced, the auxiliary resonant capacitor 7 is made conductive to reduce the resonance frequency. The increase can be suppressed, and the inductive load characteristic can be maintained. The control method of the IGBT 13 is the same as that in the second embodiment, and a description thereof will be omitted.
[0056]
(Example 10)
FIG. 16 is a block diagram of an electromagnetic induction heating apparatus according to the tenth embodiment of the present invention. In FIG. 16, the inverter 100 and the inverter 200 are driven by drive circuits 61, 62, 63 and drive circuits 64, 65, 66, respectively, and each drive circuit is controlled by a control circuit 70. The control circuit 70 includes conduction period setting units 80 and 81 for setting the conduction periods of the switching circuits of the inverters 100 and 200, the bypass circuit and the snubber capacitor switching circuit, and a variable frequency oscillator 82 for setting the drive frequency of the inverter. In the present invention, as shown in FIG. 16, when a plurality of inverters are provided to heat different objects to be heated, each inverter is driven at the same frequency output from the variable frequency oscillator 82 in order to prevent the generation of interference noise. The conduction period setting units 80 and 81 control the conduction period of the switching circuit, the bypass circuit, and the snubber capacitor switching circuit to control the input power.
[0057]
FIG. 17 shows the resonance current IL5 when the oscillation frequency of the variable frequency oscillator 82, that is, the drive frequency fs is controlled to be substantially constant without fluctuation in this embodiment. In FIG. 17, the amplitude value of IL5 changes in accordance with the power supply voltage of the inverter obtained by rectifying and smoothing the commercial AC voltage Vac, and the envelope of IL5 is substantially similar to the power supply voltage of the inverter. In this case, the noise level radiated from the inverter to the outside has a frequency characteristic as shown in FIG. 18, and decreases as the noise level Np at the drive frequency fs becomes the maximum value and becomes higher order harmonics.
[0058]
In this embodiment, by changing the oscillation frequency of the variable frequency oscillator 82 and changing the drive frequency fs, the noise frequency component can be diffused and the noise level can be reduced. FIG. 19 shows the resonance current IL5 when the drive frequency is changed in synchronization with the power supply voltage of the inverter. In FIG. 19, the drive frequency is changed by ± Δfs with reference to fs, and the drive frequency is set to be higher when the inverter power supply voltage is higher, and the frequency is lower when the voltage is lower. Since the resonance type inverter is operated at a drive frequency higher than the resonance frequency, the resonance current decreases when the drive frequency is increased.
[0059]
Therefore, by shifting the drive frequency higher when the power supply voltage of the inverter is high, the resonance current IL5 can be reduced, and when the maximum value of IL5 when the drive frequency is controlled to be constant is Ip, FIG. As shown, the maximum value of IL5 can be reduced from Ip to Id. On the other hand, when the power supply voltage of the inverter is low, the drive frequency is shifted lower, so that the resonance current IL5 can be increased, and IL5 can be increased as compared with the case where the drive frequency is controlled to be constant. In this case, the noise level radiated to the outside from the inverter has frequency characteristics as shown in FIG. 20, and the maximum noise level near the driving frequency fs is set to a level from Np to Nd, compared to the case where the driving frequency is controlled to be constant. Can be reduced.
[0060]
【The invention's effect】
According to the present invention, the resonance capacitor is provided with a bypass circuit to bypass a part of the resonance current, so that the load characteristic of the resonance circuit can be maintained inductive, the input power can be controlled by duty control, and switching The occurrence of element 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.
[Brief description of the drawings]
FIG. 1 is a block diagram of an electromagnetic induction heating device according to a first embodiment of the present invention.
FIG. 2 is a circuit configuration diagram of an electromagnetic induction heating device according to a second embodiment of the present invention.
FIG. 3 is an operation explanatory diagram in the embodiment of FIG. 2;
FIG. 4 is an explanatory diagram of a control method in the embodiment of FIG.
FIG. 5 is an explanatory diagram of a control method in the embodiment of FIG. 2;
6 is an operation explanatory diagram in the embodiment of FIG. 2;
FIG. 7 is a circuit configuration diagram of an electromagnetic induction heating device according to a third embodiment of the present invention.
FIG. 8 is an operation explanatory diagram in the embodiment of FIG. 7;
FIG. 9 is a circuit configuration diagram of an electromagnetic induction heating device according to a fourth embodiment of the present invention.
FIG. 10 is a part of a circuit of an electromagnetic induction heating device according to a fifth embodiment of the present invention.
FIG. 11 is a part of a circuit of an electromagnetic induction heating device according to a sixth embodiment of the present invention.
12 is an operation explanatory diagram of the embodiment of FIG.
FIG. 13 is a part of a circuit of an electromagnetic induction heating device according to a seventh embodiment of the present invention.
FIG. 14 is a part of a circuit of an electromagnetic induction heating device according to an eighth embodiment of the present invention.
FIG. 15 is a part of a circuit of an electromagnetic induction heating device according to a seventh embodiment of the present invention.
FIG. 16 is a block diagram of an electromagnetic induction heating device according to a tenth embodiment of the present invention.
FIG. 17 is an operation explanatory diagram in the embodiment of FIG. 16;
18 is an explanatory diagram of the embodiment of FIG.
19 is an operation explanatory diagram of the embodiment of FIG.
20 is an explanatory diagram of the embodiment of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Commercial alternating current power supply, 2 ... Rectifier circuit, 3 ... Inductor, 4, 6, 7, 31, 32, 33 ... Capacitor, 5 ... Heating coil, 10 ... Power supply, 11, 12, 13, 14, 15, 16, 17, 18, 19 ... semiconductor switching element, 20 ... switching circuit, 21, 22, 23, 24, 25, 28, 29 ... diode, 30 ... bypass circuit, 40 ... snubber capacitor switching circuit, 60 ... resonance circuit, 61, 62, 63, 64, 65, 66 ... 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, 80, 81 ... conduction period setting unit, 82 ... variable frequency oscillator, 100, 200 ... inverter.

Claims (13)

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 bypass 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 and a 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 being one terminal of the DC power supply. Connected to
The bypass circuit connected in parallel to the resonance capacitor includes a first switch element, and the control circuit allows the resonance frequency of the resonance circuit to be lower than the drive frequency of the inverter . An electromagnetic induction heating device characterized by controlling a conduction period. In the electromagnetic induction heating device according to claim 1,
The bypass circuit includes a second diode connected in series with the first switching element, and the first switching element includes a first diode connected in antiparallel. apparatus. In the electromagnetic induction heating device according to claim 1,
The bypass circuit includes a first switching element with a reverse withstand voltage function. In the electromagnetic induction heating device according to claim 1,
The bypass circuit includes a third switching element and a third diode connected in antiparallel to the third switching element. In the electromagnetic induction heating device according to claim 1,
The bypass circuit includes a first switching element and a second switching element connected in anti-series, and the first and second switching elements include first and second diodes connected in anti-parallel, respectively. An electromagnetic induction heating device comprising: In the electromagnetic induction heating device according to claim 1,
The said bypass circuit is provided with the 1st, 2nd switching element with a reverse pressure | voltage resistant function connected antiparallel, The electromagnetic induction heating apparatus characterized by the above-mentioned. The electromagnetic induction heating device according to claim 2,
The bypass circuit further includes an auxiliary induction capacitor and a fourth switching element connected in series with an electromagnetic induction heating device, and further includes a fourth diode connected in antiparallel to the fourth switching element. Electromagnetic induction heating device. 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. In the electromagnetic induction heating device according to claim 1,
The switching circuit includes a snubber capacitor switching circuit 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, and the snubber capacitor switching circuit is a second connected in series. An electromagnetic induction heating device comprising a snubber capacitor and a fifth switching element, wherein the fifth switching element comprises a seventh diode connected in antiparallel. The electromagnetic induction heating device according to claim 9,
The electromagnetic induction heating device is
A first drive circuit for driving a power semiconductor switching element of the upper arm of the switching circuit and a power semiconductor switching element of the lower arm;
A second drive circuit for driving the switching element of the bypass circuit;
A third drive circuit for driving a switching element of the snubber capacitor switching circuit;
An input power setting unit for setting the power supplied to the object to be heated;
The electromagnetic induction heating apparatus, wherein the control circuit inputs an output signal of the input power setting unit and outputs a signal for controlling the first, second, and third drive circuits. The electromagnetic induction heating device according to claim 10,
The control circuit includes a variable frequency oscillator capable of changing an oscillation frequency, and a conduction period setting unit that sets a conduction period of the power semiconductor switching element of each switching circuit and a conduction period of the power semiconductor switching element of the bypass circuit. The electromagnetic induction heating apparatus, wherein the inverter circuit is driven at an oscillation frequency output from the variable frequency oscillator. The electromagnetic induction heating device according to claim 11,
The variable frequency oscillator has an oscillating frequency that increases when a voltage of the DC power supply increases, and an oscillating frequency that decreases when the voltage of the DC power supply decreases. The electromagnetic induction heating device according to claim 12,
The electromagnetic induction heating device includes a first inverter circuit, a second inverter circuit, and a control circuit,
The first inverter circuit includes a first switching circuit, a first resonance circuit, and a first bypass circuit, and the second inverter circuit includes a second switching circuit, a second resonance circuit, And a second bypass circuit,
The control circuit includes a first conduction period setting unit, a second conduction period setting unit, and a variable frequency oscillator,
The electromagnetic induction heating device, wherein the first inverter circuit and the second inverter circuit are driven at a frequency output from the variable frequency oscillator.

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