JP7344740B2 - electromagnetic induction heating device - Google Patents

Description

The present invention relates to an electromagnetic induction heating device (IH cooking heater) that reduces the excitation noise of a pot with an inexpensive configuration.

In recent years, inverter-type IH cooking heaters (hereinafter also referred to as "electromagnetic induction heating devices") that heat objects to be heated, such as pots, without using fire have become widely used. In an IH cooking heater, a high-frequency current is passed through a heating coil placed directly under a glass top plate to generate an eddy current in a metal pot placed on the top plate, which generates heat due to the electric resistance of the pot itself. As described above, IH cooking heaters are rapidly becoming popular in place of gas ranges because they allow cooking without using a fire and offer a high level of safety and comfort in the cooking environment.

In a conventional IH cooking heater, a high frequency current is supplied to the heating coil from an inverter, and a non-smooth DC voltage obtained by full-wave rectification of a commercial power source is applied to the inverter. An IH cooking heater is a device that converts electric power into heat and has a long thermal time constant, so even if the power supply voltage of the inverter is non-smooth and pulsates as in the above configuration, the heating characteristics are not significantly affected.

FIG. 16 shows the heating coil current and the electromagnetic force acting on the pot when pot excitation noise is generated. When the power supply voltage of the inverter pulsates, depending on the material and structure of the pot, the envelope of the heating coil current is distorted and does not become a sine wave, as shown in FIG. 16. Also, the electromagnetic force acting on the pot is proportional to the square of the heating coil current, as shown in the lower diagram of Figure 16. Figure 17 shows the FFT analysis results of electromagnetic force. As shown in the lower diagram of FIG. 16, because the heating coil current is distorted, harmonic components of high frequencies of 4 kHz or higher are observed. Due to the harmonic components of this electromagnetic force, there is a problem in that an excitation sound (pot rattling noise) is generated from the pot.

Therefore, in order to improve this problem, in the electromagnetic induction heating device of Patent Document 1, a converter is placed between the commercial power source and the inverter, and the inverter power supply voltage is converted to a constant DC voltage without pulsation by the converter. By applying power to the inverter, the excitation noise of the pot is suppressed.

Japanese Patent Application Publication No. 2009-117378

However, in Patent Document 1, as shown in the internal structure of the DC power supply as shown in FIG. There is a need. For example, electrolytic capacitors are known as large-capacity capacitors, but since these are large and expensive capacitors, in the configuration of Patent Document 1, the addition of the converter itself increases the size of the DC power supply and increases the cost. In addition to the problems of increasing power consumption and complicating control, there is also the problem of increasing the size and cost of DC power supplies due to the installation of large-capacity capacitors.

Therefore, the present invention reduces the capacitance of the capacitor in the power supply circuit that supplies DC power to the inverter, and even if the power supply circuit is configured to have a smaller circuit size and lower cost, An object of the present invention is to provide an electromagnetic induction heating device that can reduce excitation noise when heating a pot even if the pulsation caused by the commercial power source remains in the DC voltage.

The electromagnetic induction heating device of the present invention includes a heating coil that inductively heats an object to be heated, a power circuit that converts an AC voltage supplied from a commercial power supply into a DC voltage and outputs the DC voltage, and a DC voltage supplied from the power supply circuit. an inverter that converts the DC voltage supplied from the power supply circuit into a high-frequency AC voltage and supplies it to the heating coil; and an envelope that detects the envelope of the resonant current flowing through the inverter. a line detection circuit; and a control circuit that controls the inverter, and the control circuit controls the inverter so that the output value of the envelope detection circuit is similar to the output value of the DC voltage detection circuit. control.

Another electromagnetic induction heating device of the present invention includes a heating coil that inductively heats an object to be heated, a power circuit that converts AC voltage supplied from a commercial power source into DC voltage and outputs the DC voltage, and an input of the power circuit. an input current detection circuit that detects a current; a DC voltage detection circuit that detects a DC voltage supplied from the power supply circuit; and a DC voltage detection circuit that converts the DC voltage supplied from the power supply circuit into a high-frequency AC voltage. and a control circuit for controlling the inverter, the control circuit controlling the input current detection circuit so that the output value of the input current detection circuit is similar to the output value of the DC voltage detection circuit. Control the inverter.

According to the electromagnetic induction heating device of the present invention, even if the DC voltage supplied to the inverter has a configuration in which pulsations caused by the commercial power supply remain, fluctuations in the electromagnetic force generated from the heating coil can be reduced, and the Excitation sound can be reduced.

1 is a block diagram of an electromagnetic induction heating device of Example 1. FIG. FIG. 2 is a configuration diagram of a power supply circuit and an inverter circuit according to the first embodiment. It is a table showing the resistance value of the object to be heated and the resistance value ratio when iron is the standard. 3 is an inverter operation waveform of the electromagnetic induction heating device of Example 1. 3 is a frequency characteristic of input power of the electromagnetic induction heating device of Example 1. It is a duty characteristic of the input power of the electromagnetic induction heating device of Example 1. 1 is a configuration example of an envelope detection circuit according to a first embodiment. 7 is another configuration example of the envelope detection circuit of the first embodiment. FIG. 4 is an operation waveform diagram of various signals when applying excitation sound reduction control in the first embodiment. FIG. 7 is an operation waveform diagram of various signals when applying excitation sound reduction control in a modified example of the first embodiment. FIG. 7 is an operation waveform diagram of various signals when applying excitation sound reduction control in a modified example of the first embodiment. FIG. 2 is an inverter circuit configuration diagram of an electromagnetic induction heating device according to a second embodiment. It is an inverter operation waveform of the electromagnetic induction heating device of Example 2. 3 is a frequency characteristic of input power of the electromagnetic induction heating device of Example 2. FIG. 3 is a configuration diagram of an inverter circuit of an electromagnetic induction heating device according to a third embodiment. Conventional heating coil waveform and electromagnetic force waveform. These are the results of conventional FFT analysis of electromagnetic force waveforms. FIG. 4 is a configuration diagram of an inverter circuit of an electromagnetic induction heating device according to a fourth embodiment.

Embodiments of the electromagnetic induction heating device (IH cooking heater) of the present invention will be described below with reference to the drawings.

First, an electromagnetic induction heating device according to a first embodiment of the present invention will be explained using FIGS. 1 to 11.

FIG. 1 is a block diagram of an electromagnetic induction heating device according to a first embodiment. As shown here, the electromagnetic induction heating device of this embodiment includes a power supply circuit 10 that outputs DC voltage, three inverters (100a, 100b, 100c) that use this power supply circuit 10 as a power supply, and controls each inverter. a drive circuit 61 that detects the input current, a current detector 31 that detects the input current, an input current detection circuit 62 that rectifies the output of the current detector 31 and detects the input current, and a DC voltage detection circuit that detects the output voltage of the power supply circuit 10. A circuit 63, a resonant current detection circuit 64 that detects the resonant current flowing in each inverter, an envelope detection circuit 65 that detects the envelope of the resonant current, and an input power used by the user to set thermal power, etc. It is equipped with a control circuit 70 that controls each inverter based on inputs from a setting section 71, a resonant current detection circuit 64, an envelope detection circuit 65, and an input power setting section 71, and a plurality of heating coils 5 corresponding to each inverter. Accordingly, an object to be heated such as a pot placed on a top plate (not shown) can be heated. Note that since the configurations of each inverter are the same, the inverter 100a will be described below as an example. Furthermore, the heating coils 5 of each inverter may be arranged in a distributed manner so that they can heat different objects to be heated placed on the top plate, or they may be placed in one place so that they can heat a single object to be heated. For example, they may be arranged concentrically.

The inverter 100a includes an inverter circuit 20, a resonance circuit 30, and a current detector 32. The inverter circuit 20 is connected between the positive electrode point P and the negative electrode point O of the power supply circuit 10, and converts the DC voltage supplied from the power supply circuit 10 into a high-frequency AC voltage and applies it to the resonance circuit 30. do. The resonant circuit 30 is a series circuit of the heating coil 5 and the resonant capacitor Cr, and the heating coil 5 is supplied with high frequency power from the inverter circuit 20. Current detector 32 detects resonant current IL flowing through resonant circuit 30.

The output of the current detector 31 is sent to the control circuit 70 via the input current detection circuit 62, and the output of the current detector 32 is sent to the control circuit 70 via the resonance current detection circuit 64 and the envelope detection circuit 65. The control circuit 70 calculates these inputs and generates a drive signal according to the signal from the input power setting section 71. The drive circuit 61 outputs a drive signal waveform for controlling the inverter circuit 20 of each inverter based on the drive signal from the control circuit 70. The input power setting unit 71 is an interface such as a touch panel through which the user sets input power (thermal power), and sends a signal corresponding to the set thermal power to the control circuit 70.

Next, the operation of inverter 100a will be explained. Generally, an electromagnetic induction heating device uses a resonant inverter. In the resonant type inverter, by setting the driving frequency fs of the inverter circuit 20 > the resonant frequency fr of the resonant circuit 30 and making the characteristics of the resonant load inductive, the resonant current IL flowing through the resonant circuit 30 is set to be higher than the resonant frequency fr of the resonant circuit 30. This is an inverter that is controlled so that the phase lags behind the output voltage. This suppresses an increase in loss in the inverter circuit 20. That is, in FIG. 1, the inverter circuit 20 is controlled so that the resonant current IL flowing through the resonant circuit 30 is delayed in phase with respect to the voltage at the output terminal point t, which is the connection point between the inverter circuit 20 and the resonant circuit 30. losses are suppressed.

However, when power control is performed by changing the conduction period of the inverter circuit 20 with the driving frequency fs of the inverter circuit 20 fixed, the polarity of the resonant current IL is reversed during the conduction period of the inverter circuit 20, and the resonant current IL is In some cases, the output voltage of the inverter circuit 20 may shift to a phase advance mode in which the phase is ahead of the output voltage of the inverter circuit 20. Since the phase advance mode causes an increase in loss in the inverter circuit 20, it is a mode that must be avoided in a resonant type inverter.

FIG. 2 shows in more detail the circuit configurations of the power supply circuit 10 and inverter circuit 20 of the electromagnetic induction heating device of this embodiment. A bridge type circuit configuration is illustrated.

This full-wave rectification passive filter type power supply circuit 10 converts an AC voltage input from a commercial power supply 1 into a DC voltage and supplies it to an inverter 100a, and includes a rectifier circuit 2 for rectifying the AC voltage, and an inductor 3 It consists of a smoothing circuit composed of a filter capacitor Cf and a filter capacitor Cf. The inverter circuit 20 of the inverter 100a is connected between the positive electrode point p and the negative electrode point o of the filter capacitor Cf. Note that since the filter capacitor Cf used here is a capacitor with a relatively small capacity, unlike the configuration using a large-capacity electrolytic capacitor as in Patent Document 1, the power supply voltage Vp output by the power supply circuit 10 is Pulsations caused by pulsations in the commercial power supply voltage will remain.

The inverter circuit 20 of the inverter 100a has power semiconductor switching elements (hereinafter referred to as "switching elements") SW1 and SW2 such as IGBTs connected in series, and diodes D1 and D2 connected in antiparallel to each switching element. . That is, the cathode terminal of each diode is connected to the collector terminal of each switching element, and the anode terminal of each diode is connected to the emitter terminal of each switching element. Hereinafter, the circuit composed of the switching element SW1 and the diode D1 will be referred to as an upper arm, the circuit composed of the switching element SW2 and the diode D2 will be referred to as a lower arm, and the combination of the upper arm and the lower arm will be referred to as an upper and lower arm. Furthermore, snubber capacitors Cs1 and Cs2 are connected in parallel to each switching element. The snubber capacitors Cs1 and Cs2 are charged or discharged by the cutoff current when each switching element is turned off. Since the capacitance of the snubber capacitors Cs1 and Cs2 is sufficiently larger than the output capacitance between the collector and emitter of the switching elements SW1 and SW2, changes in the voltage applied to both switching elements at turn-off are reduced, and turn-off loss is suppressed. .

Further, a resonant circuit 30 is connected to an output terminal point t, which is a connection point between switching elements SW1 and SW2, and a positive electrode point p and a negative electrode point o of the power supply circuit 10. The resonant circuit 30 of this embodiment is composed of a heating coil 5 and resonant capacitors Cr1 and Cr2. In the following, the direction in which the resonant current IL flows from the output terminal point t of the inverter circuit 20 toward the heating coil 5 is defined as the positive direction of the resonant current IL.

Current detector 32 detects resonant current IL flowing through resonant circuit 30. Resonant current detection circuit 64 converts the output signal level of current detector 32 of each inverter into a signal suitable for the input level of control circuit 70. The current detector 31 detects an input current input from the commercial power supply 1. The input current detection circuit 62 converts the output value of the current detector 31 into a signal suitable for the input level of the control circuit 70. The control circuit 70 determines the material and condition of the object to be heated from the relationship between the input current detected by the input current detection circuit 62 and the resonance current IL detected by the resonance current detection circuit 64, and starts or stops the heating operation. The objects to be heated are classified into magnetic materials and non-magnetic materials. The method for distinguishing is to energize with low power (about 300 W) before heating. The resonance current IL or the current value of the switching elements SW1 and SW2 at that time is detected, and the material of the object to be heated is determined based on the current value. If the current value is small, the object to be heated is determined to be a magnetic material such as iron, and if the current value is large, the object to be heated is determined to be a non-magnetic material such as non-magnetic stainless steel, aluminum, or copper.

FIG. 3 shows resistance values for each material of the heated object when the drive frequency of the inverter circuit 20 is 20 kHz. As shown in this table, the resistance value of non-magnetic stainless steel is 1/3 that of iron, 1/20 of aluminum, and about 1/25 of copper.

Further, the control circuit 70 controls the input power by setting the conduction period of the switching elements SW1 and SW2 of the inverter circuit 20 via the drive circuit 61 according to the signal from the input power setting section 75. Material detection must be performed at low power and in a short time to prevent overcurrent and overvoltage.

Here, the current flowing in the upper arm of the inverter circuit 20 is Ic1, the current flowing in the lower arm is Ic2, the voltage between the collector and emitter of switching element SW1 in the upper arm is Vc1, and the voltage between the collector and emitter of switching element SW2 in the lower arm is Vc1. The voltage between them is Vc2, the resonant voltage of the resonant capacitor Cr1 is Vcr1, the resonant voltage of the resonant capacitor Cr2 is Vcr2, and the power supply voltage of the inverter 100a is Vp.

Next, operating waveforms of the inverter of this embodiment in modes 1 to 4 will be explained using FIG. Note that in either mode, the switching elements SW1 and SW2 are driven complementary to each other with a dead time period provided. As shown here, a sinusoidal resonant current IL flows through the heating coil 5, and this resonant frequency fr is determined by the inductance value L of the heating coil 5 and the capacitance of the resonant capacitors Cr1 and Cr2 according to equation 1. Determined from C.

Detailed operations in modes 1 to 4 will be described below.

(Mode 1)
It is assumed that mode 1 starts at the timing when the current Ic1 of the switching element SW1 changes from negative to 0A. At the start of mode 1, current Ic1 does not flow through switching element SW1, but since switching element SW1 is already turned on, current Ic1 starts flowing through switching element SW1 immediately after mode 1 starts. At this time, since the voltage across the switching element SW1 (voltage Vc1) is 0V, ZVZCS turn-on occurs in which no loss occurs in the switching element SW1.

(Mode 2)
When the switching element SW1 is cut off and mode 2 is established, the resonant current IL passes through the power supply circuit 10, the snubber capacitor Cs1, the heating coil 5, and the resonant capacitor Cr2, and the heating coil 5, the resonant capacitor Cr1, and the snubber capacitor Cs1. It flows through the heating coil 5, resonance capacitor Cr2, and snubber capacitor Cs2. At this time, snubber capacitor Cs1 is charged and snubber capacitor Cs2 is discharged. As a result, the voltage across the switching element SW1 gradually increases, ZVS turn-off occurs, and switching loss can be reduced.

When the voltage Vc1 of the snubber capacitor Cs1 becomes equal to or higher than the power supply voltage Vp, the voltage Vc2 of the snubber capacitor Cs2 becomes 0V, the diode D2 is turned on, and the resonant current IL continues to flow. An on signal is input to the switching element SW2 while a current is flowing through the diode D2.

(Mode 3)
It is assumed that mode 3 starts at the timing when the current Ic2 of the switching element SW2 changes from negative to 0A. Although current Ic2 does not flow through switching element SW2 at the start of mode 3, since switching element SW2 is already turned on, current Ic2 starts flowing through switching element SW2 immediately after mode 3 starts. At this time, since the voltage (Vc2) across the switching element SW2 is 0V, ZVZCS turn-on occurs in which no loss occurs in the switching element SW2.

(Mode 4)
When the switching element SW2 is cut off and mode 4 is established, the resonant current IL passes through a path of the heating coil 5, snubber capacitor Cs2, power supply circuit 10, and resonant capacitor Cr1, and a path of the heating coil 5, snubber capacitor Cs2, and resonant capacitor Cr2. It flows through the heating coil 5, snubber capacitor Cs1, and resonance capacitor Cr1. At this time, snubber capacitor Cs2 is charged and snubber capacitor Cs1 is discharged. As a result, the voltage across the switching element SW2 gradually increases, ZVS turn-off occurs, and switching loss can be reduced.

By repeating the operations from modes 1 to 4 above and passing a high-frequency current through the heating coil 5, magnetic flux can be generated from the heating coil 5, and the magnetic flux causes the heating coil to be placed on the top plate above the heating coil 5. An eddy current flows through the heated pot, and the pot itself generates heat due to induction heating.

<Method of controlling input power to heated object>
Next, a power control method in the electromagnetic induction heating device of this embodiment will be described in detail. FIG. 5 is a graph showing an example of the relationship between the drive frequency fs of the inverter circuit 20 and the input power to the heated object. Electromagnetic induction heating devices utilize resonance phenomena to send a large, high-frequency current through a heating coil. Therefore, the frequency characteristics of the input power to the heated object exhibit resonance characteristics. As shown in the table of FIG. 3, when the object to be heated is a magnetic material such as an iron pot, the resistance is large, so the resonance Q is small and a gentle resonance characteristic is exhibited. On the other hand, when the object to be heated is a non-magnetic material such as an aluminum pot or a copper pot, the resistance is small, so the resonance Q becomes large and exhibits steep resonance characteristics. Therefore, for an iron pot or the like having a small resonance Q, it is possible to finely control the input power by frequency control by utilizing the gentle resonance characteristics. Moreover, FIG. 6 is a graph showing the relationship between the duty of the switching element SW1 and the input power to the heated object. By utilizing the relationship shown here, it is also possible to control power by controlling the duty of the switching element SW1 in an iron pot or the like with a small resonance Q.

<An example of the envelope detection circuit 64>
Here, an example of a specific configuration of the envelope detection circuit 65 will be explained. For the envelope detection circuit 65, a circuit configuration used in an AM radio demodulation circuit or the like can be used, and a typical example thereof is illustrated in FIG.

The envelope detection circuit 65 illustrated here has a resistor R1 connected between the output of a current detector 32 that detects the resonant current IL and the ground, and a resistor R2 and a capacitor C1 connected to the output of the current detector 32 via a diode D5. This is a configuration in which parallel circuits of 1 and 2 are connected between grounds.

In the envelope detection circuit 65 having such a configuration, when the output voltage of the current detector 32 becomes higher than the voltage of the capacitor C1, the diode D5 becomes conductive and charges the capacitor C1, and the output voltage of the current detector 32 becomes higher than the voltage of the capacitor C1. When the voltage becomes lower than the voltage of C1, the current of diode D5 is cut off, and capacitor C1 is discharged from resistor R2. Therefore, by setting the time constant determined by the values of the resistor R2 and the capacitor C1 to a value corresponding to the driving frequency fs of the inverter circuit 20, it is possible to detect the envelope of the resonant current IL indicated by Venv in the figure.
<Another example of the envelope detection circuit 65>
Next, another example of the specific configuration of the envelope detection circuit 65 will be described. This envelope detection circuit 65 utilizes a peak hold circuit configured with an operational amplifier, and a typical example thereof is shown in FIG.

The envelope detection circuit 65 illustrated here connects the output of the current detector 32 that detects the resonant current IL to the non-inverting input of the operational amplifier OP1, connects an input resistor R3 between the ground, and connects the inverting input of the operational amplifier OP1 to the input resistor R3. A diode D6 is connected between the terminal and the output terminal. Further, the output terminal of the operational amplifier OP1 is connected to the non-inverting input terminal of the operational amplifier OP2 via the diode D7, and a hold circuit 50 constituted by a parallel circuit of a resistor R5 and a capacitor C2 is connected between the ground and the ground. Further, a resistor R4 is connected between the inverting input terminal of the operational amplifier OP1 and the inverting input terminal of the operational amplifier OP2, and the inverting input terminal and the output terminal of the operational amplifier OP2 are connected.

In the envelope detection circuit 65 having such a configuration, when the output voltage of the current detector 32 becomes higher than the output voltage of the operational amplifier OP1, the operational amplifier OP1 outputs a voltage at the same level as the current detector 32. As a result, diode D7 becomes conductive, and capacitor C2 of hold circuit 50 is charged. Then, when the capacitor C2 is charged and becomes equal to or higher than the output voltage of the operational amplifier OP2, the operational amplifier OP2 outputs a voltage at the same level as the hold circuit 50.

On the other hand, when the output voltage of the current detector 31 becomes lower than the output voltage of the hold circuit 50, the diode D7 is turned off, and the charging current of the hold circuit 50 is cut off. Therefore, the operational amplifier OP2 outputs the charged voltage to the hold circuit 50. Therefore, by setting the time constant determined by the values of the resistor R5 and capacitor C2 of the hold circuit 50 to a value corresponding to the drive frequency fs of the inverter circuit 20, the envelope indicated by Venv in the figure can be detected.

<Method for reducing excitation noise when heating an object to be heated>
Next, a method of controlling the resonant current IL in the electromagnetic induction heating device of the present embodiment for suppressing pot ringing noise (excitation sound) during pot heating will be described.

FIG. 9 is an operation waveform diagram of various signals when the drive frequency fs of the inverter circuit 20 is controlled so that the output value of the envelope detection circuit 65 becomes similar to that of the DC voltage detection circuit 63. It shows fluctuations in the input voltage and input current from the commercial power supply 1, the output value of the DC voltage detection circuit 63, the output value of the envelope detection circuit 65, the resonance current IL, and the drive frequency fs of the inverter circuit 20.

As is clear from the figure, in this embodiment, the drive frequency fs of the inverter circuit 20 is changed so that the output value of the envelope detection circuit 65 becomes similar to the DC voltage detection circuit 63. If the drive frequency of the inverter circuit changes within the commercial cycle and the output value of the DC voltage detection circuit 63 is small, the drive frequency fs of the inverter circuit 20 is lowered, and if the input voltage detection value is large, the drive frequency of the inverter circuit 20 is lowered. Increase fs. By such control of the inverter circuit 20, the envelope of the resonant current IL becomes similar to the input voltage waveform, so that the envelope of the resonant current IL supplied to the heating coil 5 becomes approximately sinusoidal. Figure 10 shows the FFT analysis results of electromagnetic force. As is clear from the comparison with FIG. 17, which is the FFT analysis result when the present invention is not applied, the harmonic components of the electromagnetic force in the several kHz band are smaller than in FIG. 10, and the excitation noise generated in the pot is reduced. I can do it.
<Modified example of excitation sound reduction method during heating of heated object>
Next, FIG. 11 shows a modification of the method of controlling the resonant current IL of the first embodiment.

FIG. 11 is an operation waveform diagram of various signals when the duty of the lower arm (switching element SW2) is controlled so that the output value of the envelope detection circuit 65 becomes similar to the DC voltage detection circuit 63. In order, the input voltage and input current from the commercial power supply 1, the output value of the DC voltage detection circuit 63, the output value of the envelope detection circuit 65, the resonance current IL, and the duty fluctuation of the lower arm (switching element SW2) are shown.

As is clear from the figure, in this modification, the duty of the lower arm of the inverter circuit 20 is changed so that the output voltage of the envelope detection circuit becomes similar to that of the DC voltage detection circuit. The lower arm Duty of the inverter circuit changes within the commercial cycle, and when the output value of the DC voltage detection circuit 63 is small, the lower arm Duty is set to be large, and when the input voltage detection value is large, the lower arm Duty is set to be small. Due to such control of the inverter circuit 20, the envelope of the resonant current IL becomes similar to the input voltage waveform, so the envelope of the resonant current IL supplied to the heating coil 5 becomes approximately sinusoidal, as described above. As a result, the harmonic components of the electromagnetic force become smaller, and the excitation noise generated in the pot can be reduced.

The above excitation sound reduction control was performed using the output value of the envelope detection circuit. However, in the electromagnetic induction heating device of this embodiment, since the capacitance of the capacitor Cf of the power supply circuit 10 is small, the voltage between p and Pulsating in sync. Therefore, since the output value of the input current detection circuit is approximately the same as the envelope waveform of the heating coil current, the inverter circuit 20 is configured so that the output value of the input current detection circuit 62 and the DC voltage detection circuit 63 have a similar shape. A similar effect can be obtained by controlling.

According to the electromagnetic induction heating device of this embodiment described above, even if the DC voltage supplied to the inverter has a configuration in which pulsations caused by the commercial power supply remain, fluctuations in the electromagnetic force generated from the heating coil can be reduced. , it is possible to reduce the excitation sound when heating the pot.

Next, an electromagnetic induction heating device according to a second embodiment of the present invention will be described using FIG. 12. Note that redundant explanation of common points with the embodiments described above will be omitted.

FIG. 12 shows the circuit configuration of the electromagnetic induction heating device of Example 2. The inverter circuit 80 (voltage resonance inverter) of this embodiment is a series circuit of a resonance circuit 91 and a switching element SW2. The resonant circuit 91 is a parallel circuit of the heating coil 5 and the resonant capacitor Cr1. Furthermore, a diode D2 is connected in antiparallel to the switching element SW2.

Next, a normal heating operation will be explained using FIG. 13. Here, regarding the direction of the current flowing through the heating coil 5, the direction of the arrow in FIG. 12 is assumed to be positive.
(Mode 1)
Mode 1 is a period from turning off the switching element SW2 to the peak of the collector voltage Vc1 of the switching element SW2. In mode 1, when the switching element SW2 is turned off, the current Ic1 flowing through the switching element SW2 is cut off, and the energy stored in the heating coil 5 causes a current to flow through the path between the heating coil 5 and the resonant capacitor Cr1. At this time, the collector voltage Vc1 of the switching element SW2 rises in a sinusoidal manner, resulting in zero voltage switching (hereinafter referred to as ZVS).
(Mode 2)
Mode 2 is a period from the peak of the collector voltage Vc1 of the switching element SW2 to 0V. In mode 2, when the collector voltage Vc1 of the switching element SW2 reaches a peak, the current Ic1 of the heating coil 5 switches from positive to negative, the direction of the current is reversed, and the current flows through the path between the resonant capacitor Cr1 and the heating coil 5.
(Mode 3)
Mode 3 is a period during which diode D2 is energized. In mode 3, when the resonant capacitor Cr1 is discharged and the collector voltage of the switching element SW2 becomes 0V, the diode D2 is turned on, and a current flows through the path of the heating coil 5, the filter capacitor Cf, and the diode D2. The gate of the switching element SW2 is turned on during the energization period of the diode D2.
(Mode 4)
Mode 4 is a period during which switching element SW2 is energized. In mode 4, when the heating coil 5 runs out of energy, the resonant current IL switches from negative to positive. At this time, since the gate of the switching element SW2 is already turned on, current begins to flow. At this time, ZVS is achieved in which no switching loss occurs. The current flows through a path of filter capacitor Cf, heating coil 5, switching element SW2, and a path of commercial power supply 1, rectifier circuit 2, inductor 3, heating coil 5, switching element SW2, and rectifier circuit 2.

By repeatedly operating the above modes 1 to 4, a high-frequency alternating current flows through the heating coil 5 and heats the pot.

FIG. 14 shows the relationship between the drive frequency fs and the input power in the voltage resonance type inverter circuit 80. In this embodiment, the heating coil 5 and the resonant capacitor Cr1 are connected in parallel to form a parallel resonant circuit. Therefore, the frequency characteristics shown in FIG. 14 exhibit a downward convex characteristic. In this way, in parallel resonance, the power at the resonance point is the lowest power, and the power can be controlled by lowering the frequency.

Also in the circuit of this embodiment described above, the output value of the envelope detection circuit 65 becomes similar to that of the DC voltage detection circuit 63 by controlling the inverter circuit 20 explained in FIGS. 9 and 11 of the first embodiment. By controlling the resonant current IL in this way, it is possible to reduce fluctuations in the electromagnetic force generated from the heating coil, and it is possible to reduce the excitation noise generated from the pot.

Next, using FIG. 15, an electromagnetic induction heating device according to a third embodiment of the present invention will be described. Although a half-bridge inverter was used in the above embodiment, a full-bridge inverter is used in this embodiment. The same components as in FIG. 2 are given the same reference numerals to avoid redundant explanation.

As shown in FIG. 15, the full-bridge inverter used in this embodiment has an inverter circuit 20a and an inverter circuit 20b connected between the output terminals op of the power supply circuit 10, and a midpoint between the two inverter circuits t- In this configuration, a series circuit of a heating coil 5 and a resonant capacitor Cr1 is connected between r. Diodes D1a, D1b, D2a, and D2b are connected in antiparallel to the switching elements SW1a, SW1b, SW2a, and SW2b, and the cathode terminals of the diodes are connected to the collector terminals of the switching elements, and the anode terminals are connected to the emitter terminals of the diodes. By applying the same drive signal to switching elements SW1a and SW2b and applying the same drive signal to switching elements SW2a and SW1b, switching elements SW1a and SW2a are driven complementary to each other, and switching elements SW1b and SW2b are driven to be complementary to each other.

The soft switching operation of each switching element is similar to that of a half bridge, so a description thereof will be omitted. In a full bridge, the voltage applied to the series circuit of the heating coil 5 and the resonant capacitor Cr1, that is, the inverter output voltage (voltage between t and r), can generate a voltage twice that of a half bridge. Therefore, it is possible to increase the number of turns of the heating coil 5, thereby making it possible to improve heating efficiency.

The details of the power control method will be omitted since it can be controlled by using the same frequency or duty as the half-bridge inverter.

Even when using the full bridge inverter as described above, the inverter circuit 20a, By controlling the drive frequency or duty of 20b, the pulsation of the resonant current IL can be reduced, and the excitation noise generated from the pot can be reduced.

Next, using FIG. 18, an electromagnetic induction heating device according to a fourth embodiment of the present invention will be described. The same components as in FIG. 2 are given the same reference numerals to avoid redundant explanation.

This embodiment differs from the first embodiment in that a zero-cross detection circuit 66 that detects the zero-cross point of the commercial power supply 1 and a sine wave generation circuit 67 that generates a sine wave in synchronization with the output of the zero-cross detection circuit 66 are provided. That's what happened. In this way, the sine wave generation circuit 67 that generates a sine wave synchronized with the commercial power supply 1 is provided, and the reference waveform that is the output of the sine wave generation circuit 67 and the outputs of the envelope detection circuit 65 and the input current detection circuit 62 are similar. By controlling the inverter circuit 20 so as to maintain the shape, the pot excitation noise can be reduced. By doing so, it is possible to reduce pot excitation sound even in an environment where the output of the commercial power supply 1 is distorted.

Note that the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the embodiments described above are described in detail to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to having all the configurations described. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace other configurations with respect to the configuration of each embodiment.

1 Commercial power supply 2 Rectifier circuit 3 Inductor 5 Heating coil 10 Power supply circuit 20, 20a, 20b Inverter circuit 30 Resonance circuit 31, 32 Current detector
OP1, OP2 Operational amplifier 61 Drive circuit 62 Input current detection circuit 63 DC voltage detection circuit 64 Resonant current detection circuit 65 Envelope detection circuit 66 Zero cross detection circuit 67 Sine wave generation circuit 70 Control circuit 71 Input power setting section 100a, 100b, 100c Inverter Cf Filter capacitor Cr1, Cr2 Resonant capacitor Cs1, Cs2 Snubber capacitor C1, C2 Capacitor D1, D2, D3, D4, D5, D6, D7 Diode R1, R2, R3, R4, R5 Resistor SW1, SW1a, SW1b, SW2, SW2a , SW2b, SW3, SW4 switching element

Claims (6)

A heating coil that inductively heats an object to be heated;
A power supply circuit that converts AC voltage supplied from a commercial power source into DC voltage and outputs it;
a DC voltage detection circuit that detects the DC voltage supplied from the power supply circuit;
an input current detection circuit that detects an input current of the power supply circuit;
a zero-cross detection circuit that detects a zero-cross of an AC voltage supplied from the commercial power source;
a sine wave generation circuit that outputs a sine wave based on the output value of the zero cross detection circuit;
an inverter that converts the DC voltage supplied from the power supply circuit into a high-frequency AC voltage and supplies it to the heating coil;
an envelope detection circuit that detects an envelope of a resonant current flowing through the inverter;
A control circuit that controls the inverter,
The control circuit is arranged such that the output value of the envelope detection circuit is similar to the output value of the DC voltage detection circuit, and the output value of the input current detection circuit is configured to be similar to the output value of the sine wave generation circuit. An electromagnetic induction heating device characterized in that the inverter is controlled so that the shapes are similar . The electromagnetic induction heating device according to claim 1 ,
The inverter includes a resonant circuit in which the heating coil and a resonant capacitor are connected in series;
An electromagnetic induction heating device comprising: an inverter circuit connected between output terminals of the power supply circuit and having two switching elements connected in series. The electromagnetic induction heating device according to claim 1 ,
The inverter includes a resonant circuit in which the heating coil and a resonant capacitor are connected in parallel;
An electromagnetic induction heating device comprising: an inverter circuit connected between output terminals of the power supply circuit and having a switching element and the resonance circuit connected in series. The electromagnetic induction heating device according to claim 1 ,
The inverter includes a first inverter circuit connected between the output terminals of the power supply circuit and having two switching elements connected in series;
a second inverter circuit connected between the output terminals of the power supply circuit and having two switching elements connected in series;
An electromagnetic induction heating device comprising: a resonant circuit connected between the output terminals of both inverters and having the heating coil and a resonant capacitor connected in series. The electromagnetic induction heating device according to any one of claims 2 to 4 ,
The electromagnetic induction heating device is characterized in that the control circuit controls the drive frequency of the inverter circuit so that the similar shapes are obtained. The electromagnetic induction heating device according to any one of claims 2 to 4 ,
The electromagnetic induction heating device is characterized in that the control circuit controls the duty of the inverter circuit so that the similar shapes are achieved.

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