JP7397762B2 - electromagnetic induction heating device - Google Patents

Description

The present invention relates to an electromagnetic induction heating device (IH cooking heater) equipped with a current detection circuit that detects heating coil current.

In recent years, inverter-type electromagnetic induction heating devices (IH cooking heaters) that heat objects such as pots without using fire have become widely used. An IH cooking heater uses a high-frequency current to flow through a heating coil to generate an eddy current in a pot made of a material such as iron or stainless steel, which is placed close to the coil, and generates heat due to the electrical resistance of the pot itself. In this way, IH cooking heaters are rapidly becoming popular in place of gas ranges because they allow cooking without using a fire, are highly safe and provide a comfortable cooking environment.

In an IH cooking heater, a heating coil is arranged below a glass top plate, and an inverter that supplies high-frequency current is connected to the heating coil. A high frequency current of approximately 40 Arms and approximately 20 kHz to 100 kHz flows through the heating coil. Conventionally, methods using current transformers or shunt resistors have been used to detect current in heating coils.

However, some current transformers have a core with a primary winding and a secondary winding, and others have a through-type core with a secondary winding, but both methods have small component sizes. This is a big and expensive problem. Further, since a large current flows through the shunt resistor, Joule loss occurs in the shunt resistor, resulting in an increase in temperature.

Therefore, the electromagnetic cooker shown in Patent Document 1 includes a voltage detection circuit that detects the voltage across a resonant capacitor, a differentiation circuit that differentiates the output from this voltage detection circuit, and a heating coil that rectifies the output from this differentiation circuit. By providing an envelope detection circuit that outputs current information that follows the peak value of the current flowing through the heating coil, the heating coil current can be detected while solving the above-mentioned problems.

Patent No. 4448802

However, when the inverter is subjected to PWM control (Pulse Width Modulation control), the alternating current flowing through the heating coil has different peak values depending on whether it is positive or negative. As can be read from FIGS. 6 and 7 of the same document, Patent Document 1 has a configuration in which the output voltage of the differentiating circuit is half-wave rectified and a peak value is detected. However, when the inverter is subjected to PWM control, there is a problem that the effective current flowing through the heating coil cannot be accurately detected.

Therefore, the present invention solves the above-mentioned conventional problems.In an induction heating device in which an inverter is PWM-controlled, the current flowing through a resonant capacitor is shunted, the voltage generated in a resistor is detected, and the detected value is rectified. By averaging the values, the effective current flowing through the heating coil can be accurately detected.

The electromagnetic induction heating device of the present invention is an electromagnetic induction heating device that uses a heating coil to inductively heat an object to be heated, and includes a DC power source that supplies a DC voltage, and a device that converts the DC voltage into a high-frequency AC voltage. an inverter circuit that supplies the heating coil, a control circuit that controls the inverter circuit, a resonant circuit that connects the heating coil and a resonant capacitor in series, and a resonant capacitor current shunting circuit that shunts the current flowing through the resonant capacitor; The inverter circuit includes a rectifying amplifier circuit that rectifies and amplifies the output of the resonant capacitor current shunting circuit, and an averaging circuit that averages the output of the rectifying amplifier circuit. The control circuit is an electromagnetic induction heating device that controls a high-frequency AC voltage supplied to the heating coil by PWM controlling the conduction period of each switching element .

According to the electromagnetic induction heating device of the present invention, when the inverter is under PWM control, the current flowing through the resonant capacitor is shunted, the voltage generated in the resistor is detected, and the detected value is rectified and averaged. The effective current flowing through the heating coil can be accurately detected.

1 is a block diagram of an electromagnetic induction heating device according to a first embodiment. FIG. 3 is an inverter circuit configuration diagram of the electromagnetic induction heating device of Example 1. The figure which shows the resistance value of each to-be-heated object, and a resistance value ratio with respect to iron. Inverter operation waveforms of the electromagnetic induction heating device of Example 1. Frequency characteristics of input power of the electromagnetic induction heating device of Example 1. Duty characteristics of input power of the electromagnetic induction heating device of Example 1. FIG. 3 is a circuit diagram of a current detection circuit according to the first embodiment. 3 is an operation waveform of the current detection circuit of the electromagnetic induction heating device of Example 1. 3 is a graph showing the relationship between the current detection circuit and heating coil current of the electromagnetic induction heating device of Example 1. FIG. 3 is a circuit diagram of a current detection circuit according to a second embodiment. 3 is an operational waveform of the current detection circuit of the electromagnetic induction heating device of Example 2. 7 is a graph showing the relationship between the current detection circuit and heating coil current of the electromagnetic induction heating device of Example 2. FIG. 3 is a circuit diagram of a current detection circuit according to a third embodiment. FIG. 7 is an operation waveform of the current detection circuit of the electromagnetic induction heating device of Example 3. FIG. 4 is a circuit diagram of a current detection circuit according to a fourth embodiment. FIG. 4 is an operation waveform of the current detection circuit of the electromagnetic induction heating device of Example 4. A modification of the circuit diagram of the current detection circuit of Example 4. FIG. 7 is an operation waveform of a modified example of the current detection circuit of the electromagnetic induction heating device of Example 4.

Embodiments 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 9.

FIG. 1 is a block diagram of an electromagnetic induction heating device according to a first embodiment. The electromagnetic induction heating device shown here is a heating device that can simultaneously heat three objects to be heated, such as a pot placed on a top plate, and is a power source that converts AC voltage from a commercial power source 1 and outputs DC voltage. Circuit 10, input current detector 11, input current detection circuit 12, three inverters 100 (100a, 100b, 100c), drive circuit 21, rectifier amplifier circuit 50, averaging circuit 51, and control circuit 60 and an input power setting section 61. The heating coil 31 of each inverter can induction-heat the object to be heated. Note that since the configurations of each inverter are the same, the first inverter 100a will be described below as a representative.

The inverter 100a includes an inverter circuit 20, a resonant circuit 30, and a resonant capacitor current shunting circuit 40. The inverter circuit 20 is connected between the positive electrode point P and the negative electrode point N 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 a heating coil 31 and a resonant capacitor Cr, and high frequency power is supplied to the heating coil 31 from the inverter circuit 20. The resonant capacitor current shunting circuit 40 shunts the current flowing through the resonant capacitor Cr.

The output value of the resonant capacitor current shunting circuit 40 of each inverter is sent to the control circuit 60 via the rectifier amplifier circuit 50 and the averaging circuit 51. The input power setting unit 61 is an interface through which the user sets input power (thermal power), and sends a signal corresponding to the set thermal power to the control circuit 60. The control circuit 60 generates a drive signal according to the calculation result from the rectifier amplifier circuit 50 and the signal from the input power setting section 61. The drive circuit 21 generates a drive signal waveform for controlling the inverter circuit 20 of each inverter based on the drive signal from the control circuit 60.

Next, the operation of inverter 100a will be explained. Generally, an IH cooking heater uses a resonant inverter. In the resonant inverter, by setting the drive 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 current flowing through the resonant circuit 30 is adjusted to the output voltage of the inverter circuit 20. This is an inverter that is controlled to have a delayed phase. This suppresses an increase in loss in the inverter circuit 20. That is, in FIG. 1, the inverter circuit 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. 20 losses can be suppressed.

However, when power control (PWM control) is performed by changing the conduction period of the inverter circuit 20 while the drive frequency fs of the inverter circuit 20 is fixed, the polarity of the resonant current I _L is reversed during the conduction period of the inverter circuit 20. , the resonant current I _L may shift to a phase advance mode in which the phase leads 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 a more specific circuit configuration of the electromagnetic induction heating device of Example 1. This is a circuit diagram of an electromagnetic induction heating device in which the power supply circuit 10 is of a full-wave rectification passive filter type and the inverter circuit 20 has a herb bridge circuit configuration.

In FIG. 2, a power supply circuit 10 converts an AC voltage from a commercial power supply 1 into a DC voltage and supplies it to an inverter 100a, and includes a diode bridge 13 for rectifying the AC voltage, an inductor 14, and a filter capacitor Cf. configured. The inverter circuit 20 of the inverter 100a is connected between the positive electrode point p and the negative electrode point n of the filter capacitor Cf.

The inverter circuit 20 of the inverter 100a is configured by connecting IGBTs (hereinafter referred to as switching elements SW (SW ₁ , SW ₂ )) that are power semiconductor switching elements in series. A diode D (D ₁ , D ₂ ) is connected in parallel in opposite directions to each switching element SW, and the cathode terminal of the diode D is connected to the collector terminal of the switching element SW, and the anode terminal is connected to the emitter terminal. Hereinafter, the circuit composed of the switching element SW ₁ and the diode D ₁ will be referred to as an upper arm, and the circuit composed of the switching element SW ₂ and the diode D ₂ will be referred to as a lower arm. Furthermore, snubber capacitors Cs (Cs ₁ , Cs ₂ ) are connected in parallel to the switching elements SW ₁ and SW ₂ , respectively. The snubber capacitors Cs ₁ and Cs ₂ are charged or discharged by a cutoff current when the switching element SW ₁ or the switching element SW ₂ is turned off. Since the capacitance of the snubber capacitors Cs ₁ and Cs ₂ is sufficiently larger than the output capacitance between the collector and emitter of the switching elements SW ₁ and SW ₂ , the change in voltage applied to both switching elements SW at turn-off is reduced, and the change in the voltage applied to both switching elements SW at turn-off is reduced. Losses are reduced.

A resonant circuit 30 is connected to an output terminal point t, which is a connection point between switching elements SW ₁ and SW ₂ , and a positive electrode point p and a negative electrode n point of the power supply circuit 10 . This resonant circuit 30 is composed of a heating coil 31 and resonant capacitors Cr ₁ and Cr ₂ . Here, the direction in which the resonant current IL flows from the output terminal point t toward the heating coil 31 is defined as the positive direction of the resonant current _IL . The resonant capacitor current shunting circuit 40 shunts the resonant current _IL flowing through the resonant circuit 30.

Further, the input current detector 11 detects a current input from the commercial power supply 1. The input current detection circuit 12 converts the output signal level of the input current detector 11 into a signal suitable for the input level of the control circuit 60.

The control circuit 60 determines the temperature of the object to be heated based on the relationship between the input current detected by the input current detection circuit 12 and the resonance current I _L detected by the averaging circuit 51 via the resonance capacitor current shunting circuit 40 and the rectification amplifier circuit 50. Starts or stops the heating operation based on the material and condition. 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. At that time, the resonance current I _L or the current value of the switching elements SW ₁ and SW ₂ (Ic ₁ and Ic ₂ described later) is detected, and the material of the object to be heated is determined based on the detected 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 the resistance value of each heated object at a frequency of 20 kHz. As shown here, the resistance value of non-magnetic stainless steel is 1/3 of iron, 1/20 of aluminum, and about 1/25 of copper.

Further, the control circuit 60 sets the conduction period of the switching elements SW ₁ and SW ₂ of the inverter circuit 20 via the drive circuit 21 according to a signal from the input power setting section 61, and performs PWM control of the input power. Material detection must be performed at low power and in a short time to prevent overcurrent and overvoltage.

Here, as shown in FIG. 2, the current flowing through the upper arm of the inverter circuit 20 is Ic ₁ , the current flowing through the lower arm is Ic ₂ , and the resonance current is I _L . Furthermore, the voltage between the collector and emitter of the switching element SW ₁ in the upper arm is Vc ₁ , the voltage between the collector and emitter of the switching element SW ₂ in the lower arm is Vc ₂ , and the power supply voltage of the inverter is Vp.

Next, the operation will be explained. FIG. 4 shows operating waveforms in modes 1 to 4 of the inverter of this embodiment. Note that in either mode, the switching elements SW ₁ and SW ₂ are driven complementary to each other with a dead time period provided.

As shown in FIG. 4, a sinusoidal resonant current I _L flows through the heating coil 31, and this resonant frequency fr is determined by the inductance value L of the heating coil 31 and the resonant capacitor Cr ₁ as shown in Equation 1. and the combined value of the resonance capacitor _Cr2 .

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 Ic ₁ of the switching element SW ₁ increases from negative to 0A. At the start of mode 1, no current is flowing through the switching element SW ₁ , but since the switching element SW ₁ is already turned on, the current Ic ₁ starts flowing through the switching element SW ₁ immediately after the start of mode 1. At this time, since the voltage across the switching element SW ₁ (voltage Vc ₁ between the collector terminal and emitter terminal) is 0V, ZVZCS turn-on occurs in which no loss occurs in the switching element SW ₁ .

(Mode 2)
When the switching element SW ₁ is cut off and mode 2 is established, the resonant current _IL flows through the power supply circuit 10, the snubber capacitor Cs ₁ , the heating coil 31, the resonant capacitor Cr ₁ , and the heating coil 31, the resonant capacitor Cr ₂ , and the snubber capacitor. It flows through the path of Cs ₁ , the heating coil 31, the resonance capacitor Cr ₁ , and the snubber capacitor Cs ₂ . At this time, snubber capacitor Cs ₁ is charged and snubber capacitor Cs ₂ 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 Vc ₁ of the snubber capacitor Cs ₁ becomes equal to or higher than the power supply voltage (p-n voltage), the voltage Vc ₂ of the snubber capacitor Cs ₂ becomes 0V, the diode D ₂ is turned on, and the resonant current I _L continues to flow. An ON signal is input to the switching element _SW2 during a period when current is flowing through the diode _D2 .

(Mode 3)
It is assumed that mode 3 starts at the timing when the current Ic ₂ of the switching element SW ₂ increases from negative to 0A. Although no current is flowing through the switching element SW ₂ at the start of mode 3, since the switching element SW ₂ is already turned on, the current Ic ₂ starts flowing through the switching element SW ₂ immediately after the start of mode 3. At this time, since the voltage across the switching element SW ₂ (voltage Vc ₂ between the collector terminal and the emitter terminal) is 0V, ZVZCS turn-on occurs in which no loss occurs in the switching element SW ₂ .

(Mode 4)
When the switching element SW ₂ is cut off and mode 4 is established, the resonant current _IL flows through the heating coil 31, the snubber capacitor Cs ₂ , the power supply circuit 10, the resonant capacitor Cr ₂ , and the heating coil 31, the snubber capacitor Cs ₂ , and the resonant capacitor. It flows through the path of Cr ₁ and the path of the heating coil 31, snubber capacitor Cs ₁ and resonance capacitor Cr ₂ . At this time, snubber capacitor Cs ₂ is charged and snubber capacitor Cs ₁ is discharged. As a result, the voltage across the switching element _SW2 gradually increases, ZVS turn-off occurs, and switching loss can be reduced.

When the voltage Vc ₂ of the snubber capacitor Cs ₂ becomes equal to or higher than the power supply voltage (p-n voltage), the voltage Vc ₁ of the snubber capacitor Cs ₁ becomes 0V, the diode D ₁ is turned on, and the resonant current I _L continues to flow. An ON signal is input to the switching element _SW1 during a period when current is flowing through the diode _D1 .

By repeating the operations in modes 1 to 4 above and passing a high-frequency current through the heating coil 31, magnetic flux is generated from the heating coil 31. This magnetic flux causes an eddy current to flow through the pot placed on the heating coil 31, and the pot itself generates heat due to induction heating.

Next, a power control method will be explained. Figure 5 shows the relationship between frequency and input power. IH cooking heaters utilize resonance phenomena to send a large, high-frequency current through a heating coil. Therefore, the frequency characteristics of the input power exhibit resonance characteristics. As shown in FIG. 3, since the resistance of the iron pot is large, the resonance Q is small and exhibits a gentle resonance characteristic. On the other hand, low-resistance materials such as aluminum and copper have a large resonance Q and exhibit steep resonance characteristics. For iron pots with a small resonance Q, it is possible to control the power by frequency by utilizing the gentle resonance characteristics.

Further, FIG. 6 shows the relationship between the duty of the switching element _SW1 and the input power. Power control based on duty is also possible for iron pots with small resonance Q. On the other hand, in the case of aluminum or the like having steep resonance characteristics, it is difficult to perform frequency control or duty control, and power can be controlled by controlling the output voltage of the power supply circuit 10.

Next, details of the resonant capacitor current shunting circuit 40, the rectifying amplifier circuit 50, and the averaging circuit 51 that constitute the resonant current detection circuit will be described using FIGS. 2 and 7.

As shown in FIG. 2, the resonant capacitor current shunting circuit 40 is composed of a series circuit of a capacitor C ₄₀ and a resistor R ₄₀ connected in parallel with the resonant capacitor Cr ₁ of the resonant circuit 30.

_The rectifying amplifier circuit 50 of _this embodiment is an inverting amplifier circuit ₅₂ , and as shown in FIG. The other end of the resistor R _52a is connected to the connection point (VR_OUT) between the capacitor C ₄₀ and the resistor R ₄₀ of the resonant capacitor current shunting circuit 40, and the other end of the resistor R _52b is connected to the output terminal of the operational amplifier A ₅₂ . This is the configuration of an inverting amplifier circuit in which the non-inverting input terminal of the operational amplifier _A52 is grounded.

Further, as shown in FIG. 7, the averaging circuit 51 includes a parallel circuit of a capacitor C _51a and a resistor R _51a , and a series circuit of a resistor R 51b and a capacitor C 51b at the output of the inverting amplifier circuit ₅₂ (rectifying amplifier circuit ₅₀₎ . This is a configuration in which circuits are connected. Then, the voltage of the capacitor C _51b of the averaging circuit 51 becomes the output voltage V _out .

Next, the operations of the resonant capacitor current shunting circuit 40, the rectifying amplifier circuit 50 (inverting amplifier circuit 52), and the averaging circuit 51, which constitute the current detection circuit of this embodiment, will be explained using FIG. 8. The operating waveforms shown here are, from top to bottom, (a) gate voltage of the upper and lower arms, (b) current I _Cr1 of the resonant capacitor Cr ₁ , (c) output voltage VR_OUT of the resonant capacitor current shunt circuit 40, and (d) rectification. These are the output voltage Va of the amplifier circuit 50 and the output voltage V _out of the averaging circuit 51. The operating conditions are that the heating load (pot) is a stainless steel pot, the operating frequency of the inverter is 35 kHz, and the drive signals for the upper and lower arms are asymmetric PWM, with the upper arm having a duty of 0.2 and the lower arm having a duty of 0.8. In other words, the upper arm is energized for a short time and the lower arm is energized for a long time.

When the inverter 100a is operated under the above conditions, the peak current of the resonant capacitor _Cr1 of the resonant circuit 30 is 30A/-23A. Assuming that the resonant capacitor _{Cr 1} is 1 μF, the capacitor C ₄₀ of the resonant capacitor current shunting circuit ₄₀ is 470 pF, and the resistor R ₄₀ is 150 Ω, the resonant capacitor Cr is Approximately 1/2000 of the current I _Cr1 of ₁ flows into the capacitor C ₄₀ , and the peak of the output voltage VR_OUT of the resonant capacitor current shunting circuit 40 generated in the resistor R ₄₀ is 2.25V/-1.7V. This output voltage VR_OUT is input to the rectifier amplifier circuit 50. The amplification factor G of the rectifying amplifier circuit 50 (inverting amplifier circuit 52) is expressed by Equation 2 from the resistor R _52a and the resistor R _52b .

From Equation 2, the peak value of the output voltage Va of the rectifying amplifier circuit 50 (inverting amplifier circuit 52) is 5.1V. The output voltage Va of the rectifying amplifier circuit 50 (inverting amplifier circuit 52) is converted into a constant voltage by the averaging circuit 51, and the output voltage V _out of the averaging circuit 51 becomes approximately 2V. Since the resonant current I _L flowing through the heating coil 31 is the total current of the resonant capacitors Cr ₁ and Cr ₂ , if the resonant capacitors Cr ₁ and Cr ₂ have the same capacitance, the resonant current I _L will be the sum of the current of the resonant capacitors Cr 1 and Cr ₂ . The current I becomes twice as much as the current I _Cr1 . In other words, the voltage has a value proportional to the resonant current _IL .

FIG. 9 shows the relationship between the resonant current I _L and the output voltage V _out of the averaging circuit 51. As shown here, even in pans made of different materials, the resonant current I _L and the output voltage V _out show an approximately equal proportional relationship, and the resonant current I _L can be detected from the output voltage V _out regardless of the material of the pan. can do.

As described above, by dividing the current flowing through the resonant capacitor _Cr1 and rectifying and averaging the voltage generated by the resistor, it is possible to use an induction heating device where the inverter is PWM controlled without using a current transformer or shunt resistor. , the resonant current flowing through the heating coil can be detected. This can contribute to miniaturization and cost reduction of the resonant current detection circuit.

Next, an electromagnetic induction heating device according to a second embodiment of the present invention will be described using FIGS. 10 to 12. Note that redundant explanation of common points with the embodiments described above will be omitted.

The difference from the first embodiment is that the configuration of the rectifier amplifier circuit 50 is different. In the first embodiment, the output voltage VR_OUT of the resonant capacitor current shunting circuit 40 is half-wave rectified by the inverting amplifier circuit 52, which is a type of rectifier amplifier circuit 50, and then averaged by the averaging circuit 51. In the second embodiment, the output voltage VR_OUT is full-wave rectified by a full-wave rectifier circuit 53, which is a type of rectifier amplifier circuit 50, and then averaged by an averaging circuit 51.

The circuit configuration of the full-wave rectifier circuit 53, which is the rectifier amplifier circuit 50 in this embodiment, will be explained using FIG. 10. In this full-wave rectifier circuit 53, the output voltage VR_OUT of the resonant capacitor current shunting circuit 40 is connected to the inverting input terminal of the operational amplifier A _53a via a resistor R _53a . The cathode terminal of the diode D _53a is connected to the inverting input terminal of the operational amplifier A _53a , and the anode terminal of the diode D _53a is connected to the output terminal of the operational amplifier A _53a . Furthermore, the anode terminal of a diode D _53b is connected to the inverting input terminal of the operational amplifier A _53a via a resistor R _53b , and the cathode terminal of the diode D _53b is connected to the output terminal of the operational amplifier A _53a . The anode terminal of diode D _53b is connected to the inverting input terminal of operational amplifier A _53b via resistor R _53c . The inverting input terminal of operational amplifier A _53b is connected to the output terminal of operational amplifier A _53b through a resistor R _53e , and the output voltage VR_OUT is connected to the inverting input terminal of operational amplifier A _53b through a resistor R _53d . The non-inverting input terminals of operational amplifiers A _53a and A _53b are grounded. The averaging circuit 51 described in the first embodiment is connected to the output terminal of the operational amplifier A _53b .

Next, the operation of the current detection circuit of this embodiment will be explained using FIG. 11. Here, the operating waveforms are, from top to bottom, (a) current I _Cr1 of resonant capacitor Cr ₁ , (b) output voltage VR_OUT of resonant capacitor shunt circuit 40, (c) intermediate voltage Vb of full-wave rectifier circuit 53, (d ) The output voltage Vc of the full-wave rectifier circuit 53 and the output voltage V _out of the averaging circuit 51.

When the inverter 100a is operated under the same conditions as in FIG. 8, the peak current of the resonant capacitor _Cr1 of the resonant circuit 30 is 30A/-23A. Assuming that the resonant capacitor _{Cr 1} is 1 μF, the capacitor C ₄₀ of the resonant capacitor current shunting circuit ₄₀ is 1000 pF, and the resistor R ₄₀ is 82 Ω, the resonant capacitor Cr is Approximately 1/1000 of the current I _Cr1 of ₁ flows into the capacitor C ₄₀ , and the peak of the output voltage VR_OUT of the resonant capacitor current shunting circuit 40 generated in the resistor R ₄₀ is 2.5V/-1.9V.

When the output voltage VR_OUT becomes a negative voltage, the diode _D53a becomes conductive and the diode _D53b turns off, and the forward voltages of the diodes _D53a and _D53b cancel each other out, so that the intermediate voltage Vb of the full-wave rectifier circuit 53 becomes zero volts. become. On the other hand, when the output voltage VR_OUT becomes a positive voltage, the diode D _53b becomes conductive, but the diode D _53a turns off, so the forward voltages of the diodes D _53a and D _53b cancel each other out, resulting in the inversion described in Example 1. The operation is similar to that of the amplifier circuit 52, and due to the relationship between the resistors R _53a and R _53b , if the resistors R _53a and R _53b are set to 10 kΩ, the intermediate voltage Vb voltage of the full-wave rectifier circuit 53 is the output voltage VR_OUT with the positive and negative reversed. It becomes -2.5V.

The operational amplifier A _53b is a circuit that inverts and amplifies the intermediate voltage Vb and the output voltage VR_OUT and adds them together. Further, the inverting input terminal and the non-inverting input terminal of the operational amplifier A _53b are imaginary short-circuited, and since the non-inverting input terminal is grounded, the non-inverting input terminal becomes zero volts. Assuming that the resistor R _53c is 10 kΩ and the resistors R _53d and R _53e are 20 kΩ, when the output voltage VR_OUT is 2.5 V at the positive peak voltage, the resistor R _53d has a current of Ia = -125 μA (5 V/20 kΩ). flows, and since the intermediate voltage Vb is -2.5V, a current of Ib=250 μA flows through the resistor R _53c . Since the input terminal of the operational amplifier has a high impedance, no current flows into it, and Ic, which is the total current of Ia and Ib, flows through the resistor _R53e . Therefore, since Ic=125 μA flows, the output voltage Vc of the full-wave rectifier circuit 53 becomes Vc=2.5 V (125 μA×20 kΩ). On the other hand, when the output voltage VR_OUT is at a negative peak voltage of -1.9V, a current of Ia=95μA (1.9V/20kΩ) flows through the resistor _R53d , and since Vb is 0V, a current flows through the resistor _R53c . does not flow. Therefore, since Ic=95 μA flows, the output voltage Vc of the full-wave rectifier circuit 53 becomes Vc=1.9V (95 μA×20 kΩ). As a result, the output voltage Vc of the full-wave rectifier circuit 53 has a form obtained by full-wave rectifying the current I _Cr1 of the resonant capacitor _Cr1 . By averaging the output voltage Vc of the full-wave rectifier circuit 53 with the averaging circuit 51, a voltage proportional to the resonant current _IL can be detected. By configuring the full-wave rectifier circuit 53 in this manner, current information on the positive current and negative current of the resonant current _IL can be detected, so that current can be detected with high accuracy.

FIG. 12 shows the relationship between the resonant current I _L and the output voltage V _out of the averaging circuit 51. As shown here, even in pans made of different materials, the resonant current I _L and the output voltage V _out show an approximately equal proportional relationship, and the resonant current I _L can be detected from the output voltage V _out regardless of the material of the pan. can do.

As described above, by dividing the current flowing through the resonant capacitor _Cr1 and rectifying and averaging the voltage generated by the resistor, it is possible to use an induction heating device where the inverter is PWM controlled without using a current transformer or shunt resistor. , the heating coil current can be detected. This can contribute to miniaturization and cost reduction of the resonant current detection circuit.

Next, an electromagnetic induction heating device according to a third embodiment of the present invention will be described using FIGS. 13 and 14. Note that redundant explanation of common points with the embodiments described above will be omitted. Similar to the second embodiment, the resonant current detection circuit of this embodiment has a configuration in which the output voltage VR_OUT of the resonant capacitor current shunting circuit 40 is full-wave rectified and then averaged, but the difference is that the operational amplifier can be driven by a single power supply. This is different from the second embodiment. As a result, in this embodiment, the resonance current flowing through the heating coil can be detected with an inexpensive configuration without providing a negative power supply circuit.

The circuit configuration of the rectifier amplifier circuit 50 of this embodiment will be explained using FIG. 13. As shown here, the rectifying amplifier circuit 50 of this embodiment is a combination of the inverting amplifier circuit 52 of the first embodiment and the adding circuit 54.

<Inverting amplifier circuit 52>
The inverting amplifier circuit 52 has the same configuration as the first embodiment. That is, the output voltage VR_OUT of the resonant capacitor current shunting circuit 40 is connected to the inverting input terminal of the operational amplifier A ₅₂ through the resistor R _52a , and the inverting input terminal of the operational amplifier A ₅₂ is connected to the operational amplifier A through the resistor R _52b . ₅₂ output terminals.

<Addition circuit 54>
The output voltage VR_OUT of the resonant capacitor current shunting circuit 40 and the output voltage Vd of the inverting amplifier circuit 52 are input to the adder circuit 54 . Specifically, the output terminal INV_AMP of the inverting amplifier circuit 52 is connected to the non-inverting input terminal of the operational amplifier A ₅₄ via a resistor R _54d , and the output terminal VR_OUT of the resonant capacitor current shunting circuit 40 is connected to the resistor R _54c . connected via. The inverting input terminal of operational amplifier A ₅₄ is connected to the output terminal via resistor R _54b and to ground via resistor R _54a . An averaging circuit 51 is connected to the output terminal of the operational amplifier A ₅₄ , and the output of the operational amplifier A ₅₄ becomes the output voltage Ve of the rectifier amplifier circuit 50 of this embodiment.

Next, the operation of the current detection circuit of this embodiment will be explained using FIG. 14. The operating waveforms shown in FIG. 14 are, from top to bottom, (a) current I _Cr1 of resonant capacitor Cr ₁ , (b) output voltage VR_OUT of resonant capacitor current shunt circuit 40, (c) output voltage Vd of inverting amplifier circuit 52, (d) The output voltage Ve of the adding circuit 54 and the output voltage V _out of the averaging circuit 51.

When the inverter 100a is operated under the same conditions as in FIG. 8, the peak current of the resonant capacitor _Cr1 of the resonant circuit 30 is 30A/-23A. Assuming that the resonant capacitor _{Cr 1} is 1 μF, the capacitor C ₄₀ of the resonant capacitor current shunting circuit ₄₀ is 1000 pF, and the resistor R ₄₀ is 82 Ω, the resonant capacitor Cr is Approximately 1/1000 of the current I _Cr1 of ₁ flows into the capacitor C ₄₀ , and the peak of the output voltage VR_OUT of the resonant capacitor current shunting circuit 40 generated in the resistor R ₄₀ is 2.5V/-1.9V. In this case, if the resistor R _52a is 10 kΩ and the resistor R _52b is 20 kΩ, the output voltage of the inverting amplifier circuit 52 is Vd (-20k/10k), which is 3.8V.

When the resistor R _54c and the resistor R _54d are set to 10 kΩ, the non-inverting input terminal of the operational amplifier A ₅₄ has a value obtained by dividing the voltage between the output terminals VR_OUT and INV_AMP by the resistors R _54c and R _54d . Therefore, the positive peak voltage of the output voltage VR_OUT of 2.5V is 1.25V, and the negative peak voltage of -1.9V is 0.95V. Since the adder circuit 54 has a non-inverting amplifier circuit configuration, the amplification factor is expressed as Equation 3.

When the above voltage is applied to the non-inverting input terminal voltage of the operational amplifier A ₅₄ , the amplification factor becomes 4 times, and becomes 5V at the positive peak voltage of the output voltage VR_OUT and 3.8V at the negative peak voltage. This results in full-wave rectification of the resonant capacitor current. By averaging the output voltage Ve of the adding circuit 54 with the averaging circuit 51, a voltage proportional to the resonance current _IL flowing through the heating coil 31 can be detected. In this way, the output of the resonant capacitor current shunting circuit 40 is added via the non-inverting amplifier circuit and the inverting amplifier circuit, resulting in a full-wave rectified form, and the current information of the positive current and negative current of the heating coil current is obtained. Since the current can be detected, it becomes possible to detect the current with high accuracy. Furthermore, since it can be configured without using a negative power source, it is an advantageous configuration for reducing costs.

Next, an electromagnetic induction heating device according to a fourth embodiment of the present invention will be described using FIGS. 15 and 16. Note that redundant explanation of common points with the embodiments described above will be omitted.

In Examples 1 to 3, the rectifier amplifier circuit 50 with a built-in operational amplifier was used, but this example has a configuration in which the resonant current _IL flowing through the heating coil 31 can be detected without using an operational amplifier. Thereby, the number of circuit elements can be reduced, and the heating coil current can be detected with a cheaper configuration.

The circuit configuration of the resonant current detection circuit of this embodiment will be explained. In this embodiment, as shown in FIG. 15, the output voltage VR_OUT of the resonant capacitor current shunting circuit 40 is connected to the averaging circuit 51 via a diode _D15 corresponding to a rectifier circuit.

Next, the operation of the current detection circuit of this example will be explained using FIG. 16. The operating waveforms shown here are (a) current I _Cr1 of the resonant capacitor Cr ₁ , (b) output voltage VR_OUT of the resonant capacitor current shunt circuit 40, () output voltage Vh of the diode D ₁₅ and the averaging circuit 51. The output voltage is _Vout .

When the inverter 100a is operated under the same conditions as in FIG. 8, the peak current of the resonant capacitor _Cr1 of the resonant circuit 30 is 30A/-23A. Assuming that the resonant capacitor _{Cr 1} is 1 μF, the capacitor C ₄₀ of the resonant capacitor current shunting circuit ₄₀ is 1000 pF, and the resistor R ₄₀ is 150 Ω, the resonant capacitor Cr is Approximately _1/1000 of the current flows to the resistor R _51b via the capacitor C ₄₀ and the diode D ₁₅ , and the peak output voltage of the resonant capacitor current shunting circuit 40 generated in the resistor R ₄₀ is 3.0V/-3.6V. Become. The negative voltage generated in the resistor R ₄₀ is limited by the diode D ₁₅ , and the output voltage Vh outputs only a positive voltage, which is converted to a constant voltage by the resistor R _51b and the capacitor C _51b , and the resonance current _IL flowing through the heating coil 31. An output voltage V _out proportional to the effective value can be detected. Thereby, the resonant current _IL flowing through the heating coil 31 can be detected with a cheaper configuration without using an operational amplifier.

<Modified example>
Next, an electromagnetic induction heating device according to a modification of the fourth embodiment will be described using FIGS. 17 and 18. In this modification, as shown in FIG. 17, a diode _D17 , which is a rectifier circuit, is connected in parallel to the output voltage VR_OUT of the resonant capacitor current shunting circuit 40, and an averaging circuit 51 is connected in parallel with the diode _D17. This is the configuration.

The operation of the current detection circuit of this example will be explained using FIG. 18. The operating waveforms shown here are (a) the current I _Cr1 of the resonant capacitor Cr ₁ , (b) the output voltage VR_OUT of the resonant capacitor current shunting circuit 40, and the output voltage V _out of the averaging circuit 51, in order from the top.

When the inverter 100a is operated under the same conditions as in FIG. 8, the peak current of the resonant capacitor _Cr1 of the resonant circuit 30 is 30A/-23A. Assuming that the resonant capacitor _{Cr 1} is 1 μF, the capacitor C ₄₀ of the resonant capacitor current shunting circuit ₄₀ is 1000 pF, and the resistor R ₄₀ is 150 Ω, the resonant capacitor Cr is Approximately 1/1000 of the current I _Cr1 of ₁ flows through the capacitor C ₄₀ and a voltage is generated across the resistor R ₄₀ . However, at negative currents, resistor R ₄₀ generates a negative voltage but is clamped by diode D ₁₇ by the forward voltage of diode D ₁₇ . Therefore, the peak output voltage of the resonant capacitor current shunting circuit 40 is 2.93V/-0.3V. In this way, in the circuit configuration of this modification, it is possible to detect the output voltage V _out which is converted into a constant voltage by the resistor R _52b and the capacitor C _52b and is proportional to the effective value of the resonant current I _L flowing through the heating coil 31. can. Thereby, the resonant current _IL flowing through the heating coil 31 can be detected with a cheaper configuration without using an operational amplifier.

1 Commercial power supply 5 Heating coil 10 Power supply circuit 11 Input current detector 12 Input current detection circuit 13 Diode bridge 14 Inductor 20 Inverter circuit 21 Drive circuit 30 Resonance circuit 40 Resonant capacitor current shunting circuit 50 Rectification amplifier circuit 51 Averaging circuit 60 Control circuit 61 Input power setting section 100a, 100b, 100c Inverter A Operational amplifier Cf Filter capacitor Cr Resonance capacitor Cs Snubber capacitor C Capacitor D Diode R Resistor SW Switching element

Claims (5)

An electromagnetic induction heating device that inductively heats a heated object using a heating coil,
a DC power supply that supplies DC voltage;
an inverter circuit that converts the DC voltage into a high-frequency AC voltage and supplies it to the heating coil;
a control circuit that controls the inverter circuit;
a resonant circuit in which the heating coil and a resonant capacitor are connected in series;
a resonant capacitor current shunting circuit that shunts the current flowing to the resonant capacitor;
a rectifier amplifier circuit that rectifies and amplifies the output of the resonant capacitor current shunt circuit;
an averaging circuit that averages the output of the rectifier amplifier circuit;
Equipped with
The inverter circuit includes a plurality of switching elements,
The electromagnetic induction heating device is characterized in that the control circuit controls the alternating current voltage supplied to the heating coil by performing PWM control on the conduction period of each switching element . The electromagnetic induction heating device according to claim 1,
The resonant capacitor current shunting circuit is composed of a series circuit of a capacitor and a resistor,
An electromagnetic induction heating device characterized in that a voltage generated in the resistor is used as an output of the resonant capacitor current shunting circuit. The electromagnetic induction heating device according to claim 1 or 2,
The averaging circuit is
a parallel circuit of a first capacitor and a first resistor;
a series circuit of a second resistor and a second capacitor connected to both ends of the first resistor,
An electromagnetic induction heating device characterized in that the voltage across the second capacitor is the output of the averaging circuit. The electromagnetic induction heating device according to any one of claims 1 to 3,
The rectifier amplifier circuit is
connecting an inverting input terminal of a first operational amplifier to an output terminal of the resonant capacitor current shunting circuit via a first input resistor;
A first diode and a series circuit of a first feedback resistor and a second diode are connected between the inverting input terminal and the output terminal of the first operational amplifier,
connecting a series circuit of the second diode and a second input resistor between the output terminal of the first operational amplifier and the inverting input terminal of the second operational amplifier;
connecting the inverting input terminal of the second operational amplifier to the output terminal of the resonant capacitor current shunting circuit via a third input resistor;
connecting a second feedback resistor between the inverting input terminal and the output terminal of the second operational amplifier;
non-inverting input terminals of the first operational amplifier and the second operational amplifier are grounded;
An electromagnetic induction heating device characterized by a full-wave rectifier circuit. An electromagnetic induction heating device that inductively heats a heated object using a heating coil,
a DC power supply that supplies DC voltage;
an inverter circuit that converts the DC voltage into a high-frequency AC voltage and supplies it to the heating coil;
a control circuit that controls the inverter circuit;
a resonant circuit in which the heating coil and a resonant capacitor are connected in series;
a resonant capacitor current shunting circuit that shunts the current flowing to the resonant capacitor;
a rectifier circuit that rectifies the output of the resonant capacitor current shunt circuit;
an averaging circuit that averages the output of the rectifier circuit;
Equipped with
The inverter circuit includes a plurality of switching elements,
The electromagnetic induction heating device is characterized in that the control circuit controls the alternating current voltage supplied to the heating coil by performing PWM control on the conduction period of each switching element .

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