JP4444243B2 - Induction heating device - Google Patents

Description

  The present invention relates to an induction heating cooker capable of efficiently performing induction heating on an object to be heated having high conductivity and low magnetic permeability such as an aluminum pan, and an induction heating apparatus such as an induction heating type water heater, a humidifier or an iron. It is about.

  Hereinafter, as an example of a conventional induction heating apparatus, an induction heating cooker that generates a high-frequency magnetic field from a heating coil and heats a load such as a pan by eddy current due to electromagnetic induction will be described with reference to FIG.

  FIG. 5 is a diagram showing a circuit configuration of a conventional induction heating cooker. The power source 51 is a 200 V commercial power source that is a low-frequency AC power source, and is connected to an input terminal of a rectifier circuit 52 that is a bridge diode. A first smoothing capacitor 53 is connected between the output terminals of the rectifier circuit 52. A series connection body of the choke coil 54 and the second switching element 57 is further connected between the output terminals of the rectifier circuit 52. The heating coil 59 is arranged to face the aluminum pan 61 that is the object to be heated. 50 is an inverter, the low potential side terminal (emitter) of the second smoothing capacitor 62 is connected to the negative terminal of the rectifier circuit 52, and the high potential side terminal of the second smoothing capacitor 62 is the first switching element (IGBT). ) 55 is connected to the high potential side terminal (collector) of the first switching element (IGBT) 55 and the low potential side terminal of the first switching element (IGBT) 55 is the high potential side terminal (collector) of the choke coil 54 and the second switching element (IGBT) 57. Connected to the connection point. A series connection body of the heating coil 59 and the resonance capacitor 60 is connected to the second switching element 57 in parallel. The first diode 56 (first reverse conducting element) is connected in antiparallel to the first switching element 57 (the cathode of the first diode 56 and the collector of the first switching element 57 are connected), and the second The diode 58 (second reverse conducting element) is connected to the second switching element 57 in antiparallel. The snubber capacitor 64 is connected in parallel to the second switching element 57. A series connection body of the correcting resonance capacitor 65 and the relay 66 is connected to the resonance capacitor 60 in parallel. The control circuit 63 inputs detection signals of a current transformer 67 that detects an input current from the power source 51 and a current transformer 68 that detects a current of the heating coil 59, and the first switching element 55 and the second switching element. A signal is output to a gate 57 and a drive coil (not shown) of the relay 66.

  The operation of the induction cooking device configured as described above will be described below. The power source 1 is full-wave rectified by a rectifier circuit 52 and supplied to a first smoothing capacitor 53 connected to the output terminal of the rectifier circuit 52. The first smoothing capacitor 53 serves as a supply source for supplying a high-frequency current to the inverter. FIG. 6 is a diagram showing the waveform of each part in the above circuit, and FIG. 6 (A) is the one when the output is 2 kW, which is a large output. FIG. 4A shows the current waveform Ic1 flowing through the first switching element 55 and the first diode 56, and FIG. 4B shows the current waveform Ic2 flowing through the second switching element 57 and the second diode 58. FIG. 4C shows the voltage Vce2 generated between the collector and the emitter of the second switching element 57, FIG. 4D shows the drive voltage Vg1 applied to the gate of the first switching element 55, and FIG. The driving voltage Vg <b> 2 applied to the gate of the second switching element 57 and the current IL flowing through the heating coil 59 are shown in FIG. When the output is 2 kW (FIG. 6 (A)), the control circuit 63 has a driving period T2 (about 24 μsec) at the gate of the second switching element 57 as shown in (e) from time t0 to time t1. Outputs an on signal. During this driving period T2, the second switching element 57 and the second diode 58, the heating coil 59, and the resonant capacitor 60 resonate in a closed circuit, and the pot 61 is an aluminum pot. The number of turns of the heating coil 59 (40T), the capacity of the resonant capacitor 60 (0.04 μF), and the driving period so that the resonance period (1 / f) is about 2/3 times (about 16 μs) the driving period T2. T2 is set. The choke coil 54 stores the electrostatic energy of the smoothing capacitor 53 as magnetic energy during the driving period T2 of the second switching element 57. Next, the collector current is applied at the time t1, which is the timing between the second peak of the resonance current flowing in the second switching element 57 and the resonance current next becoming zero, that is, in the forward direction of the second switching element 57. At the time of flowing, the driving of the second switching element 57 is stopped. Then, since the second switching element 57 is turned off, the potential of the terminal of the choke coil 54 connected to the collector of the second switching element 57 rises, and when this potential exceeds the potential of the second smoothing capacitor 62, The second smoothing capacitor 62 is charged through the first diode 56 to release the magnetic energy stored in the choke coil 54. The voltage of the second smoothing capacitor 62 is boosted so as to be higher than the peak value (283 V) of the DC output voltage Vdc of the rectifier 52 (500 V in this conventional example). The level to be boosted depends on the conduction time of the second switching element 58, and the voltage generated in the second smoothing capacitor 62 tends to increase as the conduction time increases. As described above, the second smoothing capacitor 62, the first switching element 55, the first diode 56, the heating coil 59, and the second smoothing functioning as a DC power source when resonating in a closed circuit formed by the resonance capacitor 60. As the voltage level of the capacitor 62 is boosted, the peak value (peak value) of the resonance current flowing through the first switching element 55 shown in FIG. In such a manner that the peak value of the resonance current flowing through the second switching element 57 of FIG. 5B that resonates does not become zero or does not become small, the aluminum pan is induction-heated with high output, In addition, the output can be controlled by increasing or decreasing continuously. Then, as shown in (d) and (e) of FIG. 6 (A), the control circuit 63 starts at time t2 after an idle period provided to prevent both switching elements from conducting simultaneously from time t1. A drive signal is output to the gate of the first switching element 55. As a result, as shown in FIG. 5A, the path is changed to a closed circuit composed of the heating coil 59, the resonance capacitor 60, the first switching element 55 or the first diode 56, and the second smoothing capacitor 62, and the resonance current is changed. Will flow. In this case, the drive period T2 of the drive signal is set to substantially the same period as T1, so that the drive period T2 is about 2/3 of the drive period T1, as in the case where the second switching element 58 is conductive. Periodic resonance current flows. Therefore, the current IL flowing through the heating coil 59 has a waveform as shown in (f) of FIG. 6A, and the drive periods (the sum of T1, T2, and the idle period) of the first and second switching elements are resonant. If the current period is about three times and the first and second drive frequencies are about 20 kHz, the frequency of the resonant current flowing through the heating coil 59 is about 60 kHz. Next, at the time of start-up, the control circuit 63 turns off the relay 66 and drives the first switching element 55 and the second switching element 57 alternately at a constant frequency (about 21 kHz). The drive period of the first switching element 55 is driven in a mode shorter than the resonance period of the resonance current, the drive time ratio is minimized, and the drive time ratio is gradually increased after the minimum output is achieved. 63 detects the material of the load pan 61 from the detection output of the current transformer 67 and the detection output of the current transformer 68. When the control circuit 63 determines that the material of the load pan 61 is iron-based, the heating is stopped, the relay 66 is turned on, and heating is started again at a low output. At this time, the control circuit 63 gradually increases the first switching element 55 and the second switching element 57 from a minimum output at a constant frequency (about 21 kHz) with a minimum drive time ratio to a predetermined output. On the other hand, when it is not detected that the load is iron-based, when the predetermined drive time ratio is reached, the period of the resonance current is shorter than the drive period of the first switching element 57 as shown in FIG. Enter mode. At this time, the drive period is set so that the output is in a low output state. As described above, when a high-conductivity and low-permeability load such as aluminum or copper is heated by the magnetic field generated by the heating coil 59, the heating coil 59 and the resonant capacitor 60 that flow through the first switching element 55 and the first diode 56 are used. Since the resonance current due to the resonance current resonates at a cycle shorter than the drive period (T1) of each of the switching elements, a current having a frequency higher than the drive frequency of the first switching element 55 (1.5 times in this embodiment) Is further supplied to the heating coil 59, and further, a choke coil 54 as a boosting means and a second smoothing capacitor 62 as a smoothing means are provided to boost the voltage of the smoothing capacitor 62 as a high-frequency power source. Since the amplitude of the resonance current is increased in each drive period (T and T ′), the resonance current starts flowing after the drive is started. First cycle is completed from that in the following reached the second cycle also is capable to continue the resonance current of sufficiently large amplitude. In addition, when the maximum output is set, the control circuit 63 performs the first switching within a period in which the resonance current is flowing in the first switching element 55 after the start of driving of the first switching element 55. A signal that cuts off the conduction of the element 55 is output, or after the second switching element 57 starts to be driven, the resonance current is flowing in the second switching element 57 after the second period and flowing through the second switching element 57. Since the signal for shutting off the conduction of the second switching element is output, an increase in turn-on loss of the second switching element 57 or the first switching element 55 at the maximum output can be suppressed. In addition, at the time of start-up, load ratio is detected by changing the driving time ratio of the first switching element 55 and the second switching element 57 to increase the heating output and changing the driving frequency from the middle to increase the heating output. It can be made easier. That is, by changing the drive time ratio, the output can be monotonously changed in a low output state, whether it is a load of a material such as aluminum having a high conductivity and a low magnetic permeability or an iron load, and the control circuit 63 can detect the load. Accurate and low power state. Further, when an iron-based load or a nonmagnetic stainless steel load 61 is heated by the magnetic field generated by the heating coil 59, the resonance current resonates at a period longer than the conduction period of the first switching element 55 and the second switching element 57. When the iron-based load or the non-magnetic stainless steel load 61 is heated at the maximum output, the switching element is activated at the timing when the current flows in the first switching element 55 and the second switching element 57 in the forward direction. The correction resonance capacitor 65 is connected in parallel to the resonance capacitor 60 so as to be able to cut off, and the capacitance is switched to a larger capacity than when heating a load with high conductivity and low magnetic permeability. The correction capacitor 64 is connected in series with the heating coil 59 and has a switchable capacity. By switching the resonant capacitor 60 to a larger capacity than when heating a load with high conductivity and low permeability when heating a magnetic stainless steel load, the resonance frequency becomes longer and the current increases. Since the DC voltage Vdc is boosted by the choke coil 54, the amplitude of the resonance current increases, so the maximum output is set within a range in which the switching element can be cut off at the timing when the current flows through the switching element in the forward direction. Therefore, when it is intended to suppress an increase in switching loss when the switching element is turned on, the maximum output can be made larger than that of the conventional configuration. Further, when an aluminum pan and an iron pan are to be heated by the same inverter, conventionally, the number of turns of the heating coil 59 and the resonance capacitor are switched simultaneously to radiate the resonance frequency and the magnetic field to the object 61 to be heated. However, the coil winding number switching action can be replaced by the boosting action of the choke coil 54 and the first switching means 57, and the resonance capacitor 60 can be replaced by the same heating coil 59. By switching, there is an effect that an object to be heated of a wide range of materials can be heated. Further, the correction resonance capacitor 65 is started without being connected to the resonance capacitor 60, that is, is started with the resonance capacitor 60 having a small capacity, and the output is gradually increased. It is determined whether it has conductivity and low magnetic permeability. If it is determined that the load is an iron-based load, after the drive is stopped, the relay 60 is turned on and the correcting resonance capacitor 65 is connected in parallel. Since the capacitor 60 is switched to have a large capacity and the drive frequency is re-driven at a low frequency, the resonance frequency is increased and the current is increased. Further, the choke coil 54 as the boosting means and the second smoothing capacitor 62 are used for direct current. Since the power supply voltage is boosted, the resonance current value increases, so that the switching element is switched at the timing when the current flows in the forward direction to the first switching element 55. The when the extent possible blocking by setting the maximum output attempts to suppress the increase in switching loss at turn-on of the switching element 57 can be made larger than that of the conventional configuration the maximum output. If it is determined that the load has high conductivity and low permeability, the drive time ratio is continuously fixed and the conduction time is changed by increasing the output to a predetermined drive time ratio or a predetermined output. Since the output reaches a predetermined output, so-called soft start operation is possible to start at a low output at any load, determine the load, and stably reach the predetermined output value or limit value. It becomes.

In the induction heating cooker configured as described above, since the load detection can be performed accurately and in a low output state regardless of a load of a material such as aluminum having a high conductivity and a low permeability or an iron load, the relay is turned on and off. Thus, the resonant capacitor is switched to enable induction heating according to the material of the load.
Japanese Patent No. 3460997

  However, in the conventional configuration as seen in Patent Document 1, a high-voltage relay is required to heat a load of a material such as aluminum having a high conductivity and a low permeability and an iron load, High output was difficult. Also, sufficient output can be obtained in intermediate materials between high-conductivity and low-permeability aluminum materials such as aluminum and iron-based loads, that is, composite materials in which aluminum is combined with a relatively thick nonmagnetic stainless steel or thin stainless steel. If the drive frequency of the switching element is approximately ½ times the resonance frequency of the resonance circuit, the switching loss can be reduced without switching the resonance capacitor rather than driving at the approximately resonance frequency, but the drive is performed at approximately ３ times. The problem is that it is difficult to obtain sufficient output.

  The present invention solves the above-mentioned conventional problems, and can obtain a larger heating output with a simple configuration from high conductivity such as aluminum and copper to low conductivity such as magnetic material regardless of the material of the load. An object is to provide an induction heating apparatus.

In order to solve the conventional problem, an induction heating device of the present invention includes a heating coil for magnetically coupling a load and a resonance circuit having a resonance capacitor, an inverter having a switching element and supplying power to the resonance circuit, Heating output control means for controlling the heating output of the heating coil, rectification means for rectifying commercial alternating current, and load material detection means for detecting the material of the load, wherein the resonant capacitor includes a first capacitor and a second capacitor. a series circuit of a capacitor, a first switching means connected in parallel with the first capacitor, a series circuit of a third capacitor and a second switching means connected in parallel with said second capacitor wherein the third capacitor is to increase the electrostatic capacitance than the second capacitor, the load material detection means said load and high conductivity such as aluminum low When the magnetic material is detected, the first switching means and the second switching means are opened to switch the driving frequency of the switching element to approximately 1/3 times the resonance frequency of the resonance circuit, and the load material When the detecting means detects the load as an intermediate material such as a composite material in which a high-conductivity material such as aluminum or copper is provided on a thick non-magnetic stainless steel plate or a thin non-magnetic stainless steel plate, the first switching is performed. Short-circuiting means and opening the second switching means to switch the drive frequency to approximately 1/3 times the resonance frequency, and the load material detecting means is made of a material having a low conductivity such as iron. When detected, the first switching unit and the second switching unit are short-circuited, and the drive frequency is switched to be substantially the same as the resonance frequency . With this configuration, an induction heating apparatus that can obtain a larger heating output regardless of the material of the load from a high conductivity such as aluminum or copper to a low conductivity such as a magnetic material with an easy configuration that does not use a high-voltage relay, can do.

  The induction heating apparatus of the present invention can obtain a larger heating output with a simple configuration from a high conductivity such as aluminum or copper to a low conductivity such as a magnetic material regardless of the material of the load.

A first invention is a heating circuit for magnetically coupling a load and a resonance circuit having a resonance capacitor, an inverter having a switching element and supplying power to the resonance circuit, and a heating output control for controlling the heating output of the heating coil. Means, rectifying means for rectifying commercial alternating current, and load material detecting means for detecting the material of the load, wherein the resonant capacitor is a series circuit of a first capacitor and a second capacitor, and the first capacitor. comprising a first switching means connected in parallel, and a series circuit of a third capacitor and a second switching means connected in parallel with the second capacitor, the third capacitor and the second to increase the capacitance from capacitor, when the load material detection unit has the load detecting a material of high conductivity and low permeability like aluminum the first switch The stage and the second switching means are opened to switch the drive frequency of the switching element to approximately 1/3 times the resonance frequency of the resonance circuit, and the load material detection means switches the load to a non-magnetic stainless steel plate or When an intermediate material such as a composite material in which a high conductivity material such as aluminum or copper is provided on a thin nonmagnetic stainless steel plate is detected, the first switching means is short-circuited and the second switching means is opened. The drive frequency is
When the load material detecting means detects the load as a material having a low conductivity such as iron, the first switching means and the second switching means are short-circuited. By switching the drive frequency so as to be substantially the same as the resonance frequency, the load can be reduced from a high conductivity such as aluminum or copper to a low conductivity such as a magnetic material with an easy configuration without using a high-voltage relay. A larger heating output can be obtained regardless of the material.

  In the second invention, in particular, in the first invention, the resonance capacitor is a series circuit of two capacitors, and the capacitance of each capacitor is substantially the same. A higher heating output can be obtained regardless of the material of the load, from the rate to the low conductivity such as a magnetic material.

  According to a third aspect of the invention, in particular, in the first or second aspect of the invention, the inverter has a full bridge circuit, so that the load material can be applied more easily with an easy configuration.

A fourth invention is, in particular, in the first to third any one of the, with a power factor improving means for improving the power factor of the commercial alternating current, the power factor correction means high load the load material detection means the conductivity and the material of low permeability, if it is detected that the material of the intermediate material or low conductivity, with the configuration you supplied to the inverter boosts the rectified output from the rectifying means, more thermally efficient with a simple structure Can be better.

According to a fifth aspect of the invention, in particular, in the fourth aspect of the invention, when the load material detecting means detects that the load material detecting means is a low conductivity material, the load material detecting means is a material having a high conductivity and a low magnetic permeability. when is detected that and the load material detection means with the configuration you increase the output voltage than if it detects an intermediate material, you are possible to improve more the thermal efficiency with a simple configuration.

In a sixth aspect of the invention, in particular, in any one of the first to fifth aspects of the invention, the load material detection means includes at least the output of the heating output detection means for outputting according to the heating output, and the voltage of the resonance capacitor or the heating coil. Or, by adopting a configuration that uses the output of the resonant voltage detection means that detects current as an input, it can be easily configured to have a higher conductivity from high conductivity such as aluminum and copper to low conductivity such as magnetic material, regardless of the material of the load. A heating output can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a circuit configuration diagram of an induction heating cooker which is an induction heating apparatus according to a first embodiment of the present invention.

  In FIG. 1, a power source 51 is a 200 V commercial power source, and a power factor improvement circuit (a power factor improvement circuit ( The power source is converted into a boosted direct current by the power factor improving means 71 and stored in the second smoothing capacitor 73 so that the power factor of the commercial power source becomes close to 1. It is converted into a high frequency by the inverter 70, and a high frequency magnetic field is generated in the heating coil 59. A pan (not shown), which is a load, is installed facing the heating coil 59. The resonance capacitor 60 forms a series resonance circuit together with the heating coil 59. The resonant capacitor 60 includes a first capacitor 85, a second capacitor 86, and a third capacitor 87. In the present invention, the resonant capacitor 60 is opened and closed as a relay by opening and closing as a relay. Change the capacitance. The inverter 70 is connected to the first switching element 74, the second switching element 75, the third switching element 76, and the fourth switching element 77 so as to form a full bridge circuit having the resonance circuit as an output. The switching elements 74, 75, 76, and 77 are formed of IGBTs and diodes connected in antiparallel to the IGBTs. When the output is increased by alternately driving the first switching element 74 and the fourth switching element 77 or the second switching element 75 and the third switching element 76 by the heating output control circuit (heating output control means) 63. In this case, the switching element is driven by the heating output control circuit 63 so that the driving frequency of the switching element approaches the resonance frequency, and the heating output is detected by the heating output detecting means 67 comprising a current transformer so that a predetermined heating output can be obtained. It is a frequency controlled inverter. At the time of startup, the first switching unit 83 and the second switching unit 84 are open. The resonance frequency of the resonance circuit at this time is about 90 kHz. The heating output control circuit 63 alternately drives the first switching element 74 and the fourth switching element 77 or the second switching element 75 and the third switching element 76 at a constant frequency (about 60 kHz).

  The operation and action of the induction heating cooker configured as described above will be described below.

  FIG. 2 is a characteristic diagram of the detection input of the load material detection means 72. The drive period of the first switching element 74 and the fourth switching element 77 is driven in a mode shorter than the resonance period of the resonance current, the drive time ratio is minimized, and the drive time ratio is gradually increased after the minimum output is achieved. In the meantime, the load material detection means 72 detects the load material from the detection output of the current transformer 67 and the detection output of the resonance voltage detection means 68 comprising the second current transformer.

  When it is detected that the load is an aluminum load, when a predetermined drive time ratio is reached, the mode shifts to a mode in which the period of the resonance current is shorter than the drive period of the first switching element 74 and the fourth switching element 77. At this time, the drive period is set so that the output is in a low output state. The drive frequency of the switching elements 74, 75, 76, 77 is set to about 30 kHz which is 1/3 of the resonance frequency of the resonance circuit. At this time, each part operates as shown in FIG. The power factor correction circuit 71 operates to improve the power factor of the commercial power supply while boosting the voltage to 400V. In this way, by increasing the pressure while reducing the loss of the switching elements 74, 75, 76, 77, the metal is operated in a high conductivity material mode that can heat a metal having low magnetic permeability and high conductivity such as aluminum. It is what.

  Furthermore, when it is detected as a composite material in which a high conductivity material such as aluminum or copper is placed on an aluminum-based and iron-based intermediate material, that is, a non-magnetic stainless steel plate or a thin non-magnetic stainless steel plate, the switching element 74, 75, 76 and 77 are driven as shown in FIG. However, the first switching means is short-circuited and the second switching means is opened, so that the resonance frequency of the resonance circuit is about 66 kHz. The first switching element is driven by flowing a resonance current in the latter half period of driving the first switching element 74 and the fourth switching element 77 so that the driving frequency is about 22 kHz which is 1/3 of the resonance frequency of the resonance circuit. 74 and the fourth switching element 77 are stopped, and the second switching element 75 and the third switching element 76 are started to be driven. The third switching element 76 is operated in a medium conductivity material mode that repeatedly stops driving. At this time, the power factor correction circuit 71 operates to boost and smooth to 400V. The switching frequency is reduced by lowering the driving frequency than that of the high conductivity material mode, and the frequency of the current flowing in the resonance circuit is about 66 kHz, which is lower than that of the high conductivity material mode. If the voltage is the same, a larger heating output can be obtained.

  When the load material detecting means 72 determines that the material of the load is of low conductivity such as iron, the first switching means and the second switching means are short-circuited to set the resonance frequency of the resonance circuit to about 20 kHz. . The drive frequency is lowered so as to be approximately the resonance frequency of the resonance circuit, and heating is started again at a low output. The drive frequency of the switching elements 74, 75, 76, 77 is set to about 20 kHz which is the resonance frequency of the resonance circuit, and the switching element 74, 75, 76, 77 is operated in the low conductivity material mode starting from the minimum output and gradually increasing to a predetermined output. . At this time, each part operates as shown in FIG. At this time, the power factor correction circuit 71 can boost the voltage to 450 V and obtain a sufficient heating output.

  As described above, in this embodiment, the resonant capacitor is formed of a series circuit of at least two capacitors, and the first switching means is connected in parallel to the first capacitor, and the third capacitor is connected in parallel to the second capacitor. And the second switching means are connected in series, the third capacitor has a larger capacitance than the second capacitor, and the first switching means or the second switching means is switched according to the load material detection result. The resonance frequency of the resonance circuit is switched, and the drive frequency of the switching element is switched between approximately the resonance frequency of the resonance circuit and approximately 1 / n times the resonance frequency of the resonance circuit (n is an integer of 2 or more). Since the heating mode can be switched according to the material of the load from high conductivity to low conductivity without using a withstand voltage relay, switching element loss is further reduced. Kudeki, thus can be increased more heating power.

  Furthermore, even if the load material detection means 72 is based on the voltage detection of the resonant capacitor 60, it is possible to detect an increase in the current of the switching elements 74, 75, 76, 77, and the load material detection is performed with a simpler configuration to switch the heating mode. be able to.

  As described above, since the induction heating device according to the present invention can increase the heating output regardless of the material of the load, it can also be applied to uses such as industrial induction heating.

The circuit block diagram of the induction heating apparatus in Embodiment 1 of this invention Characteristic diagram of detection input of load material detection means of the same induction heating device The figure which shows each part waveform of the circuit of the same induction heating apparatus The figure which shows each part waveform of the circuit of the same induction heating apparatus Circuit diagram of a conventional induction heating device The figure which shows each part waveform of the circuit of the same induction heating apparatus

Explanation of symbols

59 Heating coil 60 Resonant capacitor 63 Heating output control circuit (heating output control means)
70 Inverter 71 Power factor improvement circuit (Power factor improvement means)
72 Load material detection means 74 1st switching element 75 2nd switching element 76 3rd switching element 77 4th switching element 83 1st switching means 84 2nd switching means 85 1st capacitor | condenser 86 2nd Capacitor 87 Third capacitor

Claims (6)

A heating circuit for magnetically coupling a load, a resonance circuit having a resonance capacitor, an inverter having a switching element and supplying power to the resonance circuit, a heating output control means for controlling the heating output of the heating coil, and commercial AC Rectifying means for rectifying and load material detecting means for detecting the material of the load are provided, and the resonant capacitor is connected in parallel with the first capacitor and the series circuit of the second capacitor and the first capacitor. a first switching means, said a series circuit of a third capacitor and a second switching means connected in parallel with the second capacitor, the third capacitor capacitance than the second capacitor It was increased, the load when the material detecting means has the load detecting a material of high conductivity and low permeability, such as aluminum the first switching means and said 2 switching means is opened to switch the drive frequency of the switching element to approximately 1/3 times the resonance frequency of the resonance circuit, and the load material detection means switches the load to a non-magnetic stainless steel plate or thin non-magnetic stainless steel. When detecting an intermediate material such as a composite material provided with a high conductivity material such as aluminum or copper on a plate material, the first switching means is short-circuited and the second switching means is opened to drive the drive When the frequency is switched to approximately ３ times the resonance frequency, and the load material detecting means detects the load as a material having a low conductivity such as iron, the first switching means and the second switching means. Is switched so that the drive frequency is substantially the same as the resonance frequency . The induction heating apparatus according to claim 1, wherein the resonance capacitor is a series circuit of two capacitors, and the capacitance of each capacitor is substantially the same. Inverter induction heating apparatus according to claim 1 or 2 characterized by having a full bridge circuit. Includes a power factor improvement means for improving the power factor of the commercial alternating current, the power factor correction unit load material detection means material of high conductivity and low permeability load was detected with the material of the intermediate material or low conductivity In this case, the induction heating apparatus according to any one of claims 1 to 3 , wherein the rectified output from the rectifying means is boosted and supplied to the inverter . The power factor improving means detects the load material when the load material detecting means detects that the material has a low conductivity.
Induction heating apparatus according to claim 4 you increase the output voltage than if the means when it detects the material and the load material detection means of the high conductivity and low permeability is detected as an intermediate material. Load material sensing means at least claim 1-5 for the output of the heating output detector for the corresponding to the heating output output, the output of the resonant voltage detecting means for detecting the voltage or current of resonant capacitor or heating coil and input The induction heating device according to any one of the above.

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