JP2006228541A - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a safe and user friendly induction heating device surely detecting the temperature of an object to be heated without using new temperature detection means like infrared-ray sensor. <P>SOLUTION: A detection means 7 detects the change of impedance of a resonance circuit including an induction heating coil 4, and a material quality discrimination means 8 determines the change of the characteristics of the object to be heated by the value detected by the detection means 7, and a control means 9 is made to decide an output power for heating of a high frequency inverter 1 depending on the degree of impedance-change. Thereby, since the material characteristics-change of the object to be heated 6 is determined by detecting impedance-change of the resonance circuit including the induction heating coil 4, and heating output of the high frequency inverter 1 is decided depending on the degree of impedance-change, the temperature of the object to be heated 6 is surely detected without using new temperature detection means like infrared-ray sensor, and a safe and user friendly induction heating device is realized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an induction heating device used in general homes, offices, restaurants and the like.

Conventionally, an induction heating device generates a high-frequency magnetic field from an induction heating coil, and an object to be heated such as a cooking pan on a top plate is heated due to an eddy current due to electromagnetic induction. The temperature of the body is detected by temperature detection means arranged below the top plate (see, for example, Patent Document 1).
JP 2004-247237 A

  However, in the conventional configuration, since the temperature detecting means detects the temperature of the object to be heated through the top plate, there is a problem that the thermal response is slow and appropriate control is difficult. Moreover, although it is possible to use an infrared sensor as a temperature detection means, it was expensive.

  The present invention solves the above-described conventional problems, and realizes a safe and easy-to-use induction heating device by reliably detecting the temperature of a heated object without using a new temperature detection means such as an infrared sensor. It is aimed at.

  In order to solve the above-mentioned conventional problems, in the induction heating apparatus of the present invention, the detection means detects the impedance change of the resonance circuit including the induction heating coil, and the material discrimination means detects the object to be heated from the detection value of the detection means. The material characteristic change is determined, and the control means determines the heating output of the high-frequency inverter according to the degree of impedance change.

  As a result, a change in the material characteristics of the object to be heated is detected by detecting the impedance change of the resonance circuit including the induction heating coil, and the heating output of the high-frequency inverter is determined based on the degree of the impedance change. Without using the detection means, the temperature of the object to be heated can be reliably detected, and an induction heating device that is safe and easy to use can be realized.

  The induction heating device of the present invention reliably detects the temperature of the object to be heated, and is safe and easy to use.

  A first invention is a high-frequency inverter having a switching element, an induction heating coil for heating an object to be heated, and a resonance capacitor, a power supply for supplying power to the high-frequency inverter, and electrical characteristics of each part connected to the high-frequency inverter Detecting means for detecting the material, material determining means for determining a change in material characteristics of the object to be heated from the detection value of the detecting means, and control means for controlling the high frequency inverter, wherein the detecting means includes a resonance including an induction heating coil. An impedance change of the circuit is detected, the material discrimination means determines the material property change of the object to be heated from the detection value of this detection means, and the control means determines the heating output of the high frequency inverter according to the degree of impedance change. By using a heating device, it is possible to detect the change in impedance of the resonance circuit including the induction heating coil. Since the material property change of the heat element is judged and the heating output of the high frequency inverter is determined according to the degree of impedance change, the temperature of the heated object is reliably detected without using a new temperature detection means such as an infrared sensor. Thus, an easy-to-use induction heating device can be realized.

  According to a second aspect of the invention, in particular, in the first aspect of the invention, when the degree of impedance change is smaller than a predetermined value, the control means does not change the heating output of the high-frequency inverter, thereby changing the position of the object 6 to be heated. In this case, it is possible to eliminate the need to stop heating or suppress the output due to erroneous detection, etc., and it is possible to detect the temperature state of the heated object quickly, making it safe and easy to use. Can be realized.

  In a third aspect of the invention, in particular, in the first aspect of the invention, when the degree of impedance change is greater than a predetermined value, the control means does not change the heating output of the high-frequency inverter, so that the cooking pot that is the object to be heated is used. Even when a load such as food is applied to the heat source, it is possible to quickly detect the high temperature state of the heated object without stopping heating or suppressing the output due to erroneous detection, and it is safe and easy to use A heating device can be realized.

  According to a fourth aspect of the invention, in particular, in the first aspect of the invention, the control means does not change the heating output of the high-frequency inverter within a predetermined time after the power of the high-frequency inverter becomes a constant value. Even if induction heating is performed using the difference in Curie temperature, the object to be heated quickly does not stop heating due to erroneous detection or the heating output is not suppressed by erroneous detection. Thus, it is possible to detect a high temperature state, and it is possible to realize a safe and easy-to-use induction heating apparatus.

  According to a fifth aspect of the invention, in particular, in the first aspect of the invention, after the power of the high-frequency inverter has reached a constant value, the control means determines the material property change of the heated object within a predetermined time. In the case of a heated object that does not change the heating output of the high-frequency inverter until the heating is stopped, and the temperature does not rise above the predetermined temperature even if induction heating is performed using the difference in Curie temperature In order to prevent the heating from being stopped or the output from being suppressed, it is possible to quickly detect the high temperature state of the heated object in the case of other heated objects, which is safe and easy to use. It is possible to realize an induction heating apparatus with good quality.

  In a sixth aspect of the invention, in particular, in the first aspect of the invention, the controller is connected to the high-frequency inverter within a predetermined time when the material discriminating unit determines a change in the material property of the heated object based on the impedance change. When the change in the electrical characteristics of each part is smaller than the predetermined value, it is possible to determine that any load has been applied to the heated object by not changing the heating output of the high-frequency inverter. It is possible to distinguish between the change in the electrical characteristics of each part connected to the terminal and the change in the electrical characteristics of each part connected to the high-frequency inverter due to the change in impedance due to the heated object becoming hot. Without detecting the high temperature condition of the heated object, the heating output of the high-frequency inverter is suppressed to stop the temperature rise of the heated object. It is possible to enhance the safety of the induction heating apparatus Te.

  According to a seventh aspect of the invention, in the first aspect of the invention, in the first aspect, the control means is a case where the material discrimination means determines the material property change of the heated object by the impedance change, and the control parameter of the high frequency inverter within a predetermined time is determined. When the change is smaller than a predetermined value, it is possible to determine that any load has been applied to the heated object by not changing the heating output of the high frequency inverter. The high-temperature inverter can be distinguished from the change in the control parameters of the high-frequency inverter due to the change in impedance due to the high temperature of the heated body, detecting the high-temperature state of the heated body without making a false detection, and the heating output of the high-frequency inverter To suppress the temperature rise of the object to be heated and to improve the safety of the induction heating device Possible it is.

  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)
1 and 2 show an induction heating apparatus according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the induction heating apparatus according to the present embodiment includes a high-frequency inverter 1, a power supply 2 that supplies power to the high-frequency inverter 1, and electrical characteristics of each part connected to the high-frequency inverter 1, that is, voltage. The detection means 7 for measuring and detecting the magnitude of the current and the current, the material discrimination means 8 for determining the material characteristic change of the heated object 6 such as the cooking pot from the detection value of the detection means 7, and the high frequency inverter 1 are controlled. And control means 9 for performing the operation. The detecting means 7 detects the impedance change of the resonance circuit including the induction heating coil 4, the material determining means 8 determines the material property change of the heated body 6 from the detection value of the detecting means 7, and the control means 9 is The heating output of the high frequency inverter 1 is determined according to the degree of impedance change.

  The high-frequency inverter 1 includes a switching element 3 that supplies power supplied from a power source 2 by switching a current path, and power to be heated 6 on a top plate (not shown) by switching the switching element 3. An induction heating coil 4 to be heated and a resonance capacitor 5 connected in series with the induction heating coil 4 are provided.

  The power source 2 supplies a DC power source obtained by converting a commercial single-phase 100V or 200V AC power source into a DC by a diode bridge to the high-frequency inverter 1. Usually, the DC power supply is often boosted by boosting means such as a boost converter, but is not limited thereto. Here, the power supply 2 includes the boost converter. By boosting the voltage of the power supply 2, it is possible to reduce the current when supplying the same power to the high-frequency inverter 1, so that it is possible to lower the component ratings of each component constituting the high-frequency inverter 1. Therefore, it is desirable that the voltage of the power supply 2 be higher because the components can be reduced in size and cost, and the user can benefit by making the product cheaper and smaller.

  Here, the electric power supplied from the power supply 2 is switched by the switching element 3 to supply a high-frequency current to the induction heating coil 4. A high frequency magnetic field is generated from the induction heating coil 4, an eddy current due to electromagnetic induction flows in the heated body 6, and the heated body 6 is heated by the Joule heat.

  The material discriminating means 8 determines a change in material characteristics of the heated body 6 and changes the driving frequency of the high-frequency inverter 1 or the conduction ratio that is the ratio of the conduction period of the switching element 3 at the driving frequency. Heating according to the material is performed. As shown in FIG. 2, when the resonance frequency of the induction heating coil 4 and the resonance capacitor 5 is fc, resonance by the second harmonic and the third harmonic occurs when the inverter drive frequency is fc / 2 and fc / 3, respectively. The driving frequency-input power characteristics as shown in FIG. This drive frequency-input power characteristic differs depending on the object 6 to be heated, such as the height of the peak of the resonance peak, the frequency at the center, and the way in which the base of the mountain spreads. It is determined by this drive frequency-input power characteristic that a sufficient input power can be obtained by each heated body 6 and which frequency band should be driven to protect the high-frequency inverter 1.

  The material property change of the heated object 6 is determined by the resonance current flowing through the induction heating coil 4 and the resonance capacitor 5, the voltage of the switching element 3, the resonance current frequency flowing through the induction heating coil 4 and the resonance capacitor 5, and the voltage of the resonance capacitor 5. These values are detected by the detection means 7 for the input current and the like, and the material property change of the heated body 6 can be determined by the combination thereof. The material discriminating means 8 takes in the detected value of the detecting means 7 as an input value and determines the material characteristic change, but also includes one that is also used as the control means 9 that controls the high-frequency inverter 1. . As the control of the high-frequency inverter 1, the control means 9 performs feedback control so that the input current of the high-frequency inverter 1 is detected by the detection means 7 and the power is set by the user.

  The induction heating device in the present embodiment described above detects the high temperature state of the heated body 6 without using temperature detection means such as an infrared sensor and operates the safety function. When the body 6 to be heated is a magnetic material such as iron, there is a Curie temperature, and as the temperature rises, the magnetic properties gradually weaken. The heated body 6 is mainly a cooking pan, but some cooking pans have a multilayer structure in which a plurality of different metals are laminated. Alternatively, there is one that is processed so that induction heating can be performed by pasting a metal other than the metal forming the cooking pan at the bottom of the cooking pan, and the Curie temperature is relatively low depending on the combination of these metals There is a case. Therefore, when air-cooking is performed, the temperature of the cooking pan rises in a relatively short time, and the magnetic property gradually becomes weak and may become red hot. That is, when such a heated body 6 is heated, the impedance of the resonance circuit including the induction heating coil 4 gradually changes. The change in impedance can be read from the electrical characteristics of each part connected to the high-frequency inverter 1, the change in control parameters of the high-frequency inverter 1, and the like. These are determined by judging the material characteristic change by the material discriminating means 8.

  However, the change in the electrical characteristics and the control parameters of the high-frequency inverter 1 is due to the change in impedance due to the rise in the temperature of the heated object 6, or the relative position between the cooking pan and the induction heating coil 4. When the load is applied to the heated body 6 or, specifically, when the cooked pot as the heated body 6 is filled with a cooked product such as water or food Cannot determine whether it is. Therefore, when the heated body 6 that should continue to be heated is moved or when heating is stopped, the heating is stopped or the heating output is suppressed, or when the heated body 6 is hot due to emptying. Regardless, there are cases where the heating is stopped or the control for suppressing the heating output does not work.

  Therefore, in this embodiment, when a change in the impedance of the resonance circuit including the induction heating coil 4 is detected, whether the temperature of the heated body 6 has increased or the position of the heated body 6 has changed depending on the degree of the change. Alternatively, it is determined whether a load is applied to the heated body 6 and the heating output is determined according to the content of the heated body 6 so that the heating is stopped when the heated body 6 is at a high temperature or the high frequency inverter 1 By performing the control so that the heating output is suppressed, the heated object 6 is controlled so as not to reach a dangerous temperature, and it is possible to realize a safe and easy-to-use induction heating apparatus.

(Embodiment 2)
Next, the induction heating apparatus in Embodiment 2 of this invention is demonstrated. Since the basic configuration is the same as that of the first embodiment, only the differences will be described.

  In the present embodiment, the control means 9 does not change the heating output of the high-frequency inverter 1 when the degree of impedance change is smaller than a predetermined value.

  The determination material for determining that the material of the heated body 6 has changed can be determined using the electrical characteristics of each part connected to the high-frequency inverter 1 or the control parameters of the high-frequency inverter 1. In these cases, since minute noise is added, in order to eliminate the influence, no response is made when the degree of impedance change is smaller than a predetermined value.

  In this way, when the position of the heated body 6 is changed, the heating is not stopped or the output is not suppressed due to erroneous detection, and when the temperature of the heated body 6 becomes high and a change in impedance appears. It is possible to prevent the heated body 6 from becoming dangerous at high temperature, and to detect the temperature state of the heated body quickly and safely. An apparatus can be realized.

(Embodiment 3)
Next, the induction heating apparatus in Embodiment 3 of this invention is demonstrated. Since the basic configuration is the same as that of the first embodiment, only the differences will be described.

  In the present embodiment, the control means 9 does not change the heating output of the high-frequency inverter 1 when the degree of impedance change is greater than a predetermined value.

  This is because, as described in the first embodiment, when the relative position of the cooking pan and the induction heating coil 4 is changed, or a cooked product such as water or food is put in the cooking pan which is the body 6 to be heated. In this case, the electrical characteristics of each part connected to the high frequency inverter 1 or the control parameters of the high frequency inverter 1 change. Since the degree of change is larger than that due to noise as described in the second embodiment or due to a change in impedance due to the heated body 6 becoming high temperature, it can be determined. Therefore, when a change larger than a predetermined value occurs, the relative position of the cooking pan and the induction heating coil 4 has changed, or a cooked product such as water or food is placed in the cooking pan that is the body 6 to be heated. Can be determined. In any case, since the user is on the induction heating device side, there is no need to change the heating output of the high-frequency inverter 1. On the contrary, if the heating output is changed, the thermal power is weak, and the convenience of use such that the intended cooking cannot be performed becomes worse, but such a situation can be avoided by the present embodiment.

  Therefore, it is possible to quickly detect the high temperature state of the object to be heated, and it is possible to provide an induction heating apparatus that increases the safety by changing the heating output only when necessary.

(Embodiment 4)
Next, an induction heating apparatus in Embodiment 4 of the present invention will be described. Since the basic configuration is the same as that of the first embodiment, only the differences will be described.

  In the present embodiment, the control means 9 prevents the heating output of the high-frequency inverter 1 from being changed within a predetermined time after the electric power of the high-frequency inverter 1 becomes a constant value.

  When material determination is performed during heating, there is a control limiter for protecting the components constituting the high-frequency inverter 1 as shown in FIG. 3, the impedance changes by heating, and the power of the high-frequency inverter 1 is changed. When the control value is increased in order to maintain the control value, the increase in the control value is limited by the limiter, and as a result, the power is reduced. The control value is the same as the limiter value and does not change. In such a case, even if the control parameters of the high-frequency inverter 1 and the electrical characteristics of each part connected to the high-frequency inverter 1 are viewed, it is difficult to determine whether it is due to a change in the impedance of the heated body 6, and the determination is delayed. Or the case where it cannot be judged occurs.

  In order to avoid such a situation, the material discriminating means 8 determines the material of the heated body 6 when the input power or inverter output of the high-frequency inverter 1 is constant. By doing so, it is possible to capture the change in impedance due to the change in the material of the heated body 6 by detecting the control parameters of the high-frequency inverter 1 and the electrical characteristics of each part connected to the high-frequency inverter 1.

  In such a situation, when the heated body 6 processed so that the Curie temperature becomes a relatively low temperature and a plurality of metals are laminated so as not to reach a temperature of 300 ° C. or higher is relatively short from the start of heating. Since the electrical characteristics of each part connected to the high frequency inverter 1 or the control parameters of the high frequency inverter 1 change over time, it can be determined that the material of the heated body 6 has changed.

  However, since the temperature of such an object to be heated 6 does not exceed 300 ° C., it is not in an unsafe state even if heating is continued, so heating should be continued. Since it is determined that the material of the body 6 to be heated has changed even in the inserted state, stopping or suppressing the heating output may be erroneously detected as emptying.

  Therefore, since the object to be heated 6 having the function of suppressing the temperature rise at the time of induction heating has a change in impedance at an early stage from the start of heating, the heating output is not changed in such a case. False detection can be eliminated. In other words, by utilizing the difference in Curie temperature, even if induction heating is performed, a heated object that does not rise to a predetermined temperature or more can be heated quickly without stopping heating or suppressing the heating output due to erroneous detection. It becomes possible to detect the high temperature state of the heating body, and a safe and easy-to-use induction heating apparatus can be realized.

(Embodiment 5)
Next, an induction heating apparatus in Embodiment 5 of the present invention will be described. Since the basic configuration is the same as that of the first embodiment, only the differences will be described.

  In the present embodiment, the control means 9 performs heating if the material discrimination means 8 determines a change in the material characteristics of the heated body 6 within a predetermined time after the power of the high-frequency inverter 1 reaches a constant value. The heating output of the high-frequency inverter 1 is not changed until it stops.

  The difference between the contents in the present embodiment and the fourth embodiment is that the heating output is not stopped or suppressed after it is determined that the material has changed.

  As described in the fourth embodiment, the object to be heated 6 having the function of suppressing the temperature rise during induction heating causes a change in impedance in a short time from the start of heating, and the material change can be read. Such an object to be heated 6 changes in impedance in the same way even when it is not air-fired, and since the temperature does not exceed 300 ° C., the heating output is not stopped or suppressed even if it is determined that the material has changed. Thus, cooking can be performed without erroneous detection of empty cooking. Since it is not necessary to change this condition if the heated body 6 does not change, this condition is continued until the heating stop when the heated body 6 may be changed.

  In addition, the heating stop demonstrated here also includes the case where the to-be-heated body 6 which can be induction-heated with the high frequency inverter 1 no longer exists. That is, in many cases, the induction heating device has a button for instructing heating and stopping and a display device for informing the content of the instruction. For example, when the object to be heated 6 is removed during induction heating. The heated object 6 that can be induction-heated by the high-frequency inverter 1 no longer exists, but the display device itself may be displayed as being heated. If the heated object 6 is placed again in the induction heating device in that state, the heating may be started again. This temporarily stops the heating by the safety function of the induction heating device, but when the heated body 6 exists again, the heating can be resumed. Therefore, when the heated body 6 is replaced, the stop and start of heating must not be instructed one by one. It has the convenience of being good. In this way, even if the display device indicates that heating is in progress, the high-frequency inverter 1 actually stops heating even when induction heating is not performed. Since there is a possibility that the heated body 6 has been replaced, the temperature of the heated body 6 such as emptying is abnormally changed so that the change in the material of the heated body 6 is captured again to control the heating output. Suppress temperature rise when it is rising.

  As described above, in the present embodiment, by using the difference in Curie temperature, heating is stopped or output is suppressed in the case of an object to be heated that does not rise above a predetermined temperature even if induction heating is performed. In the case of other heated objects, it is possible to quickly detect the high temperature state of the heated object, and a safe and easy-to-use induction heating device can be realized. .

(Embodiment 6)
Next, an induction heating apparatus in Embodiment 6 of the present invention will be described. Since the basic configuration is the same as that of the first embodiment, only the differences will be described.

  In the present embodiment, the control means 9 is a case where the material discrimination means 8 determines a change in the material characteristics of the heated body 6 based on the impedance change, and the electrical means of each part connected to the high frequency inverter 1 within a predetermined time. When the change in characteristics is smaller than a predetermined value, the heating output of the high-frequency inverter 1 is not changed.

  FIG. 4 shows the heating output of the high-frequency inverter 1, the electrical characteristics of a part connected to the high-frequency inverter 1, or the control parameters of the high-frequency inverter 1 of the control means 9, the ingredients in the cooking pan as the heated body 6, etc. Changes are shown when a load is applied and when the object 6 is heated.

  The electrical characteristics of a part connected to the high frequency inverter 1 indicate the voltage of the resonance capacitor 5 measured to determine the material of the heated body 6, the voltage supplied from the power source 2 to the high frequency inverter 1, and the like. ing.

  As shown in FIG. 4, when heating is started, the electrical characteristics increase as the heating output increases over time T1. When the heating output becomes stable, the electrical characteristics gradually decrease. For example, when a load such as food is put into the cooking pan which is the heated body 6 at T2, the electrical characteristics increase rapidly over time T3, and thereafter, the electrical characteristics become almost unchanged and constant. On the other hand, when the object 6 to be heated is blown, the electrical characteristics gradually increase when the impedance of the resonance circuit including the induction heating coil 4 changes at T2.

  As described above, the way of changing the electrical characteristics is different between when the load is applied and when the impedance changes due to flying. Specifically, in both cases, the electrical characteristics increase at T4 between T2 and T4, but the load is constant from T3 to T4 in the middle. On the other hand, in the case of air-fired, it gradually increases.

  Therefore, by determining whether or not there is a period with a small change such as T3 to T4 when the load is applied, the change in the electrical characteristics due to the load application and the change in the impedance due to the heated body 6 becoming a high temperature. It can be discriminated from changes in electrical characteristics, and it is not erroneously detected that the air is blown by not changing the heating output when the load is applied. When the heated body 6 is actually hot, the state is detected and the heating output of the high-frequency inverter 1 is suppressed, so that the temperature rise of the heated body 6 can be stopped and the safety of the induction heating device can be improved. It is.

(Embodiment 7)
Next, an induction heating apparatus in Embodiment 7 of the present invention will be described. Since the basic configuration is the same as that of the first embodiment, only the differences will be described.

  In the present embodiment, the control means 9 is a case where the material discrimination means 8 determines a change in the material characteristics of the heated body 6 based on the impedance change, and the change in the control parameter of the high-frequency inverter 1 within a predetermined time is a predetermined value. When smaller, the heating output of the high-frequency inverter 1 is not changed.

  The control parameters shown in FIG. 4 are parameters that control the heating output of the high-frequency inverter 1, such as parameters that control the voltage supplied from the power source 2 to the high-frequency inverter 1, the conduction ratio of the high-frequency inverter 1, and the driving cycle. ing.

  In the present embodiment, it is possible to distinguish between a change in the control parameter due to load application and a change in the control parameter due to a change in impedance due to the heated body 6 becoming high temperature. When the change in the control parameter is smaller than the predetermined value, that is, when the load is turned on, the heating output is not changed, so that false detection of empty heating is not caused. And when the to-be-heated body 6 is actually high temperature, the state is detected, the temperature output of the to-be-heated body 6 is stopped by suppressing the heating output of the high frequency inverter 1, and the safety | security of an induction heating apparatus is improved. Is possible.

  As described above, the induction heating apparatus according to the present invention reliably detects the temperature of the object to be heated and is safe and easy to use, so the induction heating cooker used in general homes, offices, restaurants, etc. As applicable.

The block diagram which shows the structure of the induction heating apparatus in Embodiment 1-7 of this invention. The figure showing the drive frequency-input electric power characteristic of the same induction heating device The figure which shows the electric power characteristic at the time of limiter operation of the same induction heating device The figure which shows the characteristic of the electrical characteristic or the control parameter at the time of loading the load of the same induction heating device and at the high temperature

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 High frequency inverter 2 Power supply 3 Switching element 4 Induction heating coil 5 Resonant capacitor 6 Heated object 7 Detection means 8 Material discrimination means 9 Control means

Claims (7)

A switching element, an induction heating coil for heating an object to be heated, and a high-frequency inverter having a resonance capacitor; a power supply for supplying power to the high-frequency inverter; and a detecting means for detecting electrical characteristics of each part connected to the high-frequency inverter And a material discriminating means for determining a material property change of the heated object from a detection value of the detecting means, and a control means for controlling the high frequency inverter, wherein the detecting means detects an impedance change of the resonance circuit including the induction heating coil. Then, the material determining means determines the material property change of the object to be heated from the detection value of the detecting means, and the control means determines the heating output of the high frequency inverter according to the degree of impedance change. The induction heating apparatus according to claim 1, wherein the control means does not change the heating output of the high-frequency inverter when the degree of impedance change is smaller than a predetermined value. The induction heating apparatus according to claim 1, wherein the control means does not change the heating output of the high-frequency inverter when the degree of impedance change is greater than a predetermined value. The induction heating apparatus according to claim 1, wherein the control means does not change the heating output of the high-frequency inverter for a predetermined time after the electric power of the high-frequency inverter becomes a constant value. The control means changes the heating output of the high-frequency inverter until the heating stops when the material discriminating means determines the material property change of the heated object within a predetermined time after the electric power of the high-frequency inverter reaches a certain value. The induction heating device according to claim 1, wherein the induction heating device is not used. The control means is the case where the material discrimination means determines the material property change of the object to be heated based on the impedance change, and the change in the electrical characteristics of each part connected to the high frequency inverter within a predetermined time is smaller than the predetermined value. The induction heating apparatus according to claim 1, wherein the heating output of the high-frequency inverter is not changed. The control means is a case where the material discriminating means determines the material property change of the object to be heated by impedance change, and if the change in the control parameter of the high frequency inverter within a predetermined time is smaller than the predetermined value, the heating output of the high frequency inverter The induction heating apparatus according to claim 1, wherein no change is made.

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