JP4992818B2 - Induction heating device - Google Patents

Description

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

Conventionally, this type of induction heating device connects a first resonance capacitor and a second resonance capacitor when heating a low resistance, low magnetic permeability object such as aluminum or an iron type object to be heated. A device that is switched by switching means is known (see, for example, Patent Document 1).
JP 2004-362798 A

  However, in the conventional configuration, in addition to the first resonant capacitor used when the object is a low resistance, low magnetic permeability object such as aluminum, the first structure is used when the object is an iron type object. The switching means operates to connect the two resonant capacitors in parallel.

  A high voltage is applied to the first resonant capacitor, and an equivalent high voltage is also applied to the switching means opened at the output to disconnect the second resonant capacitor from the circuit. An electrode is provided inside the switching means, and the capacitor is switched by short-circuiting / opening the electrode. However, both the insulation distance against high voltage and the mechanical distance that can reliably short-circuit the electrode must be achieved. I must.

  In addition, the outer shell and electrode fixing part of the switching means are generally made of resin, but if this resin does not have sufficient pressure resistance against high voltage, it is not the space between the electrodes, -It had the subject of discharge and a short circuit in the path | route of outer shell resin-electrode.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide an induction heating device that detects an abnormal phenomenon such as a discharge in a switching means and immediately stops the inverter, and is safe and reliable. .

In order to solve the conventional problems, an induction heating apparatus according to the present invention includes a heating coil that generates a high-frequency magnetic field and heats an object to be heated, a first resonance capacitor that resonates with the heating coil, and a first resonance. a plurality of capacitors constituting the capacitor in series and parallel connection, a plurality of capacitors, and a series connection body connected in parallel of the second resonant capacitor connected in series with the switching means and the switching means, the material of the object to be heated When it is discriminated as an iron-based one, the output of the switching means is controlled to be short-circuited so that the combined capacity of the first and second resonant capacitors is increased, and connected to the connection point between the switching means and the second resonant capacitor. When the output value of the resonance voltage detecting means exceeds a predetermined value, the inverter is stopped.

  As a result, in the event of an abnormal phenomenon such as discharge in the switching means, it is possible to provide a safer and more reliable induction heating device by immediately stopping the inverter by the resonance voltage detecting means.

  The induction heating device of the present invention can detect an abnormal phenomenon such as a discharge in the switching means, immediately stop the inverter, and provide a safe and highly reliable induction heating device.

According to a first aspect of the present invention, there is provided a heating coil that generates a high-frequency magnetic field and heats an object to be heated, a first resonance capacitor that resonates with the heating coil, and a plurality of first and second resonance capacitors that are connected in series and in parallel. and a capacitor connected in parallel to said first resonance capacitor, connected the switching means switches the connected short / open the connection point side of the heating coil and the first resonant capacitor and to said switching means and in series A series body of a second resonance capacitor, an inverter for supplying a high-frequency resonance current to the heating coil, a control means for controlling the switching means and controlling the output of the inverter, and detecting the magnitude of the output of the inverter wherein the control means and the inverter output detecting means for outputting a detection signal, is connected to the connection point between the switching means second resonant capacitor resonant Te Resonance voltage detection means for detecting a voltage value, and when the control means determines that the material of the object to be heated is a low-resistance nonmagnetic metal based on an output signal of the inverter output detection means, the first, When the output of the switching means is controlled to be open so that the combined capacity of the second resonant capacitor is reduced, and the material is determined as another material, the combined capacity of the first and second resonant capacitors is increased. When the output of the switching means is controlled to be short-circuited and the output value of the resonance voltage detecting means exceeds a predetermined value in the open state of the switching means, the switching means is stopped by stopping the inverter. It is possible to provide a safer and more reliable induction heating device by immediately stopping the inverter in the event of an abnormal phenomenon such as discharge.

  In a third aspect of the invention, in the first aspect of the invention, the induction heating apparatus is configured to stop the inverter when the output value of the resonance voltage detection unit exceeds a predetermined value width when the switching unit is short-circuited. It is what.

  As a result, in the event of an abnormal phenomenon such as discharge in the switching means, it is possible to provide a safer and more reliable induction heating apparatus by immediately stopping the inverter by the resonance voltage detecting means.

  According to a fourth aspect of the invention, in particular, in the first aspect of the invention, the output value of the resonance voltage detecting means is a predetermined value determined in each of the open / short-circuit states of the switching means, When the width is exceeded, the induction heating device is configured to stop the inverter.

  As a result, in the event of an abnormal phenomenon such as discharge in the switching means, it is possible to provide a safer and more reliable induction heating apparatus by immediately stopping the inverter by the resonance voltage detecting means.

  In the fifth invention, particularly in the first invention, the inverter includes a plurality of series connection bodies of two switching elements, and the heating coil and the resonance capacitor are connected between connection points of the switching elements of the respective series connection bodies. Is.

  Here, there is a limit to the capacity of the heating coil and resonant capacitor due to the design of the inverter constant, and it is difficult to ensure the heating power of the object to be heated by controlling the capacitor short-circuit / opening switching means and the driving frequency of the switching element. There is.

  In the present invention, since there are two series connection bodies of two switching elements and the heating coil and the resonance capacitor are arranged between the connection points of the switching elements of the respective series connection bodies, Any one of the switching elements arranged between the coil and the resonance capacitor can be controlled to conduct.

  That is, since the time for supplying power from the power source to the heating coil can be lengthened, the input heating power to be heated can be set high. Therefore, the degree of freedom in inverter design can be increased.

  According to a sixth aspect of the present invention, in the first aspect of the invention, the smoothing means that acts as the power source of the inverter and the boosting means that also acts as the power factor improving means are provided. By controlling the boosting amount of the boosting means and changing the smoothing means voltage, it becomes possible to set a heating power to be heated that can be input high by appropriate selection of an inverter system, etc. Design flexibility is also increased.

  When a heated object made of a low-resistance nonmagnetic metal such as aluminum is induction-heated, the high-frequency magnetic field generated from the heating coil and the induced magnetic field generated from the eddy current induced inside the heated object are repelled. To do.

  In general, many objects to be heated, such as aluminum, are very light due to the characteristics of the material. Therefore, depending on the heated object heating power, the heated object vibrates and generates sound. When the power supply of the inverter is not smoothed, the object to be heated vibrates in synchronization with twice the commercial power supply frequency, so that a very harsh sound is generated.

  In order to suppress such noise, smoothing means such as a large-capacity electrolytic capacitor may be provided as an inverter power supply. This causes problems such as a decrease in power factor and an increase in harmonic components of the input current.

  In the present invention, since the pressure boosting means that also acts as the power factor improving means is provided, it is possible to achieve both suppression of sound generated from vibration of the heated object, power factor improvement, and reduction of harmonic components of the input current. Is possible.

  Further, the heating power of the object to be heated can be variably controlled by controlling the boosting amount of the boosting means according to the inverter output and changing the voltage of the smoothing means. If the amount of pressure increase is set high, the heating power for the object to be heated can also be increased.

  In addition, the boosting means is not newly provided, and the power boosting means for both the power factor improvement and the power source boosting for the smoothing means for suppressing the vibration noise of the object to be heated is used, so that the increase in the number of parts can be suppressed. Is possible.

  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 shows a circuit diagram of an induction heating apparatus according to the first embodiment of the present invention.

  In FIG. 1, a choke coil 3 and a third switching element (MOS-FET) 4 are connected in series on the output side of a rectifying means 2 composed of a diode bridge that rectifies an AC voltage from a commercial AC power supply 1.

  Further, the anode side of the diode 5 is connected to the connection point of the choke coil 3 and the third switching element 4.

  Between the cathode side of the diode 5 and the output low potential side of the rectifying means 2, a smoothing means 6 comprising an electrolytic capacitor, a first switching element (IGBT) 7 containing a reverse conducting diode therein, and a second switching element A series connection body of (IGBT) 8 is connected.

  The smoothing means 6 acts as a power source for an inverter 9 to be described later, and is composed of an electrolytic capacitor having a sufficiently large capacity so as to suppress voltage fluctuation as much as possible. Specifically, three smoothing capacitors of 430 μF are used. Yes.

  Between the connection point of the first switching element 7 and the second switching element 8 and the output low potential side of the rectifying means 2, a heating coil 11 that generates a high-frequency magnetic field and heats the object to be heated 10 such as a pan, A first resonance capacitor 12 that resonates with the heating coil 11 is connected in series.

  A top plate (not shown) made of a heat-resistant ceramic is provided on the top of the heating coil 11, and the object to be heated 10 is placed so as to face the heating coil 11 with the top plate interposed therebetween. The

  The heating coil 11 is formed by winding a stranded wire bundled with strands on a flat plate, and has a substantially donut shape with an inner diameter of 80 mm and an outer diameter of 180 mm. The first resonant capacitor 12 is composed of a plurality of capacitors 12a, 12b, 12c, and 12d, and is composed of a series connection of a parallel connection body of capacitors 12a and 12b and a parallel connection body of capacitors 12c and 12d.

  Capacitors 12a and 12b, 12c and 12d are each selected with a capacity of 0.02 μF.

  Accordingly, the combined capacitance of the first resonant capacitor 12 is 0.02 μF. The first resonant capacitor 12 is connected in parallel with a series body of a switching means 13 that can be short-circuited / opened, which is a relay, and a second resonant capacitor 14 having a capacitance of 0.28 μF.

  The resonance capacitor combined capacity when the output of the switching means 13 is open is 0.02 μF as described above, and the resonance capacitor combined capacity when shorted is 0.3 μF.

  The inverter 9 supplies a high frequency resonance current to the heating coil 11, and includes a first switching element 7, a second switching element 8, a heating coil 11, resonance capacitors 12 and 14, and switching means 13.

  The control means 15 performs control of the switching means 13 and output control of the inverter 9, and the first switching element 7 and the second switching element are based on detection signals from various detection means, user operations, and the like. 8 conduction / cutoff is controlled.

  Specifically, the input current detection means 16 is constituted by a current transformer. The detection signal of the input current detection means 16 is connected to be output to the control means 15. The inverter output detection unit 17 is a current transformer that is a current detection unit of the heating coil 11.

The inverter output detection means 17 detects the current of the heating coil 11 that is the magnitude of the output of the inverter 9 and outputs a detection signal to the control means 15. The resonance voltage detection means 18 connected to the connection point between the switching means 13 and the second resonance capacitor 14 is specifically connected so as to output a signal divided by a resistor to the control means 15.

  The second control means 19 for controlling the driving of the third switching element 4 detects the voltage of the smoothing means 6, the input current, etc. (not shown), while the input current becomes substantially sinusoidal and the voltage of the smoothing means 6 The driving frequency and conduction ratio of the third switching element 4 are controlled so that becomes a predetermined value.

  About the induction heating apparatus comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  First, the control means 15 outputs a drive signal so that the first switching element 7 and the second switching element 8 are exclusively turned on / off based on the operation by the user, and the input current detection means 16 and the inverter A detection signal from the output detection means 17 is input.

  FIG. 2 shows the object to be heated on the detection output plane of the input current detection means 16-the detection output plane of the inverter output detection means 17 held inside the control means 15 of the induction heating apparatus in the first embodiment of the present invention. It is the figure which showed 10 material discrimination | determination areas.

  When the first switching element 7 and the second switching element 8 are driven, the input current and the inverter output change, and when the low-resistance nonmagnetic metal region such as aluminum set in the upper part of FIG. 15 continues driving the first switching element 7 and the second switching element 8 to control the output of the inverter 9 so as to obtain a predetermined input power.

  At the same time, when the control unit 15 determines that the material of the article to be heated 10 is a low-resistance nonmagnetic metal based on the output signals of the input current detection unit 16 and the inverter output detection unit 17, the combined capacity of the resonance capacitor is reduced. Control is performed so that the output of the switching means 13 is opened.

  The combined capacity of the resonant capacitor is selected so that the output of the switching means 13 is 0.02 μF when opened, and the inductance of the heating coil 11 when the object to be heated 10 is placed is designed to be 200 μH. Therefore, the resonance frequency of the heating coil 11, the first resonance capacitor 12, and the object to be heated 10 is about 90 kHz.

  FIG. 3 shows each part voltage current waveform when the low-resistance non-magnetic metal heated object 10 of the induction heating apparatus according to the first embodiment of the present invention is induction-heated.

  The first switching element 7 and the second switching element 8 are exclusively turned on / off by the control of the control means 15, and the inverter 9 supplies a high frequency resonance current to the heating coil 11 and the first resonance capacitor 12. The heating coil 11 generates a high frequency magnetic field and heats the object to be heated 10.

  As shown in FIG. 3, during the conduction period of the first switching element 7 and the second switching element 8, the control means 15 performs control so that the resonance current flows for one period or more. That is, the inverter 9 includes a plurality of switching elements 7 and 8, and the control means 15 switches the high-frequency resonance current flowing through at least one switching element when the magnetic field generated by the heating coil 11 induction-heats the low-resistance nonmagnetic metal. It has a control mode for outputting a driving signal for the switching element so as to resonate at a cycle shorter than the driving period of the element.

  This control mode is effective when the object to be heated 10 is a low-resistance nonmagnetic metal. When the object to be heated 10 is a low-resistance nonmagnetic metal, the resistance is low, so that the high-frequency resonance current is less attenuated. Therefore, the resonance is continued even if the drive time of the first switching element 7 or the second switching element 8 is set to be long.

  During the period in which the resonance current flows through the first switching element 7 or the second switching element 8, the control means 15 shuts off the switching element and controls the other switching element to conduct the first switching. The resonance can be continued without imposing a burden on the element 7 and the second switching element 8.

  Here, the frequency of the high-frequency resonance current is determined by the heating coil 11, the first resonance capacitor 12, and the article to be heated 10, and is about 90 kHz as described above, while the drive frequency of the switching element is It becomes about 30 kHz.

  Since a switching loss occurs during the transition period in which the switching element is cut off from conduction, the higher the drive frequency of the switching element, the more the number of switchings, leading to an increase in switching loss.

  In the present embodiment, since the frequency of the high-frequency resonance current supplied to the heating coil 11 is set as high as 90 kHz, the apparent high-frequency resistance can be increased even with the low-resistance nonmagnetic metal object to be heated 10. It is possible to obtain sufficient heating power with a small current of the heating coil 11.

  Furthermore, since the driving frequency of the switching element is 30 kHz which is sufficiently lower than 90 kHz, an increase in switching loss can be suppressed. The voltage of the first resonant capacitor 12 at a predetermined input power is about 3 kVrms in terms of effective value in the present embodiment, and an equivalent high voltage of about 3 kVrms is also applied to the switching means 13. .

  Further, when the object to be heated 10 is a low-resistance nonmagnetic metal, an eddy current is induced in the object to be heated 10 with respect to the high-frequency magnetic field generated from the heating coil 11.

  Since this eddy current acts to repel the high frequency magnetic field from the heating coil 11, the article to be heated 10 itself vibrates. When the voltage of the smoothing means 6 serving as the power source of the inverter 9 fluctuates in synchronization with the voltage of the commercial AC power source 1, the object to be heated 10 also vibrates in synchronism with each other.

  In the present embodiment, the capacity of the smoothing means 6 is set to be sufficiently large to suppress fluctuations in the power source of the inverter 9 so that no pan sound is generated. On the other hand, however, if the capacity of the smoothing means 6 is set large, the input current from the commercial AC power supply 1 becomes distorted, resulting in a waveform different from the original sinusoidal shape and the power factor is lowered. .

  Since this input current includes a harmonic component, it may affect other devices connected to the same commercial AC power supply 1.

  In the present embodiment, the choke coil 3, the third switching element 4, and the diode 5 are provided with a boosting means 20 that also functions as a power factor improving means.

  The control means 15 starts the operation of the inverter 9 based on the user's operation and outputs an operation start signal to the second control means 19.

  The second control means 19 detects the voltage of the smoothing means 6, the input current, etc. (not shown), and performs the third switching so that the input current becomes substantially sinusoidal and the voltage of the smoothing means 6 becomes a predetermined value. The drive frequency and conduction ratio of the element 4 are controlled.

When the third switching element 4 becomes conductive, a short-circuit current of the choke coil 3 flows and energy is accumulated in the choke coil 3.

  While the third switching element 4 is cut off, the energy stored in the choke coil 3 is sent to the smoothing means 6 through the diode 5 to increase the voltage. The second control means 19 holds a reference voltage inside and controls the same value as compared with the voltage detection signal of the smoothing means 6, but the control means 15 also detects the voltage of the smoothing means 6. As a result, the voltage of the smoothing means 6 is controlled by the control means 15.

  The control means 15 operates the voltage detection signal of the smoothing means 6 according to the output signals of the input current detection means 16 and the inverter output detection means 17 and indirectly controls the boosting amount of the boosting means 20 to smooth the smoothing means 6. The voltage has changed.

  When the object to be heated 10 is a low-resistance nonmagnetic metal, the frequency range in which the heating coil 11 and the first resonance capacitor 12 can continue to resonate is very narrow, and therefore it is very difficult to control the output of the inverter 9. However, since the smoothing means 6 also acts as a power supply for the inverter 9, the output of the inverter 9 can also be controlled by changing the voltage of the smoothing means 6.

  When the control unit 15 starts the operation of the inverter 9 and the control unit 15 determines that the material to be heated 10 is other than a low-resistance nonmagnetic metal, the control unit 15 temporarily stops the operation of the inverter 9 (about 2 seconds). Then, the output of the switching unit 13 is controlled to be short-circuited so that the combined capacity of the first resonance capacitor 12 is increased, and the second resonance capacitor 14 is connected. At this time, in this embodiment, as described above, the combined capacitance of the resonant capacitors is set to be 0.3 μF. After the switching of the switching unit 13 is completed, the control unit 15 starts the operation of the inverter 9 again.

  FIG. 4 shows each part voltage current waveform when the object to be heated 10 other than the low-resistance nonmagnetic metal is induction heated. The waveform is similar to each waveform when heating the low-resistance nonmagnetic metal, but the difference is the waveform of the current flowing through the first switching element 7 and the second switching element 8.

  When heating the object to be heated 10 other than the low-resistance nonmagnetic metal, the object to be heated 10 itself has high resistance, and therefore it is not necessary to increase the magnetic field frequency so much.

  Therefore, switching is performed so that the capacity of the resonance capacitor is increased, and the resonance frequency of the heating coil 11, the resonance capacitor, and the article to be heated 10 is set to be low (about 23 kHz in the present embodiment).

  Since the resonance frequency is low, even if the drive frequency of the first switching element 7 and the second switching element 8 is the same as the resonance frequency, the switching loss is not significantly increased.

  In addition, since the resistance of the object to be heated 10 is high, the required high-frequency resonance current is small, and the switching loss and the loss during conduction can be kept low.

More than one time, as in the present embodiment, when switching means 13 is open, i.e. when the object to be heated 10 is performing induction heating of low resistance nonmagnetic metal pot, the first and second resonance capacitor When the capacity suddenly decreases due to abnormal heat generation or the like, resulting in a short circuit state, or when the switching unit 13 shifts from the open state to the short circuit state due to some phenomenon, arc discharge occurs between the contact terminals of the voltage switching unit 13. As shown in FIG. 3 (8), an abnormal voltage is generated in the resonance voltage detecting means 18 . At this time, the output of the inverter output detecting means 17 provided in the control means 15 exceeds a predetermined value and is output as shown in FIG. Can be made.

  The same applies when the switching means 13 is short-circuited.

  In this embodiment, the resonance capacitor 12 is formed by connecting two sets of parallel connection bodies of two capacitors in series. However, the resonance capacitor 12 may be appropriately set in view of the required breakdown voltage, current capacity, and the like. Two capacitors may be connected in series, or three or more sets of capacitor parallel connections may be connected in series. The switching means 13 is not limited to a relay, and a switching element may be used as long as the withstand voltage, current capacity, etc. allow.

  Although the example of the current transformer which detects the electric current of the heating coil 11 was given as the inverter output detection means 17, the voltage of the resonance capacitor 12 may be detected, or the first current which is a part of the electric current of the heating coil 11 may be detected. The same effect can be obtained by detecting the current of the switching element 7 or the second switching element 8 and the current of the smoothing means 6 serving as the power source of the inverter 9. Although the configuration in which the second control unit 19 is provided separately from the control unit 15 is described, the operation of the second control unit 19 can be combined with the control unit 15.

(Embodiment 2)
FIG. 5 shows an induction heating apparatus according to the second embodiment of the present invention. The same elements as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In FIG. 5, between the cathode side of the diode 5 and the output low potential side of the rectifying means 2, a smoothing means 6 made of an electrolytic capacitor, a first switching element 7a containing a reverse conducting diode inside, and a second switching element. The series connection body of the element 8a and the series connection body of the first switching element 7b and the second switching element 8b are connected.

  Between the connection point of the first switching element (IGBT) 7a and the second switching element (IGBT) 8a, and the connection point of the first switching element (IGBT) 7b and the second switching element (IGBT) 8b, A heating coil 11 and a resonant capacitor 12 are connected in series.

The inverter output detector 17 is a current transformer is a current sensing means of the heating coil 11, the magnitude of the high-frequency current of at least the inverter 9 is generated, that is, detects the current of the heating coil 11 and resonant capacitor 1 2, the control means A detection signal is output to 15.

  In the case of the configuration of the present embodiment, both ends of the heating coil 11 and the resonant capacitor 12 are unstable voltages due to switching of the switching element, and thus the heating coil 11 having a close correlation with the output of the inverter 9. Although it is difficult to detect the voltage of the resonant capacitor 12, the magnitude of the high-frequency current generated by the inverter 9, that is, the current of the heating coil 11 and the resonant capacitor 12 is detected.

  Since the current can be detected in a non-contact manner with a current transformer or the like, the current can be accurately detected regardless of the voltage stability of the heating coil 11 and the resonance capacitor 12.

  About the induction heating apparatus comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

The control means 15 is based on the operation by the user, the first switching element 7a and the second switching element 8a, the first switching element 7b and the second switching element 8.
A drive signal is output so that b is exclusively turned on / off, and detection signals from the input current detection means 16 and the inverter output detection means 17 are input.

  The control means 15 discriminates the material of the object to be heated 10 based on the material discrimination area of the object to be heated 10 on the detection output plane of the input current detection means 16 -inverter output detection means 17 as shown in FIG. Then, a control signal is output to the switching element, the switching means 13 and the second control means 19.

  At this time, the control means 15 performs control so that the first switching element 7a and the second switching element 8b, and the second switching element 8a and the first switching element 7b perform the same operation.

  That is, the first switching element 7a—the heating coil 11—the resonance capacitor 12—the second switching element 8b—the path through which the high-frequency resonance current flows in the smoothing means 6, the first switching element 7b—the resonance capacitor 12—the heating coil 11— Resonance continues while the path through which the high-frequency resonance current flows through the second switching element 7a-smoothing means 6 is switched.

  When the object to be heated 10 is made of a material other than the low-resistance nonmagnetic metal, since the resistance is high, resonance does not continue and resonance current does not flow easily.

  In the present embodiment, when the object to be heated 10 is made of a material other than the low-resistance nonmagnetic metal, the resonance capacitor 12 and the switching means 13 are set so that the resonance frequency is about 23 kHz. It is possible to control the smoothing means 6 that is the power source of the inverter 9 and any of the switching elements disposed between the heating coil 11 and the resonance capacitor 12 to be conductive.

  In other words, since the time for supplying power from the power source of the inverter 9 to the heating coil 11 can be lengthened, the heating power of the input object to be heated 10 can be set high. Therefore, it is possible to increase the design freedom of the inverter 9.

More than one time, as in the present embodiment, when switching means 13 is open, i.e. when the object to be heated 10 is performing induction heating of low resistance nonmagnetic metal pot, the first and second resonance capacitor When the capacity suddenly decreases due to abnormal heat generation or the like, resulting in a short circuit state, or when the switching unit 13 shifts from the open state to the short circuit state due to some phenomenon, arc discharge occurs between the contact terminals of the voltage switching unit 13. As shown in FIG. 3 (8), an abnormal voltage is generated in the resonance voltage detecting means 18 . At this time, it exceeds the predetermined value with respect to the output of the resonance voltage detecting means 18 provided in the control means 15 and is output as shown in FIG. Can be made.

  The same applies when the switching means 13 is short-circuited.

  In the present embodiment, the inverter 9 includes a configuration in which two serially connected bodies of two switching elements are included. However, the present invention is not limited to this. Depending on the commercial AC power source 1, the same effect can be obtained even if three series-connected bodies of two switching elements are included. Further, the boosting amount of the boosting unit 20 may be controlled to change the voltage of the smoothing unit 6 to set the output of the inverter 9 high (or low).

As described above, the induction heating apparatus according to the present invention can provide an induction heating apparatus that realizes safety and high reliability in an apparatus having a switching unit that switches a resonant capacitor. Of course, it is also useful as an induction heating type water heater, induction heating type iron, or other induction heating type heating device.

The circuit diagram of the induction heating apparatus in Embodiment 1 of this invention The figure which showed the material discrimination | determination area | region of the to-be-heated object in the input current detection means detection output-inverter output detection means detection output plane currently hold | maintained inside the control means of the induction heating apparatus in Embodiment 1 of this invention The figure which showed each part voltage current waveform at the time of induction-heating the to-be-heated object made from a low resistance nonmagnetic metal of the induction heating apparatus in Embodiment 1 of this invention The figure which showed each part voltage current waveform at the time of inductively heating to-be-heated objects other than the low resistance nonmagnetic metal of the induction heating apparatus in Embodiment 1 of this invention The circuit diagram of the induction heating apparatus in Embodiment 2 of this invention

Explanation of symbols

6 Smoothing means 7, 7a, 8, 8a, 7b, 8b Switching element 9 Inverter 10 Object to be heated 11 Heating coil 12 First resonance capacitor 13 Switching means 14 Second resonance capacitor 15 Control means 16 Input current detection means 17 Inverter Output detecting means 18 Resonant voltage detecting means 19 Second control means 20 Boosting means

Claims (5)

A heating coil that generates a high-frequency magnetic field and heats an object to be heated, a first resonance capacitor that resonates with the heating coil, a plurality of capacitors that are configured by connecting the first resonance capacitors in series and in parallel, and the first of being connected in parallel to the resonance capacitor, the second resonance capacitor connected the switching means switches the connected short / open the connection point side of the heating coil and the first resonant capacitor and to said switching means and in series A series body, an inverter for supplying a high-frequency resonance current to the heating coil, a control means for controlling the switching means and controlling the output of the inverter, and detecting the magnitude of the output of the inverter to the control means an inverter output detecting means for outputting a signal, which is connected to the connection point between the switching means and the second resonance capacitor detecting the voltage value of the resonance And when the material of the object to be heated is determined to be a low-resistance nonmagnetic metal based on the output signal of the inverter output detection means, the first and second resonance voltages are detected. When the control is performed so that the output of the switching means is opened so that the combined capacity of the capacitor is small and it is determined that the other material is used, the output of the switching means is increased so that the combined capacity of the first and second resonant capacitors is increased. Inductive heating apparatus that performs control to short-circuit, and stops the inverter when the output value of the resonance voltage detection means exceeds a predetermined value in the open state of the switching means. In short-circuit state of the switching means, induction heating apparatus according to when the output value of the resonance voltage sensing means exceeds the width of a predetermined value, to claim 1 which is configured to perform stopping of the inverter. In the open or short circuit both states of the switching means, the output value of the resonance voltage sensing means, if it exceeds a predetermined value and width defined in the open or short circuit condition each of said switching means, stop of the inverter The induction heating device according to claim 1, wherein the induction heating device is configured to perform. The inverter plurality enclosing a series connection of two switching elements, said heating coil and said first resonance capacitor between the connection points in the switching element of each of said series connection to claim 1 to be connected in series The induction heating apparatus described. A smoothing means acting as a power source of the inverter also comprises a step-up means acting as a power factor improving means, the control means controls the boosting amount of the boosting unit in accordance with the output signal of the inverter output detecting means The induction heating apparatus according to claim 1, wherein the voltage of the smoothing means is changed.

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