JP4978059B2 - 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.

As a conventional induction heating device, when heating a low-resistance, low-permeability object to be heated such as aluminum or an iron-based object to be heated, the connection means between the first resonance capacitor and the second resonance capacitor is switched. 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. In other words, an additional resonant capacitor is required.

  Further, when heating an object to be heated such as aluminum having a low resistance and a low magnetic permeability, a large current and a high voltage are applied to the first resonance capacitor. Therefore, the first resonant capacitor is generally constituted by a connection body in which a plurality of capacitors are connected in series / parallel, and the area occupied by the substrate is also very large.

  Furthermore, since a high voltage is applied to the first resonance capacitor, the same high voltage is also applied to the switching means whose output is opened to disconnect the second resonance 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 the electrode fixing portion 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, -Outer shell resin-The problem of discharge and short circuit occurred in the path of the electrode.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide an induction heating apparatus that can reduce the number of parts, save space, and realize low cost.

  In order to solve the above-described conventional problems, an induction heating apparatus according to the present invention includes a resonance capacitor formed of a series connection body of a plurality of capacitors, and short-circuit / open switching means connected in parallel to at least one of the plurality of capacitors. If the material of the object to be heated is determined to be a low-resistance non-magnetic metal, control is performed to open the output of the short-circuit / open-circuit switching means so that the combined capacity of the resonant capacitor is reduced. Control is performed to short-circuit the output of the short-circuit / open-circuit switching means so that the combined capacity of the capacitors is increased.

  Thus, the short-circuit / open-circuit switching means can change the combined capacity of the entire resonant capacitor by short-circuiting / opening a part of the plurality of capacitors constituting the resonant capacitor. It is not necessary to additionally arrange a resonance capacitor for heating the object to be heated, and the number of parts can be reduced.

  The short-circuit / open-circuit switching means is connected to some of the plurality of capacitors connected in series. For example, when heating a low-resistance nonmagnetic metal heated object such as aluminum, a high voltage is applied to the entire resonant capacitor, but the ratio according to the impedance of the connected capacitor is connected to the short-circuit / open switching means. Since a part of the high voltage is applied, the required withstand voltage performance is lower than the conventional one. Accordingly, it is possible to reduce the size and cost of the short-circuit / open-circuit switching means.

  In addition, an induction heating device that can be reduced in size and reduced in cost by reducing the components and saving the space of the resonant capacitor and the short-circuit / open switching means that occupy a large board area in the circuit components. can do.

  The induction heating device of the present invention can provide an induction heating device that can reduce the number of parts and save space, and further realize low cost.

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 resonance capacitor that resonates with the heating coil, a plurality of capacitors that are configured by connecting the resonance capacitors in series, and a plurality of capacitors Short-circuit / open-circuit switching means connected in parallel to at least one capacitor, an inverter for supplying a high-frequency resonance current to the heating coil, control means for controlling the short-circuit / open-circuit switching means and output control of the inverter, Inverter output detection means for detecting the magnitude of the output of the inverter and outputting a detection signal to the control means, and the control means determines the material of the object to be heated based on the output signal of the inverter output detection means. When it is determined as a low-resistance non-magnetic metal, short-circuit / open switching is performed so that the combined capacity of the resonant capacitor is reduced. Performs control to open the output of the stage, when it is determined that other materials, have lines control to short-circuit the output of the combined capacitance becomes large as short / open switching means of said resonant capacitor, short / open switching means Is an induction heating device that sets the combined capacity of capacitors connected in parallel to be equal to or smaller than the combined capacity of other capacitors .

  Thus, the short-circuit / open-circuit switching means can change the combined capacity of the entire resonant capacitor by short-circuiting / opening a part of the plurality of capacitors constituting the resonant capacitor. It is not necessary to additionally arrange a resonance capacitor for heating the object to be heated, and the number of parts can be reduced.

  The short-circuit / open-circuit switching means is connected to some of the plurality of capacitors connected in series. For example, when heating a low-resistance nonmagnetic metal heated object such as aluminum, a high voltage is applied to the entire resonant capacitor, but the ratio according to the impedance of the connected capacitor is connected to the short-circuit / open switching means. Since a part of the high voltage is applied, the required withstand voltage performance is lower than the conventional one. Accordingly, it is possible to reduce the size and cost of the short-circuit / open-circuit switching means.

  In addition, an induction heating device that can be reduced in size and reduced in cost by reducing the components and saving the space of the resonant capacitor and the short-circuit / open switching means that occupy a large board area in the circuit components. can do.

Further, according to the first aspect of the present invention, the combined capacity of the capacitors to which the short-circuit / open-circuit switching means is connected in parallel is set equal to or smaller than the combined capacity of the other plurality of capacitors. Here, when the object to be heated is a low-resistance nonmagnetic metal such as aluminum, the resonant capacitor capacity is reduced to set the frequency of the resonant current as high as 90 kHz, for example, in order to efficiently perform induction heating. On the other hand, in the case of an iron-based object to be heated, in order to reduce inverter loss, the resonance capacitor capacity is increased so as to set the resonance current frequency as low as 23 kHz, for example. In each case, since the frequency setting of the resonance current is greatly different, it is necessary to increase the switching width of the resonance capacitor capacity.

  In the present invention, the combined capacity of the capacitors connected in parallel with the short-circuit / open-circuit switching means is set to be the same as or smaller than the combined capacity of the other plurality of capacitors. It is possible to easily set a large switching width of the resonance capacitor capacity.

According to a second aspect of the invention, in particular, in the first aspect of the invention, the inverter includes a plurality of switching elements, and the control means includes at least one switching element when the magnetic field generated by the heating coil inductively heats the low-resistance nonmagnetic metal. And a control mode for outputting a driving signal for the switching element so that the high-frequency resonance current flowing through the capacitor resonates at a cycle shorter than the driving period of the switching element. Here, when the object to be heated is a low-resistance nonmagnetic metal, even if an eddy current is induced inside the object to be heated, the high frequency resistance is small, so that Joule heat is hardly generated and sufficient induction heating is difficult. Therefore, by increasing the magnetic field frequency generated from the heating coil, the high-frequency resistance of the object to be heated is increased to facilitate the generation of Joule heat and induction heating. However, on the other hand, since the drive frequency of the switching element included in the inverter also increases, there arises a problem that the loss generated at the time of switching increases.

  The present invention has a heating mode in which the high-frequency resonance current flowing through the switching element is controlled to resonate at a cycle shorter than the switching element drive period. Therefore, it is possible to set the driving frequency of the switching element to be lower than the magnetic field frequency generated from the heating coil. Therefore, an increase in switching loss of the switching element can be suppressed.

  However, when the object to be heated is an iron-based metal, the resistance of the object to be heated is very large, so that the attenuation of the high-frequency resonance current flowing through the switching element (that is, the energy consumed by the object to be heated) is large. In such a control method, resonance does not continue. However, when the object to be heated is a low-resistance nonmagnetic metal, the attenuation of the high-frequency resonance current flowing through the switching element is small, so this control method is very effective in reducing the loss of the switching element. It is valid.

According to a third invention, in particular, in the first invention, the inverter includes a plurality of series connection bodies of two switching elements, and a heating coil and a resonance capacitor are connected between connection points of the switching elements of the respective series connection bodies. To do.

  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, it is possible to increase the degree of freedom in inverter design.

In the fourth invention, in particular, in the third invention, the inverter output detecting means detects at least the magnitude of the high-frequency current generated by the inverter.

  In order to determine the material of the object to be heated, an inverter output detecting means for detecting the magnitude of the output of the inverter and outputting a detection signal to the control means is necessary. However, in the case of the fourth invention, both ends of the heating coil and the resonant capacitor are unstable voltage due to switching of the switching element, and therefore the voltage of the heating coil and the resonant capacitor closely correlated with the inverter output is detected. Is difficult.

  In the present invention, the magnitude of the high-frequency current generated by the inverter, that is, the heating coil and resonant capacitor current is detected. Since the current can be detected electrically 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 and the resonance capacitor.

According to a fifth aspect of the invention, in particular, 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, and the control means responds to the output signal of the inverter output detection means. The smoothing means voltage is changed by controlling the boosting amount of the boosting means.

  Accordingly, it is possible to set a heating power to be heated that can be input to be high by appropriately selecting an inverter system. Furthermore, in order to make it possible to set the heating power for the object to be heated high and to increase the degree of freedom in designing the inverter, the boosting amount of the boosting means is controlled.

  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)
1 to 4 show an induction heating cooker as the 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 choke coil 103 and a third switching element on the output side of rectifying means 102 including a diode bridge that rectifies an AC voltage from a commercial AC power supply 101. (MOS-FET) 104 is connected in series. Further, the anode side of the diode 105 is connected to the connection point between the choke coil 103 and the third switching element 104.

  Between the cathode side of the diode 105 and the output low potential side of the rectifying means 102, a smoothing means 106 made of an electrolytic capacitor, a first switching element (IGBT) 107 containing a reverse conducting diode inside, and a second switching element A series connection body of (IGBT) 108 is connected.

  The smoothing means 106 acts as a power source for an inverter 117, which will 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, the smoothing means 106 uses four electrolytic capacitors of 560 μF. Yes.

  A heating coil 109 that generates a high-frequency magnetic field and heats an object to be heated 116 such as a pan between a connection point of the first switching element 107 and the second switching element 108 and an output low potential side of the rectifying means 102; A resonance capacitor 110 that resonates with the heating coil 109 is connected in series.

  A top plate (not shown), which is an insulator and is made of heat-resistant ceramic, is provided on the top of the heating coil 109, and the object to be heated 116 is placed so as to face the heating coil 109 with the top plate interposed therebetween. The The heating coil 109 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 resonant capacitor 110 includes a plurality of capacitors 110a, 110b, 110c, and 110d, and is configured by a series connection of a parallel connection body of capacitors 110a and 110b and a parallel connection body of capacitors 110c and 110d.

  Capacitors 110a and 110b are each selected to have a capacity of 0.025 μF, and capacitors 110c and 110d are each selected to have a capacity of 0.01 μF. Therefore, the combined capacitance of the resonant capacitor 110 is about 0.014 μF.

  The capacitor 110c and the capacitor 110d are connected in parallel with a short-circuit / open-circuit switching means 111 composed of a relay. That is, the short-circuit / open-circuit switching means 111 is connected in parallel to at least one capacitor constituting the resonance capacitor 110. Further, the combined capacity of the capacitors 110c and 110d to which the short-circuit / open-circuit switching means 111 is connected in parallel is set to be the same as or smaller than the combined capacity of the other capacitors 110a and 110b. As described above, the combined capacity of the resonant capacitor 110 when the output of the short-circuit / open switch 111 is open is 0.014 μF, and the combined capacity of the resonant capacitor 110 when short-circuited is 0.05 μF.

  The inverter 117 supplies a high-frequency resonance current to the heating coil 109, and includes a first switching element 107, a second switching element 108, a heating coil 109, and a resonance capacitor 110 (including a short-circuit / open-circuit switching means 111 in a broad sense). ).

  The control means 112 controls the short-circuit / opening switching means 111 and the output control of the inverter 117. Based on detection signals from various detection means, operation by the user, etc., the first switching element 107 and the second switching means 112 are controlled. The conduction / cutoff of the switching element 108 is controlled.

  Specifically, the input current detection means 113 is configured by a current transformer. The detection signal of the input current detection means 113 is connected to be output to the control means 112.

  The inverter output detection unit 114 is a current transformer that is a current detection unit of the heating coil 109. The inverter output detection means 114 detects the current of the heating coil 109 that is the magnitude of the output of the inverter 117 and outputs a detection signal to the control means 112.

  The second control means 115 that controls the driving of the third switching element 104 detects the voltage of the smoothing means 106, the input current, etc. (not shown), while the input current becomes substantially sinusoidal and the voltage of the smoothing means 106 is detected. The drive frequency and conduction ratio of the third switching element 104 are controlled so that becomes a predetermined value.

  The operation of the above configuration will be described.

  The control means 112 outputs a drive signal so that the first switching element 107 and the second switching element 108 are exclusively turned on / off based on an operation by the user, and detects the input current detection means 113 and the inverter output. A detection signal from the means 114 is input.

  FIG. 2 shows the material discrimination region of the object to be heated 116 on the detection output plane of the input current detection means 113 -the detection output plane of the inverter output detection means 114 held in the control means 112. When the first switching element 107 and the second switching element 108 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. 112 continues to drive the first switching element 107 and the second switching element 108 to control the output of the inverter 117 so as to obtain a predetermined input power.

  At the same time, when the control unit 112 determines that the material of the object to be heated 116 is a low-resistance nonmagnetic metal based on the output signals of the input current detection unit 113 and the inverter output detection unit 114, the combined capacity of the resonance capacitor 110 is small. Control is performed to open the output of the short-circuit / open switching means 111 so that

  The combined capacitance of the resonant capacitor 110 is selected so that the output of the short-circuit / opening switching unit 111 is 0.014 μF when opened, and the inductance of the heating coil 109 when the object to be heated 116 is placed is 225 μH. Therefore, the resonance frequency of the heating coil 109, the resonance capacitor 110, and the object to be heated 116 is about 90 kHz.

  FIG. 3 shows a voltage current waveform of each part when the object to be heated 116 made of a low-resistance nonmagnetic metal is induction-heated.

  The first switching element 107 and the second switching element 108 are exclusively turned on / off by the control of the control means 112, and the inverter 117 supplies a high frequency resonance current to the heating coil 109 and the resonance capacitor 110. The heating coil 109 generates a high-frequency magnetic field and heats the object 116 to be heated.

  As shown in FIG. 3, during the conduction period of the first switching element 107 and the second switching element 108, the control means 112 performs control so that the resonance current flows for one cycle or more. That is, the inverter 117 includes a plurality of switching elements 107 and 108. When the magnetic field generated by the heating coil 109 induction-heats the low-resistance nonmagnetic metal, the control unit 112 switches the high-frequency resonance current flowing through at least one switching element. It has a control mode for outputting a driving signal for the switching element so as to resonate at a cycle shorter than the element driving period.

  This control mode is effective when the object to be heated 116 is a low-resistance nonmagnetic metal. When the object to be heated 116 is a low-resistance nonmagnetic metal, the resistance is low, so that the high-frequency resonance current is less attenuated. Therefore, resonance continues even if the drive time of the first switching element 107 or the second switching element 108 is set to be long. During the period in which the resonance current is flowing through the first switching element 107 or the second switching element 108, the control means 112 shuts off the switching element and controls the other switching element to conduct the first switching. Resonance can be continued without imposing a burden on the element 107 and the second switching element 108.

  Here, the frequency of the high-frequency resonance current is determined by the heating coil 109, the resonance capacitor 110, and the object to be heated 116, and is about 90 kHz as described above, while the driving frequency of the switching element is about 30 kHz in the present embodiment. Become. 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 this embodiment, by setting the frequency of the high-frequency resonance current supplied to the heating coil 109 as high as 90 kHz, the apparent high-frequency resistance can be increased even with the low-resistance nonmagnetic metal object 116 to be heated. Sufficient heating power can be obtained with a small current of the heating coil 109. 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.

  In this embodiment, the voltage of the resonant capacitor 110 at a predetermined input power is an effective value of about 3 kVrms. When the series connection body of the short-circuit / open-circuit switching means 111 and the additional capacitor (not shown) is connected in parallel to the resonance capacitor 110 as in the conventional method, the output of the short-circuit / open-circuit switching means 111 is about 3 kVrms. High voltage is applied.

  However, in this embodiment, since the short-circuit / open-circuit switching unit 111 is connected in parallel to the capacitors 110c and 110d, the output of the short-circuit / open-circuit switching unit 111 is about 2.1 kVrms according to the capacitor capacity, about 30%. Will be reduced. The short-circuit / open-circuit switching means 111 is constituted by a relay and has an electrode inside. The distance between the electrodes is limited to some extent for sure switching, but the distance between the electrodes needs to be increased in order to increase the withstand voltage. According to this embodiment mode, the applied voltage can be lowered, so that the degree of freedom in the interelectrode distance can be increased.

  In general, the outer shell of the short-circuit / open switching means 111 is made of a resin having a high withstand voltage. However, when a high-frequency high voltage is applied, the resin acts as a dielectric, and the resin that holds the electrode. Discharge occurs between them. Therefore, measures are taken to provide as much space as possible between the electrode and the resin, but the outer shell shape can be reduced in size by lowering the applied voltage.

  When the object to be heated 116 is a low resistance nonmagnetic metal, an eddy current is induced in the object to be heated 116 with respect to the high frequency magnetic field generated from the heating coil 109. Since this eddy current acts to repel the high-frequency magnetic field from the heating coil 109, the article to be heated 116 itself vibrates.

  When the voltage of the smoothing means 106 serving as the power source of the inverter 117 fluctuates in synchronization with the commercial AC power source 101 voltage, the object to be heated 116 also vibrates in synchronism with each other. In the present embodiment, the capacity of the smoothing means 106 is set to be sufficiently large to suppress fluctuations in the power source of the inverter 117 so that no pan sound is generated.

  On the other hand, however, if the capacity of the smoothing means 106 is set large, the input current from the commercial AC power supply 101 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 101.

  In the present embodiment, the choke coil 103, the third switching element 104, and the diode 105 are provided with boosting means 118 that also functions as power factor improving means. The control means 112 starts the operation of the inverter 117 based on the user's operation and outputs an operation start signal to the second control means 115. The second control means 115 detects the voltage of the smoothing means 106, 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 106 becomes a predetermined value. The drive frequency and conduction ratio of the element 104 are controlled.

  When the third switching element 104 is turned on, a short-circuit current flows through the choke coil 103 and energy is accumulated in the choke coil 103. While the third switching element 104 is cut off, the energy stored in the choke coil 103 is sent to the smoothing means 106 through the diode 105 to increase the voltage.

  The second control means 115 holds a reference voltage inside and controls the same value as compared with the voltage detection signal of the smoothing means 106, but the control means 112 also detects the voltage of the smoothing means 106. As a result, the voltage of the smoothing means 106 is controlled by the control means 112.

  The control unit 112 operates the voltage detection signal of the smoothing unit 106 according to the output signals of the input current detection unit 113 and the inverter output detection unit 114, and indirectly controls the boosting amount of the boosting unit 118 to smooth the smoothing unit 106. The voltage has changed.

  When the object 116 to be heated is a low-resistance nonmagnetic metal, the frequency range in which the heating coil 109 and the resonance capacitor 110 can continue to resonate is very narrow, and thus the output of the inverter 117 is very difficult to control. However, since the smoothing means 106 also functions as a power supply for the inverter 117, the output of the inverter 117 can be controlled by changing the voltage of the smoothing means 106.

  When the control unit 112 starts the operation of the inverter 117 and the control unit 112 determines that the material to be heated 116 is other than a low-resistance nonmagnetic metal, the control unit 112 temporarily stops the operation of the inverter 117 (about 2 seconds). Then, the output of the short-circuit / open-circuit switching unit 111 is controlled to be short-circuited so that the combined capacity of the resonant capacitor 110 is increased. In the present embodiment, as described above, the combined capacitance of the resonant capacitor 110 is set to be 0.05 μF.

  After completing the switching of the short-circuit / opening switching unit 111, the control unit 112 starts the operation of the inverter 117 again.

  FIG. 4 shows each part voltage current waveform when the object to be heated 116 other than the low resistance nonmagnetic metal is induction heated. The waveform is similar to the waveform of each part when heating the low-resistance nonmagnetic metal, but the difference is the waveform of the current flowing through the first switching element 107 and the second switching element 108.

  When heating the object to be heated 116 other than the low-resistance nonmagnetic metal, it is not necessary to increase the magnetic field frequency so much because the object to be heated 116 has high resistance. Therefore, switching is performed so that the capacity of the resonance capacitor 110 is increased, and the resonance frequency of the heating coil 109, the resonance capacitor 110, and the article to be heated 116 is set to be low (about 43 kHz in the present embodiment).

  Since the resonance frequency is low, even if the drive frequency of the first switching element 107 and the second switching element 108 is the same as the resonance frequency, the switching loss does not increase significantly. In addition, since the resistance of the object to be heated 116 is high, the required high-frequency resonance current is small, and switching loss and loss during conduction can be kept low.

  In the case of the conventional system, an additional capacitor (not shown) is connected to be added by the short-circuit / open-circuit switching means in order to set the capacitance of the resonant capacitor 110 large, but in this embodiment, the breakdown voltage is lowered. Therefore, it is possible to employ a short-circuit / open-circuit switching means that is miniaturized and there is no need to add a capacitor, so that the board space can be reduced and the cost can be kept low.

  In the present embodiment, the resonance capacitor 110 is configured by connecting two sets of parallel connection bodies of two capacitors in series. However, the resonance capacitor 110 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.

  Further, although the short-circuit / open-circuit switching unit 111 is connected to the low-potential side capacitors 110c and 110d, it may be connected to the high-potential side capacitors 110a and 110b. What is necessary is just to set suitably in view of the insulation capacity between the output-input of the short circuit / opening switching means 111 and the substrate layout. The short-circuit / open-circuit switching unit 111 is not limited to a relay, and a switching element may be used as long as the withstand voltage, current capacity, and the like allow.

  Although an example of a current transformer that detects the current of the heating coil 109 has been given as the inverter output detection unit 114, the voltage of the resonance capacitor 110 may be detected, or the first current that is a part of the current of the heating coil 109 may be detected. The same effect can be obtained by detecting the current of the switching element 107 or the second switching element 108 and the current of the smoothing means 106 serving as the power source of the inverter 117.

  Although the second control unit 115 is provided separately from the control unit 112, the operation of the second control unit 115 can be combined with the control unit 112.

  In addition, although the object 116 to be heated is a low resistance nonmagnetic metal such as aluminum and other examples, the material may be identified as nonmagnetic stainless steel having a higher resistance than aluminum and a metal having a higher resistance than aluminum. The material discrimination is not limited to two types, it is discriminated as three or four types, and it is necessary by combining the conduction period control of the first switching element 107 and the second switching element 108, the control of the short-circuit / opening switching means 111, etc. Inverter 117 output may be obtained.

  In particular, since the pot sound is a phenomenon peculiar to a low resistance non-magnetic metal such as aluminum and a light material, if the heating target is limited to the object to be heated 116 of other materials, the smoothing means 106 It is not necessary to set the capacity too large, and it is not necessary to provide the booster 118 if the power factor is reduced and the harmonic component of the input current is within the allowable range. What is necessary is just to comprise suitably combining in view of cost and an effect.

  In the present embodiment, an example is given in which the conduction period of the first switching element 107 and the second switching element 108 is substantially the same, but the present invention is not limited to this. For example, when the object 116 to be heated of low resistance nonmagnetic metal is heated, the conduction period of the first switching element 107 is controlled to be shorter than one period of the resonance current to be heated other than the low resistance nonmagnetic metal. The current waveform when heating 116 may be similar to the current waveform, and the conduction period of the second switching element 108 may be controlled to be one period or more of the resonance current. In addition, the conduction period of the first switching element 107 and the second switching element 108 may be controlled to be switched.

  As in the present embodiment, when the low-resistance nonmagnetic metal object to be heated 116 is heated, the conduction period of the first switching element 107 and the second switching element 108 is controlled to be one period or more of the resonance current. The ratio of the time during which power is supplied from the smoothing means 106, which is the power source of the inverter 117, during one switching element drive cycle is reduced, and the heating power that can be input in principle is reduced. However, the conduction period of the first switching element 107 is shorter than one period of the resonance current, and the conduction period of the second switching element 108 is controlled to be one period or more of the resonance current (or vice versa), thereby smoothing means. The heating power that can be input in principle can be increased by increasing the time ratio for supplying power from 106.

  In that case, a loss difference is generated due to a difference in conduction period between the first switching element 107 and the second switching element 108, but the conduction period between the first switching element 107 and the second switching element 108 is controlled to be switched. By doing so, the loss can be leveled.

  Further, since it is obvious that the switching element having the longer conduction period has a large loss, the switching element having the longer conduction period may be preferentially disposed in a place where the cooling is easy.

(Embodiment 2)
FIG. 5 shows an induction heating apparatus according to Embodiment 2 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 the induction heating apparatus according to the present embodiment, a smoothing means 106 made of an electrolytic capacitor and a first switching element containing a reverse conducting diode are provided between the cathode side of the diode 105 and the output low potential side of the rectifying means 102. A series connection body of 107a and the second switching element 108a and a series connection body of the first switching element 107b and the second switching element 108b are connected.

  Between the connection point of the first switching element (IGBT) 107a and the second switching element (IGBT) 108a, and the connection point of the first switching element (IGBT) 107b and the second switching element (IGBT) 108b, A heating coil 109 and a resonant capacitor 110 are connected in series.

  The inverter output detection means 114 is a current transformer that is a current detection means for the heating coil 109, and detects at least the magnitude of the high-frequency current generated by the inverter 117, that is, the current of the heating coil 109 and the resonance capacitor 110 to control the control means 112. A detection signal is output to

  In the case of the configuration of the present embodiment, both ends of the heating coil 109 and the resonant capacitor 110 are unstable voltages due to switching of the switching element, and thus the heating coil 109 having a close correlation with the output of the inverter 117. Although it is difficult to detect the voltage of the resonant capacitor 110, the magnitude of the high-frequency current generated by the inverter 117, that is, the current of the heating coil 109 and the resonant capacitor 110 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 109 and the resonance capacitor 110.

  With the configuration as described above, the control means 112 is configured so that the first switching element 107a, the second switching element 108a, the first switching element 107b, and the second switching element 108b are exclusively based on an operation by the user. A drive signal is output so as to conduct / cut off, and detection signals from the input current detection means 113 and the inverter output detection means 114 are input.

  The control means 112 discriminates the material of the object to be heated 116 based on the material discrimination region of the object to be heated 116 on the input current detection means 113 detection output-inverter output detection means 114 detection output plane as shown in FIG. Then, a control signal is output to the switching element, the short-circuit / open-circuit switching unit 111 and the second control unit 115.

  At this time, the control means 112 performs control so that the first switching element 107a and the second switching element 108b, and the second switching element 108a and the first switching element 107b perform the same operation.

  That is, the first switching element 107a-the heating coil 109-the resonance capacitor 110-the second switching element 108b-the path through which the high-frequency resonance current flows in the smoothing means 106, the first switching element 107b-the resonance capacitor 110-the heating coil 109- Resonance continues while the path through which the high-frequency resonance current flows is switched between the second switching element 107a and the smoothing means 106.

  When the object to be heated 116 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 particular, in this embodiment, since no capacitor is added to the resonant capacitor 110 as in the conventional method, it can be said that the adjustment range of the resonant capacitor 110 is somewhat narrow.

  In the present embodiment, when the object to be heated 116 is made of a material other than the low-resistance nonmagnetic metal, the resonance capacitor 110 and the short-circuit / opening switching unit 111 are set so that the resonance frequency is about 43 kHz. Since the high-frequency resistance of the object to be heated 116 has a resistance value at 43 kHz, it is higher than about 20 kHz in the conventional method. Therefore, when the material of the object to be heated 116 is a metal having a very high resistance, a sufficient resonance current does not flow with a high frequency resistance at 43 kHz, and a predetermined heating power may not be obtained.

  However, with the configuration as in the present embodiment, it is possible to control so that either the smoothing means 106, which is the power source of the inverter 117, the switching element disposed between the heating coil 109 or the resonance capacitor 110 is conductive. It is. That is, since the time for supplying power from the power source of the inverter 117 to the heating coil 109 can be extended, the heating power of the input object to be heated 116 can be set high. Therefore, it is possible to increase the design freedom of the inverter 117.

  In the present embodiment, the inverter 117 includes two serially connected bodies of two switching elements. However, the present invention is not limited to this. Depending on the commercial AC power supply 101, 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 118 may be controlled to change the voltage of the smoothing unit 106 to set the output of the inverter 117 high (or low).

  As described above, the induction heating device according to the present invention can reduce the number of parts and save space, and can provide an induction heating device that realizes low cost. 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 same induction heating apparatus The figure which showed the voltage current waveform of each part at the time of induction heating the to-be-heated object made from a low resistance nonmagnetic metal of the induction heating device The figure which showed the voltage current waveform of each part at the time of induction heating the to-be-heated object other than the low resistance nonmagnetic metal of the same induction heating device The circuit diagram of the induction heating apparatus in Embodiment 2 of this invention

Explanation of symbols

106 Smoothing means 107, 108, 107a, 108a, 107b, 108b Switching element 109 Heating coil 110 Resonant capacitor 110a, 110b, 110c, 110d Capacitor 111 Short-circuit / opening switching means 112 Control means 114 Inverter output detection means 116 Heated object 117 Inverter 118 Boosting means

Claims (5)

A heating coil that generates a high-frequency magnetic field to heat an object to be heated, a resonance capacitor that resonates with the heating coil, a plurality of capacitors that are configured by connecting the resonance capacitors in series, and at least one of the plurality of capacitors in parallel Connected short-circuit / open-circuit switching means, an inverter for supplying a high-frequency resonance current to the heating coil, control means for performing control of the short-circuit / open-circuit switching means and output control of the inverter, and magnitude of output of the inverter And an inverter output detection means for outputting a detection signal to the control means, and the control means uses a low-resistance nonmagnetic metal as the material of the object to be heated based on the output signal of the inverter output detection means. If it is determined, the output of the short-circuit / open-switching means is opened so that the combined capacity of the resonant capacitors is reduced. Performs control to, if it is determined that other materials, have lines control to short-circuit the output of the combined capacitance becomes large as short / open switching means of said resonant capacitor, short / open switching means are connected in parallel An induction heating device that sets the combined capacity of capacitors to be the same as or smaller than the combined capacity of other capacitors . The inverter includes a plurality of switching elements, and when the magnetic field generated by the heating coil inductively heats the low-resistance nonmagnetic metal, the control means has a high-frequency resonance current flowing through at least one switching element shorter than the driving period of the switching element. The induction heating device according to claim 1, wherein the induction heating device has a control mode in which a drive signal of the switching element is output so as to resonate with a period. The induction heating apparatus according to claim 1, wherein 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. The induction heating device according to claim 3 , wherein the inverter output detection means detects at least the magnitude of the high-frequency current generated by the inverter. A smoothing unit that functions as a power source for the inverter; and a boosting unit that also functions as a power factor correction unit. The control unit controls the boosting amount of the boosting unit according to an output signal of the inverter output detection unit, and the smoothing unit. The induction heating apparatus according to claim 1, wherein the voltage is changed.

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