JP2010055760A - Induction heating device - Google Patents

Abstract

There is provided an induction heating device that has no loss bias between switching elements, that is easy in cooling design, has a long component life, and results in low cost.
A control means 116 includes a first simultaneous conduction period in which a set of first and fourth switching elements 107 and 110 are simultaneously conducted and a set of second and third switching elements 108 and 109 are simultaneously conducted. A second simultaneous conduction period, a first closed-loop resonance period composed of the first and third switching elements 107 and 109, the heating coil 112, and the resonance capacitor 113, and the second and fourth switching elements 108. , 110 and the heating coil 112 and the resonance capacitor 113, a second closed-loop resonance period is provided, and the set of the first simultaneous conduction period and the first closed-loop resonance period and the second simultaneous conduction period And the second set of closed-loop resonance periods is controlled to appear alternately.
[Selection] Figure 1

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 apparatus has a plurality of switching elements, generates a short-period resonance current in the heating coil while one switching element is on, and supplies power from the smoothing capacitor to the heating coil. Thus, there is known a technique for heating an aluminum pan or the like with little noise without causing a squealing sound due to a pulsating flow of input voltage (see, for example, Patent Document 1).

  Also, in a full-bridge inverter that uses four switching elements, a technology is known that uses a specific switching element to form a closed loop that includes a heating coil and a resonant capacitor to flow an oscillating current and heat an aluminum pan or the like. (For example, refer to Patent Document 2).

  FIG. 5 shows a circuit diagram of a conventional induction heating cooker described in Patent Document 2. As shown in FIG. FIG. 6 is a waveform diagram showing the operation of each switching element of a conventional induction heating cooker and a waveform diagram of an oscillating current flowing through this switching operation.

  As shown in FIG. 5, the control circuit 12 alternately drives the set of the first and second switching elements 4 and 5 and the set of the third and fourth switching elements 6 and 7 and drives them. At the time of switching, the second and fourth switching elements 5 and 7 are driven and controlled so that the heating coil 8 and the resonant capacitor 9 connected in series become a closed loop.

Oscillating current flows when the series circuit becomes a closed loop. A magnetic flux is generated from the heating coil 8 by the oscillating current, and an eddy current is generated in the aluminum or copper pan 11 placed on the top plate 10 by the magnetic flux, thereby heating the pan 11.
Japanese Patent Laid-Open No. 2003-257609 JP 2005-149915 A

  However, in the conventional configuration of Patent Document 2, the conduction period of the second and fourth switching elements 5 and 7 becomes longer, so that the loss of the first and third switching elements 4 and 6 is about 3 to 5 times. It will be about.

  Generally, when induction heating of an aluminum pan or the like, a very large resonance current (oscillation current) flows, so that the loss of the second and fourth switching elements 5 and 7 becomes excessive and the cooling design becomes difficult. Was.

  In addition, when induction heating is performed on an object to be heated made of aluminum, copper, or a low-permeability material having an electric conductivity substantially equal to or higher than these, the high frequency magnetic field generated from the heating coil and the repulsive force between the objects to be heated In order to suppress the vibration noise of the object to be heated, a smoothing means that functions as a DC power supply that smoothes the inverter power supply voltage and makes the inverter output substantially constant is required.

As such a smoothing means, a large-capacitance capacitor such as an electrolytic capacitor is very effective, but there is a limit to an allowable current, and a decrease in capacity rapidly proceeds due to loss and heat generated by flowing the current. In some cases, characteristic deterioration may occur. In some cases, the life of components cannot be ensured with respect to the life of the induction heating device.

  As in Patent Document 1, when a plurality of switching elements are provided, a resonance current having a short period is generated in the heating coil during the ON period of one switching element, and power is supplied from the smoothing capacitor to the heating coil, Since a current constantly flows through the smoothing capacitor, which is a means, it is necessary to select a capacitor having a particularly large allowable current, and there is a problem that the cost increases and the part shape increases.

  The present invention solves the above-mentioned conventional problems, and by controlling the simultaneous conduction period and the closed-loop resonance period of a plurality of switching elements to appear alternately, there is no loss bias between the switching elements, and the cooling design is improved. An object of the present invention is to provide an induction heating device that is easy and has a long component life and consequently low cost.

  In order to solve the conventional problem, an induction heating device of the present invention includes a DC power supply, a heating coil and a resonant capacitor connected in series with each other, first, second, third and fourth switching elements, Control means for controlling driving of the switching elements, and a first simultaneous conduction period in which the first and fourth switching elements are simultaneously conducted and a second and third switching elements are simultaneously conducted. A first closed-loop resonance period in which a resonance current flows in a first closed loop composed of the first and third switching elements, a heating coil, and a resonance capacitor, and the second and fourth switching elements and heating. A second closed loop resonance period in which a resonance current flows is provided in a second closed loop composed of a coil and a resonance capacitor, and a first simultaneous conduction period and a first closed loop resonance period Set set and the second simultaneous ON period and the second closed-loop resonant period is intended to control so as to appear alternately.

  As a result, the closed-loop resonance period is formed by a set of different switching elements, and further, the set is switched. Therefore, there is little loss bias between the plurality of switching elements, and the cooling design is easy.

  Therefore, it is possible to provide an induction heating device with a long component life and low cost.

  The induction heating device of the present invention is controlled so that a first simultaneous conduction period, a first closed loop resonance period, a second simultaneous conduction period, and a second closed loop resonance period formed by different sets of switching elements appear alternately. By doing so, it is possible to provide a low-cost induction heating device with no loss bias between switching elements, easy cooling design, long component life, and low cost.

The first invention includes a DC power source, a heating coil and a resonant capacitor connected in series with each other, an object to be heated disposed substantially above the heating coil, a high potential side of the DC power source, and the heating coil. A first switching element inserted; a second switching element inserted between a connection point of the heating coil and the first switching element and a low potential side of the DC power supply; and a high potential side of the DC power supply. And a third switching element inserted between the heating coils, a fourth switching element inserted between a connection point of the resonant capacitor and the third switching element and a low potential side of the DC power supply, Control means for controlling the driving of the first, second, third and fourth switching elements, wherein the control means comprises the first, second, third and fourth switching elements. By conducting / interrupting a child, a resonance current having a resonance frequency determined by the heating coil, the resonance capacitor, and the object to be heated is supplied to the heating coil to generate a high-frequency magnetic field to inductively heat the object to be heated. And a first simultaneous conduction period in which the first and fourth switching elements are simultaneously conducted, and the second and third.
A first simultaneous conduction period in which a set of switching elements is simultaneously conducted, and a first current that flows through a first closed loop including the first and third switching elements, the heating coil, and the resonant capacitor. A closed loop resonance period and a second closed loop resonance period in which a resonance current flows in a second closed loop composed of the second and fourth switching elements, the heating coil, and the resonance capacitor are provided, and the first simultaneous conduction is provided. Control is performed so that a set of a period and the first closed-loop resonance period and a set of the second simultaneous conduction period and the second closed-loop resonance period appear alternately.

  Thus, when induction heating an object to be heated made of aluminum, copper, or a low permeability material having an electric conductivity substantially equal to or higher than that, in order to generate sufficient eddy current and obtain Joule heat, In order to control multiple simultaneous conduction periods and closed-loop resonance periods to appear alternately, it is possible to distribute the load on multiple switching elements almost evenly. In the closed-loop resonance period, since the resonance current does not flow through the smoothing means serving as a DC power source, the current flowing through the smoothing means is reduced. Capacitors with low component costs can be used at low cost, and loss between multiple switching elements can be achieved. Bias less easily cooled design, and component life is long, can be a low-cost induction heating apparatus.

  In particular, the second invention resonates with the smoothing means serving as a DC power source by setting the control means of the first invention longer than the first or second closed loop resonance period by at least one period of the resonance current. The current flowing period can be shortened, and a magnetic field higher in frequency than the driving frequency of the switching element can be generated. Therefore, the loss of the switching element is reduced, and the high frequency resonance current such as an aluminum pan is reduced. This is very effective for induction heating of an object to be heated made of a low-resistivity nonmagnetic metal with little attenuation.

  In the third invention, in particular, the control means according to the second invention is configured such that the first conduction period-the first closed-loop resonance period-the second conduction period-the second closed-loop resonance period or the first closed-loop resonance. The first conduction period is controlled by controlling the first, second, third, and fourth switching elements in the order of period-first conduction period-second closed loop resonance period-second conduction period. In the second conduction period, a current path on the DC power supply high potential side-heating coil and resonant capacitor-DC power supply low potential side is formed, and power is transmitted from the power supply to the object to be heated. Since the first closed-loop resonance period and the second closed-loop resonance period are sandwiched between the period and the second conduction period, the object is made of a low resistivity non-magnetic metal such as an aluminum pan that has little attenuation of the high-frequency resonance current. Very effective for induction heating of heated objects Both switching of the switching element at the time of switching becomes limited to the minimum, while transferring power to the object to be heated can be a low loss, low cost induction heating apparatus.

  In particular, according to the fourth aspect of the invention, the control means of the second aspect of the invention is such that the timing at which the first switching element turns on is earlier or later than the timing at which the third switching element turns on by approximately half a period of the resonance current. By controlling in this way, the first switching element may be driven at a timing shifted by a predetermined phase with respect to the driving of the third switching element, and the control means for controlling the driving of the switching element Since it is only necessary to drive at a timing shifted by the phase, there is no need for a special circuit for determining the drive timing, and it is counted by a timer built in the control means and driven at a predetermined timing. Thus, the switching element and the inverter can be easily controlled.

The fifth aspect of the invention is particularly the control means of the second aspect of the invention, so that the timing at which the first switching element turns on is earlier or later than the timing at which the fourth switching element turns on by approximately one period of the resonance current. By controlling, it is only necessary to drive the first switching element at a timing shifted from the predetermined phase with respect to the driving of the fourth switching element, and the control means for controlling the driving of the switching element has the predetermined phase. Since it is only necessary to drive at a timing shifted by an amount, no special circuit or the like is required for determining the drive timing. By counting with a timer or the like built in the control means and driving at a predetermined timing The switching element and the inverter can be easily controlled.

  In the sixth aspect of the invention, in particular, the control means of the second aspect of the invention controls the switching elements such that the first, second, third and fourth switching elements are substantially the same in duration, so that each switching element The conduction periods are substantially the same, the bias of conduction loss between the switching elements is reduced, the cooling design is easy, the life of the parts can be extended, and a low-cost induction heating apparatus can be obtained.

  In particular, the seventh aspect of the invention relates to the input current detection means of the first invention, the resonance output detection means for detecting the magnitude of the resonance output, the output of the input current detection means, and the output of the resonance output detection means. Material discriminating means for discriminating the material of the heated object, and the control means controls the first, second, third and fourth switching elements when the material discriminating means discriminates the material to be heated as a high resistivity metal. By controlling the conduction period to be shorter than the half period of the resonance current, it is possible to perform switching before the resonance current attenuates and sustain the resonance, and to-be-heated objects made of high resistivity metals such as iron pans and others It can be set as the practical induction heating apparatus from which heating electric power is obtained with various to-be-heated objects.

  The eighth invention particularly includes switching means for switching the capacitance of the resonant capacitor according to the seventh invention, and the control means is provided when the material discrimination means discriminates the material to be heated as a high resistivity metal. By operating the switching means so as to increase the capacity of the resonant capacitor, for example, when heating an object to be heated that has a high resistivity and a high permeability metal such as magnetic stainless steel, Since the high frequency resistance of the object becomes very high, it is difficult to obtain sufficient heating power, but depending on the material of the object to be heated, the switching means is operated to increase the resonant capacitor capacity, and the resonance frequency is lowered. The high-frequency resistance of the object to be heated also decreases, and a state where a sufficient resonance current can flow can be obtained, and a practical induction heating apparatus capable of obtaining heating power with various objects to be heated is obtained. It is a function.

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

(Embodiment 1)
FIG. 1 is a schematic circuit diagram of the induction heating apparatus according to the first embodiment of the present invention, and FIG. 2 is held inside the control means 116 and the material discrimination means 117 of the induction heating apparatus according to the first embodiment of the present invention. FIG. 3 is a diagram showing a material discrimination region of the object to be heated 114 on the detection output plane of the detected input current detection means 118 -resonance output detection means 119, and FIG. 3 shows the induction heating apparatus according to the first embodiment of the present invention. FIG. 4 is a diagram showing a voltage current waveform of each part when the object to be heated 114 made of low resistance nonmagnetic metal is induction heated, and FIG. 4 is a diagram showing low resistance nonmagnetic metal of the induction heating apparatus according to the first embodiment of the present invention. The figure which showed each part voltage current waveform at the time of inductively heating the to-be-heated material 114 other than this is shown.

  In FIG. 1, a choke coil 103 and a fifth switching element 104 are connected in series on the output side of rectifying means 102 formed of a diode bridge that rectifies an AC voltage from a commercial AC power supply 101.

  Further, the anode side of the diode 105 is connected to a 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, and a first switching element 107 and a second switching element 108 containing a reverse conducting diode inside are connected in series. A connection body and a series connection body of the third switching element 109 and the fourth switching element 110 are connected.

  The smoothing means 106 acts as a direct current power source for an inverter 111, 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, four smoothing means 560 μF electrolytic capacitors are used. ing.

  A heating coil 112 and a resonant capacitor 113 are connected in series between the connection point of the first switching element 107 and the second switching element 108 and the connection point of the third switching element 109 and the fourth switching element 110. Yes.

  A top plate (not shown) made of a heat-resistant ceramic is provided on the top of the heating coil 112, and an object to be heated 114 is placed so as to face the heating coil 112 with the top plate interposed therebetween. The

  The heating coil 112 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 113 includes a plurality of capacitors 113a, 113b, 113c, 113d, and 113e. The parallel connection body of the capacitors 113a and 113b and the parallel connection body of the capacitors 113c and 113d are connected in series, and the series connection body. In parallel, a switching body 115 composed of a relay and a capacitor 113e are formed in series.

  Capacitors 113a, 113b, 113c, and 113d are each selected to have a capacity of 0.02 μF, and capacitor 113e is selected to have a capacity of 0.2 μF. Therefore, when the switching means 115 is opened, the combined capacity of the resonance capacitor 113 is 0.02 μF, and when the switching means 115 is short-circuited, it is 0.22 μF.

  The inverter 111 includes a first switching element 107, a second switching element 108, a third switching element 109, a fourth switching element 110, a heating coil 112, and a resonance capacitor 113 (including switching means 115 in a broad sense). It is configured.

  Based on detection signals from various detection means, user operations, and the like, the control means 116 controls the first switching element 107, the second switching element 108, the third switching element 109, and the fourth switching element 110. The conduction / shutoff is controlled, that is, the output of the inverter 111 is controlled.

  Moreover, the control means 116 includes the material discrimination | determination means 117 inside, and discriminate | determines the material of the to-be-heated object 114 from the detection signal from various detection means.

  Specifically, the input current detection means 118 is constituted by a current transformer. The detection signal of the input current detection unit 118 is connected to be output to the control unit 116.

  The current transformer 119 is a current detection unit that flows through the heating coil 112, and is also a resonance output detection unit that detects the magnitude of the resonance output. The resonance output detection means 119 detects the heating coil 112 current that is the magnitude of the output of the inverter 111 and outputs a detection signal to the control means 116.

  The second control means 120 for controlling the driving of the fifth 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 The drive frequency and conduction ratio of the fifth switching element 104 are controlled so as to have predetermined values.

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

  First, the control means 116 controls the first switching element 107 and the second switching element 108 to be exclusively turned on / off based on the operation by the user, and the third switching element 109 and the fourth switching element. A drive signal is output so that the element 110 is exclusively turned on / off, and detection signals from the input current detection means 118 and the resonance output detection means 119 are input.

  FIG. 2 shows an input current detection means 118 detection output-resonance output detection means 119 detection output plane held in the control means 116 and material discrimination means 117 of the induction heating apparatus in the first embodiment of the present invention. It is the figure which showed the to-be-heated object 114 material discrimination | determination area | region.

  The input current and the resonance output are changed by driving the first switching element 107, the second switching element 108, the third switching element 109, and the fourth switching element 110, and the aluminum set in the upper part of FIG. In this case, the control means 116 continues to drive the first switching element 107, the second switching element 108, the third switching element 109, and the fourth switching element 110, The output of the inverter 111 is controlled so as to obtain a predetermined input power.

  At the same time, the controller 116 and the material discriminating unit 117 discriminate the material of the article 114 to be heated from a low-resistance nonmagnetic metal based on the output signals of the input current detector 118 and the resonant output detector 119. Control is performed to open the output of the switching means 115 so that the combined capacity becomes small.

  The combined capacity of the resonant capacitor 113 is selected so that the output of the switching means 115 is 0.02 μF when opened, and the inductance of the heating coil 112 when the object to be heated 114 is placed is designed to be 160 μH. Therefore, the resonance frequency of the heating coil 112, the resonance capacitor 113, and the object to be heated 114 is about 90 kHz.

  FIG. 3 is a diagram showing a voltage current waveform of each part when the low-resistance nonmagnetic metal heating object 114 of the induction heating device according to the first embodiment of the present invention is induction-heated.

  Under the control of the control means 116, the first switching element 107 and the second switching element 108 are exclusively turned on / off, and the third switching element 109 and the fourth switching element 110 are exclusively turned on / off as well. Then, the inverter 111 supplies the heating coil 112 with a resonance current having a resonance frequency determined by the heating coil 112, the resonance capacitor 113 and the object to be heated 114. The heating coil 112 generates a high frequency magnetic field and heats the article to be heated 114.

  As shown in FIG. 3, the control means 116 has a resonance current of 1.5 during the conduction period of the first switching element 107, the second switching element 108, the third switching element 109, and the fourth switching element 110. The conduction period is controlled so that the current flows for about a cycle and the conduction periods are substantially the same.

  Furthermore, the control means 116 determines that the timing at which the first switching element 107 is turned on is approximately half a period of the resonance current earlier than the timing at which the third switching element 109 is turned on, and that the fourth switching element 110 is The timing at which the first switching element 107 is turned on is controlled to be delayed by approximately one cycle of the resonance current with respect to the turn-on timing.

  Since the control means 116 can know the approximate resonance frequency from the result of the material discrimination of the object to be heated 114, the control means 116 is predetermined with respect to the driving of the third switching element 109 and the fourth switching element 110. It is only necessary to drive the first switching element 107 at the timing of shifting the phase, and no special circuit or the like for determining the driving timing is possessed. Counting is performed by a timer built in the control means 116, and the switching element is driven at a predetermined timing.

  Focusing on the path through which the resonance current flows, the operation of the inverter 111 will be described.

  Time t0 to t1 is a first simultaneous conduction period in which the first switching element 107 and the fourth switching element 110 are brought into conduction and the smoothing means 106 voltage is applied between the heating coil 112 and the resonance capacitor 113. During this period, electrical energy is supplied to the heating coil 112 and the resonant capacitor 113.

  The current flows in the direction of the first switching element 107 → the heating coil 112 → the resonant capacitor 113 → the fourth switching element 110 → the smoothing means 106.

  From time t1 to time t3, the first switching element 107 and the third switching element 109 become conductive, and the first switching element 107, the heating coil 112, the resonance capacitor 113, and the third switching element 109 form a closed loop. 1 is a closed-loop resonance period.

  The first closed-loop resonance period has a length corresponding to approximately one period of the resonance current. A resonance current flows through the heating coil 112 and the resonance capacitor 113 based on the electrical energy supplied in the first simultaneous conduction period.

  The current flows back through first switching element 107 (and reverse conducting diode) → heating coil 112 → resonance capacitor 113 → third switching element 109 (and reverse conducting diode). At this time, since the object to be heated 114 is made of a low-resistance nonmagnetic metal, the resonance current hardly attenuates and the resonance continues. Further, the resonance current from the inverter 111 does not flow through the smoothing means 106.

  Times t <b> 3 to t <b> 4 are a second simultaneous conduction period in which the second switching element 108 and the third switching element 109 are conductive and the smoothing means 106 voltage is applied between the heating coil 112 and the resonance capacitor 113. During this period, electrical energy is supplied to the heating coil 112 and the resonant capacitor 113. The current flows in the direction of the third switching element 109 → the resonance capacitor 113 → the heating coil 112 → the second switching element 108 → the smoothing means 106.

  From time t4 to t6, the second switching element 108 and the fourth switching element 110 are conducted, and the second switching element 108, the heating coil 112, the resonance capacitor 113, and the fourth switching element 110 constitute a closed loop. 2 closed-loop resonance period. The second closed-loop resonance period has a length corresponding to approximately one cycle of the resonance current.

A resonance current flows through the heating coil 112 and the resonance capacitor 113 based on the electrical energy supplied in the second simultaneous conduction period.

  The current flows back through second switching element 108 (and reverse conducting diode) → heating coil 112 → resonance capacitor 113 → fourth switching element 110 (and reverse conducting diode). At this time, since the object to be heated 114 is made of a low-resistance nonmagnetic metal, the resonance current hardly attenuates and the resonance continues. Further, the resonance current from the inverter 111 does not flow through the smoothing means 106.

  As described above, the control unit 116 performs switching so that the set of the first simultaneous conduction period and the first closed-loop resonance period and the set of the second simultaneous conduction period and the second closed-loop resonance period appear alternately. Drive the element. Further, the order is the first simultaneous conduction period-first closed loop resonance period-second simultaneous conduction period-second closed loop resonance period.

  This operation is effective when the object to be heated 114 is a low-resistance nonmagnetic metal. When the object 114 to be heated 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, the second switching element 108, the third switching element 109, and the fourth switching element 110 is set longer than the resonance frequency. During the simultaneous conduction period, the resonance can be continued with the electric energy supplied to the heating coil 112 and the resonance capacitor 113.

  Here, the frequency of the high-frequency resonance current is determined by the heating coil 112, the resonance capacitor 113, and the object to be heated 114, and is about 90 kHz as described above, while the driving frequency of the switching element is about 30 kHz in the present embodiment. . 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 112 is set as high as 90 kHz, the apparent high-frequency resistance can be increased even with the low-resistance nonmagnetic metal heated object 114. It is possible to obtain sufficient heating power with a small heating coil 112 current.

  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.

  Further, during the operation period of the inverter 111, a period during which no resonance current flows through the smoothing means 106 occurs. Since the smoothing means 106 is a power supply for the inverter 111, it needs to be a capacitor having a relatively large capacity. However, if the inverter 111 has a full bridge configuration as in the present embodiment, a resonance current always flows. End up.

  However, by providing the first closed-loop resonance period and the second closed-loop resonance period, it is possible to reduce the burden on the smoothing means 106 by providing a period during which no resonance current flows in the smoothing means 106. As a result, smoothing The means 106 can be reduced in size, extended in life, and reduced in cost.

  When the object to be heated 114 is a low-resistance nonmagnetic metal, an eddy current is induced inside the object to be heated 114 with respect to the high frequency magnetic field generated from the heating coil 112. Since this eddy current acts to repel the high-frequency magnetic field from the heating coil 112, the article to be heated 114 itself vibrates.

When the voltage of the smoothing means 106 serving as the power source of the inverter 111 fluctuates in synchronization with the voltage of the commercial AC power source 101, the object to be heated 114 also vibrates in synchronization 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 supply of the inverter 111 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 fifth switching element 104, and the diode 105 are provided with a boosting means 121 that also functions as a power factor improving means. The control means 116 starts the operation of the inverter 111 based on the user's operation and outputs an operation start signal to the second control means 120. The second control unit 120 detects the smoothing unit 106 voltage, the input current, and the like (not shown), and the fifth switching element 104 so that the input current has a substantially sine wave shape and the smoothing unit 106 voltage has a predetermined value. The drive frequency and conduction ratio are controlled.

  When the fifth 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 120 holds a reference voltage inside and controls the same value as compared with the smoothing means 106 voltage detection signal. The control means 116 also operates the smoothing means 106 voltage detection. As a result, the voltage is applied or the resistance is switched so that the smoothing means 106 voltage is controlled by the control means 116.

  The control unit 116 operates the smoothing unit 106 voltage detection signal according to the output signals of the input current detection unit 118 and the resonance output detection unit 119, and indirectly controls the boosting amount of the boosting unit 121 to control the smoothing unit 106 voltage. Has changed.

  When the object to be heated 114 is a low-resistance nonmagnetic metal, the frequency range in which the heating coil 112 and the resonance capacitor 113 can continue to resonate is very narrow, so that the control of the output of the inverter 111 is very difficult. However, since the smoothing means 106 also acts as a power supply for the inverter 111, the output of the inverter 111 can be controlled by changing the voltage of the smoothing means 106.

  When the control unit 116 starts the operation of the inverter 111, the control unit 116 and the material discriminating unit 117 are heated by the input current detection unit 118 detection output-resonance output detection unit 119 detection output plane as shown in FIG. If the material to be heated 114 is determined to be other than a low-resistance nonmagnetic metal based on the 114 material determination region, the control means 116 temporarily stops the operation of the inverter 111 (about 2 seconds), and the combined capacity of the resonance capacitor 113 Is controlled so that the output of the switching means 115 is short-circuited. In the present embodiment, as described above, the combined capacitance of the resonant capacitor 113 is set to 0.22 μF.

  After the switching of the switching unit 115 is completed, the control unit 116 starts the operation of the inverter 111 again.

FIG. 4 is a diagram showing a voltage current waveform of each part when the object to be heated 114 other than the low-resistance nonmagnetic metal of the induction heating device according to the first embodiment of the present invention is induction-heated. It is roughly similar to the waveform of each part when heating a low-resistance nonmagnetic metal, but the major difference is the current waveform flowing in the switching element.

  When heating the object to be heated 114 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 114 itself has high resistance. Therefore, the control means 116 switches so that the capacity of the resonance capacitor 113 is increased, and sets the resonance frequency of the heating coil 112, the resonance capacitor 113, and the article to be heated 114 to be low (about 20 kHz in the present embodiment), and the first The conduction periods of the switching element 107, the second switching element 108, the third switching element 109, and the fourth switching element 110 are controlled to be shorter than the half period of the resonance current.

  Here, since the resonance frequency is low, even if the drive frequency of the switching element is substantially the same as the resonance frequency, the switching loss is not significantly increased. Further, since the resistance of the object to be heated 114 is high, the required high frequency resonance current is small, and the switching loss and the loss during conduction can be kept low.

  The switching means 115 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 heating coil 112 current was given as the resonance output detection means 119, the resonance capacitor 113 voltage may be detected, or the first switching element 107 which is a part of the heating coil 112 current. The same effect can be obtained by detecting the current of any one of the second switching element 108, the third switching element 109, and the fourth switching element 110, and the current of the smoothing means 106 serving as the DC power source of the inverter 111.

  Although the configuration in which the second control unit 120 is provided separately from the control unit 116 is described, the operation of the second control unit 120 may be combined with the control unit 116.

  Moreover, although the to-be-heated material 114 gave the low resistance nonmagnetic metal, such as aluminum, and the other examples, for example, the material may be identified as a nonmagnetic stainless steel having a higher resistance than aluminum and a metal having a higher resistance. The material discrimination is not limited to two types, but may be determined as three types or four types, and the necessary inverter 111 output may be obtained by combining the switching element conduction period control, the switching means 115 control, and the like.

  In particular, the pot sound is a phenomenon peculiar to a low-resistance non-magnetic metal such as aluminum and a light material. Therefore, if the object to be heated is limited to the heated object 114 of other materials, the capacity of the smoothing means 106 is increased. It is not necessary to set it excessively large, and it is not necessary to provide the boosting means 121 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 in which the conduction period of the switching element is substantially the same is given, but the present invention is not limited to this. For example, when heating the low-resistance nonmagnetic metal object to be heated 114, the conduction period of the first switching element 107 is controlled to be shorter than one period of the resonance current, and the object to be heated 114 other than the low-resistance nonmagnetic metal is heated. The second switching element 108 may be controlled so that the conduction period of the second switching element 108 is longer than one period 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. The same applies to the third switching element 109 and the fourth switching element 110.

When the low-resistance nonmagnetic metal object to be heated 114 is heated as in this embodiment, if the conduction period of the switching element is controlled to be one period or more of the resonance current, the inverter 111 power The ratio of the time for supplying power from the smoothing means 106 is reduced, and the heating power that can be input in principle is reduced. However, for example, 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 switched. By controlling, it is possible to level the loss.

  The same applies to the third switching element 109 and the fourth switching element 110.

  As described above, the induction heating apparatus according to the present invention can provide an induction heating apparatus that has no loss bias between switching elements, that is easy in cooling design, has a long component life, and consequently is low in cost. As an induction heating cooker, it can be applied to uses such as induction heating type water heaters, induction heating type irons, and other induction heating type heating devices.

Schematic circuit diagram of the induction heating apparatus in Embodiment 1 of the present invention Discrimination of the material of the object to be heated 114 on the plane of detection of the input current detection means 118 -resonance output detection means 119 held in the control means 116 and material discrimination means 117 of the induction heating apparatus according to Embodiment 1 of the present invention Diagram showing the area The figure which showed the voltage current waveform of each part at the time of carrying out induction heating of the to-be-heated object 114 made from the low resistance nonmagnetic metal of the induction heating apparatus in Embodiment 1 of this invention The figure which showed the voltage current waveform of each part at the time of inductively heating to-be-heated material 114 other than the low resistance nonmagnetic metal of the induction heating apparatus in Embodiment 1 of this invention Circuit diagram of conventional induction heating cooker Waveform diagram showing the operation of each switching element of a conventional induction heating cooker and the waveform diagram of the oscillating current flowing by this switching operation

Explanation of symbols

106 Smoothing means (DC power supply)
107 First switching element 108 Second switching element 109 Third switching element 110 Fourth switching element 112 Heating coil 113 Resonant capacitor 114 Object to be heated 115 Switching means (relay)
116 Control means 117 Material discrimination means 118 Input current detection means (current transformer)
119 Resonant output detection means (current transformer)

Claims (8)

A direct current power source, a heating coil and a resonant capacitor connected in series with each other, an object to be heated disposed substantially above the heating coil, and a first potential inserted between the high potential side of the direct current power source and the heating coil. A switching element; a second switching element inserted between a connection point of the heating coil and the first switching element and a low potential side of the DC power supply; and a high potential side of the DC power supply and the resonant capacitor. A third switching element inserted; a fourth switching element inserted between a connection point of the resonant capacitor and the third switching element; and a low potential side of the DC power supply, and the first, second, Control means for controlling the driving of the third and fourth switching elements, the control means conducting the first, the second, the third and the fourth switching elements. By cutting off, a resonance current having a resonance frequency determined by the heating coil, the resonance capacitor, and the object to be heated is supplied to the heating coil to generate a high-frequency magnetic field to inductively heat the object to be heated. A first simultaneous conduction period in which the first and fourth switching elements are simultaneously conducted; a second simultaneous conduction period in which the second and third switching elements are simultaneously conducted; and the first and second A first closed-loop resonance period in which a resonance current flows in a first closed loop composed of three switching elements, the heating coil, and the resonance capacitor, and the second and fourth switching elements, the heating coil, and the resonance capacitor. A second closed loop resonance period in which a resonance current flows in a second closed loop configured by: the first simultaneous conduction period; and 1 of the closed-loop induction heating apparatus the set of pairs and said second simultaneous conduction period and the second closed-loop resonant period of the resonant period is controlled to alternately appear. The induction heating apparatus according to claim 1, wherein the control means sets the first or second closed-loop resonance period to at least one period of the resonance current. The control means includes a first simultaneous conduction period, a first closed loop resonance period, a second simultaneous conduction period, a second closed loop resonance period, or a first closed loop resonance period, a first simultaneous conduction period, and a second. The induction heating device according to claim 2, wherein the first, second, third, and fourth switching elements are controlled so that the closed-loop resonance period and the second simultaneous conduction period are in this order. 3. The induction heating apparatus according to claim 2, wherein the control unit controls the timing at which the first switching element is turned on to be approximately half a cycle of the resonance current earlier or later than the timing at which the third switching element is turned on. 3. The induction heating apparatus according to claim 2, wherein the control unit controls the timing at which the first switching element is turned on to be approximately one cycle earlier or later than the timing at which the fourth switching element is turned on. The induction heating apparatus according to claim 2, wherein the control means controls the first, second, third, and fourth switching elements to have substantially the same period. Input current detection means, resonance output detection means for detecting the magnitude of the resonance output, and material determination means for determining the material of the object to be heated from the output of the input current detection means and the output of the resonance output detection means The control means controls the first, second, third and fourth switching element conduction periods to be shorter than a half cycle of the resonance current when the material discrimination means discriminates the material to be heated as a high resistivity metal. The induction heating apparatus according to claim 1. Switching means for switching the capacity of the resonant capacitor is provided, and the control means operates the switching means so that the capacity of the resonant capacitor is increased when the material determining means determines that the material to be heated is a high resistivity metal. The induction heating apparatus according to claim 7.

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