JP6775673B2 - Induction heating device - Google Patents

Description

The present invention relates to an induction heating device.

A conventional induction heating device includes a first heating coil provided on the inner peripheral side of one heating port and a second heating coil provided on the outer peripheral side of the first heating coil. The inverter circuit that supplies an alternating current to the heating coil and the second heating coil of the above is configured by using three arm circuits in which two switching elements are connected in series (see, for example, Patent Document 1).

The three arm circuits are a first arm circuit, a second arm circuit, and a common arm circuit, and a first heating coil is connected between the first arm circuit and the common arm circuit, and a second arm circuit is connected. A second heating coil was connected between the arm circuit and the common arm circuit. Further, the first heating coil and the second heating coil are connected in series to a variable capacitance capacitor whose capacitance can be switched by opening and closing a switch, respectively, and the object to be heated placed on the heating port is magnetic metal or non-magnetic metal. The opening and closing of the switch was switched depending on whether it was a magnetic metal. Then, the first arm circuit, the second arm circuit, and the common arm circuit are switched at the same frequency, and an alternating current having the same frequency is supplied to the first heating coil and the second heating coil to be heated. Was induced and heated. Further, when the object to be heated is made of a non-magnetic metal, the switching frequency of each arm circuit is set higher than that when the object to be heated is made of a magnetic metal, and the object is supplied to the first heating coil and the second heating coil. The frequency of the alternating current was increased. When the object to be heated is induced and heated by an alternating magnetic flux having a higher frequency, the depth of the epidermis in which the eddy current flows through the object to be heated becomes shallow due to the skin effect, so that the electrical resistance of the path through which the eddy current flows increases. As a result, even when the object to be heated is made of a non-magnetic metal, induction heating can be performed efficiently.

JP-A-2009-158225

However, in the conventional induction heating device described in Patent Document 1, an induction heating object made of a different material formed by joining a magnetic metal to the inner peripheral side of the bottom of the object to be heated made of a non-magnetic metal is induced and heated. In this case, since the magnetic metal is located on the first heating coil and the non-magnetic metal is located on the second heating coil, the object to be heated cannot be efficiently induced and heated. That is, in the conventional induction heating device, an alternating current having the same frequency is passed through the first heating coil and the second heating coil. Therefore, if the alternating current has a frequency suitable for the induction heating of the magnetic metal, the outer peripheral side is not. If the induction heating of the magnetic metal becomes insufficient and the alternating current has a frequency suitable for the induction heating of the non-magnetic metal, the frequency will be unnecessarily high for the induction heating of the magnetic metal on the inner peripheral side. There was a problem that the efficiency of the coil was reduced.

The present invention has been made to solve the above-mentioned problems, and even if the first heating coil and the second heating coil share a common arm circuit, the first heating coil and the second heating coil can be used. It is an object of the present invention to provide an induction heating device capable of supplying alternating currents of different frequencies to a heating coil.

The induction heating device according to the present invention is provided between a first switching element, a second switching element connected in series with the first switching element, and between the first switching element and the second switching element. An inverter circuit having a plurality of arm circuits having output ends and including a first arm circuit, a second arm circuit, and a common arm circuit in the plurality of arm circuits, and an output end and a common arm circuit of the first arm circuit. A first heating coil electrically connected to the output end of the second arm circuit and a second heating coil electrically connected to the output end of the second arm circuit and the output end of the common arm circuit. When the AC current of the first frequency is supplied to the first heating coil, the inverter circuit switches the first switching element of the common arm circuit at a predetermined frequency and the second heating coil. Even when an alternating current of a second frequency different from the first frequency is supplied to the first heating coil, the first of the common arm circuit has the same frequency as when the alternating current of the first frequency is supplied to the first heating coil. Switching the switching element.

According to the induction heating device according to the present invention, even if the first heating coil and the second heating coil share a common arm circuit, the first heating coil and the second heating coil have different frequencies of alternating current. Can be supplied.

It is a perspective view which shows the induction heating apparatus in Embodiment 1 of this invention. It is a top view which shows the heating coil in Embodiment 1 of this invention. It is a circuit diagram which shows the structure of the electric circuit of the induction heating apparatus in Embodiment 1 of this invention. It is sectional drawing which shows the state in the case where the heated object made of a single material and the heated object made of different materials are placed on the top plate of the induction heating device according to the first embodiment of the present invention. It is a perspective view which shows the state of induction heating of the object to be heated made of a single material by the induction heating apparatus in Embodiment 1 of this invention. It is a perspective view which shows the state of induction heating of the object to be heated made of different materials by the induction heating apparatus in Embodiment 1 of this invention. An example of the driving conditions in the case of induction heating of the object to be heated made of different materials in the induction heating apparatus of Embodiment 1 of this invention is shown. 6 is a time chart showing a gate signal of each switching element constituting the inverter circuit of the induction heating device according to the first embodiment of the present invention, and a voltage waveform and a current waveform output from the inverter circuit. 6 is a time chart showing a gate signal of each switching element constituting the inverter circuit of the induction heating device according to the second embodiment of the present invention, and a voltage waveform and a current waveform output from the inverter circuit. 6 is a time chart showing a gate signal of each switching element constituting the inverter circuit of the induction heating device according to the third embodiment of the present invention, and a voltage waveform and a current waveform output from the inverter circuit. 6 is a time chart showing a gate signal of each switching element constituting the inverter circuit of the induction heating device according to the fourth embodiment of the present invention, and a voltage waveform and a current waveform output from the inverter circuit. 6 is a time chart showing a gate signal of each switching element constituting the inverter circuit of the induction heating device according to the fifth embodiment of the present invention, and a voltage waveform and a current waveform output from the inverter circuit. It is a top view which shows the position of the object to be heated placed on the heating coil at the time of induction heating of the object to be heated by the induction heating apparatus in Embodiment 6 of this invention. It is a perspective view which shows the state of induction heating of two objects to be heated by the induction heating apparatus in Embodiment 7 of this invention.

Embodiment 1.
First, the configuration of the induction heating device according to the first embodiment of the present invention will be described. FIG. 1 is a perspective view showing an induction heating device according to the first embodiment of the present invention.

In FIG. 1, the induction heating device 100 is composed of a housing 1 and a top plate 2 provided on the upper portion of the housing 1. The top plate 2 has an insulating material such as glass, ceramics, or resin, and an object to be heated such as a pan or a frying pan that is induced and heated by the induction heating device 100 is located in a region composed of the insulating material of the top plate 2. It will be placed. On the top plate 2, mounting positions 3a, 3b, and 3c indicating a guideline for the position where the object to be heated is placed are displayed. When the top plate 2 is made of a transparent material such as glass, the mounting positions 3a, 3b, and 3c may be displayed on the back surface opposite to the front surface of the top plate 2 which is the mounting surface by printing or the like. Further, the mounting positions 3a, 3b, and 3c are composed of a light emitting element such as a light emitting diode provided on the back surface side of the top plate 2 and a light guide member, and the position on which the object to be heated is placed is the top plate 2. It may be configured so that it can be visually recognized from the surface side. In FIG. 1, the mounting positions 3a, 3b, and 3c are shown so as to indicate the region on which the object to be heated is placed, but the mounting positions 3a, 3b, and 3c are the centers of the positions where the objects to be heated are placed. It may be displayed as a point or the like. Since the induction heating device 100 induces and heats the object to be heated placed at the mounting positions 3a, 3b, and 3c, the mounting positions 3a, 3b, and 3c may be referred to as heating ports, respectively.

The induction heating device 100 has a grill portion 4 having an opening / closing door that can be pulled out on the front side of the housing 1. The grill portion 4 is provided with a heating means such as a heater in a heating chamber having a rectangular parallelepiped internal space. The grill portion 4 is used, for example, when grilling grilled fish or the like. The grill portion 4 is not always necessary, and the induction heating device 100 may have a configuration that does not include the grill portion 4.

The induction heating device 100 has an operation unit 5a in front of the top plate 2 and operation units 5b and 5c in front of the housing 1. The operation units 5a, 5b, and 5c start heating, stop heating, adjust the heating power, and start heating by the grill unit 4 when inducing heating the object to be heated placed at the mounting positions 3a, 3b, and 3c. , Stop heating, or adjust the heating power. The positions where the operation units 5a, 5b, and 5c are provided are not limited to the positions shown in FIG. 1, and may be any place where the user who uses the induction heating device 100 can easily operate the induction heating device 100.

A display unit 6 for displaying the state of the induction heating device 100 is provided in front of the top plate 2. The display unit 6 may be, for example, a display device such as a liquid crystal display or an organic EL (Electroluminescence) display. The position where the display unit 6 is provided may be any position as long as it is easily visible to the user of the induction heating device 100, and the display unit 6 may be provided not only in front of the top plate 2 but also on the front surface of the housing 1, for example. .. Various information is displayed on the display unit 6 according to the operating status of the induction heating device 100. For example, the electric power input to each heating port or the relative magnitude of the electric power may be displayed, or the temperature of the bottom surface of the object to be heated placed on each heating port may be displayed. Further, the display unit 6 may be configured by a display device with a touch panel, and the display unit 6 and the operation unit may be integrally formed.

Exhaust ports 7a, 7b, and 7c are provided behind the top plate 2. The exhaust ports 7a, 7b, and 7c are formed by heat generated by a grill portion 4, an electric circuit (not shown), a heating coil (not shown), etc. provided in the induction heating device 100, or heat generated in the grill portion 4. This is an exhaust port for discharging oil smoke or the like generated by cooking to the outside of the induction heating device 100. In FIG. 1, the exhaust ports 7a, 7b, and 7c are provided on the top plate 2, but the exhaust ports may be provided on the housing 1. Further, the number of exhaust ports is not limited to three, and may be one or more. When the induction heating device 100 does not have the grill portion 4, the induction heating device 100 may be configured to dissipate heat from the surface of the housing 1, for example, without providing an exhaust port.

Inside the induction heating device 100, a heating coil for inductively heating an object to be heated such as a pot placed on the top plate 2 and an electric circuit for supplying a high frequency current to the heating coil are provided. ing. The heating coil is provided on the back surface side of the top plate 2 so as to face each of the mounting positions 3a, 3b, and 3c displayed on the top plate 2. The heating coil may be formed, for example, by spirally winding a covered wire. If a litz wire formed by twisting a plurality of thin clothing wires coated with a thin wire made of a metal having high conductivity such as copper is used as the lead wire forming the heating coil, the electric resistance of the heating coil at a high frequency of 20 kHz to 100 kHz It is more preferable because the increase can be suppressed. One heating coil has two terminals connected to an electric circuit. That is, one heating coil is a two-terminal circuit component having both ends. Further, if necessary, the heating coil may have a magnetic material such as a ferrite core so as to face the surface opposite to the surface facing the object to be heated.

FIG. 2 is a plan view showing a heating coil according to the first embodiment of the present invention. 2 (a) to 2 (d) show an example of a heating coil provided in the induction heating device 100, and the induction heating device 100 of the present invention is shown in FIGS. 2 (a) to 2 (d). A heating coil other than the above shape may be provided. Here, in the induction heating device 100 shown in FIG. 1, any of the heating coils shown in FIGS. 2 (a) to 2 (d) is placed in the mounting regions 3a, 3b, and 3c on the back surface side of the top plate 2. It will be described as being provided facing each other. The mounting regions 3a, 3b, and 3c may be provided with heating coils having different shapes facing each other. For example, the heating coils 30c of FIG. 2C are provided facing the mounting regions 3a. The heating coil 30b of FIG. 2B may be provided facing the mounting region 3b, and the heating coil 30a of FIG. 2A may be provided facing the mounting region 3c.

The heating coil 30a shown in FIG. 2A is a heating coil 31 formed in a ring shape by winding a wire, and a heating coil 31 formed in a ring shape by winding a wire and arranged adjacent to the heating coil 31. It is composed of a coil 32. The heating coil 32 is arranged around the heating coil 31 so as to be separated from the heating coil 31. The heating coil 31 and the heating coil 32 each have terminals connected to an electric circuit at both ends of the conducting wire, and each is an individual heating coil. Since the heating coil 32 is provided so as to surround the heating coil 31, when the object to be heated is placed on the heating coil 30, the heating coil 31 induces and heats the region on the inner peripheral side of the object to be heated. The heating coil 32 induces and heats the region on the outer peripheral side of the object to be heated.

In FIG. 2A, the heating coil 31 may be used as the first heating coil and the heating coil 32 may be used as the second heating coil. Further, the names of the first heating coil and the second heating coil may be interchanged, and the heating coil 32 may be used as the first heating coil and the heating coil 31 may be used as the second heating coil. Although not mentioned below, in the present invention, the names of the first heating coil and the second heating coil may be interchanged with each other. That is, one of the plurality of heating coils is the first heating coil, and one of the plurality of heating coils excluding the first heating coil is the second heating coil. The first heating coil and the second heating coil are provided on the back surface side of the top plate 2 so as to face the back surface of the top plate 2.

The heating coil 30b shown in FIG. 2B is composed of a heating coil 31a, a heating coil 31b, and a heating coil 32, which are formed in a ring shape by winding a conducting wire, respectively. The heating coil 31a and the heating coil 31b are arranged adjacent to each other and separated from each other. Further, the heating coil 31b and the heating coil 32 are arranged adjacent to each other and separated from each other. The heating coil 31a, the heating coil 31b, and the heating coil 32 may be individual heating coils each having terminals at both ends of the conducting wire. For example, the heating coil 31a and the heating coil 31b are formed by continuous conducting wires. It may function as one heating coil. That is, the first heating coil may be composed of the heating coil 31a and the heating coil 31b, and the second heating coil may be composed of the heating coil 32.

The heating coil 30c shown in FIG. 2C is composed of a heating coil 31a, a heating coil 31b, a heating coil 32a, a heating coil 32b, a heating coil 32c, and a heating coil 32d, which are formed in a ring shape by winding a conducting wire. Has been done. As in the case of FIG. 2B, the heating coil 31a and the heating coil 31b may be individual heating coils, or the heating coil 31a and the heating coil 31b may form one heating coil. .. The heating coil 32a, the heating coil 32b, the heating coil 32c, and the heating coil 32d may also be individual heating coils, or, for example, the heating coil 32a and the heating coil 32c are connected to form one heating coil. Then, the heating coil 32b and the heating coil 32d may be connected to form another heating coil. That is, the first heating coil may be composed of the heating coil 31a and the heating coil 31b, and the second heating coil may be composed of the heating coil 32a and the heating coil 32c.

The heating coil 30d shown in FIG. 2D includes a heating coil 31a, a heating coil 32a, a heating coil 32b, a heating coil 32c, a heating coil 32d, a heating coil 32e, and a heating coil, which are formed in a ring shape by winding a wire. It is composed of 32f, a heating coil 32g, and a heating coil 32h. As in the case of FIG. 2C, the heating coils 31a to 31h may be individual heating coils, and some of the heating coils 31a to 31h are connected to form one heating coil. It may be configured. For example, the first heating coil may be configured by the heating coil 32, and the second heating coil may be configured by the heating coil 32a. Further, the first heating coil is composed of a heating coil 31, a heating coil 32a, a heating coil 32b, and a heating coil 32h, and the second heating coil is a heating coil 32c, a heating coil 32d, a heating coil 32e, and a heating coil 32g. It may be composed of. Further, using a switch such as a relay or a semiconductor switching element, the connection of a plurality of heating coils is rearranged according to the cooking purpose, one set of which is the first heating coil and the other set is the second. It may be used as a heating coil of.

FIG. 3 is a circuit diagram showing a configuration of an electric circuit of the induction heating device according to the first embodiment of the present invention. As shown in FIG. 3, the electric circuit 8 of the induction heating device 100 includes an inverter circuit 81, a power supply unit 82, a choke coil 83, a DC unit 84, and a control circuit 85. As described above, the electric circuit 8 is provided inside the induction heating device 100 surrounded by the housing 1 and the top plate 2.

The power supply unit 82 has a power fuse 12, an input capacitor 13, and a diode bridge 14. The input capacitor 13 is connected in parallel to the AC side terminal of the diode bridge 14, and an AC power source 9 which is an external power source is connected in parallel to the input capacitor 13. The input capacitor 13 functions as a filter. The AC power supply 9 is a so-called commercial power supply. A power fuse 12 is provided between the AC power supply 9 and the input capacitor 13 to prevent an overcurrent from flowing into the induction heating device 100 from the AC power supply 9. The diode bridge 14 rectifies the AC power input to the AC side terminal into DC power and outputs it from the DC side terminal of the diode bridge 14. The power supply unit 82 may be provided with a load detection unit 11 at the input / output terminal to which the AC power supply 9 is connected, which detects the current value of the input current and detects the material of the object to be heated. A more detailed description of the load detection unit 11 will be described later.

As shown in FIG. 3, a DC unit 84 is connected in parallel to the DC side terminal of the diode bridge 14 via a choke coil 83. The DC unit 84 may be, for example, a capacitor, and when the DC unit 84 is a capacitor, the choke coil 83 and the capacitors constituting the DC unit 84 may form a filter. Further, the DC unit 84 may be composed of a DC / DC converter such as a step-up chopper, a step-down chopper, or a buck-boost chopper, and may be configured to change the voltage value of the DC voltage input to the inverter circuit 81. Further, the DC unit 84 may be a power factor improving converter that improves the power factor of the AC power input from the AC power source 9. When the DC unit 84 is a capacitor, the DC voltage of the pulsating current in which the AC voltage is full-wave rectified and the voltage value fluctuates periodically is input to the inverter circuit 81. On the other hand, when the DC unit 84 is a DC / DC converter, a DC voltage having a substantially constant voltage value is input to the inverter circuit 81. In the following description, it is assumed that a DC voltage having a constant voltage value is input to the inverter circuit 81, but the following description is the same even when a pulsating DC voltage is input to the inverter circuit 81. is there.

As shown in FIG. 3, an inverter circuit 81 is connected in parallel to the DC unit 84. The inverter circuit 81 has a first arm circuit 21, a second arm circuit 27, and a common arm circuit 24 connected in parallel to each other. Each arm circuit is configured by connecting two switching elements such as an IGBT (Insulated Gate Bipolar Transistor) and a MOSFET (Metal-Oxide-Semiconductor Field-Effective-Transistor) in series, and outputs between the two switching elements. The edges are provided.

The first arm circuit 21 is connected to the low voltage side of the DC unit 84 by being connected in series with the first switching element 21a electrically connected to the high voltage side of the DC unit 84 and the first switching element 21a. It has a second switching element 21b, and an output terminal 23 provided between the first switching element 21a and the second switching element 21b. Further, the diode 22a is connected in antiparallel to the first switching element 21a, and the diode 22b is connected in antiparallel to the second switching element 21b. When the first switching element 21a and the second switching element 21b are MOSFETs, the diode 22a and the diode 22b are not always necessary because they have a body diode. A gate signal H1 is input to the gate terminal of the first switching element 21a, and the first switching element 21a is controlled to be turned on and off based on the gate signal H1. Similarly, the gate signal L1 is input to the gate terminal of the second switching element 21b, and the second switching element 21b is controlled to be turned on and off based on the gate signal L1.

The second arm circuit 27 is connected to the low voltage side of the DC unit 84 by being connected in series to the first switching element 27a electrically connected to the high voltage side of the DC unit 84 and the first switching element 27a. It has a second switching element 27b, and an output end 29 provided between the first switching element 27a and the second switching element 27b. Further, the diode 28a is connected in antiparallel to the first switching element 27a, and the diode 28b is connected in antiparallel to the second switching element 27b. A gate signal H7 is input to the gate terminal of the first switching element 27a, and the first switching element 27a is controlled to be turned on and off based on the gate signal H7. Similarly, a gate signal L7 is input to the gate terminal of the second switching element 27b, and the second switching element 27b is controlled to be turned on and off based on the gate signal L7.

The common arm circuit 24 is connected in series to the first switching element 24a electrically connected to the high voltage side of the DC unit 84 and the low voltage side of the DC unit 84 by being connected in series with the first switching element 24a. It has a second switching element 24b and an output terminal 26 provided between the first switching element 24a and the second switching element 24b. Further, the diode 25a is connected in antiparallel to the first switching element 24a, and the diode 25b is connected in antiparallel to the second switching element 24b. A gate signal H4 is input to the gate terminal of the first switching element 24a, and the first switching element 24a is controlled to be turned on and off based on the gate signal H4. Similarly, the gate signal L4 is input to the gate terminal of the second switching element 24b, and the second switching element 24b is controlled to be turned on and off based on the gate signal L4.

Although FIG. 3 shows a configuration in which the inverter circuit 81 has three arm circuits, the inverter circuit has four or more arm circuits, and one or more arm circuits are used as a common arm circuit. There may be. Further, each switching element constituting each arm circuit may be composed of a discrete semiconductor switching element, and is a power semiconductor module in which a plurality of semiconductor elements are incorporated in one package such as an IPM (Intelligent Power Module). It may be configured. A power semiconductor module incorporating three arm circuits is widely used in a drive inverter device for a three-phase AC motor. Therefore, by using such a power semiconductor module, the inverter circuit 81 of the induction heating device 100 is used. Can be configured at low cost. Further, each arm circuit may have a configuration in which a snubber circuit including a capacitor and a resistor is connected in parallel to the switching element to suppress a surge voltage applied to the switching element.

The first arm circuit 21 and the common arm circuit 24 form a first full bridge circuit, and the second arm circuit 27 and the common arm circuit 24 form a second full bridge circuit. The first heating coil 31 is electrically connected between the output end 23 of the first arm circuit 21 and the output end 26 of the common arm circuit 24. Further, a second heating coil 32 is electrically connected between the output end 29 of the second arm circuit 27 and the output end 26 of the common arm circuit 24. A first variable capacitor 41 is connected in series to the first heating coil 31, and a first heating coil is formed between the output end 23 of the first arm circuit 21 and the output end 26 of the common arm circuit 24. A first resonant circuit including 31 and a first variable capacitance capacitor 41 is connected. Further, a second variable capacitance capacitor 45 is connected in series to the second heating coil 32, and a second variable capacitor 45 is connected between the output end 29 of the second arm circuit 27 and the output end 26 of the common arm circuit 24. A second resonant circuit including the heating coil 32 and the second variable capacitance capacitor 45 is connected. In the present invention, the first heating coil 31, the second heating coil 32, the first variable capacitance capacitor 41, and the second variable capacitance capacitor 45 are treated as not constituting the inverter circuit 81. ..

The first variable capacitance capacitor 41 is a capacitor whose capacitance can be changed. For example, as shown in FIG. 3, the first variable capacitance capacitor 41 can be configured by connecting a capacitor 43 and a switch 44 in series and connecting them in parallel to the capacitor 42. Alternatively, a capacitor in which a switch is connected in parallel may be connected in series to another capacitor. The number of capacitors and switches used in the first variable capacitance capacitor 41 may be arbitrarily set, and the number of series and the number of parallels may be arbitrarily set. The switch may be, for example, a relay or a semiconductor switching element. The second variable capacitor 45 is the same as the first variable capacitor 41. The second variable capacitance capacitor 45 is configured by connecting a capacitor 47 and a switch 48 in series to the capacitor 46 in parallel. The switch 44 of the first variable capacitance capacitor 41 and the switch 48 of the second variable capacitance capacitor 45 are controlled to open and close by a control signal from the control circuit 85.

The control circuit 85 controls the switching of the first switching elements 21a, 24a, 27a and the second switching elements 21b, 24b, 27b of each arm circuit of the inverter circuit 81, and the switch of the first variable capacitance capacitor 41. A control signal for controlling the opening / closing of the switch 48 of the 44 and the second variable capacitor 45 is output. In FIG. 3, the signal line connecting the gate terminal of each switching element and the control circuit 85 and the signal line connecting the switches 44 and 48 and the control circuit 85 are omitted.

Further, the control circuit 85 is connected to the load detection unit 11 by a signal line and receives a signal from the load detection unit 11. Further, the control circuit 85 is connected to the operation unit 5 and the display unit 6 by a signal line, and transmits / receives signals such as an operation signal and a display signal between the operation unit 5 and the display unit 6 and the control circuit 85. .. The operation unit 5 is the operation unit 5a, 5b, 5c shown in FIG. 1, and the display unit 6 is the display unit 6 shown in FIG. Further, when the DC unit 84 is a DC / DC converter, the control circuit 85 may perform switching control of the switching element included in the DC / DC converter. The control circuit 85 may be configured by using an integrated circuit having an analog circuit or a digital circuit, or may be configured by using an arithmetic processing unit such as a microcomputer. Further, a gate drive circuit or a protection circuit for driving each switching element may be provided as needed.

The load detection unit 11 determines the material of the object to be heated mounted on the first heating coil 31 and the second heating coil 32. Since the impedance measured at both ends of each heating coil differs between the case where the object to be heated is a magnetic metal such as iron and the case where it is a non-magnetic material such as aluminum or copper, the difference in impedance is used. The material of the object to be heated mounted on the first heating coil 31 or the second heating coil 32 is determined. As the impedance, the material of the object to be heated may be determined by using the change in resistance, or the material of the object to be heated may be determined by using the change in inductance. The position where the load detection unit 11 is provided is not limited to the position shown in FIG. 3, for example, the first load detection unit is provided in series with the first heating coil 31 and the second is provided in series with the second heating coil 32. A load detection unit may be provided.

As shown in FIG. 3, when the load detection unit 11 is provided at the input end of the induction heating device 100, the control circuit 85 controls the first arm circuit 21 and the common arm circuit 24, and the first heating coil 31 Is supplied with a pulsed current. After that, the control circuit 85 controls the second arm circuit 27 and the common arm circuit 24, and supplies a pulsed current to the second heating coil 32. Then, based on the change in the input current measured by the load detection unit 11, the change in the impedance of the first heating coil 31 and the second heating coil 32 is detected, and the material of the object to be heated is determined. As shown in FIG. 2A, when the second heating coil 32 is arranged so as to surround the first heating coil 31, the object to be heated is determined by the determination result of the first heating coil 31. The material on the inner peripheral side is discriminated, and the material on the outer peripheral side of the object to be heated is discriminated based on the discrimination result of the second heating coil 32.

The load detection unit 11 may be provided separately from the control circuit 85 as shown in FIG. 3, but may be provided integrally with the control circuit 85. That is, only a current detector and a voltage detector are provided at the input end of the induction heating device 100, and the detected current value or voltage value is input to the control circuit 85, and the current value detected inside the control circuit 85 or the like. The material of the object to be heated may be determined by calculating the voltage value. That is, the control circuit 85 may have a function of a load detection unit, and in this case, the control circuit 85 may be a load detection unit. Similarly, when a current detector or a voltage detector is provided between the output end of the arm circuit and the heating coil and the control circuit 85 determines the material of the object to be heated based on the current value and the voltage value of the heating coil. The control circuit 85 may be a load detection unit.

Next, the operation of the induction heating device 100 of the present invention will be described.

FIG. 4 is a cross-sectional view showing a state in which an object to be heated made of a single material and an object to be heated made of different materials are placed on the top plate of the induction heating device according to the first embodiment of the present invention. .. FIG. 4A is a cross-sectional view when an object to be heated 110a made of a single material is placed on the top plate 2, and FIG. 4B is a cross-sectional view made of a different material on the top plate 2. It is sectional drawing when the heated object 110b is placed.

In the present invention, the object to be heated made of a single material is an object to be heated whose bottom 111 of the object to be heated 110a is made of a metal of a single material, as shown in FIG. 4A. A single material metal refers to a magnetic metal such as iron or ferritic stainless steel or a non-magnetic metal such as aluminum, copper or austenitic stainless steel, and does not mean a metal composed of a single element. Therefore, when the bottom of the object to be heated 110a is made of a single alloy such as stainless steel, the object to be heated is made of a single material.

On the other hand, the object to be heated made of a different material is configured by joining a magnetic metal portion 112 made of a metal different from the bottom 111 to the bottom 111 of the object 110b to be heated, as shown in FIG. 4B. It is a heated object. The object to be heated 110b made of different materials is, for example, attached or coated with a magnetic metal such as iron or ferritic stainless steel which is easily induced to be heated on the bottom surface of a pot made of a non-magnetic metal having a small electric resistance such as aluminum or copper. It is formed by joining with other means. Since most of the heated object 110b can be made of aluminum in the heated object 110b made of different materials, the cost of the heated object 110b can be reduced, the weight of the heated object 110b can be reduced, and the heat of the heated object 110b can be reduced. It is widely used for the purpose of improving conduction. As shown in FIG. 4B, the object to be heated 110b made of a different material is usually provided with the magnetic metal portion 112 on the inner peripheral side of the bottom surface of the object to be heated 110b, so that the inner peripheral side of the heating port is usually provided. The magnetic metal portion 112 is placed on the first heating coil 31 arranged in the above, and the bottom portion 111 made of non-magnetic metal is placed on the second heating coil 32 arranged on the outer peripheral side of the heating port. To.

FIG. 5 is a perspective view showing a state in which an object to be heated made of a single material is induced and heated by the induction heating device according to the first embodiment of the present invention. In FIG. 5, the distance between the heating coil 30 and the back surface of the top plate 2 is increased, but the heating coil 30 is separated from the back surface of the top plate 2 by about 1 to 10 mm. It is arranged closer to the back surface of the top plate 2 than shown in FIG. 5 and facing the mounting position 3.

As shown in FIG. 5, in the heated object 110a such as a pan or frying pan that is induced and heated by the induction heating device 100, the bottom surface of the heated object 110a is located on the placement position 3 displayed on the top plate 2. It is placed in. The bottom surface of the object to be heated 110a does not have to be entirely arranged on the mounting position 3, but when the bottom surface of the object to be heated 110a is not arranged on the mounting position 3 at all, the induction heating device 100 Determines that the object to be heated is not placed, and does not supply an alternating current to the heating coil 30.

As shown in FIG. 5, an operation in which the object to be heated 110a is placed at the mounting position 3 of the top plate 2 and the user of the induction heating device 100 operates the operation unit 5 to induce and heat the object to be heated 110a. When is selected, the control circuit 85 controls the inverter circuit 81 so as to supply a pulsed current to the heating coil 31 and the heating coil 32.

For example, first, from the control circuit 85, the gate signal H1 for turning on the first switching element 21a of the first arm circuit 21 of the inverter circuit 81 and the gate signal L1 for turning off the second switching element 21b are common. The gate signal H4 that turns off the first switching element 24a of the arm circuit 24 and the gate signal L4 that turns on the second switching element 24b are output. As a result, a current flows through the first heating coil 31. Then, the control circuit 85 outputs a gate signal H1 that turns off the first switching element 21a of the first arm circuit 21 and a gate signal L1 that turns on the second switching element 21b, and first heats the first. The current flowing through the coil 31 is stopped.

Next, from the control circuit 85, a gate signal H7 that turns on the first switching element 27a of the second arm circuit 27 of the inverter circuit 81, a gate signal L7 that turns off the second switching element 27b, and a common arm. The gate signal H4 that turns off the first switching element 24a of the circuit 24 and the gate signal L4 that turns on the second switching element 24b are output. As a result, a current flows through the second heating coil 32. Then, the control circuit 85 outputs a gate signal H7 for turning off the first switching element 27a of the second arm circuit 27 and a gate signal L7 for turning on the second switching element 27b, and second heating. The current flowing through the coil 32 is stopped.

At this time, the load detection unit 11 detects an increase in the input current to the induction heating device 100 due to the current flowing through the first heating coil 31 and the second heating coil 32. When the load detection unit is connected in series to each of the first heating coil 31 and the second heating coil 32, the load detection unit is connected to the first heating coil 31 and the second heating coil 32. Directly detect the flowing current. Based on the detected current, the load detection unit 11 uses the material of the object to be heated 110a placed on the first heating coil 31 and the material of the object to be heated 110a placed on the second heating coil 32. To determine.

When the load detection unit 11 determines that the material of the object to be heated 110a on the first heating coil 31 is a magnetic metal such as iron, the control circuit 85 switches the switch 44 of the first variable capacitor 41. Close and connect the capacitor 42 and the capacitor 43 in parallel. As a result, the capacitance of the first variable capacitance capacitor 41 increases, so that the resonance frequency of the first resonant circuit including the first heating coil 31 and the first variable capacitance capacitor 41 becomes low. On the other hand, when the load detection unit 11 determines that the material of the object to be heated 110 a on the first heating coil 31 is a non-magnetic metal such as aluminum or copper, the control circuit 85 determines that the first variable capacitor The switch 44 of 41 is opened to disconnect the capacitor 43 from the capacitor 42. As a result, the capacitance of the first variable capacitance capacitor 41 is reduced, so that the resonance frequency of the first resonant circuit including the first heating coil 31 and the first variable capacitance capacitor 41 is increased. In this way, the capacitance of the first variable capacitance capacitor 41 is changed according to the material of the object to be heated on the first heating coil 31 determined by the load detection unit 11. Similarly, the capacitance of the second variable capacitance capacitor 45 is changed according to the material of the object to be heated on the second heating coil 32 determined by the load detection unit 11.

In FIG. 5, since the object to be heated 110a is an object to be heated made of a single material, the load detection unit 11 uses the material of the object to be heated 110a on the first heating coil 31 and the material to be heated on the second heating coil 32. It is judged that the material is the same as that of the object to be heated 110a. Therefore, an alternating current having the same frequency is supplied from the inverter circuit 81 to the first heating coil 31 and the second heating coil 32. Therefore, the first switching element 21a of the first arm circuit 21 of the inverter circuit 81, the first switching element 27a of the second arm circuit 27, and the first switching element 24a of the common arm circuit 24 are switched at the same frequency. Will be done. The second switching element of each arm circuit is also switched at the same frequency.

Even when the object to be heated is an object to be heated made of a single material, the operation when the object to be heated is an object to be heated made of a different material, which will be described later, prevents the object to be heated from being induced and heated. It's not a thing. That is, even if the material of the object to be heated on the first heating coil and the material of the object to be heated on the second heating coil are the same, the frequency of the current flowing through the first heating coil 31 and the second The frequency of the current flowing through the heating coil 32 may be set to a different frequency. Further, the frequency of the alternating current supplied by the inverter circuit to the first heating coil and the frequency of the alternating current supplied to the second heating coil may be different frequencies.

Next, the operation when the object to be heated is an object to be heated made of different materials will be described.

FIG. 6 is a perspective view showing a state in which an object to be heated made of a different material is induced and heated by the induction heating device according to the first embodiment of the present invention. FIG. 6 is the same as FIG. 5 except that the object to be heated 110b is an object to be heated made of a different material, and thus the description of the same portion will be omitted.

The object to be heated 110b made of a different material is described as having a magnetic metal portion 112 made of a magnetic metal such as iron bonded to the inner peripheral side of a bottom portion 111 made of a non-magnetic metal such as aluminum. The object to be heated may have a non-magnetic metal portion bonded to the inner peripheral side of the bottom portion of the object to be heated made of magnetic metal. In this case, an alternating current having a higher frequency than the second heating coil 32 that induces and heats the magnetic metal portion on the outer peripheral side is supplied to the first heating coil 31 that induces and heats the non-magnetic metal portion on the inner peripheral side. You can do it.

When the object to be heated 110b is placed at the mounting position 3 of the top plate 2 and the load detection unit 11 completes the determination of the material of the object to be heated 110b, the control circuit 85 switches the first variable capacitor 41. The opening and closing of the switch 48 of the 44 and the second variable capacitor 45 is controlled. Since the load detection unit 11 determines that the material of the object to be heated 110b on the first heating coil 31 is magnetic metal, the switch 44 of the first variable capacitor 41 is closed. As a result, in the first variable capacitance capacitor 41, the capacitor 42 and the capacitor 43 are connected in parallel, so that the capacitance becomes large. On the other hand, since the load detection unit 11 determines that the material of the object to be heated 110b on the second heating coil 32 is a non-magnetic metal, the switch 48 of the second variable capacitor 45 is opened. As a result, in the second variable capacitance capacitor 45, the capacitor 47 is separated from the capacitor 46, so that the capacitance becomes small.

When the material of the object to be heated 110b on the first heating coil 31 is a magnetic metal such as iron and the material of the object to be heated 110b on the second heating coil 32 is a non-magnetic metal such as aluminum, the first The resonance frequency f2 of the second resonance circuit including the heating coil 32 of 2 and the second variable capacitance capacitor 45 is the resonance frequency f2 of the first resonance circuit including the first heating coil 31 and the first variable capacitance capacitor 41. It is set to be higher than the resonance frequency f1. Such settings are applied to the inductance of the first heating coil 31 and the second heating coil 32, the capacitance of the capacitors 42 and 43 included in the first variable capacitor 41, and the second variable capacitor 45. It can be set by appropriately selecting the capacitances of the included capacitors 46 and 47.

As an example, the inductance of the first heating coil 31 and the second heating coil 32 are the same, the inductance when an object to be heated made of a magnetic metal such as iron is placed is 300 μH, and the object to be heated such as aluminum. The inductance when is placed is 200 μH. Further, the capacitance of the capacitor 42 of the first variable capacitance capacitor 41 and the capacitance of the capacitor 46 of the second variable capacitance capacitor 45 is 0.024 μF. Further, the capacitance of the capacitor 43 connected in series with the switch 44 and the capacitor 47 connected in series with the switch 48 is set to 0.14 μF. In the following description, the inductance of the first heating coil 31 and the second heating coil 32 and the capacitance of each of the capacitors 42, 43, 46, 47 will be described as being the values shown here.

FIG. 7 shows an example of driving conditions in the case of induction heating of an object to be heated made of different materials in the induction heating apparatus according to the first embodiment of the present invention. In FIG. 7, the object to be heated by induction heating is the object to be heated 110b shown in FIG. 6, and the bottom 111 of the object to be heated made of a non-magnetic material such as aluminum has a magnetic metal portion made of a magnetic material such as iron. It is an object to be heated to which 112 is joined. The load detection unit 11 determines that the material of the object to be heated on the first heating coil 31 is a magnetic material and the material of the object to be heated on the second heating coil 32 is a non-magnetic material. The state of the switch 44 is "closed", and the state of the second switch 48 is "open".

In this case, as shown in FIG. 7, the capacitance of the first variable capacitance capacitor 41 is 0.164 μF because it is the sum of the capacitance of the capacitor 42 and the capacitance of the capacitor 43. Therefore, the resonance frequency f1 of the first resonance circuit including the first heating coil 31 and the first variable capacitance capacitor 41 is 22.7 kHz. Further, the capacitance of the second variable capacitance capacitor 45 is 0.024 μF because it is the capacitance of the capacitor 46. Therefore, the resonance frequency f2 of the second resonance circuit including the second heating coil 32 and the second variable capacitance capacitor 45 is 72.6 kHz. The resonance frequency f of each series resonance circuit is expressed by the following equation, where L is the inductance of each heating coil and C is the capacitance of each variable capacitor.

In the induction heating device 100 of the present invention, the first heating coil 31 is electrically connected between the first arm circuit 21 and the common arm circuit 24, and the second arm circuit 27 and the common arm circuit 24 are connected to each other. A second heating coil 32 is electrically connected between them, and the first frequency, which is the frequency of the alternating current flowing through the first heating coil 31, and the alternating current flowing through the second heating coil 32 are connected. The second frequency, which is the frequency of, can be a different frequency.

As shown in FIG. 7, the inverter circuit 81 of the induction heating device 100 of the present invention switches the first switching element 21a and the second switching element 21b of the first arm circuit 21, respectively, at, for example, 25 kHz. The first switching element 27a and the second switching element 27b of the second arm circuit 27 are switched at, for example, 75 kHz, respectively. Then, the first switching element 24a and the second switching element 24b of the common arm circuit 24 are switched at, for example, 25 kHz, respectively.

That is, the switching frequency of the first arm circuit 21 and the switching frequency of the common arm circuit 24 are set to the same frequency, and the switching frequencies of the second arm circuit 27 and the common arm circuit 24 are set to different frequencies, and the first heating coil is used. The alternating current flowing at the first frequency in 31 and the alternating current flowing at the second frequency in the second heating coil 32 are set to different frequencies. Even when an alternating current having a second frequency flows through the second heating coil 32, the inverter circuit 81 has a common arm circuit 24 at the same frequency as when an alternating current having a first frequency flows through the first heating coil 31. The first switching element 24a and the second switching element 24b of the above are switched.

The first frequency, which is the frequency of the alternating current flowing through the first heating coil 31, depends mainly on the resonance frequency f1 of the first resonance circuit including the first heating coil 31 and the first variable capacitance capacitor 41. The second frequency, which is the frequency of the alternating current flowing through the second heating coil 32, depends mainly on the resonance frequency f2 of the second resonant circuit including the second heating coil 32 and the second variable capacitor 45. To do. Therefore, for example, even when the first arm circuit 21, the second arm circuit 27, and the common arm circuit 24 are all switched at 25 kHz, as shown in FIG. 7, the resonance of the first resonance circuit When the frequency f1 is 22.7 kHz and the resonance frequency f2 of the second resonance circuit is 72.6 kHz, an alternating current of 25 kHz close to the resonance frequency of 22.7 kHz flows through the first heating coil 31. An alternating current having a resonance frequency close to 72.6 kHz flows through the second heating coil 32.

It is possible to make the resonance frequency of the resonance circuit consisting of the heating coil and the capacitor about three times the switching frequency of the arm circuit, and to supply an alternating current with a frequency about three times the switching frequency to the heating coil. It is based on the same principle as the 3x resonant inverter, which is well known to those skilled in the art. That is, a triple resonance inverter may be applied to the induction heating device 100 of the present invention.

In FIG. 7, the resonance frequency f1 of the first resonance circuit is 22.7 kHz, but the switching frequency of the first arm circuit 21 is 25 kHz, and the resonance frequency f2 of the second resonance circuit is 72.6 kHz. However, the switching frequency of the second arm circuit 27 is set to 75 kHz. Generally, in an inverter circuit of an induction heating device, the arm circuit is switched at a frequency higher than the resonance frequency of the resonance circuit so that the phase of the alternating current flowing through the heating coil is delayed from the switching of the arm circuit, so that the switching loss Is suppressed from increasing. This point is the same even in the induction heating device 100 of the present invention, and the switching frequency of each arm circuit is set so that the alternating current flowing through the first heating coil 31 and the second heating coil 32 has a delayed phase. It is preferable to select.

FIG. 8 is a time chart showing a gate signal of each switching element constituting the inverter circuit of the induction heating device according to the first embodiment of the present invention, and a voltage waveform and a current waveform output from the inverter circuit. The time chart of FIG. 8 is a gate signal, a voltage waveform, and a current waveform under the conditions shown in FIG. 7.

8 (a) to 8 (g) show the gate signal of each switching element. When the gate signal is ON, the switching element is turned on, and when the gate signal is OFF, the switching element is turned off. .. The first switching element on the high voltage side and the second switching element on the low voltage side of each arm circuit are switched on and off alternately, and when one switching element is on, the other switching element is off. It becomes. Therefore, the first switching element and the second switching element are switched at the same frequency. In the actual gate signal, the gate signal of the first switching element and the gate signal of the second switching element are used so that the first switching element and the second switching element of each arm circuit are not turned on at the same time. Although a dead time is required to turn off at the same time, it is omitted in FIG.

FIG. 8A is a gate signal H1 of the first switching element 21a of the first arm circuit 21, and FIG. 8B is a gate signal L1 of the second switching element 21b of the first arm circuit 21. is there. FIG. 8C is a gate signal H4 of the first switching element 24a of the common arm circuit 24, and FIG. 8D is a gate signal L4 of the second switching element 24b of the common arm circuit 24. FIG. 8 (e) shows the gate signal H7 of the first switching element 27a of the second arm circuit 27, and FIG. 8 (f) shows the gate signal L7 of the second switching element 27b of the second arm circuit 27. is there. Each gate signal shown in FIGS. 8A to 8F is a gate signal when the duty ratio of the on-time to the switching cycle is 50%.

8 (g) and 8 (i) show the output end 23 of the first arm circuit 21 and the output end 29 of the second arm circuit when the output end 26 of the common arm circuit 24 is used as the reference potential. It is an electric potential. The voltage output from the DC unit 84 and applied to each arm circuit is shown as Vo.

FIG. 8H is a waveform of an alternating current flowing through the first heating coil 31 in which the direction from the output end 23 of the first arm circuit 21 toward the first heating coil 31 is shown as positive. FIG. 8 (j) is a waveform of an alternating current flowing through the second heating coil 32 showing the direction from the output end 29 of the second arm circuit 27 toward the second heating coil 32 as positive. 8 (h) and 8 (j) show the maximum value of the current as + Io and the minimum value of the current as -Io, respectively. The alternating current flowing through the first heating coil 31 in FIG. 8 (h) and the alternating current flowing through the second heating coil 32 in FIG. 8 (j) have the same maximum value + Io and minimum value -Io. It is not necessary to be present, and the maximum value and the minimum value of the current may be different between the first heating coil 31 and the second heating coil 32.

A voltage is applied to the first resonance circuit including the first heating coil 31 and the first variable capacitance capacitor 41 by the first full bridge circuit including the first arm circuit 21 and the common arm circuit 24. To. As shown in FIGS. 8A and 8C, in the first full bridge circuit, the gate signal H1 of the first switching element 21a of the first arm circuit 21 and the first of the common arm circuit 24 The frequency is 25 kHz, which is the same as the gate signal H4 of the switching element 24a, and the phase is 180 ° out of phase. As a result, as shown in FIG. 8 (g), a rectangular wave voltage that alternates between + Vo and − Vo is applied to the first resonant circuit, and as shown in FIG. 8 (h), the first A 25 kHz sinusoidal alternating current flows through the heating coil 31 of the above. An alternating current having a switching frequency of 25 kHz of the first arm circuit 21 and the common arm circuit 24 as the first frequency flows through the first heating coil 31.

A voltage is applied to the second resonance circuit including the second heating coil 32 and the second variable capacitance capacitor 45 by the second full bridge circuit including the second arm circuit 27 and the common arm circuit 24. To. As shown in FIGS. 8 (e) and 8 (c), in the second full bridge circuit, the second arm circuit 27 is in the period when the gate signal H4 of the first switching element 24a of the common arm circuit 24 is OFF. The gate signal H7 of the first switching element 27a is changed to ON, OFF, and ON, and the first of the second arm circuit 27 during the period when the gate signal H4 of the first switching element 24a of the common arm circuit 24 is ON. The gate signal H7 of the switching element 27a of the above changes to OFF, ON, and OFF.

While the switching frequency of the first switching element 24a of the common arm circuit 24 is 25 kHz, the switching frequency of the first switching element 27a of the second arm circuit 27 is 75 kHz, which is three times as high. As a result, as shown in FIG. 8 (i), the second resonant circuit has a voltage waveform of + Vo, 0, + Vo and a voltage waveform of −Vo, 0, −Vo during a half cycle. Are applied alternately. The ratio of the + Vo period, the ratio of the 0 period, and the ratio of the −V period to the switching cycle of the common arm circuit 24 are all 1/3 each. Then, as shown in FIG. 8 (j), a 75 kHz sinusoidal alternating current flows through the second heating coil 32. An alternating current having a second frequency of 75 kHz, which is the switching frequency of the second arm circuit 27, flows through the second heating coil 32.

As described above, in the second full bridge circuit including the second arm circuit 27 and the common arm circuit 24, the second arm circuit 27 and the common arm circuit 24 are switched at different frequencies, but the second The heating coil 32 can be supplied with an alternating current having a second frequency different from the switching frequency of the common arm circuit 24. Then, in the first full bridge circuit, an alternating current of 25 kHz of the first frequency is supplied to the first heating coil 31, and in the second full bridge circuit, the second heating coil 32 is supplied with an alternating current of 75 kHz of the second frequency. It can supply alternating current.

As a result, not only the magnetic metal portion 112 of the object to be heated 110b placed on the first heating coil 31 but also the bottom portion 111 on the outer peripheral side of the object to be heated 110b made of non-magnetic metal is efficiently induced and heated. be able to. That is, by interlinking an alternating magnetic current having a frequency higher than that of the inner peripheral side on the outer peripheral side of the object to be heated 110b made of non-magnetic metal placed on the second heating coil 32, the non-magnetic metal is produced by the skin effect. Since the resistance of the path through which the eddy current flows can be increased, the bottom portion 111 on the outer peripheral side of the object to be heated 110b made of a non-magnetic metal can be efficiently induced and heated. As a result, the uniformity of the temperature distribution at the bottom of the object to be heated 110b such as a frying pan can be improved.

In FIG. 8, the inverter circuit 81 simultaneously supplies the alternating current of the first frequency supplied to the first heating coil 31 and the alternating current of the second frequency supplied to the second heating coil 32. Although the case has been described, the alternating current of the first frequency supplied to the first heating coil 31 and the alternating current of the second frequency supplied to the second heating coil 32 may be supplied at different times. That is, when the inverter circuit 81 supplies the first heating coil 31 with an alternating current of 25 kHz, which is the first frequency, the inverter circuit 81 stops the supply of the alternating current to the second heating coil 32, and the second When supplying an alternating current of 75 kHz, which is a second frequency, to the heating coil 32, the supply of the alternating current to the first heating coil 31 may be stopped. Then, the operation of supplying the AC current of the first frequency to the first heating coil 31 and the operation of supplying the AC current of the second frequency to the second heating coil 32 may be alternately repeated.

In this case, for example, the common arm circuit 24 is switched at 25 kHz, and when an alternating current of 25 kHz is supplied to the first heating coil 31, the first arm circuit 21 is switched at 25 kHz. The gate signal H7 of the first switching element 27a of the arm circuit 27 of the second arm circuit 27 and the gate signal L7 of the second switching element 27b may both be turned off so that an alternating current does not flow through the second heating coil 32. Further, when supplying an alternating current of 75 kHz to the second heating coil 32, the gate signal of the common arm circuit 24 is not changed and is switched at 25 kHz, and the second arm circuit 27 is switched at 75 kHz. , The gate signal H1 of the first switching element 21a of the first arm circuit 21 and the gate signal L1 of the second switching element 21b may both be turned off so that the alternating current does not flow through the first heating coil 31. ..

In FIG. 8, a case where the first arm circuit 21 and the common arm circuit 24 are switched at 25 kHz and the second arm circuit 27 is switched at 75 kHz has been described, but the first arm circuit 21 is switched at 25 kHz. Switching may be performed to switch the second arm circuit 27 and the common arm circuit 24 at 75 kHz.

When the first arm circuit 21 and the common arm circuit 24 are switched at 25 kHz and the second arm circuit 27 is switched at 75 kHz, it is applied to the first resonant circuit as shown in FIG. 8 (g). Since the voltage to be generated is a rectangular wave in which + Vo and −Vo are alternately repeated, there is no period during which the voltage applied to the first resonance circuit becomes 0, and the input power to the first heating coil 31 is maximized. Can be. On the other hand, as shown in FIG. 8 (i), the voltage applied to the second resonant circuit has a period in which the voltage becomes 0 in addition to the period of + Vo and −Vo, so that the voltage is applied to the second heating coil 32. The input power of is smaller than that in the case where the voltage applied to the second resonant circuit does not have a period of zero.

On the other hand, when the first arm circuit 21 is switched at 25 kHz and the second arm circuit 27 and the common arm circuit 24 are switched at 75 kHz, the voltage applied to the second resonance circuit is set to 0. Since the period of time can be eliminated, the input power to the second heating coil 32 can be maximized. On the other hand, since there is a period in which the voltage applied to the first resonance circuit becomes 0, the input power to the first heating coil 31 has a period in which the voltage applied to the first resonance circuit becomes 0. It is smaller than when there is no.

That is, as shown in FIG. 6, when the object to be heated 110b formed by joining the magnetic metal portion 112 to the inner peripheral side of the bottom portion 111 of the non-magnetic metal is induced and heated, the magnetic metal portion 112 on the inner peripheral side If you want to preferentially induce heating, the first arm circuit 21 and the common arm circuit 24 may be switched at the same frequency, and the second arm circuit 27 may be switched at a frequency different from that of the common arm circuit 24. .. On the other hand, when it is desired to preferentially induce and heat the bottom portion 111 made of non-magnetic metal on the outer peripheral side of the magnetic metal portion 112, the second arm circuit 27 and the common arm circuit 24 are switched at the same frequency, and the first The arm circuit 21 of the above may be switched at a frequency different from that of the common arm circuit 24. Such switching between preferential induction heating of the magnetic metal portion 112 on the inner peripheral side and preferential induction heating of the bottom portion 111 made of non-magnetic metal on the outer peripheral side is performed by, for example, the user. The control circuit 85 may control and switch the switching of each arm circuit based on the signal from the operation unit 5 when the operation 5 is operated. Further, the control circuit 85 of the induction heating device 100 may be automatically switched according to the cooking menu.

As described above, in the induction heating device 100 according to the first embodiment of the present invention, the inverter circuit 81 having the first arm circuit 21, the second arm circuit 27, and the common arm circuit 24 is the first heating coil. When an alternating current of the first frequency is supplied to the 31, the first switching element 24a of the common arm circuit 24 is switched at a predetermined frequency, and the second heating coil 32 has a second frequency different from the first frequency. The first switching element 24a of the common arm circuit 24 is switched at the same frequency as when the alternating current of the first frequency is supplied to the first heating coil 31 also when the alternating current of the frequency of Therefore, the first full bridge circuit and the second full bridge circuit in which one arm circuit is shared by the three arm circuits of the first arm circuit 21, the second arm circuit 27, and the common arm circuit 24 The first heating coil 31 electrically connected to the first full-bridge circuit and the second heating coil 32 electrically connected to the second full-bridge circuit are different from each other. It can supply alternating current of frequency. Therefore, it is possible to induce and heat the non-magnetic metal portion of the object to be heated made of different materials by interlinking an alternating magnetic flux having a frequency higher than that of the magnetic metal portion without increasing the number of arm circuits.

In the conventional induction heating device described in Patent Document 1, an induction heating object made of a different material formed by joining a magnetic metal portion to the inner peripheral side of the bottom portion of the object to be heated made of a non-magnetic metal is induced and heated. If so, the first arm circuit, the second arm circuit, and the common arm circuit are switched at the same frequency, and the frequency of the alternating current flowing through the first heating coil and the frequency of the alternating current flowing through the second heating coil. Was the same as.

Therefore, when the switching frequency of each arm circuit is set to a frequency suitable for induction heating of the magnetic metal portion (for example, 25 kHz), the skin effect of the non-magnetic metal portion on the outer peripheral side of the magnetic metal portion becomes small, so that the non-magnetic metal The resistance of the part was considerably smaller than the resistance of the magnetic metal part. Therefore, an overcurrent easily flows in the second heating coil on which the non-magnetic metal is placed, and it is difficult to increase the power input to the second heating coil due to the limitation due to the rated current of the switching element. .. Therefore, the temperature of the inner peripheral side of the bottom of the object to be heated made of different materials rises quickly, but the temperature rises slowly on the outer peripheral side, and as a result, the temperature uniformity of the bottom of the object to be heated is impaired.

Further, when the switching frequency of each arm circuit is set to a frequency suitable for induction heating of the non-magnetic metal portion (for example, 75 kHz), the frequency is too high for the induction heating of the magnetic metal portion and is common to the first arm circuit. Since switching with the arm circuit, the switching loss increases and the efficiency of induction heating decreases. Further, as the frequency of the current flowing through the heating coil increases, the resistance of the conducting wire constituting the heating coil also increases, so that the efficiency of induction heating decreases.

On the other hand, in the induction heating device 100 of the present invention, the first frequency (for example, 25 kHz) suitable for the induction heating of the magnetic metal is applied to the first heating coil 31 that induces and heats the magnetic metal portion on the inner peripheral side of the object to be heated. ) Is applied to the second heating coil 32 that induces and heats the non-magnetic metal portion on the outer peripheral side of the magnetic metal portion by applying an alternating current of a second frequency (for example, 75 kHz) suitable for induction heating of the non-magnetic metal. Supply. Therefore, the resistance of the non-magnetic metal portion on the outer peripheral side can be increased by the skin effect, and a large amount of electric power can be input to the non-magnetic metal portion. Therefore, the effect of improving the temperature uniformity of the bottom of the object to be heated made of different materials can be obtained.

Further, in the induction heating device 100 of the present invention, the switching frequency of the first arm circuit 21 and the common arm circuit 24 is set to the first frequency, and the switching frequency of the second arm circuit 27 is set to the second frequency. A first frequency alternating current is supplied to the heating coil 31 of the above, and a second frequency alternating current is supplied to the second heating coil 32. Therefore, alternating currents having different frequencies can be supplied to the first heating coil 31 and the second heating coil 32 without increasing the number of arm circuits of the inverter circuit 81, so that the inverter circuit 81 can be downsized. And the effect of reducing costs can be obtained.

Since the second arm circuit 27 needs to be switched at a frequency suitable for induction heating of the non-magnetic metal as described above, the first arm circuit 27 may be switched at a frequency suitable for the induction heating of the magnetic metal. Switching at a higher frequency than the arm circuit 21 is required. Therefore, the first switching element 21a and the second switching element 21b constituting the first arm circuit 21 are made of a silicon semiconductor, and the first switching element 27a and the second switching element 27a constituting the second arm circuit 27 are formed. The switching element 27b may be made of a wide bandgap semiconductor having a bandgap larger than that of silicon. As a result, the cost of the inverter circuit 81 can be reduced as compared with the case where the switching elements of both the first arm circuit 21 and the second arm circuit 27 are made of a wide bandgap semiconductor. The wide bandgap semiconductor may be, for example, silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga ₂ O ₃ ), or diamond.

Further, the common arm circuit 24 is common to the first full bridge circuit that supplies an alternating current to the first heating coil 31 and the second full bridge circuit that supplies an alternating current to the second heating coil 32. Therefore, a larger current flows than the first arm circuit 21 and the second arm circuit 27. Therefore, for the first switching element 24a and the second switching element 24b constituting the common arm circuit 24, a switching element having an on-resistance smaller than that of the first arm circuit 21 and the second arm circuit 27 is used. preferable. Therefore, the first switching element 21a and the second switching element 21b of the first arm circuit 21 are made of silicon semiconductor, and the first switching element 24a and the second switching element 24b of the common arm circuit 24 are wide band. It is preferably composed of a gap semiconductor. Similarly, the first switching element 27a and the second switching element 27b of the second arm circuit 27 are made of a silicon semiconductor, and the first switching element 24a and the second switching element 24b of the common arm circuit 24 are wide. It is preferably composed of a bandgap semiconductor. This is because when the withstand voltage is the same, the on-resistance of the switching element formed of the wide bandgap semiconductor can be made smaller than that of the switching element formed of the silicon semiconductor. This makes it possible to reduce the cost of the inverter circuit 81 as compared with the case where the switching elements of all the arm circuits are made of wide bandgap semiconductors.

In the first embodiment, as an example, a case where the switching frequency of the first arm circuit 21 and the common arm circuit 24 is 25 kHz and the switching frequency of the second arm circuit 27 is 75 kHz has been described. That is, the example in which the switching frequency of the second arm circuit 27 is three times (integer times) the switching frequency of the first arm circuit 21 and the common arm circuit 24 has been described. For example, the second arm circuit 27 The switching frequency of the first arm circuit 21 and the common arm circuit 24 may be 25 kHz. That is, the switching frequency of the second arm circuit 27 does not have to be an integral multiple of the switching frequency of the first arm circuit 21 and the common arm circuit 24. Further, the switching frequency of the first arm circuit 21 and the switching frequency of the common arm circuit 24 may be different frequencies, that is, the switching frequency of the first arm circuit 21, the switching frequency of the second arm circuit 27, and the switching frequency of the second arm circuit 27. The switching frequencies of the common arm circuit 24 may be different from each other. Further, it is preferable that each frequency has a difference of audible frequency or more. Here, the audible frequency is about 20 kHz. This is because when the difference between the different switching frequencies is less than the audible frequency, the difference in frequency becomes an interference sound (groan) and is heard by the user of the induction heating device 100, which makes the user uncomfortable.

Embodiment 2.
FIG. 9 is a time chart showing a gate signal of each switching element constituting the inverter circuit of the induction heating device according to the second embodiment of the present invention, and a voltage waveform and a current waveform output from the inverter circuit. The time chart of FIG. 9 is a time chart showing the state of the induction heating device 100 described in the first embodiment, and from the state of the time chart shown in FIG. 8, the first heating coil 31 and the second heating coil 32 The power control method for reducing the input power of the above is shown. In FIG. 9, the same description as in FIG. 8 means the same content, and the description thereof will be omitted. Further, in the second embodiment, the configuration of the induction heating device 100 and the like are the same as those of the first embodiment, and the components of the induction heating device 100 described with the same reference numerals are the same as those of the first embodiment. It is the same.

9 (a) to 9 (f) are gate signal waveforms of switching elements of each arm circuit, and FIGS. 9 (g) to 9 (j) are voltage waveforms output from the inverter circuit 81, as in FIG. And the current waveform. In the second embodiment, a method of controlling the input power of the first heating coil 31 and the second heating coil 32 by PWM (Pulse Width Modulation) will be described.

As shown in FIGS. 9A and 9B, the control circuit 85 of the induction heating device 100 sets the duty ratio of the first switching element 21a of the first arm circuit 21 to 25% on time. The control signal H1 is output, and the control signal L1 that makes the duty ratio of the second switching element 21b of the first arm circuit 21 on time 75% is output. Further, as shown in FIGS. 9 (e) and 9 (f), the control circuit 85 of the induction heating device 100 sets the duty ratio of the first switching element 27a of the second arm circuit 27 to 25% on time. The control signal H7 is output, and the control signal L7 is output to set the duty ratio of the second switching element 27b of the second arm circuit 27 to 75%.

Here, the case where the on-time duty ratios of the first switching element 21a of the first arm circuit 21 and the second switching element 27a of the second arm circuit 27 are both set to 25% has been shown. The duty ratio of the on-time of the first switching element 21a of the arm circuit 21 of 1 and the duty ratio of the on-time of the second switching element 27a of the second arm circuit 27 can be controlled independently, respectively. The on-time duty ratio may be different. Since the gate signals of the second switching elements 27a and 27b of the first arm circuit 21 and the second arm circuit 27 are uniquely determined corresponding to the gate signals of the first switching elements 21a and 27a, the description thereof is omitted. To do.

As shown in FIGS. 9 (c) and 9 (d), the control circuit 85 of the induction heating device 100 sets the duty ratio of the first switching element 24a of the common arm circuit 24 to 50% on time. H4 is output, and a control signal L4 that makes the duty ratio of the second switching element 24b of the common arm circuit 24 on time 50% is output.

As a result, as shown in FIG. 9 (g), the first heating coil 31 and the first variable connected between the output end 23 of the first arm circuit 21 and the output end 26 of the common arm circuit 24. A square wave voltage that changes from + Vo, 0, −Vo, and + Vo is applied to the first resonant circuit including the capacitive capacitor 41. The period when the voltage of the square wave voltage is + Vo is 25% of one cycle, the period when the voltage is −Vo is 50% of one cycle, and the period when the voltage is 0 is 25% of one cycle. Comparing FIG. 9 (g) and FIG. 8 (g), it can be seen that the + Vo pulse width is reduced in the rectangular wave voltage applied to the first resonant circuit. Then, as shown in FIG. 9H, the absolute values of the maximum value and the minimum value of the current flowing through the first heating coil 31 are smaller than those of Io. Comparing FIG. 9 (h) and FIG. 8 (h), it can be seen that the magnitude of the current flowing through the first heating coil 31 is smaller in FIG. 9 (h). Further, the frequency of the current flowing through the first heating coil 31 is 25 kHz, which has not changed from the state shown in FIG. 8 (h).

The electric power that is input to the object to be heated placed on the first heating coil 31 to induce and heat the object to be heated is proportional to the square of the current flowing through the first heating coil 31. Therefore, as shown in FIGS. 9A and 9B, by changing the duty ratio of the on-time of the first switching element 21a of the first arm circuit 21 , the first heating coil 31 can be used. The electric power input to the object to be heated mounted on the first heating coil 31 can be controlled by changing the current value of the supplied alternating current.

On the other hand, as shown in FIG. 9 (i), the second heating coil 32 and the second variable capacitor connected between the output end 29 of the second arm circuit 27 and the output end 26 of the common arm circuit 24 A square wave voltage that changes from + Vo, 0, + Vo, 0, −Vo, 0, −Vo, and + Vo is applied to the second resonant circuit including the capacitor 45. The period when the voltage of the square wave voltage is + Vo is 2/12 of the switching cycle of the common arm circuit 24, and the period when the voltage is −Vo is 5/12 of the switching cycle of the common arm circuit 24, and the voltage is 0. The period is 5/12 of the switching cycle of the common arm circuit 24. Comparing FIG. 9 (i) and FIG. 8 (i), in the rectangular wave voltage applied to the second resonant circuit, the pulse width of + Vo is reduced by half, and the period when the voltage is 0 and the period when the voltage is −Vo. Is increasing slightly. Then, as shown in FIG. 9 (j), the absolute values of the maximum value and the minimum value of the current flowing through the second heating coil 32 are smaller than those of Io. Comparing FIG. 9 (j) and FIG. 8 (j), the magnitude of the current flowing through the second heating coil 32 is smaller in FIG. 9 (j). Further, the frequency of the current flowing through the second heating coil 32 is 75 kHz, which has not changed from the state shown in FIG. 8 (j).

As described above, as shown in FIGS. 9 (e) and 9 (f), the second heating is performed by changing the duty ratio of the first switching element 27a of the second arm circuit 27 during the on-time. The electric power input to the object to be heated placed on the second heating coil 32 can be controlled by changing the current value of the alternating current supplied to the coil 32.

Then, by independently controlling the on-time duty ratio of the first switching element 21a of the first arm circuit 21 and the on-time duty ratio of the first switching element 27a of the second arm circuit 27, respectively. The current value of the alternating current flowing through the first heating coil 31 and the current value of the alternating current flowing through the second heating coil 32 can be controlled independently. As a result, the object to be heated placed on the first heating coil 31 and the object to be heated placed on the second heating coil 32 can be induced and heated by independently controllable electric power. Therefore, the heating temperatures on the inner peripheral side and the outer peripheral side of the object to be heated made of different materials can be controlled independently.

In the second embodiment, the first arm circuit 21 and the second arm circuit 27 are controlled by PWM so that the alternating currents flowing through the first heating coil 31 and the second heating coil 32 are independent of each other. However, it is also possible to control the common arm circuit 24 by PWM to control the alternating current flowing through the first heating coil 31 and the second heating coil 32 together. By controlling the alternating current flowing through the first heating coil 31 and the second heating coil 32 together, the input power of a frying pan or the like, which is an object to be heated made of different materials, can be integrally controlled. Convenience can be improved by using it properly according to the purpose. Whether the alternating current flowing through the first heating coil 31 and the second heating coil 32 is controlled independently or together is determined, for example, based on an operation signal when the operation unit 5 is operated by the user. The control circuit 85 may be determined.

The control of the alternating current flowing through the first heating coil 31 and the second heating coil 32 by the PWM control described in the second embodiment is the frequency of the alternating current flowing through the first heating coil 31. The frequency and the second frequency, which is the frequency of the alternating current flowing through the second heating coil 32, can be related to any relationship. That is, in the second embodiment, the case where the first frequency is 25 kHz and the second frequency is 75 kHz has been described. For example, the first frequency is 25 kHz and the second frequency is It may be the case that the second frequency is not an integral multiple of the first frequency, such as 57 kHz.

Embodiment 3.
FIG. 10 is a time chart showing a gate signal of each switching element constituting the inverter circuit of the induction heating device according to the third embodiment of the present invention, and a voltage waveform and a current waveform output from the inverter circuit. The time chart of FIG. 10 is a time chart showing the state of the induction heating device 100 described in the first embodiment, and from the state of the time chart shown in FIG. 8, the first heating coil 31 and the second heating coil 32 The power control method for reducing the input power of the above is shown. In FIG. 10, the same description as in FIGS. 8 and 9 means the same content, and the description thereof will be omitted. Further, in the third embodiment, the configuration of the induction heating device 100 and the like are the same as those of the first embodiment, and the components of the induction heating device 100 described with the same reference numerals are the same as those of the first embodiment. It is the same.

10 (a) to 10 (f) are gate signal waveforms of the switching elements of each arm circuit, and FIGS. 10 (g) to 10 (j) are output from the inverter circuit 81, as in FIGS. 8 and 9. It is a voltage waveform and a current waveform. In the third embodiment, the first arm circuit 21 that is switched at the same frequency as the common arm circuit 24 is phase-difference controlled, and the second arm circuit 27 that is switched at a frequency different from that of the common arm circuit 24 is PWM-controlled. Then, a method of independently controlling the input powers of the first heating coil 31 and the second heating coil 32 will be described.

As shown in FIG. 10A, the control circuit 85 of the induction heating device 100 changes the gate signal of the first switching element 21a of the first arm circuit 21 from OFF to ON, that is, the first switching. The gate signal H1 whose turn-on timing of the element 21a is delayed by 90 ° is output. The duty ratio of the gate signal H1 of the first switching element 21a during the on-time is 50% as in the case of FIG. Since the gate signal L1 of the second switching element 21b of the first arm circuit 21 is uniquely determined based on the gate signal H1 of the first switching element 21a, the control circuit 85 is the second switching element 21b. gate signal L1 outputs a gate signal L1 timing, i.e. the turn-off timing was 90 ° delayed et varying oN from OFF. The duty ratio of the gate signal L1 of the second switching element 21b is also 50% as in the case of FIG.

As shown in FIG. 10 (c), the switching frequency of the first switching element 24a of the common arm circuit 24 is the same 25kHz switching frequency of the first switching element 21 a of the first arm circuit 21, The on-time duty ratio is 50%. Therefore, as shown in FIG. 10A, changing the timing at which the first switching element 21a of the first arm circuit 21 turns on means that the first switching element 21a of the first arm circuit 21 turns on. It is to change the time between the timing of turning on and the timing of turning on the first switching element 24a of the common arm circuit 24. Such control is called phase difference control.

As shown in FIG. 10 (a), by delaying the turn-on timing of the first switching element 21a of the first arm circuit 21 by 90 °, as shown in FIG. 10 (g), the first arm circuit 21 In the first resonance circuit including the first heating coil 31 and the first variable capacitance capacitor 41 connected between the output end 23 of the common arm circuit 24 and the output end 26 of the common arm circuit 24, + Vo, 0,- A rectangular wave voltage that changes from Vo, 0, + Vo is applied. The period when the voltage of the square wave voltage is + Vo is 25% of one cycle, the period when the voltage is −Vo is 25% of one cycle, and the period when the voltage is 0 is 50% of one cycle. Comparing FIG. 10 (g) and FIG. 8 (g), it can be seen that the + Vo pulse width and the −Vo pulse width are reduced in the rectangular wave voltage applied to the first resonant circuit. Then, as shown in FIG. 10 (h), the absolute values of the maximum value and the minimum value of the current flowing through the first heating coil 31 are smaller than those of Io. Comparing FIG. 10 (h) and FIG. 8 (h), it can be seen that the magnitude of the current flowing through the first heating coil 31 is smaller in FIG. 10 (h). Further, the frequency of the current flowing through the first heating coil 31 is 25 kHz, which has not changed from the state shown in FIG. 8 (h).

Therefore, the state shown in FIGS. 8A and 8C is controlled to the state shown in FIGS. 10A and 10C, that is, the timing at which the first switching element 21a of the first arm circuit 21 turns on. By changing the time between the timing at which the first switching element 24a of the common arm circuit 24 turns on, the current value of the alternating current supplied to the first heating coil 31 is changed, and the first heating is performed. It is possible to control the electric power input to the object to be heated placed on the coil 31.

On the other hand, the control of each switching element of the second full bridge circuit including the second arm circuit 27 and the common arm circuit 24 is the same as that of the second embodiment. That is, the second arm circuit 27, which is switched at a frequency different from the switching frequency of the common arm circuit 24, changes the duty ratio of the first switching element 27a for the on-time and supplies it to the second heating coil 32. It controls the current value of alternating current.

As described above, as described in the third embodiment, the switching frequency of the first arm circuit 21 is the same as the switching frequency of the common arm circuit 24, and the switching frequency of the second arm circuit 27 is common. When the switching frequency is different from that of the arm circuit 24, the gate signal H1 of the first switching element 21a of the first arm circuit 21 is phase-difference controlled, and the gate of the first switching element 27a of the second arm circuit 27 is controlled. By PWM control of the signal H7, the current value of the alternating current flowing through the first heating coil 31 and the current value of the alternating current flowing through the second heating coil 32 can be controlled independently.

Similarly, when the switching frequency of the first arm circuit 21 is different from the switching frequency of the common arm circuit 24 and the switching frequency of the second arm circuit 27 is the same as the switching frequency of the common arm circuit 24, the first The first heating is performed by PWM-controlling the gate signal H1 of the first switching element 21a of the arm circuit 21 of 1 and controlling the phase difference of the gate signal H7 of the first switching element 27a of the second arm circuit 27. The current value of the alternating current flowing through the coil 31 and the current value of the alternating current flowing through the second heating coil 32 can be controlled independently.

Also in the third embodiment, the switching frequency of the arm circuit on the side of performing PWM control may be irrelevant to the switching frequency of the common arm circuit 24, and the switching frequency can be arbitrarily selected.

Embodiment 4.
FIG. 11 is a time chart showing a gate signal of each switching element constituting the inverter circuit of the induction heating device according to the fourth embodiment of the present invention, and a voltage waveform and a current waveform output from the inverter circuit. The time chart of FIG. 11 is a time chart showing the state of the induction heating device 100 described in the first embodiment, and the first heating coil 31 and the second heating coil 32 are shown from the state of the time chart shown in FIG. The power control method for reducing the input power of the above is shown. In FIG. 11, the same description as in FIGS. 8, 9, and 10 means the same content, and the description thereof will be omitted. Further, in the fourth embodiment, the configuration of the induction heating device 100 and the like are the same as those of the first embodiment, and the components of the induction heating device 100 described with the same reference numerals are the same as those of the first embodiment. It is the same.

11 (a) to (f) are the gate signal waveforms of the switching elements of each arm circuit, and FIGS. 11 (g) to 11 (j) are inverter circuits, as in FIGS. 8, 9 and 10. It is a voltage waveform and a current waveform output from 81. In the fourth embodiment, the first arm circuit 21 that is switched at the same frequency as the common arm circuit 24 is controlled for phase difference, and the second arm circuit 27 that is switched at a frequency different from that of the common arm circuit 24 is also phase difference. A method of controlling the input power of the first heating coil 31 and the second heating coil 32 independently will be described. The switching frequency of the second arm circuit 27, which is switched at a frequency different from that of the common arm circuit 24, is 2n + 1 times the switching frequency of the first arm circuit 21 and the common arm circuit 24 (n is a natural number of 1 or more).

From the first full bridge circuit including the first arm circuit 21 and the common arm circuit 24 shown in FIGS. 11 (a) to 11 (d) and 11 (g) and 11 (h) to the first heating coil 31. The current value of the supplied alternating current is controlled by phase difference control as described in the third embodiment. Since the operation is the same as that of the third embodiment, the description thereof will be omitted.

As shown in FIG. 11 (e), the gate signal H7 of the first switching element 27a of the second arm circuit 27 is shown in FIG. 8 (e) as compared with the gate signal H7 of FIG. 8 (e). ), The phase is delayed by 90 °. As can be seen from the comparison between FIGS. 11 (c) and 8 (c), the gate signal H4 of the first switching element 24a of the common arm circuit 24 is the same in FIGS. 11 (c) and 8 (c). Therefore, in FIG. 11 (e), the timing at which the first switching element 27a of the second arm circuit 27 turns on and the first switching element 24a of the common arm circuit 24 turn on from the state of FIG. 8 (e). The time between timing is changing. As a result, as can be seen from the comparison between FIGS. 11 (i) and 8 (i), the voltage applied to the second resonant circuit including the second heating coil 32 and the second variable capacitance capacitor 45 is , The period of + Vo and -Vo decreases, and the period of zero voltage increases. Therefore, as shown in FIG. 11 (j), the current value of the alternating current flowing through the second heating coil 32 decreases from the state of FIG. 8 (j).

As shown in FIG. 8 (a) of the first embodiment, when the phase difference of the gate signal H7 of the first switching element 27a of the second arm circuit 27 is 0 °, FIG. 8 (i) shows. As described above, the ratio of the period in which the absolute value of the voltage value in the voltage waveform applied to the second resonance circuit is Vo is 4/6. On the other hand, as in the fourth embodiment, when the phase difference between the common arm circuit 24 and the second arm circuit 27 having a different switching frequency is controlled to reduce the alternating current flowing through the second heating coil 32, When the phase difference of the gate signal H7 of the first switching element 27a of the second arm circuit 27 is 180 °, the alternating current flowing through the second heating coil 32 is minimized. In this case, the ratio of the period during which the absolute value of the voltage value in the voltage waveform applied to the second resonant circuit is Vo is 2/6. That is, the magnitude of the alternating current flowing through the second heating coil 32 can be reduced by half by the phase difference control described in the fourth embodiment.

When controlling the phase difference of the second arm circuit 27 having a switching frequency different from that of the common arm circuit 24 and controlling the current value of the alternating current flowing through the second heating coil 32, the switching frequency of the common arm circuit 24 and the second arm circuit 24 are controlled. The closer the switching frequency of the arm circuit 27 of 2 is, the larger the control amount of the current value can be. Since the switching frequency of the second arm circuit 27 needs to be 2n + 1 times the switching frequency of the common arm circuit 24 (n is a natural number of 1 or more), the switching frequency of the second arm circuit 27 is the common arm circuit. Most preferably three times the switching frequency of 24.

As described above, the induction heating device 100 according to the fourth embodiment controls the phase difference of the first switching element 21a of the first arm circuit 21 to control the alternating current flowing through the first heating coil 31. By controlling the phase difference of the first switching element 27a of the second arm circuit 27, it is possible to control the current value of the alternating current flowing through the second heating coil 32. it can. Further, when controlling the phase difference of the first switching element 24a of the common arm circuit 24, the current value of the alternating current flowing through the first heating coil 31 and the current value of the alternating current flowing through the second heating coil 32. Can be controlled at the same time.

Embodiment 5.
FIG. 12 is a time chart showing a gate signal of each switching element constituting the inverter circuit of the induction heating device according to the fifth embodiment of the present invention, and a voltage waveform and a current waveform output from the inverter circuit. The time chart of FIG. 12 is a time chart showing the state of the induction heating device 100 described in the first embodiment, and from the state of the time chart shown in FIG. 8, the first heating coil 31 and the second heating coil 32 The power control method for reducing the input power of the above is shown. In FIG. 12, the same description as in FIGS. 8, 9, 10 and 11 means the same content, and the description thereof will be omitted. Further, in the fifth embodiment, the configuration of the induction heating device 100 and the like are the same as those of the first embodiment, and the components of the induction heating device 100 described with the same reference numerals are the same as those of the first embodiment. It is the same.

12 (a) to 12 (f) are gate signal waveforms of the switching elements of the respective arm circuits, as in FIGS. 8, 9, 10 and 11, and FIGS. 12 (g) to 12 (j) show the gate signal waveforms of the switching elements. Is the voltage waveform and the current waveform output from the inverter circuit 81. In the fifth embodiment, the frequency of the first arm circuit 21 switched at the same frequency as the common arm circuit 24 is controlled, and the frequency of the second arm circuit 27 switched at a frequency different from that of the common arm circuit 24 is also controlled. Therefore, a method of independently controlling the input powers of the first heating coil 31 and the second heating coil 32 will be described.

Each gate signal shown in FIGS. 12 (a) to 12 (f) has an on-time duty ratio of 50% with respect to the switching cycle as compared with each gate signal shown in FIGS. 8 (a) to 8 (f). Is the same, but the period of the gate signal is changed so that the frequency of the gate signal becomes higher. In the fifth embodiment, FIGS. 8 (a) to 8 (f) are gate signals of each switching element before the frequency change, and FIGS. 12 (a) to 12 (f) are gate signals of each switching element after the frequency change. Is.

The frequency of the gate signal of each switching element of the first arm circuit 21 and the common arm circuit 24 shown in FIGS. 8 (a) to 8 (d) before the frequency change is 25 kHz, and FIGS. 8 (e) and 8 (f) show. The frequency of the gate signal of each switching element of the second arm circuit 27 shown in the above before the frequency is changed is 75 kHz. Further, the frequency of the gate signal of each switching element of the first arm circuit 21 and the common arm circuit 24 shown in FIGS. 12 (a) to 12 (d) after changing the frequency is 26 kHz, and FIGS. The frequency of the gate signal of each switching element of the second arm circuit 27 shown in f) after the frequency is changed is 78 kHz.

As shown in FIG. 12 (g), the first heating coil 31 and the first variable capacitance capacitor 41 connected between the output end 23 of the first arm circuit 21 and the output end 26 of the common arm circuit 24. A square wave voltage whose frequency changes from + Vo to −V at 26 kHz is applied to the first resonant circuit. When the frequency of the voltage applied to the first resonance circuit is 26 kHz, the frequency of the voltage applied to the first resonance circuit is the resonance frequency 22 of the first resonance circuit as compared with the case where the frequency is 25 kHz. It will move away from 0.7 kHz. As a result, as shown in FIG. 12 (h), the absolute values of the maximum and minimum values of the current flowing through the first heating coil 31 are smaller than those of Io. Comparing FIG. 12 (h) and FIG. 8 (h), it can be seen that the magnitude of the current flowing through the first heating coil 31 is smaller in FIG. 12 (h). The frequency of the current flowing through the first heating coil 31 is 26 kHz, which is different from the frequency of 25 kHz in FIG. 8 (h).

The electric power that is input to the object to be heated and induces and heats the object to be heated placed on the first heating coil 31 is proportional to the square of the current flowing through the first heating coil 31. Therefore, as shown in FIGS. 12A to 12D, the electric power is supplied to the first heating coil 31 by changing the frequency of the first arm circuit 21 which is switched at the same frequency as the common arm circuit 24. It is possible to control the electric power input to the object to be heated mounted on the first heating coil 31 by changing the current value of the alternating current.

Similarly, as shown in FIG. 12 (i), a second heating coil 32 and a second variable connected between the output end 29 of the second arm circuit 27 and the output end 26 of the common arm circuit 24. A square wave voltage whose frequency changes from + Vo, 0, + Vo, −Vo, 0, −Vo due to frequencies of 78 kHz and 26 kHz is applied to the second resonant circuit including the capacitive capacitor 45. When the frequency of the voltage applied to the second resonance circuit is 78 kHz, the frequency of the voltage applied to the second resonance circuit is the resonance frequency 72 of the second resonance circuit as compared with the case where the frequency is 75 kHz. It will move away from 6.6 kHz. As a result, as shown in FIG. 12J, the absolute values of the maximum value and the minimum value of the current flowing through the second heating coil 32 are smaller than those of Io. Comparing FIG. 12 (j) and FIG. 8 (j), it can be seen that the magnitude of the current flowing through the first heating coil 31 is smaller in FIG. 12 (j). The frequency of the current flowing through the first heating coil 31 is 78 kHz, which is different from the frequency of 75 kHz in FIG. 8 (j).

The electric power that is input to the object to be heated placed on the second heating coil 32 to induce and heat the object to be heated is proportional to the square of the current flowing through the second heating coil 32. Therefore, as shown in FIGS. 12 (e) to 12 (f), the current value of the alternating current supplied to the second heating coil 32 is changed by changing the frequency of the second arm circuit 27. It is possible to control the electric power input to the object to be heated placed on the second heating coil 32.

However, if the switching frequency of the common arm circuit 24 that is switched at the same switching frequency as that of the first arm circuit 21 is changed, the changed common is changed even if the switching frequency of the second arm circuit 27 is not changed. The current of the second heating coil 32 may change depending on the switching frequency of the arm circuit 24. For example, when the switching frequency of the first arm circuit 21 which is switched at the same frequency as the common arm circuit 24 is changed from 25 kHz to 26 kHz and the frequency of the second arm circuit 27 is maintained at 75 kHz, the first heating The magnitude of the current flowing through the coil 31 becomes smaller, and the current flowing through the second heating coil 32 becomes smaller. On the other hand, when the switching frequency of the first arm circuit 21 which is switched at the same frequency as the common arm circuit 24 is changed from 25 kHz to 24 kHz and the frequency of the second arm circuit 27 is maintained at 75 kHz, the first heating The magnitude of the current flowing through the coil 31 becomes large, and the current flowing through the second heating coil 32 becomes large. Further, depending on the frequency to be changed, the magnitude of the current flowing through the first heating coil 31 becomes large, and the current flowing through the second heating coil 32 becomes small, or the magnitude of the current flowing through the first heating coil 31 becomes large. The current may be smaller and the current flowing through the second heating coil 32 may be larger .

Therefore, when controlling the current flowing through the first heating coil 31 and the second heating coil 32, after changing the frequency of the first arm circuit 21 which is switched at the same frequency as the common arm circuit 24, , The frequency of the second arm circuit 27 may be changed for control.

Further, when the control circuit 85 grasps in advance the increase / decrease of the current and the electric power flowing through the second heating coil 32 when the frequency of the common arm circuit 24 is changed, and switches a certain amount of electric power step by step, By changing the frequency of the second arm circuit 27 while changing the frequency of the first arm circuit 21 that is switched at the same frequency as the common arm circuit 24, the first heating coil 31 and the second heating coil are changed. The current flowing through 32 may be controlled at the same time.

In the fifth embodiment, it has been described that the current flowing through the first heating coil 31 and the second heating coil 32 is reduced by moving the frequency of the gate signal away from the resonance frequency, but the gate signal is set to the resonance frequency. By bringing the frequencies closer, the current flowing through the first heating coil 31 and the second heating coil 32 may be increased.

In this way, by changing the switching frequency of the first arm circuit 21 that is switched at the same frequency as the common arm circuit 24 and changing the switching frequency of the second arm circuit 27, the first heating coil 31 can be used. The current value of the alternating current flowing and the current value of the alternating current flowing through the second heating coil 32 can be controlled independently. As a result, the object to be heated placed on the first heating coil 31 and the object to be heated placed on the second heating coil 32 can be induced and heated by independently controllable electric power. Therefore, the heating temperatures on the inner peripheral side and the outer peripheral side of the object to be heated made of different materials can be controlled independently.

Similarly, when the switching frequency of the first arm circuit 21 is different from the switching frequency of the common arm circuit 24 and the switching frequency of the second arm circuit 27 is the same as the switching frequency of the common arm circuit 24, the first By changing the switching frequency of the arm circuit 21 of 1 and changing the switching frequency of the second arm circuit 27 which is switched at the same frequency as the common arm circuit 24, the current of the alternating current flowing through the first heating coil 31 The value and the current value of the alternating current flowing through the second heating coil 32 can be controlled independently.

Also in the fifth embodiment, the switching frequency of the first arm circuit 21 or the second arm circuit 27, which is switched at different frequencies, may be independent of the switching frequency of the common arm circuit 24, and the switching frequency. Can be selected arbitrarily.

Next, frequency control when the switching frequency of each switching element is brought close to the resonance frequency will be described. As described above, in general, in the inverter circuit of the induction heating device, the arm circuit is switched at a frequency higher than the resonance frequency of the resonance circuit so that the phase of the alternating current flowing through the heating coil is delayed from the switching of the arm circuit. Therefore, the increase in switching loss is suppressed. During induction heating, for example, the impedance of the resonance circuit may change by shaking the pot as a cooking operation, resulting in a state of complete resonance or a lead phase. In this case, the current flowing through the switching element and the surge voltage may increase, and the switching element of each arm circuit may be destroyed. Therefore, even when the frequency of the gate signal is brought close to the resonance frequency, it is preferable to control the switching frequency at a frequency higher than the resonance frequency so that the lead phase does not always occur.

As a method, for example, a frequency threshold value and a load resonance frequency error are set in advance in the control circuit 85, and the switching frequency is controlled so that the difference between the resonance frequency and the switching frequency is equal to or greater than the frequency threshold value. You can do it. Further, the control circuit 85 constantly detects the resonance frequency of the load, controls the frequency of the gate signal by feeding back the difference between the resonance frequency and the switching frequency, and controls the switching frequency so as to always exceed the frequency threshold. You may. Further, the control circuit 85 may detect the voltage and current output by the inverter circuit 81 and control the switching frequency by feeding back the phase difference between the voltage and the current so that the phase is always delayed. .. Further, when the switching frequency becomes lower than the resonance frequency and becomes the lead phase, the control circuit 85 may stop the switching of each switching element as a protective operation to stop the induction heating.

In the fifth embodiment, a method of controlling both the input power of the first heating coil 31 and the input power of the second heating coil 32 by frequency control has been described, but the first heating coil 31 or The input power of one of the second heating coils 32 is controlled by the PWM control or the phase difference control shown in the second or third embodiment, and the input power of the other of the first heating coil 31 or the second heating coil 32 is controlled. May be controlled by the frequency control of the fifth embodiment. Further, the frequency control may be performed while performing the PWM control by combining the PWM control and the frequency control.

Embodiment 6.
FIG. 13 is a plan view showing the position of the object to be heated placed on the heating coil when the object to be heated is induced to be heated by the induction heating device according to the sixth embodiment of the present invention. FIG. 13A is a plan view showing a state in which the object to be heated 110b is placed in a state where the center of the object to be heated 110b made of a different material coincides with the center of the heating coil 30. FIG. Is a plan view showing a state in which the object to be heated 110b is placed in a state where the center of the object to be heated 110b made of a different material is deviated from the center of the heating coil 30. In the sixth embodiment, the configuration of the induction heating device 100 and the like are the same as those of the first embodiment, and the components of the induction heating device 100 described with the same reference numerals are the same as those of the first embodiment. is there. In the sixth embodiment, the differences from the induction heating device 100 of the first embodiment will be described.

The induction heating device 100 of the sixth embodiment periodically performs load detection for discriminating the material of the object to be heated placed on the top plate 2. The load detection unit 11 of the induction heating device 100 determines the material of the object to be heated placed on the first heating coil 31 and the second heating coil 32 at intervals of, for example, once every few seconds. , The determination result is transmitted to the control circuit 85. The control circuit 85 controls the switching of the first arm circuit 21, the common arm circuit 24, and the second arm circuit 27 of the inverter circuit 81 based on the determination result periodically transmitted from the load detection unit 11. The inverter circuit 81 supplies an alternating current to the first heating coil 31 and the second heating coil 32.

The load detection unit 11 may be provided in the power supply unit 82 to which the AC power supply 9 is connected to the induction heating device 100 as shown in FIG. However, when the load is detected by detecting the current input from the AC power source 9 to the induction heating device 100, the material of the object to be heated placed on the first heating coil 31 and the second heating coil 32 are used. Since it is not possible to simultaneously determine the material of the object to be heated placed on the device, it takes a lot of time to detect the load, which is not preferable when the load is detected regularly. The load detection unit 11 is provided with a current detection unit connected in series with the first heating coil 31 and a current detection unit connected in series with the second heating coil 32 to form a heated object on the first heating coil 31. A configuration capable of simultaneously detecting the load on the object to be heated on the second heating coil 32 is preferable. When the current detection unit is connected in series to each of the first heating coil 31 and the second heating coil 32, the load detection unit 11 induces and heats the object to be heated, and the current flows through each heating coil. The material of the object to be heated may be discriminated from the above, and the discriminant result may be periodically transmitted to the control circuit 85.

In the following, the load detection unit 11 determines the current flowing through each heating coil detected by the current detection unit connected in series with the first heating coil 31 and the current detection unit connected in series with the second heating coil 32. A case of determining the material of the object to be heated will be described. However, the configuration of the load detection unit 11 is not limited to this, and as shown in FIG. 3, the material of the object to be heated may be determined based on the current input from the AC power supply 9.

In FIG. 13, the heating coil 30 includes a first heating coil 31 that induces and heats the inner peripheral side of the bottom of the object to be heated 110b, and a second heating coil 32 that induces and heats the outer peripheral side of the bottom of the object to be heated 110b. It is composed of and. The object to be heated 110b is formed by joining a magnetic metal portion 112 made of a magnetic metal such as iron to a bottom 111 of a pan such as a frying pan made of a non-magnetic metal such as aluminum.

As shown in FIG. 13A, the user places the heated object 110b on the heating coil 30 so that the center of the heating coil 30 and the center of the heated object 110b coincide with each other, and the heated object 110b is placed on the heating coil 30. When the operation unit 5 of the induction heating device 100 is operated to start the induction heating of the induction heating device 100, the induction heating device 100 pulses to the first heating coil 31 and the second heating coil 32 as described in the first embodiment. Current is passed to determine the material of the object to be heated on the first heating coil 31 and the second heating coil 32. Then, based on the result determined by the load detection unit 11, the inverter circuit 81 supplies an alternating current having the same or different frequencies to the first heating coil 31 and the second heating coil 32.

In the case of FIG. 13A, the material of the object to be heated 110b placed on the first heating coil 31 is magnetic metal, and the material to be heated 110b placed on the second heating coil 32 Since the material is also magnetic metal, the inverter circuit 81 supplies an alternating current of the same frequency to the first heating coil 31 and the second heating coil 32. In this case, in the circuit diagram shown in FIG. 3, the control circuit 85 closes the switch 44 of the first variable capacitance capacitor 41, connects the capacitor 42 and the capacitor 43 in parallel, and opens and closes the second variable capacitance capacitor 45. The capacitor 48 is closed and the capacitor 46 and the capacitor 47 are connected in parallel.

Assuming that the inductance of each heating coil and the capacitance of each capacitor are the values illustrated in the first embodiment, in the state of FIG. 13A, the first heating coil 31 and the first variable capacitor 41 The resonance frequency of the first resonance circuit is 22.7 kHz, and the resonance frequency of the second resonance circuit including the second heating coil 32 and the second variable capacitance capacitor 45 is also 22.7 kHz. Therefore, the inverter circuit 81 switches the first arm circuit 21, the common arm circuit 24, and the second arm circuit 27 at 25 kHz, and 25 kHz for each of the first heating coil 31 and the second heating coil 32. Supply AC current.

Then, the load detection unit 11 detects the 25 kHz alternating current flowing through the first heating coil 31 and the 25 kHz alternating current flowing through the second heating coil 32 with the current detection unit, respectively, and the first heating coil 31 It is determined that the materials of the objects to be heated placed on the upper and second heating coils 32 are magnetic metals, respectively. Since this determination result is the result of determination at the start of induction heating of the object to be heated, the induction heating device 100 continues to supply an alternating current of 25 kHz to each of the first heating coil 31 and the second heating coil 32.

Here, as shown in FIG. 13B, it is assumed that the user shakes the pot or the like and the center of the object to be heated 110b is displaced from the center of the heating coil 30. In this case, since the magnetic metal portion 112 of the object to be heated 110b is placed on the first heating coil 31, the magnitude of the alternating current flowing through the first heating coil 31 does not change. On the other hand, since the magnetic metal portion 112 of the object to be heated 110b and the bottom portion 111 made of non-magnetic metal provided on the outer peripheral side of the magnetic metal portion 112 are placed on the second heating coil 32, the second heating coil 32 is placed. The inductance of the heating coil 32 is reduced, and the resistance of the object to be heated on the second heating coil 32 is also reduced. As a result, the current flowing through the second heating coil 32 changes, so that the load detection unit 11 detects that the load on the second heating coil 32 has changed. At this time, when the proportion of the portion made of non-magnetic metal among the objects to be heated placed on the second heating coil 32 exceeds a predetermined amount, the load detection unit 11 is placed on the second heating coil 32. It is determined that the material of the placed object to be heated is a non-magnetic metal.

Since the load detection unit 11 periodically determines the material of the object to be heated on the first heating coil 31 and the material of the object to be heated on the second heating coil 32 and transmits the material to the control circuit 85. When the control circuit 85 recognizes that the material of the object to be heated on the second heating coil 32 has changed from magnetic metal to non-magnetic metal, the control circuit 85 changes the capacitance of the second variable capacitor 45. ..
That is, since the control circuit 85 opens the switch 48 of the second variable capacitance capacitor 45 and disconnects the capacitor 47 from the capacitor 46, the capacitance of the second variable capacitance capacitor 45 is 0.024 μF. As shown in FIG. 13B, since the object to be heated on the second heating coil 32 is not completely a non-magnetic metal, the inductance of the second heating coil 32 is larger than 200 μH but 300 μH. It becomes smaller. As a result, the resonance frequency of the second resonance circuit including the second heating coil 32 and the second variable capacitance capacitor 45 becomes high.

Then, in the control circuit 85, the gate signal of the switching element of each arm circuit so that the inverter circuit 81 switches the second arm circuit 27 at a frequency higher than the switching frequency of the first arm circuit 21 and the common arm circuit 24. Is output. The gate signal of the switching element of each arm circuit in this case is as described in the above-described first to fourth embodiments. As a result, the first heating coil 31 is supplied with an alternating current having a first frequency, and the second heating coil 32 is supplied with an alternating current having a second frequency higher than the first frequency to be heated. The bottom 111 made of non-magnetic metal on the outer peripheral side of the magnetic metal portion 112 of the object 110b can be efficiently induced and heated. As a result, even if the position of the object to be heated is displaced, the temperature uniformity at the bottom of the object to be heated can be improved.

Embodiment 7.
FIG. 14 is a perspective view showing a state in which two objects to be heated are induced and heated by the induction heating device according to the seventh embodiment of the present invention. In FIG. 14, those having the same reference numerals as those in FIG. 5 of the first embodiment show the same or corresponding configurations, and the description thereof will be omitted. Further, in the seventh embodiment, the configuration of the induction heating device 100 and the like are the same as those of the first embodiment, and the components of the induction heating device 100 described with the same reference numerals are the same as those of the first embodiment. It is the same. The seventh embodiment is different from the first embodiment in that the first heating coil 31 and the second heating coil 32 are provided at different heating ports.

As shown in FIG. 13, the induction heating device 100 is provided with a first heating coil 31 facing the mounting position 3a displayed on the top plate 2, and a second heating coil 31 facing the mounting position 3c. A heating coil 32 is provided. A first variable capacitance capacitor 41 is connected in series to the first heating coil 31, and the first heating coil 31 and the first variable capacitance capacitor 41 form a first resonance circuit. A second variable capacitance capacitor 45 is connected in series to the second heating coil 32, and the second heating coil 32 and the second variable capacitance capacitor 45 form a second resonance circuit.

An alternating current is supplied to the first heating coil 31 and the second heating coil 32 by the inverter circuit 81 shown in the circuit diagram of FIG. 3 of the first embodiment. That is, the first heating coil 31 is electrically connected between the output end 23 of the first arm circuit 21 and the output end 26 of the common arm circuit 24, and the second heating coil 32 is the second. It is electrically connected between the output end 29 of the arm circuit 27 of 2 and the output end 26 of the common arm circuit 24.

As shown in FIG. 14, a first object to be heated 110a, which is induced and heated by an alternating current flowing through the first heating coil 31, is placed on the first heating coil 31 and is placed on the second heating coil 32. A second object to be heated 110c, which is induced and heated by an alternating current flowing through the second heating coil 32, is placed. When the user operates the operation unit 5 of the induction heating device 100 to perform an operation for inductively heating the first object to be heated 110a and the second object to be heated 110c, the load detection unit 11 moves to the second. The material of the object to be heated 110a placed on the heating coil 31 of 1 and the material of the object to be heated 110c placed on the second heating coil 32 are discriminated.

In the load detection unit 11, the material of the object to be heated 110a on the first heating coil 31 is a magnetic metal such as iron, and the material of the object to be heated 110c on the second heating coil 32 is non-magnetic such as aluminum. When it is determined to be metal, the control circuit 85 closes the switch 44 of the first variable capacitance capacitor 41, connects the capacitor 42 and the capacitor 43 in parallel, and switches 48 of the second variable capacitance capacitor 45. To disconnect the capacitor 47 from the capacitor 46. Then, as described in the first embodiment, the first arm circuit 21 and the common arm circuit 24 are switched at the first frequency, and the second arm circuit 27 is switched at the second frequency. The first frequency may be, for example, 25 kHz, and the second frequency may be, for example, 75 kHz. As a result, an alternating current of 25 kHz flows through the first heating coil 31, and the first object to be heated 110a made of magnetic metal is induced and heated by an alternating magnetic flux of 25 kHz. Further, an alternating current of 75 kHz flows through the second heating coil 32, and the second object to be heated 110c made of a non-magnetic metal is induced and heated by an alternating magnetic flux of 75 kHz.

When both the first object to be heated 110a and the second object to be heated 110c are magnetic metals or both are non-magnetic metals, the first arm circuit 21, the common arm circuit 24, and the like. The switching frequency of the second arm circuit 27 may be the same, and the alternating current flowing through the first heating coil 31 and the alternating current flowing through the second heating coil 32 may be the same frequency.

Further, the first variable capacitance capacitor 41 and the second variable capacitance capacitor 45 do not necessarily have to be variable capacitance capacitors, and may be capacitors having a constant capacitance. In this case, for example, the heating port provided with the first heating coil 31 is used as the heating port for inducing heating the object to be heated of the magnetic metal, and the heating port provided with the second heating coil 32 is covered with the non-magnetic metal. The heating port is used to induce and heat the heated object. Then, the capacitor connected in series with the first heating coil 31 is configured by removing the switch 44 from the first variable capacitance capacitor 41 and connecting the capacitor 42 and the capacitor 43 in parallel to form the second heating coil. The capacitor connected in series to 32 is composed of only the capacitor 46 by removing the switch 48 and the capacitor 47 from the second variable capacitance capacitor 45. Then, the first arm circuit 21 and the common arm circuit 24 are switched at the first frequency, the second arm circuit 27 is switched at the second frequency, and the first heating coil 31 is switched at the first frequency. The alternating current of the second frequency may be supplied to the second heating coil 32.

The embodiments 1 to 7 of the present invention have been described above. These configurations described in Embodiments 1 to 7 of the present invention can be combined with each other.

11 Load detector 21 1st arm circuit, 21a 1st switching element, 23 output terminal 24 common arm circuit, 24a 1st switching element, 26 output end 27 2nd arm circuit, 21a 2nd switching element, 29 Output end 31 1st heating coil, 32 2nd heating coil 41 1st variable capacitance capacitor, 45 2nd variable capacitance capacitor 81 Inverter circuit 100 Inductive heating device

Claims (15)

An arm circuit having a first switching element, a second switching element connected in series with the first switching element, and an output end provided between the first switching element and the second switching element. An inverter circuit including a first arm circuit, a second arm circuit, and a common arm circuit in the plurality of arm circuits.
A first heating coil electrically connected between the output end of the first arm circuit and the output end of the common arm circuit.
A second heating coil electrically connected between the output end of the second arm circuit and the output end of the common arm circuit.
With
The inverter circuit
When an alternating current having a first frequency is supplied to the first heating coil, the first switching element of the common arm circuit is switched at a predetermined frequency.
When supplying an alternating current of a second frequency different from the first frequency to the second heating coil, it is the same as supplying an alternating current of the first frequency to the first heating coil. An induction heating device that switches the first switching element of the common arm circuit at a frequency. The induction according to claim 1, wherein the inverter circuit supplies an alternating current of the first frequency to the first heating coil and at the same time supplies an alternating current of the second frequency to the second heating coil. Heating device. The inverter circuit
The first switching element of the first arm circuit is switched at the same frequency as the first switching element of the common arm circuit.
The induction heating device according to claim 1 or 2, wherein the first switching element of the second arm circuit is switched at a frequency different from that of the first switching element of the common arm circuit. The inverter circuit
The duty ratio of the on-time of the first switching element of the first arm circuit is changed to change the current value of the alternating current of the first frequency supplied to the first heating coil.
Claim 1 to change the duty ratio of the on-time of the first switching element of the second arm circuit to change the current value of the alternating current of the second frequency supplied to the second heating coil. The induction heating device according to any one of 3 to 3. The inverter circuit
The time between the timing at which the first switching element of the first arm circuit turns on and the timing at which the first switching element of the common arm circuit turns on is changed and supplied to the first heating coil. The current value of the alternating current of the first frequency is changed.
3. Claim 3 that changes the duty ratio of the on-time of the first switching element of the second arm circuit to change the current value of the alternating current of the second frequency supplied to the second heating coil. The induction heating device according to. The inverter circuit switches the first switching element of the first arm circuit at the first frequency, and switches the first switching element of the second arm circuit at the second frequency. The induction heating device according to any one of claims 1 to 5. The second frequency is 2n + 1 times the first frequency (n is a natural number of 1 or more).
The inverter circuit
The first switching element of the first arm circuit and the common arm circuit is switched at the first frequency, and the first switching element of the second arm circuit is switched at the second frequency. ,
The time between the timing at which the first switching element of the first arm circuit turns on and the timing at which the first switching element of the common arm circuit turns on is changed and supplied to the first heating coil. The current value of the alternating current of the first frequency is changed.
The time between the timing at which the first switching element of the second arm circuit turns on and the timing at which the first switching element of the common arm circuit turns on is changed and supplied to the second heating coil. The induction heating device according to claim 3, wherein the current value of the alternating current of the second frequency is changed. The inverter circuit
By changing the switching frequency of the first switching element of the first arm circuit, the current value of the alternating current supplied to the first heating coil is changed.
The induction heating device according to claim 3, wherein the switching frequency of the second switching element of the second arm circuit is changed to change the current value of the alternating current supplied to the second heating coil. A load detecting unit for determining the material of the object to be heated mounted on the first heating coil and the second heating coil is further provided.
When the load detection unit determines that the material of the object to be heated is different on the first heating coil and on the second heating coil,
The inverter circuit is any one of claims 1 to 8 that supplies an alternating current of the first frequency to the first heating coil and supplies an alternating current of the second frequency to the second heating coil. The induction heating device according to item 1. Further, a first variable capacitor connected in series with the first heating coil and a second variable capacitor connected in series with the second heating coil are further provided.
When the load detection unit determines that the material of the object to be heated is different on the first heating coil and on the second heating coil, the capacitance of the first variable capacitor capacitor is electrostatic. The induction heating device according to claim 9, wherein the capacitance or the capacitance of the second variable capacitance capacitor is changed. The induction heating device according to claim 9 or 10, wherein the load detection unit periodically discriminates between the material on the first heating coil and the material on the second heating coil of the object to be heated. The induction heating device according to any one of claims 1 to 11, wherein the first heating coil and the second heating coil induce and heat one object to be heated. The induction heating device according to any one of claims 1 to 11, wherein the first heating coil and the second heating coil induce and heat different objects to be heated. The first switching element and the second switching element of the first arm circuit are formed of a silicon semiconductor.
The induction heating according to any one of claims 1 to 13, wherein the first switching element and the second switching element of the second arm circuit are formed of a wide bandgap semiconductor having a bandgap larger than that of silicon. apparatus. The first switching element and the second switching element of the first arm circuit are formed of a silicon semiconductor.
Induction heating according to the any one of the first switching element and the second switching element from claim 1, which is formed in the band gap larger wide band gap semiconductor silicon 13 before Symbol Common arm circuits apparatus.

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