Patent Publication Number: US-11399417-B2

Title: Induction heating cooker

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. national stage application of PCT/JP2017/020783 filed on Jun. 5, 2017, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an induction heating cooker including a plurality of coils. 
     BACKGROUND ART 
     A conventional induction heating cooker includes a center coil, a plurality of peripheral coils arranged around and to be adjacent to the center coil, and a high-frequency power supply that supplies a high-frequency current to the center coil and the peripheral coils. The high-frequency power supply supplies a high-frequency current flowing in the same direction in a region in which the center coil and the peripheral coils are adjacent to each other (for example, see Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     
         
         
           
             Patent Literature 1: International Publication No. 2010/101135 
           
         
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the conventional induction heating cooker, the direction of a current flowing through an inside portion of each peripheral coil that is adjacent to the center coil is opposite to the direction of a current flowing through an outside portion of the peripheral coil that is not adjacent to the center coil. Thus, there is a problem in that a portion of the magnetic field generated by the current flowing through the inside portion of the peripheral coil and a portion of the magnetic field generated by the current flowing through the outside portion of the peripheral coil cancel each other out. 
     The present invention has been made to solve the above-described problem and provides an induction heating cooker that can suppress magnetic field cancellation in a case where a to-be-heated object is heated through induction. 
     Solution to Problem 
     An induction heating cooker according to an embodiment of the present invention has a top plate on which a heater area indication indicating a mount position of to-be-heated object is formed, and a first coil and a second coil that are formed of an annular coil arranged below the heater area indication of the top plate, the second coil includes a first winding portion extending in a circumferential direction of the first coil, and a second winding portion spaced apart from the first winding portion and extending in the circumferential direction of the first coil, and the distance between the first winding portion and the top plate is different from the distance between the second winding portion and the top plate. 
     Advantageous Effects of Invention 
     In an induction heating cooker according to an embodiment of the present invention, the distance between a first winding portion of a second coil and a top plate differs from the distance between a second winding portion of the second coil and the top plate. Thus, it is possible to reduce the degree to which the magnetic field generated by a current flowing through the first winding portion and the magnetic field generated by a current flowing through the second winding portion cancel each other out. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exploded perspective view illustrating an induction heating cooker according to Embodiment 1. 
         FIG. 2  is a plan view illustrating a first induction heating unit of the induction heating cooker according to Embodiment 1. 
         FIG. 3  is a block diagram illustrating the configuration of the induction heating cooker according to Embodiment 1. 
         FIG. 4  is a diagram illustrating a driving circuit of the induction heating cooker according to Embodiment 1. 
         FIG. 5  is a diagram illustrating a driving circuit of the induction heating cooker according to Embodiment 1. 
         FIG. 6  is a diagram illustrating the direction of a current flowing through each coil of the induction heating cooker according to Embodiment 1. 
         FIG. 7  is an enlarged view of a main portion illustrated in  FIG. 6 . 
         FIG. 8  is a cross section illustrating the arrangement of coils of the induction heating cooker according to Embodiment 1. 
         FIG. 9  is a cross section illustrating the arrangement of coils of an induction heating cooker according to Embodiment 2. 
         FIG. 10  is a diagram for describing the space between a first winding portion and a second winding portion of the induction heating cooker according to Embodiment 2. 
         FIG. 11  is a cross section illustrating modification 1 of the arrangement of the coils of the induction heating cooker according to Embodiment 2. 
         FIG. 12  is a cross section illustrating modification 2 of the arrangement of the coils of the induction heating cooker according to Embodiment 2. 
         FIG. 13  is a cross section illustrating the arrangement of coils of an induction heating cooker according to Embodiment 3. 
         FIG. 14  is a cross section illustrating modification 1 of the arrangement of the coils of the induction heating cooker according to Embodiment 3. 
         FIG. 15  is a cross section illustrating modification 2 of the arrangement of the coils of the induction heating cooker according to Embodiment 3. 
         FIG. 16  is a cross section illustrating modification 3 of the arrangement of the coils of the induction heating cooker according to Embodiment 3. 
         FIG. 17  is a cross section illustrating the arrangement of coils of an induction heating cooker according to Embodiment 4. 
         FIG. 18  is a cross section illustrating modification 1 of the arrangement of the coils of the induction heating cooker according to Embodiment 4. 
         FIG. 19  is a cross section illustrating modification 2 of the arrangement of the coils of the induction heating cooker according to Embodiment 4. 
         FIG. 20  is a cross section illustrating modification 3 of the arrangement of the coils of the induction heating cooker according to Embodiment 4. 
         FIG. 21  is a cross section illustrating the arrangement of coils of an induction heating cooker according to Embodiment 5. 
         FIG. 22  is a plan view illustrating a first induction heating unit of an induction heating cooker according to Embodiment 6. 
         FIG. 23  is a cross section illustrating the arrangement of coils of the induction heating cooker according to Embodiment 6. 
         FIG. 24  is a cross section illustrating the arrangement of coils of an induction heating cooker according to Embodiment 7. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
       FIG. 1  is an exploded perspective view illustrating an induction heating cooker according to Embodiment 1. 
     As illustrated in  FIG. 1 , an induction heating cooker  100  has, at its upper portion, a top plate  4  for mounting a to-be-heated object  5  such as a pot. The top plate  4  has a first induction heater area indication  1  and a second induction heater area indication  2  that serve as heater area indications for heating the to-be-heated object  5  through induction. The first induction heater area indication  1  and the second induction heater area indication  2  are provided side by side in a lateral direction on the front side of the top plate  4 . In addition, the induction heating cooker  100  according to Embodiment 1 also has a third induction heater area indication  3  as the third heater area indication. The third induction heater area indication  3  is provided on the depth side with respect to the first induction heater area indication  1  and the second induction heater area indication  2  and at a substantially center position in the lateral direction on the top plate  4 . 
     Below the first induction heater area indication  1 , the second induction heater area indication  2 , and the third induction heater area indication  3 , a first induction heating unit  11 , a second induction heating unit  12 , and a third induction heating unit  13  for heating the to-be-heated object  5  mounted on a corresponding heater area indication are provided, respectively. Each heating unit includes a coil. 
     The entirety of the top plate  4  is constituted by a material through which infrared rays pass such as heat-resistant tempered glass or crystallized glass. In addition, on the top plate  4 , circular pot-position marks indicating a rough pot mount position and corresponding to the heater area indications, which are s of the first induction heating unit  11 , the second induction heating unit  12 , and the third induction heating unit  13 , are formed by, for example, application of paint or printing. 
     As an input device for setting, for example, input power and a cooking menu in a case where the to-be-heated object  5  or the like is heated by the first induction heating unit  11 , the second induction heating unit  12 , and the third induction heating unit  13 , an operation unit  40  is provided on the front side of the top plate  4 . Note that, in Embodiment 1, the operation unit  40  is divided on an induction heating coil basis, and includes an operation unit  40   a , an operation unit  40   b  and an operation unit  40   c.    
     In addition, a display unit  41  for displaying, for example, an operation state of each induction heating coil and an input and the content of an operation from the operation unit  40  is provided as a notification unit near the operation unit  40 . Note that, in Embodiment 1, the display unit  41  is divided on the induction heating coil basis, and includes a display unit  41   a , a display unit  41   b , and a display unit  41   c.    
     Note that the operation unit  40  and the display unit  41  are not specifically limited to, for example, a case where the units  40  and  41  are provided on an induction heating unit basis as described above and a case where the units  40  and  41  are provided as units common to the induction heating units. In this case, the operation unit  40  is constituted by, for example, mechanical switches such as a push switch and a tact switch and a touch switch that detects an input operation on the basis of a change in the capacitance of an electrode. In addition, the display unit  41  is constituted by, for example, a liquid crystal device (LCD) and a light-emitting diode (LED). 
     Note that the operation unit  40  and the display unit  41  may also be integrally constituted as an operation display unit  43 . The operation display unit  43  is constituted by, for example, a touch panel obtained by arranging a touch switch on the top plate surface of an LCD. 
     Inside the induction heating cooker  100 , there are provided a driving circuit  50  for supplying high frequency power to the coils of the first induction heating unit  11 , second induction heating unit  12 , and third induction heating unit  13  and a controller  45  for controlling the entire induction heating cooker including the driving circuit  50 . 
     The driving circuit  50  supplies high frequency power to the first induction heating unit  11 , the second induction heating unit  12 , and the third induction heating unit  13 , so that high frequency magnetic fields are generated from the coils of the induction heating units. Note that the configuration of the driving circuit  50  will be described in detail later. 
     The first induction heating unit  11 , the second induction heating unit  12 , and the third induction heating unit  13  are configured, for example, as in the following. Note that the first induction heating unit  11 , the second induction heating unit  12 , and the third induction heating unit  13  are configured substantially the same. Thus, as a representative, the configuration of the first induction heating unit  11  will be described in the following. 
       FIG. 2  is a plan view illustrating the first induction heating unit of the induction heating cooker according to Embodiment 1. 
     In  FIG. 2 , the first induction heating unit  11  is constituted by an inner periphery coil  11   a  arranged at the center of the heater area indication and an outer periphery coil  11   e  and an outer periphery coil  11   d  arranged around the inner periphery coil  11   a . The periphery of the first induction heating unit  11  has a substantially circular shape corresponding to the first induction heater area indication  1 . 
     The inner periphery coil  11   a  is constituted by an inner-periphery inner coil  111   a  and an inner-periphery outer coil  112   a  that are arranged concentrically. The inner-periphery inner coil  111   a  and the inner-periphery outer coil  112   a  have a circular planar shape and are constituted by a circumferentially wound insulating-coated conductive line composed of an arbitrary metal. Note that examples of a material for the conductive line include copper and aluminum. 
     The inner-periphery inner coil  111   a  and the inner-periphery outer coil  112   a  are connected in series and are driven and controlled by a driving circuit  50   a , which is a single driving circuit. Note that the inner-periphery inner coil  111   a  and the inner-periphery outer coil  112   a  may also be connected in parallel, and may also be each driven by an independent driving circuit. 
     The outer periphery coil  11   d  is constituted by an outer-periphery upper coil  111   d  and an outer-periphery lower coil  112   d . The outer periphery coil  11   e  is constituted by an outer-periphery left coil  111   e  and an outer-periphery right coil  112   e . The outer-periphery upper coil  111   d  and the outer-periphery lower coil  112   d  are connected in series and are driven and controlled by a driving circuit  50   d , which is a single driving circuit. The outer-periphery left coil  111   e  and the outer-periphery right coil  112   e  are connected in series and are driven and controlled by a driving circuit  50   e , which is a single driving circuit. 
     The outer-periphery upper coil  111   d , the outer-periphery lower coil  112   d , the outer-periphery left coil  111   e , and the outer-periphery right coil  112   e  are arranged around the inner periphery coil  11   a  and substantially along the contour of the circle shape of the inner periphery coil  11   a . Note that, in the following description, the outer-periphery upper coil  111   d , the outer-periphery lower coil  112   d , the outer-periphery left coil  111   e , and the outer-periphery right coil  112   e  may also referred to as “individual outer periphery coils”. 
     The four individual outer periphery coils have a substantially ¼ arc-shaped planar shape and are constituted by winding an insulating-coated conductive line composed of an arbitrary metal along the ¼ arc-shaped shape of the individual outer periphery coil. That is, the individual outer periphery coils are configured to extend substantially along the circular planar shape of the inner periphery coil  11   a  in ¼ arc-shaped regions adjacent to the inner periphery coil  11   a . Note that examples of a material for the conductive line include copper and aluminum. Note that the individual outer periphery coils may also be connected in parallel to each other. In addition, the outer-periphery upper coil  111   d  and the outer-periphery lower coil  112   d  may also be driven by using a single driving circuit. 
     Note that the number of individual outer periphery coils is not limited to four. In addition, the shape of the individual outer periphery coils is not limited to this, and for example the individual outer periphery coils may also be configured using a plurality of circular outer periphery coils. In addition, the shape of the individual outer periphery coils may also be, for example, an oval shape, a triangle shape, or a rectangle shape. 
     Note that, in Embodiment 1, the individual outer periphery coils are arranged around the inner periphery coil  11   a . The reason why the individual outer periphery coils and the inner periphery coil  11   a  are not concentrically arranged is to improve power controllability of each coil by weakening electromagnetic coupling between the individual outer periphery coils and the inner periphery coil  11   a  and by reducing interference between the coils. 
       FIG. 3  is a block diagram illustrating the configuration of the induction heating cooker according to Embodiment 1. 
     As illustrated in  FIG. 3 , the first induction heating unit  11  is driven and controlled by the driving circuit  50   a , the driving circuit  50   d , and the driving circuit  50   e . That is, the inner periphery coil  11   a  is driven and controlled by the driving circuit  50   a . In addition, the outer-periphery upper coil  111   d  and the outer-periphery lower coil  112   d  are driven and controlled by the driving circuit  50   d . In addition, the outer-periphery left coil  111   e  and the outer-periphery right coil  112   e  are driven and controlled by the driving circuit  50   e.    
     By supplying a high-frequency current from the driving circuit  50   a  to the inner periphery coil  11   a , a high frequency magnetic field is generated from the inner periphery coil  11   a . By supplying a high-frequency current from the driving circuit  50   d  to the outer-periphery upper coil  111   d  and the outer-periphery lower coil  112   d , a high frequency magnetic field is generated from the outer-periphery upper coil  111   d  and the outer-periphery lower coil  112   d . By supplying a high-frequency current from the driving circuit  50   e  to the outer-periphery left coil  111   e  and the outer-periphery right coil  112   e , a high frequency magnetic field is generated from the outer-periphery left coil  111   e  and the outer-periphery right coil  112   e.    
     The controller  45  is constituted by a dedicated hardware device or a central processing unit (CPU) that executes programs stored in a memory  48 . Note that the CPU is also called a central processor, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, or a processor. 
     In a case where the controller  45  is a dedicated hardware device, the controller  45  corresponds to, for example, a single circuit, a multiple circuit, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination of these. Function units realized by the controller  45  may be realized by individual hardware devices, or the function units may also be realized by a single hardware device. 
     In a case where the controller  45  is a CPU, the functions executed by the controller  45  are realized by software, firmware, or a combination of software and firmware. The software or the firmware is described as programs and is stored in the memory  48 . The CPU reads out and executes the programs stored in the memory  48  to realize the functions of the controller  45 . In this case, the memory  48  is, for example, a nonvolatile or volatile semiconductor memory such as a random access memory (RAM), a read-only memory (ROM), a flash memory, an electrically programmable read-only memory (EPROM), or an electrically erasable programmable ROM (EEPROM). 
     Note that some of the functions of the controller  45  may be realized by a dedicated hardware device and some of the functions may be realized by software or firmware. 
       FIG. 4  is a diagram illustrating a driving circuit of the induction heating cooker according to Embodiment 1. 
     Note that the driving circuit  50  is provided on a heating unit basis, and the circuit configuration may be identical or may also be changed from heating unit to heating unit.  FIG. 4  illustrates the driving circuit  50   a  for driving the inner periphery coil  11   a.    
     As illustrated in  FIG. 4 , the driving circuit  50   a  is constituted by a full bridge inverter circuit having two pairs of arms. Each arm of the driving circuit  50   a  is constituted by two switching elements (IGBTs) connected in series between positive and negative bus bars and diodes connected in anti-parallel to the respective switching elements. 
     In addition, the driving circuit  50   a  includes a direct-current power supply circuit  22 , a resonant capacitor  24   a , and an input current detection unit  25   a.    
     The input current detection unit  25   a  is constituted by, for example, a current sensor, detects a current input from an alternating-current power supply  21  to the direct-current power supply circuit  22 , and outputs a voltage signal corresponding to the input current value to the controller  45 . 
     The direct-current power supply circuit  22  includes a diode bridge  22   a , a reactor  22   b , and a smoothing capacitor  22   c , and converts an alternating voltage input from the alternating-current power supply  21  into a direct-current voltage. 
     The two pairs of arms are connected between the positive and negative bus bars to which output is performed from the direct-current power supply circuit  22 . In one of the arms, IGBTs  231   a  and  231   b , which are switching elements, are connected in series and diodes  231   c  and  231   d , which are flywheel diodes, are connected in parallel to the respective IGBTs  231   a  and  231   b . In the other arm, IGBTs  232   a  and  232   b , which are switching elements, are connected in series, and diodes  232   c  and  232   d , which are flywheel diodes, are connected in parallel to the respective IGBTs  232   a  and  232   b.    
     The IGBT  231   a , the IGBT  231   b , the IGBT  232   a , and the IGBT  232   b  are driven on and off with a driving signal output from the controller  45 . The controller  45  places the IGBT  231   b  in an off state while the IGBT  231   a  is on, places the IGBT  231   b  in an on state while the IGBT  231   a  is off, and outputs a driving signal for alternately performing switch-on and switch-off. In addition, the controller  45  places the IGBT  232   b  in an off state while the IGBT  232   a  is on, places the IGBT  232   b  in an on state while the IGBT  232   a  is off, and outputs a driving signal for alternately performing switch-on and switch-off. 
     As a result, the driving circuit  50   a  converts direct-current power output from the direct-current power supply circuit  22  into a high-frequency alternating-current power of about 20 kHz to 100 kHz, and supplies the power to a resonant circuit constituted by the inner periphery coil  11   a  and the resonant capacitor  24   a.    
     With this configuration, a high-frequency current of about a few tens of amperes flows through the inner periphery coil  11   a , and the high-frequency magnetic flux generated by the flowing high-frequency current causes the to-be-heated object  5  mounted on the top plate  4  directly above the inner periphery coil  11   a  to be induction heated. 
     Note that the IGBT  231   a , the IGBT  231   b , the IGBT  232   a , and the IGBT  232   b , which are switching elements, are configured using, for example, a silicon-based semiconductor. Note that they may also be configured using silicon carbide or a wide band gap semiconductor material such as a gallium nitride based material. By using a wide band gap semiconductor material for the switching elements, the loss at the switching elements can be reduced. In addition, heat dissipation from the driving circuit is preferably performed even when the switching frequency is high, and thus the heat dissipation fin of the driving circuit can be more compact, thereby realizing a reduction in the size and cost of the driving circuit. 
     A coil current detection unit  25   b  is connected to the resonant circuit constituted by the inner periphery coil  11   a  and the resonant capacitor  24   a . The coil current detection unit  25   b  is constituted by, for example, a current sensor, detects a current flowing through the inner periphery coil  11   a , and outputs a voltage signal corresponding to the coil current value to the controller  45 . 
       FIG. 5  is a diagram illustrating a driving circuit of the induction heating cooker according to Embodiment 1. 
       FIG. 5  illustrates the driving circuit  50   d  for driving the outer periphery coil  11   d , and the driving circuit  50   e  for driving the outer periphery coil  11   e.    
     As illustrated in  FIG. 5 , the driving circuit  50   d  and the driving circuit  50   e  include three pairs of arms constituted by two switching elements (IGBTs) connected in series between positive and negative bus bars and diodes connected in anti-parallel to the respective switching elements. Note that, hereinafter, one of the three pairs of arms is called a common arm, and the other two pairs are called a first arm and a second arm. 
     The common arm is an arm connected to the outer periphery coil  11   d  and the outer periphery coil  11   e , and is constituted by an IGBT  234   a , an IGBT  234   b , a diode  234   c , and a diode  234   d.    
     The first arm is an arm to which the outer periphery coil  11   d  is connected, and is constituted by an IGBT  233   a , an IGBT  233   b , a diode  233   c , and a diode  233   d.    
     The second arm is an arm to which the outer periphery coil  11   e  is connected, and is constituted by an IGBT  235   a , an IGBT  235   b , a diode  235   c , and a diode  235   d.    
     The IGBT  234   a  and the IGBT  234   b  of the common arm, the IGBT  233   a  and the IGBT  233   b  of the first arm, and the IGBT  235   a  and the IGBT  235   b  of the second arm are driven on and off with a driving signal output from the controller  45 . 
     The controller  45  places the IGBT  234   b  of the common arm in an off state while the IGBT  234   a  is on, places the IGBT  234   b  in an on state while the IGBT  234   a  is off, and outputs a driving signal for alternately performing switch-on and switch-off. Likewise, the controller  45  outputs a driving signal for alternately switching on and off the IGBT  233   a  and the IGBT  233   b  of the first arm and the IGBT  235   a  and the IGBT  235   b  of the second arm. 
     As a result, the common arm and the first arm constitute a full-bridge inverter for driving the outer periphery coil  11   d . In addition, the common arm and the second arm constitute a full-bridge inverter for driving the outer periphery coil  11   e.    
     A load circuit constituted by the outer periphery coil  11   d  and a resonant capacitor  24   c  is connected between a connection point that is an output point of the common arm and at which the IGBT  234   a  is connected to the IGBT  234   b  and a connecting point that is an output point of the first arm and at which the IGBT  233   a  is connected to the IGBT  233   b.    
     A load circuit constituted by the outer periphery coil  11   e  and a resonant capacitor  24   d  is connected between the output point of the common arm and a connecting point that is an output point of the second arm and at which the IGBT  235   a  is connected to the IGBT  235   b.    
     A coil current flowing through the outer periphery coil  11   d  is detected by a coil current detection unit  25   c . The coil current detection unit  25   c  detects, for example, the peak of the current flowing through the outer periphery coil  11   d , and outputs a voltage signal corresponding to a peak value of the heating coil current to the controller  45 . 
     A coil current flowing through the outer periphery coil  11   e  is detected by a coil current detection unit  25   d . The coil current detection unit  25   d  detects, for example, the peak of the current flowing through the outer periphery coil  11   e , and outputs a voltage signal corresponding to a peak value of the heating coil current to the controller  45 . 
     The controller  45  inputs a high-frequency driving signal to the switching elements (IGBTs) of each arm in accordance with input power and adjusts power to be supplied to each coil. The controller  45  causes the driving signals for the arms to have the same frequency and performs phase difference control on the driving signal for the first arm and the second arm with respect to the driving signal for the common arm to adjust power to be supplied to each coil. Note that the driving signals for the arms have the same on duty ratio. 
     In this manner, by sharing one of the arms of the two full bridge inverter circuits as the common arm, the number of parts of the inverters is reduced by reducing the number of IGBTs from eight to six, thereby achieving a low cost configuration. 
     Note that, in  FIG. 5 , the example has been illustrated in which the outer-periphery upper coil  111   d  and the outer-periphery lower coil  112   d , which constitute the outer periphery coil  11   d , are connected in series and the outer-periphery left coil  111   e  and the outer-periphery right coil  112   e , which constitute the outer periphery coil  11   e , are connected in series; however, the embodiment of the present invention is not limited to this. Needless to say, the four outer coils may also be driven by individual driving circuits. 
     Note that the inner periphery coil  11   a  corresponds to a “first coil” in the present invention. 
     In addition, the outer periphery coil  11   d  and the outer periphery coil  11   e  correspond to a “second coil” in the present invention. 
     In addition, the driving circuit  50   a  corresponds to a “first inverter circuit” in the present invention. 
     In addition, the driving circuit  50   d  and the driving circuit  50   e  correspond to a “second inverter circuit” in the present invention. 
     In addition, the controller  45  corresponds to a “controller” in the present invention. 
     In addition, the high-frequency current supplied from the driving circuit  50   a  to the inner periphery coil  11   a  corresponds to a “first high-frequency current” in the present invention. 
     In addition, the high-frequency current supplied from the driving circuit  50   d  to the outer periphery coil  11   d  corresponds to a “second high-frequency current” in the present invention. 
     In addition, the high-frequency current supplied from the driving circuit  50   e  to the outer periphery coil  11   e  corresponds to a “second high-frequency current” in the present invention. 
     Operation 
     Next, the operation of the induction heating cooker according to Embodiment 1 will be described. 
     The user mounts the to-be-heated object  5  on a heater area indication of the induction heating cooker  100 , and performs an input operation for starting a heating operation using the operation display unit  43 . 
     The controller  45  performs a heating operation for induction heating the to-be-heated object  5  by bringing each of the driving circuits  50   a ,  50   d , and  50   e  into operation in accordance with the input operation. That is, a high-frequency current is supplied to each of the inner periphery coil  11   a , the outer-periphery upper coil  111   d  and the outer-periphery lower coil  112   d  as well as the outer-periphery left coil  111   e  and the outer-periphery right coil  112   e.    
     The controller  45  drives the driving circuits  50   a ,  50   d , and  50   e  at the same frequency. The controller  45  drives the driving circuits  50   a ,  50   d , and  50   e  within a range of from 20 kHz to 100 kHz, for example, at a frequency of 21 kHz. As a result, the to-be-heated object  5  arranged on the top plate  4  is heated through induction. Note that the controller  45  may determine whether the to-be-heated object  5  is mounted above each coil and stop driving coils that are in a no-load state in which no to-be-heated object  5  is mounted. For example, the controller  45  performs a load determination in accordance with a relationship between a coil current and an input current. 
     In addition, the controller  45  drives the driving circuits  50   a ,  50   d , and  50   e  at the same frequency such that the directions of the high-frequency currents are the same in adjacent portions of the inner periphery coil  11   a  and the individual outer periphery coils. Note that, the direct-current power supply circuit  22 , the controller  45 , and the operation display unit  43  may be common or shared elements shared between the circuits of  FIGS. 4 and 5 . 
       FIG. 6  is a diagram illustrating the direction of a current flowing through each coil of the induction heating cooker according to Embodiment 1. 
     As illustrated in  FIG. 6 , a current direction  15  of the inner periphery coil  11   a  flows in the same direction as a direction  16  of a current flowing through portions of the individual outer periphery coils adjacent to the inner periphery coil  11   a . In contrast, the current direction  15  of the inner periphery coil  11   a  flows in the opposite direction to a direction  17  of a current flowing through outer portions of the individual outer periphery coils. 
     The direction of a current flowing through each coil will be described in detail using  FIG. 7 . Note that since the individual outer periphery coils are configured the same, the outer-periphery right coil  112   e  will be described as an example. 
       FIG. 7  is an enlarged view of a main portion illustrated in  FIG. 6 . Note that  FIG. 7  illustrates a portion of the inner periphery coil  11   a  and the outer-periphery right coil  112   e.    
     As illustrated in  FIG. 7 , the outer-periphery right coil  112   e  is formed of an annular coil obtained by performing winding. In addition, the outer-periphery right coil  112   e  has a first winding portion  112   e   1  extending in a circumferential direction of the inner periphery coil  11   a  and a second winding portion  112   e   2  spaced apart from the first winding portion  112   e   1  and extending in the circumferential direction of the inner periphery coil  11   a . In addition, the outer-periphery right coil  112   e  has a third winding portion  112   e   3  and a fourth winding portion  112   e   4  between the first winding portion  112   e   1  and the second winding portion  112   e   2 . 
     The current direction  16  of a high-frequency current flowing through the first winding portion  112   e   1  flows in the same direction as the current direction  15  of a high-frequency current flowing through the inner periphery coil  11   a  adjacent to the first winding portion  112   e   1 . 
     As a result, the magnetic fields around the adjacent portions of the outer-periphery right coil  112   e  and the inner periphery coil  11   a  strengthen each other, and the amount of heat generated by induction heating can be increased. That is, heating at the corresponding portion can be intensified. 
     In contrast, the current direction  17  of the high-frequency current flowing through the second winding portion  112   e   2  flows in the opposite direction to the current direction  15  of the high-frequency current flowing through the inner periphery coil  11   a  adjacent to the first winding portion  112   e   1 . 
     Thus, for example, when the first winding portion  112   e   1  and the second winding portion  112   e   2  are arranged on the same plane, a portion of the magnetic field generated by the high-frequency current flowing through the first winding portion  112   e   1  and a portion of the magnetic field generated by the high-frequency current flowing through the second winding portion  112   e   2  cancel each other out. That is, the amount of heat generated by induction heating the to-be-heated object  5  becomes small. 
     Thus, the induction heating cooker  100  according to Embodiment 1 is configured such that the distance between the first winding portion  112   e   1  of the individual outer periphery coil and the top plate  4  is different from the distance between the second winding portion  112   e   2  and the top plate  4 . A specific example will be described using  FIG. 8 . 
     Coil Arrangement 
       FIG. 8  is a cross section illustrating the arrangement of the coils of the induction heating cooker according to Embodiment 1. 
     Note that  FIG. 8  schematically illustrates an X-X longitudinal section of  FIG. 2 . In addition,  FIG. 8  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 8  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 8 , the inner periphery coil  11   a  and the first winding portion  112   e   1  of the outer-periphery right coil  112   e  are arranged on a reference plane B that is a plane parallel to the top plate  4 . The second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged on an upper plane U that is a plane parallel to the top plate  4  and located at a distance to the top plate  4 , the distance being shorter than a distance from the reference plane B to the top plate  4 . That is, the second winding portion  112   e   2  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being shorter than a distance from the first winding portion  112   e   1  to the top plate. 
     As described above, in Embodiment 1, the distance between the first winding portion  112   e   1  and the top plate  4  is different from the distance between the second winding portion  112   e   2  and the top plate  4 . 
     Thus, when compared with the case where the first winding portion  112   e   1  and the second winding portion  112   e   2  are arranged on the same plane, it is possible to reduce the degree to which the magnetic field generated by the high-frequency current flowing through the first winding portion  112   e   1  and the magnetic field generated by the high-frequency current flowing through the second winding portion  112   e   2  cancel each other out. Thus, a reduction in heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5  can be suppressed, and the temperature irregularity at the outer periphery region of the to-be-heated object  5  can be reduced. 
     In particular, in a case where the distance between the inner side and the outer side corresponding to the width of the individual outer periphery coil is short, an advantageous effect in further reducing the temperature irregularity at the outer periphery region of the to-be-heated object  5  and an advantageous effect in further increasing heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5  can be obtained. 
     In addition, in Embodiment 1, the controller  45  drives the driving circuits  50   a ,  50   d , and  50   e  at the same frequency. In addition, the high-frequency current flowing through the first winding portion of the individual outer periphery coil has the same direction as the high-frequency current flowing through the inner periphery coil  11   a  adjacent to the first winding portion. 
     Thus, the occurrence of noise due to magnetic interference can be suppressed by high-frequency currents having different frequencies flowing through the adjacent coils. 
     In addition, since the second winding portion  112   e   2  arranged on the outer periphery side of a heater area indication is arranged at a position closer to the top plate  4  than is the first winding portion  112   e   1 , it is easier to heat the outer periphery region of the to-be-heated object  5  corresponding to the outer periphery side of the heater area indication, and an advantageous effect in reducing the temperature irregularity at the outer periphery region of the to-be-heated object  5 , an example of which is a large pot, can be obtained. Thus, an advantageous effect in increasing heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5 , an example of which is a large pot, can be obtained. 
     Embodiment 2 
     The arrangement of the individual outer periphery coils of an induction heating cooker  100  according to Embodiment 2 will be described mainly on the differences from Embodiment 1 described above. 
     Coil Arrangement 
       FIG. 9  is a cross section illustrating the arrangement of the coils of the induction heating cooker according to Embodiment 2. 
     Note that  FIG. 9  schematically illustrates an X-X longitudinal section of  FIG. 2 . In addition,  FIG. 9  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 9  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 9 , the inner periphery coil  11   a  and the first winding portion  112   e   1  of the outer-periphery right coil  112   e  are arranged on the reference plane B that is a plane parallel to the top plate  4 . The outer-periphery right coil  112   e  is arranged on an upward inclined plane S 1  that is inclined upward from the outer peripheral side of the inner periphery coil  11   a  toward the outer peripheral side of the heater area indication and that intersects the reference plane B. That is, the second winding portion  112   e   2  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being shorter than a distance from the first winding portion  112   e   1  to the top plate. In addition, both the first winding portion  112   e   1  and the second winding portion  112   e   2  of the outer-periphery right coil  112   e  are arranged obliquely with respect to the top plate  4 . 
     With this configuration, substantially the same advantageous effects as those of Embodiment 1 described above can also be obtained. In addition, in Embodiment 2, since the first winding portion and the second winding portion of the individual outer periphery coil are arranged on the same plane, a coil bending process can be omitted in a manufacturing process of the individual outer periphery coil, and thus the manufacturing process can be simplified. 
     In addition, in Embodiment 2, compared with an outer periphery coil having the same coil width, the space between the first winding portion  112   e   1  and the second winding portion  112   e   2  can be widened. A specific example will be described using  FIG. 10 . 
       FIG. 10  is a diagram for describing the space between the first winding portion and the second winding portion of the induction heating cooker according to Embodiment 2. 
     The lower part of  FIG. 10  illustrates a configuration in which the outer-periphery right coil  112   e  is arranged on the reference plane B. In this case, a coil width Win a plan view is the sum of a width W 1  of the first winding portion  112   e   1 , a width W 2  of the second winding portion  112   e   2 , and a space G 2 . 
     The upper part of  FIG. 10  illustrates a configuration in which the outer-periphery right coil  112   e  is arranged on the upward inclined plane S 1 . In a case where the same coil width W is used for the outer-periphery right coil  112   e  in a plan view, a space G 1  between the first winding portion  112   e   1  and the second winding portion  112   e   2  arranged on the upward inclined plane S 1  is wider than the space G 2 . 
     In this manner, with the configuration according to Embodiment 2, the space between the first winding portion  112   e   1  and the second winding portion  112   e   2  can be wider than in a case where the outer periphery coil having with the same coil width W is arranged on the reference plane B. 
     Modification 1 
       FIG. 11  is a cross section illustrating modification 1 of the arrangement of the coils of the induction heating cooker according to Embodiment 2. 
     Note that  FIG. 11  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 11  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 11  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 11 , the inner periphery coil  11   a  is arranged on the reference plane B that is a plane parallel to the top plate  4 . The first winding portion  112   e   1  of the outer-periphery right coil  112   e  is arranged on an upward inclined plane S 1  that is a plane inclined upward from the outer peripheral side of the inner periphery coil  11   a  toward the outer peripheral side of the heater area indication and intersecting the reference plane B. The second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged on the upper plane U that is a plane parallel to the top plate  4  and located at a distance to the top plate  4 , the distance being shorter than a distance from the reference plane B to the top plate  4 . That is, the second winding portion  112   e   2  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being shorter than a distance from the first winding portion  112   e   1  to the top plate. In addition, the first winding portion  112   e   1  of the outer-periphery right coil  112   e  is arranged obliquely with respect to the top plate  4 . 
     With this configuration, substantially the same advantageous effects as those of Embodiment 1 described above can also be obtained. In addition, compared with the configuration in Embodiment 1 described above, a coil bending amount can be reduced for the individual outer periphery coil, and thus the manufacturing can be easily performed. 
     Modification 2 
       FIG. 12  is a cross section illustrating modification 2 of the arrangement of the coils of the induction heating cooker according to Embodiment 2. 
     Note that  FIG. 12  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 12  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 12  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 12 , the inner periphery coil  11   a  and the first winding portion  112   e   1  of the outer-periphery right coil  112   e  are arranged on the reference plane B that is a plane parallel to the top plate  4 . The second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged on the upward inclined plane S 1  that is a plane inclined upward from the outer peripheral side of the inner periphery coil  11   a  toward the outer peripheral side of the heater area indication and intersecting the reference plane B. That is, the second winding portion  112   e   2  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being shorter than a distance from the first winding portion  112   e   1  to the top plate. In addition, the second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged obliquely with respect to the top plate  4 . 
     With this configuration, substantially the same advantageous effects as those of Embodiment 1 described above can also be obtained. In addition, compared with the configuration in Embodiment 1 described above, the coil bending amount can be reduced in a manufacturing process for bending the outer periphery coil, and thus the manufacturing can be easily performed. 
     Embodiment 3 
     The arrangement of the individual outer periphery coils of an induction heating cooker  100  according to Embodiment 3 will be described mainly on the differences from Embodiments 1 and 2 described above. 
     Coil Arrangement 
       FIG. 13  is a cross section illustrating the arrangement of the coils of the induction heating cooker according to Embodiment 3. 
     Note that  FIG. 13  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 13  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 13  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 13 , the inner periphery coil  11   a  and the first winding portion  112   e   1  of the outer-periphery right coil  112   e  are arranged on the reference plane B that is a plane parallel to the top plate  4 . The second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged on a lower plane L that is a plane parallel to the top plate  4  and located at a distance to the top plate  4 , the distance being longer than a distance from the reference plane B to the top plate  4 . That is, the second winding portion  112   e   2  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being longer than a distance from the first winding portion  112   e   1  to the top plate. 
     As described above, in Embodiment 3, the distance between the first winding portion  112   e   1  and the top plate  4  is different from the distance between the second winding portion  112   e   2  and the top plate  4 . 
     Thus, when compared with the case where the first winding portion  112   e   1  and the second winding portion  112   e   2  are arranged on the same plane, it is possible to reduce the degree to which the magnetic field generated by the high-frequency current flowing through the first winding portion  112   e   1  and the magnetic field generated by the high-frequency current flowing through the second winding portion  112   e   2  cancel each other out. Thus, a reduction in heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5  can be suppressed, and the temperature irregularity at the outer periphery region of the to-be-heated object  5  can be reduced. 
     In particular, in a case where the distance between the inner side and the outer side corresponding to the width of the individual outer periphery coil is short, an advantageous effect in further reducing the temperature irregularity at the outer periphery region of the to-be-heated object  5  and an advantageous effect in further increasing heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5  can be obtained. 
     In addition, in Embodiment 3, the controller  45  drives the driving circuits  50   a ,  50   d , and  50   e  at the same frequency. In addition, the high-frequency current flowing through the first winding portion of the individual outer periphery coil has the same direction as the high-frequency current flowing through the inner periphery coil  11   a  adjacent to the first winding portion. 
     Thus, the occurrence of noise due to magnetic interference can be suppressed by high-frequency currents having different frequencies flowing through the adjacent coils. 
     In addition, the first winding portion  112   e   1  arranged on the inner periphery side of the heater area indication is arranged at a position closer to the top plate  4  than the second winding portion  112   e   2 . Thus, it is easier to heat the central portion of the to-be-heated object  5  corresponding to the inner periphery side of the heater area indication, and an advantageous effect in reducing the temperature irregularity at the outer periphery region of the to-be-heated object  5 , an example of which is a medium pot or a small pot, can be obtained. Generally a large number of medium pots and small pots are diffused. Thus, an advantageous effect in increasing heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5 , an example of which is a medium pot or a small pot, can be obtained. 
     Modification 1 
       FIG. 14  is a cross section illustrating modification 1 of the arrangement of the coils of the induction heating cooker according to Embodiment 3. 
     Note that  FIG. 14  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 14  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 14  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 14 , the inner periphery coil  11   a  is arranged on the reference plane B that is a plane parallel to the top plate  4 . The outer-periphery right coil  112   e  is arranged on a downward inclined plane S 2  that is inclined downward from the outer peripheral side of the inner periphery coil  11   a  toward the outer peripheral side of the heater area indication and that intersects the reference plane B. That is, the first winding portion  112   e   1  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being shorter than a distance from the second winding portion  112   e   2  to the top plate. In addition, both the first winding portion  112   e   1  and the second winding portion  112   e   2  of the outer-periphery right coil  112   e  are arranged obliquely with respect to the top plate  4 . 
     With this configuration, the above-described advantageous effects can also be obtained. In addition, since the first winding portion and the second winding portion of the individual outer periphery coil are arranged on the same plane, the coil bending process can be omitted in the manufacturing process of the individual outer periphery coil, and thus the manufacturing process can be simplified. 
     In addition, similarly to as in Embodiment 2 described above, compared with an outer periphery coil having the same coil width, the space between the first winding portion  112   e   1  and the second winding portion  112   e   2  can be widened. 
     Modification 2 
       FIG. 15  is a cross section illustrating modification 2 of the arrangement of the coils of the induction heating cooker according to Embodiment 3. 
     Note that  FIG. 15  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 15  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 15  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 15 , the inner periphery coil  11   a  is arranged on the reference plane B that is a plane parallel to the top plate  4 . The first winding portion  112   e   1  of the outer-periphery right coil  112   e  is arranged on the downward inclined plane S 2  that is a plane inclined downward from the outer peripheral side of the inner periphery coil  11   a  toward the outer peripheral side of the heater area indication and intersecting the reference plane B. The second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged on the lower plane L that is a plane parallel to the top plate  4  and located at a distance to the top plate  4 , the distance being longer than a distance from the reference plane B to the top plate  4 . That is, the first winding portion  112   e   1  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being shorter than a distance from the second winding portion  112   e   2  to the top plate. In addition, the first winding portion  112   e   1  of the outer-periphery right coil  112   e  is arranged obliquely with respect to the top plate  4 . 
     With this configuration, the above-described advantageous effects can also be obtained. In addition, compared with the configuration illustrated in  FIG. 13 , the coil bending amount can be reduced for the individual outer periphery coil, and thus the manufacturing can be easily performed. 
     Modification 3 
       FIG. 16  is a cross section illustrating modification 3 of the arrangement of the coils of the induction heating cooker according to Embodiment 3. 
     Note that  FIG. 16  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 16  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 16  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 16 , the inner periphery coil  11   a  and the first winding portion  112   e   1  of the outer-periphery right coil  112   e  are arranged on the reference plane B that is a plane parallel to the top plate  4 . The second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged on the downward inclined plane S 2  that is a plane inclined downward from the outer peripheral side of the inner periphery coil  11   a  toward the outer peripheral side of the heater area indication and intersecting the reference plane B. That is, the first winding portion  112   e   1  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being shorter than a distance from the second winding portion  112   e   2  to the top plate. In addition, the second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged obliquely with respect to the top plate  4 . 
     With this configuration, the above-described advantageous effects can also be obtained. In addition, compared with the configuration illustrated in  FIG. 13 , the coil bending amount can be reduced for the individual outer periphery coil, and thus the manufacturing can be easily performed. 
     Embodiment 4 
     The arrangement of the individual outer periphery coils of an induction heating cooker  100  according to Embodiment 4 will be described mainly on the differences from Embodiments 1 to 3 described above. 
     Coil Arrangement 
     An individual outer periphery coil among the individual outer periphery coils according to Embodiment 4 is arranged such that, in a plan view, at least a portion of the first winding portion is at a position superposed with the inner periphery coil  11   a . A specific example will be described using  FIG. 17 . 
       FIG. 17  is a cross section illustrating the arrangement of the coils of the induction heating cooker according to Embodiment 4. 
     Note that  FIG. 17  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 17  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 17  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 17 , the inner periphery coil  11   a  and the second winding portion  112   e   2  of the outer-periphery right coil  112   e  are arranged on the reference plane B that is a plane parallel to the top plate  4 . The first winding portion  112   e   1  of the outer-periphery right coil  112   e  is arranged on the lower plane L that is a plane parallel to the top plate  4  and located at a distance to the top plate  4 , the distance being longer than a distance from the reference plane B to the top plate  4 . That is, the first winding portion  112   e   1  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being longer than a distance from the second winding portion  112   e   2  to the top plate  4 . In addition, in a plan view, at least a portion of the first winding portion  112   e   1  is arranged at a position underlying the inner periphery coil  11   a.    
     As described above, in Embodiment 3, the distance between the first winding portion  112   e   1  and the top plate  4  is different from the distance between the second winding portion  112   e   2  and the top plate  4 . 
     Thus, when compared with the case where the first winding portion  112   e   1  and the second winding portion  112   e   2  are arranged on the same plane, it is possible to reduce the degree to which the magnetic field generated by the high-frequency current flowing through the first winding portion  112   e   1  and the magnetic field generated by the high-frequency current flowing through the second winding portion  112   e   2  cancel each other out. Thus, a reduction in heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5  can be suppressed, and the temperature irregularity at the outer periphery region of the to-be-heated object  5  can be reduced. 
     In particular, in a case where the distance between the inner side and the outer side corresponding to the width of the individual outer periphery coil is short, an advantageous effect in further reducing the temperature irregularity at the outer periphery region of the to-be-heated object  5  and an advantageous effect in further increasing heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5  can be obtained. 
     In addition, in Embodiment 4, the controller  45  drives the driving circuits  50   a ,  50   d , and  50   e  at the same frequency. In addition, the high-frequency current flowing through the first winding portion of the individual outer periphery coil has the same direction as the high-frequency current flowing through the inner periphery coil  11   a  adjacent to the first winding portion. 
     Thus, the occurrence of noise due to magnetic interference can be suppressed by high-frequency currents having different frequencies flowing through the adjacent coils. 
     In addition, the individual outer periphery coil according to Embodiment 4 is arranged such that, in a plan view, at least a portion of the first winding portion is at a position superposed with the inner periphery coil  11   a . Thus, the magnetic field near the outer peripheral side of the inner periphery coil  11   a  can be strengthened. Thus, it is easier to heat the central portion of the to-be-heated object  5  corresponding to the inner periphery side of the heater area indication, and, regarding the to-be-heated object  5 , an example of which is a medium pot or a small pot, the amount of heat generated at the outer periphery portion of the to-be-heated object  5  where the temperature tends to be on the lower side can be increased. Generally a large number of medium pots and small pots are diffused. 
     Modification 1 
       FIG. 18  is a cross section illustrating modification 1 of the arrangement of the coils of the induction heating cooker according to Embodiment 4. 
     Note that  FIG. 18  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 18  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 18  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 18 , the inner periphery coil  11   a  and the second winding portion  112   e   2  of the outer-periphery right coil  112   e  are arranged on the reference plane B that is a plane parallel to the top plate  4 . The first winding portion  112   e   1  of the outer-periphery right coil  112   e  is arranged on the upper plane U that is a plane parallel to the top plate  4  and located at a distance to the top plate  4 , the distance being shorter than a distance from the reference plane B to the top plate  4 . That is, the first winding portion  112   e   1  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being shorter than a distance from the second winding portion  112   e   2  to the top plate. In addition, in a plan view, at least a portion of the first winding portion  112   e   1  is arranged at a position overlying the inner periphery coil  11   a.    
     With this configuration, the above-described advantageous effects can also be obtained. 
     Modification 2 
       FIG. 19  is a cross section illustrating modification 2 of the arrangement of the coils of the induction heating cooker according to Embodiment 4. 
     Note that  FIG. 19  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 19  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 19  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 19 , the inner periphery coil  11   a  is arranged on the reference plane B that is a plane parallel to the top plate  4 . The first winding portion  112   e   1  of the outer-periphery right coil  112   e  is arranged on the lower plane L that is a plane parallel to the top plate  4  and located at a distance to the top plate  4 , the distance being longer than a distance from the reference plane B to the top plate  4 . The second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged on the upward inclined plane S 1  that is a plane inclined upward from the outer peripheral side of the inner periphery coil  11   a  toward the outer peripheral side of the heater area indication and intersecting the reference plane B. That is, the first winding portion  112   e   1  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being longer than a distance from the second winding portion  112   e   2  to the top plate. In addition, the second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged obliquely with respect to the top plate  4 . 
     With this configuration, the above-described advantageous effects can also be obtained. In addition, compared with the configuration illustrated in  FIG. 18 , the coil bending amount can be reduced for the individual outer periphery coil, and thus the manufacturing can be easily performed. 
     Modification 3 
       FIG. 20  is a cross section illustrating modification 3 of the arrangement of the coils of the induction heating cooker according to Embodiment 4. 
     Note that  FIG. 20  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 20  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 20  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 20 , the inner periphery coil  11   a  is arranged on the reference plane B that is a plane parallel to the top plate  4 . The first winding portion  112   e   1  of the outer-periphery right coil  112   e  is arranged on the upper plane U that is a plane parallel to the top plate  4  and located at a distance to the top plate  4 , the distance being shorter than a distance from the reference plane B to the top plate  4 . The second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged on the downward inclined plane S 2  that is a plane inclined downward from the outer peripheral side of the inner periphery coil  11   a  toward the outer peripheral side of the heater area indication and intersecting the reference plane B. That is, the first winding portion  112   e   1  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being shorter than a distance from the second winding portion  112   e   2  to the top plate. In addition, the second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged obliquely with respect to the top plate  4 . 
     With this configuration, the above-described advantageous effects can also be obtained. In addition, compared with the configuration illustrated in  FIG. 13 , the coil bending amount can be reduced for the individual outer periphery coil, and thus the manufacturing can be easily performed. 
     Embodiment 5 
     The configuration of an induction heating cooker  100  according to Embodiment 5 will be described mainly on the differences from Embodiments 1 to 4 described above. Note that the arrangement of the individual outer periphery coils is the same as any of those in Embodiments 1 to 4 described above. 
       FIG. 21  is a cross section illustrating the arrangement of the coils of the induction heating cooker according to Embodiment 5. 
     Note that  FIG. 21  schematically illustrates the X-X longitudinal section of  FIG. 2 . In addition,  FIG. 21  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 21  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 21 , the induction heating cooker  100  according to Embodiment 5 includes a flat plate-shaped magnetic member  200   a  arranged radially below the inner periphery coil  11   a  in a plan view. The magnetic member  200   a  is formed of, for example, a magnetic material such as ferrite. 
     In addition, the induction heating cooker  100  includes a first magnetic member  200   e   1  arranged to surround at least a portion of both side surfaces and the bottom of the first winding portion  112   e   1  of the outer-periphery right coil  112   e . In addition, the induction heating cooker  100  includes a second magnetic member  200   e   2  arranged to surround at least portion of both side surfaces and the bottom of the second winding portion  112   e   2  of the outer-periphery right coil  112   e . The first magnetic member  200   e   1  and the second magnetic member  200   e   2  are each formed of a U-shaped magnetic material. The first magnetic member  200   e   1  and the second magnetic member  200   e   2  are formed of, for example, a magnetic material such as ferrite. 
     For example, as illustrated in  FIG. 21 , the top ends of the first magnetic member  200   e   1  and second magnetic member  200   e   2  are formed to be arranged at positions above the top ends of the outer-periphery right coil  112   e . In addition, the distance from the top ends of the first magnetic member  200   e   1  to the top plate  4  is the same as the distance from the top ends of the second magnetic member  200   e   2  to the top plate  4 . 
     With this configuration, a magnetic path that passes through the first magnetic member  200   e   1  and the to-be-heated object  5  on the top plate  4  is formed around the first winding portion  112   e   1 . In addition, a magnetic path that passes through the second magnetic member  200   e   2  and the to-be-heated object  5  on the top plate  4  is formed around the second winding portion  112   e   2 . 
     Thus, it is possible to further reduce the degree to which the magnetic field generated by the high-frequency current flowing through the first winding portion  112   e   1  and the magnetic field generated by the high-frequency current flowing through the second winding portion  112   e   2  cancel each other out. 
     In addition, the top ends of the first magnetic member  200   e   1  and second magnetic member  200   e   2  are formed such that the distance from the top ends of the first magnetic member  200   e   1  to the top plate  4  is the same as the distance from the top ends of the second magnetic member  200   e   2  to the top plate  4 . Thus, the magnetic field leakage from the first winding portion  112   e   1  to the second winding portion  112   e   2  side and the magnetic field leakage from the second winding portion  112   e   2  to the first winding portion  112   e   1  side can be reduced. 
     Note that the shape of the first magnetic member  200   e   1  and that of the second magnetic member  200   e   2  are not limited to the U shape. The shape of the first magnetic member  200   e   1  and that of the second magnetic member  200   e   2  may also be, for example, a concave shape. In addition, the first magnetic member  200   e   1  and the second magnetic member  200   e   2  may also be formed by combining a plurality of plate-shaped ferrite materials. In addition, the adjacent portions of the first magnetic member  200   e   1  and the second magnetic member  200   e   2  may also be formed of a common member. 
     Embodiment 6 
     The configuration of an induction heating cooker  100  according to Embodiment 6 will be described mainly on the differences from Embodiments 1 to 5 described above. 
     Coil Arrangement 
       FIG. 22  is a plan view illustrating the first induction heating unit of the induction heating cooker according to Embodiment 6. 
       FIG. 23  is a cross section illustrating the arrangement of the coils of the induction heating cooker according to Embodiment 6. 
     Note that  FIG. 23  schematically illustrates a Y-Y longitudinal section of  FIG. 22 . In addition,  FIG. 23  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 23  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIGS. 22 and 23 , the outer-periphery right coil  112   e  is arranged in a plan view such that the first winding portion  112   e   1  overlies the second winding portion  112   e   2 . That is, the individual outer periphery coil is arranged such that the center axis of a tubular-shaped winding obtained by performing winding is in a direction parallel to the top plate  4 . 
     In addition, the inner periphery coil  11   a  and the first winding portion  112   e   1  of the outer-periphery right coil  112   e  are arranged on the reference plane B that is a plane parallel to the top plate  4 . The second winding portion  112   e   2  of the outer-periphery right coil  112   e  is arranged on the lower plane L that is a plane parallel to the top plate  4  and located at a distance to the top plate  4 , the distance being longer than a distance from the reference plane B to the top plate  4 . That is, the first winding portion  112   e   1  of the outer-periphery right coil  112   e  is located at a distance to the top plate  4 , the distance being shorter than a distance from the second winding portion  112   e   2  to the top plate. 
     Note that an area parallel to the top plate  4  may also be increased by widening the width of the first winding portion  112   e   1  of the outer-periphery right coil  112   e.    
     Note that the first winding portion  112   e   1  does not have to be arranged so as to entirely overlie the second winding portion  112   e   2  in a plan view, and the first winding portion  112   e   1  and the second winding portion  112   e   2  may also be arranged such that at least a portion of the first winding portion  112   e   1  overlies at least a portion of the second winding portion  112   e   2 . 
     As described above, in Embodiment 6, the distance between the first winding portion  112   e   1  and the top plate  4  is different from the distance between the second winding portion  112   e   2  and the top plate  4 . 
     Thus, when compared with the case where the first winding portion  112   e   1  and the second winding portion  112   e   2  are arranged on the same plane, it is possible to reduce the degree to which the magnetic field generated by the high-frequency current flowing through the first winding portion  112   e   1  and the magnetic field generated by the high-frequency current flowing through the second winding portion  112   e   2  cancel each other out. Thus, a reduction in heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5  can be suppressed, and the temperature irregularity at the outer periphery region of the to-be-heated object  5  can be reduced. 
     In addition, in Embodiment 6, the controller  45  drives the driving circuits  50   a ,  50   d , and  50   e  at the same frequency. In addition, the high-frequency current flowing through the first winding portion of the individual outer periphery coil has the same direction as the high-frequency current flowing through the inner periphery coil  11   a  adjacent to the first winding portion. 
     Thus, the occurrence of noise due to magnetic interference can be suppressed by high-frequency currents having different frequencies flowing through the adjacent coils. 
     In addition, the first winding portion  112   e   1  is arranged so to overlie the second winding portion  112   e   2  in a plane view. 
     Thus, the width of the first winding portion  112   e   1  can be wider than those in Embodiments 1 to 5 described above. Thus, an advantageous effect in further reducing the temperature irregularity at the outer periphery region of the to-be-heated object  5  and increasing heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5  can be obtained. 
     Embodiment 7 
     The configuration of an induction heating cooker  100  according to Embodiment 7 will be described mainly on the differences from Embodiment 6 described above. Note that the arrangement of the individual outer periphery coils is the same as that in Embodiment 6 described above. 
       FIG. 24  is a cross section illustrating the arrangement of the coils of the induction heating cooker according to Embodiment 7. 
     Note that  FIG. 24  schematically illustrates the Y-Y longitudinal section of  FIG. 22 . In addition,  FIG. 24  illustrates only the right side of the heater area indication from the center C. Note that  FIG. 24  illustrates the outer-periphery right coil  112   e  among the individual outer periphery coils; however, the other outer periphery coils are configured substantially the same. 
     As illustrated in  FIG. 24 , the induction heating cooker  100  according to Embodiment 7 includes the flat plate-shaped magnetic member  200   a  arranged radially below the inner periphery coil  11   a  in a plan view. The magnetic member  200   a  is formed of, for example, a magnetic material such as ferrite. 
     In addition, the induction heating cooker  100  includes the first magnetic member  200   e  arranged so as to surround at least a portion of both side surfaces and the bottom of the first winding portion  112   e   1  of the outer-periphery right coil  112   e . The first magnetic member  200   e  is formed of a U-shaped magnetic material. The first magnetic member  200   e   1  is formed of, for example, a magnetic material such as ferrite. For example, as illustrated in  FIG. 24 , the top ends of the first magnetic member  200   e   1  are formed so as to be arranged at positions above the top ends of the first winding portion  112   e   1  of the outer-periphery right coil  112   e.    
     With this configuration, a magnetic path that passes through the first magnetic member  200   e   1  and the to-be-heated object  5  on the top plate  4  is formed around the first winding portion  112   e   1 . Thus, it is possible to further reduce the degree to which the magnetic field generated by the high-frequency current flowing through the first winding portion  112   e   1  and the magnetic field generated by the high-frequency current flowing through the second winding portion  112   e   2  cancel each other out. 
     In addition, since the top ends of the first magnetic member  200   e   1  are positioned above the top ends of the first winding portion  112   e   1 , the magnetic field leakage from the first winding portion  112   e   1  to the second winding portion  112   e   2  side can be reduced. 
     Note that the shape of the first magnetic member  200   e   1  is not limited to the U shape. The shape of the first magnetic member  200   e   1  may also be, for example, a concave shape. In addition, the first magnetic member  200   e   1  may also be formed by combining a plurality of plate-shaped ferrite materials. 
     Embodiment 8 
     An operation of an induction heating cooker  100  according to Embodiment 8 will be described mainly on the differences from Embodiments 1 to 7 described above. Note that the configuration of the induction heating cooker  100  according to Embodiment 8 is the same as any of those in Embodiments 1 to 7 described above. 
     Operation 
     When an input operation for starting a heating operation is performed using the operation display unit  43 , the controller  45  drives each of the driving circuits  50   a ,  50   d , and  50   e  in accordance with the input operation, and performs the heating operation to heat the to-be-heated object  5  through induction. 
     The controller  45  increases the driving frequency of the driving circuit  50   d  and the driving circuit  50   e , so that the driving frequency of the driving circuit  50   d  and the driving circuit  50   e  is higher than the driving frequency of the driving circuit  50   a  by at least an audio frequency. That is, the controller  45  drives each of the driving circuits  50   d  and  50   e  such that the frequency of the high-frequency current flowing through the individual outer periphery coil becomes higher than the frequency of the high-frequency current flowing through the inner periphery coil  11   a  by at least the audio frequency. For example, the controller  45  drives the driving circuit  50   a  at a driving frequency of 23 kHz, and drives the driving circuit  50   d  and the driving circuit  50   e  at a driving frequency of 90 kHz. 
     In this case, the audio frequency is the frequency of a sound that can be recognized by the sense of hearing of people. The lower limit of the audio frequency is substantially 20 kHz. 
     As a result of the operation described above, the occurrence of noise due to magnetic interference can be suppressed by high-frequency currents having different frequencies flowing through the adjacent coils. 
     In addition, the high-frequency current flowing through the individual outer periphery coil arranged on the outer side of the heater area indication has a higher frequency than the current flowing through the inner periphery coil  11   a . Thus, it is easier to heat the outer periphery region of the to-be-heated object  5  corresponding to the outer periphery side of the heater area indication, and an advantageous effect in increasing heat at and the amount of heat generated at the outer periphery region of the to-be-heated object  5  can be obtained. 
     In this case, examples of the to-be-heated object  5  include an item formed of a composite material obtained by attaching a magnetic material to a non-magnetic material. For example, the to-be-heated object  5  is formed by attaching a magnetic material such as stainless steel to the center portion of the bottom of a flying pan made of a non-magnetic material such as aluminum. Note that the magnetic material is attached to the non-magnetic material by using an arbitrary method, examples of which include sticking, welding, thermal spraying, crimping, inlaying, calking, and embedding. 
     In general, regarding a to-be-heated object  5  formed of a composite material, a magnetic material is attached to a center flat portion of the bottom surface of the base of a non-magnetic material, and no magnetic material is attached to an outer periphery region where the bottom surface is curved. When this to-be-heated object  5  is mounted on a heater area indication among the heater area indications, the magnetic material is mounted on the center of the heater area indication, and the non-magnetic material is mounted on the outer periphery side of the heater area indication. 
     In the induction heating cooker  100  according to Embodiment 8, since a higher-frequency current flows through the individual outer periphery coils than through the inner periphery coil  11   a , when the to-be-heated object  5  formed of the above-described composite material is induction heated, high frequency heating can be performed to the non-magnetic material corresponding to the outer periphery region of the to-be-heated object  5  formed of the composite material. Thus, induction heating appropriate for the material of the to-be-heated object  5  can be performed. 
     Note that a wide band gap semiconductor material may also be used for the switching elements of the driving circuit  50   d  and the driving circuit  50   e  that drive the individual outer periphery coils. By using a wide band gap semiconductor material for the switching elements driven at a high frequency, power loss at the switching elements can be reduced. In addition, heat dissipation from the driving circuits is preferably performed even when the switching frequency is high, and thus the heat dissipation fins of the driving circuits can be more compact, thereby realizing a reduction in the size and cost of the driving circuits. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  first induction heater area indication  2  second induction heater area indication  3  third induction heater area indication  4  top  5  to-be-heated object  11  first induction heating unit  11   a  inner periphery coil  11   d  outer periphery coil  11   e  outer periphery coil  12  second induction heating unit  13  third induction heating unit  15  current direction  16  current direction  17  current direction  21  alternating-current power supply  22  direct-current power supply circuit  22   a  diode bridge  22   b  reactor  22   c  smoothing capacitor  24   a  resonant capacitor  24   c  resonant capacitor  24   d  resonant capacitor  25   a  input current detection unit  25   b  coil current detection unit  25   c  coil current detection unit  25   d  coil current detection unit  40  operation unit  40   a  operation unit  40   b  operation unit  40   c  operation unit  41  display unit  41   a  display unit  41   b  display unit  41   c  display unit  43  operation display unit  45  controller  48  memory  50  driving circuit  50   a  driving circuit  50   d  driving circuit  50   e  driving circuit  100  induction heating cooker  111   a  inner-periphery inner coil  111   d  outer-periphery upper coil  111   e  outer-periphery left coil  112   a  inner-periphery outer coil  112   d  outer-periphery lower coil  112   e  outer-periphery right coil  112   e   1  first winding portion  112   e   2  second winding portion  112   e   3  third winding portion  112   e   4  fourth winding portion  200   a  magnetic member  200   e   1  first magnetic member  200   e   2  second magnetic member  231   a  IGBT  231   b  IGBT  231   c  diode  231   d  diode  232   a  IGBT  232   b  IGBT  232   c  diode  232   d  diode  233   a  IGBT  233   b  IGBT  233   c  diode  233   d  diode  234   a  IGBT  234   b  IGBT  234   c  diode  234   d  diode  235   a  IGBT  235   b  IGBT  235   c  diode  235   d  diode