Patent Publication Number: US-2022240354-A1

Title: Induction heating apparatus and method for controlling induction heating apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0011744, filed in Korea on Jan. 27, 2021, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to an induction heating apparatus and a method for controlling the induction heating apparatus. 
     2. Background 
     An induction heating apparatus is a mechanism that heats a container by generating an eddy current in a metal container, using a magnetic field generated around a working coil. When the induction heating apparatus is driven, an alternating current may be applied to the working coil. Accordingly, an induction magnetic field may be generated around the working coil disposed in the induction heating apparatus. When a magnetic force line of the induced magnetic field generated in this way passes through the bottom of the container having a metal component placed on the working coil, an eddy current may be generated inside the bottom of the container. When the eddy current generated in this way flows through the container, the container itself may be heated. 
     In general, AC current for driving a working coil is supplied by an inverter circuit including a plurality of switching elements. The magnitude of the AC current supplied to the working coil varies based on the driving frequency of the inverter circuit. The driving frequency of the inverter circuit is determined based on the required power value of the working coil, and the required power value of the working coil is a value determined based on a power level set for a heating region (or heating area) corresponding to the working coil. 
     That is, when a user sets the power level for the heating region, the required power value of the working coil corresponding to the set power value is determined. To heat a container according to the power level set by the user, the actual output power value of the working coil has to match the required power value. Therefore, in the process of controlling the induction heating apparatus, it is necessary to measure the output power value of the working coil and adjust the driving frequency of the inverter circuit based on the output power value. 
     Cited document 1 (Korean Patent Publication No. 10-2008-0057399), the subject matter of which is incorporated herein by reference, discloses a method and apparatus for controlling an inverter.  FIG. 1  is a block diagram illustrating the configuration of the apparatus for controlling the inverter disclosed in Cited document 1. The apparatus for controlling the inverter disclosed in Cited document 1 (hereinafter, the inverter controlling apparatus) includes a DC converter  71  supplied DC power, a power circuit  72 , a power voltage sensing circuit  73  configured to sense the power voltage supplied through the DC converter  71 , a motor  74 , an inverter IC (IPM)  75  configured to supply power to power to the motor  74 , a shunt resistor  76  configured to detect the current flowing through the inverter IC (IMP)  75  to prevent overcurrent, a comparator  77  configured to compare the voltage Va applied to the shunt resistor  76  with a preset reference voltage Vb, thereby transmitting the result of comparison, a microcomputer  78  configured to output a three-phase power control signal to the inverter IC (IPM)  75  to control the driving of the motor  74  and the driving of other loads based on the comparison result of the comparator  77 , and a load drive part  79  configured to drive a load such as a heater  80  based on a control signal of the microcomputer  78 . 
     In Cited document 1 as shown in  FIG. 1 , a control signal is supplied to IC (IPM)  75  to control the driving of the motor and other loads. The control signal is generated based on the result of the comparison between the voltage Va applied to the shunt resistor  76  and the reference voltage Vb. 
     The inverter controlling apparatus according to Cited document 1 has to include not only the shunt resistor  76  for controlling the inverter IC (IPM) and the driving of the load but also the voltage measuring circuit and the current measuring circuit for measuring the voltage and the current applied to the shunt resistor  76 . 
     Cited document 2 (Korean Patent Publication No. 10-2009-0061863), the subject matter of which is incorporated herein by reference, discloses an inverter heating cooker and a method for controlling the same.  FIG. 2  is a block diagram illustrating the configuration of the inverter heating cooker (or the induction heating cooker) disclosed in Cited document 2. 
     Referring to  FIG. 2 , the inverter heating cooker includes a power source part  81  receiving and supplying commercial power for home use, an IGBT drive part  85 , a power element  86 , a heating coil  87 , an inverter circuit including a resonance capacitor and generating and outputting a resonance voltage for heating food contained in a container or vessel, an input voltage sensor  82 , an input current sensor  83 , a microcomputer  84  controlling the operation of the induction heating cooker, and a trigger part  88  outputting a trigger signal when the resonance voltage generated in the inverter circuit reaches a preset voltage level. 
     In Cited document 2, power consumption may be calculated based on the input voltage value detected by the input voltage sensor  82  and the input current detected by the input current sensor  83 , and the inverter circuit may be controlled based on the calculated power consumption. 
     Ultimately, according to the prior art, an element or circuit (e.g., the shunt resistor, the input voltage sensing circuit and the input current sensing circuit) is additionally required in order to control the inverter circuit and control the output of the load. Accordingly, the prior art has a disadvantage in that the device configuration is complicated and the manufacturing cost is increased. 
     According to the prior art, the output power value of the load or heating coil is not calculated based on the actual voltage value and the actual current input to the load or the heating coil, but the output power value is calculated based on the magnitude of the voltage and current input from the outside. Therefore, it is difficult to calculate an accurate output power value, and accordingly, it is difficult to accurately control the driving of the load or heating coil. 
     In addition, according to the prior art, the calculation of the output power value and the control of the load or heating coil may be performed based on the detected value using a hardware detection circuit such as the input voltage detection circuit or the input current detection circuit, so that it can be difficult to quickly control the load or heating coil in response to change in the output power value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Arrangements and embodiments may be described in detail with reference to the following drawings in which like reference numerals refer to like elements and wherein: 
         FIG. 1  is a block diagram illustrating the configuration of the apparatus for controlling the inverter disclosed in Cited document 1; 
         FIG. 2  is a block diagram illustrating the configuration of the inverter heating cooker (or the induction heating cooker) disclosed in Cited document 2; 
         FIG. 3  is an exploded perspective diagram illustrating an induction heating apparatus according to one embodiment of the present disclosure; 
         FIG. 4  is a circuit diagram of the induction heating apparatus according to one embodiment; 
         FIG. 5  is a graph illustrating a DC link voltage function of an inverter circuit according to one embodiment; 
         FIG. 6  is a graph illustrating a switching function of the inverter circuit according to one embodiment; 
         FIG. 7  is a graph illustrating the result of combining the DC link voltage function shown in  FIG. 5  and the switching function of the inverter circuit shown in  FIG. 6 ; 
         FIG. 8  is a flow chart illustrating a method for controlling the induction heating apparatus according to one embodiment; and 
         FIG. 9  is a flow chart illustrating a method for controlling the induction heating apparatus according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The above-described aspects, features and advantages are specifically described hereunder with reference to the accompanying drawings such that one having ordinary skill in the art to which the present disclosure pertains can easily implement the technical spirit of the disclosure. In the disclosure, detailed description of known technologies in relation to the disclosure is omitted if it is deemed to make the gist of the disclosure unnecessarily vague. Below, preferred embodiments according to the disclosure are specifically described with reference to the accompanying drawings. In the drawings, identical reference numerals can denote identical or similar components. 
       FIG. 3  is an exploded perspective diagram illustrating an induction heating apparatus according to one embodiment of the present disclosure. Referring to  FIG. 3 , an induction heating apparatus according to one embodiment of the present disclosure may include a case  102  defining a body thereof and a cover plate  104  coupled to the case  102  and sealing the case  102 . 
     The cover plate  104  may be coupled to an upper surface of the case to close the space formed in the case  102  from the outside. The cover plate  104  may include a top plate  106  on which an object to be heated (i.e., a container for cooking food) is placed. The top plate  106  may be made of a tempered glass material such as ceramic glass, but is not limited thereto. The material of the top plate  106  may vary according to embodiments. 
     Heating regions  12  and  14  (or heating areas) corresponding to working coil assemblies  122  and  124 , respectively, may be formed in the top plate  106 . Lines or figures corresponding to the heating regions  12  and  14  may be printed or displayed on the top plate  106  in order for a user to clearly recognize the positions of the heating regions  12  and  14 . 
     The case  102  may have a hexahedral shape with an open top. The working coil assembly  122  and  124  for heating a container or vessel may be disposed in the space formed inside the case  102 . In addition, an interface unit  114  (or interface) may be provided inside the case  102  and have functions to adjust a power level of each heating region  12  and  14  and display related information to the induction heating apparatus  10 . The interface unit  114  may be a touch panel that is capable of both inputting information and displaying information by touch, but the interface unit  114  having a different structure may be provided according to embodiments. 
     A manipulation region  118  may be formed in a position corresponding to the interface unit  108  in the top plate  106 . For user manipulation, characters or images may be printed on the manipulation region  118 . The user may perform a desired operation by touching a specific point of the manipulation region  118  with reference to the characters or images pre-printed on the manipulation region  118 . 
     The user may set the power level of each heating region  12  and  14  through the interface unit  114 . The power level may be indicated by a number (e.g., 1, 2, 3, . . . , 9) on the manipulation region  118 . When the power level for each heating region  12  and  14  is set, the required power value and the heating frequency of the working coil assemblies responding to the respective heating regions  12  and  14  may be determined. A controller may drive each working coil so that the actual output power value can match the required power value set by the user based on the determined heating frequency. In the space formed inside the case  102  may be further provided a power source part  112  (or power source) for supplying power to the working coil assemblies  122  and  124  or the interface unit  114 . 
     In the embodiment of  FIG. 3 , two working coil assemblies (i.e., a first working coil assembly  122  and a second working coil assembly  124 ) are disposed inside the case  102 . However, three or more working coil assemblies may be provided in the case  102  according to embodiments. 
     Each working coil assembly  122  and  124  may include a working coil configured to an induced magnetic field using a high frequency alternating current supplied by the power source part  112 , and an insulating sheet configured to protect the coil from heat generated by the container. For example, the first working coil  122  shown in  FIG. 3  may include a first working coil  132  for heating the container put in the first heating region  12  and a first insulating sheet  130 . Although not shown in the drawings, the second working coil  124  may include a second working coil and a second insulating sheet. The insulating sheet may not be provided according to embodiments. 
     A temperature sensor  134  may be provided at the center of each working coil. For example, the temperature sensor  134  may be provided in the center of the first working coil  132  as shown in  FIG. 3 . The temperature sensor may measure the temperature of the container put in each heating region. In one embodiment of the present disclosure, the temperature sensor may be a thermistor temperature sensor having a variable resistance of which a resistance value changes according to the temperature of the container, but is not limited thereto. 
     In the embodiment, the temperature sensor may output a sensing voltage corresponding to the temperature of the container, and the sensing voltage output from the temperature sensor may be transmitted to the controller. The controller may check the temperature of the container based on the magnitude of the sensing voltage output from the temperature sensor. When the temperature of the container is a preset reference value or more, the controller may perform an overheat protection operation of lowering the actual power value of the working coil or stopping the driving of the working coil. 
     Although not shown in  FIG. 3 , a circuit board on which a plurality of circuits or elements including the controller may be disposed in the space formed inside the case  102 . The controller may perform a heating operation by driving each working coil based on the user&#39;s heating start command input through the interface unit  114 . When the user inputs a heating terminating command through the interface unit  114 , the controller may stop the driving of the working coil to terminate the heating operation. 
       FIG. 4  is a circuit diagram of an induction heating apparatus according to one embodiment. Referring to  FIG. 4 , the induction heating apparatus  10  according to one embodiment may include a rectifier circuit  202 , a smoothing circuit L 1  and C 1 , an inverter circuit  204 , a working coil  132 , a controller  2  and a drive circuit  22 . Other components may also be provided, as may be discussed below. 
     The rectifier circuit  202  may include a plurality of diodes D 1 , D 2 , D 3  and D 4 . As shown in  FIG. 4 , the rectifier circuit  202  may be a bridge diode circuit and it may be another type circuit according to embodiments. The rectifier circuit  202  may be configured to rectify the AC input voltage supplied from a power source  20 , thereby outputting a voltage having a pulsating waveform. 
     The smoothing circuit L 1  and C 1  may smooth the voltage rectified by the rectifier circuit  202  and output a DC link voltage. The smoothing circuit L 1  and C 1  may include a first inductor L 1  and a DC link capacitor C 1 . 
     A voltage sensor  212  may sense a magnitude of the voltage output (or voltage value) from the DC link capacitor C 1  and transmit the sensed voltage value to the controller  2 . A current sensor  214  may sense a magnitude of the current output (or current value) from the inverter circuit  204  and transmit the sensed current value to the controller  2 . 
     When the voltage value measured by the voltage sensor  212  exceeds a first reference value or the current value measured by the current sensor  214  exceeds a second reference value, the controller  2  may perform a protection function for stopping the driving of the working coil by stopping the supply of a control signal to the drive circuit  22 . 
     The inverter circuit  204  may include a first switching element SW 1 , a second switching element SW 2 , a third switching element SW 3  and a fourth switching element SW 4 . As shown in  FIG. 4 , the inverter circuit  204  of the induction heating apparatus  10  according to one embodiment may be configured as a full-bridge circuit including four switching elements SW 1 , SW 2 , SW 3  and SW 4 . However, in another embodiment, the inverter circuit  204  may be configured as a half-bridge circuit including two switching elements (e.g., a first switching element SW 1  and a second switching element SW 2  as shown in  FIG. 4 ). 
     The first switching element SW 1 , the second switching element SW 2 , the third switching element SW 3  and the fourth switching element SW 4  may be turned on and off by a first switching signal S 1 , a second switching signal S 2 , a third switching signal S 3  and a fourth switching signal S 4 , respectively. Each of the switching elements SW 1 , SW 2 , SW 3  and SW 4  may be turned on when each of the switching signals S 1 , S 2 , S 3  and S 4  is at a high level, and each of the switching elements SW 1 , SW 2 , SW 3  and SW 4  may be turned off when each of the switching signals S 1 , S 2 , S 3  and S 4  is at a low level. 
     In the embodiment of  FIG. 4 , each of the switching elements SW 1 , SW 2 , SW 3 , and SW 4  is an IGBT element, but each of the switching elements SW 1 , SW 2 , SW 3  and SW 4  may be a different type of a switching elements (e.g., BJT or FET, etc.) according to embodiments. 
     Any of the switching elements SW 1 , SW 2 , SW 3  and SW 4  may be turned on and off to complement each other. For example, in any one of the operation modes, the second switching element SW 2  may be turned off (turned on) while the first switching element SW 1  is turned on (turned off). In the present disclosure, the switching elements that are turned on and off complementary to each other may be referred to as switching elements ‘complementary to each other’. 
     In addition, any of the switching elements SW 1 , SW 2 , SW 3  and SW 4  may be turned on and off in the same manner as each other. For example, in any of the operation modes, the first switching element SW 1  may be turned on and off at the same timing as that of the third switching element SW 3 . In the present disclosure, the switching elements that are turned on and off at the same timing may be referred to as the switching elements ‘belonging to the same group’. 
     The first switching element SW 1  and the third switching element SW 3  may be referred to as the switching elements belonging to a first group (i.e., a high side), and the second switching element SW 2  and the fourth switching element SW 4  may be referred to as the switching elements belonging to a second group (i.e., a low side). 
     If the inverter circuit  204  according to another embodiment is configured as a half-bridge circuit (i.e., a circuit including only the first switching element SW 1  and the second switching element SW 2 ), the first switching element SW 1  may belong to the first group and the second switching element SW 2  may belong to the second group. 
     The DC link voltage input to the inverter circuit  204  may be converted into the AC link voltage by the turned-on and turned-off (i.e., the switching operation) of the switching elements SW 1 , SW 2 , SW 3  and SW 4  provided in the inverter circuit  204 . The AC current converted by the inverter circuit  204  may be supplied to the working coil  132 . As a resonance phenomenon occurs in the working coil  132 , an eddy current may flow through the container (or vessel), thereby heating the container (or vessel). 
     The first switching signal S 1 , the second switching signal S 2 , the third switching signal S 3  and the fourth switching signal S 4  may be pulse width modulation (PWM) signals each having a predetermined duty cycle. 
     When the AC current output from the inverter circuit  204  is supplied to the working coil  132 , the working coil  132  may be driven. While eddy current flows through the container provided on the working coil, with the driving of the working coil  132 , the container may be heated. The amount of thermal energy supplied to the container may vary based on the amount of power actually generated by the driving of the working coil (i.e., the actual output power value of the working coil). 
     When the user changes a current state of the induction heating apparatus  10  into a power on state by manipulating the interface unit, the input power source may supply power to the induction heating apparatus  10  and the induction heating apparatus may enter a driving standby state. The user may put a container on the working coil and set a power level for the container to input a heating start command for the working coil. Once the user inputs the heating start command, a power value required for the working coil (i.e., a required power value) may be determined based on the power level set by the user. 
     The controller  2  having received the heating start command from the user may determine a frequency corresponding to the required power value of the working coil  132  (i.e., a heating frequency), and supply a control signal corresponding to the determined heating frequency to the drive circuit  22 . Accordingly, switching signals S 1 , S 2 , S 3  and S 4  may be output from the drive circuit  22 . As the switching signals S 1 , S 2 , S 3  and S 4  are input to the switching elements SW 1 , SW 2 , SW 3  and SW 4 , respectively, the working coil  132  may be driven. Once the working coil  132  is driven, an eddy current may flow through the container, and the container may be heated. 
     In an embodiment of the present disclosure, the controller  2  may determine a heating frequency corresponding to the power level set for the heating region. For example, when the user sets a power level (or power value) for the heating region, the controller  2  may gradually lower the driving frequency of the inverter circuit  204  until the output power value of the working coil  132  in a state where the driving frequency of the inverter circuit  204  is set to a predetermined reference frequency matches the required power value corresponding to the power level set by the user. The controller  2  may determine a frequency detected when the output power value of the working coil  132  matches the required power value as the heating frequency. 
     The controller  2  may supply a control signal corresponding to the determined heating frequency to the drive circuit  22 . The drive circuit  22  may output switching signals S 1 , S 2 , S 3  and S 4  having a duty ratio corresponding to the heating frequency determined by the controller  2  based on the control signal output from the controller  2 . While the switching elements SW 1 , SW 2 , SW 3  and SW 4  are turned on and off complementary to each other in response to the input of the switching signals S 1 , S 2 , S 3  and S 4 , the alternating current may be supplied to the working coil  132 . 
     In order for the controller  2  to determine the heating frequency as discussed above, the actual output power value of the working coil  132  has to be calculated during the driving of the working coil  132 . In one embodiment, the controller  2  may calculate the output power value of the working coil  132  based on the magnitude of the output voltage of the DC link capacitor C 1  measured by the voltage sensor  212  (i.e., the DC link voltage value), and the magnitude of the output current of the inverter circuit  204  measured by the current sensor  214  (i.e., the inverter based on the output current value of the inverter circuit  204 ). 
     To accurately calculate the output power value of the working coil during the driving of the working coil  132 , the magnitude of the voltage input to the working coil  132  and the magnitude of the current input to the working coil  132  may be required. 
     The magnitude of the current input to the working coil  132  may be substantially equal to the magnitude of the current output from the inverter circuit  204  (i.e., the output current value of the inverter circuit  204 ). 
     Similarly, in one embodiment, the magnitude of the voltage input to the working coil  132  may be substantially equal to the magnitude of the voltage output from the inverter circuit  204  (i.e., the output voltage value of the inverter circuit  204 ). In the embodiment, the output voltage value of the inverter circuit  204  may be calculated based on a DC link voltage function or a switching function of the inverter circuit  204 . 
       FIG. 5  is a graph illustrating a DC link voltage function of an inverter circuit according to one embodiment.  FIG. 6  is a graph illustrating a switching function of the inverter circuit according to one embodiment.  FIG. 7  is a graph illustrating the result of combining the DC link voltage function shown in  FIG. 5  and the switching function of the inverter circuit shown in  FIG. 6 . 
     In one embodiment, while the working coil  132  is being driven, the controller  2  may measure the DC link voltage value through the voltage sensor  212 . The controller  2  may calculate the DC link voltage function based on the measured DC link voltage value as shown in  FIG. 5 . 
     In one embodiment, the controller  2  may calculate the output voltage value of the inverter circuit  204  by using a predetermined switching function of the inverter circuit  204 . The switching function of the inverter circuit  204  may be a function representing a voltage level supplied from the inverter circuit  204  to the working coil  132  based on the combination of the switching signals supplied to the inverter circuit  204 . As shown in  FIG. 6 , the switching function may be predetermined during the manufacturing process of the induction heating apparatus  10  and stored in a storage. Accordingly, the controller  2  may refer to a pre-stored switching function. 
     The switching function shown in  FIG. 6  may be a function having a period (T′). The period T′ of the switching function shown in  FIG. 5  may be smaller than the period T of the DC link voltage function. The period T′ of the switching function may repeatedly appear within one period T of the DC link voltage function. 
       FIG. 7  is a graph illustrating the result of combining the DC link voltage function shown in  FIG. 5  and the switching function of the inverter circuit  204  shown in  FIG. 6 . In  FIG. 7 , V DC  represents the magnitude of the DC link voltage. Specifically, when the DC link voltage function and the switching function of the inverter circuit  204  are combined, the magnitude V DC  of the DC link voltage may be directly reflected in the waveform of the switching function of the inverter circuit  204 . 
     The result of combining the DC link voltage function and the switching function of the inverter circuit  204  may be considered to be substantially the same as the output voltage of the inverter circuit  204 . Accordingly, the controller  2  may calculate the output power value of the working coil  132  based on the output current function based on the result of combining the DC link function and the switching function of the inverter circuit  204  and the output current value of the inverter circuit  204  measured by the current sensor  214 . 
     In one embodiment, the output power value of P of the working coil  132  may be defined as [Equation 1]: 
     
       
         
           
             
               
                 
                   P 
                   = 
                   
                     
                       1 
                       T 
                     
                     ⁢ 
                     
                       
                         ∫ 
                         0 
                         T 
                       
                       
                         
                           
                             ν 
                             o 
                           
                           ( 
                           t 
                           ) 
                         
                         ⁢ 
                         
                           
                             i 
                             o 
                           
                           ( 
                           t 
                           ) 
                         
                         ⁢ 
                         d 
                         ⁢ 
                         t 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     In [Equation 1], T is the period of the DC link voltage function. In addition, V o  (t) is a function of the output voltage of the inverter circuit  204  and i o  (t) is a function of the output current of the inverter circuit  204 . 
     As discussed above, the output voltage function of the inverter circuit  204  according to one embodiment may be regarded as the combination of the DC link voltage function and the switching function of the inverter circuit  204 . Accordingly, [Equation 1] may be transformed as [Equation 2]: 
     
       
         
           
             
               
                 
                   P 
                   = 
                   
                     
                       1 
                       T 
                     
                     ⁢ 
                     
                       
                         ∫ 
                         0 
                         T 
                       
                       
                         
                           
                             v 
                             
                               D 
                               ⁢ 
                               C 
                             
                           
                           ( 
                           t 
                           ) 
                         
                         ⁢ 
                         
                           Ψ 
                           ⁡ 
                           ( 
                           t 
                           ) 
                         
                         ⁢ 
                         
                           
                             i 
                             o 
                           
                           ( 
                           t 
                           ) 
                         
                         ⁢ 
                         dt 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     In [Equation 2], V DC  (t) represents a DC link voltage function, and ψ(t) represents a switching function of the inverter circuit  204 . 
     As shown in  FIG. 5 , the period T′ of the switching function is smaller than the period T of the DC link voltage function, and the period T′ of the switching function appears repeatedly within one period T of the DC link voltage function. Accordingly, [Equation 2] can be finally transformed as [Equation 3]: 
     
       
         
           
             
               
                 
                   P 
                   = 
                   
                     
                       1 
                       N 
                     
                     ⁢ 
                     
                       
                         ∑ 
                         
                           j 
                           = 
                           1 
                         
                         N 
                       
                       
                         
                           [ 
                           
                             
                               
                                 
                                   v 
                                   
                                     D 
                                     ⁢ 
                                     C 
                                   
                                 
                                 ( 
                                 
                                   t 
                                   j 
                                 
                                 ) 
                               
                               
                                 T 
                                 ′ 
                               
                             
                             ⁢ 
                             
                               
                                 ∫ 
                                 
                                   t 
                                   
                                     j 
                                     - 
                                     1 
                                   
                                 
                                 
                                   t 
                                   j 
                                 
                               
                               
                                 
                                   Ψ 
                                   ⁡ 
                                   ( 
                                   τ 
                                   ) 
                                 
                                 ⁢ 
                                 
                                   
                                     i 
                                     o 
                                   
                                   ( 
                                   τ 
                                   ) 
                                 
                                 ⁢ 
                                 dτ 
                               
                             
                           
                           ] 
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     In [Equation 3], V DC  (t j ) is a DC link voltage function, ψ(T) is a switching function of the inverter circuit  204 , and Io (T) is an output current function of the inverter circuit  204 . T′ is the period of the switching function, and N is the value obtained by driving the period T of the DC link voltage function by the period T′ of the switching function. 
     According to [Equation 3], the output power value of the working coil  132  may be defined as an integral value of the output voltage function of the inverter circuit calculated based on the DC link voltage value and the output current function of the inverter circuit. 
     Accordingly, the controller  2  may calculate the output voltage value of the working coil  2  in real time and in software based on [Equation 3]. The output voltage value of the working coil  132  during the driving of the working coil  132  may be calculated quickly and accurately. Since the output voltage value of the working coil  132  is calculated quickly and accurately, the heating operation of the working coil  132  may be controlled more precisely. The control response to the change in the output voltage value of the working coil  132  may be accelerated, so that the control speed of the induction heating apparatus may be improved. 
       FIG. 8  is a flow chart illustrating a method for controlling the induction heating apparatus according to one embodiment of the present disclosure. Referring to  FIG. 8 , the controller  2  may receive a power level (or power value) for the heating region (or heating area) input through the interface unit  114  ( 402 ). Once the power level for the heating region is input, a required power value corresponding to the input power level may be determined. 
     When the power level is input, the controller  2  may supply a control signal to the drive circuit  22  based on a preset reference frequency (e.g., 60 kHz) and then supply a switching signal to the inverter circuit  204  ( 404 ). Accordingly, the working coil  132  may start to output power corresponding to the reference frequency. 
     While the working coil  132  is being driven, the controller  2  may measure the output current value of the inverter circuit  204  through the current sensor  214  ( 406 ). The controller  2  may calculate an output current function of the inverter circuit  204  based on the measured output current value of the inverter circuit  204 . 
     Additionally, while the working coil  132  is being driven, the controller  2  may measure a DC link voltage value through the voltage sensor  212  ( 408 ). The controller may calculate a DC link voltage function based on the measured DC link voltage value. 
     The controller  2  may calculate the output power value of the working coil  132  based on the output current value of the inverter circuit  204  and the DC link voltage value ( 410 ). 
     In one embodiment, the output power value of the working coil  132  may be defined as an integral value of the output voltage function of the inverter circuit calculated based on the DC link voltage value and the output current function of the inverter circuit. Additionally, the output voltage function of the inverter circuit  204  may be calculated by combining the DC link voltage function and the switching function of the inverter circuit. 
     In one embodiment, the controller  2  may calculate the output power value of the working coil  132  based on [Equation 3]. 
     The controller  2  may compare the calculated output power value with the required power value, and determine the heating frequency of the inverter circuit  204  based on the result of the comparison ( 412 ). 
     The determining of the heating frequency ( 412 ) may include adjusting the driving frequency of the inverter circuit  204  until the output power value of the working coil  132  matches the required power value, and determining the driving frequency of the inverter circuit  204  when the output power value of the working coil  132  matches the required power value as the heating frequency. 
     When the heating frequency is determined, the controller  2  may supply a control signal to the drive circuit  22  based on the heating frequency and supply a switching signal to the inverter circuit  204  ( 414 ). Accordingly, the working coil  132  may output power corresponding to the power level, thereby heating the container. 
       FIG. 9  is a flow chart illustrating a method for controlling the induction heating apparatus according to another embodiment of the present disclosure. Referring to  FIG. 9 , the controller  2  may receive a power level (or power value) for the heating region input through the interface unit  114  ( 602 ). Once the power level for the heating region is input, a required power value corresponding to the input power level may be determined. 
     When the power level is input, the controller  2  may set the driving frequency of the inverter circuit  204  to be a preset reference frequency (e.g., 60 kHz) ( 604 ). The size of the reference frequency may vary according to embodiments. 
     The controller  2  may supply a control signal to the drive circuit  22  based on the preset reference frequency and then supply a switching signal to the inverter circuit  204  ( 606 ). Accordingly, the working coil  132  may start to output power corresponding to the reference frequency. 
     While the working coil  132  is being driven, the controller  2  may measure the output current value of the inverter circuit  204  through the current sensor  214  ( 608 ). The controller  2  may calculate an output current function of the inverter circuit  204  based on the measured output current value of the inverter circuit  204 . 
     Additionally, while the working coil  132  is being driven, the controller  2  may measure a DC link voltage value through the voltage sensor  212  ( 610 ). The controller may calculate a DC link voltage function based on the measured DC link voltage value. 
     The controller  2  may calculate the output power value of the working coil  132  based on the output current value of the inverter circuit  204  and the DC link voltage value ( 612 ). 
     In the embodiment, the output power value of the working coil  132  may be defined as an integral value of the output voltage function of the inverter circuit calculated based on the DC link voltage value and the output current function of the inverter circuit. In addition, the output voltage function of the inverter circuit  204  may be calculated by combining the DC link voltage function and the switching function of the inverter circuit. 
     In one embodiment, the controller  2  may calculate the output power value of the working coil  132  based on [Equation 3]. 
     The controller  2  may compare the calculated output power value with the required power value, and determine the heating frequency of the inverter circuit  204  based on the result of the comparison ( 614 ). 
     Unless the output power value matches (or equals) the required power value in the process or operation ( 614 ), the controller  2  may reduce the driving frequency of the inverter circuit  204  by a predetermined unit size (e.g., 1 kHz) ( 616 ), and return to the process or operation ( 606 ). Accordingly, the driving frequency of the inverter circuit  204  may be reduced until the output power value matches the required power value. 
     When the output power value matches the required power value in the process or operation ( 614 ), the controller may determine the current driving frequency of the inverter circuit  204  as the heating frequency ( 618 ) and set the driving frequency of the inverter circuit  204  as the heating frequency ( 620 ). 
     Once determining the heating frequency, the controller may supply switching signals to the inverter circuit  204  by supplying the control signals to the drive circuit  22  based on the heating frequency ( 622 ). Accordingly, the working coil  132  may heat the container by outputting power corresponding to the power level. 
     An object of the present disclosure is to provide an induction heating apparatus that may calculate the output power value of a working coil and the driving of the working coil only with existing elements or circuits, without additional elements or circuits (e.g., a shunt resistor, an input voltage detection circuit and an input current detection circuit), and a method for controlling the induction heating apparatus. 
     An object of the present disclosure is to provide an induction heating apparatus that may calculate a more accurate output power value based on the actual voltage value and an actual current value to the working coil and control accurate driving of the working coil, and a method for controlling the induction heating apparatus. 
     An object of the present disclosure is to provide an induction apparatus that may improve control speed and responsiveness to changes in the output power value by calculating the output power value of the working coil by using software. 
     Aspects according to the present disclosure are not limited to the above ones, and other aspects and advantages that are not mentioned above can be clearly understood from the following description and can be more clearly understood from the embodiments set forth herein. 
     In embodiments of the present disclosure, an output power value of a working coil may be calculated based on an output voltage of an inverter circuit and an output current. The output voltage of the inverter circuit may be calculated based on a DC link voltage function of the inverter circuit and a switching function of the inverter circuit. 
     In embodiments, the output power value of the working coil may be an integral value of the output voltage function of the inverter circuit calculated based on the DC link voltage value and the output current function of the inverter circuit. 
     Embodiments of the present disclosure may provide a method for controlling an induction heating apparatus including steps of: receiving a power level for a heating region; supplying a switching signal to an inverter circuit based on a predetermined reference frequency; measuring an output current value of the inverter circuit; measuring a DC link voltage value; calculating an output power value of the working coil based on the output current value of the inverter circuit and the DC link voltage value; determining a heating frequency of the inverter circuit based the result of comparison by comparing the output power value of the working coil with a required power value; and supplying a switching signal to the inverter circuit based on the heating frequency. 
     The output power value of the working coil may be an integral value of the output voltage function of the inverter circuit calculated based on the DC link voltage value and the output current function of the inverter circuit. 
     The output voltage function of the inverter circuit may be calculated by combining the DC link voltage function and the switching function of the inverter circuit. 
     The DC link voltage may be obtained by rectifying an AC voltage supplied by an external power source and smoothing the rectified voltage. 
     The output power value of the working coil may be calculated based on the following [Equation 4]: 
     
       
         
           
             
               
                 
                   P 
                   = 
                   
                     
                       1 
                       N 
                     
                     ⁢ 
                     
                       
                         ∑ 
                         
                           j 
                           = 
                           1 
                         
                         N 
                       
                       
                         [ 
                         
                           
                             
                               
                                 v 
                                 
                                   D 
                                   ⁢ 
                                   C 
                                 
                               
                               ( 
                               
                                 t 
                                 j 
                               
                               ) 
                             
                             
                               T 
                               ′ 
                             
                           
                           ⁢ 
                           
                             
                               ∫ 
                               
                                 t 
                                 
                                   j 
                                   - 
                                   1 
                                 
                               
                               
                                 t 
                                 j 
                               
                             
                             
                               
                                 Ψ 
                                 ⁡ 
                                 ( 
                                 τ 
                                 ) 
                               
                               ⁢ 
                               
                                 
                                   i 
                                   o 
                                 
                                 ( 
                                 τ 
                                 ) 
                               
                               ⁢ 
                               d 
                               ⁢ 
                               τ 
                             
                           
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     In the [Equation 4], VDC (tj) is a DC link voltage function, and ψ(T) is a switching function of the inverter circuit, and io (T) is an output current function of the inverter circuit, and T′ is a period of the switching function, and N is the value obtained by driving the period of the DC link voltage function by the period T′ of the switching function, and P is the output power value of the working coil. 
     The step of determining the heating frequency of the inverter circuit based the result of comparison by comparing the output power value of the working coil with a required power value may include steps of adjusting a driving frequency of the inverter circuit until the output power value of the working coil matches the required power value; and determining the driving frequency of the inverter circuit, when the output power value of the working coil matches the required power value, as the heating frequency. 
     Embodiments of the present disclosure may also provide an induction heating apparatus including a working coil provided in a position corresponding to a heating region; an inverter circuit comprising a plurality of switching elements and configured to supply current to the working coil; a drive circuit configured to supply switching signals to the switching elements provided in the inverter circuit, respectively, and a controller configured to determine a driving frequency of the inverter circuit and drive the working coil by supplying a control signal to the drive circuit based on the driving frequency. The controller may be configured to perform a method according to any one of the herein described embodiments. 
     The controller may receive a power level for a heating region, supplies a switching signal to an inverter circuit based on a predetermined reference frequency, measures an output current value of the inverter circuit, measure a DC link voltage value, calculate an output power value of the working coil based on the output current value of the inverter circuit and the DC link voltage value, determine a heating frequency of the inverter circuit based the result of comparison by comparing the output power value of the working coil with a required power value, and supplies a switching signal to the inverter circuit based on the heating frequency. 
     The output power value of the working coil may be an integral value of the output voltage function of the inverter circuit calculated, e.g. by the controller, based on the DC link voltage value and the output current function of the inverter circuit. The output voltage function and/or the output current function of the inverter circuit may be stored and/or predetermined for the inverter circuit. 
     The DC link voltage may be obtained by rectifying an AC voltage supplied by an external power source and smoothing the rectified voltage. 
     The output voltage function of the inverter circuit may be calculated by combining the DC link voltage function and the switching function of the inverter circuit. 
     The output power value of the working coil may be calculated based on the following [Equation 5]: 
     
       
         
           
             
               
                 
                   P 
                   = 
                   
                     
                       1 
                       N 
                     
                     ⁢ 
                     
                       
                         ∑ 
                         
                           j 
                           = 
                           1 
                         
                         N 
                       
                       
                         [ 
                         
                           
                             
                               
                                 v 
                                 
                                   D 
                                   ⁢ 
                                   C 
                                 
                               
                               ( 
                               
                                 t 
                                 j 
                               
                               ) 
                             
                             
                               T 
                               ′ 
                             
                           
                           ⁢ 
                           
                             
                               ∫ 
                               
                                 t 
                                 
                                   j 
                                   - 
                                   1 
                                 
                               
                               
                                 t 
                                 j 
                               
                             
                             
                               
                                 Ψ 
                                 ⁡ 
                                 ( 
                                 τ 
                                 ) 
                               
                               ⁢ 
                               
                                 
                                   i 
                                   o 
                                 
                                 ( 
                                 τ 
                                 ) 
                               
                               ⁢ 
                               d 
                               ⁢ 
                               τ 
                             
                           
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     5 
                   
                   ] 
                 
               
             
           
         
       
     
     In the [Equation 5], VDC (tj) is a DC link voltage function, and ψ(T) is a switching function of the inverter circuit, and io (T) is an output current function of the inverter circuit, and T′ is a period of the switching function, and N is the value obtained by driving the period of the DC link voltage function by the period T′ of the switching function, and P is the output power value of the working coil. 
     The controller may adjust a driving frequency of the inverter circuit until the output power value of the working coil matches the required power value, and determine the driving frequency of the inverter circuit, when the output power value of the working coil matches the required power value, as the heating frequency. 
     According to an embodiment of the present disclosure, there is an advantage in that the output power value calculation and driving control of the working coil are possible only with the existing elements or circuits without additional elements or circuits (e.g., shunt resistors, input voltage sensing circuits, input current sensing circuits). 
     According to an embodiment of the present disclosure, there is an advantage in that a more accurate output power value is calculated based on the actual voltage value and the actual current value input to the working coil, and thus accurate driving control of the working coil is possible. 
     According to an embodiment of the present disclosure, there is an advantage in that the control speed of the induction heating device and the responsiveness to changes in the output power value are improved by calculating the output power value of the working coil by using software. 
     The embodiments are described above with reference to a number of illustrative embodiments thereof. However, the present disclosure is not intended to limit the embodiments and drawings set forth herein, and numerous other modifications and embodiments can be devised by one skilled in the art. Further, the effects and predictable effects based on the configurations in the disclosure are to be included within the range of the disclosure though not explicitly described in the description of the embodiments. 
     It will be understood that when an element or layer is referred to as being “on” another element or layer, the element or layer can be directly on another element or layer or intervening elements or layers. In contrast, when an element is referred to as being “directly on” another element or layer, there are no intervening elements or layers present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
     Spatially relative terms, such as “lower”, “upper” and the like, may be used herein for ease of description to describe the relationship of one element or feature to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “lower” relative to other elements or features would then be oriented “upper” relative to the other elements or features. Thus, the exemplary term “lower” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Embodiments are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.