Patent Description:
Various types of cooking apparatuses are used to heat food at homes or restaurants. Conventionally, gas stoves fueled by gas have been widely used. However, in recent years, apparatuses for heating a cooking vessel using electricity are used.

Methods for heating a vessel using electricity are broadly classified as a resistance heating method and an induction heating method. The resistance heating method is a method by which a vessel is heated by thermal energy that is generated when electric energy is supplied to a metallic resistance wire, or a non-metallic heating element such as silicon carbide. The induction heating method is a method by which a metallic vessel itself is heated by eddy currents that are generated in the vessel, using a magnetic field that is generated around a working coil when electric energy is supplied to the working coil.

A theory about the induction heating method is specifically described as follows. As power is supplied to an induction heating device, a high-frequency voltage having predetermined magnitude is supplied to a working coil. Accordingly, an induction field is produced around the working coil in the induction heating device. When a magnetic line of force of the produced induction field passes through a bottom of a metallic vessel placed on an upper portion of the working coil, eddy currents are generated at an inside of the bottom of the vessel. As the generated eddy currents flow through the vessel, the vessel itself is heated.

The induction heating device may include two or more heating areas, and two or more working coils corresponding to the heating areas. For example, when a user places a vessel respectively in two heating areas and cooks a load of food in the vessels at the same time, using an induction heating device with two heating areas, power for driving is supplied respectively to two working coils. Each working coil is driven at a driving frequency corresponding to a required power value set by the user.

<FIG> is a graph showing a relationship between a driving frequency of a working coil and an output power value of the same.

The driving frequency of the working coil, as illustrated in <FIG>, is inversely proportional to an output power value of the working coil. For example, when the driving frequency of the working coil increases from fa to fb, the output power value of the working coil decreases from Pa to Pb. That is, an increase in the driving frequency of the working coil results in a decrease in the output power value of the working coil. Accordingly, an amount of thermal energy due to eddy currents generated in a vessel is reduced.

In the case of an absolute value of a difference between driving frequencies of two working coils is included in a range of audio frequencies (e.g., <NUM> to <NUM>) when the two working coils are driven at the same time, interference noise caused by the driving of the working coils may occur. The interference noise causes inconvenience to a user and may cause the user to think that a failure of the induction heating device has occurred.

To remove interference noise caused by the driving of two or more working coils, the driving frequencies of the working coils may be adjusted such that an absolute value of a difference between the driving frequencies of the working coils is out of a range of audio frequencies. For example, according to <CIT>, switching elements respectively connected to a plurality of working coils in an induction heating device are consecutively turned on/off on the basis of time division, and thus even when the plurality of working coils are driven simultaneously, interference noise is prevented.

<FIG> is a graph showing a change in output power values when a driving frequency of a working coil is adjusted to reduce interference noise generated at the time of driving of two working coils.

In the embodiment of <FIG>, a driving frequency of a first working coil, which corresponds to P1 - a required power value of the first working coil, is f1, a driving frequency of a second working coil, which corresponds to P2 - a required power value of the second working coil, is f2, and an absolute value of a difference between f1 and f2 is included in a range of audio frequencies (e.g., <NUM> to <NUM>). Accordingly, when the first working coil and the second working coil are driven at the same time, interference noise may occur.

To remove the interference noise, the driving frequency of the second working coil may be adjusted from f2 to f3. When the driving frequency of the second working coil increases to f3, an absolute value of a difference between f1and f3 is out of the range of audio frequencies. Accordingly, interference noise does not occur.

However, the increase in the driving frequency of the second working coil to f3 leads to a decrease in an output power value of the second working coil from P2 to P3, and an amount of thermal energy generated in a vessel by the second working coil is reduced. Thus, cooking time is lengthened, causing inconvenience to a user and may cause the user to think that the induction heating device is not operating correctly.

Documents <CIT>, <CIT> or <CIT> disclose controlling methods for avoiding inter-modulation noise in an induction heating device having at least two coils.

The present disclosure is directed to an induction heating device and a method for controlling the same that may help solve a problem associated with a reduction in an output power value of a working coil when a driving frequency of the working coil is adjusted to remove interference noise.

Aspects of the present disclosure are not limited to the above-described ones. Additionally, other aspects and advantages that have not been mentioned may be clearly understood from the following description and may be more clearly understood from embodiments. Further, it will be understood that the aspects and advantages of the present disclosure may be realized via means and combinations thereof that are described in the appended claims.

A method for controlling an induction heating device according to one embodiment may include acquiring a temperature value of a high-power working coil, when an absolute value of a difference between a first final driving frequency of a first working coil and a second final driving frequency of a second working coil is equal to or greater than a predetermined noise avoidance value and when a final driving frequency of a low-power working coil differs from a target frequency of the low-power working coil, determining whether the temperature value satisfies a predetermined output change condition, setting a required power value of the high-power working coil to a predetermined minimum power value when the temperature value satisfies the output change condition, and determining the first final driving frequency of the first working coil and the second final driving frequency of the second working coil again.

In one embodiment, the output change condition is satisfied when the temperature value is equal to or greater than a predetermined reference temperature value.

In one embodiment, the output change condition is satisfied when the temperature value is maintained within a range of predetermined reference temperatures for a predetermined reference period.

In one embodiment, the method may further include determining a first target frequency of the first working coil based on a required power value of the first working coil, determining a second target frequency of the second working coil based on a required power value of the second working coil, calculating an absolute value of a difference between the first target frequency and the second target frequency, and determining a driving mode of the induction heating device based on the absolute value of the difference between the first target frequency and the second target frequency.

In one embodiment, the step of determining a driving mode based on the absolute value of the difference between the first target frequency and the second target frequency may include determining the driving mode as a coupling mode when the absolute value of the difference between the first target frequency and the second target frequency is equal to or greater than a predetermined first reference value and less than a predetermined second reference value, determining the driving mode as a dividing mode when the absolute value of the difference between the first target frequency and the second target frequency is equal to or greater than the second reference value and is less than or equal to a predetermined third reference value, and determining the driving mode as a normal mode when the absolute value of the difference between the first target frequency and the second target frequency is less than the first reference value or greater than the third reference value.

In one embodiment, when the driving mode is the coupling mode, the first final driving frequency and the second final driving frequency may be set to the same value, when the driving mode is the dividing mode, a difference between the first final driving frequency and the second final driving frequency may be set to equal to or greater than the noise avoidance value, and when the driving mode is the normal mode, the first final driving frequency is set equal to the first target frequency, and the second final driving frequency is set equal to the second target frequency.

In one embodiment, the method may further include driving the first working coil and the second working coil at a predetermined adjusted frequency, and adjusting a driving frequency of the first working coil to the first final driving frequency and adjusting a driving frequency of the second working coil to the second final driving frequency.

An induction heating device according to one embodiment may include a first working coil corresponding to a first heating area, a second working coil corresponding to a second heating area, and a controller configured to respectively drive the first working coil and the second working coil according to an instruction to drive the first working coil and an instruction to drive the second working coil. The controller may acquire a temperature value of a high-power working coil when an absolute value of a difference between a first final driving frequency of the first working coil and a second final driving frequency of the second working coil is equal to or greater than a predetermined noise avoidance value and a final driving frequency of a low-power working coil differs from a target frequency of the low-power working coil, may determine whether the temperature value satisfies a predetermined output change condition, may set a required power value of the high-power working coil to a predetermined minimum power value when the temperature value satisfies the output change condition, and may determine a first final driving frequency of the first working coil and a second final driving frequency of the second working coil again.

In one embodiment, the controller may determine a first target frequency of the first working coil, based on a required power value of the first working coil, may determine a second target frequency of the second working coil, based on a required power value of the second working coil, may calculate an absolute value of a difference between the first target frequency and the second target frequency, and may determine a driving mode of the induction heating device, based on the absolute value of the difference between the first target frequency and the second target frequency.

In one embodiment, the controller may determine the driving mode as a coupling mode when the absolute value of the difference between the first target frequency and the second target frequency is equal to or greater than a predetermined first reference value and less than a predetermined second reference value, may determine the driving mode as a dividing mode when the absolute value of the difference between the first target frequency and the second target frequency is equal to or greater than the second reference value and is less than or equal to a predetermined third reference value, and may determine the driving mode as a normal mode when the absolute value of the difference between the first target frequency and the second target frequency is less than the first reference value or greater than the third reference value.

In one embodiment, when the driving mode is the coupling mode, the first final driving frequency and the second final driving frequency may be set to the same value, when the driving mode is the dividing mode, a difference between the first final driving frequency and the second final driving frequency may be set equal to or greater than the noise avoidance value, and when the driving mode is the normal mode, the first final driving frequency may be set equal to the first target frequency and the second final driving frequency may be set equal to the second target frequency.

In one embodiment, the controller may drive the first working coil and the second working coil at a predetermined adjusted frequency, and may respectively adjust driving frequencies of the first working coil and the second working coil to the first final driving frequency and the second final driving frequency.

According to the present disclosure, a problem associated with a reduction in an output power value of a working coil may be solved when a driving frequency of the working coil is adjusted to remove interference noise during the driving of an induction heating device.

The accompanying drawings constitute a part of this specification, illustrate one or more embodiments of the present disclosure, and together with the specification, explain the present disclosure, wherein:.

The above-described aspects, features and advantages are specifically described with reference to the accompanying drawings hereunder such that one having ordinary skill in the art to which the present disclosure pertains may easily implement the technical spirit of the disclosure. During description 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 present disclosure unnecessarily vague. Below, preferred embodiments according to the disclosure are described with reference to the accompanying drawings. Throughout the drawings, identical reference numerals may denote identical or similar components.

<FIG> is a perspective view of an exemplary induction heating device.

Referring to <FIG>, the exemplary induction heating device <NUM> may include a case <NUM> forming an exterior of the induction heating device <NUM>, and a cover plate <NUM> coupled to the case <NUM> and configured to seal the case <NUM>.

The cover plate <NUM> having less surface than an upper plate <NUM> may be coupled to an upper surface of the case <NUM> to seal a space formed in the case <NUM> from the outside. The upper plate <NUM>, on which an object to be heated - i.e. a vessel for cooking food - is placed, may be formed on the upper surface of the cover plate <NUM>. The upper plate <NUM> may be made of a variety of materials, e.g. tempered glass such as ceramic glass.

Working coils <NUM>, <NUM>, 106a, 106b for heating a vessel may be disposed in the case <NUM>'s inner space formed by the coupled cover plate <NUM> and case <NUM>. Specifically, a first working coil <NUM>, a second working coil <NUM>, and a third working coil 106a, 106b may be disposed in the case <NUM>.

Conductive wire, made of a conductive material such as copper, may be wound many times to respectively manufacture the first working coil <NUM>, the second working coil <NUM> and the third working coil 106a, 106b. In <FIG>, the first working coil <NUM> and the second working coil <NUM> may have a rectangular shape with its edges curved, and the third working coil 106a, 106b may have a circular shape. However, the shape of each of the working coils may vary depending on embodiments.

Additionally, the number and disposition of working coils in the induction heating device <NUM> may vary depending on embodiments.

In one embodiment, the third working coil 106a, 106b may include two working coils - i.e. an inner coil 106a and an outer coil 106b. <FIG> shows the third working coil 106a, 106b including two coils. However, the number of coils constituting the third working coil, and the number of coils constituting the inner coil and the outer coil may vary depending on embodiments.

As an example, the third working coil may include four coils. In this case, two coils disposed at an inner side of the third working coil may be defined as an inner coil and the remaining two coils disposed at an outer side of the third working coil may be defined as an outer coil. As another example, three coils disposed at the inner side of the third working coil may be defined as an inner coil, and the remaining coil disposed at the outer side of the third working coil may be defined as an outer coil.

Additionally, a first heating area <NUM>, a second heating area <NUM>, and a third heating area <NUM> may be respectively displayed on a surface of the upper plate <NUM> of the cover plate <NUM>. Positions of the first heating area <NUM>, the second heating area <NUM> and the third heating area <NUM> may respectively correspond to those of the first working coil <NUM>, the second working coil <NUM> and the third working coil 106a, 106b.

Further, an interface <NUM> allowing a user to supply power or to adjust output of the working coils <NUM>, <NUM>, 106a, 106b, or configured to display information on the induction heating device <NUM> may be disposed in the inner space of the case <NUM>. In one embodiment, the interface <NUM> according to the present disclosure may be implemented as a touch panel capable of inputting and displaying information as a result of a touch. Description of the interface <NUM> is provided hereunder. However, the interface <NUM> may be implemented in different forms and structures depending on embodiments.

Furthermore, a manipulation area <NUM>, disposed at a position corresponding to that of the interface <NUM>, may be formed on the upper plate <NUM> of the cover plate <NUM>. In the manipulation area <NUM>, a specific character, a specific image and the like for the user's manipulation or a display of information may be displayed. The user may perform a desired manipulation by manipulating (e.g. touching) a specific point of the manipulation area <NUM> considering a character or an image displayed in the manipulation area <NUM>. For example, to input an instruction for driving a working coil corresponding to a heating area, the user may set a heating level of a vessel placed on at least one of the first heating area <NUM>, the second heating area <NUM> and the third heating area <NUM> by touching the manipulation area <NUM>. Additionally, as a result of the user's manipulation or operation of the induction heating device <NUM>, various pieces of information outputted by the interface <NUM> may be displayed through the manipulation area <NUM>.

Further, a power supply circuit (not illustrated) for supplying power to the working coils <NUM>, <NUM>, 106a, 106b or the interface <NUM> may be disposed in the inner space of the case <NUM>. The power supply circuit may electrically connect to the working coils <NUM>, <NUM>, 106a, 106b or the interface <NUM>, and may convert power, supplied by an external power supply, into power appropriate for driving of the working coils <NUM>, <NUM>, 106a, 106b or the interface <NUM> and may supply the converted power to the same.

<FIG> shows an embodiment in which three working coils <NUM>, <NUM>, 106a, 106b are disposed in the inner space of the case <NUM>. In another embodiment, a single working coil or four or more working coils may be disposed in the inner space of the case <NUM>.

Though not illustrated in <FIG>, a controller (not illustrated) may be disposed in the inner space of the case <NUM>. The controller (not illustrated) may control driving of the working coils <NUM>, <NUM>, 106a, 106b on the basis of the user's instruction for heating (e.g. an instruction to start driving, an instruction to end driving, an instruction to adjust a heating level and the like) inputted through the interface <NUM>.

After placing a vessel in a desired heating area among the first heating area <NUM>, the second heating area <NUM> and the third heating area <NUM>, the user may give an instruction for heating and for setting a heating level of the heating area, in which the vessel is placed, through the manipulation area <NUM>.

The user's instruction for heating, inputted through the manipulation area <NUM>, may be inputted to the controller (not illustrated) as an instruction for driving a working coil corresponding to the heating area in which the user places the vessel. The controller (not illustrated), having received the instruction for driving, may drive the working coil subject to the instruction for driving to heat the vessel.

<FIG> is a circuit diagram of an exemplary induction heating device.

<FIG> shows a circuit diagram in the case of an exemplary induction heating device provided with two working coils - i.e. the first working coil <NUM> and the second working coil <NUM>. However, the exemplary induction heating device, as described above, may be provided with two or more working coils, and a below-described method for controlling an induction heating device may also be applied to an induction heating device provided with two or more working coils.

Referring to <FIG>, the exemplary induction heating device may include two heating modules, i.e., a first heating module <NUM> and a second heating module <NUM>. The first heating module <NUM> and the second heating module <NUM> may convert AC power supplied by an external power supply <NUM> and may supply power for driving to each of the first working coil <NUM> and the second working coil <NUM>.

The first heating module <NUM> may include a rectifier <NUM> and a smoother <NUM>. The rectifier <NUM> may rectify an AC voltage, supplied by the external power supply <NUM>, and may output a rectified voltage. The smoother <NUM> may include a first inductor (L1) and a first capacitor (C1), and may convert the rectified voltage, outputted from the rectifier <NUM>, into a DC voltage, and may output the DC voltage.

The second heating module <NUM> may include a rectifier <NUM> and a smoother <NUM>. The rectifier <NUM> may rectify an AC voltage, supplied by the external power supply <NUM>, and may output a rectified voltage. The smoother <NUM> may include a second inductor (L2) and a fourth capacitor (C4), and may convert the rectified voltage, outputted from the rectifier <NUM>, into a DC voltage, and may output the DC voltage.

Additionally, the first heating module <NUM> may include a plurality of switching elements (SW1 and SW2) and a plurality of capacitors (C2 and C3).

A first switching element (SW1) and a second switching element (SW2) may connect to each other in series and may be turned on and turned off alternatively according to a first switching signal (S1) and a second switching signal (S2) outputted from a first driver <NUM>. In the present disclosure, the turn-on and the turn-off operations of the switching elements are referred to as a "switching operation".

A second capacitor (C2) and a third capacitor (C3) may connect to each other in series. The first switching element (SW1) and the second switching element (SW2) may connect to the second capacitor (C2) and the third capacitor (C3) in parallel.

The first working coil <NUM> may connect between a point, at which the first switching element (SW1) and the second switching element (SW2) connect, and a point, at which the second capacitor (C2) and the third capacitor (C3) connect. When the first switching signal (S1) and the second switching signal (S2) are respectively supplied to the first switching element (SW1) and the second switching element (SW2), and the first switching element (SW1) and the second switching element (SW2) perform switching operations, alternating current may be supplied to the first working coil <NUM>, and a vessel may be inductively heated.

Further, the second heating module <NUM> may include a plurality of switching elements (SW3 and SW4) and a plurality of capacitors (C5 and C6).

A third switching element (SW3) and a fourth switching element (SW4) may connect to each other in series, and may be alternatively turned on and turned off according to a third switching signal (S3) and a fourth switching signal (S4) outputted from a second driver <NUM>.

A fifth capacitor (C5) and a sixth capacitor (C6) may connect to each other in series. The third switching element (SW3) and the fourth switching element (SW4) may connect to the fifth capacitor (C5) and the sixth capacitor (C6) in parallel.

The second working coil <NUM> may connect between a point, at which the third switching element (SW3) and the fourth switching element (SW4) connect, and a point, at which the fifth capacitor (C5) and the sixth capacitor (C6) connect. When the third switching signal (S3) and the fourth switching signal (S4) are respectively supplied to the third switching element (SW3) and the fourth switching element (SW4), and the third switching element (SW3) and the fourth switching element (SW4) perform switching operations, alternating current may be supplied to the second working coil <NUM>, and a vessel may be inductively heated.

The first driver <NUM> may supply the first switching signal (S1) and the second switching signal (S2) respectively to the first switching element (SW1) and the second switching element (SW2) that are included in the first heating module <NUM>. Additionally, the second driver <NUM> may supply the third switching signal (S3) and the fourth switching signal (S4) respectively to the third switching element (SW3) and the fourth switching element (SW4) that are included in the second heating module <NUM>. In one embodiment, the first switching signal (S1), the second switching signal (S2), the third switching signal (S3) and the fourth switching signal (S4) may be respectively a pulse width modulation (PWM) signal. A duty ratio of the first switching signal (S1) and the second switching signal (S2) may be determined based on a driving frequency of the first working coil <NUM>, and a duty ratio of the third switching signal (S3) and the fourth switching signal (S4) may be determined based on a driving frequency of the second working coil <NUM>.

The controller <NUM> may determine a driving frequency of the first working coil <NUM> and a driving frequency of the second working coil <NUM>, and may output control signals corresponding to the determined driving frequencies. The controller <NUM> may be an electronic processor. The controller <NUM> may supply a control signal to each of the first driver <NUM> and the second driver <NUM> independently. Magnitude of power, i.e., an output power value, output by the first working coil <NUM> or the second working coil <NUM>, may vary as a result of the controller <NUM>'s adjustment of the driving frequencies.

Voltage sensors <NUM>, <NUM> may measure a magnitude of a voltage input to the heating modules <NUM>, <NUM>, i.e., a magnitude of an input voltage. Current sensors <NUM>, <NUM> may measure a magnitude of electric current input to the first working coil <NUM> and the second working coil <NUM>, i.e., a magnitude of input current.

The controller <NUM> may receive the magnitude of an input voltage from the voltage sensors <NUM>, <NUM> and may receive the magnitude of input current from the current sensors <NUM>, <NUM>. The controller <NUM> may calculate output power values of the first working coil <NUM> and the second working coil <NUM>, i.e., a power value supplied to a vessel by the first working coil <NUM> and the second working coil <NUM>, using the received magnitude of the input voltage and input current. When the first working coil <NUM> and the second working coil <NUM> are driven, the controller <NUM> may calculate an output power value of each working coil in real time using various well-known methods.

Though not illustrated in <FIG>, a temperature sensor may be disposed on one side of each of the first working coil <NUM> and the second working coil <NUM>. The temperature sensor may measure a temperature in real time respectively at the first working coil <NUM> and the second working coil <NUM>, and may deliver the measured temperature values to the controller <NUM>.

After placing a vessel in a desired heating area, the user may set a heating level of the heating area, in which the vessel is placed, through the manipulation area <NUM>, and may give an instruction to heat the vessel. The user's instruction for heating inputted through the manipulation area <NUM> may be inputted to the controller <NUM> as an instruction to drive a working coil corresponding to the heating area in which the vessel is placed. The controller <NUM>, having received the instruction for driving, may drive the working coil subject to the instruction for driving, to heat the vessel.

In the case of a single working coil being driven, the above- described interference noise may not occur. However, in the case the where the user inputs an instruction to drive another working coil in the state where a single working coil is being driven, the interference noise may be made depending on the magnitude of a driving frequency of each working coil.

The controller <NUM> of the induction heating device according to the present disclosure may determine a target frequency of each working coil and may control a frequency to reduce interference noise on the basis of the determined target frequency of each working coil, in the case where the user inputs an instruction to drive another working coil in the state where a single working coil is being driven.

The target frequency of each working coil may denote a driving frequency of each working coil when an output power value of each working coil reaches a power value corresponding to a heating level set by the user, i.e., a required power value. For example, when the user sets a heating level of the first heating area to <NUM>, a required power value of the first working coil <NUM> corresponding to the first heating area may be <NUM> W. When the first working coil <NUM> is driven and outputs a power value of <NUM> W, a driving frequency (e.g. <NUM>) of the first working coil <NUM> may be defined as a target frequency of the first working coil <NUM>.

The controller <NUM> of the induction heating device according to the present disclosure may determine a second target frequency of the second working coil <NUM> in the case where driving of the second working coil <NUM> is requested in a state where the first working coil <NUM> is being driven at a first target frequency. The controller <NUM> may determine a driving mode (a coupling mode, a dividing mode and a normal mode) of the induction heating device on the basis of the determined first target frequency and second target frequency.

The controller <NUM> may determine a final driving frequency of the first working coil <NUM> and the second working coil <NUM>, based on the determined driving mode. The controller <NUM> may drive each working coil based on the determined final driving frequency. When the first working coil <NUM> and the second working coil <NUM> are driven respectively at the final diving frequency, interference noise, which is generated when two working coils are driven at the same time, may be removed.

A frequency control method for removing interference noise of the induction heating device according to the present disclosure is described hereunder with reference to the accompanying drawings. The frequency control method may be performed by the controller <NUM> according to instructions stored in a memory. Below, f1 denotes a driving frequency of the first working coil <NUM>, and f2 denotes a driving frequency of the second working coil <NUM>. Additionally, t denotes a driving period of each working coil.

<FIG> is a graph for describing a process of controlling driving frequencies of a first working coil and a second working coil when the exemplary induction heating device is driven in a coupling mode. <FIG> is a graph for describing a process of controlling driving frequencies of a first working coil and a second working coil when the exemplary induction heating device is driven in a dividing mode. <FIG> is a graph for describing a process of controlling driving frequencies of a first working coil and a second working coil when the exemplary induction heating device is driven in a normal mode.

Referring to <FIG>, in a state where the second working coil <NUM> is not yet driven, the user places a vessel in the first heating area and sets a heating level of the first heating area. Accordingly, an instruction to drive the first working coil <NUM> may be inputted to the controller <NUM>.

The controller <NUM>, having received the instruction to drive the first working coil <NUM>, may drive the first working coil <NUM> at a predetermined first adjusted frequency, e.g., <NUM>. In the disclosure, magnitude of the first adjusted frequency may vary depending on embodiments. As illustrated in <FIG>, the first working coil <NUM> may start to be driven in the first adjusted frequency of <NUM> at a time point (<NUM>).

The controller <NUM> may reduce a driving frequency of the first working coil <NUM> while measuring an output power value of the first working coil <NUM> such that power the same as a required power value corresponding to the heating level of the first working coil <NUM>, which is set by the user, is supplied to the first working coil <NUM>.

For example, the controller <NUM> may measure an output power value of the first working coil <NUM> while gradually reducing a driving frequency of the first working coil <NUM> from the first adjusted frequency, e.g., <NUM>, in a section between a time point (<NUM>) and a time point (T1) in <FIG>. In this case, the output power value of the first working coil <NUM> may be calculated based on an input voltage value received from a voltage detector <NUM> and an input current value received from a current detector <NUM>.

The controller <NUM> may determine a frequency value (e.g. <NUM>) at a time point (T1), when the output power value of the first working coil <NUM>, measured while the driving frequency of the first working coil <NUM> is reduced, matches a required output amount, as the first target frequency of the first working coil <NUM>. Accordingly, the first working coil <NUM> may be driven at the first target frequency (<NUM>).

Depending on embodiments, the controller <NUM> may determine a first target frequency corresponding to the instruction to drive the first working coil <NUM> with reference to a table where target frequencies corresponding to heating levels of the first working coil <NUM>, set by the user, are recorded.

When the first working coil <NUM> is driven at the first target frequency, the user may place a vessel in the second heating area and may set a heating level of the second heating area. Accordingly, the controller <NUM> may receive an instruction to drive the second working coil <NUM>. When receiving the instruction to drive the second working coil <NUM>, the controller <NUM> may stop the driving of the first working coil <NUM> at a time point (T2) to determine a target frequency (a second target frequency) of the second working coil <NUM>.

The controller <NUM> may drive the second working coil <NUM> at the first adjusted frequency, e.g., <NUM> at the same time as the controller <NUM> stops the driving of the first working coil <NUM> at the time point (T2). Depending on embodiments, the second working coil <NUM> may be driven at the first adjusted frequency after the driving of the first working coil <NUM> stops and then a predetermined period passes.

According to the present disclosure, the driving of the first working coil <NUM> may temporarily stop to find a target frequency of the second working coil <NUM> when driving of the second working coil <NUM> is requested in the state where the first working coil <NUM> is being driven, as described above. Accordingly, the driving frequency of the first working coil <NUM> may be <NUM> in a section (T2~T3) where a target frequency of the second working coil <NUM> is searched. On the basis of the control, interference noise caused by the first working coil <NUM> and the second working coil <NUM> may not occur in the section (T2~T3) where the target frequency of the second working coil <NUM> is searched.

The controller <NUM> may calculate an output power value of the second working coil <NUM> while gradually reducing a driving frequency of the second working coil <NUM> in the above-described process of searching the target frequency of the first working coil <NUM>. When the output power value of the second working coil <NUM> matches a required power value of the second working coil <NUM> at a time point (T3), the controller <NUM> may determine a frequency value (<NUM>) at the time point (T3) as a second target frequency of the second working coil <NUM>.

Depending on embodiments, the controller <NUM> may determine a second target frequency corresponding to the instruction to drive the second working coil <NUM> with reference to a table where target frequencies corresponding to heating levels of the second working coil <NUM>, set by the user, are recorded.

The controller <NUM> may compare the target frequencies of the first working coil <NUM> and the second working coil <NUM> without driving the working coils at their own target frequency at the time point (T3) when the second target frequency of the second working coil <NUM> is determined. As a result of comparison, the controller <NUM> may determine a driving mode of the induction heating device among the coupling mode, the dividing mode and the normal mode.

Specifically, the controller <NUM> may calculate an absolute value (M) of a difference between the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM>. The controller <NUM> may determine a driving mode by comparing the absolute value (M) of the difference between the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM> with a predetermined reference value.

In the case where the absolute value (M) of the difference of the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM> is equal to or greater than a predetermined first reference value and is less than a predetermined second reference value, the controller <NUM> may determine the driving mode of the induction heating device as a coupling mode. In the coupling mode, the controller <NUM> may set a final driving frequency of the first working coil <NUM> and a final driving frequency of the second working coil <NUM> to the same value.

For example, in the case where the controller <NUM> determines a first target frequency of the first working coil <NUM> as <NUM> at the time point (T1), and a second target frequency of the second working coil <NUM> as <NUM> at the time point (T3), as in the embodiment of <FIG>, the controller <NUM> may calculate a difference between the two target frequencies (<NUM>-<NUM>=<NUM>). On the assumption that a first reference value is <NUM> and a second reference value is <NUM>, an absolute value (M) of the calculated difference is equal to or greater than the first reference value and less than the second reference value. Accordingly, the controller <NUM> may determine the driving mode of the induction heating device as a coupling mode.

When determining the driving mode of the induction heating device as a coupling mode, the controller <NUM>, as illustrated in <FIG>, may set a final driving frequency of the first working coil <NUM> and a final driving frequency of the second working coil <NUM> to the greater (<NUM>) of the two target frequencies - the first target frequency (<NUM>) of the first working coil <NUM> and the second target frequency (<NUM>) of the second working coil <NUM>.

In another embodiment, the controller <NUM> may set the final driving frequency of the first working coil <NUM> and the final driving frequency of the second working coil <NUM> to the less (<NUM>) of the two target frequencies - the first target frequency (<NUM>) of the first working coil <NUM> and the second target frequency (<NUM>) of the second working coil <NUM>.

According to the present disclosure, when a difference between the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM> is equal to or greater than the first reference value and less than the second reference value, the final driving frequencies of the two working coils may be matched such that interference noise, caused by a difference between the driving frequencies of the two working coils, is removed, as described above.

In another embodiment of the disclosure, when the driving mode of the induction heating device is a coupling mode, the controller <NUM> may set the final driving frequencies of the two working coils to a value (e.g. an average of the target frequencies of the two working coils or any set value) different from the target frequencies of the two working coils.

When the absolute value (M) of the difference between the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM> is equal to or greater than the second reference value and less than or equal to a predetermined third reference value, the controller <NUM> may determine the driving mode of the induction heating device as a dividing mode. In the dividing mode, the controller <NUM> may set a final driving frequency of the first working coil <NUM> and a final driving frequency of the second working coil <NUM> such that a difference between the final driving frequency of the first working coil <NUM> and the final driving frequency of the second working coil <NUM> is set equal to or greater than a predetermined noise avoidance value (k).

For example, in the case where the controller <NUM> determines a first target frequency of the first working coil <NUM> as <NUM> at the time point (T1), and a second target frequency of the second working coil <NUM> as <NUM> at the time point (T3), as in the embodiment of <FIG>, the controller <NUM> may calculate an absolute value of a difference between the two target frequencies (<NUM>-<NUM>=<NUM>). On the assumption that a second reference value is <NUM> and a third reference value is <NUM>, the absolute value (M) of the difference is equal to or greater than the second reference value and less than or equal to the third reference value. Accordingly, the controller <NUM> may determine the driving mode of the induction heating device as a dividing mode.

When determining the driving mode of the induction heating device as a dividing mode, the controller <NUM> may set a final driving frequency of the first working coil <NUM> to <NUM> the same as the first target frequency. Additionally, the controller <NUM> may set a final driving frequency of the second working coil <NUM> to <NUM> increased by a predetermined noise avoidance value (k) of <NUM> from <NUM> that is the final driving frequency of the first working coil <NUM>. Magnitude of the noise avoidance value (k) may be set to different values (e.g. <NUM>) depending on embodiments.

In another embodiment of the disclosure, the controller <NUM> may set the final driving frequency of the first working coil <NUM> to a value (e.g. <NUM>) less than the first target frequency (<NUM>), and may set the final driving frequency of the second working coil <NUM> to a value (e.g. <NUM>) increased by the noise avoidance value (k) from the final driving frequency of the first working coil <NUM>.

According to the present disclosure, when an absolute value (M) of a difference between the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM> is equal to or greater than the second reference value and less than the third reference value, the final driving frequency of each working coil may be set such that a difference between the final driving frequencies of the working coils is set equal to or greater than a predetermined noise avoidance value (k). On the basis of the control, the difference (<NUM>) between the driving frequencies of the two working coils is out of a range of audio frequencies (e.g. <NUM> to <NUM>). Accordingly, interference noise, caused by operation of the working coils may be removed.

When an absolute value (M) of a difference between the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM> is less than the first reference value or greater than the third reference value, the controller <NUM> may determine the driving mode of the induction heating device as a normal mode. When the calculated absolute value (M) of the difference is less than the first reference value or greater than the third reference value, the absolute value (M) of the difference between the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM> may be out of the range of audio frequencies (e.g. <NUM> to <NUM>). Accordingly, when determining the driving mode of the induction heating device as a normal mode, the controller <NUM> may determine the first target frequency of the first working coil <NUM> as a final driving frequency of the first working coil <NUM>, and may determine the second target frequency of the second working coil <NUM> as a final driving frequency of the second working coil <NUM>.

For example, in the case where the controller <NUM> determines a first target frequency of the first working coil <NUM> as <NUM> and a second target frequency of the second working coil <NUM> as <NUM> at the time point (T3), as in the embodiment of <FIG>, the controller <NUM> may calculate an absolute value of a difference between the two target frequencies (<NUM>-<NUM>=<NUM>). Since the calculate absolute value (<NUM>) of the difference is greater than the third reference value (<NUM>), the controller <NUM> may set a final driving frequency of the first working coil <NUM> to <NUM>, and may set a final driving frequency of the second working coil <NUM> to <NUM>.

When determining an output control method of each working coil, as described above, the controller <NUM> may simultaneously drive the first working coil <NUM> and the second working coil <NUM> at a second adjusted frequency.

For example, as illustrated in <FIG>, the first working coil <NUM> and the second working coil <NUM> may be simultaneously driven at the second adjusted frequency, e.g., <NUM>, at the time point (T3). According to the disclosure, the final driving frequencies of the first working coil <NUM> and the second working coil <NUM> may be determined after the second target frequency of the second working coil <NUM> is determined, and the first working coil <NUM> and the second working coil <NUM> may be simultaneously driven at the same frequency, i.e., the second adjusted frequency.

In the case where a driving frequency of the first working coil <NUM> increases to the final driving frequency while maintaining the final driving frequency of the second working coil <NUM> at the time point (T3) after the determination of the final driving frequencies of the first working coil <NUM> and the second working coil <NUM>, a difference between driving frequencies of the first working coil <NUM> and the second working coil <NUM> may be included in the range of audio frequencies and may cause interference noise. To prevent this from happening, the first working coil <NUM> and the second working coil <NUM> may be respectively driven simultaneously at the same frequency - i.e. at the second adjusted frequency - at the time point (T3) after the determination of the final driving frequency of each working coil, in the disclosure.

In the present disclosure, simultaneous operation of the first working coil <NUM> and the second working coil <NUM> at the second adjusted frequency after the determination of the final driving frequencies is referred to as a "soft start" operation. The second adjusted frequency may be set to a frequency the same as or different from the first adjusted frequency.

After the soft start operation, the controller <NUM> may adjust, i.e., reduce, the driving frequencies of the first working coil <NUM> and the second working coil <NUM> respectively to the previously determined final driving frequencies. After the driving frequencies are adjusted, the first working coil <NUM> and the second working coil <NUM> may heat a vessel without causing interference noise while respectively being driven at its final driving frequency.

On the basis of the control of the driving frequencies, interference noise, which is generated when the first working coil <NUM> and the second working coil <NUM> are driven at the same time, may be removed.

When the driving mode of the induction heating device is a coupling mode as in the embodiment of <FIG>, the final driving frequencies of the first working coil <NUM> and the second working coil <NUM> may be the same as the target frequencies or there is little difference between the final driving frequencies and the target frequencies. Additionally, when the driving mode of the induction heating device is a normal mode as in the embodiment of <FIG>, the final driving frequencies of the first working coil <NUM> and the second working coil <NUM> may be the same as the target frequencies. Accordingly, when the driving mode of the induction heating device is a coupling mode or a normal mode, an output power value of the first working coil <NUM> and the second working coil <NUM> may satisfy a required power value set by the user respectively.

However, when the driving mode of the induction heating device is a dividing mode as in the embodiment of <FIG>, the final driving frequency of the second working coil <NUM> may be <NUM> or <NUM> which is greater than <NUM> that is the second target frequency of the second working coil <NUM>. When the final driving frequency of the second working coil <NUM> increases to <NUM> or <NUM>, as described above with reference to <FIG>, an output power value of the second working coil <NUM> may be less than when the driving frequency is <NUM>. That is, an output power value when the second working coil <NUM> is driven at the final driving frequency may be less than a required power value set by the user. Thus, the second working coil <NUM> may not supply thermal energy, corresponding to a heating level set by the user, to a vessel.

To prevent the output power value of the second working coil <NUM> from being less, the controller <NUM> may reset an output power value of the first working coil <NUM> based on a temperature value measured at the first working coil <NUM>, and then may reset final driving frequencies of the first working coil <NUM> and the second working coil <NUM>.

<FIG> is a graph showing a change in temperature values measured in a high-power working coil when an exemplary induction heating device is driven in a dividing mode.

When the driving mode of the induction heating device is a dividing mode, and a first final driving frequency of the first working coil <NUM> and a second final driving frequency of the second working coil <NUM> are determined in the embodiment of <FIG>, the controller <NUM> may drive the first working coil <NUM> at the first final driving frequency and may drive the second working coil <NUM> at the second final driving frequency (see the time point (T4) in <FIG>).

After the time point (T4), the controller <NUM> may acquire a temperature value of a high output power value of a working coil, i.e., a high-power working coil, of the first working coil <NUM> and the second working coil <NUM>. For example, in the embodiment of <FIG>, the first final driving frequency of the first working coil <NUM> may be less than the second final driving frequency of the second working coil <NUM>, and an output power value of the first working coil <NUM> may be greater than an output power value of the second working coil <NUM>. Accordingly, in the embodiment of <FIG>, the first working coil <NUM> is referred to as a high-power working coil, and the second working coil <NUM> is referred to as a low-power working coil. The controller <NUM> may acquire the high-power working coil's temperature value, i.e., the first working coil <NUM>'s temperature value that are measured through a temperature sensor after the time point (T4).

The controller <NUM> may determine whether the temperature value of the high-power working coil, i.e., the first working coil <NUM>, satisfies a predetermined output change condition.

In one embodiment, in the predetermined output change condition, the acquired temperature value of the high-power working coil may be set equal to or greater than a predetermined reference temperature value. For example, when the reference temperature value is set to <NUM> in the embodiment of <FIG>, the controller <NUM> may compare a temperature value of the first working coil <NUM> with the reference temperature value of <NUM>. In the case where the temperature value of the first working coil <NUM> is <NUM> or greater at the time point (T5), the controller <NUM> may confirm that the output change condition is satisfied.

In another embodiment, the output change condition is set such that the acquired temperature value of the high-power working coil is maintained within a range of predetermined reference temperatures for a predetermined reference period. For example, when the reference period is set to TR and the range of reference temperatures is set to <NUM> ± <NUM>, i.e., <NUM> to <NUM> in the embodiment of <FIG>, the controller <NUM> may confirm whether the temperature value of the first working coil <NUM> is maintained within the range of <NUM> to <NUM> for the reference period of TR. The controller <NUM> may confirm that the output change condition is satisfied at a time point (T6) when the controller <NUM> confirms that the temperature value of the first working coil <NUM> is maintained within the range of <NUM> to <NUM> for the reference period of TR.

The above-described reference temperature value, reference period and range of reference temperatures may vary depending on embodiments. Additionally, the reference temperature value may be set equal to or greater than a boiling point of a load (e.g. water or cooking oil) contained in a vessel heated by the high-power working coil. Further, the range of reference temperatures may be set to a value that is high or low with respect to the reference temperature value, i.e., a value that is greater or less than the reference temperature value by a predetermined offset value (e.g. <NUM>).

When confirming that a temperature value of the high-power working coil satisfies the output change condition, the controller <NUM> may set a required power value of the high-power working coil to a predetermined minimum power value.

When a temperature value of the high-power working coil satisfies the output change condition, a load (e.g. water) in a vessel heated by the first working coil <NUM> is boiling. As long as a minimum amount of thermal energy is supplied to keep the load boiling, the load in the vessel in the first heating area may keep boiling. According to the disclosure, after the controller <NUM> confirms that the temperature value of the high-power working coil satisfies the output change condition, the required power value of the high-power working coil is reset to a predetermined minimum power value such that high-power working coil supplies a minimum amount of power for enabling the load in the vessel heated by the high-power working coil to keep boiling. The minimum power value may vary depending on embodiments.

For example, when a temperature value of the first working coil <NUM> satisfies the output change condition at the time point (T5) or the time point (T6) in the embodiment of <FIG>, the controller <NUM> may set a required output value of the first working coil <NUM> to a minimum power value, e.g. <NUM> W, rather than a required output value set by the user.

When the required output value of the first working coil <NUM> is reset to the minimum power value as described above, the controller <NUM> may reset a driving mode of the induction heating device as describe below.

<FIG> is a graph for describing a process of re-determining a driving mode of an exemplary induction heating device after the induction heating device is driven in a dividing mode.

Referring to <FIG>, the first working coil <NUM> and the second working coil <NUM> may be respectively driven at final driving frequencies of <NUM> and <NUM> at the time point (T4) after the controller <NUM> determines the driving mode of the induction heating device as a dividing mode, as described with reference to the embodiment of <FIG>. Accordingly, interference noise, caused by operation of the first working coil <NUM> and the second working coil <NUM>, may be removed, but an output power value of the second working coil <NUM> is less than a required power value.

After the first working coil <NUM> is driven at a first final driving frequency and the second working coil <NUM> is driven at a second final driving frequency, the controller <NUM> may calculate an absolute value (N) of a difference between the first final driving frequency and the second final driving frequency. The controller <NUM> may determine whether the calculated absolute value (N) of the difference between the first final driving frequency and the second final driving frequency is equal to or greater than a predetermined noise avoidance value (k).

When the absolute value (N) of the difference of the first final driving frequency and the second final driving frequency is less than the noise avoidance value (k), it may denote that the driving mode of the induction heating device is a coupling mode, or that an absolute value (M) of a difference between a first target frequency and a second target frequency is less than a first reference value while the driving mode of the induction heating device is a normal mode. In this case, the above-mentioned reduction in the output power value of the working coil may not occur. Accordingly, when the absolute value (N) of the difference between the first final driving frequency and the second final driving frequency is less than the noise avoidance value (k), the controller (<NUM>) may maintain a driving frequency of the first working coil <NUM> at the first final driving frequency and may maintain a driving frequency of the second working coil <NUM> at the second final driving frequency.

When the absolute value (N) of the difference between the first final driving frequency and the second final driving frequency is equal to or greater than the noise avoidance value (k), it may denote that the driving mode of the induction heating device is a dividing mode, or that the absolute value (M) of the difference between the first target frequency and the second target frequency is greater than a third reference value while the driving mode of the induction heating device is a normal mode. When the driving mode of the induction heating device is a dividing mode, the above-mentioned reduction in the output power value of the working coil may occur. Accordingly, when the absolute value (N) of the difference between the first final driving frequency and the second final driving frequency is equal to or greater than the noise avoidance value (k), the controller <NUM> may compare a final driving frequency of a less-output working coil with a target frequency of the low-power working coil.

When the final driving frequency of the low-power working coil is the same as the target frequency of the low-power working coil, it may denote that the driving mode of the induction heating device is a normal mode. Accordingly, when the final driving frequency of the low-power working coil is the same as the target frequency of the low-power working coil, the controller <NUM> may maintain the driving frequency of the first working coil <NUM> at the first final driving frequency and may maintain the driving frequency of the second working coil <NUM> at the second final driving frequency.

When the final driving frequency of the low-power working coil is different from the target frequency of the low-power working coil, it may denote that the driving mode of the induction heating device is a dividing mode. For example, in the embodiment of <FIG>, the controller <NUM> may confirm that the final driving frequency (<NUM>) of the second working coil <NUM>, which is a low-power working coil, is different from a target frequency (<NUM>) of the second working coil <NUM>. In this case, the driving mode of the induction heating device is a dividing mode, and the low-power working coil - i.e. the second working coil <NUM> - is being driven at the final driving frequency (<NUM>) greater than the target frequency (<NUM>). Accordingly, an output power value of the second working coil <NUM> may be less than a required power value.

When confirming that the final driving frequency of the low-power working coil is different from the target frequency of the low-power working coil, the controller <NUM> may acquire a temperature value of a high-power working coil and may determine whether the acquired temperature value of the high-power working coil satisfies a predetermined output change condition.

After the first working coil <NUM> and the second working coil <NUM> are respectively driven at the final driving frequencies of <NUM> and <NUM>, the temperature value of the high-power working coil, i.e., the first working coil <NUM> satisfies the output change condition at the time point (T5) or at the time point (T6) as described with reference to the embodiment of <FIG>. Accordingly, the controller <NUM> may reset a required power value of the high-power working coil, i.e., the first working coil <NUM>, to a minimum power value (e.g. <NUM> W).

Then the controller <NUM> may stop all the first working coil <NUM> and the second working coil <NUM> from operating to -determine a driving mode of the induction heating device again. At a time point (T7), the controller <NUM> may drive the first working coil <NUM> at a predetermined first adjusted frequency, e.g., <NUM>, and then may reduce the driving frequency of the first working coil <NUM> until the output power value of the first working coil <NUM> matches the required power value.

In the embodiment of <FIG>, a first target frequency of the first working coil <NUM> may be <NUM> that is a frequency when the output power value of the first working coil <NUM> matches the preset required power value of <NUM> W, at a time point (T8). Compared to the embodiment of <FIG>, as the required power value of the first working coil <NUM> is reduced, the first target frequency of the first working coil <NUM> may increase from <NUM> to <NUM>.

Then the first working coil <NUM> may temporarily stop operating, and, at a time point (T9), the second working coil <NUM> may be driven at the first adjusted frequency, e.g., <NUM>. In this case, a required power value of the second working coil <NUM> may be the same as the required power value in the embodiment of <FIG>. Accordingly, at a time point (T10), a second target frequency of the second working coil <NUM> may be reset to <NUM>.

In the embodiment of <FIG>, the first target frequency of the first working coil <NUM> is searched first by the controller <NUM> at the time point (T7) to the time point (T8). However, the second target frequency of the second working coil <NUM> may be searched first, depending on embodiments.

Then the controller <NUM> may calculate an absolute value (M) of a difference between the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM>. In the embodiment of <FIG>, the absolute value (M) of the difference between the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM> may be <NUM>.

On the assumption that a first reference value, a second reference value, and a third reference value are the same as those in the above-described embodiment of <FIG>, <NUM> is equal to or greater than the first reference value (<NUM>) and less than the second reference value (<NUM>). Accordingly, the controller <NUM> may determine the driving mode of the induction heating device as a coupling mode, and may set a first final driving frequency of the first working coil <NUM> and a second final driving frequency of the second working coil <NUM> to the same value (e.g. <NUM>).

When determining the final driving frequencies, the controller <NUM> may simultaneously drive the first working coil <NUM> and the second working coil <NUM> at a second adjusted frequency, e.g., <NUM>, at a time point (T11). Then driving frequencies of the first working coil <NUM> and the second working coil <NUM> may be reduced to a final driving frequency of <NUM> at a time point (T12).

Accordingly, interference noise, caused by operation of the first working coil <NUM> and the second working coil <NUM>, may not occur after the time point (T12). Additionally, after the time point (T12), a minimum amount of thermal energy may be supplied to a vessel in the first heating area corresponding to the first working coil <NUM> such that a load in the vessel may keep boiling. Further, after the time point (T12), the driving frequency of the second working coil <NUM> is maintained at <NUM> corresponding to a required power value set by the user. Accordingly, less output power of the second working coil <NUM>, which is caused temporarily between the time point (T4) and the time point (T5) (or the time point (T6)), may be dealt with.

Unlike the embodiment of <FIG>, the controller <NUM> may determine the driving mode of the induction heating device as a dividing mode or a normal mode between the time point (T10) and the time point (T11), depending on an absolute value (M) of a difference between the first target frequency of the first working coil <NUM> and the second target frequency of the second working coil <NUM>, which are determined at the time point (T8) and the time point (T10).

When the controller <NUM> determines the driving mode of the induction heating device as a dividing mode between the time point (T10) and the time point (T11), the processes from the time point (T4) to the time point (T10) may be repeated. However, when the controller <NUM> determines the driving mode of the induction heating device as a normal mode between the time point (T10) and the time point (T11), the first working coil <NUM> and the second working coil <NUM> may be driven respectively at the final driving frequency determined between the time point (T10) and the time point (T11), and the processes from the time point (T4) to the time point (T10) may not be repeated.

On the basis of the control method, even when the first working coil <NUM> and the second working coil <NUM> are driven at the same time, interference noise may not occur. Further, when the controller <NUM> determines the driving mode of the induction heating device as a dividing mode, an output power value of the low-power working coil may be temporarily less. However, the output power value of the low-power working coil increases again after a time point when a load in a vessel heated by the high-power working coil reaches a reference temperature, or reaches a range of reference temperatures for a reference period. Finally, according to the present disclosure, interference noise may be prevented and thermal energy satisfying the user's needs may be supplied to the vessel.

<FIG> is a flow chart showing a process of driving a first working coil and a second working coil respectively at a final driving frequency in one embodiment. The flow chart may be performed by the controller <NUM> according to instructions stored in the memory.

Referring to <FIG>, the controller <NUM> of the exemplary induction heating device may determine a first target frequency of the first working coil <NUM> on the basis of a required power value of the first working coil (<NUM>). Additionally, the controller <NUM> may determine a second target frequency of the second working coil <NUM> on the basis of a required power value of the second working coil <NUM> (<NUM>).

Then the controller <NUM> may calculate an absolute value (M) of a difference between the first target frequency and the second target frequency that are determined in previous steps (<NUM>).

The controller <NUM> may determine a driving mode of the induction heating device, a first final driving frequency of the first working coil <NUM> and a second final driving frequency of the second working coil <NUM> on the basis of the absolute value (M) of the difference between the first target frequency and the second target frequency that are calculated in step <NUM> (<NUM>).

When determining the driving mode of the induction heating device, the first final driving frequency of the first working coil <NUM> and the second final driving frequency of the second working coil <NUM>, the controller <NUM> may drive the first working coil <NUM> at the first final driving frequency (<NUM>), and may drive the second working coil <NUM> at the second final driving frequency (<NUM>).

<FIG> is a flow chart showing a process of determining a final driving frequency of a first working coil and a second working coil in one embodiment. The flow chart may be performed by the controller <NUM> according to instructions stored in the memory.

Referring to <FIG>, the controller <NUM> may compare the absolute value (M) of the difference between the first target frequency and the second target frequency, which is calculated in step <NUM>, with a predetermined first reference value, a predetermined second reference value and a predetermined third reference value (<NUM>).

In the case where the absolute value (M) of the difference between the first target frequency and the second target frequency is equal to or greater than the first reference value and less than the second reference value, the controller <NUM> may determine the driving mode as a coupling mode (<NUM>), and may set a final driving frequency of the first working coil <NUM> and a final driving frequency of the second working coil <NUM> to the same value (<NUM>).

In case the absolute value (M) of the difference between the first target frequency and the second target frequency is equal to or greater than the second reference value and less than or equal to the third reference value, the controller <NUM> may determine the driving mode as a dividing mode (<NUM>), and may set a final driving frequency of each working coil such that a difference between the final driving frequency of the first working coil <NUM> and the final driving frequency of the second working coil <NUM> is equal to or greater than a predetermined noise avoidance value (k) (<NUM>).

In case the absolute value (M) of the difference between the first target frequency and the second target frequency is less than the first reference value or greater than the third reference value, the controller <NUM> may determine the driving mode as a normal mode (<NUM>), and may respectively set a first final driving frequency of the first working coil <NUM> as a first target frequency and a second final driving frequency of the second working coil <NUM> as a second target frequency (<NUM>).

<FIG> is a flow chart showing a process of controlling an induction heating device to solve a problem associated with a reduction in an output power value of working coils when a first working coil and a second working coil are respectively driven at a final driving frequency, in one embodiment. The flow chart may be performed by the controller <NUM> according to instructions stored in the memory.

After the first working coil <NUM> is driven at the first final driving frequency in step <NUM> and the second working coil <NUM> is driven at the second final driving frequency in step <NUM>, the controller <NUM> may calculate an absolute value (N) of a difference between the first final driving frequency and the second final driving frequency. The controller <NUM> may confirm whether the calculated absolute value (N) of the difference between the first final driving frequency and the second final driving frequency is equal to or greater than a predetermined noise avoidance value (k) (<NUM>).

In the case where the absolute value (N) of the difference between the first final driving frequency and the second final driving frequency is less than the noise avoidance value (k), it may denote that the driving mode of the induction heating device is a coupling mode, or may denote that the driving mode of the induction heating device is a normal mode and that the absolute value (M) of the difference between the first target frequency and the second target frequency is less than the first reference value. In this case, the above-described reduction in the output power value of the working coil does not occur. Accordingly, in case the absolute value (N) of the difference between the first final driving frequency and the second final driving frequency is less than the noise avoidance value (k) in step <NUM>, the controller <NUM> may maintain a driving frequency of the first working coil <NUM> at the first final driving frequency and may maintain a driving frequency of the second working coil <NUM> at the second final driving frequency.

In the case where the absolute value (N) of the difference between the first final driving frequency and the second final driving frequency is equal to or greater than the noise avoidance value (k), it may denote that the driving mode of the induction heating device is a dividing mode, or may denote that the driving mode of the induction heating device is a normal mode and that the absolute value (M) of the difference between the first target frequency and the second target frequency is greater than the third reference value. When the driving mode of the induction heating device is a dividing mode, the above-described reduction the output power value of the working coil may occur. Accordingly, in case the absolute value (N) of the difference between the first final driving frequency and the second final driving frequency is equal to or greater than the noise avoidance value (k) in step <NUM>, the controller <NUM> may compare a final driving frequency of the low-power working coil with a target frequency of the low-power working coil (<NUM>).

When the final driving frequency of the low-power working coil is the same as the target frequency of the low-power working coil, it may denote that the driving mode of the induction heating device is a normal mode. Accordingly, in case the final driving frequency of the low-power working coil is the same as the target frequency of the low-power working coil in step <NUM>, the controller <NUM> may maintain a driving frequency of the first working coil <NUM> at the first final driving frequency and may maintain a driving frequency of the second working coil <NUM> at the second final driving frequency.

In the case where the final driving frequency of the low-power working coil is different from the target frequency of the low-power working coil, it may denote that the driving mode of the induction heating device is a dividing mode. In the embodiment of <FIG>, the controller <NUM> may confirm that the final driving frequency (<NUM>) of the second working coil <NUM>, which is the low-power working coil, is different from the target frequency (<NUM>) of the second working coil <NUM>. In this case, the driving mode of the induction heating device is a dividing mode, and the low-power working coil, i.e., the second working coil <NUM>, is being driven at the final driving frequency (<NUM>) greater than the target frequency (<NUM>). Accordingly, the output power value of the second working coil <NUM> may be less than a required power value.

When confirming that the final driving frequency of the low-power working coil is different from the target frequency of the low-power working coil in step <NUM>, the controller <NUM> may acquire a temperature value of the high-power working coil (<NUM>), and may determine whether the acquired temperature value of the high-power working coil satisfies a predetermined output change condition (<NUM>).

In the output change condition according to one embodiment, the temperature value of the high-power working coil is equal to or greater than a predetermined reference temperature value. In the output change condition according to another embodiment, the temperature value of the high-power working coil is maintained within a range of predetermined reference temperatures for a predetermined reference period.

In case the temperature value of the high-power working coil does not satisfy the output change condition in step <NUM>, the controller <NUM> may perform step <NUM> and step <NUM> again while maintaining current driving states of the first working coil <NUM> and the second working coil <NUM>.

In case the temperature value of the high-power working coil satisfies the output change condition in step <NUM>, the controller <NUM> may set a required power value of the high-power working coil to a predetermined minimum power value (<NUM>). In the embodiment of <FIG>, the required power value of the first working coil <NUM>, which is the high-power working coil, may be set to the minimum power value.

When the required power value of the high-power working coil is set to the minimum power value, the controller <NUM> may perform steps <NUM> to <NUM> illustrated in <FIG> to re-determine a driving mode of the induction heating device, a first final driving frequency and a second final driving frequency, and may drive the first working coil <NUM> and the second working coil <NUM> respectively at the determined final driving frequencies (<NUM>, <NUM>).

Claim 1:
A controlling method by an induction heating device, comprising:
between a high-power working coil and a low-power working coil among a first working coil (<NUM>) and a second working coil (<NUM>), acquiring (<NUM>) a temperature value of the high-power working coil, when an absolute value of a difference between a first final driving frequency of the first working coil (<NUM>) and a second final driving frequency of the second working coil (<NUM>) is equal to or greater than a predetermined noise avoidance value (<NUM>), and when a final driving frequency of the low-power working coil differs from a target frequency of the low-power working coil (<NUM>);
determining (<NUM>) whether the temperature value satisfies a predetermined output change condition;
setting (<NUM>) a required power value of the high-power working coil to a predetermined minimum power value when the temperature value satisfies the output change condition; and
determining the first final driving frequency of the first working coil (<NUM>) and the second final driving frequency of the second working coil (<NUM>) again based on the required power value of the high-power working coil set to the predetermined minimum value.