Patent Description:
Induction heating apparatuses are devices that generate eddy current in a metallic container and heat the container, using a magnetic field generated around a working coil. When an induction heating apparatus is driven, high-frequency current is supplied to the working coil. Then, an induced magnetic field is generated around the working coil disposed in the induction heating apparatus. When magnetic line of force of the induced magnetic field generated passes through a bottom of the metallic container over the working coil, eddy current is generated inside the bottom of the container. Accordingly, the eddy current generated flows in the container, and the container itself is heated.

<FIG> is a view showing a state in which a container is abnormally placed in a heating zone formed on an upper plate of an induction heating apparatus, and <FIG> is a view showing a state in which a container is normally placed in a heating zone formed on an upper plate of an induction heating apparatus.

The induction heating apparatus includes a heating zone in which a container is placed. For example, the heating zone is formed on an upper plate <NUM> of the induction heating apparatus, and the heating zone corresponds to a working coil <NUM>, as illustrated in <FIG>. That is, the heating zone is formed in a zone corresponding to a position of the working coil <NUM>.

When a user places the container <NUM> on the upper plate <NUM>, sets a power level of the heating zone, and then inputs an instruction to initiate heating, the working coil <NUM> operates, to heat the container.

When the container <NUM> is placed on the upper plate <NUM>, heating performance of the working coil <NUM> may vary depending on a distance between a center point A1 of the working coil <NUM> and a center point A2 of the container <NUM>. For example, when the container <NUM> is heated, as the center point A1 of the working coil <NUM> becomes farther from the center point A2 of the container <NUM> as illustrated in <FIG>, the heating performance of the working coil <NUM> deteriorates. Thus, it takes a long time to heat the container <NUM>. When the center point A1 of the working coil <NUM> is spaced from the center point A2 of the container <NUM> as illustrated in <FIG>, the container is in a state of being eccentric.

When the center point A1 of the working coil <NUM> completely matches the center point A2 of the container <NUM> as illustrated in <FIG>, the heating performance of the working coil <NUM> is maximized. Thus, time taken to heat the container <NUM> is minimized. When the center point A1 of the working coil <NUM> matches the center point A2 of the container <NUM> as illustrated in <FIG>, the container is in a state of being concentric.

<FIG> is a view showing frequency-output power value curves when a container is placed in a heating zone abnormally and normally.

In <FIG>, a curve <NUM> shows output power values of the working coil <NUM>, corresponding to driving frequencies of the working coil <NUM>, when the container <NUM> is in the state of being eccentric as illustrated in <FIG>. In <FIG>, a curve <NUM> shows output power values of the working coil <NUM>, corresponding to driving frequencies of the working coil <NUM>, when the container <NUM> is in the state of being concentric as illustrated in <FIG>. As illustrated in <FIG>, a resonance frequency of the working coil <NUM> when the container <NUM> is in the state of being eccentric are less than a resonance frequency of the working coil <NUM> when the container <NUM> is in the state of being concentric.

In each of the frequency-output power value curves <NUM>, <NUM> of <FIG>, a left area, i.e., an area in which frequencies are less than the resonance frequencies F1, F2, is referred to as capacitive areas CA1, CA2, with respect to the resonance frequencies F1, F2, and a right area, i.e., an area in which frequencies are greater than the resonance frequencies F1, F2, is referred to as inductive areas IA1, IA2, with respect to the resonance frequencies F1, F2.

When a driving frequency of the working coil <NUM> is set to a frequency included in the inductive areas IA1, IA2 in a state in which the resonance frequencies F1, F2 of the working coil <NUM> are fixed, the induction heating apparatus operates normally.

When a driving frequency of the working coil <NUM> is set to a frequency included in the capacitive areas CA1, CA2 in a state in which the resonance frequencies F1, F2 of the working coil <NUM> are fixed, the induction heating apparatus operates abnormally. Specifically, when the working coil <NUM> operates in the capacitive areas CA1, CA2, zero voltage switching (ZVS) of switching elements included in an inverter circuit configured to supply current to the working coil <NUM> fails. Thus, switching loss among the switching elements increases, and power efficiency of the inverter circuit and the working coil <NUM> decrease. Further, as the switching loss among the switching elements increases due to the failure of ZVS, the switching elements may be damaged due to heat generation of the switching elements.

When the user inputs a power level and an instruction to initiate heating in the state in which the container <NUM> is in the state of being eccentric as illustrated in <FIG>, a resonance frequency F1 of the working coil <NUM> is determined, and a driving frequency FL of the working coil <NUM> is determined based on an output power value corresponding to the power level input by the user. Accordingly, the working coil <NUM> may be driven at the driving frequency FL. In this case, since the driving frequency FL of the working coil <NUM> is greater than the resonance frequency F1, the induction heating apparatus operates in the inductive area IA1.

By the way, when the user moves the container <NUM> to a different position such that the container <NUM> is in the state of being concentric as illustrated in <FIG>, while the working coil <NUM> operates at the driving frequency FL in the state in which the container <NUM> is in the state of being eccentric as illustrated in <FIG>, the driving frequency FL of the working coil <NUM> remains the same, and the resonance frequency the working coil <NUM> changes from F1 to F2. As a result, the driving frequency FL of the working coil <NUM> becomes less than the resonance frequency F2, and the induction heating apparatus operates in the capacitive area CA2. Thus, as switching loss of the switching elements included in the inverter circuit increases, the switching elements can be burned out. Documents <CIT>, <CIT>, <CIT> and <CIT> disclose induction heating apparatuses and their corresponding control methods according to the prior art.

The objective of the present disclosure is to provide an induction heating apparatus and a method for operating the same, which prevent a switching element from being burnt out.

It is an objective of the present disclosure to provide an induction heating apparatus and a method for operating the same, which adapt the driving frequencies, when moving the container during operation of the working coil.

This is in particular achieved by stopping operation of an induction heating apparatus when the induction heating apparatus is sensed operating abnormally due to a change in the position of a container during normal operation of the induction heating apparatus.

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. Additionally, the aspects and advantages in the present disclosure can be realized via means and combinations thereof that are described in the appended claims.

In one aspect of the disclosure, an induction heating apparatus, is provided comprising: a working coil disposed in a position corresponding to a position of a heating zone; an inverter circuit comprising a plurality of switching elements and configured to supply current to the working coil; a driving circuit configured to supply a switching signal to each of the switching elements included in the inverter circuit; and a controller configured to determine a driving frequency of the working coil, corresponding to a power level of the heating zone, when the power level is input, supply a control signal based on the driving frequency to the driving circuit, and drive the working coil.

Preferably, the controller may measure a resonance current value of the working coil, may measure a driving voltage value supplied to a switching element included in the inverter circuit configured to supply current to the working coil.

The controller may measure a resonance current value of the working coil and measure a driving voltage value supplied to a switching element and may determine whether the induction heating apparatus is driven in abnormal or normal and may control driving of the working coil based on thereon.

Operating the induction heating apparatus with driving frequencies less than a resonance frequency may represent a capacitive area and operating the induction heating apparatus with driving frequencies greater than the resonance frequency may represent an inductive area.

The controller may determine or generate an overlapped period of the resonance current value and the driving voltage value, may compare a time point of appearance of the overlapped period with a predetermined reference time point to thereby determine a driving state of the induction heating apparatus, and may control driving of the working coil based on the driving state of the induction heating apparatus.

In one or more embodiments, the overlapped period may be a period for which the resonance current value and the driving voltage value are all positive numbers.

In one or more embodiments, the diving voltage value may be magnitude of voltage supplied between a second terminal and a third terminal of the switching element.

In one or more embodiments, the reference time point may be a middle time point of a period for which the resonance current value is positive numbers.

In one or more embodiments, when the time point at which the overlapped period appears is later than the reference time point, the controller may determine that the driving state of the induction heating apparatus is normal.

When the time point at which the overlapped period appears is earlier than the reference time point, the controller may determine that the driving state of the induction heating apparatus is abnormal.

In one or more embodiments, when determining that the driving state of the induction heating apparatus is normal, the controller may keep the working coil operating.

When determining that the driving state of the induction heating apparatus is abnormal, the controller may stop driving of the working coil.

In one or more embodiments, the controller may determine a re-driving frequency of the working coil, corresponding to the power level after the working coil stops operating, and may drive the working coil based on the re-driving frequency.

In another aspect a method for controlling an induction heating apparatus is provided, comprising: receiving an input power level of a heating zone; determining a driving frequency of a working coil, corresponding to the power level; driving the working coil based on the driving frequency; measuring a resonance current value of the working coil; measuring a driving voltage value supplied to a switching element included in an inverter circuit configured to supply current to the working coil; determine whether the driving state of the induction heating apparatus is normal or abnormal based on the measured resonance current value of the working coil and the measured a driving voltage.

The determining of the driving state may include determining an overlapped period of the resonance current value and the driving voltage value; comparing a time point at which the overlapped period appears with a predetermined reference time point to determine a driving state of the induction heating apparatus; and controlling driving of the working coil based on the driving state of the induction heating apparatus.

In one or more embodiments, determining a driving state of the induction heating apparatus may comprise: determining that the driving state of the induction heating apparatus is normal when the time point at which the overlapped period appears is later than the reference time point; and determining that the driving state of the induction heating apparatus is abnormal when the time point at which the overlapped period appears is earlier than the reference time point.

In one or more embodiments, controlling driving of the working coil, may comprise: keeping the working coil operating when determining that the driving state of the induction heating apparatus is normal; and stopping driving of the working coil when determining that the driving state of the induction heating apparatus is abnormal.

In one or more embodiments, controlling driving of the working coil, may further comprise: determining a re-driving frequency of the working coil, corresponding to the power level, after the working coil stops operating; and driving the working coil based on the re-driving frequency. A controller of an induction heating apparatus in one embodiment may generate an overlapped period of a resonance current value of a working coil, and a driving voltage value of a switching element included in an inverter circuit. In the present disclosure, the overlapped period may be a period for which the resonance current value and the driving voltage value are all positive numbers.

The controller may determine whether a driving state of the induction heating apparatus is abnormal, based on a time point of appearance of the overlapped period.

In the disclosure, the abnormal driving state of the induction heating apparatus denotes driving of the induction heating apparatus in a capacitive area. Additionally, in the disclosure, the normal driving state of the induction heating apparatus denotes driving of the induction heating apparatus in an inductive area.

When determining that the driving state of the induction heating apparatus is abnormal, the controller may stop the driving of the working coil. When the induction heating apparatus operates in the capacitive area, the switching element is likely to be burnt out. The driving of the working coil may be stopped to prevent the switching element from being burnt out.

The induction heating apparatus in one embodiment may include a working coil disposed in a position corresponding to a position of a heating zone, an inverter circuit including a plurality of switching elements and configured to supply current to the working coil, a driving circuit configured to supply a switching signal to each of the switching elements included in the inverter circuit, and a controller configured to determine a driving frequency of the working coil, corresponding to a power level of the heating zone, when the power level is input, supply a control signal based on the driving frequency to the driving circuit, and drive the working coil.

In one embodiment, the controller may measure a resonance current value of the working coil, measure a driving voltage value supplied to the switching element included in the inverter circuit configured to supply current to the working coil, generate an overlapped period of the resonance current and the driving voltage, compare a time point of appearance of the overlapped period with a predetermine reference time point to determine a driving state of the induction heating apparatus, and control driving of the working coil based on the driving state of the induction heating apparatus.

A method for controlling an induction heating apparatus in one embodiment may include receiving an input power level of a heating zone, determining a driving frequency of a working coil, corresponding to the power level, driving the working coil based on the driving frequency, measuring a resonance current value of the working coil, measuring a driving voltage value supplied to a switching element included in an inverter circuit configured to supply current to the working coil, generating an overlapped period of the resonance current and the driving voltage, comparing a time point of appearance of the overlapped period with a predetermined reference time point to determine a driving state of the induction heating apparatus, and controlling driving of the working coil based on the driving state of the induction heating apparatus.

In one embodiment, when an induction heating apparatus is sensed operate abnormally due to a change in the position of a container during normal operation of the induction heating apparatus, the induction heating apparatus stops operating. Thus, the burning out of switching elements are prevented, which would be caused when the induction heating apparatus continues to operate abnormally.

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 idea of the disclosure. In the disclosure, detailed descriptions of known technologies in relation to the disclosure are omitted if they are 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> is an exploded perspective view showing an induction heating apparatus in one embodiment.

Referring to <FIG>, an induction heating apparatus <NUM> in one embodiment may include a case <NUM> constituting a main body, and a cover plate <NUM> coupled to the case <NUM> and sealing the case <NUM>.

The cover plate <NUM> may be coupled to an upper surface of the case <NUM> and seal a space, formed inside the case <NUM>, from the outside. The cover plate <NUM> may include an upper plate <NUM> on which a container for cooking a food item is placed. In one embodiment, the upper plate <NUM> may be made of tempered glass such as ceramic glass. However, a material for the upper plate <NUM> may vary depending on embodiments.

Heating zones <NUM>, <NUM> respectively corresponding to working coil assemblies <NUM>, <NUM> may be formed on the upper plate <NUM>. For a user to recognize positions of the heating zones <NUM>, <NUM> easily, lines or figures corresponding to the heating zones <NUM>, <NUM> may be provided, printed or displayed on the upper plate <NUM>.

The case <NUM> may be formed as a cuboid, an upper portion of which is open. The working coil assemblies <NUM>, <NUM> for heating a container may be disposed in the space formed inside the case <NUM>. Additionally, an interface <NUM> may be disposed inside the case <NUM>. The interface <NUM> may allow the user to input a desired supply power or be used to adjust a power level of each of the heating zones <NUM>, <NUM>. The interface may further display information on the induction heating apparatus <NUM>. However, such information may be also displayed at a different position. The interface <NUM> may be implemented as a touch panel that is capable of inputting based on a touch input at the touch panel and/or displaying information. However, an interface <NUM> having a different structure may be used depending on embodiments.

Additionally, on the upper plate <NUM>, a manipulation zone <NUM> may be disposed in a position corresponding to a position of the interface <NUM>. For the user's manipulation, characters or images and the like may be printed in the manipulation zone <NUM>, in advance. The user may perform desired manipulation by touching a specific point of the manipulation zone <NUM> with reference to the characters or images that are printed in the manipulation zone <NUM> in advance. Additionally, information output by the interface <NUM> may be displayed through the manipulation zone <NUM>.

The user may set a power level of one or more of the heating zones <NUM>, <NUM> through the interface <NUM>. The power level may be displayed in the manipulation zone <NUM> as numbers (e.g., <NUM>, <NUM>, <NUM>,. When a power level of the one or more of the heating zones <NUM>, <NUM> is set, a required power value and a driving frequency of a working coil corresponding to the one or more of the heating zones <NUM>, <NUM> may be determined. A controller may drive each working coil, based on the determined driving frequency, such that an actual output power value of the one or more working coils matches a required power value set by the user.

Further, a power supply <NUM> for supplying power to the working coil assemblies <NUM>, <NUM> or the interface <NUM> may be disposed in the space formed inside the case <NUM>.

In the embodiment of <FIG>, two working coil assemblies, i.e., a first working coil assembly <NUM> and a second working coil assembly <NUM>, are disposed inside the case <NUM>, for example. However, three or more working coil assemblies may be disposed inside the case <NUM>, depending on embodiments.

The working coil assemblies <NUM>, <NUM> may include a working coil that forms an induced magnetic field using a high-frequency alternating current supplied by the power supply unit <NUM>, and/or an insulating sheet for protecting a coil from heat generated by a working coil forming an induced magnetic field. In <FIG>, the first working coil assembly <NUM> may include a first working coil <NUM> for heating a container placed in a first heating zone <NUM>, and a first insulating sheet <NUM>, for example. Additionally, though not illustrated, the second working coil assembly <NUM> may include a second working coil and a second insulating sheet. Depending on embodiments, the insulating sheet may not be provided.

Further, one or more of the working coils may be provided with one or more temperature sensors, preferably in a central portion thereof. In <FIG>, a temperature sensor <NUM> may be disposed in a central portion of the first working coil <NUM>, for example. The temperature sensor may measure a temperature of a container placed in the heating zones. In one embodiment, the temperature sensor may be a thermistor temperature sensor having a variable resistance whose resistance value changes according to the temperature of the container, but the type of the temperature sensor is not limited thereto.

In one embodiment, the temperature sensor may output a sensing voltage corresponding to a temperature of a container. The sensing voltage output from the temperature sensor may be delivered to the controller. The controller may determine the temperature of the container, based on magnitude of the sensing voltage output from the temperature sensor. When the temperature of the container is a predetermined reference value or greater, the controller may perform an overheat preventing operation by decreasing an actual power value of a working coil or stopping driving of a working coil.

Furthermore, though not illustrated in <FIG>, a substrate may be disposed in the space formed inside the case <NUM>, and a plurality of circuits or elements including the controller may be mounted onto the substrate. The controller may drive the one or more working coils according to the user's instruction to initiate heating, input through the interface <NUM>, to perform a heating operation. When the user inputs an instruction to end heating through the interface <NUM>, the controller may stop the driving of the working coils to end the heating operation.

<FIG> is a circuit diagram of the induction heating apparatus in one embodiment.

Referring to <FIG>, the induction heating apparatus <NUM> in one embodiment may include a rectifying circuit <NUM>, smoothing circuits L1, C1, an inverter circuit <NUM>, and a working coil <NUM>.

The rectifying circuit <NUM> may include a plurality of diode elements D1, D2, D3, D4. The rectifying circuit <NUM> may be a bridge diode circuit, as illustrated in <FIG>, and may be another circuit depending on embodiments. The rectifying circuit <NUM> may rectify AC voltage supplied by a power supplying device <NUM> and output voltage having a pulse waveform.

The smoothing circuits L1, C1 may smooth the voltage rectified by the rectifying circuit <NUM> and output DC link voltage. The smoothing circuits L1, C1 may include a first inductor L1 and a DC link capacitor C1.

The inverter circuit <NUM> may include a first switching element SW1, a second switching element SW2, a first capacitor C2, and a second capacitor C3.

As illustrated in <FIG>, the inverter circuit <NUM> of the induction heating apparatus <NUM> in one embodiment may be implemented as a half-bridge circuit including two switching elements SW1, SW2. In another embodiment, the inverter circuit <NUM> may be implemented as a full-bridge circuit including four switching elements.

The first switching element SW1 and the second switching element SW2 may be respectively turned on and turned off by a first switching signal S1 and a second switching signal S2. For example, each of the switching elements SW1, SW2 may be turned on when each of the switching signals S1, S2 is at a high level, and turned off when each of the switching signals S1, S2 is at a low level.

In <FIG>, each of the switching elements SW1, SW2 is an IGBT element, for example. However, each of the switching elements SW1, SW2 may be another type of switching element (e.g., a BJT or an FET and the like), depending on embodiments.

The switching elements SW1, SW2 may be turned on and turned off complementarily. For example, in any operation mode, the second switching element SW2 may be turned off (turned on) while the first switching element SW1 is turned on (turned off).

DC link voltage input to the inverter circuit <NUM> may be converted into alternating voltage (alternating current) as a result of the turn-on and turn-off operations, i.e., a switching operation, of the switching elements SW1, SW2 included in the inverter circuit <NUM>. The alternating current output from the inverter circuit <NUM> may be supplied to the working coil <NUM>. When the alternating current is supplied by the inverter circuit <NUM>, a resonance phenomenon may occur in the working coil <NUM>, and thermal energy may be supplied to the container.

In the disclosure, each of the first switching element S1 and the second switching element S2 may output a pulse width modulation (PWM) signal having a predetermined duty cycle.

When the alternating current output from the inverter circuit <NUM> is supplied to the working coil <NUM>, the working coil <NUM> may be driven. As a result of the driving of the working coil <NUM>, a container placed over the working coil <NUM> may be heated while eddy current flows in the container. During the driving of the working coil <NUM>, magnitude of thermal energy supplied to the container may vary depending on magnitude of power actually generated as a result of the driving of the working coil, i.e., an actual output power value of the working coil.

When the induction heating apparatus <NUM> is powered on as a result of manipulation of the interface of the induction heating apparatus <NUM> by the user, the induction heating apparatus may be put on standby for driving as power is supplied to the induction heating apparatus from an input power supply <NUM>. Then the user may place a container over a working coil of the induction heating apparatus and set a power level for the container, to give the working coil an instruction to initiate heating. When the instruction to initiate heating is given by the user, a power value required for the working coil <NUM>, i.e., a required power value of the working coil <NUM> may be determined based on the power level set by the user.

Having received the user's instruction to initiate heating, the controller <NUM> may determine a driving frequency, corresponding to the required power value of the working coil <NUM>, and supply a control signal corresponding to the determined driving frequency to the driving circuit <NUM>. Accordingly, the switching signals S1, S2 may be output from the driving circuit <NUM>, and as the switching signals S1, S2 are respectively input to the switching elements SW1, SW2, the working coil <NUM> may be driven. As a result of the driving of the working coil <NUM>, the container may be heated while eddy current flows in the container.

In one embodiment, the controller <NUM> may determine a driving frequency of the working coil <NUM> such that the driving frequency corresponds to a power level of a heating zone, set by the user. For example, when the user sets a power level of a heating zone, the controller <NUM> may set a driving frequency of the working coil <NUM> to a predetermined maximum frequency, and then gradually decrease the driving frequency of the working coil <NUM> until an output power value of the working coil <NUM> matches a required power value corresponding to the power level set by the user. The controller <NUM> may determine a frequency at a time when the output power value of the working coil <NUM> matches the required power value as the driving frequency of the working coil <NUM>.

The controller <NUM> may supply a control signal corresponding to the determined driving frequency to the driving circuit <NUM>. The driving circuit <NUM> may output switching signals S1, S2 that have a duty ratio corresponding to the driving frequency determined by the controller <NUM>, based on the control signal output from the controller <NUM>. As a result of input of the switching signals S1, S2 alternating current may be supplied to the working coil <NUM> while the switching elements SW1, SW2 are turned on and turned off complementarily.

When the container is heated as a result of the driving of the working coil <NUM>, the controller <NUM> may obtain magnitude of resonance current, i.e., a resonance current value, of the working coil <NUM>, measured through a current sensor <NUM>.

Further, the controller <NUM> may obtain magnitude of voltage, which is supplied to the switching elements SW1, SW2, and measured through a voltage sensor <NUM> when the switching elements SW1, SW2 are turned on and turned off complementarily, SW2, i.e., a driving voltage value that is magnitude of driving voltage of the switching elements SW1, SW2. For example, when the switching elements SW1, SW2 are an IGBT element, a driving voltage value of the switching elements SW1, SW2 may be the magnitude of voltage between a second terminal (a collector terminal) and a third terminal (an emitter terminal), among a first terminal (a base terminal), the second terminal (a collector terminal) and the third terminal (an emitter terminal) included in the IGBT element, i.e., magnitude of collector-emitter voltage VCE.

<FIG> shows an embodiment in which the voltage sensor <NUM> measures a driving voltage value of the switching element SW2. However, a driving voltage value of the switching element SW1 may be also or alternatively measured depending on the application.

In one embodiment, the controller <NUM> may compare the resonance current value obtained through the current sensor <NUM> with the driving voltage value of the switching element obtained through the voltage sensor <NUM>, and may generate an overlapped period.

<FIG> is a view showing a waveform of resonance current of a working coil and a waveform of driving voltage of a switching element when an induction heating apparatus is driven in an inductive area, and <FIG> is a view showing a waveform of resonance current of a working coil and a waveform of driving voltage of a switching element when an induction heating apparatus is driven in a capacitive area.

In one embodiment, when the container is heated as a result of the driving of the working coill <NUM>, the controller <NUM> may respectively obtain a resonance current value <NUM>, <NUM> of the working coil <NUM> and a driving voltage value <NUM>, <NUM> of the switching element SW2, as illustrated in <FIG>.

The controller <NUM> may compare the obtained resonance current value <NUM>, <NUM> of the working coil <NUM> with the obtained driving voltage value <NUM>, <NUM> of the switching element SW2, and may derive or generate a period for which the resonance current value <NUM>, <NUM> of the working coil <NUM> and the driving voltage value <NUM>, <NUM> of the switching element SW2 are all positive numbers, i.e., an overlapped period. In <FIG>, the overlapped periods <NUM>, <NUM> that are the periods, for which the resonance current value <NUM>, <NUM> of the working coil <NUM> and the driving voltage value <NUM>, <NUM> of the switching element SW2 are all positive numbers, are illustrated respectively.

After determining the overlapped periods <NUM>, <NUM>, i.e. when the overlapped periods <NUM>, <NUM> are obtained, the controller <NUM> may compare a time point OT1 at which the overlapped periods <NUM>, <NUM> appear or starts with a predetermined reference time point RT.

In the disclosure, the reference time point RT may be defined as a middle time point of the period for which the resonance current value of the working coil is positive numbers. For example, in <FIG>, a middle time point RT of the period <NUM> for which the resonance current value <NUM> of the working coil <NUM> is positive numbers may be a reference time point. Likewise, in <FIG>, a middle time point RT of the period <NUM> for which the resonance current value <NUM> of the working coil <NUM> is positive numbers may be a reference time point.

As illustrated in <FIG>, when the induction heating apparatus is driven in the inductive area, i.e., when the induction heating apparatus is driven normally, a time point OT1 at which the overlapped period <NUM> appears may be later than the reference time point, i.e., the middle time point RT. When the container is not moved in a state of being eccentric (see <FIG>) or in a state of being concentric (see <FIG>) and the working coil <NUM> is driven, the induction heating apparatus may be driven in the inductive area.

When the induction heating apparatus is driven in the capacitive area as illustrated in <FIG>, i.e., when the induction heating apparatus is driven abnormally, a time point OT2 at which the overlapped period <NUM> appears may be earlier than the reference time point RT, i.e., the middle time point RT. When the container is in a state of being eccentric (see <FIG>) and is then moved into a state of being concentric (see <FIG>) during the driving of the working coil <NUM>, as described above, the induction heating apparatus may be driven in the capacitive area.

Accordingly, the controller <NUM> may compare the time point OT at which the overlapped period, generated during the driving of the working coil <NUM>, appears with the reference time point RT, to determine a driving state of the induction heating apparatus.

In one embodiment, when the time point OT at which the overlapped period appears is later than the reference time point RT, the controller <NUM> may determine that the driving state of the induction heating apparatus is normal, and when the time point OT at which the overlapped period appears is earlier than the reference time point RT, determine that the driving state of the induction heating apparatus is abnormal.

The controller <NUM> may determine whether the working coil <NUM> is driven, based on the overlapped period OT1 and the driving state of the induction heating apparatus. For example, when determining that the driving state of the induction heating apparatus is normal, the controller <NUM> may keep the working coil <NUM> operating.

However, when determining that the driving state of the induction heating apparatus is abnormal, the controller <NUM> may stop the driving of the working coil <NUM>. Thus, the switching elements SW1, SW2 included in the inverter circuit <NUM> may be prevented from being burnt out.

In one embodiment, after the working coil <NUM> stops operating since the controller <NUM> determines that the driving state of the induction heating apparatus is abnormal, the controller <NUM> may calculate a driving frequency for driving the working coil <NUM> again, i.e., a re-driving frequency, based on a required power value set by the user.

For example, as illustrated in <FIG>, after the working coil <NUM> stops operating since the controller determines that the driving state of the induction heating apparatus is abnormal while the working coil <NUM> is being driven at a driving frequency FL, the controller <NUM> may calculate a re-driving frequency FN of the working coil <NUM>, corresponding to the required power value PW. The controller <NUM> may drive the working coil <NUM> again, based on the re-driving frequency FN, such that the working coil <NUM> starts to heat the container again. Since the re-driving frequency FN of the working coil <NUM> is greater than a resonance frequency F2 as illustrated in <FIG>, the induction heating apparatus may be driven reliably in the inductive area.

<FIG> is a flow chart showing a method for controlling an induction heating apparatus in one embodiment.

Referring to <FIG>, a controller <NUM> may receive an input power level of a heating zone <NUM>. The controller <NUM> may determine a driving frequency of a working coil <NUM>, corresponding to the input power level <NUM>.

When the driving frequency of the working coil <NUM> is determined, the controller <NUM> may supply a control signal to a driving circuit <NUM> to drive the working coil <NUM> based on the driving frequency <NUM>.

While the working coil <NUM> is being driven, the controller <NUM> may measure a resonance current value of the working coil <NUM><NUM>. Further, while the working coil <NUM> is being driven, the controller <NUM> may measure <NUM> a driving voltage value supplied to a switching element e.g., SW2 included in an inverter circuit <NUM> configured to supply current to the working coil <NUM>.

The controller <NUM> may determine or generate an overlapped period OT of the resonance current value and the driving voltage value <NUM>.

The controller <NUM> may compare a time point at which the overlapped period OT appears with a predetermined reference time point RT to thereby determine a driving state of the induction heating apparatus <NUM>.

In one embodiment, when the time point at which the overlapped period OT appears is later than the reference time point RT, the controller <NUM> may determine the driving state of the induction heating apparatus is normal. Then no change in driving the induction heating apparatus is made.

However, when the time point at which the overlapped period OT appears is earlier than the reference time point RT, the driving state of the induction heating apparatus is determined as being abnormal.

The controller <NUM> may control the driving of the working coil, based on the determined driving state of the induction heating apparatus <NUM>.

In one embodiment, when determining that the driving state of the induction heating apparatus is normal, the controller <NUM> may keep the working coil <NUM> operating.

When determining that the driving state of the induction heating apparatus is abnormal, the controller <NUM> may stop the driving of the working coil <NUM>.

Though not illustrated, the method for controlling an induction heating apparatus in one embodiment may further include determining a re-driving frequency of the working coil <NUM>, corresponding to the power level, after stopping the driving of the working coil <NUM>, and driving the working coil <NUM> at the re-driving frequency.

<FIG> is a flow chart showing a method for controlling an induction heating apparatus in another embodiment.

When a user places a container in a heating zone and inputs a power level <NUM>, a controller <NUM> may determine a driving frequency of a working coil <NUM>, corresponding to the power level <NUM>.

When the driving frequency is determined, the controller <NUM> may supply a control signal corresponding to the driving frequency to a driving circuit <NUM>. Accordingly, the working coil <NUM> may be driven at the driving frequency <NUM>.

When the working coil <NUM> is driven at the driving frequency, the controller <NUM> may obtain <NUM> a resonance current value of the working coil <NUM> measured through a current sensor <NUM>. Further, the controller <NUM> may obtain a driving voltage value of a switching element SW2, measured through a voltage sensor <NUM> when the working coil <NUM> is driven <NUM>.

The controller <NUM> may determine or generate <NUM> an overlapped period OT of resonance current value of the working coil <NUM> and the driving voltage value of the switching element SW2.

The controller <NUM> may compare <NUM> a time point at which the overlapped period OT generated appears with a predetermined reference time point RT.

When the time point at which the overlapped period OT appears is later than the reference time point RT as a result of the comparison in step <NUM>, it means that the induction heating apparatus is driven in an inductive area. Accordingly, the controller <NUM> may determine that a driving state of the induction heating apparatus is normal.

When determining that the driving state of the induction heating apparatus is normal, the controller <NUM> may perform step <NUM> to step <NUM> again.

When the time point at which the overlapped period OT appears is earlier than the reference time point RT as a result of the comparison in step <NUM>, it means that the induction heating apparatus is driven in a capacitive area. Accordingly, the controller <NUM> may determine that the driving state of the induction heating apparatus is abnormal.

When determining that the driving state of the induction heating apparatus is abnormal, the controller <NUM> may stop the driving of the working coil <NUM> (<NUM>). Thus, the switching elements SW1, SW2 may be prevented from being burnt out.

Claim 1:
An induction heating apparatus (<NUM>), comprising:
a working coil (<NUM>) disposed in a position corresponding to a position of a heating zone (<NUM>, <NUM>);
an inverter circuit (<NUM>) comprising a plurality of switching elements (SW1, SW2) and configured to supply current to the working coil (<NUM>);
a driving circuit (<NUM>) configured to supply a switching signal (S1, S2) to each of the switching elements (SW1, SW2) included in the inverter circuit (<NUM>); and
a controller (<NUM>) configured:
to determine a driving frequency of the working coil (<NUM>), corresponding to a power level of the heating zone (<NUM>, <NUM>), when the power level is input, and
to supply a control signal based on the driving frequency to the driving circuit (<NUM>) for driving the working coil (<NUM>) correspondingly,
characterised in that
the controller (<NUM>) is configured to measure a resonance current value of the working coil (<NUM>), measure a driving voltage value supplied to the plurality of switching elements (SW1, SW2), determine an overlapped period (OT) of the resonance current value and the driving voltage value, compare a time point of appearance of the overlapped period (OT) with a predetermined reference time point (RT) to determine a driving state of the induction heating apparatus, and control driving of the working coil (<NUM>) based on the driving state of the induction heating apparatus.