JP6021516B2 - Induction heating cooker and control method thereof - Google Patents

Description

  The present invention relates to an induction heating cooker and a control method thereof.

  Several induction heating cookers having a plurality of heating coils have been proposed so far to control the heating power supplied to the heating coil according to the size of the pan bottom.

  For example, the induction heating cooker described in Patent Document 1 controls the heating power by changing the setting of the voltage variable means and controlling the power after setting the operating frequency of the driving means within a predetermined setting range. It is.

  The induction heating cooker described in Patent Document 2 performs rough adjustment of input power by changing the switching frequency of the inverter circuit, and finely adjusts the DC voltage supplied to the inverter circuit, thereby setting the target power value of the input power. It is realized.

  The induction heating cooker described in Patent Literature 3 has a plurality of inverters, sets a first maximum power when operating these inverters simultaneously, and a second maximum power when operating these inverters alone, Interference noise is prevented by operating at a constant driving frequency of the plurality of inverters at least up to the first maximum power, and the conduction time of the semiconductor switch of each inverter up to the second maximum power exceeding the first maximum power The power is adjusted by changing the ratio.

  The induction heating cooker described in Patent Document 4 is equipped with a plurality of induction heating coils, performs output control by changing the frequency of the current to be supplied to each induction heating coil, and is used for one induction heating coil. By setting the lowest frequency of the frequency band used for the other induction heating coil to be 15 kHz or more higher than the maximum frequency of the band, interference sound when operating simultaneously is prevented. Further, in Patent Document 4, when continuously controlling the drive frequency of the inverter as the maximum frequency, on / off control of energization of the inverter is used together when power lower than the minimum power of one induction heating coil is input to the load. It is described.

Japanese Patent Laid-Open No. 2005-093088 JP 2006-351371 A JP 2011-103225 A JP 2011-1555022 A

  However, according to the induction heating cooker described in Patent Document 1, voltage varying means is required, the overall circuit configuration and control method are complicated, the manufacturing work becomes complicated, and the production cost increases.

  In addition, according to the induction heating cooker described in Patent Document 2, when heating control is performed by distinguishing between a pan made of a magnetic material (for example, iron) and a pan made of a non-magnetic material (for example, aluminum), aluminum is used. Although it is necessary to set the driving frequency when heating the pan to about 90 kHz, it is necessary to provide a circuit for controlling the load power separately. As in Patent Document 1, the circuit configuration is complicated and avoids an increase in production cost. I can't.

  In addition, the induction heating cooker described in Patent Document 3 is configured to heat pans made of materials having different frequency characteristics, and keeps the driving frequency of the high-frequency current supplied to each heating coil constant. Power adjustment is performed by adjusting the time ratio, but when heating an aluminum pan or the like using a high drive frequency, it is difficult to adjust the desired wide range of power only by adjusting the conduction time ratio. It is. Moreover, when the drive frequency difference of a some inverter enters into a frequency variable area | region, an interference sound (beat sound) will generate | occur | produce and there exists a possibility of giving a user discomfort.

  Furthermore, according to the induction heating cooker described in Patent Document 4, when an electric power lower than the minimum electric power of the other induction heating coil is input to one of the plurality of induction heating coils, the energization of the inverter However, there may be a problem that magnetostrictive sound that is annoying to the user is generated by the on / off control of the inverter when the power is turned on.

  Therefore, the present invention does not require a voltage variable means or a load power control circuit, and with a simple circuit configuration, does not control on / off of the inverter when the power is turned on, and extremely wide range of thermal power (output power) is very delicate. It is an object of the present invention to provide an induction heating cooker that can be adjusted and a control method thereof.

The present invention has been made to solve the above problems, and relates to an induction heating cooker,
A plurality (i, i is a natural number of 2 or more) of heating coils that are adjacent to each other and cooperate to inductively heat a single object to be heated;
A plurality of power supply units individually supplying a high-frequency current having a predetermined driving frequency to each heating coil;
A detecting unit that detects a driving current flowing through each heating coil and a driving voltage applied to both ends of each heating coil, and calculates a load resistance and a resonance frequency of each heating coil from the detected driving current and driving voltage. When,
An operation unit capable of setting a desired target heating power consumed by each heating coil by a user;
A control unit connected to the detection unit and the operation unit,
The controller is
a) To each of a plurality of thermal power bands corresponding to a desired target thermal power of each of the heating coils set by the user to the maximum (Fr ₀ ) of the calculated resonance frequencies (Fr _i ) of the respective heating coils. The drive frequency (F _D = Fr ₀ + ΔFr) is determined by adding the same differential frequency (ΔFr) set for
b) A high-frequency current having a drive frequency (F _D ) determined based on a desired target heating power of each heating coil set by the user and a calculated load resistance of each heating coil is periodically generated in each heating coil. The power supply units are controlled so as to adjust the time interval (t) supplied to the power supply.

  According to the embodiment of the present invention, by calculating the load resistance and resonance frequency of each heating coil, and determining the specific drive frequency according to the thermal power desired by the user, a plurality of thermal power ranges that can be supplied to the pan By roughly setting and adjusting the magnitude of the high-frequency current flowing through the switching element of the inverter circuit by fixing the driving frequency, controlling the driving phase relationship of the switching element, and adjusting the application time of the driving voltage It is possible to provide an induction heating cooker capable of finely adjusting a predetermined heating power.

It is a perspective view showing the whole induction heating cooking appliance 1 concerning the present invention roughly. It is the top view which omitted a part of top plate and looked at the IH heating part from the top. It is sectional drawing seen from the III-III line | wire of FIG. 2 of the IH heating part which concerns on Embodiment 1. FIG. It is the conceptual diagram which showed typically the electrical structure of the induction heating cooking appliance of this invention. 2 is a schematic diagram showing an electrical configuration of the power supply device according to Embodiment 1. FIG. 2 is a circuit block diagram showing an electrical configuration of the power supply device according to Embodiment 1. FIG. It is a circuit block diagram of a general LCR resonance circuit. 3 is a flowchart showing a control method according to the first embodiment. It is a top view which shows the detailed form of an operation part. It is a top view which shows the detailed form of a display part. It is a graph which shows transition of the drive frequency adjusted with respect to target thermal power. It is the graph which plotted the magnitude | size of the high frequency current when supplying the high frequency current which has various drive frequencies to the pan which has a predetermined resonant frequency. (A) is a timing chart of the control signal supplied to the high-voltage side and low-voltage side switching elements of the first and second arms of the inverter circuit, and (b) is the timing of the high-frequency current flowing through the LCR induction heating unit. It is a chart. (A) is a timing chart of the control signal supplied to a switching element by another phase difference, (b) is a timing chart of the high frequency current which flows into a LCR induction heating part. It is a graph with which the variation | change_quantity of the output thermal power by a phase difference changes discretely with respect to the adjustment amount of a thermal power adjustment dial. It is a graph with which the variation | change_quantity of the output thermal power by the single control phase difference changes continuously with respect to the adjustment amount of a thermal power adjustment dial. (A) is a graph which shows the variation | change_quantity of the phase difference with respect to the adjustment amount of a thermal-power adjustment dial, (b) is a graph which shows the thermal-power variation | change_quantity (gradient) with respect to a phase difference step. It is a graph which shows another relationship between a thermal power adjustment amount and setting thermal power. In Embodiment 1, it is a graph which shows distribution of the output power of the central coil and each peripheral coil with respect to setting output. It is a flowchart which shows the control method when the setting thermal power by Embodiment 2 is changed. It is the same flowchart as FIG. 20 which shows another control method when the setting thermal power by Embodiment 2 is changed. 6 is a schematic diagram showing an electrical configuration of a power supply device according to Embodiment 3. FIG. FIG. 6 is a circuit block diagram illustrating an electrical configuration of a power supply device according to a third embodiment. In Embodiment 3, it is a graph which shows distribution of the output power of the central coil and each peripheral coil with respect to setting output. It is a top view when the frying pan for egg-baking is mounted above the top plate of an IH heating part. 6 is a plan view of an IH heating unit according to Embodiment 4. FIG.

  Embodiments of an induction heating cooker according to the present invention will be described below with reference to the accompanying drawings. In the description of each embodiment, terms indicating directions (for example, “upward”, “downward”, “right”, “left”, etc.) are used as appropriate for easy understanding. However, these terms do not limit the present invention.

Embodiment 1 FIG.
The first embodiment of the induction heating cooker according to the present invention will be described in detail below with reference to FIGS. FIG. 1 is a perspective view schematically illustrating the entire induction heating cooker 1 according to the present invention. In FIG. 1 and FIG. 2, the induction heating cooker 1 is roughly arranged on the left and right sides of a casing 2 mainly composed of sheet metal, a top plate 3 formed of glass or the like covering almost the entire upper surface thereof. A pair of IH heating units 10 and 11, a central heating unit 4 disposed in the center, and a cooking grill 5 are provided.

  In FIG. 1, the IH heating unit 10 shown on the left side in the drawing is illustrated and described as an IH heating unit according to the present invention, but both of the IH heating units 10 and 11 may adopt the present invention. Moreover, the center heating part 4 arrange | positioned in the center back may employ | adopt any heating system of an IH (induction heating) system or a radiant system. Similarly, the central heating unit 4 may be configured as an IH heating unit according to the present invention. Further, in the induction heating cooker 1 according to the present invention, the number and arrangement positions of the IH heating parts are not limited to those shown in FIG. 1, and more IH heating parts are provided and arranged in a horizontal row or an inverted triangle shape. It may be a thing.

  Further, in this embodiment, the induction heating cooker 1 having a so-called center grille structure in which the cooking grill 5 is arranged in the approximate center of the casing 2 will be described as an example. It is not limited, and the cooking grill 5 is biased to one of the side surfaces (the induction heating cooker having a so-called side grill structure) or the induction heating cooker that does not include the cooking grill 5 as well. Can be applied.

  The induction heating cooker 1 includes an operation unit (operation panel) 6 used for a user to operate each of the IH heating units 10 and 11, the central heating unit 4 and the cooking grill 5, and “thermal power (output power)”. There are provided display units 8a, 8b, and 8c using thermal power adjustment dials 7a and 7b to be adjusted, and liquid crystal display elements for displaying the control states and operation guides thereof. Although not shown here, the display unit 8 may include a light emitting unit (LED level meter) that displays the magnitude and setting state of the thermal power adjusted by the user. Regarding the operation unit 6 and the display unit 8, their configuration, arrangement position, and the like are not limited to those illustrated. Further, the heating power adjustment dial 7 may also be collectively arranged on the side opposite to the cooking grill 5 in the induction cooking device having the side grill structure.

The induction heating cooker 1 has an exhaust port 9 a and a pair of intake ports 9 b and 9 c provided on the rear surface side of the top plate 3. Furthermore, as will be described later, the induction heating cooker 1 includes a power supply device (power supply unit) 12 that supplies a high-frequency current to the IH heating units 10 and 11. FIG. 1 shows an example of the number, size, arrangement position, and the like of the exhaust port 9a and the intake ports 9b and 9c, and the present invention is not limited to these.
In the following detailed description, when the user sets the heating power using the operation unit 6, “adjustment”, when the control circuit in the present invention sets / controls the operation of the component parts such as the power supply device 12. Uses the term “adjustment”.

  FIG. 2 is a plan view of the IH heating unit 10 as viewed from above with a part of the top plate 3 omitted. As illustrated, the IH heating unit 10 includes at least one heating coil (hereinafter simply referred to as “central coil”) 20 disposed in the center, and a plurality of (first embodiment) disposed around the central coil 20. Then, four heating coils (hereinafter simply referred to as “peripheral coils”) 30a to 30d. That is, the IH heating unit 10 heats a single pot K in cooperation with (as a set) at least one central coil 20 and a plurality of peripheral coils 30a to 30d.

  The central coil 20 according to the first embodiment includes concentric circles, an inner central coil 20a and an outer central coil 20b connected in series, and a conductive wire (for example, a litz wire) made of any metal having an insulating coating. Etc.) are wound in a spiral shape. On the other hand, each of the peripheral coils 30a to 30d has a ¼ arc shape (banana shape or pepper shape) planar shape, and the same conductive wire follows the ¼ arc shape of each of the peripheral coils 30a to 30d. It is formed by winding. That is, each of the peripheral coils 30a to 30d is configured to extend substantially along the circular planar shape of the outer central coil 20b in a quarter arc region adjacent to the outer central coil 20b.

  As shown in FIG. 2, the arrows shown on the central coil 20 and the peripheral coils 30a to 30d indicate an example of the direction of the high-frequency current at a certain point in time. In the figure, the central coil 20 and the peripheral coils It is preferable that the current flowing inside 30a to 30d is controlled so as to be in the same direction in the adjacent portion of the coil.

  FIG. 3 is a schematic configuration diagram including a cross-sectional view of the IH heating unit 10 according to Embodiment 1 as viewed from the line III-III in FIG. 2. As described above, the IH heating unit 10 includes a central coil 20 and a plurality of peripheral coils 30 (only the peripheral coils 30a and 30c are shown in FIG. 3) supported on the upper surface of the coil base 14, and a lower surface of the coil base 14. A plurality of supported magnetic bodies (ferrite cores) 15 and a magnetic cancel ring 18 fixed to the peripheral portion of the coil base 14 are provided. Each of the magnetic bodies 15 is disposed below the central coil 20 and the peripheral coil 30. Each ferrite core 15 is for reducing the radial magnetic resistance. The ferrite core 15 may be formed in a rod shape and arranged along the radial direction (radially). The magnetic cancel ring 18 blocks magnetic flux that does not contribute to the heating of the pan K from leaking outward in the radial direction.

  Next, the power supply device 12 according to the present invention will be described. FIG. 4 is a conceptual diagram schematically showing the electrical configuration of the induction heating cooker 1 of the present invention. The induction heating cooker 1 shown in FIG. 4 includes a central inverter circuit (central drive circuit) 40 for supplying a high frequency current to the central coil 20, and a peripheral inverter circuit for supplying a high frequency current to each of the peripheral coils 30a to 30d. (Peripheral drive circuit) It has the power supply device (power supply part) 12 which consists of 50a-50d. The induction heating cooker 1 detects the driving voltage V at both ends of the central coil 20 and each of the peripheral coils 30a to 30d and the driving current I flowing therethrough to detect load information (load resistance (impedance) and resonance frequency of the pan K. Etc.) and a control unit 80 for controlling the inverter circuits 40, 50a to 50d based on the load information.

  Returning to FIG. 3, the central inverter circuit 40 that supplies power to the central coil 20 and the peripheral inverter circuits 50 a and 50 c that supply power to the peripheral coils 30 a and 30 c are illustrated. These are connected to the detection units 60 and 70 and the control unit 80 described above. The operation unit 6 and the display unit 8 are connected to the control unit 80.

  Since a temperature sensor (not shown) is disposed between the inner central coil 20a and the outer central coil 20b so as to come into contact with the top plate 3, for example, a gap of about 20 mm is provided. On the other hand, a gap of about 10 mm, for example, is provided between the outer central coil 20b and the peripheral coils 30a to 30d. Further, a gap d1 of about 3 mm, for example, is provided between the top surfaces of the central coils 20a and 20b and the peripheral coils 30a to 30d and the top plate 3. In addition, such a space | interval shows an example and does not limit this invention.

  The inner central coil 20a and the outer central coil 20b may be connected in series (FIG. 2), and each of the peripheral coils 30a-30d is connected to a separate peripheral inverter circuit 50a-50d and independently a high frequency current. May be configured to be supplied (FIG. 4). FIG. 5 is another schematic diagram of the power supply device 12 that supplies a high-frequency current to the central coil 20 and the peripheral coils 30a to 30d. Each of the central coil 20 and each of the peripheral coils 30a to 30d includes, for example, full-bridge inverter circuits 40 and 50a to 50d including a pair of arms 16 and 17 (FIG. 6), and each of the heating coils 20 and 30a to 30d. Detection units 60, 70a to 70d that detect load information of the pan K (loading state and size of the pan, or load resistance and resonance frequency indicating the constituent material of the pan), each inverter circuit based on the load information of the pan K The control part 80 which controls 40, 50a-50d, the operation part 6, and the display part 8 are illustrated similarly.

  Since each of the full-bridge inverter circuits 40 and 50a to 50d has the same circuit configuration, the power supply device 12 including the full-bridge inverter circuit 40 that supplies a high-frequency current to the central coil 20 will be described as a representative example. FIG. 6 is a circuit block diagram showing an electrical configuration of the power supply device 12 according to the present invention. The power supply device 12 generally includes a rectifier (for example, a diode bridge) 92 for full-wave rectifying the commercial power supply AC, a filter circuit 94 for smoothing the full-wave rectified waveform, and a central inverter circuit 40 for the central coil 20 (enclosed by a broken line). ). The bus voltage output from the filter circuit 94 is supplied to the inverter circuit 40.

The inverter circuit 40 according to the present invention can be a half-bridge inverter circuit as well, but here, a full-bridge inverter circuit will be described. The full-bridge inverter circuit 40 includes a first arm 16 including first high-voltage side and low-voltage side switching elements SW _1U and SW _1D , and second high-voltage side and low-voltage side switching elements SW _2U and SW _2D. And a second arm 17 including As each of the switching elements SW _1U , SW _1D , SW _2U , SW _2D , any switching element known to those skilled in the art can be used, and for example, an IGBT (insulated gate bipolar transistor) may be used.

In FIG. 6, the central coil 20 is shown as an equivalent circuit of an inductance L and a resistance R, and constitutes a central LCR induction heating unit 22 together with a resonance capacitor C connected in series therewith. The central LCR induction heating unit 22 includes switching points SW _1U and SW _1D on the high pressure side and low pressure side of the first arm 16 and switching elements SW _2U and SW on the high pressure side and low pressure side of the second arm 17. Connected to the _2D midpoint. When the pan K is placed on the heating coil 20, the inductance L and the resistance R become the combined inductance L and combined resistance (load resistance) R of the pan K and the heating coil 20.

The control unit 80 supplies a high frequency current to the central coil 20 under an arbitrary driving condition by supplying a control signal to each of the switching elements SW _1U , SW _1D , SW _2U , SW _2D. When a high frequency current is supplied, an alternating magnetic field is formed around it (alternating magnetic field is linked to the heated object K made of a conductor), an eddy current is formed in the pan bottom K, and the pan bottom K itself is heated. The

The central inverter circuit 40 in FIG. 6 _generates a drive voltage V between the high-voltage side switching elements SW _1U and SW _2U and the low-voltage side switching elements SW _1D and SW _2D (that is, both ends of the central LCR induction heating unit 22). A drive voltage detector 24 for detecting and a drive current detector 25 for detecting the drive current I flowing through the central LCR induction heating unit 22 are included. That is, the detection units 60 and 70a to 70d associated with the inverter circuits 40 and 50a to 50d detect the drive voltage V and the drive current I of the LCR induction heating units 22 and 32a to 32d. Although the drive current detector 25 is illustrated as an ammeter that directly detects the drive current I flowing through the central LCR induction heating unit 22, the drive current detector 25 detects the drive current I by detecting the voltage across the resonance capacitor C. It may be. Further, although not explicitly shown here, it goes without saying that each of the inverter circuits 50a to 50d also has a drive voltage detector and a drive current detector.

  Further, the detection units 60, 70a to 70d are connected to the load resistance of the central coil 20 and the peripheral coils 30a to 30d from the detected drive current I flowing through the LCR induction heating units 22, 32a to 32d and the drive voltages V at both ends thereof. R (impedance Z) and resonance frequency Fr can be calculated. That is, the detection units 60 and 70a to 70d are known to those skilled in the art as long as they can calculate the load resistance R and the resonance frequency Fr of the central coil 20 and the peripheral coils 30a to 30d from the drive current I and the drive voltage V. It may have an arbitrary configuration.

  As a specific example, the detection units 60 and 70 calculate the load resistance R and the resonance frequency Fr by extracting the primary components of the drive current I and the drive voltage V detected by the drive current detector 25 and the drive voltage detector 24. The configuration and operation of the configuration (primary component extraction unit) configured as described above will be described below.

As described above, each of the inverter circuits 40, 50a to 50d includes a plurality of switching elements SW _1U , SW _1D , SW _2U , SW _2D and is a control signal (gate signal) having a predetermined drive frequency (for example, 25 kHz). when driving, the driving voltage detector 24 and the drive current detector 25, a high frequency modulated drive voltage V and the drive current I, that is, detects a composite waveform including a natural-number multiple high-order frequency component of the driving frequency F _D .

The detection units (primary component extraction units) 60 and 70 convert the drive voltage V and the drive current I detected as analog signals into digital signals at a high sampling frequency and sample them (not shown). having the drive voltage V and the drive current I has a higher-order frequency components, for example by discrete Fourier transform by using a sampling frequency of an integral multiple of the driving frequency F _D (e.g. 30 times), the drive voltage V and the drive Only the primary component of the current I is extracted. Note that any method and algorithm for extracting a signal of only the primary component from a signal having a high-order frequency component can be used, and generally one of the drive voltage V and the drive current I is obtained using commercially available software. Only the next component can be extracted.

  At this time, the detection units (primary component extraction units) 60 and 70 can complex display the primary components of the drive voltage V and the drive current I as in the following equations.

ここでＶ_１，Ｉ_１は駆動電圧Ｖおよび駆動電流Ｉの１次成分を示し、Ｖ_１Re，Ｉ_１ReはＶ_１，Ｉ_１の実部、Ｖ_１Im，Ｉ_１ImはＶ_１，Ｉ_１の虚部、そしてｊは虚数単位を示す。

Here, V ₁ and I ₁ indicate primary components of the driving voltage V and the driving current I, V _1Re and I _1Re are real parts of V ₁ and I ₁ , and V _1Im and I _1Im are imaginary _values of V ₁ and I ₁ . Part and j are imaginary units.

Further, the detection units (primary component extraction units) 60 and 70 include the impedance Z of the LCR induction heating units 22 and 32 and the phase of the drive voltage V ₁ and the drive current I ₁ (the phase of the drive voltage V ₁ with respect to the drive current I ₁₎ . Or the phase of the impedance Z) φ can be calculated by the following equation.

ここでＩｍ（Ｚ）およびＲｅ（Ｚ）はそれぞれインピーダンスＺの虚部および実部を意味する。なお、駆動電圧Ｖおよび駆動電流Ｉの位相は、arctanの代わりにarcsinまたはarccosを用いて算出してもよい。位相差φが９０度付近ではarctanは発散し、誤差を多く含み得るので、arcsinまたはarccosを用いて位相差φを算出することが好ましい場合がある。

Here, Im (Z) and Re (Z) mean an imaginary part and a real part of the impedance Z, respectively. Note that the phases of the drive voltage V and the drive current I may be calculated using arcsin or arccos instead of arctan. When the phase difference φ is around 90 degrees, arctan diverges and may contain many errors, so it may be preferable to calculate the phase difference φ using arcsin or arccos.

Further detection unit (primary component extraction unit) 60 and 70, the driving voltages _{V 1} and the drive current _{I 1} of the first-order component of the complex notation, the effective power value _{W E,} and the current effective value _{I E,} the following equation Can be calculated.

ここでＩ_１ ^＊はＩ_１の複素共役を示す。

Here, I ₁ ^* represents a complex conjugate of I ₁ .

  On the other hand, in a general LCR circuit including the LCR induction heating units 22 and 32, the load resistance R, impedance Z, inductance L of the heating coils 20 and 30, and resonance frequency Fr are expressed by the following equations.

ここでωは１次成分の駆動周波数Ｆ_Ｄ（ω＝２πＦ_Ｄで表される）であり、Ｃは共振コンデンサＣの静電容量であって、ともに既知である。したがって検知部（１次成分抽出部）６０，７０は、［数２］で算出したφを用いて、［数４］から共振周波数Ｆｒと負荷抵抗Ｒ（＝Ｒ_Ｃ＋Ｒ_Ｌ）を求めることができる。

Here, ω is the driving frequency F _{D of the} primary component (expressed by ω = 2πF _D ), and C is the capacitance of the resonance capacitor C, both of which are known. Therefore, the detection units (primary component extraction units) 60 and 70 obtain the resonance frequency Fr and the load resistance R (= _RC + _RL ) from [Expression 4] using φ calculated in [Expression 2]. it can.

The impedance Z of the LCR induction heating units 22 and 32 varies depending on the presence / absence of the heated body K or the mounting state (alternating magnetic field linked to the heated body K). That is, the load resistance R in the above formula [Equation 4] is the apparent resistance of the pan K due to the pan K being placed on the wire resistance _RC of the heating coils 20 and 30 when the pan K is not placed. This corresponds to a load resistance R _L added (R = R _C + R _L ). Therefore, the detection units (primary component extraction units) 60 and 70 can detect the material of the pan K (for example, SUS, copper, or aluminum having iron, magnetism, or nonmagnetism) from the calculated resonance frequency Fr. At the same time, the placement area of the pan K placed above the heating coils 20 and 30 can be detected from the apparent load resistance _{RL of} the pan K. Load resistance shows the the placing area of the heating coils 20 and 30 above the material and pot K these pots K R and the resonant frequency Fr and (inductance L) such that the load information of the pot K is in the present invention.

As described above, the control unit 80 according to the embodiment includes the resonance frequency Fr and the load resistance R calculated by the detection units (primary component extraction units) 60 and 70, and the desired thermal power P set by the user through the operation unit 6. _{According to T} , each inverter circuit 40, 50a-50d can be controlled so as to supply an appropriate high-frequency current to the central coil 20 and each peripheral coil 30. The detectors 60 and 70 detect the drive voltage V and the drive detected in a single cycle of the drive voltage and drive current modulated at high frequency (that is, when the drive frequency is 25 kHz, one cycle is 40 microseconds). From the current I, the resonance frequency Fr and the load resistance R can be calculated in a very short time for each of the central coil 20 and each peripheral coil 30. Therefore, the control unit 80 obtains the load information from the detection units 60 and 70 instantaneously, and each inverter circuit 40 , 50a to 50d provides an appropriate high frequency current to each of the central coil 20 and each peripheral coil 30. it can be controlled in so that to supply.

FIG. 7 shows a resonance circuit model of a general LCR resonance circuit. The power P with which the LCR induction heating units 22 and 32 heat the pan K is proportional to the square of the drive current I flowing through the LCR induction heating units 22 and 32 and the load resistance (combined resistance) R. As shown, this corresponds to the line resistance R _C of the heating coils 20, 30 itself plus the apparent load resistance R _L of the pan K due to the pan K being placed (R = R _C + R _L ).

For example, when the load resistance R (combined resistance R = R _L + R _C ) detected by the detection units 60 and 70 does not exceed a predetermined value, the control unit 80 has a small apparent load resistance R _L due to the pan K. When it is determined that the pan K is not placed on the central coil 20 or the peripheral coils 30a to 30d or only a part of the pan K is placed, the central coil 20 or the peripheral coils 30a to 30a The supply of high-frequency current to 30d can be stopped or suppressed.

Specifically, in addition to the load information from the detection units 60 and 70, the control unit 80 responds to setting information from the operation unit 6 or the thermal power adjustment dial 7 (set thermal power or target thermal power P _T desired by the user). Thus, an appropriate control signal is supplied to each of the inverter circuits 40, 50a to 50d.

Control unit 80 which, inter alia according to the present invention, as described in detail below, the resonance frequency Fr, the phase difference between the drive frequency F _D and the inverter circuits of appropriate control signals in response to the load resistor R, and setting thermal power P _T theta By controlling this, effective and precise thermal power adjustment is realized.

  Next, the control method of the induction heating cooker by the control part 80 which concerns on this invention is demonstrated, referring FIGS. 8-19. FIG. 8 is a flowchart showing an outline of a control method of the control unit 80 according to the present invention.

[ST01: Resonance frequency calculation]
In step ST01 of FIG. 8, as described above, the detection units 60 and 70 are used to calculate the resonance frequency Fr, the load resistance R, and the like of the heating coils 20 and 30 (LCR induction heating units 22 and 33).

[ST02: Determination of drive frequency]
In step ST02 of FIG. 8, the user sets and inputs a desired heating power using the operation unit 6. The operation unit 6 may have a configuration as shown in FIGS. 9A to 9C. The operation unit 6 in FIG. 9A includes a button 6a for selecting “weak” thermal power, “medium” thermal power, and “strong” thermal power, and adjustment buttons 6b and 6c for increasing / decreasing the thermal power. The thermal power adjustment dial 7 shown in FIG. 9B is a rotary dial type thermal power adjustment dial, and is configured so that “strong” thermal power is obtained when rotated to the right and “weak” thermal power is obtained when rotated to the left. Has been. The operation unit 6 in FIG. 9C (not shown in FIG. 1) has a button 6d for selecting a heating power that increases in accordance with a given number, as in FIG. It has a “3kW” button.

On the other hand, the display unit 8 may be configured by using an LED level meter as shown in FIG. 10 in addition to the one shown in FIG. 1, and displays the set thermal power _PT set in 12 steps. For example, in FIG. 10, “thermal power 1” is 100 W, “thermal power 2” is 200 W, “thermal power 3” is 400 W, “thermal power 7” is 700 W, “thermal power 10” is 2000 W, “thermal power 12” is 3000 W may be allocated. Then, when the button 6a for selecting “weak” thermal power is pressed, “thermal power 2” is set, when “medium” thermal power button 6a is pressed, “thermal power 7” is set, and when “strong” thermal power button 6a is pressed, “thermal power 10” is set. May be set. In order to set “thermal power 4”, after pressing the “weak” thermal power button 6a, further press the adjustment button 6c for increasing the thermal power to set the thermal power, and to set “thermal power 6”, After pressing the “middle” thermal power button 6a, the thermal power decrease adjustment button 6b is further pressed to set the thermal power, and when “thermal power 12” is to be set, after the “strong” thermal power button 6a is pressed, the thermal power increase adjustment button 6c. the may be the heating power setting for 2 Kai押. Note that these numerical values, buttons and thermal power allocation, operation methods, and the like are examples of operations for setting thermal power, and do not limit the present invention.

Figure 11 is a graph showing a change in the driving frequency F _D to be adjusted with respect to the set thermal power P _T. Control unit 80, the resonance frequency _(Fr i of the detected central coil 20 and each of the peripheral coils 30a~30d by the detection unit 60, 70, i correspond to the respective center coil 20 and each of the peripheral coils 30a~30d identifier, The drive frequency (F _D = Fr ₀ + ΔFr) is determined by adding the offset frequency (ΔFr, also referred to as a difference frequency) to the maximum (Fr ₀ ) of i = 1 to 5).

Figure 12 is a graph plotting the Okiki of the high frequency current I _HF when supplying a high-frequency current having various driving frequencies in the pot K made of a material having a resonant frequency Fr. As apparent from FIG. 12, the high-frequency current I _HF is a function of the driving frequency F _D, to remain at Cauchy distribution curve having a peak resonant frequency Fr. That high-frequency current _{I HF} is closer to the resonance frequency Fr, exponentially increases, also the drive current I flowing through the switching element SW of the inverter circuits 40,50A～50d, the driving frequency _{F D} approaches the resonance frequency Fr It increases. However the drive current I exceeds the maximum allowable drive current _{I MAX} of the switching element SW, there is a possibility that the switching element SW is destroyed, the driving frequency _{F D} frequencies higher than the resonant frequency Fr and _(F D> Fr) It is better to choose.

On the other hand, the driving frequency band (IH heating frequency band) of the switching element used in the inverter circuit of the power supply device 12 of a general induction heating cooker is defined as 20 kHz to 100 kHz by law, and each inverter circuit 40, 50a. without destroying the switching element SW of ～50D, more safely, and to supply a high-frequency current _{I HF} with high reliability, in the range of 20 kHz to 100 kHz, and a predetermined offset frequency ΔFr than the resonance frequency Fr it is preferably driven by (difference frequency) that is higher driving frequency F _D. In other words, the driving frequency F _D can be more offset frequency ΔFr is smaller, by supplying a larger high-frequency current I _HF in a pot, to achieve greater thermal power P.

However, as is clear from FIG. 12, the high-frequency current I _HF, since the driving frequency F _D decreases as the exponentially increases beyond the resonant frequency Fr, the pot K by adjusting only the driving frequency F _D Although it is possible to adjust the flowing high-frequency current _IHF , there is an aspect that it is somewhat difficult to control in terms of delicate adjustment. Accordingly the present invention, as described in detail later, is set to (first adjusting means), a plurality of predetermined thermal range firepower supplied to the pot K by adjusting the driving frequency F _D in the first, second fixing the driving frequency F _D in, the (second adjusting means), a predetermined thermal power range by adjusting the high-frequency current flows time the switching element SW of the inverter circuits 40,50A～50d (phase difference) This is to finely adjust the set thermal power _PT .

As a specific example, it is assumed that the pan K is made of iron and the maximum resonance frequency Fr ₀ of the resonance frequencies Fr of the heating coils 20 and 30 detected by the detection units 60 and 70 is 20 kHz. At this time, the user uses the operation unit 6 as shown in FIG.
i) If you select "weak" thermal less than 500 W, the offset frequency .DELTA.fr _A as 3 kHz, the drive frequency _{F D} and 23 kHz (the driving frequency _{F DA),}
If you select "medium" firepower ii) 500W~1500W, the offset frequency .DELTA.fr _B as 2.5 kHz, the drive frequency _{F D} and 22.5 kHz (the driving frequency _{F DB),}
If you choose "strong" firepower iii) 1500W~3000W, as 2kHz the offset frequency .DELTA.fr _C, the driving frequency _{F D} is determined as 22.0KHz (driving frequency _{F DC) (F DA> F} DB> F DC) .
These offset frequencies ΔFr and the driving frequency F _D is determined by the control unit 80.

Thus, the three offset frequencies ΔFr have a relationship of ΔFr _A > ΔFr _B > ΔFr _C , and these offset frequencies ΔFr are added to the maximum resonance frequency Fr ₀ in accordance with the thermal power selected by the user to drive frequency F _D is determined, and as shown in FIG. 11, three thermal power zones (“weak” thermal zone, “medium” thermal zone, and “strong” thermal zone) are set. In this embodiment, three thermal power zones are set. However, the present invention is not limited to this, and the number of thermal zones may be two or four or more. That is, the offset frequency ΔFr applied to the maximum resonance frequency is the smallest in the maximum thermal power or a region (thermal power zone) including the maximum thermal power, and the highest value in the minimum thermal power or the region including the thermal power zone (thermal power zone).

[ST03: Determination of phase difference]
Next, a method for determining the time (time interval t) during which the high-frequency current flows in the switching elements of the inverter circuits 40, 50a to 50d in step ST03 in FIG. 8 will be described.
FIG. 13A shows switching elements SW _1U and SW _1D on the high voltage side and low voltage side of the first arm 16 and the high voltage side and low voltage side of the second arm 17 constituting the central inverter circuit 40 shown in FIG. of a timing chart showing an example of the switching element _SW 2U, control signal supplied to the _{SW 2D.} When a high-frequency current flows directly from the high-voltage side switching element SW _1U of the first arm 16 to the low-voltage side switching element SW _1D without passing through the load (LCR induction heating unit 22), the switching elements SW _1U and SW _1D Loss and thus overcurrent breakdown can occur. In order to prevent this, a period (on phase and off phase) when the control signals supplied to the high voltage side switching element SW _1U and the low voltage side switching element SW _1D of the first arm 16 are on and off. Is normally controlled by the control unit 80 so as to be complementary (or exclusive). For the same reason, the control unit 80 ensures that the ON phase and the OFF phase of the control signal supplied to the high voltage side switching element SW _2U and the low voltage side switching element SW _2D of the second arm 17 are always complementary. Be controlled. It is on phase and the off phase total driving signal one period T of, expressed by the reciprocal of the driving frequency F _D from the definition _{(T = 1 / F D)} .

On the other hand, in the generally available switching element SW, the control signal supplied from the control unit 80 does not have a complete rectangular shape but has distortion and delay. There may be a delay from when the signal is supplied until the high frequency current starts to flow through the load (LCR induction heating unit 22). Therefore, in order to prevent the high-frequency current from flowing directly from the high-voltage side switching element SW _1U of the first arm 16 to the low-voltage side switching element SW _1D without passing through the LCR induction heating unit 22, A dead time d (driving suspension period) is provided between the timing at which the on / off control signal is supplied to the SW _1U and the timing at which the off / on control signal is supplied to the low-voltage side switching element SW _1D. Controlled by the control unit 80 . If each switching element uses an ideal switching element in which distortion and delay do not occur and the dead time d is set to zero (0), for example, the control signal in FIG. In the case of a signal, that is, a signal with a so-called duty of 50%, the time during which the on / off control signal is supplied is equal to ½ of the driving cycle T at maximum.

As shown in FIG. 13A, when an on / off control signal is supplied to the switching elements SW _1U , SW _1D , SW _2U , and SW _2D , the timing shown in FIG. A drive voltage is applied. That is, when the high-voltage side switching element SW _1U of the first arm 16 and the low-voltage side switching element SW _2D of the second arm 17 are in the on state, the LCR induction heating unit 22 is moved from the left to the right in FIG. direction) high-frequency current I flows, when the low voltage side switching element _{SW 1D} of the high voltage side switching element _{SW 2U} and the first arm 16 of the second arm 17 is in the oN state, in FIG. 6 to LCR induction heating section 22 A high-frequency current I flows from left to right (negative direction).

14A similarly supplies the first high-voltage side and low-voltage side switching elements SW _1U and SW _1D and the second high-voltage side and low-voltage side switching elements SW _2U and SW _{2D shown} in FIG. It is a timing chart which shows an example of the control signal to be performed. The difference between FIG. 13 (a) and FIG. 14 (a) is that the on / off control signal is supplied to the second high-voltage side and low-voltage side switching elements SW _2U and SW _2D (on phase and Compared to the timing (on phase and off phase) at which the on / off control signal is supplied to the first high-voltage side and low-voltage side switching elements SW _1U and SW _1D (off phase), FIG. ) Is delayed by π, and in FIG. 14A, it is delayed by the delay time τ. That is, the delay time τ in the driving cycle T is expressed by the following equation by the delay phase difference θ.

よって、デッドタイムｄをゼロ（０）としたとき、オン制御信号が供給されている最大時間が駆動周期Ｔの１／２となるので、遅延位相差θの設定範囲は次式で表される。

Therefore, when the dead time d is set to zero (0), the maximum time during which the ON control signal is supplied is ½ of the drive cycle T, and therefore the setting range of the delay phase difference θ is expressed by the following equation. .

ただし、デッドタイムｄ(＞０）を考慮すると、遅延時間τに２倍のデッドタイムｄを加えた時間が駆動周期Ｔの１／２となるので、遅延位相差θは次式で表される。

However, considering the dead time d (> 0), the time obtained by adding the double dead time d to the delay time τ is ½ of the driving cycle T, and therefore the delay phase difference θ is expressed by the following equation. .

デッドタイムｄは、上述のとおり、スイッチング素子ＳＷの損失を低減し、過電流破壊を回避するためのものであるので、スイッチング素子ＳＷの特性および駆動周波数Ｆ_Ｄに依存するが、たとえば２．５μ秒であってもよい。

Dead time d, as described above, to reduce the loss of the switching elements SW, since it is intended to avoid over-current breakdown depends on the characteristics and the driving frequency F _D of the switching element SW, for example, 2.5μ It may be seconds.

At this time, when the on / off control signal is supplied to the switching elements SW _1U , SW _1D , SW _2U , and SW _2D at the timing shown in FIG. 14A, the first high voltage is supplied at the timing shown in FIG. 14B. When the side switching element SW _1U and the second low voltage side switching element SW _2D are in the ON state, a positive current flows through the LCR induction heating unit 22, and the second high voltage side switching element SW _2U and the first low voltage side When the switching element SW _1D is in the ON state, a negative current flows through the LCR induction heating unit 22.

As apparent from a comparison of the timing charts of FIG. 13B and FIG. 14B, the time interval t periodically supplied to each of the heating coils 20 and 30, that is, a pair of full-bridge inverter circuits is formed. The phase difference (delayed phase) θ between the arms 16 and 17, that is, SW _1U of the first arm 16 and SW _{2D of} the second arm 17 (or SW _2U of the second arm 17 and SW _{1D of} the first arm 16). ) Are simultaneously turned on, the high-frequency current (target heating power or output power) supplied to the LCR induction heating unit 22 can be adjusted. Although not detailed description, even when adopting a half-bridge type inverter circuit, by adjusting the ON time of the switching element, similarly, the high-frequency current the LCR induction heating with a constant driving frequency F _D by adjusting the time interval t which is periodically supplied to the parts 22 and 32, it is possible to adjust the thermal power P. These delay times τ (phase difference θ) are determined by the control unit 80 in accordance with the heating power P set by the user using the operation unit 6.

As described above, the driving frequency _{F D} is maintained at maximum resonance frequency of the resonance frequencies of the respective heating coils 20 and 30 detected by the detecting portion 60, 70 (Fr ₀₎ constant as plus an offset frequency ΔFr Thus, the thermal power supplied to each heating coil 20 and 30 is determined as a thermal power zone composed of “weak” thermal power less than 500 W, “medium” thermal power less than 500 W to 1500 W, or “strong” thermal power less than 1500 W to 3000 W. be able to. Furthermore, in this embodiment, based on the load resistance R or impedance Z of each heating coil 20, 30 detected by the detection units 60, 70, a full bridge inverter that supplies a high frequency current to each heating coil 20, 30. The delay phase of the circuit (or the time interval t (delay time τ) periodically supplied to each of the LCR induction heating units 22 and 32, hereinafter simply referred to as “phase difference θ”) can be adjusted. In this case the driving frequency _{F D,} so is maintained constant in each inverter circuit 40,50A～50d, interference noise arising when the driving frequency _{F D} differed supplied to each heating coil 20 and 30 (beat sound) occurring Can be prevented.

More specifically, when using an AD converter or a microcontroller (not shown) having 8-bit information (256 (= 2 ⁸ ) steps resolution), the control unit 80 can obtain a phase difference θ of 256 steps at maximum. Can be realized. That is, in a “weak” thermal power zone of less than 500 W, it is theoretically possible to realize a delicate thermal power adjustment by about 2 W (= 500/256). Control unit 80, for example if it is desired to firepower 200 W, to fix the drive frequency F _DA, about 2W as a single step, to determine the phase difference θ corresponding to about 100 steps, the inverter circuits in the phase difference θ 40, 50a to 50d are controlled. Even if the AD converter or the like of the control unit 80 has 4-bit information (16 (= 2 ⁴ ) step resolution), fine adjustment of about 31 W (= 500/16) can be performed.

Similarly, when the AD converter or the like of the control unit 80 has a resolution equivalent to 8 bits (256 (= 2 ⁸ ) steps), in the “medium” thermal power zone of less than 1500 W, about 5.9 W (= 1500/256). ) And a “strong” thermal zone of less than 3000 W, the thermal power of about 11.7 W (= 3000/256) can be finely adjusted. In other words, according to this embodiment, the user can adjust the heating level very precisely in a dish that is slowly cooked over low heat. This controls the by adjusting the phase difference θ firepower as, in comparison with the case where by adjusting only the driving frequency F _D for adjusting the heating power (high frequency current), the high-frequency current is dependent on the driving frequency F _D This supplements the difficulty of adjusting the thermal power due to the exponential increase / decrease.

  In addition, fine adjustment is possible, so that resolution | decomposability of the AD converter etc. of the control part 80 is large. On the other hand, in an actual AD converter or the like, the power supply voltage for driving the AD converter is generally as small as about 5V, and when exogenous noise or the like is superimposed, the sensitivity to the change amount of 1 bit is reduced, May adversely affect the resolution. Therefore, in order to eliminate adverse effects such as noise as much as possible, in order to secure a margin for noise, the sensitivity (resolution) is intentionally decreased, the adjustment step (adjustable thermal power unit) is increased, and the discrete thermal power is increased. Adjustments may be made.

As described above, when the AD converter or the like of the control unit 80 has 4-bit information (resolution of 16 (= 2 ⁴ ) steps), the “weak” thermal power band (F _DA ) of less than 500 W, “ In the “medium” thermal zone (F _DB ) and the “strong” thermal zone (F _DC ) of less than 3000 W, the phase difference θ corresponding to the resolution of one step (hereinafter referred to as “unit phase difference θ”) is about each. This corresponds to a regulated heating amount of 31 W (= 500/16), about 93 W (= 1500/16), and about 187 W (= 3000/16). Figure 15 is set to determine the driving frequency F _D from thermal P _T, is a graph showing the actual output thermal relationship when adjusting the phase difference θ (X / 16 steps). At this time, since the high-frequency current I does not flow when the value X becomes 0, the thermal powers adjustable by the unit phase difference θ are 500 W (low thermal power), 1500 W (medium thermal power), and 3000 W (high thermal power), respectively. Note that it is 1/16 of the maximum value of.

Table 1 below shows the thermal power adjustment amount when the resolution step of the phase difference θ is changed in each thermal power band (drive frequency F _D ). For example, when the phase difference θ step is set to 5/16 or 4/16 in the middle thermal power zone, it can be adjusted to a thermal power of less than 500 W belonging to the weak thermal power zone. doing.
Similarly, when the step of the phase difference θ is 4/16 to 7/16 in the strong thermal power zone, it can be adjusted to a thermal power of less than 1500 W belonging to the middle thermal power zone.

When three thermal power zones are set in this way, for example, when shifting from the “weak” thermal zone to the “medium” thermal zone, the “medium” thermal power is set so as to enable continuous thermal power adjustment. The 6/16 step that realizes the minimum thermal power adjustment amount in the belt may be set in advance as a phase difference step that indicates the boundary between adjacent thermal belts. That control unit 80 includes a thermal to be adjusted in 16/16 Step phase difference θ of the drive frequency F _DA of "weak" thermal zone, in 6/16 step phase difference θ of the drive frequency F _DB "medium" thermal zone It is preferable to control each inverter circuit 40, 50a to 50d after recognizing that the adjusted thermal power is continuous. Similarly, the control unit 80 controls the thermal power adjusted by the 16/16 step phase difference θ of the driving frequency F _{DB in} the “medium” thermal power zone and the 9/16 step phase difference of the driving frequency F _{DC in} the “strong” thermal power zone. It is preferable that the inverter circuits 40 and 50a to 50d are controlled by recognizing that the heating power adjusted by θ is continuous.

Further, the AD converter or the like of the control unit 80 is designed to have a sufficiently large resolution (for example, the AD converter or the like of the control unit 80 is designed to have a resolution equivalent to 16 bits (65536 (= 2 ¹⁶ ) steps)). Then, by making the thermal power units adjustable by a plurality of step phase differences θ in the “weak”, “medium”, and “strong” thermal power zones constant, as shown in FIG. Can be made linear in accordance with the user's tactile sense, for example, to adjust the heating power of 1 W, corresponding to about 131/65536 steps of the driving frequency F _DA of the “weak” heating zone. phase difference theta _a, a phase difference equivalent to approximately 44/65536 step of driving frequency _{F DB} "medium" thermal zone theta _B, approximately 22/65536 step of driving frequency _{F DC} "strong" thermal zone By controlling the respective inverter circuits 40,50a~50d those phase difference theta _C, as a single controlled phase difference, it is possible to realize a linear output fired as shown in FIG. 16.

  The control unit 80 according to this embodiment controls the step amount of a discrete value corresponding to the resolution by using an AD converter or the like that is a digital circuit in correspondence with the phase difference θ. The phase difference θ may be continuously adjusted using an analog signal circuit (not shown in detail) widely known to those skilled in the art. When the phase difference θ is continuously adjusted, the user can perform smooth thermal power adjustment that is more suitable for the tactile sensation according to the adjustment amount of the thermal power adjustment dial 7.

  As shown in FIG. 17, the amount of change in output thermal power due to a single control phase difference may be changed non-linearly with respect to the adjustment amount (control amount) of the thermal power adjustment dial 7 by the user. For example, the control unit 80 may be configured so that the control amount of the output thermal power by a single control phase difference responds gently in the “weak” thermal power zone and sharply in the “strong” thermal power zone. . Thereby, a thermal power (output electric power) can be changed nonlinearly. That is, since the output thermal power due to a single control phase difference in each thermal power zone changes, the thermal power change amount (gradient) in an arbitrary thermal power zone can be set freely (FIG. 17B).

In addition to FIG. 17 (b), the relationship between the thermal power adjustment value (control amount of the output thermal power based on a single control phase difference) and the set thermal power _PT is as shown in FIGS. 18 (a) to 18 (c). The control unit 80 stores in advance a functional expression and a numerical table representing the relationship between the two, and sets the relationship together with the product specification (adjustment specification) of the induction heating cooker 1. You can also

[ST04: Control of inverter circuit]
In step ST04 of FIG. 8, as described above, the control unit 80 determines the driving frequency F _D (thermal power band) according to the adjustment amount of the heating power adjustment dial 7, fixes the driving frequency F _D , By adjusting the phase difference θ between the inverter circuits 40, 50a to 50d, each inverter circuit 40, 50a to 50d is controlled so that an arbitrary delicate set thermal power _PT can be obtained.

In addition, the detection units 60 and 70 according to this embodiment detect the impedance Z (load resistance R), thereby determining whether or not the pan K is placed above the heating coils 20 and 30. Therefore, the set thermal power _PT can be distributed on the basis of the load resistance R of each heating coil 20, 30 and the like.

Based on the load resistance R of each heating coil 20, 30, the control unit 80 is configured such that the ratio of the output power P 1 to be supplied to the central coil 20 and the output power P 2 to be supplied to the peripheral coils 30 a to 30 d (P1: P2). ) Is set to 4 to 1, for example, and when the overall target thermal power _PT is 2000 W, the power supply device 12 is controlled so that 1000 W is supplied to the central coil 20 and 250 W is supplied to each of the peripheral coils 30 a to 30 d. (P _T = P1 + 4 × P2, see FIG. 19). The ratio of the output power to be supplied to the central coil 20 and each peripheral coil 30 is arbitrary, and may be changed depending on the load resistance R of each central coil 20 and each peripheral coil 30. The timing chart showing the phase differences of the central coil 20 and the peripheral coils 30 is not shown because it is considered to be understood by those skilled in the art.

  In the above embodiment, the pan K is made of a magnetic material such as iron, and the resonance frequency Fr is 20 kHz. However, the present invention provides a pan K made of a constituent material having an arbitrary resonance frequency Fr. It can be employed in the case of induction heating.

For example, when the detection units 60 and 70 detect that the resonance frequency Fr of the aluminum pan K is 60 kHz,
i) If you select "weak" thermal less than 500 W, the offset frequency ΔFr as 7 kHz, the drive frequency _{F D} and 67 kHz (the driving frequency _{F DA),}
If you select "medium" thermal below ii) 500W~1500W, the offset frequency ΔFr as 5 kHz, the drive frequency _{F D} and 65 kHz (the driving frequency _{F DB),}
If you select iii) "strong" below 1500W~3000W firepower, the offset frequency ΔFr as 2 kHz, the drive frequency _{F D} is determined as 62.0KHz (driving frequency _{F DC) (F DA> F} DB> F DC) .
The "weak", "medium", the thermal zone of "strong", the control unit 80, to fix the drive frequency F _D, to control the phase difference θ the user according to the adjusted amount of thermal power adjusting dial 7 Thus, the set thermal power _PT desired by the user can be realized.

As described above, according to the present invention, the maximum heating frequency Fr ₀ of each heating coil detected by the detection units 60 and 70 is set to the desired heating power (set heating power P _T ) of each heating coil set by the user. the plus corresponding predetermined offset frequency ΔFr determine the drive frequency F _D (first thermal adjusting means), while fixing the driving frequency F _D, steps corresponding to the desired setting thermal power P _T By controlling the phase difference θ manually or continuously, the heating power can be further finely adjusted (second heating power adjusting means). Therefore, according to the present invention, by detecting the resonant frequency Fr of the respective heating coils, for supplying a high-frequency current having the drive frequency F _D, which only added offset frequency ΔFr thereto, pass a larger current to the pot K Power can be supplied very efficiently. According to the present invention, since the high-frequency current varies exponentially depending on the driving frequency F _D, to achieve a precise thermal adjustment in comparison with the case of controlling only the drive frequency F _D, the phase difference Compared to controlling only θ, a very wide range of thermal power can be adjusted.

Embodiment 2. FIG.
A second embodiment of the induction heating cooker according to the present invention will be described with reference to FIGS. 20 and 21. In the first embodiment, after the user adjusts the heating power using the heating power adjustment dial 7, the control unit 80 controls each inverter circuit 40, 50 a to 50 d with respect to a constant setting heating power _PT of each heating coil 20, 30. but in which it was to control the, in the second embodiment, when the setting thermal power P _T is changed by the user, and determines the driving frequency F _D and the phase difference θ again each inverter circuit 40,50a~50d Since it has the same structure as the induction heating cooking appliance 1 of Embodiment 1 except the point to control, description is abbreviate | omitted about the overlapping content.

FIG. 20 is a flowchart showing a control method of induction heating cooker 1 according to Embodiment 2 when the setting thermal power _PT desired by the user is changed, and FIG. 21 is a flowchart showing another control method. First, the control method shown in FIG. 20 will be described.

Initially, the user selects a “medium” thermal power (ie, a “medium” thermal power band) of 500 W to 1500 W, and the control unit 80 determines and maintains the drive frequency F _DB to each inverter circuit 40, 50a. It is assumed that the inverter circuits 40 and 50a to 50d are controlled so as to obtain the desired set heating power _PT by adjusting the phase difference θ of ˜50d.

In step ST11, the control unit 80 detects that the user has changed the heating power using the heating power adjustment dial 7, and the changed heating power (hereinafter simply referred to as “target heating power P _T ”) is the same “medium”. Judge whether it belongs to thermal zone.

When the control unit 80 determines that the target thermal power _PT belongs to the “medium” thermal power zone, in step ST <b> 17, the control unit 80 compares the target thermal power P _T with the current thermal power P _C to determine the target thermal power P _T. Recalculate the phase difference θ required to obtain When determining that the heating power needs to be increased, the control unit 80 increases the phase difference θ in step ST18, and when determining that the heating power needs to be decreased, the control unit 80 decreases the phase difference θ in step ST19. The inverter circuits 40, 50a to 50d are controlled.

On the other hand, when the control unit 80 determines that the target thermal power _PT belongs to the “strong” thermal power zone in steps ST11 and ST12, the control unit 80 changes the driving frequency to F _DC (<F _DB ) in step ST13. In ST14, the phase difference θ is changed to a smaller value than before, for example, the minimum phase difference θ that realizes the “strong” heating power (for example, the phase difference θ corresponding to 8/16 step of [Table 1]). As small as the driving frequency F _D, when the phase difference θ as it is, the high frequency current increases rapidly, is the switching element SW of the respective inverter circuits 40,50a~50d is prevented from being destroyed . In other words, when the control unit 80 determines that the driving frequency of the high-frequency current that realizes the target thermal power _PT is two or more of the driving frequency F _DC of the “strong” thermal power and the driving frequency F _DB of the “medium” thermal power, with changing the driving frequency F _DC "strong" thermal, it is preferable to change the phase difference theta a minimum phase difference theta.

The control unit 80, as described above in step ST17～ST19, the target thermal P _T and compares the current thermal power P _C, to adjust the phase difference θ required to obtain the target thermal P _T by an inverter circuit 40, 50a to 50d are controlled. However, if the control unit 80 has changed the phase difference θ to the minimum phase difference θ (for example, 1500 W of thermal power) that realizes “strong” thermal power in step ST14, the control unit 80 increases the phase difference θ in step ST18. Thus, the inverter circuits 40, 50a to 50d are controlled.

On the other hand, when the control unit 80 determines that the target thermal power _PT belongs to the “weak” thermal power zone in steps ST11 and ST12, the control unit 80 changes the driving frequency to F _DA (> F _DB ) in step ST15 and In ST16, the phase difference θ is left as it is or is changed to a smaller value than before. Steps ST13 and ST14 and steps ST15 and ST16 may be interchanged.

Then step ST17~ST19 as above described, compares the target firepower _{P T} and the current thermal power _{P C,} the target thermal _{P T} adjust to the phase difference θ required to obtain an inverter circuit 40,50a~50d To control. If necessary, in step ST16, the phase difference θ is changed to, for example, the maximum phase difference θ that realizes the “weak” heating power (for example, the phase difference θ corresponding to the 16/16 step of [Table 1]). Alternatively, the fire power may be weakened in two stages in step ST19.

Next, another control method will be described with reference to the flowchart of FIG. This control method is substantially the same as the control method shown in FIG. However, in this control method, when the control unit 80 detects that the target thermal power _PT has been changed by the user in step ST21, power supply to the pan K is temporarily stopped in step ST40, and the pan K is placed in step ST41. The point of detecting load information such as the state again is different from the control method of FIG. That is, the detection units 60 and 70 newly calculate the resonance frequency Fr in step ST41, and the control unit 80 determines whether or not the target thermal power _PT belongs to a higher thermal power zone in step ST22. For example, when the control unit 80 determines that the target thermal power _PT belongs to a higher thermal power zone, the control unit 80 reduces the offset frequency ΔFr to a drive frequency F _DC (<F _DB ) in step ST23, while the target thermal power P _When it is determined that _T belongs to a lower thermal power zone, the offset frequency ΔFr is increased and changed to the drive frequency F _DA (> F _DB ) in step ST26, and heating is resumed in steps ST24 and ST27. According to the control method of FIG. 21, since power supply to the pan K is stopped in step ST40, the resonance frequency Fr and the load resistance R are updated to the latest state by redetecting the load information in step ST41. and, with the drive frequency F _D, it is possible to re-calculate the phase difference θ realizing the target thermal P _T. Alternatively, in the above specific example, when the driving frequency is changed to _FDA , the maximum phase difference θ that realizes the “weak” heating power (for example, the step corresponding to 16/16 steps of [Table 1]). change in phase difference theta), when it is changed to the drive frequency F _DC is the smallest phase difference to realize a "strong" thermal theta (e.g. phase difference corresponding to 8/16 step of Table 1] theta) It may be changed.

Thereafter, as described above in step ST17～ST19, in step ST29～ST31, compares the target firepower _{P T} and the current thermal power _{P C,} by adjusting the phase difference θ required to obtain the target thermal _{P T} The inverter circuits 40, 50a to 50d are controlled.

As described above, when the detectors 60 and 70 update the resonance frequency Fr, when the position of the pan K is changed while the pan K is being heated (the position of the pan is shifted due to a pan shake or the like). The load resistance R and the resonance frequency Fr in the latest state are detected and the optimum output power ratio is also coped with when there is a change in the circuit characteristics due to the rise in the temperature of the heating coils 20 and 30. or it is possible to select the driving frequency F _D, it is possible to drive control of the inverter circuit 40,50a~50d in a more proper heating conditions, reduction and the circuit loss, the heating between the respective heating coils 20 and 30 Uniformity can be maintained.

Incidentally, as described above, the present invention first by adjusting the driving frequency F _D (first adjusting means) adjusts the heating power to be supplied to the pot K to a plurality of predetermined thermal range, then the drive fixing the frequency F _D, (second adjusting means) by adjusting the time the high-frequency current flows through the switching elements of the inverter circuits 40,50A～50d (phase), finer heating power at a given thermal range It is what you want to adjust.

By the way, when the target thermal power _PT less than 500 W is set by the user, the control unit 80 selects the “weak” thermal power band, that is, the drive frequency F _DA to control the phase difference θ. Referring to Table 1, even when the “medium” thermal power band, that is, the driving frequency F _DB is selected and the phase difference θ is controlled, the target thermal power P _T (for example, the phase difference θ is 4/16 steps or 5 / 16 steps) can be realized. Similarly, if the target heating power _{P T} of 500W~1500W is set, usually, the control unit 80, "medium" thermal zone, i.e. by selecting a drive frequency _{F DB,} but to control the phase difference theta, "strong Even if the thermal power zone, that is, the driving frequency _FDC is selected and the phase difference θ is controlled, the target thermal power P _T of the “medium” thermal power zone (for example, the phase difference θ is 4/16 step to 7/16 step) is realized. can do.

At this time, as described with reference to FIG. 12, it is possible to better drive frequency F _D is closer to the resonance frequency Fr is efficiently supplied to the high-frequency current. Accordingly, when two combinations of the driving frequency F _DA and the phase difference θ _A , and the driving frequency F _DB and the phase difference θ _B can be used to realize the target thermal power _PT , the smaller driving frequency F _DB and by controlling the respective inverter circuits 40,50a~50d using a smaller phase difference theta _B, it is possible to realize a less efficient feed of power loss.

Thus, the control unit 80, the driving frequency F _D and the phase difference theta, set in advance, is stored in a memory (not shown), the driving frequency F _D and position required to achieve the target thermal P _T The phase difference θ is not necessarily limited to the thermal power zone, and may be appropriately selected according to the use.

Embodiment 3 FIG.
A third embodiment of the induction heating cooker according to the present invention will be described with reference to FIGS. In the first embodiment, the peripheral coils 30a to 30d are supplied with high-frequency currents by the individual inverters 50a to 50d. However, in the third embodiment, the peripheral coils 30a and 30c and the peripheral coils 30b, Except for the point that 30d is connected in series, since it has the same configuration as the induction heating cooker 1 of the first and second embodiments, description of the overlapping contents will be omitted.

  FIG. 22 is a schematic diagram similar to FIG. 5 (Embodiment 1) of power supply device 12 that supplies high-frequency current to central coil 20 and peripheral coils 30a to 30d, and in Embodiment 3, as described above. The peripheral coils 30a and 30c and the peripheral coils 30b and 30d are connected in series. FIG. 23 is a circuit block diagram of the power supply device 12 of the third embodiment. The full-bridge inverter circuits 40 and 50a for supplying a high-frequency current to the central coil 20 and the peripheral coils 30a and 30c are the circuit block diagram of FIG. Have the same electrical configuration. In FIG. 23, the full-bridge inverter circuit 50b for supplying a high-frequency current to the peripheral coils 30b and 30d is omitted for clarity.

Although not limited to this, as shown in FIG. 23, the inverter circuits 40 and 50a for supplying a high-frequency current to the central coil 20 and the peripheral coils 30a + 30c may share the first arm 16, The number of points can be reduced and the production cost can be reduced. That is, the full-bridge inverter circuits 40 and 50a that supply high-frequency current to the central coil 20 and the peripheral coils 30a + 30c include the first shared arm 16 including SW _1U and SW _1D, and SW _2U and SW connected to the central coil 20. The second arm 17a including _2D and the third arm 17b including SW _3U and SW _3D connected to the peripheral coils 30a + 30c are included. Since the high frequency currents of both the central coil 20 and the peripheral coils 30a + 30c flow through the switching elements SW _1U and SW _1D used in the first shared arm 16, a high output power composed of silicon carbide (SiC) or the like is used. It is preferable to use a switching element.

In the induction heating cooker 1 configured in this way, the control unit 80 is similar to the first and second embodiments.
i) Using the detection units 60 and 70, the resonance frequency Fr (and load resistance R) of each heating coil 20 and 30 is calculated,
ii) An offset frequency ΔFr, that is, a thermal power band (driving frequency F _D ) is determined based on a desired target thermal power P input by the operation unit 6 (first thermal power adjusting means),
iii) securing the drive frequency F _D, central inverter circuit 40 determines the peripheral inverter circuits 50a, 50b the time flowing through the switching element (phase difference theta),
iv) By controlling each inverter circuit 40, 50a, 50b, the target thermal power _PT can be finely adjusted (second thermal power adjusting means).

Therefore, according to Embodiment 3, since it can drive on the conditions suitable for the impedance Z in the state in which the pan K was mounted, a bigger electric current can be sent and electric power can be supplied very efficiently. The inverter circuit 40, 50a, 50b is controlled so as to be supplied with a high frequency current having a constant driving frequency F _D and a phase difference θ corresponding to a desired heating power, thereby realizing precise heating power adjustment. Can do.

Moreover, the control part 80 may control each output electric power based on the load resistance R which shows the load state of the pan K which exists above each heating coil 20 and 30. FIG. For example, as shown in FIG. 24, with respect to a set thermal power _PT set by the user in a certain thermal power band (driving frequency F _D ), the detection units 60 and 70 detect the loading state of the pan K, When the placement area of the pan K on the coils 30a + 30c and the peripheral coils 30b + 30d is S1, S2, S3 (S1>S2> S3), the control unit 80 controls the central coil 20, the peripheral coils 30a + 30c, and the peripheral coils 30b + 30d. By determining the ratio (for example, 4 to 2 to 1) of the output powers P ₁ , P ₂ and P ₃ to be supplied to each of the inverter circuits 40, 50a and 50b, You may control the firepower. At this time, the target (set) thermal power _PT set by the user is the total value of the output powers P ₁ , P ₂ , P ₃ of the central coil 20, the peripheral coils 30a + 30c, and the peripheral coils 30b + 30d (P _T = P ₁ + P _2). + _P 3), the control unit 80, and the driving frequency _{F D} constant, the inverter circuits 40, 50a, the output power _{P 1,} P 2, phase difference theta ₁ corresponding to _{P 3} of 50b, θ _2, θ ₃ And the heating power obtained by each of the heating coils 20 and 30 may be controlled. Note that the timing chart showing the phase differences of the heating coils 20 and 30 is understood by those skilled in the art, and is not shown.

Further, as shown in FIG. 25, when the frying pan K for egg baking is placed on the top plate 3, it is not substantially placed on the peripheral coils 30a + 30c, and the apparent pan K is detected by the detection unit 70a. The load resistance _RL becomes small. When determining that the load resistance _RL of the peripheral coil 30a + 30c is smaller than the predetermined threshold, the control unit 80 may stop the power supply to the peripheral coil 30a + 30c. Thus, according to the present invention, an appropriate and effective high-frequency current can be supplied based on the load information detected by the detection units 60 and 70.

Embodiment 4 FIG.
A fourth embodiment of the induction heating cooker according to the present invention will be described with reference to FIG. Although the induction heating cooker 1 which concerns on Embodiment 1-3 has the center coil 20 (the inner center coil 20a and the outer center coil 20b connected in series) and the four peripheral coils 30a-30d, The induction heating cooker 1 according to the fourth embodiment is the same as the induction heating cooker 1 according to the first to third embodiments, except that the central coil 20 and the outer peripheral coil 30 arranged concentrically therewith are included. The description of the overlapping contents is omitted.

  FIG. 26 is a plan view of the IH heating unit 10 according to the fourth embodiment, in which the top plate 3 and the like are omitted, and is the same as FIG. The IH heating unit 10 includes a central coil 20 (an inner central coil 20a and an outer central coil 20b connected in series) and an outer peripheral coil 30 independent of the central coil 20 and is also referred to as a triple ring coil type IH heating unit. . Similar to the first embodiment, a temperature sensor is disposed between the inner central coil 20a and the outer central coil 20b so as to contact the top plate 3.

  Since the circuit configuration of the power supply device 12 according to the fourth embodiment is basically the same as that of the above-described embodiment, a description thereof will be omitted, but it is equivalent to FIG. 23 (the inverter circuit 50b is omitted). is there. Further, the first arm of each of the inverter circuits 40 and 50 may be a common arm (similar to FIG. 23) or may be configured as an individual one.

In the induction heating cooker 1 configured as described above, the control unit 80 is similar to the first to third embodiments.
i) Using the detection units 60 and 70, calculate the resonance frequency Fr (and load resistance R) of the central coil 20 and the outer coil 30;
ii) An offset frequency ΔFr, that is, a thermal power band (driving frequency F _D ) is determined based on a desired thermal power _PT input by the operation unit 6 (first thermal power adjusting means),
iii) securing the drive frequency F _D, to determine the time interval at which the high-frequency current flows through the switching elements of the central inverter circuit 40 and the outer peripheral inverter circuit 50 t (≒ phase difference theta),
iv) The target heating power _PT can be finely adjusted by controlling the inverter circuits 40 and 50 (second heating power adjusting means).

Therefore, according to Embodiment 4, since it can drive on the conditions suitable for the impedance Z in the state in which the pan K was mounted, a bigger electric current can be sent and electric power can be supplied very efficiently. The inverter circuits 40 and 50 are controlled so that a high-frequency current having a constant drive frequency F _D and a phase difference θ corresponding to a desired heating power is supplied to the central coil 20 and the outer coil 30, Thermal power adjustment can be realized.

Moreover, the control part 80 can control each output electric power based on the load resistance R (or impedance) which shows the load state of the pan K above each heating coil 20,30. For example, as shown in FIG. 26, when the small pan K is placed on the top plate 3, the apparent load of the pan K on the outer peripheral coil 30 is not substantially placed above the outer peripheral coil 30. The resistance _RL becomes small. At this time, the detection units 60 and 70 detect the mounting state of the pan K, determine that the pan K is not placed above the outer peripheral coil 30, and supply a high-frequency current only to the central coil 20. preferable. At this time the detection unit 60 obtains the drive frequency F _D of the central coil 20, the control unit 80 determines a drive frequency F _D and the phase difference θ in accordance with the target thermal P _T desired by the user, appropriate and effective The central inverter circuit 40 is controlled so that a high frequency current is supplied.

As described above, according to the fourth embodiment, as in the first to third embodiments, a large current can flow through the pan K, power can be supplied very efficiently, and a constant drive frequency F Each of the inverter circuits 40 and 50 can be controlled so as to be supplied with a high-frequency current having a phase difference θ corresponding to _{D 1} and a desired heating power, thereby realizing precise heating power adjustment.

DESCRIPTION OF SYMBOLS 1 ... Induction cooking device, 2 ... Housing | casing, 3 ... Top plate, 4 ... Central heating part, 5 ... Cooking grill, 6 ... Operation part (operation panel), 7 ... Thermal power adjustment dial, 8 ... Display part, 9a ... exhaust port, 9b, 9c ... intake port, 10, 11 ... IH heating unit, 12 ... power supply device (power source unit), 14 ... coil base, 15 ... magnetic body (ferrite core), 16 ... first arm, 17 ... second arm, 18 ... magnetic cancel ring, 20 ... center coil, 20a ... inner center coil, 20b ... outer center coil, 22,32 ... LCR induction heating unit, 24 ... drive voltage detector, 25 ... drive current detection 30a-30d ... peripheral coil, 40 ... central inverter circuit, 50a-50d ... peripheral inverter circuit, 60, 70 ... detection part (primary component extraction part), 80 ... control part, K ... pan, SW ... switching element .

Claims (14)

A plurality (i, i is a natural number of 2 or more) of heating coils that are adjacent to each other and cooperate to inductively heat a single object to be heated;
A plurality of power supply units individually supplying a high-frequency current having a predetermined driving frequency to each heating coil;
A detecting unit that detects a driving current flowing through each heating coil and a driving voltage applied to both ends of each heating coil, and calculates a load resistance and a resonance frequency of each heating coil from the detected driving current and driving voltage. When,
An operation unit capable of setting a desired target heating power consumed by each heating coil by a user;
A control unit connected to the detection unit and the operation unit,
The controller is
a) To each of a plurality of thermal power bands corresponding to a desired target thermal power of each of the heating coils set by the user to the maximum (Fr ₀ ) of the calculated resonance frequencies (Fr _i ) of the respective heating coils. The drive frequency (F _D = Fr ₀ + ΔFr) is determined by adding the same differential frequency (ΔFr) set for
b) A high-frequency current having a drive frequency (F _D ) determined based on a desired target heating power of each heating coil set by the user and a calculated load resistance of each heating coil is periodically generated in each heating coil. The induction heating cooker characterized by controlling each said power supply part so that the time interval (t) supplied to may be adjusted.   The differential frequency (ΔFr) set for a thermal power band corresponding to a larger desired target thermal power is smaller than that set for a thermal power band corresponding to a smaller desired target thermal power. Item 2. An induction heating cooker according to item 1. The power supply unit has a full bridge circuit composed of first and second arms including switching elements on the high voltage side and the low voltage side,
The heating coil is connected between an intermediate point of the high-voltage side and low-voltage side switching elements of the first arm and an intermediate point of the high-voltage side and low-voltage side switching elements of the second arm,
The control unit is a drive applied from the high-voltage side switching element of the first arm to the low-voltage side switching element of the second arm based on a desired target heating power of each heating coil set by the operation unit. Controlling the phase difference (θ) between the phase of the voltage and the phase of the drive voltage applied from the high-voltage side switching element of the second arm to the low-voltage side switching element of the first arm. The induction heating cooker according to claim 1 or 2. The time interval (t) set by the phase difference θ is shorter than the half cycle (T / 2) of the high-frequency current having the drive frequency (F _D ) by a time that is twice the dead time (d) (τ = The induction heating cooker according to claim 3, characterized in that T / 2-2d). The control unit stores a plurality of discrete difference frequencies (ΔFr), and adds the difference frequency determined according to the desired target heating power to the maximum resonance frequency (Fr ₀ ) to thereby increase the drive frequency (F _D ). It determines, The induction heating cooking appliance of any one of Claims 1-4 characterized by the above-mentioned.   When the control unit determines that there are two or more driving frequency options for the high-frequency current that can supply the desired target heating power to the heating coil, the control unit changes the driving frequency to a smaller driving frequency and changes to a shorter time interval (t). The induction heating cooker according to any one of claims 1 to 5, wherein:   The induction heating cooker according to any one of claims 1 to 6, wherein the heating coil includes a central coil and at least one or more peripheral coils arranged around the central coil. The detector
A drive voltage detection unit for detecting a drive voltage applied to both ends of an LCR induction heating unit including a heating coil and a resonance capacitor connected in series to the heating coil;
A drive current detection unit for detecting a drive current flowing in the LCR induction heating unit;
A primary component extraction unit that extracts a primary drive voltage and a primary drive current including a primary component having the same frequency as the drive frequency from the detected drive voltage and drive current;
The control unit calculates the load resistance and resonance frequency of each heating coil from the primary drive voltage and the primary drive current, and when the calculated load resistance and resonance frequency are greater than a predetermined threshold, the LCR induction heating unit The induction heating cooker according to any one of claims 1 to 7, wherein a high-frequency current is supplied to the heater. A plurality of (i, i is a natural number of 2 or more) heating coils that are adjacent to each other and cooperate to inductively heat a single object to be heated, and a high-frequency current having a predetermined driving frequency is individually applied to each of the heating coils. A plurality of power supply units to be supplied to each of the heating coils, a driving current flowing through each of the heating coils and a driving voltage applied to both ends of each of the heating coils, and a load of each of the heating coils from the detected driving current and the driving voltage. An induction including a detection unit that calculates resistance and resonance frequency, an operation unit that allows a user to set a desired target heating power consumed by each heating coil, and a control unit that is connected to the detection unit and the operation unit A control method of the heating cooker, in this control unit,
a) To each of a plurality of thermal power bands corresponding to a desired target thermal power of each of the heating coils set by the user to the maximum (Fr ₀ ) of the calculated resonance frequencies (Fr _i ) of the respective heating coils. Determining the drive frequency (F _D = Fr ₀ + ΔFr) by adding the same differential frequency (ΔFr) set for
b) A high-frequency current having a drive frequency (F _D ) determined based on a desired target heating power of each heating coil set by the user and a calculated load resistance of each heating coil is periodically generated in each heating coil. And controlling each of the power supply units so as to adjust the time interval (t) supplied to the control unit. Determining whether a thermal power zone corresponding to the desired target thermal power after the change is different from a thermal power zone corresponding to the desired target thermal power before the change;
When it is determined that the thermal power bands corresponding to the desired target thermal power before and after the change are different, the step of stopping the supply of the high-frequency current to each of the heating coils;
Calculating the resonance frequency of the heating coil (Fr _i) again,
For each of the plurality of thermal power bands corresponding to the desired target thermal power of each of the heating coils set by the user, the resonance frequency (Fr _i ) of the heating coils calculated again is the maximum (Fr ₀ ). 10. The control method according to claim 9, further comprising a step of determining a drive frequency (F _D = Fr ₀ + ΔFr) by adding the same differential frequency (ΔFr) set in the above. The power supply unit includes a full bridge circuit including first and second arms including switching elements on the high voltage side and the low voltage side, and the heating coil includes the switching elements on the high voltage side and the low voltage side of the first arm. Connected between an intermediate point and an intermediate point of the switching element on the high-voltage side and the low-voltage side of the second arm;
Based on the desired target heating power of each heating coil set by the operation unit, the phase of the drive voltage applied from the high-voltage side switching element of the first arm to the low-voltage side switching element of the second arm And a step of controlling a phase difference (θ) between the high-voltage side switching element of the second arm and the phase of the drive voltage applied to the low-voltage side switching element of the first arm. The control method according to claim 9 or 10. The time interval (t) set by the phase difference θ is shorter than the half cycle (T / 2) of the high-frequency current having the drive frequency (F _D ) by a time that is twice the dead time (d) (τ = The control method according to claim 11, wherein T / 2-2d). Storing a plurality of discrete differential frequencies;
13. A step of determining a drive frequency (F _D ) by adding a difference frequency determined according to a desired target heating power to a maximum resonance frequency (Fr ₀ ). Or the control method according to claim 1.   When it is determined that there are two or more driving frequency options of the high-frequency current that can supply a desired target heating power to the heating coil, the method includes a step of changing to a lower driving frequency and a shorter time interval (t). The control method according to any one of claims 9 to 12, wherein:

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