WO2015063942A1

WO2015063942A1 - Induction heating cooker

Info

Publication number: WO2015063942A1
Application number: PCT/JP2013/079664
Authority: WO
Inventors: 浩志郎 ▲高▼野; 吉野　勇人; 匡薫伊藤; 木下　広一
Original assignee: 三菱電機株式会社; 三菱電機ホーム機器株式会社
Priority date: 2013-11-01
Filing date: 2013-11-01
Publication date: 2015-05-07
Also published as: CN105684551B; DE112013007556B4; JP6038345B2; JPWO2015063942A1; DE112013007556T5; CN105684551A

Abstract

To obtain an induction heating cooker capable of accurately determining a material of a subject to be heated. This induction heating cooker obtains a change quantity (I1) of an input current and/or a coil current during a period of time from a time when power supply to a heating coil (11a) starts to a time when a first heating period (t1) elapses, and on the basis of the change quantity (I1) of the current, a material of a subject to be heated (5) is determined.

Description

Induction heating cooker

This invention relates to an induction heating cooker.

Some conventional induction heating cookers determine the material of an object to be heated based on an output current flowing through a heating coil (see, for example, Patent Document 1).
The induction heating cooker of Patent Document 1 determines whether the material of the object to be heated is aluminum, stainless steel, or iron based on the output current of the heating coil.

Moreover, in the conventional induction heating cooking appliance, there exist some which determine the temperature of a to-be-heated object with the input electric current or controlled variable of an inverter (for example, refer patent document 2, 3).
The induction heating cooker of Patent Document 2 has a control means for controlling the inverter so that the input current of the inverter becomes constant, and when there is a change in the control amount within a predetermined time, The output of the inverter is suppressed by judging that the temperature change is large. In addition, it is disclosed that when a predetermined control amount change or less is reached during a predetermined time, it is determined that boiling is completed, and the drive frequency is decreased to reduce the output of the inverter.
Patent Document 3 discloses an input current change amount detecting means for detecting a change amount of an input current, and a temperature determination processing means for determining the temperature of an object to be heated from the change amount of the input current detected by the input current change amount detecting means. An induction heating cooker equipped with the above has been proposed. It is disclosed that when the temperature determining means determines that the heated object has blown up, a stop signal is output to stop heating.

JP-A-63-2284 (pages 2 to 4) JP 2008-181892 A (page 3 to page 5, FIG. 1) Japanese Patent Laid-Open No. 5-62773 (pages 2 to 3, FIG. 1)

In the induction heating cooker described in Patent Document 1, it is possible to roughly determine whether the object to be heated is aluminum, stainless steel, or iron. That is, it is possible to roughly discriminate depending on the property of the material, such as whether the object to be heated is a magnetic material or a non-magnetic material. However, there is a problem that the material of the object to be heated cannot be further subdivided. For example, both the aluminum object to be heated and the copper object to be heated are low resistance non-magnetic materials, and therefore, there is a problem that it is not possible to determine a material obtained by subdividing them.

In the induction heating cooker described in Patent Document 2, the drive frequency of the inverter is controlled so that the input power is constant, and the temperature change of the object to be heated is determined by this control amount change (Δf). However, depending on the material of the object to be heated, there is a problem that the control amount change (Δf) of the driving frequency becomes minute and the temperature change of the object to be heated cannot be detected.

In the temperature detection device of the induction heating cooker described in Patent Document 3, when the material of the object to be heated changes, the input current may be excessive depending on the drive frequency of the inverter, and the inverter may become hot and break down. There was a problem that there was.

The present invention has been made to solve at least one of the above-described problems, and provides an induction heating cooker that can accurately determine the material of an object to be heated. Moreover, the induction heating cooking appliance which can detect the temperature change of a to-be-heated object irrespective of the material of a to-be-heated object is obtained.

An induction heating cooker according to the present invention includes a heating coil that induction-heats an object to be heated, a drive circuit that supplies high-frequency power to the heating coil, a load determination unit that performs a load determination process on the object to be heated, A control unit that controls driving of the drive circuit and controls high-frequency power supplied to the heating coil, input current detection means that detects an input current to the drive circuit, and a coil current that flows through the heating coil A coil current detection unit, wherein the load determination unit is a change amount (I1) of at least one of the input current and the coil current from the start of power supply to the heating coil until the first heating period elapses. ) And determining the material of the object to be heated based on the change amount (I1) of the current, and the control unit drives the drive circuit according to the determination result of the load determination unit. And controlling.

This invention can accurately determine the material of the object to be heated.

It is a disassembled perspective view which shows the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a figure which shows the drive circuit of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a functional block diagram which shows an example of the control part of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a load discrimination | determination characteristic view of the to-be-heated object based on the relationship between the heating coil current and input current in the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is an interphase figure of the input current with respect to the drive frequency at the time of the temperature change of the to-be-heated material of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is the figure which expanded the part shown with the broken line of FIG. It is a figure which shows the relationship between the drive frequency of the induction heating cooking appliance which concerns on Embodiment 1, temperature, an electric current, and time. It is a flowchart which shows the operation example of the hot water heating mode of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a load discrimination | determination characteristic view of the to-be-heated object based on the relationship between the heating coil current and input current in the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a figure which shows the relationship between the drive frequency of the induction heating cooking appliance which concerns on Embodiment 1, temperature, an electric current, and time. It is a figure which shows the relationship between the drive frequency of the induction heating cooking appliance which concerns on Embodiment 1, temperature, an electric current, and time. It is a figure which shows another drive circuit of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a figure which shows a part of drive circuit of the induction heating cooking appliance which concerns on Embodiment 2. FIG. 6 is a diagram illustrating an example of a drive signal for a half-bridge circuit according to Embodiment 2. FIG. It is a figure which shows a part of drive circuit of the induction heating cooking appliance which concerns on Embodiment 3. FIG. 6 is a diagram illustrating an example of a drive signal of a full bridge circuit according to a third embodiment. FIG.

Embodiment 1 FIG.
(Constitution)
1 is an exploded perspective view showing an induction heating cooker according to Embodiment 1. FIG.
As shown in FIG. 1, an induction heating cooker 100 has a top plate 4 on which an object to be heated 5 such as a pan is placed. The top plate 4 includes a first heating port 1, a second heating port 2, and a third heating port 3 as heating ports for inductively heating the object to be heated 5, and corresponds to each heating port. The first heating unit 11, the second heating unit 12, and the third heating unit 13 are provided, and the object to be heated 5 can be placed on each heating port to perform induction heating. Is.
In the first embodiment, the first heating means 11 and the second heating means 12 are provided side by side on the front side of the main body, and the third heating means 13 is provided at substantially the center on the back side of the main body. .
In addition, arrangement | positioning of each heating port is not restricted to this. For example, three heating ports may be arranged side by side in a substantially straight line. Moreover, you may arrange | position so that the position of the depth direction of the center of the 1st heating means 11 and the center of the 2nd heating means 12 may differ.

The top plate 4 is entirely composed of a material that transmits infrared rays, such as heat-resistant tempered glass or crystallized glass, and a rubber packing or a sealing material is interposed between the upper surface opening outer periphery of the induction heating cooker 100 main body. Fixed in a watertight state. The top plate 4 has a circular pan showing a rough placement position of the pan corresponding to the heating range (heating port) of the first heating unit 11, the second heating unit 12 and the third heating unit 13. The position display is formed by applying paint or printing.

On the front side of the top plate 4, the heating power and cooking menu (boiling mode, fried food mode when heating the article 5 to be heated by the first heating means 11, the second heating means 12, and the third heating means 13. Etc.) are provided as an input device for setting the operation unit 40a, the operation unit 40b, and the operation unit 40c (hereinafter may be collectively referred to as the operation unit 40). Further, in the vicinity of the operation unit 40, as the notification unit 42, a display unit 41 a, a display unit 41 b, and a display unit 41 c (display unit 41 a that displays the operation state of the induction heating cooker 100 and the input / operation contents from the operation unit 40. Hereinafter, the display unit 41 may be collectively referred to). The operation units 40a to 40c and the display units 41a to 41c are not particularly limited, for example, when the

operation units

40a and 41c are provided for each heating port, or when the operation unit 40 and the display unit 41 are provided collectively.

A first heating means 11, a second heating means 12, and a third heating means 13 are provided below the top plate 4 and inside the main body, and each heating means is a heating coil (not shown). Z).

Inside the main body of the induction heating cooker 100, there are a drive circuit 50 for supplying high frequency power to the heating coils of the first heating means 11, the second heating means 12, and the third heating means 13, and the drive circuit 50. And a control unit 45 for controlling the overall operation of the induction heating cooker 100.

The heating coil has a substantially circular planar shape, and is configured by winding a conductive wire made of an arbitrary metal with an insulating film (for example, copper, aluminum, etc.) in the circumferential direction. Is supplied to each heating coil, whereby an induction heating operation is performed.

FIG. 2 is a diagram showing a drive circuit of the induction heating cooker according to the first embodiment. In addition, although the drive circuit 50 is provided for every heating means, the circuit structure may be the same and may be changed for every heating means. In FIG. 2, only one drive circuit 50 is shown. As shown in FIG. 2, the drive circuit 50 includes a DC power supply circuit 22, an inverter circuit 23, and a resonance capacitor 24a.

The input current detection means 25a detects a current input from the AC power supply (commercial power supply) 21 to the DC power supply circuit 22 and outputs a voltage signal corresponding to the input current value to the control unit 45.

The DC power supply circuit 22 includes a diode bridge 22a, a reactor 22b, and a smoothing capacitor 22c, converts an AC voltage input from the AC power supply 21 into a DC voltage, and outputs the DC voltage to the inverter circuit 23.

The inverter circuit 23 is a so-called half-bridge type inverter in which

IGBTs

23a and 23b as switching elements are connected in series to the output of the DC power supply circuit 22, and

diodes

23c and 23d are parallel to the

IGBTs

23a and 23b as flywheel diodes, respectively. It is connected to the. The inverter circuit 23 converts the DC power output from the DC power supply circuit 22 into a high-frequency AC power of about 20 kHz to 50 kHz, and supplies the AC power to the resonance circuit including the heating coil 11a and the resonance capacitor 24a. The resonance capacitor 24a is connected in series to the heating coil 11a, and this resonance circuit has a resonance frequency according to the inductance of the heating coil 11a, the capacity of the resonance capacitor 24a, and the like. The inductance of the heating coil 11a changes according to the characteristics of the metal load when the object to be heated 5 (metal load) is magnetically coupled, and the resonance frequency of the resonance circuit changes according to the change in the inductance.

With this configuration, a high-frequency current of about several tens of A flows through the heating coil 11a, and the object to be heated placed on the top plate 4 directly above the heating coil 11a by the high-frequency magnetic flux generated by the flowing high-frequency current. 5 is induction heated. The

IGBTs

23a and 23b, which are switching elements, are composed of, for example, a silicon-based semiconductor, but may be configured using a wide band gap semiconductor such as silicon carbide or a gallium nitride-based material.

By using a wide bandgap semiconductor for the switching element, the conduction loss of the switching element can be reduced, and since the heat radiation of the driving circuit is good even when the switching frequency (driving frequency) is high (high speed), the driving circuit Therefore, the size and cost of the driving circuit can be reduced.

The coil current detection means 25b is connected between the heating coil 11a and the resonance capacitor 24a. For example, the coil current detection unit 25 b detects a current flowing through the heating coil 11 a and outputs a voltage signal corresponding to the heating coil current value to the control unit 45.

The temperature detecting means 30 is constituted by a thermistor, for example, and detects the temperature by the heat transferred from the heated object 5 to the top plate 4. In addition, you may use arbitrary sensors, such as not only a thermistor but an infrared sensor.

FIG. 3 is a functional block diagram illustrating an example of a control unit of the induction heating cooker according to the first embodiment. The control unit 45 will be described with reference to FIG.
The control unit 45 controls the operation of the induction heating cooker 100 including a microcomputer or a DSP (digital signal processor), and includes a drive control unit 31, a load determination unit 32, a drive frequency setting unit 33, a current. A change detection unit 34, a power adjustment unit 35, and an input / output control unit 36 are provided.

The drive control means 31 drives the inverter circuit 23 by outputting a drive signal DS to the

IGBTs

23a and 23b of the inverter circuit 23 to perform a switching operation. And the drive control means 31 controls the heating to the to-be-heated material 5 by controlling the high frequency electric power supplied to the heating coil 11a. The drive signal DS is a signal having a predetermined drive frequency of, for example, about 20 to 50 kHz with a predetermined on-duty ratio (for example, 0.5).

The load determination means 32 performs a load determination process for the object to be heated 5 and determines the material of the object to be heated 5 as a load. Details of the load determination process will be described later.

The drive frequency setting means 33 sets the drive frequency f of the drive signal DS output to the inverter circuit 23 when the inverter circuit 23 supplies the heating coil 11a. In particular, the drive frequency setting unit 33 has a function of automatically setting the drive frequency f according to the determination result of the load determination unit 32. Specifically, the drive frequency setting means 33 stores a table for determining the drive frequency f according to, for example, the material of the article to be heated 5 and the set thermal power. The drive frequency setting means 33 determines the value fd of the drive frequency f by referring to this table when the load determination result and the set thermal power are input. The drive frequency setting means 33 sets a frequency higher than the resonance frequency of the resonance circuit so that the input current does not become excessive.

Thus, since the drive frequency setting means 33 drives the inverter circuit 23 with the drive frequency f corresponding to the material of the article to be heated 5 based on the load determination result, an increase in input current can be suppressed. The reliability of the circuit 23 can be improved by suppressing the high temperature of the circuit 23.

When the inverter circuit 23 is driven at the drive frequency f = fd set by the drive frequency setting means 33, the current change detection means 34 has a current change amount ΔI per predetermined time of at least one of the input current and the coil current. Is detected. The predetermined time may be a preset period, or may be a period that can be changed by operating the operation unit 40.

The power adjustment means 35 sets the adjustment amount of the drive signal DS when the current change amount ΔI detected by the current change detection means 34 becomes equal to or less than the threshold value. Specifically, the power adjustment unit 35 determines a preset increase amount Δf of the drive frequency as the adjustment amount. Then, the drive control unit 31 releases the fixation of the drive frequency f, increases the drive frequency f by the adjustment amount Δf (f = fd + Δf), and drives the inverter circuit 23.

The drive control means 31 reduces the electric power supplied to the heating coil 11a according to the adjustment amount set by the power adjustment means 35. The drive control means 31 releases the fixation of the drive frequency f = fd, increases the drive frequency f by the increase amount Δf (f = fd + Δf), and drives the inverter circuit 23.

(Operation)
Next, an operation example of the induction heating cooker 100 according to Embodiment 1 will be described.
First, the operation in the case where the object to be heated 5 placed on the heating port of the top plate 4 is induction-heated by the thermal power set by the operation unit 40 will be described.

When the heated object 5 is placed on the heating port by the user and an instruction to start heating (heating power input) is given to the operation unit 40, the load determination unit 32 of the control unit 45 performs a load determination process. The load determination process performed by the load determination unit 32 includes “a load determination process at the start of heating” and “a load determination process during a heating operation”.

(Load judgment process at the start of heating)
The material of the heated object 5 (pan) serving as a load is roughly classified into a magnetic material, a high-resistance nonmagnetic material, and a low-resistance nonmagnetic material depending on the magnetic characteristics and impedance characteristics. Examples of the magnetic material include iron and ferritic stainless steel (for example, 18Cr: Japanese Industrial Standard SUS430). Examples of the high resistance nonmagnetic material include austenitic stainless steel (for example, 18Cr-8Ni: Japanese Industrial Standard SUS304). Examples of the low resistance nonmagnetic material include aluminum and copper.

In the load determination process at the start of heating, the load determination unit 32 uses a magnetic material, a high-resistance non-magnetic material, and a low-resistance non-magnetic material based on the correlation between the input current and the coil current. The classification is roughly classified. Moreover, the load determination means 32 is based on the correlation of an input electric current and a coil current, the state to which the to-be-heated material 5 is not mounted in the top plate 4, or the to-be-heated material 5 of sufficient magnitude | size is mounted. It is determined whether or not there is no load, which is not in the state.

FIG. 4 is a load discrimination characteristic diagram of the object to be heated based on the relationship between the heating coil current and the input current in the induction heating cooker according to the first embodiment.
As shown in FIG. 4, the relationship between the coil current and the input current differs depending on the material of the heated object 5 (pan) placed on the top plate 4. The load determination means 32 stores therein in advance a load determination table in which the relationship between the coil current and the input current shown in FIG. 4 is tabulated. By storing the load determination table therein, the load determination unit 32 can be configured with an inexpensive configuration.

In the load determination process at the start of heating, the control unit 45 drives the inverter circuit 23 for a predetermined determination time at a preset drive frequency for load determination, and detects the input current from the output signal of the input current detection means 25a. To do. At the same time, the control unit 45 detects the coil current from the output signal of the coil current detection means 25b. The control part 45 determines the classification of the material of the to-be-heated object (pan) 5 mounted from the detected coil current and input current, and the load determination table showing the relationship of FIG. Thus, the load determination means 32 determines roughly the material of the to-be-heated object 5 mounted above the heating coil 11a based on the correlation between the input current and the coil current.

After performing the load determination process at the start of heating, the control unit 45 performs a control operation based on the load determination result.
When the load determination result is no load, the control unit 45 notifies the notification means 42 that heating is impossible, and prompts the user to place the pan. At this time, high frequency power is not supplied from the drive circuit 50 to the heating coil 11a.
When the load determination result is a magnetic material, a high-resistance nonmagnetic material, or a low-resistance nonmagnetic material, these pans are materials that can be heated by the induction heating cooker 100 of the first embodiment. Therefore, the control unit 45 determines a driving frequency according to the determined material. This drive frequency is set to a frequency higher than the resonance frequency so that the input current does not become excessive. The drive frequency can be determined by referring to a frequency table or the like corresponding to the material of the article 5 to be heated and the set heating power, for example.
The controller 45 drives the inverter circuit 23 with the determined drive frequency fixed, and starts the induction heating operation. In the state where the drive frequency is fixed, the on-duty (on / off ratio) of the switching element of the inverter circuit 23 is also fixed.

In this way, the material of the object to be heated 5 placed above the heating coil 11a is roughly classified and the drive frequency of the inverter circuit 23 is determined according to the material of the object to be heated 5, and the drive frequency is determined according to the drive frequency. The inverter circuit 23 is driven. For this reason, the inverter circuit 23 can be fixed and driven by the drive frequency according to the material of the to-be-heated material 5, and the increase in input current can be suppressed. Therefore, the high temperature of the inverter circuit 23 can be suppressed and the reliability can be improved.

(Load judgment processing during heating operation)
FIG. 5 is a phase diagram of current with respect to the drive frequency when the temperature of the object to be heated of the induction heating cooker according to Embodiment 1 changes.
In FIG. 5, a thin line is a characteristic when the to-be-heated object 5 (pan) is low temperature, and a thick line is a characteristic when the to-be-heated object 5 is high temperature.
As shown in FIG. 5, the characteristics change depending on the temperature of the object to be heated 5 because the electrical resistivity of the object to be heated 5 increases and the magnetic permeability decreases due to the temperature rise. This is because the magnetic coupling of the heated object 5 changes.

6 is an enlarged view of a portion indicated by a broken line in FIG.
The controller 45 heats the article to be heated 5 by supplying power to the heating coil 11a with the drive frequency of the inverter circuit 23 fixed. At this time, as shown in FIG. 6, as the heated object 5 changes from a low temperature to a high temperature, the current value (operating point) at the driving frequency changes from the point A to the point B, and the temperature of the heated object 5 increases. Along with this, the current gradually decreases.

The amount of change in current varies depending on the type of material to be heated, and there are materials having a large amount of current change and materials having a small amount of current change.
As shown in FIG. 4, the heated object 5 (current change “large” pan) plotted with ◆ and the heated object 5 (current change “small” pan) plotted with ■ are at the initial low temperature. In, the values of the input current and the output current are almost the same. In the above-described load determination process at the start of heating, it is determined that both the materials of the object to be heated 5 are magnetic materials.

When the temperature of the article to be heated 5 rises due to the heating operation, the current greatly decreases in the current change “large” pan, as plotted by ◇. On the other hand, the current change “small” pan has a smaller amount of current decrease than the current change “large” pan, as plotted by □.
For this reason, the load determination unit 32 is configured to perform at least one of the input current and the coil current from the start of power supply to the heating coil 11a until the first heating period elapses in the load determination process during the heating operation. Is obtained. And based on the variation | change_quantity I1 of an electric current, the material of the to-be-heated material 5 is subdivided and determined. That is, it is determined which material is the material among the plurality of materials belonging to the broadly classified section in the above-described load determination process at the start of heating.

For example, the load determination unit 32 stores in advance the relationship between the current change amount I1 and the material type corresponding to the value of the input current and the value of the coil current based on experimental data or the like.
Then, the load determination means 32 is based on at least one of the input current detected by the input current detection means 25a and the coil current detected by the coil current detection means 25b. By referring to the information on the relationship with the type, the type of material of the object to be heated 5 is subdivided and determined.
Thereby, for example, it can be determined by subdividing which material is the material of the object 5 to be heated, such as iron or ferrite stainless steel belonging to the magnetic material category.

Since the input current and the coil current both decrease as the temperature of the object to be heated 5 rises, in the load determination process during the heating operation, the amount of change I1 of one of the input current and the coil current is used. It is possible to determine the material of the heated object 5. When both the input current and the coil current are used, the current change amount I1 = sqrt {(input current change amount) ² + (output current change amount) ² }. By using both the input current and the coil current, it is possible to further improve the accuracy of determining the material of the article to be heated 5.

It should be noted that the first heating period may be a preset time, or may be determined by the heating power set by the operation unit 40 or the cooking mode.

After performing the load determination process during the heating operation, the control unit 45 performs a control operation based on the load determination result. For example, the drive frequency may be corrected in accordance with the type of material of the object to be heated 5 determined in detail. Further, for example, an upper limit value of the input heating power may be set according to the type of material of the article 5 to be heated.

Thus, based on the amount of change in current from the start of power supply to the heating coil 11a until the first heating period elapses, the material of the object to be heated 5 is any of a plurality of materials belonging to the broadly classified section. Since the material is subdivided, the material of the object to be heated 5 can be accurately determined.

(Temperature change detection)
In a state where the driving frequency is fixed, the current (input current and coil current) decreases according to the temperature of the object to be heated 5. As shown in FIG. 6, the current value (operating point) at the driving frequency changes from the point A to the point B as the heated object 5 changes from the low temperature to the high temperature, and as the heated object 5 increases in temperature. The current gradually decreases.
From this, the control unit 45 obtains a change amount (current change amount ΔI) per predetermined time of the current (input current or coil current) with the drive frequency of the inverter circuit 23 fixed, and this current change amount ΔI. Based on the above, the temperature change of the object to be heated 5 is detected.

Thus, since the temperature change of the object to be heated 5 can be detected by the change of the current, the temperature change of the object to be heated 5 can be detected at a higher speed than the temperature sensor or the like.

(Hot water mode)
Next, an operation when the water heating mode for performing the water heating operation of the water charged in the article to be heated 5 is selected as the cooking menu (operation mode) by the operation unit 40 will be described.

FIG. 7 is a diagram showing the relationship between the drive frequency, temperature, current, and time of the induction heating cooker according to the first embodiment.
FIG. 7 shows the elapsed time and changes in each characteristic when water is put into the article to be heated 5 and operated in the water heating mode. 7A shows the drive frequency, FIG. 7B shows the temperature (water temperature), and FIG. 7C shows the current (input current or coil current). Note that the display such as ■ in FIG. 7C corresponds to the plot such as ■ in FIG.

When the inverter circuit 23 is controlled with the drive frequency fixed as shown in FIG. 7A, the temperature (water temperature) of the article to be heated 5 gradually increases until it boils, as shown in FIG. 7B. As it rises and boils, the temperature remains constant at about 100 ° C. At this time, as shown in FIG. 7 (c), as the temperature of the object to be heated 5 increases, the current gradually decreases, and when the water boils and the temperature becomes constant, the input current also becomes constant. Become. That is, when the current becomes constant, the water boils and the boiling is completed.
As shown in FIG. 7C, the current gradually decreases regardless of whether the object to be heated 5 is a current change “large” pan or a current change “small” pan. When the water boils and the temperature becomes constant, the input current also becomes constant.

For this reason, the control unit 45 according to the first embodiment obtains a change amount of current per unit time (current change amount ΔI) with the drive frequency of the inverter circuit 23 fixed, and the current change amount ΔI is calculated as follows. When it becomes below the threshold value, it is determined that the boiling is completed.
The details of such a water heater mode will be described with reference to FIG.

FIG. 8 is a flowchart showing an operation example of the hot water mode of the induction heating cooker according to the first embodiment.
First, the user places the object to be heated 5 on the heating port of the top plate 4, and instructs the operation unit 40 to start heating (heat power input). Then, the load determination means 32 performs a load determination process at the start of heating. In the load determination process at the time of heating start, the classification of the material of the to-be-heated material (pan) 5 placed is roughly classified using a load determination table indicating the relationship between the input current and the coil current (step ST1). ). When it is determined that there is no load, the control unit 45 notifies the notification means 42 to that effect, and controls the high frequency power not to be supplied from the drive circuit 50 to the heating coil 11a.

Next, the drive frequency setting means 33 determines the value fd of the drive frequency f according to the material classification determined based on the result of the load determination process at the start of heating (step ST2). At this time, the drive frequency f is set to a drive frequency f = fd higher than the resonance frequency of the resonance circuit so that the input current does not become excessive.

In step ST2, the drive frequency setting unit 33 sets the value fd of the drive frequency f so that the high-frequency power supplied to the heating coil 11a becomes the maximum value according to the classification roughly classified by the load determination unit 32. May be determined. For example, when the material of the object to be heated 5 is a magnetic material, the value fd of the driving frequency f that sets the power supplied to the heating coil 11a to 3 kW is determined. Further, for example, when the material of the object to be heated 5 is a low-resistance nonmagnetic material, the value fd of the drive frequency f that sets the power supplied to the heating coil 11a to 1 kW is determined.
In this way, by setting the high-frequency power supplied to the heating coil 11a to the maximum value, the temperature change speed of the article to be heated 5 is increased, and the current change amount I1 in the load determination process during the heating operation is increased. Becomes larger. Therefore, the accuracy of determination of the material of the article to be heated 5 can be further improved.

Thereafter, the drive control means 31 starts the induction heating operation by driving the inverter circuit 23 with the drive frequency f fixed at fd (step ST3). The load determination unit 32 starts measuring the first heating period t1 along with the start of the induction heating operation.

When the driving frequency is fixed and heating is started, the temperature (water temperature) of the object to be heated 5 gradually rises until boiling (FIG. 7 (b)). In the control with the driving frequency fixed, as shown in FIG. 6, the input current value (operating point) at the driving frequency changes from the point A to the point B, and as the temperature of the heated object 5 increases, The current gradually decreases.

During the induction heating operation, the current change detecting means 34 calculates the current change amount ΔI at a predetermined sampling interval (step ST4).

Next, the load determination means 32 determines whether or not the first heating period t1 has elapsed from the start of heating (step ST5). If the first heating period t1 has not elapsed since the start of heating, the process returns to step ST4.

When the first heating period t1 has elapsed from the start of heating, the load determination unit 32 determines whether the material of the article to be heated 5 is one of a plurality of materials belonging to the broadly classified section by the load determination process during the heating operation described above. The material is subdivided (step ST6).

In step ST6, when the first heating period has elapsed, the control unit 45 may drive the inverter circuit 23 for a predetermined determination time at a preset driving frequency for load determination. That is, the control unit 45 sets the inverter circuit 23 at a predetermined determination time for a predetermined determination time when starting the supply of power to the heating coil 11a and when the first heating period t1 has elapsed. The load determination means 32 is driven for a period of time, and the material of the object to be heated 5 is based on the amount of change I1 between the current when starting the power supply to the heating coil 11a and the current when the first heating period t1 has elapsed. May be determined.

Next, the control unit 45 sets a threshold value (Iref) of the current change amount ΔI according to the material of the heated object 5 determined by the load determination unit 32 in step ST6 (step ST7). Note that the initial value of the threshold value (Iref) may be set in advance or may be input from the operation unit 40 or the like. Or you may determine from the result of the load determination process at the time of the heating start in step ST1.
This threshold value (Iref) is set to be larger as the change amount I1 of the current in the first heating period t1 of the material of the object to be heated 5 determined by the load determination unit 32 is larger. That is, when the material of the object to be heated 5 is a material having a small current change amount I1, the boiling determination condition is made strict (threshold value is small), and the current change amount ΔI per predetermined time is determined by the current detection amount. Makes it difficult to be buried in the noise. In addition, when the material of the object to be heated 5 is a material having a large current change amount I1, it is possible to boil accurately according to the material of the object to be heated 5 by loosening the boiling judgment condition (increasing the threshold). Detection is possible.

After step ST7, the controller 45 determines whether or not the current change amount ΔI is equal to or less than a threshold value (Iref) set according to the material of the article to be heated 5 (step ST8).
As the object to be heated 5 changes from a low temperature to a high temperature, the current change amount ΔI decreases (FIG. 7C). When water boils and the temperature becomes constant, the current also becomes constant (FIG. 7 (c)). Thereby, in the 1st heating period t1, the control part 45 determines with the electric current variation | change_quantity (DELTA) I having become below a threshold value (Iref).

When the current change amount ΔI becomes equal to or less than the threshold value, the drive control unit 31 of the control unit 45 releases the fixed drive frequency and increases the drive frequency f of the inverter circuit 23 by the increase amount Δf (f = fd + Δf ), The high-frequency power (thermal power) supplied to the heating coil 11a is reduced (step ST9). That is, since the heating power to raise the temperature is not necessary when the object to be heated 5 is kept warm, the amount of heating from the heating coil 11a to the object to be heated 5 is suppressed.

The control unit 45 uses the notification means 42 to notify that the water heating has been completed (step ST10). Here, the notification means 42 is not particularly limited, for example, displaying the completion of boiling on the display unit 41 or notifying the user by voice using a speaker (not shown).

As described above, in the water heating mode for setting the water boiling operation, the amount of change ΔI per predetermined time of the current is obtained with the drive frequency of the inverter circuit 23 fixed, and the amount of change per predetermined time is the threshold value. When it becomes below, the notification means 42 notifies the completion of the boiling.
For this reason, it is possible to promptly notify the completion of boiling of water, and an easy-to-use induction heating cooker can be obtained.

In addition, since the control unit 45 does not require a high-precision microcomputer when obtaining the current change amount ΔI of the input current, an induction heating cooker that can detect boiling water by an inexpensive method can be obtained.

In addition, since the material of the object to be heated 5 is subdivided and determined by the load determining means 32, and the threshold value (Iref) is set according to the material of the object to be heated 5, the accuracy is determined according to the material of the object to be heated 5. Water heater detection can be performed.

(Modification)
Next, a modification of the load determination process during the heating operation will be described.

(Judgment considering the temperature at the beginning of heating)
Since the change amount I1 of the current from the start of heating until the first heating period t1 elapses depends on the temperature change amount of the article 5 to be heated, it is affected by the initial temperature of the article 5 to be heated. For this reason, the material can be determined with higher accuracy by performing the material determination in consideration of the temperature of the article 5 to be heated at the start of heating.

FIG. 9 is a load discrimination characteristic diagram of the object to be heated based on the relationship between the heating coil current and the input current in the induction heating cooker according to the first embodiment.
In FIG. 9, the heated object 5 (current change “large” pan) plotted with ◆ and the heated object 5 (current change “small” pan) plotted with ■ are when the initial heating temperature is medium Is shown.
Compared with the case where the temperature in the initial stage of heating in FIG. 4 is low, the plot position is different, and the amount of change in current until the temperature becomes high is reduced.

For this reason, the load determination unit 32 acquires the temperature of the article to be heated 5 detected by the temperature detection unit 30 at the start of heating. In the load determination process during the heating operation, the load determination unit 32 calculates the temperature of the object to be heated 5 detected by the temperature detection unit 30 at the start of heating and the current from the start of heating until the first heating period t1 elapses. Based on the amount of change I1, the material of the article to be heated 5 is subdivided into which of a plurality of materials belonging to the broadly classified section.
For example, the relationship between the amount of change in current I1 and the type of material is stored in advance according to experimental data or the like, corresponding to the initial temperature of heating. And the load determination means 32 refers to the information on the relationship between the current change amount I1 and the material type stored in advance based on the temperature of the heated object 5 at the start of heating and the current change amount I1. Thus, the type of the material to be heated 5 is subdivided and determined.
Thereby, the material of the to-be-heated material 5 can be determined still more accurately.

(Judgment considering high frequency power)
The speed of temperature change of the article 5 to be heated depends on the high frequency power (thermal power) supplied to the heating coil 11a, and the current change amount I1 from the start of heating until the first heating period t1 elapses is the high frequency power. to be influenced. For this reason, the material can be determined with higher accuracy by performing the material determination in consideration of the high-frequency power (drive frequency) from the start of heating until the first heating period t1 elapses.

FIG. 10 is a diagram showing the relationship between the drive frequency, temperature, current, and time of the induction heating cooker according to the first embodiment.
FIG. 10 shows the elapsed time and changes in each characteristic when the drive frequency is high (high-frequency power is low) compared to the example of FIG. 10A shows the drive frequency, FIG. 10B shows the temperature (water temperature), and FIG. 10C shows the current (input current or coil current).
As shown in FIG. 10B, when the high frequency power supplied to the heating coil 11a is low, the temperature rise until boiling is moderate. Further, as shown in FIG. 10 (c), even when the object to be heated 5 is either a current change “large” pan or a current change “small” pan, the current gradually decreases, The amount of current change I1 during one heating period t1 is smaller than that in the example of FIG.

For this reason, in the load determination process during the heating operation, the load determination unit 32 changes the high-frequency power (drive frequency) of the drive circuit 50 and the current from the start of heating until the first heating period t1 has elapsed. Based on the amount I1, the material of the article to be heated 5 is subdivided into which of a plurality of materials belonging to the broadly classified section.
For example, the relationship between the current change amount I1 and the type of material is stored in advance by experimental data or the like corresponding to the high frequency power. Then, the load determination unit 32 refers to the information on the relationship between the current change amount I1 and the material type stored in advance based on the high frequency power and the current change amount I1 in the first heating period t1. The material type of the article to be heated 5 is subdivided and determined.
Thereby, the material of the to-be-heated material 5 can be determined still more accurately.

(Setting of the first heating period t1)
In the above-described load determination process in the water heater mode, load determination is performed before heating is started and boiling is detected. That is, it is desirable that the first heating period t1 is before the boiling time.

For this reason, in the load determination process during the heating operation, the load determination unit 32 has at least the input current and the coil current from the start of heating until the second heating period t2 shorter than the first heating period t1 elapses. The first heating period t1 is set according to the change amount I2 of one of the currents.

FIG. 11 is a diagram showing the relationship between the drive frequency, temperature, current, and time of the induction heating cooker according to Embodiment 1.
In FIG. 11, compared with the example of FIG. 7, the elapsed time and the change in each characteristic when the amount of water in the article to be heated 5 is reduced are shown. 11A shows the driving frequency, FIG. 11B shows the temperature (water temperature), and FIG. 11C shows the current (input current or coil current).
As shown in FIG. 11B, when the amount of water in the article to be heated 5 is small, the heating time until boiling is shortened. Moreover, as shown in FIG.11 (c), even if the to-be-heated material 5 is any case of a current change "large" pan and a current change "small" pan, an electric current falls rapidly.

For this reason, the load determination means 32 sets the 1st heating period t1 short, when the variation | change_quantity I2 of the electric current until the 2nd heating period t2 passes since a heating start is large.
Conversely, when the amount of change in current I2 is small, such as when the amount of water in the object to be heated 5 is large or the high frequency power is small, the first heating period t1 is set to be long.
For example, the relationship between the current change amount I2 and the first heating period t1 is stored in advance by experimental data or the like. And the load determination means 32 sets the 1st heating period t1 by referring the information memorize | stored beforehand based on the variation | change_quantity I2 of the electric current in the 2nd heating period t2.
Thereby, the material of the to-be-heated material 5 can be determined still more accurately.

The first heating period t1 may be set according to the rate of change of at least one of the input current and the coil current from the start of heating until the second heating period t2 elapses. For example, when the rate of change is large, the current rapidly decreases, so the first heating period t1 is set short. In addition, when the rate of change is small, the change in current is gentle, so the first heating period t1 is set to be long.

Note that the setting operation for the first heating period t1 may be periodically performed a plurality of times.

(Combination of each modification)
The modification examples of the load determination process during the heating operation described above can be arbitrarily combined. For example, in the load determination process during the heating operation, the load determination unit 32 drives the temperature of the heated object 5 detected by the temperature detection unit 30 at the start of heating and the time from the start of heating until the first heating period t1 elapses. Based on the drive frequency of the circuit 50 and the amount of change in current I1, the material of the article to be heated 5 may be subdivided from among a plurality of materials belonging to a broadly divided category.
Thereby, the material of the to-be-heated material 5 can be determined still more accurately.

(Configuration example of another drive circuit)
Next, an example using another drive circuit will be described.
FIG. 12 is a diagram showing another drive circuit of the induction heating cooker according to the first embodiment.
A drive circuit 50 shown in FIG. 12 is obtained by adding a resonance capacitor 24b to the configuration shown in FIG. Other configurations are the same as those in FIG. 2, and the same parts are denoted by the same reference numerals.

As described above, since the resonance circuit is configured by the heating coil 11a and the resonance capacitor, the capacity of the resonance capacitor is determined by the maximum heating power (maximum input power) required for the induction heating cooker. In the drive circuit 50 shown in FIG. 10, by connecting the

resonant capacitors

24a and 24b in parallel, the respective capacities can be halved, and an inexpensive control circuit can be obtained even when two resonant capacitors are used. .

In addition, by arranging the coil current detection means 25b on the resonance capacitor 24a side of the resonance capacitors connected in parallel, the current flowing through the coil current detection means 25b is half of the current flowing through the heating coil 11a. The capacity coil current detection means 25b can be used, a small and inexpensive control circuit can be obtained, and an inexpensive induction heating cooker can be obtained.

In the first embodiment, the half-bridge type inverter circuit 23 has been described. However, a configuration using a full-bridge type or one-stone voltage resonance type inverter may be used.

Further, the method of using the relationship between the coil current and the primary current in the load determination process at the start of heating by the load determination unit 32 has been described. However, the method of performing the load determination process by detecting the resonance voltage at both ends of the resonance capacitor is used. The method for determining the load is not particularly limited.

In the above description, the method of controlling the high frequency power (thermal power) by changing the drive frequency has been described. However, the thermal power is controlled by changing the on-duty (on / off ratio) of the switching element of the inverter circuit 23. A method may be used.

Embodiment 2. FIG.
In the second embodiment, details of the drive circuit 50 in the first embodiment will be described.

FIG. 13 is a diagram showing a part of the drive circuit of the induction heating cooker according to the second embodiment. In FIG. 13, only a part of the configuration of the drive circuit 50 of the first embodiment is illustrated.
As shown in FIG. 13, the inverter circuit 23 includes two switching elements (

IGBTs

23a and 23b) connected in series between the positive and negative buses, and

diodes

23c and 23d connected in antiparallel to the switching elements, respectively. One set of arms is provided.

The IGBT 23 a and the IGBT 23 b are driven on and off by a drive signal output from the control unit 45.
The control unit 45 turns off the IGBT 23b while turning on the IGBT 23a, turns on the IGBT 23b while turning off the IGBT 23a, and outputs a drive signal that turns on and off alternately.
Thereby, the half bridge inverter which drives the heating coil 11a is comprised by IGBT23a and IGBT23b.

The IGBT 23a and the IGBT 23b constitute the “half bridge inverter circuit” in the present invention.

The control part 45 inputs a high frequency drive signal into IGBT23a and IGBT23b according to input electric power (thermal power), and adjusts a heating output. The drive signal output to the IGBT 23a and the IGBT 23b is variable in a drive frequency range higher than the resonance frequency of the load circuit constituted by the heating coil 11a and the resonance capacitor 24a, and the current flowing through the load circuit is applied to the load circuit. It is controlled to flow with a lagging phase compared to the voltage to be transmitted.

Next, the control operation of the input power (thermal power) by the drive frequency and on-duty ratio of the inverter circuit 23 will be described.

FIG. 14 is a diagram illustrating an example of a drive signal of the half bridge circuit according to the second embodiment. FIG. 14A shows an example of a drive signal for each switch in a high thermal power state. FIG. 14B is an example of the drive signal of each switch in the low thermal power state.
The control unit 45 outputs a high-frequency drive signal higher than the resonance frequency of the load circuit to the IGBT 23 a and the IGBT 23 b of the inverter circuit 23.
By varying the frequency of the drive signal, the output of the inverter circuit 23 increases or decreases.

For example, as shown in FIG. 14A, when the drive frequency is lowered, the frequency of the high-frequency current supplied to the heating coil 11a approaches the resonance frequency of the load circuit, and the input power to the heating coil 11a increases. .
As shown in FIG. 14B, when the drive frequency is increased, the frequency of the high frequency current supplied to the heating coil 11a is separated from the resonance frequency of the load circuit, and the input power to the heating coil 11a is reduced. .

Furthermore, the control unit 45 controls the application time of the output voltage of the inverter circuit 23 by changing the on-duty ratio of the IGBT 23a and the IGBT 23b of the inverter circuit 23, along with the control of the input power by changing the drive frequency described above, It is also possible to control the input power to the heating coil 11a.
When increasing the thermal power, the ratio (on duty ratio) of the on-time of the IGBT 23a (the off-time of the IGBT 23b) in one cycle of the drive signal is increased to increase the voltage application time width in one cycle.
When reducing the thermal power, the ratio (on duty ratio) of the on-time of the IGBT 23a (the off-time of the IGBT 23b) in one cycle of the drive signal is reduced to reduce the voltage application time width in one cycle.

In the example of FIG. 14A, the ratio between the ON time T11a of the IGBT 23a (the OFF time of the IGBT 23b) and the OFF time T11b of the IGBT 23a (the ON time of the IGBT 23b) in one cycle T11 of the drive signal is the same (on duty ratio). Is 50%).
In the example of FIG. 14B, the ratio between the on-time T12a of the IGBT 23a (the off-time of the IGBT 23b) and the off-time T12b of the IGBT 23a (the on-time of the IGBT 23b) in one cycle T12 of the drive signal is on (on). The case where the duty ratio is 50%) is illustrated.

In the state where the drive frequency of the inverter circuit 23 is fixed when the controller 45 determines the current change amount ΔI per predetermined time of the input current (or coil current) described in the first embodiment, the control circuit 45 23, the on-duty ratio of the IGBT 23a and the IGBT 23b is fixed.
Thus, the current change amount ΔI per predetermined time of the input current (or coil current) can be obtained in a state where the input power to the heating coil 11a is constant.

Embodiment 3 FIG.
In the third embodiment, an inverter circuit 23 using a full bridge circuit will be described.
FIG. 15 is a diagram illustrating a part of the drive circuit of the induction heating cooker according to the third embodiment. In FIG. 15, only the differences from the drive circuit 50 of the first embodiment are illustrated.
In the third embodiment, two heating coils are provided for one heating port. For example, the two heating coils have different diameters and are arranged concentrically. Here, the heating coil having a small diameter is referred to as an inner coil 11b, and the heating coil having a large diameter is referred to as an outer coil 11c.
In addition, the number and arrangement | positioning of a heating coil are not limited to this. For example, the structure which arrange | positions a some heating coil around the heating coil arrange | positioned in the center of a heating port may be sufficient.

The inverter circuit 23 includes three arms each composed of two switching elements (IGBTs) connected in series between the positive and negative buses and diodes connected to the switching elements in antiparallel. Hereinafter, one of the three sets of arms is called a common arm, and the other two sets are called an inner coil arm and an outer coil arm.

The common arm is an arm connected to the inner coil 11b and the outer coil 11c, and includes an IGBT 232a, an IGBT 232b, a diode 232c, and a diode 232d.
The inner coil arm is an arm to which the inner coil 11b is connected, and includes an IGBT 231a, an IGBT 231b, a diode 231c, and a diode 231d.
The outer coil arm is an arm to which the outer coil 11c is connected, and includes an IGBT 233a, an IGBT 233b, a diode 233c, and a diode 233d.

The common arm IGBT 232a and IGBT 232b, the inner coil arm IGBT 231a and IGBT 231b, and the outer coil arm IGBT 233a and IGBT 233b are driven on and off by a drive signal output from the control unit 45.

The controller 45 turns off the IGBT 232b while turning on the IGBT 232a of the common arm, turns on the IGBT 232b while turning off the IGBT 232a, and outputs a drive signal that turns on and off alternately.
Similarly, the control unit 45 outputs drive signals for alternately turning on and off the IGBTs 231a and IGBT 231b for the inner coil arms and the IGBTs 233a and IGBT 233b for the outer coil arms.
As a result, the common arm and the inner coil arm constitute a full bridge inverter that drives the inner coil 11b. The common arm and the outer coil arm constitute a full bridge inverter that drives the outer coil 11c.

In addition, the “full bridge inverter circuit” in the present invention is constituted by the common arm and the inner coil arm. The common arm and the outer coil arm constitute a “full bridge inverter circuit” in the present invention.

The load circuit constituted by the inner coil 11b and the resonance capacitor 24c is connected between the output point of the common arm (the connection point of the IGBT 232a and the IGBT 232b) and the output point of the arm for the inner coil (the connection point of the IGBT 231a and the IGBT 231b). Is done.
The load circuit constituted by the outer coil 11c and the resonance capacitor 24d is connected between the output point of the common arm and the output point of the outer coil arm (the connection point between the IGBT 233a and the IGBT 233b).

The inner coil 11b is a heating coil with a small outer shape wound in a substantially circular shape, and an outer coil 11c is disposed on the outer periphery thereof.
The coil current flowing through the inner coil 11b is detected by the coil current detection means 25c. For example, the coil current detection means 25c detects the peak of the current flowing through the inner coil 11b and outputs a voltage signal corresponding to the peak value of the heating coil current to the control unit 45.
The coil current flowing through the outer coil 11c is detected by the coil current detection means 25d. For example, the coil current detection unit 25d detects the peak of the current flowing through the outer coil 11c and outputs a voltage signal corresponding to the peak value of the heating coil current to the control unit 45.

The control unit 45 inputs a high-frequency drive signal to the switching element (IGBT) of each arm according to the input power (thermal power), and adjusts the heating output.
The drive signal output to the switching elements of the common arm and the inner coil arm varies in a drive frequency range higher than the resonance frequency of the load circuit constituted by the inner coil 11b and the resonance capacitor 24c, and flows to the load circuit. Control is performed so that the current flows in a delayed phase compared to the voltage applied to the load circuit.
Further, the drive signal output to the switching elements of the common arm and the outer coil arm can be varied within a drive frequency range higher than the resonance frequency of the load circuit constituted by the outer coil 11c and the resonance capacitor 24d, and the load circuit Control is performed so that the current flowing in the current flows in a delayed phase compared to the voltage applied to the load circuit.

Next, the control operation of the input power (thermal power) due to the phase difference between the arms of the inverter circuit 23 will be described.

FIG. 16 is a diagram illustrating an example of a drive signal of the full bridge circuit according to the third embodiment.
FIG. 16A is an example of the drive signal of each switch and the energization timing of each heating coil in the high thermal power state.
FIG. 16B is an example of the drive signal of each switch and the energization timing of each heating coil in the low thermal power state.
Note that the energization timings shown in FIGS. 16A and 16B are related to the potential difference between the output points of each arm (connection point of IGBT and IGBT), and the output points of the inner coil arm and the outer coil A state where the output point of the common arm is lower than the output point of the arm is indicated by “ON”. Further, the state where the output point of the common arm is higher than the output point of the inner coil arm and the output point of the outer coil arm and the state of the same potential are indicated by “OFF”.

As shown in FIG. 16, the control unit 45 outputs a high-frequency drive signal higher than the resonance frequency of the load circuit to the IGBTs 232a and IGBTs 232b of the common arm.
Further, the control unit 45 outputs a drive signal having a phase advanced from the drive signal of the common arm to the IGBT 231a and IGBT 231b of the inner coil arm and the IGBT 233a and IGBT 233b of the outer coil arm. In addition, the frequency of the drive signal of each arm is the same frequency, and the on-duty ratio is also the same.

The positive bus potential or the negative bus potential, which is the output of the DC power supply circuit, is switched at a high frequency and output at the output point of each arm (the connection point between the IGBT and IGBT) in accordance with the on / off state of the IGBT and IGBT. As a result, a potential difference between the output point of the common arm and the output point of the inner coil arm is applied to the inner coil 11b. Further, a potential difference between the output point of the common arm and the output point of the outer coil arm is applied to the outer coil 11c.
Therefore, the high frequency voltage applied to the inner coil 11b and the outer coil 11c can be adjusted by increasing / decreasing the phase difference between the driving signal to the common arm and the driving signals to the inner coil arm and the outer coil arm. The high frequency output current and the input current flowing through the inner coil 11b and the outer coil 11c can be controlled.

When increasing the thermal power, the phase α between the arms is increased to increase the voltage application time width in one cycle. The upper limit of the phase α between the arms is in the case of reverse phase (phase difference 180 °), and the output voltage waveform at this time is almost a rectangular wave.
In the example of FIG. 16A, the case where the phase α between the arms is 180 ° is illustrated. Further, the case where the on-duty ratio of the drive signal of each arm is 50%, that is, the case where the ratio of the on-time T13a and the off-time T13b in one cycle T13 is the same is illustrated.
In this case, the energization on time width T14a and the energization off time width T14b of the inner coil 11b and the outer coil 11c in one cycle T14 of the drive signal have the same ratio.

When lowering the thermal power, the phase α between the arms is made smaller than in the high thermal power state to reduce the voltage application time width in one cycle. Note that the lower limit of the phase α between the arms is set to a level at which an excessive current does not flow into the switching element and breaks due to the phase of the current flowing in the load circuit at the time of turn-on, for example.
In the example of FIG. 16B, the case where the phase α between the arms is made smaller than that in FIG. The frequency and on-duty ratio of the drive signal for each arm are the same as in FIG.
In this case, the energization on time width T14a of the inner coil 11b and the outer coil 11c in one cycle T14 of the drive signal is a time corresponding to the phase α between the arms.
Thus, the input power (thermal power) to the inner coil 11b and the outer coil 11c can be controlled by the phase difference between the arms.

In the above description, the case where both the inner coil 11b and the outer coil 11c are heated is described. However, the driving of the inner coil arm or the outer coil arm is stopped, and either the inner coil 11b or the outer coil 11c is stopped. Only one of them may be heated.

When the control unit 45 determines the current change amount ΔI per predetermined time of the input current (or coil current) described in the first embodiment, the control unit 45 does not operate between the arms in a state where the drive frequency of the inverter circuit 23 is fixed. And the on-duty ratio of the switching element of each arm are fixed. Other operations are the same as those in the first embodiment.
Thereby, the current change amount ΔI per predetermined time of the input current (or coil current) can be obtained in a state where the input power to the inner coil 11b and the outer coil 11c is constant.

In the third embodiment, the coil current flowing through the inner coil 11b and the coil current flowing through the outer coil 11c are detected by the coil current detecting means 25c and the coil current detecting means 25d, respectively.
Therefore, when both the inner coil 11b and the outer coil 11c are heated, even if either the coil current detection means 25c or the coil current detection means 25d cannot detect the coil current value due to a failure or the like. The other detection value makes it possible to detect the current change amount ΔI of the coil current per predetermined time.
The control unit 45 also includes a current change amount ΔI per predetermined time of the coil current detected by the coil current detection means 25c, and a current change amount ΔI per predetermined time of the coil current detected by the coil current detection means 25d. And the determination operation described in the first embodiment may be performed using the larger one of the current change amounts ΔI. Further, each determination operation described in the first embodiment may be performed using an average value of each current change amount ΔI.
By performing such control, even if the detection accuracy of either the coil current detection means 25c or the coil current detection means 25d is low, the current change amount ΔI per predetermined time of the coil current can be obtained more accurately. be able to.

In Embodiments 1 to 3, the IH cooking heater has been described as an example of the induction heating cooker of the present invention. However, the present invention is not limited to this. The present invention can be applied to any induction heating cooker that employs an induction heating method, such as a rice cooker that performs cooking by induction heating.

1 1st heating port, 2nd heating port, 3rd heating port, 4 top plate, 5 object to be heated, 11 1st heating means, 11a heating coil, 11b inner coil, 11c outer coil, 12 2nd heating means, 13 3rd heating means, 21 AC power supply, 22 DC power supply circuit, 22a diode bridge, 22b reactor, 22c smoothing capacitor, 23 inverter circuit, 23a, 23b IGBT, 23c, 23d diode, 24a-24d Resonance capacitor, 25a, input current detection means, 25b to 25d, coil current detection means, 30 temperature detection means, 31 drive control means, 32 load determination means, 33 drive frequency setting means, 34 current change detection means, 35 power adjustment means, 36 Input / output control means, 40a to 40c, operation unit, 41a to 41 Display unit, 42 notification means, 45 control unit, 50 drive circuit, 100 induction heating cooker, 231a, 231b IGBT, 232a, 232b IGBT, 233a, 233b IGBT, 231c, 231d diode, 232c, 232d diode, 233c, 233d diode .

Claims

A heating coil for inductively heating an object to be heated;
A drive circuit for supplying high-frequency power to the heating coil;
Load determination means for performing load determination processing of the object to be heated;
A controller that controls driving of the driving circuit and controls high-frequency power supplied to the heating coil;
Input current detection means for detecting an input current to the drive circuit;
Coil current detection means for detecting a coil current flowing in the heating coil,
The load determination means includes
Obtaining a change amount (I1) of at least one of the input current and the coil current from the start of power supply to the heating coil until the first heating period elapses,
Based on the amount of change in current (I1), the material of the object to be heated is determined,
The controller is
An induction heating cooker that controls driving of the drive circuit according to a determination result of the load determination means.
The controller is
2. The induction heating cooker according to claim 1, wherein the drive frequency of the drive circuit is fixed from the start of power supply to the heating coil until the first heating period elapses.
The load determination means includes
Based on the correlation between the input current and the coil current, whether the material of the object to be heated is at least two of a magnetic material, a high resistance nonmagnetic material, and a low resistance nonmagnetic material. Broadly divided
Based on the change amount (I1) of the current from the start of power supply to the heating coil until the first heating period elapses, the material of the object to be heated is selected from among a plurality of materials belonging to the broadly classified section. The induction heating cooker according to claim 1 or 2, wherein the material is subdivided into any material.
The controller is
The driving circuit is driven so that the high-frequency power supplied to the heating coil has a maximum value according to the classification roughly classified by the load determination unit,
4. The induction heating cooker according to claim 3, wherein the driving frequency of the driving circuit is fixed from the start of power supply to the heating coil until the first heating period elapses.
Temperature detecting means for detecting the temperature of the object to be heated;
The load determination means includes
The temperature of the heated object detected by the temperature detecting means at the start of power supply to the heating coil; and
Based on the amount of change in current (I1) from the start of power supply to the heating coil until the first heating period elapses,
5. The induction heating cooker according to claim 3, wherein the material of the object to be heated is subdivided into any of a plurality of materials belonging to the broadly classified section.
The controller is
From the start of power supply to the heating coil until the elapse of the first heating period, the driving frequency of the driving circuit is fixed,
The load determination means includes
Based on the drive frequency of the drive circuit and the amount of change in current (I1) from the start of power supply to the heating coil until the first heating period elapses,
The induction heating cooker according to any one of claims 3 to 5, wherein a material of the object to be heated is subdivided into any one of a plurality of materials belonging to the roughly classified section. .
Temperature detecting means for detecting the temperature of the object to be heated;
The load determination means includes
Based on the correlation between the input current and the coil current, whether the material of the object to be heated is at least two of a magnetic material, a high resistance nonmagnetic material, and a low resistance nonmagnetic material. Broadly divided
The controller is
According to the classification roughly classified by the load determination means, the driving circuit is driven, and the driving frequency of the driving circuit is fixed,
The load determination means includes
The temperature of the heated object detected by the temperature detecting means at the start of power supply to the heating coil; and
Based on the drive frequency of the drive circuit and the amount of change in current (I1) from the start of power supply to the heating coil until the first heating period elapses,
The induction heating cooker according to claim 1, wherein a material of the object to be heated is subdivided into which of a plurality of materials belonging to the roughly classified section.
The controller is
When starting to supply power to the heating coil, and when the first heating period has elapsed, the drive circuit is driven at a preset drive frequency for load determination for a predetermined determination time,
The load determination means includes
The difference between the current when the power supply to the heating coil is started and the current when the first heating period has elapsed is obtained as the amount of change in current (I1), and the material of the object to be heated is determined. The induction heating cooker according to any one of claims 1 to 7, characterized in that:
The load determination means includes
Depending on the amount of change or rate of change of at least one of the input current and the coil current from the start of power supply to the heating coil until the second heating period shorter than the first heating period elapses. The induction heating cooker according to any one of claims 1 to 8, wherein a heating period is set.
The controller is
In a state where the drive frequency of the drive circuit is fixed, a change amount (ΔI) per predetermined time of at least one of the input current and the coil current is obtained,
When the amount of change per predetermined time (ΔI) is equal to or less than a threshold set according to the material of the object to be heated,
The induction heating cooker according to any one of claims 1 to 9, wherein the drive of the drive circuit is controlled to vary the high-frequency power supplied to the heating coil.
An operation unit for selecting an operation mode;
An informing means,
The controller is
When the water heating mode for setting the water heating operation of water is selected as the operation mode, the driving circuit is driven,
In a state where the drive frequency of the drive circuit is fixed, a change amount (ΔI) per predetermined time of at least one of the input current and the coil current is obtained,
When the amount of change per predetermined time (ΔI) obtained with the drive frequency of the drive circuit fixed is equal to or less than a threshold set according to the material of the heated object, The induction heating cooker according to any one of claims 1 to 10, wherein the induction heating device is notified by a notification means.
The controller is
The induction heating cooker according to claim 10 or 11, wherein the threshold value is set to be larger as the change amount (I1) of the current of the material to be heated determined by the load determination means is larger. .
The controller is
The induction heating cooker according to any one of claims 1 to 12, wherein an on-duty ratio of a switching element of the drive circuit is fixed in a state where the drive frequency of the drive circuit is fixed. .
The drive circuit is
A full-bridge inverter circuit having at least two arms in which two switching elements are connected in series;
The controller is
In the state where the driving frequency of the switching element of the full bridge inverter circuit is fixed, the driving phase difference of the switching element between the two arms and the on-duty ratio of the switching element are fixed. The induction heating cooker according to any one of claims 1 to 12, wherein
The drive circuit is
It is composed of a half-bridge inverter circuit having an arm in which two switching elements are connected in series,
The controller is
The on-duty ratio of the switching element is fixed in a state where the driving frequency of the switching element of the half-bridge inverter circuit is fixed. Induction heating cooker.