WO2014068646A1

WO2014068646A1 - Induction heating cooker

Info

Publication number: WO2014068646A1
Application number: PCT/JP2012/077942
Authority: WO
Inventors: 吉野　勇人; 浩志郎 ▲高▼野; 雄一郎伊藤; 西　健一郎
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: 2012-10-30
Filing date: 2012-10-30
Publication date: 2014-05-08
Also published as: WO2014069008A1; JP5980344B2; JPWO2014069008A1

Abstract

In this induction heating cooker, an inverter circuit (23) is driven corresponding to determination results obtained from a load determining means, an amplification factor of an amplifying means is set corresponding to a detection value of an input current and/or a detection value of a coil current, or corresponding to the determination results obtained from the load determining means, a change quantity of a detection value amplified by means of the amplifying means is obtained per predetermined time in a state wherein the drive frequency of the inverter circuit (23) is fixed, and a temperature change of a subject to be heated is detected on the basis of the change quantity per predetermined time.

Description

Induction heating cooker

This invention relates to an induction heating cooker.

Some conventional induction heating cookers determine the temperature of an object to be heated based on the input current or control amount of an inverter.
For example, it has a control means for controlling the inverter so that the input current of the inverter becomes constant, and when the control amount changes more than a predetermined amount within a predetermined time, it is determined that the temperature change of the object to be heated is large. An induction heating cooker that suppresses the output of an inverter has been proposed (see, for example, Patent Document 1).
Further, for example, a temperature detection device for an induction heating cooker comprising temperature determination processing means for determining a temperature corresponding to the change amount of the input current detected by the input current change amount detection means for detecting only the change amount of the input current Has been proposed (see, for example, Patent Document 2).

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, 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 for an induction heating cooker described in Patent Document 2, when the material of the object to be heated changes, the input current may become 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 the above-described problems, and provides an induction heating cooker that can detect a temperature change of a heated object regardless of the material of the heated object. Moreover, the highly reliable induction heating cooking appliance which suppressed the increase in input current 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, load determination means that performs load determination processing of the heating coil, and the drive Amplifying means for amplifying a detected value of at least one of an input current to the circuit and a coil current flowing in the heating coil, and a control for controlling the driving of the drive circuit and the high-frequency power supplied to the heating coil And the control unit drives the drive circuit according to a determination result of the load determination unit, and detects a detected value of at least one of the input current and the coil current, or the load determination unit. In accordance with the determination result, the amplification factor of the amplification unit is set, and the detection frequency amplified by the amplification unit in a state where the drive frequency of the drive circuit is fixed Determine the amount of change per predetermined time, based on the amount of change per predetermined time, the which detects the temperature change of the heated object.

This invention can detect the temperature change of the heated object regardless of the material of the heated object. Further, an increase in input current can be suppressed, and reliability can be improved.

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 load discrimination | determination characteristic view of the to-be-heated object based on the relationship between the heating coil electric 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, input 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, input current, and an amplifier output, 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 the drive frequency of the induction heating cooking appliance which concerns on Embodiment 2, temperature, an input current, and the relationship between an amplifier part output and time. It is a figure explaining the determination process of the electric current variation | change_quantity of the to-be-heated material based on the relationship between the heating coil current and input current in the induction heating cooking appliance which concerns on Embodiment 2. 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 made of a material that transmits infrared rays, such as heat-resistant tempered glass or crystallized glass, and a rubber packing or sealing material is interposed between the upper surface and the outer periphery of the upper surface 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, there is a 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 41a, a display unit 41b, and a display unit 41c for displaying the operation state of the induction heating cooker 100, the input / operation content from the operation unit 40, and the like. Is provided. Note that 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 control unit 45 in the present embodiment constitutes a “control unit” and a “load determination unit” in the present invention.

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 illustrating a drive circuit of the induction heating cooker according to the first embodiment. In addition, the drive circuit 50 is provided for every heating means, and the structure is the same. 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.

Amplifying

units

48a and 48b and a switching unit 49 are provided between the input current detecting means 25a and the control unit 45. The amplifying

units

48a and 48b amplify the voltage signal (detected value) output from the input current detecting unit 25a. The

amplifiers

48a and 48b are configured by an amplifier circuit that amplifies and outputs an input voltage signal. The

amplification units

48a and 48b have different amplification factors, and the switching unit 49 switches the connection with the input current detection means 25a. In the first embodiment, a case where the amplification unit 48b has a higher amplification factor than the amplification unit 48a will be described.
In the first embodiment, the case where two amplifying

units

48a and 48b are provided will be described. However, the present invention is not limited to this, and three or more amplifying units having different amplification factors may be provided. Further, only one amplifying unit is provided, and the case where the detection value is input to the control unit 45 without going through the amplifying unit and the case where the detection value amplified through the amplifying unit is input to the control unit 45 are switched. May be. Further, an amplification unit that can vary the amplification factor may be provided, and the amplification factor may be set by 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.

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.

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 25b detects the peak of the current flowing through the heating coil 11a and outputs a voltage signal corresponding to the peak value of the heating coil current to the control unit 45.

The temperature detection means 30 is composed of, for example, a thermistor, 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.

(Operation)
Next, operation | movement of the induction heating cooking appliance 100 which concerns on Embodiment 1 is demonstrated.
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 control unit 45 (load determination means) performs a load determination process.

FIG. 3 is a load discrimination characteristic diagram of an 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.
Here, the material of the heated object 5 (pan) serving as a load is largely divided into a magnetic material such as iron or SUS430, a high resistance nonmagnetic material such as SUS304, and a low resistance nonmagnetic material such as aluminum or copper. Separated.

As shown in FIG. 3, the relationship between the coil current and the input current differs depending on the material of the pan load placed on the top plate 4. The control unit 45 stores therein in advance a load determination table in which the relationship between the coil current and the input current shown in FIG. 3 is tabulated. By storing the load determination table therein, the load determination means can be configured with an inexpensive configuration.

In the load determination process, the control unit 45 drives the inverter circuit 23 with a specific drive signal for load determination, and detects the input current from the output signal of the input current detection means 25a. 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 material of the to-be-heated material (pan) 5 mounted from the detected coil current and input current, and the load determination table showing the relationship of FIG. Thus, the control part 45 (load determination means) determines the material of the article 5 to be heated placed on the heating coil 11a based on the correlation between the input current and the coil current.

After performing the above load determination processing, the control unit 45 performs a control operation based on the load determination result.

When the load determination result is a low-resistance non-magnetic material, the induction heating cooker 100 according to the first embodiment cannot be heated. Encourage people to change the pan.

Also, even if the load determination result is no load, the notification means 42 is notified that heating is impossible, and the user is prompted to place the pan.

When the load determination result is a magnetic material or a high-resistance nonmagnetic material, these pans are materials that can be heated by the induction heating cooker 100 of the first embodiment, and thus the control unit 45 has determined. Determine the drive frequency according to the pan 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 control unit 45 fixes the determined drive frequency and drives the inverter circuit 23 to start the induction heating operation.

FIG. 4 is a phase diagram of the input current with respect to the drive frequency when the temperature of the heated object of the induction heating cooker according to Embodiment 1 is changed. In FIG. 4, 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. 4, the characteristics change depending on the temperature of the object to be heated 5 because the resistivity of the object to be heated 5 increases and the magnetic permeability decreases due to the temperature rise, so that the heating coil 11a and the object to be heated are heated. This is because the magnetic coupling of the object 5 changes.

In the control unit 45 of the induction heating cooker 100 according to the first embodiment, a frequency higher than the frequency at which the input current shown in FIG. 4 is maximized is determined as the driving frequency, and this driving frequency is fixed and the inverter circuit 23 is controlled.

FIG. 5 is an enlarged view of a portion indicated by a broken line in FIG.
When the inverter circuit 23 is controlled by fixing the drive frequency according to the pan material determined in the load determination process described above, the input current value (operating point) at the drive frequency increases as the heated object 5 changes from low temperature to high temperature. The point A changes from point A to point B, and the input current gradually decreases as the temperature of the article to be heated 5 rises.
At this time, the control unit 45 obtains a change amount (time change) of the input current per predetermined time with the drive frequency of the inverter circuit 23 fixed, and based on the change amount per predetermined time, the object to be heated 5 Detects temperature changes in

For this reason, it is possible to detect the temperature change of the heated object 5 regardless of the material of the heated object 5. Moreover, since the temperature change of the to-be-heated object 5 can be detected by the change of input current, a temperature change can be detected at high speed compared with a temperature sensor etc.

Moreover, the material of the to-be-heated object 5 mounted above the heating coil 11a is determined, the drive frequency of the inverter circuit 23 is determined according to the material of the to-be-heated object 5, and the inverter circuit 23 is determined by the drive frequency. Drive. 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.

(Water heating mode 1)
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.

Similarly to the above-described operation, the control unit 45 performs a load determination process, determines a drive frequency corresponding to the determined pan material, drives the inverter circuit 23 with the determined drive frequency fixed, and performs an induction heating operation. carry out. And the control part 45 judges completion of boiling by the time change of input current. Here, the elapsed time and the change of each characteristic when performing water boiling will be described with reference to FIG.

FIG. 6 is a diagram showing the relationship between the drive frequency, temperature, input current and time of the induction heating cooker according to the first embodiment. In FIG. 6, the elapsed time and the change of each characteristic when water is poured into the article to be heated 5 and the boiling of water are shown, FIG. 6 (a) shows the driving frequency, and FIG. 6 (b) shows the temperature ( Water temperature), FIG. 6 (c) shows the input current.

As shown in FIG. 6A, the inverter circuit 23 is controlled with the drive frequency fixed. As shown in FIG. 6B, the temperature (water temperature) of the article to be heated 5 gradually rises until it boils, and when it boils, the temperature becomes constant. As shown in FIG. 6C, the input current gradually decreases as the temperature of the article 5 to be heated increases, and when the water boils and the temperature becomes constant, the input current also becomes constant. That is, when the input current becomes constant, the water boils and the boiling is completed.

For this reason, the control unit 45 in the present embodiment obtains a change amount (time change) of the input current per predetermined time with the drive frequency of the inverter circuit 23 fixed, and the change amount per predetermined time. When the value becomes equal to or less than the predetermined value, it is determined that the water heater has been completed.
The predetermined value information may be set in the control unit 45 in advance, or may be input from the operation unit 40 or the like.

And the control part 45 alert | reports that the kettle was completed using the alerting | reporting means 42. FIG. 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 in which the water boiling operation is set, the amount of change per predetermined time of the input current is obtained with the drive frequency of the inverter circuit 23 being fixed. When the value is less than or equal to the value, the notification means 42 notifies the completion of 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.

(Water heater mode 2)
Next, another control operation when the water heating mode is selected by the operation unit 40 will be described.

The magnitude of the input current depends on the magnitude of the high-frequency power (thermal power) supplied to the heating coil 11a. The larger the thermal power, the larger the input current, and the smaller the thermal power, the smaller the input current. In addition, when the thermal power is small, the temperature rises more slowly than when the thermal power is large, and the input current also decreases slowly. For this reason, when the high-frequency power (thermal power) supplied to the heating coil 11a is small, the change amount of the input current per predetermined time becomes small, and it may be impossible to detect the completion of boiling.

In the hot water heating mode 2, the control unit 45 selects either the

amplification unit

48a or 48b by switching the switching unit 49 according to the detected value of the input current detected by the input current detection means 25a. Here, the control unit 45 selects so that the amplification factor of the amplification unit increases as the detected value of the input current decreases. The control unit 45 obtains a change amount per predetermined time of the detection value amplified by the selected amplification unit. Then, when the amount of change per predetermined time becomes equal to or less than a predetermined value (substantially constant), it is determined that the water has boiled and the boiling has been completed. Details of such operation will be described with reference to FIG.

FIG. 7 is a diagram illustrating the relationship between the drive frequency, temperature, input current, and amplification unit output of the induction heating cooker according to Embodiment 1 and time. In FIG. 7, the elapsed time and the change of each characteristic when water is poured into the article to be heated 5 and the boiling of water are shown, FIG. 7 (a) shows the drive frequency, and FIG. 7 (b) shows the temperature ( Water temperature), FIG. 7C shows the input current, and FIG. 7D shows the input current value amplified by the

amplifiers

48a and 48b (hereinafter referred to as “amplifier output”). Moreover, in each figure of FIG. 7, a continuous line shows the characteristic at the time of operation | movement (control) with high thermal power, and a broken line shows the characteristic at the time of controlling with low thermal power.
In the following explanation, the driving frequency, the input current, etc., and the length of the time and the length of the time are not particularly determined in relation to absolute values, and when the set thermal power is high thermal power and low thermal power It shall be relatively determined by comparison of cases.

In the case of high thermal power, the drive frequency of the inverter circuit 23 is set low, the drive frequency is fixed, and heating is started (solid line in FIG. 7A). In this case, since the heating power is high, the temperature (water temperature) of the object to be heated 5 rises in a short time (solid line in FIG. 7B). As indicated by the solid line in FIG. 7C, the input current decreases as the temperature of the object to be heated 5 increases. When the input current decreases and the water boils and the temperature becomes constant, the input current also becomes constant. Thus, at the time of high thermal power, since the high frequency power supplied to the heating coil 11a is high and the value of the input current is also high, the amount of change in the input current until the water boils increases.
On the other hand, in the case of low thermal power, the drive frequency of the inverter circuit 23 is set high, the drive frequency is fixed, and heating is started (broken line in FIG. 7A). In this case, since the heating power is low, the temperature (water temperature) of the article 5 to be heated rises gently as compared with the high heating power (broken line in FIG. 7B). As shown by the broken line in FIG. 7 (c), when the temperature of the article 5 to be heated increases, the input current decreases slowly as compared with the high heating power, and the water boils and the temperature becomes constant. The input current is also constant.
In this way, at the time of decreasing force, the high frequency power supplied to the heating coil 11a is low and the value of the input current is also low, so the amount of change in the input current until the water boils is also small.

For this reason, in the kettle mode 2, the control unit 45 determines the input current of the

amplifiers

48a and 48b according to the heating power set at the start of the kettle mode 2, that is, the value of the input current detected first. Switch the amplification section to be amplified. In other words, when the input current is lower than a preset threshold value, the input current is amplified by the amplification unit 48b having a high amplification factor among the

amplification units

48a and 48b (broken line in FIG. 7D). This increases the amount of change per unit time of the input current. When the input current is equal to or greater than a preset threshold, the input current is amplified by the amplifying unit 48a having a low amplification factor among the amplifying

units

48a and 48b (solid line in FIG. 7D). It should be noted that the selection of the amplifying unit to be used is preferably immediately after the start of the control in the water heating mode 2.

Here, the case of switching to one of the two amplifying

units

48a and 48b has been described, but the present invention is not limited to this, and the amplification factor for amplifying the input current increases as the detected value of the input current decreases. Any configuration can be used. For example, it may be switched to any of three or more amplifiers having different amplification factors, and the presence or absence of amplification may be switched by one amplifier. Further, the amplification factor may be set steplessly by an amplification unit that can vary the amplification factor.

The control unit 45 obtains a change amount (time change) of the amplified detection value per predetermined time with the drive frequency of the inverter circuit 23 fixed, and the change amount per predetermined time becomes equal to or less than the predetermined value. If it is determined that the water heater has been completed.
The threshold value and the predetermined value information may be set in the control unit 45 in advance, or may be input from the operation unit 40 or the like.

As described above, in the water heating mode for setting the water heating operation of the water, the amplification unit that amplifies the detection value is selected according to the detection value of the input current, and the change amount of the amplified detection value per predetermined time is obtained. When the amount of change per predetermined time becomes equal to or less than the predetermined value, it is determined that the boiling is completed.
For this reason, irrespective of the high frequency power (thermal power) supplied to the heating coil 11a, the completion of boiling of water can be detected with high accuracy, and a highly reliable induction heating cooker can be obtained. In addition, a user-friendly induction heating cooker can be obtained.

When the controller 45 determines that the kettle has been completed, the fixed driving frequency is released, the driving frequency of the inverter circuit 23 is increased, the input current is decreased, and the high-frequency power supplied to the heating coil 11a. You may make it reduce (thermal power). In the case of boiling water (boiling water), even if the heating power is increased more than necessary, the water temperature does not become 100 ° C. or higher, so that the water temperature can be maintained even if the driving frequency is increased to lower the heating power.
Thus, when the amount of change per predetermined time of the input current correction value is equal to or less than the predetermined value, the drive of the inverter circuit 23 is controlled to reduce the high frequency power supplied to the heating coil 11a. Energy can be saved by reducing power.

(Configuration example of another drive circuit)
Next, an example using another drive circuit will be described.
FIG. 8 is a diagram illustrating another drive circuit of the induction heating cooker according to the first embodiment.
The drive circuit 50 shown in FIG. 8 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. 8, 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. .

Further, 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 becomes 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

amplification units

48 a and 48 b and the control unit 45 are described separately. However, the

amplification units

48 a and 48 b may be configured as a part of the control unit 45.

Embodiment 2. FIG.
Another control operation when the water heating mode is selected by the operation unit 40 will be described.
In addition, the structure of the induction heating cooking appliance 100 in this Embodiment 2 is the same as that of the said Embodiment 1. FIG.

(Water heater mode 3)
The amount of change in input current from the start of heating to the boiling of water (hereinafter referred to as “current change amount”) also varies depending on the load (material) of the article 5 to be heated. That is, even with the same thermal power, there are materials having a large current change amount and materials having a small amount of current change. For this reason, when the object to be heated 5 with a small amount of current change is induction-heated and water is heated, depending on the material of the object to be heated 5, the amount of change in the input current per predetermined time becomes small and the water heater is heated. Completion may not be detected.
In the second embodiment, the control unit 45 (load determination unit) determines the magnitude of the current change amount of the object to be heated 5 immediately after the start of the hot water heating mode control, and the amplification unit 48a or One of 48b is selected. Details of such an operation will be described with reference to FIG.

FIG. 9 is a diagram illustrating the relationship between the drive frequency, temperature, input current, and amplification unit output of the induction heating cooker according to Embodiment 2 and time. In FIG. 9, the elapsed time and the change of each characteristic when water is poured into the article to be heated 5 and the boiling of water are shown, FIG. 9 (a) shows the drive frequency, and FIG. 9 (b) shows the temperature ( 9C shows the input current, and FIG. 9D shows the input current value (hereinafter referred to as “amplifier output”) amplified by the

amplifiers

48a and 48b. In FIGS. 9C and 9D, the solid line shows the characteristics when a load (material) with a small amount of current change is heated, and the broken line shows the characteristics when a load (material) with a large amount of current change is heated. Indicates.
In the following description, the magnitude of the input current and the like and the magnitude of the current change amount are not particularly determined in relation to the absolute value, but by comparing the load (material) of the object 5 to be heated, It shall be relatively determined.

When heating is started with the driving frequency fixed (FIG. 9 (a)), the temperature (water temperature) of the article to be heated 5 gradually rises until boiling (FIG. 9 (b)). As shown in FIG. 9 (c), the input current gradually decreases as the temperature of the article 5 to be heated increases, and when the water boils and the temperature becomes constant, the input current also becomes constant. At this time, when the object to be heated 5 is made of a material having a large amount of change in input current, the input current decreases as shown by the solid line in FIG. 9C, whereas the object to be heated 5 is made of a material having a small input current. In such a case, as shown by the broken line in FIG.

For this reason, in the hot water heating mode 3, the control unit 45 (load determination means) determines the magnitude of the current change amount of the heated object 5 immediately after the start of the control in the hot water heating mode 3.

Here, an example of determination of the current change amount of the object to be heated 5 in the control unit 45 (load determination unit) will be described.
FIG. 10 is a diagram for explaining a determination process of the current change amount 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 second embodiment.
As described in Embodiment 1 above, based on the correlation between the input current and the coil current, the type of material of the heated object 5 (pan) serving as a load can be determined. Even if it is the thing 5, the to-be-heated object 5 with a large amount of current changes and the to-be-heated object 5 with a small amount of current changes exist. Therefore, as shown in FIG. 10, the control unit 45 (load determination means) stores the magnitude relation of the current change amount in advance according to the value of the input current and the value of the coil current based on experimental data or the like. Keep it. Then, the control unit 45 (load determination unit) determines the magnitude relation of the current change amount stored in advance based on the input current detected by the input current detection unit 25a and the coil current detected by the coil current detection unit 25b. By referring to the information, the magnitude of the current change amount when the object to be heated 5 is heated is determined.
In the example of FIG. 10, the case where the current change amount is “large” and the case of “small” are shown, but the present invention is not limited to these two cases, and in three or more stages. You may judge.

Next, the control unit 45 switches the amplification unit that amplifies the input current among the

amplification units

48a and 48b according to the determination result of the current change amount.
That is, when it is determined that the amount of change in current is small, the input current is amplified by the amplification unit 48b having a high amplification factor among the

amplification units

48a and 48b (broken line in FIG. 9D). This increases the amount of change per unit time of the input current. When it is determined that the amount of current change is large, the input current is amplified by the amplifier 48a having a low amplification factor among the

amplifiers

48a and 48b (solid line in FIG. 9D). It should be noted that the selection of the amplifying unit to be used is preferably immediately after the start of the control in the water heating mode 2.

The control unit 45 obtains a change amount (time change) of the amplified detection value per predetermined time with the drive frequency of the inverter circuit 23 fixed, and the change amount per predetermined time becomes equal to or less than the predetermined value. If it is determined that the water heater has been completed.
The predetermined value information may be set in the control unit 45 in advance, or may be input from the operation unit 40 or the like.

As described above, in the water heating mode for setting the water boiling operation of water, the amplification unit that amplifies the detection value is selected according to the current change amount of the object to be heated 5, and the change in the amplified detection value per predetermined time An amount is obtained, and when the amount of change per predetermined time becomes equal to or less than a predetermined value, it is determined that the boiling is completed.
For this reason, it is possible to accurately detect the completion of boiling of water regardless of the amount of current change during induction heating of the article 5 to be heated, and it is possible to obtain a highly reliable induction heating cooker. In addition, a user-friendly induction heating cooker can be obtained.

In the above description, the method for controlling the thermal power by changing the drive frequency is described. However, the method for controlling the thermal power by changing the on-duty (on / off ratio) of the switching element of the inverter circuit 23 is used. Also good.

In the first and second embodiments, the example in which the amount of change in the input current detected by the input current detection unit 25a is detected has been described. However, instead of the input current, the change in the coil current detected by the coil current detection unit 25b is described. The amount may be detected, or the amount of change in both the input current and the coil current may be detected. In the case of using a coil current,

amplification units

48a and 48b and a switching unit 49 are provided between the coil current detection means 25b and the control unit 45, and the detection value is selected by the selected amplification unit in the same manner as described above. Amplify.

In the first and second embodiments, the half-bridge type inverter circuit 23 has been described. However, a configuration using a full-bridge type or a single-voltage resonance type inverter may be used.

Furthermore, although the method of using the relationship between the coil current and the primary current in the load determination of the pot material has been described, a method of determining the load by detecting the resonance voltage at both ends of the resonance capacitor may be used. It doesn't matter.

In

Embodiments

1 and 2, the IH cooking heater has been described as an example of the induction heating cooker of the present invention, but 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.

DESCRIPTION OF SYMBOLS 1 1st heating port, 2nd heating port, 3rd heating port, 4 top plate, 5 to-be-heated object, 11 1st heating means, 11a heating coil, 12 2nd heating means, 13th Three 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, 24b resonance capacitor, 25a input current detection means 25b, coil current detection means, 30 temperature detection means, 35 primary voltage detection means, 35a, 35b resistance, 40a-40c operation section, 41a-41c display section, 42 notification means, 45 control section, 48a, 48b amplification section, 49 Switching unit, 50 drive circuit, 100 induction heating cooker.

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 heating coil;
Amplifying means for amplifying a detected value of at least one of an input current to the drive circuit and a coil current flowing in the heating coil;
A controller that controls driving of the driving circuit and controls high-frequency power supplied to the heating coil;
The controller is
Depending on the determination result of the load determination means, the drive circuit is driven,
According to a detection value of at least one of the input current and the coil current, or a determination result of the load determination unit, an amplification factor of the amplification unit is set,
In a state where the drive frequency of the drive circuit is fixed, the amount of change per predetermined time of the detection value amplified by the amplification means is determined,
An induction heating cooker that detects a temperature change of the object to be heated based on a change amount per predetermined time.
The controller is
The induction heating cooker according to claim 1, wherein the amplification factor of the amplification means is set to be larger as the detection value is smaller.
The load determination means includes
Based on the correlation between the input current and the coil current, determine the amount of current change when the object to be heated is induction-heated,
The controller is
The induction heating cooker according to claim 1, wherein the amplification factor of the amplification means is set to be larger as the current change amount is smaller.
The controller is
When the amount of change per predetermined time obtained in a state where the drive frequency of the drive circuit is fixed becomes a predetermined value or less,
The induction heating cooker according to any one of claims 1 to 3, wherein the driving circuit is controlled to vary the high-frequency power supplied to the heating coil.
The controller is
The induction heating cooker according to claim 4, wherein the high-frequency power supplied to the heating coil is varied by varying a driving frequency of the driving circuit or an on-duty ratio of the switching element.
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,
2. The notification means that the boiling of water has been completed when the amount of change per predetermined time obtained with the drive frequency of the drive circuit fixed is below a predetermined value. The induction heating cooker according to any one of 1 to 5.
The load determination means includes
The induction heating cooker according to any one of claims 1 to 6, wherein a load determination process for the object to be heated is performed based on a correlation between the input current and the coil current.