WO2015001610A1 - Induction heating cooker - Google Patents

Abstract

This induction heating cooker is characterized by the following: finding the time change amount (ΔI) for a current input to a drive circuit (50) and/or a coil current flowing in a heating coil (11a), in a state where the drive frequency of the drive circuit (50) is constant; measuring the heating time (t1) from the start of power supply to the heating coil (11a) until the time change amount (ΔI) becomes a value that is no more than a set value; and controlling the high frequency power supplied to the heating coil (11a) in accordance with the heating time (t1) and the current change amount (I1) for the input current and/or the coil current during the heating time (t1).

Description

Induction heating cooker

The present 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 (see, for example, Patent Documents 1 and 2). The induction heating cooker of Patent Document 1 has control means for controlling the inverter so that the input current of the inverter is constant, and the temperature of the object to be heated when there is a change in the control amount over a predetermined time within a predetermined time. Judging that the change is large, the output of the inverter is suppressed. 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 2 discloses an input current change amount detecting means for detecting an input current change amount, and a temperature determination processing means for determining the temperature of an object to be heated from the input current change amount 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 2008-181892 A (paragraph 0025, FIG. 1) Japanese Patent Laid-Open No. 5-62773 (paragraph 0017, FIG. 1)

However, like the induction heating cookers of Patent Documents 1 and 2, when the temperature is simply stopped when reaching a predetermined temperature, temperature control suitable for the contents of the heated object is performed after the heated object is heated. There is a problem that can not be. That is, when the content of the object to be heated is maintained at a predetermined temperature (for example, in a boiling state), the amount of heat to be supplied differs depending on the heat load (such as the initial temperature and amount of the content) in the initial stage of heating the object to be heated. For example, if a large amount of heat is supplied when the initial temperature of the content of the object to be heated is high, power is wasted, and if the initial temperature of the content of the object to be heated is low, a heat corresponding to that must be supplied. Therefore, it cannot be kept at a predetermined temperature.

The present invention has been made to solve the above-described problems, and provides an induction heating cooker that can perform an optimal operation efficiently according to the heat load of the contents of the object to be heated. It is intended.

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, and a drive circuit that controls driving of the drive circuit and is supplied to the heating coil. A control unit that controls high-frequency power, and the control unit is configured to fix at least one of an input current to the drive circuit and a coil current that flows to the heating coil in a state where the drive frequency of the drive circuit is fixed. A change amount (ΔI) is obtained, a first time (t1) from the start of power supply to the heating coil until the time change amount (ΔI) becomes equal to or less than a set value is measured, and the first time (t1) ) And the current change amount (I1) of at least one of the input current and the coil current between the first time (t1) and the high frequency power supplied to the heating coil It is characterized by controlling.

According to the present invention, an optimal operation can be efficiently performed according to the heat load of the contents of the object to be heated. In addition, it is possible to provide an energy-saving and easy-to-use induction heating cooker that can perform a heat retaining operation while suppressing wasteful power supply.

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 an example of 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 in the hot water heating mode 1 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 in the hot water heating mode 2 of the induction heating cooking appliance concerning Embodiment 1, temperature, input current, and time. It is the figure which expanded the part shown with the broken line of FIG. It is a flowchart which shows the operation example of the hot water heating mode 2 of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a flowchart which shows the operation example of the initial stage water temperature detection of FIG. It is a figure which shows the relationship between reference time and reference current variation | change_quantity, and the thermal load of a heating initial stage. It is a figure which shows the relationship between the drive frequency, temperature, input electric current, and time in the water heating mode 3 of the induction heating cooking appliance which concerns on Embodiment 1. FIG. 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 that display the operation state of the induction heating cooker 100 and input / operation contents from the operation unit 40 are provided. Is provided. 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 operation of the whole induction heating cooker.

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 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.

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 period measurement 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. In addition, the load determination means 32 is, for example, iron, a magnetic material such as SUS430, a high resistance nonmagnetic material such as SUS304, or a low resistance nonmagnetic material such as aluminum or copper. It is roughly classified and judged.

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.

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

The period measuring means 35 measures the heating time t1 from the start of power supply to the heating coil 11a until the time change amount ΔI becomes equal to or less than the set value in the current change detecting means 34. The period measuring means 35 measures the current change amount I1 of the input current during the heating time t1.
The heating time t1 corresponds to the “first time” in the present invention.

The drive control means 31 reduces the electric power supplied to the heating coil 11a according to the heating time t1 and the current change amount I1 measured by the period measuring 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. In particular, the drive control means 31 sets the increase amount Δf to be larger as the heating time t1 is shorter and the current change amount I1 is smaller.

(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.

FIG. 4 is a graph showing how the input current with respect to the drive frequency changes according to the temperature change of the object to be heated in the drive circuit of FIG.
Here, the material of the heated object 5 (pan) serving as a load is largely divided into a magnetic material such as iron and SUS430, a high-resistance nonmagnetic material such as SUS304, and a low-resistance nonmagnetic material such as aluminum and copper. Separated.

As shown in FIG. 4, 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 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, 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 object (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 32) determines the material of the to-be-heated object 5 mounted above the heating coil 11a based on the correlation between an input current and a 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. At this time, high frequency power is not supplied from the drive circuit 50 to the heating coil 11a.

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. In this case as well, high-frequency power is not supplied to the heating coil 11a.

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. 5 is a graph showing how the input current with respect to the drive frequency varies with the temperature change of the object to be heated in the drive circuit of FIG. 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.

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. 5 is maximized is determined as the drive frequency, and this drive frequency is fixed and the inverter circuit 23 is controlled.

6 is an enlarged graph of a portion indicated by a broken line in the graph of 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 of the input current per time (time change amount ΔI) in a state where the drive frequency of the inverter circuit 23 is fixed, and based on this time change amount ΔI, the heating object 5 Detect temperature changes.

For this reason, the temperature change of the heated object 5 can be detected 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 an input current, the temperature change of the to-be-heated object 5 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. Then, the control unit 45 determines the completion of boiling based on the time variation ΔI of the input current. Here, the elapsed time and the change of each characteristic when performing boiling of water will be described with reference to FIG.

FIG. 7 is a graph showing the temperature and input current over time when driven at the predetermined drive frequency of FIG.
In FIG. 7, the elapsed time and the change of each characteristic when water is thrown into the to-be-heated material 5 and it was made to operate | move in the kettle mode are shown, FIG. 7 (a) is a drive frequency, FIG.7 (b). Is the temperature (water temperature), and FIG. 7C shows the input current.

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. 7C, the input current gradually decreases as the temperature of the article to be heated 5 increases, and when the water boils and the temperature becomes constant, the input current also becomes constant. It becomes. 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 first embodiment obtains a change amount (time change amount ΔI) of the input current per time with the drive frequency of the inverter circuit 23 fixed, and this time change amount ΔI. When becomes below the set value, it is determined that the water heating is completed.
The setting 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 boiling 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 time change amount ΔI of the input current is obtained with the drive frequency of the inverter circuit 23 fixed, and this time change amount ΔI becomes equal to or less than the set value. When the hot water is heated, the notification means 42 notifies the user that the boiling is completed.
For this reason, the completion of boiling of water can be notified promptly, 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 time variation ΔI of the input current, an induction heating cooker capable of detecting boiling water by an inexpensive method can be obtained.

(Hot water mode 2)
Next, another control operation when the water heating mode is selected 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. Then, the control unit 45 determines the completion of boiling based on the time variation ΔI of the input current.
Further, the control unit 45 cancels the fixing of the driving frequency when the time change amount ΔI obtained in a state where the driving frequency of the inverter circuit 23 is fixed becomes equal to or less than the set value. Then, the control unit 45 varies the drive frequency of the inverter circuit 23 according to the heating time t1 until the time change amount ΔI becomes equal to or less than the set value and the current change amount I1 of the input current during the heating time t1. Thus, the high frequency power supplied to the heating coil 11a is varied. Details of such an operation will be described with reference to FIGS.

FIG. 8 is a diagram showing the relationship between the drive frequency, temperature, input current, and time in the hot water mode 2 of the induction heating cooker according to the first embodiment.
In FIG. 8, the elapsed time and the change of each characteristic when water is thrown into the to-be-heated material 5 and boiling is performed are shown.
FIGS. 8A to 8C show characteristics when the initial temperature of water charged into the object to be heated 5 is high. FIG. 8A shows the driving frequency, and FIG. 8B shows the temperature (water temperature). 8 (c) shows the input current.
8D to 8F show characteristics when the initial temperature of the water charged into the object to be heated 5 is low, FIG. 8D shows the driving frequency, and FIG. 8E shows the temperature (water temperature). 8 (f) shows the input current.
FIG. 9 is an enlarged view of a portion indicated by a broken line in FIG.
Here, the initial temperature refers to a temperature in a range from the start of heating to a predetermined period, and is not limited to the start of heating.
In FIG. 8, description will be made assuming that the amount of water (contents) when the initial temperature is high and when the initial temperature is low is substantially the same. That is, the heat load of the contents of the article 5 to be heated in the initial stage of heating is determined by the temperature and amount of the contents. However, if the amounts of the contents are equal, the heat load depends on the initial temperature.

FIG. 10 is a flowchart illustrating an operation example of the hot water mode 2 of the induction heating cooker according to the first embodiment.
FIG. 11 is a flowchart showing an operation example of the initial water temperature detection of FIG.
Hereinafter, description will be made based on the flowcharts of FIGS. 10 and 11 with reference to FIGS.

First, the heated object 5 is placed on the heating port of the top plate 4 by the user, and an instruction to start heating (heating power input) is given to the operation unit 40. Then, in the load determination means 32, the material of the to-be-heated object (pan) 5 is determined as a load using the load determination table which shows the relationship between input current and coil current (step ST1). When it is determined that the load determination result is a material that cannot be heated or that there is no load, the notification means 42 notifies that and the high frequency power is controlled from being 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 pot material determined based on the load determination result of the load determination means 32 (step ST2). At this time, the drive frequency f is set to a frequency f = fd higher than the resonance frequency of the resonance circuit so that the input current does not become excessive.

Thereafter, the drive control means 31 fixes the drive frequency f to fd and the inverter circuit 23 is driven to start the induction heating operation (step ST3). Simultaneously with the start of the induction heating operation by the start of power supply, the measurement of the heating time t1 and the current change amount I1 by the period measuring means 35 is started.

When heating is started with the driving frequency fixed (FIGS. 8A and 8D), the temperature (water temperature) of the article to be heated 5 gradually rises until boiling (FIGS. 8B and 8E). . In the control with the driving frequency fixed, as shown in FIG. 9, the input current value (operating point) at the driving frequency changes from the point A to the point B, and the temperature of the article 5 to be heated increases. The input current gradually decreases.

While the induction heating operation is performed, the current change detecting means 34 calculates the time change amount ΔI at a predetermined sampling interval (step ST4).
Then, it is determined whether or not the time change amount ΔI is equal to or less than a set value (Iref) (step ST5). As the heated object 5 changes from a low temperature to a high temperature, the time change amount ΔI decreases (FIGS. 8C and 8F). When water boils and the temperature becomes constant, the input current also becomes constant (FIGS. 8C and 8F). Thereby, in the heating time t1, the control part 45 determines with the time variation | change_quantity (DELTA) I of input current having become below setting value (Iref).

When the time change amount ΔI becomes equal to or less than the set value, the period measuring means 35 detects the heating time t1 (step ST6). Further, the period measuring means 35 detects the current change amount I1 of the input current between the heating start and the heating time t1 (step ST7).
Thereafter, the drive control means 31 performs an initial water temperature detection process, and an increase amount Δf of the drive frequency f is determined from the heating time t1 and the current change amount I1 (step ST8).

Since the driving frequency is fixed during the heating time t1, the heating time t1 and the current change amount I1 vary depending on the initial temperature of the water charged into the article 5 to be heated. That is, when the initial temperature (T0) of water is high (FIG. 8B), the heating time t1 is short and the current change amount I1 is small. On the other hand, when the initial temperature of water is low (FIG. 8E), the heating time t1 is long and the current change amount I1 is large.
From this, the initial temperature of water (heat load at the initial stage of heating) can be determined based on the heating time t1 and the current change amount I1.

Details of this initial water temperature detection process will be described with reference to FIG.
The controller 45 determines whether or not the heating time t1 is shorter than the predetermined reference time t_ref1 and the current change amount I1 is smaller than the predetermined reference current change amount I_ref1 (step ST81).

When satisfy | filling the conditions of step ST81, the control part 45 determines with the initial temperature of water being high (strong hot start) (step ST82). For example, if the amount of water is known, it can be estimated that the initial temperature (T0) of water is equal to or higher than T_ref1.

On the other hand, when the condition of step ST81 is not satisfied, the control unit 45 determines whether or not the heating time t1 is equal to or less than the predetermined reference time t_ref2 and the current change amount I1 is equal to or less than the predetermined reference current change amount I_ref2. (Step ST83). Here, the reference time t_ref2 is longer than the reference time t_ref1. The reference current change amount I_ref2 is larger than the reference current change amount I_ref1.

If the condition of step ST83 is satisfied, the control unit 45 determines that the initial temperature of water is lower (weak hot start) than the strong hot start (step ST84). For example, if the amount of water is known, it can be estimated that the initial temperature (T0) of water is T_ref2 or more and less than T_ref1.

On the other hand, when the condition of step ST83 is not satisfied, the control unit 45 determines that the initial temperature of water is lower (normal heating) than the weak hot start (step ST85). For example, if the amount of water is known, it can be estimated that the initial temperature (T0) of water is less than T_ref2.

FIG. 12 is a diagram illustrating the relationship between the reference time and the reference current change amount and the heat load in the initial stage of heating.
As shown in FIG. 12, according to the initial water temperature determination process in steps ST81 to ST85, the control unit 45 causes the heating time t1 to be shorter and the current change amount I1 to be smaller according to the heating time t1 and the current change amount I1. It is estimated that the heat load of the contents of the article 5 to be heated in the initial heating stage is small (water temperature is high).
In addition, although the case where the reference time and the reference current change amount are each two has been described here, it may be determined by setting three or more reference times and the reference current change amount.

Here, since the heating time t1 and the current change amount I1 change not only with the initial temperature but also with the amount of water, each reference time and each reference current change amount in the processing of the initial water temperature determination in steps ST81 to ST85 is the water temperature. It is necessary to set according to the amount. For this reason, for example, information on each reference time and each reference current change amount corresponding to the amount of water (content amount) is stored in advance as a table, and information on the amount of water (content amount) is acquired. Thus, each reference time and each reference current change amount may be determined. Thereby, the initial temperature (heat load) of water can be detected more accurately. Information on the amount of water may be input from the operation unit 40 or the like. For example, the amount of water may be determined from the weight of the object to be heated 5 using a gravity sensor or the like. Note that the amount of water does not need to be a strict value, and may be, for example, three levels such as small, medium, and large.

Next, the drive control means 31 of the control unit 45 releases the fixed drive frequency and increases the drive frequency of the inverter circuit 23 to lower the input current, thereby supplying high-frequency power (thermal power) supplied to the heating coil 11a. ). 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.
At this time, the drive control means 31 of the control part 45 controls the high frequency electric power supplied to the heating coil 11a according to the estimated initial temperature (heat load). In the drive control means 31, the drive frequency of the inverter circuit 23 is changed from f = fd to f = fd + Δf, and the reduced high-frequency power is supplied from the inverter circuit 23 to the heating coil 11a (step ST86, FIGS. 8A and 8D). ).

Here, the increase amount (Δf) of the drive frequency will be described.
When the heating time t1 is short and the current change amount I1 is small, that is, in the case of strong hot start, as shown in FIG. 8A, the drive control means 31 greatly increases the drive frequency f, and the drive frequency f = The inverter circuit 23 is driven by the drive signal DS of fd + Δf1.
On the other hand, when the heating time t1 is long and the current change amount I1 is large, that is, in the case of weak hot start, as shown in FIG. 8D, the drive control means 31 increases the drive frequency f to a small value, The inverter circuit 23 is driven by the drive signal DS of f = fd + Δf2.
When the heating time t1 is longer and the current change amount I1 is larger, that is, in the case of normal heating, the drive control means 31 drives the inverter circuit 23 by increasing the drive frequency f to be smaller than Δf2.
The information on the increase amounts Δf1 and Δf2 of the drive frequency may be set in the control unit 45 in advance, or may be input from the operation unit 40 or the like.

As shown in FIG. 9, even if the driving frequency f is increased to lower the heating power, the increase amounts Δf1 and Δf2 are set so that the water temperature hardly decreases and keeps a constant temperature, and the operating point is changed from the point B to the point C1. (Or point C2). Then, even if the driving frequency f is increased and the thermal power is lowered, the water temperature is hardly lowered and the heat retaining state is maintained.

Thus, for the high-frequency power (thermal power) input after the heating time t1, when the thermal load at the initial stage of heating is small (the initial temperature is high), the thermal power is set low, and the thermal load at the initial stage of heating is large ( If the initial temperature is low), set the heating power higher.
For this reason, it is possible to obtain an energy-saving and easy-to-use induction heating cooker that can perform a heat retaining operation while suppressing wasteful power supply.
In particular, in the case of boiling water (boiling water) mode, even if the heating power is increased more than necessary, the water temperature will not exceed 100 ° C. Therefore, even if the driving frequency f is increased and the heating power is decreased, the boiling state is maintained. can do.

As described above, when the time variation ΔI of the input current becomes equal to or less than the set value, the drive of the inverter circuit 23 is controlled to reduce the high frequency power supplied to the heating coil 11a. Energy saving can be achieved.
That is, when the set value is simply increased to a predetermined driving frequency f as in the conventional case, the optimum heat retaining state cannot be maintained according to the heat load (temperature and amount) of the contents. There is. For example, when the initial temperature of the contents of the article to be heated 5 is low, the amount of heat is insufficient and the temperature gradually decreases, and reheating is required. On the other hand, when the initial temperature of the contents of the article to be heated 5 is high, excessive power is consumed.
In the first embodiment, if the heat load (temperature and amount) of the contents of the article to be heated 5 is different, the heating time t1 and the current change amount I1 are different even if the drive frequency f is the same (the same thermal power). Focusing on this point, the drive control means 31 determines the increase amount Δf in accordance with the heating time t1 and the current change amount I1, and changes the drive frequency f when the temperature is kept. Thereby, since necessary and sufficient electric power can be supplied to the heating coil 11a according to the thermal load of the article 5 to be heated, energy saving can be achieved efficiently.

Refer to FIG. 10 again. After step ST8, the drive control means 31 notifies the user of the completion of boiling by the notifying means 42 after a predetermined additional time Δt has elapsed after the time change amount ΔI becomes equal to or less than the set value (t2 = t1 + Δt). Is performed (step ST9).
The control unit 45 determines that the heating time t1 is shorter than the reference time t_ref1 (time reference value) and the current change amount I1 is smaller than the reference current change amount I_ref1 (current reference value) (strong hot start). When the time change amount ΔI becomes equal to or less than the set value, the notification means 42 may notify that the hot water has been heated.

(Water heating mode 3)
Next, another control operation when the water heating mode is selected 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. Then, the control unit 45 determines the completion of boiling based on the time variation ΔI of the input current.
Further, the control unit 45 performs the same control continuously for a predetermined time after the time variation ΔI obtained with the drive frequency of the inverter circuit 23 fixed becomes equal to or less than the set value. The fixed frequency is released, the drive frequency of the inverter circuit 23 is varied, and the high frequency power supplied to the heating coil 11a is varied. Details of such an operation will be described with reference to FIGS.

FIG. 13 is a diagram showing a relationship among drive frequency, temperature, input current, and time in the water heating mode 3 of the induction heating cooker according to the first embodiment.
In FIG. 13, the elapsed time and the change of each characteristic when water is poured into the article 5 to be heated and the water is heated are shown.
13 (a) to 13 (c) show characteristics when the initial temperature of water charged into the object to be heated 5 is high. FIG. 13 (a) shows the driving frequency, and FIG. 13 (b) shows the temperature (water temperature). FIG. 13C shows the input current.
FIGS. 13D to 13F show characteristics when the initial temperature of the water charged into the object to be heated 5 is low, FIG. 13D shows the drive frequency, and FIG. 13E shows the temperature (water temperature). FIG. 13F shows the input current.
In FIG. 13, description will be made assuming that the amount of water (contents) when the initial temperature is high and low is approximately the same. That is, the heat load of the contents of the article 5 to be heated in the initial stage of heating is determined by the temperature and amount of the contents. However, if the amounts of the contents are equal, the heat load depends on the initial temperature.

Similar to the operation in the water heating mode 1 described above, when heating is started with the driving frequency fixed (FIGS. 13A and 13D), the temperature (water temperature) of the article to be heated 5 gradually increases until boiling. (FIGS. 13B and 13E). In the control with the driving frequency fixed, as shown in FIG. 9, the input current value (operating point) at the driving frequency changes from the point A to the point B, and the temperature of the article 5 to be heated increases. The input current gradually decreases.

As described above, the input current gradually decreases as the temperature of the object to be heated 5 rises. The electrical resistivity and magnetic permeability of the object to be heated 5 change as the temperature rises. This is because the magnetic coupling of the heated object 5 changes. That is, the state in which the input current is constant means that the temperature of the article to be heated 5 (particularly, the portion adjacent to the heating coil 11a) is constant.

In the heating time t1 in which the input current is constant in FIGS. 13C and 13F, the temperature of the object to be heated 5 reaches about 100 ° C., but the water charged into the object to be heated 5 has a temperature of There may be unevenness and the water as a whole may not have boiled.
In the hot water boiling mode 3, the entire water can be boiled reliably in a short time by driving with the driving frequency fixed until the heating time t2 obtained by adding the additional time Δt to the heating time t1. At the heating time t2, the control unit 45 determines that the boiling of water has been completed.
The additional time Δt corresponds to the “second time” in the present invention.

Here, the heating time t2 and the additional time Δt will be described.
The additional time Δt is a difference between the heating time t2 and the heating time t1, and is expressed by Δt = t2−t1. In the hot water heating mode 3, the controller 45 measures the heating time t1 from the start of heating until the input current becomes constant, and according to the length of the heating time t1 and the magnitude of the current change amount I1 until the heating time t1. The additional time Δt is changed.

In the initial heating stage of the water heating mode 3, since the driving frequency is fixed, the heating time t1 and the current change amount I1 are changed by the thermal load (initial temperature and amount) of water charged into the article 5 to be heated. Change. That is, when the initial temperature of water is high (FIG. 13B), the heating time t1 is short and the current change amount I1 is small. When the initial temperature of water is low (FIG. 13 (e)), the heating time t1 becomes long and the current change amount I1 becomes large. When the heating time t1 is short and the current change amount I1 is large, as shown in FIG. 13C, the control unit 45 sets the additional time Δt to be short. On the other hand, when the heating time t1 is long and I1 is large, the control unit 45 sets the additional time Δt to be long as shown in FIG.

When the initial temperature of the water is low, the temperature unevenness of the water inside the article to be heated 5 is often larger than when it is high, and more time is required to boil the whole water reliably. .
Therefore, in the water heating mode 3, the initial temperature of the water inside the article to be heated 5 is detected by measuring the heating time t1 and the current change amount I1, and the additional time Δt corresponding to the initial temperature of the water is set. In addition, it is possible to obtain an energy-saving and easy-to-use induction heating cooker that can suppress wasteful power supply necessary for boiling and can surely boil the entire water in a short time.

Next, after the additional time Δt has elapsed from the heating time t1, the control unit 45 releases the fixing of the driving frequency and increases the driving frequency of the inverter circuit 23 to reduce the input current, thereby heating the heating coil 11a. The high frequency power (thermal power) supplied to is reduced. The control for increasing the drive frequency is the same as in the hot water mode 2. Even if the driving frequency is increased to lower the thermal power, the water temperature hardly decreases, so that the operating point moves (changes) from point B to point C1 (point C2) as shown in FIG.

Further, at the heating time t2, the control unit 45 increases the drive frequency of the inverter circuit 23 and notifies the user of the completion of boiling by the notification means 42. Note that the user may be notified before or after raising the drive frequency.

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.

Further, by using the temperature information detected by the temperature detecting means 30, a more reliable induction heating cooker can be obtained.

(Configuration example of another drive circuit)
Next, an example using another drive circuit will be described.
FIG. 14 is a diagram illustrating another drive circuit of the induction heating cooker according to the first embodiment.
A drive circuit 50 shown in FIG. 14 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 example in which the time change amount of the input current detected by the input current detection unit 25a is detected has been described. However, instead of the input current, the time of the coil current detected by the coil current detection unit 25b is described. The change amount ΔI may be detected, or the time change amount ΔI of both the input current and the coil current may be detected.

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.

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

Moreover, although the case where the initial temperature of the water thrown into to-be-heated material is determined by the above embodiment has been described, the load determination unit is configured by setting a threshold for each determination result of the load determination unit 32. Depending on the determination result of 32, the initial temperature of the water charged into the object to be heated may be estimated.

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

FIG. 15 is a diagram illustrating a part of the drive circuit of the induction heating cooker according to the second embodiment. In FIG. 15, only a part of the configuration of the drive circuit 50 of the first embodiment is illustrated.
As shown in FIG. 15, 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. 16 is a diagram illustrating an example of a drive signal of the half bridge circuit according to the second embodiment. FIG. 16A shows an example of a drive signal for each switch in the high thermal power state. FIG. 16B 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. 16A, 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. 16B, 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. 16A, 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. 16B, 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 the same (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 control unit 45 obtains the time variation 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.
Thereby, the time 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. 17 is a diagram illustrating a part of the drive circuit of the induction heating cooker according to the third embodiment. Note that FIG. 17 shows only the differences from the drive circuit 50 of the first embodiment.
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. The peak of the current flowing through the coil current detection means 25d, for example, the outer coil 11c, is detected, and a voltage signal corresponding to the peak value of the heating coil current is output 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. 18 is a diagram illustrating an example of a drive signal of the full bridge circuit according to the third embodiment.
FIG. 18A shows an example of the drive signal of each switch and the energization timing of each heating coil in the high thermal power state.
FIG. 18B 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. 18A and 18B 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. 18, 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. 18A, 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. 18B, 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 determining the time change amount ΔI per predetermined time of the input current (or coil current) described in the first embodiment, the control unit 45 determines whether the drive frequency of the inverter circuit 23 is fixed between the arms. 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 time 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 time variation ΔI of the coil current per predetermined time.
The control unit 45 also includes a time change amount ΔI per predetermined time of the coil current detected by the coil current detection means 25c, and a time 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 time change amounts ΔI. Further, each determination operation described in the first embodiment may be performed using an average value of each time change amount ΔI.
By performing such control, even if the detection accuracy of either the coil current detection unit 25c or the coil current detection unit 25d is low, the time change amount ΔI per predetermined time of the coil current is 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 period measurement 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 (14)

1. A heating coil for inductively heating an object to be heated;
   A drive circuit for supplying high-frequency power to 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
   In a state where the drive frequency of the drive circuit is fixed, the time change amount (ΔI) of at least one of the input current to the drive circuit and the coil current flowing through the heating coil is obtained,
   Measure the first time (t1) from the start of power supply to the heating coil until the time variation (ΔI) becomes below a set value,
   The heating coil according to the current change amount (I1) of at least one of the input current and the coil current between the first time (t1) and the first time (t1). An induction heating cooker characterized by controlling the high-frequency power supplied to the.
2. The controller is
   The induction heating cooker according to claim 1, wherein the high frequency power supplied to the heating coil is reduced as the first time (t1) is shorter and the current change amount (I1) is smaller.
3. The controller is
   As the first time (t1) is short and the current change amount (I1) is small, it is estimated that the heat load of the contents of the heated object in the initial heating stage is small,
   The induction heating cooker according to claim 1 or 2, wherein high-frequency power supplied to the heating coil is controlled in accordance with the estimated heat load.
4. The controller is
   The time change amount (ΔI) obtained with the drive frequency of the drive circuit fixed is supplied to the heating coil after a second time (Δt) has elapsed since it became equal to or less than the set value. Control to reduce the high-frequency power,
   The induction according to any one of claims 1 to 3, wherein the second time (Δt) is determined according to the first time (t1) and a current change amount (I1). Cooking cooker.
5. The controller is
   The induction heating cooker according to claim 4, wherein the second time (Δt) is shortened as the first time (t1) is short and the current change amount (I1) is small.
6. The controller is
   After the time variation (ΔI) obtained with the drive frequency of the drive circuit fixed is less than or equal to the set value, the drive frequency of the drive circuit is increased and the high frequency supplied to the heating coil Control to reduce power,
   The induction heating cooking according to any one of claims 1 to 5, wherein the increase amount of the driving frequency is determined according to the first time (t1) and the current change amount (I1). vessel.
7. The controller is
   The induction heating cooker according to claim 6, wherein the amount of increase in the drive frequency is reduced as the first time (t1) is shorter and the current change amount (I1) is smaller.
8. The controller is
   The induction according to any one of claims 1 to 7, wherein the high frequency power supplied to the heating coil is reduced by changing a driving frequency of the driving circuit or an on-duty ratio of the switching element. Cooking cooker.
9. 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,
   The induction heating cooking according to any one of claims 1 to 8, wherein after the time change amount (ΔI) becomes equal to or less than the set value, the notification means notifies the completion of boiling. vessel.
10. The controller is
    When the first time (t1) is shorter than the time reference value and the current change amount (I1) is smaller than the current reference value,
    10. The induction heating cooker according to claim 9, wherein when the time change amount (ΔI) becomes equal to or less than the set value, the notification means notifies the completion of boiling.
11. Load determining means for performing load determination processing of the heated object,
    The controller is
    The induction heating cooker according to any one of claims 1 to 10, wherein a driving frequency for driving the driving circuit is set according to a determination result of the load determining means.
12. The controller is
    The induction heating cooker according to any one of claims 1 to 11, 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. .
13. 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 11, wherein
14. 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.

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