CN204377176U - Induction heating cooking instrument - Google Patents

Abstract

The utility model provides an induction heating cooker capable of detecting temperature changes of heated objects. The induction heating cooker of the present invention comprises: a heating coil for inductively heating an object to be heated; a drive circuit for supplying high-frequency power to the heating coil; a control unit for controlling the drive driving of the circuit, and controls the high-frequency power supplied to the heating coil; an input current detection unit that detects the input current to the driving circuit; and a coil current detection unit that detects the For a coil current flowing in the heating coil, the control unit is configured to select either one of the input current and the coil current based on the input current and fluctuations in the coil current, and to select one of the input current and the coil current based on the selected one. The amount of change detects the temperature change of the object to be heated.

Description

induction heating cooker

technical field

The utility model relates to an induction heating cooker.

Background technique

Among conventional induction heating cookers, there is an induction heating cooker that determines the temperature of an object to be heated based on an input current or a control amount of an inverter.

For example, an induction heating cooker has been proposed that has a control unit that controls the inverter so that the input current of the inverter is constant, and when there is a predetermined time or more When the control amount changes, it is judged that the temperature of the object to be heated changes greatly, and the output of the inverter is suppressed (for example, refer to Patent Document 1).

In addition, for example, a temperature detection device for an induction heating cooker has been proposed that includes a temperature determination processing unit that determines the temperature corresponding to the change in input current detected by the input current change detection unit. temperature, the above-mentioned input current change amount detection unit detects only the change amount of the input current (for example, refer to Patent Document 2).

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2008-181892 (pages 3 to 5, FIG. 1 )

Patent Document 2: Japanese Patent Application Laid-Open No. 5-62773 (pages 2 to 3, FIG. 1 )

In the induction heating cooker described in Patent Document 1, the driving 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 based on the change (Δf) of the control amount. However, depending on the material of the object to be heated, there is a problem that the change in the control amount (Δf) of the driving frequency is so small that it is impossible to detect the temperature change of the object to be heated.

In the temperature detection device of the induction heating cooker described in Patent Document 2, there is a problem that, when the material of the object to be heated changes, the input current becomes too large depending on the driving frequency of the inverter, and there is an inverter. There is a possibility that the inverter may become damaged due to high temperature.

Utility model content

This invention was made in order to solve the above-mentioned subject, and it intends to obtain the induction heating cooker which can detect the temperature change of a to-be-heated object regardless of what kind of material it is. In addition, it is intended to obtain an induction heating cooker capable of suppressing an increase in input current and having high reliability.

The technical solution 1 of the present utility model relates to an induction heating cooker, which is characterized in that:

The induction heating cooker described above has:

A heating coil, which inductively heats the object to be heated;

a drive circuit that supplies high-frequency power to the heating coil;

a control unit that controls the driving of the driving circuit and controls the high-frequency power supplied to the heating coil;

an input current detection unit that detects an input current to the drive circuit; and

a coil current detection unit that detects a coil current flowing in the heating coil,

The control unit is configured to select one of the input current and the coil current based on fluctuations in the input current and the coil current, and detect a temperature change of the object to be heated based on a change amount of the selected one.

The induction heating cooker according to Claim 2 is characterized in that, in the induction heating cooker according to Claim 1,

The control unit is configured to detect the input current and the coil current based on a change in the input current and the coil current from the start of power supply to the heating coil to the elapse of the first heating period, whichever is greater in the amount of change or the greater rate of change. The temperature change of the object to be heated.

The induction heating cooker according to Claim 3 is characterized in that, in the induction heating cooker according to Claim 2,

The control unit is configured to set the first heating period based on a fluctuation amount or a fluctuation rate of at least one of the input current and the coil current from the start of power supply to the heating coil to the elapse of the second heating period, However, the second heating period is shorter than the first heating period.

The induction heating cooker according to claim 4 is characterized in that, in the induction heating cooker according to claim 2 or 3,

The control unit includes an AD converter for converting an analog value detected by the input current detection unit and the coil current detection unit into a digital value,

And the control unit sets, as the variation rate, a fluctuation amount of the digital value of the input current and the coil current with respect to the maximum current value converted into a digital value by the AD converter.

The induction heating cooker according to claim 5 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The induction heating cooker described above has:

a load determination unit that performs load determination processing of the object to be heated,

The control unit is configured to drive the drive circuit based on the determination result of the load determination unit, and detect a temperature change of the object to be heated based on the change amount in a state where the drive frequency of the drive circuit is fixed.

The induction heating cooker according to claim 6 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The control unit is configured to control the drive of the drive circuit to vary the high-frequency power supplied to the heating coil when the amount of change is equal to or less than a threshold while the drive frequency of the drive circuit is fixed.

The induction heating cooker according to claim 7 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The control unit is configured to release the fixation of the drive frequency and increase the drive frequency of the drive circuit to drive the heating coil to The supplied high-frequency power is reduced.

The induction heating cooker according to claim 8 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The control unit is configured to control driving of the driving circuit to increase high-frequency power supplied to the heating coil when the amount of change increases by a second threshold value or more while the driving frequency of the driving circuit is fixed.

The induction heating cooker according to claim 9 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The control unit is configured to control so as to stop the drive of the drive circuit and to stop supplying high voltage to the heating coil when the amount of change is lower than a fourth threshold value while the drive frequency of the drive circuit is fixed. frequency power.

The induction heating cooker according to Claim 10 is characterized in that, in the induction heating cooker according to Claim 7,

The control unit may vary the high-frequency power supplied to the heating coil by varying the drive frequency of the drive circuit or the conduction duty of the switching element.

The induction heating cooker according to Claim 11 is characterized in that, in the induction heating cooker according to Claim 8,

The control unit may vary the high-frequency power supplied to the heating coil by varying the drive frequency of the drive circuit or the conduction duty of the switching element.

The induction heating cooker according to claim 12 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The above-mentioned control unit is composed of:

When the amount of change is below the threshold in the state where the driving frequency of the driving circuit is fixed, the fixing of the driving frequency is released, the driving frequency of the driving circuit is increased, and the high-frequency power supplied to the heating coil is reduced. reduce, and then fix the drive frequency of the above drive circuit, after that,

When the amount of change increases above the second threshold while the drive frequency of the drive circuit is fixed, the fixation of the drive frequency is released, the drive frequency of the drive circuit is reduced, and the high voltage supplied to the heating coil is reduced. The frequency power is increased, and then the driving frequency of the above driving circuit is fixed, after that,

When the change amount is equal to or less than the threshold value in the state where the driving frequency of the driving circuit is fixed, the fixing of the driving frequency is released, the driving frequency of the driving circuit is increased, and the high frequency supplied to the heating coil is reduced. The electric power is reduced, and then the driving frequency of the above-mentioned driving circuit is fixed.

The induction heating cooker according to claim 13 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The above-mentioned control unit is composed of:

When the amount of change is below the threshold in the state where the driving frequency of the driving circuit is fixed, the fixing of the driving frequency is released, the driving frequency of the driving circuit is increased, and the high-frequency power supplied to the heating coil is reduced. reduce, and then fix the drive frequency of the above drive circuit, after that,

When the amount of change increases above the second threshold while the drive frequency of the drive circuit is fixed, the fixation of the drive frequency is released, the drive frequency of the drive circuit is reduced, and the high voltage supplied to the heating coil is reduced. The frequency power is increased, and then the driving frequency of the above driving circuit is fixed, after that,

When the change amount is equal to or less than the threshold value in the state where the driving frequency of the driving circuit is fixed, the fixing of the driving frequency is released, the driving frequency of the driving circuit is increased, and the high frequency supplied to the heating coil is reduced. The power is reduced, and then the driving frequency of the above driving circuit is fixed, after that,

When the amount of change is lower than the fourth threshold with the driving frequency of the driving circuit fixed, control is performed to stop the driving of the driving circuit, thereby stopping supply of high-frequency power to the heating coil.

The induction heating cooker according to claim 14 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The induction heating cooker described above has:

an operation unit for performing a selection operation of an operation mode; and

reporting unit,

When the control unit selects the boiling mode for setting the boiling operation of water as the operation mode, the control unit drives the driving circuit,

When the amount of change is equal to or less than a threshold in a state in which the driving frequency of the driving circuit is fixed, the reporting unit reports completion of boiling.

The induction heating cooker according to claim 15 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The induction heating cooker described above has:

an operation unit for performing a selection operation of an operation mode; and

a temperature detection unit that detects the temperature of the object to be heated,

The above-mentioned control unit is composed of:

When the deep-frying mode in which the oil is heated to the target temperature is selected as the above-mentioned operation mode, the above-mentioned driving circuit is driven,

When the detected temperature of the above-mentioned temperature detection unit exceeds the above-mentioned target temperature, the drive of the above-mentioned drive circuit is controlled so that the high-frequency power supplied to the above-mentioned heating coil is reduced, and the drive frequency of the above-mentioned drive circuit is fixed,

When the amount of change increases by the third threshold value or more with the driving frequency of the driving circuit kept constant, the driving of the driving circuit is controlled to increase the high-frequency power supplied to the heating coil.

The induction heating cooker according to Claim 16 is characterized in that, in the induction heating cooker according to Claim 5,

The load judging means is configured to perform a load judging process of the object to be heated based on a relationship between the input current and the coil current.

The induction heating cooker according to claim 17 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The control unit is configured to maintain a constant on-duty ratio of the switching elements of the drive circuit in a state in which the drive frequency of the drive circuit is fixed.

The induction heating cooker according to claim 18 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The driving circuit is composed of a full-bridge inverter circuit having at least two bridge arms, and the bridge arms are formed by connecting two switching elements in series,

The control unit is configured to set a drive phase difference between the two bridge arms and a phase difference between the switching elements and the switching elements in a state where the driving frequency of the switching elements of the full-bridge inverter circuit is fixed. A state in which the on-duty ratio is fixed.

The induction heating cooker according to claim 19 is characterized in that, in the induction heating cooker according to claim 1 or 2,

The driving circuit is composed of a half-bridge inverter circuit having a bridge arm formed by connecting two switching elements in series,

The control unit is configured to maintain a constant on-duty ratio of the switching elements in a state in which the driving frequency of the switching elements of the half-bridge inverter circuit is constant.

According to the utility model, no matter what material the heated object is, the temperature change of the heated object can be detected. In addition, an increase in input current can be suppressed, and reliability can be improved.

Description of drawings

FIG. 1 is an exploded perspective view showing an induction heating cooker according to Embodiment 1. FIG.

FIG. 2 is a diagram showing a drive circuit of the induction heating cooker according to Embodiment 1. FIG.

FIG. 3 is a functional block diagram showing an example of a control unit of the induction heating cooker according to Embodiment 1. FIG.

Fig. 4 is a load discrimination characteristic diagram of an object to be heated in the induction heating cooker according to Embodiment 1, and is a diagram based on a relationship between a heating coil current and an input current.

Fig. 5 is a correlation diagram of electric current with respect to drive frequency when the temperature of the object to be heated changes in the induction heating cooker according to the first embodiment.

FIG. 6 is an enlarged view of a portion indicated by a dotted line in FIG. 5 .

(a), (b), (c) of FIG. 7 is a figure which shows the relationship among the drive frequency of the induction heating cooker concerning Embodiment 1, temperature, electric current, and time.

(a), (b), (c) of FIG. 8 is a figure which shows the relationship among drive frequency, temperature, electric current, and time of the induction heating cooker concerning Embodiment 1. FIG.

(a), (b), (c) of FIG. 9 is a figure which shows the relationship among drive frequency, temperature, electric current, and time of the induction heating cooker concerning Embodiment 1. FIG.

FIG. 10 is an enlarged view of a portion indicated by a dotted line in FIG. 5 .

(a), (b), (c) of FIG. 11 is a figure which shows the relationship among drive frequency, temperature, electric current, and time of the induction heating cooker concerning Embodiment 1. FIG.

FIG. 12 is a diagram showing another drive circuit of the induction heating cooker according to Embodiment 1. FIG.

(a), (b), (c) of FIG. 13 are figures which show the relationship among drive frequency, temperature, electric current, and time of the induction heating cooker concerning Embodiment 2. FIG.

FIG. 14 is a diagram showing a part of the drive circuit of the induction heating cooker according to Embodiment 3. FIG.

(a) and (b) of FIG. 15 are diagrams showing an example of driving signals of the half bridge circuit according to the third embodiment.

FIG. 16 is a diagram showing a part of a drive circuit of the induction heating cooker according to Embodiment 4. FIG.

(a) and (b) of FIG. 17 are diagrams showing an example of drive signals of the full bridge circuit according to the fourth embodiment.

Label description

1: first heating port; 2: second heating port; 3: third heating port; 4: top plate; 5: object to be heated; 11: first heating unit; 11a: heating coil; 12: second heating unit; 13: third heating unit; 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: resonant capacitor; 25a: input current detection unit; 25b: coil current detection unit; 30: temperature detection unit; 31: drive control unit; 32: load determination unit; 33: drive frequency setting unit; 34: current change detection unit; 35: current selection unit; 36: input and output control unit; 37: AD converter; 40a~40c: operation part; 41a~41c: display part; 42: report unit; 50: drive circuit; 100: induction heating cooker; 11b: inner coil; 11c: outer coil; 24c, 24d: resonance capacitor; 25c, 25d: coil current detection unit; 231a, 231b, 232a, 232b, 233a, 233b: IGBT; 231c, 231d, 232c, 232d, 233c, 233d: diodes.

Detailed ways

Implementation mode 1.

(structure)

FIG. 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 on an upper portion. The top plate 4 is provided with a first heating port 1, a second heating port 2, and a third heating port 3 as heating ports for inductively heating the object 5 to be heated, and a first heating unit 11 is provided corresponding to each heating port. , The second heating unit 12 and the third heating unit 13 can place the object to be heated 5 on each heating port and perform induction heating.

In Embodiment 1, the first heating unit 11 and the second heating unit 12 are arranged side by side on the front side of the main body, and the third heating unit 13 is arranged substantially in the center on the inner side of the main body.

In addition, the arrangement of each heating port is not limited to this. For example, three heating ports may be arranged side by side in a substantially straight line. Alternatively, the center of the first heating unit 11 and the center of the second heating unit 12 may be disposed at different positions in the depth direction.

The top plate 4 is entirely made of heat-resistant tempered glass or crystallized glass or other infrared-transmissive material, and is fixed in a watertight state to the outer periphery of the upper surface opening of the main body of the induction heating cooker 100 via rubber gaskets or seals. On the top plate 4, corresponding to the heating range (heating port) of the first heating unit 11, the second heating unit 12 and the third heating unit 13, a circular pot position display is formed by coating or printing of paint, etc., to The approximate placement position of the pot is shown.

On the near side of the top plate 4, as the first heating unit 11, the second heating unit 12 and the third heating unit 13 are used to set the heating power and the cooking menu (boiling mode, frying mode) when the object to be heated 5 is heated. etc.) is provided with an operation unit 40a, an operation unit 40b, and an operation unit 40c (hereinafter collectively referred to as the operation unit 40 in some cases). In addition, in the vicinity of the operation part 40, as the report unit 42, a display part 41a, a display part 41b, and a display part 41c (sometimes hereinafter) are provided to display the operating state of the induction heating cooker 100 and the input/operation content from the operation part 40, etc. collectively referred to as the display unit 41). In addition, the operation part 40a-40c and the display part 41a-41c may be provided for each heating port, or the operation part 40 and the display part 41 may be provided collectively for all heating ports, etc., and it is not specifically limited.

Below the top plate 4 and inside the main body are provided a first heating unit 11 , a second heating unit 12 and a third heating unit 13 , each of which is composed of a heating coil (not shown).

Inside the main body of the induction heating cooker 100, a drive circuit 50 and a control unit 45 are provided, and the drive circuit 50 supplies high-frequency power to the heating coils of the first heating unit 11, the second heating unit 12, and the third heating unit 13, The control unit 45 controls the overall operation of the induction heating cooker 100 including the drive circuit 50 .

The heating coil has a nearly circular planar shape, and is formed by winding a conductive wire made of any metal (such as copper, aluminum, etc.) with an insulating coating in the circumferential direction, and is supplied to each heating coil by the drive circuit 50 . High-frequency power is used for induction heating.

FIG. 2 is a diagram showing a drive circuit of the induction heating cooker according to Embodiment 1. FIG. In addition, the drive circuit 50 is provided for each heating unit, and its circuit configuration may be the same or may be changed for each heating unit. Only one drive circuit 50 is shown in FIG. 2 . As shown in FIG. 2 , the drive circuit 50 includes a DC power supply circuit 22 , an inverter circuit 23 , and a resonant capacitor 24 a.

The input current detection unit 25 a detects the 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 22 a , a reactor 22 b , and a smoothing capacitor 22 c , converts the AC voltage input from the AC power supply 21 into a DC voltage, and outputs it to the inverter circuit 23 .

The inverter circuit 23 is a so-called half-bridge type inverter. IGBTs 23a and 23b as switching elements are connected in series to the output of the DC power supply circuit 22, and IGBTs 23a and 23b are connected in parallel to the IGBTs 23a and 23b respectively. Diodes 23c, 23d. 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 it to a resonance circuit composed of the heating coil 11 a and the resonance capacitor 24 a. The resonance capacitor 24a is connected in series to the heating coil 11a, and the resonance frequency of this resonance circuit corresponds to the inductance of the heating coil 11a, the capacitance of the resonance capacitor 24a, and the like. In addition, the inductance of the heating coil 11a changes according to the characteristics of the metal load after 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 several tens of amperes (A) flows through the heating coil 11a, and the top plate 4 placed directly above the heating coil 11a is connected to the top plate 4 by the high-frequency magnetic flux generated by the flowing high-frequency current. The object to be heated 5 on the surface is heated by induction. The IGBTs 23a and 23b as switching elements are made of, for example, silicon-based semiconductors, but they may also be made of wide-bandgap semiconductors such as silicon carbide or gallium nitride-based materials.

By forming the switching element using a wide bandgap semiconductor, the conduction loss of the switching element can be reduced, and even if the switching frequency (drive frequency) is set to a high frequency (high speed), the heat dissipation of the drive circuit is good, so the heat sink of the drive circuit can be made compact Miniaturization and cost reduction of the drive circuit can be realized.

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

The temperature detecting unit 30 is constituted by, for example, a thermistor, and detects the temperature based on the amount of heat transferred from the object to be heated 5 to the top plate 4 . In addition, it is not limited to a thermistor, and arbitrary sensors, such as an infrared sensor, may be used.

FIG. 3 is a functional block diagram showing an example of a control unit of the induction heating cooker according to Embodiment 1. FIG. The control unit 45 will be described with reference to FIG. 3 .

The control unit 45 is composed of a microcomputer or a DSP (Digital Signal Processor), controls the operation of the induction heating cooker 100, and includes a drive control unit 31, a load determination unit 32, a drive frequency setting unit 33, and a current change detection unit 34. , a current selection unit 35 , an input/output control unit 36 and an AD converter 37 .

The drive control unit 31 outputs a drive signal DS to the IGBTs 23a and 23b of the inverter circuit 23 to perform switching operations, thereby driving the inverter circuit 23. Further, the drive control unit 31 controls the high-frequency power supplied to the heating coil 11 a, thereby controlling the heating of the object 5 to be heated. The drive signal DS is, for example, a signal composed of a predetermined drive frequency of about 20 to 50 kHz with a predetermined on-duty ratio (for example, 0.5).

The load determination unit 32 performs load determination processing of the object to be heated 5 , and determines the material of the object to be heated 5 as a load. In addition, the load determining unit 32, for example, determines the material of the object to be heated 5 (pot) as a load roughly according to the following categories: magnetic materials such as iron and SUS 430; high-resistance non-magnetic materials such as SUS304; and low-resistance non-magnetic materials such as aluminum and copper. Material.

The drive frequency setting unit 33 sets the drive frequency f of the drive signal DS output to the inverter circuit 23 when electric power is supplied from the inverter circuit 23 to the heating coil 11 a. 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 unit 33 stores, for example, a table for determining the drive frequency f in accordance with the material of the object 5 and the set heating power. Then, after inputting the load determination result and the set heating power to the driving frequency setting unit 33 , the driving frequency setting unit 33 determines the value fd of the driving frequency f by referring to the above table. In addition, the drive frequency setting unit 33 sets a frequency higher than the resonance frequency of the resonance circuit so that the input current does not become too large.

In this way, the drive frequency setting unit 33 drives the inverter circuit 23 with the drive frequency f corresponding to the material of the object to be heated 5 based on the load determination result, thereby suppressing an increase in the input current, and thus suppressing the inverter circuit from increasing. 23 high temperature to improve reliability.

The AD converter 37 converts the analog value of the input current detected by the input current detection unit 25a and the analog value of the coil current detected by the coil current detection unit 25b into digital values. For example, if the resolution is 8 bits, it will be converted into a total of 256 levels of digital values (count values) ranging from 0 to 255.

The current selection unit 35 selects either one of the input current and the coil current according to fluctuations in the input current and the coil current. Details of the current selection operation will be described later.

The current change detection unit 34 detects: when the inverter circuit 23 is driven at the drive frequency f=fd set in the drive frequency setting unit 33, every regulation of the current selected by the current selection unit 35 among the input current and the coil current The amount of change in time ΔI (time change). In addition, the predetermined time period may be a period set in advance, or may be a period that can be changed by the operation of the operation unit 40 .

When the amount of change ΔI detected by the current change detection unit 34 is below the threshold, the drive control unit 31 releases the fixation of the drive frequency f=fd, and increases the drive frequency f by Δf (f=fd+Δf ), and drive the inverter circuit 23.

(action)

Next, the operation of induction heating cooker 100 according to Embodiment 1 will be described.

First, the operation in the case of inductively heating the object 5 placed on the heating port of the top plate 4 with the heating power set by the operation unit 40 will be described.

When the user places the object to be heated 5 on the heating port and instructs the operation unit 40 to start heating (apply heating power), the control unit 45 (load determination means) performs load determination processing.

Fig. 4 is a load discrimination characteristic diagram of an object to be heated in the induction heating cooker according to Embodiment 1, and is a diagram based on a relationship between a heating coil current and an input current.

Here, the material of the heated object 5 (pot) as a load is roughly divided into: magnetic materials such as iron and SUS 430; high-resistance non-magnetic materials such as SUS 304; and low-resistance non-magnetic materials such as aluminum and copper.

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 internally 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 inside, it is possible to configure the load determination unit 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 based on the output signal of the input current detection means 25a. And at the same time, the control part 45 detects a coil current based on the output signal of the coil current detection means 25b. The control unit 45 judges the material of the placed object to be heated (pan) 5 based on the load judgment table expressing the relationship in FIG. 4 and the detected coil current and input current. In this way, the control unit 45 (load judging means) judges the material of the object to be heated 5 placed above the heating coil 11 a based on the relationship 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 no load, the control unit 45 causes the reporting unit 42 to report that heating is impossible, and urges the user to place the pan. At this time, high-frequency power is not supplied from the drive circuit 50 to the heating coil 11 a.

When the load determination result is any one of a magnetic material, a high-resistance non-magnetic material, or a low-resistance non-magnetic material, since the above-mentioned pan is a material that can be heated by the induction heating cooker 100 of the first embodiment, the control The unit 45 determines a drive frequency corresponding to the determined material. The drive frequency is set higher than the resonance frequency so that the input current does not become too large. The driving frequency can be determined by referring to a table of frequencies corresponding to the material of the object to be heated 5 and the set heating power, for example.

The control unit 45 drives the inverter circuit 23 with the determined driving frequency fixed, and starts the induction heating operation. In addition, in the state where the driving frequency is fixed, the on-duty ratio (on-off ratio) of the switching elements of the inverter circuit 23 is also in a constant state.

Fig. 5 is a correlation diagram of electric current with respect to drive frequency when the temperature of the object to be heated changes in the induction heating cooker according to the first embodiment. In FIG. 5 , the thin line is the characteristic when the temperature of the object 5 (pot) is low, and the thick line is the characteristic when the temperature of the object 5 is high.

As shown in FIG. 5 , the characteristics change according to the temperature of the object to be heated 5. This is because the resistivity of the object to be heated 5 increases and the magnetic permeability decreases as the temperature rises, whereby the heating coil 11a and the object to be heated 5 changes in magnetic coupling.

In the control unit 45 of the induction heating cooker 100 according to Embodiment 1, the drive frequency is determined to be higher than the frequency at which the current (input current or coil current) shown in FIG. The frequency is fixed and the inverter circuit 23 is controlled.

FIG. 6 is an enlarged view of a portion indicated by a dotted line in FIG. 5 .

If the inverter circuit 23 is controlled with a fixed drive frequency corresponding to the pan material determined by the above-mentioned load determination process, the current value (operating point) at the drive frequency as the object to be heated changes from a low temperature to a high temperature. From point A to point B, the current gradually decreases as the temperature of the object to be heated 5 rises.

At this time, the control unit 45 obtains the change amount ΔI of the current (input current or coil current) per predetermined time while the drive frequency of the inverter circuit 23 is fixed, and detects The temperature of the object to be heated 5 changes.

Therefore, the temperature change of the object to be heated 5 can be detected regardless of the material of the object to be heated 5 . In addition, since the temperature change of the object to be heated 5 can be detected from the change of the electric current, it is possible to detect the temperature change at a higher speed than a temperature sensor or the like.

In addition, the material of the object to be heated 5 placed above the heating coil 11a is determined, the driving frequency of the inverter circuit 23 is determined according to the material of the object to be heated 5, and the inverter circuit 23 is driven by the driving frequency. . Therefore, the inverter circuit 23 can be driven at a constant drive frequency according to the material of the object to be heated 5 , and an increase in input current can be suppressed. Accordingly, the increase in temperature of the inverter circuit 23 can be suppressed, and the reliability can be improved.

(Current selection action)

As the temperature of the object to be heated 5 rises, both the input current detected by the input current detection means 25a and the coil current detected by the coil current detection means 25b decrease. However, depending on the material of the object to be heated 5, the amount of current fluctuation between the coil current and the input current differs. That is, there are materials with a large amount of change (amount of drop) in the coil current and materials with a large amount of change (amount of drop) in the input current.

Therefore, the control unit 45 according to Embodiment 1 pays attention to the variation amount of the current, and selects either one of the input current and the coil current according to the variation of the input current and the coil current. Then, the current change detection unit 34 obtains the change amount ΔI of the current selected by the current selection unit 35 per predetermined time.

In this way, by selecting a current with a large amount of current change among the input current and the coil current, the temperature change of the object to be heated 5 can be captured more largely, and the temperature change of the object to be heated 5 can be detected with high precision. In addition, the accuracy of boiling detection can be improved, and an induction heating cooker with good usability can be obtained.

In addition, reliability can be further improved by comparing the actually measured input current with the coil current.

(boil mode 1)

Next, the operation when the boiling mode is selected as the cooking menu (operation mode) by the operation unit 40 will be described. In the boiling mode, the boiling operation of water added to the object 5 to be heated is performed.

The control unit 45 performs load determination processing in the same manner as the above operation, 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. Then, the control unit 45 judges whether or not the boiling is completed based on the time change of the electric current. Here, the elapsed time when boiling water and changes in various characteristics will be described using (a), (b) and (c) of FIG. 7 .

(a), (b), (c) of FIG. 7 is a figure which shows the relationship among the drive frequency of the induction heating cooker concerning Embodiment 1, temperature, electric current, and time. In (a), (b) and (c) of Fig. 7, the elapsed time and the change of each characteristic when water is added to the object to be heated 5 and boiled are shown, and (a) of Fig. 7 shows the driving frequency, (b) of FIG. 7 shows temperature (water temperature), and (c) of FIG. 7 shows electric current (input current and coil current).

As shown in (a) of FIG. 7 , the inverter circuit 23 is controlled while the drive frequency is fixed. As shown in (b) of FIG. 7 , the temperature (water temperature) of the object to be heated 5 gradually rises until it boils, and the temperature becomes constant after boiling.

As shown in (c) of FIG. 7 , as the temperature of the object to be heated 5 rises, both the input current detected by the input current detection means 25 a and the coil current detected by the coil current detection means 25 b decrease.

The current selection unit 35 obtains the coil current variation I1 and the input current variation I2 from the start of power supply to the heating coil 11a (start of heating) to the elapse of the first heating period td1. Then, the fluctuation amount I1 and the fluctuation amount I2 are compared, and a current having a larger fluctuation amount among the input current and the coil current is selected.

In addition, the first heating period td1 may be a preset time, or may be determined according to the heating power or the cooking mode set by the operation unit 40 .

In addition, as shown in (c) of FIG. 7 , the current (input current and coil current) gradually decreases according to the temperature rise of the object to be heated 5 , and the current becomes constant after the water boils and the temperature becomes constant. That is, when the current becomes constant, the water boils and the boiling is completed.

In this way, the control unit 45 of this embodiment selects a current with a large fluctuation amount among the input current and the coil current, and obtains the change amount (time change) of the selected current per predetermined time. When the change amount per predetermined time is When it is below a predetermined value, it is judged that boiling is complete.

In addition, the information of the predetermined value 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 reports completion|finish of boiling using the reporting means 42. Here, as the notification unit 42 , the display unit 41 performs a display such as completion of boiling, or uses a speaker (not shown) to notify the user by voice, and the method is not particularly limited.

As described above, in the boiling mode for setting the boiling operation of water, in the state where the drive frequency of the inverter circuit 23 is fixed, the change amount of the current per predetermined time is obtained, and when the change amount per predetermined time is a predetermined When it is below the value, the reporting unit 42 reports that the boiling is complete.

Therefore, it is possible to quickly report that the boiling of water is completed, and it is possible to obtain an induction heating cooker with good usability.

In addition, by selecting a current with a large current variation among the input current and the coil current, the temperature change of the object 5 to be heated can be captured more largely, and the temperature change of the object 5 to be heated can be detected with high precision. In addition, the accuracy of boiling detection can be improved, and an induction heating cooker with good usability can be obtained. In addition, reliability can be further improved by comparing the actually measured input current with the coil current.

In addition, in the control unit 45 of the first embodiment, the current selection unit 35 obtains the fluctuation amount I1 of the coil current and the fluctuation amount I2 of the input current from the start of heating to the elapse of the first heating period td1. I1 is compared with the fluctuation amount I2, and a current with a large fluctuation amount among the input current and the coil current is selected.

Therefore, compared with, for example, selecting either one of the input current and the coil current based on the magnitude relationship between the input current and the coil current at the start of heating, a current with a large fluctuation in current can be selected regardless of the current value at the start of heating. , the temperature change of the object to be heated 5 can be detected with high precision.

For example, as shown in (c) of FIG. 8, although the relationship of coil current>input current is the relationship at the start of heating, the amount of current fluctuation from the start of heating to the elapse of the first heating period td1 is within the fluctuation amount of coil current I1<input current. In this case, regardless of the current value at the start of heating, an input current with a large current fluctuation amount is selected. Therefore, it is possible to select a current with a large amount of current fluctuation among the input current and the coil current, and it is possible to capture the temperature change of the object 5 to be heated to a greater extent, and to detect the temperature change of the object to be heated 5 with high precision.

(Modification)

Next, a modified example of the current selection operation will be described.

(selection based on the rate of change of current)

The analog value of the input current detected by the input current detection means 25 a and the analog value of the coil current detected by the coil current detection means 25 b are converted into digital values by the AD converter 37 . The detection accuracy of the current differs depending on the maximum value of the current converted into a digital value by the AD converter 37 and the resolution of the AD converter 37 .

For example, if the maximum value of the current converted into a digital value by the AD converter 37 is 100A, and the resolution of the AD converter 37 is 8 bits (256 steps), the current per count value is about 0.39A. In this case, if the analog value of the current fluctuates by 3 A, for example, the digital value fluctuates by 7 counts (≈3/0.39). That is, the current value converted by the AD converter 37 is about 2.74A (≈100/256×7).

On the other hand, for example, if the maximum value of the current converted into a digital value by the AD converter 37 is 50 A, and the resolution of the AD converter 37 is 8 bits (256 steps), the current per count value is about 0.20 a. In this case, if the analog value of the current varies by, for example, 3A, the digital value varies by 15 counts (≈3/0.20). That is, the current value converted by the AD converter 37 is about 2.93 A (≈50/256×15).

In this way, even if the fluctuation amount of the current is the same, the accuracy of the current value obtained by the control unit 45 using the AD converter 37 varies depending on the maximum value of the current converted into a digital value by the AD converter 37 and the resolution of the AD converter 37. .

In this way, the current selection unit 35 obtains the variation (count) of the digital value of the input current and the coil current with respect to the maximum current value converted into a digital value by the AD converter 37 from the start of heating to the elapse of the first heating period td1. value), and set it as the rate of change of the current. Then, the rate of change of the input current and the rate of change of the coil current are compared, and a current with a greater rate of change among the input current and the coil current is selected.

Thereby, the temperature change of the to-be-heated object 5 can be caught more largely, and the temperature change of the to-be-heated object 5 can be detected with high precision. In addition, the accuracy of boiling detection can be improved, and an induction heating cooker with good usability can be obtained.

(Setting of the first heating period td1)

In the above-described load determination processing in the boiling mode, the load determination is performed before heating is started and boiling is detected. That is, it is preferable that the first heating period td1 is before the time when boiling occurs.

In this way, in the current selection operation, the current selection unit 35 sets the first heating period corresponding to the variation I1 of the coil current and the variation I2 of the input current from the start of heating to the elapse of the second heating period td2. td1, wherein the second heating period td2 is shorter than the first heating period td1.

(a), (b), (c) of FIG. 9 is a figure which shows the relationship among drive frequency, temperature, electric current, and time of the induction heating cooker concerning Embodiment 1. FIG.

In (a), (b) and (c) of FIG. 9, compared with the example of (a), (b) and (c) of FIG. In the case of elapsed time and changes in each characteristic. (a) of FIG. 9 shows a drive frequency, (b) of FIG. 9 shows a temperature (water temperature), and (c) of FIG. 9 shows a current (input current and a coil current).

As shown in (b) of Figure 9, when the amount of water in the object to be heated 5 is small, the heating time until boiling is shortened. In addition, as shown in (c) of FIG. 9 , both the input current and the coil current drop sharply.

Therefore, when the current fluctuation amount I2 from the start of heating to the elapse of the second heating period td2 is large, the current selection means 35 sets the first heating period td1 to be short.

Conversely, when the amount of water in the object to be heated 5 is large or the high-frequency power is small, and the current fluctuations I1 and I2 are small, the first heating period td1 is set to be long.

For example, the relationship between the current fluctuations I1 and I2 and the first heating period td1 is stored in advance based on experimental data or the like. Then, the current selection unit 35 sets the first heating period td1 based on the fluctuation amounts I1 and I2 of the current in the second heating period t2 and referring to pre-stored information.

Thereby, the precision of boiling detection can be further improved, and the induction heating cooker with good usability can be obtained.

In addition, the setting operation|movement of this 1st heating period t1 may be performed regularly several times.

(boiling mode 2)

Next, another control operation when the boiling mode is selected by the operation unit 40 will be described.

The control unit 45 performs load determination processing in the same manner as the above operation, determines the drive frequency corresponding to the determined pan material, drives the inverter circuit 23 with the determined drive frequency fixed, and performs the induction heating operation. . In addition, the above-mentioned current selection operation is performed to select either one of the input current and the coil current. And the control part 45 judges whether boiling is complete or not based on the change amount per predetermined time of the selected electric current (henceforth abbreviated as "current") among the input electric current or a coil electric current.

Then, when the amount of change per predetermined time obtained while the drive frequency of the inverter circuit 23 is fixed is equal to or less than a predetermined value, the control unit 45 releases the drive frequency from being fixed, and makes the drive frequency of the inverter circuit 23 The drive frequency is variable, so that the high-frequency power supplied to the heating coil 11a is variable. Details of such an operation will be described with reference to FIGS. 10 and 11 ( a ), ( b ), and ( c ).

FIG. 10 is an enlarged view of a portion indicated by a dotted line in FIG. 5 .

(a), (b), (c) of FIG. 11 is a figure which shows the relationship among drive frequency, temperature, electric current, and time of the induction heating cooker concerning Embodiment 1. FIG. In (a), (b) and (c) of Fig. 11, the elapsed time and the change of each characteristic when water is added to the object to be heated 5 and boiled are shown, and (a) of Fig. 11 shows the driving frequency, (b) of FIG. 11 shows a temperature (water temperature), and (c) of FIG. 11 shows a current (current selected by the current selection means 35).

Similar to the operation of the above-mentioned boiling mode 1, when the driving frequency is fixed and heating is started ((a) in FIG. 11 ), the temperature (water temperature) of the object to be heated 5 gradually rises until it boils ((b) in FIG. 11 ). In the control in the state where the driving frequency is fixed, as shown in FIG. 10, the current value (operating point) of the driving frequency changes from point E to point B, and the current gradually decreases as the temperature of the object to be heated 5 rises. .

When water boils and the temperature becomes constant, the electric current also becomes constant ((c) of FIG. 11). Thereby, at time t1, the control part 45 judges that the change amount per predetermined time of electric current is below predetermined value, and judges that boiling is complete.

Next, the control unit 45 releases the fixation of the drive frequency, and increases the drive frequency of the inverter circuit 23 to decrease the current, thereby reducing the high-frequency power (heating power) supplied to the heating coil 11a. At this time, even if the driving frequency is increased to reduce the thermal power, the temperature hardly decreases, so the operating point moves (varies) from point B to point C as shown in FIG. 10 .

Then, the control unit 45 fixes the driving frequency of the inverter circuit 23 again, and continues heating with the lowered heating power.

In the case of boiling (water boiling), the water temperature does not exceed 100° C. even if the heating power is increased more than necessary, so even if the driving frequency is increased to lower the heating power, the water temperature can be maintained.

In this way, when the amount of change in current per predetermined time is equal to or less than a predetermined value, the drive of the inverter circuit 23 is controlled to reduce the high-frequency power supplied to the heating coil 11a, thereby reducing input power and saving energy.

And at time t1, the control part 45 raises the drive frequency to the inverter circuit 23, and uses the notification means 42 to notify the user that boiling is complete. In addition, the report may be made to the user before the driving frequency is increased, or may be reported to the user after the driving frequency is increased.

There is a case where the user adds ingredients to the object to be heated 5 (pot) due to the report that the boiling is complete. Here, the case of adding ingredients to the object to be heated 5 at time t2 will be described as an example.

As shown in (c) of FIG. 11 , when a food material is added to the object to be heated 5 at time t2, the temperature of the object to be heated 5 decreases as shown in (b) of FIG. 11 . When the temperature of the foodstuffs to be added is low, such as frozen food, the above-mentioned temperature drop is more remarkable. In addition, as the temperature decreases, as shown in (c) of FIG. 11 , the current increases sharply.

At this time, as shown in FIG. 10 , the operating point moves (fluctuates) from point C to point D.

When the amount of change per predetermined time obtained while the drive frequency of the inverter circuit 23 is fixed is equal to or greater than the second predetermined value, the control unit 45 determines that the change is due to the food addition operation, water addition operation, etc. Instead, the temperature decreases (time t3).

In addition, the information of the second predetermined value may be set in the control unit 45 in advance, or may be input from the operation unit 40 or the like.

Then, at time t3, the control unit 45 releases the fixation of the drive frequency, decreases the drive frequency of the inverter circuit 23 to increase the current, and increases the high-frequency power (heating power) supplied to the heating coil 11a. Thereby, as shown in FIG. 10 , the operating point moves (varies) from point D to point E. FIG.

Then, the control unit 45 fixes the driving frequency of the inverter circuit 23 again, and continues heating with the increased heating power.

At time t3, since the drive frequency was lowered in the low temperature state, the current further increased, but the current gradually decreased as the temperature increased ((b) and (c) of FIG. 11 ). At this time, the operating point moves (varies) from point E to point B as shown in FIG. 10 .

Thereby, at time t4, the control part 45 judges that the change amount per predetermined time of electric current is below a predetermined value, and judges again that boiling is complete.

Next, the control unit 45 releases the fixation of the drive frequency, and increases the drive frequency of the inverter circuit 23 again to decrease the current to decrease the high-frequency power (heating power) supplied to the heating coil 11a. Thereafter, the above-mentioned operation is repeated until the operation of heating stop (end of boiling mode) is performed from the operation unit 40 .

By such an operation, the operating point in FIG. 10 is moved (varied) in the order of point E→point B→point C.

As described above, when the amount of change per predetermined time obtained while the drive frequency of the inverter circuit 23 is fixed is equal to or greater than the second predetermined value, the fixation of the drive frequency is released, and the inverter circuit 23 is controlled. By driving, the high-frequency power supplied to the heating coil 11a is increased, so that the temperature drop of the object to be heated 5 can be quickly detected to increase the heating power, and cooking can be realized in a short time. In addition, by realizing cooking in a short time, usability can be improved and energy saving can be achieved.

In addition, for example, when adding food or adding water after boiling, if the drive frequency is kept constant, there is a problem that the heating power required for heating the food (water) cannot be obtained sufficiently. The cooking time is extended so that the convenience of use is poor, and the overall power consumption increases.

In addition, in the above description, the method of controlling the heating power by changing the driving frequency has been described, but the method of controlling the heating power by changing the on-duty ratio (on-off ratio) of the switching elements of the inverter circuit 23 may also be used. The way.

(frying mode)

Next, the operation when deep-frying cooking is performed will be described. In deep-frying cooking, the oil in the object to be heated 5 is heated to a predetermined temperature.

In the case of heating oil, unlike boiling of water, even if the drive frequency is kept constant and controlled continuously, the change in current is not constant, the temperature of the oil continues to rise, and in the worst case, there is a possibility that the oil may catch fire sex.

In this embodiment, as shown in FIG. 2 , a temperature detection unit 30 such as a thermistor or an infrared sensor that detects the temperature of the object to be heated 5 is used, and the detection of the change amount of the current is performed together with the use of the temperature detection unit 30 . By performing temperature detection, a highly reliable induction heating cooker that suppresses overheating of oil is realized.

If the deep-frying mode is selected as the cooking menu (operation mode) by the operation unit 40, the control unit 45 performs load determination processing in the same manner as described above, determines a drive frequency suitable for the material of the object to be heated 5, and The determined driving frequency is fixed, and the induction heating operation is performed.

In addition, by outputting the value of the current during heating and the temperature detected by the temperature detection means 30 to the control unit 45 , the control unit 45 can store the relationship between the temperature and the current.

When the temperature detected by the temperature detection unit 30 reaches a temperature (predetermined temperature) suitable for frying, the control unit 45 releases the fixation of the drive frequency, and gradually increases the drive frequency to reduce the heating power while maintaining the temperature. At this time, that is, even when the driving frequency is gradually increased, the value of the input current detected by the input current detection unit 25 a and the temperature detected by the temperature detection unit 30 are stored together with the changed driving frequency by the control unit 45 .

The control unit 45 notifies the user that the preheating of the fried cooking is completed through the notification unit 42, fixes the driving frequency of the inverter circuit 23 again, and continues heating with the lowered heating power. In addition, the report may be made to the user before the driving frequency is increased, or may be reported to the user after the driving frequency is increased.

After the completion of preheating is reported, if the user adds ingredients to the object to be heated 5, the temperature of the oil will drop. When the food material to be added is a frozen food, since the temperature difference between the food material and the oil is large, if the amount of food material to be added is large, the temperature of the oil will drop rapidly.

When the amount of change per predetermined time in the input current or coil current obtained with the drive frequency of the inverter circuit 23 fixed is equal to or greater than a third predetermined value, the control unit 45 controls the inverter circuit 23 to Driving increases the high-frequency power supplied to the heating coil 11a.

In addition, the information of the third predetermined value 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, when the detected temperature of the temperature detection unit 30 exceeds a predetermined temperature, the high-frequency power supplied to the heating coil 11a is reduced, and the current obtained with the driving frequency of the inverter circuit 23 is fixed every predetermined time. When the amount of change is equal to or greater than the third predetermined value, the driving of the inverter circuit 23 is controlled to increase the high-frequency power supplied to the heating coil 11a. Therefore, the drop in temperature of the oil can be suppressed, the temperature suitable for frying can be maintained, and an induction heating cooker with good usability that shortens the time of frying can be obtained.

In addition, in the case of only using the temperature detection unit 30 such as a thermistor or an infrared sensor to detect the temperature, there is a problem that the detection of the temperature change of the oil when the food is added is delayed. In the present embodiment, since the electric current under the constant drive frequency control changes rapidly, it is possible to detect the drop in oil temperature by detecting the amount of change in the electric current.

(Structure example of another drive circuit)

Next, an example using another drive circuit will be described.

FIG. 12 is a diagram showing another drive circuit of the induction heating cooker according to Embodiment 1. FIG.

The driving circuit 50 shown in FIG. 12 has a resonant capacitor 24 b added to the structure shown in FIG. 2 . In addition, other structures are the same as those in FIG. 2 , and the same reference numerals are assigned to the same parts.

As described above, since the heating coil 11a and the resonant capacitor constitute a resonant circuit, the capacitance of the resonant capacitor is determined according to the maximum heating power (maximum input power) required by the induction heating cooker. In drive circuit 50 shown in FIG. 12 , by connecting resonant capacitors 24 a and 24 b in parallel, the respective capacitances can be reduced to half, and an inexpensive control circuit can be obtained even when two resonant capacitors are used.

In addition, by arranging the coil current detection unit 25b on the resonant capacitor 24a side among the resonant capacitors connected in parallel, the current flowing in the coil current detection unit 25b is half of the current flowing in the heating coil 11a, so it is possible to use a small and small-capacity The coil current detecting unit 25b can obtain a small and inexpensive control circuit, and can obtain an inexpensive induction heating cooker.

Implementation mode 2.

(a), (b), (c) of FIG. 13 are figures which show the relationship among drive frequency, temperature, electric current, and time of the induction heating cooker concerning Embodiment 2. FIG. In (a), (b) and (c) of Fig. 13, the elapsed time and the change of each characteristic when water is added to the object to be heated 5 and boiled are shown, and (a) of Fig. 13 shows the driving frequency, (b) of FIG. 13 shows the temperature (the bottom temperature of the object to be heated 5), and (c) of FIG. 13 shows the current.

(boiling mode 3)

Another control operation when the boiling mode is selected by the operation unit 40 will be described.

The control unit 45 performs load determination processing in the same manner as the operation described in Embodiment 1, determines the drive frequency corresponding to the determined pan material, and drives the inverter circuit while the determined drive frequency is fixed. 23, so as to implement the induction heating action. And the control part 45 judges whether boiling is complete or not based on the temporal change of electric current.

Then, when the amount of change per predetermined time obtained while the drive frequency of the inverter circuit 23 is fixed is equal to or less than a predetermined value, the control unit 45 releases the drive frequency from being fixed, and makes the drive frequency of the inverter circuit 23 The drive frequency is variable, so that the high-frequency power supplied to the heating coil 11a is variable. The details of this operation will be described with reference to (a), (b) and (c) of FIG. 13 .

Same as above-mentioned boiling modes 1 and 2, if the driving frequency is fixed and heating is started ((a) of FIG. 13 ), the bottom temperature of the heated object 5 will gradually rise until the water in the heated object 5 boils (FIG. 13 (a)). (b)). In the control when the drive frequency is fixed, the current gradually decreases as the temperature of the object to be heated 5 rises.

When water boils and the temperature becomes constant, the electric current also becomes constant ((c) of FIG. 13). Thereby, at time t1, the control part 45 judges that the change amount per predetermined time of electric current is below predetermined value, and judges that boiling is complete.

Next, the control unit 45 releases the fixation of the drive frequency, and increases the drive frequency of the inverter circuit 23 to decrease the current, thereby reducing the high-frequency power (heating power) supplied to the heating coil 11a. At this time, even if the driving frequency is increased to reduce the thermal power, the temperature hardly decreases. Then, the control unit 45 fixes the drive frequency of the inverter circuit 23 again, and continues heating with the reduced heating power.

In the case of boiling (water boiling), the water temperature does not exceed 100° C. even if the heating power is increased more than necessary, so even if the driving frequency is increased to lower the heating power, the water temperature can be maintained.

In this way, when the amount of change in current per predetermined time is equal to or less than a predetermined value, the drive of the inverter circuit 23 is controlled to reduce the high-frequency power supplied to the heating coil 11a, thereby reducing input power and saving energy.

Moreover, at time t1, the control part 45 raises the drive frequency to the inverter circuit 23, and uses the notification means 42 to notify the user that boiling is complete. In addition, the report may be made to the user before the driving frequency is increased, or may be reported to the user after the driving frequency is increased.

There are cases where the water continues to boil even though the user ignores the report that the boiling is complete. Here, a case where all the water in the object to be heated 5 evaporates at time t2 will be described as an example.

When water exists in the object to be heated 5, the temperature of the object to be heated 5 (the temperature of the bottom of the pot) changes at a temperature that is almost the same as or slightly higher than the water temperature. That is, during boiling of water, the temperature of the object to be heated 5 is constant at about 100°C.

When all the water in the object to be heated 5 evaporates at time t2, the temperature of the object to be heated 5 rises rapidly, and as the temperature of the object to be heated 5 rises, the current drops sharply as shown in (c) of FIG. 13 .

When the change amount (decrease amount) per predetermined time obtained while the drive frequency of the inverter circuit 23 is fixed is equal to or greater than the fourth predetermined value (in the case of decreasing by an amount equal to or greater than the fourth predetermined value) , the control unit 45 determines that all the water has evaporated (time t3).

In addition, the information of the 4th predetermined value may be previously set in the control part 45, and may also be input from the operation part 40 grade|etc.,.

Then, at time t3, the control unit 45 stops supplying high-frequency electric power (heating power) to the heating coil 11a. At this time, the control unit 45 notifies the user that all the water has evaporated using the reporting unit 42 .

As described above, when the amount of reduction (change amount) per predetermined time obtained in the state where the drive frequency of the inverter circuit 23 is fixed is equal to or greater than the fourth predetermined value (in the case of decreasing the amount equal to or greater than the fourth predetermined value) Bottom), the fixation of the driving frequency is released, the driving of the inverter circuit 23 is stopped, and the supply of high-frequency power to the heating coil 11a is stopped, thereby suppressing the rapid increase in the temperature of the object to be heated 5 and achieving safety. High performance induction heating cooker. In addition, by notifying the user that all the water has evaporated, safety can be further improved, and an induction heating cooker with good usability can be obtained.

In addition, for example, even if a contact-type thermistor or a non-contact infrared sensor is used as the temperature detection unit 30, it is possible to detect the complete evaporation of water, but it is difficult to instantaneously detect the heating object 5 accompanied by the complete evaporation of water. There is a danger (problem) that the temperature of the object to be heated 5 will rise rapidly due to the drastic temperature change.

In addition, in the above description, the method of controlling the heating power by changing the drive frequency has been described, but a method of controlling the heating power by changing the on-duty ratio (on-off ratio) of the switching elements of the inverter circuit 23 may also be used.

In addition, it is also possible to combine the operation modes described in Embodiments 1 and 2 above. For example, it is also possible to form an operation mode in which the operation of the boiling mode 2 and the operation of the boiling mode 3 are combined.

In addition, in Embodiments 1 and 2 above, the half-bridge type inverter circuit 23 has been described, but a full-bridge type or a single-switch voltage resonant type inverter (Single-switch voltage resonant type inverter) may also be used. ) and other structures.

In addition, the method of using the relationship between the coil current and the primary current in the load judgment of the pot material is described, but the method of detecting the resonance voltage at both ends of the resonant capacitor can also be used to judge the load, and the method of the load judgment is not special. limit.

Implementation mode 3.

In Embodiment 3, details of the drive circuit 50 in Embodiments 1 and 2 described above will be described.

FIG. 14 is a diagram showing a part of the drive circuit of the induction heating cooker according to Embodiment 3. FIG. In addition, in FIG. 14, only the structure of a part of the drive circuit 50 of Embodiment 1 and 2 mentioned above is shown in figure.

As shown in FIG. 14 , the inverter circuit 23 has a set of bridge arms (arms), and the set of bridge arms consists of two switching elements (IGBT 23a, 23b) connected in series between the positive and negative bus bars and the switching elements respectively connected to the above-mentioned switching elements. Diodes 23c and 23d connected in antiparallel are formed.

The IGBT 23a and IGBT 23b are driven on and off by the drive signal output from the control unit 45.

The control unit 45 turns the IGBT 23b off while the IGBT 23a is turned on, and keeps the IGBT 23b on while the IGBT 23a is turned off, and outputs alternately on-off drive signals.

Thus, a half-bridge inverter for driving the heating coil 11a is constituted by the IGBT 23a and the IGBT 23b.

In addition, IGBT 23a and IGBT 23b are used to form the "half-bridge inverter circuit" of the present invention.

The control unit 45 inputs a high-frequency drive signal to the IGBT 23a and the IGBT 23b in accordance with the applied electric power (heating power), and adjusts the heating output. And control is performed so that the frequency of the drive signal output to IGBT23a and IGBT23b is variable within the range of drive frequency higher than the resonance frequency of the load circuit composed of heating coil 11a and resonance capacitor 24a, and the current flowing in the load circuit Flows in a phase delayed from the voltage applied to the load circuit.

Next, the control operation of the applied electric power (heating power) by the driving frequency and the on-duty ratio of the inverter circuit 23 will be described.

(a) and (b) of FIG. 15 are diagrams showing an example of driving signals of the half bridge circuit according to the third embodiment. (a) of FIG. 15 is an example of a drive signal of each switch in a high heating power state. (b) of FIG. 15 is an example of a drive signal of each switch in a low heating power state.

The control unit 45 outputs, to the IGBT 23a and the IGBT 23b of the inverter circuit 23, a high-frequency drive signal having a frequency higher than the resonance frequency of the load circuit.

By varying the frequency of the drive signal, the output of the inverter circuit 23 increases and decreases.

For example, as shown in (a) of FIG. 15 , when the driving 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 power applied to the heating coil 11a increases.

Also, as shown in (b) of FIG. 15 , when the driving frequency is increased, the frequency of the high-frequency current supplied to the heating coil 11a deviates from the resonance frequency of the load circuit, and the power applied to the heating coil 11a decreases.

Furthermore, the control unit 45 controls the inverter circuit 23 by varying the on-duty ratios of the IGBT 23a and the IGBT 23b of the inverter circuit 23 while performing the above-mentioned control of the applied power realized by varying the driving frequency. The application time of the output voltage of the inverter circuit 23 can also be controlled thereby to control the power applied to the heating coil 11a.

In the case of increasing the thermal power, the ratio (on-duty ratio) of the on-time of IGBT 23a (off-time of IGBT 23b) in one cycle of the drive signal is increased so that The voltage application time width increases.

In addition, in the case of 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 so that one cycle The voltage application time width in is reduced.

In the example of (a) in FIG. 15 , 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 off-time of the IGBT 23b ) in one cycle T11 of the drive signal are shown in the figure. The ratio of the on-time) is the same (the on-duty cycle is 50%).

In addition, in the example of (b) of FIG. 15 , the on-time T12a of the IGBT 23a (the off-time of the IGBT 23b) and the off-time T12b of the IGBT 23a ( IGBT 23b on-time) ratio is the same (on-duty ratio is 50%).

The control unit 45 forms the IGBT of the inverter circuit 23 in a state where the drive frequency of the inverter circuit 23 is fixed when obtaining the amount of change of the current per predetermined time described in Embodiments 1 and 2 above. 23a and the state in which the on-duty ratio of IGBT 23b is fixed.

This makes it possible to obtain the amount of change in current per predetermined time in a state where the electric power applied to the heating coil 11 a is constant.

Implementation mode 4.

In Embodiment 4, an inverter circuit 23 using a full bridge circuit will be described.

FIG. 16 is a diagram showing a part of a drive circuit of the induction heating cooker according to Embodiment 4. FIG. In addition, in FIG. 16 , only points of difference from the drive circuits 50 of Embodiments 1 and 2 described above are illustrated.

In Embodiment 4, two heating coils are provided for one heating port. The two heating coils have different diameters, for example, and are concentrically arranged. Here, the heating coil with a small diameter is called an inner coil 11b, and the heating coil with a large diameter is called an outer coil 11c.

In addition, the number and arrangement of heating coils are not limited to these. For example, a configuration in which a plurality of heating coils are arranged around a heating coil arranged in the center of the heating port is also possible.

The inverter circuit 23 has three sets of bridge arms composed of two switching elements (IGBTs) connected in series between positive and negative bus bars and diodes connected in antiparallel to these switching elements. In addition, hereinafter, one of the three sets of arms will be referred to as a common arm, and the other two sets will be referred to as an inner coil arm and an outer coil arm.

The common bridge arm is a bridge arm connected to the inner coil 11b and the outer coil 11c, and is composed of IGBT 232a, IGBT 232b, diode 232c, and diode 232d.

The bridge arm for the inner coil is a bridge arm to which the inner coil 11b is connected, and is composed of an IGBT 231a, an IGBT 231b, a diode 231c, and a diode 231d.

The bridge arm for the outer coil is a bridge arm to which the outer coil 11c is connected, and is composed of an IGBT 233a, an IGBT 233b, a diode 233c, and a diode 233d.

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

The control unit 45 keeps the IGBT 232b in the off state while the IGBT 232a of the common arm is turned on, and keeps the IGBT 232b in the on state while the IGBT 232a is turned off, and outputs alternately on-off drive signals.

Similarly, the control unit 45 outputs a drive signal for alternately turning on and off the IGBT 231a and IGBT 231b of the bridge arm for the inner coil and the IGBT 233a and IGBT 233b of the bridge arm for the outer coil.

Thus, a full-bridge inverter that drives the inner coil 11b is configured by using the common arm and the inner-coil arm. In addition, a full-bridge inverter that drives the outer coil 11c is configured by using the common arm and the arm for the outer coil.

In addition, the "full-bridge inverter circuit" of the present invention is constituted by using the common bridge arm and the bridge arm for the inner coil. In addition, the "full-bridge inverter circuit" of the present invention is constituted by using the common bridge arm and the bridge arm for the outer coil.

A load circuit composed of the inner coil 11b and the resonant capacitor 24c is connected between the output point of the common arm (the connection point between the IGBT 232a and the IGBT 232b) and the output point of the inner coil arm (the connection point between the IGBT 231a and the IGBT 231b). between.

A load circuit composed of the outer coil 11c and the resonant 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 small heating coil wound in a substantially circular shape, and the outer coil 11c is disposed on its outer periphery.

The coil current flowing in the inner coil 11b is detected by the coil current detection unit 25c. Coil current detection means 25 c detects, for example, the peak value of the current flowing in inner coil 11 b, and outputs a voltage signal corresponding to the peak value of the heating coil current to control unit 45 .

The coil current flowing in the outer coil 11c is detected by the coil current detection means 25d. The coil current detection means 25d detects, for example, the peak value of the current flowing through the outer coil 11c, and outputs a voltage signal corresponding to the peak value of the heating coil current to the control unit 45 .

The control unit 45 inputs a high-frequency drive signal to the switching element (IGBT) of each arm in accordance with the applied electric power (heating power) to adjust the heating output.

It is controlled so that the frequency of the drive signal output to the switching element of the common bridge arm and the bridge arm for the inner coil is variable within the range of the drive frequency higher than the resonance frequency of the load circuit composed of the inner coil 11b and the resonance capacitor 24c, Also, the current flowing in the load circuit flows in a phase delayed from the voltage applied to the load circuit.

In addition, control is performed so that the frequency of the drive signal output to the switching element of the common arm and the arm for the outer coil is within the range of the drive frequency higher than the resonance frequency of the load circuit composed of the outer coil 11c and the resonance capacitor 24d. change, and the current flowing in the load circuit flows in a phase delayed from the voltage applied to the load circuit.

Next, the control operation of the applied electric power (heating power) realized by the phase difference between the bridge arms of the inverter circuit 23 will be described.

(a) and (b) of FIG. 17 are diagrams showing an example of drive signals of the full bridge circuit according to the fourth embodiment.

(a) of Fig. 17 is an example of the drive signal of each switch and the energization timing of each heating coil in the high heating power state.

(b) of FIG. 17 is an example of the drive signal of each switch and the energization timing of each heating coil in a low heating power state.

In addition, the energization timing shown in (a) and (b) of Fig. 17 is related to the potential difference of the output point of each bridge arm (the connection point between the IGBT and the IGBT), and the common bridge is shown as "on". The potential of the output point of the arm is lower than the potential of the output point of the bridge arm for the inner coil and the output point of the bridge arm for the outer coil. In addition, "OFF" indicates a state in which the potential of the output point of the common arm is higher than that of the output points of the inner coil arm and the output point of the outer coil arm and the state in which the potential is the same.

As shown in (a) and (b) of FIG. 17, the control unit 45 outputs a high-frequency drive signal having a frequency higher than the resonance frequency of the load circuit to the IGBT 232a and the IGBT 232b of the common arm.

In addition, the control unit 45 outputs a drive signal whose phase is advanced from that of 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 driving signal of each bridge arm is the same, and the conduction duty ratio is also the same.

Corresponding to the on-off state of the IGBT and the IGBT, the output of the DC power supply circuit, that is, the positive bus potential or the negative bus potential is switched at high frequency at the output point of each bridge arm (the connection point between the IGBT and the IGBT). Thus, the 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. Also, the potential difference between the output point of the common arm and the output point of the arm for the outer coil 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 or decreasing the phase difference between the drive signal for the common arm and the drive signals for the inner coil arm and the outer coil arm. , it is possible to control the high-frequency output current and input current flowing in the inner coil 11b and the outer coil 11c.

To increase the firepower, the phase difference α between the bridge arms is increased to increase the voltage application time width in one cycle. In addition, in the case of phase inversion (phase difference 180°), the phase difference α between the bridge arms reaches the upper limit, and the output voltage waveform at this time is almost a rectangular wave.

In the example of (a) of FIG. 17 , the diagram shows the case where the phase difference α between the bridge arms is 180°. In addition, the figure shows 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 to the off-time T13b in one cycle T13 is the same.

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 the thermal power is to be lowered, the phase difference α between the arms is reduced compared to the high thermal power state, thereby reducing the voltage application time width in one cycle. In addition, the lower limit of the phase difference α between the arms is set, for example, at a level that does not cause excessive flow in the switching element due to the relationship with the phase of the current flowing in the load circuit when turned on. current thereby destroying the switching element.

In the example of FIG. 17( b ), a case is shown in which the phase difference α between the bridge arms is made smaller than the phase difference α in the example of FIG. 17( a ). In addition, the frequency and on-duty ratio of the drive signal of each bridge arm are the same as the example of (a) of FIG. 17 .

In this case, the conduction 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 difference α between the bridge arms.

In this way, the electric power (heating power) applied to the inner coil 11b and the outer coil 11c can be controlled using the phase difference between the bridge arms.

In addition, in the above description, the case of heating the inner coil 11b and the outer coil 11c together has been described, but it is also possible to stop the drive of the inner coil arm or the outer coil arm and only make the inner coil 11b or the outer coil 11c Either one of the outer coils 11c performs a heating operation.

The control unit 45 forms the phase difference between the bridge arms in a state where the driving frequency of the inverter circuit 23 is fixed when obtaining the amount of change of the current per predetermined time described in the first and second embodiments. α and the state where the on-duty ratio of the switching element of each arm is fixed. In addition, other operations are the same as those of Embodiments 1 and 2 described above.

Thereby, it is possible to obtain the change amount of the electric current every predetermined time in a state where the electric power applied to the inner coil 11b and the outer coil 11c is constant.

In addition, in Embodiment 4, the coil current flowing in the inner coil 11b and the coil current flowing in the outer coil 11c are detected by the coil current detecting means 25c and the coil current detecting means 25d, respectively.

Therefore, when the heating operation of the inner coil 11b and the outer coil 11c is performed together, even when either the coil current detection means 25c or the coil current detection means 25d fails to detect the coil current value, etc. The amount of change in the coil current per predetermined time can be detected using the other detection value.

In addition, the control unit 45 may obtain the amount of change per predetermined time in the coil current detected by the coil current detection means 25c and the amount of change in the coil current per predetermined time detected by the coil current detection means 25d, and use Each of the determination operations described in Embodiments 1 and 2 above is performed on the larger one of the respective amounts of change. In addition, the respective determination operations described in Embodiments 1 and 2 above may be performed using an average value of each change amount.

By performing such control, even when the detection accuracy of either the coil current detection means 25c or the coil current detection means 25d is low, the change amount of the coil current per predetermined time can be calculated|required more accurately.

In addition, in the above-mentioned Embodiments 1 to 4, the IH cooking heater (cooking heater) was described as an example of the induction heating cooker of the present invention as an example, but the present invention is not limited thereto. The utility model can be applied to any induction heating cooker using induction heating, such as an electric rice cooker for heating and cooking by induction heating.

Claims (19)

1. an induction heating cooking instrument, is characterized in that,

Described induction heating cooking instrument possesses:

Heater coil, this heater coil carries out induction heating to heating object;

Drive circuit, this drive circuit is to described heater coil supply high frequency electric power;

Control part, this control part controls the driving of described drive circuit, and the High frequency power that control supplies to described heater coil;

Input electric cur-rent measure unit, this input electric cur-rent measure unit inspection is to the input current of described drive circuit; And

Coil current detecting unit, this coil current detecting unit detects the coil current flowed at described heater coil,

Described control part is configured to: either party in described input current and described coil current is selected in the variation based on described input current and described coil current, and detects the variations in temperature of described heating object based on the selected variable quantity of either party.

2. induction heating cooking instrument according to claim 1, is characterized in that,

Described control part is configured to: based in described input current and described coil current to till described heater coil supply electric power plays through between first period of heating, the variable quantity of the electric current of variation or the large side of the rate of change, detect the variations in temperature of described heating object.

3. induction heating cooking instrument according to claim 2, is characterized in that,

Described control part is configured to: based on to till described heater coil supply electric power plays through between second period of heating, the variation of at least one party of described input current and described coil current or the rate of change, set between described first period of heating, wherein, between described second period of heating than short between described first period of heating.

4. the induction heating cooking instrument according to Claims 2 or 3, is characterized in that,

Described control part possesses AD converter, and the analogue value detected by described input electric cur-rent measure unit and described coil current detecting unit is converted to digital value by this AD converter,

And the digital value of described input current and described coil current is set as the described rate of change relative to the variation of the lowest high-current value being converted to digital value by described AD converter by described control part.

5. induction heating cooking instrument according to claim 1 and 2, is characterized in that,

Described induction heating cooking instrument possesses:

Load determination unit, this load determination unit carries out the load determination processing of described heating object,

Described control part is configured to: the result of determination based on described load determination unit makes described drive circuit drive, and based on the described variable quantity under the state of the driving frequency of described drive circuit being fixed, detects the variations in temperature of described heating object.

6. induction heating cooking instrument according to claim 1 and 2, is characterized in that,

Described control part is configured to: when variable quantity described under the state of the driving frequency of described drive circuit being fixed is below threshold value, control the driving of described drive circuit, makes the High frequency power that supplies to described heater coil variable.

7. induction heating cooking instrument according to claim 1 and 2, is characterized in that,

Described control part is configured to: when variable quantity described under the state of the driving frequency of described drive circuit being fixed is below threshold value, remove the fixing of described driving frequency, and improve the driving frequency of described drive circuit, the High frequency power supplied to described heater coil is reduced.

8. induction heating cooking instrument according to claim 1 and 2, is characterized in that,

Described control part is configured to: when variable quantity described under the state of the driving frequency of described drive circuit being fixed increases more than Second Threshold, control the driving of described drive circuit, and the High frequency power supplied to described heater coil is increased.

9. induction heating cooking instrument according to claim 1 and 2, is characterized in that,

Described control part is configured to: when variable quantity described under the state of the driving frequency of described drive circuit being fixed reduces more than 4th threshold value, control in the mode of the driving stopping described drive circuit, stop described heater coil supply high frequency electric power.

10. induction heating cooking instrument according to claim 7, is characterized in that,

Described control part, by the conducting variable duty ratio of the driving frequency or switch element that make described drive circuit, makes the High frequency power that supplies to described heater coil variable.

11. induction heating cooking instruments according to claim 8, is characterized in that,

Described control part, by the conducting variable duty ratio of the driving frequency or switch element that make described drive circuit, makes the High frequency power that supplies to described heater coil variable.

12. induction heating cooking instruments according to claim 1 and 2, is characterized in that,

Described control part is configured to:

When variable quantity described under the state of the driving frequency of described drive circuit being fixed is below threshold value, remove the fixing of described driving frequency, the driving frequency of described drive circuit is made to increase, thus the High frequency power supplied to described heater coil is reduced, again the driving frequency of described drive circuit is fixed, afterwards

When variable quantity described under the state of the driving frequency of described drive circuit being fixed increases more than Second Threshold, remove the fixing of described driving frequency, the driving frequency of described drive circuit is reduced, thus the High frequency power supplied to described heater coil is increased, again the driving frequency of described drive circuit is fixed, afterwards

When variable quantity described under the state of the driving frequency of described drive circuit being fixed is below described threshold value, remove the fixing of described driving frequency, the driving frequency of described drive circuit is made to increase, thus the High frequency power supplied to described heater coil is reduced, then the driving frequency of described drive circuit is fixed.

13. induction heating cooking instruments according to claim 1 and 2, is characterized in that,

Described control part is configured to:

When variable quantity described under the state of the driving frequency of described drive circuit being fixed is below threshold value, remove the fixing of described driving frequency, the driving frequency of described drive circuit is made to increase, thus the High frequency power supplied to described heater coil is reduced, again the driving frequency of described drive circuit is fixed, afterwards

When variable quantity described under the state of the driving frequency of described drive circuit being fixed increases more than Second Threshold, remove the fixing of described driving frequency, the driving frequency of described drive circuit is reduced, thus the High frequency power supplied to described heater coil is increased, again the driving frequency of described drive circuit is fixed, afterwards

When variable quantity described under the state of the driving frequency of described drive circuit being fixed is below described threshold value, remove the fixing of described driving frequency, the driving frequency of described drive circuit is made to increase, thus the High frequency power supplied to described heater coil is reduced, again the driving frequency of described drive circuit is fixed, afterwards

When variable quantity described under the state of the driving frequency of described drive circuit being fixed reduces more than 4th threshold value, control in the mode of the driving stopping described drive circuit, thus stop described heater coil supply high frequency electric power.

14. induction heating cooking instruments according to claim 1 and 2, is characterized in that,

Described induction heating cooking instrument possesses:

Operating portion, this operating portion carries out the selection operation of pattern; And

Reporting unit,

Described control part when have selected setting water the boil mode of boiling action as described pattern, described drive circuit is driven,

When under the state that the driving frequency of described drive circuit is fixing, described variable quantity is below threshold value, this situation complete is boiled in described reporting unit report.

15. induction heating cooking instruments according to claim 1 and 2, is characterized in that,

Described induction heating cooking instrument possesses:

Operating portion, this operating portion carries out the selection operation of pattern; And

Temperature detecting unit, this temperature detecting unit detects the temperature of described heating object,

Described control part is configured to:

When have selected oil is heated to target temperature fried pattern as described pattern, described drive circuit is driven,

When the detected temperatures of described temperature detecting unit exceedes described target temperature, the driving of described drive circuit is controlled, thus the High frequency power supplied to described heater coil is reduced, then the driving frequency of described drive circuit is fixed,

When variable quantity described under the state of the driving frequency of described drive circuit being fixed increases more than 3rd threshold value, the driving of described drive circuit is controlled, thus the High frequency power supplied to described heater coil is increased.

16. induction heating cooking instruments according to claim 5, is characterized in that,

Described load determination unit is configured to: the relation based on described input current and described coil current carries out the load determination processing of described heating object.

17. induction heating cooking instruments according to claim 1 and 2, is characterized in that,

Described control part is configured to: under the state that the driving frequency of described drive circuit is fixing, is formed the fixing state of the conducting duty ratio of the switch element of described drive circuit.

18. induction heating cooking instruments according to claim 1 and 2, is characterized in that,

Described drive circuit is made up of the full-bridge inverter circuit with at least 2 brachium pontis, described brachium pontis by 2 switch elements in series are connected and composed,

Described control part is configured to: under the state that the driving frequency of the described switch element by described full-bridge inverter circuit is fixing, forms the state of being fixed with the conducting duty ratio of described switch element by the driving phase difference of described 2 brachium pontis described switch element each other.

19. induction heating cooking instruments according to claim 1 and 2, is characterized in that,

Described drive circuit is made up of the half-bridge inverter circuit with brachium pontis, described brachium pontis by 2 switch elements in series are connected and composed,

Described control part is configured to: under the state that the driving frequency of the described switch element by described half-bridge inverter circuit is fixing, is formed the fixing state of the conducting duty ratio of described switch element.