JPH04262391A - Induction heating cooking apparatus - Google Patents

Abstract

PURPOSE:To prevent impression of an excessive voltage and current on a switching element of an induction heating cooking apparatus for domestic use, which is free from risk of firing of a cooking oil even in the event of malfunction of the temp. control. CONSTITUTION:A deep pan 6 is made of a material whose Curie point lies between the temp. at which cooking oil goes into firing and the max. normally used cooking temp. Temp. control in normal cooking is carried out in the form of input control for an inverter circuit 5 using signals from a temp. sensing means 7, but if as the worst case this temp. control goes in malfunction to permit the pan temp. to rise continued. the self-temp. control action of the pan 6 is actuated at the Curie point to prevent firing of the cooking oil.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker having a safety device.

0002

BACKGROUND OF THE INVENTION In recent years, induction heating cookers have become popular in general households as their superior features of safety, cleanliness, and high efficiency have been recognized. Induction heating cookers generate high-frequency magnetic flux by applying a high-frequency current of several tens of kHz to a heating coil wound on a spiral flat plate, and inductively heats a cooking pot, which serves as a load that is magnetically coupled to the heating coil. It is something. Therefore, depending on the properties of the metal that makes up the pot, i.e. how easily magnetic flux can penetrate and how easily it generates heat (relative magnetic permeability, skin thickness, specific resistance), there may be differences in the input power, or there may be differences in the input power, or the ease with which the induction heating cooker is equipped. The load detection circuit installed may determine that the load is inappropriate and stop heating. Taking advantage of this property, we have developed a material for pots with a Curie point of approximately 300.
A method has been devised to automatically adjust the temperature of the pot so that the temperature does not exceed the Curie point by utilizing changes in the properties of the pot, such as relative magnetic permeability, that occur at the Curie point by using a metal with a temperature below the Curie point. Here, the Curie point is about 300
The temperature is set at below ℃ because the temperature of the pot that causes cooking oil to ignite is approximately 300℃, and considering the danger of this, the temperature is set to be appropriate based on the normal cooking temperature required for a cooking pot. be.

[0003] A conventional induction heating cooker will be explained below with reference to the drawings. In FIG. 6, 1 is an AC power supply;
2 is a heating coil, 3 is a switching element, 4 is an input current detection circuit that detects the input current from the AC power supply 1, 5 is an inverter circuit that supplies high-frequency current to the heating coil 2 by turning on and off the switching element 3, 6 is about 30
A cooking pot 8 made of a material having a Curie point of 0° C. or lower is a control unit that controls the on/off of the switching element 3, but the internal signals of the inverter circuit 5, such as the voltage generated in the switching element 3 and the element current, The signal from the input current detection circuit 4 detects small items that are unloaded or unsuitable for heating.
It also has a load detection function for aluminum pots, etc.

FIG. 7 shows the operation of the pot in the vicinity of the Curie point in the above configuration. The vertical axis shows the pot temperature and the presence or absence of induction heating.
The horizontal axis shows the passage of time. When the temperature of the pot is below the Curie point, the magnetic flux from the heating coil is concentrated on the lower surface of the bottom of the pot, so the bottom of the pot exhibits a high electrical resistance value and the pot is heated. However, when the temperature of the pot rises and exceeds the Curie point, the magnetic permeability of the pot changes, and the magnetic flux from the heating coil is no longer concentrated on the lower surface of the bottom of the pot, resulting in a lower electrical resistance and lower calorific value. At this time, the load detection function of the control section determines that the load is inappropriate, and induction heating is stopped. after that,
When the temperature of the pot drops below the return point, the pot's magnetic permeability is restored, heating starts again, and the temperature of the pot begins to rise. In this way, temperature control is performed by repeatedly heating and stopping between the Curie point and the return point of the pot material.

[0005]

[Problem to be Solved by the Invention] However, according to the induction heating cooker with the conventional configuration, there is a sudden change in characteristics such as magnetic permeability at the Curie point of the pot, and at that time, excessive voltage and current are generated in the inverter circuit. There is a risk. This is because the resonance frequency of the LC resonance inside the inverter circuit changes rapidly, and the oscillation circuit that determines the on/off period cannot keep up with the change. As a result, excessive voltage and current are applied to the switching element, causing the switching element to be destroyed.

[0006] The present invention solves the above-mentioned conventional problems, and allows temperature control without applying harmful excessive voltages and currents to switching elements, and even if temperature control malfunctions, cooking can be continued. To provide an induction heating cooker in which the oil temperature does not reach the ignition point.

[0007] Furthermore, even when the temperature control malfunctions and self-temperature control is performed to prevent the cooking oil temperature from reaching the ignition point using the property of the pot at its Curie point, excessive voltage and current are not generated. A second object is to provide an induction heating cooker.

A third object of the present invention is to provide means for detecting that the temperature of the pot has reached the Curie point.

[0009]

[Means for Solving the Problems] To achieve this object, the induction heating cooker of the present invention includes an AC power source, a heating coil, a switching element, and an input current detector that detects an input current from the AC power source. a circuit, an inverter circuit that supplies high-frequency current to the heating coil by turning on and off the switching element, and a material having a Curie point between the temperature at which the cooking oil ignites and the highest point of the normal cooking temperature. the pot, a temperature detecting means for directly or indirectly detecting the temperature of the pot, and a control section for controlling the input current of the inverter circuit based on a signal from the temperature detecting means, the control section for controlling the input current of the inverter circuit. The pot is configured to control the temperature of the pot at a temperature lower than the Curie point of the pot.

Furthermore, in order to achieve the second object, the present invention includes, in addition to the above-mentioned configuration, a Curie point detection means and a voltage/current limiting circuit.

Furthermore, in order to achieve the third object, the present invention includes a switching element voltage change detection circuit or a heating coil current change detection circuit.

0012

[Operation] According to the first configuration described above, during cooking, the temperature of the pot is controlled in a temperature range lower than the Curie point, so there is no sudden change in characteristics such as magnetic permeability, and there is no excessive voltage or voltage applied to the inverter circuit. No current is generated. As a result, there is no destruction of switching elements. In addition, the automatic temperature control function that uses the Curie point of the pot does not work at all times, but if the temperature control function of the induction heating cooker malfunctions, the pot itself will self-control so that the temperature does not exceed the Curie point temperature. Ignition due to excessive temperature rise of the oil is prevented.

Furthermore, according to the second configuration, even when the pot itself self-controls itself so that the temperature does not exceed the Curie point, when the temperature reaches near the Curie point, the voltage applied to the switching element and the heating coil current are reduced to below a predetermined value. Since the limiting voltage/current limiting circuit lowers the limiting value, it is possible to suppress excessive voltage/current that occurs when the pot reaches the Curie point.

According to the third configuration, it is possible to detect a change in the voltage applied to the switching element and determine that the Curie point has been reached when the voltage exceeds a preset value. This can be detected because the voltage change when the temperature of the pot reaches the Curie point is much larger than the voltage change that occurs when the pot is moved manually.

According to the fourth configuration, it is possible to detect a change in the current applied to the heating coil and determine that the Curie point has been reached when the current applied to the heating coil exceeds a predetermined value.

[0016]

[Embodiment] (Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an AC power supply, 2 is a heating coil, 3 is a switching element, 4 is an input current detection circuit that detects the input current from the AC power supply 1, and 5 is a heating element that turns on and off the switching element 3. An inverter circuit that supplies high-frequency current to the coil 2; 6, a pot made of a material having a Curie point of about 250°C; 7, temperature detection means for directly or indirectly detecting the temperature of the pot 6; 8, temperature detection means 7; In response to the signal from the current detection circuit 4, the temperature of the pot is adjusted to approximately 140°C, which is the normal temperature range for cooking, using a predetermined input current.
Switching element 3
This is a control unit that controls the on/off of the

The operation of the induction heating cooker constructed as described above will be explained using FIG. 2. First, during normal cooking, the high frequency current flowing through the heating coil 2 is controlled by the control section 8 controlling the on/off of the switching element 3 based on the signal from the temperature detection means 7.
The temperature of the pot 6 is controlled and maintained within a range of about 140°C to about 190°C, which is suitable for cooking. Next, in the unlikely event that the control malfunctions and the temperature of the pot 6 continues to rise beyond the normal temperature range for cooking, the pot temperature will be approximately 3.5 degrees, at which point the cooking oil will ignite.
Since the Curie point of the pot is reached at about 250.degree. C., which is lower than 00.degree. C., the pot 6's self-temperature control action based on changes in characteristics such as magnetic permeability comes into play, and the pot temperature does not rise above about 250.degree. The ignition temperature of normal cooking oil is around 370 degrees Celsius, but taking into account the time difference between the detected pan temperature and oil temperature in the example when the temperature suddenly rises due to overheating, the pan temperature at which cooking oil ignites has been adjusted. was set at approximately 300°C.

In this way, in the induction heating cooker according to the present embodiment, the pot does not reach the Curie point during normal cooking, so there is no sudden change in the pot's characteristics such as magnetic permeability, and the inverter circuit is prevented from overheating. No excessive voltage or current is generated. Furthermore, even in the unlikely event that the temperature control function malfunctions, the self-temperature control at the Curie point of the pot works, preventing the cooking oil from igniting.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3, 1 is an AC power supply, 2 is a heating coil, 3 is a switching element, 4 is an input current detection circuit,
5 is an inverter circuit, 6 is a pot, 7 is a temperature detection means, and 8 is a control section, which is the same as the configuration shown in FIG. 1. Figure 1
The configuration differs from that in that a Curie point detection means 9 and a voltage/current limiting circuit 10 are added.

The operation of the induction heating cooker constructed as described above will be explained below. First, the temperature control operation of the pot during normal cooking and the self-temperature control operation when the temperature of the pot reaches the Curie point are the same as those of the first embodiment. The difference in operation from the first embodiment is that when the Curie point detection means 9 detects that the temperature of the pot has reached around the Curie point, the voltage/current limiting circuit 1
0 limits the voltage applied to the switching element to a maximum of 900V and the heating coil current to a maximum of 70A.

As described above, in the induction heating cooker according to the second embodiment, the Curie point detection means 9 and the voltage/voltage
By adding the current limiting circuit 10, in the first embodiment, even when the temperature control function malfunctions and the self-temperature control at the Curie point of the pot is activated, excessive voltage of the inverter circuit that destroys the switching element can be prevented. Electric current can be prevented.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings.

In FIG. 4, the configuration is similar to that of FIG. 3 except that the Curie point detection means 9 in the configuration of FIG. 3 includes a voltage change detection circuit 11 for detecting changes in the voltage applied to the switching element. be.

In the induction heating cooker constructed as described above, the Curie point detection means 9 of the second embodiment has the following features:
The operation is similar to that of the second embodiment except that it is implemented more concretely. That is, when the temperature of the pot reaches around the Curie point, the voltage applied to the switching element starts to rise, and by detecting the voltage change, it is known that the temperature has reached around the Curie point.

(Embodiment 4) Similar to the third embodiment, the fourth embodiment provides another concrete implementation means for the Curie point detection means 9 of the second embodiment, and includes a heating coil. It has a heating coil current detection circuit that detects changes in the current applied to the heating coil.

[0028]

As is clear from the above embodiments, according to the present invention, even if the temperature control function malfunctions, the self-temperature control at the Curie point of the pot works to prevent the cooking oil from igniting. Since the temperature of the pot is lower than the Curie point during cooking, excessive voltage and current will not be generated in the inverter circuit due to sudden changes in characteristics such as magnetic permeability at the Curie point of the pot. , the switching element will be destroyed, but this can be prevented. It also provides a means for detecting the Curie point of the pot by detecting changes in the voltage applied to the switching element and the current flowing through the heating coil, and further reduces the limiting value of the switching element voltage and heating coil current at that time. By doing so, it is possible to prevent the switching element from being destroyed even when the pot reaches the Curie point.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an induction heating cooker according to a first embodiment of the present invention.

[Fig. 2] Temperature-related diagram for explaining the operation of the induction heating cooker in the first embodiment.

FIG. 3 is a circuit diagram showing the configuration of an induction heating cooker according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing the configuration of an induction heating cooker according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing the configuration of an induction heating cooker according to a fourth embodiment of the present invention.

[Fig. 6] Circuit diagram showing the configuration of a conventional induction heating cooker

[Figure 7] Diagram for explaining the operation of a conventional induction heating cooker

[Explanation of symbols]

1 AC power supply 2 Heating coil 3 Switching element 4 Input current detection circuit 5 Inverter circuit 6 Pot 7 Temperature detection means 8 Control section 9 Voltage/current limiting circuit 10 Curie point detection means 11 Voltage change detection circuit 12 Current change detection circuit

Claims (4)

[Claims] 1. An AC power supply, a heating coil, a switching element, an input current detection circuit for detecting an input current from the AC power supply, and supplying a high-frequency current to the heating coil by turning on and off the switching element. an inverter circuit; a cooking pot made of a material having a Curie point between the temperature at which cooking oil ignites and the highest point of the normal cooking temperature; and temperature detection means for directly or indirectly detecting the temperature of the pot. , a control section that controls the input current of the inverter circuit based on the signal of the temperature detection means,
In the induction heating cooker, the control unit controls the temperature of the pot at a temperature lower than the Curie point of the pot. 2. A Curie point detection means and a voltage/current limiting circuit, wherein when the Curie point detection means detects that the temperature of the pot has reached near the Curie point, the voltage/current limiting circuit reduces the switching element voltage. The induction heating cooker according to claim 1, wherein the limit value of the heating coil current and the limit value of the heating coil current are reduced. 3. The induction heating cooker according to claim 2, further comprising a voltage change detection circuit for detecting a change in the voltage applied to the switching element as the Curie point detection means of the pot. 4. The induction heating cooker according to claim 2, further comprising a heating coil current change detection circuit for detecting a change in the current applied to the heating coil as the Curie point detection means of the pot.