JPH0541274A - Electromagnetic induction heating cooker - Google Patents

Abstract

PURPOSE:To lower induction voltage as well as to prevent a man from being struck by electricity by clarifying two heating coils in positional relation when flat heating coils are formed into a two stage construction. CONSTITUTION:The positional relation between the high and low voltage sides of a double heating coil is so clarified that a heating coil 3b at the high voltage side is placed at the lower stage apart from a metallic pan 1, and a heating coil 3a at the lower voltage side is placed at the upper stage close to the metallic pan 1 while they are over-lapped in two stages coaxially about their winding centers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a flat plate heating coil in an electromagnetic induction heating cooker.

[0002]

2. Description of the Related Art FIG. 6 is a structural diagram around a flat plate heating coil of a conventional electromagnetic induction heating cooker. In FIG. 6, 1 is a metal pan that is an object to be heated, 2 is a mounting table on which the metal pan 1 is placed, 3 is a flat plate heating coil that generates high-frequency alternating magnetic flux for inductively heating the metal pan 1, 4 Is a flat plate heating coil 3
The metal pan 1 is heated by Joule heat loss of the eddy current that flows when the generated high-frequency alternating magnetic flux permeates the bottom surface of the metal pan 1.

Further, as a high frequency power converter for driving the flat plate heating coil 3, a single end push pull (SEPP) circuit shown in FIG. 7 or a single-stone resonance inverter circuit shown in FIG. 8 is generally used. Target.

Most of the conventional flat plate heating coils have a single-stage structure. As a two-stage heating coil according to the present invention, two heating coils are connected in series for the purpose of heating a non-magnetic metal pot. Japanese Patent Publication No. 2-31472 discloses a flat plate heating coil having a two-stage structure in which the inductance value is increased and the amount of high frequency alternating magnetic flux from the flat plate heating coil is increased.

[0005]

In the above high-frequency power converter, since the flat plate heating coil 3 and the resonance capacitor 7 are driven under the series resonance condition, the coil current flowing in the heating coil 3 is charged in the resonance capacitor 7 to cause resonance. Capacitor 7
Generate high voltage across both ends of. This resonant voltage is also applied to the heating coil. At this time, the generated voltage Vc is
The coil current flowing through the heating coil 3 is I _L , and the heating coil 3
The inductance value of L and the capacitance of the resonance capacitor 7 are C
Then,

[0006]

[Equation 1]

Therefore, the resonance voltage Vc is proportional to the inductance value of the heating coil 3. Therefore, in the case of a two-stage heating coil in which two heating coils are connected in series, the inductance value is larger than that of a normal one-stage coil, and the resonance voltage Vc
In the case of a high output type electromagnetic induction heating cooker, the voltage reaches several tens of kV. This high voltage is also generated at the connection point of the heating coil on the side of the resonance capacitor. At this time, the two heating coils are divided into a high voltage side on the resonance capacitor side and a low voltage side on the power supply side.

On the other hand, the heating coil 3 and the heated metal pot 1 are
In order to efficiently permeate the high frequency alternating magnetic flux generated from the heating coil 3 to the bottom surface of the metal pan 1, it is preferable to bring them as close as structurally possible, usually several mm, and between the heating coil 3 and the metal pan 1. In consideration of heat resistance and strength, a certain mounting table 2 generally uses a dielectric material such as ceramic or glass as its material.
There is a floating capacitance 5 between the and the metal pot 1.

Due to the electrostatic coupling due to the presence of the floating electrostatic capacitance 5, a high voltage generated in the heating coil 3 is induced in the metal pot 1 and a voltage is generated between the ground and the metal pot.

In the conventional two-stage heating coil, no distinction is made between the low-voltage side and the high-voltage side of the two heating coils, and if the heating coil on the high-voltage side is in the upper stage close to the metal pot, The above-mentioned induced voltage of the metal pot 1 also becomes large, and there is a drawback that the human body receives an electric shock when touching the pot, and especially when the hand of the cooker is wet, there was a strong electric shock, which was a problem.

Further, in the conventional heating coil, the connection points of the first and second stages are not clarified. If the insides of the two-stage heating coils are connected to each other, the height between the outsides of the two-stage heating coils is increased. A voltage is applied and corona discharge occurs between the first and second stages.

[0012]

The present invention has been made in view of the above drawbacks, and the positional relationship between the high-voltage side and the low-voltage side of the two-stage heating coil is clarified, and the high-pressure side heating coil is attached to the metal pan 1.
The lower coil is separated from the lower coil, and the winding center is the same so that the low-voltage side heating coil is in the upper coil close to the metal pan 1.

Further, the connection points of the first stage and the second stage are set to the inner side of the first stage and the outer side of the second stage, or the outer side of the first stage and the inner side of the second stage.

[0014]

Since the induced voltage generated in the metal pot 1 is caused by the stray capacitance 5 existing between the metal pot 1 and the heating coil 3, the distance between the metal pot 1 and the heating coil 3 is physically adjusted. The floating electrostatic capacitance 5 can be reduced by separating it to
As a result, the induced voltage generated in the metal pot 1 can also be reduced. Therefore, the positional relationship between the high-voltage side on the resonance capacitor side and the low-voltage side on the power supply side of the two-stage heating coil connected in series is clarified, and the low-voltage side of the two-stage heating coil is provided in the upper stage close to the metal pot 1, By providing the high voltage side in the lower stage far from the pot 1, the induced voltage generated in the metal pot can be reduced, and the problem of electric shock to the human body can be solved.

Further, by connecting the connection points of the two-stage heating coil to the inside (outside) of the first stage and the outside (inside) of the second stage, the voltage between the first and second stages can be set at any position. It becomes the same and the voltage is lowered.

[0016]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is an explanatory view showing the structure of a two-stage heating coil of an electromagnetic induction heating cooker of the present invention, and FIGS. 2 and 3 are circuit diagrams of a high-frequency power converter relating to the two-stage heating coil of the present invention. is there.

In FIG. 1, the difference from FIG. 4 is a heating coil, which is connected in series in order to increase the inductance value, and is wound in two steps with the same winding center. There is. The upper stage close to the metal pan 1 is the low-voltage side heating coil 3a, and the lower stage far from the metal pan 1 is the high-voltage side heating coil 3b, and the holding plate / insulating plate 6 for the upper stage heating coil is provided between them. As the insulating plate 6, an insulating material such as a mica plate having a thickness of several mm is used.

Electrically, as shown in FIG. 2 or 3,
The heating coil connected to the power source side (point A in the figure) is the low voltage side heating coil 3a, and the alternating voltage (100
Rectifying circuit 12 and smoothing capacitor 1
A voltage above the DC voltage smoothed by 1 will not be applied. On the other hand, the heating coil connected to the resonance capacitor 7 side (point B in the figure) is the high-voltage side heating coil 3b, and since the heating coil 3 and the resonance capacitor 7 resonate in series, a very high resonance voltage (usually several tens of kV) is generated. It is generated at the connection point and applied to the heating coil 3b.

As for the electric leakage to the metal pan 1, the high-voltage resonance voltage generated in the series resonance circuit composed of the heating coil 3 and the resonance capacitor 7 is applied to the heating coil 3, and the voltage is applied to the heating coil 3 and the metal pan. Since it is generated by induction in the metal pot 1 by electrostatic coupling with 1, the ground voltage Vr of the metal pot 1 causes the capacitance of the floating electrostatic capacity 5 between the heating coil 3 and the metal pot 1 to be C. If the ground voltage of the coil 3 is Vc, the ground resistance of the metal pot 1 is R, and the drive frequency of the inverter is f.

[0021]

[Equation 2]

(See FIG. 4)

The capacitance C of the floating electrostatic capacitance 5 between the heating coil 3 and the metal pot 1 is ε ₀ : vacuum dielectric, where S is the facing area between the heating coil 3 and the metal pot 1 and d is the facing distance. , Ε _s : As the relative permittivity,

[0024]

[Equation 3]

[0025]

Here, when the high-pressure side 3b of the two-stage heating coil is set to the lower stage as in the present invention, the facing distance d in the above equation is 3
It becomes larger than when b is set to the upper stage. When the facing distance d increases, the floating capacitance 5 between the heating coil 3 and the metal pot 1
On the contrary, as a result, the ground voltage V of the metal pot 1 becomes smaller.
r also becomes small.

The distance between the metal pot 1 and the heating coil 3 is
In order to efficiently permeate the high frequency alternating magnetic flux generated from the heating coil 3 to the bottom surface of the metal pot, the magnetic flux is as close as possible structurally, and is usually several mm. On the other hand, the thickness of one stage of the heating coil is several mm for the coil alone, and the holder and the insulating plate 6
The thickness of the metal pan will be about 5 mm including the thickness of the heating pan.
The facing distance d between the heating coil 3 and the heating coil 3 is two to three times different. As a result, by setting the low-voltage side 3a of the heating coil to the upper stage and the high-voltage side 3b to the lower stage, the induced voltage induced in the metal pot 1 is reduced to 1/2 to 1/3 as compared with the opposite structure.

Further, since the heating efficiency is not affected by whichever of the low-pressure side 3a and the high-pressure side 3b of the two-stage heating coil is in the upper stage, even if the low-pressure side 3a of the heating coil is in the upper stage as in the present invention, the performance is completely reduced. No problem with.

As shown in FIG. 5 (a), when the connecting points of the two-stage heating coil are inside, the outsides of the two-stage heating coils are connected to the resonance capacitor side and the power supply side, respectively. The voltage V is applied to the insulating plate 6 not only on the outside of the heating coil. However, if the connection points are connected from the inside of the first stage 3a to the outside of the second stage 3b as shown in FIG. 5 (b), the voltage applied to the insulating plate 6 is V / 2 ( (When the heating coils in the first and second stages are the same). On the contrary, even if the outer side of the first stage and the inner side of the second stage are connected, the effect is the same.

As a result, generation of corona discharge is suppressed between the two-stage heating coils, the thickness of the insulating plate can be reduced, and the first-stage and second-stage couplings are improved, resulting in a high-performance two-stage heating coil. it can.

[0031]

As is apparent from the above description, in the two-stage heating coil of the present invention, the induced voltage to the metal pot due to the high frequency / high voltage resonance voltage generated in the inverter circuit of the electromagnetic induction heating cooker is applied. It is possible to reduce the electric shock from the metal pot to the cook.

Further, in the structure of the present invention, it is not necessary to insert a shield plate between the metal pan and the heating coil to suppress the voltage induced in the metal pan, and conversely, by inserting the shield plate, the high frequency alternating magnetic flux There is no problem such as reduction of heating efficiency due to suppression or increase of the spatial distance between the metal pan and the heating coil, and the structure can be simplified.

[Brief description of drawings]

FIG. 1 is a structural diagram of an induction heating cooker with a two-stage heating coil according to the present invention.

FIG. 2 is a circuit diagram of a high frequency power converter for an induction heating cooker according to the present invention.

FIG. 3 is a circuit diagram of a high frequency power converter for an induction heating cooker according to the present invention.

FIG. 4 is an explanatory diagram illustrating a leakage state.

5 (a) and 5 (b) are views showing connection points of the two-stage heating coil of the present invention.

FIG. 6 is a structural diagram of a conventional induction heating cooker having a one-stage heating coil.

FIG. 7 is a circuit diagram of a conventional high-frequency power converter for an induction heating cooker.

FIG. 8 is a circuit diagram of a conventional high-frequency power converter for an induction heating cooker.

[Explanation of symbols]

 1 Metal Pan 3 Heating Coil 7 Resonant Capacitor 8 Transistor 9 Diode 10 Inverter Drive Control Circuit 11 Smoothing Capacitor 12 Rectifier Circuit 13 Commercial Power Supply

Claims (2)

[Claims] 1. A flat-plate heating coil having the same winding center and stacked in two stages, and a high-frequency power converter for generating a high-frequency alternating magnetic flux from the flat-plate heating coil, wherein the structure of the flat-plate heating coil is the upper stage. An electromagnetic induction heating cooker having a two-stage structure in which a low-voltage side heating coil and a high-pressure side heating coil are arranged in the lower part. 2. The two-stage heating coil according to claim 1, wherein an insulating plate is inserted between the first stage and the second stage,
An electromagnetic induction heating cooker characterized in that the connection points of the tiers are inside (outside) of the first tier and outside (inner) of the second tier.