JPH07326471A - Electromagnetic cooker heating coil and electromagnetic cooker - Google Patents

Abstract

PURPOSE:To provide an electromagnetic cooker heating coil which can be molded with a large diameter without having excessive inductance or an excessive equivalent resistance value and an electromagnetic cooker using the same. CONSTITUTION:Two conductors (a), (b) having both end portions are arranged in a flat shape on the same plane and tightly wound together into a spiral, with the ends of the two litz wires (a), (b) electrically connected to each other by terminals 11, 12 to obtain a heating coil 1. The ends 11, 12 of the heating coil 1 are connected to the output terminals of an inverter circuit having a half-bridged semiconductor switching circuit, to constitute a high-output electromagnetic cooker.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating coil used in an electromagnetic cooker and a structure of an electromagnetic cooker constructed by using the heating coil.

[0002]

2. Description of the Related Art As an electromagnetic cooker, a flat heating coil in which a conducting wire such as a litz wire is wound closely in a spiral shape from a central portion to an outer peripheral portion is arranged in parallel with a coil surface of the heating coil. There is known a structure including a non-magnetic top plate and a power supply for supplying high-frequency power to the heating coil. In this type of electromagnetic cooker, an object to be heated, such as a cooking container made of a conductive material, is placed on the top plate, and in this state, a high-frequency current is passed from the power supply to the heating coil. Induction heating of the object to be heated is performed by the eddy current.

As a power source, a structure in which a commercial power source supplied from the outside is converted into a high frequency by an inverter circuit is generally used, but in an electromagnetic cooker having a higher output, a half bridge is used in the inverter circuit of the power source. Type and full-bridge type semiconductor switching circuits are used. In such a power supply, an optimum equivalent resistance value (load equivalent resistance value) as a load is specified in order to obtain a rated output by matching the impedance on the load side. For example, the optimum equivalent resistance value of a half-bridge type semiconductor switching circuit is around 2.8Ω in a three-phase 200V input type electromagnetic cooker, but actually, considering the type of cooking container, etc. It becomes about 3Ω.

[0004]

By the way, the only part of the electromagnetic cooker that heats the object to be heated is the part of the heating coil arranged under the top plate that faces the object to be heated. For this reason, when constructing an electromagnetic cooker corresponding to a large object to be heated, it is necessary to make the diameter of the heating coil as large as possible. However, as a conventional heating coil for an electromagnetic cooker, one conductor wire wound in a flat spiral shape is usually used. The number of turns increases. Therefore, the inductance of the heating coil becomes very large, and the degree of electromagnetic coupling between the object to be heated and the heating coil becomes large. As a result, the equivalent resistance value on the load side as seen from the power supply becomes large, and in the case of a configuration using a power supply having a small optimum load equivalent resistance value, such as a power supply having the above half bridge type inverter circuit, There is a problem that the rated resistance cannot be obtained because the equivalent resistance value on the load side becomes a large value larger than the optimum value.

Here, in the case of using the large-diameter heating coil as described above, in order to reduce the equivalent resistance value on the load side, the interval between the top plate and the heating coil is increased so that the object to be heated and the heating coil are A method of reducing the degree of electromagnetic coupling of is conceivable. However, this method has the following (1)-
There was a problem like (3). (1) The height of the cooker body is unnecessarily high. (2) As the inductance of the heating coil increases, the high-frequency voltage across the coil increases, resulting in insulation failure and the like, resulting in reduced safety. (3) As the apparent voltage of the heating coil increases, the power capacity of the tank capacitor for high frequency generation provided inside the power supply increases. Therefore, it is necessary to use a tank capacitor with a large capacity, resulting in an increase in cost.

Further, as a method of reducing the inductance and increasing the coil diameter with a single conductor, it is conceivable to widen the gap between the conductors when wound in a flat spiral shape. However, in the case of this method, the manufacturing cost of the heating coil is increased, and the equivalent resistance of the heating coil alone cannot be reduced.
There is a drawback that the coil loss becomes large. In addition, it is possible to use a conductor with a flat cross section in the radial direction of the heating coil.However, even in this method, when forming the vicinity of the center of the heating coil, which is important in the heating pattern, the bending radius of the flat conductor is However, there is a drawback that molding is difficult because the size cannot be reduced.

In view of the above problems and drawbacks, an object of the present invention is to provide a heating coil for an electromagnetic cooker which is easy to form without excessively increasing the equivalent resistance value seen from the power source, and the heating coil. The purpose is to provide the electromagnetic cooker that was used.

[0008]

A heating coil for an electromagnetic cooker provided by the present invention has a plurality of conducting wires having both ends arranged on the same plane and spirally wound, and one end portion of each conducting wire is adjacent to each other. And the other ends are electrically connected to each other.

The electromagnetic cooker provided by the present invention has an inverter circuit having a pair of output terminals, and a heating coil that receives power from the output terminals of the inverter circuit to induction-heat an object to be heated. In this heating coil, a plurality of conducting wires are arranged in a plane parallel to the heating part of the object to be heated and spirally wound, and both ends of each conducting wire are connected in parallel to the output terminal. It is characterized by The inverter circuit in this configuration is preferably an inverter circuit including a half-bridge type semiconductor switching circuit.

[0010]

By arranging a plurality of conducting wires on the same plane and winding them in a spiral shape, the diameter from the center portion becomes larger than that when one conducting wire of the same length is wound. In addition, by electrically connecting the ends of the plurality of conductors to each other, it is equivalent to a case where the conductors are electrically connected in parallel. Therefore, in the heating coil having such a configuration, the combined inductance and the equivalent resistance value of the conductive wire are smaller than those in the case where one conductive wire is wound in a spiral shape with a large diameter, which corresponds to a large object to be heated. A heating coil having a diameter can be formed without increasing inductance or equivalent resistance.

Further, in the electromagnetic cooker of the present invention, the inductance and the equivalent resistance value of the heating coil viewed from the output terminal of the inverter circuit are smaller than those of the heating coil composed of one conductor wire. Therefore, the degree of electromagnetic coupling between the heating coil and the object to be heated is correspondingly reduced, and the distance between the heating object and the heating coil can be narrowed. As a result, the efficiency of induction heating of the object to be heated by the heating coil is increased, and the voltage value applied to the heating coil can be lowered. Further, since the equivalent resistance value seen from the output terminal of the inverter circuit becomes small, impedance matching with the half-bridge type semiconductor switching circuit becomes easier.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a front view of a heating coil for an electromagnetic cooker according to an embodiment of the present invention. This heating coil 1
For example, it is composed of two conducting wires a and b such as a litz wire.
More specifically, two conductors a and b having both ends are arranged in a flat shape on the same plane, and in this state, they are closely wound together in a spiral shape, and the ends of these two litz wires a and b are Are electrically connected by terminals 11 and 12. In the heating coil 1 having such a configuration, the two conductive wires are the terminals 11 and 1.
Since it is equivalent to the case where the heating coil 1 is electrically connected in parallel, the inductance and the equivalent resistance value of the heating coil 1 are smaller than in the case where one conductor wire is spirally wound with the same diameter.
In other words, if the same inductance or equivalent resistance value is used, a heating coil having a larger diameter can be formed.

FIG. 2 is a side view of an essential part of an electromagnetic cooker 10 using the heating coil 1. This electromagnetic cooker 1
Reference numeral 0 includes a heating coil 1, a top plate 3 made of a non-magnetic material, and a high frequency power supply unit 4 for supplying high frequency power to the heating coil 1. On the top of the top plate 3, a large cooking container 2 which is an object to be heated is placed. The high-frequency power supply unit 4 includes, for example, an inverter circuit including a half-bridge type semiconductor switching circuit, the input side is connected to a commercial power supply (not shown), and the pair of output terminals is the heating coil 1 shown in FIG. It is electrically connected to the terminals 11 and 12. In the electromagnetic cooker 10 having the above-described configuration, when high frequency power is supplied to the heating coil 1 from the inverter circuit of the high frequency power supply unit 4, a high frequency magnetic field is generated in the heating coil 1, which causes the cooking container 2 on the top plate 3 to be induction-heated. To be done.

Here, as an example, when the bottom of the cooking vessel 2 is about 40 cm and the coil diameter of the heating coil is about 36 mm, in the conventional heating coil formed by spirally winding one litz wire. , Its inductance is about 130 μH
Becomes The equivalent resistance value when the cooking container 2 is placed on the top plate of the electromagnetic cooker configured by the conventional heating coil is several Ω when the power supply frequency is 25 kHz. Therefore, when the inverter circuit of the high frequency power supply unit 4 has a half-bridge type semiconductor switching circuit, a mismatch occurs and almost no output is obtained.

On the other hand, the inductance of the heating coil 1 of this embodiment having the above coil diameter is about 60 μH, and the equivalent resistance value when the cooking vessel 2 is placed on the top plate 3 is the power frequency. Is about 25 kHz, it is about 1 to 2Ω. Therefore, even if the half bridge type semiconductor switching circuit is used for the inverter circuit of the high frequency power supply unit 4, an appropriate load condition can be obtained.

The distance between the upper surface of the top plate and the heating coil under the above conditions needs to be about 40 mm or more when the conventional heating coil is used, but when the heating coil of this embodiment is used, Since the equivalent resistance value becomes small, it can be narrowed to 15 mm or less, and the electromagnetic cooker body can be made thin. Further, since the distance between the top plate 3 and the heating coil 1 can be narrowed as described above, the efficiency of induction heating of the cooking container 2 is also increased. Furthermore, the voltage applied to the heating coil in the conventional electromagnetic cooker is about 1.0
The same heating effect as when it is set to 00 V can be achieved with the electromagnetic cooker 10 of the present embodiment at a voltage value of about 500 V, and accordingly, the power capacity of the tank capacitor inside the power supply can be reduced to about half. The cost can be reduced.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and various design changes can be made without departing from the scope of the invention. For example, the heating coil of this embodiment has two conducting wires a,
Although b is wound closely and both ends thereof are electrically connected, three or more conducting wires may be electrically connected in parallel. In addition, in the present embodiment, an example in which the inverter circuit included in the power supply of the electromagnetic cooker 10 is provided with a half-bridge type semiconductor switching circuit has been described as an example in which impedance matching is difficult. So, not necessarily limited to this example,
The one using the inverter circuit of the full bridge system or another system can be similarly used.

[0018]

As is apparent from the above description, according to the heating coil for an electromagnetic cooker of the present invention, the equivalent resistance value seen from both ends of each conducting wire is significantly reduced as compared with the conventional heating coil having the same diameter. Has the effect of Therefore, coil loss when high frequency power is supplied to both ends is suppressed. In addition, it becomes easy to form a spiral shape, especially near the center.

Further, according to the electromagnetic cooker of the present invention, the efficiency of induction heating of the object to be heated by the heating coil is higher than that of the conventional electromagnetic cooker, so that the power supply voltage can be suppressed to a low level and the end portion of the heating coil can be reduced. Insulation failure at the point of is also prevented, which has the effect of improving safety. Moreover, even when using an inverter circuit (power supply) equipped with a half-bridge type semiconductor switching circuit to obtain high output, it is not necessary to raise the height of the electromagnetic cooker body more than necessary, Since it is possible to reduce the power capacity of the tank capacitor for high frequency generation provided in the above, it is advantageous in terms of cost.

[Brief description of drawings]

FIG. 1 is a plan view of a heating coil for an electromagnetic cooker according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a main part of the electromagnetic cooker of the present embodiment configured by using the heating coil for the electromagnetic cooker of FIG.

[Explanation of symbols]

 1 heating coil 2 cooking container 3 top plate 4 high frequency power supply unit 10 electromagnetic cooker

Claims (3)

[Claims] 1. A plurality of conductors having both ends are arranged on the same plane and wound in a spiral shape, and one end of each conductor and the other end thereof are electrically connected. A heating coil for an electromagnetic cooker. 2. An inverter circuit having a pair of output terminals, and a heating coil that receives electric power from the output terminals of the inverter circuit to induction-heat an object to be heated, wherein the heating coil is the object to be heated. An electromagnetic cooker characterized in that a plurality of conducting wires are arranged in a plane parallel to a heating portion of an object and are spirally wound, and both ends of each conducting wire are connected in parallel to the output terminal. 3. The electromagnetic cooker according to claim 2, wherein the inverter circuit is an inverter circuit including a half-bridge type semiconductor switching circuit.