JPH01246782A - Electromagnetic cooking apparatus - Google Patents

Abstract

PURPOSE:To reduce the power loss and increase the output power by providing a plurality of heating coils, furnishing each coil with an inverter operating independently, and by installing a means to shelter magnetic effects of the heating coils upon one another, CONSTITUTION:Inverter control circuits 21A, 21B independently drive inverter circuits 3A, 3B which operate in compliance with control signals in analog amount given by an output control circuit 25, and a large output is obtained by heating coils 1A, 1B. In case control signals from the output control circuit 25 are directed only to the inverter circuit 2A, for ex., the inverter circuit 3A is driven to heat only the heating coil 1A, and the output is set to a low value. Between these heating coils 1A, 1B wound approx. in a sector on a coil base 11, a ferrite 13 of a magnetic shelter means is provided so that they are free from magnetic influence upon each other, and thus the drive is conducted without generation of any power loss.

Description

Detailed Description of the Invention [Objective of the Invention 1 (Field of Industrial Application) The present invention provides an electromagnetic cooker that heats an object by generating an eddy current in the object through the electromagnetic induction action of a heating coil. In particular, the present invention relates to an electromagnetic cooker that can obtain a large power output while reducing power loss.

(Prior art) Electromagnetic rXAl! l! The device is highly safe because it does not generate flames, and the top plate on which the heated object is placed is made of crystallized glass, so it is clean, and the heated object is heated directly, so it has high thermal efficiency. has. For this reason, conventional electromagnetic cookers use various circuit methods, such as a method in which the heating coil is driven by an inverter circuit using an E-class amplifier circuit, or a method in which the heating coil is driven by an inverter circuit using a so-called half-bridge circuit. An electromagnetic cooker using this has been developed. On the other hand, for example, Chinese cooking requires a large amount of heat, so it has been desired to increase the output of the electromagnetic cooker.

In an electromagnetic cooker that uses a method of driving a heating coil by an inverter circuit using an El & amplifier circuit, the heating coil and a semiconductor switching element are connected in series, and the heating coil and a resonance capacitor are connected in series. ing. By utilizing the series resonance between the heating coil and the resonance capacitor, the object to be heated is heated by electromagnetic induction between the heating coil and the object to be heated, such as a pot.

In such an electromagnetic cooker using a class E amplifier circuit, the output of the electromagnetic cooker is varied by changing the period during which the semiconductor switching element is turned on.

(Problem to be Solved by the Invention) However, in an electromagnetic cooker using an inverter circuit system using a class E amplifier circuit, if the ON time of the semiconductor switching element is set to be long in order to set the output power high, this semiconductor switching element The voltage between the collector and emitter increases in proportion to the length of the ON time, which may destroy the semiconductor switching element, making it difficult to obtain large output power.

In addition, in conventional electromagnetic cookers using an inverter circuit system using a so-called half-bridge circuit, in order to set the output power to a high level, it is necessary to supply a large current to the switching element, which slows down the switching speed of the switching element. The disadvantage was that losses would be large. Furthermore, conventional electromagnetic cookers using an inverter system using a half-bridge circuit have the disadvantage that the output power cannot be continuously changed from low power to high power.

The present invention has been made in view of the above, and provides an electromagnetic cooker that can continuously vary power output from low to high power output while reducing power loss, and can obtain large output power. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a plurality of heating coils that heat an object to be heated by electromagnetic induction, and a plurality of heating coils provided between the plurality of heating coils, The heating coil is configured to include a magnetic shielding means for partitioning off the mutual magnetic influence of the respective heating coils, and a plurality of inverter circuits provided for each of the plurality of heating coils and operating each heating coil independently.

(Function) In the present invention, a plurality of heating coils are provided, and a plurality of inverter circuits are provided corresponding to the heating coils so that each heating coil is operated independently. In addition, magnetic shielding means is provided between each heating coil to prevent each heating coil from being magnetically influenced by each other, and each heating coil is separated from magnetic influences from other heating coils. . Therefore, power loss is reduced and the object to be heated is effectively heated.

(Embodiment) An embodiment of the present invention will be described below in detail with reference to the drawings.

First, the overall structure of the electromagnetic cooker according to the present invention will be explained with reference to FIG.

As shown in FIG. 3, a plurality of heating coils 1A and 1B are provided. These heating coils are formed by winding a litz wire into a disk shape, for example.

Heating coils IA and IB are each inverter circuit 3A,
Connected to 3B.

Next, the circuit configuration of the heating coil 1A and the inverter circuit 3A will be explained with reference to FIG.

A heating coil 1A is connected to the terminal P1, and a resonance capacitor 5A is connected in series to the heating coil 1A. This resonance capacitor 5A has a diode 7A
and transistor 9A are connected in parallel. When a rectangular pulse signal is input to the base of the transistor 9A via the terminal P3, the transistor 9A repeats on and off operations based on the input pulse signal.

As a result, the heating coil 1A and the resonance capacitor 5A resonate in series, and a large resonant voltage and current are generated in the heating coil 1A.As a result, the magnetic flux generated from the heating coil 1A causes an electromagnetic induction effect on the object to be heated, such as steel. It generates an induced current and heats it up.

The circuit configuration described above is the same for the heating coil 1B and the inverter circuit 3B.

Next, referring to FIGS. 1 and 2, a plurality of heating coils IA
, the arrangement of the IB and its peripheral devices will be explained.

On the coil base 11, heating coils 1A and 1B wound into a substantially fan-shaped shape are arranged.

The fan-shaped heating coils 1A and 1B are set to form a substantially circular shape. Further, a ferrite 13 serving as a magnetic shielding means is provided between the heating coils 1A and 1B so that they are not magnetically influenced by each other.

Furthermore, a ferrite 15a and a ferrite 15b are provided on the lower side of the coil base 11. This ferrite 15a
is formed in a shape corresponding to the heating coil 1A, and
It is provided at a position corresponding to this heating coil 1A.

Similarly, the ferrite 15b is formed in a shape corresponding to the heating coil 1B, and is provided at a position corresponding to the heating coil 1B. These ferrites 15a and 15b reduce leakage of magnetic flux from the corresponding heating coils IA and IB, respectively, and also reduce the leakage of magnetic flux from the corresponding heating coils 1A and 1A.
, IB. The ferrite 13 and ferrites 15a and 15b described above are made of metal oxide magnetic material.

A top plate 17 made of crystallized glass or the like is provided above the coil base 11 on which the heating coils IA and IB are arranged. A pot 19 as an object to be heated is placed on top plate 17.

Referring again to FIG. 3, the inverter circuit 3A is connected to the inverter a+l+ control circuit 21A. Similarly, inverter circuit 3B is connected to inverter control circuit 21B. Further, each of the inverter control circuits 21A and 21B is connected to an output control circuit 25. These inverter control circuits 21A and 21B drive corresponding inverter circuits 3A and 3B based on analog control signals from the output w4 control circuit 25. The inverter control circuit 21A independently operates the inverter circuit 3A, and the inverter w4111 circuit 21B independently operates the inverter circuit 3B. Therefore, output control circuit 2
When the same analog quantity command signal is output from 5 to the inverter control circuits 21A and 21B, the inverter control circuits 21A and 21B operate the corresponding inverter circuits 3A and 3B, so that the l119 heats both of them. It is heated by the coils 1A and 1B, and a large output can be obtained.

For example, if the control signal from the output control circuit 25 is output only to the inverter control diameter 21A, and the control signal from the output 1jJtl11 circuit 25 is not sent to the inverter control circuit 21B,
Since only the heating coil 1A is driven and the inverter circuit 3B stops its operation, the pot 19 is heated only by the heating coil 1A. This allows the output of the electromagnetic cooker to be set to a low value.

The load detection circuit 23A inputs a signal corresponding to the current value flowing through the heating coil 1A, and also inputs a signal corresponding to the input current from a commercial power source (not shown), and by comparing both signals, the heating coil It is detected whether a pot 19, which is an object to be heated, is present above 1A. The load detection circuit 23A is connected to the inverter control circuit 21A, and when the load detection circuit 23A detects a no-load state, that is, there is no steel 19 above the heating coil 1A, it stops the operation of the inverter &lJ a11 circuit 21A. As a result, the heating operation by the heating coil 1A can be prohibited.

Similarly, the load detection circuit 23b inputs a signal corresponding to the current value flowing through the heating coil 1B, and also inputs a signal corresponding to the input current from the commercial power supply, and by comparing both signals, the heating coil 1B It is detected whether a pot 19 exists on top of the pot 19. The load detection circuit 23B is connected to the inverter 1. When the II control circuit 21B is connected and the load detection circuit 23b determines that 119 is not present on the heating coil 1B, the heating operation of the heating coil 1B is prohibited by stopping the operation of the inverter control circuit 21B. .

Next, the operation will be explained with reference to FIGS. 5 and 6.

The operation when the maximum output power is generated from the electromagnetic cooker as shown in period A in FIG. 6 will be described.

The output control circuit 25 sends out an analog control signal, and the period f! in FIG. The output control circuit 25 as shown in IA
A signal at level L1 is output from the inverter control circuit 21A to the inverter control circuit 21A, and a signal at level L1 is output to the inverter control circuit 1B.

First, the operation of the heating coil 1A will be explained. When the inverter control circuit 21A receives a signal of level L+ from the output full control circuit 25, it outputs a pulse signal with a pulse width corresponding to this level L1 to the inverter circuit 3A. In inverter circuit 3A, transistor 9AIf conducts only during a period corresponding to the pulse width of the pulse signal. When the transistor 9A is conductive for a period corresponding to the pulse width, a sawtooth collector current 1c flows to the collector of the transistor 9A via the heating coil 1A to drive the heating coil 1A, as shown in FIG. 5(A). When transistor 9A turns off after a period of time corresponding to the pulse width,
Since the driving current of the heating coil 1A is suddenly cut off, the heating coil 1A causes series resonance with the resonance capacitor 58,
As shown in FIG. 5(B), a large resonant voltage having a substantially sinusoidal shape, that is, a voltage yce between the collector and emitter of the transistor 9A is generated, and at the same time, a large resonant current is generated.

An eddy current is generated in the pot 19 due to the electromagnetic induction effect caused by the magnetic flux generated by this large resonant current, and the steel 19 is heated.

The heating operation described above is performed by the inverter control circuit 2113,
The same applies to the inverter circuit 3B and the heating coil 1B.

Next, the operation when the output power of the electromagnetic cooker is set to about half of the maximum value as shown in period B in FIG. 6 will be described.

The output control circuit 25 outputs an analog signal of level L2, which is approximately half the level of level 1, to the inverter control circuit 21A.
and 21B, respectively.

First, the operation on the side of the heating coil 1A will be described. When the inverter liI1m circuit 21A converts the level 2 analog signal, it outputs a pulse signal with a pulse width corresponding to the level of the input L2 to the inverter circuit 3A. That is, the inverter control circuit 21A sets the pulse width of the pulse signal short based on the analog signal at level L2. The inverter circuit 3A operates based on the pulse signal from the inverter control circuit 21A, and drives the heating coil 1A. As a result, the heating coil 1A heats the pot 19 with about half of the maximum output power.

The heating operation described above is the same in the inverter control circuit 21B, inverter circuit 3B, and heating coil 1B. That is, the heating coils 1A and 1B heat the pot 19 with approximately half of the maximum output power.

Next, the operation when the output power of the electromagnetic cooker is set to a low value as shown in period C in FIG. 6 will be described.

The output control circuit 25 prohibits sending analog signals to the inverter control circuit 21A, and
The analog signal at level L2 is output only to the No. 11 circuit 21B. Inverter circuit 3B drives heating coil 1B based on pulse signals from inverter control circuit 21B. As a result, the heating coil 1B heats the pot 19 with about half of the maximum output power, similarly to the period B described above.

In addition, since the inverter circuit 3A cannot obtain a pulse signal from the inverter control circuit 21A, the heating coil 1A
Prohibits the operation of Therefore, WA 19 is heated only by heating coil 1B. As a result, the electromagnetic cooker heats the steel 19 with an output power of about 1/4 of the maximum output.

As shown in period A or period B in FIG. 6, the output control circuit 2
When the heating coils 1A and 1B are driven simultaneously based on the control signal from the heating coils 1A and 1B, since the ferrite 13 is provided between the heating coils 1A and 1B, each heating coil is connected to the other heating coils. Each heating coil 1 is free from magnetic influence from the coil.
A and 1B reliably use steel 19 without causing power loss of 10
can be heated.

Further, a ferrite 15a is provided on the lower side of the heating coil 1A, and a ferrite 15b is provided on the lower side of the heating coil 1B.
are provided, and by interposing these ferrites 15a and 15b, impedance matching between the corresponding heating coils IA and IB is achieved, and each heating coil 1A and 1B efficiently heats the pot 19.

Next, a second embodiment of the present invention will be described with reference to FIG.

In the example shown in FIG. 7, the heating coil 1A is wound approximately circularly.
The heating coil 1B is arranged concentrically outside the
A feature is that a concentric ferrite 13a is provided between the heating coil 1A and the heating coil 1B.

In the example shown in FIG. 7, a heating coil 1A is arranged approximately at the center of the top plate 17, and a heating coil 1B is arranged outside this heating coil 1A. Therefore, the heating coil 1A provided on the inside and the heating coil 1B provided on the outside are arranged so as not to be magnetically influenced by each other due to the interposition of the ferrite 13a.

In the configuration example shown in FIG. 7, when setting the output power of the electromagnetic cooker to a low value, the heating coil 1
By activating only the heating coil A and stopping the operation of the heating coil 1B disposed outside, it is possible to efficiently heat the object to be heated, such as steel, which has a small area to be heated.

[Effects of the Invention] As explained above, according to the present invention, a plurality of heating coils are provided, an inverter circuit that operates independently for each of these heating coils is provided, and these heating coils are magnetically partitioned. Because of this, by driving both heating coils independently, it is possible to freely obtain a large power output to a small power output while preventing power loss, and it is possible to efficiently heat the object to be heated. .

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a main part of an electromagnetic cooker to which the present invention is applied, FIG. 2 is a cross-sectional explanatory view showing a cross section of a main part of an electromagnetic cooker to which the present invention is applied, and FIG. 4 is a block diagram showing the overall configuration of an electromagnetic cooker to which the present invention is applied, FIG. 4 is a circuit diagram showing the circuit configuration of the heating coil and inverter circuit in FIG. 3, and FIG. 5 is a diagram showing each part of FIG. 4. Signal waveform diagram, No. 6
The figure is an explanatory diagram showing the operation of FIG. 3, and FIG. 7 is a cross-sectional explanatory diagram showing a main part of another embodiment of the present invention. IA, IB... Heating coil 3A, 3B... Inverter circuit

Claims (1)

[Scope of Claims] A plurality of heating coils that heat an object to be heated by electromagnetic induction; a magnetic shielding means that is provided between the plurality of heating coils and partitions off the magnetic influence of each of the heating coils; and the plurality of heating coils. An electromagnetic cooking device characterized by having a plurality of inverter circuits provided for each heating coil and operating each heating coil independently.