JPH05251172A - Electromagnetic induction heating cooker - Google Patents

Abstract

PURPOSE:To heat various cooking pans having different magnetic permeability and specific resistance. CONSTITUTION:A high frequency inverter circuit 16 is structured with full-bridge circuit system, which consists of two pairs of conventional half-bridge circuit systems. The full-bridge circuit system of this high frequency inverter circuit 16 is can be functioned as a half-bridge circuit system. Furthermore, a pan material discriminating circuit 8 for performing the discrimination whether a cooking pan is made of magnetic material or non-magnetic material is provided, and the high frequency inverter circuit 16 can be switched to the full- bridge circuit system and a half-bridge circuit system on the basis of a result of the discrimination.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic induction heating cooker, particularly by improving a high frequency inverter circuit system.
The present invention relates to a heating cooker capable of heating both magnetic and non-magnetic cooking pots having different magnetic permeability.

[0002]

2. Description of the Related Art Generally, when both a magnetic pot and a non-magnetic pot having different magnetic permeability and specific resistance are heated by a single heating coil and a single high-frequency inverter circuit, the magnetic pot should satisfy the rated output. If it is designed, the non-magnetic pot cannot be driven within the rating of the high-frequency inverter circuit, and conversely if the non-magnetic pot is designed to match the output, the magnetic pot will not be able to obtain output.

Therefore, in the conventional electromagnetic induction heating cooker as disclosed in Japanese Patent Laid-Open No. 2-3008, as shown in FIG. 5, two kinds of heating coils are switched or heating is performed according to the material of the cooking pot. A method is disclosed in which a tap is provided in the middle of a coil and the connection with a high frequency inverter circuit is switched to heat.

In FIG. 5, 1 is a commercial AC power supply, 2 is a rectifier circuit, 3 is a smoothing yoke, 4 is a smoothing capacitor, 16
Are transistors 5a and 5b and diodes 6a and 6b
A high-frequency inverter circuit of a half-bridge circuit type composed of 7;
Inverter drive circuit for switching a and 5b, 8 is a pan material discriminating circuit for discriminating a magnetic pot and a non-magnetic pot from the current value detected by the current transformer 13, and 10 is a value of the output setting volume 15 and a current transformer A control circuit for controlling the inverter drive circuit 7 so that the magnitudes of the power supply currents detected from 14 become equal, 11a and 11b are heating coils, and 12 is a resonance capacitor.

In the above electromagnetic induction heating cooker, the commercial AC power source 1 is converted into direct current through the rectifier circuit 2 and the smoothing capacitor 4, and further converted into high frequency current by the high frequency inverter circuit 16, which is then heated by the heating coil 11a. , 11b
When the high frequency magnetic field generated in the heating coils 11a and 11b is applied to the cooking pot placed on the heating coils 11a and 11b, the taps 21a and 21b of the switching relay 17 are changed according to the determination result of the pot material determination circuit 8. ON / OFF respectively
Then, by switching the connection with the inverter circuit 16, the heating coils 11a and 11b are used properly according to the material of the pot.

[0006]

[Prior Art] However, in order to generate a high frequency magnetic field from the heating coil, it is necessary to flow a large current of 50 to 60 A through the heating coil. Further, the heating coil and the resonance capacitor 12 constitute a resonance circuit, and a resonance voltage of several kV is generated at both ends of the heating coil.

For this reason, in the case of the method of switching the heating coil as shown in FIG. 5 or the method of heating by switching the intermediate tap, if switching is performed by the switch 17 such as a relay, the above-mentioned large current and high voltage portions are switched. A switching device 17 that satisfies this spec is required.
The shape is large and the cost is high. Also, two types of heating coils and intermediate taps are required, which complicates the design of the heating coil portion.

Therefore, the applicant of the present invention can heat either a magnetic or non-magnetic pot with a single heating coil, and does not require a switching relay of high voltage and large current specifications.
We provided an inexpensive cooking device (see Japanese Patent Application No. 3-5076).

As shown in FIG. 6, a high-frequency transformer is inserted between the high-frequency inverter circuit and the heating coil so that differences in permeability and specific resistance are matched by the high-frequency transformer and heating is performed by a single heating coil. Is. That is, FIG.
Instead of switching the heating coil as described above, taps 31a, 31 are provided to determine whether the high frequency transformer 18 is inserted between the high frequency inverter circuit 16 and the heating coil 11.
By switching ON / OFF of b and 31c respectively, the difference in the material of the pan is matched by the high frequency transformer.

[0010]

However, in the technique of the prior application in which the high frequency transformer 18 matches the differences in the magnetic permeability and the specific resistance to heat, it is not necessary to switch the heating coils, but the switching in the high frequency transformer section is not required. is necessary. In this case, there is no switching in the portion where the high voltage is generated as described above, but there is no change in that a large current flows. Therefore, as in the case of FIG. 5, the shape of the switch 17 is large and the cost is high.

Further, since the high frequency transformer 18 is inserted between the high frequency inverter circuit 16 and the heating coil 11, the heating efficiency of the electromagnetic induction heating cooker itself is lowered due to the loss in the high frequency transformer portion.

Further, since the high frequency transformer itself flows a large current, the winding becomes thick and the shape becomes large.

In view of the above, the present invention eliminates the need for a switching device such as a high withstand voltage / high current specification relay or a high frequency transformer.
An object of the present invention is to provide an electromagnetic induction heating cooker capable of heating a cooking pot having different magnetic permeability and specific resistance.

[0014]

As shown in FIGS. 1 and 2, a means for solving the problem according to the present invention is provided with a pan material discriminating circuit 8 for discriminating whether a cooking pot is a magnetic pot or a non-magnetic pot, and a high frequency The inverter circuit 16 is a full bridging circuit that also functions as a half bridging circuit, and a switching means 9 for switching the circuit system of the high frequency inverter circuit 16 between the full bridging circuit system and the half bridging circuit system according to the discrimination result of the pan material discrimination circuit 8. It is provided.

[0015]

In the above means for solving the problems, generally, when a magnetic pot and a non-magnetic pot are placed on the same heating coil 11, it is more difficult for a current to flow in the heating coil 11 in the magnetic pot than in the case where the non-magnetic pot is placed. Therefore, power consumption is reduced. This is the equivalent resistance R3 when the heating coil 11 and the pan are connected.
This is because the magnetic pot becomes larger (see FIG. 4), and if the output voltage of the high frequency inverter circuit 16 is the same, the magnetic pot becomes less likely to flow current.

From the above, the high frequency inverter circuit 1
If the output voltage of 6 is increased when using a magnetic pot, heating coil 1
A current can be made to flow through the device 1, and the power consumption can be made constant.

Therefore, the high-frequency inverter circuit 16 is switched between the full-bridge circuit system and the half-bridge circuit system to change the output voltage of the high-frequency inverter circuit 16. Then, the voltage applied to the heating coil 11 is twice as much as in the half-bridge method when the full-bridge method is used.

As described above, the circuit system of the high-frequency inverter circuit 16 is switched according to the result of the determination of the pot material determining circuit 8 so that either the magnetic or non-magnetic pot can be heated by the single heating coil 11. ..

[0019]

Embodiments of the electromagnetic induction heating cooker according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a commercial AC power supply, 2 is a rectifying circuit, 3 is a smoothing yoke, 4 is a smoothing capacitor, 16 is a full bridge circuit consisting of transistors 5a, 5b, 5c and 5d and diodes 6a, 6b, 6c and 6d. It is a high frequency inverter circuit.

Reference numeral 7 is an inverter drive circuit for switching each of the transistors 5a to 5d in the high frequency inverter circuit 16, and 8 is a pot material discriminating circuit for discriminating a magnetic pot and a non-magnetic pot from the current value detected by the current transformer 13. Is. Reference numeral 10 is a control circuit that controls the inverter drive circuit 7 so that the value of the output setting volume 15 and the magnitude of the power supply current detected by the current transformer 14 become equal. 1
Reference numeral 1 is a heating coil, and 12 is a resonance capacitor.

The high frequency inverter circuit 16 supplies a high frequency current to the heating coil 11 to generate a high frequency alternating magnetic field. As a result, an eddy current is generated in the cooking pot placed on the heating coil 11, and this eddy current is generated. Heats the cooking pot.

Switching means 9 for switching the circuit system of the high-frequency inverter circuit 16 between the full-bridge circuit system and the half-bridge circuit system according to the determination result of the pan material determination circuit 8.
Is provided.

The control circuit 10 controls the inverter drive circuit 7 to adjust the switching frequency so that the value of the output setting volume 15 and the magnitude of the power supply current detected by the current transformer 14 become equal. That is, when the power supply current is small, the switching frequency is brought close to the resonance frequency determined by the series resonance circuit of the heating coil 11 and the resonance capacitor 12. On the contrary, when the power supply current is large, the control is performed so as to increase the load impedance formed by the heating coil 11 and the resonance capacitor 12 to decrease the current by moving away from the resonance frequency.

Here, the power consumption P of the electromagnetic induction heating cooker
Is the output voltage V of the high frequency inverter circuit 16 and the equivalent resistance R3,

[0025]

[Equation 1]

It is represented by

When the cooking pot is placed on the heating coil 11 (the heating coil and the pot are magnetically coupled), the cooking pot is also considered to be an induction coil, so its equivalent circuit is as shown in FIG. become. In this figure, R1 is the resistance of the heating coil, L1 is the inductance of the heating coil, R2 is the resistance of the pot, L2 is the inductance of the pot, and M is the mutual inductance.

When this equivalent circuit is converted into an equivalent circuit viewed from the primary side, it becomes B in FIG. In this figure, R3 is an equivalent resistance when the heating coil and the pan are connected, and L3 is an equivalent inductance when the heating coil and the pan are connected. The equivalent resistance R3 of the coupling circuit between the heating coil and the pan in this case is

[0029]

[Equation 2]

It is represented by However, A = 1 / ω ² , ω =
2πf.

Here, the time constant τ of the pot is a value determined by the material of the pot, that is, the magnetic permeability and the specific resistance.

From the above, the equivalent resistance R3 is determined by the constants (resistance value, inductance value) of the heating coil and the material of the pot.

Usually, when placed on the same heating coil 11, the magnetic pan has a large equivalent resistance R3, and the non-magnetic pan has a small equivalent resistance R3. Therefore, in order to satisfy the rated power consumption with the non-magnetic pan, the resistance value R1 of the heating coil 11,
When the inductance value L1 is designed, the time constant of the pan in the magnetic pot becomes smaller, so that it becomes larger than the equivalent resistance R3 in the case of the non-magnetic pot, and as a result, the power consumption becomes smaller.

On the contrary, if the magnetic pot is designed to satisfy the rated power consumption, the equivalent resistance R3 will be small and the power consumption P will be large in the non-magnetic pot, but a high current will flow through the high frequency inverter circuit 16 within the rated range. It becomes impossible to drive in.

From the above, the power consumption P changes depending on the equivalent resistance R3 determined by the material of the pot. Therefore, if the value of the equivalent resistance R3 is quadrupled from the equation (1), the output voltage V of the high frequency inverter will be 2 By doubling, the power consumption P becomes constant.

On the contrary, if the value of the equivalent resistance R3 becomes 1/4,
It can be seen that the power consumption P becomes constant when the output voltage is halved.

If the heating coil constant and the driving frequency of the high frequency inverter circuit 16 are set under certain conditions, the ratio of the equivalent resistance R3 of the magnetic pot and the non-magnetic pot can be set to 4: 1.

From this, the output voltage of the high frequency inverter is set to 2 when heating the magnetic pot when heating the magnetic pot.
If the voltage is doubled, the power consumption P becomes constant and both the magnetic pot and the non-magnetic pot can be heated in the same manner.

Therefore, in the present embodiment, in order to switch the output voltage of the high frequency inverter circuit 16, the high frequency inverter circuit 16 is realized by switching between the full bridge circuit system and the half bridge circuit system.

Next, this switching method will be described. When the high frequency inverter circuit 16 is of a full bridge circuit type, it is configured as shown in A of FIG. When the half-bridge circuit system is adopted, the structure is as shown in B of FIG.

That is, as shown in FIG. 2A, when the high frequency inverter circuit 16 is made to function as a full bridge circuit system, the inverter switching means 9 causes the drive system in the inverter drive circuit 7 to change to the transistors 6a, 6d.
A driving unit 7a for driving the pair of transistors and a transistor 6b,
6c and a driving unit 7b that drives the pair. Then, when the pair of transistors 6a and 6d are turned on, the drive signal is given so that the other pair of transistors 6b and 6c are turned off. As a result, the heating coil 1
As shown in A of FIG. 3, a voltage of ± V is applied to No. 1.

When the high frequency inverter circuit 16 is made to function as a half-bridge circuit system, the transistor 6c is used.
Is controlled so that it is always turned off, and the transistor 6d
Is controlled to always turn on. When the transistors 6c and 6d are replaced with switches and the high frequency inverter circuit 16 of the full bridge type is rewritten, it becomes as shown in FIG. 2B. As a result, the transistors 6a and 6b become similar to the conventional half-bridge circuit type high frequency inverter circuit, and the heating coil 11 has the same structure as shown in FIG.
A voltage of + V will be applied. In FIG. 2B, 7c and 7d are transistors 6a and 6b, respectively.
The drive part which drives is shown.

From the above, in the case of the full-bridge circuit system, twice the voltage can be applied to the heating coil 11 as compared with the case of the half-bridge circuit system. As a result, both the magnetic pan and the non-magnetic pan can be heated similarly.

The present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention. For example, in the above embodiment, the ratio of the equivalent resistance R3 of the magnetic pot and the non-magnetic pot is set to 4: 1. However, even when the ratio is different, the output voltage of the high frequency inverter circuit is calculated based on the above equation (1). Can be determined and the power consumption can be made constant.

[0045]

As is apparent from the above description, according to the present invention, the high frequency inverter circuit portion is switched between the full bridging circuit system and the half bridging circuit system to heat the magnetic pan and the non-magnetic pan. As described above, heating can be performed with a single heating coil without switching the heating coil or providing an intermediate tap, and a switching device such as a relay is not necessary.

Therefore, the design of the heating coil can be simplified, and it is not necessary to use an expensive high withstand voltage and large current relay or the like in the switching portion, the cost can be reduced, and the volume of the high frequency inverter portion is small. can do.

Further, unlike the prior art, since a high frequency transformer is not required, it is possible to solve problems such as a decrease in heating efficiency, a cost increase, and an increase in weight due to the insertion of the high frequency transformer.

[Brief description of drawings]

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

FIG. 2 is a block diagram relating to a switching system of a high frequency inverter circuit according to the present invention, where A is a block diagram when functioning as a full-bridge circuit system, and B is a block diagram when functioning as a half-bridge circuit system.

FIG. 3 is an output voltage waveform diagram relating to the switching system of the high-frequency inverter circuit of the present invention, where A is a voltage waveform diagram applied to the heating coil when functioning as a full-bridge circuit system, and B is a case where it is functioning as a half-bridge circuit system. Waveform diagram of the heating coil

FIG. 4 is an equivalent circuit diagram of the heating coil and the pan, where A is an equivalent circuit when the cooking pan is placed on the heating coil (a state where the heating coil and the pan are magnetically coupled), and B is an equivalent circuit of A. Figure converted to an equivalent circuit viewed from the primary side

FIG. 5 is a block diagram of a conventional electromagnetic induction heating cooker.

FIG. 6 is a block diagram of an electromagnetic induction heating cooker according to the prior application.

[Explanation of symbols]

 1 Commercial AC Power Supply 2 Rectifier Circuit 3 Smoothing Chioke 4 Smoothing Capacitor 5a to 5d Transistor 6a to 6d Diode 7 Inverter Drive Circuit 8 Pot Material Discrimination Circuit 9 Switching Means 10 Control Circuit 11 Heating Coil 12 Resonant Capacitor 13, 14 Current Transformer 15 Output Setting volume 16 High frequency inverter circuit

Claims (1)

[Claims] 1. A commercial AC power source is converted into a direct current through a rectifier circuit, further converted into a high frequency current by a high frequency inverter circuit, and this is passed through a heating coil, and a high frequency alternating magnetic field generated from the heating coil is placed on the heating coil. In an electromagnetic induction heating cooker that heats a cooking pot by generating an eddy current by adding it to the cooked pot, a pot material determination circuit is provided to determine whether the cooking pot is a magnetic pot or a non-magnetic pot. The high-frequency inverter circuit has a full-bridge circuit that also functions as a half-bridge circuit, and switches the circuit system of the high-frequency inverter circuit between a full-bridge circuit system and a half-bridge circuit system according to the determination result of the pot material determination circuit. An electromagnetic induction heating cooker having a switching means.