JPS5949187A - Electromagnetic induction heating system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention uses a high frequency magnetic field to
The present invention relates to an electromagnetic induction heating method for an electromagnetic induction cooker that cooks food in a cooking pot by induction heating a cooking pot.

[Technical background of the invention]

In general, an electromagnetic induction heating cooker generates a high-frequency magnetic field with a frequency of 20 kHz from the heating coil by supplying a high-frequency current from an inverter circuit to the heating coil, and transmits it to the 8 yen buried pot which is the load. The cooking pot is heated by induction.

[Problems with background technology]

However, such an electric induction cooker has the drawback that only an iron cooking pot can be used, and an aluminum cooking pot cannot be used.

In other words, when an aluminum cooking pot is used, an excessively high curvature flows through the heating coil. 1.4 A protection circuit is adopted to prevent the implementation of the principles.

[Purpose of the invention]

This invention was made in view of the above-mentioned circumstances;
The object of the present invention is to provide a magnetic induction heating system that enables the use of a pot.

[Requires invention]

This invention uses a one-parameter magnetic field with a frequency of 50 kHz or more.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

In Fig. 1, 1 is an AC source, and this Iq iMi
A fan motor 3 for cooling the transistor and a primary coil 4a of a transformer are connected to the transistor 1 via power switches 2, 2, respectively. Furthermore, a DC power supply circuit 5 is connected to the j7 source 1 via the power switch 2.2. This DC power supply circuit 5 includes a diode bridge rectifier bit circuit 6, a chiroku coil 7, and a flat capacitor 8.
Consists of. Therefore, the output terminals P and N of the DC power supply circuit 5
An inverter circuit 10 is connected between them. This inverter circuit 10 employs a so-called 5EEP circuit, and is an NPN
It consists of 11 and 12 type transistors connected in series.
As each of the transistors, a pieborad 2 insulator capable of switching at a frequency of about 100 kHz is used. A heating coil 13 is connected between the interconnection point of the transistors 11 and 12 in the inverter circuit 10 and the terminal N. A series resonant circuit between the content 14 and the content 14 is connected. -The force 15 is the drive control circuit and is obtained by the secondary coil 4b of the transformer? The lj pressure is the operating 1L pressure, and the transistor 1 in the inverter circuit 10 has an operating voltage of 1L.

12 is turned on and off to supply high frequency current to the heating coil 13. In this way, the heating coil 13
from about 50 kHz, for example about IQ OkIl
A high frequency liG field with a frequency of z is emitted. This high frequency (magnetic field) of about 100 kHz is applied to the a circumference of the aluminum plate set near the heating coil 3.

It is adopted as a line. In addition, the heating coil 13 has a configuration in which multiple stages, for example three stages, are stacked, and the number of turns is twice that of the conventional one.Furthermore, the resonance capacitor 14 has a high A pressure-resistant model was adopted.

Therefore, Takaoka's pot 2o can last a long time.

The wave magnetic field produces an eddy current, and the resulting eddy current J
jt generates self-heat and heats the food inside.

Here, J! l calamity 2
Whether it is possible to use 0 will be discussed below.

First of all, when cooking, make sure to use the
The pot has a certain resistance value, which makes the key 1! ) It is a necessary condition that the input to one pot can be kept constant.

In other words, conventional cookers use high-frequency energy with a frequency of about 20 kHz, and a
The use of a hot pot is used, but this costs about 20k.
Cook at Hz frequency! M! This is because a skin effect occurs on the steel plate 'M. This skin effect is caused by the fact that the area where the current flows is concentrated in a certain range (the broken line area in the figure) from the surface of the iron plate 31 (the side to which the 1+G flux φ is applied), as shown by the broken line in FIG. When this happens, the resistance value of the iron plate 3 will be constant regardless of the thickness K.
Is l12 even more strengthened? The bundle φ begins to permeate (leak). Note that the iron plate 3 in Fig. 2(b) shows a state in which no skin effect occurs, and since the 't:j flow flows in all parts, the resistance value is constant depending on the thickness'! 9
, further given (, the μ flux φ becomes transparent (both companies).

For aluminum pots, the following methods are available to keep the resistance constant.

(1) A method of shaping the thickness of the aluminum plate of the cooking pot into a thin shape.

Although this arrangement allows the frequency of the inverter circuit to be low, it has the disadvantage that cooking M is limited. Also,
There is also the disadvantage that the magnetic flux will carve the cooker.
It's not realistic.

(2) A method of stopping the frequency of the inverter circuit, taking into account that the skin effect appears on aluminum plates when the frequency of the high-frequency magnetic field is 50 kHz or more.

In this case, there is no need to limit cooking f1F6, and the magnetic flux is iiA! On the one hand, there is a problem in that it does not transmit 11.4, but on the other hand, there is a problem in that the frequency of the inverter circuit must be increased. Well, the inverter circuit is
Normally, a transistor is used as a switching element, and its switching speed is limited.
I... - Seriously, for example, Bahia 1'? -Switching at a frequency of approximately 100 kHz is possible for the power MO3/1i'ET transistor.
In this case, switching at frequencies from 1200 kHz to 300 kHz is possible, and is it possible to fully realize the difference in adopting these transistors in the inverter circuit?Ii
It is J-Noh.

According to experiments, the image frequency 1. ? It was found that the optimum skin effect for the cooking pot occurs when the field frequency is approximately 100 klIz and the thickness of the aluminum plate of the 45-circumferential cooking pot, Q, is 5 mm or more.

Therefore, as mentioned above, in this case, approximately 1.
By using a high frequency 1 commercial world with a frequency of 0.00 kHz, this made it possible to use an aluminum 111 cooking pot for one year. .

However, this alone will cause various problems in the soil where the fruit is cooked.

In other words, the heating coil can be regarded as one transformer, and the resistance between the primary side resistance of the heating coil side and the secondary side equivalent resistance of the 5A buried pot 111]. has a major problem in terms of heating efficiency.

Here, i: "J 4i 4i
To calculate the L resistance, create the situation shown in Figure 3. As shown in Figure 3, a metal of thickness d (iron or aluminum forming the entire cooking pot) is placed on the surface of the water,
A coil 13a is arranged on the ground at a distance from rj. This coil 1.9a is made by winding one turn of copper with a radius of ψ and is considered to correspond to a part of the heating coil 13.

However, bottom) i1'! Using Nu 5U in the table,
Metal side secondary (Ill q + 7-valent LW 4)'c R
and the equivalent inductance are expressed by the following formula.

ξ = □ No divination J In this case, 1; (ξ) is the 1st x 0 perfect elliptic integral, K (
ξ) 1 2nd god complete agony 1”J 7/< min, f←j sieve frequency I 1 frequency of the initial world, It2 is the magnetic flux of the metal, μ.'IIJ
'b'A"E's chance of 1 offspring, σ2" of gold &bow;, q +
, -1j ratio, δ is the skin depth.

Therefore, the metal is an iron plate, -so! Thickness of iron plate J-Q
, 5 MIL, upper layer II (iB field frequency f=2
0kHz, 1-turn coil 13a (D-winding Sakae E')
a = l O/, 7++, radius ψ of coil #lIl wire
= 05 points, distance between iron plate and coil t411 = 1 cn
+, the secondary 41+114+p curve Ja resistance is 5 mΩ in R.

Is it 51 metal or aluminum plate, and the aluminum plate's 11 height d=Q, 5a? Frequency f of J high frequency foundation field =
100 kI (z, the winding radius a-10 m of the one-turn coil 13a, the radius ψ of the coil conduction A' spring = 0.5
1 Distance between the aluminum plate and the coil 1'j1M h =
When 1 cm, the secondary side equivalent is 41 [, anti-RFi,, 0.5 mΩ in R.

In other words, the equivalent resistance R on the secondary side when the cooking pot is made of aluminum is iil・!I When the sinking pot is made of iron, although it varies to some extent depending on the sinking rate and transmission rate (1!) If the value is about 1/10 higher than 9, the coil loss will increase, resulting in a significantly lower heating efficiency.

By the way, the deviation considering the actual number of turns (number of turns) of the heating coil 13 is calculated by the quadratic 1111 etc. ll1li resistance RIri f
The calculation results are as shown in Figure M4.

That is, if the copper pot is 20 aluminum, the thickness of the aluminum is 0.5M or more, and the R11 wave number of the high frequency magnetic field is 100 kHz, R=0.14Ω is approximately constant.

On the other hand, the resistance value of the coil conductor of the heating coil J3 is actually measured to be 0295Ω due to the skin effect.Furthermore, in addition to the heating coil 13, there are other resistances such as 1Wonostar, and because these resistances are added, the primary side Resistance R' is 0.4-050
It will be about.

Therefore, under such a situation where the primary resistance is much larger than the secondary equivalent resistance, the heating efficiency is extremely low.
<becoming-f'').

To deal with this problem, the present invention has been developed by bundling a large number of thin copper wires into one conducting wire, and employing this as the winding wire of the heating coil No. 3, so that the resistance of the heating coil 13 is (Skin resistance) decreased R1, which also decreased primary elevation resistance.

However, this alone cannot sufficiently suppress the decrease in heating efficiency since it is obvious that there is a resistor other than the heating coil 13. Therefore, in this invention, the heating coil 1
30, the number of wires was forcibly increased, and the secondary side equivalent resistance was forcibly increased.

In this case, even if the number of turns of the coil 130 is increased by the coil 1, the size of the heating coil 13 will be adjusted to I8! There is a limit depending on the size of the pot, etc. Therefore, the heating coil 13 is stacked in multiple stages, for example, 13 stages.By doing this, the secondary side equivalent 1't: Jj'+: R becomes: quadratic (+1!1 equivalent υ(anti-R1
71 Since it is proportional to the square of the number of turns of the heating coil 13, R=O, 14ΩX3−1.260.

In this way, the resistance of the heating coil 3 is reduced and the resistance of the heating coil 2 is reduced.
Since the next-side equivalent resistance R is increased, a decrease in heating efficiency can be sufficiently suppressed.

However, since the heating coil 13 is made of 31'a Ji+), it is necessary to perform the following process IKt. That is, when the inductance L when the heating coil 13 is in one stage (same as in the case of ilC) is calculated, L=14.4μ11. The inductance L is also proportional to the square of the winding, so in three stages, L = 14.4 x 3 stages 130 μH.

Therefore, in order to resonate at a frequency of 100kHz, the capacitance C of the resonance capacitor 14 needs to be as follows.

In addition, in such a case, the resistors other than the heating coil 13 should be set to 0.
．． 50 and deviation C:, P=1.05 kW.

η=72%, V (4m"" 405 (l V, 1m = 48.8A.

In this case, Pt, l is the power saving, η is the efficiency, ■o□V is the maximum both openings of the capacitor 14: 11i city 1Lhi, IIn is the capacitor 14 /+Ir,; b)

In addition, in Jin's invention, the confine 14 was designed for high voltage resistance of several kV.

In addition, although a high-frequency 1111 field with a frequency of about 100 kHz was used in the embodiment described above, it is not necessarily determined by this, and for the reasons mentioned above (in the case of aluminum, the skin is affected by The effect is visible)
Therefore, a high frequency magnetic field of at least about 50 kHz or more can be similarly implemented.

Map (9) A series resonant circuit was constructed with the heating coil 13 and the capacitor 14, but as shown in the ε+S5 diagram,
71 heating coils 131, 132 and capacitor 14
A parallel resonant circuit may be configured by Furthermore, as shown in Figure n6, a single-end type injector circuit 10 may be used. Moreover, it is also possible to use a T108-FET as the Tosinnostar used in the inverter circuit 10.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an electromagnetic induction heating method that allows the use of an aluminum cooking pot.

[Brief explanation of drawings]

1 shows an embodiment of the present invention, FIG. 1 shows +i+ of the control circuit, FIG. 2 shows (a) (b) v, x
A diagram to explain the skin effect that occurs in all sets of 'aura logic 1j' 7M, F+43 diagram is secondary side etc. Jiff tj
! , 1'2'l to derive the division formula for the resistance, 4th
Figure e is a diagram showing the correspondence relationship between the frequency of the high-frequency magnetic field and the secondary side equivalent resistance, and Figures 5 and 6 each show a 1θ variation of the shape of Figure 1. Yes. 10... Inverter circuit, 13... Heating coil, 1
4... Capacitor, 15..., 1, ν1<suspension control circuit, 20... Cooking pot (load). Out: r4 agents BenjA1 Sat Suzu Jiang Wu Pig Figure 3 Figure 4 Temple, L I Momme (ni Hid) □ Figure 5 riS6 Figure II? (7'u I158.1)・1 Mr. Kazuo Wakasugi, Commissioner of the Japan Patent Office■, Indication of small matter l)￥￥57-159327-shi) 2. Name of the invention Electromagnetic heating system 3. Relationship with the case of the person making the amendment Patent 1-11 Applicant (307) Tokyo Shibaura Electric Co., Ltd., Ki Co., Ltd. 4, Agent 6 Specification subject to amendment ++ ``r; ) on page 10, line 3 of the specification" [164d/δruO

Claims (1)

[Claims] An electromagnetic induction heating method that uses a high frequency magnetic field to heat a load by conduction, using a high frequency magnetic field with a frequency of 50 k) or more.