JPH0357191A - High frequency heating device - Google Patents

Abstract

PURPOSE:To prevent the generation of corona between each wire, and to lengthen longevity of an electric wire by winding a winding that forms a pressure rise transformer almost in a line, so as to make voltage between each winding almost the same as the voltage applied to the winding divided by the number of windings. CONSTITUTION:A pressure rise transformer is composed of a primary winding 1, a bobbin 2 for the primary winding, a secondary winding 3, a ferrite core 4, and a gap 5. Since the primary winding 1 of the pressure rise transformer is wound in a line by the number of winding of approximately five turns, the voltage generated between wire 5 of the primary winding 1 is approximately 100V at a peak value. The potential difference generated between the wire of the primary winding 1 can thus be made lower than that generated between the wire of a primary winding of a conventional pressure rise transformer of the power source whose resonance frequency fr is approximately 20kHz. Insulation between each winding can be assured, and the generation of corona is prevented, and the longevity of the winding can be ensured thereby.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-frequency heating device for cooking food using dielectric heating, and particularly to a high-frequency heating device that is equipped with a frequency converter, a so-called inverter, as a power source of the high-frequency heating device. This paper concerns the power supply circuit for high-frequency heating equipment. BACKGROUND ART Below, a conventional technique will be explained with reference to the drawings.

FIG. 6 is a circuit diagram showing the circuit configuration of a power source of a conventional high-frequency heating device. In the same figure, 50Hz or 60Hz
A commercial power supply 12 is rectified by a diode bridge 13 and converted into a DC voltage. The DC voltage passes through a filter l4, an inductor l1, a capacitor l5, and a transistor 1.
Applied to 1. The inductor l and the capacitor 15 form a resonant circuit, and the resonant frequency f1 of the resonant circuit in actual operation is given by the following equation. 1 ” ” ”x2x JT7T ””” Here, Ll is the inductance of the inductor 1 of the resonant circuit, and C is the capacitance of the capacitor 5 of the resonant circuit. The transistor 1l has a resonant frequency 1 expressed by equation (1).
1, the resonant operation of the resonant circuit is maintained.

The inductor 1 of the resonant circuit also serves as the primary winding l of the step-up transformer l6. A voltage with a waveform as shown in Fig. 7 is generated in the primary winding l due to the resonant operation of the resonant circuit. The step-up transformer 16 boosts the voltage of the primary winding 1 and generates a high voltage in the secondary winding 3. The high voltage is converted into a DC high voltage by the voltage doubler rectifier circuit 17 and applied to the magnetron 18. Magnetron 1B generates microwaves,
The microwaves are irradiated onto the food inside the oven of the high-frequency heating device, dielectrically heating the food. Figure 8 shows a cross-sectional view of the structure of a conventional step-up transformer 16. A conventional step-up transformer 16 is flifed from a primary winding l, a secondary winding 3, a core 4 and a gap 9.

The primary winding 1 has about 25 turns, the secondary winding 3 has about 380 turns, the core 4 is made of ferrite, and a gap is provided below the primary winding l. 1
As mentioned above, the secondary winding 1 also serves as the inductor l of the resonant circuit, and therefore the inductance L of the primary winding 1
, determines the resonant frequency of the resonant circuit, as shown by the equation ( ]).

The inductance L1 of the primary winding l is determined by the number of turns, and the number of turns of the primary winding l is set to N. Then, it is given by the following formula.

LL = k (N+)" ... (2) where k is a proportional constant. The electric current flowing in the primary winding 1 (excitation t; Ur, is the magnetic flux Φ = I
+L+, a part of the magnetic east Φ interlinks with the secondary winding &93, and induces a high voltage in the secondary winding 3. The electromotive force E2 at this time is expressed by the following formula. E! ceN, r, Φ
・(3) However, N2 is the number of turns of secondary winding 3, f1
is the resonance frequency, and Φ is the magnetic flux interlinking with the secondary Sm3.

Problems to be Solved by the Invention Making the step-up transformer used for the power source of the high-frequency heating device smaller makes it possible to make the 1-ton source itself compact and lightweight.
Moreover, it is possible to reduce costs. In order to downsize a step-up transformer, a method is used to increase the resonant frequency of the resonant circuit. As the resonant frequency r is increased, the electromotive force E increases as shown in equation (3), so in order to maintain a constant electromotive force, the magnetic flux Φ should be reduced. If the magnetic flux Φ is reduced, the cross-sectional area of the core of the step-up transformer through which the magnetic flux passes can be reduced, and the core can be made smaller. Furthermore, in order to increase the resonant frequency, the inductance L1 may be reduced as shown in equation (1).

L, is the number of turns N1 of the primary S wire l as shown in equation (2)
Since it is proportional to the square of , you can reduce the number N. By increasing the resonant frequency in this way, the size of the core can be reduced and the number of turns of the primary winding 1 can be reduced, making it possible to make the step-up transformer smaller, lighter, and lower in cost. However, the resonant frequency f1 is 10
If the value is greater than 0kHz, the lth order t! &Il number of turns N,
As shown in Figure 9, it takes about 6 to 8 turns. In the figure, the primary winding 1 is wound in the order indicated by arrow 19. A voltage with a peak value of about 500V is generated in the primary wA1 as shown in FIG. Therefore, the ninth
As shown in the figure, for example, if the number of turns of the L-order winding tiill is 8 turns, approximately 62.5 (V) will be generated per turn. Therefore, a potential difference of about 312 (V) is generated between the electric wire 20 at the beginning of winding of the primary winding and the electric wire 2l in the second row. In a conventional step-up transformer as shown in Fig. 8, the primary t
The number of turns of one wire l is about 25 turns, so the primary winding l
Wire 22 at the beginning of winding and tIli in the second row! 23, only a potential difference of about 180 (V) occurs.

In other words, as shown in Figure 9, the resonance frequency is approximately 100k.
A step-up transformer used for a power supply with a frequency of Hz or higher generates nearly twice as much voltage between the lines of the primary winding as compared to a conventional step-up transformer used in a power supply with a resonant frequency of about 20k}fz (Figure 8). Therefore, there is a problem in that corona discharge occurs between the glands, and the life of the insulating film of the electric wire is significantly reduced.

In order to prevent corona discharge between wires, it is effective to thicken the insulation coating of the wire, but if the insulation coating of each wire is thickened, the primary winding will use approximately 150 strands of wire. Therefore, there was a problem that the size of the primary winding became large and expensive. iI! Means for Solving the Problems The present invention has been made to solve these conventional problems, and is an extremely effective means that can solve the conventional problems with a simple configuration. That is, a DC power source obtained by rectifying a battery or commercial power source, a frequency converter that converts the DC power source into a high frequency power source, and a step-up transformer that boosts the output of the frequency converter to drive the magnetron. This step-up transformer is equipped with multiple SW
A and a core made of a magnetic material such as ferrite, and some or all of the plurality of windings are wound approximately in a line. In addition, the windings wound in a row are arranged so that the area facing the other windings is large. Effects of the present invention The windings constituting the step-up transformer are wound in a substantially straight line, so that the line-to-line voltage of the windings is approximately 1/the number of turns of the voltage applied to the windings. By using a small number of turns, the potential difference generated between the wires of the winding can be reduced, preventing the generation of corona between the wires, ensuring the life of the wire, and increasing reliability.
In addition, there is no need to thicken the insulating film on the wire, so the cost does not increase. In addition, because it is a simple horizontal winding method that winds the wire almost in a row, there is no need to make major changes to the structure of the bobbin, which is the frame for winding the wire, so conventional production equipment such as winding machines can be used. This has the effect that it can be used as is. By winding the windings in approximately one row, when forced air cooling is performed using a fan, etc., the wind hits the entire winding, resulting in a very high cooling effect, and suppressing heat generation in the windings even at high frequencies of 100kHz or higher. It has this effect. In addition, by arranging the windings wound in a row so that the area facing other windings is large, the magnetic flux interlinking with other @ wires through the core can be reduced. This has the effect of making the core more compact. Embodiment The circuit configuration of the power source of the high-frequency heating device of the present invention is the same as that of the conventional example shown in FIG. 6, so a description thereof will be omitted. An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a sectional view showing the structure of a step-up transformer that is an embodiment of the present invention. In the same figure, the step-up transformer is 1
Secondary winding 1. Consists of a bobbin 2 for the primary winding, a secondary winding 3, a ferrite core 4, and a gap 5. The primary winding, III, is wound in a row with approximately 5 turns as shown in the figure. As described in the prior art, a voltage with a peak value of about 500 V is generated in the primary winding l, as shown in FIG. However, since the primary winding l of the step-up transformer according to the present invention is wound in a row with approximately 5 turns, the voltage generated between the lines 5 of the primary winding 1 in FIG. 1 has a peak value. It is about IOOV. Therefore, even in a step-up transformer used for a power supply with a resonant frequency f1 of 100 kHz or more, by winding the primary port wire l in a single row as described above, it is possible to It is possible to make the potential difference between the primary @ wires of a step-up transformer of a conventional power supply with a resonant frequency f7 of about 20 kHz lower than the potential difference that occurs between the lines, ensuring insulation between the windings and preventing corona generation. , the life of the winding can be guaranteed. FIG. 2 shows another embodiment of the present invention. This figure is a sectional view showing a configuration in which the primary winding l wound in a row is arranged horizontally so that the area 6 facing the secondary winding 3 is wide. In the figure, most of the magnetic flux generated by the primary winding l passes through the core 4, but some of the magnetic flux directly interlinks with the secondary winding 3. Therefore, as shown in the figure, by arranging the primary winding l wound in a row horizontally so that the area 6 facing the secondary winding 3 is wide, the primary winding l
Of the magnetic flux created by the coil, the amount of magnetic flux 8 that directly interlinks with the secondary winding 3 can be increased. Therefore, the magnetic flux 7 that passes through the core and interlinks with the secondary winding 3 can be reduced. As a method of reducing the magnetic flux 7 passing through the core, it is effective to position the gap 9 at the position of the primary cotton 1.

By taking such precautions, the magnetic flux 7 passing through the core can be reduced, so the cross-sectional area of the core can be reduced, and the core can be made smaller and lighter.

The diagram shown in FIG. 3 is also another embodiment of the present invention.

This figure shows the configuration of a step-up transformer in which the size of the gap 9 is made small, the magnetic resistance is made small, and the gap 9 is placed between the primary winding 1 and the secondary S wire 3. This is a cross-sectional view. As the frequency increases, the loss of wires increases due to the skin effect. For this reason, it is preferable that the amount of winding is small.

Therefore, if the configuration is as shown in the figure, the magnetic resistance of the step-up transformer can be reduced, so the number of turns of the primary winding I can be reduced and the necessary inductance can be obtained. Even if the number of turns of the primary winding l is reduced, insulation between the windings of the primary winding l can be ensured because the primary winding l is wound in a single row. Generally, the loss in the winding is divided into the loss due to the skin effect mentioned above and the loss due to the generation of eddy current etc. in the winding due to the magnetic flux leaking from the gap 9 (leakage magnetic flux) interlinking with the winding. Ru. Therefore, by arranging the gap 9 between the primary winding 1 and the secondary winding 3 as shown in the figure, the primary winding 1 and the secondary winding &! By moving the gear amplifier 9 away from both windings of l3, it is possible to reduce loss in the windings due to the influence of leakage magnetic flux in the gap 9. However, when the magnetic resistance of the core is reduced in this way, the magnetic coupling between the primary wire 1 and the secondary winding 3 becomes extremely strong. If the magnetic coupling is too strong, the loss in the transistors that perform switching operations to maintain the resonant operation of the resonant circuit tends to increase. Therefore, when using a step-up transformer with low magnetic resistance as shown in Fig. 3, an inductor is connected in series with the inductor 1 of the resonant circuit, which is the primary winding 1, as shown in the circuit configuration shown in Fig. 4. By inserting a transistor 10, it is possible to prevent an increase in the loss of the transistor l1. FIG. 5 is another embodiment of the present invention, and is a sectional view of a step-up transformer in which the primary SvA1 and the secondary winding 2 are wound in a line. As the resonant frequency] increases, the number of turns of the secondary winding 2, like the primary winding 1, decreases. Therefore, by winding the secondary winding 2 in a single row in the same way as the primary winding 1, insulation between the windings can be guaranteed.
The secondary S fastener 3 has an extremely small cross-sectional area but a large number of turns compared to the secondary winding l, so the primary winding l and the secondary winding 3 are each wound in a row, and the primary winding Secondary winding 3 on top of l
If we plan to rearrange the step-up transformer, the height of the step-up transformer will become very high, the magnetic path length of the core will become long, and the loss of the core will increase. Therefore, as shown in Figure 5, the primary winding 1
By winding the secondary winding vA3 and the secondary winding vA3 in an overlapping manner, the height of the step-up transformer can be lowered. Effects of the Invention As described above, the step-up transformer of the present invention has a structure in which the windings are wound approximately in a row, so that even with a small number of turns, insulation between the windings can be ensured, and reliability and The life of the S line is guaranteed. In particular, according to the present invention, since the winding wire is wound in a simple line, it can be realized without major changes to the conventional bobbin structure for winding the winding wire, making the conventional winding equipment effective. It has the advantage that it can be used for

[Brief explanation of drawings]

1, 2, 3, and 5 are cross-sectional views showing the structure of a step-up transformer installed in a high-frequency heating device according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view of an inverter circuit of the same high-frequency heating device Circuit diagram, Fig. 6 is an inverter circuit diagram of a conventional high-frequency heating device, Fig. 7 is a waveform diagram showing the voltage generated in the primary winding of a step-up transformer, and Fig. 8 is a cross section showing the configuration of a conventional step-up transformer. 9 are cross-sectional views showing the structure of a step-up transformer used at frequencies of 100 kHz or higher. 1...Primary winding, 3...Secondary winding, 4
...Core, l2...Commercial power supply, l6.
...Step-up transformer, l8... Magnetron.

Claims (2)

[Claims] (1) A DC power source obtained by rectifying a battery or commercial power source, a frequency converter that converts the DC power source into a high frequency power source, and a booster that boosts the output of the frequency converter to drive the magnetron. The step-up transformer is comprised of a plurality of windings and a core made of a magnetic material such as ferrite, and a part or all of the plurality of windings are wound substantially in a row, Above, a high-frequency heating device configured to set the line voltage to 1/the number of turns of the voltage applied to the windings. (2) The high-frequency heating device according to claim 1, wherein the windings are arranged in a line so that the area facing the other windings is large.