KR101834910B1

KR101834910B1 - Induction Heating device by Using Resonant Inverter with Dual Frequency Output

Info

Publication number: KR101834910B1
Application number: KR1020150054653A
Authority: KR
Inventors: 성환호
Original assignee: 주식회사 피에스텍
Priority date: 2015-04-17
Filing date: 2015-04-17
Publication date: 2018-03-09
Also published as: KR20160124381A; WO2016167501A1

Abstract

An induction heating apparatus using a dual frequency resonance inverter is disclosed.
According to an embodiment of the present invention, there is provided a power supply apparatus for supplying power to an inductive load of an induction heating apparatus, the power supply apparatus comprising: an oscillation unit for selectively outputting AC power of a first frequency or a second frequency; And a resonance circuit unit configured to form a resonance circuit with the inductive load corresponding to a frequency of the alternating-current power output from the oscillation unit, wherein the first frequency is higher than the second frequency, and the resonance circuit unit includes: And operates as a series-parallel resonance circuit when AC power is applied, and operates as a series resonance circuit when AC power of the second frequency is applied.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating apparatus using a dual frequency resonance inverter,

This embodiment relates to an induction heating apparatus using a dual frequency resonance inverter.

The contents described in this section merely provide background information on the present embodiment and do not constitute the prior art.

Induction heating is a method of heating a conductor using electromagnetic induction phenomenon and is widely used for non-contact heating, soldering, welding, and heat treatment.

When the conductor is heated by the induction heating method, only the specific region can be rapidly heated, thereby reducing the material cost and the processing cost, and shortening the working time. Particularly, it is possible to control the depth of fineness and to obtain extremely shallow depth of fineness, so that precise processing is possible. Other advantages include automation of the process and less pollution.

The principle of induction heating is that when a high frequency power source is applied, curing is concentrated intensively on the high temperature region of the object to be heated. On the other hand, when a low-frequency power source is applied, curing is intensively performed on the gingival region of the object to be heated.

For this reason, induction heating using a resonant inverter outputting only a single frequency has made it difficult to fill out the contour, which must be uniformly hardened at the tip of the object to be heated. Therefore, by using an induction heating device capable of selectively outputting two or more frequencies, contour filling is performed by outputting a high frequency and outputting a low frequency.

However, even if an induction heating apparatus capable of selectively outputting two or more frequencies is used, there is a need to change the setting of the induction heating apparatus every time the frequency is changed. In order to reduce the inconvenience of changing the setting of the induction heating device every time the frequency is changed, a resonant inverter system capable of simultaneous dual frequency driving has been developed (Korean Patent Publication No. 10-1134419).

First, the present embodiment aims at quickly contouring a complex shape component in a single process by using a dual frequency resonance inverter.

Second, the present embodiment aims at reducing the manufacturing cost by using only one inverter in the dual frequency resonance type inverter.

Third, the present embodiment aims at improving the heating efficiency by removing the filter in the dual frequency resonance type inverter.

Fourth, the present embodiment aims at reducing the switching loss by removing the mechanical switch in the dual frequency resonance inverter.

According to an aspect of the present invention, there is provided a power supply unit for a vehicle, comprising: a power supply unit for supplying DC power; a full bridge inverter for converting DC power supplied from the power supply unit into AC power, And a resonance circuit connected to the full bridge inverter and the heating coil (Lc) to form a resonance frequency, wherein the induction heating device has two resonance frequencies And an induction heating apparatus characterized by the following.
According to another aspect of the present invention, there is provided a power supply apparatus for a vehicle, comprising: a power supply unit for supplying a DC power supply; a half bridge inverter for converting DC power supplied from the power supply unit into AC power and outputting the AC power; And a resonance circuit connected to the half bridge inverter and the heating coil (Lc) to form a resonance frequency, wherein the induction heating device has two resonance frequencies And an induction heating apparatus characterized by the following.

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According to the present embodiment, by using the dual frequency resonance inverter, it is possible not only to quickly outline the complicated shape components in a single process but also to reduce the manufacturing cost by using only one inverter since two inverters were used before .

According to this embodiment, the heating efficiency can be improved by removing the filter from the dual frequency resonance type inverter, and the switching loss can be reduced by removing the mechanical switch from the dual frequency resonance type inverter.

1 is a diagram illustrating a process of contouring a gear using a heating coil manufactured in accordance with the shape of a gear.
2 is a diagram illustrating a process of contouring a gear by applying a high frequency power source to a circular heating coil.
3 is a diagram illustrating a process of contouring a gear by applying a low frequency power to a circular heating coil.
FIG. 4 is a graph comparing a process of contouring a gear by applying a high frequency power to a circular heating coil, a process of contouring the gear by applying a high frequency power source, and a process of contouring the gear by applying a dual frequency power source FIG.
5 is a diagram showing a current waveform when a simultaneous dual frequency resonance inverter is connected to a heating coil.
6 is a circuit diagram illustrating a circuit of an induction heating apparatus using a simultaneous dual frequency resonance inverter.
7 is a diagram showing a current waveform when a time division duplex resonance type inverter is connected to a heating coil.
8 is a circuit diagram illustrating a circuit of an induction heating apparatus using a conventional time division duplex resonance inverter.
9 is a circuit diagram illustrating a series resonant circuit used for induction heating.
10 is a circuit diagram illustrating a series-parallel resonant circuit used for induction heating.
11 is a circuit diagram illustrating a full bridge circuit of an induction heating apparatus using a dual frequency resonance inverter according to the present embodiment.
12 is an example of a circuit in which the induction heating apparatus using the dual frequency resonance inverter according to the present embodiment is implemented as a half bridge.
13 is another example of a circuit in which an induction heating apparatus using a dual frequency resonance inverter according to the present embodiment is implemented as a half bridge.
FIG. 14 is an example of a circuit implemented as a half bridge circuit by replacing a switch in a pole in a full bridge circuit of FIG. 11 with a capacitor.
Fig. 15 shows an example of a circuit that performs impedance matching using three switches when two windings of N turns are on the primary side of the current transformer and one winding of M turns is on the secondary side of the current transformer.
Fig. 16 shows an example of a circuit that performs impedance matching using three switches when there are two N-turn windings and two L-turn windings on the primary side of the current transformer and one M-turn winding on the secondary side of the current transformer.
17 is an example of a circuit for adjusting the winding ratio in such a manner that a tap is provided on the primary side of the current transformer.
18 is another example of a circuit for adjusting the winding ratio in such a manner that a tap is provided on the primary side of the current transformer.

Hereinafter, some embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that, in the drawings, like reference numerals are used to denote like elements in the drawings, even if they are shown in different drawings. In the following description of the present invention, detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

In describing the constituent elements of this embodiment, first, second, i), ii), a), b) and the like can be used. Such a code is intended to distinguish the constituent element from other constituent elements, and the nature of the constituent element, the order or the order of the constituent element is not limited by the code. It is also to be understood that when an element is referred to as being "comprising" or "comprising", it should be understood that it does not exclude other elements unless explicitly stated to the contrary, do. Also, the terms 'module', 'module', and the like described in the specification mean units for processing at least one function or operation, and may be implemented as 'hardware' or 'software' or 'combination of hardware and software' have.

Hereinafter, the principle of induction heating will be briefly described.

If the coil is wound on the conductor and current is applied to the coil, the magnetic flux in the conductor changes. In this case, the electromotive force is induced in the opposite direction of the coil in order to prevent the change of the magnetic flux in the conductor. This is called the induced electromotive force (see Equation 1).

The current generated in the conductor by the induced electromotive force is called eddy current or eddy current. When an eddy current flows through a conductor, the conductor itself acts as a kind of resistance, causing eddy current loss. Soldering, welding, and heat treatment are performed while the conductor is heated by the thermal energy generated by eddy currents (see Equation 2).

In Equation (2), k _e is a proportional constant, f is the frequency of the power source, and B _max is the maximum magnetic flux density.

As shown in equation (2), the eddy current is proportional to the square of the frequency f and proportional to the square of the maximum magnetic flux density B _max . Thus, as the high frequency power is applied, the conductor is heated to a high temperature by high eddy currents.

When the conductor to be induction-heated is a magnetic body such as iron or nickel, hysteresis loss occurs as well as eddy currents due to the coil. When a coil is wound around a magnetic body and alternating current flows, the magnetic flux generated by the coil magnetizes the magnetic body. When the magnetic body is magnetized by the alternating current, the magnetic flux density changes along the hysteresis curve, and energy loss occurs in the process, which is called a hysteresis hand (see Equation 3).

In Equation (3),? Is a hysteresis constant, f is the frequency of the power source, B _max is the maximum magnetic flux density, and V is the volume.

As shown in Equation (3), the hysteresis hand is proportional to the frequency f and proportional to the maximum magnetic flux density _Bmax . Thus, as the high frequency power is applied, the conductor is heated to a high temperature by high eddy currents.

Comparing Equations 2 and 3, it can be seen that the eddy current hand is proportional to the square of the frequency f, but the hysteresis hand is proportional to the frequency f.

Hysteresis hands can be ignored compared to eddy current hands when the used frequency is higher than 10 KHz. In an induction heating apparatus using a resonant inverter that outputs a high frequency, hysteresis is negligible, and eddy currents are the main energy for heating the conductor.

The phenomenon that the eddy currents generated by the induced electromotive force concentrate on a portion near the surface of the conductor when the eddy current flows through the conductor is called a skin effect (see Equation 4).

In the equation (4), I _o is the current intensity at the conductor surface, I _x is the current intensity at the point x [cm] away from the conductor surface, P is the depth at which the current value decreases to 1 / (epsilon is a natural logarithm value).

As shown in equation (4), eddy currents are concentrated on the surface of the conductor due to the skin effect.

In induction heating systems using resonant inverters that output high frequencies, eddy currents are the main energy to heat the conductor. Eddy currents are concentrated on the conductor surface due to the skin effect. As a result, in the induction heating apparatus using a resonant inverter that outputs a high frequency, heat energy is concentrated on the surface of the conductor.

An induction heating device using a resonant inverter outputting a high frequency can be used for surface hardening heat treatment of gears.

Gears in which the cogs of the cogwheel move can not be used for cars, bikes, clocks, elevators, escalators, aircraft, ships, and heavy equipment. However, since the gears are engaged with each other, if the surface of the gear is not hardened by heat treatment, the gears are easily worn out and can not perform their functions.

Although the deformation of a material is very small, the degree of destruction of the material is called brittleness. The hardened region increases abrasion resistance, but the brittleness is increased and broken. Therefore, when the gear is heat-treated, the whole surface is not heat-treated but only the surface thereof is heat-treated so as to increase abrasion resistance and prevent breakage.

In this way, when the gear is subjected to the surface hardening heat treatment, the hardened layer is formed in parallel with the gear surface.

1 is a diagram illustrating a process of contouring a gear using a heating coil manufactured in accordance with the shape of a gear.

As shown in Fig. 1, in order to outline a component having a complex shape such as a gear at a single frequency, the heating coil of the induction heating apparatus must have a complicated shape corresponding to the shape of the gear. In this case, since the shape of the heating coil must be changed every time the shape of the gear changes, there is a problem that the heat treatment process is complicated and the cost is increased.

In the gears, hit the highest end of the teeth of the gear (齒高) and say between the teeth and the teeth of the gear.

Herein, in the present specification, 'high frequency' does not refer to a commonly used high frequency region band (HF) but refers to a frequency range of about 60 Hz to 1 MHz used for induction heating It means a relatively high frequency.

In this specification, 'low frequency' does not refer to the commonly used low frequency region band (LF), but refers to a relative frequency which is relatively high enough to form a hardened layer in the gingival region among the power frequency (approximately 60 Hz to 1 MHz) Which means low frequency.

2 is a diagram illustrating a process of contouring a gear by applying a high frequency power source to a circular heating coil.

As shown in Fig. 2, when a high-frequency power source is applied to the circular heating coil, eddy currents are concentrated in the fixation area. As a result, the hardened layer of the scalp area is formed thick, and the hardened layer of the dental area is formed thinly.

3 is a diagram illustrating a process of contouring a gear by applying a low frequency power to a circular heating coil.

As shown in Fig. 3, when a low-frequency power source is applied to the circular heating coil, eddy currents are concentrated in the gingival region. As a result, the hardened layer of the dental gland is formed thick, and the hardened layer of the hardened area is formed thin.

Referring to FIGS. 2 and 3, in the induction heating apparatus using a resonant inverter outputting a high frequency, it is known that the tooth root is mainly hardened, and in the induction heating apparatus using a resonant inverter outputting a low frequency, .

In order to form a uniform hardened layer on the teeth and dentures of gears, it is necessary to make the heating coil of the induction heating device according to the shape of the gear, or to make the heating coil of the induction heating device circular, A hardening part is cured by applying a high-frequency power to the tooth part, or iii) a heating coil of a induction heating device is made into a circular shape, and a high frequency power is applied to harden the hard part, Lt; / RTI >

Generally, complicated parts are outlined by alternately applying a low-frequency power source and a high-frequency power source, since it is inefficient to change the shape of the heating coil of the induction heating apparatus every time the shape of the material to be heated changes.

Specifically, in an induction heating apparatus using a resonance inverter that outputs a low frequency, a process is performed by curing a tooth region and then moving the material to be heated by a induction heating apparatus using a resonance inverter that outputs high frequency, It proceeds. If the process movement is slow, full heating may occur and the material to be heated may be deformed, so that the process movement must be quick and there is a problem such as a double investment of facilities.

In order to solve problems such as process difficulty and cost increase, a dual frequency resonance inverter has recently been used. The use of a dual frequency resonant inverter not only solves the problem of double investment in equipment but also eliminates the need to move parts to be hardened, which simplifies the process and prevents deformation of parts due to full heating.

FIG. 4 is a graph comparing a process of contouring a gear by applying a high frequency power to a circular heating coil, a process of contouring the gear by applying a high frequency power source, and a process of contouring the gear by applying a dual frequency power source FIG.

As shown in Fig. 4, when a high-frequency power source is applied to a circular heating coil, the fixation site is intensively cured (Fig. 4 (a)) and when the low-frequency power source is applied to the circular heating coil, the fixation site is intensively cured 4 (b)). It can be seen that when the dual-frequency power source is applied to the circular heating coil, the teeth area and the dorsal area are uniformly cured (Fig. 4 (c)).

There are two types of dual frequencies: Simultaneous Dual Frequency and Time Sharing Dual Frequency.

5 is a diagram showing a current waveform when a simultaneous dual frequency resonance inverter is connected to a heating coil.

As shown in FIG. 5, the simultaneous dual-frequency resonant inverter outputs a dual frequency having a high-frequency component and a low-frequency component at the same time by synthesizing a high-frequency output and a low-frequency output.

6 is a circuit diagram illustrating a circuit of an induction heating apparatus using a simultaneous dual frequency resonance inverter.

As shown in FIG. 6, the simultaneous dual frequency resonance inverter is composed of a low frequency inverter section and a high frequency inverter section.

The low frequency inverter unit receives the DC power from the converter and outputs the low frequency power. The low frequency power is supplied to the heating coil through the resonance circuit and the low pass filter.

The high frequency inverter section receives the direct current power from the converter and outputs the high frequency power. The high frequency power is supplied to the heating coil through the resonance circuit and the high pass filter.

Simultaneous dual-frequency resonant inverter provides simultaneous dual-frequency power supply to heating coil by combining low-frequency power and high-frequency power in heating coil. As an example of simultaneous dual-frequency resonant inverter, 'resonant inverter system (Korean Registered Patent Application No. 10-1134419).

7 is a diagram showing a current waveform when a time division duplex resonance type inverter is connected to a heating coil.

As shown in FIG. 7, the time division duplex resonant inverter alternately outputs the high frequency output and the low frequency output so that the high frequency component and the low frequency component are separated in time.

8 is a circuit diagram illustrating a circuit of an induction heating apparatus using a conventional time division duplex resonance inverter.

As shown in FIG. 8, the conventional time division duplex resonance type inverter supplies a time division duplex power source to the heating coil through a mechanical switch which alternately connects a capacitor outputting a high frequency and a capacitor outputting a low frequency.

Unlike a dual frequency resonant inverter using two inverters (Korean Patent Registration No. 10-1134419), a conventional time division duplex resonant inverter uses only one inverter. However, in the conventional time division duplex resonance type inverter, since the switch which alternately connects the capacitor outputting the high frequency and the capacitor outputting the low frequency is a mechanical switch using mechanical switching, loss due to spark or contact resistance occurs when the switch is opened .

The dual frequency resonance inverter according to the present embodiment configures a resonance circuit having a plurality of resonance frequencies so that it can output a time division duplex frequency without a mechanical switch that alternately connects a capacitor outputting a high frequency and a capacitor outputting a low frequency.

The use of the dual frequency resonance inverter according to the present embodiment makes it possible to operate the single inverter and thus to lower the production cost and to improve the heating efficiency by eliminating the filter and by eliminating the mechanical switch, Thereby reducing the switching loss caused by the switching operation.

Hereinafter, the dual frequency resonance inverter according to the present embodiment will be described in detail.

Since the induction heating load is an air-core transformer having a large electrical leakage inductance, even if a material having an electrical resistance characteristic is inserted, the reactive power (Q) is large, so that most of the supplied power has an ineffective component. In other words, although the inductance of the heating coil and the equivalent resistance of the heating material are connected in series, the induction heating circuit has a power factor between 0.03 and 0.08 because the resistance is very small compared to the inductance. Therefore, a resonant circuit in which capacitors are connected is necessary to cancel the reactive power due to the inductance and to make the apparent power of the power supply equal to the active power. When the resonance circuit is constituted, since the impedance becomes low at the resonance frequency, the effective power supplied to the equivalent resistance of the material to be heated becomes large.

For example, FIG. 9 is a circuit diagram illustrating a series resonance circuit used for induction heating, and FIG. 10 is a circuit diagram illustrating a series-parallel resonance circuit used for induction heating.

In summary, the inductive impedance due to the inductor component of the heating coil is often much larger than the equivalent resistance of the material to be heated, so a method of improving the power factor by adding a capacitor with capacitive impedance to the inverter is generally used .

11 is a circuit diagram illustrating a full bridge circuit of an induction heating apparatus using a dual frequency resonance inverter according to the present embodiment.

The full bridge circuit of the induction heating apparatus according to the present embodiment includes a power supply unit 110, an inverter unit 120, and a heating unit 130.

DC power is applied to the power supply unit 110. At this time, DC power may be directly applied to the power supply unit 110, or alternatively, the AC power may be converted to DC power via the converter and applied to the power supply unit 120.

The inverter unit 120 has a serial resonance capacitor of FIG. 9 added to the series-parallel resonance circuit of FIG. The inverter unit 120 includes a full bridge inverter composed of four switches and a resonance circuit that forms a resonance frequency when connected to the heating coil.

The heating unit 130 includes a heating coil. When a DC power source is applied to the power source unit 110 after inserting the material to be heated into the heating coil, the material to be heated is heated by induction heating.

9, the capacitor C _lf connected in series with the heating coil in the inverter unit 120 is connected to the capacitor C _l connected in parallel with the heating coil, _hf . That is, C _lf >> C _hf .

The induction heating apparatus according to this embodiment has two resonance points. Among them, a high resonance frequency is referred to as f _hr and a low resonance frequency is referred to as f _lr .

In the circuit of Fig. 11, L _s , C _hf and the equivalent inductance L _c of the heating coil form a high resonance frequency. The resonance frequency formed by L _s , C _hf and the equivalent inductance L _c of the heating coil is expressed by Equation (5).

In Equation (5), L _s // L _c denotes an inductance value when L _s and L _c are connected in parallel.
When the circuit of FIG. 11 is operated at a high resonance frequency (f _hr ), since C _lf >> C _hf , a voltage lower than C _hf is applied to C _lf . I.e. the impedance of C is lowered enough in the f _lf _hr operates as if there is no C _lf. When the circuit of FIG. 11 is operated at a high resonance frequency (f _hr ), the low-frequency resonance capacitor C _lf acts like a high pass filter. Therefore, there is no problem that the circuit of FIG. 11 operates at a high resonance frequency f _hr .
In the circuit of Fig. 11, L _s , C _lf and the equivalent inductance L _c of the heating coil form a low resonance frequency. The resonance frequency formed by the equivalent inductance L _c of L _s , C _lf and the heating coil is expressed by Equation (6).

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When the circuit of Fig. 11 is operated at a low resonance frequency (f _lr ), a resonance current having a high resonance frequency (f _hr ) superimposed on parasitic resonance flows.

The operation of the high resonance frequency (f _hr ) and the low resonance frequency (f _lr ) can be independently controlled. Therefore, when only the high frequency is operated, a single frequency of high frequency is outputted, and when the low frequency is operated only, a low frequency single frequency is outputted.

In addition, by operating the high frequency and the low frequency in a time division manner, the same effect as when the material to be heated is heated simultaneously at two frequencies can be obtained. That is, if the low-frequency operation and the high-frequency operation are repeated by dividing the number of times by a sufficiently large number of times as compared with the total heating time, the same effect as heating by two frequencies can be obtained simultaneously.

12 is an example of a circuit in which the induction heating apparatus using the dual frequency resonance inverter according to the present embodiment is implemented as a half bridge.

An example of the half bridge circuit of the induction heating apparatus according to the present embodiment shown in FIG. 12 includes a power supply unit 210, an inverter unit 220, and a heating unit 230.

DC power is applied to the power supply unit 210.

The inverter unit 220 is obtained by modifying the full bridge circuit of Fig. 11 into a half bridge circuit. The inverter unit 220 includes a half bridge inverter composed of two switches and a resonance circuit that forms a resonance frequency when connected to the heating coil.

Because of the half-bridge circuit, the number of switches has been reduced from four to two. Also, a capacitor C _lf connected in series with the heating coil in the resonance circuit is connected to the negative (-) terminal of the power supply unit 210. 12, the capacitor C _lf connected in series with the heating coil may be connected to the positive (+) terminal of the power supply unit 210.

The heating section 230 includes a heating coil. When a DC power source is applied to the power supply unit 210 after inserting a material to be heated into the heating coil, the material to be heated is heated by induction heating.

13 is another example of a circuit in which an induction heating apparatus using a dual frequency resonance inverter according to the present embodiment is implemented as a half bridge.

Another example of the half bridge circuit of the induction heating apparatus according to the present embodiment shown in FIG. 13 includes a power supply unit 310, an inverter unit 320, and a heating unit 330.

DC power is applied to the power supply unit 310.

The inverter unit 320 is a modification of the full bridge circuit of FIG. 11 to a half bridge circuit. The inverter unit 320 includes a half bridge inverter composed of two switches and a resonance circuit that forms a resonance frequency when connected to the heating coil.

Because of the half-bridge circuit, the number of switches has been reduced from four to two. In addition, the capacitor C _lf connected in series with the heating coil in the resonance circuit is divided into two and connected to the plus (+) terminal and the minus (-) terminal of the power supply unit 310, respectively.

The heating section 330 includes a heating coil. When a DC power source is applied to the power supply unit 310 after inserting the material to be heated into the heating coil, the material to be heated is heated by induction heating.

12 and 13, the full bridge circuit of FIG. 11 may be implemented by various types of half bridge circuits, as those skilled in the art will appreciate.

A half bridge circuit may be implemented by replacing the switch in the full bridge circuit with a capacitor having a sufficiently large capacity.

For example, FIG. 14 is an example of a circuit that is implemented to operate as a half bridge circuit by replacing a switch in a pole in a full bridge circuit of FIG. 11 with a capacitor.

In this embodiment, if the equivalent resistance or impedance of the high-frequency output and the low-frequency output are different, efficient heating may be difficult. In this case, impedance matching can be performed by using a current transformer to adjust the equivalent resistance or impedance of the input side differently from the high frequency and the low frequency, respectively, so that efficient heating can be achieved.

Fig. 15 shows an example of a circuit that performs impedance matching using three switches when two windings of N turns are on the primary side of the current transformer and one winding of M turns is on the secondary side of the current transformer.

In the circuit of Fig. 15, when SW1 and SW2 are turned OFF and SW3 is turned ON, the primary side of the current transformer is connected in series and becomes a 2N turn. As a result, the impedance of the secondary side appears to be (2N / M) ² times on the primary side. On the other hand, when SW1 and SW2 are turned on and SW3 is turned off, the primary side of the current transformer is connected in parallel and becomes N turns. As a result, the impedance of the secondary side appears to be (N / M) ² times on the primary side.
The impedance at the two matches is four times the difference.

Fig. 16 shows an example of a circuit that performs impedance matching using three switches when there are two N-turn windings and two L-turn windings on the primary side of the current transformer and one M-turn winding on the secondary side of the current transformer.

In the circuit of Fig. 16, when SW1 and SW2 are turned OFF and SW3 is turned ON, the primary side of the current transformer is serially connected to become 2 (N + L) turns. As a result, the impedance of the secondary side appears to be (2 (N + L) / M) ² times on the primary side. On the other hand, when SW1 and SW2 are turned on and SW3 is turned off, the primary side of the current transformer is connected in parallel and becomes N turns. As a result, the impedance of the secondary side appears to be (N / M) ² times on the primary side.
The impedance at both matches is 4 ((N + L) / N) ² times the difference.

In the examples of Figs. 15 and 16, the switch for impedance matching may be fabricated using a semiconductor, or a mechanical switch may be used. However, it is preferable to use a semiconductor switch for a fast switching speed.

In the impedance matching using the current transformer, the winding ratio can be adjusted by tapping the primary side of the current transformer. An example of a circuit for adjusting the winding ratio in such a manner as to tap the primary side of the current transformer is shown in Figs.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as defined by the appended claims. It will be possible.

The present invention is not intended to limit the scope of the present invention but to limit the scope of the present invention. The scope of protection of the present invention should be construed according to the claims, and all technical ideas considered to be equivalent or equivalent thereto should be construed as being included in the scope of the present invention.

110: power supply unit 120: inverter unit
130: heating section 210: power source section
220: inverter unit 230: heating unit
310: power supply unit 320: inverter unit
330:

Claims

A full bridge inverter for converting DC power supplied from the power supply unit to AC power and outputting the AC power, a heating coil Lc for heating the material to be heated by receiving AC power from the full bridge inverter, An induction heating device including a full bridge inverter and a resonance circuit connected to the heating coil Lc to form a resonance frequency and a current transformer connected to the heating coil Lc,
The induction heating apparatus has two resonant frequencies,
The full bridge inverter outputs a high resonance frequency (hereinafter referred to as a 'high frequency') and a low resonance frequency (hereinafter referred to as a 'low frequency') of the two resonance frequencies,
The current transformer performs impedance matching of the heating coil Lc by adjusting the impedance when the high frequency is output and the impedance when the low frequency is output,
Wherein the primary side of the current transformer includes a plurality of windings and a plurality of switches connected to the plurality of windings,
Wherein the current transformer adjusts the impedance when the high frequency is outputted and the impedance when the low frequency is outputted by individually turning on or off the plurality of switches.

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The method according to claim 1,
The resonance circuit includes a first capacitor Chf connected in parallel to the heating coil Lc, a second capacitor Clf connected in series with the heating coil Lc, and an inductor connected in series with the heating coil Lc Ls). &Lt; / RTI >

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The method according to claim 1,
And a plurality of taps are provided on the primary side of the current transformer to adjust a winding ratio.

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The induction heating apparatus according to claim 1, wherein the plurality of switches are semiconductor switches.

A half bridge inverter for converting the DC power supplied from the power supply unit to AC power and outputting the AC power, a heating coil Lc for heating the material to be heated by receiving the AC power outputted from the half bridge inverter, An induction heating device including a half bridge inverter and a resonance circuit connected to the heating coil Lc to form a resonance frequency and a current transformer connected to the heating coil Lc,
The induction heating apparatus has two resonant frequencies,
The half bridge inverter outputs a high resonance frequency (hereinafter referred to as a 'high frequency') and a low resonance frequency (hereinafter referred to as a 'low frequency') of the two resonance frequencies,
The current transformer performs impedance matching of the heating coil Lc by adjusting the impedance when the high frequency is output and the impedance when the low frequency is output,
Wherein the primary side of the current transformer includes a plurality of windings and a plurality of switches connected to the plurality of windings,
Wherein the current transformer adjusts the impedance when the high frequency is outputted and the impedance when the low frequency is outputted by individually turning on or off the plurality of switches.

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11. The method of claim 10,
The resonance circuit includes a first capacitor Chf connected in parallel to the heating coil Lc, a second capacitor Clf connected in series with the heating coil Lc, and an inductor connected in series with the heating coil Lc Ls). &Lt; / RTI >

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11. The method of claim 10,
And a plurality of taps are provided on the primary side of the current transformer to adjust a winding ratio.

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11. The induction heating apparatus according to claim 10, wherein the plurality of switches are semiconductor switches.