JP2005078959A - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device decreasing a low-frequency magnetic field included in a heating coil. <P>SOLUTION: A low-frequency magnetic field canceling means 12 fitted inside a high-frequency oscillation part 11 supplying high-frequency current to the heating coil 1, and structured with the use of wiring with the same frequency component as that of the current flowing in the heating coil 1 is arranged in a circular shape in the vicinity of the heating coil 1 so as to generate the low-frequency magnetic field having a direction reversed to that of the heating coil 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an induction heating device such as an electromagnetic cooker that heats an object to be heated by using induction heating by a high frequency magnetic field.

  A conventional method for reducing a leakage magnetic field of a heating coil for an induction heating device (for example, see Patent Document 1) will be described with reference to the drawings. FIG. 6 shows a conventional leakage magnetic field reduction method for a heating coil for an induction heating device. By disposing the electromagnetic shield ring 2 on the outer periphery of the heating coil 1, the 20 k to 50 kHz high frequency leakage magnetic field leaking from the heating coil 1 can be reduced. This is because a high-frequency magnetic field generated in the heating coil 1 causes a current to flow in the electromagnetic shield ring 2, and a high-frequency magnetic field opposite to that of the heating coil 1 is generated by the current. This is because it acts to cancel out. The electromagnetic shield ring 2 is made of an aluminum plate, a lead wire or the like that is annular.

On the other hand, another leakage magnetic field reduction method (for example, refer to Patent Document 2) of the conventional induction heating apparatus will be described. FIG. 7 shows a leakage magnetic field reduction method of a conventional induction heating apparatus. The inductance 5 is formed by winding the vicinity of the outer periphery of the heating coil 1, and the high-frequency magnetic field generated from the heating coil 1 and the high-frequency magnetic field component generated by the inductance 5 are arranged to cancel each other. FIG. 8 shows a circuit example of a conventional induction heating apparatus. The induction heating apparatus of FIG. 8 includes a power supply unit 3 constituted by a commercial power source, a high-frequency oscillation unit 11 that converts the power of the power supply unit 3 into high-frequency power, and a heating coil 1 that converts the power of the high-frequency oscillation unit 11 into a high-frequency magnetic field. The high-frequency oscillating unit 11 includes a rectifying unit 4 that rectifies the commercial power supply, an inductor 5 and a smoothing capacitor 6 that smooth the output of the rectifying unit 4, and a load 15 that generates heat upon receiving a magnetic field from the heating coil 1. The semiconductor switch 8 controls the power supply to the heating coil 1 and the resonance capacitor 7 that smoothes the switching operation of the semiconductor switch 8. In the conventional example of FIG. 8, the inductor 5 is composed only of windings, so that the core material of the inductance 5 is not required, so that the apparatus can be reduced in size and the high frequency noise can be reduced.
JP-A-57-115795 Japanese Patent Publication No. 63-7672

  However, in the conventional method for reducing the leakage magnetic field of the heating coil for the induction heating device as shown in FIG. 6, the high-frequency leakage magnetic field can be reduced by the effect of the electromagnetic shield ring 2, but the power source generated from the heating coil 1 A magnetic field having a frequency or twice the frequency of the power source (hereinafter referred to as a low-frequency magnetic field) is hardly absorbed by the load 15 and released to the outside, and the electromagnetic shield ring 2 generates a reverse magnetic field that only cancels the low-frequency magnetic field. Therefore, there is a problem that the low frequency magnetic field is not reduced and is emitted to the outside of the device. On the other hand, in the conventional induction heating apparatus of FIG. 7, since the winding is operated as an inductance (about several hundred μH), the number of winding turns increases. At this time, the low-frequency magnetic field emitted from the winding becomes larger than the low-frequency magnetic field emitted from the heating coil, resulting in an increase in the low-frequency magnetic field emitted to the outside. Further, the conventional induction heating device aims to cancel the high-frequency magnetic field, and the winding for reducing the leakage magnetic field is limited to the outside of the outermost peripheral portion of the heating coil, and there is a problem that there is no degree of freedom in arrangement. Become.

  SUMMARY OF THE INVENTION The present invention solves the above-described problems, and an object thereof is to provide an induction heating apparatus that can reduce noise of unnecessary electromagnetic waves by reducing the emission of a low-frequency magnetic field from a heating coil. .

  In order to solve the above-described problems, the present invention provides a heating coil that generates a high-frequency magnetic field for inductively heating an object to be heated, a high-frequency oscillation unit that supplies a high-frequency current to the heating coil, and a commercial frequency for the high-frequency oscillation unit. A low frequency magnetic field canceling means comprising a power supply section for supplying electric power and a wiring having the same frequency component as the low frequency component of the current flowing in the heating coil in the high frequency oscillation section, and the low frequency magnetic field canceling means Is formed in an annular shape in the vicinity of the heating coil, and the induction heating apparatus is configured such that the low frequency magnetic field canceling means and the low frequency magnetic field generated by the heating coil cancel each other.

  As a result, the low-frequency magnetic field generated from the heating coil can be easily canceled out without significantly affecting the high-frequency magnetic field for heating the load, and an induction heating apparatus with a low low-frequency leakage magnetic field is realized.

  As described above, according to the present invention, an induction heating apparatus that can cancel out a low-frequency magnetic field generated from a heating coil and has a low low-frequency leakage magnetic field is realized.

  According to a first aspect of the present invention, there is provided a heating coil that generates a high-frequency magnetic field for inductively heating an object to be heated, a high-frequency oscillation unit that supplies a high-frequency current to the heating coil, and a commercial frequency power supply to the high-frequency oscillation unit. And a low-frequency magnetic field canceling means comprising a wiring having the same frequency component as the low-frequency component of the current flowing in the heating coil in the high-frequency oscillation unit, and the low-frequency magnetic field canceling means The induction heating apparatus is configured to be provided in the vicinity of the heating coil in an annular shape so that the magnetic field of the low frequency magnetic field canceling means and the low frequency magnetic field generated by the heating coil cancel each other.

  As a result, the low-frequency magnetic field generated from the heating coil can be easily canceled without affecting the high-frequency magnetic field that heats the load, and an induction heating device with a low low-frequency leakage magnetic field is realized. .

  In addition to the above, the invention according to claim 2 has a heating coil divided into a plurality of parts, and the low-frequency magnetic field canceling means is annularly applied in the vicinity of the heating coil arranged on the outer peripheral side of the plurality of heating coils. The induction heating device is configured as described above.

  As a result, the magnetic field generated from the canceling coil can be strengthened, and an induction heating apparatus with less low-frequency leakage magnetic field can be realized.

  In addition to the above, the invention according to claim 3 is an induction heating device in which the low-frequency magnetic field canceling means is configured such that a wiring having the same frequency component as the low-frequency component of the current flowing in the heating coil is provided in a ring shape a plurality of times.

  As a result, the magnetic field generated from the canceling coil can be strengthened, and an induction heating apparatus with less low-frequency leakage magnetic field can be realized.

  In addition to the above, the invention according to claim 4 is an induction heating device in which the low-frequency magnetic field canceling means is annularly provided on the outer side of the magnetic-shielding ferrite disposed in the vicinity of the heating coil.

  As a result, it is possible to reduce the influence of the low-frequency canceling means on the high-frequency magnetic field, and to realize an induction heating apparatus that can reduce the low-frequency leakage magnetic field in a state in which the heating distribution hardly changes.

  In the invention according to claim 5, in addition to the above, the low-frequency magnetic field canceling means is an induction heating apparatus using a wiring immediately before or after the inductance in the high-frequency oscillation section.

  As a result, the inductor component of the wiring is absorbed by the inductor on the circuit, so there is no need to consider the influence on the wiring equipment used for the low-frequency magnetic field canceling means, and the low-frequency can be set in a state where the wiring location can be easily set. An induction heating apparatus that can reduce the leakage magnetic field is realized.

  In addition to the above, the invention according to claim 6 is an induction heating device in which the low frequency magnetic field canceling means uses a wiring in which a current in a direction opposite to that of the inductor in the high frequency oscillation section flows.

  As a result, an inductor component due to wiring is generated in another phase of the inductor 5, and as a result, the circuit imbalance between phases can be improved, and the low frequency leakage magnetic field can be reduced in a state where common mode noise can be reduced. An induction heating device that can be realized is realized.

  According to the seventh aspect of the present invention, in addition to the above, the low frequency magnetic field canceling means is an induction heating device using a wiring to which a heating coil is not connected among wirings from a semiconductor switch in a high frequency transmission section.

  Thereby, the induction heating apparatus which can reduce a low frequency magnetic field while reducing a high frequency magnetic field is implement | achieved.

  In addition to the above, the present invention according to claim 8 is an induction heating device in which a plurality of heating coils are connected in parallel, and the heating coils are all wound in the same direction.

  This makes it possible to use the same low-frequency magnetic field canceling means for a plurality of heating coils, and realize an induction heating device that can reduce low-frequency leakage magnetic fields generated from the plurality of heating coils with a simple configuration. To do.

(Example 1)
A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of the induction heating apparatus of this embodiment. A power supply unit 1 including a commercial power supply and a filter is connected to a high frequency oscillation unit 11, and the high frequency oscillation unit 11 is connected to the heating coil 1. The heating coil 1 is installed at the upper part in such a manner that a load 15 such as a pan is magnetically coupled to the heating coil 1, and a magnetic shield ferrite 13 is arranged at the lower part to enhance the magnetic coupling with the load 15. The high-frequency oscillation unit 11 includes a rectifying unit 4 connected to the power source unit 3, a series connection of an inductor 5 and a smoothing capacitor 6 connected in series with the rectifying unit 4, and a resonant capacitor connected in parallel to the smoothing capacitor 6. 7 and the semiconductor switch 8 are connected in series, and the resonant capacitor 7 is connected in parallel with the heating coil 1. On the other hand, the wiring of the inductor 5 is wound a plurality of times in the vicinity of the outer periphery of the heating coil around the lower part of the ferrite in the direction opposite to the winding direction of the heating coil 1 to constitute a low-frequency canceling means.

  In the present embodiment, a general circuit configuration used in the induction heating apparatus is shown, but there is no particular limitation as long as it is a circuit configuration in which a low-frequency magnetic field from the heating coil 1 is generated.

  Next, the operation of this embodiment will be described. FIG. 2 is a diagram showing a current path in each section of the inverter circuit. I3 is an input current, I5 is a current flowing through the inductor 5 and the low-frequency magnetic field canceling means 12, and I1 is a current flowing through the heating coil. The power supply unit 3 includes a commercial power supply and a filter, and supplies commercial frequency power to the high-frequency oscillation unit 11. Therefore, the input current I3 is a current having a commercial frequency component. In the high-frequency oscillating unit 11, the commercial power is rectified by the rectifying means 4 to be converted into power having a frequency component twice that of the commercial power supply, and further converted into high-frequency power of about 20 k to 50 kHz using the semiconductor switch 8. This high frequency power is supplied to the heating coil 1 and supplied from the heating coil 1 to the load 15 in the form of a high frequency magnetic field. The load 15 generates eddy current in the surface layer portion due to the high frequency magnetic field, and as a result, generates heat. For this reason, the current I5 having a frequency twice the commercial frequency flows through the inductor 5 and the low-frequency magnetic field canceling means 12, and when the semiconductor switch 8 becomes conductive in the heating coil 1, the power source 1 → rectifier A current I11 in which a low-frequency current having a component twice the commercial frequency generated in the loop of means 4 → heating coil 1 → semiconductor switch 8 and a high-frequency component flowing in the heating coil 1 according to the frequency of the semiconductor switch 8 flows.

  And the low frequency magnetic field which generate | occur | produces from the heating coil 1 can be negated by arrange | positioning mutually so that the low frequency magnetic field of the heating coil 1 and the low frequency magnetic field cancellation means 12 may mutually cancel. Further, the low frequency magnetic field canceling means 12 is preferably arranged in the vicinity of the outer heating coil 1 when the heating coil 1 is divided into a plurality of parts, and more canceling magnetic fields are generated by winding a plurality of times. It becomes possible to make it. However, when the low-frequency magnetic field canceling means 12 is wound a plurality of times, the magnetic field from the low-frequency magnetic field canceling means 12 increases conversely when the number of turns is large, and therefore the number of turns of the heating coil 1 is approximately ½ or less. It consists of the number of turns.

  On the other hand, by disposing the low-frequency magnetic field canceling means 12 below the magnetic-shielding ferrite 13, the high-frequency magnetic field transmitted from the heating coil 1 to the load 15 is not greatly disturbed, and as a result, a good heating distribution can be obtained. .

  Further, in this embodiment, the low frequency magnetic field canceling means 12 is taken immediately after the inductor 5. This is advantageous because the wiring inductor generated when the wiring of the low-frequency magnetic field canceling means 12 is long is sufficiently smaller than the inductor 5 and is absorbed capacitively, so that the influence of noise superimposed on the wiring is small. Because.

  As described above, in this embodiment, the low-frequency magnetic field canceling means 12 using the wiring that generates the low-frequency magnetic field opposite to the heating coil 1 is disposed in the vicinity of the heating coil 1, thereby reducing the low-frequency generated from the heating coil 1. It is possible to cancel the high frequency magnetic field easily and with little influence on the high frequency magnetic field that heats the load 15, and to realize an induction heating device with a low low frequency leakage magnetic field.

(Example 2)
A second embodiment of the present invention will be described with reference to the drawings. The configuration of this embodiment is shown in FIG. The present embodiment is different from the first embodiment in that the low-frequency magnetic field reducing unit 12 uses a wiring positioned in the opposite phase of the inductor 5.

  The operation in the above configuration will be described. In this embodiment, as shown in FIG. 3, the low-frequency magnetic field canceling means 12 is configured by using the wiring through which the reverse-phase current of the inductor 5 flows. In this way, by using the reverse-phase wiring of the inductor 5 in the normal mode, the inductance of the wiring is added to the circuit, and the impedance viewed from the power supply unit 1 can be made closer between both phases. As a result, common mode noise is reduced, and the filter configuration of the power supply unit 1 is simplified.

  As described above, according to the present embodiment, the low frequency magnetic field canceling means 12 uses a wiring having a phase opposite to that of the inductor 5 so that the impedance viewed from the power source unit 1 is made symmetrical, and as a result, induction heating with less common mode noise is achieved. A device can be realized.

(Example 3)
A third embodiment of the present invention will be described with reference to the drawings. The configuration of this embodiment is shown in FIG. The present embodiment is different from the first embodiment in that the low frequency magnetic field reducing means 12 is taken from the emitter line of the semiconductor switch 8.

  The operation in the above configuration will be described. In this embodiment, as shown in FIG. 4, the low frequency magnetic field canceling means 12 is configured by using the emitter line wiring of the semiconductor switch 8. By doing so, it is possible to reduce high-frequency leakage magnetic fields in addition to low-frequency magnetic fields. By doing so, the electromagnetic shield ring 2 can be eliminated, and low frequency and high frequency leakage magnetic fields can be reduced with a simple configuration.

  As described above, according to the present embodiment, by using the wiring of the emitter line of the semiconductor switch 8 for the low frequency magnetic field canceling means 12, it is possible to reduce the high frequency leakage magnetic field in addition to the low frequency magnetic field by a simple method. A simple induction heating device can be realized.

Example 4
A fourth embodiment of the present invention will be described with reference to the drawings. The configuration of this embodiment is shown in FIG. The present embodiment is different from the first embodiment in that the series circuit of the inner heating coil 1a and the semiconductor switch a8a, the outer heating coil 1b and the semiconductor switch 8b are connected in parallel. A resonance capacitor 7a is connected in parallel to the inner heating coil 1a, and a resonance capacitor 7b is connected in parallel to the outer heating coil.

  The operation of this embodiment will be described. In this embodiment, the semiconductor switch a8a and the semiconductor switch b8b do not conduct at the same time, and operate alternately according to control means (not shown). Therefore, power can be supplied to the load 15 without being affected by the high frequency magnetic field. However, when the inner heating coil 1a and the outer heating coil 1b are reversed, the low-frequency magnetic field increases while one of the heating coils is energized due to the winding direction of the low-frequency magnetic field reduction means 12. Become. Therefore, by winding the inner heating coil 1a and the outer heating coil 1b in the same direction, it is possible to reduce the low frequency magnetic field generated in both heating coils by arranging the low frequency magnetic field reducing means 12.

  As described above, in the present embodiment, it is possible to reduce the low frequency magnetic field by using the same low frequency magnetic field canceling means 12 by winding a plurality of heating coils in the same direction, and the plurality of heating coils with a simple configuration. The induction heating device that can reduce the low-frequency leakage magnetic field generated from the above is realized.

The figure which shows the induction heating apparatus of 1st Example of this invention. The figure which shows the operation | movement waveform of the induction heating apparatus of a 1st Example of this invention. The figure which shows the induction heating apparatus of the 2nd Example of this invention. The figure which shows the induction heating apparatus of the 3rd Example of this invention. The figure which shows the induction heating apparatus of the 4th Example of this invention. Diagram showing a conventional induction heating device Diagram showing a conventional induction heating device The figure which shows the circuit structure of the conventional induction heating heating apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating coil 2 Electromagnetic shield ring 3 Power supply part 4 Rectification means 5 Inductor 6 Smoothing capacitor 7 Resonance capacitor 8 Semiconductor switch 11 High frequency oscillation part 12 Low frequency magnetic field cancellation means 13 Magnetic shield ferrite 15 Load 1a Internal heating coil 1b External heating coil 7a Resonance capacitor a
7b Resonant capacitor b
8a Semiconductor switch a
8b Semiconductor switch b

Claims (8)

A heating coil that generates a high-frequency magnetic field for induction heating of an object to be heated, a high-frequency oscillation unit that supplies a high-frequency current to the heating coil, a power supply unit that supplies commercial frequency power to the high-frequency oscillation unit, and the high frequency A low-frequency magnetic field canceling means comprising a wiring having the same frequency component as the low-frequency component of the current flowing in the heating coil in the oscillating unit, wherein the low-frequency magnetic field canceling means is annularly applied in the vicinity of the heating coil. An induction heating apparatus configured to cancel the magnetic field of the low frequency magnetic field canceling unit and the low frequency magnetic field generated by the heating coil. The induction heating apparatus according to claim 1, further comprising: a heating coil divided into a plurality of portions, wherein the low-frequency magnetic field canceling unit is annularly provided in the vicinity of the heating coil disposed on the outer peripheral side of the plurality of heating coils. . The induction heating apparatus according to claim 1 or 2, wherein the low-frequency magnetic field canceling means is configured such that a wire having the same frequency component as the low-frequency component of the current flowing through the heating coil is annularly formed a plurality of times. The induction heating device according to any one of claims 1 to 3, wherein the low-frequency magnetic field canceling means is configured to be provided in an annular shape on the outer side of the magnetic-shielding ferrite disposed near the heating coil. The induction heating apparatus according to any one of claims 1 to 4, wherein the low-frequency magnetic field canceling means uses wiring connected to an inductance in the high-frequency oscillation unit. The induction heating apparatus according to any one of claims 1 to 4, wherein the low-frequency magnetic field canceling means uses a wiring through which a current in a direction opposite to that of the inductor in the high-frequency oscillation unit flows. The induction heating apparatus according to any one of claims 1 to 4, wherein the low-frequency magnetic field canceling means uses a wiring to which the heating coil is not connected among the wiring from the semiconductor switch in the high-frequency transmission section. The induction heating apparatus according to any one of claims 1 to 7, wherein a plurality of heating coils are connected in parallel, and the heating coils are all wound in the same direction.

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