KR900004445B1 - High Frequency Induction Current Heating Device - Google Patents

Abstract

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Description

High Frequency Induction Current Heating Device

1 is a block diagram of a conventional high frequency induction heating device.

2 is a block diagram of a conventional high frequency induction heating apparatus of FIG.

3 is a block diagram of a third conventional high frequency induction heating device.

4 is a diagram of waveforms showing the principle of a high frequency induction current heating apparatus according to the present invention.

5 is a block diagram of a high frequency induction current heating apparatus according to the present invention.

6A and 6B are waveform diagrams showing additional principles of the high frequency induction heating apparatus according to the present invention.

The present invention relates to an induction current heating device that is driven by power supplied from a high frequency inverter. In particular, the present invention relates to a high frequency inductive current heating apparatus capable of heating different parts of an object almost simultaneously under different conditions.

If a good electrical conductor, such as a metal, is placed in a rapidly alternating magnetic field, an eddy current occurs in the conductor as a result of electromagnetic induction, resulting in eddy current loss. If the good conductor is a magnetic material, hysteresis loss also occurs. High frequency induction heaters utilize both heat generated by eddy current losses and hysteresis losses, and the principle of operation of such devices is known.

According to the so-called "epidermal effect", the eddy currents generated in the object heated by the induction phenomenon are intended to be integrated in the surface area, not the deep part of the object. As the frequency of the current flowing in the induction heating coil increases, the depth at which the eddy current penetrates decreases. It is also known that the amount of eddy current loss increases as the current flowing in the induction heating coil increases and as the frequency increases.

A representative arrangement of such a high frequency induction heater is schematically shown in FIG. The heater has a rectifier 1 for achieving AC-to-DC conversion, and has a capacitor for leveling the resulting DC voltage, and also generates a high frequency voltage supplied to the induction heating coil 4. Inverter 3 is provided, wherein the induction heating coil 4 is wound around the conductor 5 to be heated. The rectifier 1 is required only when the high frequency heater receives energy from an AC power source. Therefore, the rectifier 1 is not necessary when the heater is operated by being supplied with DC power. In the rectifier 1, the capacitor 2 is also unnecessary as long as the sofa-like voltage generated by the AC-to-DC conversion is negligible. The DC voltage supplied by the three-phase or single-phase power converted to the DC voltage in the rectifier 1 and leveled by the capacitor 2, or the DC voltage supplied by the DC power source is input to the high frequency inverter 3 to induce high frequency AC current. This alternating current is supplied to the heating coil (4). The resulting eddy currents in an object located in or around the heating coil generate sufficient thermal energy to heat the object. The above is the known operating principle of the high frequency induction current heating apparatus.

In some cases where an induction heater is used, for example when quenching heated iron, it is necessary to heat different temperatures on the surface and inside of the iron. Conventionally, to meet this need, two separate high frequency induction heaters are used which generate different outputs and different frequencies, which are installed side by side and move the objects to be heated into these two heaters. The surface of the object was heated by one heater and the interior of the object was heated by him and another heater.

Referring to FIG. 2, a case of using two induction heating apparatuses to heat the surface portion and the inner portion of the object to be heated to different temperatures is shown. The first induction heating device includes a rectifier 11, a capacitor 21, a first high frequency inverter 31, a coil 4l, and the like. The second induction current heating device includes a rectifier 12, a capacitor 22, a second high frequency inverter 32, a coil 42, and the like. An output of different power and different frequency than the output of the first inverter is calculated. The coils 41 and 42 surround the heated object 5. By sequentially moving the object 5 into the coils 41 and 42, high frequency energy of different outputs is supplied to the object.

As is apparent from the above description, heating as two induction heating devices requires a separate rectifier and an inverter for each heating device, which costs a lot.

A less expensive system has been developed, which is shown schematically in FIG. In this system, the rectifier 1 'and the capacitor 2' are commonly used for two high frequency inverters 31 and 32. The output of the inverter 31 is supplied to the common coil 4 through the cross current dissipation reactors 611 and 612, in which the output is superimposed with the output of the other inverter 32, and the inverter 32 Output is passed through cross current quenching reactors 621 and 622 before being fed to coil 4. By this arrangement, the surface layer and the inner portion of the object 5 to be heated in the coil 4 are heated to different temperatures. Because the two outputs have different frequencies. However, this system is also not very economical because it requires two high frequency inverters and four cross-current quench reactors.

It is therefore an object of the present invention to provide a device capable of heating a surface layer and an internal portion of an object to a different temperature almost simultaneously using one high frequency induction current type device.

It is another object of the present invention to provide a high frequency induction current heating apparatus using one high frequency inverter capable of variable output and variable frequency.

This and other objects are achieved by a high frequency induction current heating device having the following component elements. That is, the device has a voltage source, has a high frequency inverter connected to the voltage source and capable of generating an AC output, and has a device for applying an electric current to the object to heat the object by an induction phenomenon. And a frequency control device for controlling the high frequency inverter to output the first current and the second current. Wherein the first current has a first frequency for heating the internal portion of the object, and the second current has a second frequency that is higher than the frequency of the first current for heating the external portion of the object.

The above objects, features and advantages of the present invention will be apparent from the following description in more detail with reference to the drawings.

The embodiment of the high frequency induction heating apparatus according to the present invention is similar to that of the conventional apparatus as shown in FIG. However, one voltage source is provided, which is a direct DC voltage source or uses a rectifier 101 connected to the leveling capacitor 201.

To inductively heat an object, a voltage is applied to the high frequency input unit 301 which supplies a high frequency alternating current to a device that supplies a current to the object. As shown in the embodiment, a device for applying a current includes a coil 401, which induces an eddy current to an object located in or near the coil. That is, as described above, the eddy current generates heat energy, thereby heating the object portion corresponding to the frequency of the current.

The apparatus also includes a frequency controller 601, which controls a high frequency inverter 301 that applies power to the coil 401, where the first current is used to heat an internal portion of the object. It has one frequency, and the second current has a second frequency higher than the frequency of the first current for heating the external portion of the object. The frequency controller 601 is formed by any suitable circuit arrangement. This circuit device controls the inverter 30 to output a current having one or more selectable frequencies, which are output as soon as it is input to the controller 601, and the frequency selection signal of the controller 601 indicates the selected frequency. The period selection signal indicates a time sequence for outputting the selected frequency. If the output frequency of the high frequency inverter is changed, the time taken to realize this change is preferably not longer than the thermal time constant of the object to be heated.

In the present invention, the frequency of the high frequency inverter output can be periodically changed by the controller 60l at an appropriate time interval as shown in FIG. 4, so that heat is generated not only on the surface layer of the object to be heated but also on the deep portion thereof. do. When the system is operated at low frequency, the object 501 can be heated to a certain depth within the surface, while when operated at a high frequency, generally only the surface layer of the object 501 is heated. The frequency controller 601 controls the inverter 301 to be changed from one frequency to another frequency rather than a constant time interval, which is not longer than the thermal time constant of the object to be heated. Therefore, two different but continuous frequencies can heat an object as if it were heated at the same time.

If it is desired to control not only the frequency but also the energy input to the heated object, the voltage control may be performed using the rectifier 101 in a thyrister inverter. However, for economic reasons, the voltage control can be better performed by the controller 601 controlling the inverter 301 as shown in FIGS. 6A and 6B. In the case shown in Fig. 6A, the inverter is operated by applying current in the opposite direction at alternating time intervals of t / 2.

6B shows an alternating method for realizing the output voltage control of the inverter. That is, the current is supplied during the selectable period ta, the current supply is suppressed during the to period, and the output is not calculated. ta + to is the whole period t. The output voltage of the inverter can be controlled by controlling the " no output period " to and the period length from 0 to t.

Instead of controlling the output voltage of the inverter 301, by controlling the ratio of the two periods to be described later, a low cost device can be manufactured to inject selected levels of energy into the outside and inside of the object, respectively. The two periods, that is, one means a period during which the low frequency output is calculated, and the other means a period during which the high frequency output is calculated.

The above description relates to the following cases. That is, the output frequency of the high frequency inverter is changed from a low level to a high level based on a periodic time interval of periodicity, or vice versa. It should be understood that the object of the present invention is satisfactorily achieved even when frequency changes are made for three or more frequencies.

Claims (6)

A voltage source, a high frequency inverter connected to the voltage source and outputting an alternating current, a current applying device of an object for inductively heating an object, and controlling the high frequency inverter for outputting a first current and a second current to the current applying device. And a first current outputted therefrom inductively heats the internal portion of the object by the first frequency, and the second current is an external portion of the object by a second frequency higher than the first frequency. High frequency induction current heating device for heating the object, characterized in that the heating. The high frequency induction of claim 1, wherein the frequency controller controls the inverter to periodically replace the first frequency and the second frequency at a time interval shorter than a thermal time constant of an object to be heated. Current heater. The high frequency induction current heating device according to claim 1, wherein the current application device is constituted by a coil to induce eddy currents in an object. A voltage source, a high frequency inverter connected to the voltage source to output an alternating current, a current applying device for heating the object inductively, and a frequency control device for controlling the high frequency inverter, the voltage level of the output current from the inverter High frequency induction current heating device for heating an object, characterized in that to change periodically. 5. The apparatus of claim 4, wherein the frequency control device controls the inverter to change the voltage between the first voltage and the voltage of zero at a time interval shorter than the thermal time constant of the object to be heated. High frequency induction heating system. The high frequency induction current heating device according to claim 5, wherein the current application device is constituted by a coil to induce an eddy current to an object.

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