• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1997.10a
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• pp.41-44
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• 1997

본 논문에서는 뉴로퍼지제어기를 이용한 유도가열기의 시변부하에 대한 적응 정전력 제어를 하고자 한다. 유도가열기의 정전력 조절을 위해 IGBT를 사용한 위상전이형 펄스폭변조(PWM)와 PLL에 의한 부하공진주파수 추종형 펄스 주파수변수(PFM)가 조절되는 공진 고주파 인버터를 유용한 유도가열기를 설명하고, 실험 제작된 유도가열기에서의 부하에 대한 규정 전력 추종이 잘되고 있음이 실제적으로 논증되어졌다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.805-808
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• 2003

기존에 적용중인 유전가열 합성수지 접착기술의 경우 진공관 소자를 사용하여 10MHz 대역 이상의 스위칭 주파수를 사용하고, 유전손실이 비교적 높은 PVC 소재에 제한적으로 적용해 왔다. 다른 합성수지 소재에 비해서 유전손실이 낮은 친환경적인 소재에 대해서는 적용이 어려운 기술인 관계로 최근들어 부각되는 친환경적 소재의 적용 확대로 인하여 기존 유전가열 방식의 접착기술은 한계에 접하고 있다. 본 논문에서는 고주파 유도가열 관련 기술을 응용하여 친환경적인 합성소재의 직접가열의 문제점을 간접가열에 의한 온도제어를 적용하여 고주파 유도가열 접착기를 설계하였다.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.506-507
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• 2010

유도가열용 공진형 인버터는 부하에 전류가 흐르면 전자유도 작용에 의해서 와전류가 발생된다. 이 와전류에 의해 발열체가 가열되는 시스템이다. 그러나 유도가열용 인버터에 사용되는 IGBT나 MOSFET와 같은 스위칭 소자들은 스위칭 시 순간 과전류의 발생이나 외부의 이상과전류로 인해서 소자가 파괴 되거나 오작동을 일으키게 되어 전기기기의 손상을 가져올 수 있다. 이를 방지하기 위하여 공급 전원에 비교기를 사용하여 전류의 변화를 감지하고 전류를 차단하는 고주파 직렬 공진형 인버터를 이용한 유도가열 시스템의 안정화에 관한 연구를 하고자 한다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.99-102
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• 2004

In rheo forming process, slurry making is very important factor because the microstructure of slurry affects the quality of final products. To control the microstructure of slurry, slurry making by new rheo die casting was studied. In new rheocasting method, processes parameters are degree of overheat in molten metal, cooling condition, high frequency induction heating condition and cup temperature. Microstructures according to these parameters were observed. By image analysis, equivalent diameter and roundness of grain were investigated and discussed. To find out mechanical properties of grain controlled aluminum part by rheo die casting, tensile tests were carried out to the T6 heat treatment.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.395-396
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• 2013

고주파 유도가열 시스템은 고효율 및 생산의 편의성으로 산업 전반에 걸쳐 다양하게 적용되고 있다. 이러한 고주파 유도 가열 시스템은 크게 정류부, 전압조절부, 공진형 인버터로 구분된다. 공진형 인버터는 공진 주파수로 스위칭 시, 순수 실수 어드미턴스만 남게 되어 최대 효율을 얻는다. 공진 주파수는 공진회로의 입력 어드미턴스에 의해 결정되는데, 용융과정에서 피가열체의 저항 값은 시간에 따라 변화한다. 이는 전체 입력 어드미턴스의 변화와 공진 주파수의 변화로 나타나고, 효율이 저하되는 단점이 있다. 본 논문에서는 공진 인버터의 공진 주파수를 스스로 추종하는 자기공진 추종 토폴로지를 제안한다. 제안된 토폴로지는 고주파 유도가열 시스템의 용융과정에서 피가열체의 저항 값이 시변하여 공진 주파수가 이동하더라도 반주기 내에 정확하게 추종 동작을 한다. 본 논문에서는 제안된 자동 공진 추종회로를 기존의 병렬 공진 유도가열 시스템에 적용하여 타당성을 검증하였다.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.303-305
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• 1996

A strategy that can maximize the efficiency of the inverter system for the non-magnetic material is proposed. Frequency control and variable DC-Link voltage control are compared and analyzed by the experimental results. The experimental results show the variable DC-Link voltage control is superior to the frequency control with respect to improve the efficiency of the inverter system. MOSFETs and IGBTs are used as switching devices and IGBTs are considerable as better switching devices for improving the efficiency of the inverter system.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.1
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• pp.94-102
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• 2003

This paper describes the load parallel type full-bridge high frequency resonant inverter can be used as power source. Output control method of proposed circuit is compared with pulse frequency modulation(PFM), pulse width modulation(PWM) and pulse phase variation(Phase-Shift). The analysis of the proposed circuit is generally described by using the normalized parameters. The principle of basic operating and the its characteristics are estimated according to the parameters such as switching frequency(${\mu}$), pulse width($\theta$d) the variation of phase angle($\phi$) by three driving signal patterns. Experimental results are presented to verify the theoretical analysis result. In future, Characteristics by three driving signal control method is provided as useful data in case of output control of a power supply in various fields as induction heating application, DC-DC converter etc.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2004.11a
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• pp.98-99
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• 2004

(1) Using high-frequency induction heating sintering and spark plasma sintering method, the densification of WC-Ni hard materials was accomplished using ultra fine power of Ni and WC. (2) Nearly fully dense WC-Ni could be obtained within 1 min. (3) Relative density and mechanical properties of WC-Ni obtained by HFIHS were high than those obtained by SPS. And WC grain size made by HFIHS was smaller than that made by SPS. (4) The fracture toughness and hardness values of WC-8Ni, WC-10Ni, and WC-12Ni made by HFIHS were $13MPa{\cdot}m^{1/2}\;and\;1950kg/mm^2,\;13.5Mpa{\cdot}m^{1/2}\;and\;1810kg/mm^2,\;14.4MPa{\cdot}m^{1/2}\;and\;1690kg/mm^2$, respectively for 60MPa and an induced current for 90% output of total capacity, 15KW. (5) The fracture toughness and hardness values of WC-8Ni, WC-10Ni, and WC-12Ni made by SPS were $12.2MPa{\cdot}m^{1/2}\;and\;1796kg/mm^2,\;12.9MPa{\cdot}m^{1/2}\;and\;1725kg/mm^2,\;13.6MPa{\cdot}m^{1/2}\;and\;1597kg/mm^2$, respectively for 60MPa and the electric current of 2500 A

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.1
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• pp.24-31
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• 2019

The current study demonstrates an efficient procedure to create ingots from $Al_2O_3$ powder using the skull melting method to use these ingots as a starting material in conventional methods for growing synthetic single-crystal sapphire. Dimension of the cold crucible was 24 cm in inner diameter and 30 cm in inner height, 15 kg of $Al_2O_3$ powder was completely melted within 1 h at an oscillation frequency of 2.75 MHz, maintained in the molten state for 3 h, and finally air-cooled. The areal density and components of the cooled ingot by parts were analyzed through scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). The areal density and $Al_2O_3$ content of the ingot were related to the temperature distribution inside the cold crucible during high-frequency induction heating, and the area with high temperature was high tends to be high in areal density and purity.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.32 no.4
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• pp.381-392
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• 2022

Objectives: Objective of this study is to review briefly exposure characteristics, monitoring instruments and threshold limit values for extremely low frequency-magnetic field (ELF-MF) methods. This study was undertaken through brief literature review. We performed a literature search in PubMed to identify ELF-MF studies conducted in workplaces. Initial search keywords such as 'extremely low frequency-magnetic field (ELF-MF)' and 'electromagnetic fields (EMF)' combined or singly. We limited our review to occupational rather than general nonworkplace environmental exposures. Methods: The contents we reviewed: key industry and occupations generating ELF-MF, several direct-reading instruments monitoring ELF-MF and threshold limit values (TLV) preventing health effects may be caused by the exposure to ELF-MF. Results: The industries related to the generation and supply of electricity, electrolytic installations, welding, and induction heating and more were regarded as high ELF-MF exposure industries. All jobs handling or employed performed in power cable lines, electrical wiring, and electrical equipment are found to be exposed to ELF-MF. Threshold or ceiling limit, 1,000 µT, is established to prevent acute effects of exposure to low-frequency EMFs on the nervous system: the direct stimulation of nerve and muscle tissues and the induction of retinal phosphenes. The International Agency for Research on Cancer (IARC) has classified ELF-MF as possibly carcinogenic to humans chiefly based on epidemiological studies on childhood leukemia. However, a causal relationship between magnetic fields and several types of cancer including childhood leukemia has not been established nor has any other long-term effects. Risk management using precautionary measures, has been initiated by the US and EU to prevent chronic health effects related to ELF-MF exposure in workplaces. Conclusion: This study recommends the implementation of various measures such as theestablishment of occupational exposure limit values for ELF-MF and precautionary principle to prevent potential chronic occupational health effects may be caused by ELF-MF in Korea.