• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.5
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• pp.857-864
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• 2020

The multi-functional VoIP phone supports the Ethernet protocol in the TIPS(: Tactical IP Switch), which is one of the sub-systems of the tactical information and communication system (TICN). It provides secured voice / video calls in conjunction with VoIP exchanges and supports differential services such as multi-party calls and command functions. In this paper, improving methods have been proposed to reduce power supply defects in the field of multi-functional VoIP phones. The power supply part was improved by applying TVS of the output voltage inlet of the dedicated adapter of the multi-functional VoIP phone, TVS of the PoE module input, adding blocking diodes, and adding DC / DC converters behind the poly-switch. Also, functional and environmental tests were performed to verify the validity of the proposed methods.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.4
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• pp.385-394
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• 2006

The application areas of traditional push-pull converters are limited because the voltage stress of switches is high (twice of the input voltage). But the push - pull converter topology is suitable for unregulated low-voltage to high-voltage power conversion such as the fuel cell. This paper presents a novel power converter structure that is very suitable for the DC/DC converter in fuel cell systems. Based on this structure, a ZVS- ZCS push-pull converter is proposed. The switches of the proposed push-pull converter can operate under ZVS or ZCS condition with the help of a new passive clamping circuit. The passive clamping techniques solves the voltage overshoot problem. Because the buck converter circuit operates at twice the synchronous switching frequency of the push-pull converter, the peak current in the current-fed inductor and transformer is reduced. The operation principle of the proposed converter is analyzed and verified by simulations and experimental results. A 1 kW DC/DC converter was implemented with DSP TMS320F2812, from which experimental results have shown that efficiency improvement and surge suppression can be achieved effectively.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.10a
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• pp.61-62
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• 2017

In this study, we introduce some main functions and specifications of a recently commercialized potable compact high voltage generator. USB killer has been designed to test surge protection circuitry of electronic equipments using USB ports. USB killer transforms 5V DC power supplied by USB port into a sufficiently high voltage over 200V DC through oscillator, transformer, voltage multiplier, and rectifier. The power charged in a high-capacity condenser can be applied back into the electronic equipments as an electric shock to destroy them or test protection circuits. USB killer is a readily available item, and one can test a variety of electronic equipments. We introduce some test results known over the internet and those obtained from our tests.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1212-1213
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• 2011

PWM(pulse width modulation) rectifier has unit power factor and low harmonic distortion with high power conversion efficiency in entire loading range. These merits of PWM rectifier help the spread of DC distribution system. In addition, if multiple PWM rectifiers can be operated in parallel connection, maintenance process can be simple and reliability of power source can be advanced because of the hot swapping is available. The other way, the load unbalance among rectifiers can force a converter to stop by over current. The surge current by closed circuit composition between rectifiers can force switching devices damage. In this paper, some problems that can occur in case of parallel operation of PWM rectifiers and problem eliminating methods are considered.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.265-266
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• 2011

본 논문에서는 가정용 직류배전시스템 도입 시 가전기기 입력단 커패시터의 용량 산정 및 최적화 가능성 검증을 위하여 직류배전시스템용 가전기기 입력단 및 PWM 컨버터 출력단 사이의 관계를 전압방정식의 형태로 모델링 한다. 또한 모델링된 전압방정식을 이용하여 대용량 부하변화 시 발생가능 한 Sag 및 Surge 규격에 부합하는 커패시터의 용량을 산정하고 시뮬레이션을 통하여 검증한 뒤 직류배전시스템 가전기기 설계의 가이드라인을 제시한다.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2019_2020
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• 2009

A recurrent surge oscillograph(RSO) test was performed at the Taean thermal power plant on #5 turbine generator. The test was conducted using a rotor reflectometer and digital oscilloscope. A DC voltage step is applied to each end of the rotor winding in turn. Each reflected wave, at the input end of the winding, is monitored and the two waveforms are superimposed automatically and monitored on a single channel oscilloscope. As the half windings in a rotor are identical, the two waveforms monitored at each end of the rotor will also be identical for a healthy winding. A winding with a fault will cause different voltages to be monitored at the two ends.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1285_1286
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• 2009

본 논문에서는 지하철 인버터 회로에 사용 환경에 적합하면서 높은 과도 전압(dV/dt)에 견딜 수 있는 건식형 스너버용 커퍼시터를 설계 및 제작하여 특성을 검토하고자 한다. 필름 커패시터는 환경적 측면을 고려하여 에폭시 몰드형 건식형을 적용하였다. 증착 필름에 적용되는 금속은 Zn 전극에 비하여 Al 전극이 우수한 커패시터 특성을 나타내었으며 패턴의 경우에도 T-pattern에서 정전용량 및 손실의 변화율이 작게 나타났다. Al 금속전극에 wave-cut를 적용한 T - pattern 필름으로 DC 1650V, 12 uF, 정격전류 40 A의 커패시터를 제작하여 ESR 및 유전 손실이 적은 제품을 구현할 수 있으며 내구성 및 surge test 결과 신뢰성 규격을 만족하였다.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.25-26
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• 2008

A, B 변전소간에 345kV 지중선로 4회선으로 Loop 운전 중 1개의 지중선로에 절연파괴 고장이 발생하였으며, 이때 4개의 지중송전선로가 모두 운전정지 되는 고장이 발생하였다. 고장이 발생한 선로는 정상적으로 보호계전기가 동작하였으나, 그 외 다른 선로의 보호계전기가 오동작하여 원인규명시험을 한 결과 외부고장시 CT 포화로 인해 보호계전기가 자단고장으로 인식하여 동작된 것으로 분석되었다. 본 논문에서는 CT 포화와 관련하여 DC성분, Surge, 2차 부담 등 여러가지 조건에 대하여 고찰함으로서 향후 전력계통의 다양한 고장에 대비하는데 도움이 되기를 기대한다.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.1044-1047
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• 1999

This paper deals with the dynamic property of ground overvoltage relay in large turbine generator. Relay operation is based on detecting the fundamental voltages originating from the generator. Calculations of fault voltage and current are reviewed for the neutral ground resistance. The frequency, ampitude and waveform of individual harmonics were measured using power quality analyzer and memory hi-corder at the secondary side of ground potential transformer. The ac and dc high-potential tests were applied to evaluate the condition of generator, main and auxiliary transformer, isolated phase bus, potential transformer, surge capacitor and arrester.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.292-294
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• 2005

A new zero voltage switching (ZVS) 2-transformer boost converter is proposed in this paper. The proposed converter has the advantage that the magnetizing inductor of the transformer acts for the boost inductor without additional inductor. Moreover, ZVS of main switches and auxiliary switches can be achieved, and the switch turn-off surge problem of conventional isolated boost converter is effectively solved. The operational principle, DC voltage gain, and ZVS characteristics are analyzed. To confirm the validity of the proposed converter, simulation results with 200w, 24Vdc/200Vdc specification are presented.