• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.6
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• pp.491-496
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• 2005

In this paper, test on characteristics of 3-phase line-interactive UPS system, known as delta conversion UPS system, is studied. Delta conversion UPS system is new line-interactive UPS system using two series-parallel PWM converters instead of using series inductor in conventional single conversion line-interactive UPS system. It is known that the characteristics of input and output in delta conversion UPS system is much improved by controlling source current of AC lines directly. Here the results on load test, normal/backup mode test, and normal/bypass mode test, which are very important in the test on characteristics of UPS system, is presented. And finally overall evaluation on delta conversion UPS system is given.

• Proceedings of the KIEE Conference
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• 2006.04a
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• pp.288-290
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• 2006

An efficiency improving method for Uninterruptible Power Supply System(UPS) was developed by using OP-AMP based application circuits such as voltage detection device, current detection device and static switch control device. The efficiency improving algorithm was made by mixing the operating concepts of On-Line type UPS with the operating concepts of Off-Line type UPS. The UPS' inverter does not work if the UPS' output load current is not higher than the low load operating current which is about 0-30(%) of the UPS' output load capacity. The low load operating current is adjustable within the half of the UPS' output load capacity. If the UPS' output load current is rising over than the low load operating current, the UPS' inverter starts working and the inverter output power feeds to the loads of UPS. If UPS' input power breaks out while UPS' inverter does not operate because the load current is low, the inverter starts working within 4(ms) with excessive output voltage which is ${\pm}$8(%) of normal UPS' output voltage. Like these. UPS can continuously feeds power to it's load device and reduce power consumptions.

• Journal of Power Electronics
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• v.5 no.2
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• pp.160-165
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• 2005

In a parallel operation of UPS, there are two types of circulating currents between UPS. One is the low order circulating current with a fundamental frequency caused by the amplitude and phase differences of UPS output voltages, and the other is the harmonic circulating current with PWM switching frequency caused by non-synchronized PWM waveforms among UPS. The elimination of the low order circulating current is essential for optimal load sharing in parallel operations of UPS, which can be accomplished by the phase and magnitude control at each UPS. The harmonic circulating current may cause troubles and deteriorate in performance of the controller for optimal load sharing in parallel operation of UPS. This paper presents a PWM synchronizing method to eliminate the harmonic circulation current in parallel operation of UPS. The effectiveness of the proposed scheme has been investigated and verified through experiments by a 50kVA UPS.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.603-604
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• 2015

본 논문은 UPS(Uninterrupted Power Supply)의 기능을 확장하여 ESS(Energy Storage System)로서 충방전 제어를 수행하는 hybrid UPS[1][2]인 UES(UPS+ESS)의 실제 구축사례를 기술한다. 기존 시스템의 변경을 최소화 하고 UPS 기능을 우선 동작하기 위해 UES는 UPS와 battery을 각각 제어하는 별도의 외부 제어장치를 이용하여 UES로서 시스템을 통합하며 각 부분 구성품의 호환성을 확보한다.

• Proceedings of the KAIS Fall Conference
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• 2004.11a
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• pp.174-178
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• 2004

본 논문에서는 일명 델타변환 무정전전원장치(UPS)로서 알려져 있는 3상 라인 인터랙티브 UPS 시스템의 성능 시험에 대해서 다루고 있다. 델타변환 UPS는 종래의 단일 변환 라인 인터랙티브 UPS 시스템에서 직렬 인덕터를 제거하고 직렬 및 병렬 PWM 컨버터를 사용하는 새로운 라인 인터랙티브 UPS 시스템으로 전원 전류를 직접 제어함으로써 UPS 시스템의 입출력 특성들이 상당히 개선되는 것으로 알려져 있다. 여기서는 UPS 시스템의 성능 시험에서 중요한 내용들인 부하시험, 정전/복전시험, 동기절체 시험 등에 대한 결과들을 제시하고 델타변환 UPS 시스템에 대한 전반적인 평가를 한다.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.818-823
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• 1998

A three-arm PWM UPS is realizable low price and small size UPS. In this UPS configuration, the center arm operates in both PWM converter mode and PWM inverter mode. Therefore, the operation of this UPS differs from the conventional UPS. In this paper, the three-arm PWM UPS is analyzed and a trial product is realized.

• Proceedings of the KIEE Conference
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• 2005.11c
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• pp.131-135
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• 2005

Stabilization of electric power is the most important thing is such place as computing center having business critical equipment. However, ability to cope with electrical quality shift and power failure is very weak from UPS output side to load in those electricity system, though UPS is generally used for power stabilization. this problem can be solved by duplication of power source using newly configured UPS and small sized transfer switch even in case of UPS failure.

• KDI Journal of Economic Policy
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• v.40 no.2
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• pp.75-96
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• 2018

Recently, the government has been pursuing various policies to create new industries and jobs through the invigoration of start-ups. For the sustained growth of start-ups, it is necessary to look not only at the supply of risk capital but also at policies for venture capital firms that nurture and foster start-ups. The purpose of this study is to estimate the effects of the nurturing and fostering role of risk capital, such as mentorship on the performance of start-ups, and to do this we analyzed the effects, as a newly introduced form of venture capital, of mentoring by an accelerator and investor ties on the performance outcomes of start-ups. We find that mentoring and investor ties for start-up enterprises positively influence follow-up investment in start-ups. In addition, this study finds that with a younger CEO of a start-up, it is more likely that the performance of the start-up will improve. Meanwhile, when examining increases in employment as a measure of the business performance of start-ups, mentoring and investor ties are found to have a positive effect on the increase of employment at start-ups. These results suggest that there is a need to promote policies that strengthen the mentoring role of venture capital in Korea's equity finance policies and in the government's SME support policies.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.199-200
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• 2011

Uninterruptible Power Supply(UPS) is largely divided into passive-standby, line-interactive and double-conversion methods. This paper proposes the double-conversion UPS for low cost and high performance. The proposed UPS are composed of PFC, inverter, battery charger and discharger. Finally, the validity of proposed UPS was verified by experiments.

• Proceedings of the IEEK Conference
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• 2002.06e
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• pp.75-78
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• 2002

Since power failures in high-speed communication network, especially in HFC(Hybrid Fiber Coaxial cable) network are critical, microcontroller-based UPS(Uninterrupted Power Supply) are commonly used in the network. Hardware and software of UPS management system is designed and implemented to monitor and control UPS status to supply electric power to ONU and TBA in the HFC network. The result of laboratory tests and field tess of this system shows the scan rate to be 1 to 10 minutes to sufficiently monitor the status of UPS in the network.