• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.954-955
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• 2008

In this paper, the voltage harmonics are investigated in terms of the voltage sag versus the time constants of electric machinery under the source voltage variation condition. The electric machinery and compensation equipment are established on the proposed design scheme based on voltage quality effect assessment technology. It have been analyzed how the variation of harmonic order, the output current, the DC-Link voltage and the induction motor speed is carried out under the voltage sag and switching frequency variation.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.321-322
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• 2015

An area of severity (AOS) assessment is defined as a set of the fault positions that can result in the voltage sag bigger than certain level for sensitive buses simultaneously. Using the AOS assessment, the location of devices for compensating voltage sag can be determined as the site expected to less voltage sag at the sensitive bus. The energy storage system based on the control strategy emulating the traditional synchronous generator can contribute the fault current with fast response. Therefor are of venerability (AOV) can be reduced. The energy storage system installed by the AOS assessment has function which can experience relatively less voltage sag in addition to the conventional role of energy storage.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.315-319
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• 2003

This paper presents modeling and analysis of static and dynamic characteristics in PWM Boost AC-AC converter used for input voltage sag compensation of custom power. Especially, using circuit DQ transformation technique, an equivalent circuit in fundamental frequency domain is obtained which has all the system characteristics. Moreover, voltage gain and input power factor is analytically induced and linearized state equation at the specific operating point is given. Finally, simulation results show the validity of the proposed modelling and analyses.

• Proceedings of the KIEE Conference
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• 2002.11d
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• pp.218-220
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• 2002

본 연구에서는 정상상태에서 고조파 전류와 순시전압 강하에 대한 보상성능이 우수한 3상 전압 Sag 및 고조파 전류 보상 시스템을 제안하고 있다. 제안된 시스템의 보상 알고리즘으로는 구현하기 쉽고 간단한 직접 필터링 알고리즘이 사용되고 있으며 하이브리드 직렬형 능동전력필터에 적용하였다. 제안된 알고리즘은 전원전압이 순간적으로 왜형과 sag가 발생되더라도 비선형 부하에 인가되는 전압은 일정한 정현파로 제어 가능하며 동시에 전원전류의 고조파와 기본파 무효전류도 보상 가능하다. 정상상태와 과도상태에서 전력전자전용 시뮬레이터인 PSIM에 의해 제안된 이론의 타당성을 입증하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.10-13
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• 2008

Fuel cell systems have witnessed remarkable development in recent years as they offer a clean and efficient alternative for power generation. Testing was conducted to determine the safety performance of a residential fuel cell system when subjected to abnormal operation condition, especially for voltage sag and fuel cut. In case of voltage sag to 198V, its arriving time at rated power had shown a slight lag but there wasn't any noticeable change when operating it between rated voltage(220V) and 10% voltage sag(198V). In case of fuel cut, it also showed stable shut-down characteristics. The test results are being used to develop a new safety evaluation for residential fuel cell system.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1014-1015
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• 2006

In this paper, a new single phase voltage sag/swell compensator using direct power conversion is introduced. A new compensator consists of input/output filter, series transformer and direct at-ac converter, which is a single-phase back-to-back PWM converter without dc-link capacitors. Advantages of the proposed compensator include: simple power circuit by eliminating dc-link electrolytic capacitors and thereby, improved reliability and increased life time of the entire compensator; simple PWM strategy to compensate voltage sag/swell at the same time and reduced switching losses in the ac-ac converter. Further, the proposed scheme is able to adopt simple switch commutation method without requiring complex four-step commutation method commonly required in the direct power conversion. Simulation results are shown to demonstrate the advantages of the new compensator and PWM strategy.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.972-977
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• 2009

For the improvement of a train speed in the conventional line from overhead system point of view, it is necessary to approach not only in the aspect of the increasement of tension for catenary but the application of a pre-sag. A certain tension acting on a dropper is removed when it is slack by the pantograph passing. Right after the pantograph passes, the dynamic force caused by the mass of contact wire acts on the dropper. If the pre-sag is applied to the catenary, the static force on the dropper is increased. For the assurance of the safety for the dropper, it is necessary to predict the dynamic force. The purpose of this study is to predict and analyze the force on the dropper according to the applied pre-sag.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.12
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• pp.65-73
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• 2014

In this paper, the detection scheme of the voltage variation using a two difference voltage is proposed. The conventional sag detector is from a single-phase digital phase-locked loop (DPLL) that is based on a d-q transformation using an all-pass filter (APF). The APF generates a virtual q-axis voltage component with $90^{\circ}$ phase delay but the APF cannot generate the virtual q-axis voltage depending on the phase of the grid voltage. To overcome the problem, q-axis voltage component is generated from difference between the current and previous value of d-axis voltage component in the stationary reference frame. However, the difference voltage around the zero crossing is not enough to detect the voltage sag. Therefore, the new detection scheme using the two difference voltage which can detect the sag around the zero crossing voltage is proposed.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.9
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• pp.165-171
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• 2010

There are many researches on Power Quality Device to protect the critical load and power system as the nonlinear load and precision load are adopted into the power system recently. To analyze the voltage compensation of voltage sag and voltage swell by DVR, which is connected to the important load in series, this paper shows PSCAD/EMTDC simulation and its verification by comparing with the actual DVR output of 2MVA. DVR control scheme in this paper is applicable to compensate single-phase, 2-phases or 3-phases voltage sag as well as DVR for distribution system.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.157-159
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• 2003

To improve power quality, it is important to find the location of disturbance source. This paper presents a method to find the location of disturbance source that leads to voltage sag. The relative location of the source is defined and the method to determine the relative location of voltage sag is proposed. With this method, this paper shows that the location of disturbance source can be identified under distributed monitoring system.