• Journal of Electrical Engineering and Technology
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• 제11권5호
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• pp.1108-1115
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• 2016

• Journal of Electrical Engineering and Technology
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• 제4권4호
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• pp.429-437
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• 2009

This paper proposes a hybrid voltage controller based on a hierarchical control structure for implementation in the Jeju power system. The hybrid voltage controller utilizes the coordination of various reactive power devices such as generators, switched shunt devices and LTC to regulate the pilot voltage of an area or zone. The reactive power source can be classified into two groups based on action characteristics, namely continuous and discrete. The controller, which regulates the pilot bus voltage, reflects these characteristics in the coordination of the two types of reactive power source. However, the continuous type source like generators is a more important source than the discrete type for an emergency state such as a voltage collapse, thereby requiring a more reactive power reserve of the continuous type to be utilized in the coordination in order to regulate the pilot bus voltage. Results show that the hybrid controller, when compared to conventional methods, has a considerable improvement in performance when adopted to control the pilot bus voltage of the Jeju island system.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 춘계학술대회논문집
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• pp.398-401
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• 2005

This paper presents a user-friendly application for voltage sag analysis and effective visualization for analysis date. This developed tool provides basic functions for voltage sag analysis such as load flow analysis, short circuit analysis and determination of vulnerability of sensitive equipments. Particularly it has the ability to visualize analysis results effectively using computer graphic and animation. In order to give the real sense, analysis results are displayed with geographical information in an intuitive and rapid manner. The developed voltage sag simulator is applied to the Jeju-Island power system in order to show its capabilities.

• 전기학회논문지
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• 제64권8호
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• pp.1168-1179
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• 2015

This paper presents voltage and frequency control methods for a stand-alone Gasa Island Microgrid in South Korea that can be fully energized by renewable energy resources such as photovoltaic systems and wind turbines. To mitigate the variations of the output of renewable energy resources and supply more reliable electricity to customers, battery energy storage systems (BESSs) are employed in the stand-alone microgrid. The coordination between BESSs and pre-existing diesel generators is an important issue to manage the microgrid more securely. This paper presents voltage and frequency control schemes considering the coordination of BESSs and DGs. The effectiveness for the operating method is validated via simulation studies.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1777-1788
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• 2017

This paper presents the design and dynamic analysis of a stand-alone microgrid with high penetration of renewable energy. The optimal sizing of various components in the microgrid is obtained considering two objectives: minimization of levelized cost of energy (LCOE) and maximization of renewable energy penetration. Integrating high renewable energy in stand-alone microgrid requires special considerations to assure stable dynamic performance, we therefore develop voltage and frequency control method by coordinating Battery Energy Storage System (BESS) and diesel generators. This approach was applied to the design and development of Gasa Island microgrid in South Korea. The microgrid consists of photovoltaic panels, wind turbines, lithium-ion batteries and diesel generators. The dynamic performance of the microgrid during different load and weather variations is verified by simulation studies. Results from the real microgrid were then presented and discussed. Our approach to the design and control of microgrid will offer some lessons in future microgrid design.

• Journal of the Optical Society of Korea
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• 제16권4호
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• pp.349-353
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• 2012

Uniform spreading of injection current in light-emitting diodes (LEDs) is one of the crucial requirements for better device performances. It is reported that non-uniform current spreading leads to low output power, high current crowding, heating, and reliability degradation of the LED device. This paper reports on the effects of different surface and electrode geometries in the LEDs. To increase the output power of LEDs and reduce the series resistance, a rectangular-type LED (RT-LED) with a centered island cathode has been fabricated and investigated by comparison with a conventional LED (CV-LED). The performances of RT-LEDs were prominently enhanced via uniform current spreading and low current crowding. Performances in terms of increased output power and lower forward voltage of simulated RT-LEDs are much superior to those of CV-LEDs. Based on these results, we investigated the correlation between device geometries and optical characteristics through the fabricated CV and RT-LEDs. The measured output power and forward voltage of the RT-LEDs at 100 mA are 64.7% higher and 8% smaller compared with those of the CV-LEDs.

• 한국산학기술학회논문지
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• 제19권9호
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• pp.526-535
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• 2018

최근, 도서지역에서는 $CO_2$ 배출의 저감을 위하여, 디젤발전기의 가동률을 줄이고 신재생에너지전원의 비중을 높여, 계통을 안정적으로 운용할 수 있는 방안들이 연구되고 있다. 특히, Carbon free를 목표로 하는 도서지역용 Micro-grid에서는 CVCF(constant voltage & constant frequency) 인버터를 기반으로 운용되는데, CVCF 인버터용 배터리의 SOC(state of charge) 상태에 따라, 계통의 부하소비 보다 신재생에너지전원의 출력이 큰 경우에 CVCF 인버터 내에서 발생하는 에너지 Sinking에 의하여, 배터리측 전압이 급격히 상승하여, 인버터의 과전압 보호동작에 의해 CVCF 인버터가 급격하게 탈락되어 계통에 정전이 발생하는 문제점이 일어날 수 있다. 따라서, 본 논문에서는 CVCF 인버터를 기반으로 한 도서지역용 Micro-grid의 안정적인 운용을 위하여, 에너지 Sinking 시에 발생 가능한 CVCF 인버터의 탈락을 사전에 방지하는 과도상태 운용알고리즘을 제안한다. 또한, PSCAD/EMTDC의 모델링을 이용하여, 제안한 알고리즘을 적용한 Micro-grid의 과도상태 운용특성을 분석한 결과, 배터리의 전압과 SOC에 따라 CVCF 인버터가 탈락하는 과도상태를 사전에 방지할 수 있어, 본 논문의 유용성을 확인하였다.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1052-1059
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• 2018

This paper deals with commutation failure of the line-commutated converter high voltage direct current (LCC HVDC) system caused by a three phase fault in the ac power system. An analytic calculation method is proposed to estimate the maximum permissible voltage drop at the LCC HVDC station on various operating point and to assess the area of vulnerability for commutation failure (AOV-CF) in the power system based on the residual phase voltage equation. The concept is extended to multi-infeed HVDC power system as the area of severity for simultaneous commutation failure (AOS-CF). In addition, this paper presents the implementation of a shunt compensator applying to the proposed method. An analysis and simulation have been performed with the IEEE 57 bus sample power system and the Jeju island power system in Korea.

• 전력전자학회논문지
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• 제15권1호
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• pp.69-74
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• 2010

풍력발전기가 계통에 연계되어 운전 중 바람의 변동에 따라 유효전력이 변동하면 연계지점에서는 전압변동이 발생하며 풍력발전기의 연계 위치 (PCC, Point of Common Coupling) 에 따라 그 값은 변동한다. 본 논문에서는 이러한 계통 연계 지점의 전압변동이 이상 전원에서 PCC지점까지의 등가 선로 임피던스와 풍력발전기 출력 전류의 곱에 비례함을 보였으며 이러한 전압변동을 억제하기 위하여 필요한 무효전력 요구량을 해석적인 방법으로 구하였다. 만일 풍력발전기 출력단 인버터의 용량 제한에 의해 무효전력 주입량에 한계가 있거나 전압변동 허용범위가 주어진 경우에는 그에 따라 무효전력 주입량을 변화시킬 수 있다. 제안된 알고리즘을 가변속 풍력발전시스템의 출력단 인버터에 사용하면 수시로 변동하는 유효전력에 따라 무효전력 요구량을 실시간으로 계산함으로서 PCC전압변동을 최소화할 수 있다. 제안된 알고리즘의 타당성을 검증하기 위해 실제 서해 도서지역에 설치된 소형 풍력발전기 및 전력 시스템 파라메터를 사용하여 Matlab과 PSCAD/EMTDC 시뮬레이션을 수행하였다.

• 전기학회논문지
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• 제59권12호
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• pp.2190-2194
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• 2010

Wind power generation system (WPGS) of Ulleung Island causes frequency and voltage fluctuation due to wind speed variation during night time. Superconducting magnetic energy storage (SMES) system can overcome the fluctuations through the fast response time of energy charging and discharging. The SMES system should be connected to the terminal of the WPGS for frequency stabilization. To demonstrated the effectiveness of SMES system for power quality improvement, Ulleung Island power network was modeled in a real time digital simulator (RTDS). The RTDS-based simulation results of power quality improvement with SMES are investigated and discussed in detail.