• 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.

• 한국초전도ㆍ저온공학회논문지
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• 제13권2호
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• pp.1-4
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• 2011

This paper describes current status of High Temperature Superconductor (HTS) rotating machinery development in Japan. Recent advances in production technology of HTS materials have continuously stimulated the development of high performance rotating machines. One of the most promising applications for such machines is the ship propulsion, and then some major projects have been underway. Also, energetic challenges for the HTS drive motor, e.g., automobile, have started. Furthermore, low speed and large capacity HTS generators are considered to be exciting candidates for wind turbines. The technology trends of the HTS rotating machines is introduced and discussed in this review paper.

• Journal of Electrical Engineering and Technology
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• 제12권3호
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• pp.1064-1072
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• 2017

The power of controlled generators in microgrids randomly fluctuate because of the stochastic volatility of the outputs of photovoltaic systems and wind turbines as well as the load demands. To address and dispatch these stochastic factors for daily operations, a dynamic economic dispatch model with the goal of minimizing the generation cost is established via chance-constrained programming. A Monte Carlo simulation combined with particle swarm optimization algorithm is employed to optimize the model. The simulation results show that both the objective function and constraint condition have been tightened and that the operation costs have increased. A higher stability of the system corresponds to the higher operation costs of controlled generators. These operation costs also increase along with the confidence levels for the objective function and constraints.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.23-24
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• 2007

Most of modern wind turbines employs a doubly-fed induction generator (DFIG) system because it has many advantages due to variable-speed operation, relatively high efficiency and it small converter size. The DFIG system uses a wound rotor induction machine so that the magnetizing current of the generator can be fed from both the stator and the rotor. This paper presents a protection relaying algorism for DFIG using the DQ equivalent circuits. The induced voltages calculated from the stator and rotor sides are nearly the same in the steady state. They become different in the DQ equivalent circuits during an internal fault. The proposed algorithm compares the inducted voltages estimated from the stator and the rotor circuit converted into the stationary reference frame. If the difference between the induced voltages exceeds the threshold, the proposed algorithm detects an turn-to-turn fault.

• Ocean Systems Engineering
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• 제12권4호
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• pp.439-459
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• 2022

This paper describes experimental studies of impact pressure generated by breaking regular waves in shallow water on a vertical cylinder. Experimental work was carried out in a shallow water flume using a 1:30 - scale model of a vertical rigid circular hollow cylinder with a diameter 0.2 m. This represents a monopile for shallow water offshore wind turbines, subjected to depth induced breaking regular waves of frequencies of 0.8 Hz. The experimental setup included a 1 in 10 sloping bed followed by horizontal bed with a constant 0.8 m water depth. To determine the breaking characteristics, plunging breaking waves were generated. Free surface elevations were recorded at different locations between the wave paddle to the cylinder. Wave impact pressures on the cylinder at a number of elevations along its height were measured under breaking regular waves. The depth-induced wave breaking characteristics, impact pressures, and wave run-up during impact for various cylinder locations are presented and discussed.

• 전력전자학회논문지
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• 제28권1호
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• pp.1-7
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• 2023

A grid-connected 3-level NPC inverter is a power conversion device that connects renewable energy generators, such as photovoltaic or wind turbines to the grid. Although many studies have focused on this inverter, commercializing it requires strictly satisfying various safety and power quality-related standards. Among many standards, leakage current and grid current total harmonic distortion(THD) can be affected by external factors such as installation environment, aging, and grid conditions. Hence, inverter operations that can satisfy these standards need to be explored. In this study a 3-level NPC inverter operation algorithm using the Phase Opposition Disposition-PWM method that can effectively reduce leakage current and switching frequency adjustment to reduce THD effectively has been proposed.

• 한국항공우주학회지
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• 제46권1호
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• pp.10-17
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• 2018

풍력발전기의 효율을 증가시키기 위하여 피치제어가 주로 사용되어 왔으나 피로파괴와 효율의 감소를 일으키는 날개의 국부적인 유동을 제어할 수 없는 단점이 있다. 본 논문에서는 기존의 풍력발전기 블레이드에 합성제트 구동기 모듈을 설치하여 국부 유동을 제어하고 날개의 공력성능을 향상시키고자 한다. 합성제트 구동기는 작은 구멍을 통해 유체를 흡입/분출하여 유동 박리를 지연시켜 공력성능을 향상시킨다. 압전디스크를 사용하여 탈부착이 가능한 합성제트 구동기 모듈을 제작하고 풍동실험을 통해 오리피스 형상과 합성제트 속도에 따른 공력성능을 측정하였다. 직사각형 오리피스 형상을 사용하고 합성제트 속도가 커질수록 날개의 항력이 감소하고 양력이 증가하는 것을 확인하였다.

• 대한조선학회논문집
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• 제50권6호
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• pp.365-372
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• 2013

In this study, the flow characteristics and structural safety of a 500W class vertical-axis wind turbines(VAWT) for a fishing boat are investigated by numerical simulations. Guide vanes to increase the performance of the VAWT are investigated. And the best guide vane in the numerical simulations is applied to the VAWT. Also, modal analyses are performed to find out the natural frequencies of the VAWT, and the resonance safety of the VAWT is evaluated. The structural analysis of the VAWT is carried out by one-way FSI(Fluid Structure Interaction). And the results are used for the evaluation of structural safety according to IEC 61400-1 code. Finally, the possibility of the installation of the VAWT on the wheelhouse of a 9.77ton class fishing boat is checked. The results of the present research could be used as one of the fundamental data to design a VAWT for a fishing boat.

• 한국기계가공학회지
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• 제19권2호
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• pp.38-46
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• 2020

The purpose is to evaluate the structural characteristics of 750 mm diameter injection spiral blades under various operating conditions. A fiber-glass reinforced polypropylene material was employed to the injection blades, and mechanical tests on two kinds of glass-reinforced polypropylene were performed to evaluate the mechanical properties and to select a suitable candidate material. Also, three kinds of spiral blade geometries were studied to observe the influence of fixing rods between blades. For this, structural analyses were conducted to understand the role of fixing rods under a range of rotating speed. In addition, modal analysis was performed to confirm the resonance in the operating speed range. One-way fluid-structure interaction (FSI) analysis was carried out to know its mechanical integrity under dangerous wind speed conditions. Through this work, the structural characteristics of the proposed spiral blade geometries were studied under various operating conditions, and the requirements of mechanical properties of blades were determined.

• 한국지반공학회논문집
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• 제36권2호
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• pp.29-42
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• 2020

본 연구에서는 모래지반에 설치된 해상풍력 지지용 직경 7m 모노파일의 p-y 곡선에 대한 수평하중-모멘트 조합의 영향을 분석하기 위하여 원심모형실험을 수행하였다. 이를 위하여 원심모형실험시스템을 구축하였고, 다수의 게이지를 부착한 계측용 모노파일 모형을 사용하여 68.83g에서 원심모형실험을 수행하였다. 지표면으로부터 직경의 1배와 직경의 5배 높이에서 하중재하를 하는 2개의 수평하중-모멘트 조합으로 재하시험이 수행되었다. 모형지반은 중간밀도의 모래로 조성되었다. 원심모형실험결과로부터 실험 p-y 곡선을 산정하였고 기존 문헌의 p-y 곡선과 비교하였다. 결과적으로 p-y 곡선에 대한 모멘트 조합의 영향이 미미함을 확인하였다. 또한, 근입깊이가 모노파일의 p-y 곡선에 영향을 미치는 것을 확인하였다