• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 학술대회 논문집
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• pp.251-255
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• 2005

This paper proposes a new soft switching technique for a phase-shift controlled bi-directional DC-DC converter. The described converter employs a low profile high frequency transformer and two active full-bridge converters for bidirectional power flow capability. A new soft switching technique is proposed, which guarantees soft switching over wide range (no load to full load) without any additional circuit components. In the proposed switching scheme, the switch pairs in the diagonal position of the converter each are turned on/off simultaneously by the switching signals with a variable duty ratio depending on the phase shift amount, and the converter is operated without freewheeling interval.

• Current Photovoltaic Research
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• 제4권4호
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• pp.131-139
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• 2016

This paper shows the series power device in the massive roof-top PVs and domestic loads. D-UPFC as the series power device controls the distribution voltage during voltage rise (or fall) condition. D-UPFC consists of the bi-directional ac-ac converter and the transformer. In order to verify the D-UPFC voltage control, the distribution model is used in the case study. D-UPFC enables the voltage control in the distribution voltage range. Dynamic voltage control from voltage rise and voltage fall conditions is performed. Scaled-down experimental test of the D-UPFC is verified the voltage control and it is well performed without high voltage spikes in the inductive load.

• 디지털산업정보학회논문지
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• 제10권3호
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• pp.197-205
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• 2014

In applications of adaptive noise control or active noise control, the presence of a transfer function in the secondary path following the adaptive controller and the error path, been shown to generally degrade the performance of the Least Mean Square (LMS) algorithm. Thus, the convergence rate is lowered, the residual power is increased, and the algorithm can become unstable. In general, in order to solve these problems, the filtered-x LMS (FX-LMS) type algorithms can be used. But these algorithms have slow convergence speed and weakness in the environment that the secondary path and error path are varied. Therefore, I present the new algorithm called the "Bi-directional Filtered-x (BFX) LMS" algorithm with nearly equal computation complexity. Through experimental study, the proposed BFX-LMS algorithm has better convergence speed and better performance than the conventional FX-LMS algorithm, especially when the secondary path or error path is varied and the impulsive disturbance is flow in.

• 한국기계가공학회지
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• 제4권4호
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• pp.39-47
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• 2005

In this paper, a novel high power micropump using active check valves in place of conventional passive check valves employed at the inlet and outlet ports is presented. It actively controls open/close motion of check valves using piezoelectric actuator for expansion/contraction of pump chamber. A prototype micropump having an effective size of $17mm{\times}8mm{\times}11mm$ is fabricated. Frequency-dependent flow rate characteristics, bi-directional flow characteristics and load characteristics are experimentally investigated using a timing control method for valve closing motion. From the obtained experimental results, it is ascertained that optimal values of the phase shift compared to the voltage to drive pump chamber are $15^{\circ}$ for inlet check valve and $195^{\circ}$ for outlet. Based on the obtained results, a sheet-type active shuttle valve that has a unified valve-body for inlet and outlet check valves is proposed. A micropump with an effective size of $10mm{\times}10mm{\times}10mm$ is fabricated and the basic characteristics are experimentally investigated.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.163.1-163.1
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• 2011

세계는 지금 지구 온난화 및 화석연료의 고갈로 인해 대체 에너지 자원의 확보문제가 급속히 대두되고 있다. 이에 조류발전은 오염이 발생하지 않는 친환경 에너지원으로서, 날씨나 계절에 상관없이 항상 발전할 수 있는 신뢰성 있는 에너지이며, 높은 밀도를 가지는 작동유체가 수차에 미치는 영향 또한 크므로 지속적으로 예측이 가능한 장점을 가지고 있다. 이러한 조류에너지는 실 해역에 적용하기 위해서는 전격유효 전력이 생산 가능한 지리적 요인에 대한 고찰과 더불어 조류발전 터빈의 개념설계가 고려되어야 한다. 본 연구는 다양한 설치 공간을 형성할 수 있으며, 장, 단점이 보완될 수 있는 조류발전 터빈의 개념설계 연구 단계로서, 내부 유동 특성을 고려하여 입구를 설계하였으며, 일정한 속도로 유입되는 유량을 노즐의 장착을 통해 에너지 밀도를 높일 수 있게 된다. 이러한 개념형상 설계로 추가 작동이나, 장치의 사용 없이 양방향 발전이 가능해 진다.

• 한국정보통신학회논문지
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• 제25권11호
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• pp.1603-1611
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• 2021

본 연구에서는 에너지 저장장치인 배터리를 기존의 발전기 전력계통에 연계하기 위하여 양방향 전력의 흐름이 가능한 BDC(Bi-Directional Converter) 적용을 위해 모델링을 통하여 제어 프로세스를 설계하고, 해상 상황에 따라 변화하는 부하에 최적화된 전력 공급이 가능한 배터리의 충전 혹은 방전 메커니즘에 대하여 제안한다. 본 연구는 MATLAB/Simulink를 이용하여 BDC를 모델링 하였으며 부하 시나리오에 따라 배터리 충전 및 방전 시의 전류 제어 및 SOC(State Of Charge) 최적화를 시뮬레이션 하였다. 이를 통해 선내 운전되는 발전기가 최적운전 범위에 운전될 수 있도록 배터리와 전력 및 부하를 연동할 수 있도록 하였으며, 발전기가 높은 연료효율 범위에서 운전될 수 있도록 전력제어관리를 수행하였다.

• 드라이브 ㆍ 컨트롤
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• 제17권2호
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• pp.55-62
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• 2020

There are two types of IMV for MCV, the spool type and the poppet type. The spool type is used in the existing excavator MCV and easily meets large-capacity flow conditions, but has a flow force problem which affects the spool control. The poppet type stably blocks the flow and has excellent rapid response. However, the larger the capacity, the larger the diameter of the poppet needed, requiring a strong spring to withstand the oil pressure. In this study, a bi-directional three-stage IMV for MCV that can be used in medium and large hydraulic excavators was proposed. This is a poppet type, enabling bi-directional flow control and resolves the problem of proportional solenoid suction force limitation. To investigate the validity of the proposed valve, the system was mathematically modeled and the static and dynamic characteristics were investigated through the simulation using commercial software. It has been concluded that the reverse flow is possible in a regeneration circuit and that the proposed IMV can be used to perform various excavation modes.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 전력전자학술대회
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• pp.180-181
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• 2017

Recently as distributed source has increased, the distribution system has changed from unidirectional power flow to bi-directional power flow. This power flow causes the PCC voltage variation, which can adversely affect voltage sensitive loads. In this paper, the relation between the active power, reactive power and PCC voltage of the distributed source is analyzed, and the PCC voltage control scheme by reactive power compensation is proposed in the distributed source itself. In addition, limitations and conditions according to the standard for interconnecting distributed resources are specified and verified through simulation.

• 조명전기설비학회논문지
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• 제26권7호
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• pp.70-76
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• 2012

In general, the unidirectional power flow is normal in distribution feeders before activation of distributed power source such as PV. However, the interactive power flow is likely to occur in case of the power system under distributed generation. This interactive power flow can cause an unexpected effect on convectional protection coordination systems designed based only on the unidirectional power flow system. When the power line system encounters a problem, the interactive power flow can be a contributed current source and this makes the fault current bigger or smaller compared to the unidirectional case. The effect of interactive power flow is varied depending on the location of the point to ground fault, relative location of the PV, and connection method. Therefore it is important to analyse characteristics of fault current and interactive flow for various transformer connection and location of the PV. This paper proposes a method of improved protection coordination which can be adopted in the protective device for customers in distribution feeders interconnected with the PV. The proposed method is simulated and analysed using PSCAD/EMTDC under various conditions.

• International Journal of Fluid Machinery and Systems
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• 제9권3호
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• pp.222-228
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• 2016

Almost 70% of the earth is covered by the ocean. Extracting the power available in the ocean using a wave energy converter has been seen to be eco-friendly and renewable. This study focuses on developing a method for analyzing a wave energy device that uses a cross-flow turbine. The motion of the ocean wave causes an internal bi-directional flow of water and the cross-flow turbine is able to rotate in one direction. This device is considered of double-hull structure, and because of this structure, sea water does not come into contact with theturbine. Due to this, the problem of befouling on the turbine is avoided. This study shows specific relationship for wave length and several motions.