• 동력기계공학회지
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• 제17권5호
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• pp.52-57
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• 2013

In this paper, an analysis on exergy efficiency of high-efficiency R717 OTEC power system for the efficiency and pressure drop in main components were investigated theoretically in order to optimize the design for the operating parameters of this system. The operating parameters considered in this study include turbine and pump efficiency, and pressure drop in a condenser and evaporator, respectively. As the turbine efficiency of R717 OTEC power system increases, the exergy efficiency of this system increases. But pressure drop in the evaporator of R717 OTEC power system increases, the exergy efficiency of this system decreases, respectively. And, in case of exergy efficiency of this OTEC system, the turbine efficiency and pressure drop in a condenser on R717 OTEC power system is the largest and the lowest among operation parameters, respectively.

• Journal of Power Electronics
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• 제11권4호
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• pp.561-567
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• 2011

This paper presents a high-efficiency power conditioning system (PCS) for grid-connected photovoltaic (PV) modules. The proposed PCS consists of a step-up DC-DC converter and a single-phase DC-AC inverter for the grid-connected PV modules. A soft-switching step-up DC-DC converter is proposed to generate a high DC-link voltage from the low PV module voltage with a high-efficiency. A DC-link voltage controller is presented for constant DC-link voltage regulation. A half-bridge inverter is used for the single-phase DC-AC inverter for grid connection. A grid current controller is suggested to supply PV electrical power to the power grid with a unity power factor. Experimental results are obtained from a 180 W grid-connected PV module system using the proposed PCS. The proposed PCS achieves a high power efficiency of 93.0 % with an unity power factor for a 60 Hz / 120 Vrms AC power grid.

• Journal of Power Electronics
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• 제11권4호
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• pp.551-560
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• 2011

This paper proposes a grid-tied power conditioning system for the fuel cell power generation, which consists of a 2-stage DC-DC converter and a 3-phase PWM inverter. The 2-stage DC-DC converter boosts the fuel cell stack voltage of 26-48V up to 400V, using a hard-switching boost converter and a high-frequency unregulated LLC resonant converter. The operation of the proposed power conditioning system was verified through simulations with PSCAD/EMTDC software. Based on the simulation results, a laboratory experimental set-up was built with a 1.2kW PEM fuel-cell stack to verify the feasibility of hardware implementation. The developed power conditioning system shows a high efficiency of 91%, which is a very positive result for the commercialization.

• 한국수소및신에너지학회논문집
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• 제19권5호
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• pp.417-422
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• 2008

In this paper, a novel DC/DC low-voltage high-current converter circuit is proposed to improve the efficiency of power converter used in the grid-connected fuel-cell generator system. We proposed a novel high efficiency grid-connected power conditioning system for RPG fuel cell. On the result of that, the loss of system was decreased rapidly by driving stack within the condition of maximum efficiency. The peak currents of the current-type inductor and the transformer's coil are reduced by synchronizing switching frequency of Buck-type converter is increased twice as the Push-Pull converter's switching frequency. The novel structure of DC/DC converter is able to realize ZVS-ZCS in fuel-cell system is proposed. The proposed switching component of Push-Pull converter has the ZVS and ZCS function by using the circuit of new passive clamp.

• 동력기계공학회지
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• 제18권5호
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• pp.88-93
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• 2014

In this paper, the performance analysis of condensation and evaporation capacity, turbine work and efficiency of the OTEC power system using vapor-liquid Ejector is presented to offer the basic design data for the operating parameters of the system. The working fluid used in this system is $CO_2$. The operating parameters considered in this study include the vapor quality at heat exchanger outlet, pressure ratio of ejector and inlet pressure of low turbine, mass flow ratio of separator at condenser outlet. The main results were summarized as follows. The efficiency of the OTEC power cycle has an enormous effect on the mass flow ratio of separator at condenser outlet. With a thorough grasp of these effects, it is possible to design the OTEC power cycle proposed in this study.

• 마이크로전자및패키징학회지
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• 제13권1호통권38호
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• pp.57-61
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• 2006

연료전지는 연료(수소)의 화학적 반응에 의해 축적된 화학에너지를 전기에너지로 변환하여 직류 전기를 발생시키는 에너지원이다. 연료전지는 질소나 유황산화물 등의 유해한 물질을 방출하지 않으며 기계적 동력부가 없고 거의 무소음으로 운전되는 이점을 가진다. 수소연료에 의한 연료전지는 그들의 부산물로써 열과 물을 방출한다. 연료전지를 이용한 응용분야의 확대로 인해 화석연료나 수입 석유의 의존도를 현저히 감소시킬 수 있다. 본 논문에서는 이러한 연료전지 (PEMFC, Proton Exchange Membrane Fuel Cell)의 출력을 치대한 활용하고 발전시스템의 안전운전을 위한 전력변환기(PCS, Power Conditioning System)에 대해 연구하였다. 본 논문에서는 고효율로 운전하는 새로운 전력변환 회로토폴로지를 설계하고, 발전시스템에 적용하여 각종 실험을 통하여 그 타당성을 입증하였다. 그 결과 연료전지 발전시스템은 고성능으로 동작되는 전력변환기에 의해 발전시스템의 효율과 성능을 향상시키게 된다.

• Journal of Power Electronics
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• 제10권4호
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• pp.335-341
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• 2010

In this paper, an interleaved soft switching boost converter for a Photovoltaic Power Conditioning System (PV-PCS) with high efficiency is proposed. In order to raise the efficiency of the proposed converter, a 2-phase interleaved boost converter integrated with soft switching cells is used. All of the switching devices in the proposed converter achieve zero current switching (ZCS) or zero voltage switching (ZVS). Thus, the proposed circuit has a high efficiency characteristic due to low switching losses. To analyze the power losses of the proposed converter, two experimental sets have been built. One consists of normal devices (MOSFETs, Fast Recovery (FR) diodes) and the other consists of advanced power devices (CoolMOSs, SiC-Schottky Barrier Diodes (SBDs)). To verify the validity of the proposed topology, theoretical analysis and experimental results are presented.

• 동력기계공학회지
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• 제21권3호
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• pp.45-50
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• 2017

This paper presents the Coefficient of performance(COP) and mass flow ratio of cascade refrigeration system with respect to refrigerants appling to high temperature cycle. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporating temperature, condensing temperature and internal heat exchanger effectiveness in high temperature cycle. The result of this study is as follows : The COP of cascade system increases with increasing degree of superheating and subcooling, compressor efficiency and internal heat exchanger effectiveness except increasing condensing temperature. The mass flow ratio of low and high temperature cycle increases with increasing evaporating temperature and condensing temperature, but decreases with increasing internal heat exchanger effectiveness, degree of superheating and subcooling. Also, the mass flow ratio has no correlation with compressor efficiency at high temperature cycle.

• Journal of Advanced Marine Engineering and Technology
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• 제37권8호
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• pp.829-835
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• 2013

본 논문은 제안된 고효율 R717용 해양온도차 발전 시스템의 운전변수에 대한 최적의 설계를 위해 엑서지 효율을 이론적으로 분석하였다. 본 연구에서 고려된 작동변수로는 증발기 출구압력, 고단터빈 출구압력, 응축기 입구압력 그리고 냉각기 출구건도이다. 분석한 결과를 요약하면 다음과 같다. R717용 OTEC 발전 사이클의 증발기 출구압력, 냉각기 출구건도가 증가할수록 엑서지 효율은 증가한다. 그러나 고단터빈 출구압력, 응축기 입구압력이 증가할수록 엑서지 효율이 감소한다. 그리고 이러한 작동변수들 중에서 증발기 출구압력이 R717용 OTEC 발전 사이클의 엑서지 효율에 가장 크게 영향을 미치고, 고단터빈 출구압력이 가장 적게 영향을 미친다.

• Journal of Power Electronics
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• 제13권2호
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• pp.296-303
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• 2013

This paper proposes a high efficiency three-phase cascaded phase shifted H-bridge multi-level inverter without DC/DC converters for grid-tied multi string photovoltaic (PV) applications. The cascaded H-bridge topology is suitable for PV applications since each PV module can act as a separate DC source for each cascaded H-bridge module. The proposed phase shifted H-bridge multi-level topology offers advantages such as operation at a lower switching frequency and a lower current ripple when compared to conventional two level topologies. It is also shown that low ripple sinusoidal current waveforms are generated with a unity power factor. The control algorithm permits the independent control of each DC link voltage with a maximum power point for each string of PV modules. The use of the controller area network (CAN) communication protocol for H-bridge multi-level inverters, along with localized PWM generation and PV voltage regulation are implemented. It is also shown that the expansion and modularization capabilities of the H-bridge modules are improved since the individual inverter modules operate more independently. The proposed topology is implemented for a three phase 240kW multi-level PV power conditioning system (PCS) which has 40kW H-bridge modules. The experimental results show that the proposed topology has good performance.