• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1336-1337
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• 2011

본 논문은 최근 이슈가 되고 있는 해양에너지 중 해류의 흐름을 이용한 조류발전 시스템에 관한 것으로 대학 실험실규모에서 조류발전 시스템의 성능 및 특성을 효율적으로 시험 평가할 수 있도록 구성된 모의실험 장치에 관한 것이다. 조류발전은 타 에너지원에 비해 발전의 제한조건과 단점이 거의 없으며 국내 자연환경에 적용하기에 적합한 많은 장점을 가지고 있다. 본 논문에서는 조류발전 시스템의 성능 및 특성을 시험할 수 있도록 Motor-Generator Set(M-G Set)을 구성하였고, 최대출력제어를 위해 사전에 PSIM을 이용하여 시뮬레이션을 수행하여 최대 출력제어 알고리즘을 검증하였다. 구축된 조류 발전 모의실험 장치는 해양의 기후, 시간 변화에 따른 조류 속도 변화를 효율적으로 모의할 수 있도록 전동기 속도 제어를 가능하도록 하였다. 조류발전 시스템에서는 와류등으로 인해 유속을 측정하기 힘들고, 오차가 발생할 가능성이 많다. 그래서 유속 정보 없이 최대출력제어가 가능한 알고리즘을 시뮬레이션하여 수행하였다. 본 연구는 향후 실시간 발전 사항을 모니터링 할 수 있도록 LabVIEW 기반 모니터링 시스템에서 최대 출력제어 시스템을 구축하기 위한 좋은 자료로 쓰일 것이라 판단된다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2189-2195
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• 1992

The performance of heat exchanger as an energy conversion device can be described by the available energy output and efficiency. The efficiency is defined as the ratio of the available energy output and the exergy of the heat source flow. In present study, a counterflow heat exchanger is analyzed and the conditions to obtain maximum output is numerically determined. As a result, the avilable energy obtained by the cold flow can be determined as functions of the heat capacity flow, the cold flow inlet temperature and the heat transfer capacity of heat exchanger. At the maximum output condition the heat capacity flow of the cold fluid is larger than that of the heat source, and the heat capacity flow ratio is equal to the ratio of the cold flow inlet temperature and the atmospheric temperature. And the avilable energy output increases as the heat transfer capacity of the heat exchanger become larger, but in the economic point of view there is also an optimum heat transfer capacity for a given heat source flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.172-181
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• 1993

Pseudo-Brayton cycle is defined as an ideal Brayton cycle admitting the difference between heat capacities of working fluid during heating and cooling processes. The endo-pseudo-Brayton cycle which is a pseudo-Brayton cycle with heat transfer processes is analyzed with the consideration of maximum power conditions and the results were compared with those of the endo-Carnot cycle and endo-Brayton cycle. As results, the maximum power is an extremum with respect to the cycle temperature and the flow heat capacities of heating and cooling processes. At the maximum power condition, the heat capacity of the cold side is smaller than that of heat sink flow. And the heat capacity of endo-Brayton cycle is always between those of heat source and sink flows and those of the working fluids of pseudo-Brayton cycle. There is another optimization problem to decide the distribution of heat transfer capacity to the hot and cold side heat exchangers. The ratios of the capacies of the endo-Brayton and the endo-pseudo-Braton cycles at the maximum power condition are just unity. With the same heat source and sink flows and with the same total heat transfer caqpacities, the maximum power output of the Carnot cycle is the least as expected, but the differences among them were small if the heat transfer capacity is not so large. The thermal efficiencies of the endo-Brayton and endo-Carnot cycle were proved to be 1-.root.(T$_{7}$/T$_{1}$) but it is not applicable to the pseudo-Brayton case, instead it depends on comparative sizes of heat capacities of the heat source and sink flow.w.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.110-111
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• 2013

전원의 변동이 심한 전압원을 사용하는 선박, 전기자동차 등에서는 DC-Link전압이 가변하기 때문에 낮은 영역의 전압에서는 최대출력 운전을 할 수가 없다. 낮은 영역의 전압에서 최대 출력을 하기 위하여 유도전동기 ${\Delta}$결선 운전을 해야 하지만 ${\Delta}$결선 운전시 높은 입력 전류로 인하여 인버터 전력소자의 온도가 상승하게 된다. 따라서 유도전동기 Y결선 운전을 하고 부족한 출력은 유도전동기 약계자 제어를 하여야 한다. 본 논문은 가변 DC-Link 전압에서 최소의 상전류로 전력소자와 유도 전동기의 상태에 따라 최대출력 운전을 하는 약계자 제어 알고리즘을 제안하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.150-156
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• 1986

A Rankine cycle including heat exchange processes in the steam generator has been analyzed by the concept of available energy. The operation condition of the cycle can be expressed with the evaporation temperature, and there exists an optimum power condition at which the thermal efficiency of the cycle is almost the same as that of the Carnot cycle at the maximum power condition. The mass flow rate of the working fluid increases sharply as the evaporation temperature approaches to the critical point, and the regenerative system is needed to operate the cycle at the maximum power condition.

• Nuclear Engineering and Technology
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• v.16 no.4
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• pp.181-194
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• 1984

The in-core fuel management problem was studied by use of the calculus of variations. Two functions of interest to a public power utility, the profit function and the cost function, were subjected to the constraints of criticality, the reactor turnup equations and an inequality constraint on the maximum allowable power density. The variational solution of the initial profit rate demonstrated that there are two distinct regions of the reactor, a constant power region and a minimum inventory or flat thermal flux region. The transition point between these regions is dependent on the relative importance of the profit for generating power and the interest charges for the fuel. The fuel cycle cost function was then used to optimize a three equal volume region reactor with a constant fuel enrichment. The inequality constraint on the maximum allowable power density requires that the inequality become an equality constraint at some points in the reactor. and at all times throughout the core cycle. The finite difference equations for reactor criticality and fuel burnup in conjunction with the equality constraint on power density were solved, and the method of gradients was used to locate an optimum enrichment. The results of this calculation showed that standard non-linear optimization techniques can be used to optimize a reactor when the inequality constraints are properly applied.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.24-26
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• 2018

본 논문은 일사량 변화 시, 최대 출력점을 추종하는 태양광 발전시스템의 동적 응답특성을 향상시키기 위해 가변 스텝 사이즈 기반의 P&O (perturb & observe) 알고리즘을 제안하였다. 제안된 기법은 일사량과 PV (photovoltaic) 전류 관계로부터 일사량 변화에 따른 최대 전력점 전류 $I_{MPP}$변화 특성을 이용하며, 새로운 I-V 곡선에서 PV 동작점을 최대 출력점으로 빠르게 이동시키는 고속모드와 정상상태 부근에서 정상상태 효율 향상을 위한 가변 스텝 모드로 구성된다. 시뮬레이션 및 실험을 통해 $500W/m^2$와 $1000W/m^2$ 일사량 증감 조건에서 제안된 MPPT(maximum power point tracking) 기법의 추종 성능을 검증하였으며, MPPT 주기가 2초이고 일사량 $500W/m^2$과 $1000W/m^2$ 증감을 할 때 추종시간은 약 30초 정도이며, 정상상태 PV 전압변동은 약 0.1V로써 일사량 변화 조건에서 제안된 MPPT 기법의 알고리즘 성능을 검증하였다.

• Proceedings of the KIPE Conference
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• 2013.11a
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• pp.139-140
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• 2013

본 연구는 군 항공용 레이더 프로세서 유닛용 다중 출력 스위칭 전원공급기 개발 과제의 효율 요구조건 만족을 위해 선행 연구 과제로 실시되었다. 전원공급기의 다중 출력 전원 중 출력 전력이 크고, 효율 측면에서 구현 난이도가 높은 +3.3VDC/55A 전원을 대상으로 선정하였다. 주요 개발 목표 사양은 입력전압 범위 230VDC~330VDC, 전압 안정도 ${\pm}2%$, 효율 85% 이상이다. 이를 만족하기 위해 DC/DC 컨버터의 메인 토폴로지는 하프 브릿지 컨버터이며, 효율 특성 개선을 위하여 동기정류방식을 적용하였다. 본 논문은 DC/DC 컨버터의 설계와 Prototype을 제작하고, 고찰된 실험결과를 제시한 내용으로, 230VDC~330VDC 범위의 입력 조건 및 +3.3VDC/55A 출력 조건에서 최대 89%의 효율 특성을 확인한 내용을 기술한다.

• Korean Journal of Optics and Photonics
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• v.4 no.1
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• pp.57-65
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• 1993

Small XeCl laser of charge transfer discharge excitation was fabricated and output charateristics were investigated according to gas mixture ratio. Beam cross section of 2.7cm${\times}$1.5cm was obtained by constructing excimer laser which preionization is operated automatically and which has chang profile electrode. According to the component gas mixture ratio, the condition of maximum output energy, efficiency were investigated. The maximum energy, efficiency and specific energy were obtained 230 mJ, 1.6% and 1.1 J/l, respectively. The long pulse effect is observed by constructing low peaking to main capacitance ratio of 1:3.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.225-229
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• 1990

As a basic study of optimal design conditions of refrigeration systems, the reversed carnot cycle, including heat transfer processes through the finite temperature differences between heat sources and the working fluids, is analyzed with the capacity of heat exchanger as a design parameter. When the temperatures of heat sources and the input work are fixed as constants, the optimal design condition is obtained as an optimum ratio of capacities of heat exchangers, which is exactly unity when the exergy output and effectiveness are maximum. In addition, the optimum ratio is slightly increased from unity as the irreversibility of the cycle increases.