• The KSFM Journal of Fluid Machinery
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• v.17 no.3
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• pp.52-58
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• 2014

The development of efficient systems for water quality improvement for water sources such as lakes, dams and reservoirs has become a necessity to provide not only a cleaner and safer water to the urban society, but also to provide a cleaner and safer environment for the aquatic organisms living in lakes, dams and reservoirs. This study concentrates on the outlet design and internal flow analysis of an axial flow pump used in a floating type water treatment system completely powered by renewable energy source. The treatment system is designed to raise water from depths of about 3~5m up to the water surface where it is naturally mixed with air as it is released back to the reservoir. The outlet of a typical axial flow pump is modified to suit the floating type water mixer. The performance of the axial flow pump is studied by investigating the internal flow of the system. Results show that the change in outlet shape does not alter the performance of the original pump at the maximum efficiency point as long as the cross sectional area of inlet is the same as the outlet. The axial pump for floating type water treatment system has good cavitation performance in the whole flow passage.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.1
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• pp.27-32
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• 2008

Recently, we have a lot of interest in alternative fuels to provide energy independence from oil producing country and to reduce exhaust emissions for air pollution prevention. Biodiesel, which can be generated from natural renewable sources such as new or used vegetable oils or animal fats, may be used as fuel in diesel engine of compression ignition engine. In this paper, the test results on specific fuel consumption and exhaust emissions of neat diesel oil and biodiesel blends(10 vol.% biodiesel and 20 vol.% biodiesel) were presented using four stroke, direct injection diesel engine, especially this biodisel was produced from soybean oil at our laboratory. This study showed that Soot and CO emission were decreased as the blending ratios of biodiesel to diesel oil increased, on the other hand NOx emission was slightly increased because of the oxygen content in biodiesel. Also, the biodiesel blends yielded slightly higher specific fuel consumption than that of diesel oil because of lower heating value of biodiesel.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.2
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• pp.89-94
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• 2014

Tidal generation has become one of environmentally friendly new and renewable future sources of energy. The Sihwa Tidal Power Plant in South Korea, which was imported from abroad by turnkey type in 2011, connected to the power system in 2012, and is currently under commercial operation. However, leading companies are reluctant to disclose their technologies associated with the control systems and are not cooperative in technology transfers, making it a high priority to develop core technologies in South Korea. In order to develop a start stop control system for tidal generation, this paper presents the optimal algorithm for decision making and prototype of hardware design. First, control systems in tidal power, such as plant operation control, data interfaces between systems, monitoring and control points of the control system, are analyzed. The software development and PC based emulator processes for optimization algorithm processing are described. Finally, verification of the algorithm implementation, hardware platform for start stop control device, and implementation of prototype control system were discussed.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.11.2-11.2
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• 2010

Photovoltaic devices are promising candidates as affordable and large-area renewable energy sources, which can replace the fossil-fuel-based resources. Especially, thin film solar cells have attracted increasing research attention, since they have a great advantage of low production cost. From the physical point of view, the photovoltaic devices can provide us interesting questions, how to enhance the light absorption and the carrier collection efficiency. A lot of approaches would be possible to address these issues. We have focused on two major topics relevant to photovoltaic device physics; (1) light management using surface plasmons and (2) junction characterizations aiming at proper interface engineering. Regarding the first topic, we have investigated the influences of Ag under-layer morphology on optical properties of ZnO thin films. The experimental results suggested that coupling between the surface plasmon polaritons at the ZnO/Ag interface and excitons in ZnO should play important roles in reflectivity of the ZnO/Ag thin films, which are widely used back reflector structures in thin film solar cells. For the second topic, we have carried out scanning probe microscopy studies of Schottky junctions consisting of photovoltaic materials. Such a research is very helpful to understand the correlation between the defects (e.g., grain boundaries) and local electrical properties. We will introduce some of the recent experimental results and discuss the physical significance.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.175.1-175.1
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• 2011

A rotating activated bacillus contactor (RABC) process with a series of aerobic reactors was tested in pilot scale to treat digested liquid from an anaerobic digester treating swine wastewater and sewage sludge. The influent (digested liquid) for the RABC process showed C/N ratios less than 2 as a typical feature of effluent from anaerobic digesters. The pilot process, which consists of three 3 RABC reactors, four aerobic tanks and a sedimentation tank, was operated for 210 days with a hydraulic retention time of 20 days without pH and temperature control. Since the Bacillus-enriched aerobic reactors shows high efficiencies of nitrogen removal at low DO levels less than 1.0 mg/L, they were operated at reduced aeration intensities. With relatively low concentrations of organics in comparison with nitrogen concentrations, the RABC process tested in this study showed stable and high nitrogen and organics removal efficiencies over 80%. The nitrogen removal process tested in this study was proven to be an effective and operation-cost saving (lower aeration) method to remove nitrogen without adding external carbon sources to meet the optimum C/N ratio.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.5
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• pp.39-45
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• 2013

Wind power is one of the fastest growing renewable energy sources. In these days, wind turbine shifts from onshore to offshore because the offshore wind farm has a abundant wind resource. However, offshore wind turbine is not easy to access, it has a long downtime when the failures of the wind turbine component occur. Therefore, the appropriate wind turbine maintenance plan is required to meet the economic and reliability of the components. This paper proposes the maintenance planning method based on the RCM(Reliability Centered Maintenance) to determine an economical maintenance cycle to satisfy the appropriate reliability of the wind turbine components. In order to compare the proposed method with the conventional RCM method, critical components are selected in the case study because they have a long downtime and a large amount of total cost.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.3
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• pp.188-196
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• 2009

Due to its high power density, long cycle life and clean nature supercapacitors are widely used for improving the dynamic characteristics of the new and renewable energy sources and extending the battery run-time and life. In this paper improved dynamic model of the supercapacitor is developed by the electrochemical impedance spectroscopy technique. The developed model can be used to accurately estimate the dynamic behaviour of the supercapacitor and calculate the exact capacitance value at a certain state of charges. The model of the supercapacitor in the frequency domain is equivalently transformed into that in the time domain for Matlab/Simulink simulaton. The simulation data shows fine agreements with experimental results, thereby proving the validity and the accuracy of the developed model.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.5
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• pp.358-368
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• 2020

Grid-connected inverters (GCIs) based on renewable energy sources play an important role in enhancing the sustainability of a society. Harmonic standards, such as IEEE 519 and P1547, which require the total harmonic distortion (THD) of the output current to be less than 5%, should be satisfied when GCIs are connected to a grid. However, achieving a current THD of less than 5% is difficult for GCIs with an output filter under a distorted grid condition. In this study, a novel harmonic compensation method that uses a digital lock-in amplifier (DLA) is proposed to eliminate harmonics effectively at the output of GCIs. Accurate information regarding harmonics can be obtained due to the outstanding performance of DLA, and such information is used to eliminate harmonics with a simple proportional-integral controller in a feedforward manner. The validity of the proposed method is verified through experiments with a 5 kW single-phase GCI connected to a real grid.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.3
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• pp.465-470
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• 2011

Recently fault currents are increasing in a network. It is caused by increase in electric demand and high penetration of distributed generation with renewable energy sources. Moreover, distribution network has become more and more complex as mesh network to improve the distribution system reliability and increase the flexibility and agility of network operation. Accordingly, the fault current will exceed capacity of circuit breakers soon and all the various rational solutions to solve this problem are taken into account. Under these circumstances, superconducting fault current limiter(SFCL) is a new alternative in the viewpoint of technical and economic aspects. This study presents operation processes for a resistive-type of SFCL, and it proposes reliability model for the SFCL. When a SFCL is installed into a network, the contribution of decreased fault currents to failure for distribution equipments can be quantified. As a result, it is expected that a SFCL makes the reliability of adjacent equipments on existing network improve and these changes are analyzed. We propose a methodology to evaluate the reliability in the distribution network where a SFCL is installed considering a reliability model for resistive-type of SFCL and reliability changes for adjacent equipments which are proposed in this paper.

• Journal of Electrical Engineering and Technology
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• v.12 no.3
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• pp.1027-1037
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• 2017

Penetration of renewable energy sources makes the modern interconnected power systems to have more intelligence and flexibility in the control. Hence, it is essential to maintain the system frequency and tie-line power exchange at nominal values using Load Frequency Control (LFC) for efficient, economic and reliable operation of power systems. In this paper, intelligent tuning of the Proportional Integral Derivative (PID) controller for LFC in an interconnected power system is considered as a main objective. The chosen problem is formulated as an optimization problem and the optimal gain parameters of PID controllers are computed with three innovative swarm intelligent algorithms named Particle Swarm Optimization (PSO), Bacterial Foraging Optimization Algorithm (BFOA) and hybrid Bacterial Foraging Particle Swarm Optimization (BFPSO) and a comparative study is made between them. A new objective function designed with necessary time domain specifications using weighted sum approach is also offered in this report and compared with conventional objective functions. All the simulation results clearly reveal that, the hybrid BFPSO tuned PID controller with proposed objective function has better control performances over other optimization methodologies.