• Journal of the Korea Convergence Society
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• 제2권2호
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• pp.47-56
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• 2011

Korea Ministry of Knowledge Economy has estimated that wind power (WP) will be occupied 37% in 2020 and 42% in 2030 of the new energy sources, and also green energies such as photovoltaic (PV) and WP are expected to be interconnected with the distribution system because of Renewable Portfolio Standard (RPS) starting from 2012. However, when a large scale wind power plant (over 3[MW]) is connected to the traditional distribution system, protective devices (mainly OCR and OCGR of re-closer) will be occurred mal-function problems due to changed fault currents it be caused by Wye-grounded/Delta winding of interconnection transformer and %impedance of WP's turbine. Therefore, when Double-Fed Induction Generator (DFIG) of typical WP's Generator is connected into distribution system, this paper deals with analysis three-phase short, line to line short and a single line ground faults current by using the symmetrical components of fault analysis and PSCAD/EMTDC modeling.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• 제13권6호
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• pp.523-529
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• 2020

Power distribution management system is essential for the efficient management and operation of power distribution networks. The power distribution system is a system that manages the distribution network based on IT, and has been evolving along with the development of the power industry. The current power distribution system is designed to operate at a relatively low network transmission speed based on the independent operation of the main equipment. However, due to distributed resources such as photovoltaic or energy storage devices, which are rapidly increasing in popularity in recent years, the operation of future distribution environments is becoming more complex, and various information needs to be collected in real time. In this study, the requirements of the next-generation power distribution system were derived to overcome the limitations of the existing power distribution system, and based on this, the communication network system and performance requirements for the distribution system were defined. In order to verify the performance of the designed system, a software-based terminal device simulator was developed because it takes excessive time and cost to introduce a large-scale system such as a power distribution system. Using the simulator, a test environment similar to the actual operation was established, and the number of terminal devices was increased up to 1,000. The proposed system was shown to satisfy the requirements to support the functions of the next-generation power distribution system, recording less than 10 % of the communication network bandwidth.

• Journal of Korean Society of Environmental Engineers
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• 제34권10호
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• pp.694-701
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• 2012

The main purpose of this study is to evaluate of backwash system of hydrodynamic separator filter (HSF) with solar powered submerged pumps. It consists of a photovoltaic solar array, control electronics, battery, and two submersible pump powered by a 12 voltage DC motor. The laboratory scale study on treatable potential of micro particles using backwash HSF that was a combined with perlite filter cartridge and backwash nozzles. Since it was not easy to use actual storm water in the scaled-down hydraulic model investigations, it was necessary to reproduce ranges of particle sizes with synthetic materials. The synthesized storm runoff was made with water and addition of particles; ion exchange resin partices, silica gel particles, and commercial area manhole sediment particles. HSF was made of acryl resin with 250 mm of diameter filter chamber and overall height of 800 mm. Four case test were performed with different backwashing conditions and determined the SS removal efficiency with various surface loading rates. The operated range of surface loading rate was about 308~$1,250m^3/m^2/day$. It was found that SS removal efficiency of HSF using two submersible pumps improved by about 18% compared with HSF without backwash. Nonpoint control devices with solar water pumping systems would be useful for backwashing the filter in areas with not suppling electricity and reduce filter media exchange cost.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제21권6호
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• pp.662-671
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• 2020

Recently, for the purposes of reducing carbon dioxide(CO₂) emissions in the island area, countermeasures to decrease the operation rate of diesel generator(DG) and to increase one of renewable energy sources(RES) is being studied. In particular, the demonstration and installation of stand-alone micro-grid(MG) system which is composed of DG, RES and energy storage system(ESS) has been implemented in some island areas such as Gapa-do, Gasa-do and Ulleung-do island. However, many power quality(PQ) problems may be occurred due to an intermittent output of RES including photovoltaic(PV) system and wind power(WP) system in a normal operating of constant voltage & constant frequency(CVCF) inverter-based MG system. Therefore, this paper presents a modeling of the 30kW scale MG system using PSCAD/EMTDC, and also implements a 30kW scale CVCF inverter-based MG system as test devices to analyze normal operating characteristics of MG system. From the simulation and test results, it is confirmed that the proposed methods are useful and practical tools to improve PQ problems such as under-voltage, over-voltage and unbalanced load in CVCF inverter-based MG system.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제13권3호
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• pp.1288-1295
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• 2012

Korea Ministry of Knowledge Economy has estimated that wind power (WP) will be occupied 37% in 2020 and 42% in 2030 of the new energy sources, and also green energies such as photovoltaic (PV) and WP are expected to be interconnected with the distribution system because of Renewable Portfolio Standard (RPS) starting from 2012. However, when a large scale wind power plant (over 3[MW]) is connected to the traditional distribution system, protective devices (mainly OCR and OCGR of re-closer) will be occurred mal-function problems due to changed fault currents it be caused by Wye-grounded/Delta winding of interconnection transformer and %impedance of WP's turbine. Therefore, when Double-Fed Induction Generator (DFIG) of typical WP's Generator is connected into distribution system, this paper deals with analysis three-phase short, line to line short and a single line ground faults current by using the symmetrical components of fault analysis and PSCAD/EMTDC modeling.

• Bulletin of the Korean Chemical Society
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• 제32권2호
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• pp.417-423
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• 2011

A series of new quinoxaline-based thiophene copolymers (PQx2T, PQx4T, and PQx6T) was synthesized via Yamamoto and Stille coupling reactions. The $M_ws$ of PQx2T, PQx4T, and PQx6T were found to be 20,000, 12,000, and 29,000, with polydispersity indices of 2.0, 1.2, and 1.1, respectively. The UV-visible absorption spectra of the polymers showed two distinct absorption peaks in the ranges 350 - 460 nm and 560 - 600 nm, which arose from the ${\pi}-{\pi}^*$ transition of oligothiophene units and intramolecular charge transfer (ICT) between a quinoxaline acceptor and thiophene donor. The HOMO levels of the polymer ranged from -5.37 to -5.17 eV and the LUMO levels ranged from -3.67 to -3.45 eV. The electrochemical bandgaps of PQx2T, PQx4T, and PQx6T were 1.70, 1.71, and 1.72 eV, respectively, thus yielding low bandgap behavior. PQx2T, PQx4T, and PQx6T had open circuit voltages of 0.58, 0.42, and 0.47 V, and short circuit current densities of 2.9, 5.29 and 9.05 mA/$cm^2$, respectively, when $PC_{71}BM$ was used as an acceptor. For the solar cells with PQx2T-PQx6T:$PC_{71}BM$ (1:3) blends, an increase in performance was observed in going from PQx2T to PQx6T. The power conversion efficiencies of PQx2T, PQx4T, and PQx6T devices were found to be 0.69%, 0.73%, and 1.80% under AM 1.5 G (100 mW/$cm^2$) illumination.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.493-493
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• 2014

The manufacturing cost of thin-film photovoltics can potentially be lowered by minimizing the amount of a semiconductor material used to fabricate devices. Thin-film solar cells are typically only a few micrometers thick, whereas crystalline silicon (c-Si) wafer solar cells are $180{\sim}300\mu}m$ thick. As such, thin-film layers do not fully absorb incident light and their energy conversion efficiency is lower compared with that of c-Si wafer solar cells. Therefore, effective light trapping is required to realize commercially viable thin-film cells, particularly for indirect-band-gap semiconductors such as c-Si. An emerging method for light trapping in thin film solar cells is the use of metallic nanostructures that support surface plasmons. Plasmon-enhanced light absorption is shown to increase the cell photocurrent in many types of solar cells, specifically, in c-Si thin-film solar cells and in poly-Si thin film solar cell. By proper engineering of these structures, light can be concentrated and coupled into a thin semiconductor layer to increase light absorption. In many cases, silver (Ag) nanoparticles (NP) are formed either on the front surface or on the rear surface on the cells. In case of poly-Si thin film solar cells, Ag NPs are formed on the rear surface of the cells due to longer wavelengths are not perfectly absorbed in the active layer on the first path. In our cells, shorter wavelengths typically 300~500 nm are also not effectively absorbed. For this reason, a new concept of plasmonic nanostructure which is NPs formed both the front - and the rear - surface is worth testing. In this simulation Al NPs were located onto glass because Al has much lower parasitic absorption than other metal NPs. In case of Ag NP, it features parasitic absorption in the optical frequency range. On the other hand, Al NP, which is non-resonant metal NP, is characterized with a higher density of conduction electrons, resulting in highly negative dielectric permittivity. It makes them more suitable for the forward scattering configuration. In addition to this, Ag NP is located on the rear surface of the cell. Ag NPs showed good performance enhancement when they are located on the rear surface of our cells. In this simulation, Al NPs are located on glass and Ag NP is located on the rear Si surface. The structure for the simulation is shown in figure 1. Figure 2 shows FDTD-simulated absorption graphs of the proposed and reference structures. In the simulation, the front of the cell has Al NPs with 70 nm radius and 12.5% coverage; and the rear of the cell has Ag NPs with 157 nm in radius and 41.5% coverage. Such a structure shows better light absorption in 300~550 nm than that of the reference cell without any NPs and the structure with Ag NP on rear only. Therefore, it can be expected that enhanced light absorption of the structure with Al NP on front at 300~550 nm can contribute to the photocurrent enhancement.

• Applied Chemistry for Engineering
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• 제4권2호
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• pp.393-402
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• 1993

Redox flow secondary battery have been studied actively as one of the most promising electrochemical energy storage devices for a wide range of applications, such as electric vehicles, photovoltaic arrays, and excess power generated by electric power plants. In all-vanadium redox flow battery using solution of vanadium-sulfuric acid as a active material, the difficulty in developing an efficient ion selective membrane can still be identified. The asymmetric cation exchange membrane(M-30) as a separator of all-vanadium redox flow battery which were obtained by the reaction of chlorosulfonation for 30 minutes under the irradiation of UV, showed its superiority in the transport number of 0.94 and electrical resistivity of $0.5{\Omega}{\cdot}cm^2$. The base membrane were prepared by lamination a low density polyethlene film of $10{\mu}m$ thickness on polyolefin membrane(HIPORE 120). The electrical resistivity of M-30 membrane in real solution of vanadium-sulfuric acid was $3.79{\Omega}{\cdot}cm^2$ and it was similar to that of Nafion 117 membrane. Also the cell resistivity was $6.6{\Omega}{\cdot}cm^2$and lower than that of Nafion 117. In considertion of electrochemical properties and costs of membranes, M-30 membrane was better than that of Nafion 117 and CMV of Asahi glass Co. as a separator of all-vanadium redox flow battery.

• JSTS:Journal of Semiconductor Technology and Science
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• 제7권3호
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• pp.196-208
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• 2007

An analytical model is proposed for an optically controlled Metal Semiconductor Field Effect Transistor (MESFET), known as Optical Field Effect Transistor (OPFET) considering the diffusion fabrication process. The electrical parameters such as threshold voltage, drain-source current, gate capacitances and switching response have been determined for the dark and various illuminated conditions. The Photovoltaic effect due to photogenerated carriers under illumination is shown to modulate the channel cross-section, which in turn significantly changes the threshold voltage, drainsource current, the gate capacitances and the device switching speed. The threshold voltage $V_T$ is reduced under optical illumination condition, which leads the device to change the device property from enhancement mode to depletion mode depending on photon impurity flux density. The resulting I-V characteristics show that the drain-source current IDS for different gate-source voltage $V_{gs}$ is significantly increased with optical illumination for photon flux densities of ${\Phi}=10^{15}\;and\;10^{17}/cm^2s$ compared to the dark condition. Further more, the drain-source current as a function of drain-source voltage $V_{DS}$ is evaluated to find the I-V characteristics for various pinch-off voltages $V_P$ for optimization of impurity flux density $Q_{Diff}$ by diffusion process. The resulting I-V characteristics also show that the diffusion process introduces less process-induced damage compared to ion implantation, which suffers from current reduction due to a large number of defects introduced by the ion implantation process. Further the results show significant increase in gate-source capacitance $C_{gs}$ and gate-drain capacitance $C_{gd}$ for optical illuminations, where the photo-induced voltage has a significant role on gate capacitances. The switching time ${\tau}$ of the OPFET device is computed for dark and illumination conditions. The switching time ${\tau}$ is greatly reduced by optical illumination and is also a function of device active layer thickness and corresponding impurity flux density $Q_{Diff}$. Thus it is shown that the diffusion process shows great potential for improvement of optoelectronic devices in quantum efficiency and other performance areas.

• Journal of the Korean Solar Energy Society
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• 제28권2호
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• pp.64-69
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• 2008

As the grid-connected photovoltaic power conditioning systems (PVPCS) are installed in many residential areas, these have raised potential problems of network protection on electrical power system. One of the numerous problems is an Islanding phenomenon. There has been an argument that it may be a non-issue in practice because the probability of islanding is extremely low. However, there are three counter-arguments: First, the low probability of islanding is based on the assumption of 100% power matching between the PVPCS and the islanded local loads. In fact, an islanding can be easily formed even without 100% power matching (the power mismatch could be up to 30% if only traditional protections are used, e.g. under/over voltage/frequency). The 30% power-mismatch condition will drastically increase the islanding probability. Second, even with a larger power mismatch, the time for voltage or frequency to deviate sufficiently to cause a trip, plus the time required to execute a trip (particularly if conventional switchgear is required to operate), can easily be greater than the typical re-close time on the distribution circuit. Third, the low-probability argument is based on the study of PVPCS. Especially, if the output power of PVPCS equals to power consumption of local loads, it is very difficult for the PVPCS to sustain the voltage and frequency in an islanding. Unintentional islanding of PVPCS may result in power-quality issues, interference to grid-protection devices, equipment damage, and even personnel safety hazards. Therefore the verification of anti-islanding performance is strongly needed. In this paper, improved RPV method is proposed through considering power quality and anti-islanding capacity of grid-connected single-phase PVPCS in IEEE Std 1547 ("Standard for Interconnecting Distributed Resources to Electric Power Systems"). And the simulation results are verified.