• Korean Journal of Materials Research
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• v.20 no.10
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• pp.501-507
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• 2010

Changes in surface morphology and roughness of dc sputtered ZnO:Al/Ag back reflectors by varying the deposition temperature and their influence on the performance of flexible silicon thin film solar cells were systematically investigated. By increasing the deposition temperature from $25^{\circ}C$ to $500^{\circ}C$, the grain size of Ag thin films increased from 100 nm to 1000 nm and the grain size distribution became irregular, which resulted in an increment of surface roughness from 6.6 nm to 46.6 nm. Even after the 100 nm thick ZnO:Al film deposition, the surface morphology and roughness of the ZnO:Al/Ag double structured back reflectors were the same as those of the Ag layers, meaning that the ZnO:Al films were deposited conformally on the Ag films without unnecessary changes in the surfacefeatures. The diffused reflectance of the back reflectors improved significantly with the increasing grain size and surface roughness of the Ag films, and in particular, an enhanced diffused reflectance in the long wavelength over 800 nm was observed in the Ag back reflectors deposited at $500^{\circ}C$, which had an irregular grain size distribution of 200-1000 nm and large surface roughness. The improved light scattering properties on the rough ZnO:Al/Ag back reflector surfaces led to an increase of light trapping in the solar cells, and this resulted in a noticeable improvement in the $J_{sc}$ values from 9.94 mA/$cm^2$ for the flat Ag back reflector at $25^{\circ}C$ to 13.36 mA/$cm^2$ for the rough one at $500^{\circ}C$. A conversion efficiency of 7.60% ($V_{oc}$ = 0.93, $J_{sc}$ = 13.36 mA/$cm^2$, FF = 61%) was achieved in the flexible silicon thin film solar cells at this moment.

• Journal of the Korea Convergence Society
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• v.2 no.4
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• pp.21-27
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• 2011

Recently, new distributed power sources such as photovoltaic, wind power, fuel cell systems etc. are energetically interconnected and operated in the distribution feeders, as one of the national projects for alternative energy. When new power sources are considered to be interconnected to distribution systems, bi-directional power flow and interconnection conditions of new power sources may cause several power quality problems like voltage sag, voltage swell, harmonics, since new power sources can change typical characteristics of distribution systems. Under these situations, this paper deals with the analysis the power quality problems at primary and secondary feeders in distribution systems, when new power sources like photovoltaic (PV) systems are interconnected, by using the test devices for PV systems based on the LabVIEW S/W. This paper presents the test device which is consisted with model distribution system and model PV systems. By performing the simulation for power quality operation characteristic based on the test facilities, this paper presents the optimal countermeasures for power quality.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.100-102
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• 1998

In recent years, for the viewpoint of environment and electric power demand for stable secure, new energy such as photovoltaic system (PV) become increasingly popular. In case of interconnecting PV to the commercial electric company, two problems will occur when operating in isclation with the other general consumers. One is doing harm to the power quality. And the other is the security problem caused by charching a part of commercial system line that has to be no voltage. In this paper, a simple modelling of distribution system and grid-connected PV system and simulation result were proposed.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.4
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• pp.241-245
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• 2011

In this paper, when photovoltaic (PV) systems are connected to power distribution system, most effective capacity and connected-point of PV system are presented considering power distribution system reliability. The reliability model of PV system is presented considering the duration of sunshine. Also the model of time-varying load and reliability test system bus2 model are used. To simulate the effects of PV system, various cases are selected; (1) base case which is no connection of PV system to power distribution system when faults are occurred, (2) 3MW case which is 3[MW] connection of PV system (3) 4[MW] case, and (4) 20[MW] case which is 20[MW] connection of PV system to the bus of power distribution system. The capacity limit of connected PV system is settled to 14[MW] for all cases except case 4. The reliability for residential, general, industrial, and educational customer is evaluated.

• Journal of Korea Society of Industrial Information Systems
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• v.21 no.3
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• pp.29-33
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• 2016

Development of the distributed energy resources such as photovoltaic, wind, and fuel cell has increased rapidly due to the rising demand for clean energy utilization. On the other hand, the distribution system became complex and has problems such as degradation of power factor and current unbalance caused by power converters, reactive power and unbalanced loads. To solve these problems, this paper proposes a 3-phase 4-leg type power conditioning system with compensation control algorithm for the reactive power and unbalance current in distribution system using photovoltaic resource. It is simulated in PSCAD/EMTDC and the effectiveness is confirmed.

• Journal of Electrical Engineering and Technology
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• v.4 no.2
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• pp.185-193
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• 2009

This paper presents a methodology for photovoltaic (PV) system allocation in distribution systems using a discrete particle swarm optimization (DPSO). The PV allocation problem is in the category of mixed integer nonlinear programming and its formulation may include multi-valued dis-crete variables. Thus, the PSO requires a scheme to deal with multi-valued discrete variables. This paper introduces a novel multi-level quantization scheme using a sigmoid function for discrete particle swarm optimization. The technique is employed to a standard PSO architecture; the same velocity update equation as in continuous versions of PSO is used but the particle's positions are updated in an alternative manner. The set of multi-level quantization is defined as integer multiples of powers-of-two terms to efficiently approximate the sigmoid function in transforming a particle's position into discrete values. A comparison with a genetic algorithm (GA) is performed to verify the quality of the solutions obtained.

• International conference on construction engineering and project management
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• 2022.06a
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• pp.937-944
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• 2022

Electric vehicles (EVs) have been growing to reduce energy consumption and greenhouse gas (GHG) emissions in the transportation sector. The increasing number of EVs requires adequate recharging infrastructure, and at the same time, adopts low- or zero-emission electricity production because the GHG emissions are highly dependent on primary sources of electricity production. Although previous research has studied solar photovoltaic (PV) -integrated EV charging stations, it is challenging to optimize spatial areas between where the charging stations are required and where the renewable energy sources (i.e., solar photovoltaic (PV)) are accessible. Therefore, the primary objective of this research is to support decisions of siting EV charging stations using a spatial data clustering method integrated with Geographic Information System (GIS). This research explores spatial relationships of PV power outputs (i.e., supply) and traffic flow (i.e., demand) and tests a community in the state of Indiana, USA for optimal sitting of EV charging stations. Under the assumption that EV charging stations should be placed where the potential electricity production and traffic flow are high to match supply and demand, this research identified three areas for installing EV charging stations powered by rooftop PV in the study area. The proposed strategies will drive the transition of existing energy infrastructure into decentralized power systems. This research will ultimately contribute to enhancing economic efficiency and environmental sustainability by enabling significant reductions in electricity distribution loss and GHG emissions driven by transportation energy.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.9
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• pp.1674-1683
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• 2011

More than 80% of electric loads need DC electricity rather than AC at the moment. If DC power could be supplied directly to the terminal loads, power conversion stages including rectifiers, converters, and power adapters can be reduced or simplified. Therefore, DC microgrids may be able to improve energy efficiency of power distribution systems. In addition, DC microgrids can increase the penetration level of renewable energy resources because many renewable energy resources such as solar photovoltaic(PV) generators, fuel cells, and batteries generate electric power in the form of DC power. The integration of the DC generators to AC electric power systems requires the power conversion circuits that may cause additional energy loss. This paper discusses the capability and feasibility of DC microgrids with regard to energy efficiency analysis through detailed dynamic simulation of DC and AC microgrids. The dynamic simulation models of DC and AC microgrids based on the Microgrid Test System in KEPCO Research Institute are described in detail. Through simulation studies on various conditions, this paper compares the energy efficiency and advantages of DC and AC microgrids.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.5
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• pp.280-286
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• 2006

The paper proposes a new protection algorithm for reliable operation of grid-interfaced PV system, which can flexibly interact with conventional protective schemes of power utility grid not only to prevent damages to utility or public persons and utility apparatus caused by malfunction or failure in distribution network protection system, but also to protect a PV system itself from faults or abnormal conditions of the network. The proposed algorithm is based on reclosing characteristics of the distribution system. As a network fault occurs, the new scheme determines whether it is momentary or permanent and responds in a pre-programmed way to the fault. For permanent outage, the proposed algorithm shuts down inverter's operations but monitoring system voltage and frequency at the point of common coupling with grid. When it comes to the momentary outage, Inverter starts stand-by operation mode so that it can be automatically connected to the grid without start-up procedures as soon as the system voltage and frequency returns into the normal operation range. In order to investigate' and evaluate the PV system operation, simulation study based on PSCAD/EMTDC has been carried out to verify the performance of the proposed protection scheme.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.177-178
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• 2008

Recently, the concern of PV(Photovoltaic) systems has increased because of an environmental problem and limitation of fossil fuel. In this paper, distribution system of existing one-way power flow and distribution system generating bidirectional power flow analyze voltage variation at distribution system interconnected multiple PV systems. Also, we analyze a supply voltage range of distribution system using LDC and ULTC voltage regulation method by case study.