• Journal of Power Electronics
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• v.13 no.5
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• pp.829-840
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• 2013

The modified sinusoidal pulse-width modulation (SPWM) is one of the PWM techniques used in three-phase AC-DC buck converters. The modified SPWM works without the current sensor (the converter is current sensorless), improves production of sinusoidal AC current, enables obtainment of near-unity power factor, and controls output voltage through modulation gain (ranging from 0 to 1). The main problem of the modified SPWM is the huge starting current and voltage (during transient) that results from a large step change from the reference voltage. When the load changes, the output voltage significantly drops (through switching losses and non-ideal converter elements). The single-input single-output (SISO) approach with minor-loop voltage feedback controller presented here overcomes this problem. This approach is created on a theoretical linear model and verified by discrete-model simulation on MATLAB/Simulink. The capability and effectiveness of the SISO approach in compensating start-up current/voltage and in achieving zero steady-state error were tested for transient cases with step-changed load and step-changed reference voltage for linear and non-linear loads. Tests were done to analyze the transient performance against various controller gains. An experiment prototype was also developed for verification.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.9
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• pp.1315-1322
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• 2015

This paper proposes an active islanding detection method for the BESS (Battery Energy Storage System) with 3-phase inverter which is connected to the AC grid. The proposed method adopts the DDSRF (Decoupled Double Synchronous Reference Frame) PLL (Phase Locked-Loop) so that the independent control of positive-sequence and negative-sequence current is successfully carried out using the detected phase angle information. The islanding state can be detected by sensing the variation of negative-sequence voltage at the PCC (Point of Common Connection) due to the injection of 2-3% negative-sequence current from the BESS. The proposed method provides a secure and rapid detection under the variation of negative-sequence voltage due to the sag and swell. The feasibility of proposed method was verified by computer simulations with PSCAD/EMTDC and experimental analyses with 5kW hardware prototype for the benchmark circuit of islanding detection suggested by IEEE 1547 and UL1741. The proposed method would be applicable for the secure detection of islanding state in the grid-tied Microgrid.

• Steel and Composite Structures
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• v.23 no.1
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• pp.31-40
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• 2017

This article aims at presenting multi objective optimization of parameters that affect crashworthiness characteristics of bi-tubular structures using Taguchi method with grey relational analysis. To design the experiments, the $L_9$ orthogonal array has been used and based on that, the inner tubes have been fabricated by varying the three influence factors such as reference diameter, length difference and numbers of sides of the polygon with three levels, but all the outer cylinders have the same diameter and length 90 mm and 135 mm respectively. Then, the tailor made bi-tubular steel structures were subjected into quasi static axial compression. From the test results it is found that the crushing behaviors of bi-tubular structures with different combinations were fairly significant. The important responses (crashworthiness indicators) specific energy absorption and crush force efficiency have been evaluated from load - displacement curve. Finally optimal levels of parameters were identified using grey relational analysis, and significance of parameters was determined by analysis of variance. The optimum crashworthiness parameters are reference diameter 80 mm, length difference 0 mm and number of sides of polygon is 3, i.e., triangle within the selected nine bi-tube combinations.

• Radiation Oncology Journal
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• v.11 no.2
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• pp.455-461
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• 1993

Experimental measurements of dose characteristics with pentagonal applicator at nominal energy of 4, 6, 9, 12 and 15 MeV electron beam were performed for intraoperative radiotherapy (IORT) in ML-15MDX linear accelerator. This paper presents the percent depth dose, surface dose, beam flatness and output factors of using the IORT applicator in different electron beam energy. The output factor showed as a 24 percent higher in IORT applicator than that of reference $10{\times}10cm^2$ applicator. The surface dose of using the IORT applicator showed 7.7 and 2.7 percent higher than that of reference field in 4 and 15 MeV electron beam, respectively. In our experiments, the variation of percent depth dose was very small but the output factor and flatnees at 0.5 cm depth have showed a large value in IORT applicator.

• Journal of the Korean Solar Energy Society
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• v.29 no.3
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• pp.1-11
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• 2009

Heliostat sun tracking accuracy could be the most important requirement in solar thermal power plant, since it determines the overall efficiency of power plant. This study presents the effect of geometrical errors on the heliostat sun tracking performance. The geometrical errors considered here are the mirror canting error, encoder reference error, heliostat position error. pivot offset and tilt error, gear backlash and mass unbalanced effect error. We first investigate the effect of each individual geometrical error on the sun tracking accuracy. Then, the sun tracking error caused by the combination of individual geometrical error is computed and analyzed. The results obtained using the solar ray tracing technique shows that the sun tracking error due to the geometrical error is varying almost randomly. It also shows that the mirror canting error is the most significant error source, while the encoder reference error and gear backlash are second and the third dominant source of errors.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.1
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• pp.89-99
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• 2018

This study analyzed the change of the dam inflow and evapotranspiration in the Soyanggang dam basin using the results of 26 CMIP5 GCMs based on AR5 RCP 4.5 and RCP 8.5 scenarios. The SWAT model was used to simulate the dam inflow and evapotranspiration in the target watershed. The simulation was performed during 2010~2016 as the reference year and during 2010~2099 as the analysis period. Bias correction of input data such as precipitation and air temperature were conducted for the reference period of 2006~2016. Results were analyzed for 3 different periods, 2025s (2010~2040), 2055s (2041~2070), and 2085s (2071~2099). It demonstrated that the change of dam inflow gradually increases 9.5~15.9 % for RCP 4.5 and 13.3~29.8 % for RCP 8.5. The change of evapotranspiration gradually increases 1.6~8.6 % for RCP 4.5 and 1.5~8.5 % for RCP8.5.

• Journal of the Korean Society for Marine Environment & Energy
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• v.2 no.2
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• pp.78-85
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• 1999

Tracking model of a drifted ship lot the search and rescue mission in southern sea of Korea is studied. In this model, search area is determined by considering standard deviation of position around reference point. The reference point is estimated for a given type of ship when marine environmental conditions such as wind and current are given. A database for environmental data, which is necessary for the real-lime tracking of drilled ship, is gel)elated on southern sea and western sea of Korea. Using this database, the real-time prediction of wind and current is possible. The simulated trajectories and search area of our model ate validated by comparing with reported real data.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.2
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• pp.110-118
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• 2015

Weather routing method is one of the best practices of SEEMP (Ship Energy Efficiency Management Plan) for fuel-efficient operation of ship. KR is carrying out a basic research for development of the weather routing algorithm and making a monitoring system by FOC (Fuel Oil Consumption) analysis compared to the reference, which is the great circle route. The added resistances applied global sea/weather data can be calculated using ship data, and the results can be corrected to ship motions. The global sea/weather data such as significant wave height, ocean current and wind data can be used to calculate the added resistances. The reference route in a usual navigation is the great circle route, which is the shortest distance route. The global sea/weather data can be divided into grids, and the nearest grid data from a ship's position can be used to apply a ocean going vessel's sea conditions. Powell method is used as an optimized routing technique to minimize FOC considered sea/weather conditions, and FOC result can be compared with the great circle route result.

• Journal of the Korean Home Economics Association
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• v.34 no.5
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• pp.183-196
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• 1996

The purposes of this study were to review the effects of textiles production on the environment, and to investigate the environmental consciousness and environmental preservation behavior of textile producers. This study was conducted by reference analysis and empirical research. To develope theoretical framework of dimensions of environmental behavior, references concerned were analyzed. And for empirical study, researcher developed a questionnaire based on the free writing by producers and references. The questionnaire included problems about environmental consciousness, environmental behavior, demographic variables, and environmental variables. 135 questionnaires were used for final data analysis. ANOVA and factor analysis were used. The results were as follows: First, the level of global environmental problem consciousness was relatively high. The conscious level of water pollution caused by the waste water from textile mills was the highest, and that of desertation of mountain caused by timber cutting was the lowest. The effects of textile dyers and finishers on the environment were the highest, and that of designers were the lowest. Second, the results of reference analysis showed that the dimensions of textile producers environmental behavior were resource and energy saving, solid waste reduction, and green product production. And the results of empirical study were resource and energy saving, resource reuse or recycling, solid waste reduction, and green product production, and total variances was 62.3%. The practice was the lowest. Third, global environment problem consciousness, environment problem consciousness caused by the textile life-cycle concerned, and clothing seperate-collection or not at residing place were effective on environmental behavior, and 52.45% of environmental behavior was explained with above variables.

• The Transactions of the Korean Institute of Power Electronics
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• v.28 no.1
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• pp.30-38
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• 2023

In this paper, a constant current(CC) and constant voltage(CV) control method using a primary-side regulated(PSR) fly-buck converter is proposed. Because the primary-side structure of the fly-buck converter is the same as that of the synchronous buck converter, it always operates in continuous conduction mode(CCM). Therefore, in the proposed method, the load information on the secondary side can always be easily estimated by measuring the primary inductor current at the midpoint of the switch-on period. An accurate CC/CV control can be achieved through simple calculations based on this estimated information. Consequently, the proposed method is advantageous for optimizing the control performance of the PSR converter. The validity of the proposed control was verified using a 5 W prototype of a PSR fly-buck converter. The experimental results confirmed that the current reference of 500 mA was followed within the error range of 1.2%, and that the voltage reference of 12 V was followed within the error range of 1.8% despite the indirect control of the load current and output voltage from the primary side.