• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1501-1510
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• 2014

Low voltage direct current (LVDC) distribution system is a suitable techno-economic candidate which can create an innovative solution for distribution network development with respect to rural electrification. This research focuses on the use of LVDC distribution system to replace some of KEPCO's existing traditional medium voltage alternating current (MVAC) distribution network for rural electrification in South Korea. Considering the technical and economic risks and benefits involved in such project, a comparative techno-economic analysis on the LVDC and the MVAC distribution networks is conducted using economic assessment method such as the net present value (NPV) on a discounted cash flow (DCF) basis as well as the sensitivity analysis technique. Each would play a role in an economic performance indicator and a measure of uncertainty and risk involved in the project. In this work, a simulation model and a computational tool are concurrently developed and employed to aid the techno-economic analysis, evaluation, and estimation of the various systems efficiency and/or performance.

• The Journal of Industrial Distribution & Business
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• v.8 no.2
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• pp.21-31
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• 2017

Purpose - The total amount of advanced Corporate Pension Insurance products exceed 148 trillion Korean Won at the end of 2016. For a firm with over 300 employees, when a bill on compulsion of introduction of Corporate Pension Insurance products, currently pending in court, is passed, Corporate Pension shall be an essential. The findings of the paper will provide a guideline for understanding on firm's attributes and its effects towards introduction of Corporate Pension Insurance products. Research design, data, and methodology - The data were collected using statistics of employer panel survey from Korea Labour Institute in 2013. The study analyses a sample survey on 1,775 outstanding enterprises and their HR department among whole corporations in Korea. For analysis of data, empirical testing by Logistic Regression was utilized. Results - As an outcome of empirical testing, variables on share of regular employees and the aged employees in over 50's generates a significant statistical meaning. It eventually gives a great impact on purchase of Corporate Pension scheme. Moreover, variables on corporate financial statement, current sales, current net income, total amount of the debts, labor cost per person also has a vital influence on introduction of Corporate Pension Insurance products. Lastly, variables on firm's labor relationship have no effect except for the execution or non-execution of HR consulting. Meanwhile, Variables affecting a choice on pension schemes types among firm's attributes are a share of regular employees, current net income, execution or non-execution of HR consulting etc. These variables represents a statistical implication. According to their each features, they prefer DB or DC plan. Conclusions - Introduction of corporate pension scheme is apposite to contemporary Korea's situation entering a hyper-aging society and firms with a high share of regular employees, the weight of aging, current sales, current net income and labor cost per person are exceedingly active in purchasing Corporate Pension Insurance products. However, after the introduction of corporate pension scheme, firms which has an implementation of consultation on human resource management, flexible benefits plan, job security and welfare system prefer DC plan whereas from financial perspective firms with high net income prefer DB plan.

• Journal of radiological science and technology
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• v.43 no.6
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• pp.431-441
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• 2020

The purpose of this study was to construct a model of MVCT(Megavoltage Computed Tomography) dose calculation by using Dosimetry Check™, a program that radiation treatment dose verification, and establish a protocol that can be accumulated to the radiation treatment dose distribution. We acquired sinogram of MVCT after air scan in Fine, Normal, Coarse mode. Dosimetry Check™(DC) program can analyze only DICOM(Digital Imaging Communications in Medicine) format, however acquired sinogram is dat format. Thus, we made MVCT RC-DICOM format by using acquired sinogram. In addition, we made MVCT RP-DICOM by using principle of generating MLC(Multi-leaf Collimator) control points at half location of pitch in treatment RP-DICOM. The MVCT imaging dose in fine mode was measured by using ionization chamber, and normalized to the MVCT dose calculation model, the MVCT imaging dose of Normal, Coarse mode was calculated by using DC program. As a results, 2.08 cGy was measured by using ionization chamber in Fine mode and normalized based on the measured dose in DC program. After normalization, the result of MVCT dose calculation in Normal, Coarse mode, each mode was calculated 0.957, 0.621 cGy. Finally, the dose resulting from the process for acquisition of MVCT can be accumulated to the treatment dose distribution for dose evaluation. It is believed that this could be contribute clinically to a more realistic dose evaluation. From now on, it is considered that it will be able to provide more accurate and realistic dose information in radiation therapy planning evaluation by using Tomotherapy.

• Journal of Korea Society of Industrial Information Systems
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• v.29 no.3
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• pp.41-49
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• 2024

In this paper, we validate simulation results for the design optimization of a Superconducting Fault Current Limiter (SFCL) intended for use in Medium Voltage Direct Current systems (MVDC). With the increasing integration of renewable energy and grid connections, researchers are focusing on medium-voltage systems for balancing energy in new and renewable energy networks, rather than traditional transmission or distribution networks. Specifically, for DC distribution networks dealing with fault currents that must be rapidly blocked, current-limiting systems like superconducting current limiters offer distinct advantages over the operation of DC circuit breakers. The development of such superconducting current limiters requires finite element analysis (FEM) and an extensive design process before prototype production and evaluation. To expedite this design process, the design outcomes are assimilated using a Reduced Order Model (ROM). This approach enables the verification of results akin to finite element analysis, facilitating the optimization of design simulations for production and mass production within existing engineering frameworks.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.528-535
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• 2020

Recently, the protection coordination method of DC systems has been presented because renewable energy and distributed resources are being installed and operated in distribution systems. On the other hand, it is difficult to detect ground faults because there is no significant difference compared to a steady-state current in ungrounded IT systems, such as DC load networks and urban railways. Therefore, this paper formulates the detection principle of IMD (Insulation Monitoring Device) to use it as a protection coordination device in a DC system. Based on the signal injection method of IMD, which is analyzed by a wavelet transform, this paper presents an algorithm of detecting ground faults in a DC system in a fast and accurate manner. In addition, this paper modeled an IMD and an ungrounded DC system using the PSCAD/EMTDC S/W and performed numerical analysis of a wavelet transform with the Matlab S/W. The simulation results of a ground fault case in an ungrounded DC system showed that the proposed algorithm and modeling are useful and practical tools for detecting a ground fault in a DC system.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.6
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• pp.1-6
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• 2010

We present simulation results on DC characteristics of AlGaN/GaN HEMT having stair-type gate electrodes, in comparison with those of the conventional single gate AlGaN/GaN HEMTs and field-plate enhanced AlGaN/GaN HEMTs. In order to reduce the internal electric field near the gate electrode of conventional HEMT and thereby to increase their DC characteristics, we applied three-layered stacking electrode schemes to the standard AlGaN/GaN HEMT structure. As a result, we found that the internal electric field was decreased by 70% at the same drain bias condition and the transconductance (gm) was improved by 11.4% for the proposed stair-type gate AlGaN/GaN HEMT, compared with those of the conventional single gate and field-plate enhanced AlGaN/GaN HEMTs.

• Journal of Power Electronics
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• v.16 no.2
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• pp.464-472
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• 2016

This study applies the selective harmonic elimination (SHE) technique to design and operate a regulated AC/DC/AC power supply suitable for maritime military applications and underground trains. The input is a single 50/60 Hz AC voltage, and the output is a 400 Hz regulated voltage. The switching angles for a multi-level inverter and transformer turns ratio are determined to operate with special connected transformers with equal power ratings and produce an almost sinusoidal current. As a result of its capability of directly controlling harmonics, the SHE technique is applicable to apparatus with congenital immunity to specific harmonics, such as series-connected transformers, which are specially designed to equally share the total load power. In the present work, a single-phase 50/60 Hz input source is rectified via a semi-controlled bridge rectifier to control DC voltage levels and thereby regulate the output load voltage at a constant level. The DC-rectified voltage then supplies six single-phase quazi-square H-bridge inverters, each of which supplies the primary of a single-phase transformer. The secondaries of the six transformers are connected in series. Through off-line calculation, the switching angles of the six inverters and the turns ratios of the six transformers are designed to ensure equal power distribution for the transformers. The SHE technique is also employed to eliminate the higher-order harmonics of the output voltage. A digital implementation is carried out to determine the switching angles. Theoretical results are demonstrated, and a scaled-down experimental 600 VA prototype is built to verify the validity of the proposed system.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.4
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• pp.135-141
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• 2021

Interest is growing in the design and development of square wave driven BLDC permanent magnet motors suitable for industrial automation, and the development of position detection circuits and drivers. However, this motor is somewhat limited in its application despite the price and functional advantages due to the decrease in efficiency due to switching loss and vibration and noise. In the process of designing and assembling a BLDC motor, the magnetic pole angle is not uniform or the magnetic flux distribution is distorted due to problems in magnetic circuit design or product non-uniformity in the assembly process. Therefore, these things cause position detection deviation and deteriorate the motor characteristics. In addition, the sine wave driven BLDC system can operate stably only when the signal generated from the position sensor is accurately fed back to the driver. However, since the generated signal cannot perform stable position detection due to the occurrence of DC offset component due to magnetic flux density deviation or magnetization technology, which is an external influence, this study intends to study the proposed circuit that can remove the DC offset component.

• The Korean Journal of Franchise Management
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• v.7 no.2
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• pp.27-35
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• 2016

Purpose - The primary objective of this study is to investigate the impact of employee characteristics on employees' preference towards corporate pension products. This study can provide a guidance for maximization of benefits for employees and their affiliated corporation. Employee characteristics include average length of labour, wage system of annual salary, age, types of interest rates and size of corporation. Existing research generally concentrate on vitalizations of corporate pension product raising an imperfection, improvements, tax benefit analysis and legal consideration. Thus, this study intensively analyses the effect of employee attributes on firms' decision for corporate pension products, such as DB(defined benefit) and DC(defined contribution) type. Research design, data, and methodology - The data were collected using self-administrated questionnaire survey on corporate pension products from CEOs or HR directors 250 foreign-invested companies', purchasing pension plans in practice with domestic financial trustees (insurance companies, banks and security companies). Hypotheses testing was conducted using Logistic Regression analysis with SPSS/PC+ 21.0. Results - The findings of the study are as follows. Employees with the long length of labour are more likely to have DB plan; more likely to prefer DC plan with the dividend distribution product regarding the types of interest rate. SMEs(less than 100 employees) are more likely to select DC plan whereas high fluctuation in wage with annual salary has no impacts. In addition, the ages has no significant effect on the preference. Conclusions - This study has examined with the empirical testing that employees' variable attributes and qualities are one of the vital factors for corporation pension plan selection. Currently, majority employees are highly likely to join DB plan and Defined interest types. Corporation with less than 10 employees prefer IRP scheme while most of corporation are intended to join DC plan. In a very near future, corporation more than 300 employees will be required to purchase mandatory plan under national regulation. For maximization of employees' contentment to corporation pension insurance and for complementing the flaws of existing plans, the future studies shall also research in a perspective of employee benefit.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.11c
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• pp.2021-2024
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• 2003

Information security is becoming a more important factor in distribution of digital contents. Generally, illegal facsimile of high-quality multimedia products such as DVDs, MP3s and AACs is possible without damaging quality. Thus, the illegal distribution of duplicated contents on the Web is causing digital content providers great economic loss. Therefore, a study of security and efficient distribution of digital contents is required. The most important issues in the design of a digital content distribution system are user convenience, execution speed and security. In this study, we designed a digital contents distribution system that uses web caching technology and encryption/decryption techniques in hierarchical structures. We propose a digital content distribution system that improves user convenience, security and execution speed. The superior performance of the proposed system has been proven in the tests. The results of experiment show that the developed system has improved the security of DC without decreasing process speed.