• Journal of Power Electronics
• /
• 제18권2호
• /
• pp.627-639
• /
• 2018

The fact that the reliability of IGBTs has become a more and more significant aspect of power converters has resulted in an increase in the research on the open circuit (OC) fault location of IGBTs. When an OC fault occurs, a zero-current phenomena exists and frequently appears, which can be found in a lot of the existing literature. In fact, fault variables have a very high correlation with the zero-current interval. In some cases, zero-current interval actually decides the most significant fault feature. However, very few of the previous studies really explain or prove the zero-current phenomena of the fault current. In this paper, the zero-current phenomena is explained and verified through mathematical derivation, based on two-level and three-level NPC static var generators (SVGs). Mathematical models of single OC fault are deduced and it is concluded that a zero-current interval with a certain length follows the OC faults for both two-level and NPC three-level SVGs. Both inductive and capacitive reactive power situations are considered. The unbalanced load situation is discussed. In addition, simulation and experimental results are presented to verify the correctness of the theoretical analysis.

• The Journal of Korean Physical Therapy
• /
• 제23권2호
• /
• pp.77-84
• /
• 2011

Purpose: This study was designed to investigate the level of recognition and utilization of Korean physical therapists for assistive technology. Methods: The subjects of this study were 218 physical therapists who worked in various institutions in Seoul, Kyonggi-do, and Choongchung area. A questionnaire was developed using a related article. Simple descriptive statistics were used for respondent characteristics, and for the level of recognition and utilization. Results: The physical therapists reported having a less-than-average level of recognition and utilization for assistive technology. They were cognizant that the use of assistive technology devices were used mainly for specific outcome such as mobility, seating and position, and ADL. Conclusion: Our findings indicate that physical therapists need more opportunities for training in assistive technology. For effective clinical applications of assistive technology, there should be continuous support, such as college education, continued education, and related seminars.

• 한국정보시스템학회지:정보시스템연구
• /
• 제12권2호
• /
• pp.189-208
• /
• 2003

The purpose of this study was to survey current status of information technology literacy in Korean teachers and to give some suggestions for the preparation of prospective teachers in Korea. To achieve the purpose, data were collected using on- and off-line surveys containing questionnaires developed by the researchers. The survey items were categorized into 11 groups such as operation capability, computer use and communication, word processing, ethics, computer fundamentals, understanding of educational IT, information instruments use, application s/w use, work processing with computer, and internet use capability. Major findings were as follows: (1) Female teachers rated their IT literacy level higher than male teachers. (2) Teachers with longer teaching experience rated their IT literacy level lower than those of shorter experience. (3) There were no signigicant differences among sex, school, job grade of teachers at the present level of literacy, but there were significant differences among sex, age, carreer, job grade, and subject matter at the expectation level except for school grade.

• Safety and Health at Work
• /
• 제6권4호
• /
• pp.345-352
• /
• 2015

Background: Goal-oriented communication of risk of hazards is necessary in order to reduce risk of workers' exposure to chemicals. Adequate training of workers and enterprise priority setting are essential elements. Cleaning enterprises have many challenges and the existing paradigms influence the risk levels of these enterprises. Methods: Information on organization and enterprises' prioritization in training programs was gathered from cleaning enterprises. A measure of enterprises' conceptual level of importance of chemical health hazards and a model for working out the risk index (RI) indicating enterprises' conceptual risk level was established and used to categorize the enterprises. Results: In 72.3% of cases, training takes place concurrently with task performances and in 67.4% experienced workers conduct the trainings. There is disparity between employers' opinion on competence level of the workers and reality. Lower conceptual level of importance was observed for cleaning enterprises of different sizes compared with regional safety delegates and occupational hygienists. Risk index values show no difference in risk level between small and large enterprises. Conclusion: Training of cleaning workers lacks the prerequisite for suitability and effectiveness to counter risks of chemical health hazards. There is dereliction of duty by management in the sector resulting in a lack of competence among the cleaning workers. Instituting acceptable easily attainable safety competence level for cleaners will conduce to risk reduction, and enforcement of attainment of the competence level would be a positive step.

• Geomechanics and Engineering
• /
• 제18권1호
• /
• pp.71-83
• /
• 2019

This investigation presented conventional triaxial and creep-permeability tests on sandstones considering thermally-induced damage (TID). The TID had no visible effects on rock surface color, effective porosity and permeability below $300^{\circ}C$ TID level. The permeability enlarged approximately two orders of magnitude as TID increased to $1000^{\circ}C$ level. TID of $700^{\circ}C$ level was a threshold where the influence of TID on the normalized mass and volume of the specimen can be divided into two linear phases. Moreover, no prominent variations in the deformation moduli and peak strength and strain appeared as TID< $500^{\circ}C$ level. It is interesting that the peak strength increased by 24.3% at $700^{\circ}C$ level but decreased by 11.5% at $1000^{\circ}C$ level. The time-related deformation and steady-state creep rate had positive correlations with creep loading and the TID level, whereas the instantaneous modulus showed the opposite. The strain rates under creep failure stresses raised 1-4 orders of magnitude than those at low-stress levels. The permeability was not only dependent on the TID level but also dependent on creep deformation. The TID resulted in large deformation and complexity of failure pattern for the sandstone.

• 자동차안전학회지
• /
• 제12권4호
• /
• pp.61-69
• /
• 2020

As a sales volume of autonomous vehicle continually grows up, regulations on this new technology are being introduced around the world. For example, safety standards for the Level 3 automated driving system was promulgated in December 2019 by the Ministry of Land, Infrastructure and Transport of Korean government. In order to promote the development of autonomous vehicle technology and ensure its safety simultaneously, the regulations on the automated driving systems should be phased in to keep pace with technology progress and market expansion. However, according to SAE J3016, which is well known to classify the level of the autonomous vehicle technologies, the description for classification is rather abstract. Therefore it is necessary to describe the automated driving system in more detail in terms of the 'Level.' In this study, the functions and characteristics of automated driving system are carefully classified at each level based on the commentary in the Informal Working Group (IWG) of the UN WP29. In particular, regarding the Level 4, technical issues are characterized with respect to vehicle tasks, driver tasks, system performance and regulations. The important features of the autonomous vehicles to meet Level 4 are explored on the viewpoints of driver replacement, emergency response and connected driving performance.

• Nuclear Engineering and Technology
• /
• 제48권1호
• /
• pp.98-113
• /
• 2016

A reactor vessel level monitoring system measures the water level in a reactor during normal operation and abnormal conditions. A drop in the water level can expose nuclear fuel, which may lead to fuel meltdown and radiation spread in accident conditions. A level monitoring system mainly consists of a sensing line and pressure transmitter. Over a period of time boron sediments or other impurities can clog the line which may degrade the accuracy of the monitoring system. The aim of this study is to determine blockage in a sensing line using the energy of the composite signal. An equivalent Pi circuit model is used to simulate blockages in the sensing line and the system's response is examined under different blockage levels. Composite signals obtained from the model and plant's unblocked and blocked channels are decomposed into six levels of details and approximations using a wavelet filter bank. The percentage of energy is calculated at each level for approximations. It is observed that the percentage of energy reduces as the blockage level in the sensing line increases. The results of the model and operational data are well correlated. Thus, in our opinion variation in the energy levels of approximations can be used as an index to determine the presence and degree of blockage in a sensing line.

• 무역학회지
• /
• 제44권4호
• /
• pp.51-66
• /
• 2019

This study analyzes trade competitiveness by classifying the classification by item among Korea and the 10 ASEAN member countries into high level and medium-high level technology industry groups, medium level, medium-low level, and low-level technology industry groups. Before analyzing each of the 10 member states, I investigate the trade competitiveness between Korea and ASEAN, and analyze the trade competitiveness of Korea, especially among the 10 member countries, with Korea having a competitive industrial force. The study results revealed that trade with Vietnam was actively promoted, with Korea-Vietnam trade volume also growing far above that of other member states. And trade with Korea was brisk in the order of Singapore, Indonesia, Malaysia and the Philippines. The analysis of the trade structure of the 10 ASEAN member states, confirmed that imports were also being made while exporting items in the high- and medium-level technology industry groups. The possibility of entering the Korean market was quite high, given that Korea imported high- and medium- and high-tech industrial forces while exporting low-tech industrial forces.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1996년도 하계학술대회 논문집 A
• /
• pp.585-587
• /
• 1996

A simple regenerative snubber structure is proposed, which is applicable to multi-level inverter with series-connected GTOs for high power applications. The novel snubber structure can solve large energy loss problems and guarantee safe operation of power converter can be achieved. The proposed new snubber has the potential of high performance and high reliability and is particularly suitable to high power and multi-level application with series connected power devices. The snubber voltage and current waveforms are analized and shown the simulation and experimental results for a GTO 3-level inverter circuit with inductive load.

• Journal of Power Electronics
• /
• 제18권2호
• /
• pp.407-417
• /
• 2018

A novel family of Buck mode three-level direct ac converters with a high frequency link is proposed. These converters can transfer an unsteady high ac voltage with distortion into a regulated sinusoidal voltage with a low THD at the same frequency. The circuit configuration is constituted of a three-level converter, high frequency transformer, cycloconverter, as well as input and output filters. The topological family includes forward, push-pull, half-bridge, and full-bridge modes. In order to achieve a reliable three-level ac-ac conversion, and to overcome the surge voltage and surge current of the cycloconverter, a phase-shifted control strategy is introduced in this paper. A prototype is presented with experimental results to demonstrate that the proposed converters have five advantages including high frequency electrical isolation, lower voltage stress of the power switches, bi-directional power flow, low THD of the output voltage, and a higher input power factor.