• Journal of Power Electronics
• /
• v.17 no.4
• /
• pp.914-922
• /
• 2017

Multilevel converters have attracted a lot of attention in recent years. The efficiency parameters of a multilevel converter such as the switching losses and total harmonic distortion (THD) mainly depend on the modulation strategy used to control the converter. Among all of the modulation techniques, the selective harmonic elimination (SHE) method is particularly suitable for high-power applications due to its low switching frequency and high quality output voltage. This paper proposes a new expression for the SHE problem in five-level converters. Based on this new expression, a simple analytical method is introduced to determine the feasible modulation index intervals and to calculate the exact value of the switching angles. For each selected harmonic, this method presents three-level or five-level waveforms according to the value of the modulation index. Furthermore, a flowchart is proposed for the real-time implementation of this analytical method, which can be performed by a simple processor and without the need of any lookup table. The performance of the proposed algorithm is evaluated with several simulation and experimental results for a single phase five-level diode-clamped inverter.

• 한국연소학회:학술대회논문집
• /
• 2001.11a
• /
• pp.51-56
• /
• 2001

An experiment using preheated air in the coaxial diffusion flame burner was carried out in order to decrease NOx emission and improve the thermal efficiency. Preheated air combustion generally produces high NOx emissions but it was known very well to reduce NOx emission by diluting the combustion air with inert gas in preheated air combustion. In our study, $N_2$ gas was used for diluent and propane was utilized for fuel. We set the combustion air temperature on 300K, 500K, 700K, 900K and dilution level from 21% to 10% in terms of oxygen concentration. NOx emission increased along increment of combustion air temperature and decreased along increment of dilution level(lowering of oxygen concentration in combustion air). Flame-off limit with dilution level enhanced, flame length became longer and the location of maximum flame temperature became lower with increasing of combustion air temperature.

• Journal of Information Science Theory and Practice
• /
• v.3 no.4
• /
• pp.35-48
• /
• 2015

The aim of this study is to compare country output and citation impact as well as to assess the level of interdisciplinarity in the field of tribology research during the period 1998-2012, based on the SCOPUS database. Macro-level scientometric indicators such as growth rate, share of international collaborative papers, citation per paper, share of un-cited papers, and publication efficiency index were employed. Further, the Simpson Index of Diversity was used to measure the level of interdisciplinarity. The performance of top countries contributing more than 1000 papers during the study period was discussed. Contributions and share of continents and countries by income groups were examined. Further research contributions and citation impact of selected country groups were analyzed. This study reveals that high levels of interdisciplinarity exist in tribology research. Asia outperforms the other world regions and China contributes most of the papers (25%), while the United States receives most of the citations (22%).

• Proceedings of the KSR Conference
• /
• 2008.06a
• /
• pp.1946-1954
• /
• 2008

In urban railways operated by 10 cars or 8 cars per trainset, passengers split up and board a train. On-board passengers for each car are not aware of congestion level of other cars of the train. Passengers waiting at stations can not predict congestion rate of the car which they get on. Therefore, the number of passengers is not equally distributed. The cars with a relatively low congestion level and the ones with a high level coexist in the train. The objective of this paper is to enhance passenger convenience and improve train operational efficiency through operational headway adjustments according to congestion level of each car. It also aims to spread passengers out evenly and assess the degree of congestion on each car by measuring the weight of each car including passengers during peak and off-peak hours.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.12 no.12
• /
• pp.6079-6097
• /
• 2018

Safety-related systems (SRSs) has widely used in shipbuilding and power generation to prevent fatal accidents and to protect life and property. Thus, SRS performance is a high priority. The safety integrity level (SIL) is the relative performance level of an SRS with regard to its ability to operate reliably in a safe manner. In this article, we proposed an optimal design procedure to achieve the targeted SIL of SRSs. In addition, a more efficient failure mode and effects diagnostic analysis (FMEDA) process and optimization model were developed to improve cost efficiency. Based on previous IEC 61508 diagnostic analyses that revealed unnecessary costs associated with excessive reliability, the new approach consists of two phases: (i) SIL evaluation by FMEDA, and (ii) solution optimization for achieving the target SIL with minimal cost using integer-programming models. The proposed procedure meets the required safety level and minimizes system costs. A case study involving a gas-detection SRS was conducted to demonstrate the effectiveness of the new procedure.

• Herbal Formula Science
• /
• v.19 no.1
• /
• pp.219-231
• /
• 2011

Objectives : This study was designed to determine the effects of the GGEx18 ethyl acetate fraction(EF) on body weight gain, feeding efficiency ratio, and obesity-related factors in plasma as well as histology of liver and adipose tissues using high fat diet-fed male C57BL/6N obese mice. Methods : 8 weeks old, high fat diet-fed obese male mice were divided into 5 groups: C57BL/6N normal, control, EF(1), EF(2) and EF(3). After mice were treated with EF for 9 weeks, we measured body weight gain, food intake, feeding efficiency ratio, fat weight, plasma leptin and lipid levels. We also analysed histology of liver and adipose tissues on high fat diet-fed male C57BL/6N obese mice. Results : Compared with control, EF-treated mice had significantly lower body weight gain and feeding efficiency ratio. Consistent with the effects on body weight gain, EF significantly decreased the adipose tissue weight compared with control. Consistent with the effects on feeding efficiency ratio, EF significantly decreased plasma leptin concentrations compared with control. EF reduced the size of adipocytes as well as hepatic lipid accumulation compared with control. EF seems to be safe since not only the plasma levels of ALT and AST are within the normal range, but also EF did not show any toxic effects on organs. EF(3) was most effective among EF(1), EF(2), and EF(3) at doses of 25, 50, and 100 mg/kg, respectively. Conclusions : These results demonstrate that EF effectively reduces body weight gain, feeding efficiency ratio in high fat diet-fed obese mice, leading to the modulation of obesity. In addition, EF decreases the size of adipocytes and improves plasma lipids and controls hepatic lipid accumulation, suggesting that EF may act as a therapeutic agent for obesity.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.5
• /
• pp.3298-3303
• /
• 2014

In order to recycle the waste bumper, techniques removing coated paint on a bumper is crucial. Chemical methods are known to be much more effective in removing the paint compared to physical methods. However, the chemical methods generally use toxic solvents and consequently cause environmental pollution. In this study, we tested a new method which combines the chemical and physical method to reduce the amount of solvent and increase the paint removal efficiency. We found that mechanical stirring increases the paint removal efficiency in soaking stage of solvent. When solid particles as a stress transfer media are incorporated into the solvent and high mechanical stirring is applied, the paint removal efficiency is very high. It was proved that the combined method can accomplish high level of the paint removal efficiency maintaining low amount of solvent consumed.

• Journal of Power Electronics
• /
• v.9 no.6
• /
• pp.866-873
• /
• 2009

In general, the output voltage level of a PV array varies widely at various irradiances and temperatures. The MPP (Maximum Power Point) range of a medium- or high-power PV PCS is normally 450~830Vdc or 300~600Vdc. This means the PV PCS should operate in a wide range of modulation indexes. The PV PCS should satisfy the harmonic current requirement that the TDD (Total demand distortion) shall not exceed 5%. This paper proposes a new PWM control method for a medium- or high-power PV PCS which increases the efficiency of power conversion in all operation ranges with acceptable harmonic ripple currents. This paper compares and analyzes appropriate PWM schemes for the PV PCS in the view points of conversion efficiency and current harmonics.

• Proceedings of the KIPE Conference
• /
• 2004.07b
• /
• pp.963-966
• /
• 2004

The torque of SRM depends on the level of phase current and the derivative of phase inductance. But the phase inductance of SRM is not linearly changed according to rotor position angle because of saturation in magnetic circuit. Therefor it is difficult to control the desired torque. This paper proposes a model of control system for high efficiency drive of SRM. The GA-Neural Network is used to simulate the reasonable switching angle which is nonlinearly varied with rotor speed and load.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.27 no.10
• /
• pp.16-23
• /
• 1990

In this paper, the shaped offset Cassegrain antenna with low sidelobe, low cross-polar level, and high efficiency is designed. The design data is presented for shaping scheme. The validity of radi-ation characteristics is accomplished by comparing the result of measurement with numerical calculation and design goal. Experimental results of designed antenna are in good agreement with design goal except efficiency.