• Journal of Electrical Engineering and Technology
• /
• v.6 no.1
• /
• pp.48-58
• /
• 2011

In this paper, an attempt has been made to design the current and speed proportional and integral (PI) regulators of self-commutating current source inverter-fed induction motor drive having capacitors at the machine end and to investigate the transient performance of the same for step changes in reference speed. The mathematical model of the complete drive system is developed in closed loop, and the characteristic equations of the systems are derived using perturbation about steady-state operating point in order to develop the characteristic equations. The D-partition technique is used for finding the stable region in the parametric plane. Frequency scanning technique is used to confirm the stability region. Final selection of the regulator parameters is done by comparing the transient response of the current and speed loops for step variations in reference. The performance of the drive is observed analytically through MATLAB simulation.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2005.05a
• /
• pp.461-466
• /
• 2005

This paper presents a new speed control scheme of the spindle induction motor (IM) using fuzzy-logic control in fold weakening region. The implementation of the proposed FLC-based spindle IM are investigated and compared to those obtained from the conventional PI controller based drive system, we have confirmed good simulation and experimental results at different dynamic operating conditions such as sudden change in command speed, step change, etc.

• Proceedings of the KIPE Conference
• /
• 2004.07a
• /
• pp.303-307
• /
• 2004

This paper presents a new speed control scheme of the spindle induction motor (IM) using fuzzy-logic control in field weakening region. The implementation of the proposed FLC-based spindle IM are investigated and compared to those obtained from the conventional PI controller based drive system, we have confirmed good simulation and experimental results at different dynamic operating conditions such as sudden change in command speed, step change, etc.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2007.08b
• /
• pp.1172-1175
• /
• 2007

We have investigated the threshold voltage shifts(${\Delta}Vth$) and drain current level shift (${\Delta}Ids$) in subthreshold region of a-Si:H TFTs induced by DC Bias (Vgs and Vds) - Temperature stress (BTS) condition. We plotted the transfer curves and the ${\Delta}Vth$ contour maps as Vds-Vds stress bias and Temperature to examine the severe damage cases on TFTs. Also, by drawing out the time-dependent transfer curve (Ids-Vgs) in the region of $10^{-8}\;{\sim}\;10^{-13}$ (A) current level, we can estimate the failure time of TFTs in a operating condition.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.05c
• /
• pp.193-198
• /
• 1996

The effect of dynamic strain aging (DSA) on the leak-before-break (LBB) analysis was estimated through the evaluation of leakage-size-crack and flaw stability in SA106 Gr.C piping steel. Also. the results were represented as a form of "LBB allowable load window". In the DSA temperature region. the leakage-size-crack length was smaller than that at other temperatures and it increased with increasing tensile strain rate. In the results of flaw stability analysis. the lowest instability load appeared at the temperature corresponding to minimum J- R curve which was caused by DSA. The instability load near the plant operating temperature depended on the loading rate of J-R data. and decreased with increasing tensile strain rate. These are due to the strain hardening characteristic and strain rate sensitivity of DSA. In the "LBB allowable load window". LBB allowable region was the narrowest at the temperature and loading conditions where DSA occurs.

• Journal of Information Technology Applications and Management
• /
• v.23 no.4
• /
• pp.83-100
• /
• 2016

In this paper, we present the DEA (Data Envelopment Analysis) application case study to investigate the regionally distinctive telco management characteristics of the Asia-Pacific countries. This study attempts to exploit the implications of DEA for the assessments of core process capabilities of telcos. Accordingly, we extract input variables of CAPEX (capital expenditure), operating expense, marketing expense, and number of employees, each to reflect the competitiveness of the core processes such as fixed asset utilization, operation & sales efficiency, and white collar productivity. In conjunction with the input variables, the output variables are chosen as EBITDA (Earnings Before Interest, Taxes, Depreciation and Amortization), ARPU (Average Revenue per User), and number of subscribers. The computational testing results, conducted with total 37 telcos of the 12 Asia-Pacific countries, are analyzed in various ways to understand the distinctive performance characteristics across the region. The managerial implication captured from this study provides useful insight for using DEA as the international telco management purpose.

• Proceedings of the IEEK Conference
• /
• 2002.07b
• /
• pp.1184-1187
• /
• 2002

In this paper, we propose a Rail-to-Rail OTA using equivalent MOSFETs without cutoff region, which operate in triode and saturation regions. The proposed circuit has a merit that its input range is not limited due to voltage drop of current mirrors. The simulation results of the proposed circuit are shown. From the simulation results, the linearity of the proposed circuit is improved when input voltage is from 2V to 3V.

• Journal of Mechanical Science and Technology
• /
• v.19 no.9
• /
• pp.1821-1832
• /
• 2005

This study realizes the conceptual method to predict combustion instability in actual full-scale combustion chamber of rocket engines by experimental tests with model (sub-scale) chamber. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions, and hot-fire test procedures were followed to obtain stability boundaries. From the experimental tests, two instability regions are presented by the parameters of combustion-chamber pressure and mixture (oxidizer/fuel) ratio, which are customary for combustor designers. It is found that instability characteristics in the chamber with the adopted jet injectors can be explained by the correlation between the characteristic burning or mixing time and the characteristic acoustic time: In each instability region, dynamic behaviors of flames are investigated to verify the hydrodynamically-derived characteristic lengths of the jet injectors. Large-amplitude pressure oscillation observed in upper instability region is found to be generated by lifted-off flames.

• Proceedings of the IEEK Conference
• /
• 1999.11a
• /
• pp.251-254
• /
• 1999

In this paper V-I(Voltage to Current) converter using the series composite transistor is presented. Due to the series composite transistor employs operating in the saturation region and triode region, the proposed circuit has wide input range at low voltage. The designed V-I converter has simulated by HSPICE using 0.6${\mu}{\textrm}{m}$ n-well CMOS process with a $\pm$2.5V supply voltage. Simulation results show that the THD can be 0.81% at 4 $V_{p-p}$ differential input voltage when frequency of input signal is 10MHz.z.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.526-529
• /
• 2008

Air Conditioner has become a popular comfort providing device since two decades, whether in an office or home especially for warm and wet climate countries. The RAC (Room Air Conditioner) is widely used in various working spaces and residences. It composed of heat exchager, cross-flow fan, stabilizer, rearguider and blade of diffuser region, etc. In this study, numerical analyses based on the prediction of transient phenomena were carried out to investigate the flow characteristics in the RAC, including the impeller, the rearguider, the stabilizer and the blade of the diffuser region. Using a commercial code, FLUENT, the velocity, pressure and streamlines were obtained with unsteady, turbulent flow and no-slip condition. The angular velocities of impeller are located in the 900 rpm. Turbulent closure was achieved using a standard k-${\varepsilon}$ model. A moving reference frame (MRF) approach was adopted to simulate the flow field generated by impeller in the RAC. Results were graphically depicted with various geometrical configurations and operating conditions.