• The Korean Journal of Health Service Management
• /
• v.12 no.2
• /
• pp.75-87
• /
• 2018

Objectives : This study aimed to investigate factors affecting multicultural acceptability of adolescents at individual and environmental levels. Methods : Participants were 2,032 first-year high school students who participated in the 4th-year Korean Children and Youth Panel Survey in 2013. Data were analyzed using descriptive statistics, t-test, one-way ANOVA, Pearson's correlation, and multilevel analysis. Results : Individual factors affecting multicultural acceptability of adolescents were health status, ego-resilience, and experience of visiting foreign countries. Learning activity, school regulation, relationship with teachers, and community spirit were significant factors at environmental level. Conclusions : Findings suggest that it is necessary to consider health status, improve positive resilience, activate a multicultural experience program, establish friendly relations with teachers, adhere to social norms, and strengthen community spirit for multicultural acceptability.

• Journal of information and communication convergence engineering
• /
• v.1 no.3
• /
• pp.163-168
• /
• 2003

This paper presents a cascade multilevel PWM rectifier without the isolation transformers for energy build-up at each inverter modules. The features and advantages of the proposed PWM rectifier can be summarized as follows; I) It realizes the high power high voltage AC/DC power conversion, 2) It uses no transformer which is bulky and heavy, 3) It has hybrid structure so that switching devices can be effectively utilized, 4) It produces high quality AC current even in high power high voltage applications, 5) The input power factor remains unity by simple modulation index control. The multilevel rectifier is analyzed by using the circuit DQ transformation whereby the characteristics and control equations are obtained. Finally, it will be shown that the system simulation reveals the validity of analyses.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.51 no.11
• /
• pp.645-651
• /
• 2002

In this paper, a multilevel PWM inverter employing a cascaded transformer is presented to reduce the harmonics of output voltage and load currents. The proposed PWM inverter consists of two full-bridge modules and their corresponding transformers. The secondarics of each transformer are series-connected. So continuous output voltage levels can be synthesized from the suitable selection of the turns ratio of trasformer. And it appears an integral ratio to input DC source. Because of the cascaded connection of transformers, output filter inductor is not necessary. The operational principles and analysis are explained, and it is compared with a conventional isolated H-bridge PWM inverter. The validity of proposed multilevel inverter is verified through simulated and experimental waveform and their FFT results.

• Journal of Power Electronics
• /
• v.16 no.3
• /
• pp.861-871
• /
• 2016

With high penetration of renewable energies, power electronic transformers (PETs) will be one of the most important infrastructures in the future power delivery and management system. In this study, an isolated bidirectional modular multilevel DC/DC converter is proposed for PET applications. A modular multilevel structure is adopted as switching valves to sustain medium voltages to achieve modular design and high reliability. Only one high-frequency transformer is used in the proposed converter, which significantly simplifies the circuit and galvanic insulation design. A dual-phase-shift modulation strategy is proposed to regulate the output power and achieve a simple voltage balancing control. A down-scaled (2 kW/20 kHz) prototype is constructed to demonstrate the proposed converter and verify the control strategy. The experimental results comply with the theoretical analysis well, with the highest power efficiency reaching 97.6%.

• Journal of Power Electronics
• /
• v.10 no.4
• /
• pp.357-364
• /
• 2010

In this paper, a novel analysis of a carrier based PWM method for multilevel inverters is presented. The space vector PWM and carrier based PWM correlations in multilevel inverters are investigated in a nominal two-level switching diagram. The obtained results can be applied to design various carrier PWM techniques. In this paper, a carrier based single-state PWM technique, which reduces the switching number and optimizes the active voltage errors, is presented. This PWM technique can be advantageous if there are a large number of levels. The proposed method is mathematically formulated and demonstrated by simulations and experimental results.

• Proceedings of the KIPE Conference
• /
• 2002.07a
• /
• pp.618-621
• /
• 2002

This paper proposes a static vu compensator using hybrid cascade 5-level PWM inverter, Circuit DQ transformation is used for modeling and analysis of the system, and it reveals the important characteristics and related equations of the system. Also, a multilevel PWM technique suitable to hybrid structure Is proposed for less harmonics in the input currents of the system. Finally, the validity of tile characteristics analysis is shown through PSIM simulations.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.40 no.11
• /
• pp.17-26
• /
• 2003

To reduce the nonlinear distortion of high power amplifier(HPA) in down link OFCDM system to employ time domain spreading, we apply technology which transmits MPSK(Multilevel-PSK) signal after clipping on multilevel input signal of IFFT subcarrier. In case that the nonlinear distortion of HPA is considered in AWGN channel, performacne of clipping OFCDM system using extended m sequence is over 2.2㏈ better than that of OFCDM system using extended m sequence when the number of user is 8 and 16. In case that the nonlinear distortion of HPA is considered in quasi-static channel, performacne of clipping OFCDM system using extended m code is over 2㏈ better than that of OFCDM system using extended m sequence when the number of user is 8 and 16.

• Journal of Power Electronics
• /
• v.15 no.2
• /
• pp.504-517
• /
• 2015

This paper presents a novel switching voltage model and an offset-based pulse width modulation (PWM) scheme for multilevel inverters with unbalanced DC sources. The switching voltage model under a DC voltage imbalance will be formulated in general form for multilevel neutral-point-clamped topologies. Analysis of the reference switching voltages from active and non-active switching voltage components in abc coordinates can enable voltage implementation for an unbalanced DC-source condition. Offset voltage is introduced as an indispensable variable in the switching voltage model for multilevel voltage-source inverters. The PWM performance is controlled through the design of two offset components in a subsequence. One main offset may refer to the common mode voltage, and the other offset restricts its effect on the quality of PWM control in related DC levels. The PWM quality can be improved as the switching loss is reduced in a discontinuous PWM mode by setting the local offset, which is related to the load currents. The validity of the proposed algorithm is verified by experimental results.

• Journal of the Korean institute of surface engineering
• /
• v.49 no.5
• /
• pp.467-471
• /
• 2016

In order to investigate the Na gettering, PSG/$SiO_2$/Al-1%Si multilevel thin films were fabricated. DC magnetron sputter techniques and APCVD (atmosphere pressure chemical vapor deposition) were utilized for the deposition of Al-1%Si thin films and PSG/$SiO_2$ passivations, respectively. Heat treatment was carried out at $300^{\circ}C$ for 5 h in air. SIMS (secondary ion mass spectrometry) depth profiling and XPS (X-ray Photoelectron Spectroscopy) analysis were used to determine the distribution and binding energies of Na, Al, Si, O, P and other elements throughout the PSG/$SiO_2$/Al-1%Si multilevel thin films. Na peaks were mainly observed at the the PSG/$SiO_2$ interface and at the $SiO_2$/Al-1%Si interfaces. Na impurity gettering in PSG/$SiO_2$/Al-1%Si multilevel thin films is considered to be caused by a segregation type of gettering. The chemical state of Si and O elements in PSG passivation appears to be $SiO_2$.

• Physical Therapy Rehabilitation Science
• /
• v.10 no.3
• /
• pp.328-336
• /
• 2021

Objective: The purpose of this study was to investigate the effect of cervical range of motion training on the change in respiratory function growth rate at the group and individual level in stroke patients and stroke patients with tracheostomy tube. Design: A Multilevel Growth Model Methods: 8 general stroke patients and 6 stroke patients who had a tracheostomy tube inserted were subjected to cervical range of motion training 3 times a week for 4 weeks. Force vital capacity (FVC), Forced expiratory volume in the first second (FEV1), Forced expiration ratio (FEV1/FVC) and Manual assist peak cough flow (MPCF) were measured. Data were analyzed using descriptive statistics and multilevel analysis with HLM 8.0. Results: A significant difference was found in the respiratory function analysis growth rate of the entire group (p<0.05), and two groups were added to the research model. The linear growth rate of respiratory function in patients with general stroke increased with the exception of FEV1/FVC (p<0.05). Stroke patients with tracheostomy tube showed a decreasing pattern except for FVC. In particular, MPCF showed a significantly decreased result (p<0.05). Conclusions: This study found that the maintenance of improved respiratory function in stroke patients with tracheostomy tube decreased over time. However, cervical range of motion training is still a useful method for respiratory function in general stroke patients and stroke patients with tracheostomy tube.