• The Journal of the Korea Contents Association
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• v.5 no.3
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• pp.167-173
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• 2005

In a speech coding system using excitation source of voiced and unvoiced, it would be involved a distortion of speech quality in case coexist with a voiced and unvoiced consonants in a frame. So, I propose TSIUVC(Transition Segment Including Unvoiced Consonant) extraction method by using pitch pulses and Zero Crossing Rate in order to unexistent with a voiced and unvoiced consonants in a frame. And this paper present a TSIUVC approximate-synthesis method by using frequency band division. As a result, this method obtains a high quality approximation-synthesis waveform within TSIUVC by using frequency information of 0.547kHz below and 2.813kHz above. And the TSIUVC extraction rate was $91\%$ for female voice and $96.2\%$ for male voice respectively This method has the capability of being applied to a new speech coding of Voiced/Silence/TSIUVC, speech analysis, and speech synthesis.

• Journal of Power Electronics
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• v.19 no.2
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• pp.454-462
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• 2019

When compared to traditional bridge-type inverters, the dual-buck inverter has a higher reliability due to the fact that its bridge legs do not have a shoot-through problem. In this paper, the working principle of the dual-buck inverter is analyzed. A comparison of the working modes under full-cycle and half-cycle control is discussed. With half-cycle control, the inverter can realize a higher efficiency. However, this results in current zero-crossing distortion. The corresponding control strategy of the dual-buck inverter is proposed in order to realize both high efficiency and low current harmonic distortion. In addition, the system stability is analyzed. Dead-time is unnecessary due to the advantages of the topology. Thus, the current harmonic distortion can be further reduced. An inverter with the proposed control strategy has the advantages of high reliability, high efficiency and low current harmonic distortion. Finally, simulation and experimental results are given to verify the theoretical analysis.

• Journal of Power Electronics
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• v.14 no.2
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• pp.249-256
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• 2014

A novel topology generation method for the no dead-time three-phase AC/DC converter is proposed in this study. With this method, a series of no dead time topologies are generated and their operation principles are analyzed. The classic three-phase bridge AC/DC converter can realize a bidirectional operation. However, dead-time should be inserted in the driving signals to avoid the shoot-through problem, which would cause additional harmonics. Compared with the bridge topology, the proposed topologies lack the shoot-through problem. Thus, dead time can be avoided. All of the no dead time three-phase AC/DC converters can realize bidirectional operation. The operating principles of the converters are analyzed in detail, and the corresponding control strategies are discussed. Comparisons of waveform distortion and efficiency among the converters are provided. Finally, 9 KW DSP-based principle prototypes are established and tested. Simulation and experimental results verify the theoretical analysis.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.169-170
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• 2011

PFC(Power Factor Correction) converters are commonly designed for CCM(Continuous Conduction Mode). However, DCM(Discontinuous Conduction Mode) appears in the input current near the ZCP(Zero Crossing Point) at light loads, resulting in input current distortion. It is caused by inaccurate average current values obtained in DCM. This paper studies a simple digital control scheme that can be operated in both CCM and DCM with minimal changes to the CCM average current control structure.

• Journal of Power Electronics
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• v.15 no.4
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• pp.876-885
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• 2015

High frequency alternating current (HFAC) has been widely used in a wide range of power distribution systems (PDS) due to its superior performance. A high frequency AC/DC converter plays the role of converting HFAC voltage to DC voltage. In this paper, a new LCL-T resonant AC/DC converter has been proposed, and an easier control method based on input voltage comparison is presented, without the complicated calculation of the zero-crossing point. Both a low distortion and near-to-unity power factor can be achieved by the proposed resonant converter and control strategy. The operational principle and steady-state analysis are given for the proposed resonant converter. A simulation model and experimental prototype are implemented with an operation frequency of 25kHz and a rated power of 20W. The simulation and experimental results verify the accuracy of the analysis and the excellent performance of the proposed topology.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.281-285
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• 2002

The photophysical properties and the singlet oxygen generation efficiencies of meso-tetraphenyl-trithiasapphyrin $(S_3TPS)$ and meso-tetmkis(p-methoxy phenyl)-trithiasapphy rin ((p-MeO)-$S_3TPS$) have been investigated, utilizing steady-state and time-resolved spectroscopic methods to elucidate the possibility of their use as photosensitizers for photodynamic therapy (PDT). The observed photophysical properties were compared with those of other porphyrin-like photosensitizers in geometrical and electronic structural aspects, such as extended ${\pi}$ conjugation, structural distortion, and internal heavy atoms. The steady-state electronic absorption and fluorescence spectra were both red-shifted due to the extended ${\pi}$-conjugation. The fluorescence quantum yields were measured as very small. Even though intersystem crossing rates were expected to increase due to the increment of spin orbital coupling, the triplet quantum yields were measured as less than 0.15. Such characteristics can be ascribed to the more enhanced internal conversion rates compared with the intersystem crossing rates. Furthermore, the triplet state lifetimes were shortened to -1.0 ${\mu}s$ as expected. Therefore, the singlet oxygen quantum yields were estimated to be near zero due to the fast triplet state decay rates and the inefficient energy transfer to the oxygen molecule as well as the low triplet quantum yields. The low efficiencies of energy transfer to the oxygen molecule can be attributed to the lower oxidation potential and/or the energetically low lying triplet state. Such photophysical factors should be carefully evaluated as potential photosensitizers that have extended ${\pi}$-conjugation and heavy core atoms synthesized for red-shifted absorption and high triplet state quantum yields.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.1
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• pp.91-98
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• 1999

An integrated ZCS quasi-resonant converter(QRC) for the power factor correction with a single switch is presented in this paper. The power factor correction can be achieved by the discontinuous conduction mode(DCM) operation of the input current. The proposed converter gives the good power factor, low line current harmonics, and tight output regulation. The input current waveform of the prototype designed using design equations shows about 15% of total harmonic distortion at rated condition. Also, the efficiency and power factor can be obtained about 86% and 0.985, respectively, at rated condition. The proposed converter is suitable for a low power level converter with a tightly regulated low output voltage and switching frequency of more than several hundreds kHz.

• IEMEK Journal of Embedded Systems and Applications
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• v.8 no.3
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• pp.129-136
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• 2013

In this paper, a motion control system based on 2-axis gimbal system is designed and implemented to drive a high speed and precision. The proposed system consists of the RS-422 interface, 2-axis gimbal platform, servo control unit integrated with a high speed DSP chip-set, servo amplifier unit, potentiometer sensor unit, and resolver sensor unit. The servo control unit using the high speed DSP firmware is designed to get a fast response without an overshoot with step input and a RMS error of low probability with ramp input. The servo amplifier unit using a voltage control is designed to resolve the zero-crossing distortion for precise motion. To verify the performance and stability of the implemented system, experiments are performed through a measurement of the time and frequency domain response in a laboratory environment by using a PXI(PCI eXtentions for Instrumentation).

• Journal of Korea Multimedia Society
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• v.7 no.9
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• pp.1233-1239
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• 2004

In a speech coding system using excitation source of voiced and unvoiced, it would be involved a distortion of speech qualify in case coexist with a voiced and an unvoiced consonants in a frame. This paper present a new multi-pulse coding method by using V/S/TSIUVC switching, individual pitch pulses and TSIUVC approximation-synthesis method in order to restrict a distortion of speech quality. The TSIUVC is extracted by using the zero crossing rate and individual pitch pulse. And the TSIUVC extraction rate was 91% for female voice and 96.2% for male voice respectively. The important thing is that the frequency information of 0.347kHz below and 2.813kHz above can be made with high quality synthesis waveform within TSIUVC. I evaluate the MPC use V/UV and the FBD-MPC use V/S/TSIUVC. As a result, I knew that synthesis speech of the FBD-MPC was better in speech quality than synthesis speech of the MPC.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.6
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• pp.1180-1184
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• 2006

In a speech coding system using excitation source of voiced and unvoiced, it would be a distortion of speech quality in a voiced and an unvoiced consonants in a frame. In this paper, I propose a new multi-pulse coding method make use of V/S/TSIUVC switching and TSIUVC approximation-synthesis method in order to restrict a distortion of speech quality. The TSIUVC is extracted by using the zero crossing rate and individual pitch pulse. And the TSIUVC extraction rate was 91% for female voice and 96.2% for male voice. The important thing is that the frequency information of 0.547kHz below and 2.813kHz above can be made with high quality synthesis waveform within TSIUVC. I evaluated the MPC of V/UV and FBD-MPC of V/S/TSIUVC. As a result, the synthesis speech of FBD-MPC was better in speech quality than the MPC.