• Proceedings of the KOSOMBE Conference
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• v.1995 no.11
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• pp.167-170
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• 1995

An frequency modulated (FM) DANTE pulse sequence generates a quadratic phase toward the transverse of image by an FM RF pulse. In the image of a serious susceptibility effect, the phase due to the difference of the susceptibility in the pixel occurs susceptibility error which arise signal loss. But the signal loss due to the susceptibility effect in the pixel is reduced when the quadratic phase adds in the pixel. In this paper, we have generated a quadratic function toward the transverse (X-Y) using FM DANTE sequence and the susceptibility effect is reduced in the gradient echo (GE) imaging. Computer simulation and experimental results is obtained by using a whole-body KAIS 2.0T NMR system.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.7
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• pp.49-57
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• 2008

This paper presents a voltage source type half-bridge series resonant high frequency (HF) inverter for induction heated fixing roller in copy machines. This high-frequency inverter works under zero current soft switching (ZCS) commutation and has wide power regulation range due to employing a pulse density modulation (PDM) scheme. Transient and steady state operating modes of the inverter are presented in this paper together with its PDM-based power regulation system. Experimental operating performances of the developed HF-ZCS inverter as well as power losses and actual efficiency are discussed and compared with computer simulation results.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1421-1428
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• 2015

The efficiency and reliability of the dual-buck inverter (DBI) were greatly improved by eliminating the shoot-through problem and optimally designing the freewheeling diode. The traditional DBI suffers from large harmonic components with low output voltage and large capacity output filter inductor. To overcome the aforementioned disadvantages, a modified DBI (MBDI) was proposed by adopting a quasi-resonant link and pulse density modulation (PDM). This paper first introduces the working principle of the MBDI and PDM, and then the selection principle of system parameters is presented. Finally, a mathematical model of the MBDIis built, and an experiment prototype is set up. Simulation and experimental results verify the correctness of the theoretical analysis and the feasibility of the scheme.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1314-1321
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• 2014

A new simplified topology for a dynamic voltage restorer (DVR) based on direct converter with a reduced number of switches is presented. The direct converter is fabricated using only three bi-directional controlled switches. The direct converter is connected between the grid and center-tapped series transformer. The center-tapped series transformer is used to inject the compensating voltage synthesized by the direct converter. The DVR can properly compensate for long-duration, balanced, and unbalanced voltage sag and swell by taking power from the grid. The switches are driven by ordinary pulse width modulation signals. Simulation and hardware results validate the idea that the proposed topology can mitigate sag of 50% and swell of unlimited quantity.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.1044-1048
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• 2001

This paper proposes a nonlinear impedance circuit composed by diodes and inductors or capacitors. This circuit needs no control circuits and switches, and the impedance value is changed by the polarity of current or voltage. This paper presents one of these applications to improve the input current of capacitor input diode rectifiers. The rectifier using the nonlinear impedance circuit id constructed with four diodes and four capacitors in addition to the conventional rectifiers, that is, it has eight diodes and five capacitors, including a DC link capacitor. It makes harmonic components of the input current reduce and the power factor improve. A circuit design method is shown by experimentation and confirmed simulation. It explained that compared conventional pulse-width modulated (PWM)inverter with half pulse-width modulated (HPWM) inverter proposed HPWM inverter eliminated dead-time by lowering switching loss and holding over-shooting.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.11
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• pp.1819-1828
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• 1989

In this paper, we determined the modulation index for minimization of speed ripple and position error using maximum speed ripple (SRF) and maximum position error(PEF) in current source TPWM inverter. Through computer simulation, we compared with total current harmonic distortion, SRF and PEF for square wave modulation method and TPWM method. As a result, it turns out that square wave modulation method is superior to TPWM method of 3 pulses per half cycle in speed ripple and position error contents. And TPWM is better than square wave method when pulse number is more than 5. Also, in these pulse numbers, moduladtion index of minimum speed ripple and munimum position error is 0.91.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.204-207
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• 2003

The present paper reports high-fidelity simulation of direct initiation processes of cylindrical detonation waves by concentrated energy deposition. The goal is to understand the underpinning mechanisms in failed or successful detonation initiation processes. We employed the Space-Time CESE method to solve the reacting flow equations, including realistic finite-rate chemistry model of the nine species and twenty-four reactions for H$_2$-O$_2$-Ar mixtures. Detailed results of sub-critical, critical. and supercritical initiation process are reported.

• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.633-636
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• 1989

The simulation results of the third harmonic conversion with 1.064 um Nd :YAG laser using polarization mismatch method are reported. The third harmonic conversion efficiency was over 65% for the Gaussian incident pulse of $300{\sim}400MW/cm^2$ peak intensity, and over 80% for $3{\sim}4GW/cm^2$ peak intensity pulse. The dependence of the third harmonic conversion efficiency' on the variation of incident polarization angle ${\theta}_p$ and angular discrepancy ${\Delta}{\theta}$ of phase matched angle ${\theta}_m$ is discussed.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.12
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• pp.739-750
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• 2004

In case while M(modulation index) is more than 0.7, the spectrum of motor voltage and current of a conventional two-phase SRP-PWM scheme are not reduced considerably. To solve the problems of a conventional two-phase SRP-PWM, this paper proposes a two-phase SRP-PWM(DZSRP-PWM) with double zero vector mode which zero vector is selected as V(111) in case of M >0.7, and zero vector is selected as V(000) if M < 0.7. For the validity of the proposed method, the PSIM simulations and experiments were achieved. And the simulation and experiment results show that the voltage and current harmonics all over the modulation index are spread to a wide band area.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2559-2561
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• 1999

The life of a fluorescent lamp is greatly affected by starting scenario and crest factor. This paper will propose a new crest factor control method in electronic ballast for fluorescent lamp using Pulse Frequency Modulation (PFM), which employs a passive Power Factor Correction (PFC) circuit in the input stage. The operation of parellel-loaded circuit, the switching frequency. and the characteristics of electronic ballast with the proposed PFM control scheme are described in detail, and its validity is verified by the simulation results.