• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.3
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• pp.239-246
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• 2015

A novel control method of a three-phase PWM inverter with LC filter is proposed. The transfer function of LC filter is the same as that of second-order low pass filter(LPF), which has a zero damping ratio. A simple method of implementing second-order LPF with damping ratio is to add a resistor in an LC circuit. However, in a real power system, adopting damping resistors is impractical because it results in losses proportional to the square of the current flowing through the resistors. Instead of inserting resistors, the proposed control strategy utilizes the measured capacitor voltages to control the oscillation of LC circuit. The overall transfer function of the proposed method is the same as a second-order LPF, and its damping ratio is controllable via control variables. The current controller can have overshoots caused by LC filter. Improved current controller is implemented by an equivalent second-order of LC filter. A 7.5 kVA PWM converter and a PWM inverter with a 5.5 kW induction motor are set up to verify the proposed control algorithm. Test waveforms are also presented to verify the proposed LC filter control algorithm.

• Korean Journal of Optics and Photonics
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• v.16 no.1
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• pp.103-108
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• 2005

Second harmonic generation(SHG) by guided phase matching is observed in waveguide structure using the anomalous dispersion of a poled polymer. The second harmonic TM$_{0}$ guided mode could be generated from the fundamental TM$_{0}$ guided mode and then the second harmonic power was higher than any other phase matchable mode because the overlap integral between the fundamental and the second harmonic wave was the largest in the theoretical analysis. Near UV SHG(370 nm) was obtained from the fundamental wavelength of Ti-sapphire laser(740 nm).

• Journal of the Korean Mathematical Society
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• v.51 no.1
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• pp.163-187
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• 2014

We present a multi-stage Roe-type numerical scheme for a model of two-phase flows arisen from the modeling of deflagration-to-detonation transition in granular materials. The first stage in the construction of the scheme computes the volume fraction at every time step. The second stage deals with the nonconservative terms in the governing equations which produces states on both side of the contact wave at each node. In the third stage, a Roe matrix for the two-phase is used to apply on the states obtained from the second stage. This scheme is shown to capture stationary waves and preserves the positivity of the volume fractions. Finally, we present numerical tests which all indicate that the proposed scheme can give very good approximations to the exact solution.

• Journal of Information Technology Applications and Management
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• v.11 no.3
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• pp.35-62
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• 2004

Recently, IT outsouricng has been one of the major concerns of many companies. This paper explores the relationship between information technology outsourcing risk factors and outsourcing performance. It is based upon a three-phase process utilizing IPO (Input-Process-Output) system. The first phase means the outsourcing planning risks t~at arise from overall environment of outsourcing, organizational refuse, and wrong contracts. The second phase implies outsourcing operational risks, which are occurred while out-sourcing perform and consist of organizational acceptances of outsourcing, partnership and hidden costs. The last phase is outsourcing performance based on four perspective of BSC(Blanced Scored Card). The survey was performed on the IT/IS firms, and the data was collected from 53 service receivers. The result of the analysis are as follows. First, Outsourcing planning risks positively affects the operational risks. Second, Outsourcing operational risks negatively affects the Outsourcing Performance.

• Journal of the Korean Society for Railway
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• v.16 no.4
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• pp.348-351
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• 2013

The aim of this research is to analyze and periodize the relationship between railroad and river transportation as one aspect of the transformation of the land transportation system in Korea. As a result, three phases can be observed: a first phase of equality and interdependence (1910s); a second phase, subordinating rivers to feeder lines under railroad's dominance; and a third phase when trucks and buses became a major means for local transportation in place of traditional shipping routes. River ports were among the main planned destinations during the first and second phases, but such plans were changed or withdrawn after the third phase. This relationship between river and rail illustrates one geopolitical factor relating to the development of Korea's rail transportation network.

• Journal of the Semiconductor & Display Technology
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• v.7 no.2
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• pp.1-5
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• 2008

Silicide formation process and the formation sequence were investigated in this study. It was postulated that the formation of the second silicide phase involves glass formation between the first silicide phase and Si given that a thin metal film is deposited on a Si substrate. The concentration of glass was assumed to be located where the free energy of the liquid alloy with respect to the first nucleated compound and solid Si (${\Delta}$G') is most negative. It was also mentioned that the glass concentration is close to the composition of the second phase in order to achieve the maximum energy degradation. It was shown that the minimum ${\Delta}$G' concentration can be estimated by interpolating the portion of the liquidus where the liquid alloy is in equilibrium with the two solid constituents, namely the first compound phase and Si, thereby forming a hypothetical eutectic.

• Journal of Power Electronics
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• v.14 no.3
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• pp.598-607
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• 2014

This paper proposes a frequency-locked loop (FLL) scheme for a single-phase grid-connected converter. A second-order generalized integrator (SOGI) based on fuzzy logic (FL) is applied to this converter to achieve precise phase angle detection. The use of this method enables the compensation of the nonlinear characteristic of the frequency error, which is defined in the SOGI scheme as the variation of the central frequency through the self-tuning gain. With the proposed scheme, the performance of the SOGI-FLL is further improved at the grid disturbances, which results in the stable operation of the grid converter under grid voltage sags or frequency variation. The PSIM simulation and experimental results are shown to verify the effectiveness of the proposed method.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.35 no.11
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• pp.529-534
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• 1986

In recent year, there have been much techniques for designing globally stable adaptive control systems when the unknown plant is minimum phase. This paper presents a new seheme for indirect adaptive control structure for nonminimum phase plant of which parameters are estimated from the least-square algorithm. Its effectiveness has been demonstrated by computer simulation carried out for a second-order plant.

• The Korean Journal of Ceramics
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• v.6 no.1
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• pp.6-8
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• 2000

The specific heat of a partly deuterated triglycine selenage (DTGSe) crystal under $\gamma$-irradiation was measured. It was shown that $\gamma$-irradiation defects changed the thermodynamic behavior of DTGSe crystal in a small dose region. The order of the phase transition changed from the first to the second at D=0.3 MR.

• 전기의세계
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• v.13 no.2
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• pp.1-4
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• 1964

Phase transformation is used to change some phase from phase in A.C. system. We have been used Scott or Fork connection in phase transformation the otherwise phase transformation was constructed from M-G set. From this M-G set, we could make phase shift facilities by mannual. Now, I can derive more easy phase transformation from taking another method. I believe this new phase transformation method in the first thing in the world. And so, I am going to explain about phase transformer construction process. The first, we could devide into equal part of core around the iron core as to be same size. The second, you will make primary and secondary winding on the core. The third, when you will supplied three phase A.C. at the terminal of primary winding you can get e.m.f. inducing of some phase at secondary. And so, we could make phase change from some phase A.C. We can apply this principle in many fields, i.e., freequency changer, phase leader of no use condenser, voltage regulator in keeping balance, and D.C. generator. And more, I will introduce in details concerning main pinciple and theory through following chapter.