• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.453-454
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• 2016

The ESS(Energy Storage System) connected with distributed generation is drawing attention due to improving the quality load leveling, peak shaving for enhancing reliability of the power grid. The grid-connected inverter makes frequency adjustment to the active power's charge discharge according to the load variation. In addition, the inverter is possible to act as a reactive power compensation device to eliminate harmonic operates as power factor change inhibiting, anti-transient voltage fluctuation, active filter. In this paper, we propose a design method of igbt stack considering the reactive power supply capacity to improve the quality and reliability of the inverter. Moreover, the grid-connected inverter considering the four-quadrant rated operation designed stack and verified the feasibility of the design through a thermal analysis.

• Journal of the Korean Society of Visualization
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• v.14 no.1
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• pp.46-50
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• 2016

Direct numerical simulations (DNSs) of turbulent pipe flows with temporal deceleration were performed to examine response of the turbulent flows to the deceleration. The simulations were started with a fully-developed turbulent pipe flow at the Reynolds number, $Re_D=24380$, based on the pipe radius and the laminar centerline velocity, and three different constant temporal decelerations were applied to the initial flow with varying dU/dt = -0.001274, -0.00625 and -0.025. It was shown that the mean flows were greatly affected by temporal decelerations with downward shift of log law, and turbulent intensities were increased in particular in the outer layer, compared to steady flows at a similar Reynolds number. The analysis of Reynolds shear stress showed that second- and fourth-quadrant Reynolds shear stresses were increased with the decelerations, and the increase of the turbulence was attributed to enhancement of outer turbulent vortical structures by the temporal decelerations.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.217-220
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• 2002

The assessment of PIV to measure the mean velocity and turbulence was carried out over a train of fixed two-dimensional dunes. The agreement between the PIV and LDV is good enough even in regions of flow reversals and high shear. Though limited in the wall normal direction field-of-view, PIV provides instantaneous flow fields, which reveal the complex nature of flow over dunes, as well as more sophisticated analyses such as two-point space correlation and quadrant analysis with a reasonable accuracy.

• Proceedings of the KIEE Conference
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• 1997.07a
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• pp.130-132
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• 1997

In this paper, we propose a new type of tubular linear induction motor(TLIM) with two-dimensional motion. The proposed motor consists of four short primary LIMs arranged on a same circumference and a common secondary. By adopting independently energized ring-windings to the primary, we can expect the reduction of coil-end region and the freedom of alternating current supply. The secondary conductor is capable of producing anyone of rotary, linear, and helical motions by controlling the phase of supply currents in each primary winding. From the 3-D finite element analysis and the experiment, we derive the feeding conditions to increase the subsidiary rotary-force and an optimal arrangement of primary currents to reduce the number of slot.

• Journal of the Korean Institute of Telematics and Electronics
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• v.2 no.2
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• pp.9-16
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• 1965

The characteristics of electronic multipliers and their accuracy are analyzed. From the analysis a low cost, four-quadrant timedivision electronic multiplier jis built. This multiplier produces an output voltage equal to 0.01 of the instantaneous product of two input voltage representing independent variables. Each input may either be constant or vary with time over a range of ${\pm}$100 volts. Drift and noise in this multiplier are kept at very low level and dynamic response is below 0.5 decibels up to 700 cycles per second. Methods of testing this multiplier and the results are also described. It is shown that the results agree with theoretical values satisfactorily.

• 전기의세계
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• v.14 no.2
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• pp.14-24
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• 1965

The characteristics of servo-multipliers and its accuracies are analyzed. From the analysis a low cost high accuracy four quadrant servo-multiplier with first derivative output feedback is built. The multiplier servomechanism has a second order system response with a damping ratio of 0.8 and computing bandwidth of 4 cycles per second, and its tracking accuracy at low speed of 0.5 volt per second is 0.9 per cent of maximum output voltage and static accuracy is better than 0.6 per cent. Method of testing this multiplier and the results are also described. The test on the characteristics of the multiplier shows that the results agree with theoretical values satisfactorily, and justifies the use of the servo-multiplier for slow type analog computers.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.356-357
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• 2013

ITER(국제 열핵융합 실험로) 핵융합 토카막 장치의 초전도 코일 부하에는 대용량 AC-DC 4상한 컨버터가 필요하다. 4상한 컨버터는 대용량 부하에 전력을 공급하기 위해서 12펄스 위상 제어 정류기의 양방향성 병렬 구조로 이루어져 있다. 컨버터의 안정된 정역 변환 동작을 위한 방법으로 순환 전류를 이용한 알고리즘이 필요하며, 본 논문에서는 4상한 컨버터의 안정된 동작을 위한 순환전류의 알고리즘을 해석 및 연구하였다. 또한 RTDS(Real Time Digital Simulator)의 RSCAD 시뮬레이션을 통해 동작 모드에 따른 컨버터의 스위칭 동작을 확인하였으며, 실제 4상한 컨버터를 RTDS와 연계하여 순환전류를 이용한 정역 운전 변환에 대한 실험 결과를 입증하였다.

• Proceedings of the KIEE Conference
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• summer
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• pp.992-994
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• 2004

In this paper, hybrid electromagnets using NdFeB permenant magnet are designed by 3-dimensional finite element analysis. Four hybrid magnets levitate the carrier of which total weight including control circuits and battery is 14[kg]. The nominal air gap length of the hybrid magnet is 3[mm]. The control circuit consists of DSP, 4-quadrant chopper, and gap sensor as feedback sensors. As a result, some experimental results for the magnetic levitation control by PI feedback control theory are shown.

• Journal of Power Electronics
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• v.5 no.4
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• pp.247-256
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• 2005

In order to harvest power in an efficient manner from a micro piezoelectric (PZT) device for charging the battery of a remote system, a new AC/DC resonant pulse power converter is proposed. The proposed power converter has two stages in the power conversion process. The first stage includes N-type MOSFET full bridge rectifier. The second stage includes a boost converter having an N-type MOSFET and a P-type MOSFET. MOSFETs work in the $1^{st}$ or $3^{rd}$ quadrant region. A small inductor for the boost converter is assigned in order to make the size of the power converter as small as possible, which makes the on-interval of the MOSFET switch of the boost converter ultimately short. Due to this short on-interval, the parasitic junction capacitances of MOSFETs affect the performance of the power converter system. In this paper, the performance of the new converter is analytically and experimentally evaluated with consideration of the parasitic capacitance of switching devices.

• The Pure and Applied Mathematics
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• v.17 no.4
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• pp.389-396
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• 2010

We investigate the existence of homoclinic orbits of the following systems of $Li{\'{e}}nard$ type: $a(x)x^'=h(y)-F(x)$, $y^'$=-a(x)g(x), where $h(y)=m{\mid}y{\mid}^{p-2}y$ with m > 0 and p > 1 and a, F, 9 are continuous functions such that a(x) > 0 for all $x{\in}{\mathbb{R}}$ and F(0)=g(0)=0 and xg(x) > 0 for $x{\neq}0$. By a series of time and coordinates transformations of the above system, we obtain sufficient conditions for the positive orbits of the above system starting at the points on the curve h(y) = F(x) with x > 0 to approach the origin through only the first quadrant. The method of this paper is new and the results of this paper cover some early results on this topic.