• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1746-1752
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• 2014

This paper presents an application of proportional-resonant (PR) current controllers in modular multilevel converter-high voltage direct current (MMC-HVDC) system under unbalanced voltage conditions. The ac currents are transformed and controlled in the stationary reference frame (${\alpha}{\beta}$-frame). Thus, the complex analysis of the positive and negative sequence components in the synchronous rotating reference frame (dq-frame) is not necessary. With this control method, the ac currents are kept balanced and the dc-link voltage is constant under the unbalanced voltage fault conditions. The simulation results based on a detailed PSCAD/EMTDC model confirm the effectiveness of the proposed control method.

• Journal of Power Electronics
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• v.15 no.2
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• pp.431-442
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• 2015

Dead-time element must be set into space vector pulsed width modulation signals to avoid short circuits of the inverter. However, the dead-time element distorts the output voltage vector, which deteriorates the performance of electrical machine drive system. In this paper, dead-time effect and its compensation control strategy are analyzed. Based on the analysis, the voltage distortion caused by dead-time is regarded as two disturbances imposed on dq axes in the rotor reference frame, which degenerates the current tracking performance. To inhibit the adverse effect caused by the dead-time, a control scheme using two linear extended state observers is proposed. This method provides a strong ability to suppress dead-time effects. Simulations and experiments are conducted on a permanent magnet synchronous motor drive system to demonstrate the effectiveness of the proposed method.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.395-396
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• 2014

3상 독립형 인버터의 비대칭 출력 전압은 부하의 불평형에 의하여 야기되며 암 단락을 방지하기 위한 데드타임은 출력 전압에 비선형적인 특성을 발생시킨다. 인버터가 불평형부하 구동 시 3상 출력전압은 불평형의 홀수배 고조파를, 동기좌표계 상에서 dq전압은 서로 크기가 다른 짝수배 고조파를 발생시킨다. 본 논문에서는 불평형부하에 따른 불평형 출력 전압을 평형으로 유지하는 동시에 공진제어를 이용하여 데드타임에 의한 불평형 고조파를 보상하는 전압제어기를 제안하였으며 10kW 용량의 독립형 인버터를 제작하여 제안한 제어기법의 타당성을 입증하였다. 실험을 통해 출력 전압의 THD는 4.3%에서 1.5%로, 불평형율은 4.3%에서 1.1%로 감소함을 확인하였다.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.367-368
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• 2015

This paper introduces a shunt active power filter with a small DC bus capacitor by adding additional low-pass filter (LPF). The DC link voltage fluctuation is impressively suppressed with a small value in spite of the low value of DC-link capacitor under the steady-state condition. Consequently, the cost and volume of power converter are significantly reduced thanks to the reduced value of DC-bus capacitor. On the other hand, an indirect control strategy is used to maintain grid-side current when non-linear loads are connected to the system. By using proportional-integral (PI) and modified repetitive controller (RC) in dq0 frame, the calculation time is greatly decreased by 6 times compared with the conventional RC, and the number of measurement devices is also minimized. As a result, the acquired total harmonic distortion (THD) is lower than 2% regardless of the load conditions. Simulation results are carried out in order to verify the effectiveness of the proposed control strategy.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.764-766
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• 1993

A new static var compensator(SVC) system using three-level inverter is proposed for high voltage and high power applications. A general and simple model for the overall system is obtained using circuit DQ-transform and DC and AC analyses are achieved to characterize the open-loop system. Using the proposed model, a new control method which controls both the phase angle and modulation index of switching pattern simultaneously is suggested to provide fast response of SVC system without using independent voltage source. Finally, predicted results are verified by computer simulation.

• Proceedings of the KIEE Conference
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• 1999.07h
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• pp.21-25
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• 1999

This paper proposes a novel control strategy of SVC(Static var compensator) using cascade multilevel inverter. To control the reactive power instantaneously, the dq-dynamic system model is described and analyzed. A single pulse pattern based on the SHE(Selective Harmonic Elimination) technique is determined from the look-up table to reduce the line current harmonics and a rotating fundamental frequency switching scheme is applied to adjust the DC capacitor voltage at the scheme level. From the simulation, it is verified that this proposed control scheme make the dynamic control response of SVC fast, the current harmonics low, and the DC capacitor voltage balanced.

• Journal of the Korean Vacuum Society
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• v.4 no.3
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• pp.334-341
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• 1995

IB-AI-VIB2 및 IB-AI-VIB2 :Co2+ 결정을 고순도 원소를 출발 물질로 하고 iodine을 수송 매체로 사용하여 chemical transport reaction method로 성장시켰다. 성장된 결정의 결정구조는 chalcopyrite 구조였으며, energy gap은 direct band gap으로 3.514~1.814 eV 정도로 주어졌으며, cobalt를 불순물로 첨가할 때 energy gap은 감소하였다. IB-AI-VIB2 :Co2+ 결정에서 첨가된 cobalt가 모체결정의 Td symmetry site에 Co2+ ion으로 위치하여, Co2+ ion의 energy 준위 사이의 전자전이에 기인하는 불순물 광흡수 peaks가 나타났다. 이 불순물 광흡수 peaks에 결정장 이론을 적용하여 구산 1st-order spin-orbit coupling parameter(λ)는 -183~ -189cm-1정도였고, 2nd-order spin-orbit coupling parameter(P)는 225~239 cm-1정도였으며, crystal field parameter(Dq)는 328~395cm-1, Racah parameter(B)는 531~552cm-1정도였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.105-108
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• 2014

기업에서 사용하는 시스템에서는 대량의 데이터를 실시간으로 처리해야 하며 또한 시스템 장애로 인한 생산 중단이 발생하지 않도록 하기 위해 서버 이중화 구성에 많은 투자를 하고 있다. 장애를 최소화하기 위해 서버 구성을 Active-Standby 구조로 이중화를 구성하여 사용하고 있으며, 이로 인해 시스템에 대한 많은 비용을 투자하고 있다. 서버 부하 감소 및 서버 가용성 향상을 통한 투자 비용을 절감하기 위해 서버 분산 처리에 대한 방법이 나오고 있다. 그러나 Network 스위치나 라우터 등의 Hardware 적인 분산 시스템을 이용한 방법으로는 특정한 데이터만을 분산하여 처리할 수 없고 Hardware 의 투자 비용 또한 증가하게 된다. 또한 서버의 Active-Standby 구성에서 Standby 서버는 Active 서버의 문제 발생시에만 이용하게 됨으로 인해 서버의 가용성이 떨어지는 불합리가 발생함으로 인해 이를 개선하기 위한 연구를 통해 Active-Active 구성을 통해 서버의 가용성을 확보하고자 한다. 본 논문에서는 서버 가용성 향상을 위한 방법으로 DQ(Distributed Queue)를 이용하여 응용프로그램에서의 데이터 분산을 통한 응용프로그램에서의 부하를 분산하여 서버 내 리소스를 최대한 활용하면서 응용프로그램에서의 부하를 감소화할 수 있는 방법을 검증하고자 한다.

• Structural Engineering and Mechanics
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• v.73 no.5
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• pp.481-486
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• 2020

This paper deals with the buckling and optimization of a nanocomposite beam. The agglomeration of nanoparticles was assumed by Mori-Tanaka model. The harmony search optimization algorithm is adaptively improved using two adjusted processes based on dynamic parameters. The governing equations were derived by Timoshenko beam model by energy method. The optimum conditions of the nanocomposite beam- based proposed AIHS are compared with several existing harmony search algorithms. Applying DQ and Hs methods, the optimum values of radius and FS were obtained. The effects of thickness, agglomeration, volume percent of CNTs and boundary conditions were assumed. The results show that with increasing the volume percent of CNTs, the optimum radius of the beam decreases while the FS was improved.

• Smart Structures and Systems
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• v.23 no.4
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• pp.387-392
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• 2019

This research deals with the vibration analysis of embedded smart concrete plate reinforced by zinc oxide (ZnO). The effective material properties of structure are considered based on mixture rule. The elastic medium is simulated by orthotropic visco-Pasternak medium. The motion equations are derived applying Sinusoidal shear deformation theory (SSDT). The differential quadrature (DQ) method is applied for calculating frequency of structure. The effects of different parameters such as volume percent of ZnO, boundary conditions and geometrical parameters on the frequency of system are shown. The results are compared with other published works in the literature. Results indicate that the ZnO have an important role in frequency of structure.