• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.5
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• pp.307-314
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• 2021

Even though the LCL filters have superior harmonic attenuation ability to L filters, stability has always been an issue. The system could be unstable because of the resonance phenomenon, especially when digital controller is used. Adding a notch filter to the compensator is one approach to solve the problem. Resonance phenomenon can be inhibited by aligning notch frequency to system resonance frequency. However, resonance frequency variation can be obtained because the actual system has a nonstationary characteristic. Therefore, the system could be unstable, where the system parameters are changed when the conventional notch filter is used. An adaptive digital notch filter that stabilizes the system even system parameters are changed. Simulation and experiment results are provided to verify the validity of the proposed adaptive filter.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.338-339
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• 2019

본 논문에서는 LCL 필터를 사용하는 계통연계형 인버터에서 시스템을 안정시키기 위해 피드백 경로에 2차 저역 통과 필터(LPF)가 사용되었을 때 전류센서의 위치에 따른 출력 전류의 고조파 성분을 분석한다. LCL 필터를 사용하는 계통 연계형 인버터에서는 필터의 공진으로 시스템은 불안정해 지기 쉬우며 또한 안정조건은 전류센서의 위치에 따라서 바뀐다. 전류센서의 위치에 따라 바뀌는 계통측 전류의 고조파 성분을 시뮬레이션을 통해 분석한다.

• Journal of Navigation and Port Research
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• v.33 no.6
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• pp.409-414
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• 2009

As Korea has the economic structure heavily depending on exporting commodities, the importance of both maritime and air transportation mode is significant. Accordingly, for the sustainable and stable export the freight transportation market by mode needs to be developed complementarity each other. This paper, therefore, aims at analysing the LCL commodities transported by the two mode in terms of unit price, freight charge bearability and price structure. For this around 500 bill of lading(B/L) are collected and analysed resulting in deriving the distinctive characteristics of commodities by mode and the implication for price policy.

• Applied Microscopy
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• v.38 no.4
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• pp.353-361
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• 2008

We aimed to investigate whether the extracts of Lycii fructus, Lycii folium, and estradiol can attenuate on the level of cholesterol on serum and ultrastructure alteration of hepatocytes isolated from ovariectomized rats. Experimental groups are divided into five: Sham (sham-operated), OVX (ovariectomized animal), LCF (OVX, Lycii fructus), LCL (OVX, Lycii folium), and $E_2$ (OVX, estradiol). The body weights of OVX group showed increase compared with Sham, LCF, and LCL groups. The levels of total cholesterol and low-density lipoprotein (LDL) cholesterol were significantly decreased in the LCF and LCL groups compared with those of OVX group. Moreover, the High-density lipoprotein (HDL) cholesterol level was increased in the LCL group. As the results of electron microscopical observation, lipid droplets in the OVX group showed increase compared with Sham group. But in the LCF group not showed lipid droplets. In conclusion, administration of Lycii fructus or Lycii folium lowers the serum cholesterol content of the ovariectomized rats and also the damage of the hepatocytes and formation of lipid droplets.

• The Transactions of the Korean Institute of Power Electronics
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• v.2 no.2
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• pp.19-28
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• 1997

A simple AC complex circuit analysis for LCL type series resonant converter with phase shift control is proposed. Based on these analyses, a set of characteristic curves which allows a optimal design procedure for this converter is shown, without increasing the volt-ampere rating of tank circuit. Especially, inverter output peak current can be minimized in both full load and partial load conditions. The presented design considerations can make the load range wide from full loads to light loads achieving turn-on with zero voltage switching (ZVS) operation. The simulation and experimental results show the effectiveness of the proposed design algorithms.

• Journal of Power Electronics
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• v.16 no.4
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• pp.1565-1577
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• 2016

For grid-connected LCL-filtered inverters, dual-loop current control with an inner-loop active damping (AD) based on capacitor current feedback is generally used for the sake of current quality. However, existing studies on capacitor current feedback AD with a control delay do not reveal the mathematical relation among the dual-loop stability, capacitor current feedback factor, delay time and LCL parameters. The robustness was not investigated through mathematical derivations. Thus, this paper aims to provide a systematic study of dual-loop current control in a digitally-controlled inverter. At first, the stable region of the inner-loop AD is derived. Then, the dual-loop stability and robustness are analyzed by mathematical derivations when the inner-loop AD is stable and unstable. Robust design principles for the inner-loop AD feedback factor and the outer-loop current controller are derived. Most importantly, ensuring the stability of the inner-loop AD is critical for achieving high robustness against a large grid impedance. Then, several improved approaches are proposed and synthesized. The limitations and benefits of all of the approaches are identified to help engineers apply capacitor current feedback AD in practice.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1178-1189
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• 2018

In grid-connected voltage-source inverters (VSIs), when compared with a simple inductive L filter, the LCL filter has a better performance in attenuating the high frequency harmonics caused by the pulse-width modulation of power switches. However, the resonance peaks generated by the filter inductors and capacitors can make a system unstable. In terms of simplicity and filter design cost, a passive damping method is generally preferred. However, its high power loss and degradation in high frequency harmonic attenuation are significant demerits. In this paper, a mathematical design solution for a passive LCL filter to derive filter parameters suppressing the high frequency current harmonics to 0.3% is proposed. The minimum filter inductance can be obtained to reduce the size of the filter. Furthermore, a minimum damping resistance design considering a current controller is analyzed for a stable closed-loop system. The proposed design method is verified by experimental results using a 5-kW three-phase prototype inverter.

• Journal of Power Electronics
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• v.13 no.5
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• pp.896-908
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• 2013

Under high grid impedance conditions, it is difficult to guarantee the stability of grid-connected inverters with an LCL filter designed based on ideal grid conditions. In this paper, the theoretical basis for output impedance calculation is introduced. Based on the small-signal model, the d-d channel closed-loop output impedance models adopting the converter-side current control method and the grid-side current control method are derived, respectively. Specifically, this paper shows how to simplify the stability analysis which is usually complemented based on the generalized Nyquist stability criterion (GNC). The stability of each current-controlled grid-connected system is analyzed via the proposed simplified method. Moreover, the influence of the LCL parameters on the stability margin of grid-connected inverter controlled with converter-side current is studied. It is shown that the stability of grid-connected systems is fully determined by the d-d channel output admittance of the grid-connected inverter and the inductive component of the grid impedance. Experimental results validate the proposed theoretical stability analysis.

• Journal of Navigation and Port Research
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• v.28 no.1
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• pp.69-74
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• 2004

Container Freight Station(CFS), which would be located inside terminal or outside, plays the role of consolidating less than container load(LCL) cargo gathered from multi shippers and deconsolidating full container load cargo into individual consignment. When CFS is allocated inside terminal it muses several problem such as traffic gam around terminal, high social and logistics cost and deterioration of terminal condition. This study, therefore, tries to evaluate the location of CFS, inside and outside of terminal, with respect to the social and logistics costs.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.85-87
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• 2008

The demand of a three phase PWM inverter for the purpose of power control or grid-connecting is increasing. This inverter is connected to a grid through an L-filter or LCL-filter to reduce the harmonics caused by switching. An LCL-filter can reduce the harmonic of a low switching frequency and generate a satisfactory level of grid side current with a relatively low-inductance than an L-filter. But the additional poles caused by the LC part affects a stability problem due to induced resonance of the system. This paper presents a compensation method using a power theory to improve performance, the designed LCL-filter system and to reduce the stability problems caused by resonance. The effectiveness of the proposed algorithm is verified by simulations.