• Journal of Power Electronics
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• v.11 no.2
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• pp.237-243
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• 2011

Lithium batteries are widely used in mobile electronic devices due to their higher voltage and energy density, lighter weight and longer life cycle when compared to other secondary batteries. In particular, a high demand for lithium batteries is expected for electric cars. In the case of the lithium batteries used in electric cars, driving distance must be calculated accurately and discharging should not be done below a level that makes it impossible to crank. Therefore, accurate information on the state-of-charge (SOC) becomes an essential element for reliable driving. In this paper, a novel method for estimating the SOC of lithium polymer batteries using AC impedance is proposed. In the proposed method, the parameters are extracted by fitting the measured impedance spectrum on an equivalent impedance model and the variation in the parameter values at each SOC is used to estimate the SOC. Also to shorten the long length of time required for the measurement of the impedance spectrum, a novel method is proposed that can extract the equivalent impedance model parameters of lithium polymer batteries with the impedance measured at only two specific frequencies. Experiments are conducted on lithium polymer batteries, with similar capacities, made by different manufacturers to prove the validity of the proposed method.

• 전기의세계
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• v.21 no.1
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• pp.7-12
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• 1972

General steady state equivalent circuits are derived for the family of single phase motor having two windings with non-quadrature. First, the fundamental voltage equations of motor are derived by Faraday-Krichhoff's low in the fiew of the flux distribution in the modified motor with Kron primitive machine. Those equations are arranged in to f-b equations by transformation matrix. To using the above equations for circuit; 1) The concept of current-source was much help to sove the realtions between matrix impedance equation and circuit analysis 2) The simplification of the circuit to the mutual impedance matrix elements is easy to considerations of motor characteristics in the case of inserted external auxiliary winding impedance. Finally, this equivalent circuit showing as a single phase induction motor with quadrature winding is described by each conditions.

• Journal of electromagnetic engineering and science
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• v.15 no.1
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• pp.26-30
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• 2015

In this paper, a simple equivalent circuit model for a defected ground structure (DGS) microstrip line with stepped impedance slot-lines in the ground plane is presented. In addition, an analytic expression for the resonance frequency of the proposed structure is derived. In equivalent circuit modeling, the capacitance and the inductance of the resonance circuit are evaluated from the dimensions of the etched pattern in the ground plane. The resonance frequencies calculated from the proposed method are compared with those obtained with an electromagnetic (EM) simulation.

• Journal of Magnetics
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• v.20 no.1
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• pp.57-61
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• 2015

In this paper wireless power transmission system based on magnetic resonance coupling circuit was carried out. With the research objectives based on the mutual coupling model, mathematical expressions of optimal coupling coefficients are examined. Equivalent circuit parameters are calculated by Maxwell software, and the equivalent circuit was solved by Matlab software. The power transfer efficiency of the system was derived by using the electrical parameters of the equivalent circuit. System efficiency was analyzed depending on the different air gap values for various characteristic impedances. Hence, magnetic resonance coupling involves creating a resonance and transferring the power without radiating electromagnetic waves. As the air gap between the coils increased the coupling between the coils were weakened. The impedance of circuit varied as the air gap changed, affecting the power transfer efficiency.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.510-510
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• 2012

반도체, 디스플레이, 태양광 등의 공정에서 사용되는 웨이퍼의 크기가 증가하고, 생산률이 플라즈마의 밀도에 비례한다는 연구 결과가 발표되면서 대면적 고밀도 플라즈마 소스 개발에 대한 연구가 활발히 진행되고 있다. 특히, ECR, ICP, Helicon plasma 등 고밀도 플라즈마 소스에 대한 관심이 높아지고 있다. 이에 따라, 여러 개의 ICP를 결합한 multiple ICP를 이용해 대면적 고밀도 플라즈마 소스 개발을 진행했다. Multiple ICP의 경우 각 ICP 소스에 같은 power (current)를 공급해야만 균일한 플라즈마 방전이 발생되어 균일도를 확보 할 수 있다. Current controller 같은 추가적인 장비를 설치하지 않고, power를 분배하는 transmission line을 coaxial 형태로 설계하고 같은 길이로 병렬 연결함으로써 각각의 ICP소스에서 균일한 플라즈마를 방전시킬 수 있었다. Power generator에서 보는 각 ICP의 total impedance는 각 ICP 소스의 impedance와 coaxial 형태의 transmission line의 characteristic impedance, frequency, 길이의 함수로 구할 수 있고, 이 total impedance가 일정하기 때문에 current가 균등하게 분배되어 각 ICP소스에 균등한 power 분배가 가능한 것이다. 실질적으로 ICP 소스의 impedance는 플라즈마 방전 유무에 따라 변화하기 때문에 일정하게 유지하는 것은 어렵다. Transmission line의 characteristic을 사용함으로써 ICP의 impedance의 변화에 상관없이 Total impedance를 일정하게 유지시킴으로써 균등한 power 분배가 가능하다는 것을 연구했다. Frequency는 13,56MHz, characteristic impedance를 $50{\Omega}$ (coaxial cable)으로 고정하고, ICP 소스의 플라즈마 방전 유무/antenna turn/소스 위치에 따른 total impedance를 transmission line의 길이에 따라 측정하고, 이를 이론값, 그래프와 비교하였다. 특정 length에서 플라즈마 방전 유무(ICP의 impedance 변화)와 상관없이 비교적 일정한 total impedance를 유지하는 것을 확인 했다. 이것은 특정 길이를 갖는 coaxial형태의 transmission line를 연결하면, total impedance는 플라즈마 방전 유무로 발생하는 ICP의 impedance 변화와 상관없이 일정하게 유지되어 각 ICP소스에 균등한 파워 분배가 가능하다는 것을 보여준 결과이다. 이것을 토대로 frequency에 따라(또는 characteristic impedance에 따라) 균등한 파워 분배가 가능한 coaxial 형태 transmission line의 특정 길이를 구할 수 있고, 대면적 소스에서 균등한 파워 분배를 위한 병렬연결에 적용할 수 있을 것이다.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.11 no.5
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• pp.97-102
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• 2012

In this paper, each electrical length and harmonics of the multi-stage SIR are calculated by using the input impedance for the variable application of SIR in the microwave systems. The size reduced ratio of the SIR is slightly reduced as increasing of the number of stage. The impedance ratio between lower and higher impedance of the SIR has the dominant effect on the size reduced ratio and harmonic characteristics. Also the equivalent impedance of the SIR is a geometric mean between lower and higher impedance and the quality factor of the SIR is similar to the half-wavelength resonator's.

• Journal of Power Electronics
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• v.16 no.1
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• pp.319-328
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• 2016

In this study, we first briefly introduce the effect of circulating current control on the modulation signal of a modular multilevel converter (MMC). The maximum modulation index is also theoretically derived. According to the optimal modulation index analysis and the model in the continuous domain, different DC-side output impedance equivalent models of MMC with/without compensating component are derived. The DC-side impedance of MMC inverter station can be regarded as a series xR + yL + zC branch in both cases. The compensating component of the maximum modulation index is also related to the DC equivalent impedance with circulating current control. The frequency characteristic of impedance for MMC, which is observed from its DC side, is analyzed. Finally, this study investigates the prediction of the DC voltage ripple transfer between two-terminal MMC high-voltage direct current systems under unbalanced conditions. The rationality and accuracy of the impedance model are verified through MATLAB/Simulink simulations and experimental results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.6
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• pp.230-237
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• 2004

In this paper the effects of inverter ripple currents to the Proton Exchange Membrane Fuel Cell Stack (PEMFCS) is analyzed by the impedance model. The proposed method employs the frequency analysis technique to derive an equivalent impedance model of the fuel cell stack and the effects of the inverter ripple current are investigated. The calculated results m then verified by means of experiments on commercially available PEMFCSs. The experimental results show that the ripple current can contribute up to 10[%] reduction in the available output power.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.438-439
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• 2006

We have used ITO/$Alq_3$/Al structure to study complex impedance in $Alq_3$ based organic light emitting diode. Equivalent circuit was analyzed in a device structure of ITO/$Alq_3$/Al by varying the thickness of $Alq_3$ layer from 60 to 400nm. The impedance results can be fitted using equivalent circuit model of parallel combination resistance $R_p$ and capacitance $C_p$ with a small series resistance $R_s$.

• Journal of Electrochemical Science and Technology
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• v.4 no.4
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• pp.157-162
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• 2013

First of all, we express our deepest sympathies for the passing of Professor Su-Moon Park. In the present paper, an electrochemical impedance spectroscopy (EIS), which Professor Su-Moon Park also used frequently for the investigation of electroconducting polymer, is introduced as a recent evaluation tool for a commercially available lithium-ion battery (LIB). The paper surveys how to design equivalent circuits while explaining physical and chemical phenomena in the LIB and how to get more accurate impedance spectra with varying the measuring temperatures. Additionally, a square current EIS (SC-EIS) technique, which we have suggested, is introduced for the larger LIB system as a promising technique for the future.