• Journal of the Korean Electrochemical Society
• /
• v.11 no.1
• /
• pp.33-36
• /
• 2008

In the present study, impedance spectrometry has been used for predicting State-of-Charge (SoC) of gel type, Valve Regulated Lead Acid (VRLA), battery. The impedance measurements of VRLA battery (2V/1.2 Ah) at various SoC were made over the frequency range from 100kHz to 10mHz with an amplitude 10 mV. The impedance parameters have been evaluated by the analysis of the data using an equivalent circuit and a complex non-linear least squares (CNLS) fitting method. The charge transfer resistance values and double layer capacitance values of the positive electrode were higher than those of the negative electrode. The gel resistance values increased with decreasing in SoC. This indicates that the gel resistance is an important parameter for predicting SoC of VRLA battery.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.14 no.3
• /
• pp.226-232
• /
• 2003

In this paper, design rule of power island is studied. Power island have a defect that increase transfer noise when each power bus structure is resonant. So, in this paper, resonances are suppressed for various noise source positions and in order to improve noise characteristics, it is suggested EGI in order to improve noise characteristic. At the simulation result, the least resonance is showed for various noise source position and transfer impedance with power bus resonance is reduced about 11 $\Omega$ by EGI.

• Journal of Power Electronics
• /
• v.18 no.4
• /
• pp.1190-1200
• /
• 2018

A current sourced bi-directional wireless power transfer (WPT) system is proposed to solve the problems that exist in the bi-directional WPT for vehicle-to-grid (V2G) systems. These problems include the fact that these systems are not safe enough, the output power is limited and the control methods are complicated. Firstly, the proposed system adopts two different compensation and control methods on both the primary and secondary sides. Secondly, based on an AC impedance analysis, the working principle is analyzed and the parameter configuration method with frequency stability is given. In order to output a constant voltage, a bi-directional DC/DC circuit and a controllable rectifier bridge are adopted, which are based on the "constant primary current, constant secondary voltage" control strategy. Finally, the effectiveness and feasibility of the proposed methods are verified by experimental results.

• Proceedings of the KIEE Conference
• /
• 2002.11b
• /
• pp.151-153
• /
• 2002

Using UPFC(Unified Power Flow Controlled), it is possible to control three parameters(voltage, impedance, and phase angle). The UPFC can generate or absorb reactive power rapidly so as to enhance the transient and voltage stability and also influence the power flow. In this paper, the effects of application of the UPFC to the power system are analyzed from a viewpoint of improving the total transfer capability by enhancing voltage stability. The IPLAN, which is a high level language used with PSS/E program, is employed for evaluating the total transfer capability from a f-V curve.

• Proceedings of the KIEE Conference
• /
• 2007.07a
• /
• pp.1704-1705
• /
• 2007

A step-down procedure employing low voltage thermal transfer standard(LVTS) and micropotentiometer is described for the establishing the ac low voltage standards in the range of 2 mV to 200 mV below 1 MHz. Techniques are given for measuring input impedance with insertion method and calculating the loading error for the ac-dc transfer difference of the LVTS.

• Korean Chemical Engineering Research
• /
• v.53 no.5
• /
• pp.638-645
• /
• 2015

Vanadium redox flow batteries (VRFBs) have been investigated for their potential utility as large energy storage systems due to their advantageous performances in terms of long cycle life, high energy efficiency, low cost, and flexible design. Carbon materials are typically used as electrodes in redox reactions and as a liquid electrolyte support. The activities, surface areas, and surface morphologies of porous carbon materials must be optimized to increase the redox flow battery performance. Here, to reduce the resistance in VRFBs, surface-modified carbon felt electrodes were fabricated, and their structural, morphological, and chemical properties were characterized. The surface-modified carbon felt electrode improved the cycling energy efficiencies in the VRFBs, from 65% to 73%, due to the improved wettability with electrolyte. From the results of impedances analysis with proposed fitting model, the electrolyte-coupled polarization in VRFB dramatically decreased upon modification of carbon felt electrode surface. It is also demonstrated that the compressibility of carbon felt electrodes was important to the VRFB polarization, which are concerned with mass transfer polarization. The impedance analysis will be helpful for obtaining better and longer-lived VRFB performances.

• Journal of Power Electronics
• /
• v.16 no.4
• /
• pp.1483-1493
• /
• 2016

Multiple parallel inverters have multiple resonant frequencies that are influenced by many factors. This often results in stability and power quality problems. This paper develops a multiple input multiple output model of grid-connected inverter systems using a closed-loop transfer function. The influence factors of the resonant characteristics are analyzed with the developed model. The analysis results show that the resonant frequency is closely related to the number, type and composition ratio of the parallel inverters. To suppress resonance, a scheme based on virtual impedance is presented, where the virtual impedance is emulated in the vicinity of the resonance frequency. The proposed scheme needs one inverter with virtual impedance control, which reduces the design complexity of the other inverter controllers. Simulation and experimental tests are carried out on two single phase converter-based setups. The results validate the correctness of the model, the analytical results and the resonant suppressing scheme.

• Applied Chemistry for Engineering
• /
• v.10 no.3
• /
• pp.382-387
• /
• 1999

The processes and the kinetics of the lithium intercalation into the spin coated $V_2O_5$ xerogel prepared by the sol-gel processing have been studied employing impedance analyzer. Homogeneous and quasi-isotropic thin films of the xerogel can be obtained as a result of random distribution of the $V_2O_5$ gels on the substrate by the use of the spin coating. Effective diffusion coefficient and charge transfer resistance vary more than one order of magnitude at high and low lithium composition in $V_2O_5$ xerogel, respectively.

• Corrosion Science and Technology
• /
• v.16 no.6
• /
• pp.298-304
• /
• 2017

Coil spring steels from the automobile suspension part after field exposure for 10 years and those after anti-corrosion validation test in proving ground of 5,000 ~ 10,000 km were examined for corrosion damages. Partial loss of paint, accumulation of corrosion product, and cracking of paint and superficial material were observed. The surface and subsurface region of spring steels had compressive residual stress and high hardness by shot peening. The surface hardness values of the specimens were 620 ~ 670 Hv. They were 60 ~ 80 Hv higher than those of the samples taken from the middle part of the spring. The maximum compressive stress was -916 ~ -1208 MPa measured at depth of about $100{\mu}m$. Electrochemical impedance spectroscopy showed that the resistances of charge transfer and the paint layer of the spring steels ranged from several tens to millions ${\Omega}{\cdot}cm^2$. The resistance of the field samples was much higher than that of the proving ground samples used in this study, implying that the proving ground test condition would be more corrosive than the field environment.

• Proceedings of the KIEE Conference
• /
• 2003.07c
• /
• pp.1674-1676
• /
• 2003

The factors affecting the accuracy of lightning current measuring system are figured out the materials and length of down-conductor, and impedance matching between grounding resistance and characteristic impedance of cable. The cable with the low characteristic impedance used to transfer the lightning current from the top of the tower is too long to measure the waveform of lightning current, exactly. Especially, the height of the tower can cause the change of front time and magnitude of lightning stroke current. Basically, in this experiment. It was found that the magnitude and rise time of the lightning current are extremely dependant in the length of down-conductor in lightning current measuring system.