• Journal of the Korean Society for Precision Engineering
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• v.20 no.3
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• pp.140-148
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• 2003

An analysis fur the warping process has been performed to design the warper beam. Nonlinear material response is included in the physical model of polyester yarn. Large deformation finite element simulation considering contact and frictional analysis are used to obtain the pressure on the barrel of the warper beam. Loading condition on the flange is assumed by using the pressure on the barrel, winding number of yarn, Poisson's ratio of fiber, and fiber volume fraction. By using the above loading conditions NASTRAN finite element simulation is performed to calculate stress distribution and deformation of the warper beam. By comparing the deformed shape of the flange with experimental result, loading condition on the flange has been obtained. The obtained loading conditions on the barrel and flange can be utilized to design the warper beam.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.2
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• pp.157-164
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• 2022

This study proposes an enhanced quadruple-Active-Bridge (QAB) converter that can solve power coupling problems. By adopting a multiple winding transformer, the equivalent circuit of a conventional QAB converter has power couplings between arbitrary output ports. This coupling is an unintended power relationship that complicates the regulation of output voltage of the multiple ports. The proposed converter can carry out power decoupling by changing the arrangement of the coupling inductor. Power transfer equations for the proposed converter and its operating principles are analyzed in detail. The power coupling caused by the transformer's leakage inductance is verified by using a proposed coupling factor that presents the relationship between inductance ratio and coupling power. In addition, the decoupling power control performance of the proposed converter is verified by simulation and a 3 kW prototype converter.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.184-185
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• 2006

The flux-lock type superconducting fault current limiter (SFCL) has the attractive characteristics that can adjust the current limiting level by the turns ratio between two coils. Since the recovery characteristics of a superconducting element m the flux-lock type SFCL were dependent on the turns ratio between two coils, the analysis for the recovery characteristics of this type SFCL together with the current limiting characteristic is necessary to apply it to power system. When the applied voltage and load impedance were same, the recovery time of the superconducting element was 0.32sec in case that the turn's ratio between the primary and secondary windings was 63:21. In the meantime, when the turn's ratio of secondary winding increased to 3 times, the recovery time became longer to 0.58sec.

• Journal of Platform Technology
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• v.6 no.4
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• pp.59-68
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• 2018

The objective of this study is to develop an embedded antenna structure with NFC and WPC composite functions. By selecting stable materials, the optimal component ratio of the polymer sheet was determined. The low cost embedded winding method compared to the existing FPCB was devised. During the winding process, characterization and process technology were developed. We also fabricated a ferrite mold to process the WPC grooves and developed the process technology for optimizing the WPC antenna. The following conclusions were obtained. (1) Optimum composition ratio was derived as Fe 87.5%, Si 7%, Al 5.5% and selected as the final material. (2) Optimal sheet conditions were derived from the experimental evaluation method and the experimental design method through the combination test of the optimized sheet and the conventional mass production FPCB. (3) According to coil diameter and inner diameter, Q value fluctuation, resistance value and efficiency fluctuation are obtained. Therefore, the most suitable coil condition is selected and Rx matching is performed. (4) The EMV load modulation test and the cognitive distance test of the polymer sheet and the ferrite sheet showed that the recognition distance of the polymer sheet at 1k and 4K was 32-33 mm and the recognition distance of the ferrite sheet at the same condition was 30-31 mm.

• Composites Research
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• v.35 no.3
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• pp.139-146
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• 2022

In this study, we study fabrication methods suitable for CNT fibers-based composite. We try to fabricate a composite material using a small amount of CNT fiber preparation of woven fabrics or stitched unidirectional fabrics consisting of CNT fiber is not achievable currently. The composite materials on the basis of CNT fibers have been mainly manufactured filament winding method due to productivity issues and difficulties in composite processes. We develop a new method to prepare CNT fibers-based composite using resin infiltrated CNT fibers-based films. Because CNT fibers have numerous nanopores inside, unnecessary resin can remain after curing and decrease the mechanical properties of the composites. To remove the excess resin, pressure should be applied during the process, but the pressure applied through VaRTM was not enough to remove the excess resin. To obtain the composite with high ratio of CNT fibers, higher pressure using hot press machine and foams next to the resin-infiltrated CNT fibers are necessary. We can obtain the composite having a mass ratio of 58.5 wt% based on the new suggested method and diluted epoxy. The specific strength of the composite reach 0.525 N/tex. This study presents a new process method that can be applied to the manufacturing of CNT fiber composite materials in the future.

• Proceedings of the KIEE Conference
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• 2006.10b
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• pp.208-211
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• 2006

We have analyzed operating characteristics of hybrid-type superconducting fault current limiter (SFCL) according to the parallel connection of secondary windings with $YBa_{2}Cu_{3}O_{7}$ (YBCO) films. The turn ratio between the primary and secondary windings of each reactor was 63:21. Hybrid-type SFCL using a transformer with parallel reactors could reduce the unbalanced quench caused by differences of the critical current density between YBCO films. We found that hybrid-type SFCL having parallel connection induced simultaneous quench between the superconducting elements. The quench-starting point at this time was almost same. When the applied voltage was 200V, the limiting current in the hybrid-type SFCL with a serial connection was lowered to 34 percent than that in the SFCL with a parallel connection. In the meantime, when the voltage generated in the superconducting elements was the same, the current value in the parallel connection was 60 percent less than in the serial connection. The voltage generated in the primary winding also showed the similar behavior. In conclusion, we found that the fault current was limited more effectively in the SFCL with the serial connection but the power burden of the superconducting elements was reduced in the parallel connection.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.3
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• pp.299-306
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• 2008

The electromagnet in Maglev vehicles controls the voltage in its winding to maintain the air gap, a clearance between the electromagnet and guideway, within an allowable deviation, with strongly interacting with the flexible guideway. Thus, the vibration characteristics of guideway plays important role in dynamics of Maglev vehicles using electromagnet as an active suspension system. The effects of the guideway's vibrational characteristics on dynamics of the Maglev vehicle UTM-01 are analyzed. The coupled equations of motion of the vehicle/guideway with 3 DOFs are derived. Eigenvalues are calculated and frequency response analysis is also performed for a clear understanding of the dynamic characteristics due to guideway vibration characteristics. To verify the results, tests of the urban Mgalev vehicle UTM-02 are carried out. It is recommended that the natural frequency of the guideway be minimized and its damping ratio in the Maglev vehicle with a 5-states feedback control law as a levitation control law.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.1
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• pp.79-84
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• 2009

In order to increase the capacity of the superconducting fault current limiter(SFCL), the current and voltage grades of the SFCL must be increased. As a method for the increase of the current and voltage grades of the SFCL, we compared the various characteristics between the flux-lock type SFCL "With three superconducting units connected in series and the transformer type SFCL using the transformer with three secondary circuits. One of three superconducting units had not quenched in the flux-lock type SFCL. Therefore, the unbalanced power burden happened because of the voltage difference generated by unbalanced quenching between the superconducting units. In the meantime, the three superconducting units were all quenched in the transformer type SFCL using the transformer, and the voltage difference generated between the superconducting units was decreased. Therefore, the difference of critical characteristics was complemented by distribution of fault current in accordance with the turn's ratio between primary and secondary windings. The unbalanced power burden of the superconducting units was reduced due to flux-share between the superconducting units in the transformer. In conclusion, the capacity increment of the SFCL using a transformer was easier due to equal distribution of voltages generated by simultaneous quench of the superconducting units. We think that the characteristics is improved more because of the decrease of saturation in the iron core if the secondary winding is increased in the SFCL using the transformer.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.3
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• pp.256-263
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• 2014

Torque ripple is a very essential index for evaluating the effectiveness of a switched reluctance motor (SRM). Many common design strategies for reducing torque ripples of a SRM are changing the excitation trigger angle of stator windings, delaying the cut-off time of winding excitation, adjusting the ratio of arc angle between stator and rotor, and changing the geometric shape of rotor. However, the output torque or the efficiency of the SRM may drop as the above design strategies are solely adopted. In this paper, a hybrid design model which is obtained by the Taguchi Method for optimally designing a SRM with lower torque ripple and higher efficiency is presented. A 12S/8P motor is taken as a study case, and the 3D finite element method (FEM) is applied to analyze the characteristics of the motor and optimize the design process. The results have shown that the proposed method can achieve the design goal of obtaining a high-performance SRM for light electric vehicle applications.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.65 no.2
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• pp.77-83
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• 2016

The electric quality of train is represented by voltage and current harmonics at PT(Ratio 25,000/15/[V]) which is located between pantograph and primary winding of train transformer. In this paper, voltage and current harmonics were measured on the test EMU(electric multiple unit)train with maximum speed of 180km/h in existing railway lines(chungbuk, Taeback, Honam). As a results of test, it is found that the electric quality of train depends on the mostly operation conditions which is accelerating mode and braking mode on each sections. Voltage THD is above all 3[%] and current harmonics is monitored from lowest Harmonic to highest Harmonic in case of accelerating mode. But, highest current harmonics is not monitored in case of breaking mode. The results in this paper can help to stabilize the power device and power converter of the test EMU train.