Hyung-Woo Lee

The performance prediction of controlled-PM LSM in various design schemes by FEM

This paper presents the various design schemes of controlled-permanent magnet (PM) linear synchronous motor (LSM). The motor performance on various design schemes, such as slot shapes, magnetizing patterns of PM and skewing, have been investigated in detail by using FEM and experiment. From this study, it is known that in various design schemes, skewing is most efficient to this system in all aspects.

Copolymerization characteristics of homogeneous and in situ supported [(CH2)5(C5H4)2][(C9H7)ZrCl2]2 catalyst

Abstract A newly synthesized catalyst, a pentamethylene bridged dinuclear zirconocene ([(CH2)5(C5H4)2][(C9H7)ZrCl2]2), and its in situ supported catalyst were tested in a ethylene/1-hexene copolymerization and their performance was compared with those of Cp2ZrCl2 and rac-Et(Ind)2ZrCl2. When homogeneous [(CH2)5(C5H4)2][(C9H7)ZrCl2]2 catalyst was used in the copolymerization, its activity decreased with comonomer incorporation (a negative comonomer effect) and it produced copolymer with a lower comonomer content than other catalysts, both of which were ascribed to the steric effect of the [(CH2)5(C5H4)2][(C9H7)ZrCl2]2 catalyst. With in situ supported catalysts, the activity did not change much with the increase of 1-hexene content in contrast to the homogeneous catalysts. In situ supported catalysts produced copolymers with higher content of 1-hexene and lower melting point and crystallinity. The changes in the molecular weight and its distribution of the copolymer with in situ supporting were significant and dependant on the nature of the catalyst.

Polymerization characteristics of in situ supported pentamethylene bridged dinuclear zirconocene

Abstract An in situ supporting method was applied to newly synthesized [(CH2)5(C5H4)2][(C9H7)ZrCl2]2 catalyst and other commercial catalysts, and its effects on the polymerization characteristics of these catalysts were examined through reaction experiments. The changes in the molecular weight distribution varied depending on the metallocene catalyst while the changes in the catalytic activity, average molecular weight and the melting point showed the same trend. The reason for the decrease in the molecular weight with in situ supporting was discussed in relation to the co-catalysts. The polymerization characteristics of each catalyst also varied according to the alkyl aluminum, and so it is important to select a proper co-catalyst or a combination of co-catalysts to obtain a desired polymer product from each metallocene catalyst supported by in situ method.

Effect of magnetic field on the magnetic domain structure of MnAs film on GaAs(001)

In this work, the effects of external magnetic field were studied, on the magnetic domain structure and the magnetic properties of epitaxial MnAs films on GaAs.

Information hiding for EC: public key traitor tracing for digital copyright protection

The authors present a software copyright protection model based on information hiding concepts with a public key scheme. A number of schemes for information hiding have been proposed such as digital watermarking, fingerprinting and traitor tracing scheme. Among these schemes, the authors focus on traitor tracing schemes. They first introduce digital copyright protection schemes. The proposed model provides secure software installation and an illegal copying protection scheme based on an information hiding scheme. It also provides a software live-update scheme based on a traitor tracing scheme. They propose a new model which uses the traitor tracing scheme and an electronic legal license tracing scheme for copyright protection. The live-update scheme of the proposed model is based on the traitor tracing scheme and reliable multicast guarantees security and efficiency.

Transient analysis of a superconducting AC generator using the compensated 2-D model

This paper presents a 2-D transient analysis of a superconducting AC generator (SCG) using the finite element method (FEM). The compensated 2-D model obtained by lengthening the airgap of the original 2-D model is proposed for the accurate and efficient transient analysis. The accuracy of the compensated 2-D model is verified by the small error 6.4% compared to experimental data. The transient characteristics of the 30KVA SCG model have been investigated in detail and the damper performance on various design parameters is examined.

THE FAILURE ANALYSIS IN TRACTION POWER SYSTEM

This paper presents a failure analysis of traction power systems. The electric railway consists of traction power systems, various vehicles, operating equipment, track, overhead line and electric equipment. It is a fundamental function of traction power systems that they supply customers with acceptable reliability and high quality power. Perhaps the most commonly used reliability assessment for railway systems has been the failure analysis of the traction signal system. The reliability assessment of traction power systems has also been an indispensable issue for reliability assessment. This paper deals with the classification of railway accidents caused by electrification problems, the estimation of failure rate in power equipments and failure analysis using fault trees. In study cases, the fault tree method for failure analysis is applied to railway substations in South Korea.

A study on the improvement of high power in interior permanent magnet

Recently, electric motors are required to show high efficiency/power/torque within low cost/size and noise in every application field, such as home appliance and industrial field. This paper proposed a design method that can result in motors that show low-cost and high output characteristics. An optimally designed flat type IPMSM and a V type IPMSM was design. For the design, a novel method considering d-axis armature reaction was used and a novel design equation is proposed. The validation of design method was done by comparing the manufactured motors.

Compensated phase method of current for reducing torque ripple of multi-degree of freedom surfaced permanent-magnet motor

In this paper, the torque characteristics of multi degree of freedom surfaced permanent-magnet motor (multi-D.O.F. SPM) are introduced. The multi-D.O.F. SPM can rotate a shaft while the rotor tilts to one side [1]. To decrease the torque ripple, the locus of summed wave forms of motor driving current have to be in an ellipse. Because the axis of electro motive force is generated by many numbers of currents as considering rotor position, the currents have different phase while the rotor is tilting. Therefore the phase of each current is defined as function of rotor position as using compensated phase method in this paper. The modified current is verified by comparison of analytic simulation results to experimentation results.

Trade-off optimal design in single-phase Line-start Permanent Magnet synchronous motor

A single phase LSPM (Line-Start Permanent Magnet Motor) has been investigated to improve the efficiency. Single phase LSPM has a permanent magnet (PM) inserted rotor which generates magnet torque and reluctance torque. The torques fluctuate due to asynchronous motion during transient state. The torques act as a breaking torque which make the motor not to start. To obtain good design of single phase LSPM, there is trade off design between efficiency and starting torque which are strongly relative to the magnet volume and inserted position. This paper presents the trade off optimal design of single phase LSPM.