• Journal of Electrical Engineering and Technology
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• v.6 no.4
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• pp.474-483
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• 2011

Solid-state fault current limiters (SSFCL) in power systems are alternative devices to limit prospective short circuit currents from reaching lower levels. Fault current limiters (FCL) can be classified into two categories: R-type (resistive) FCLs and L-type (inductive) FCLs. L-type FCL uses an inductor to limit fault level and is more efficient in suppressing voltage drop during a fault. In contrast, R-type FCL is constructed with a resistance and is more effective in consuming the acceleration energy of generators during a fault. Both functions enhance the transient stability of the power system. In the present paper, a novel SSFCL is proposed to enhance power system transient stability and power quality. The proposed SSFCL uses both functions of an L-type and R-type FCL. SSFCL consists of four diodes, one self-turn-off IGCT, a current-limiting by-pass inductor (L), and a variable resistance parallel with an inductor for improvement of power system stability and prevention of over-voltage across SSFCL. The main advantages of the proposed SSFCL are the simplicity of its structure and control, low steady-state impedance, fast response, and the existence of R-type and Ltype impedances during the fault, all of which improve power system stability and power quality. Simulations are accomplished in PSCAD/EMTDC.

• Journal of Information Technology Services
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• v.14 no.3
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• pp.117-129
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• 2015

For the continuous growth of firms, the contributions of effective risk management system are required. This research analyzes the impact on the firm's performance related to risk management structure which includes the risk management system, risk management activity and risk management competency. In this research, the structural equation model considering the variable which contains enterprise risk management system, risk management activity and risk management competency was suggested. Also risk management organization and management procedures are identified as in enterprise risk management system. The implementation activity and control activity were the factors related in risk management activity. And risk management competency can be described as the response level of managing risk in outside and inside the firms' environment. Finally this model was analysed empirically for 112 firms in Korea using SPSS 18.0 and Amos 16.0. As the results, the suggested hypothesis were adopted. So as to manage risk performance for their firms, the development of systematic Risk Management Framework is important for their risk management activity and risk management competency. Ultimately, we can conclude that the focusing to the systematic risk management approach could be effective on the firm's risk management performance.

• Computational Structural Engineering : An International Journal
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• v.1 no.2
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• pp.89-96
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• 2001

A study on the topology optimization of a Hard-Disk-Driver(HDD) actuator arm is presented. The purpose of the present wert is to increase the natural frequency of tole first lateral mode of the HDD actuator arm under the constraint of total moment of inertia, so as to facilitate the position control of the high speed actuator arm. The first lateral mode is an important factor in the position control process. Thus the topology optimization for 2-D model of the HDD actuator arm is considered. A new objective function corresponding to multieigenvalue optimization is suggested to improve the solution of the eigenvalue optimization problem. The material density of the structure is treated as the design variable and the intermediate density is penalized. The effects of different element types and material property functions on the final topology are studied. When the problem is discretized using 8-node element of a uniform density, tole smoothly-varying density field is obtained without checker-board patterns incurred. AS a result of 7he study, an improved design of the HDD actuator arm is suggested. Dynamic characteristics of the suggested design are compared computationally with those of the old design. With the same amount of the moment of inertia, the natural frequency of the first lateral mode of the suggested design is subsequently increased over the existing one.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.48 no.6
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• pp.8-14
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• 2011

In this note, a proof of Utkin's theorem is presented for SI(Single input) uncertain linear systems. The invariance theorem with respect to the two transformation methods so called the two diagonalization methods is proved clearly and comparatively for SI uncertain linear systems. With respect to the sliding surface transformation, the equation of the sliding mode i.e., the sliding surface is invariant. The control inputs by the two transformation methods both have the same gains. By means of the two transformation methods, the same results can be obtained. Through an illustrative example and simulation study, the usefulness of the main results is verified.

• Wind and Structures
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• v.30 no.2
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• pp.211-217
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• 2020

Vibrations of a wind turbine blade have a negative impact on its performance and result in failure of the blade, therefore an approach to effectively control vibration in turbine blades are sought by wind industry. The small domestic horizontal axis wind turbine blades induce flap wise (out-of-plane) vibration, due to varying wind speeds. These flap wise vibrations are transferred to the structure, which even causes catastrophic failure of the system. Shape memory alloys which possess physical property of variable stiffness across different phases are embedded into the composite blades for active vibration control. Previously Shape memory alloys have been used as actuators to change their angles and orientations in fighter jet blades but not used for active vibration control for wind turbine blades. In this work a GFRP blade embedded with Shape Memory Alloy (SMA) and tested for its vibrational and material damping characteristics, under martensitic and austenite conditions. The embedment portrays 47% reduction in displacement of blade, with respect to the conventional blade. An analytical model for the actuated smart blade is also proposed, which validates the harmonic response of the smart blade.

• Journal of Electrical Engineering and Technology
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• v.13 no.5
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• pp.1886-1900
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• 2018

This paper proposes a confronting feedback control structure and controllers for positive output elementary super lift Luo converters (POESLLCs) working in discontinuous conduction mode (DCM). The POESLLC offers the merits like high voltage transfer gain, good efficiency, and minimized coil current and capacitor voltage ripples. The POESLLC working in DCM holds the value of not having right half pole zero (RHPZ) in their control to output transfer function unlike continuous conduction mode (CCM). Also the DCM bestows superlative dynamic response, eliminates the reverse recovery troubles of diode and retains the stability. The proposed control structure involves two controllers respectively to control the voltage (outer) loop and the current (inner) loop to confront the time-varying ON/OFF characteristics of variable structured systems (VSSs) like POESLLC. This study involves two different combination of feedback controllers viz. the proportional integral controller (PIC) plus sliding mode controller (SMC) and the fuzzy logic controller (FLC) plus SMC. The state space averaging modeling of POESLLC in DCM is reviewed first, then design of PIC, FLC and SMC are detailed. The performance of developed controller combinations is studied at different working states of the POESLLC system by MATLAB-Simulink implementation. Further the experimental corroboration is done through implementation of the developed controllers in PIC 16F877A processor. The prototype uses IRF250 MOSFET, IR2110 driver and UF5408 diodes. The results reassured the proficiency of designed FLC plus SMC combination over its counterpart PIC plus SMC.

• Journal of Navigation and Port Research
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• v.29 no.8 s.104
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• pp.747-753
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• 2005

In this paper, as an anti-sway control strategy of container cranes, we investigate a variable structure control in which the moving load follows a given trajectory, whereas both the trolley and hoist controllers achieve their positioning problems. It is crucial, in an automated container terminal, that collisions should be avoided during the transference of containers from one place to another. It is also necessary, in the case of a quay crane, to select suitable loading and unloading trajectories of containers, so that possible collisions with surrounding obstacles are avoided. After a brief introduction of the mathematical model, a robust control scheme (i.e., a second-order sliding mode control that guarantees a fast and precise transference and a suppression of the resulted swing) is presented. Despite model uncertainties and unmodeled actuators dynamics, the swing suppression from the given trajectory is obtained by constraining the system motion on suitable sliding surfaces, which include both the desired path and the swing angle. The proposed controller has been tested with a laboratory-size pilot crane. Experimental results are provided.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.1
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• pp.45-54
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• 2003

Turbo compressor needs high speed rotation of impeller in structure, high rated gearbox and conventional induction motor. This mechanical system increased the moment of inertia and mechanical friction loss. Resently, the study of turbo compressor applied super high speed motor and drive, removing gearbox made its sire small and mechanical friction loss minimum. This paper describes the implementation of the vector control schemes for a variable-speed 131㎾ PMSM(Permanent Magnet Synchronous Motor) drive in super-high speed application.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.170-173
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• 2002

시스템이 슬라이딩모드의 존재조건을 만족하는 경우, 전동기의 상태가 전동기의 파라미터에 의존하지 않고 결정되는 절환 초평면에 수렴하기 때문에 파라미터에 불감한 응답을 나타낸다. 본 연구는 소형 유도전동기에 의한 외란 및 파라미터의 변동에 대하여 로바스트(robust)와 동시에 정확한 응답을 나타내는 교류서보 전동기 구동시스템을 실현하는 것이다. 이를 실현하기 위해서 가변구조 제어이론에 기초한 슬라이딩모드 제어를 적용하여 유도전동기 자계 슬립주파수형 벡터제어를 실현한다. 이상적인 전동기에 대한 시뮬레이션의 결과에 의해서 관성, 점성마찰계수, 부하 토오크 등 의 파라미터의 변동 및 외란에 대하여 로바스터성이 있다는 것을 알 수 있고 슬라이딩모드 제어의 도입이 교류전동기 서보제어에 유효한 것을 확인하였다.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.711-720
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• 2001

An enlarging a scale of logical domain organizing Internet, security policy association among entities become complicated. Establishment and control of security policies for each system is a hard problem to solve because of the environment and composite factors with variable properties. In this paper, to solve this actual problems, we orgainze a hierarchical structure of network and than we design the structure of database to apply security policies for secure communication. This enables efficient management of security data and association of security policy by using designed data structure between different domain in hierarchical structure with make secure communication possible.