• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.12
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• pp.2233-2239
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• 2007

The pantograph-catenary system is one of important components for high-speed rail system that are powered electrically. Electrical power is delivered from a catenary structure to the train via a pantograph and thus it is very important to regulate the contact force between catenary and pantograph. Although a lot of research results for active pantograph have been reported, most of them have made an unrealistic assumption that the catenary displacement is constant with respect to the time. In this paper, we present a new pantograph model that regards the catenary displacement as an unknown disturbance input. Moreover, a disturbance observer based controller is proposed to remove the effect of disturbance, i.e., the catenary displacement variation. The computer simulation result shows that the substantial improvement in regulating the contact force can be achieved by the proposed controller.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.5
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• pp.435-441
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• 2003

Dynamic Voltage Restorers (DVR)s are known as the best effective and economic means to compensate for voltage sags and swells. This paper proposes a novel method to generate reference voltages synchronized with the grid whether the line voltages are distorted by a fault or not. The proposed reference wave generator (RWG) looks for the original wave forms from the corrupted line voltages and synthesizes the expected positive sequence reference waves for DVRs. There is no transient problem on the generated reference waves when the line voltages are distorted by the fault.

• Proceedings of the KIPE Conference
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• 2003.11a
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• pp.36-40
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• 2003

On analyzing the power circuit of a DVR system, control limitations and control targets are presented for the voltage compensation in DVRs. The control delay in digital controllers increases the dimension of the system transfer function one degree higher which makes the control system more complicate and more unstable. Based on the power stage analysis, a novel controller for the compensation voltages in DVRs is proposed by a feedforward control scheme. Proposed controller works well with the time delay in the digital control system. This paper also proposes a guide line to design the control gain, appropriate output filter parameters and inverter switching frequency for DVRs in digital controllers. Proposed theory is verified by an experimental DVR system with a typical digital controller.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.458-459
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• 2010

일반적으로 전력 품질을 저하시키는 여러 문제들 중에서 가장 빈도가 높고 민감한 부하를 가지고 있는 수용가에 많은 영향을 주고 있는 것이 순간적인 전압상승(voltage swell)과 전압 강하(voltage sag)인데, 순간 전압 강하는 짧은 시간 동안 공급 전압의 크기가 줄어드는 것으로 대부분 인접한 배전 선로에서의 사고가 그 원인으로 작용한다. 이러한 순간 전압 강하는 제조공정의 제어를 위한 자동화 기기 등의 오동작이나 작업정지 등의 문제를 유발하여 경제적으로 큰 손실을 일으키게 되는데 이러한 순간 전압 강하의 문제를 해결하기 위한 대표적인 전력 전자 기기로는 일반적으로 동적 전압 보상기(Dynamic Voltage Restore: DVR)가 있다. 본 논문에서는 새로운 3상 Quasi Z-소스 DVR을 제안하였다．

• Proceedings of the Korea Information Processing Society Conference
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• 2001.04b
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• pp.1077-1080
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• 2001

본 논문에서는 트래픽 상태를 기반으로 네트워크 패킷의 상호관계에 따라 트래픽을 제어하는 방화벽 모델을 제시한다. 기존의 방화벽은 단순한 필터링 메커니즘과 보안 정책으로 복잡하고 다양해진 네트워크 트래픽 패턴에 효과적으로 대응할 수 없었다. 그러나, 본 논문에서는 네트워크 트래픽의 정보를 정적인 상태 정보와 동적인 상태 정보로 구분하여 수집하고 이러한 정보를 보안 정책에 의하여 생성된 상태 그래프의 의사 결정에 반영함으로서 트래픽의 미세한 변화에도 효과적이고 다양한 대응을 할 수 있도록 하였다. 그리고, 트래픽 분석기, 네트워크 에이전트, 관리자 인터페이스로 구분함으로서 관리자 인터페이스의 형태와 위치의 독립성을 높임으로서 보다 효과적인 사용환경을 제공하도록 하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1229-1234
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• 2006

This paper is concerned with the dynamic modeling and controller design for a cylindrical shell equipped with MFC actuators. The dynamic model was derived by using Ravleigh-Ritz method based on Donnel-Mushtari shell theory. The boundary conditions at both ends were assumed to be shear diaphragm. To verify the theoretical results, a cylindrical shell structure made of aluminum was built ana tested by using impact hammer. Experimental results show that there are little discrepancies compared to theoretical results because of the boundary conditions at both ends. The MFC actuators were glued to the cylindrical shell in longitudinal and circumferential directions. The PPF controller were designed for lowest two modes and applied to the MFC actuators. The experimental results show that vibrations can be successfully suppressed.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.2308-2310
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• 2000

In adaptive fuzzy control, fuzzy systems are used to approximate the unknown plant nonlinearities. Until now, most of the papers in the field of controller design for nonlinear system using fuzzy systems considers the affine system with fixed grid-rule structure. This paper considers general nonlinear systems and dynamic fuzzy rule structure. Adaptive laws for fuzzy parameters and fuzzy rule structrue are established so that the whole system is stable in the sense of Lyapunov.

• Proceedings of the KIEE Conference
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• 1987.07a
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• pp.252-255
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• 1987

High performance requirements such as high speed operation. accuracy and versatility have led to the consideration of structural flexibility in robot arms. The purpose of this study is to investigate the interrelationships between the robot structural flexibility and a linear controller for the rigid body motion. This paper employs an assumed modes method to model both the rigid and flexible motion of the robot arm. The simulation results illustrate the differences between leadscrew driven and unconstrainted axes of the robot.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.11
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• pp.2066-2072
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• 2010

In this paper, a variable structure dynamic output feedback controller with an transformed sliding surface is designed for the improved robust control of a uncertain system under unmatched system uncertainty, matched input matrix uncertainty, and disturbance satisfying some conditions. This paper is extended from the results of the static output feedback VSS in [9]. To effectively remove the reaching phase problems, an initial condition of the dynamic output is determined. The previous some limitations on the dynamic output feedback variable structure controller is overcome in this systematic design. A stabilizing control is designed to generate the sliding mode on the predetermined sliding surface S=0 and as a results the closed loop exponential stability is obtained and proved together with the existence condition of the sliding mode on S=0 for all unmatched system matrix uncertainties. To show the usefulness of the algorithm, a design example and computer simulations are presented.

• The KIPS Transactions:PartC
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• v.12C no.2 s.98
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• pp.229-234
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• 2005

We propose a fuzzy logic-based buffer management algorithm to improve internet traffic over ATM-GFR service. The proposed algorithm employs the strategies of early congestion detection and selective packet discard to achieve its design goals. A key feature of proposed algorithm is its ability to accept or drop a new incoming packet dynamically based on buffer condition and load rate of VCs. This is achieved by using fuzzy logic controller for the production of a drop factor. Simulation results show that proposed scheme significantly has improved fairness and TCP throughput compared with previous schemes.