• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.1
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• pp.129-137
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• 2016

In the present study we verified performance of feed-forward control algorithm using short term prediction of ship motion information by taking advantage of developed numerical simulation model of FPSO motion. Up until now, various studies have been conducted about thrust control and allocation for dynamic positioning systems maintaining positions of ships or marine structures in diverse sea environmental conditions. In the existing studies, however, the dynamic positioning systems consist of only feedback control gains using a motion of vessel derived from environmental loads such as current, wind and wave. This study addresses dynamic positioning systems which have feedforward control gain derived from forecasted value of a motion of vessel occurred by current, wind and wave force. In this study, the future motion of vessel is forecasted via Brown's Exponential Smoothing after calculating the vessel motion via a selected mathematical model, and the control force for maintaining the position and heading angle of a vessel is decided by the feedback controller and the feedforward controller using PID theory and forecasted vessel motion respectively. For the allocation of thrusts, the Lagrange Multiplier Method is exploited. By constructing a simulation code for a dynamic positioning system of FPSO, the performance of feedforward control system which has feedback controller and feedforward controller was assessed. According to the result of this study, in case of using feedforward control system, it shows smaller maximum thrust power than using conventional feedback control system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.11
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• pp.934-943
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• 2018

In these days, demand for agile spacecraft is gradually increasing, due to the fact that agile spacecraft can improve mission capability. In this paper, an attitude control logic based on reaction wheels that can enhance agility of spacecraft is proposed. Three methods are suggested, and all three or part of them can be integrated to the existing attitude control system. First, a feedforward/feedback controller is introduced, and its pros and cons are provided, compared to the conventional feedback controller. Second, an attitude command generation method that fully utilizes torque/momentum capacities of reaction wheels is proposed. Third, a torque (current) control mode for internal wheel control is introduced. Numerical results verify that the settling time can be significantly reduced by employing the feedforward/feedback control method, especially for large angle maneuver.

• Journal of IKEEE
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• v.17 no.1
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• pp.83-88
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• 2013

This paper presents the output feedback control design for feedforward nonlinear systems with input and output delay. The proposed output feedback controller is composed of a linear observer and a linear controller. It is shown that by using Lyapunov-Krasovskii theorem, the proposed controller ensures a global asymptotic stability for arbitrarily large delay. Finally, an illustrative example is given in order to show the effectiveness of our design method.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.5
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• pp.442-449
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• 2003

This paper discusses how to generate the reference compensation voltages in Dynamic Voltage Restorers (DVR) by use of PQR instantaneous power theory. Sensed three-phase terminal voltages are transformed to PQR coordinates without time delay. Since the reference voltage in PQR coordinates is a single dc value, the voltage controller for DVRs is simple and easy to design. Proposed control method can be implemented by feedforward controllers or by feedback controllers. This paper verified the theory by a feedforward controller of a DVR with simulation and experiment.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.4
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• pp.839-848
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• 2012

In this paper, we propose a robust control scheme of AC servo motors to suppress disturbance torques effectively. The proposed controller consists of both a model based feed-forward controller and a stabilizing feedback controller. The feed-forward controller is designed such that the output of the nominal plant tracks perfectly the reference velocity command with desired dynamic characteristics. The feedback controller stabilizes the overall closed loop system. Furthermore, the feedback controller contains a free function that can be chosen arbitrarily. The free function can be designed so as to achieve both suppression of disturbances and robustness to model uncertainties. In order to illuminate the superior performance of the proposed control scheme to the conventional ones, we present some simulation results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.556-560
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• 2007

In this paper, the research results for the improvement of tracking performance of a hydraulic shaking table are presented. A servo-hydraulic shaking table is not only highly nonlinear but also has a lot of time delay. In addition, the shaking table, which consists of multi axial hydraulic actuators, is a MIMO system coupled by kinematics and dynamics of each other's actuators. And it is demanded for the shaking table to track arbitrary trajectories up to high frequency even at the extreme situations such as substantial external loads and large disturbances. For this purpose, an iterative feed-forward control based on the inverse of a measured frequency response function is used for the shaking table. To solve the dynamic coupling, a pressure feedback control as numerical damping is used. It is shown through numerical simulations that the tracking performance of shaking table is improved up to 100Hz.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.41 no.3
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• pp.17-24
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• 2004

We present a P-type iterative learning control(ILC) scheme for uncertain robotic systems that perform the same tasks repetitively. The proposed ILC scheme comprises a linear feedback controller consisting of position error, and a feedforward and feedback teaming controller updated by current velocity error. As the learning iteration proceeds, the joint position and velocity mrs converge uniformly to zero. By adopting the learning gain dependent on the iteration number, we present joint position and velocity error bounds which converge at the arbitrarily tuned rate, and the joint position and velocity errors converge to zero in the iteration domain within the adopted error bounds. In contrast to other existing P-type ILC schemes, the proposed ILC scheme enables analysis and tuning of the convergence rate in the iteration domain by designing properly the learning gain.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.272-274
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• 2005

본 논문은 PWM DC-DC 변환기의 입력 임피던스를 Middlebrook의 EET (Extra Element Theorem)를 사용하여 해석할 수 있는 방법을 제시하고, 이를 이용하여 실제로 전압 제어, 전류 제어 승압형 변환기에 대한 입력 임피던스를 해석하였다. 유도된 수식은 간략화, 근사화를 통하여 보드 선도 (Bode plot)화 하였고, 입력 임피던스 특성 및 전류 루프, 피드백/피드포워드 루프, 전압루프의 영향을 해석하였다. 또한 이론적 해석은 컴퓨터시뮬레이션 결과 및 실제 제작된 PWM DC-DC 변환기의 실험 결과로 비교, 검증하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.162-166
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• 1996

This paper presents a position control of ultra-precision machine tool post using piezoelectric material. A stack-type piezoelectric actuator Is employed in a hinge-type tool holder. An assumed linear transfer function of the practical nonlinear plant is established through the comparison of transfer functions and step responses in the experiments and the simulations. Several types of feedforward/feedback controllers are designed via computer simulations using the assumed linear transfer function. The position tracking control experiments are undertaken to show the control efficiency of each controller.

• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.1815-1816
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• 2006

소음은 환경 오염원의 하나로서 사람에게 육체적, 정신적 피해를 발생시킨다. 이에 소음 제어 기술의 필요성이 증대하였고, 그 중에서 제어가 까다롭고 고비용을 요구하는 저주파 소음 제어 기술의 개발이 확대되고 있다. 따라서 본 연구에서는 저주파의 주기적인 특성을 가지는 1차원 평면파 소음에 대한 능동 제어를 위해 기존의 적응 피드포워드 방법의 단점을 보완하는 적응 피드백 방법을 이용한 능동 소음 제어 시스템을 구성하고 능동 소음 제어 실험을 수행하였다. 이를 위해 소음원과 제어 음원을 가지는 덕트 형상의 실험 장치를 구성하였다. 제어기 설계를 위해 전파 소음을 예측하는 선형 예측법을 적용한 적응 디지털 필터를 구성하였으며 적응 알고리즘으로 Filtered-X LMS 알고리즘을 이용하였다. 제어기는 제어 알고리즘을 프로그램화하여 DSP에 입력함으로써 구성하였다. 실험에 사용된 소음은 500[Hz] 이하의 단일 주파수의 정현파 소음을 사용하였으며, 실험결과 음압 감소의 효과를 볼 수 있었다. 능동 소음 제어의 기술을 개발하여 하드웨어(덕트)의 모양 및 구조, 제어기의 종류 및 처리 속도, 주파수나 크기와 같은 특성이 급격히 변하는 소음의 경우에 능동적으로 소음을 제어할 수 있으며, 저주파 소음을 발생시키는 관형 연소기와 같은 장치 및 여러 분야에 응용이 가능하도록 하였다.