• 대한기계학회논문집
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• 제11권6호
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• pp.923-934
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• 1987

본 연구에서는 유연한 로봇 조각기를 허브가 있는 첨단질량이 부착된 유연한 외팔보로 모델링하고 Hamilton의 원리에 의하여 유도된 운동방정식을 Galerkin의 모우 드 합 방접을 이용하여 유한차원화하여 상태방정식으로 표시하였다. 계를 제어 모우 드부(controlled mode part)와 잔류 모우드부(residual mode part)로 나누어 제어 모 우드부에 대해 최적제어 이론을 도입하여 귀환계수(feedback ccefficient)를 구하였으 며 측정이 불가능한 상태변수(inaccessible state)를 근사적으로 추정하기 위하여 Lu- enberger 관측기가 사용되었다.2차 성능계수(quadratic performance index)내의 입 력에 대한 가중치의 변화에 따른 제어효과 및 계의 여러 모우드중 중요 모우드만 제어 하는 제어기를 사용함에 따른 Spillover 효과가 계의 제어효과에 미치는 영향을 시뮬 레이션을 통하여 고찰하였으며, 또한 실험을 통하여 이론의 타당성을 검토하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.986-988
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• 2001

This paper presents a digitally speed sensorless control system for induction motor with direct torque control (DTC). Some drawbacks of the classical DTC are the relatively large torque ripple in a low speed range and notable current pulsation during steady state. They are reflected speed response and increased acoustical noise. In this paper, the DTC quick response are preserved at transient state, while better qualify steady state performance is produced by space vector modulation (SVM). The system are closed loop stator flux and torque observer for wide speed range that inputs are currents and voltages sensing of motor terminal, model reference adaptive control (MRAC) with rotor flux linkages for the speed fuming signal at low speed range, two hysteresis controllers and optimal switching look-up table. Simulation results of the suggest system for the 2.2 [kW] general purposed induction motor are presented and discussed.

• Journal of Power Electronics
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• 제16권2호
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• pp.598-609
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• 2016

The good control performance of permanent magnet linear synchronous motor (LSM) drive systems is difficult to achieve using linear controllers because of uncertainty effects, such as fictitious forces. A backstepping control system using adaptive modified recurrent Laguerre orthogonal polynomial neural network uncertainty observer (OPNNUO) is proposed to increase the robustness of LSM drive systems. First, a field-oriented mechanism is applied to formulate a dynamic equation for an LSM drive system. Second, a backstepping approach is proposed to control the motion of the LSM drive system. With the proposed backstepping control system, the mover position of the LSM drive achieves good transient control performance and robustness. As the LSM drive system is prone to nonlinear and time-varying uncertainties, an adaptive modified recurrent Laguerre OPNNUO is proposed to estimate lumped uncertainties and thereby enhance the robustness of the LSM drive system. The on-line parameter training methodology of the modified recurrent Laguerre OPNN is based on the Lyapunov stability theorem. Furthermore, two optimal learning rates of the modified recurrent Laguerre OPNN are derived to accelerate parameter convergence. Finally, the effectiveness of the proposed control system is verified by experimental results.

• Archives of Plastic Surgery
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• 제40권5호
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• pp.570-574
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• 2013

Background The elliptical excision is the standard method of removing benign skin lesions, such as congenital melanocytic nevi. This technique allows for primary closure, with little to no dog-ear deformity, but may sacrifice normal tissue adjacent to the lesion, resulting in scars which are unnecessarily long. This study was designed to compare the predicted results of elliptical excision with those resulting from our excision technique. Methods Eighty-two patients with congenital melanocytic nevus on the face were prospectively studied. Each lesion was examined and an optimal ellipse was designed and marked on the skin. After an incision on one side of the nevus margin, subcutaneous undermining was performed in the appropriate direction. The skin flap was pulled up and approximated along several vectors to minimize the occurrence of dog-ear deformity. Results Overall, the final wound length was 21.1% shorter than that achieved by elliptical excision. Only 8.5% of the patients required dog-ear repair. There was no significant distortion of critical facial structures. All of the scars were deemed aesthetically acceptable based on their Patient and Observer Scar Assessment Scale scores. Conclusions When compared to elliptical excision, our technique appears to minimize dogear deformity and decrease the final wound length. This technique should be considered an alternative method for excision of facial nevi.

• Journal of Electrical Engineering and Technology
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• 제7권3호
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• pp.443-450
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• 2012

As power grids are integrated into one big umbrella (i.e., Smart Grid), communication network plays a key role in reliable and stable operation of power grids. For successful operation of smart grid, interoperability and security issues must be resolved. Security means providing network system integrity, authentication, and confidentiality service. For a cyber-attack to a power grid system, which may jeopardize the national security, vulnerability of communication infrastructure has a serious impact on the power grid network. While security aspects of power grid network have been studied much, security mechanisms are rarely adopted in power gird communication network. For security issues, strict timing requirements are defined in IEC 61850 for mission critical messages (i.e., GOOSE). In this paper, we apply security algorithms (i.e., MD-5, SHA-1, and RSA) and measure their processing time and transmission delay of secured mission critical messages. The results show the algorithms satisfying the timing requirements defined in IEC 61850 and we observer the algorithm that is optimal for secure communication of mission critical messages. Numerical analysis shows that SHA-1 is preferable for secure GOOSE message sending.

• 대한전기학회논문지:전력기술부문A
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• 제50권1호
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• pp.13-19
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• 2001

This paper deals with decentralized control scheme and its application to multi-machine power systems. Decentralized control scheme has several practical advantages, because power system has geographically distributed characteristics. In this paper, decentralized observer-based optimal Power System Stabilizer(PSS) and Thyristor-Controlled Series Capacitor(TCST) controller are designed and tested in WSCC 9 bus system with one TCSC installed. Simulation results show that the proposed decentralized controller has satisfactory performances comparable to the centralized controller. In addition, using modal analysis, this paper shows that the proposed decentralized controller significantly affects only one pair of eigenvalues which have high participation with each generator, while slightly affects other eigenvalues. This result indicates that the application of the decentralized control scheme to enhance power system dynamic stability via excitation control have potential advantages because each low-damped mode occurs dominantly by each decentralized subsystem.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 학술대회 논문집 전문대학교육위원
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• pp.135-141
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• 2002

This paper presents an implementation of high-dynamic performance of position sensorless motion control system of Reluctance Synchronous Motor(RSM) drives for an industrial servo system with direct torque control(DTC), The problems of DTC for high-dynamic performance and maximum efficiency RSM drive due to a saturated stator linkage flux and nonlinear inductance curve with various load currents, The accurate estimation of the stator flux and torque are obtained using stator flux observer of which a saturated inductance Ld and Lq can be compensated by adapting from measurable the modulus and angle of the stator current space vector. To obtain fast torque response and maximum torque/current with varying load current, the reference command flux is ensured by imposing Ids=Iqs. This control strategy is proposed to fast response and optimal efficiency for RSM drive. In order to prove rightness of the suggested control algorithm, the actual experiment carried out at ${\pm}$20 and ${\pm}$1500 rpm. The developed digitally high-performance control system are shown some good response characteristic of control results and high performance features using 1.0kW RSM of which has 2.57 Ld/Lq salient ratio.

• 전기학회논문지
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• 제67권6호
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• pp.782-788
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• 2018

This paper proposes a novel method for the omnidirectional camera-based image rendering synchronization system using head mounted display. There are two main processes in the proposed system. The first one is rendering 360-degree images which are remotely photographed to head mounted display. This method is based on transmission control protocol/internet protocol(TCP/IP), and the sequential images are rapidly captured and transmitted to the server using TCP/IP protocol with the byte array data format. Then, the server collects the byte array data, and make them into images. Finally, the observer can see them while wearing head mounted display. The second process is displaying the specific region by detecting the user's head rotation. After extracting the user's head Euler angles from head mounted display's inertial measurement units sensor, the proposed system display the region based on these angles. In the experimental results, rendering the original image at the same resolution in a given network environment causes loss of frame rate, and rendering at the same frame rate results in loss of resolution. Therefore, it is necessary to select optimal parameters considering environmental requirements.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1126-1131
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• 2001

Excessive vibration in rotating machinery is a problem encountered in many different fields, causing such difficulties as fatigue of machinery components and failure of supporting bearings. Passive techniques, though sometimes limited in their capabilities, have been used in the past to attenuated vibrations. Recently active techniques have been developed to provide vibration control perform beyond that provided by their passive counters. Most often, the focus of active control methods has been to suppress rotating machinery displacements. In cases where vibration results in bearing failures, displacement suppression may not be the best choice of control approaches (it can, in fact, increase dynamic bearing loads which would be even more harmful to bearings). This paper presents two optimal control methods for attenuating steady state vibrations in rotating machinery. One method minimizes shaft displacements while the other minimizes dynamic bearing reaction forces. The two methods are applied to a model of a typical rotating machinery system and their results are compared. It is found that displacement minimization can increase bearing loads, while bearing load minimization, on the other hand, decreases bearing loads.

• 한국방사선학회논문지
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• 제15권7호
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• pp.999-1005
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• 2021

본 연구에서는 검사시간을 단축시키면서 해상도를 증가시키는 Compressed SENSE를 TOF에 적용하여 SENSE와 CS 기법에 대한 영상의 질을 비교하고 SNR, CNR을 평가하여 최적의 기법을 알아보고 이러한 정보를 토대로 임상적 기초자료로 제공하고자 한다. 충청도 소재 한 대학병원에서 TOF MRA 검사를 시행한 환자 32명(남자 15명, 여자 17명, ICA stenosis:10, M1 aneurysm:10, 평균나이 53 ± 4.15)을 대상으로 데이터를 분석하였다. 검사에 적용된 장비는 Ingenia CX 3.0T, Archieva 3.0 T 두 기기를 이용하였고 데이터 획득을 위한 방법으로 32 Channel Head Coil과 3D Gradient echo 이었다. 정량적 분석으로 각 영상의 SNR과 CNR을 측정하고 정성적 평가를 위해 관찰자의 시각적 견해에 대하여 5등급으로 나누어 영상의 질을 평가하였다. 영상평가는 paired t-test와 Wilcoxon 검정을 하였으며 p 값이 0.05 이하 일 때 유의성이 있는 것으로 간주하였다. TOF MRA 영상에서 SNR과 CNR에 대한 정량적 분석 결과 SENSE 기법에 비해 CS 기법이 높게 측정되었다(p<0.05). 관찰자의 시각적 평가로서 혈관의 선예도: CS(4.45 ± 0.41), 전반적인 영상의질: CS(4.77 ± 0.18), 영상의 배경소거: CS(4.57 ± 0.18)는 모두 CS 기법이 높은 결과를 얻었다(p=0.000). 결론적으로, 유속증가 자기공명혈관 조영술에서 SENSE 와 Compressed SENSE 기법을 비교하여 평가했을 때 Compressed SENSE TOF MRA 기법이 우위의 결과를 보여주었다. 이러한 결과는 뇌 질환 3D TOF MRA 검사에서 향후 임상적 기초자료가 될 것이라고 생각한다.