• Journal of Power Electronics
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• 제15권3호
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• pp.753-762
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• 2015

This paper presents a nonlinear sliding mode control (SMC) scheme with a variable damping ratio for interior permanent magnet synchronous motors (IPMSMs). First, a nonlinear sliding surface whose parameters change continuously with time is designed. Actually, the proposed SMC has the ability to reduce the settling time without an overshoot by giving a low damping ratio at the initial time and a high damping ratio as the output reaches the desired setpoint. At the same time, it enables a fast convergence in finite time and eliminates the singularity problem with the upper bound of an uncertain term, which cannot be measured in practice, by using a simple adaptation law. To improve the efficiency of a system in the constant torque region, the control system incorporates the maximum torque per ampere (MTPA) algorithm. The stability of the nonlinear sliding surface is guaranteed by Lyapunov stability theory. Moreover, a simple sliding mode observer is used to estimate the load torque and system uncertainties. The effectiveness of the proposed nonlinear SMC scheme is verified using comparative experimental results of the linear SMC scheme when the speed reference and load torque change under system uncertainties. From these experimental results, the proposed nonlinear SMC method reveals a faster transient response, smaller steady-state speed error, and less sensitivity to system uncertainties than the linear SMC method.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2003년도 추계종합학술대회
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• pp.699-702
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• 2003

현재 대부분의 쇼핑몰들은 관리자의 주관에 따라 상품배열과 제안을 획일적이며 포괄적으로 제시하기 때문에 모든 개인에게 만족을 주지 못한다. 오히려 모두 비슷한 형태로 쇼핑몰이 선택의 기준이 아닌 가격 비교만이 상품 구매에 결정적인 역할을 할 뿐이다. 쇼핑몰에서 고객의 구매성향은 세대별, 성별, 소득별, 직업별, 취미생활 등에 따라 그룹으로 구분해서 볼 때 서로 다르게 나타나며, 개인마다 관심분야와 실제 구매력도 다르다. 또한 경제원리에 따라 환경요인인 유행, 계절과 환경변수인 천재지변 등을 바탕으로 좀 더 빠른 판매전략 수립과 구현은 소비자의 구매력을 극대화 시킬 것이다. 본 논문에서는 고객의 성향을 지속적으로 분석 업데이트 하여 그룹으로 나누고 최적의 상품을 자동으로 구성할 수 있으며 환경변수에 따른 판매자의 전략을 가미한 지능형 쇼핑몰을 설계 및 구현하였다.

• 한국정밀공학회지
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• 제33권11호
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• pp.911-918
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• 2016

A conical roll-shaping process was proposed for fabrication of a metallic spiral blade applied to a small-scale wind turbine system. A spiral blade has continuously different curvatures, with a range of 100 to 350 mm radius. To fabricate this complex shape, we developed a conical roll-shaping process having two main conical rollers for feeding a blank sheet, and two cylindrical side rollers for control of local bending. For clear understanding of the process parameters, numerical analyses were conducted using a commercial code, Pam-Stamp. This study optimized the effects of process parameters, such as gap and angle between the main rollers and side rollers, and also the movement of side rollers. In order to increase the forming efficiency, a central rotation point was also calculated by the analytical approach. This developed rolling process can thus be utilized in a sheet metal forming process for obtaining spirally curved sheet metal shapes.

• 한국광학회지
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• 제10권2호
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• pp.152-156
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• 1999

여기밀도 변화에 따른 펄스폭 연속 가변 Quenched Dye Laser(Q이)를 설계 제작하여 그 동작 특성을 분석하였다. 펌핑광원은 펄스폭 20 ns(FWHM), 에너지 150mJ의 XecCl 엑시머 레이저를 사용하였으며, 색소레이저의 활성매질은 Rhodamine 6G로서 에탄올(ethanol)용액에 2.5$\times$10-3[mol/l]의 농도로 용해되었다. 활성길이 5 nm인 색소셀에서 서로 평행한 양면을 공진기로 구성하여 색소레이저의 이완발진 출력특성을 얻었다. 이완발진의 펄스열에서 단일 펄스를 추출하기 위해 QDL를 구성하였다. QDL의 펄스폭을 가변하기 위해 초점거리 f=150 mm 접속렌즈를 이동시켜 색소셀에 조사되는 공간적 펌핑폭을 조절함으로써 여기밀도를 8.8$\times$1023[cm-3s-1]~2.8$\times$1023[cm-3s-1]까지 가변시켰다. 공간적 펌핑폭에 따른 펄스폭 가변 실험을 수행한 결과 QDL의 발진 펄스폭이 86 ps~201 ps 사이에서 연속적으로 가변됨을 알 수 있었다.

• 정보교육학회논문지
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• 제17권4호
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• pp.393-407
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• 2013

대학 컴퓨터 정보화 분야 특기자 특별전형은 1997학년도부터 수도권 소재 대학을 중심으로 수시모집 기간에 주로 실시되었으나, 전체 선발인원과 선발대학은 지속적으로 감소추세이며, 2013학년도에는 2개 대학 14명을 선발하는 등 우수 특기생 양성 선발과 중등학교의 정보화 관련 교육에 긍정적 영향을 기대하기 어려운 수준이다. 이러한 현상은 중등학교의 정보화 관련 교육활동이 미흡하고, 컴퓨터 정보화 부분에 대한 사회적 인식이 반영된 결과이며, 중등학교의 정보화 관련 교육과정의 운영과 국가적 차원의 관련 인재 육성 정책에 대학입학전형이라는 영향력 높은 주요 변수가 적절하게 고려되지 못하고 있음을 나타낸다. 따라서 향후 관련 정책을 수립함에 있어 대학의 학생선발전형과 방법, 기준 등을 고려한 종합적인 접근이 필요하다.

• 유통과학연구
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• 제14권12호
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• pp.53-59
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• 2016

Purpose - The concept of lifetime job has disappeared, and men are interested in business foundation to work continuously with similar jobs. The value of business foundation is thought to be important in accordance with the viewpoint of society, government, individuals and family. Research design, data, and methodology - The economic exchange between South Korea and China has been expanded, and they are likely to play an important role in entry into China by business foundation in accordance with economic exchange between the two countries. As Korean residents inflow overseas, small businessmen business foundation shall be given attention scientifically and Korean Chinese business foundation shall be given attention as well. Results - The study investigated the effects on psychological characteristics and small business foundation motives upon business foundation will by using models. Self-efficacy and self achievement had positive influence upon small business foundation of Korean Chinese. The use of control variable had explanatory power (29.6%). Conclusions - The findings would help the government's small business foundation system to promote small business foundation and to be a guide for expansion in Korean Chinese's small business markets. An education program should be developed to strengthen Korean Chinese's self efficacy considering psychological characteristics.

• 드라이브 ㆍ 컨트롤
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• 제15권1호
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• pp.38-49
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• 2018

This research describes the development model and testing of a hybrid damper which can be applicable to a vehicle suspension. The hybrid damper is devised to improve the performance of a conventional passive oil damper using a magneto-rheological (MR) accumulator which consists of a gas accumulator and a MR device. The level of damping is continuously variable by the means of control in the applied current in a MR device fitted to a floating piston which separates the gas and the oil chamber. A simple MR device is used to resist the movement of floating piston. At first a mathematical model which describes all flows within the conventional oil damper is formulated, and then a small MR device is also devised and adopted to a mathematical model to characterize the performance of the device.

• Smart Structures and Systems
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• 제5권3호
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• pp.209-221
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• 2009

A control algorithm for seismic protection of building structures based on the theory of variable structural control or sliding mode control is presented. The paper focus in the design of sliding surface. A method for determining the sliding surface by pole assignment algorithm where the poles of the system in the sliding surface are obtained on-line, based on the frequency content of the incoming earthquake signal applied to the structure, is proposed. The proposed algorithm consists of the following steps: (i) On-line FFT process is applied to the incoming part of the signal and its frequency content is recognized. (ii) A transformation of the frequency content to the complex plane is performed and the desired location of poles of the controlled structure on the sliding surface is estimated. (iii) Based on the estimated poles the sliding surface is obtained. (iv) Then, the control force which will drive the response trajectory into the estimated sliding surface and force it to stay there all the subsequent time is obtained using Lyapunov stability theory. The above steps are repeated continuously for the entire duration of the incoming earthquake. The potential applications and the effectiveness of the improved control algorithm are demonstrated by numerical examples. The simulation results indicate that the response of a structure is reduced significantly compared to the response of the uncontrolled structure, while the required control demand is achievable.

• 한국안전학회지
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• 제38권1호
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• pp.87-92
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• 2023

The number of unmanned light rail train operators is continuously increasing in Korea. In a failure event during an operation due to the nature of the unmanned operation, recovery is performed based on the remote control. However, if remote recovery is not feasible, safety personnel arrive at the train to resume the train operation. There are regulations on safety personnel and the suspension time of the train operation. However, there is currently no rule for safety personnel deployment. Currently, railway operating organizations operate in three scenarios: safety personnel on board trains, stationed at stations, and deployed at major stations. Four major factors influence the downtime for each emergency response scenario. However, these four influencing factors vary too much to predict results with simple calculations. In this study, four influencing factors were considered as random variables with high uncertainty. In addition, the Monte Carlo method was applied to each scenario for the safety personnel deployment to predict train service downtime. This study found a 17% difference in train service suspension by safety personnel deployment scenario. The results of this study can be used in setting service goals, such as standards for future safety personnel placement and frequency of service interruptions.

• Steel and Composite Structures
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• 제48권2호
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• pp.191-206
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• 2023

The present research investigates how micromechanical models affect the behavior of Functionally Graded (FG) plates under different boundary conditions. The study employs diverse micromechanical models to assess the effective material properties of a two-phase particle composite featuring a volume fraction of particles that continuously varies throughout the thickness of the plate. Specifically, the research examines the vibrational response of the plate on a Winkler-Pasternak elastic foundation, considering different boundary conditions. To achieve this, the governing differential equations and boundary conditions are derived using Hamilton's principle, which is based on a four-variable shear deformation refined plate theory. Additionally, the Galerkin method is utilized to compute the plate's natural frequencies. The study explores how the plate's natural frequencies are influenced by various micromechanical models, such as Voigt, Reuss, Hashin-Shtrikman bounds, and Tamura, as well as factors such as boundary conditions, elastic foundation parameters, length-to-thickness ratio, and aspect ratio. The research results can provide valuable insights for future analyses of FG plates with different boundaries, utilizing different micromechanical models.