• Communications for Statistical Applications and Methods
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• 제14권1호
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• pp.111-119
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• 2007

In this paper, we develop a nonparametric Bayesian methodology of estimating an unknown distribution function F at the given survival time with current status data under the assumption of Dirichlet process prior on F. We compare our algorithm with the nonparametric maximum likelihood estimator through application to simulated data and real data.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 학술대회 논문집 전문대학교육위원
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• pp.47-52
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• 2001

This paper presents a high-performance control system for Reluctance Synchronous Motor (RSM) drives with direct torque control (DTC). The system consist of stator flux observer, rotor position/speed estimator, torque estimator, two hysteresis band controllers, an optimal switching look-up table, IGBT voltage source inverter, and F240/C31DSP controller by using fully integrated control software. The stator flux observer is based on the combined voltage and current model with stator flux feedback adaptive control that inputs are current and voltage sensing of motor terminal with estimated rotor angle for wide speed range. The rotor position is estimated by the observed stator flux-linkage space vector. The estimated rotor speed can be determinated by differentiation of the rotor position used only in the current model part of the flux observer for a low speed operating area. To prove the suggested control algorithm, we have a simulation and testing at actual experimental system. The developed digitally high-performance position sensorless control system are shown a good motion control response characteristic results and high performance features using 1.0Kw RSM.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.161-164
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• 2001

This paper presents a digital speed sensorless control system for Reluctance Synchronous Motor (RSM) drives with direct torque control (DTC). The system consist of stator flux observer, rotor speed estimator, torque estimator two hysteresis band controllers, an optimal switching look-up table. IGBT voltage source inverter, and TMS320C31DSP controller by using fully integrated control software. The stator flux observer is based on the combined voltage and current model with stator flux feedback adaptive control that inputs are current and voltage sensing of motor terminal with estimated rotor angle for wide speed range. The rotor speed is estimated by the observed stator flux-linkage space vector. The estimated rotor speed can be determinated by differentiation of the rotor position used only in the current model part of the flux observer for a low speed operating area. In order to prove the suggested speed sensorless control algorithm. There are some simulation and testing at actual experimental system. The developed digitally high- performance speed sensorless control system are shown a good speed control response characteristic results and high Performance features using 1.0Kw RSM.

• The Journal of Asian Finance, Economics and Business
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• 제8권9호
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• pp.287-300
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• 2021

The study is conducted to find out the impact of the country- and corporate-level governance and firm internationalization on stock liquidity of 120 listed firms in Japan, Hong Kong, Pakistan, and India. Panel data is used in the current study. The annual time span covered in the current study is 10 years. The current study explores results based on secondary data. The findings of the 'robust panel corrected standard error' estimator shows that the internationalization strategy of firms positively influences the stock liquidity. The internationalization strategy of multinational corporations proves to be an effective methodology for improving stock liquidity in the home market as well as abroad. The study also shows that a stronger relationship exists between stock liquidity and internationalization in those countries where the regulatory settings are effective, the judiciary system is efficient and shareholders' rights are protected. Corporate governance and stock liquidity are negatively associated. The study also finds a negative relationship between country-level governance mechanisms and stock liquidity. Whereas the 'robust panel corrected error' estimator shows a positive association between corporate governance mechanisms and firm internationalization. The study depicts that effective corporate governance motivates multinational companies to expand their business abroad.

• 전자공학회논문지SC
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• 제46권1호
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• pp.55-62
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• 2009

본 논문에서 증폭 후 전달 전송 기법을 사용하는 중계망의 채널 추정을 하는데 있어서 일어나는 문제점을 해결할 수 있는 방법으로 학습 계열(training sequence)을 이용하는 방법을 제안하였다. 현재의 고속 페이딩 채널 환경에서 기존 파일럿의 추정이 적절하지 않아 송신국(source)과 중계국(relay) 사이의 채널과 중계국(relay)과 수신국(destination) 사이의 채널을 결합하여 추정할 경우 많은 문제점이 초래되기에$^{[1{\sim}2]}$ 전송한 신호의 주파수 영역을 선택하여 얻은 정규(Gaussian) 분포에 대하여 최대 우도 함수의 평균을 내어 채널 추정량(estimator)을 유도해 낼 수 있는, 즉, 파일럿 대신에 하나의 OFDM 신호를 사용하여 모든 채널 충격 응답(CIR)을 추정할 수 있는 새로운 방법을 살펴보았다. 컴퓨터 모의실험으로 높은 SNR 영역에서 제안한 채널 추정기(estimator)의 성능이 [1]과 비교하여 약 1dB 정도 높음을 확인할 수 있었다.

• 제어로봇시스템학회논문지
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• 제13권6호
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• pp.589-595
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• 2007

This paper presents a new method on controller design of brushless dc motors. In such drives the current ripples are generated by motor inductance in stator windings and the back EMF. To suppress the current ripples the current controller is generally used. To minimize the size and the cost of the drives it is desirable to control motors without the current controller and the current sensing circuits. To estimate the motor CUlTent it is modeled by a neural network that is contigured as an output-error dynamic system. The identified model is essentially a one step ahead prediction structure in which past inputs and outputs are used to calculate the current output. Using the model, a state feedback controller to compensate the effects of disturbance has been designed. The controller is implemented by a 16-bit microprocessor and the effectiveness of the proposed control method is verified through experiments.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.260-265
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• 1999

This paper describes a novel control method of a three-phase PWM inverter for uninterruptible power supply(UPS) applications. To obtain the fast dynamics and excellent harmonic characteristics, a new state feedback control technique is proposed. The proposed control consists of the inner-loop current and outer-loop voltage controllers with a load current estimator to reduce the effects of the load variations and nonlinearity. In order to verify the effectiveness of the proposed control, the simulation is carried out for various load condition.

• 전력전자학회논문지
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• 제4권4호
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• pp.357-367
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• 1999

매입형 영구자석 동기전동기와 인버터, 그리고 추진제어기로 구성된 추진시스템을 갖는 독립 구동형 전기자동차에 대하여 파라미터 변동특성을 반영하는 전동기 제어기법과 주행특성을 개선한 새로운 추진제어기 기법을 제시하였다. 기존의 방식과는 다르게 전동기의 등가파라미터인{{{{ { L}_{d } }} 와{{{{ { L}_{q } }} 의 변동을 전류의 크기뿐만 아니라 전류 위상각의 관점에서 고려하였으며, 해석적인 방법으로 전 영역에 대한 변동 곡선을 제시하였다. 그리고{{{{ { L}_{d } }}와 {{{{ { L}_{q } }}에 대한 변동을 신경회로망을 이용하여 추정기를 구성한 후 신경회로망 추정기를 갖는 매입형 영구자석 동기 전동기용 벡터제어 기법을 제시하였다. 또한, 추진제어기는 토크분배 기능과 토크약화제어 기능을 구비하도록 만들어졌으며, 선회 조종성과 슬립율이 안정 영역 내에서 운전 되도록 개선된 추진 제어기를 제시하였다. 제안된 제어기의 동특성을 실험과 모의 실험을 통하여 검증하였다.

• 대한전자공학회논문지SP
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• 제49권2호
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• pp.69-75
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• 2012

본 논문은 MAP (maximum a posterior) 예측기에 기반하여 움직임 보상 예측 오차를 보정해주는 방식의 순차주사화 (de-interlacing) 알고리즘을 제안한다. 먼저, 현재 필드와 인접한 필드 간의 적절한 정합 (registration)을 수행 한 후, 계산된 정합 정보에 기반한 MAP 예측기를 통해 현재 필드에 대응하는 순차 주사 (progressive) 프레임을 찾아낸다. 안정적인 결과를 얻기 위하여 잘 알려진 BTV (bilateral total variation) 기반의 평활화 (regularization) 과정이 추가된다. 한편, 잘못된 정합 정보로 인한 소위 깃털 현상 (feathering artifact)을 억제하기 위하여 블록 단위로 깃털 현상 발생 여부를 판단하여 발생되었다고 판단된 블록 영역에 대해서는 앞서 설명한 MAP기반 순차주사화 대신 에지 방향성에 기반한 공간적 순차주사화를 적용한다. 실험 결과에 따르면, 제안된 기법은 종래 기법들에 비하여 평균 약 4dB의 PSNR 성능 개선을 보이고 있으며, 우수한 주관적 화질을 보여주고 있다.

• Journal of Advanced Marine Engineering and Technology
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• 제27권7호
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• pp.930-936
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• 2003

A new method of direct current motor drive, which requires neither shaft encoder nor speed estimator, is presented. The proposed scheme is based on decreasing current gap between a numerical model and an actual motor. By supplying the identical instantaneous voltage to both model and motor in the direction of reducing the current difference, the rotor approaches to the model speed, that is, reference value. The performance of direct current motor drives without speed sensor is generally poor at very low speed. However, in this system, it is possible to obtain good speed performance in the low speed range.