• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.156-157
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• 2003

A simple method is proposed to split the flux vector of the Euler equations by introducing two artificial wave speeds. The direction of wave propagation can be adjusted by these two wave speeds. This idea greatly simplifies the upwinding, and leads to a new family of upwind schemes. Numerical flux function for multi-dimensional Euler equations is formulated for any grid system, structured or unstructured. A remarkable simplicity of the scheme is that it successfully achieves one-sided approximation for all waves without recourse to any matrix operation. Moreover, its accuracy is comparable with the exact Riemann solver. For 1-D Euler equations, the scheme actually surpasses the exact solver in avoiding expansion shocks without any additional entropy fix. The scheme can exactly resolve stationary contact discontinuities, and it is also freed of the carbuncle problem in multi­dimensional computations.

• Journal of Power Electronics
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• 제13권4호
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• pp.609-618
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• 2013

This paper proposes a primary side constant power control scheme for TRIAC dimmer compatible LED drivers. The LED driver is a Flyback converter operated in boundary conduction mode (BCM) to minimize the switching loss. With the proposed control scheme, the input power of the Flyback converter can be controlled by the TRIAC dimming angle, which is not affected by AC input voltage variations. Since the output voltage is almost constant for LED loads, the output current can be changed by controlling the input power with a given conversion efficiency. The isolated feedback circuit is eliminated with the proposed primary side control scheme, which dramatically simplifies the whole circuit. In addition, the input current automatically follows the input voltage due to the BCM operation, and the resistive input characteristic can be achieved which is attractive for TRIAC dimming applications. Experimental results from a 15W prototype verify the theoretical analysis.

• 한국산업정보학회:학술대회논문집
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• 한국산업정보학회 2001년도 춘계학술대회논문집:21세기 신지식정보의 창출
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• pp.318-324
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• 2001

In this paper we propose the adaptive scheme to place more search points as long as the operation tapability of the motion estimator in the video codec permits. And the proposed algorithm takes advantage of the intuitive fact that the quality of the decoded video is more degraded as the spatial frequency of the corresponding block is increased due to the augmentation of local minima per unit area. Thererore, we propose the scheme to enhance the quality by locating relatively more search points in the block with high frequency components by analyzing the spatial frequencies of the video sequence. As a result, the proposed scheme can adaptively place more search points possibly permitted by the motion estimator and guarantees better quality compared to the TSS and FS.

• Journal of Power Electronics
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• 제16권6호
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• pp.2067-2075
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• 2016

Cascaded H-bridge multilevel inverters are currently used because it enables the integration of various sources, such as batteries, ultracapacitors, photovoltaic array and fuel cells in a single system. Conventional modulation schemes for multilevel inverters have concentrated mainly on the generation of a low harmonic output voltage, which results in less effective utilization of connected sources. Less effective utilization leads to a difference in the charging/discharging of sources, causing unsteady voltages over a long period of operation and a reduction in the lifetime of the sources. Hence, a charge balance control scheme has to be incorporated along with the modulation scheme to overcome these issues. In this paper, a new approach for charge balancing in symmetric cascaded H-bridge multilevel inverter that enables almost 100% charge balancing of sources is presented. The proposed method achieves charge balancing without any additional stages or complex circuit or considerable computational requirement. The validity of the proposed method is verified through simulation and experiments.

• 한국통신학회논문지
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• 제21권9호
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• pp.2402-2414
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• 1996

Registration is the process by which a base station gets the information of location and status about mobile stations. Registration will become an increasingly important issue in mobile cellular communications, especially in microcellular system with the increase of location updating traffic. Four typesof registration schemes, which are specified in US standard IS-95 and Korean standard TTA-KO-0062, power up registration scheme, power down registration scheme, distance based registration scheme and zone based registration scheme, will be mainly used in the future. In this paper, we derive the combined cost of signaling traffic of paging and registration for various parameters of mobile stations behavior(unencumbered call duration, power up and down rate, velocity, etc.) then we present numerical results for the perfroamnce of four registration schemes. The size of location area is provided for optimal operation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1998년도 제13차 학술회의논문집
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• pp.513-518
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• 1998

In this paper, a robust fault-tolerant control scheme for robot manipulators overcoming actuator failures is presented. The joint(or actuator) fault considered in this paper is the free-swinging joint failure and causes the loss of torque on a joint. The presented fault-tolerant control framework includes a normal control with normal(non-failed) operation, a fault detection and a fault-tolerant control to achieve task completion. For both no uncertainty case and uncertainty case, a stable normal con-troller and an on-line fault detection scheme are presented. After the detection and identification of joint failures, the robot manipulator becomes the underactuated robot system with failed actuators. A robust adaptive control scheme of robot manipulators with the detected failed-actuators using the brakes equipped at the failed(passive) joints is proposed in the presence of parametric uncertainty and external disturbances. To illustrate the feasibility and validity of the proposed fault-tolerant control scheme, simulation results for a three-link planar robot arm with a failed joint are presented.

• 조명전기설비학회논문지
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• 제15권1호
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• pp.112-117
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• 2001

본 논문은 전력설비 피해 감소를 위한 배전시스템의 지능형 재폐로방식을 제안하였다. 재폐로 시도횟수를 늘릴수록 공급신뢰도는 향상될 수 있지만, 전력설비에는 사고전류에 의한 충격이 누적된다. 제안된 방식은 사고전류의 크기에 따라 재폐로 시도횟수와 무전압시간을 결정하여 배전시스템 공급신뢰도를 유지하면서 전력설비의 피해를 감소시킬 수 있다. 사례연구에서는 현장 운전 데이터를 사용하여 제안된 지능형 재폐로방식에 대한 효율성을 입증하였다.

• Journal of Power Electronics
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• 제14권3호
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• pp.598-607
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• 2014

This paper proposes a frequency-locked loop (FLL) scheme for a single-phase grid-connected converter. A second-order generalized integrator (SOGI) based on fuzzy logic (FL) is applied to this converter to achieve precise phase angle detection. The use of this method enables the compensation of the nonlinear characteristic of the frequency error, which is defined in the SOGI scheme as the variation of the central frequency through the self-tuning gain. With the proposed scheme, the performance of the SOGI-FLL is further improved at the grid disturbances, which results in the stable operation of the grid converter under grid voltage sags or frequency variation. The PSIM simulation and experimental results are shown to verify the effectiveness of the proposed method.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.454-458
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• 2008

This article describes an interference reduction scheme for Mobile WiMAX in an indoor environment. The feasibility of user deployed femtocells in the same frequency channel as an existing macro cell network is investigated. One of the important requirements for co-channel operation of femtocells such as auto-configuration and self optimization are discussed. In femtocell deployments, leakage of the pilot signal to the outside of a house can result of the higher number of mobility events caused by passing user of macrocell. This interference effect can be minimized by reducing the pilot power using proper scheme. This paper introduces existing auto-configuration method of power control and proposed interference reduction scheme using power control for Mobile WiMAX in an indoor environment.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2015년도 전력전자학술대회 논문집
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• pp.189-190
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• 2015

This paper investigates an economic and highly efficient power converter topology and its modulation scheme for 60kW rapid EV charger system. The target system consists of three-phase three-switch buck-type rectifier topology. A new Carrier Based PWM scheme along with its simple implementation using logic gates is introduced in this paper. This PWM scheme replaces the diode rectifier equivalent switching state with an active switching state producing the effectively same current flowing path. As a result, the distortion of input current during the polarity reversal of capacitor line voltage can be mitigated. The proposed modulation technique is confirmed through simulation verification. The proposed modulation technique and its implementation scheme can expand the operation range of the three-phase three-switch buck-type rectifier having ac input and capacitor ripple current of high quality.