Dongho Lee

The three level voltage source inverter (VSI) is a good topology for high voltage and high power applications where no semiconductor devices are available. However, it has an inherent problem of midpoint charge balance. The problem becomes critical when the load is nonlinear and/or has large phase angle and harmonics. If it exceeds the critical points, there is no way to control the midpoint voltage by itself. The midpoint balancing problem is analyzed with respect to the reactive loads with har

A tournament-shaped magnetically coupled power-combiner architecture for a fully integrated RF CMOS power amplifier is proposed. Various 1 : 1 transmission line transformers are used to design the power combiner. To demonstrate the new architecture, a 1.81-GHz CMOS power amplifier using the tournament-shaped power combiner was implemented with a 0.18-mum RF CMOS process. All of the matching components, including the input and output transformer, were fully integrated. The amplifier achieved a dr

Abstract In this paper, we study the Multi-Start Team Orienteering Problem (MSTOP), a mission re-planning problem where vehicles are initially located away from the depot and have different amounts of fuel. We consider/assume the goal of multiple vehicles is to travel to maximize the sum of collected profits under resource (e.g., time, fuel) consumption constraints. Such re-planning problems occur in a wide range of intelligent UAS applications where changes in the mission environment force the

A series of wind tunnel tests were conducted for Korean high-speed train model with various shape components to assess the contributions to aerodynamic drag. In order to elucidate the ground effects, two different wind tunnels, one with a moving ground system and the other with a fixed ground, were used for the same model and the results of both were compared and analyzed in detail. The results show that a suitable ground simulation is necessary for the test of a train model with many cars and d

A 1.8 GHz power amplifier for a polar transmitter application is implemented with 0.18 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m RF CMOS technology, and a differential line inductor is proposed for the differential circuit. The differential line inductor is used as a low power matching network in the stage-convertible power amplifier in order to increase the efficiency of a low output power region. The power amplifier achieved a power-ad

An on-chip implementation of a low loss 1:9 transmission line transformer (TLT) is presented. The TLT was fabricated with broadside coupled microstrip lines in a GaAs HBT process. The wide metal transmission lines allow the high-quality factor and the high-current capability. The measured insertion loss is 0.88 dB at 880 MHz. The equivalent circuit model of the TLT is also presented. The model shows good agreement with the measured data. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett

Existing techniques for soft-switching DC-DC converters are for either zero-voltage-turn-on or zero-current-turn-off with the exception of several specialized cases. A new type of soft-switching converter is proposed which has both zero-voltage-turn-on and zero-current-turn-off functions. Its implementation requires even fewer auxiliary circuit components and almost no intentional circulating energy. An experimental converter is built to verify the concept.

A monolithic quadrature signal generator is presented, using PLL technique for automatic calibration. The quadrature signal generator consists of a quadrature signal generation block and a phase control loop to calibrate quadrature signals in real-time. The phase of a phase shifter is tuned by a control current from the phase control loop. The phase error of quadrature signals is detected by two phase detectors. A charge pump generates a feedback voltage to control the phase of the phase shifter

Flow field near the turbine blade platform is very complex due to the secondary flow motions such as horseshoe vortices, passage vortices and endwall cross flows. It is therefore extremely difficult to predict the platform heat transfer distribution. As the secondary flows are largely affected by platform profile/shape, a number of investigators have studied different platform profiles to minimize aerodynamic loss and heat load. Understanding of the platform heat transfer has become especially c

Gravity ventilators rely simply on air buoyancy to extract air and are widely used to exhaust air contaminants and heat from workplaces using minimal energy. They are designed to maximize the exhaust flow rate, but the rain penetration sometimes causes malfunctioning. In this study, the characteristics of rain penetration through a ventilator were examined as a preliminary study to develop a ventilator with the maximum exhaust capacity while minimizing rain penetration. A model ventilator was bu

본 연구는 복잡한 다수 무인기 시스템을 효율적으로 운용하기 위해 이산 사건 모델 기반의 다수 무인기 이종 임무 할당 기법을 제안한다. 이종 임무의 생성, 임무 할당, 무인기 출동, 임무 수행, 무인기 수리 및 정비에 이르는 무인기의 임무 시작에서 종료까지 일련의 과정을 이산 사건 모델링을 통해 수학적으로 정의하고, 이를 기반으로 주어진 임무 상황에서 필요한 최적 무인기 대수를 도출한다. 도출된 최적 무인기 대수를 적용하여 이산 사건 모델 기반의 반복 시뮬레이션을 통해 그 결과를 검증한다. 제안된 이종 임무 할당 기법으로 운용자는 제한된 무인기 자원을 효율적으로 활용하여 주어진 임무 상황에서 최적의 임무 계획을 수립할 수 있다.

소프트웨어 프로젝트 데이터를 이용한 각종 분석·예측 모델 생성시 직면하는 문제 중 하나는 데이터에 포함된 결측값이며 이에 대한 효과적인 방안은 결측값 대치법이다. 대표적인 결측값 대치법인 K 최근접 이웃 대치법은 대치과정에서 결측값을 포함하는 인스턴스의 관측정보를 활용하지 못한다는 단점이 있다. 본 연구에서는 이러한 단점을 극복하기 위해 K 최근접 이웃 대치법과 최대 우도 추정법을 결합한 새로운 소프트웨어 프로젝트 수치 데이터용 결측값 대치법을 제안한다. 또한 결측값 대치법의 정확도를 비교하기 위한 새로운 측도를 함께 제안한다.

We study noncooperative games, in which each player's objective is composed of a sequence of ordered—and potentially conflicting—preferences. Problems of this type naturally model a wide variety of scenarios: for example, drivers at a busy intersection must balance the desire to make forward progress with the risk of collision. Mathematically, these problems possess a nested structure, and to behave properly players must prioritize their most important preference, and only consider less importan