Heung-Kwan Choi

Voltage Shift Acceleration Control for Anti-Islanding of Distributed Generation Inverters

This paper proposes voltage-shift acceleration control for islanding detection of distributed-generation (DG) inverters. The proposed method is conceptually based on a traditional dq -based voltage positive feedback control. A main improvement of the proposed control is that the anti-islanding performance and its impact on inverter output control can be consistent regardless of inverter operation points. An analytical approach based on a small-signal model of an inverter controller is used to prove the proposed control. Also, an analytical design method is proposed to obtain proper control gain that satisfies two conflicting issues: successful anti-islanding and limited impact on inverter control. Simulation and experimental tests were conducted to validate the proposed detection algorithm and its design method. In addition, simulation results on a two DGs system are shown to investigate the performance in multiple DGs operation.

Establishment of a pilot plant for KERI microgrid system based on power IT development program in Korea

This paper introduces a microgrid system having been developed in Korea. Firstly, the Korean Power IT (Information Technology)” development program and its environment are shortly described including the concept of Korean microgrid and characteristics of its components. And then, the microgrid system, the functions of its components and test facilities are explained which are established in KERI (Korea Electrotechnology Research Institute). Finally, some system operation results according to two operational modes are shown.

Controller-Hardware-In-The Loop Simulation Based Analysis of Photovoltaic Power Generation System under Variable Conditions of Utility

This paper presents a controller-hardware-in-the loop simulation (CHILS) based test system as a controller for testing phtovotaic (PV) power generation system. The analysis of grid-connected PV power generation system to observe the phenomenon and confirm the stability on the PV power generation system under the variable conditions occured in utility was performed. The utility is stable in the steady state but the utility condition can be changed by unexpected phenomenon. The effect of grid condition should be analyzed to make sure the stability of the grid-connected PV power generation system. The PV power generation system is connected to a utility grid through a inverter and several conditions of grid are modeled by using RTDS. A RTDS is employed to calculate the variable conditions of grid. The voltage source inverter (VSI) is controlled by a digital signal processor connected between gigabit transceiver analogue output card and a gigabit transceiver digital input card in the RTDS interface boards. Experiment results are presented and analyzed to show the effect of a variable conditions to the PV system.

Soft x-ray generation using CNT based liquid hybrid target

Summary form only given. In order to image soft biological tissues that are consisted of living animal or plants, water window (2.1-4.4 nm) region of soft X-ray is generally required. However, conventional X-ray source that is based on tungsten filament tube generally produces hard X-ray. In order to solve this problem, laser based soft X-ray sources have been studied recently. In this technique solid metal or liquid-jet target has been generally applied. However, debris problem was issued for the former and small intensity of the generated soft X-ray was the problem for the latter. In this research, liquid target, which is added with carbon nanotubes (CNTs) or other metal nanopowders, was proposed as new targets for laser based soft X-ray generation. Detailed descriptions of the experimental method and results were presented in this study

Generation of x-ray images using a CNT-based cathode as an field emission electron source

Summary form only given. Conventional X-ray source reveals several problems such as short lifetime, immovability with bulky size, and relatively low resolution. For solving these problems, laser based X-ray sources have been applied but they were insufficient for X-ray source because of its low conversion efficiency. Recently, O. Zhou et al., has developed a new X-ray emission method by using field emission of carbon nanotubes. Carbon nanotubes (i.e., CNTs) are tubular carbon molecules with properties that make them potentially useful in extremely small scale electronic and mechanical applications. In the present study, CNTs were applied for an X-ray emitter. CNTs were grown by thermal CVD method and the length of the grown CNTs was about 30~50 mm. The electrical properties of the grown CNT emitter were tested in a vacuum chamber. Electron beam focusing characteristics were also investigated by using Opera 3D code and the positions of individual electrodes in the mode were optimized for the best X-ray generation. Typical X-ray images were obtained and the detailed descriptions of the manufactured X-ray mode were discussed

Optimal Design of Resistive Type HTS-FCL Using Monte Carlo Method

Abstract Nowadays, one of the serious problems in KEPCO system is much higher fault current than the SCC(Short Circuit Capacity) of circuit breaker. As the superconductivity technology has developed, the HTS-FCL(High Temperature Superconductor-Fault Current Limiter) can be one of the attractive alternatives to solve the fault current problem. But the parameters of HTS-FCL should be designed optimally to have the best performance. Under this background, this paper presents the optimal design method of parameters for resistive type HTS-FCL using Monte Carlo technique.

Application Effects of SFCL in Korean Power System

Abstract As power systems grow more complex and power demands increase, the fault current tends to gradually increase. In the near future, the fault current will exceed a circuit breaker rating for some substations, which is an especially important issue in the Seoul. metropolitan area In this paper, the resistive and inductive SFCLs are applied to reduce the fault current in Korean power system and their technical and economic impacts are evaluated