• Journal of Power Electronics
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• v.16 no.4
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• pp.1526-1540
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• 2016

This work mainly discusses an accurate and fast islanding detection based on fractional wavelet packet transform (FRWPT)for multibus microgrid systems. The proposed protection scheme uses combined desirable features retrieved from discrete fractional Fourier transform (FRFT) and wavelet packet transform (WPT) techniques, which provides precise time-frequency information on minute perturbation signals introduced in the system. Moreover, this study focuses on the design of decoupling control with a distributed controller based on state feedback for the efficient operation of microgrid systems that are transitioning from the grid-connected mode to the islanded mode. An IEEE 9-bus test system with inverter based distributed generation (DG) units is considered for islanding assessment and smooth operation. Finally, tracking errors are greatly reduced with stability improvement based on the proposed controller. FRWPT based islanding detection is demonstrated via a time domain simulation of the system. Simulated results show an improvement in system stability with the application of the proposed controller and accurate islanding detection based on the FRWPT technique in comparison with the results obtained by applying the wavelet transform (WT) and WPT.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.240-241
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• 2006

Islanding operations of DG usually occur when power supply from the main utility is interrupted due to several reasons but the DG keeps supplying power into the distribution networks. These kinds of islanding conditions cause negative impacts on protection, operation, and management of distribution systems. Therefore, it is necessary to effectively detect the islanding conditions and swiftly disconnect DG from distribution network. This paper proposes the islanding detection algorithm for DG using the change of the voltage unbalance and the output power of DG. The proposed method effectively combines the conventional parameters for detecting the islanding conditions. The proposed methods were verified using the radial distribution network of IEEE 34 bus.

• Proceedings of the KIEE Conference
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• 2006.11a
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• pp.302-304
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• 2006

본 연구에서 개발한 실시간 시뮬레이터에 적용 가능한 발전단 사고 모의를 위한 정밀 모델 개발 목적은 발전단에서 발생되는 다양한 사고 중 전기적 형태로 모의 가능한 사고를 분류하고 실시간 시뮬레이터로 모의하도록 발전기 모델 및 보호계전요소 모델을 개발하여 이를 현장 실무 교육 및 훈련에 활용하기 위한 것이다. 본 연구에서는 RTDS/RSCAD로 구현 가능한 6가지 계전 요소(거리계전, 주파수, 역전력, 과여자, 과전압, 동기탈조)에 대해 모델링하였다. 그리고 보호계전기가 효과적인 보호계전을 수행할 수 있도록 계전기 신호 처리 모듈, 거리계전기 모듈, 역전력 모듈, 과여자 모듈, 주파수 모듈, 과전압 모듈, 동기탈조 모듈을 UDC를 이용하여 개발하였다. 그리고, 각 요소의 출력에 대해서 Flex Logic을 이용하여 최종적으로 계전기의 트립을 결정하는 모듈을 개발하였다. 또한 발전단 사고에 따른 발전기 보호 과정을 모의함으로써 발전회사 발전기 운전원들이 실제적인 발전기 동특성 및 발전기 보호계전기의 동작을 이해할 수 있도록 하였다.

• Progress in Superconductivity and Cryogenics
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• v.7 no.1
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• pp.37-41
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• 2005

This paper describes the construction scheme of new distribution system using HTS(High Temperature Superconducting) power equipments such as cable, transformer and FCL(fault current limiter). At present, one of the most serious problems in distribution power system, especially for metropolitan complex city, is to obtain the ROW for cable line routes, space for downtown substations and satisfy the environmental protection caused by NIMBY phenomena. Unfortunately, it is expected that this situation will get more and more worse. As the HTS technology to apply in power system Is developed, HTS cable utilizing mass-capacity characteristic can be a useful countermeasure to overcome this problem. This paper describes the application methodology of 22.9kV HTS cable with low-voltage, mass-capacity characteristics replacing the 154kV conventional cable. By applying 22.9kV HTS cable, the HTS transformer with higher capacity for the reduction of space and transformer numbers of downtown substation is necessary. Also, if the leakage Impedance of HTS transformer is same as or lower than that of conventional transformer, the fault current of 22.9kV bus will increase because the HTS transformer capacity is larger than that of the conventional transformer. This means the parallel application of HTS-FCL to reduce the fault current in addition to the HTS cable and transformer can be necessary. With the basic construction scheme of new distribution system, this paper describes the future study points to realize this new distribution system using HTS equipments.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.2
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• pp.155-163
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• 2008

This paper presents a novel framework for analysis of power system wide-area blackout based on so called fault cascading scenarios. For a given power system operating state, "triggering" faults or a "seed faults" are chosen based on the probabilities estimated from the hazard rates. The fault probabilities reflect both the load and the weather conditions. Effects of hidden failures in protection systems are also reflected in establishing the fault propagation scenarios since they are one of the major causes for the wide-area blackouts. A tree type data structure called a PS-BEST(Power System Blackout Event Scenario Tree) is proposed for construction of the fault cascading scenarios, in which nodes represent various power system operating states and the arcs are the events causing transitions between the states. Arcs can be either probabilistic or deterministic. For a given initial fault, the total probability of leading to wide-area blackout is estimated by aggregating the individual probability of each fault sequence route leading to wide-area blackout. A case study is performed on the IEEE RTS-79(24 bus) system based on the fault data presented by the North American Electrical Reliability Council(NERC). Test results demonstrate the potentials and the effectiveness of the proposed technique for the future wide-area blackout analysis.

• Journal of Electrical Engineering and Technology
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• v.8 no.3
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• pp.446-452
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• 2013

Under frequency load shedding (UFLS) is an effective way to prevent system blackout after a serious disturbance occurs in a power system. A novel centralized adaptive under frequency load shedding (AUFLS) scheme using the synchronous phase measurement unit (PMU) is proposed in this paper. Two main stages are consisted of in the developed technique. In the first stage, the active power deficit is estimated by using the simplest expression of the generator swing equation and static load model since the frequency, voltages and their rate of change can be obtained by means of measurements in real-time from various devices such as phase measurement units. In the second stage, the UFLS schemes are adapted to the estimated magnitude based on the presented model. The effectiveness of the proposed AUFLS scheme is investigated simulating different disturbance in IEEE 10-generator 39-bus New England test system.

• Wind and Structures
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• v.14 no.1
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• pp.55-70
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• 2011

This study investigates the design criteria required for wind barriers to protect vehicles running on an expressway under a high side wind. At the first stage of this study, the lateral deviations of vehicles in crosswinds were computed from the commercial software, CarSim and TruckSim, and the critical wind speeds for a car accident were then evaluated from a predefined car accident index. The critical wind speeds for driving stability were found to be 35 m/s for a small passenger car, yet 30 m/s for a truck and a bus. From the wind tunnel tests, the minimum height of a wind barrier required to reduce the wind speed by 50% was found to be 12.5% of the road width. In the case of parallel bridges, the placement of two edge wind barriers plus one wind barrier at center was recommended for a separation distance larger than 20 m (four lanes) and 10 m (six lanes) respectively, otherwise two wind barriers were recommended.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.6
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• pp.610-617
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• 2005

A variable speed wind turbine simulation model for grid connection is developed based on PSCAD/EMTDC. The model consists of wind model, rotor dynamics, synchronous generator, power converter, transformer, distribution line and infinite bus. Implementation of blade characteristics and power converter control strategies are included. Several transient case studies are performed including wind speed change, local load change and grid-side voltage unbalance using developed simulation model. The results of this work can be utilized for study of actual interaction between wind turbine and grid for reliable operation and protection of power system.

• Journal of Power Electronics
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• v.14 no.4
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• pp.733-741
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• 2014

The integration of photovoltaic (PV) energy sources into DC grid has gained considerable attention because of its enhanced conversion efficiency with reduced number of power conversion stages. During the integration process, a local control unit is normally included with every power conversion stage of the PV source to accomplish the process of maximum power point tracking. A centralized monitoring and supervisory control unit is required for monitoring, power management, and protection of the entire system. Therefore, we propose a field-programmable gate array (FPGA) based centralized control unit that integrates all local controllers with the centralized monitoring unit. The main focus of this study is on the process of integrating many local control units into a single central unit. In this paper, we present design and optimization procedures for the hardware implementation of FPGA architecture. Furthermore, we propose a transient analysis and control design methodology with consideration of the nonlinear characteristics of the PV source. Hardware experiment results verify the efficiency of the central control unit and controller design.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3347-3352
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• 2022

In 2013, the International Atomic Energy Agency (IAEA) changed the recommended maximum range of the Emergency Planning Zone (EPZ) to 30 km, and the Kori Nuclear Power Plant in Republic of Korea has also expanded the EPZ to 30 km, following the recommendation. As a result, metropolitan cities with a high population density are contained within the EPZ, and evacuating millions of people should be considered if the 30 km range of evacuation is to take place. This study proposes an evacuation plan using buses (public transportation) to transport people outside of the EPZ, quickly and efficiently. To verify the appropriate mode share ratio of buses that can guarantee the right of vulnerable road users and reduce traffic congestion, a model was built simulating the Kori Nuclear Power Plant in Ulsan Metropolitan City. The scenarios were established by changing the mode share ratio of buses and passenger cars by 10%. Considering a large-scale network analysis at the city level, a cell transmission model was applied to calculate the evacuation time in each scenario. The result shows that the optimal mode share ratio of buses is 40%, with a total evacuation time of 132 min, considering feasible bus fleets in Ulsan Metropolitan City.