• Journal of Power Electronics
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• 제18권1호
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• pp.204-211
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• 2018

At present, one of two LCC-HVDC systems is responsible for controlling the grid frequency of the Jeju Island Power System (JIPS). The grid voltage is regulated by using STATCOMs. However, these two objectives can be achieved in one device that is called by a modular multilevel converter-high voltage direct current (MMC-HVDC) system. Therefore, this paper proposes frequency and voltage control strategies for the JIPS based on a MMC-HVDC system. In this case, the ancillary frequency and voltage controllers are implemented into the MMC-HVDC system. The modelling of the JIPS is done based on the parameters and measured data from the real JIPS. The simulation results obtained from the PSCAD/EMTDC simulation program are confirmed by comparing them to measured data from the real JIPS. Then, the effect of the MMC-HVDC system on the JIPS will be tested in many cases of operation when the JIPS operates with and without STATCOMs. The objective is to demonstrate the effectiveness of the proposed control strategy.

• JSTS:Journal of Semiconductor Technology and Science
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• 제16권6호
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• pp.832-841
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• 2016

The voltage-frequency island (VFI) design paradigm has strong potential for achieving high energy efficiency in communication centric manycore system-on-chip (SoC) design called network-on-chip (NoC). However, because of the diminished scaling of wire-dimension and supply voltage as well as threshold voltage in modern CMOS technology, the vulnerability to link failure in VFI NoC is becoming a crucial challenge. In this paper, we propose an energy-optimized topology generation technique for VFI NoC to cope with permanent link failures. Based on the energy consumption model, we exploit the on-chip communication traffic patterns and characteristics of link failures in the early design stage to accommodate diverse applications and architectures. Experimental results using a number of multimedia application benchmarks show the effectiveness of the proposed three-step custom topology generation method in terms of energy consumption and latency without any degradation in the fault coverage metric.

• 전자공학회논문지
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• 제53권8호
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• pp.66-75
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• 2016

반도체 공정 초미세화에 따라 에이징 (aging)과 공정 변이 (process variation)로 인한 칩에서의 물리적인 결함은 더욱 증가하고 있으며, 특히 금속 배선 스케일링 제한과 온 칩 데이터 통신량 증가에 따라 다수의 프로세서 코어로 구성된 네트워크-온-칩(Network-on-Chip, NoC)에서의 결함 감내 기법 연구가 활발히 진행되고 있다. 그러나 NoC에서 저전력 설계 기법으로 널리 채용되고 있는 VFI (Voltage-Frequency-Island)를 적용한 경우에서의 신뢰성 측면에 대한 연구가 부족한 실정이다. 본 논문에서는 신뢰성과 에너지 소모를 고려하여 VFI NoC에서 링크 고장이 발생하는 경우에도 정상적으로 통신을 유지할 수 있는 테이블 기반 라우팅 기법을 제안한다. 에너지 소모와 성능을 고려한 최적 경로와 고장 감내를 위한 우회 경로를 제공하며, 이때 우회 경로의 경우 필요한 최소한의 노드에만 라우팅 테이블을 저장하여 구현 복잡도를 완화하였다. 모의실험 결과를 통해 제안하는 기법은 전체 링크의 1%에서 고장이 발생하는 경우에도 정상적으로 통신함을 보였다. 또한 실시간으로 우회 경로를 탐색하는 고장 감내 라우팅 기법인 $d^2$-LBDR에 비해 링크에 고장이 발생하는 경우 평균 15.9%의 에너지 소모가 감소함을 보였으며, 실행 시간 측면에서는 평균 0.8% 감소하는 것을 확인 할 수 있었다.

• 대한전자공학회논문지SD
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• 제46권8호
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• pp.22-30
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• 2009

네트워크 온 칩 (Network-on-Chip, NoC) 기술은 기존 시스템-온-칩(System-on-Chip, SoC) 설계에서 IP 블록 수 증가와 이에 수반된 상호 연결 네트워크 복잡화 및 데이터 대역폭 제한 등의 문제점을 해결하기 위한 새로운 설계 패러다임이다. 더불어 동작 주파수 증가에 따른 급격한 전력 소모 클럭 신호의 분배와 동기화 문제 역시 중요한 이슈이며, 이에 대한 대안으로 광역적으로는 비동기, 국부적으로는 동기식 (Globally Asynchronous Locally Synchronous, GALS) 인 시스템 설계 방법론이 저전력 기술과 결합되어 에너지 소모를 줄이고 모듈적인 설계를 위해서 고려되어 왔다 GALS 방식의 설계 스타일은 정밀한 시스템 수준 전력 관리를 적용하기 위해 최근 소개되고 있는 전압 주파수 구역 (Voltage-Frequency-Island, VFI) 의 개념과 매우 잘 어울린다. 본 논문에서는 VFI를 적용한 NoC 시스템에서 최적의 전압선택을 통해 에너지 소모를 최소화하는 효율적인 알고리즘을 제시한다. 최적의 코어(또는 처리 소자) 전압과 VFI를 찾기 위해 통신량을 고려한 코어 그래프 분할, 통신-경쟁 시간을 고려한 타일 매핑, 전력 변화량을 고려한 코어의 동적 전압 조절 그리고 효율적인 VFI 병합 및 VFI 동적 전압 재 조절을 포함한다. 본 논문에서 제안한 설계 방법론은 기존 연구결과 대비 평균적으로 10.3%의 에너지 효율 향상이 있다는 것을 실험 결과를 통해 보여준다.

• 전기학회논문지
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• 제64권8호
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• pp.1168-1179
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• 2015

This paper presents voltage and frequency control methods for a stand-alone Gasa Island Microgrid in South Korea that can be fully energized by renewable energy resources such as photovoltaic systems and wind turbines. To mitigate the variations of the output of renewable energy resources and supply more reliable electricity to customers, battery energy storage systems (BESSs) are employed in the stand-alone microgrid. The coordination between BESSs and pre-existing diesel generators is an important issue to manage the microgrid more securely. This paper presents voltage and frequency control schemes considering the coordination of BESSs and DGs. The effectiveness for the operating method is validated via simulation studies.

• 전기학회논문지
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• 제65권5호
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• pp.724-729
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• 2016

Nowadays high-cost energy storage system using flywheel or secondary battery is applying to hybrid generation system with WT(Wind Turbine) and diesel generator in island areas for stable operation. This paper proposes an operating algorithm and modeling method of the hybrid generation system that can operate for variable wind speed and load, which is composed of energy storage system, variable-speed PMSG(Permanent Magnet Synchronous Generator) WT and diesel generator applied in island areas. Initially, the operating algorithm was proposed for frequency and voltage to be maintained within the proper ranges for load and wind speed changes. Also, the modeling method is proposed for variable speed PMSG WT, diesel generator and BESS(Battery Energy Storage System). The proposed operating algorithm and modeling method were applied to a typical island area. The frequency and voltage was kept within the permissible ranges and the proposed method was proven to be appropriate through simulations.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.1159-1160
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• 2006

As the grid-connected photovoltaic power conditioning systems (PVPCS) are installed in many residential areas, this has raised potential problems of network protection on electrical power system. One of the numerous problems is an Island phenomenon. There has been an argument that because the probability of islanding is extremely low it may be a non-issue in practice. However, there are three counter-arguments: First, the low probability of islanding is based on the assumption of 100% power matching between the PVPCS and the islanded local loads. In fact, an island can be easily formed even without 100% power matching (the power mismatch could be up to 30% if only traditional protections are used, e.g. under/over voltage/frequency). The 30% power-mismatch condition will drastically increase the islanding probability. Second, even with a larger power mismatch, the time for voltage or frequency to deviate sufficient to cause a trip, plus the time required to execute the trip (particularly if conventional switchgear is required to operate), can easily be greater than the typical re-close time on the distribution circuit. And, third, the low-probability argument is based on the study of PVPCS. Especially, if the output power of PVPCS equals to power consumption of local loads, it is very difficult for the PVPCS to sustain the voltage and frequency in an island. Unintentional islanding of PVPCS may result in power-quality issues, interference to grid-protection devices, equipment damage, and even personnel safety hazards. So the verification of anti-islanding performance is strongly needed. In this paper, the authors propose the improved RPV method through considering power quality and anti-islanding capacity of grid-connected three-phase PVPCS in IEEE Std 1547 ("Standard for Interconnecting Distributed Resources to Electric Power Systems"). And the simulation and experimental results are verified.

• 전기학회논문지
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• 제59권12호
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• pp.2190-2194
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• 2010

Wind power generation system (WPGS) of Ulleung Island causes frequency and voltage fluctuation due to wind speed variation during night time. Superconducting magnetic energy storage (SMES) system can overcome the fluctuations through the fast response time of energy charging and discharging. The SMES system should be connected to the terminal of the WPGS for frequency stabilization. To demonstrated the effectiveness of SMES system for power quality improvement, Ulleung Island power network was modeled in a real time digital simulator (RTDS). The RTDS-based simulation results of power quality improvement with SMES are investigated and discussed in detail.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1777-1788
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• 2017

This paper presents the design and dynamic analysis of a stand-alone microgrid with high penetration of renewable energy. The optimal sizing of various components in the microgrid is obtained considering two objectives: minimization of levelized cost of energy (LCOE) and maximization of renewable energy penetration. Integrating high renewable energy in stand-alone microgrid requires special considerations to assure stable dynamic performance, we therefore develop voltage and frequency control method by coordinating Battery Energy Storage System (BESS) and diesel generators. This approach was applied to the design and development of Gasa Island microgrid in South Korea. The microgrid consists of photovoltaic panels, wind turbines, lithium-ion batteries and diesel generators. The dynamic performance of the microgrid during different load and weather variations is verified by simulation studies. Results from the real microgrid were then presented and discussed. Our approach to the design and control of microgrid will offer some lessons in future microgrid design.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.250-254
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• 2007

As photovoltaic(PV) power generation systems become more common, it will be necessary to investigate islanding detection method for PV systems. Islanding of PV systems can cause a variety of problems and must be prevented. However, if the real and reactive powers of the load and PV system are closely matched, islanding detection by passive methods becomes difficult. Also, most active methods lose effectiveness when there are several PV systems feeding the same island. The active frequency drift positive feedback method(AFDPF) enables islanding detection by forcing the frequency of the voltage in the island to drift up or down. In this paper the research for the minimum value of chopping fraction gain applied digital phase-locked-loop (DPLL) to AFDPF considering output power quality and islanding prevention performance are performed by simulation and experiment according to IEEE Std 929-2000 islanding test.