• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.1
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• pp.45-50
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• 2014

A vibration test coupon is prepared with nine plastic ball grid array packages on a printed circuit board using SnPb solders, and a random vibration test is conducted on the coupon. Life data from the test are analyzed, and it is shown that over the board, life data is location-dependent. For investigating this location dependency, a finite element model is developed and the equivalent stresses, which are defined based on the stress response functions at each node, are investigated. It is shown that one of the corner solder balls has the maximum equivalent stress at a package during the test. Finally, it is demonstrated that the maximum equivalent stress and durability life are inversely proportional.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.10
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• pp.1916-1922
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• 2009

Introducing distributed generators(DGs) to utility distribution system can cause malfunction of relay on the grid when ground faults or severe load unbalances are occurred on the system. Because DGs interconnected to the grid can contribute fault currents and make bidirectional power flows on the system, fault currents from DGs can cause an interference of relay operation. A directional over current relay(DOCR) can determine the direction of power flow whether a fault occurs at the source side or load side through detecting the phases of voltage and current simultaneously. However, it is identified in this paper that the contributed fault current(Ifdg) from the ground source when was occurred to contribute single-line-to-ground(SLG) fault current, has various phases according to the distances from the ground source. It means that the directionality of Ifdg may not be determined by simply detecting the phases of voltage and current in some fault conditions. The magnitude of Ifdg can be estimated approximately as high as 3 times of a phase current and its maximum is up to 2,000 A depending on the capacity of generation facilities. In order to prevent malfunction of relay and damage of DG facilities from the contribution of ground fault currents, Ifdg should be limited within a proper range. Installation of neutral ground reactor (NGR) at a primary neutral of interconnection transformer was suggested in the paper. Capacity of the proposed NGR can be adjusted easily by controlling taps of the NGR. An algorithm for unidirectional relay was also proposed to prevent the malfunction of relay due to the fault current, Ifdg. By the algorithm, it is possible to determine the directionality of fault from measuring only the magnitude of fault current. It also implies that the directionality of fault can be detected by unidirectional relay without replacement of relay with the bidirectional relay.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.1
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• pp.23-30
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• 2016

Wake effects cause wind turbine generators (WTGs) within a wind power plant (WPP) to produce different levels of active power and subsequent reactive power capabilities. Further, the impedance between a WTG and the point of interconnection (POI)-which depends on the distance between them-impacts the WPP's reactive power injection capability at the POI. This paper proposes a voltage control scheme for a WPP based on the available reactive current of the doubly-fed induction generators (DFIGs) and its impacts on the POI to improve the reactive power injection capability of the WPP. In this paper, a design strategy for modifying the gain of DFIG controller is suggested and the comprehensive properties of these control gains are investigated. In the proposed scheme, the WPP controller, which operates in a voltage control mode, sends the command signal to the DFIGs based on the voltage difference at the POI. The DFIG controllers, which operate in a voltage control mode, employ a proportional controller with a limiter. The gain of the proportional controller is adjusted depending on the available reactive current of the DFIG and the series impedance between the DFIG and the POI. The performance of the proposed scheme is validated for various disturbances such as a reactive load connection and grid fault using an EMTP-RV simulator. Simulation results demonstrate that the proposed scheme promptly recovers the POI voltage by injecting more reactive power after a disturbance than the conventional scheme.

• Journal of Software Engineering Society
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• v.24 no.3
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• pp.111-115
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• 2011

With the emergence of the smart grid era, the interest in green energy which reduce carbon emissions and environment-friendly smart grid which combines the advantages of power and IT technology is increasing around the world. To use the smart grid effectively heterogeneous systems such as EMS, MOS and WIS must be linked together. However, additional interface should be developed to link EMS and heterogeneous systems since IEC has only defines the interface for EMS. Especially, to link legacy system and new system, some software might need to be designed and developed because separate interfaces for connection can be developed depending on each system and environment. In this paper, we propose an integrated interface based on CIM for interconnection between systems. A proposed interface can integrate messages of heterogeneous system and will be able to reduce costs that could be incurred by the removal of the existing system and the addition of the new system.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.484-485
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• 2008

A micro-grid (MG) is a new concept to aggregate distributed generations (DGs) and loads in a small area. The difference between MG and DG is that MG can supply power to loads even in islanding conditions. The magnitude of the fault current depending on interconnection between the MG and utility and the number of DGs in the MG. Therefore, the setting value of the OCR must be changed depending on operating conditions of the MG. This paper proposes the over-current relay considering operating conditions of the MG. In the proposed algorithm, the supervisory control and data acquisition decides the operating conditions of the MG and sends the proper setting values to each OCR. The performance of the algorithm was investigated in the case of the various operating conditions.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.4B no.4
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• pp.217-224
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• 2004

A novel anti-islanding method for the distributed power generation system (DPGS) is proposed in this paper. Three different islanding scenarios are explored and presented based on the analysis of real and reactive power mismatch. It is shown via investigation that islanding voltage is a function of real power alone, where its frequency is a function of both real and reactive power. Following this analysis, a robust anti-islanding algorithm is developed. The proposed algorithm continuously perturbs ($\pm$5%) the reactive power supplied by the DPGS while simultaneously monitoring the utility voltage and frequency. In the event of islanding, a measurable frequency deviation takes place, upon which the real power of the DPGS is further reduced to 80%. A drop in voltage positively confirms islanding and the DPGS is then safely disconnected. This method of control is shown to be robust: it is able to detect islanding under resonant loads and is also fast acting (operable in one cycle). Possible islanding conditions are simulated and verified through analysis. Experimental results on a 0.5kW fuel cell system connected to a utility grid are discussed.

• Proceedings of the KIPE Conference
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• 2013.11a
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• pp.113-114
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• 2013

일본은 동일본 대지진 이후로 원자력 발전 가동을 점차 중단시켜 가고 있는 추세이고 이에 발 맞추어 신재생에너지 발전 비중은 높아지고 있다. 특히 태양광 발전에 대한 관심은 주택용 뿐 아니라 발전소 수준의 메가솔라 시장으로 확대 되어 가고 있다. 본 논문에서는 일본형 대용량 계통연계형 태양광 인버터들이 가져야 할 기능 중 FRT 기능에 관해 일본 계통연계 규정인 JEAC 9701-2010을 기반으로 알아보고자 한다.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.714-716
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• 2004

Owing to the environmental problems as well as increasing energy prices and power plant construction costs, many researches have been made for the safe operation of distributed generations. In order to be more popularly used in parallel with the distribution network, the distributed generation and its correlation with the power system should be exactly monitored at any time. This paper presents a monitoring system which displays the important states of the distributed generation in operation and stores various measurements of the system. The proposed system constructs a data-base for developing algorithms against any faults of the interconnected system, and monitors efficiently at any place with the communication network function.

• Proceedings of the KIEE Conference
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• 2008.11a
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• pp.194-196
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• 2008

우리나라 전력시장은 2001년 4월부터 구조개편 초기모델로 원가반영발전시장(Cost Based Pool)으로 새로운 경쟁적 시장환경이 도입되면서 지역간 연계를 위한 송전망의 확충은 개별 시장참여자뿐만 아니라 다양한 이익주체들에게 경제적 편익에 큰 영향을 미칠 수 있다. 따라서 국내 전력시장 환경에 적합한 송전망 투자의 경제성 평가 절차와 방법을 개발하고 전산모형을 활용하여 실제 계통계획(안)에 적용하여 시장참여자별 경제적 효과를 평가한다.

• Proceedings of the KIEE Conference
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• 2004.04a
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• pp.205-207
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• 2004

This paper presents experimental operation with utility invertactive 3kW photovoltaic generation system. And that describe configuration of utility interactive photovoltaic system which power supply for Demonstration experiment. The status of photovoltaic generation system components and interconnection and safety equipment will be summarized. This paper discusses property operation state which system endure division of power for demonstration experiment.