• Proceedings of the KIPE Conference
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• 2008.10a
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• pp.36-38
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• 2008

본 논문에서는 여러 대의 인버터를 동시에 사용하는 분산전원 환경하에서 Anti-islanding을 효과적으로 할 수 있는 방안을 제안한다. 제안하는 Anti-islanding기법은 SMS(Sliding Mode Frequency Shift)를 근간으로 하면서 공진 Q가 높을 때 검출이 어려운 단점을 해결하는 방법을 제시한다. SMS위상의 변동 값을 판단근거를 사용하지 않고 SMS위상의 적분 값을 판단근거로 사용한다. Run on시간이 0.5초 이내로 국내외 규격을 모두 만족시킨다. 여러 대의 인버터를 병렬로 접속해도 islanding 검출이 탁월하다. 출력전력의 품질 면에 있어서도 다른 Anti-islanding기법에 비해 우수하다. 본 알고리즘의 우수성을 시뮬레이션과 실험을 통해 검증하였다.

• Proceedings of the KIEE Conference
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• summer
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• pp.217-219
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• 2004

The installation of small sized dispersed generation(DG) units operating in parallel with the utility supply presents several technical problems for the protection and control of the system. One of the critical concerns is the occurrence of islanding. Hence, this paper propose the Digital Universal Relay(DUR) including anti-islanding function as DG interconnection interface. The existent islanding detection algorithms are examined. And the most effective and reliable method of those is modified for DUR application. The modified algorithm is evaluated through the modeling of the test system by PSCAD/EMTDC.

• 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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.10
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• pp.3898-3904
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• 2010

In order to analyze the transient characteristics for distributed generation located with the secondary feeders, this paper constructs a Distributed Generations Filed Test Center which can produce transient characteristics such as voltage sag, swell, interruption, harmonic and so on. And also this paper proposes the test results for the interconnection of distributed generations. The results show the effectiveness for the utility technical guidelines for distributed generations with the secondary feeders.

• 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.

• Journal of Sensor Science and Technology
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• v.28 no.5
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• pp.284-288
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• 2019

A calibration-free analog neuron circuit is proposed as a viable alternative to the power hungry digital neuron in implementing a deep neural network. The conventional analog neuron requires calibrations because a voltage-mode link is used between the soma and the synapse, which results in significant uncertainty in terms of current mapping. In this work, a current-mode link is used to establish a robust link between the soma and the synapse against the variations in the process and interconnection impedances. The increased hardware owing to the adoption of the current-mode link is estimated to be manageable because the number of neurons in each layer of the neural network is typically bounded. To demonstrate the utility of the proposed analog neuron, a simple neural network with $4{\times}7{\times}3$ architecture has been designed for classifying iris flowers. The chip is now under fabrication in 0.35 mm CMOS technology. Thus, the proposed true current-mode analog neuron can be a practical option in realizing power-efficient neural networks for edge computing.

• KEPCO Journal on Electric Power and Energy
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• v.5 no.4
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• pp.295-309
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• 2019

This paper demonstrates that the verification and analysis of the increase of hosting capacity of distributed energy resources in distribution system for the high penetration of distributed energy resources. In the case of generally designed distribution feeders in South Korea, it can host up to 10 MVA of distributed energy resources and the over voltage due to reverse power flow is prohibited beyond the range by the law of electric utility. However, it should take into consideration that there are some factors of extra hosting capacity such as generation characteristics of distributed energy resources and minimum loads that always exist to distribution system. For these reason, we choose a specific distribution system hosted 10 MVA of distributed energy resources monitored by distribution system operator and verify the impact of increasing hosting capacity such as power flow and voltage profile of distribution system. By the result, we could find that it is possible to increase the hosting capacity and define the factors to expand the hosting capacity of distributed energy resources in distribution system.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.4 no.1
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• pp.43-51
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• 2010

In this paper, we developed a digital Taekwondo trainer system based on the electronic protector was authorized by the World Taekwondo Federation for the improvement of user's training effects and athletic performances. Our system consists of E-Kick Bag with sensors for sensing hits, taekwondo trainer program and receiver for interconnection of E-kick Bag to program. Taekwondo trainer system also has an advantage to improve training effects and athletic performances such as hit-accuracy and reaction velocity by appointing a hitting target for users with 6 LED indicators. The taekwondo trainer program is a user interface to provide training courses such as progress training of response time and stamina, preparation training for real sparring by training scenario. It has also characteristics which are to strengthen and supplement user's pros and cons by analyzing hitting intensity and accuracy from training. In this paper, we implemented a test targeting eight taekwondo players on the playing list include a member of the Korea national team and conducted a survey in order to evaluate the utility of our system.