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Choi, Kyungwho,Choi, Woongchul,Yu, Choongho,Park, Yong Tae Hindawi Limited 2017 Journal of nanomaterials Vol.2017 No.-
<P>In contrast to commercial piezoelectric ceramics, lead-free materials such as ZnO and a polymer matrix are proper candidates for use in ecofriendly applications. In this article, the authors represent a technique using ZnO nanowires with a polyvinylidene fluoride (PVDF) matrix in a piezoelectric polymer composite. By aligning the nanowires in the matrix in a desired direction by AC dielectrophoresis, the piezoelectric behavior was enhanced. The dielectric constant of the composite was improved by increasing the concentration of the ZnO nanowires as well. Specifically, the resulting dielectric constant shows an improvement of 400% with aligned ZnO nanowires by increasing the poling effect compared to that of a randomly oriented nanowire composite without a poling process.</P>
Woongchul Choi 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.7 No.4
Global climate change is affecting human life more seriously than ever before. Countries around the world have identified cars as a significant source of pollution, leading to an increased interest in eco-friendly automobiles. Electric vehicles (EVs), which are characteristically eco-friendly, have become a choice for future transportation system. In this paper, we proposed a strategy for determining the appropriate placement of large-scale charging stations using K-mean algorithm. Also, the initial results were validated utilizing actual electricity usage data from the existing chargers. Currently in Korea, a typical public charging station has two to three chargers to support EV users. As EVs become more popular, new problems arise, such as charger hopping and/or long waiting lines. In order to address these new issues, a large-scale charging station concept which houses more than ten chargers, is suggested. In doing so, a strategic approach for selecting close-to-ideal locations for the charging stations is introduced to maximize the charging station’s effectiveness. In this study, Jeju Island, Korea, which has many EVs, was used as a testbed. With the wealth of EV chargers and their usage data, initial validation of the proposed methodology was made possible. During the evaluation of the best possible locations for the largescale charging stations, we considered the locations of tourist attractions and convenient support facilities, as well as the population. After the evaluations, the proposed locations were validated using actual long-term charger usage data on Jeju Island. The demonstrated strategy for identifying appropriate locations for large-scale charging stations can be used by other tourist heavy islands or even small countries.
Chulyoung Choi(최철영),Woongchul Choi(최웅철) 대한전기학회 2017 전기학회논문지 Vol.66 No.12
Global automobile manufacturers are developing electric vehicles (EVs) to eliminate the pollutant emissions from internal combustion vehicles and to minimize fossil fuel consumptions for the future generations. However, EVs have a disadvantage of shorter traveling distance than that of conventional vehicles. To answer this shortfall, more batteries are installed in the EV to satisfy the consumer expectation for the driving range. However, as the energy capacity of the battery mounted in the EV increases, the amount of heat generated by each cell also increases. Naturally, a better battery thermal management system (BTMS) is required to control the temperature of the cells efficiently because the appropriate thermal environment of the cells greatly affects the power output from the battery pack. Typically, the BTMS is divided into an active and a passive system depending on the energy usage of the thermal management system. Heat exchange materials usually include gas and liquid, semiconductor devices and phase change material (PCM). In this study, an application of PCM for a BTMS was investigated to maintain an optimal battery operating temperature range by utilizing characteristics of a PCM, which can accumulate large amounts of latent heat. The system was modeled using Dymola from Dassault Systems, a multi-physics simulation tool. In order to compare the relative performance, the BTMS with the PCM and without the PCM were modeled and the same battery charge/discharge scenarios were simulated. Number of analysis were conducted to compare the battery cooling performance between the model with the aluminum case and PCM and the model with the aluminum case only.
실제 전기자동차 사용 패턴 분석을 통한 충전 인프라 보급 방향과 확산 전략에 대한 고찰
최영석(Youngsuk Choi),김현준(Hyunjun Kim),최웅철(Woongchul Choi) 대한전기학회 2019 대한전기학회 학술대회 논문집 Vol.2019 No.5
본 논문에서는 각종 환경문제의 무분별한 확산을 방지하는데 기여하고, 인류와 산업이 상생할 수 있는 지구 환경을 만들기 위한 여러 가지 노력 중 하나인 전기자동차 산업이 성공적으로 안착하기 위한 방안들에 대해 논의하고자 한다. 최근, 전 세계적으로 진행되고 있는 자동차 동력원의 변화(즉, 내연기관을 기반으로 하는 기존 자동차 형태에서 전기모터와 배터리 팩을 기반으로 하는 전기자동차로의 패러다임 변화)는 기존의 주유 시설과는 다른 전기 충전 인프라의 구축을 요구하고 있다. 다만, 아직까지는 충전 인프라 구축에 대한 경험이 부족하고, 전기자동차의 충전 패턴 등에 대해 연구가 부족하여, 효율적인 충전 인프라의 구축과 그 운영방안에 대해 적절한 전략이 부재한 상황이다. 따라서 본 연구에서는 제반 충전 인프라의 효율적 구축과 정착 그리고 보다 현실적인 충전 인프라의 운영 방안 모색을 통하여, 전기자동차 충전 인프라의 자생적 확산 방향에 대해 논의하였다. 그 연구의 기반으로는 PHEV와 BEV를 포함한 실제 전기자동차 사용자들의 충전 인프라 이용사례와 패턴을 분석하였다. 또한, 전기자동차의 지속적 보급과 확산, 그리고 함께 준비되고 마련되어야 할 효용성 높은 충전 인프라 구축과 더불어 점진적이고 궁극적으로 나아가야 할 전기자동차 충전 인프라 산업의 비전과 방향성을 고찰하였다.