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Highly isolated switching mode power supply for solid-state transformers in railway vehicles
Lee, Yejun,Bu, Hanyoung,Lee, Dohong,Cho, Younghoon The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.4
This paper discusses an isolated switching mode power supply (SMPS) with an AC 30 kV<sub>rms</sub> insulation capability for application to the solid-state transformers (SSTs) in railway vehicles. The insulation capability of the SMPS should be higher than AC 25 kV<sub>rms</sub> for application at the SSTs in railway vehicles. The proposed highly isolated SMPS is superior to commercial isolated power supplies with low insulation capability, which is normally less than 20 kV. The input side of the proposed isolated SMPS is physically separated from its output side by a specially designed miniature high-frequency (HF) transformer to obtain high insulation capability. The core of the miniature HF transformer is separated by insulation material. The primary and secondary coils are wound around each separated core. A CLLC resonant converter that consists of a primary resonant capacitor (C), two inductors (LL), and a secondary resonant capacitor (C) is applied as the proposed isolated SMPS topology to improve the output voltage regulation performance, which varies due to a large leakage inductance derived from the airgap of the proposed miniature HF transformer. Experiments are carried out to verify the CLLC resonant converter of the proposed isolated SMPS. Electrostatic finite element method (FEM) simulations and high potential (HiPot) tests are carried out to verify the AC 30 kV<sub>rms</sub> insulation capability of the proposed isolated SMPS. The electrostatic FEM simulations demonstrate the DC 42.43 kV insulation capability, and the HiPot tests verify the insulation capability from AC 5 kV<sub>rms</sub> to AC 30 kV<sub>rms</sub>.
Leaky-Wave Antenna for a Car-to-Satellite Link
Yejune Seo(서예준),Munsu Jeon(전문수),Junghyun Cho(조정현),Yejin Lee(이예진),Jiyeon Jang(장지연),Changhyeong Lee(이창형),Inyeol Moon(문인열),Sungtek Kahng(강승택) 한국통신학회 2021 한국통신학회 학술대회논문집 Vol.2021 No.11
In this paper, a CRLH (Composite Right and Left Handed) leaky-wave antenna is proposed for V2X communication. The unit cell is composed of series chip capacitors and via for metamaterial properties. Also, the ground length is varied to attach on the automobiles. The size of the unit cell is 20×40 mm2 and the EM Simulation was used to see the results.
습열 노화 및 산소 유량이 마그네슘 파우더의 열 화학적 성질에 미치는 영향 파악
이예준(Yejun Lee),오주영(Juyoung Oh),여재익(Ja-ick Yoh) 한국추진공학회 2023 한국추진공학회 학술대회논문집 Vol.2023 No.5
마그네슘은 충분한 에너지 밀도와 저렴한 가격으로 다양한 분야에서 사용되고 있다. 하지만, 마그네슘은 노화를 겪으면서 열화학적 성능 저하가 발생하는데, 아직 이것에 대해 밝혀진 바가 없었다. 습열 노화는 마그네슘에 열과 습기 모두 영향을 줘서, 마그네슘의 산화 반응을 지연시키는 산화 마그네슘과 가속시키는 마그네슘 수산화물로 이뤄진 산화막을 형성한다. 마그네슘 산화 반응은 표면 산화와 코어 산화로 이뤄지는데 장기 노화에서 산화막이 마그네슘 입자를 모두 둘러싸 표면 산화가 발생하지 않는다. 이로 인해, 장기 노화의 열 거동은 코어 산화의 열 거동과 유사한 형태를 가졌고, 낮은 반응률에서 높은 활성화 에너지를 형성했다. 게다가, 산소 유량이 증가하면서 마그네슘-산소 반응이 fuel-rich 조건에서 fuel-lean 조건으로 변화한다. 이러한 변화는 반응하는 마그네슘의 양을 증가시켜 더 높은 활성화 에너지를 유발했다. 따라서, 본 연구는 노화로 인한 마그네슘의 열화학적 성질 변화를 밝히고, 노화가 장기화될 때 생기는 현상을 규명했다. Magnesium is widely used in various fields due to its high energy density and low price. However, the degradation of thermochemical performance of magnesium subjected to hygrothermal aging has not yet been identified. Hygrothermal aging affects magnesium to form an oxide film consisting of magnesium oxide that retards the magnesium oxidation and magnesium hydroxide that accelerates it. The magnesium oxidation consists of surface oxidation and core oxidation. In long-term aging, the oxide film surrounds all magnesium surface, which results in the skip of surface oxidation. Because of this, the thermal behavior of long-term aged samples had a similar form to core oxidation, and forme a high activation energy at a low reaction rate. In addition, as the oxygen flow rate increases, the magnesium-oxygen reaction changes from fuel-rich condition to fuel-lean condition. These changes increased the amount of magnesium that reacted, resulting in higher activation energy. Thus, this study investigated changes in the thermochemical properties of magnesium subjected to hygrothermal aging and identified the phenomenon that occurs when aging is prolonged.
이예준(Yejun Lee),조정찬(Jungchan Cho) 대한전자공학회 2023 대한전자공학회 학술대회 Vol.2023 No.11
Recently, research using text information has attracted attention in computer vision, but PAR(Pedestrian Attribute Recognition) is only using simple text extraction methods. However, language models have the flexibility to utilize a variety of prompts, so finding good prompts plays an important role in improving the performance of the PAR model. In this paper, we propose a PAR training method using CLIP and multiple template prompts. Experimental results show that the proposed method outperformed a comparison method. This demonstrates that it is important to use textual information extracted through the appropriate prompts to improve visual model performance.