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Characteristics of Energy Harvesting in Flywheel Energy Storage System Based on Efficiency Map
Jeonghyun Cho,Hongsik Hwang,Gwansoo Park,Cheewoo Lee Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4
In this paper, the characteristics of energy discharge in a flywheel energy storage system (FESS) are analyzed according to load condition mapped in the efficiency of a generator. As time goes by, the electromotive force (EMF) of a generator decreases in an FESS as a power source, but output power is maintained by boosting the generator voltage in a bidirectional power converter (BPC). Using the principle of operation of a boost converter, the variation of voltage gain in a BPC is investigated under the condition of load change, and current is compensated for the reduction of back EMF in a generator as its speed goes down. The loss of the FESS is separated into that of its generator, bearings, and BPC through experimental evaluation, and it has been verified that the generator plays a significant role in the efficiency of the FESS.
Jeonghyun Cho,Hongsik Hwang,Cheewoo Lee 한국자기학회 2020 Journal of Magnetics Vol.25 No.1
In this paper, the energy consumption of PMSM was compared simultaneously in direct and indirect drive systems, considering the efficiency of the operating point in the washing and dehydration modes. DD (Direct Drive) washing machines have the disadvantage of high-power consumption due to the difference in driving point efficiency of washing and dehydration. Therefore, in this paper, a method of changing the washing operation point using a gear is proposed. Two types of miniaturization models that satisfies the output level under two gear conditions are designed, and energy consumption with respect to the operating mode of the washing machine is analyzed and compared. From the viewpoint of power consumption, optimal stacking and gear combination model is selected. In conclusion, the energy consumption of the optimum gear model is decreased about 97 Wh and material cost of the motor down by 57.3 % compared with base DD motor.
회전자 위치추정을 위해 자기적 돌극성을 고려한 표면 부착형 영구자석 동기 전동기 설계
조정현(Jeonghyun Cho),이치우(Cheewoo Lee) 대한전기학회 2017 전기학회논문지 Vol.66 No.5
This paper presents concurrent design methods of surface permanent magnet synchronous machines for saliency-tracking self-sensing position estimation. Magnetic saliency for the self-sensing is created by stator pole saturation due to the rotor zigzag leakage flux. The power conversion properties such as saliency ratio, torque ripple, and efficiency vary according to motor design. The property change due to design modification is analysed by using finite element analysis, and with the appropriate design modification, proper saliency is created while preserving their power conversion capabilities.
Cho, Daehwan,Kim, Moonkyoung,Hwang, Jeonghyun,Park, Jay Hoon,Joo, Yong Lak,Jeong, Youngjin Springer US 2015 NANOSCALE RESEARCH LETTERS Vol.10 No.1
<P>We report a facile fabrication of porous silicon nanofibers by a simple three-stage procedure. Polymer/silicon precursor composite nanofibers are first fabricated by electrospinning, a water-based spinning dope, which undergoes subsequent heat treatment and then reduction using magnesium to be converted into porous silicon nanofibers. The porous silicon nanofibers are coated with a graphene by using a plasma-enhanced chemical vapor deposition for use as an anode material of lithium ion batteries. The porous silicon nanofibers can be mass-produced by a simple and solvent-free method, which uses an environmental-friendly polymer solution. The graphene-coated silicon nanofibers show an improved cycling performance of a capacity retention than the pure silicon nanofibers due to the suppression of the volume change and the increase of electric conductivity by the graphene.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s11671-015-1132-8) contains supplementary material, which is available to authorized users.</P>
Cho, Eun-Bum,Park, Jeonghyun,Jaroniec, Mietek American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.41
<P>Periodic mesoporous thiophene-silicas with hexagonal (<I>p</I>6<I>mm</I>) symmetry were synthesized using a 2,5-bis(triethoxysilyl)thiophene (BTET) precursor in the presence of Pluronic P123 (EO<SUB>20</SUB>PO<SUB>70</SUB>EO<SUB>20</SUB>) and PLGE (EO<SUB>17</SUB>(L<SUB>28</SUB>G<SUB>7</SUB>)EO<SUB>17</SUB>) triblock copolymers at different acidic conditions. P123-templated mesoporous thiophene-silicas with <I>p</I>6<I>mm</I> ordered structure were prepared in the presence of hydrochloric acid and iron(III) chloride hexahydrate used as acid catalysts. However, it was found that a relatively large fraction of the Si–C bonds in thiophene-bridging groups were decomposed during the synthesis process. On the other hand, thiophene-silicas synthesized at lower acidic conditions were disordered and nonporous structures. In contrast, PLGE-templated thiophene-silicas with <I>p</I>6<I>mm</I> ordered mesostructure were prepared using copper(II) perchlorate hexahydrate and boric acid as well as hydrochloric acid. Importantly, up to 97.3% of the Si–C bonds in mesoporous thiophene-silica prepared in the presence of boric acid were retained. Solid state <SUP>29</SUP>Si MAS NMR clearly showed that the structural stability of the Si–C bond is dependent on the acidity and time of the initial self-assembly stage. Also, the thermal stability of the thiophene-bridging groups was shown to be dependent on the acidity of the synthesis gel.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-41/jp408385t/production/images/medium/jp-2013-08385t_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp408385t'>ACS Electronic Supporting Info</A></P>