• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.3
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• pp.257-265
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• 2000

Brushless DC(BLDC) motors are widely used as AC servo motors in factory automation fields because of their quick instantaneous mobility, good energy saving efficiency and easiness of design for control system comparing with induction motors. Recently, a Two-Degree-of-Freedom(2DOF) PI control law has been adopted to some application parts to accomplish an advanced speed control of BLDC motors. The method can treat the two conflicting performances, minimum tracking errors versus reference inputs without large overshoot and rejection of some disturbances including modeling errors, independently. However, the method can not design the optimal system which is able to minimize tracking errors and energy consumption simultaneously. In this paper, a 2DOF integral type optimal servo control method is investigated to promote the speed control performances of BLDC motors considering energy consumption. In order to applicate the method to the speed servo system of the BLDC motor, the motor is modeled in the state space using the vector control and decoupling technique. To verify the validity of the suggested method, some simulations and experiments are performed.

• Journal of the Korean Applied Science and Technology
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• v.37 no.2
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• pp.260-267
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• 2020

In this study, supercapacitor based on the all solid state electrolyte with PVA(polyvinyl alcohol), ionic liquid as a BMIMBF4(1-buthyl-3-methylimidazolium tetrafluoroborate) and activated carbon/Ni-MOF composite was fabricated and characterized its electrochemical properties with function of MOF. In order to analysis and comparison that electrochemical performances [including cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS) and galvanostatic charge/discharge test] of prepared supercapacitor based on activated carbon/Ni-MOF composite and all solid state electrolyte. As a result, specific capacitance of the supercapacitor without Ni-MOF was 380 F/g which value decreased to 340 F/g after adding Ni-MOF to activated carbon as a electrode material. This result exhibited that decreased electrochemical property of the supercapacitor effected on physical hinderance in the electrode. In further, it needs to optimization of the Ni-MOF amount (wt%) in the electrode composite to maximize its electrochemical performances.

• Korean Journal of Materials Research
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• v.8 no.9
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• pp.813-818
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• 1998

Ultrafine powders of $\textrm{In}_{2}\textrm{O}_{3}$-doped $\textrm{SnO}_{2}$ were synthesized by a coprecipitation method and the effects of pH value and the amount of In2Q addition on particle size were investigated. The influence of pH value on particle size could be negligible, whereas the amount of $\textrm{In}_{2}\textrm{O}_{3}$ has influenced on particle size and specific surface area. The gas sensitivity to hydrocarbOn($\textrm{C}_{3}\textrm{H}_{8}$, $\textrm{C}_{4}\textrm{H}_{10}$) increased with $\textrm{In}_{2}\textrm{O}_{3}$ addition and reached a maximum at 3wt.% addition. From the results of impedance analysis and I-V characteristics. it was showed that the agglomeration structure of particles and the boundaries between agglomerates were the important factors to determine the gas sensing mechanism.

• Journal of the Korean Electrochemical Society
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• v.6 no.4
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• pp.229-235
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• 2003

A precursor of lithium manganese oxide was synthesized by mixing $(CH_3)_2CHOLi\;with\;Mn(CH_3COO)_2{\cdot}4H_2O$ in ethanol using a sol-gel method, then heat-treated at $400^{\circ}C\;and\;800^{\circ}C$ in air atmosphere. The condition of heat treatment was determined by thermogravimetric analysis/differential thermogravimetric analysis (TGA/DTA). The characterization of the lithium manganese oxide was done by X-ray diffraction (XRD) spectra and scanning electron microscopy (SEM). The electrochemical characteristics of lithium manganese oxide electrode for lithium ion battery were measured by cyclic voltammetry (CV), chronoamperometry and AC impedance method using constant charge/discharge process. The electrochemical behaviors of the electrode have been investigated in a 1.0M $LiClO_4/propylene$ carbonate electrolyte solution. The diffusivity of lithium ions, $D^+\;_{Li}\;^+$, as determined by AC impedance technique was $6.2\times10^{-10}cm^2s^{-1}$.

• Journal of the Korean Chemical Society
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• v.42 no.4
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• pp.422-431
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• 1998

Tridentate Schiff base ligands such as $SIPH_2,\;SIPCH_2,\;HNIPH_2,\;and\; HNIPCH_2$ were prepared by the reaction of salicylaldehyde and 2-hydroxy-l-naphthaldehyde with 2-aminophenol and 2-amino-p-cresol. The structures and properties of ligands and their Co(II) complexes were investigated by elemental analysis, $^1H$NMR, IR, UV-visible spectra, and thermogravimetric analysis. The molar ratio of Schiff base to the metal of complexes was found to be 1:1. Co(II) complexes were contemplated to be hexa-coordinated octahedral configuration containing three water molecules. The redox process of ligands and complexes in DMSO solution containing 0.1 M TBAP as a supporting electrolyte were investigated by cyclic voltammetry with glassy carbon electrode. The redox process of the tridentate Schiff base ligands was totally irreversible. The redox process of Co(II) complexes were irreversible and one electron processes by two steps in diffusion controlled reaction. The reduction potential of the Co(II) complexes was shifted to the positive direction in the order [Co(Ⅱ)$(HNIPC)(H_2O)_3$]>[Co(Ⅱ)$(HNIP)(H_2O)_3$]>[Co(II)$(SIPC)(H_2O)_3$]>[Co(Ⅱ)$(SIP)(H_2O)_3], and their dependence on ligands were not so high.

• Journal of the Korean Applied Science and Technology
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• v.36 no.1
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• pp.200-207
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• 2019

In this study, flexible supercapacitor based on the all solid state electrolyte with PVA (polyvinyl alcohol)-$H_3PO_4$, ionic liquid as a BMIMBF4 (1-buthyl-3-methylimidazolium tetrafluoroborate) and reduced graphene oxide/conductive polymer composite was fabricated and characterized electrochemical properties with function of its flexibility. In order to measure and compare that electrochemical performances (including cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS) and galvanostatic charge/discharge,after 0~100th bending test) of prepared flexible supercapacitor based on reduced graphene oxide/conducting polymer composite and all solid state electrolyte, we have conducted press machine with constant pressure ( 0.01/cm2) for $100^{th}$ bending test. As a result, specific capacitance of the flexible supercapacitor was 43.9 F/g which value decreased to 42.0 and 40.1 F/g after 50 and $100^{th}$ bending test, respectively. This result exhibited that decreased electrochemical property of the flexible supercapacitor effected on physical stress on the electrode after repeated bending test. In addition, we have measured that electrode surface morphology by SEM to prove its decreased electrochemical property of the flexible supercapacitor after prolonged bending test.

• Applied Chemistry for Engineering
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• v.22 no.2
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• pp.167-172
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• 2011

In this work, the effect of surface treatment on mesoporous carbons (MCs) supports was investigated by analyzing surface functional groups. MCs were prepared by a conventional templating method using mesoporous silica (SBA-15) for using catalyst supports in direct methanol fuel cells (DMFCs). The MCs were treated with different phosphoric acid ($H_3PO_4$) concentrations i.e., 0, 1, 3, 4, and 5 M at 343 K for 6 h. And then Pt-Ru was deposited onto surface treated MCs (H-MCs) by chemical reduction method. The characteristics of Pt-Ru catalysts deposited onto H-MCs were determined by specific surface area and pore size analyzer, X-ray diffraction, X-ray photoelectron, transmission electron microscopy, and inductive coupled plasma-mass spectrometer. The electrochemical properties of Pt-Ru/H-MCs catalysts were also analyzed by cyclic voltammetry experiments. From the results of surface analysis, an oxygen functional group was introduced to the surface of carbon supports. From the results, the H4M-MCs carbon supports surface treated with 4 M $H_3PO_4$ led to uniform dispersion of Pt-Ru onto H4M-MCs, resulting in enhancing the electro-catalytic activity of Pt-Ru catalysts.

• Solar Energy
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• v.10 no.3
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• pp.60-65
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• 1990

[ $n^+-p^+$ ] InP homojunction solar cells were fabricated by thermal diffusion of sulphur into a $p^+$-InP wafer($p=4{\times}10^{18}cm^{-3}$), and a SiO film($600{\AA}$ thick) was coated on the $n^+$ layer as an antireflection(AR) coating by an e-beam evaporator. The volume of the cells were $5{\times}5{\times}0.3mm^3$. The front contact grids of the cells with 16 finger pattern of which width and space were $20{\mu}m$ and $300{\mu}m$ respectively, were formed by photo-lithography technique. The junction depth of sulphur were as shallow as about 0.4r m We found out the fabricated solar cells that, with increasing the diffusion time, short circuit current densities($J_{sc}$), series resistances($R_s$) and energy conversion efficiencies(${\eta}$) were increased. The cells show good spectral responses in the region of $5,000-9,000{\AA}$. The short circuit current density, the open circuit voltage( $V_{oc}$), the fill factor(F.F) and the energy conversion efficiency of the cell were $13.16mA/cm^2$, 0.38V, 53.74% and 10.1% respectively.

• Journal of the Korean Electrochemical Society
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• v.17 no.1
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• pp.57-64
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• 2014

Carbon electrodes for capacitive deionization were fabricated through mixing two different carbon powders (activated carbon powder, carbon black) with different particle sizes to investigate physical or electrochemical properties and finally desalination performances of the electrodes with various compositions of two carbon powders in weight and were compared with the electrode consisting of activated carbon. As a result, the electrode structure became more packed as increasing the amount of carbon black and resulted in 10% increase in mesopore fraction. The specific capacitance obtained from cyclic voltammograms of various electrodes showed that the electrode containing carbon black only had 107.4 F/g, while the specific capacitance of the electrode having more amount of carbon black increased and was higher than the one having no carbon black. The results of desalination runs in a capacitive deionization cell exhibited that the electrode having the highest amount of carbon black (1 wt%) in this study had the highest desalting efficiency, and no significant pH variation was observed during the runs. It was analyzed using accumulated charge that the fraction of non-Faraday current increased as the amount of carbon black increased in the electrodes. It can be concluded that the addition of carbon black changed the electrode structure resulting in an increase in the fraction of mesopore and finally enhanced the desalting efficiency by decreasing Faraday current.

• Journal of Digital Contents Society
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• v.18 no.6
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• pp.1199-1205
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• 2017

Global energy consumption is rapidly increasing yearly due to drastic industrial advances, requiring the development of new energy storage devices. For this reason, supercapacitors with fast charge-discharge, long life cycle and high power density is getting attention, and have been considered as one of the potential energy storage systems. In this research, we developed a supercapacitor that consists of amorphous manganese oxide($MnO_2$) electrodes deposited onto carbon cloth substrates using the hydrothermal method. The Fe-doped amorphous $MnO_2$ samples were characterized by X-ray diffraction(XRD), Energy Dispersive X-ray spectroscopy(EDX), as well as scanning electron microscopy(SEM). The electrochemical analysis of the prepared samples were performed using cyclic voltammetry and galvanostatic charge-discharge measurements in 1M $Na_2SO_4$ electrolyte. The test results demonstrate that the supercapacitor based on the Fe-doped amorphous $MnO_2$ electrodes has a specific capacitance as high as 163F/g at 1A/g current density, and good cycling stability of 87.34% capacitance retention up to 1000 cycles.