• Solar Energy
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• v.19 no.3
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• pp.23-28
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• 1999

The thermal performance of storage brick, containing microencapsulated PCM(phase change material), was investigated for utilization as a floor heating system. Sodium acetate trihydrate($CH_3COONa{\cdot}3H_2O$) was selected for the PCM and was encapsulated. The thermal storage brick was manufactured with mixing cement mortar having 10%, 20% PCM contents, respectively. Four different flow rates and three different cooling temperatures was used in this work for analyzing the heat charging and discharging characteristics of the thermal storage brick. The result showed that cycle time was shortened as the PCM content was increased and as the mass flow rate was increased. The same effect was obtained when the cooling temperature was decreased. For each thermal storage brick the overall heat transfer coefficient(U-value) was constant for a 0% brick, but was increased with time for the bricks containing microencapsulated PCM.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.424-430
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• 2001

Cut-off 전압 변화에 따른 충방전 특성을 알아보기 위하여 Mn을 다른 전이 금속이 Co와 Ni로 소량 치환시킨 Li(M $n_{1-{\delta}}$ $n_{\delta}$)$_2$ $O_4$(M=Ni, Co, $\delta$=0, 0.05, 0.1, 0.2)를 고상 반응법으로 80$0^{\circ}C$에서 48시간 동안 유지하여 합성하였다. 충방전의 cut-off 전압은 2.5~4.4V, 3.0~4.5V, 3.5~4.5V, 3.5V~4.7V의 네 가지 전압범위고 하였다. 충방전 실험결과, Li(M $n_{1-{\delta}}$ $n_{\delta}$)$_2$ $O_4$의 용량은 각각 Co와 Ni의 $\delta$=0.1에서 최대를 보였다. Co 치환 조성 재료와 순물질 모두에서 최대의 용량을 보인 cut-off 전압대는 3.5~4.5V 이었는데 이때의 Li(M $n_{0.9}$ $Co_{0.1}$)$_2$ $O_4$와 LiM $n_2$ $O_4$의 초기 충전용량과 초기 방전용량은 각각 118, 119mAh/g과 114, 104mAh/g 이었다. 또한 모든 cut-off 전압대에서 Li(M $n_{0.9}$ $Co_{0.1}$)$_2$ $O_4$는 순수한 LiM $n_2$ $O_4$보다 더 높은 용량과 우수한 싸이클 성능을 보였으며 그 결과는 밀착형 전지구성에서도 일치하였다.하였다.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.6
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• pp.587-593
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• 2011

A new high power density and low cost Photovoltaic Power Conditioning System (PV PCS) with energy storage system is proposed. Its high power density and cost effectiveness can be achieved through the unification of the maximum power point tracker and battery charger/discharger. Despite of the reduced power stage, the proposed system can achieve the same performances of maximum power point tracking and battery charging/discharging as the conventional system. Moreover, the high voltage stress across the link-capacitor can be relieved through the series-connected link-capacitor with the battery. Therefore, a large number of series/parallel-connected link-capacitors can be reduced by 4-times. Especially, when the utility power failure happens, both photovoltaic and battery energies can be supplied to the load with only one power stage. Therefore, it features a simpler structure, less mass, lower cost, and fewer devices. Finally, to confirm the operation, validity, and features of the proposed system, theoretical analysis and experimental results from a single phase AC 220Vrms/1.5kW prototype are presented.

• Journal of Digital Convergence
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• v.14 no.7
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• pp.193-200
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• 2016

Research and development of energy self-consumption introducing photovoltaic and energy storage system at home is very active. This system can manage the home energy in which it charges the electricity generated during the day and uses it during high electricity bills. However, it not yet made up the residential real-time pricing in Korea but it can reduce electricity usage to a certain target on the progressive. In order to introduce the home photovoltaic, it requires PCS(Power Conditioning System). This converts the direct current into alternating current by the electricity generated and used to perform charging and discharging of the energy storage system. The market for self-consumption smart home system is currently increasing because the interests of the general public about solar power, energy storage systems increased. The result of this study is installed on the room environment and the effect was analyzed on the assumption of real-time pricing.

• Journal of the Korean Institute of Telematics and Electronics
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• v.10 no.1
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• pp.18-26
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• 1973

In AM detection system, when the ratio of the frequency of the carrier to that of the modulating signal becomes less than a ratio of approximately 10:1, AM detectors become unable to detect the impressed signal in a satisfactory waveform. The failure of detecting such a super wide-band AM signal resulting from charging and discharging transient phenomena in associated diode circuit during the detecting of AM signal, has been a cause of limiting the channel capacity in AM or FM super multiplexing systems. This Paper presents the "Poly-phase Envelope Detection System" as a suitable method to solve the problem and the analyses of the system suggested. This system will make it possible to take the envelope out of the impressed AM signal to any desired degree of accuracy even when the ratio of the frequency of the carrier to that of the modulating signal approaches unity. Experiments were carried out to verify the validity of the theory of Poly-phase Envelope Detection System by adopting the frequency conversion method from among the two proposals.proposals.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.5
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• pp.37-42
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• 2012

In this paper, a new charge pump is proposed to reduce the timing mismatch in the conventional current-steering charge pumps. Conventional current-steering charge pumps used NMOS input stages both for UP and DOWN signals, which resulted in different numbers of stage for UP and DOWN delay paths. The proposed charge pump has equalized the numbers of stages for UP and DOWN signals by using a PMOS stage for the DOWN signal. The simulation results show that the conventional current-steering charge pump has 14ns and 6ns for optimized timing mismatches between UP and DOWN signals for turn-on and turn-off, respectively. On the other hand, the proposed charge pump has improved timing mismatches of 6ns and 5ns for turn-on and turn-off, respectively. As a result, the reference spurs are reduced from -26dBc to -39dBc for the proposed charge pump. The proposed charge pump was designed by using $0.18{\mu}m$ CMOS technology. The measurement results show that the maximum variation of the charging and discharging current over the charge pump output voltage range of 0.3~1.5V is approximately 1.5%.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.5
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• pp.362-366
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• 2000

$Li_{0.44}MnO_2$cathode material has high reversibility during lithium insertion processes and is not easily damaged through over-charging or over-discharging. $Mn_2O_3$is often present as an impurity phase, and reduce the electrochemical capacity of electrode because this phase is electrochemically inert. Adding of excess NaOH reduced the $Mn_2O_3$to the content under undetectable by X-ray diffraction. Because the capacity can be increased in the cathode materials with larger unit cell, some of the manganese was replaced with titanium having larger ion size, and powders with the formula $Li_{0.44}T_{iy}Mn_{1-y}O_2$(where y = 0.11, 0.22, 0.33, 0.44, and 0.55) was synthesized and characterized. A maximum reversible capacity of 150 mAh/g was obtained for $Li/P(EO)_8$LiTFSI/$Li_{0.44}Ti_{0.22}Mn_{0.78}O_2$cells in electrochemical potential spectroscopy (ECPS) experiments. Cells with the titanium-doped manganese oxides exhibited a fade rate of 0.12 % or less per cycle.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.433-436
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• 2013

Carbon-coated $Li_3V_2(PO_4)_3-LiMnPO_4$ composite cathode materials are first reported in this work, prepared by the mechanochemical process with a complex metal oxide as the precursor and sucrose as the carbon source. X-ray diffraction pattern of the composite material indicates that both olivine $LiMnPO_4$ and monoclinic $Li_3V_2(PO_4)_3$ co-exist. We further investigated the electrochemical properties of our $Li_3V_2(PO_4)_3-LiMnPO_4$ composite cathode materials using galvanostatic charging/discharging tests, where our $Li_3V_2(PO_4)_3-LiMnPO_4$ composite electrode materials exhibit the charge/discharge efficiency of 91.9%, while $Li_3V_2(PO_4)_3$ and $LiMnPO_4$ exhibit the efficiency of 87.7 and 86.7% in the first cycle. The composites display unique electrochemical performances in terms of overvoltage and cycle stability, displaying a reduced gap of 141.6 mV between charge and discharge voltage and 95.0% capacity efficiency after $15^{th}$ cycles.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.33-38
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• 2015

Energy storage systems (ESSs) have been utilized widely in the world to optimize the power operation system and to improve the power quality. As lithium secondary batteries are the main power supplier for ESSs, it is very important to predict its cycle and power degradation behavior. In particular, the power, one of the hardest electrochemical properties to measure, needs lots of resources such as time and facilities. Due to these difficulties, computer modelling of lithium secondary batteries is applied to predict the DC-IR and power value during charging and discharging as a function of state of charge (SOC) by using pulse-based measurement methods. Moreover, based on the hybrid pulse power characteristics (HPPC) and J-Pulse (JEVS D 713, Japan Electric Vehicle Association Standards) methods, their electrochemical properties are also compared and discussed.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.228-238
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• 2010

There is an increasing interest in research to help overcome the energy crisis that has been focused on energy storage applications in various parts of power systems. Energy storage systems are good at enhancing the reliability or improving the efficiency of a power system by creating a time gap between the generation and the consumption of power. As a contribution to the various applications of storage devices, this paper describes a novel algorithm that determines the power and storage capacity of selected energy storage devices in order to improve upon railroad system efficiency. The algorithm is also demonstrated by means of simulation studies for the Korean railroad lines now in service. A part of this novel algorithm includes the DC railroad powerflow algorithm that considers the mobility of railroad vehicles, which is necessary because the electric railroad system has a distinct distribution system where the location and power of vehicles are not fixed values. In order to derive a more accurate powerflow result, this algorithm has been designed to consider the rail voltage as well as the feeder voltage for calculating the vehicle voltage. By applying the resultant control scheme, the charging or discharging within a specific voltage boundary, energy savings and a substation voltage stabilization using storage devices are achieved at the same time.