• International Journal of Air-Conditioning and Refrigeration
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• 제6권
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• pp.113-123
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• 1998

The present study is to investigate the effect of experimental parameters on the heat transfer characteristics of a spherical capsule storage system using paraffins. N-Tetradecane and mixture of n-Tetradecane 40% and n-Hexadecane 60% were used as paraffins. Water with inorganic material was also tested for the comparison. The experimental parameters were varied for the Reynolds number from 8 to 16 and for the inlet temperature from -7 to 2$^{\circ}C$. Measured local temperatures of spherical capsules in the storage tank were utilized to calculate charging and discharging times, dimensionless thermal storage amount, and the average heat transfer coefficients in the tank. Local charging and discharging times in the storage tank were significantly different. The effect of inlet temperature on charging time was larger than that on discharging time, but the effect of Reynolds number on charging time was smaller than that on discharging time. Charging time of paraffins was faster by 11~72% than that of water with inorganic material, but little difference of discharging time was found among them. The effect of Reynolds number on the dimensionless thermal storage was less during charging process and more during discharging process than the effect of inlet temperature. The effect of the inlet temperature and the Reynolds number on the average heat transfer coefficient of the storage tank was stronger during discharging process than during charging process. The average heat transfer coefficients of the spherical capsule system using paraffins were larger by 40% than those using water.

• 설비공학논문집
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• 제9권3호
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• pp.354-363
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• 1997

The purpose of the present work is to show the best thermal storage material and the sensitivity of the parameters on the thermal performance by experimentally investigating the effects of the parameters on the thermal performance of the spherical capsule system using paraffins superior to the commercial one. The paraffins were n-Tetradecane and the mixture of n-Tetradecane 40% and n-Hexadecane 60%. The experimental parameters were the Reynolds number of 8, 12, and 16 and the inlet temperature of-7, -4, -1, and $2^{\circ}C$. The charging and the discharing time, the dimensionless thermal storage amount, and the averge heat transfer coefficient in the tank were obtained by utilizing the local temperature variation in the tank. The local charging and discharging time in the tank was axially and radially different a lot. The effects of the inlet temperature on the charging and the discharging time were larger during the charging process than during the discharging process, but the effects of the Reynolds number on the charging and the discharging time were in reverse order. The paraffins were better by 11~72% than the water with the inorganic material in the charging time aspect, but no difference in the discharging time aspect. The effects of the Reynolds number on the dimensionless thermal storage amount were smaller than the effects of the inlet temperature during the charging process, but in reverse order during the discharging process within the working range of the experimental parameters. The effects of the inlet temperature and the Reynolds number on the average heat transfer coefficient were larger during the discharging process than during the charging process. The average heat transfer coefficient for the paraffins was larger by 40% maximum than that for the commercial material during the charing and the discharging process.

• Journal of Electrical Engineering and Technology
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• 제9권3호
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• pp.803-811
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• 2014

The moment when Electrical Vehicle (EV) starts charging or discharging is one of the most important parameters in estimating the impact of EV load on the grid. In this paper, a decision-making problem of determining the start time of charging and discharging during allowed period is proposed and studied under the uncertainty of real-time price. Prospect theory is utilized in the decision-making problem of this paper for it describes a kind of decision making behaviors under uncertainty. The case study uses the parameters of Springo SGM7001EV and adopts the historical realtime locational marginal pricing (LMP) data of PJM market for scenario reduction. Prospect values are calculated for every possible start time in the allowed charging or discharging period. By comparing the calculated prospect values, the optimal decisions are obtained accordingly and the results are compared with those based on Expected Utility Theory. Results show that with different initial State-of-Charge ($SoC_0$) and different reference points, the optimal start time of charging can be the one between 12 a.m. to 3 a.m. and optimal discharging starts at 2 p.m. or 3p.m. Moreover, the decision results of Prospect Theory may differ from that of the Expected Utility Theory with the reference points changing.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1146-1148
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• 2007

This paper proposes a method to improve the charging speed and discharging performance of a high voltage capacitor used in a portable medical device. The improvement of the charging speed was achieved by duty cycle control. The discharging performance was carried out by varying the phase duration and the leading edge voltage of the output according to the transthoracic impdedance of the patient. As a result, the improvement in the charging speed and the performance of the discharging parameters shorten the patient treatment time.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.2089-2091
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• 2000

Pulsed power systems consist of a capacitor bank, an isolated high-voltage charging power-supply, high-current bus-work for charging and discharging and a control system. In such pulsed power systems, the operating-lifetime of the capacitors is closely dependent on the voltage reversal. Hence, most capacitor-discharging systems includes crowbar circuits. The crowbar circuit prevents the capacitor recharging with reverse voltage. Usually it consists of crowbar resistors and high pulse-current diode-stacks connected in series. The requirements for the diode-stacks are fast-recovery time and high-voltage and large-current ratings, which results in the high cost of the pulsed-power system. This paper presents a protection scheme of a charging and discharging system of a 500kJ capacitor bank using a low-cost crowbar circuit and safety-fuses.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2011년도 전력전자학술대회
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• pp.429-430
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• 2011

This paper presents a simple and cost-effective stand-alone rapid battery charging system of 30kW for electric vehicles. The proposed system mainly consists of active front-end rectifier of neutral point clamped 3-level type and non-isolated bi-directional dc-dc converter of multi-phase interleaved half-bridge topology with coupled inductors. The charging system is designed to operate for both lithium-polymer and lithium-ion batteries. The complete charging sequence is made up of three sub-interval operating modes; pre-charging mode, constant-current mode, and constant-voltage mode. The pre-charging mode employs the staircase shaped current profile to accomplish shorter charging time while maintaining the reliable operation of the battery. The proposed system is able to reach the full-charge state within less than 16min for the battery capacity of 8kWh by supplying the charging current of 67A. The optimal discharging algorithm for Vehicle to the Grid (V2G) operation has been adopted to maintain the discharging current of 1C. Owing to the simple and compact power conversion scheme, the proposed solution has superior module-friendly mechanical structure which is absolutely required to realize flexible power expansion capability in a very high-current rapid charging system.

• 조명전기설비학회논문지
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• 제29권8호
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• pp.40-48
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• 2015

In this paper, battery charging and discharging circuit with a single voltage power supply is proposed. The proposed circuit has the separated current path and charging-monitoring sequence control scheme. In the charging sequence, the proposed 2-level comparator combined with control signal of the micro-processor can control the constant charging current to protect the over current of the battery. Furthermore, the proposed circuit uses a periodic main power switch control to detect the discharging characteristics to estimate the approximated battery life-time. In the experiments, the proposed emergency power supply for emergency call system has 89% efficiency with 98% power factor. And the proposed sequence control scheme is well operated in the designed emergency power system.

• 플랜트 저널
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• 제16권4호
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• pp.40-44
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• 2020

본 연구에서는 2 V 연축전지의 극판에 펄스파를 인가하여 충전과 방전을 반복한 후 충전용량을 분석하였다. 발전소에서 비상용 전원으로 많이 사용하고 있는 연축전지는 충전과 방전이 반복됨에 따라 방전시 극판에 달라붙어 있던 황산염이 충전 시 이탈하지 아니하고 극판에 피막형태로 달라붙어 절연막을 형성하여 연축전지의 전기반응 통로를 차단하기 때문에 충전용량이 줄어들게 된다. 이에 12 V 연축전지에 많이 사용하고 있는 펄스파를 2 V 연축전지 극판에 인가하고 충전용량을 분석하였다. 펄스파로는 4 V, 20 mA의 전압과 전류에 각각 10 kHz, 20 kHz, 30 kHz 주파수의 펄스파를 사용하였다. 실험결과를 분석한 결과 펄스파를 인가하지 않은 연축전지는 초기 충전용량보다 약 18 % 충전용량이 감소한 반면, 펄스파를 인가한 연축전지는 충전용량의 감소가 훨씬 적었고, 특히 20 kHz 주파수의 펄스파에서 충전용량이 0.56 %만 감소되었다. 이것은 20 kHz 주파수의 펄스파가 다른 주파수의 펄스파보다 극판의 황산염 피막을 분해하는데 더 적합하여 양전하와 음전하의 이동이 활발해진 것으로 판단된다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 추계종합학술대회 논문집
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• pp.216-219
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• 1999

A simple two-terminal cyclic current-voltage(I-V) technique is used to measure the current-transients in MOS capacitors. Distinct charging/discharging currents were measured and analyzed as a function of (1) the hold time. (2) the gate polarity during the FNT electron injection, (3) the injection fluence and (4) the annealing time after the injection had stopped. Discharging and charging current-transients were strongly dependent upon the conditions for forming the inversion layer and the density of interface traps caused during the FNT electron injection, respectively. Several tentative mechanisms were suggested in the current work.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2227-2235
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• 2018

Under the current policies and compensation rules in South Korea, Photovoltaic (PV) generation supplier can maximize the profit by combining PV generation with Energy Storage System (ESS). However, the existing operational strategy of ESS is not able to maximize the profit due to the limitation of ESS capacity. In this paper, new ESS scheduling algorithm is introduced by utilizing the System Marginal Price (SMP) and PV generation forecasting to maximize the profits of PV generation supplier. The proposed algorithm determines the charging time of ESS by ranking the charging schedule from low to high SMP when PV generation is more than enough to charge ESS. The discharging time of ESS is determined by ranking the discharging schedule from high to low SMP when ESS energy is not enough to maintain the discharging. To compensate forecasting error, the algorithm is updated every hour to apply the up-to-date information. The simulation is performed to verify the effectiveness of the proposed algorithm by using actual PV generation and ESS information.