• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.679-679
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• 2013

태양전지는 계속되는 유가상승과 무소음 무공해의 녹색에너지원이라는 점에서 각광받고 있다. 더욱이 발전단가가 높기 때문에 특히 저가의 다결정 실리콘 태양전지의 연구가 활발히 진행되고 있다. 태양전지의 texturing 공정은 광 포획 효과를 극대화 시킨다. 이에 따라 웨이퍼 표면에 텍스쳐를 형성하여, 광학적 손실을 줄이는데, 일반적으로 alkaline etching (WET) 공정과 reactive ion etching (RIE) 공정이 사용된다. 본 연구에서는 RIE, WET 공정을 사용하여 만든 texturing 구조의 태양전지를 모듈 공정 진행 전 특성평가를 한 후 다시 모듈 공정 후 특성평가를 진행하였다. 특성평가는 태양전지의 전류-전압 곡선을 통해 개방전압, 단락전류, 곡선인자 을 측정하고, 파장에 따른 양자효율 및 반사율을 측정하였다. 또한 태양전지의 전기에너지를 가하여 생성되는 전계발광 현상과 NIR camera를 이용하여 Grain의 Dark Area 및 Micro crack을 검출하였다. 이와 같은 모듈 공정 전/후 특성을 측정하고, 이를 비교 분석하여 BIPV 적용 시 태양전지의 동작특성을 확인하였다.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.185-187
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• 2000

Fault current is flowed into 154/23kV M. Tr when line-to-ground fault occurs in power system. NGR(Neutral Grounded Reactor) is set up in order to prevent M.Tr fault by limiting magnitude of fault currents. Here, disconnection of NGR causes voltage increase by L-C resonance and line-to-ground fault in an unearthed system results in voltage increase at healthy phases. So Over Voltage Ground Relay(OVGR) is used for tripping M.Tr. Also, buses at second phases of M.Trs are all connected with section circuit breakers closed for the purpose of parallel operation and load shedding. In case of speciality buses are comprised of power cable in part for GIS connection. When no-load charged cable or bus is open by a section CB, unbalanced voltage charged on the bus is induced. Also discrepant opening time for circuit breakers on different phases gives rise to unbalanced zero sequence voltage. It was observed that this zero sequence voltage detected in the 22.9kV P.T (Potential Transformer for bus) mal-operated 59GT and tripped M.Tr. The zero sequence voltage of which vanishing time is longer than relay operating time came out by EMTDC simulation. Also, it was shown that the voltage waves of actual test are similar to those of simulation. On the basis of above results, R-C circuit complement on the relay without any effect on a power system made operating time of the relay longer than vanishing time of distorted waves. Consequently, operating time of the relay was delayed and magnitude of distorted waves was decreased by increasing time constant of the relay.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.3
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• pp.75-84
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• 2005

Since an unexpected fault of induction motor drive systems can cause serious troubles in many industrial applications, which the technique is required to diagnose faults of a voltage-fed PWM inverter for induction motor drives. The considered fault types are rectifier diodes, switching devices and input terminals with open-circuit faults, and the signal for diagnosis is derived from motor currents. The magnitude of dq-current trajectory is used for the feature extraction of a fault and PCA LDA are applied to diagnose. Also, we show results with respect to the execution time because of the possibility to use that a diagnosis software is embedded in the controllers of medium and small size induction motors drive for real-time diagnosis. After we performed various simulations for the fault diagnosis of the inverter, the usefulness of proposed algerian was verified.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.329.2-329.2
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• 2014

지난 수년간 태양전지의 광전변환효율을 높이기 위해 자가 조립된 InAs 또는 GaSb와 같은 양자점을 GaAs 단일 p-n 접합에 적용하는 연구를 개발해 왔다. 그러나 양자점의 흡수 단면적에 의한 광 흡수도는 양자점층을 수십 층을 쌓으면 증가하지만 활성층에 결함을 생성시킨다. 생성된 결함은 운반자트랩으로 작용하여 태양전지의 광전변환효율을 감소시킨다. 본 실험에서는 양자점이 적용된 태양전지와 적용되지 않은 태양전지의 광전변환 효율을 비교하고, 깊은준위 과도용량 분광법을 이용하여 결함상태를 측정 및 비교함으로써, 활성층 내부에 생성된 결함이 광전변환 효율에 미치는 영향을 분석하였다. 소자구조는 분자선 증착 방법을 이용하여, 먼저 n+-형 GaAs기판위에 n+-형 GaAs를 250 nm 증착한 후, 도핑이 되지 않은 GaAs활성층을 $1{\mu}m$ 두께로 증착하였다. 마지막으로 n+ 와 p+-형 GaAs를 각각 50, 750 nm 증착함으로써 p-i-n구조를형성하였다. 여기서, n+-형 GaAs 과 p+-형 GaAs의 도핑농도는 동일하게 $5{\times}1018cm-3$로 하였다. 또한 양자점을 태양전지 활성층에 20층을 형성하였다. 이때 p-i-n 태양전지 와 양자점 태양전지의 광전변환 효율은 각각 5.54, 4.22 % 를 나타내었다. p-i-n 태양전지의 개방 전압과 단락전류는 847 mV, 8,81 mA이며 양자점 태양전지는 847 mV, 6.62mA로 확인되었다. 태양전지의 전기적 특성을 측정하기 위해 소자구조 위에 Au(300nm)/Pt(30nm)/Ti(30nm)의 전극을 전자빔증착장치로 증착하였으며, 메사에칭으로 직경 $300{\mu}m$의 태양전지 구조를 제작하였다. 정전용량-전압 특성 및 깊은준위 과도용량 분광법을 이용하여 태양전지의 결함분석 및 이에 따른 광전변환 특성인자와의 상관관계를 논의할 것이다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.236-236
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• 2010

단일접합 $n^+-p/p^+$ (p-emitter) 및 $p^+-n/n^+$ (n-emitter) GaAs 태양전지 (Solar Cell)를 각각 제작하여, 그 소자특성을 비교 분석하였다. AM 1.5 (1 sun, $100\;mW/cm^2$) 표준광을 조사할 경우, p-emitter/n-emitter 소자의 개방회로전압 (Voc), 단락회로전류 (Jsc), 충전율 (FF), 효율 (Eff)은 각각 0.910/0.917 V, $15.9/16.1\;mA/cm^2$, 78.7/78.9, 11.4/12.1%로서, n-emitter 소자가 다소 크지만 거의 비슷한 값을 가지고 있었다. 태양전지의 집광 특성을 분석하기 위하여 조사광의 출력에 따른 태양전지의 소자 특성을 측정하였다. 조사광 강도가 높아짐에 따라 p-emitter 소자의 특성은 점진적으로 증가하는 반면, n-emitter는 1.3 sun에서 약 1.4 배의 최대 효율 (17%)을 나타내고 조사광이 더 증가함에 따라 급격히 감소하는 특성을 보여 주었다. (그림 참고) 본 연구에서 사용한 2종류 소자의 층구조는 서로 반대되는 대칭구조로서, 모두 가까이에 위치하고 있는 표면전극 (surface finger) 방향으로 소수전하 (minority carrier)가 이동하고 다수전하 (majority carrier)는 기판 (두께 $350\;{\mu}m$)을 통한 먼 거리의 후면전극 (back electrode)으로 표류 (drift)되도록 설계되어 있다. 이때, n-emitter에서는 이동도 (mobility)와 확산길이 (diffusion length)가 높은 전자가 후면전극으로 이동하기 때문에 적정밀도의 전자-정공 쌍 (EHP)이 여기될 경우에는 Jsc와 Eff가 극대화되지만, 조사광 강도 또는 EHP가 더 높아질 경우에는 직렬저항의 증가와 함께 전류-전압 (I-V)의 이상인자 (ideality factor)가 커짐으로서 FF와 효율이 급격히 감소한 결과로 분석된다. 현재 전산모사를 통한 자세한 분석을 진행하고 있으며, 본 결과는 효율 극대화를 위한 최적 층구조 및 도핑 밀도 설계에 활용할 수 있을 것으로 판단된다.

• Applied Chemistry for Engineering
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• v.28 no.1
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• pp.118-124
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• 2017

An air cooling, open cathode type polymer electrolyte membrane fuel cell (PEMFC) has the advantages of system simplification and cost effectiveness. Open cathode PEMFC could suffer from reduced performance due to the membrane dehydration in low humidity of air. Effects of the cathode air flow rate, anode purge interval and long term storage on PEMFC performance were investigated in this work. Fan voltage is an important factor on air cooling PEMFC performance because the cathode air flow rate and stack temperature were controlled by fan voltage. The dead ended anode (DEA) method was applied to increase hydrogen usage. Periodical purge was used to discharge accumulated water and gas. The influence of long term non-operating condition on PEMFC performance degradation due to the membrane dehydration was also studied and the quick recovery method was developed.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.346-349
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• 2013

This paper describes a triple-input energy harvesting circuit using solar, vibration and thermoelectric energy with MPPT(Maximum Power Point Tracking) control. The designed circuit employs MPPT control to harvest maximum power available from a solar cell, PZT vibration element and thermoelectric generator. The harvested energies are simultaneously combined and stored in a storage capacitor, and then managed and transferred into a sensor node by PMU(Power Management Unit). MPPT controls are implemented using the linear relation between the open-circuit voltage of an energy transducer and its MPP(Maximum Power Point) voltage. The proposed circuit is designed in a CMOS 0.18um technology and its functionality has been verified through extensive simulations. The designed chip occupies $945{\mu}m{\times}995{\mu}m$.

• Journal of IKEEE
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• v.19 no.2
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• pp.201-209
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• 2015

This paper describes a battery charger using photovoltaic energy harvesting with MPPT control. The proposed circuit harvests maximum power from a PV(photovoltaic) cell by employing MPPT(Maximum Power Point Tracking) control and charges an external battery with the harvested energy. The charging state of the battery is controlled according to the signals from a battery management circuit. The MPPT control is implemented using linear relationship between the open-circuit voltage of a PV cell and its MPP voltage such that a pilot PV cell can track the MPP of a main PV cell in real time. The proposed circuit is designed in a $0.35{\mu}m$ CMOS process technology and its functionality has been verified through extensive simulations. The maximum efficiency of the designed entire system is 86.2% and the chip area including pads is $1.35mm{\times}1.2mm$.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.577-580
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• 2014

In this paper an auto-switching dual-input energy harvesting circuit is proposed. Since the maximum power points of a thermoelectric generator(TEG) output and a vibration device(PEG) output is 1/2 of their open-circuit voltage, an identical MPPT controller can be used for both energy sources. The proposed circuit monitors the outputs of the TEG and PEG, and chooses the energy source generating a higher output using an auto-switching controller, and then harvests the maximum power from the selected device using a MPPT controller. The harvested energy is boosted through a charge pump and stored in a storage capacitor. The stored energy is provided to a load through a PMU(Power Management Unit). The proposed circuit is designed in a $0.35{\mu}m$ CMOS process and its functionality has been verified through extensive simulations. The designed chip occupies $1.4mm{\times}1.2mm$ including pads.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.1
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• pp.71-76
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• 2022

Since brightness is proportional to the operating current, a method of connecting several LEDs in series and driving with a constant current source is widely used for driving circuits of LED lights. Because several LEDs are connected in series, if some LEDs open due to a fault, the current path is broken and all other LEDs connected in series are turned off. In this paper, we designed a circuit to solve this problem by connecting a Zener diode having a breakdown voltage of about 0.4V higher than the LED operating voltage in parallel with each LED to create a current bypass in case of LED failure. Through simulations and experiments, it was confirmed that the current of the Zener diode hardly flows when the LED is operating normally, and that the Zener diode stably operates as a current bypass when the LED fails.