• 전기학회논문지
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• 제64권2호
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• pp.353-356
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• 2015

Due to high oil prices, environmental pollution, the study of electric vehicles have been actively promoted. Charger for the electric vehicle is being developed using wireless rather than cable options. In this paper, we got more efficiency from using a superconducting transmission coil compared to using a normal coil. We implemented a wireless power transmission system using a magnetic induction at a frequency of 63.1 kHz. For comparison, a transmitter was designed using a superconducting coil and a normal coil. In addition, a receiver used a normal coil to apply for electric vehicles. The applied voltage and current were12 V and 5 A. Efficiency at a distance of 40 ~ 80 mm was measured. As a result, the superconducting transmission coil had a higher efficiency than the normal transmission coil. However, the receiving coil should be normal conductor for stable operation considering that it was put in moving electric vehicle. The efficiency was increased to 44 % at a distance of 40 mm when the diameter of normal receiving coil was 120 mm.

• 유공압시스템학회논문집
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• 제3권4호
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• pp.1-7
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• 2006

A water hydraulic pump is likely to have serious problems of high leakage, friction and low energy efficiency. A water hydraulic pump has commonly a fixed displacement type and its outlet flow is adjusted by controlling rotation speed of the pump, which can be implemented by using an electric inverter. This study aims to investigate energy efficiency of the water hydraulic pump system which is driven by an electric inverter. The study is based on the experimental results. The pump which is used in the study shows relatively good efficiency and low leakage, low friction as well. The reasons for the good performance of pump is also investigated.

• Journal of Power Electronics
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• 제16권1호
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• pp.268-276
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• 2016

A hybrid sinusoidal-pulse current (HSPC) charging method for the Li-ion batteries in electric vehicle applications is proposed in this paper. The HSPC charging method is based on the Li-ion battery ac-impedance spectrum analysis, while taking into account the high power requirement and system integration. The proposed HSPC method overcomes the power limitation in the sinusoidal ripple current (SRC) charging method. The charger shares the power devices in the motor inverter for hardware cost saving. Phase shifting in multiple pulse currents is employed to generate a high frequency multilevel charging current. Simulation and experimental results show that the proposed HSPC method improves the charger efficiency related to the hardware and the battery energy transfer efficiency.

• Journal of Power Electronics
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• 제16권1호
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• pp.102-110
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• 2016

Contactless power transfer technology is gaining increasing attention in city transportation applications because of its high mobility and flexibility in charging and its commensurate power level with conductive power transfer method. In this study, an inductively coupled contactless charging system for a 48 V light electric vehicle is proposed. Although this study does not focus on system efficiency, the generic problems in an inductively coupled contactless power transfer system without ferromagnetic structure are discussed. An active load matching method is also proposed to control the power transfer on the receiving side through a load matching converter. Small signal modeling and linear control technology are applied to the load matching converter for port voltage regulation, which effectively controls the power flow into the load. A prototype is built, and experiments are conducted to reveal the intrinsic characteristics of a series-series resonant inductive power charger in terms of frequency, air gap length, power flow control, coil misalignment, and efficiency issues.

• Journal of electromagnetic engineering and science
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• 제15권3호
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• pp.129-133
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• 2015

This paper presents the dosimetry of a resonance-based wireless power transfer (RBWPT) system for electric vehicles applications. The compact RBWPT system is designed to transfer power at 150-mm distance. The electric and magnetic fields generated by the RBWPT system and the specific absorption rate in the human body model, which stands around the system, are calculated. These analyses are conducted in two cases: the alignment and the misalignment between the transmitter and the receiver. The matching loops are adjusted to maximize the power transfer efficiency of the RBWPT system for the misalignment condition. When the two cases were compared for the best power transfer efficiency, the specific absorption rates (SAR) in the misalignment case were larger than those in the alignment case. The dosimetric results are discussed in relation to the international safety guidelines.

• Journal of Power Electronics
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• 제13권3호
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• pp.497-506
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• 2013

This paper proposes a new method to improve the available battery capacity in electric vehicles by connecting lead-acid batteries with lithium-ion battery in parallel to supply power. In addition, this method combines the discharge characteristics of batteries to improve their efficiency and lower their cost for electric vehicles. A lithium-ion battery set is used to connect with N sets of lead-acid batteries in parallel. The lead-acid battery supplies the initial power. When the lead-acid battery is discharged by the load current until its output voltage drops to the cut-off voltage, the power management unit controls the lead-acid battery and changes it to discharge continuously with a small current. This discharge can be achieved by connecting the lead-acid battery to a lithium-ion battery in parallel to supply the load power or to discharge its current to another lead-acid or lithium-ion battery. Experimental results demonstrates that the available capacity can be improved by up to 30% of the rated capacity of the lead-acid batteries.

• 전기학회논문지
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• 제60권5호
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• pp.955-964
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• 2011

In renewable energy system such as flywheel energy storage system, wind power and solar power, the motor/generator is the important key for offering the electric energy to the electric loads. For example, the heavy and large flywheel is rotated by electromagnetic torque of pemanent magnet synchronous motor (PMSM) and, in case of a breakdown of electric current, the PMSM used as generator supplies electric energy for the various electric utilities using mechanical rotation energy of the flywheel. Thus, design of a motor/generator should be performed in effort to reduce cogging torque and electromagnetic loss for high efficiency. In our paper, a slotless permanent magnet synchronous motor/generator (SPMSM/G) with output power 15kW at the rotor speed 18000rpm is designed from electromagnetic analysis and dynamic performance analysis. In analytical approach, design parameters such as back electro-motive force (back EMF), inductance and electromagnetic torque are derived from analytical method which is one of the electromagnetic analysis method. And using the design parameters, this paper deal with system design considering the driving characteristics and electric load in required power. Finally, the analytical results are verified by the experiment and finite element method (FEM).

• KEPCO Journal on Electric Power and Energy
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• 제1권1호
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• pp.93-97
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• 2015

The combustion tests for Korean anthracite-bituminous coal blend were carried out in the 200 MW utility boiler. The burning characteristics of the blend were studied with a thermogravimetric analyzer (TGA). From the observation of TGA burning profiles, it was found that the presence of bituminous coal in the blend appeared to enhance the reactivity of anthracite in the higher temperature region, indicating certain interactions between the two coals. The plant test showed the boiler operation was reasonably stable with somewhat poor combustion efficiency, and some modification of the combustion environment in the furnace is necessitate for the further stable plant operation.

• 조명전기설비학회논문지
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• 제22권8호
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• pp.38-44
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• 2008

급격한 IT 산업 발전의 산물인 인터넷데이터센터(IDC)는 서버 시스템이 집적된 고밀도 디지털 부하로 구성되는 특징을 가지고 있다. IDC의 디지털 부하 특성을 고려하여 직류배전시스템을 도입하는 경우 전력 변환 체계의 단순화로 효율 향상의 가능성이 일부 제기되어 왔으나, 국내 IDC 환경에서의 효율성이 검증된 사례는 없었다. 본 논문에서는 교류배전방식을 적용한 KT 분당 IDC와 직류배전방식을 적용한 KT 남수원 IDC의 전력 효율을 비교 분석함으로써 국내 IDC 배전체계의 직류화에 따른 효율 개선 효과를 제시하였다. DC 48[V]를 배전하였을 때 직류배전 방식의 효율이 13.2[%] 높은 것으로 도출되었으며, DC 380[V]의 공급을 가정하였을 때에는 25[%] 이상의 효율 향상을 기대할 수 있었다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 전력전자학술대회 논문집
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• pp.3-4
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• 2014

Power line in electric power tunnel generate heat around during power transmission. Rising temperature inside the electric power tunnel reduces the transmission efficiency of the power line. In this study, trying to understand the change in temperature in the electric power tunnel by forced ventilation and natural ventilation when the temperature rise of the electric power tunnel. The results show that average temperature in electric power tunnel by natural ventilation, forced ventilation is $56.55^{\circ}C$, $23.25^{\circ}C$. Therefore electric power tunnel during power transmission needs cooling or ventilation system.