• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.6
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• pp.461-468
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• 2008

This paper presents a novel series connected DC/DC converter and a proper variable phase shift switching method in order to obtain high voltage ratio for fuel cell system. The proposed series connected DC/DC converter has same rectifier and LC filter for DC output voltage, so it can reduce the number of passive devices regardless of the converter number. In the conventional constant phase shift switching method, the proposed series connected DC converters have inverse bias output voltage. In order to overcome this problem, a simple but proper variable phase shift switching method is proposed in the a novel series connected DC/DC converter. In order to verify the proposed system, simulation and experiments are implemented.

• Nuclear Engineering and Technology
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• v.27 no.1
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• pp.141-153
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• 1995

SNU 1.5-MV 직렬형 반데그라프 가속기로부터 얻은 0.5~2.2 MeV He$^{++}$ 빔을 이용하여 러더포드 후방산란 분광법 (RBS, Rutherford Backscattering Spectrometry)으로 여러가지 시료의 표면적층을 분석하였다. 먼저 RBS 분석계통의 신뢰성을 확인하기 위하여 Micromatter사와 Charles Evans & Associates에서 제작한 14종 33개의 표준시료들에 대한 후방산란 실험을 수행하여, 각 층의 두께, 원소조성비 및 주입 이온의 깊이, 분포폭을 측정하였다. 결정된 이 값들은 제시된 값과 3% 이내로 일치하였다 이와 같이 본 RBS 분석계통의 신뢰성을 확인한 후, 분석을 의뢰받은 22종 87개의 시료에 대해, 빔에너지. 후방산란의 기하학적 구조 등의 최적 조건하에서 후방산란 실험을 수행하였다 그 결과, 분석가능한 두께의 한계를 벗어난 2종 3개의 시료를 제외한 나머지 모든 시료에 대해 각 층의 두께, 원소조성비 및 농도분포를 결정할 수 있었으며, 측정치의 통계오차는 8% 이내였다. 다양한 종류의 많은 시료들에 대한 표면적층 분석을 수행한 경험을 통하여, RBS 분석에서 신뢰도 높은 결과를 얻기 위해 분석계통에서 필수적으로 고려해야 할 요소들을 파악할 수 있었으며, 분석 결과에 대한 신뢰도는 분석 계통의 체계화뿐만 아니라 시료의 상태에 따라 크게 좌우됨을 알 수 있었다. 결론적으로 주의 깊은 시료준비와 RBS 분석계통의 최적화를 통해 신뢰도 높은 표면적층 분석이 가능함을 확인하였다.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.170-175
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• 2003

A control algorithm is developed for highly efficient operation of auxiliary power unit (APU) that consists of a diesel engine and a directly coupled induction generator in series hybrid electric Bus (SHEB). In a series hybrid configuration the APU supplies the electric power needed for maintaining the state of charge (SOC) of the battery unit in various conditions of vehicle operation. As the rotational speed of generator does not depend on the vehicle speed, an optimized operation of engine-generator unit based on the efficiency map of each component can be achieved. The output torque of diesel engine can be controlled by the amount of fuel injection, and the power converted from mechanical to electrical energy can be adjusted by generate control unit (GCU) using the decoupling vector control of torque and flux. As for the given reference of the generating power, the multiply of speed and torque, many combinations of operating speed and torque are possible. The algorithm decides the new operating point based on the engine efficiency map and generator characteristic curve. During the transition of operating points, the speed controller saturation is avoided using variable limit and filtering of generator torque reference. A test rig and SHEB consist of a 1.5L diesel engine and a 30kw induction generator are constructed by Hyundai Motor Company.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.1
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• pp.53-58
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• 2016

Modeling of engine coolant temperature was conducted for a series hybrid powertrain system. The purpose of this modeling was a simplification of complex heat transfer process inside a engine cooling system in order to apply it to the vehicle powertrain simulation software. A basic modeling concept is based on the energy conservation equation within engine coolant circuit and are composed of heat rejection from engine to coolant, convection heat transfer from an engine surface and a radiator to ambient air. At the final stage, the coolant temperature was summarized as a simple differential equation. Unknown heat transfer coefficients and heat rejection term were defined by theoretical and experimental methods. The calculation result from this modeling showed a reasonable prediction by comparison with the experimental data.

• The Korean Journal of Applied Statistics
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• v.5 no.2
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• pp.193-209
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• 1992

We consider a Step Life Testing which is deviced for a two-component serial system with the considerably long life time. In the modelling stage we discuss the bivariate exponential distribution suggested by Block and Basu as the bivariate survival function for the two-component system, and develope the cumulative exposure model introduced by Nelson so that it can be used under the bivariate function. We consider inference on the component life time when the components are at work in the system by combining the information from system life test and that from the component tests carried out separately under the controlled environment. In data analysis, maximum likelihood estimators are discussed with the initial value obtained by an weighted least square method. Finally we discuss the optimal time for changing the stress in the simple step stress life testing.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.1
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• pp.92-98
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• 2013

There are lots of studies about hybrid electric vehicles (HEVs) because of the global warming and energy problems. Series and parallel HEVs are the common types of many developing hybrid vehicle types. Series HEV uses engine only as the generator for the battery but parallel HEV utilizes engine for driving and generating of the vehicle. In this paper, backward simulations based on dynamic programming were conducted for the fuel economy analysis of two different types of hybrid transit buses depending on driving cycles. It is shown that there is a relation between the type of HEV and the characteristics of driving cycles. Regarding the aggressiveness, the series hybrid bus is more efficient than the parallel system on highly aggressive driving cycle. On the other hand, the parallel hybrid bus is more efficient than the series system on low aggressive driving cycle. Based on this results of the paper, it is expected to choose more efficient type of the hybrid buses according to the driving cycle.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.1
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• pp.35-41
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• 1997

A series-fed microstrip array antenna of beamwidth $10^{\circ}$, squint angle $80^{\circ}$ and SLL -15 dB below is designed. Series-fed arrays are formed by interconnecting all the elements by high-impedance transmission lines and feeding the power at the first element and it is a traveling-wave antenna which is terminated with a matched load. Radiation patterns and impedance matching of the antenna are analyzed by Ensemble 4.0, which is a popular software package for designing printed antennas and arrays. The squint angle of beam can be controlled by the spacing between the elements. The major advantages of series-fed array antennas are that feed arangement is compact and the losses associated with the feeding network are less than those of a corporate feed type. The antennas are fabricated on the RT/Duroid Laminates of 62 mil thickness. The experimental results are very close to the specifications to be designed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.12
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• pp.935-941
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• 2018

In this study, we propose a suitable magnetic resonant wireless power transfer(WPT) system topology for size-limited implant medical devices(IMDs). The proposed modified series-parallel topology(mSPT) can be implemented by adding an inductor in series to the parallel-connected Rx coil and a capacitor. The topology achieves high efficiency when the Rx coil has a small inductance. The validity and operating conditions of the system are verified theoretically through circuit analysis. Experiments were conducted with bio-blocks, which are made of pork fat and muscle. When the Rx coils were inserted into the blocks at a depth of 2.5~10 mm, mSPT showed 17.79 % improved efficiency on average compared with the conventional series-series topology(SST). In the case of 32 dBm WPT in air, the Rx coil's heating rate for the mSPT was $0.18^{\circ}C/s$, whereas the SST was $0.75^{\circ}C/s$. It was confirmed that the mSPT is more suitable for an IMD-targeted WPT system.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.6
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• pp.432-440
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• 2010

In this paper, a LC series resonant boost converter using a single switch is proposed. The proposed topology contains additional passive elements in the conventional boost converter and performs Zero Voltage Switching(ZVS) without an additional auxiliary switch when a main switch turned on and off. The switch off time of the proposed system determined by LC series resonance, thus a on-time variable Pulse Frequency Modulation(PFM) method is adapted to control output voltage in the proposed converter. Operational modes of the proposed topology are divided with respected to the current conduction paths and then through the theoretical analysis and experimental results, operational modes and characteristics of the proposed converter are verified.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.21-24
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• 1999

멀티미디어 시대로의 진입에 따른 인터넷에서의 실시간 데이터 전송을 위한 어플리케이션의 요구에도 불구하고 현재의 인터넷은 최선형 서비스만을 제공할 뿐 QoS(quality of service)를 제공하지 못하고 있다. 이에 인터넷 표준화 기구에서는 종합서비스(IS : integrate service)모델을 정했다. 〔5〕 그러나 기존의 shared LAN 환경에 이를 적용하기에는 자원의 공유로 인한 어려움이 있다. 반면. 직렬 버스의 표준으로 자리잡은 IEEE 1394 고속 직렬 버스〔1〕〔2〕는 예약된 대역폭을 보장할 수 있을 뿐만 아니라 고속통신이 가능하여 IS 모델의 적용에 적합한 기술이라고 할 수 있다. IS over 1394 프로토콜〔8〕은 IS 모델을 IEEE 1394 고속 직렬 버스에 적용하기 위한 프로토콜로써 본 논문에서는 이의 구현을 위한 구조를 고찰하였다.