• The Transactions of the Korean Institute of Power Electronics
• /
• v.19 no.1
• /
• pp.15-22
• /
• 2014

Recently, parallel operation of dc-dc converters has been widely used in distributed power systems. In this paper, a control method to achieve parallel operation of three-phase bi-directional isolated interleaved dc-dc converters is discussed for the battery charging and discharging system which consists of the 32 battery charger/dischargers and two three-phase bi-directional isolated interleaved dc-dc converters. In the boost mode, the battery energy is delivered to the grid, whereas the grid energy is transferred to the battery in the buck mode operation. The average current sharing control method is employed to obtain an equal conducting of each phase current in the three-phase dc-dc converter. By using the proposed method, the imbalance factor is gratefully reduced from 8 percent to 1 percent. Two 2.5kW three-phase bi-directional dc-dc converter prototype have been built and the proposed method has been verified through experiments.

• Journal of Astronomy and Space Sciences
• /
• v.38 no.3
• /
• pp.165-173
• /
• 2021

Apophis is a near-Earth object with a diameter of approximately 340 m, which will come closer to the Earth than a geostationary orbit in 2029, offering a unique opportunity for characterizing the object during the upcoming encounter. Therefore, Korea Astronomy and Space Science Institute has a plan to propose a space mission to explore the Apophis asteroid using scientific instruments such as a laser altimeter. In this study, we evaluate the performance metrics of a laser altimeter using a pseudorandom noise modulation technique for the Apophis mission, in terms of detection probability and ranging accuracy. The closed-form expression of detection probability is provided using the cross correlation between the received pulse trains and pseudo-random binary sequence. And the new ranging accuracy model using Gaussian error propagation is also derived by considering the sampling rate. The operation range is significantly limited by thermal noise rather than background noise, owing to not only the low power laser but also the avalanche photodiode in the analog mode operation. However, it is demonstrated from the numerical simulation that the laser altimeter can achieve the ranging performance required for a proximity operation mode, which employs commercially available components onboard CubeSat-scale satellites for optical communications.

• Journal of Power Electronics
• /
• v.19 no.3
• /
• pp.691-701
• /
• 2019

To solve the problems in the contact charging of inspection robots, a wireless charging system for inspection robots and a control strategy are introduced in this paper. Circuit models of a wireless power system with a compound compensation circuit and a three-phase Class-D resonant inverter are set up based on circuit theory. An output voltage control method based on the equal spread regulation of the phase difference between adjacent phases and the parameter correction method in the primary compound compensation circuit are proposed. The dynamic characteristics of the key parameters varying with the secondary coil position are obtained to further investigate the adaptive location scheme during the access and exit processes of moving robots. Combining the output voltage control method and the adaptive location scheme, a transition control strategy for the standby and operation modes of the wireless charging systems for inspection robots is put forward to realize the system characteristics including the low standby power in the standby mode and the high receiving power in the operation mode. Finally, experiments are designed and conducted to verify the correctness of the theoretical research.

• Geomechanics and Engineering
• /
• v.34 no.3
• /
• pp.303-316
• /
• 2023

With the development and utilization of urban underground space, the artificial ground freezing technology has been widely used in the construction of underground engineering in soft soil areas. The mechanical properties of soft clay changed greatly after freezing and thawing, which affected the seismic performance of underground structures. In this paper, a series of triaxial tests were carried out to study the dynamic response of the freezing-thawing clay under the seismic load considering different dynamic stress amplitudes and different confining pressures. The reduction factor of dynamic shear stress was determined to correct the amplitude of the seismic load. The deformation development mode, the stress-strain relationship and the energy dissipation behavior of the soft clay under the seismic load were analyzed. An empirical model for predicting accumulative plastic strain was proposed and validated considering the loading times, the confining pressures and the dynamic stress amplitudes. The relevant research results can provide a theoretical reference to the seismic design of underground structures in soft clay areas.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 1999.10a
• /
• pp.123-130
• /
• 1999

The bus as a feeder trip should supply equality service to the whole community. But in spite of the change of latent demand to the bus by the variety of regional structural change, the existing bus route can not supply effective feeder service. For cope with the latent demand to the bus, this study establish a concept that frame of the bus operation and management. This study tackled to evidence this fact by analyzing the bus transport problems in terms of the urban growth, and following issues were discussed: 1) the strategy for improvement of bus operation, 2) the land use control which is appropriate for the public transport network, 3) the economical range to justify the bus operation, 4) the allowance for the private transport mode. On the second part of this study, the difference on the bus operation was compared to determine the range within which the bus operation can be justified. This would provide the direction to improve the management for bus operation and fundamental information to develop the bus operation system.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.17 no.9
• /
• pp.2133-2138
• /
• 2013

In this paper, the variation of a steep subthreshold slope at elevated temperature in nanowire n-channel junctionless and inversion mode MuGFETs has been compared. It has been observed that the subthreshold slopes are increased with the increase of the operation temperature in junctionless and inversio-mode transistors. The variation of a subthreshold slope with operation temperature is more significant in junctionless transistor than inversion-mode transistor. The temperature dependence on the variation of a subthreshold slope for different fin widths shows a similar behavior regardless of fin width. From the temperature dependence on the variation of a subthreshold slope for different substrate biases, it has been observed that the variation of a subthreshold slope is less significant when the substrate bias was applied. It is worth noting that one can achieve a subthreshold slope of below 41mV/dec at elevated temperature of 400K using the junctionless MuGFETs with a positive substrate bias.

• Journal of Advanced Marine Engineering and Technology
• /
• v.41 no.3
• /
• pp.245-250
• /
• 2017

Worldwide environmental regulations have been enhanced for emission reduction of greenhouse gases and air pollutants; accordingly, some measures were prepared. Furthermore, the need for effective and reasonable energy-saving methods is growing in accordance with that for environmental pollution minimization. In the case of marine engineering, techniques for the development of eco-friendly vessels have been actively studied, including reduction of exhaust gas emissions, development of alternative fuel, and development of a new propulsion system. In this study, we presented the basic concepts and analyzed the speed, current, voltage, and output power characteristics of each operating mode, i.e., operating mode of battery, generator, and full power.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.22 no.3
• /
• pp.42-49
• /
• 2014

The gasoline direct injection (GDI) system is considerably spreading in automotive market due to its advantages. Nevertheless, since GDI system emit higher particle matter (PM) due to its combustion characteristics, it is difficult to meet strengthened emission regulation in near future. For this reason, a combined GDI with MPI system, so-called, dual injection (DUI) system is being investigated as a supplemental measure for the GDI system. This paper focused on power and fuel consumption effect by injection mode strategy of DUI system in part load and idle engine operating condition. In this study, port fuel injectors are installed on 2.4 liters GDI production engine in order to realize DUI system. And, at each injection mode, DOE (design of experiment) method is used to optimize engine control parameters such as dual injection ratio, start of injection timing, end of injection timing, CAM position and so on. As a consequence, DUI mode shows slightly better or equivalent fuel efficiency compared to conventional GDI engine on 9 points fuel economy mode as well as MPI mode shows less fuel consumption than GDI mode during idle operation. Furthermore, DUI system shows improvement potential of maximum 2.0% fuel consumption and 1.1% performance compared to GDI system in WOT operating condition.

• The Magazine of the IEIE
• /
• v.30 no.3
• /
• pp.287-287
• /
• 2003

• The Magazine of the IEIE
• /
• v.30 no.3
• /
• pp.73-80
• /
• 2003