• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1721-1735
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• 2016

Power-efficient base station (BS) operation is one of the important issues in future green cellular networks. Previously well-known BS operation schemes, the cell zooming scheme and the cell wilting and blossoming scheme, require tight cooperation between cells in cellular networks. With the previous schemes, the non-cooperative BSs of a serving cell and neighboring cells could cause coverage holes between the cells, thereby seriously degrading the quality of service as well as the power saving efficiency of the cellular networks. In this paper, we propose a novel power-efficient BS operation scheme for green downlink heterogeneous cellular networks, in which the networks virtually adjust the coverage of a serving macrocell (SM) and neighboring macrocells (NMs) without adjusting the transmission power of the BSs when the SM is lightly loaded, and the networks turn off the BS of the SM when none of active users are associated with the SM. Simulation results show that our proposed scheme significantly improves the power saving efficiency without degrading the quality of service (e.g., system throughput) of a downlink heterogeneous LTE network and outperforms the previous schemes in terms of system throughput and power saving efficiency. In particular, with the proposed scheme, macrocells are able to operate independently without the cooperation of a SM and NMs for green heterogeneous cellular networks.

• Journal of Electrical Engineering and Technology
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• v.8 no.4
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• pp.704-711
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• 2013

Data center is an information hub and resource for information-centric society. Since data center houses hundreds to ten thousands servers, networking and communication equipment, and supporting systems energy saving is one of the hottest issues for green data center. Among several solutions for green data center this paper introduces higher voltage direct current (DC) power feeding system. Contrary to legacy alternating current (AC) power feeding system equipped with Uninterruptible Power Supply (UPS), higher voltage DC power feeding system is reported to be a more energy efficient and reliable solution for green data center thanks to less AC/DC and DC/AC conversions. Main focus of this paper is on reliability issue for reliable and continuous operation of higher voltage DC power feeding system. We present different types of configuration of the power feeding systems according to the level of reliability. We analyze the reliability of the power feeding systems based on M/M/1/N+1/N+1 queueing model. Operation of the power feeding system in case of failure is also presented.

• KIEE International Transactions on Power Engineering
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• v.3A no.3
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• pp.148-154
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• 2003

This paper describes the development of KEPCO's 80MVA UPFC electromagnetic transient model and the analysis of its performance in the actual Korean power system. KEPCO's 80MVA UPFC is currently undergoing installation and will be ready for commercial operation from the year 2003. In order to apply a new FACTS device such as the UPFC to the actual power system, the utility needs, in advance, both load flow stability studies and transient studies. Therefore, KEPRI, the research institute of KEPCO, developed a detailed transient analysis model that is based on the actual UPFC S/W algorithm and H/W specifications. This simulation model is implemented by an EMTDC/PSCAD package. The results of the simulation show the effectiveness of UPFC operation in the KEPCO power system.

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

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.57-60
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• 2008

KEPRI has studied planar type SOFC stacks using anode-supported single cells and kW class co-generation systems for residential power generation. A 1kW class SOFC system consisted of a hot box part, a cold BOP part and a water reservoir. A hot box part contains a SOFC stack made up of 48 single cells and ferritic stainless steel interconnectors, a fuel reformer, a catalytic combustor and heat exchangers. Thermal management and insulation system were especially designed for self-sustainable operation. A cold BOP part was composed of blowers, pumps, a water trap and system control units. When a 1kW class SOFC system was operated at $750^{\circ}C$ with hydrogen after pre-treatment process, the stack power was 1.2kW at 30 A and 1.6kW at 50A. Turning off an electric furnace, the SOFC system was operated using hydrogen and city gas without any external heat source. Under self-sustainable operation conditions, the stack power was about 1.3kW with hydrogen and 1.2kW with city gas respectively. The system also recuperated heat of about 1.1kW by making hot water.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1350-1352
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• 2003

For developing a 100 kW MCFC power generation system, Several design parameters for a fuel cell stack and system analysis results by Cycle Tempo, a processing computer soft ware, were described. Approximately two substacks with 90 cells are required to generate 100 kW at a current density of $125\;mA/cm^2$ with $6000\;cm^2$ of cells. An overall heat balance was calculated to predict exit temperature. The 100 kW power is expected only under pressurized operation condition at 3 atm. Recycle of cathode gas by more than 50% is recommended to run the stack at $125\;mA/cm^2$ and 3 atm. Manifolds should be designed based on gas flow rates for the suggested operating condition. The fuel cell power generation system was designed conceptually with several choices of utilization of anode exhaust gas. To operate and evaluate the MCFC system, control and measurement system and operation mode are designed before 100 MCFC system construction. In system control schematics, OS, PLC and MMI were consisted and have roles for MCFC system control. For operation of 100 kW MCFC system, NS, PS PR mode were considerated step by step and simulated.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.5
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• pp.120-126
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• 2009

This paper presents an optimal operating scheme by integrating Sihwa tidal power into NamSihwa systems. For optimal operation of NamSihwa systems, the sea levels of 1 minute interval using cubic interpolation based on the forecasted levels of high and low water are calculated. Especially, it is compared by three schemes to purchase total power from transmission system to purchase total power from tidal power system in time period that can generate tidal power and to purchase total power by comparing purchase costs from transmission system and tidal power system. The scheme may contribute to energy save in Korea that natural resources are lacking.

• Proceedings of the KIEE Conference
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• 1997.07b
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• pp.603-605
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• 1997

The systematic and efficient operation of telecommunication power equipments is very important to the safe operation of telecommunication system. To achive that, Korea Telecom has developed a new centralized management system for telecommunication power equipments. The system configuration and main functions for the new developed system are described in this paper.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1322-1324
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• 2002

For developing a 100 kW MCFC power generation system, Several design parameters for a fuel cell stack and system analysis results by Cycle Tempo, a processing computer soft ware, were described. Approximately 170 cells are required to generate 100 kW at a current density of 125 mA/$cm^2$ with 6000 $cm^2$ cells. An overall heat balance was calculated to predict exit temperature. The 100 kW power is expected only under pressurized operation condition at 3 atm. Recycle of cathode gas by more than 50% is recommended to run the stack at 125 mA/$cm^2$ and 3 atm. Manifolds should be designed based on gas flow rates for the suggested operating condition. The fuel cell power generation system was designed conceptually with several choices of utilization of anode exhaust gas. Also system efficiency was calculated at various type of system and operation conditions.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.1300-1302
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• 2001

For developing a 100 kW MCFC power generation system. Several design parameters for a fuel cell stack and system analysis results by Cycle Tempo, a processing computer soft ware, were described. Approximately 170 cells are required to generate 100 kW at a current density of $125mA/cm^2$ with $6000cm^2$ cells. An overall heat balance was calculated to predict exit temperature. The 100 kW power is expected only under pressurized operation condition at 3 atm. Recycle of cathode gas by more than 50% is recommended to run the stack at $125mA/cm^2$ and 3 atm. Manifolds should be designed based on gas flow rates for the suggested operating condition. The fuel cell power generation system was designed conceptually with several choices of utilization of anode exhaust gas. Also system efficiency was calculated at various type of system and operation conditions.