• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.97-99
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• 2008

It is possible to suppress voltage drops, power loading fluctuations and regeneration power lapses for DC railway systems by applying an energy storage system. Recently the electric double layer capacitor (EDLC) of the rapid charge/discharge type has been developed and used in wide ranges. The on board energy storage system with supercapacitor for railway vehicles presented in this paper seems to be a reliable technical solution with an enormous energy saving potential. In this paper, an efficient charge and discharge control method of a bidirectional DC-DC converter using the supercapacitor is proposed.

• Proceedings of the KIEE Conference
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• 1998.07g
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• pp.2393-2395
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• 1998

Today it is hard to imagine the operation of power network and its facilities without the control systems such as EMS/SCADA/DAS. In KEPCO, data links to the upper layer of control system (SCABA) is required to launched DAS project lately, in terms of the needs of saving cost for the data gathering facilities (RTU) in the substation that previously equipped SCADA RTU. In this Paper we researched the circumstance of the KEPCO SCADA systems for data link and present the scheme of the data link between DAS and SCADA.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.7
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• pp.2530-2547
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• 2015

In the recent years, femtocell technology has received a considerable attention due to the ability to provide an efficient indoor wireless coverage as well as enhanced capacity. However, under the spectrum sharing between femtocell user equipment (FUEs) and the owner of spectrum macrocell user equipment (MUEs), both may experience higher uplink interference to each other. This paper proposes a novel distributed power control algorithm for the interference management in two-tier femtocell networks. Due to the assignment of licensed radio frequency to the outdoor macrocell users, the access priority of MUEs should be higher than FUEs. In addition, the quality of service (QoS) of MUEs that is expressed in the target signal-to-interference-plus-noise ratio (SINR) must always be achieved. On the other hand, we consider an efficient QoS provisioning cost function for the low-tier FUEs. The proposed algorithm requires only local information and converges even in cases where the frontiers of available power serve the target SINRs impossible. The advantage of the algorithm is the ability to implement in a distributed manner. Simulation results show that the proposed algorithm based on our cost function provides effective resource allocation and substantial power saving as compared to the traditional algorithms.

• The KIPS Transactions:PartA
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• v.19A no.3
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• pp.139-146
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• 2012

In the server cluster environment, one of the ways saving energy is to control server's power according to traffic conditions. This is to determine the ON/OFF state of servers according to energy usage of data center and each server. To do this, we need a way to estimate each server's energy. In this paper, we use a software-based power consumption estimation model because it is more efficient than the hardware model using power meter in terms of energy and cost. The traditional software-based power consumption estimation model has a drawback in that it doesn't know well the computing status of servers because it uses only the idle status field of CPU. Therefore it doesn't estimate consumption power effectively. In this paper, we present a CPU field based power consumption estimation model to estimate more accurate than the two traditional models (CPU/Disk/Memory utilization based power consumption estimation model and CPU idle utilization based power consumption estimation model) by using the various status fields of CPU to get the CPU status of servers and the overall status of system. We performed experiments using 2 PCs and compared the power consumption estimated by the power consumption model (software) with that measured by the power meter (hardware). The experimental results show that the traditional model has about 8-15% average error rate but our proposed model has about 2% average error rate.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.61 no.1
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• pp.18-22
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• 2012

In this paper, we propose a sensor-based LED lighting system that can significantly reduce standby powers. The proposed LED lighting system has the more advanced power circuit and control mechanism compared to existing one. The whole power circuit consists of two subcircuits. One is designed to apply electric powers to controller, PIR(Pyroelectric Infrared Ray) sensor and CdS, and the other one is designed to apply electric powers to LED module. Such a power circuit configuration makes the standby powers reduction of LED lighting system possible. From the experimental results, we confirmed that the standby powers saving performance of the developed power circuit is superior to that of the conventional one.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1947-1948
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• 2008

This paper presents the implementation of Power Line Communication(PLC) module which can reduce standby-power consumption. The suggested PLC module consists of PLC modem, coupling circuit, ZCP(Zero-Cross Point) Circuit and main SMPS control relay. The test results under power line communication test-bed used home appliance show the 77% saving of standby-power.

• 한국태양에너지학회:학술대회논문집
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• 2011.04a
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• pp.168-173
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• 2011

Recently, from a saving energy and environmental lighting sources point of view, using LED lighting have been increased rapidly. The colors of light was applied to the control of dimmers that is composed of red, green, blue, and white(RGBW) to improve the quality of visual environment. Moreover this study has been processed to develop adjustable dynamic LED lighting system on SPD and definitize the various spectral power distribution and color temperature of light through the control of the four dimmers. It is possible to combine up to $432^4$ kinds of light. Measurement of illuminance of range on working surface was as 7~l,831 lux. Application of visual environment for occupants can be expected according to control of lighting performance.

• Journal of Digital Convergence
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• v.12 no.2
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• pp.271-276
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• 2014

The life-time and performance of a wireless sensor network is closely related to energy-efficiency of sensor nodes. In this paper, to increase energy-efficiency, each sensor node operates in one of three operational modes which are normal, power-saving, and inactive. In normal mode sensor nodes sense and transmit data with normal period, whereas sensor nodes in power-saving mode have three-times longer period. In inactive mode, sensor nodes do not sense and transmit any data, which makes the energy consumption to be minimized. Plus, the proposed algorithm can avoid unnecessary energy consumption by preventing transmitting duplicate sensed data. We implemented and simulated the proposed algorithm using Tiny OS based ZigbeX platfom and NS-2, respectively. Performance evaluation results show that the proposed algorithm can prolong sensor networks' lifespan by efficiently reducing energy consumption and its standard deviation of all sensor nodes.

• Journal of Electrical Engineering and Technology
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• v.2 no.1
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• pp.89-97
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• 2007

This paper presents a new circuit topology of active edge resonant snubbers assisted half-bridge soft switching PWM inverter type DC-DC high power converter for DC bus feeding power plants. The proposed DC-DC power converter is composed of a typical voltage source-fed half-bridge high frequency PWM inverter with a high frequency planar transformer link in addition to input DC busline side power semiconductor switching devices for PWM control scheme and parallel capacitive lossless snubbers. The operating principle of the new DC-DC converter treated here is described by using switching mode equivalent circuits, together with its unique features. All the active power switches in the half-bridge arms and input DC buslines can achieve ZCS turn-on and ZVS turn-off commutation transitions. The total turn-off switching losses of the power switches can be significantly reduced. As a result, a high switching frequency IGBTs can be actually selected in the frequency range of 60 kHz under the principle of soft switching. The performance evaluations of the experimental setup are illustrated practically. The effectiveness of this new converter topology is proved for such low voltage and large current DC-DC power supplies as DC bus feeding from a practical point of view.

• Proceedings of the KWS Conference
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• 1994.10a
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• pp.89-92
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• 1994

According to the industrial development welding technology is necessitated to develop in the direction of full automation, high efficiency, energy saving, and full safety. In this study, thus, a simple holder ampere controller for welding systems is developed and applied to arc welders and its capability is examined and tested. The results are as follows: 1. It has a simple structure, since the primary AC power for the welder can be directly control led using a triac. 2. It can control the electric power strength in several steps as well as on and off easily, since a small-sized variable resistance is installed in the small controller on the welding holder. 3. In real field applications a welding system with this controller increases the working efficiency greatly compare to the conventional arc welders without the system, because the controller can control the ampere onsite far from the main power supply. 4. It can reduce the probability of the electrical mishap due to electrical leakage, since the electricity is disconnected as soon as the switch is off or welding person's hand is taken off from the welder after the work or for rest. 5. It can control the welding depth in the beginning and do the crater treatment well in the ending of welding, since it always supplies the relevent amount of electrical current. Therefore, it can improve the mechanical properties of the welding zone.