• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.10
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• pp.4781-4803
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• 2017

Environmental monitoring systems using Wireless Sensor Networks (WSNs) face the challenge of high power consumption, due to the high levels of multi-hop data communication involved. In order to overcome the issue of fast energy depletion, a proof-of-concept implementation proves that adopting a clustering algorithm in environmental monitoring applications will significantly reduce the total power consumption for environment sensor nodes. In this paper, an energy-efficient WSN-based environmental monitoring system is proposed and implemented, using eight sensor nodes deployed over an area of $1km^2$, which took place in the city of Tabuk in Saudi Arabia. The effectiveness of the proposed environmental monitoring system has been demonstrated through adopting a number of real experimental studies.

• Journal of the Korean Institute of Intelligent Systems
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• v.8 no.5
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• pp.72-82
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• 1998

Power transformer protective relay should block the tripping during magnetizing imrush and rapidly operate the tripping during internal faults. But traditional approaches maloperate in the case of magnetizing inrush with low second harmonic component and internal faults with high second harmounic component. To enhance the fault detection sensitivities of conventional technuques, flux-differential current derivative curve by fuzzy theory approaches is used. This paper deals with fuzzy logic based protective relaying for power transformer. The proposed fuzzy based relaying algorithm consisits of flux-differential current derivative curve, harmonics restraint, and precentage differential characteristic curv. The proposed relaying was tested with relaying signals obtained from Salford EMTP simulation package and showed a fast and accurate trip operation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.1
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• pp.296-308
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• 2015

Advanced Encryption Standard (AES) is widely used for protecting wireless sensor network (WSN). At the Workshop on Cryptographic Hardware and Embedded Systems (CHES) 2012, G$\acute{e}$rard et al. proposed an optimized collision attack and break a practical implementation of AES. However, the attack needs at least 256 averaged power traces and has a high computational complexity because of its byte wise operation. In this paper, we propose a novel double sieve collision attack based on bitwise collision detection, and an improved version with an error-tolerant mechanism. Practical attacks are successfully conducted on a software implementation of AES in a low-power chip which can be used in wireless sensor node. Simulation results show that our attack needs 90% less time than the work published by G$\acute{e}$rard et al. to reach a success rate of 0.9.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.3
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• pp.401-406
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• 2012

The aim of this research is to develop more actual high-frequency power generators that includes various noise, to make flexible control systems for test or performance analysis of electric and electronic machines. It proposed power generating circuits using basic amplifier, B-level Push-Pull type, and FPGA for the easier control to get data and transmit. And it also testify to realize the proposed systems to report output data by input waveform and designed the digital LPF with MATLAB, universal simulation tools, for this study.

• Journal of Power Electronics
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• v.8 no.4
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• pp.345-353
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• 2008

In this paper, a novel loss minimization of an induction generator in wind energy generation systems is presented. The proposed algorithm is based on the flux level reduction, for which the generator d-axis current reference is estimated using support vector regression (SVR). Wind speed is employed as an input of the SVR and the samples of the generator d-axis current reference are used as output to train the SVR algorithm off-line. Data samples for wind speed and d-axis current are collected for the training process, which plots a relation of input and output. The predicted off-line function and the instantaneous wind speed are then used to determine the d-axis current reference. It is shown that the effect of loss minimization is more significant at low wind speed and the loss reduction is about to 40% at 4[m/s] wind speed. The validity of the proposed scheme has been verified by experimental results.

• International Journal of Fluid Machinery and Systems
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• v.10 no.3
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• pp.209-217
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• 2017

The paper presents two novel concepts of increasing the energy storage capacity at pumped storage power plants, both existing and new projects. The concepts utilize compressed air as a working medium to displace water from a volume originally not available for storage. The concepts are likely to give additional storage volume at a low cost, however, much development and many investigations are needed before the concepts can be shown to be technical and economical feasible solutions for energy storage. The concepts are disclosed so that researchers and utilities can start those investigations, hopefully helping the green transition by providing highly valuable energy storage for a future renewable energy having a much higher share of renewable energies than the current systems.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.31B no.8
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• pp.172-180
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• 1994

Implantable biotelemetry systems are indispensable tools not only in animal research but also in clinical medicine as such systems enable the acquisition of otherwise unavailable physiological data. We present the manufacture of CMOS IC and its system for implantable multichannel biotelemeter system. The internal circuits of this system are designed not only to achieve as multiple functions and low power dissipation as possible but also to enable continuous measurement of physiological data. Its main functions are to enable continuous measurement of physiological data and to accomplish on-off power swiching of an implantable battery by receiving appropriate commanc signals from an external circuit. The implantable circuits of this system are designed and fabricated on a single silicon chip using $1.5\mu$m n-well CMOS process technology. The total power dissipation of implantable circuits for a continuous operation was 6.7mW and for a stand-by operation was 15.2$\mu$ W. This system used together with approriate sensors is expected to contribute to clinical medicine telemetry system of measuring and wireless transmitting such significant physiological parameters as pressure pH and temperature.

• Journal of the Korea Institute of Military Science and Technology
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• v.23 no.3
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• pp.237-245
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• 2020

In this paper, I introduce Phase-Change Cooling for thermal management of high power devices that can be applied to High Power Laser and Electric Propulsion Systems which are composed of multiple distributed superheat sources. Phase-Change Cooling can be good used to efficient cooling of their heat sources. Phase-Change Cooling has extremely high efficiency of two-phase heat transport by utilizing heat of vaporization, relatively low flow rates and reduced pumps power. And I suggest TPI(Thermal Performance Index) which is a quantitative performance index of Phase-Change Cooling for thermal management. I quantify the performance of Phase-Change Cooling by introducing TPI. I present the test results of TPI's changing refrigerant, heat sink and flow rate of the Phase-Change Cooling system through the experiments and analyze these results.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.665-672
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• 2002

In this paper, the utilization of waste foundry sand produced in the molding process is studied as a backfill material for underground electric utility systems such as concrete box structures and pipe lines for power supply. The physical, chemical and thermal properties for waste foundry sand are investigated for mechanical stability, environmental hazard and power transmission capacity. Also its properties are compared with the natural river sand. The test results show that waste foundry sand can be utilized for underground concrete box structures as a backfill material; however, it can not be applied to underground pipe lines due to high thermal resistivity or low power transmission capacity.

• Proceedings of the KIEE Conference
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• summer
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• pp.60-63
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• 2004

AGC is widely used to regulate the frequency of power systems. It is also used to control the frequency of Korean Power System. Control strategies depends on systems to which it is applied. Korean Power System consists of one control area and it has no tie-line. In this research, we have developed a simulation tool to confirm AGC dynamics. The developed tool has been verified by two-machine three-bus system. Moreover an AGC control strategy has been suggested to avoid contradiction with governor dynamics. Low pass filter with relatively long time constant showed good regulation performance. This simple strategy is expected to be applied to New EMS in KPX to get reasonable AGC regulation performance.