• The Journal of the Korea Contents Association
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• v.11 no.6
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• pp.51-58
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• 2011

One of the objectives of research on routing methods in wireless sensor networks is maximizing the energy life of sensor nodes that have limited energy. In this study, we tried to even energy use in a wireless sensor network by giving a weight to the transition probability of ACS(Ant Colony System), which is commonly used to find the optimal path, based on the amount of energy in a sensor and the distance of the sensor from the sink. The proposed method showed improvement by 46.80% on the average in energy utility in comparison with representative routing method GPSR (Greedy Perimeter Stateless Routing), and its residual energy after operation for a specific length of time was 6.7% more on the average than that in ACS.

• Applied Chemistry for Engineering
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• v.33 no.2
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• pp.202-209
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• 2022

Effects of the support and amount of NiCl₂ on ammonia adsorption capacity were investigated to improve the ammonia adsorption performance. NiCl₂ was impregnated onto the surface of various supports under ultrasonic irradiation. The physicochemical properties and ammonia adsorption performance of NiCl₂-impregnated adsorbents were investigated. Among the various supports, it was found that the adsorption capacity of ammonia was the best when NiCl₂ was impregnated on activated carbon (AC) with the highest specific surface area. As a result of changing the amount of NiCl₂ impregnated on AC, the NiCl₂(2.0)/AC adsorbent impregnated with 2 mmol·g^-1 of NiCl₂ showed the highest ammonia adsorption capacity of 5.977 mmol·g^-1. In addition, the adsorption capacity was found to be maintained at an almost constant level in five repeated cycle tests under the condition that low-temperature heat could be utilized. This indicates that the adsorbent has excellent regeneration ability.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.39-46
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• 2015

A outdoor termination installed at the outdoor substation is required to connect undergroud cables and overhead transmission lines. The joint box for AC transmission system is already developed and widely used to interconnect overhead and undergroud systems. But the development of the joint box for DC transmission system was only introduced from China and Japan, but theire developemnt staus and core technologies were not fully reported. In order to implement HVDC systems connecting ovehead transmission lines and undergroud cables, a outdoor termination should be developed, but the detailed specifications and information of this device were not reported. It is estimated that the development of the joint box for DC environment has some technical obstacles including insulating materials, electric field mitigation, thermal temperature rise, and space charge accumuations. Among this, the most important one is the DC elctrical insualtion design. Therefore, in order to investigate the DC elctrical insualton design of outdoor termination, the design of AC slip-on type outdoor termination is reffered, and DC electric field analysis performed to verify the possiblity of application of AC joint box into DC joint box. Especially for DC electric field analysis, temperature rise of insualting materials of a joint box was considered, because the conductivity of materials could be changed due to temperature rise. Furthermore, DC electric field analysis considering transinet state, and polarity reversal state were also investigated to verify which state is the most severe condition for the DC joint box. From the simualtion resulsts, it was shown that the value and the position of maximum electric field was obtained comparing AC state, DC state without temperaure rise, and DC state with temperaure rise. And it was confimred that severe DC electric field was observed considing temperaure rise. Finally, in order to reduce DC eletric field intensifation, different configuration of the joint box was applied and it was not possible to obtain satisfactory results. It means that the slight change of configuration of AC joint box was not the suitable soluton for DC joint box. It is essential to establish novel DC insulaton design skills and method for DC joint box to commercialze this product in the near future.

• Nuclear Engineering and Technology
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• v.27 no.1
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• pp.53-66
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• 1995

Since the current licensed system codes for Non-LOCA safety analysis are applicable only for a specific type PWR, it is necessary to develope a new system analysis code applicable for all apes of PWRs. As a R&D program, KAERI is developing TASS code as an interactive and faster-than-real-time code for the NSSS transient simulation of both CE and Westinghouse plane. It is flexible tool for PWR analysis which gives the user complete control over the simulation through convenient input and output options. In this paper the code applicability to Westinghouse ape plants was verified by comparing the TASS prediction to plant data of loss of AC power and loss of load transients, and comparing to the prediction of RELAP5/MOD3 for feedline break, locked rotor, steam generator tube rupture and steam line break accidents.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.39-42
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• 2018

In this paper, a low-power MPPT interface circuit for vibration energy harvesting sources is presented. The designed circuit rectifies the harvested ac type energy to the dc type energy required to drive the system, and periodically samples and holds the open circuit voltage (Voc) through the MPPT controller, and transfers the harvested power to the load while maintaining the input voltage at 1/2 of the maximum available power point. All circuits have been designed using a 0.35-um CMOS technology, and the operation has been verified through simulation. Simulation results show that the designed circuit consumes 98nA of current at 3V input voltage and the maximum power efficiency is 99.21%. The designed chip occupies $1.281mm{\times}1.236mm$.

• Journal of Sensor Science and Technology
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• v.28 no.5
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• pp.311-317
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• 2019

Rotating devices are commonly installed in power plants and factories. This study proposes a self-powered sensor node that is powered by converting the vibration energy of a rotating device into electrical energy. The self-powered sensor consists of a piezoelectric harvester for self-power generation, a rectifier circuit to rectify the AC signal, a sensor unit for measuring the vibration frequency, and a circuit to control the light emitting diode (LED) lighting. The frequency of the vibration source was measured using a piezoelectric-cantilever-type vibration frequency sensor. A green LED was illuminated when the measured frequency was within the normal range. The power generated by the piezoelectric harvester was determined, and the LED operation was assessed in terms of the vibration frequency. The piezoelectric harvester was found to generate a power of 3.061 mW or greater at a vibration acceleration of 1.2 g ($1g=9.8m/s^2$) and vibration frequencies between 117 and 123 Hz. Notably, the power generated was 4.099 mW at 122 Hz. As such, our self-powered sensor node can be used as a module for monitoring rotating devices, because it can convert vibration energy into electrical energy when installed on rotating devices such as air compressors.

• Journal of the Korean Electrochemical Society
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• v.16 no.3
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• pp.129-137
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• 2013

From the cooked-rice as a raw material, activated carbons throughout a hydrothermal synthesis and vacuum soak of KOH for chemical activation were obtained. Activated carbon electrodes for electric double layer supercapacitors were prepared and electrochemical characteristics were examined. Including the specific surface area by BET method and pore size distribution by NLDFT method, physical properties of activated carbons were investigated by means of SEM, EDS, XRD, and TG analyses. Cycle voltammetry and AC-impedance measurements were conducted to confirm the electrochemical characteristics for the electrodes. From hydrothermal synthesis, $5{\sim}7{\mu}m$ diameters of spherical carbons were obtained. After the activation at $800^{\circ}C$, it was notable for the activated carbon to be the specific surface $1631.8cm^2/g$, pore size distribution in 0.9~2.1 nm, and micro-pore volume $0.6154cm^3/g$. As electrochemical characteristics of the activated carbon electrode in 6M KOH electrolyte, it was confirmed that the specific capacitances of 236, 194, and 137 F/g at the scan rate of 5, 100, and 500 mV/s respectively were exhibited and 91.2% of initial capacitance after 100,000 cycles at 200 mV/s was maintained.

• Korean Chemical Engineering Research
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• v.55 no.3
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• pp.332-340
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• 2017

This study aims to propose a new optimization-based approach for design and analysis of the stand-alone hybrid energy supply system using renewable energy sources (RES). In the energy supply system, we include multiple energy production technologies such as Photovoltaics (PV), Wind turbine, and fossil-fuel-based AC generator along with different types of energy storage and conversion technologies such as battery and inverter. We then select six different regions of Korea to represent various characteristics of different RES potentials and demand profiles. We finally designed and analyzed the optimal RES stand-alone energy supply system in the selected regions using multiobjective optimization (MOOP) technique, which includes two objective functions: the minimum cost and the minimum $CO_2$ emission. In addition, we discussed the feasibility and expecting benefits of the systems by comparing to conventional systems of Korea. As a result, the region of the highest RES potential showed the possibility to remarkably reduce $CO_2$ emissions compared to the conventional system. Besides, the levelized cost of electricity (LCOE) of the RES-based energy system is identified to be slightly higher than conventional energy system: 0.35 and 0.46 $/kWh, respectively. However, the total life-cycle emission of $CO_2$ ($LCE_{CO2}$) can be reduced up to 470 g$CO_2$/kWh from 490 g$CO_2$/kWh of the conventional systems.

• Journal of the Korean Solar Energy Society
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• v.32 no.spc3
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• pp.255-261
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• 2012

Since PV PCS uses output current sensor for ac output current control, the sensor's sensing value includes unnecessary offset inevitably. If PV inverter is controlled by the included offset value, it's output current will generate DC offset. The DC offset of output current for trans-less PV inverter is fatal to grid, which results in saturating grid side transformer. Usually DSP controller of PV inverter reads several times sensing value during initial operation and, finally, it's average value is used for offset calibration. However, if temperature changes, the offset changes, too. And also, the switch device is not ideal, both each switching element of the voltage drop difference and on & off time delay difference generate DC offset. Thus, to compensate for deadtime and the switch voltage drop, feedback control by output current DC offset should be provided to compensate additional distortion of the output current. The validity of the proposed method is confirmed through PSIM simulation.

• Journal of the Korean Solar Energy Society
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• v.32 no.spc3
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• pp.199-206
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• 2012

The purpose of this study is to understand the change of impression by comparing the uniformity lighting with the compound lighting. In previous study, we proposed a light controlling method to harmonize daylight from a window and artificial lights from a ceiling and obtained the results to support our method. We referred this method as the Adjusted Compound-Lighting Model (AC Model). The experiment is carried out with the scaled-models and mock-up spaces that were supposed to be an office space. One is lit by the uniform lighting and the other by the compound lighting in each experimental space. In order to present varying illuminance distributions, the two variables were used in this study. Subjects were asked to evaluate the point of difference by semantic differential rating on their overall impression after comparing with two rooms. The results showed that the impressions of compound lighting were more positive score than that of uniformity lighting on the items of 'dim-bright', 'dislike-like', 'artificial-natural' and 'closed-open', and that there was no significant difference in impressions between two spaces on other items.