• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.10
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• pp.926-934
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• 2016

In this paper, we designed a compact frequency synthesizer with multi-function for Ka-band seeker. DDS(Direct Digital Synthesizer) is applied to generate various waveform and to cover high-speed frequency sweep. In order to reduce size, waveform generator and frequency up-converter are integrated in one module. Proposed frequency synthesizer provides precise detection and tracking waveform for low and high speed targets. It is observed that fabricated synthesizer performs $0.45{\mu}sec$ frequency switching time and -93.69 dBc/Hz phase noise at offset 1 kHz. The size of the synthesizer is kept within 120 mm width, 120 mm length and 22 mm height.

• Journal of Power Electronics
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• v.15 no.2
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• pp.455-468
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• 2015

A microgrid (MG) with integrated renewable energy resources can benefit both utility companies and customers. As a result, they are attracting a great deal of attention. The control of a MG is very important for the stable operation of a MG. The droop-control method is popular since it avoids circulating currents among the converters without using any critical communication between them. Traditional droop control methods have the drawback of an inherent trade-off between power sharing and voltage and frequency regulation. An adaptive droop control method is proposed, which can operate in both the island mode and the grid-connected mode. It can also ensure smooth switching between these two modes. Furthermore, the voltage and frequency of a MG can be restored by using the proposed droop controller. Meanwhile, the active power can be dispatched appropriately in both operating modes based on the capacity or running cost of the Distributed Generators (DGs). The global information (such as the average voltage and output active power of the MG and so on) required by the proposed droop control method to restore the voltage and frequency deviations can be acquired distributedly based on the Multi Agent System (MAS). Simulation studies in PSCAD demonstrate the effectiveness of the proposed control method.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1587-1599
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• 2017

This paper proposes a real-time implementation of an optimal operation of a double stage grid connected wind power system incorporating an active power filter (APF). The system is used to supply the nonlinear loads with harmonics and reactive power compensation. On the generator side, a new adaptive neuro fuzzy inference system (ANFIS) based maximum power point tracking (MPPT) control is proposed to track the maximum wind power point regardless of wind speed fluctuations. Whereas on the grid side, a modified predictive current control (PCC) algorithm is used to control the APF, and allow to ensure both compensating harmonic currents and injecting the generated power into the grid. Also a type 2 fuzzy logic controller is used to control the DC-link capacitor in order to improve the dynamic response of the APF, and to ensure a well-smoothed DC-Link capacitor voltage. The gained benefits from these proposed control algorithms are the main contribution in this work. The proposed control scheme is implemented on a small-scale wind energy conversion system (WECS) controlled by a dSPACE 1104 card. Experimental results show that the proposed T2FLC maintains the DC-Link capacitor voltage within the limit for injecting the power into the grid. In addition, the PCC of the APF guarantees a flexible settlement of real power exchanges from the WECS to the grid with a high power factor operation.

• Nuclear Engineering and Technology
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• v.43 no.2
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• pp.187-194
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• 2011

Korea Nuclear Fuel is developing the X-GEN fuel which shows high performance and robust reliability for the worldwide supply. However, the simplified code systems such as CESEC-III which were developed in 1970s are still used in the current Non-LOCA safety analysis of OPR1000 and APR1400 plants. Therefore, it is essential to secure an advanced safety analysis methodology to make the best use of the merits of X-GEN fuel. To accomplish this purpose, the $\b{i}$ntegrated $\b{s}$afety $\b{a}$nalysis $\b{m}$ethodology (iSAM), is developed by selecting the best-estimate thermal-hydraulic code RETRAN. iSAM possesses remarkable advantages, such as generality, integrity, and designer-friendly features. That is, iSAM can be applied to both OPR1000 and APR1400 plants and uses only one computer code, RETRAN, in the whole scope of the non-LOCA safety analyses. Also the iSAM adopts the unique and automatic initialization and run tool, $\b{a}$utomatic $\b{s}$teady-$\b{s}$tate $\b{i}$nitialization and $\b{s}$afety analysis too l (ASSIST), to enable unhandy designers to use the new design code RETRAN without difficulty. In this paper, a brief overview of the iSAM is given, and the results of applying the iSAM to typical non-LOCA transients being checked during the reload design are reported. The typical non-LOCA transients selected are the single control element assembly withdrawal (SCEAW) accident, the asymmetric steam generator transients (ASGT), the locked rotor (LR) accident, and bank CEA withdrawal (BCEAW) event. Comparison to current licensing results shows a close resemblance; thus, it reveals that the iSAM can be applied to the non-LOCA safety analysis of OPR1000 and APR1400 plants.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.6
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• pp.527-534
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• 2018

The segment of the piston type wave board has been expressed as a submerged vertical line segment in the two dimensional wave flume. Either end of vertical line segment representing wave board could be located in fluid domain from free surface to the bottom of the flume. Naturally the segment could be extended from the bottom to the free surface of the flume. It is assumed that the piston motion of the wave board could be defined by the sinusoidal oscillation in horizontal direction. Simplified analytic solution of the submerged segment of wave board has been derived through the first order perturbation method in water of finite depth. The analytic solution has been utilized in expressing the wave generated by the piston type wave board installed on the upper or lower half of the flume. The wave form derived by the analytic solution have been compared with the wave profile obtained through the CFD calculation for the either of the above cases. It is appeared that the wave length and the wave height are coincided each other between analytic solution and CFD calculation. However the wave form obtained by CFD calculations are more closer to real wave form than those from analytic calculation. It is appeared that the linear solutions could be not only superposed by segment but also integrated by finite elements without limitation. Finally it is proven that the wave generated by the oscillation of flap type wave board could be derived by integrating the wave generated by the sinusoidal motion of the finite segment of the piston type wave board.

• Fashion & Textile Research Journal
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• v.21 no.3
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• pp.300-307
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• 2019

This study develops a user centered outdoor jacket capable of energy harvesting based on consumer needs. Jackets are designed for typical outdoor activities such as hiking, trekking, and climbing, integrated with an energy harvesting module that can generate electric power from arm swing in outdoor and daily life walking. Textile based energy generators developed by the previous research of Lee & Roh (2018) were used. A prototype was created based on the arm swing motion experiment for location options and energy harvesting system functions, the simulation by the design sketch, and evaluation of the wearing test by experts. In-depth interviews were later conducted for the prototype with 10 outdoor experts to derive the optimal location of an energy harvesting system in three ways, and the prototype was revised to 5 styles that reflected reviews by experts on function and appearance. Research indicated that the energy harvesting jacket design signifies a user-centered design based on expert interviews and usability evaluation as well as previous research on energy generation and storage device. The jacket is convenient because it combines an energy generator in an optimal position to maximize energy generation with a storage and charging device that can be inserted into various position options for accessibility.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.470-475
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• 2019

This paper deals with a 30kW grid-connected PCS (Power Conversion System) for an Oscillating Water Column (OWC) wave-power generation system. Wave power generation in marine energy is suitable for Korea with the characteristics of a peninsula with three sides facing the sea. In the case of coastal disasters, wave generators can act as a breakwater to reduce damage, and can be integrated with other marine power generation systems to increase efficiency. Wave power generation systems are classified into various types, such as oscillating bodies, OWC, and overtopping according to the operation principle, and they can also be classified into two types according to the installation method: a fixed structure and floating structure. This paper proposes a 30kW grid-connected PCS topology and model for OWC wave power generation that is structurally stable with a turbine and generator that are relatively easy to maintain, and then provide a control method required for grid connection, including DC link voltage control. Simulation verification was performed to verify the proposed PCS.

• Journal of the Korea Society of Computer and Information
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• v.14 no.10
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• pp.123-131
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• 2009

In this paper, we design ZigBee RF based framework for mobile web service on collected data by sensor node and transmitting data to data base by sensor network and remote sensing server through wireless connection. The proposed system is an integrated platform of sensor network for the sensor management and providing SOA based sensor web access. This paper combines SOA technology with sensor network. composes sensor node as web view, and provides high capability. extensiveness, reliability, and usability to the user who accesses to sensor web. The mobile message conversion module, SOAP message processing module. WSDL message generator, and mobile web service module is embodied for improving the capacity of the framework. The capacity evaluation of local wireless communication system which is proposed in this paper is analyzed through NS-2 simulation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.139-147
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• 2021

Livestock manure is used as an organic fertilizer to replace chemical fertilizers after sufficient fermentation in an aerobic bioreactor. On the other hand, liquid manure disposal problems occur repeatedly because soil spraying is restricted during the summer when the crops are growing. To use liquid fertilizer (LF) as an additional nutrient source for crops, it is necessary to reduce the amount of suspended solids (SS) in the liquid fertilizer and secure stability problems against pathogenic microorganisms. This study examined the effects of the simultaneous SS removal and E.coli sterilization in the LF using the microbubble (MB) generator (FeMgO catalyst insertion). The remaining SS were further removed using the integrated microbubble and microfilter system. During the floating process in the MB device, the SS were removed by 57.9%, and the coliform group was not detected (16,200→0 MPN/100 mL). By optimizing the HRT of the integrated system, the removal efficiency of the SS was improved by 92.9% under the 0.1h of HRT condition. After checking the properties of the treated LF, 64.5%, 70.1%, 54.9%, and 51.5% of the TCOD, SCOD, PO4-P, and TN, respectively, were removed. The treated effluent from such an integrated system has a lower SS content than that of the existing LF and does not contain coliforms; therefore, it can be used directly as an additional fertilizer.

• Journal of the Korean Society of Radiology
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• v.6 no.6
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• pp.447-454
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• 2012

To examine the performance of a diagnostic X-ray system, we tested a linearity, reproducibility, and Half Value Layer(HVL). The linearity was examined 4 times of irradiation with a given condition, and we recorded a level of radiation. We then calculated the mR/mAs. And the measured value should not be more than 0.1. If the measured value was more than 0.1, we could know that the linearity was decreased. The reproducibility was analyzed 10 times of irradiations at 80kVp, 200mA, 20mAs and 120kVp, 300mA, 8mAs. The values from these analyses were integrated into CV equation, and we could get outputs. The reproducibility was good if the output was lower than 0.05. HVL was measured 3 times of irradiation without a filter, and we inserted additional HLV filters with 0, 1, 2, 4 mm of thickness. We tested the values until we get the measured value less than a half of the value measured without additional filter. We tested the linearity, the reproducibility, and HVL of 5 diagnostic X-ray generators in this facilities. The linearity of No. 1 and No. 5 generator didn't satisfy the standard for radiation safety around 300mA~400mA and 100mA~200mA, respectively. HVL of No.1 generator was not satisfied at 80kVp. The outputs were higher in the three-phase equipment than the single-phase equipment. The old generators need to maintain and exchange of components based on the these results. Then, we could contribute to getting more exact diagnosis increasing a quality of the image and decreasing an expose dose of radiation.