• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.1
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• pp.75-80
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• 2011

In the cooperative communication, The relay that transmit signal to destination can achieve diversity gain. But transmitter and relay must have own frequency to transmit signal to destination. If Relay is secondary user and does not have own frequency, relay can't transmit signal to destination. So, To analysis performance of cognitive radio We need to consider detection probability of secondary user. In the paper we propose cooperative communication system considering detection probability. And to compare proposed system and conventional, we also simulate incremental cooperative communication. Through the simulation result, we can know that BER performance of proposed scheme is better than incremental relaying in the cognitive radio.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.3
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• pp.290-295
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• 2005

The incremental encoder has been mostly used to measure the speed and position of the motor. As the output signals of encoder are high frequency digital signals, they have much influence on radiation noises due to switching of the power semiconductor circuits. It is so difficult to suppress the noises with the conventional LPF. In this paper, the hardware digital filter for suppressing noises in the output signals of the encoder signals is developed. As both the clock frequency and counter in the digital filter for encoder are easily adjusted according to the kinds of noises, any noises in the encoder can be entirely eliminated. The performance of the digital filter has been verified by simulation and experimental results.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.120-126
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• 2011

The fatigue damages in structural details of offshore plants can be accumulated due to various environmental loadings such as swell, wave, wind and current. It is known that load histories acting on mooring and riser systems show stationary and ergodic bimodal wide-banded process. This paper provides refined approach to obtain time signals representing stress range histories from wide-banded bimodal spectrum which consists of ideally narrow-banded and fully separated two spectrums. Variations of the probabilistic characteristics for time signals according to frequency and sampling time increments are compared with the reference data to be the probabilistic characteristics such as zero-crossing period, peak period, and irregularity factor obtained from an assumed ideal spectrum. It is proved that the sampling time increment more affects on the probabilistic characteristics than frequency increment. The fatigue damages according to the frequency and sampling time increments are also compared with the ones with minimum increment condition which are thought to be exact fatigue damage. It is concluded that the maximum sampling time increment to obtain reliable time signals should be determined that ratio of applied maximum sampling time increment and minimum period is less than approximately 0.08.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.4
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• pp.633-642
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• 2021

Growing demand for electricity, when combined with the need to limit carbon emissions, drives a huge increase in renewable energy industry. In the electric power system, electricity supply always needs to be balanced with electricity demand and network losses to maintain safe, dependable, and stable system operation. There are three broad challenges when it comes to a power system with a high penetration of renewable energy: transient stability, small signal stability, and frequency stability. Transient stability analyze the system response to disturbances such as the loss of generation, line-switching operations, faults, and sudden load changes in the first several seconds following the disturbance. Small signal stability refers to the system's ability to maintain synchronization between generators and steady voltages when it is subjected to small perturbations such as incremental changes in system load. Frequency stability refers to the ability of a power system to maintain steady frequency following a severe system upset resulting in significant imbalance between generation and load. In this paper, we discusses these stability using system simulation by renewable energy deployment plan, and also analyses the influence of the renewable energy sources to the grid stability.

• Journal of the Korean Electrochemical Society
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• v.2 no.3
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• pp.130-133
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• 1999

In this work, a capacitance-type alcohol gas sensor using porous silicon layer is developed to apply for breath alcohol measurement and its characteristics are estimated at room temperature. Current alcohol sensors using metal oxides such as tin-oxide are not only difficult to measure low alcohol concentration, but also should heat at $200\;to\;400^{\circ}C$ to improve the sensitivity. But the sensor using porous silicon layer has good sensitivity even at room temperature by very large effective surface area and suitable structure to fabricate integrated micro sensors. In the experiment, the capacitance was measured for the range of 0 to $0.5\%$ alcohol concentration with the interval of $0.05\%$, in which alcohol solution was kept at 25, 36, and $45^{\circ}C$ by a heater. As the result, good linearity was observed and the capacitance increased about 1.1, 2.6 and $4.6\%$ per the increment of $0.1\%$ alcohol concentration each temperature, respectively, at the frequency of 120 Hz.

• Journal of IKEEE
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• v.27 no.4
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• pp.477-485
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• 2023

In this paper, the effect of AC ripple on the lifetime of lithium-ion batteries is experimentally analyzed. Bidirectional power conversion system(PCS) is used to increase the efficiency of energy storage systems (ESS). When connected to the grid, a current ripple with a frequency twice the grid frequency is applied to the battery due to its structure. Therefore, to analyze the effect of AC ripple on Li-ion battery aging, cycle life test are performed by applying charge/discharge profiles of DC current and DC+AC current ripple specifications. Based on the experimental results, direct current internal resistance (DCIR), incremental capacitance (IC), and surface temperature were analyzed. As a result, it is confirmed that AC ripple does not directly affect degradation and that battery degradation slows down after a certain cycle. These results can serve as a guideline for optimizing filters to reduce ripple on the battery side in applications where AC ripple occurs.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.3
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• pp.11-22
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• 2010

An analysis method is proposed for the transient linear or nonlinear analysis of dynamic interactions between a flexible dam body and reservoir impounding compressible water under earthquake loadings. The coupled dam-reservoir system consists of three substructures: (1) a dam body with linear or nonlinear behavior; (2) a semi-infinite fluid region with constant depth; and (3) an irregular fluid region between the dam body and far field. The dam body is modeled with linear and/or nonlinear finite elements. The far field is formulated as a displacement-based transmitting boundary in the frequency domain that can radiate energy into infinity. Then the transmitting boundary is transformed for the direct coupling in the time domain. The near field region is modeled as a compressible fluid contained between two substructures. The developed method is verified and applied to various earthquake response analyses of dam-reservoir systems. Also, the method is applied to a nonlinear analysis of a concrete gravity dam. The results show the location and severity of damage demonstrating the applicability to the seismic evaluation of existing and new dams.