• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 추계학술대회 논문집
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• pp.206-207
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• 2016

The intermittent characteristics of wind power (WP) may have negative effect on grid stability, especially in weak grid. WP fluctuation rate can be reduced by using energy storage system (ESS) through charging and discharging. The operation of ESS will decide its losses and lifetime of batteries. From this point, this paper proposes WP smoothing control by using short-term average of WP. In this case, the ESS will only operate at high WP fluctuation rate. Then, the output power of ESS will be estimated by short-term average value. The effectiveness of proposed method will be verified by comparing with conventional method. The simulation results will be carried out by using Matlab program.

• 한국전기전자재료학회논문지
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• 제21권3호
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• pp.272-278
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• 2008

This paper investigated the a-si:H gate driver with the stepwise gate signal. In 1-chip type mobile LCD application the stepwise gate signal for low power consumption can be used by adding simple switching circuit. The power consumption of the a-Si:H gate driver can be decreased by employing the stepwise gate signal in the conventional circuit. In conventional one, the effect of stepwise gate signal can decrease slew rate and increase the fluctuation of gate-off state voltage, In order to increase the slew rate and decrease the gate off state fluctuation, we proposed a new a-Si:H TFT gate driver circuit. The simulation data of the new circuit show that the slew rate and the gate-off state fluctuation are improved, so the circuit can work reliably.

• Journal of Welding and Joining
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• 제13권4호
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• pp.85-102
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• 1995

Weld quality of GMA welding processes is closely related to arc stability. Although many researches on arc stability have been performed, real-time estimation of arc stability has not been attempted. For instance, Mita proposed a off-line statistical method in which short circuiting and arcing time, and voltage and current wave forms were sampled to assess arc stability. But this method is not suitable to assess arc stability for GMA welder which employ inverter power source due to its controlled current and voltage wave forms. In this paper, the relationship between are stability and wire feed rate fluctuation is analyzed to propose new criterion for inverter power source. When arc voltage and arc current and arcing time are analyzed, we can assess arc stability only for short circuit transfer mode. When wire feed rate is analyzed, we can estimate arc stability udner the condition of spray transfer mode as well. Hence, the wire feed rate is chosen for monitoring process variable to cover possible metal transfer modes in GMAW. Through this research, it has been identified that arc stability in GMA welding processes is closely related to wire fed rate. When inverter power source is used, conventional statistical method of estimating arc stability, such as Mita index, is no longer valid due to its controlled voltage and current wave forms. Arc stability has been also examined in phase plane diagram.

• 한국태양에너지학회 논문집
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• 제37권6호
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• pp.59-68
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• 2017

In accordance with the policy of local government, the large scale of wind farms have been installed in Jeju power system. However, The intermittent characteristics of wind power output may cause grid voltage and frequency variation, especially in weak power system. One of the solution to solve this problem is installation of Energy storage system (ESS). In this case, the ESS will regulate the active power generated from wind farm to mitigate fluctuation. Actually, the local government of Jeju island constructed ESS connected to Hangwon wind turbine in 2016. From this point, this paper analyzes requirement capacity of ESS to mitigate wind power fluctuation based on measured data from Hangwon wind turbine and ESS. The simulation results will be carried out by Matlab program.

• 감성과학
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• 제18권3호
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• pp.63-70
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• 2015

본 연구는 1/f fluctuation의 ${\alpha}$기울기 따라 구성된 사운드를 들었을 때 감정 스트레스 업무에 종사하고 있는 피험자들의 심박 변화를 확인하고자 하였다. 기존의 연구에서는 주로 사용자의 심리상태 안정시키는 효과 또는 생리적 안정성에 1/f fluctuation의 ${\alpha}$기울기가 관계가 있는 것으로 보고되었다. 본 연구에서는 1/f fluctuation 수준을 총 3가지 나누어 제작한 사운드를 독립변수로 사용하였다. 독립변수는 감정노동 종사자에게 제시하여 그에 따른 심장반응을 측정하였다. 종속변수는 네 가지로 BPM(Beat Per Minute), VLF(Very Low Frequency), SDNN(Standard Deviation of NN intervals), 그리고 HF(High Frequency) 파워(Power)값을 확인하였다. 분석결과 기울기가 3인 1/fluctuation 사운드는 각성효과를 보였다. 기울기 1, 2인 사운드는 이완효과가 있는 것을 통계적으로 검증하였다. 이러한 1/f fluctuation 사운드의 특성을 활용해 감정 노동자들의 스트레스를 완화시키기 위한 서비스에 응용될 수 있을 것으로 사료된다.

• 한국압력기기공학회 논문집
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• 제19권2호
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• pp.155-162
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• 2023

In nuclear power plants, the flow rate information is a major indicator of the performance of rotating equipment such as pumps, and is a very important one required for facility operation and maintenance. To measure a flow rate, various types of methods have been developed and used. Among them, the differential pressure type using orifice and the direct doppler type using ultrasonic waves are the most commonly used. However, these flow rate measurement methods have limitations in installation, conditions and status of the measuring part, etc. To solve this problem, we have studied a new technique for measuring flow rate from scratch. In this paper, we have devised a technique to estimate the flow rate using an average moving velocity of large-scale eddy in turbulence that occurs in the piping flow field. The velocity of the large-scale eddy can be measured using the pressure fluctuation signals on the inner surface of the pipe. To estimate the flow rate, at first a cross-correlation function is applied to the two pressure fluctuation signals located at different positions in the down stream for calculating the time delay between the moving eddies. In order to validate the proposed flow rate estimation method, CFD analyses for the internal turbulence flow in pipe are conducted with a fixed flow condition, where the pressure fluctuation signals on the pipe inner surface are simulated. And then the average flow velocity of the large scale eddy is to be estimated. The estimated flow velocity is turned out to be similar to the fixed (known) flow rate.

• 한국표면공학회지
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• 제51권5호
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• pp.316-324
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• 2018

Harsh seawater environment is subdivided into marine atmosphere, splash zone, tidal zone, submerged zone and bottom of sea depending on the exposed part. Since corrosion rate depends on the conditions of the exposed parts, proper protection and maintenance for each parts are essential for long-term use of steel structures in seawater environment. For steel structures which were installed in Shiwha Lake, a special maintenance system is required to guarantee its long-term durability and safety. As the tidal power plant has recently been operated, the salinity has risen due to the rapid influx of seawater upstream into Sihwa Lake and the corrosion tendency of the structure is variable according to the water level fluctuation. In this study, corrosion properties of steel structures under water level fluctuation was evaluated by corrosion rate measurement, visual inspection and natural potential measurement and their durability and life management were discussed in view of the effect of variation in of seawater level fluctuations in Shihwa Lake.

• 한국태양에너지학회 논문집
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• 제32권1호
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• pp.25-31
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• 2012

This paper presents the characteristics of power generation output at Haeng-won wind farm and how to determine the optimized ESS capacity for power stabilizing. Depend on the fluctuation rate of wind power output variation, wind farm capacity and site, power stabilization will be impacted. Therefore, we need to determine proper ESS capacity. Using the actual data of Haeng-won wind farm from 2009. 3 to 2010.2., capacity of ESS was determined by moving average value. To verify the proposed algorithm, simulations are carried out with PSCAD/EMTDC program. As a result, optimal ESS capacity of Haeng-won wind farm in Jeju is estimated about 1.63 MWh.

• Nuclear Engineering and Technology
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• 제33권1호
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• pp.83-92
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• 2001

The properties of off-gas generated from vitrification process of ion-exchange resin were characterized. Theoretical composition and flow rate of the off-gas were calculated based on chemical composition of resin and it＇s burning condition inside CCM. The calculated off-gas flow rate was 67.9Nm$^3$/h at the burning rate of 40kg/h. And the composition of off-gas was avaluated as $CO_2$(41.4%), steam(40.0%), $O_2$(13.3%), NO(3.6%), and SO$_2$(1.6%) in order. Then, actual flow rate and composition of off-gas were measured during pilot-scale demonstration tests and the results were compared with theoretical values. The actual flow rate of off-gas was about 1.6 times higher than theoretical one. The difference between theoretical and actual flow rates was caused by the in-leakage of air to the system, and the in-leakage rate was evaluated as 36.3Nm$^3$/h. Because of continuous change in the combustion parameters inside CCM, during demonstration tests, the concentration of toxic gases showed wide fluctuation. However, the concentration of CO, a barometer of incompleteness of combustion inside CCM, was stabilized soon. The result showed quasi-equilibrium state was achieved two hours after feeding of resin.

• 한국의학물리학회지:의학물리
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• 제6권2호
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• pp.103-109
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• 1995

자율신경계는 서로 상반되게 작용하는 교감신경과 부교감신경으로 구성되어 그 활성의 균형에 의해 신체의 향상성이 유지된다. 자율신경계는 각종 스트레스나 질환에 의해 그 활성이 변화한다. 그러나 자율신경계의 메카니즘은 너무나 복잡하여 해석이 용이하지 않은 관계로 인체에서 유기되는 여러가지 생체신호중에서 자율신경에 의해 지배되는 심전도 신호와 호흡을 매개변수로하여 자율신경의 활성도를 측정하는 시스템의 설계와 제작이 본 연구의 목적이다. 본 논문을 수행하기 위해서 심전도 신호 증폭기, 호흡변위 증폭기, interval time generator 및 처리 소프트웨어 등을 제작하였다. 그리고 심전도 신호와 호흡요소에 대한 power spectrum을 나타낼 뿐만 아니라 이들을 합성하여 하나의 graph로 표현할 수 있도록 하였다.