• Journal of Power Electronics
• /
• v.18 no.4
• /
• pp.1111-1126
• /
• 2018

In modern power systems, distributed generators (DGs) result in high stress on system frequency stability. Apart from the intermittent nature of DGs, most DGs do not contribute inertia or damping to systems. As a result, a new control method referred to as a virtual synchronous machine (VSM) has been proposed, which brought new characteristics to inverters such as synchronous machines (SM). DGs employing an energy storage system (ESS) provide inertia and damping through VSM control. Meanwhile, energy storage presents some physical constraints in the VSM implementation level. In this paper, a VSM mathematical model is built and analyzed. The dynamic responses of the output active power are presented when a step change in the frequency occurs. The influences of the inertia constant, damping factor and operating point on the ESS volume margins are investigated. In addition, physical constraints are proposed based on these analyses. The proposed physical constraints are simulated using PSCAD/EMTDC software and tested through RTDS experiment. Both simulation and RTDS test results verify the analysis.

• Korean Journal of Soil Science and Fertilizer
• /
• v.47 no.1
• /
• pp.23-27
• /
• 2014

Nutrient accumulation in surface soil has become a serious problem for cucumber production in greenhouse. However, still in many cases, soil management practices are only focused on maintaining crop yield, regardless of sustainability related with soil chemical properties. This study was conducted to propose a sustainable soil management practice by investigating the impact of cover crop species and nitrogen rate of fertigated solution on cucumber yield and soil chemical properties in greenhouse condition. Rye and hairy vetch were tested as a fallow cover crop, and each amount of urea (1/2, 3/4, 1 times of N fertilizer recommendations), determined by soil testing result, was supplied in fertigation plots as an additional nitrogen source. The result showed that the yield of cucumber was higher in rye treatment than control and hairy vetch treatment. In addition, rye effectively reduced EC and accumulated nutrients from the soil. Meanwhile, N concentration of fertigated solution showed no significant effect on the growth and yield of cucumber. Consequently, these results suggest that it is desirable to choose rye as a fallow catch crop for sustainable cucumber production in greenhouse.

• ALGAE
• /
• v.27 no.4
• /
• pp.283-294
• /
• 2012

The physico-chemical and environmental factors of stoneworks were examined from March 2009 to October 2010, and aerial algae living on 24 stoneworks in Korea were identified. Fifty aerial algae were found in 24 stoneworks. Of the 50 taxa, 30 taxa were cyanophytes, 16 taxa were bacillariophytes, 3 taxa were chlorophytes, and 1 taxon was a xanthophyte. Nine species, including Aphanocapsa rivularis, which is known to only live in aquatic conditions, inhabited both aquatic and aerial environments. Synechococcus aeruginosus, Scytonema coactile var. thermalis, S. coactile var. minor, Stigonema ocellatum f. ocellatum, and Oscillatoria boryana were newly recorded in Korea. As a result of a correlation analysis between algae and the physico-chemical and ecological environmental factors, the taxa were divided into the bryophyte group, the humidity group, and the dry group. Although the bryophyte group was included within the humidity group, it was separated from the dry group. Taxa in the bryophyte group including Nostoc commune which was distributed in more humid areas than those in the humidity group. However, dry group taxa including Chroococcus pallidus were distributed in lower humidity than that of the two other groups. Correlations among other environmental factors were tested to identify other factors that could substitute for humidity and light intensity. As a result, tree distance, water distance, and plant coverage were replaceable environmental factors.

• Journal of Astronomy and Space Sciences
• /
• v.15 no.2
• /
• pp.373-389
• /
• 1998

The test result of the X-ray observation system is presented which have been developed at Korea Astronomy Observatory for 3 years(1995 -1997). The instrument, which is composed of detector and signal processing parts, is designed for the future observations of compact X-ray sources. The performance of the instrument was tested by mounting on the two-stage Korean Sounding Rocket, which was launched from Taean rocket flight center on June 11 at 10:00 KST 1998. Telemetry data was received from individual parts of the instrument for 32 and 55.7 sec, respectively, since the launch of the rocket. In this paper, the result of the data analysis based on the received telemetry data and discussion about the performance of the instrument is reported.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.56 no.1
• /
• pp.206-213
• /
• 2007

In this paper, The monitoring system for TV advertisement is implemented using video watermark. The functions of the advertisement monitoring system are monitoring the time, length, and index of the on-air advertisement, saving the log data, and reporting the monitoring result. The performance of the video watermark used in this paper is tested for TV advertisement monitoring. This test includes LAB test and field test. LAB test is done in laboratory environment and field test in actually broadcasting environment. LAB test includes PSNR, distortion measure in image, and the watermark detection rate in the various attack environment such as AD/DA(analog to digital and digital to analog) conversion, noise addition, and MPEG compression. The result of LAB test is good for the TV advertisement monitoring. KOBACO and SBS are participated in the field test. The watermark detection rate is 100% in both the real-time processing and the saved the processing. The average deviation of the watermark detection time is 0.2 second, which is good because the permissible average error is 0.5 second.

• Journal of the Korean Society of Safety
• /
• v.17 no.2
• /
• pp.16-21
• /
• 2002

At present the Polyethylene piping, on supporting LNG is widely used because of it's disposition which are anti-corrosion flexible and so on. However, it has a few kinds of risk which are the possibility of piping leak, the character of easily corroded and so on. For giving solution, this study is intended to experiment the intension of the PE pipe after melted and when it is melting, the condition which are temperature and pressure is changed. the melting condition in temperature and pressure is adapted identically. After melting, it's joint is tested as intension. The result is that the effect of temperature in intension is more effective than pressure. In $210^{\circ}C$, $20kg/cm^{2}$ condition, the melting intension has the highest. Compare to the Butt melting joint and the Saddle melting joint, the former was $214kg/cm^{2}$ and the latter was $50kg/cm^{2}(bead\;2{\sim}3mm)$ and $73kg/cm^{2}(bead\;5{\sim}7mm)$. It means that the Butt melting method has more intensive than saddle. Consequently, the result shows that the liability and safety when pipe melting method is used will improve in pipe installation.

• Journal of the Korean Society of Combustion
• /
• v.14 no.1
• /
• pp.25-30
• /
• 2009

Propagation rates ($U_{edge}$) of various premixed, twin edge-flames were measured as a function of global strain rate ($\sigma$), mixture strength, and Lewis number (Le). Using a counterflow slot-jet burner with electrical heaters at each end, both advancing (positive $U_{edge}$) and retreating (negative $U_{edge}$) edge-flames can be studied as they propagate along the long dimension of the burner. Experimental results are presented for premixed methane/air twin flames in terms of the effects of $\sigma$ on $U_{edge}$. Both low-$\sigma$ and high-$\sigma$ extinction limits were discovered for all mixtures tested. As a result, the domain of edge-flame stability was obtained in terms of heat loss factor and normalized flame thickness, and comparison with the numerical result of other researchers was also made. For low ($CH_4/O_2/CO_2$) and high ($C_{3}H_{8}$/air) Lewis number cases, propagation rates clearly show a strong dependence on Le.

• The Journal of Korea Robotics Society
• /
• v.4 no.4
• /
• pp.298-304
• /
• 2009

This paper describes an algorithm that improves 3D reconstruction result using a multi-sensor fusion disparity map. We can project LRF (Laser Range Finder) 3D points onto image pixel coordinatesusing extrinsic calibration matrixes of a camera-LRF (${\Phi}$, ${\Delta}$) and a camera calibration matrix (K). The LRF disparity map can be generated by interpolating projected LRF points. In the stereo reconstruction, we can compensate invalid points caused by repeated pattern and textureless region using the LRF disparity map. The result disparity map of compensation process is the multi-sensor fusion disparity map. We can refine the multi-sensor 3D reconstruction based on stereo vision and LRF using the multi-sensor fusion disparity map. The refinement algorithm of multi-sensor based 3D reconstruction is specified in four subsections dealing with virtual LRF stereo image generation, LRF disparity map generation, multi-sensor fusion disparity map generation, and 3D reconstruction process. It has been tested by synchronized stereo image pair and LRF 3D scan data.

• The Journal of Asian Finance, Economics and Business
• /
• v.7 no.1
• /
• pp.249-257
• /
• 2020

This paper focused on the level of managerial centralization on chief executive officer (CEO) as a factor to affect the shared growth activities of corporate. As service corporations are becoming active in shared growth activities recently, this paper thus used CEO. Pay Slice (CPS) information to measure the level of managerial centralization on CEO of service corporation and tested the influence of the level of managerial centralization on whether shared growth activities are executed and the level of such activities respectively. The result of test shows that companies with high managerial centralization on CEO are more passive toward shared growth activities than those without such centralization. This can be interpreted that a CEO with more powerful influence may consider shared growth activities as to be negative and take a passive attitude to them. On the other hand, such result was supported by additional analysis with companies committing shared growth activities as well. This paper is expected to contribute to bring about interest on shared growth activities as the gap between major companies and small and medium sized companies is currently expanding in terms of operating profit ratio and even salary of employees.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.25 no.7
• /
• pp.49-54
• /
• 2011

Now the world will regulate the CO2 emission due to environmental issues. For an alternative plan photovoltaic system is watched. So, photovoltaic system is trend of big city and it is mandatory for renovation of construction. Oil & gas filling station existed in city is suitable to found the photovoltaic system. But the general photovoltaic system in oil & gas filling station is difficult to found because it is classified into hazardous area. This paper evaluates intrinsic safety evaluation of solar cell for making basic data to found for the photovoltaic system on hazardous area. The intrinsic safety characteristic is evaluated by short-circuit ignition test using IEC type spark ignition test apparatus and temperature rising test. The result of short-circuit ignition test, propane-air mixture gas is exploded on condition that 4 solar cells(9[V], 90[mA]) are connected serially under insolation 800[W/$m^2$]. So, if a larger solar module will be used at oil & gas filling station than we were tested, it needs explosion proof. As the result of rising temperature test, the temperature rising due to short circuit is not so much, but when the temperature rises due to radiant heat, it demands careful consideration for environmental influence.