• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.738-744
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• 2017

Recently, the installation of energy storage systems (ESSs) has increased in parallel with the extension of renewable energy resources. However, there has been no concrete analysis ofthe performance verification and economic evaluation of ESSs,which makes it difficult to perform aneffective installation and operation of an ESS. In particular, there are no international technical standards and guidelines on electric ESS for frequency regulation applications. Therefore, acomprehensive study on the power quality, impact on grid, extent of contribution, and cost benefit study of ESS are strongly being required. Under these backgrounds, this paper proposes a performance verification algorithm on ESS for frequency regulation application based on ananalysis of the AGC(Automatic Generation Control) performance verification method of PJM in USA. In addition,this paper proposes an economic evaluation algorithm on a 500 MW installation of ESS for frequency regulation applications using the account settlement of an expensive gas-fired generation plant and coal-fired power generation plant. From the simulation with real ESS operation data and 500 MW installation case, it wasconfirmed that the ESS showssuperior performance toany other conventional generators and provides anannual benefit of 500 MW ESS are between 345~429 billon won.

• Tunnel and Underground Space
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• v.13 no.6
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• pp.486-494
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• 2003

When the orientations of joints are measured on a rock exposure, there are frequent cases that are difficult to approach by the surveyor to the target joints or to set up scanlines on the slope. In this study, to complement such limit and weak points, a new algorithm was developed to interpret joint orientation from analyzing the images of rock slope. As a method of arranging the multiple images of a rock slope, the multistage convergent photographing system was introduced to overcome the limitation of photographing direction which existing method such as parallel stereophotogrammetric system has and to cover the range of image measurement, which is the overlapping area between the image pair, to a maximum extent. To determine camera parameters in the perspective projection equation that are the main elements of the analysis method, a new method was developed introducing three ground control points and single ground guide point. This method could be considered to be very simple compared with other existing methods using a number of ground control points and complicated analysis process. So the global coordinates of a specific point on a rock slope could be analyzed with this new method. The orientation of a joint could be calculated using the normal vector of the joint surface which can be derived from the global coordinates of several points on the joint surface analyzed from the images.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.12
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• pp.3235-3245
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• 1996

A DDFS(Direct Digital Frequency Synthesizer) used in spread spectrum communication systems must need fast switching speed, high resolution(the step size of the synthesizer), small size and low power. The chip has been designed with four parallel sine look-up table to achieve four times throughput of a single DDFS. To achieve a high processing speed DDFS chip, a 24-bit pipelined CMOS technique has been applied to the phase accumulator design. To reduce the size of the ROM, each sine ROM of the DDFS is stored 0-.pi./2 sine wave data by taking advantage of the fact that only one quadrant of the sine needs to be stored, since the sine the sine has symmetric property. And the 8 bit of phase accumulator's output are used as ROM addresses, and the 2 MSBs control the quadrants to synthesis the sine wave. To compensate the spectrum purity ty phase truncation, the DDFS use a noise shaper that structure like a phase accumlator. The system input clock is divided clock, 1/2*clock, and 1/4*clock. and the system use a low frequency(1/4*clock) except MUX block, so reduce the power consumption. A 107MHz DDFS(Direct Digital Frequency Synthesizer) implemented using 0.8.mu.m CMOS gate array technologies is presented. The synthesizer covers a bandwidth from DC to 26.5MHz in steps of 1.48Hz with a switching speed of 0.5.mu.s and a turing latency of 55 clock cycles. The DDFS synthesizes 10 bit sine waveforms with a spectral purity of -65dBc. Power consumption is 276.5mW at 40MHz and 5V.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.12 s.103
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• pp.1229-1238
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• 2005

OFDM(Orthogonal Frequency Division Multiplexing) communications system is very attractive for the high data rate wireless transmission. However, it may be distorted in the nonlinear HPA(High Power Amplifier) since OFDM signal has hish PAPR(Peak-to-Average Power Ratio). In this paper, a new method using control tone is studied for reducing the PAPR and we call it PCT(PAPR Control Tone) method. This proposed PCT method is to assign control tones for PAPR reduction at the predefined sub-carriers. After IFFT(Inverse Fast Fourier Transform) and PAPR calculation, the OFDM data signal of the lowest PAPR is selected to transmit. Unlike the conventional method, it can cut down the computational complexity because it does not require the transmission and demodulation process of side information about the phase rotation. Furthermore, if this method is made up in parallel configuration, it can solve the time delay problem so that it can be processed in real time processing. This proposed method is compared with the conventional selected mapping(SLM) technique. We find out the PAPR reduction performance and BER when the number of control tone is 6 and nonlinear HPA is considered.

• Journal of Korea Spatial Information System Society
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• v.11 no.3
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• pp.9-18
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• 2009

Recently, due to the advanced technologies of mobile devices and wireless communication, there are many studies on telematics and LBS(location-based service) applications. because moving objects usually move on spatial networks, their locations are updated frequently, leading to the degradation of retrieval performance. To manage the frequent updates of moving objects' locations in an efficient way, a new distributed grid scheme, called DS-GRID (distributed S-GRID), and k-NN(k-nearest neighbor) query processing algorithm was proposed[1]. However, the result of k-NN query processing technique may be invalidated as the location of query and moving objects are changed. Therefore, it is necessary to study on continuous k-NN query processing algorithm. In this paper, we propose both MCE-CKNN and MBP(Monitoring in Border Point)-CKNN algorithmss are S-GRID. The MCE-CKNN algorithm splits a query route into sub-routes based on cell and seproves retrieval performance by processing query in parallel way by. In addition, the MBP-CKNN algorithm stores POIs from the border points of each grid cells and seproves retrieval performance by decreasing the number of accesses to the adjacent cells. Finally, it is shown from the performance analysis that our CKNN algorithms achieves 15-53% better retrieval performance than the Kolahdouzan's algorithm.

• Journal of Korean Society on Water Environment
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• v.24 no.6
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• pp.659-669
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• 2008

Two sets of four parallel activated sludge reactors (ASRs) maintaining an MLSS of 3000 mg/L were operated to investigate the effect of DO, HRTs and bio-contact media (BCM) packing ratios on the removal efficiency of organic matters and nitrogen. Packing ratios of BCM to BCM-ASR systems 1, 2, 3, and 4 were 0% (suspended growth only), 10%, 15% and 20%, respectively. All systems were operated at an HRT of 4 hr, 6 hr, and 8 hr, respectively; DO concentration was maintained 0.5~1.0 mg/L and 1.5~2.0 mg/L for each HRT condition. In terms of TSS, TCODcr and SCODcr removal efficiency, all systems had a similar level of the removal efficiency under varied HRTs, and DO. But organic removal efficiency of systems with BCM was approximately 3~5% higher than systems without BCM at the same HRT and the DO. About the nitrification efficiency, with high DO (1.5~2.0 mg/L), as HRT (4 hr, 6 hr, 8 hr) or BCM packing ratio increased, the slight increment of nitrification efficiency was observed. However, under the low DO (0.5~1.0 mg/L), increase of BCM packing ratio and HRT resulted in large increase of the nitrification efficiency. At the same HRT and BCM packing ratio, the nitrification efficiency increased greatly with up to 15% as DO increased. When the HRT increased from 4hr to 8hr, the denitrification efficiency slightly increased by 5~10% only, under all DO conditions. Systems with BCM had higher denitrification efficiency, ranged 62.7~91.1% than systems without BCM showed 32.1~65.6%. And the increase in BCM packing ratio from 10% to 20% resulted in about 14~16% denitrification efficiency increment. BCM packing ratio showed great effect on the denitrification. The increase of the DO (from 0.5~1.0 mg/L to 1.5~2.0 mg/L) at the same HRT and BCM packing ratio resulted in slight decrease of denitrification efficiency with up to 7% for systems with BCM. But for systems without BCM, the denitrification efficiency decreased with up to 28%. In all system, the denitrification efficiency had more influence on the TN removal efficiency than nitrification efficiency. So, BCM packing ratio (0%, 10%, 15%, 20%) has greater effect on the TN removal than HRT and DO. The TN removal efficiency increased as packing ratio of BCM increased with up to 45%. As a result, the highest TN removal efficiency was observed 73.7% at the condition showed the highest denitrification efficiency that DO of 0.5~1.0 mg/L, an HRT of 8 hr, and 20% of BCM packing ratio was maintained.

• Journal of environmental and Sanitary engineering
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• v.7 no.2
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• pp.1-10
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• 1992

Since 1960's along with industrialization and urbanization, economic growth has been . achieved, however, at the same time, environmental condition has been seriously deteriorated. . Currently, volume of wastewater has been increasing at annual rate of 7% in sewage and 20% in industrial wastewater. However, the nation's sewage treatment serves only 33% of the municipal wastewater as of 1991. Major portion of air pollutants comes from combustion of oil and coal which comprise 81% of total energy use and emission gases from motor vehicles increasing at an accelerated rate. It is known that Korea generates the highest amount of waste per capta. Nevertheless, it is not sufficient to reduce the volume of waste by means of resources recovery and recycling. Recognizing the importance of global environmental problems such as ozone layer depletion, global warming and acid rain, international society has been making various efforts since the 1972 Stockholm conference. In particular, it is expected that the Rio conference which has adopted the Rio declaration and Agenda 21 will form a crucial turning point of the emerging new world order after the Cold War confrontation. To cope with such issues as domestic pollution and global environmental problems, the fundamental national policy aims at harmonizing "environmental protection and sustainable development". The Ministry of Environment has recently set up a mid-term comprehensive plan which includes annual targets for environmental protection. According to the government plan, gradual improvement of various environmental conditions and specific measures to achieve them is planned in time frame. Additional sewage treatment plants will be constructed in urban areas with the target to treat 65% of the nation's municipal sewage by 1996. Supply of clean fuels such as LNG will also be expanded starting from large cities as a cleaner substitute energy for coal and oil. In parallel with expansion of LNG, emphasis will be placed on installation of stack monitoring system. Due to the relatively limited land, government's basic policy for solid waste treatment is to develop large scale landfill facilities rather than small sized ones. Thirty three regional areas have been designated for the purpose of waste management. For each of these regions, big scale landfill site is going to be developed. To increase the rate of waste recycling the government is planning to reinforce separate collection system and to provide industries with economic incentives. As a part of meeting the changing situation on global environmental problems after UNCED, and accommodation regulatory measures stipulated in the global environmental conventions and protocols, national policy will try to alter industrial and economic structure so as to mitigate the increasing trends of energy consumption, by encouraging energy conservation and efficiency. In this regard, more attention will be given to the policy on the development of the cleaner technology. Ultimately, these policies and programs will contribute greatly to improving the current state of national public health.

• Journal of KIISE:Databases
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• v.29 no.3
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• pp.180-192
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• 2002

We investigate the effect of the data skew of join attributes on the performance of a pipelined multi-way hash join method, and propose two new harsh join methods in the shared-nothing multiprocessor environment. The first proposed method allocates buckets statically by round-robin fashion, and the second one allocates buckets dynamically via a frequency distribution. Using harsh-based joins, multiple joins can be pipelined to that the early results from a join, before the whole join is completed, are sent to the next join processing without staying in disks. Shared nothing multiprocessor architecture is known to be more scalable to support very large databases. However, this hardware structure is very sensitive to the data skew. Unless the pipelining execution of multiple hash joins includes some dynamic load balancing mechanism, the skew effect can severely deteriorate the system performance. In this parer, we derive an execution model of the pipeline segment and a cost model, and develop a simulator for the study. As shown by our simulation with a wide range of parameters, join selectivities and sizes of relations deteriorate the system performance as the degree of data skew is larger. But the proposed method using a large number of buckets and a tuning technique can offer substantial robustness against a wide range of skew conditions.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.2
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• pp.81-92
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• 2011

High resolution seismic profiles (chirp and sparker system) were analyzed for the interpretation of nearshore sedimentary environments of Suyeong Bay, Busan. The sedimentary sequence is classified into three seismic units (SU1a, SU1b, and SU2), overlying acoustic basement, and each units can be defined as erosional and disconformable strata. The lowermost SU1a is characterized by the acoustically parallel and prolonged inner reflections, compared with the upper SU1b displays irregular internal reflectors. The uppermost unit, SU2, is acoustically transparent. The acoustic basement is incised with channels, probably due to the active erosion during the early period of transgression. The acoustic basement deepens eastward in the study area, suggesting primary association with the Suyeong River. The upper SU1a and SU1b units constitute lowland-fill strata. SU2 is widely distributed over the study area. High resolution seismic profiles of Suyeong Bay provide significant information crucial to the interpretation of sedimentary environmental history, which is closely related to the sea level change, estuarine environment and influx of terrestrial sediments from the adjacent rivers.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.7
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• pp.38-45
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• 2006

The superconducting fault current limiters(SFCLs) provide the effect such as enhancement in power system reliability due to limiting the fault current within a few miliseconds. Among various SFCLs we have developed a flux-lock type SFCL and exploited a special design to effectively reduce the fault current according to properly adjustable magnetic field after the short-circuit test. This SFCL consists of two copper coils wound in parallel on the same iron core and a component using the YBCO thin film connected in series to the secondary copper coil. Meanwhile, operating characteristics can be controlled by adjusting the inductances and the winding directions of the coils. To analyze the operational characteristics, we compared closed-loop with open-loop iron core. When the applied voltage was 200[Vrms] in the additive polarity winding, the peak values of the line current the increased up to 30.71[A] in the closed-loop and 32.01[A] in the open-loop iron core, respectively. On the other hand, in the voltages generated at current limiting elements were 220.14[V] in the closed-loop and 142.73[V] in the opal-loop iron core during first-half cycle after fault instant under the same conditions. We confirmed that the open-loop iron core had lower power burden than in the closed-loop iron core. Consequently, we found that the structure of iron core enabled the flux-lock type SFCL at power system to have the flexibility.