• Journal of Power Electronics
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• v.16 no.3
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• pp.946-959
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• 2016

A novel Virtual Space Vector (VSV) modulation strategy for complete control of potential neutral point (NP) issues is proposed in this paper. The neutral point potential balancing problems of multi-level converters, which include elimination of low frequency oscillations and self-balancing for NP dc unbalance, are investigated first. Then a set of improved virtual space vectors with dynamic adjustment factors are introduced and a multi-objective optimization algorithm which aims to optimize these adjustment factors is presented in this paper. The improved virtual space vectors and the multi-objective optimization algorithm constitute the novel Virtual Space Vector modulation. The proposed novel Virtual Space Vector modulation can simultaneously recover NP dc unbalance and eliminate low frequency oscillations of the neutral point. Experiment results show that the proposed strategy has excellent performance, and that both of the neutral point potential issues can be solved.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2529-2539
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• 2022

Stochastic and an empirical Green's function (EGF) methods are preliminarily applied to simulate strong ground motions (SGMs) at seismic stations within nuclear power plant (NPP) sites in South Korea by an assumed large earthquake with M_W6.5 (scenario earthquake) on the causative fault of the 2016 Gyeongju earthquake with M_W5.5 (mainshock). In the stochastic method, a ratio of spectral amplitudes of observed and simulated waveforms for the mainshock is assumed to be an adjustment factor. In the EGF method, SGMs by the mainshock are simulated assuming SGMs by the 2016 Gyeongju earthquake with M_W5.0 (foreshock) as the EGF. To simulate SGMs by the scenario earthquake, a ratio of fault length to width is assumed to be 2:1 in the stochastic method, and SGMs by the mainshock are assumed to be EGF in the EGF method. The results are similar based on a bias of the simulated response spectra by the two methods, and the simulated response spectra by the two methods exceeded commonly standard design response spectra anchored at 0.3 g of NPP sites slightly at a frequency band above 4 Hz, but considerable attention to interpretation is required since it is an indirect comparison.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.634-642
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• 2016

This research investigated the relationship among character, interpersonal relations, and adjustment to college life of university nursing students as well as to identify the factors that affect college life. A self-report type survey was conducted on a total of 180 nursing students in a city between May 30 and Jun 09 of 2016. According to our findings, the relationship between the adjustment to school life and character (r=.506, p<.001) as well as between the adjustment to school life and personal relations (r=.585, p<.001) showed a significantly positive correlation in the medium level. With improved personal relationships and with higher level of character, nursing students appear to more successfully adjust to college life. It was also found that an explanatory power for the adjustment to college life of these factors is 46% (F=75.28, p<.001). The study results indicate that it is necessary to develop a program that can improve interpersonal relationships and character of nursing students in order to enhance the adjustment process to college life.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.8
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• pp.517-526
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• 2016

The purpose of this study was to investigate the self-resilience, professional self-concept, and major satisfaction on nursing students' adjustment to college life and to present the basic data to assist in healthy adaption of college life. The study included 310 students from two universities in Gwangju and Jeonnam. A questionnaire survey was conducted on the subjects to determine their self-resilience, professional self-concept, major satisfaction, and adjustment to college life with nursing as a major. The data were collected from 1, April, 2016 to 15, April using self-report, questionnaires and analyzed through descriptive statistics, percentage, mean, standard deviation, t-test, ANOVA, and Pearson correlation coefficient, using SPSS 20.0. As a result, self-esteem, professional self-concept, major satisfaction, and adjustment to college life averaged 3.80 (out of 4), 2.81 (4), 3.86 (5), and 2.75 (5) respectively. In terms of correlations, there was a significant positive correlation between adjustment to college life and self-resilience (r=.404, p<.001) and professional self-concept (r=.404, p<.001) and major satisfaction(r=.455, p<.001). In addition, self-resilience (${\beta}=.252$, p<.001) and major satisfaction (${\beta}=.309$, p<.001) of variance in adjustment to college life and the explanatory power of the model was 27.2%. Based on these results, improvement programs are necessary to help nursing students get adjusted to college life.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.3
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• pp.425-431
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• 2016

Supply Capability of the generator, if the maximum demand occurs, refers to the maximum power that can be stably supplied and it is possible to maintain stable power supply to be greater than actual load. However, unexpected power demand and reduction in supply Capability due to stop of unexpected generator in operation can temporarily make a big chaos in power system. In fact, due to a lack of power supply Capability in the country, enforced emergency load adjustment to the September 15, 2011, the circulation power outage has occurred in several cities. As the result, interrupted operation of the elevator and stopped hospital medical equipment led to a great deal of trouble to people's lives, causing a social problem. At that time, it was found that a failed frequency control because of smaller actual supply Capability than that of predicted. The difference was about 1,170 MW with Gas turbine power plant. By accurately calculating the generator supply capability, we can not only grasp the power reserve rate, but also correspond to the time of power supply instability.

• Proceedings of the KIEE Conference
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• 2003.07e
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• pp.31-33
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• 2003

Power amplifier linearity plays a major role in the design of RF communication systems. In this paper, predistortion type linearizer was designed an independently controllable AM/AM and AM/PM predistortion linearizers. This linearizer allows independent adjustment of the AM/AM and AM/PM curves by using two adjustable voltages to compensate the power amplifier non-linearities. The predistortion linearizer was improved the ACPR by 6dB with cdma2000 multi carrier signals. Applying this linearizer to two-tone 880MHz power amplifier, an improvement of adjacent channel leakage power up to 5dBm has been achieved.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.50 no.3
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• pp.101-108
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• 2001

Frequency is an important operating parameter of a power system. Electric power systems sustain transient frequency swings whenever the balance between generation and load does not no longer hold. To cope with this constraints, it requires an accurate and high speedy frequency deviation estimation technique and suitable adjustment to obtain the Power system energy balance. This paper describes a digital signal processing technique for measuring the operating frequency of a power system. The fundamental frequency component of 3-phase signal is first extracted by using an algorithm based on FIR filter. The rate change of the phase angle is used for estimation. To confirm the validity of the proposed algorithm, the simulation studies carried out on a typical 154KV double T/L system by using EMTP software. Some test results are presented in the paper.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.53 no.3
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• pp.188-196
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• 2004

Amplifier linearity plays a major role in the quality of mordern communication systems. The Power amplifier should be operated near saturation region to achieve high efficiency But at this region amplitude and phase distortions of the amplifier remarkably increase with the input power increase and cause a significant adjacent channel interference. In this paper, an independently controllable AM/AM and AM/PM predistortion linearizers consisted of two bias feed resistance linearizers is proposed. This linearizer allows independent adjustment of the AM/AM and AM/PM curves by using two adjustable voltages to compensate tile power amplifier non-linearities. The predistortion linearizer can improve the ACPR by 5.3dB with cdma2000 multi carrier signals. And by applying this linearizer to two-tone(880MHz) power amplifier, third order IMD products are improved up to 8(dB).

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.8
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• pp.2797-2820
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• 2015

In order to accommodate huge number of antennas in a limited antenna size, a large scale antenna array is expected to have a three dimensional (3D) array structure. By using the Active Antenna Systems (AAS), the weights of the antenna elements arranged vertically could be configured adaptively. Then, a degree of freedom (DOF) in the vertical plane is provided for system design. So the three-dimension MIMO (3D MIMO) could be realized to solve the actual implementation problem of the massive MIMO. However, in 3D massive MIMO systems, the pilot contamination problem studied in 2D massive MIMO systems and the inter-cell interference as well as inter-vertical sector interference in 3D MIMO systems with vertical sectorization exist simultaneously, when the number of antenna is not large enough. This paper investigates the interference management towards the above challenges in 3D massive MIMO systems. Here, vertical sectorization based on vertical beamforming is included in the concerned systems. Firstly, a cooperative joint vertical beams adjustment and pilot assignment scheme is developed to improve the channel estimation precision of the uplink with pilots being reused across the vertical sectors. Secondly, a downlink interference coordination scheme by jointly controlling weight vectors and power of vertical beams is proposed, where the estimated channel state information is used in the optimization modelling, and the performance loss induced by pilot contamination could be compensated in some degree. Simulation results show that the proposed joint optimization algorithm with controllable vertical beams' weight vectors outperforms the method combining downtilts adjustment and power allocation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.8
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• pp.994-1001
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• 2018

In this paper, to studied about future power system construction using PSS / E-Python API. Python-based future system automatical construction methods and modeling of renewable sources. it confirmed the stability of the powert system for each renewable area by calculating the weighted short circuit ratio (WSCR) index. it calculated the short circuit ratio (SCR) and selected the transmission line linkage scenario to improve the stability of vulnerable areas. it confirmed the WSCR index improvement through the selected transmission line linkage of scenario, and analyzed the stability of the renewable power system applying the scenario. It describes Facts and Shunt devices adjustment for the load flow convergence. It describes the stable methed of the bus voltage through the transformer Ratio Tap adjustment. By performing PSS/E ASCC using the Python it was performed three-phase short circuit fault capacity analysis, it is confirmed whether excess of the fault current circuit breaker capacity. In order to contingency accident analysis, it have described the generation of one or two line list of each areas using the Python. The list is used to contingency analysis and describe the soluted of the transmission line overload through comparison before and after adding the scenario line.