• Journal of Mechanical Science and Technology
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• v.19 no.5
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• pp.1131-1137
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• 2005

Methods for measuring surface roughness based on light reflectivity have advantages over methods based on light interference or diffraction, especially in in-situ, on-the-machine and in-process applications. However, measurement inconsistencies caused by changes in the specimen are still a drawback for field applications. In this study, we propose a new feedback-based algorithm to enhance the consistency against changes in the specimen. The algorithm is deduced from simulations based on light reflectance theory with typical modeled surfaces. The proposed method is similar to a digital controller and regulates the power of reflected light. Experiments varying heights and materials, verified the improvements in robustness of the method against measurement disturbances caused by specimen changes.

• Journal of Power Electronics
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• v.10 no.1
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• pp.79-84
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• 2010

This paper presents a grid connected photo-voltaic system using a quasi-Z-source inverter (QZSI) for power stage reduction. The power stage can be reduced because of an additional shoot-through stage which is a characteristic of QZSI. Therefore, by utilizing a QZSI the system's efficiency can be increased. In this paper, for applying a QZSI to a PV system, control methods such as maximum power point tracking (MPPT), point of common coupling (PCC) current control and PWM are studied and verified through simulation and experiment. In order to explain the above controllers, the characteristics of a QZSI are first analyzed. Then the MPPT control technique with a modified P&O method, the PCC current control for the regulation of the dc-link capacitor voltage and the PWM methods for the proposed system are explained. The feasibility of the proposed algorithm is verified through simulation and experiment with a 3kW system.

• Advances in Computational Design
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• v.2 no.3
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• pp.211-223
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• 2017

This research presented a numerical and experimental study on the seismic performance of first-generation base-isolated and fixed-base nuclear power plants (NPP). Three types of the base isolation system were applied to rehabilitate the first-generation nuclear power plants: frictional pendulum (FP), high-damping rubber (HDR) and lead-rubber (LR) base isolation. Also, an Excel program was proposed for the design of the abovementioned base isolators in accordance with UBC 97 and the Japan Society of Base Isolation Regulation. The seismic assessment was performed using the pushover and nonlinear time history analysis methods in accordance with the FEMA 356 regulation. To validate the adequacy of the proposed design procedure, two small-scale NPPs were constructed at Universiti Teknologi Malaysia's structural laboratory and subjected to a pushover test for two different base conditions, fixed and HDR-isolated base. The results showed that base-isolated structures achieved adequate seismic performance compared with the fixed-base one, and all three isolators led to a significant reduction in the containment's tension, overturning moment and base shear.

• Journal of Electrical Engineering and Technology
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• v.5 no.1
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• pp.103-115
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• 2010

This paper discusses a DC distribution system which has been supplied by external AC systems as well as local microturbine distributed generation system in order to demonstrate an overall solution to power quality issue. Based on the dynamic model of the converter, a design procedure has been presented. In this paper, the power flow control in DC distribution system has been achieved by network converters. A suitable control strategy for these converters has been proposed, too. They have DC voltage droop regulator and novel instantaneous power regulation scheme. Also, a novel control system has been proposed for MT converter. Several case studies have been studied and the simulation results show that DC distribution system including microturbine unit can provide the premium power quality using proposed methods.

• Journal of Korean Academy of Nursing
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• v.52 no.1
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• pp.36-51
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• 2022

Purpose: The purpose of this study was to examine the effects of electroencephalogram (EEG) biofeedback training for emotion regulation and brain homeostasis on anxiety about COVID-19 infection, impulsivity, anger rumination, meta-mood, and self-regulation ability of late adolescents in the prolonged COVID-19 pandemic situation. Methods: A non-equivalent control group pretest-posttest design was used. The participants included 55 late adolescents in the experimental and control groups. The variables were evaluated using quantitative EEG at pre-post time points in the experimental group. The experimental groups received 10 sessions using the three-band protocol for five weeks. The collected data were analyzed using the Shapiro-Wilk test, Wilcoxon rank sum test, Wilcoxon signed-rank test, t-test and paired t-test using the SAS 9.3 program. The collected EEG data used a frequency series power spectrum analysis method through fast Fourier transform. Results: Significant differences in emotion regulation between the two groups were observed in the anxiety about COVID-19 infection (W = 585.50, p = .002), mood repair of meta-mood (W = 889.50, p = .024), self-regulation ability (t = - 5.02, p < .001), self-regulation mode (t = - 4.74, p < .001), and volitional inhibition mode (t = - 2.61, p = .012). Neurofeedback training for brain homeostasis was effected on enhanced sensory-motor rhythm (S = 177.00, p < .001) and inhibited theta (S = - 166.00, p < .001). Conclusion: The results demonstrate the potential of EEG biofeedback training as an independent nursing intervention that can markedly improve anxiety, mood-repair, and self-regulation ability for emotional distress during the COVID-19 pandemic.

• Journal of Power Electronics
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• v.14 no.2
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• pp.302-314
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• 2014

Due to advancements in power electronics and inverter topologies, the current controlled multilevel voltage-source pulse width modulated (PWM) inverter is usually preferred for accurate control, quick response and high dynamic performance. A multilevel topology approach is found to be best suited for overcoming many problems arising from the use of high power converters. This paper presents a comprehensive review and comparative study of several current control (CC) techniques for multilevel inverters with a special emphasis on various approaches of the hysteresis current controller. Since the hysteresis CC technique poses a problem of variable switching frequency, a ramp-comparator controller and a predictive controller to attain constant switching frequency are described along with its quantitative comparison. Furthermore, various methods have been reviewed to achieve hysteresis current control PWM with constant switching frequency operation. This paper complies various guidelines to choose a particular method suitable for application at a given power level, switching frequency and dynamic response.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.4
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• pp.555-560
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• 2016

Recently, many countries have placed great attention on energy security and climate changes. Governments are promoting the construction of renewable energy projects with regulatory support in Korea. Despite an increasing penetration of renewable resources, however, the photovoltaic and wind power are underutilized due to the endemic problems such as difficulties of output control and intermittent output. The Energy Storage System (ESS) is proposed as a good solution for solving the problems and has been studied in both the private business and the government. However, because of inefficient aspects, the research has been carried out for improving high costs and a small capacity. In addition, the ESS is currently installed for using only one purpose which is frequency regulation or transmission congestion relief such that has an economic limitation. Therefore, methods which are becoming economically justifiable to increase the penetration of the ESS is required. Thus, this paper presents in terms of operation efficiency to improve economic feasibility of the ESS currently used. mainly, there are two aspects for the operation efficiency. Firstly, it is intended to improve the utilization rate through a process that can utilize the ESS for various purposes. It is necessary to be able to use for other purposes by classifying and clustering for increasing the efficiency of availability. The clustering method is proposed to conduct the grouping the ESS. Especially, it is proposed to utilize ESS for frequency regulation service which is the one of ancillary services in the power system. Through case studies, it is confirmed to secure the necessary resources by clustering small size ESS.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1869-1883
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• 2016

In recent years, some converter structures and analyzing methods for the voltage regulation of stand-alone self-excited induction generators (SEIGs) have been introduced. However, all of them are concerned with the three-phase voltage control of three-phase SEIGs or the single-phase voltage control of single-phase SEIGs for the operation of these machines under balanced load conditions. In this paper, each phase voltage is controlled separately through separated converters, which consist of a full-bridge diode rectifier and one-IGBT. For this purpose, the principle of the electronic load controllers supported by fuzzy logic is employed in the two-different proposed converter structures. While changing single phase consumer loads that are independent from each other, the output voltages of the generator are controlled independently by three-number of separated electronic load controllers (SELCs) in two different mode operations. The aim is to obtain a rated power from the SEIG via the switching of the dump loads to be the complement of consumer load variations. The transient and steady state behaviors of the whole system are investigated by simulation studies from the point of getting the design parameters, and experiments are carried out for validation of the results. The results illustrate that the proposed SELC system is capable of coping with independent consumer load variations to keep output voltage at a desired value for each phase. It is also available for unbalanced consumer load conditions. In addition, it is concluded that the proposed converter without a filter capacitor has less harmonics on the currents.

• Proceedings of the KAIS Fall Conference
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• 2009.12a
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• pp.834-836
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• 2009

The authors have been discussed the optimal voltage regulation method and on-line real time method using artificial neural networks in the distribution system interconnected with Distributed Generation and Storage(DSG) systems. However, these methods have difficulty in dealing with the random load variations and operation characteristics of a number of DSG systems. To overcome these problems, this paper shows the basic concepts of smart grid system which is considered as one of the power delivery system in the near future and presents an evaluation method on the impacts of customer voltages by the operation of smart grid system. The smart grid system can change the system configuration in a flexible manner by using the static switches and offer the different power qualities in power services through the power quality control centers.

• Journal of Environmental Impact Assessment
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• v.14 no.4
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• pp.195-202
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• 2005

The health risks from the magnetic fields exposure have been brought out difficulties in the construction of transformer substation. According to several epidemiologic studies and the relevant international organizations, magnetic fields should not exceed the exposure limits of 3mG for the people living near electric power lines. The rigid regulation of the exposure levels for the elementary school and residental areas has been established already in Switzerland and Italy. Since 1998, the environmental impact assessment system in Korea has been reviewed for power-frequency magnetic field by precautionary policies. In this study, the possible application of Prior Environmental Performance Review System for the transformer substation was reviewed from the points of the properties of the powerfrequency magnetic fields. The ranges and survey methods of the assessment for the transformer substation were proposed. The ranges of magnetic fields was between 300m to 500m for the 345kV transformer substation. It is necessary to develop further specific assessment methods for various high-voltage transformer substations.