• Nuclear Engineering and Technology
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• v.28 no.3
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• pp.265-273
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• 1996

Among those tests performed during the Yonggwang Nuclear Power Plant Units 3 and 4 (YGN 3&4) Power Ascension Test period, the Loss of a Main Feedwater Pump test at l00% power is one of the major test which characterize the capability of YGN 3&4. In this event, one of the two normally operating main feedwater pumps is tripped resulting in a 50% reduction in the feedwater flow. Unless the NSSS and Turbine/Generator control systems actuate properly, the reactor will be tripped on low SG water level or high pressurizer pressure. The test performed at Unit 3 was successful by meeting all acceptance criteria, and the plant was stabilized at a reduced power level without reactor trip. The measured test data for the major plant parameters are compared with the predictions made by the KISPAC computer code, an updated best-estimate plant performance analysis code, to verify and validate its applicability. The comparison results showed good agreement in the magnitude as well as the trends of the major plant parameters. Therefore, the KISPAC code can be utilized for the best-estimate nuclear power plant design and simulation tool after a further verification using other plant test data.

• New & Renewable Energy
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• v.5 no.4
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• pp.11-18
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• 2009

Wind energy resources are recently considered as an important power generation alternative in the future. The fact that the investment of wind turbine installation continues to increase has motivated a need to develop more widely applicable methodologies for evaluating the actual benefits of adding wind turbines to conventional generating systems. This study is aiming to estimate the future wind resources with various estimation methods. The wind power is calculated at the hub height 75m of 800KW and 1,500KW wind turbines in Wolryong site, Jeju island, South Korea. Three equations - logarithmic, profile, and power law methods are applied for the accurate prediction of wind profile. In addition, yearly wind power can be calculated by using Weibull & Rayleigh distribution. It is found that predicted wind speed is highly affected by friction velocity, atmospheric stability, and averaged roughness length. It is concluded that Rayleigh distribution provides greater power generation than the Weibull distribution, especially for low wind-speed condition.

• Journal of Power Electronics
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• v.19 no.1
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• pp.179-189
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• 2019

Four-quadrant converters (4QCs) are widely used as AC-DC power conversion interfaces in many areas. A control delay commonly exists in the digital implementation process of 4QCs, especially for high power 4QCs with a low switching frequency. This usually results in alternating current distortion, increased current harmonic content and system instability. In this paper, the control delay is divided into a computation delay and a PWM delay. The impact of the control delay on the performance of a 4QC is briefly analyzed. To obtain a fundamental value of AC current that is as accurately as possible, a specific sampling method considering the PWM pattern is introduced. Then a current predictive control based on a modified z-transform is proposed, which is effective in reducing the control delay and easy in terms of digital implementation. In addition, it does not depend on object models and parameters. The feasibility and effectiveness of the proposed predictive current control method is verified by simulation and experimental results.

• Journal of Drive and Control
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• v.18 no.4
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• pp.84-90
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• 2021

Viscosity of hydraulic oils decreases due to loss reduction and efficiency increase of fluid power systems. However, low viscosity is not always appropriate due to the induction of large leakage and small lubricity. Therefore, a detailed study on the optimum viscosity of hydraulic oils is necessary. In this study, based on the thermohydrodynamic lubrication theory, numerical simulation was conducted using the slipper model of swashplate-type axial piston pumps and motors. The viscosity grades' (VG) effects of oils on power losses are mainly discussed numerically in fluid film lubrication, including changes in temperature and viscosity. The simulation results reveal that the flow rate increases and the friction torque decreases as VG decreases. The film temperature and power loss were minimised for a specific oil with a VG. The minimum conditions regarding the temperature and loss were different and closed. Under various operating conditions, the film temperature and power loss were minimised, suggesting that an optimum hydraulic oil with a specific VG could be selected for given operating conditions of pressure and speed. Otherwise, a preferable operating condition must be established to determine a specific VG oil.

• Journal of Information Processing Systems
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• v.19 no.2
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• pp.258-266
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• 2023

Aiming at the problems of poor customer satisfaction and poor accuracy of customer classification, this paper proposes a customer classification model based on speech recognition. First, this paper analyzes the temporal data characteristics of customer demand data, identifies the influencing factors of customer demand behavior, and determines the process of feature extraction of customer voice signals. Then, the emotional association rules of customer demands are designed, and the classification model of customer demands is constructed through cluster analysis. Next, the Euclidean distance method is used to preprocess customer behavior data. The fuzzy clustering characteristics of customer demands are obtained by the fuzzy clustering method. Finally, on the basis of naive Bayesian algorithm, a customer demand classification model based on speech recognition is completed. Experimental results show that the proposed method improves the accuracy of the customer demand classification to more than 80%, and improves customer satisfaction to more than 90%. It solves the problems of poor customer satisfaction and low customer classification accuracy of the existing classification methods, which have practical application value.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.11
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• pp.2149-2154
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• 2009

Electric power quality in power transmission/distribution systems has considerably been deteriorated with the increase in the capacity of distributed generators (DGs). It is because inverters, connecting DGs to conventional power grids, tend to generate harmonic current and voltage. For harmonic mitigation, a large amount of research has been done on passive and active filters, which have been operating successfully in many countries. This paper, therefore, presents how to adopt the filters to an inverter-based DG, with considering a system consisting of both inverter-based DG and harmonic filters. In particular, this paper describes the simulation results using the PSCAD/EMTDC: firstly, the relationship between total harmonic distortion(THD) of current and output power of DG: secondly, the harmonic mitigation ability of passive and active filters. The system, furthermore, is obliged to satisfy the regulations made by Korean Electric Power Corporation(KEPCO). In the regulations, power factor should be maintained between 0.9 and 1 in a grid-connected mode. Thus, this paper suggests two methods for the system to control its power factor. First, the inverter of DG should control power factor rather than an active filter because it brings dramatic decrease in the capacity of the active filter. Second, DG should absorb reactive power only in the range of low output power in order to prevent useless capacity increase of the inverter. This method is expected to result in the variable power factor of the system according to its output power.

• Journal of Korean Institute of Industrial Engineers
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• v.29 no.4
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• pp.259-270
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• 2003

In order to properly design warning sounds that are affectively suitable to computer users, warning sounds used in Windows operating system were analyzed in terms of their sound properties; frequency band, spectral characteristics and physical intensity. A total of 36 warning sounds (3*4*3) were generated and tested with respect to three experimental variables. Among 178 collected affective adjectives that are related to hearing and sounds, seven representative affective adjectives were abstracted by statistical grouping techniques. In the experiment, subjective preference tests were performed for the 36 warning sounds according to the seven affective factors. From the result, the affective factors were again grouped into three major factors and the 60dB boost-type warning sounds at the low frequency band were, in general, the most preferred. followed by the 70dB cut-type sounds at the middle frequency band. These warning sounds have a characteristic of boost power spectrum below 1000Hz frequency band and received good scores on simplicity, clarity and accurateness.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.12 s.354
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• pp.55-64
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• 2006

This work proposes a calibration-free 14b 70MS/s 0.13um CMOS ADC for high-performance integrated systems such as WLAN and high-definition video systems simultaneously requiring high resolution, low power, and small size at high speed. The proposed ADC employs signal insensitive 3-D fully symmetric layout techniques in two MDACs for high matching accuracy without any calibration. A three-stage pipeline architecture minimizes power consumption and chip area at the target resolution and sampling rate. The input SHA with a controlled trans-conductance ratio of two amplifier stages simultaneously achieves high gain and high phase margin with gate-bootstrapped sampling switches for 14b input accuracy at the Nyquist frequency. A back-end sub-ranging flash ADC with open-loop offset cancellation and interpolation achieves 6b accuracy at 70MS/s. Low-noise current and voltage references are employed on chip with optional off-chip reference voltages. The prototype ADC implemented in a 0.13um CMOS is based on a 0.35um minimum channel length for 2.5V applications. The measured DNL and INL are within 0.65LSB and l.80LSB, respectively. The prototype ADC shows maximum SNDR and SFDR of 66dB and 81dB and a power consumption of 235mW at 70MS/s. The active die area is $3.3mm^2$.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.4
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• pp.595-606
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• 2022

Korea has the characteristics of traditional power system such as large-scale power generation and large-scale power transmission systems, including 20 GW large-scale power generation complexes in several regions with unit generator capacity exceeding 1.4 GW, 2-3 ultra-high-voltage transmission lines that transport power from large-scale power generation complexes, and 6 ultra-high-voltage transmission lines that transport power from non-metropolitan areas to the metropolitan area. Due to the characteristics of the power system, the penetration level for renewable energy is low, but due to frequency stability issue, some generators are reducing the output of generators. In the future, the issue of maintaining the stability of the power system is expected to emerge as the most important issue in accordance with the policy of expanding renewable energy. When non-inertial inverter-based renewable energy, such as solar and wind power, surges rapidly, the means to improve the power system stability in an independent system is to install a natural inertial resource synchronous condenser (SC) and a virtual inertial resource BESS in the system. In this study, we analyzed the effect of renewable energy on power system stability and the BESS effect to maintain the minimum frequency through a power system simulation. It was confirmed that the BESS effect according to the power generation constraint capacity reached a maximum of 122.81 %.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.414.2-414.2
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• 2016

The optimal configuration of a transmutation reactor based on a low aspect ratio tokamak is determined using coupled analysis of tokamak systems and neutron transport. The inboard radial build of the reactor components is obtained from plasma physics and engineering constraints, while outboard radial builds are mainly determined by constraints on a neutron multiplication, a tritium-breeding ratio, and a power density. It is shown that a breeding blanket model has an impact on the radial build of a transmutation blanket. A burn cycle has to be determined to limit a fast neutron fluence of a plasma facing material below a radiation damage limit.