• 전력전자학회:학술대회논문집
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• 전력전자학회 2020년도 전력전자학술대회
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• pp.373-374
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• 2020

This paper proposes an optimal control algorithm which determines active damping resistor values considering load variation and grid side current THD. Proposed optimal control algorithm improves grid side current THD of the interlinking converter without passive damping resistor and is verified by simulation under variable load conditions.

• 대한산업공학회지
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• 제32권1호
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• pp.51-60
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• 2006

When the nature of measuring a performance variable is destructive or very expensive, it is attractive to use a surrogate variable which is highly correlated with the performance variable and less expensive to measure. In this paper, we propose rectifying screening procedures using the performance and surrogate variables. Two screening procedures are considered; a statistically-based screening procedure to reduce the current proportion of nonconforming items to a specified lower value after screening, and an economically-based screening procedure where the screening limit is determined so that the expected cost is minimized. It is assumed that the surrogate variable given the performance variable is normally distributed with known mean and standard deviation. For two screening procedures, methods of finding the optimal solutions are presented and numerical examples are also given.

• Communications for Statistical Applications and Methods
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• 제30권6호
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• pp.577-587
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• 2023

Conventional categorical data imputation techniques, such as mode imputation, often encounter issues related to overestimation. If the variable has too many categories, multinomial logistic regression imputation method may be impossible due to computational limitations. To rectify these limitations, we propose a two-stage imputation method. During the first stage, we utilize the Boruta variable selection method on the complete dataset to identify significant variables for the target categorical variable. Then, in the second stage, we use the important variables for the target categorical variable for logistic regression to impute missing data in binary variables, polytomous regression to impute missing data in categorical variables, and predictive mean matching to impute missing data in quantitative variables. Through analysis of both asymmetric and non-normal simulated and real data, we demonstrate that the two-stage imputation method outperforms imputation methods lacking variable selection, as evidenced by accuracy measures. During the analysis of real survey data, we also demonstrate that our suggested two-stage imputation method surpasses the current imputation approach in terms of accuracy.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.225-229
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• 2017

This paper describes the loss analysis based on load conditions of the air conditioning compressor motors using variable dc-link voltage. The losses of PMSM (Permanent Magnet Synchronous Motor) should be analyzed by the PWM (Pulse Width Modulation) output of inverter. The harmonic loss by the PWM cannot consider that using the current source analysis of the inverter. In addition, when the voltage of dc-link is variable with the condition of variable speed and load conditions in motor, the losses of motor are also changeable, however it is hard to analyze those losses by only electromagnetic finite element method (FEM). Therefore, this paper proposes the analysis method considering the carrier frequency of the inverter and the varying state of the dc-link voltage through the FEM-control coupled analysis. Using proposed analysis method, additional core loss and eddy current loss of permanent magnet caused by PWM could be analyzed. Finally, the validity of the proposed analysis method is verified through the comparison the result of coupled analysis with experiment.

• Journal of Power Electronics
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• 제7권2호
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• pp.97-108
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• 2007

This paper describes simple control structures for a vector controlled stand-alone induction generator (IG) for use under variable speeds. Different control principles, indirect vector control and deadbeat current control, are developed for a voltage source PWM converter and the three-phase variable speed squirrel-cage IG to regulate DC-link and generator voltages with a newly designed phase locked loop circuit. The required reactive power for the variable speed IG is supplied by means of a PWM converter and a capacitor bank to buildup the voltage of the IG without the need for a battery, to reduce the rating of the PWM converter while using only three sensors and to eliminate the harmonics generated by the PWM converter. These proposed schemes can be used efficiently for variable speed wind energy conversion systems. The measurements of the IG systems at various speeds and loads are given and show that these systems are capable of good AC and DC voltage regulation.

• 전자공학회논문지SC
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• 제39권3호
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• pp.191-200
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• 2002

본 논문에서는 다변수 다치 논리함수에 대하여 구간함수를 절단 차분 함수로 변환하는 방법을 제시하였고, 절단 차분 함수를 전류모드 CMOS에 의한 전류 미러 회로와 금지회로를 사용하여 일정한 패턴을 갖는 다치 논리회로로 구현하는 방법을 제시하였다. 또한 제시한 방법을 2변수 4치 MOD(4) 가산 진리표와 2변수 4치 유한체 GF(4)상의 승산 진리표를 실현하는 회로의 구현에 적용하였다. PSpice 시뮬레이션을 통하여 이 회로들에 대하여 동작특성을 보였다. 회로들의 시뮬레이션은 2㎛ CMOS 표준 기술을 이용하였고, 단위 전류를 15㎂로 하였으며, 전원전압은 3.3V를 사용하였다. 본 논문에서 제시한 전류모드 CMOS에 의해 구현된 회로들은 일정한 패턴, 상호연결의 규칙성을 가지며, 다치 논리함수의 변수의 확장성을 가지므로 VLSI 실현에 적합할 것으로 생각된다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 F
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• pp.1999-2001
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• 1997

The main two drawbacks of the Sin91e Stage PFC (SS-PFC) converters employing a DCM Boost PFC cell are relatively high voltage stress on the bulk capacitor and the input current harmonic distortion. The high voltage stress on bulk capacitor makes the SS-PFC converter impractical in a universal input application and the input current harmonic distortion lowers power factor. In this paper a selective variable frequency control that reduces the voltage stress on the bulk capacitor and the input current harmonic distortion is proposed. Computer simulation results of the proposed control method are presented.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 A
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• pp.389-391
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• 1994

This paper proposes an approach to control the current amplitude and phase simultaneously. To do this, variable structure control and adaptive parameter estimation arc applied to the current control of a single-phase PWM inverter with unknown R-L series load. The load parameters, R and L, are estimated by using the recursive least square method and these parameters are used to adjust the feedback gains of control input. The inverter system is modelled in a 2nd-order system by treating load current variation caused by inductive component as a disturbance. Simulation and experiment based on the 2nd -order model are done and the results show good dynamic response and low THD.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전력기술부문
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• pp.250-252
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• 2008

DC traction system generates leakage current because running rails are used in return circuit. And it is very important to estimate the leakage current to the train operation situation. Therefore this paper presents dynamic simulation technique that is very similar to the real operation situation using TPS and PSCAD/EMTDC. For this we model DC traction system included in DC substation, variable feeding circuit model and variable train model. And we extract train location and power using TPS program and use these data for dynamic simulation. Finally we can estimate leakage current to the various operation condition using dynamic simulation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.1101-1104
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• 2001

This paper describes a newly developed power conditioner with variable current loop gain. The power conditioner consists of a do-link capacitor and three phase inverter with coupled inductor. This system is very well operated to compensate current harmonics and asymmetries caused by nonlinear load and unbalance loads. The power conditioner shapes the source current sinusoidal in phase with source voltage. A 100kVA power conditioner was built and the controller is realized with DSP Experimental results for many load conditions are presented to verify the performance of the controller.