• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1999년도 하계학술대회 논문집 F
• /
• pp.2568-2571
• /
• 1999

Recently, new trend in telecommunication device is to apply low voltage, about 3.3V-1.5V. However, it is undesirable in view of high efficiency and power desity which is the most important requirement in the distributed power system. Rectification loss in the output stage in on-board converter for distributed power system are constrained to obtain high efficience at low output voltage power suppies. This paper is investigated conduction power loss in synchronouss rectifier with a parallel -connected Schottky Barrier Diode(SBD). Conduction losses are calculated for both MOSFET and SBD respectively. The SBD conduction power loss dissipates more than the MOSFET rectifier conduction power loss.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2006년도 전력전자학술대회 논문집
• /
• pp.213-215
• /
• 2006

Islanding phenomenon is undesirable because it lead to a safety hazard to utility service personnel and may cause damage to power generation and power supply facilities as a result of unsynchronized reclosure. In order to prevent the phenomenon, various anti-islanding methods have been studied. This paper proposes the variation method of inverter output current magnitude to prevent the islanding phenomenon as a novel method, which causes the large frequency variation of inverter output voltage after islanding. Unlike most active anti-islanding method deteriorating power quality, this novel method will have high performance of islanding detection and good power quality. For the verification of the proposed method, the simulated result and analyses are presented.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1998년도 하계학술대회 논문집 F
• /
• pp.1973-1976
• /
• 1998

Recently, new trend in telecommunication device is to apply low voltage, about 3.3V-1.5V. However, it is undesirable in view of high efficiency and power desity which is the most important requirement in the distributed power system. Rectification loss in the output stage, in on-board converter for distributed power system are constrained to obtain high efficience at low output voltage power suppies. This paper explains the basic operational principles of three kinds of ZVS DC/DC converters with self-driven synchronous rectifier. The three topologies are analyzed by simulation and exprimentation, and the characteristics comparisons of high efficience converter are carried out in view of the minimized rectification losses in the out stage.

• 자원ㆍ환경경제연구
• /
• 제30권1호
• /
• pp.79-105
• /
• 2021

본 연구는 기후변화 이슈가 부각되는 환경에서 온실가스 배출량 고려 유무에 따른 연근해어업의 업종별 효율성을 비교하고, 분석 결과를 바탕으로 정책적 대안을 제시하는 데 목적이 있다. 분석을 위해 전통적인 자료포락분석(DEA) 모형과 잔여기반측정(SBM) 모형, 비소망재 SBM 모형을 이용하고, Robust Analysis of Variance (ANOVA) 검정과 Wilcoxon Signed-rank 검정을 시행하였다. 분석결과, 전통적인 DEA 모형에서 여분을 고려한 SBM 모형, 온실가스 배출량을 고려한 비소망재 SBM 모형으로 확장될수록 어업의 평균 효율성은 감소하는 것으로 분석되었다. 구체적으로 전통적인 DEA 모형과 SBM 모형, 비소망재 SBM 모형의 평균 효율성은 각각 0.7350, 0.5820, 0.4976으로 추정되었다. 또한 Robust ANOVA 검정과 Wilcoxon Signedrank 검정결과, 전통적인 DEA, SBM, 비소망재 SBM 모형 간 효율성 차이와 근해어업과 연안어업의 효율성 차이도 통계적으로 유의하게 분석되었다. 분석의 정책적 대안으로, 연근해어업의 효율성 개선을 위해서는 신조어선사업의 적극적 시행과 함께 스마트어선 및 전기복합어선 개발 등이 필요함을 제안하였다.

• 디지털융복합연구
• /
• 제17권5호
• /
• pp.117-125
• /
• 2019

본 연구는 부실채권을 산출요소에 포함시켜 2004년부터 2013년까지 금융위기 전후 10년간 자료를 이용하여 가중평균 러셀 방향거리함수 모형(Weighted Rusell Directional Distance Model: WRDDM)에 의해 은행산업의 비효율성을 측정하였다. 그리고 이를 기초로 투입산출요소의 비효율성 기여효과를 산출하였으며 이 중 비정상적 유해산출물인 부실채권의 영향이 가장 큼을 실증하였다. 분석결과, 은행산업의 비효율성은 연평균 0.3912이며 이 중 무수익여신이 0.1883, 산출요소 0.098, 투입요소는 0.098 순으로 무수익여신의 비중이 가장 컸으며 금융위기 전 비효율성은 0.2995에서 금융위기 후 0.4829로 크게 증가하였는데 이는 부실책권의 비효율성이 금융위기 전 0.1088에서 금융위기 후 0.2678로 크게 증가한데 기인하였다. 결론적으로 투입산출 요소 중에서 인력, 총수신액, 투자증권 보다 부실채권인 무수익여신이 은행산업의 비효율성에 가장 중요한 영향을 미치고 있었으며 이에 은행산업의 기술적 효율성 측정시 정상 산출물 뿐만 아니라 비정상적인 유해산출물을 함께 고려하여야 함을 실증적으로 제시하였다. 그러나 본 연구는 은행의 효율성에 영향을 미치는 금융환경요인을 가중평균 러셀 방향거리함수모형에 통제하지 못한 한계점이 있다.

• Journal of Power Electronics
• /
• 제5권2호
• /
• pp.151-159
• /
• 2005

The errors generated from current measurement paths are inevitable, and they can be divided into two categories: offset error and scaling error. The current data including these errors cause periodic speed ripples which are one and two times the stator electrical frequency respectively. Since these undesirable ripples bring about harmful influences to motor driving systems, a compensation algorithm must be introduced to the control algorithm of the motor drive. In this paper, a new compensation algorithm is proposed. The signal of the integrator output of the d-axis current regulator is chosen and processed to compensate for the current measurement errors. Usually the d-axis current command is zero or constant to acquire the maximum torque or unity power factor in the ac drive system, and the output of the d-axis current regulator is nearly zero or constant as well. If the stator currents include the offset and scaling errors, the respective motor speed produces a ripple related to one and two times the stator electrical frequency, and the signal of the integrator output of the d-axis current regulator also produces the ripple as the motor speed does. The compensation of the current measurement errors is easily implemented to smooth the signal of the integrator output of the d-axis current regulator by subtracting the DC offset value or rescaling the gain of the hall sensor. Therefore, the proposed algorithm has several features: the robustness in the variation of the mechanical parameters, the application of the steady and transient state, the ease of implementation, and less computation time. The MATLAB simulation and experimental results are shown in order to verify the validity of the proposed current compensating algorithm.

• 한국IT서비스학회지
• /
• 제10권2호
• /
• pp.177-188
• /
• 2011

This paper proposes a DEA model for the performance evaluation of each brand of coking coals in an integrated steel mill. The performance is defined as the efficiency which is the ratio of two linear combinations of the output factors to the input factors. There is only one input factor considered in the model : unit price of each brand based on CIF. Five output factors are chosen in consideration of their impact to the quality of cokes such as Ash, VM, LMF, TD, and Rm. Some of the output factors are treated as undesirable in DEA model because the quality criteria are given by the range. The CCR and BCC efficiencies are derived by the DEA model, and the scale efficiency is calculated, too. Each brand of coking coal is classified into four categories according to the CCR and BCC efficiencies, and the most inferior brands are identified as a result. The impact of the input and output factors to the efficiency is analyzed using a multiple regression, then the unit price is revealed as the most critical among them. Also, ANOVA results show that there exist efficiency differences among the coal types and the countries imported, respectively. Finally, the quantitative projection for the inefficient brands is performed if they are to be efficient. The result could be utilized in selecting the good or bad brands of coking coal based on the efficiency in an integrated steel mill. Also, this model will be used to assess the relative efficiency of a new brand of coking coal if it is a candidate to be imported.

• 자원ㆍ환경경제연구
• /
• 제22권2호
• /
• pp.329-365
• /
• 2013

본 연구의 목적은 2000-2009년 국가별로 환경과 화석에너지의 제약 하에서 경제와 환경의 효율을 측정하고자 함이다. 본 연구는 국가별 소득수준에 따른 OECD국가, 중고소득국가, 저소득국가 등 세 그룹으로 구분하여, 생산가능집합에서 바람직한 산출물인 GDP와 오염물을 동시에 포함한 '환경지향형, 경제지향형, 환경-경제지향형, Two-stage DEA모형' 등의 네 가지 방법을 제시하여 비교한다. OECD국가는 상대적으로 경제효율성이 높으나 환경효율성은 낮았고 비OECD국가는 환경효율성이 높고 경제효율성이 낮았다. 화석에너지와 온실가스의 저감의 여지는 OECD국가가 더 높았다.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2004년도 추계학술대회 논문집
• /
• pp.32-36
• /
• 2004

In order to achieve high performance vector control, it is essential to measure accurate ac current. The errors generated from current path are inevitable, and they could be divided into two categories: offset error and scaling error. The current data including these errors cause periodic speed ripples which are one and two times of stator electrical frequency respectively. Since these undesirable ripples bring about bad influences to motor driving system, a compensation algorithm must be needed in the control algorithm of the motor drive. In this paper, a new compensation algorithm is proposed. The signal of the integrator output of the d-axis current regulator is chosen and processed to compensate the current measurement errors. The compensation of the current measurement errors is easily implemented to smooth the signal of the integrator output of the d-axis current regulator by subtracting the DC offset value or rescaling the gain of the hall sensor. Therefore, the proposed algorithm has several features: the robustness of the variation of the mechanical parameters, the application of the steady and transient state, the easy implementation, and less computation time.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
• /
• 제48권11호
• /
• pp.646-654
• /
• 1999

This paper deals with PWM patterns for harmonic reduction in inverter fed traction motors and the gear changing techniques for the variable speed drive of traction motor. GTOs are used as switching device of inverter because traction motor is a large load. To derive PWM rattern which can minimize the harmonics with the limited switching frequency, the output current and torque characteristic of SPWM and SHE PWM was analyzed. GTO inverter used for traction motor drive includes harmonics in the output current and torque by the limitation of switching frequency. However, the hybrid PWM method that adopt SPWM in the range of low frequency and SHE PWM in upper frequency range can achieve less harmonic characteristics in GTO inverters. If the traction motor is driven in variable speed by the proposed PWM pattern, 7 times of gear changing is needed. At the instant of the mode change, magnetic flux and torque may be altered and the large current flow. To reduce such an undesirable transient behavior, it is also presented the technique for the gear changing of inverter fed traction motor drive operated with the hybrid PWM. The results are verified by simulations and experiments.