• 전력전자학회논문지
• /
• 제18권5호
• /
• pp.492-500
• /
• 2013

A balanced forward-flyback converter for high efficiency and high power factor using a foward and flyback converter topologies is proposed in this paper. The conventional AC/DC flyback converter can achieve a good power factor but it has the high offset current through the transformer magnetizing inductor, which results in a large core loss and low power conversion efficiency. And, the conventional forward converter can achieve the good power conversion efficiency with the aid of the low core loss but the input current dead zone near zero cross AC input voltage deteriorates the power factor. On the other hand, since the proposed converter can operate as the forward and flyback converters during switch turn-on and turn-off periods, respectively, it cannot only perform the power transfer during an entire switching period but also achieve the high power factor due to the flyback operation. Moreover, since the current balanced capacitor can minimize the offset current through the transformer magnetizing inductor regardless of the AC input voltage, the core loss and volume of the transformer can be minimized. Therefore, the proposed converter features a high efficiency and high power factor. To confirm the validity of the proposed converter, theoretical analysis and experimental results from a prototype of 24W LED driver are presented.

• Journal of Power Electronics
• /
• 제17권3호
• /
• pp.590-600
• /
• 2017

This paper presents a ripple-free input current modified interleaved boost converter for high step-up applications. By integrating dual coupled inductors and voltage multiplier techniques, the proposed converter can reach a high step-up gain without an extremely high turn-ON period. In addition, a very small auxiliary inductor employed in series to the input dc source makes the input current ripple theoretically decreased to zero, which simplifies the design of the electromagnetic interference (EMI) filter. In addition, the voltage stresses on the semiconductor devices of the proposed converter are efficiently reduced, which makes high performance MOSFETs with low voltage rated and low resistance $r_{DS}$(ON) available to reduce the cost and conduction loss. The operating principles and steady-state analyses of the proposed converter are introduced in detail. Finally, a prototype circuit rated at 400W with a 42-50V input voltage and a 400V output voltage is built and tested to verify the effectiveness of theoretical analysis. Experimental results show that an efficiency of 95.3% can be achieved.

• Journal of Biosystems Engineering
• /
• 제29권5호
• /
• pp.441-450
• /
• 2004

This study was performed to estimate mid and long term demands of a tractor, a rice transplanter, a combine and a grain dryer by using logistic curve function and Markov chain model. Field survey was done to decide some parameters far logistic curve function and Markov chain model. Ceiling values of tractor and combine fer logistic curve function analysis were 209,280 and 85,607 respectively. Based on logistic curve function analysis, total number of tractors increased slightly during the period analysed. New demand for combine was found to be zero. Markov chain analysis was carried out with 2 scenarios. With the scenario 1(rice price $10\%$ down and current supporting policy by government), new demand for tractor was decreased gradually up to 700 unit in the year 2012. For combine, new demand was zero. Regardless of scenarios, the replacement demand was increased slightly after 2003. After then, the replacement demand is decreased after the certain time. Two analysis of logistic owe function and Markov chain model showed the similar trend in increase and decrease for total number of tractors and combines. However, the difference in numbers of tractors and combines between the results from 2 analysis got bigger as the time passed.

• 전기학회논문지
• /
• 제63권1호
• /
• pp.35-41
• /
• 2014

This paper presents a design method of programmable low pass filter(PLPF) which reduce an estimation error of a zero crossing point(ZCP) for a high speed brushless DC(BLDC) motor drive. BLDC motor sensorless drive is possible by estimation of ZCP. The ZCP estimated by detecting a change of back-EMF polarity has the estimation error because noises exist on the measured back-EMF. Therefore a calculated commutation timing using the ZCP is inaccurate. And the inexact commutation timing leads to ripples of 3-phase current and degradation of drive performance. This paper proposes the design method of the PLPF to overcome these problems. First, a speed calculated a inaccurate period of the ZCP is analyzed in the frequency domain. Then, the PLPF that has varying cut-off frequency according to change of the speed is designed on the frequency analysis result. The proposed method is verified by the experiment.

• 한국해안해양공학회지
• /
• 제4권2호
• /
• pp.72-82
• /
• 1992

현지 해안에서 발생하는 해빈류를 정확히 예측하기 위해서는, 해빈류의 기인력인 다방향불 규칙파낭에 의해서 발생하는 방사응력(radiation stress)에 대해서 충분히 파악해 둘 필요가 있다. 본 연구에서는, 이차원수리실험에 있어서 단일성분파, 이성분합성 파, Bretschneider-광역형의 불규칙파를 발생시켜서, 그들의 천수쇄파변형에 따른 전파특성에 대해서 고찰하고, 불규칙파의 천수쇄파변형을 해석할 경우 가정되어지는 3가지 방법, 즉 (1) 파별해석법, (2) 성분파법, (3) 대표파법의 적용성에 대해서 檢討했다. 파별해석법에 대해서는, zero-down cross 법에 의해, 파별해석되어진 불규칙파의 전파특성으로서, 통계파(최대파, 1/3유의파, rms파 등) 및 시계열중의 임의 특정의 개개파의 파고 및 주기의 천수변화라고 하는 관점으로부터 검토했다. 또한, 성분파법에 대해서는 Spectrum 해석에 의해, 입력신호인 기본주파수성분파 및 천수비파변형에 따라 증가하는 간섭주파수 성분파에 대한 파속 및 파고의 천수변형이라고 하는 관점으로부터 그 타당성에 대해서 검토했다.

• 한국정보통신학회논문지
• /
• 제13권5호
• /
• pp.922-930
• /
• 2009

유도 전동기를 전압 제어하기 위한 최적 PWM 스위칭 방법을 제시하려한다. 전압 인버터의 공간 벡터 변조 방식은 DC-버스 이용을 향상시키고 정류 손실을 감소시키기 때문에 디지털 구현의 경우 특히 선호하는 PWM 방법이다. 유도 전동기 전압 제어를 위한 최적 PWM 스위칭 방법은 제시한 최적 PWM 알고리즘을 사용하여 두 개의 활성 전압 벡터(active voltage vector)와 하나의 영 전압 벡터(zero voltage vector)로 구성하였다. 선택된 스위칭 순차 열은 변조 지수(modulation index)와 운송파(carrier wave) 주기의 함수로 정의 된다. 순차 열은 인버터 스위칭 손실과 전류 리플 값을 기준으로 사용하여 선택된다. 실험 결과 중 저 전력용으로 사용할 경우 스위칭 주파수를 증가시킴에 따라 고조파 왜곡이 감소하고 동특성이 좋아짐을 확인할 수 있었다.

• 전력전자학회논문지
• /
• 제5권4호
• /
• pp.386-393
• /
• 2000

본 논문에서는 고전력, 고주파 응용에 적합한 저 도통손실 특성을 갖는 향상된 양전압 부분 직렬 공진행 DC/DC 컨버터를 제안한다. 제안된 컨버터는 많은 범위에서 주 스위치의 영전압 스위칭을 보장히며 주 스위치의 전류 스트레스 감소에 의해 저도통 손실 특성올 이룬다. 또한 제안된 컨버터의 보조회로는 주 전력 흐름과 분리되어 있어 주 회로의 공진 시간동안 유효 듀티비 감소는 발생하지 않는다. 보조 회로는 인덕터, 커피시터, 다이오드 그리고 과포화 리엑터의 수동 소자들만으로 구성 되어있다. 따라서 향상된 ZVS PSRC는 전체 시스템의 효율과 전류 스트레스 감소면 에서 개선된 특성을 지닌다. 제안한 컨버터의 동작 원리를 자세히 설명하고 그 타당성올 시뮬레이션과 실험을 통하여 검증하고자 한다.

• 한국항행학회논문지
• /
• 제15권3호
• /
• pp.349-354
• /
• 2011

본 논문에서는 스트립 폭과 격자주기, 유전체 층의 비유전율과 두께, 그리고 transverse electric (TE) 평면파의 입사각에 따른 접지된 유전체 평면위의 스트립 양끝에서 0 저항율을 갖는 저항띠 격자구조에 의한 H-분극산란 문제를 Fourier-Galerkin Moment Method (FGMM)를 이용하여 해석하였다. 저항띠의 변하는 저항율은 저항띠의 양끝에서 0으로 변하는 경우를 취급하였고, 이때 저항띠 위에서 유도되는 전류밀도는 직교다항식의 일종인 2종 Chebyshev 다항식의 급수로 전개하였다. 반사전력의 급변점들은 공진효과에 기인한 것으로 과거에 wood's anomallies라고 불리워지며, 반사전력에 대한 수치결과들은 기존 논문의 균일 저항율의 수치 결과들과 비교하였다.

• 한국연초학회지
• /
• 제26권1호
• /
• pp.35-42
• /
• 2004

This study was carried out to examinate the effect of aging period on chromatic, chemical and organoleptic characteristics, and to evaluate of optimum aging period for each grade in burley leaf tobacco. The leaf tobaccos were produced in 2000, and threshed, redried and packed in carton box under the current methods. Four grades of processed leaf(A3T, B1T, C1W and D3W) were stored during 24 months (May 10, 2001 to April 31, 2003) in warehouse of Chungju Leaf Tobacco Processing Factory. The leaf tobaccos were sampled at three month intervals for analysis of chromatic, chemical and organoleptic properties. pH values of four grades, and Yellow(b) of A3T and BIT were also significantly decreased during the aging. Filling values, tar, nicotine and CO contents of tobacco smoke, and puff number of cigarettes were not significantly changed during the aging. Positive correlation coefficients were significantly observed between irritation of the calculated attributes from contents of volatile oil components in leaf tobacco and that of the panel sensory attributes. The ratio of maximum change in irritation attribute was larger than that in taste attribute during aging. The calculated irritations of 18～24 months aging for A3T and B1T were significantly lower than zero-aging, while those of C1W and D3W were not significant among aging periods. The panel irritations of 12～15 months aging for four grades were low tendency. The results suggest that decrease of aging period for thin leaf from 21～24 to 12～15 months may be beneficial to save storage cost in burley tobacco.

• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2008년도 학술발표회 논문집
• /
• pp.67-74
• /
• 2008

The regional-scale transient groundwater-river interaction model is developed to gain a better understanding of the regional-scale relationships and interactions between groundwater and river system and quantify the residual river flow after groundwater abstraction from the aquifers with climate variability in the Waimea Plains, New Zealand. The effect of groundwater abstraction and climate variability on river flows is evaluated by calculating river flows at the downstream area for three different drought years (a 1 in 10 drought year, 1 in 20 drought year, and 1 in 24 drought year) and an average year with metered water abstraction data. The effect of future water demand (50 year projection) on river flows is also evaluated. A significant increase in the occurrence of zero flow, or very low flow of 100 L/sec at the downstream area is predicted due to large groundwater abstraction increase with climate variability. Modeling results shows the necessity of establishing dynamic cutback scenarios of water usage to users over the period of drought conditions considering different climate variability from current allocation limit to reduce the occurrence of low flow conditions at the downstream area.