• Journal of Power Electronics
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• 제17권2호
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• pp.533-541
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• 2017

This paper presents a novel Parameter-Independent Fictive-Axis (PIFA) approach for the Voltage-Oriented Control (VOC) algorithm used in grid-tied single-phase inverters. VOC is based on the transformation of the single-phase grid current into the synchronous reference frame. As a result, an orthogonal current signal is needed. Traditionally, this signal has been obtained from fixed time delays, digital filters or a Hilbert transformation. Nevertheless, these solutions present stability and transient drawbacks. Recently, the Fictive Axis Emulation (FAE) VOC has emerged as an alternative for the generation of the quadrature current signal. FAE requires detailed information of the grid current filter along with its transfer function for signal creation. When the transfer function is not accurate, the direct and quadrature current components present steady-state oscillations as the fictive two-phase system becomes unbalanced. Moreover, the digital implementation of the transfer function imposes an additional computing burden on the VOC. The PIFA VOC presented in this paper, takes advantage of the reference current to create the required orthogonal current, which effectively eliminates the need for the filter transfer function. Moreover, the fictive signal amplitude and phase do not change with a frequency drift, which results in an increased reliability. This yields a fast, linear and stable system that can be installed without fine tuning. To demonstrate the good performance of the PIFA VOC, simulation and experimental results are presented.

• 조명전기설비학회논문지
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• 제29권4호
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• pp.11-17
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• 2015

While most switching devices are based on PN junctions, a single layer can realize a switching device in the case of vanadium dioxide($VO_2$) thin films. In this paper, bidirectional current triggering(switching) is demonstrated in a two-terminal planar device based on a $VO_2$ thin film by illuminating the film with an infrared laser at 1550nm. To begin with, a two-terminal planar device, which had a $30{\mu}m$-wide $VO_2$ conducting layer and an electrode separation of $10{\mu}m$, was fabricated. A specific bias voltage range for stable bidirectional laser triggering was experimentally obtained by measuring the current-voltage characteristics of the fabricated device in a current-controlled mode. Then, by constructing a test circuit composed of the device, a standard resistor, and a DC voltage source, connected in series, the transient response of laser-triggered current and its response time were investigated with a DC bias voltage, included in the above specific bias voltage range, applied to the device. In the test circuit with a DC voltage source of 3.35V and a $10{\Omega}$ resistor, bidirectional laser triggering could be realized with a maximum on-state current of 15mA and a switching contrast of ~78.95.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.295-300
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• 2001

A variety of high voltage DC power supplies employing the high frequency inverter are difficult to achieve soft switching considering a quick response and no overshoot response under the wide load variation ranges which are used in medical-use x-ray high voltage generator from 20kV to 150kV in the output voltage and from 0.5mA to 1250mA, respectively. The authors develops soft switching high voltage DC power supply designed for x-ray power generator applications, which uses series resonant inverter circuit topology with a multistage voltage multiplier instead of a conventional high voltage diode rectifier connected to the second-side of a high-voltage transformer with a large turn ratio. A constant on-time dual mode frequency control scheme operating under a principle of zero-current soft switching commutation is described. Introducing the multistage voltage multiplier, the secondary transformer turn-numbers and stray capacitance of high-voltage transformer is effective to be greatly reduced. It is proved that the proposed high-voltage converter topology with dual mode frequency modulation mode control scheme is able to be the transient response and steady-state performance in high-voltage x-ray tube load. The effectiveness of this high voltage converter is evaluated and discussed on the basis of simulation analysis and observed data in experiment.

• 대한의용생체공학회:의공학회지
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• 제22권5호
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• pp.393-402
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• 2001

전체 심혈관계의 혈류역학적 특성을 분석할 수 있는 수치해석 방법을 개발하였다. 이는 12개의 요소들로 구성된 lumped parameter모델에 기초하고 있으며 인체의 신경계에 의한 자율조절기능을 모사하기 위해 주로 혈압의 단기적 조절을 위한.baroreflex system뿐 아니라 cardiopulmonary reflex 메커니즘가지도 구현하여 모델에 포함시켰다. 또한 교감 및 부교감 신경에 의한 자극-반응 전달을 구현함에 있어 생리학적 데이터에 기초한 방법을 사용하였다. 본 연구의 수치해석 코드를 검증하기 위하여 우선 보통 상태의 심혈관계에 대하여 혈류역학적 계산 결과를 기존의 참고문헌들에서의 값들과 비교 검토하였다. 심혈관계 모델의 혈류역학적 자극에 대한 반응 결과를 조사하기 위하여. 20% 출혈이 발생하는 경우와 LBNP(Lower Body Negative Pressure) 모사를 수행하였다. 두 경우 모두. 비교적 실험치와 잘 일cl하고 있음을 확인할 수 있었다. 특히 LBNP 수행 시, 외부압력의 크기가 커질수록 baroreflex만을 포함하고 있는 방법은 baroreflex와 cardiopulmonary reflex 모두를 포함하고 있는 방법에 비하여 다소 부정확한 결과를 보여주고 있는데. 이는 cardiopulmonary reflex 메커니즘의 중요성을 보여주고 있다.

• 한국지능시스템학회논문지
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• 제8권6호
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• pp.37-47
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• 1998

본 논문은 진화 연산 알고리즘과 퍼지 로직을 이용하여 고속 열처리 공정기의 웨이퍼 온도를 제어하는 제어기 설계 방법을 제안한다. 전체 제어기는 기준 온도의 정상 상태의 추종을 위한 앞먹임 정적 제어기, 과도 상태의 추종을 위한 앞먹임 동적 제어기, 그리고 온라인 상에서 모델링 오차나 외란을 극복하기 위한 되먹임 오차 제어기로 구성된다. 앞먹임 제어기들은 퍼지 로직을 이용하여 모든 동작점에서 제어 입력을 구해주는 전역적 비선형 제어기로 구성된다. 각 제어기들의 제어 파라미터는 진화 연산 알고리즘을 이용하여 추정되므로 수학적 모델식을 모르는 경우에도 제어기를 설계할 수 있는 장점이 있다. 끝으로 모의 실험을 통하여 제어기의 성능을 검증한다.

• 대한토목학회논문집
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• 제31권4C호
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• pp.127-136
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• 2011

기초사석 위에서 진동하중을 받는 진동다짐판의 침하는 일시적인 진폭과 소성침하로 나타낼 수 있다. 최대 진동하중이 사석의 지지력을 초과하지 않는 한, 소성침하량은 극한값으로 수렴하며 궁극적으로 정상적인 진동을 한다. 이러한 진동다짐의 침하거동에 대한 실내실험은 수평방향이 구속된 시료에 대하여 진동하중이 전체면적에 작용하도록 수행되었거나 진동대에 시료를 놓고 실험을 수행한 것이 대부분이다. 그러나 실제 현장에서는 진동하중이 기초사석 표면적의 일부에만 적용되고 있다. 본 연구에서는 현장조건에 맞게 쇄석에 진동하중을 작용토록 하였다. 쇄석에 대한 진동다짐실험에 따르면 전체 침하량의 약 90%가 2분 이내에 발생하며, 정적 및 동적응력을 포함한 진동응력 수준이 증가할수록 침하는 증가하였다. 진동다짐시, 진동다짐수, 진폭, 침하량, 재하폭, 진동응력의 상관관계를 나타내는 식을 제안하였다.

• 지질공학
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• 제19권2호
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• pp.205-215
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• 2009

지표하 다공성매체에서 비정상상태의 유동을 해석하기 위한 종래의 수치적 모형들은 초기 건조한 토양으로의 강우로 인한 침투와 같은 한계적인 유입경계조건인 경우에 국지적 유동영역으로 인해 수치적 진동 및 불안정성을 초래한다. 이러한 경우 주로 공간적으로 세분된 격자와 작은 계산시간 간격을 요구하는데 이는 계산의 효율성을 떨어뜨린다. 따라서 본 연구에서는 유입 경계조건을 포함하는 비정상 상태의 지표하 유동해석을 위해 입자추적 알고리즘을 적용하여 불연속영역에서의 수치적 불안정성을 제거하고자 하였다. 즉, 수치적 안정성이 개선된 혼합 LE 유한요소기법을 제시하였다. 제시된 모형의 수치적 검증을 위해 비정상 균일 유동장과 불균일 유동장의 가상예제에 적용한 결과 해석해와 유사한 결과를 얻을 수 있었고 이를 토대로 함양 및 양수에 대한 3차원 가상유역 모의에 적용되었다. 본 연구에서 제시한 입자추적 알고리즘은 포화 및 불포화 다공성 매체의 유동을 보다 실질적으로 모의할 수 있으며 계산의 정확성 및 안정성에 크게 기여할 것으로 판단되었다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회 논문집
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• pp.143-148
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• 2005

The main purpose of this study is to suggest and evaluate an operational method for assessing the potential impact of climate change on hydrologic components and water resources of regional scale river basins. The method, which uses large scale climate change information provided by a state of the art general circulation model(GCM) comprises a statistical downscaling approach and a spatially distributed hydrological model applied to a river basin located in Korea. First, we construct global climate change scenarios using the YONU GCM control run and transient experiments, then transform the YONU GCM grid-box predictions with coarse resolution of climate change into the site-specific values by statistical downscaling techniques. The values are used to modify the parameters of the stochastic weather generator model for the simulation of the site-specific daily weather time series. The weather series fed into a semi-distributed hydrological model called SLURP to simulate the streamflows associated with other water resources for the condition of $2CO_2$. This approach is applied to the Yongdam dam basin in southern part of Korea. The results show that under the condition of $2CO_2$, about $7.6\% of annual mean streamflow is reduced when it is compared with the observed one. And while Seasonal streamflows in the winter and autumn are increased, a streamflow in the summer is decreased. However, the seasonality of the simulated series is similar to the observed pattern and the analysis of the duration cure shows the mean of averaged low flow is increased while the averaged wet and normal flow are decreased for the climate change.

• International Journal of Concrete Structures and Materials
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• 제10권sup3호
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• pp.19-31
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• 2016

The objective of this paper is to investigate the effect of thickness and moisture on temperature distributions of reinforced concrete walls under fire conditions. Toward this goal, the first three wall specimens having different thicknesses are heated for 2 h according to ISO standard heating curve and the temperature distribution through the wall thickness is measured. Since the thermal behavior of the tested walls is influenced by thickness, as well as moisture content, three additional walls are prepared and preheated to reduce moisture content and then tested under fire exposure. The experimental results clearly show the temperatures measured close to the fire exposed surface of the thickest wall with 250 mm thickness is the highest in the temperatures measured at the same location of the thinner wall with 150 mm thickness because of the moisture clog that is formed inside the wall with 250 mm of thickness. This prevents heat being transferred to the opposite side of the heated surface. This is also confirmed by the thermal behavior of the preheated walls, showing that the temperature is well distributed in the preheated walls as compared to that in non-preheated walls. Finite element models including moisture clog zone are generated to simulate fire tests with consideration of moisture clog effect. The temperature distributions of the models predicted from the transient heat analyses are compared with experimental results and show good agreements. In addition, parametric studies are performed with various moisture contents in order to investigate effect of moisture contents on the thermal behaviors of the concrete walls.

• 전기학회논문지
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• 제61권10호
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• pp.1432-1441
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• 2012

In this study, an improved LCCT(Inductor-Capacitor-Capacitor-Trans) Z-source inverter(Improved LCCT ZSI) with characteristics of Quasi Z-source inverter(QZSI) and LCCT Z-source inverter(LCCT ZSI) is proposed. The proposed inverter can also reduce the voltage stress and input current/capacitor voltage ripples compared with conventional LCCT ZSI and Quasi ZSI. A two winding trans in Z-impedance network of the conventional LCCT ZSI is replaced by a three winding trans in the proposed inverter. To verify the validity of the proposed inverter, a DSP controlled hardware was made and PSIM simulation was executed for each method. Comparing the current and voltage ripples of each method under the condition of input DC voltage 70[V] and output AC voltage 76[Vrms], the input current and capacitor voltage ripple factors of the proposed inverter were low as 11[%] and 1.4[%] respectively. And, for generation of the same output AC voltage of each method, voltage stress of the proposed inverter was low as 175[V] under the condition of duty ratio D=0.15. As mentioned above, we could know that the proposed inverter have the characteristics of low voltage stress, low ripple factor and low operation duty ratio compared with the conventional methods. Finally, the efficiency according to load change/duty ratio and the transient state characteristics were discussed.