• 전력전자학회논문지
• /
• 제14권2호
• /
• pp.134-141
• /
• 2009

전원사고로 인하여 야기되는 전원급변상황에서 위상각의 새로운 PLL 방법은 추종속도를 개선시키기 위하여 제안되었다. 일반적으로 측정된 전원이 이상적이지 않고 고조파가 포함되어 있으며 센서의 노이즈 때문에 동기좌표계 PLL의 피드백 루프에는 LPF를 사용하고 있다. 그러므로 과도상태의 빠른 동특성을 얻기 위해서 LPF를 고려한 PLL시스템의 모델링을 제안하였다. 또한 전원의 급변 시에 빠른 위상각 검출을 위한 방법으로 자동으로 제어기 대역폭과 LPF의 차단주파수를 변동시키는 가변 파라미터 PLL방법을 제안하였다. 이를 시뮬레이션과 실험을 통해 검증하여 유효성을 보이고자 한다.

• 대한기계학회논문집B
• /
• 제37권11호
• /
• pp.1009-1014
• /
• 2013

본 연구는 연료전지 공기극에서 리브의 높이를 변화시켰을 때, 이에 따른 응답성과 성능의 변화를 평가하였다. 전류 밀도의 순간적인 변화에 따른 과도 상태의 전압 신호를 분석하기 위해 당량비와 상대습도가 일정한 상태에서 연료전지의 주 작동 전압 구간인 0.5V~0.7V의 범위에서 전류 밀도를 $0.8A/cm^2$에서 $1.0A/cm^2$으로 변화를 주어 응답성을 분석하였고, 체결압력을 1.5MPa, 2.0Mpa로 다르게 했을 경우 언더슈트의 정도를 확인하였다. $100{\mu}m$의 리브 높이를 변화시킨 채널의 경우, 1.5MPa의 체결압에서 기존의 경우에 비해 빠르게 안정적인 상태에 도달했으며 최대 언더슈트 전압값이 낮게 측정되었다. 하지만 성능은 접촉 저항의 증가로 인해 기존의 분리판에 비해 낮은 값을 나타냈다.

• 한국자동차공학회논문집
• /
• 제21권1호
• /
• pp.99-106
• /
• 2013

DME (Di-Methyl Ether) is synthetic product that is produced through dehydration of methanol or a direct synthesis from syngas. And it is able to save fossil fuel and reduce pollutants of emission such as PM and $CO_2$. In spite of its advantages it is difficult to design DME fuelled engine system because DME fuel may cause to severely generate cavitation and corrosion in fuel delivery system due to physical properties of DME. Therefore, in this study three-dimensional internal flow characteristics with consideration of cavitation were predicted in the DME injector using diesel and DME fuel. Moving grid technique was employed to describe needle motion and 1-D hydraulic simulation of injector was also simulated to obtain transient needle motion profiles. The results of simulation show that cavitations was generated at the inlet of nozzle near high velocity region both diesel and DME. And mass flow rate of DME is reduced by 4.73% compared to that of diesel at maximum valve lift because cavitation region of DME is much more larger. To increase flow rate of DME injector, internal flow simulation has been conducted to investigate the nozzle hole inner R-cut effect. The flow rates of diesel and DME increase as R-cut increases, and flow coefficient of DME fuel injector was increased by 6.3% on average compared with diesel fuelled injector. Finally, optimum shape of DME injector nozzle is suggested through the comparison of flow coefficient with variation of nozzle hole inner R-cut.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2002년도 하계학술대회 논문집 B
• /
• pp.1309-1312
• /
• 2002

The electric power network paralleled with wind turbine generator may have the negative impacts on the protection, operation, and management caused by the operation of wind turbine generator. Therefore, it is necessary to investigate the operating characteristic of wind turbine generator. This paper describes model of a squirrel-cage type wind turbine induction generator and the soft cut-in connection method for reducing the transient state on power network, and simulates various cases of wind turbine operations. The radial distribution network of IEEE 13-bus are modeled and tested by PSCAD/EMTDC.

• Transactions on Electrical and Electronic Materials
• /
• 제7권5호
• /
• pp.224-229
• /
• 2006

Many studies have been done on the application of residual charge measurement in cable degradation diagnosis. In this paper, the behavior of residual charges measured with water-tree degraded XLPE sheets and cable are discussed. At charge injection process, the charge is injected by applying dc voltage as a conventional method, suddenly cut-off ac voltage or impulse voltage. Therefore the residual charge is influenced by the applying process. At charge release process, transient dc current flows when applying ac high voltage and also ac high voltage superimposed to dc low voltage. From the results, new diagnosis method is suggested.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2009년도 제40회 하계학술대회
• /
• pp.2065_2066
• /
• 2009

In this paper, we have developed high performance SPD(surge protective device) and evaluated the characteristics in comparison with typical SPD used in the inside and outside of the country. The new SPD was composed of MOV(metal oxide varistor), GDT(gas discharge tube) and impedance such as resistors, capacitors or varistors. To estimate operating the characteristic of the SPD which was developed, it was measured surge voltage caused by fault current or surge according to IEC 61000-4-5. As a result it was found that the power supply was cut off by high performance SPD when caused a short-circuit. In addition we could know that it could prevent ELB(earth leakage breaker)'s malfunction caused by surge.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
• /
• pp.8-13
• /
• 2001

In the turning process, the feed is usually selected by a machining operator considering workpiece, cutting tool and depth of cut. Even if this selection can avoid power saturation or tool breakage, it is usually conservative compared to the capacity of the machine tools and can reduce the productivity significantly. This paper proposes a selection method of the feed and the reference cutting force based on MRR(material removal rate), maximum spindle power and specific energy. In order to estimate and control cutting force accurately in transient and steady state, this study utilizes a synthesized cutting force estimation method and a Fuzzy controller. The experimental results present that these systems can be useful for the FMS(flexible manufacturing system) and unmanned automation system.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2002년도 ICCAS
• /
• pp.88.5-88
• /
• 2002

A new floating power supply for the current measurement system of a high voltage power line is developed. It is confirmed that, the current measurement system can stably transfer the signal of the power line current about 50 - 300 A by using the proposed power supply. The excellent characteristics are obtained by the steady-state and transient experiments of the proposed circuit. $\textbullet$ The right figure shows the external view of the trial measurement system for 6.6 kV. In order to see the inside, 120 degrees of the insulator is cut. The toroidal coil for the power supply and the Rogowskii coil for the current sensor are both divided into two and fixed on the power line as...$\textbullet$ The proposed circuit can supply +5V and -5V voltages without using a solar cell and/or a battery.

• 대한기계학회논문집A
• /
• 제26권7호
• /
• pp.1446-1452
• /
• 2002

In the turning process, the feed is usually selected by a machining operator considering workpiece, cutting tool and depth of cut. Even if this selection can avoid power saturation or tool breakage, it is usually conservative compared to the capacity of the machine tools and can reduce the productivity significantly. This paper proposes a selection method of the feed and the reference cutting force based on MRR(material removal rate), maximum spindle power and specific energy. In order to estimate and control cutting force accurately in transient and steady state, this study utilizes a synthesized cutting force estimation method and a Fuzzy controller. The experimental results show that these systems can be useful for the unmanned turning process.

• 대한기계학회논문집B
• /
• 제29권1호
• /
• pp.27-34
• /
• 2005

We analyze in detail axially symmetric theoretical study for the photothermal pulsed radiometry of a cylindrical model. The theoretical solutions describe the transient infrared radiation from the sample heated by short-duration pulsed heating. In the conventional transmission radiometry technique, the excitation source and the detector are on opposite sides of the sample, otherwise in the new single ended radiometry technique, the excitation source and the detector are on same sides of the sample. The analytical solution described for photothermal radiometry in this study would not need to cut or polish samples to measure the thermal diffusivity. Therefore the radial area and axial thickness of samples are not limited. The effects of excitation pulse duration and the area of heat source are discussed.