• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.2116-2118
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• 2000

In the technique of Q-switching, very fast electronically controlled optical shutters can be made by using the electro-optic effect in crystals or liquids. The driver for the Pockels cell must be a high-speed, high-voltage switch which also must deliver a sizeable current. Common switching techniques include the use of vacuum tubes, cold cathode tubes, thyratrons, SCRs, and avalanche transistors. Semiconductor devices such as SCRs, avalanche transistors, and MOSFETs have been successfully employed to drive Pockels cell Q-switch. In this study, a simple driver for the Pockels cell Q-switch was developed by using SCRs, pulse transformer and TTL ICs. The Pockels cell Q-switch which was operated by this driver was employed in pulsed Nd:YAG laser system to investigate the operating characteristics of this Q-switch. And we have investigated the output characteristics of this Q-switch as a function of the Q-switch delay time to Xe flashlamp current on.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.990-992
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• 2002

30kW electrical power conversion system is delveloped for the variable speed wind turbine system. In the wind energy conversion system(WECS) a synchronous generator with field current excitation converts the mechanical energy into electrical energy. As the voltage and frequency of generator output vary according to the wind speed, a dc/dc boosting chopper is utilized to maintain constant dc link voltage. Grid connection type PWM inverter supply currents into the utility line by regulating the dc link voltage. The active power is controlled by q-axis current which the reactive power can be controlled by d-axis current reference change. The phase angle of utility voltage is detected using s/w PLL(Phased Locked Loop) in d-q synchronous reference frame. This scheme gives a low cost power solution for variable speed WECS.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.433-439
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• 2001

An experimental study was carried out on the characteristics of the mixed-convection heat transfer from a protruding heat source module which had uniform heat flux and was located on a flat plate in the inclined channel. The effects of the inclined channel(${\varphi}=0{\sim}90^{\circ}$) was studied for the input power($Q=3,\;7W$) and inlet air velocities($V_{i}=0.1{\sim}0.9m/s$). Experimental results indicate that the input power was most effective parameter on the temperature differences between inlet air and module. The effects of the inclined angle was negligible when the inlet velocities were above 0.5m/s and 0.9m/s at Q = 3W, 7W respectively. As the inclined angle of the channel increases, the temperatures of the module are decreased. So we obtained the best condition on the adiabatic board at the vertical channel.

• 전기학회논문지
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• 제57권10호
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• pp.1796-1801
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• 2008

In this paper, a new current based maximum power point tracking (CMPPT) method is proposed for a single phase photovoltaic power conditioning system and the current based MPPT modifies incremental conductance method. The current based MPPT method makes the entire control structure of the power conditioning system simple and uses an inherent current source characteristic of solar cell array. In addition, digital phase locked loop using an all pass filter is introduced to detect phase of grid voltage as well as peak voltage. Controllers about dc/dc boost converter, dc-link voltage, dc/ac inverter is designed for a coordinated operation. Furthermore, PI current control using a pseudo synchronous d-q transformation is employed for grid current control with unity power factor. 3kW prototype photovoltaic power conditioning system is built and its experimental results are given to verify the effectiveness of the proposed control schemes.

• Journal of Power Electronics
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• 제15권6호
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• pp.1628-1639
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• 2015

Line-interactive uninterruptible power supply (UPS) systems are good candidates for providing energy storage within a microgrid. In this paper, a control scheme for a line-interactive UPS system applied in a low-voltage microgrid is presented. It is based on the Q-w and P-E droop control to achieve a seamless transition between grid-connected and stand-alone operation modes. Moreover, a new model for designing the controllers is built in the dq-frame based on the instantaneous power definition. The new-built model takes into account the dynamic performance of the output impedance of the inverter in the dq-frame and can be evaluated in the time domain. Compared to the traditional model based on the instantaneous power definition, the new-built model is more accurate to describe the dynamic performance of the system. Simulation and experimental results obtained with a microgrid consisting of two 40-kW line-interactive UPS systems are given to validate the control strategy of the line-active UPS system and the accuracy of the new-built model.

• 대한기계학회논문집
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• 제12권4호
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• pp.825-832
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• 1988

본 연구에서는 1차원 열흐름하에서 상부가 가열된 다공물질내의 열파이프 현 상과 관련하여 2상영역의 존재와 그 길이에 영향을 미치는 인자들을 실험적으로 관찰, 조사하였다.

• 전력전자학회논문지
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• 제5권2호
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• pp.123-129
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• 2000

본 논문은 실용화 보급단계에 있는 대표적인 대체에너지 전원으로서, 태양전지, 직·교류(DC/AC) 인버터, 전력계통으로 구성되는 계통연계형 태양광발전시스템의 설계 및 시험결과에 대하여 기술하고자 한다. 계통연계를 위한 시스템 특성을 검증하기 위해 3상 직·교류 인버터를 포함한 50kW 계통연계 태양광발전시스템이 설계 제작되었다. 또한 d-q 변환을 이용한 PI 제어기를 갖는 전류제어방식의 3상 PWM 인버터 제어기법이 제시되었다. 실험결과들은 제안된 시스템이 계통연계 동작에 있어서 단위 역율로 안정하게 동작함을 보여준다.

• 한국전기전자재료학회논문지
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• 제16권5호
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• pp.397-403
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• 2003

Microwave dielectric properties of (1-x)ZnW $O_4$-xTi $O_2$ ceramic systems were investigated with calcination temperatures and Ti $O_2$ contents. The ZnW $O_4$ ceramic could be suitably sintered at 1075$^{\circ}C$ and showed the dielectric constant of 13.6, quality factor(Q$\times$ $f_{O}$value) of 22,000 and temperature coefficient of resonant frequency($\tau$$_{f}$) of -65$\pm$2ppm/$^{\circ}C$. Increasing the amount of Ti $O_2$ in the range of 0.25 to 0.45 mol, the dielectric constant and $\tau$$_{f}$ increased due to the role of Ti $O_2$ but the quality factor decreased due to the increase of phase boundaries. The 0.7ZnW $O_4$-0.3Ti $O_2$ ceramic showed the dielectric constant of 19.8, qualify factor(Q$\times$ $f_{0}$) of 20,000 and $\tau$$_{f}$ of -3$\pm$1ppm/$^{\circ}C$.>.EX>.>.>.

• 한국전기전자재료학회논문지
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• 제11권5호
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• pp.394-399
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• 1998

High power characteristics with vibration velocity were studied in $Pb(Y_{2/3}W_{1/3})O_3-Pb(Zr,Ti)O_3$(PYW-PZT) ceramics by using the constant current method. Young s modulus $Y_0^E$ and mechanical quality factor $Q_m$ are a function of the square of effective vibration velocity \upsilon_0$. The nonlinear proportional constants of the above functions indicate the degree of stability under the vibration level change. The stability of PYW-PZT ceramics estimated by these constants coincides with the results obtained through the heat generation. It was found that $Q_m$ was markedly decreased with increasing the vibration velocity, accompanying a lot of heat generation. The vibration hysteresis and dielectric loss according to the vibration velocity was reduced by doping $Fe_2O_3$to the ceramics. On the contrary, these losses was increased by doping $Nb_2O_5$.

• 한국ITS학회 논문지
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• 제7권4호
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• pp.76-85
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• 2008

본 논문에서는 TETRA 단말기용 800 MHz 대역 1 W급 cartesian feedback 선형전력증폭기를 설계 및 제작하였다. 200 kHz 협대역을 갖는 TETRA 신호를 증폭 시, cartesian feedback 선형화기를 통해서 ${\pm}25$ kHz 오프셋 주파수에서 30 dBc 이상의 전력증폭기 선형성을 개선하였다. 선형화의 성능은 I/Q 신호간의 이득과 위상의 불일치 및 DC offset 성분에 의해서 영향을 받음을 알 수 있으며 이러한 문제를 보상 시 선형화를 극대화 할 수 있음을 알 수 있었다. Cartesian feedback 선형화기는 협대역 QAM 신호의 선형화 기술로 적합함을 확인하였으며 이를 이용하여 다른 변조방식을 갖는 신호들의 선형화방법으로도 적용 가능하다.