• Journal of electromagnetic engineering and science
• /
• 제13권3호
• /
• pp.189-191
• /
• 2013

This letter presents a compact metamaterial-based tunable zeroth-order resonant antenna. It is based on the double-negative unit cell with a function of tunable inductance realized by a varactor and impedance convertor in the shunt branch. The resonant frequency of the designed antenna ranges from 2.31 to 3.08 GHz, depending on the capacitance of the used varactor. Its size is very compact ($0.05{\lambda}_0{\times}0.2{\lambda}_0$) with a relatively wide tunable range of 29.1%. The impedance bandwidth of the antenna is from 20 to 50 MHz for the resonant center frequency. The measured maximum total realized gain is from -0.68 dBi (2.43 GHz) to 1.69 dBi (2.97 GHz). The EM-simulated and measured results are in good agreement.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2006년도 전력전자학술대회 논문집
• /
• pp.25-27
• /
• 2006

This paper proposes a new full ZVS-range asymmetrical half bridge converter. It uses the variable transient current build-up technique with the load variations. The current build-up is accomplished by using the secondary synchronous switch control. Due to the blocking capacitor in secondary side, the voltage applied to leakage inductor varies with the load variations during current build-up period. Therefore, the unnecessary current build-up of leakage inductor current in heavy load condition is prevented and more current build-up in medium and light load condition is achieved for ZVS operation. That is, the variant current build-up with the load variation is accomplished for the ZVS operation. Furthermore, the DC offset of the transformer magnetizing current is also eliminated and the utilization of magnetic core is maximized.

• Journal of Power Electronics
• /
• 제16권2호
• /
• pp.399-413
• /
• 2016

This paper presents a topology for a modular power electronic transformer (PET) and a control scheme. The proposed PET consists of a cascaded H-Bridge rectifier on the primary side, a high-frequency DC/DC conversion cell in the center, and a cascaded H-Bridge inverter on the secondary side. It is practical to use PETs in power systems to reduce the cost, weight and size. A detailed analysis of the structure is carried out by using equivalent circuit. An algorithm to control the voltages of each capacitor and to maintain the power flow in the PET is established. The merits are analyzed and verified in theory, including the bi-directional power flow, variable voltage/frequency and high power factor on the primary side. The experimental results validated the propose structure and algorithm.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2013년도 전력전자학술대회 논문집
• /
• pp.388-389
• /
• 2013

This paper presents the method for the fluctuation smoothing control by using relaxation time variable control of battery. When the output power of wind farm is changed suddenly, it is necessary to control the output power of wind farm. The smoothing relaxation time is changed within limits of battery output power. Using the hybrid energy storage system (HESS) combined with battery energy storage system and electric double layer capacitor, it is possible to control the output power of wind farm. The capacity of battery is determined by considering the case of the disconnecting wind farm from the grid. To verify the proposed method, simulations are carried out by using PSCAD/EMTDC with actual data of wind farm in the Jeju Island.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1995년도 하계학술대회 논문집 B
• /
• pp.571-573
• /
• 1995

This paper presents a method for optimal dispatch which minimizes transmission losses and improves voltage profile of power systems using genetic algorithm based on the mechanism of natural genetics and natural selection. The constraints are VAR sources(transformer tap, generator voltage magnitude and shunt capacitor/reactor), load bus voltages and generator reactive power. Real variable-based genetic algorithms which can save coding times and maintain the accuracy are applied for optimal dispatch of reactive power. The genes of genetic algorithm consisted of integers for considering discrete VAR sources. A efficient operator for crossover is proposed to consider the effect of close genes. The algorithm proposed can apply to problems for large scale power systems with multi-variables and complex nonlinear functions efficiently. The proposed method is applied to IEEE 30 buses model system to show its effectiveness.

• 전기전자학회논문지
• /
• 제14권2호
• /
• pp.9-15
• /
• 2010

In this study, we have been proposed the new type of a transcranial magnetic stimulation adopted a variable voltage capacitor with Cockcroft-Walton circuit and constant-frequency current resonant half-bridge inverter. This a transcranial magnetic stimulation has some merits compared with the conventional one. First, it doesn't require the high voltage transformer. And second, it has less switching losses, compact size and capability in adjusting the transcranial magnetic stimulation output energy precisely. In this paper, we have performed the output characteristics of a transcranial magnetic stimulation system which is well known as magnetic stimulation. The tested results are described as a function of pulse repetition rate and switching numbers of the half-bridge inverter.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2014년도 전력전자학술대회 논문집
• /
• pp.303-304
• /
• 2014

This paper describes Four Switch Three-Phase Z-Source rectifier with reduced value capacitors. This configuration has some advantages in term of small size of the circuit. The rectifier has buck-boost function by shoot-through state. Also, the rectifier has the advantage of decreasing inrush current in start-up and transient states. In order to reduce harmonics PWM modulation technique with a variable index has been suggested. Four Switch Three-Phase Z-Source rectifier with reduced value capacitors can output stable DC. Principles and dynamics of the system are discussed in detail.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2015년도 전력전자학술대회 논문집
• /
• pp.143-144
• /
• 2015

전기추진선박은 디젤엔진과 프로펠러의 회전축이 기계적으로 연결된 기존의 선박과 달리 엔진의 기계적 에너지를 전기 에너지로 변환하여 전동기 회전을 통해 추진력을 얻는 선박으로서 시추선, 군함, OSV(Offshore Support Vessel)등 높은 조종성능이 요구되는 선종에 주로 적용되고 있다. 이러한 선종은 추진력을 얻는데 가장 큰 전력을 사용하므로 날씨에 따른 전력부하량의 변동이 크다. 본 논문에서는 슈퍼커패시터로 구성된 전력버퍼모듈을 이용하여 전기추진선박의 효율적인 전력 운용 전략을 제안한다. 추진전동기의 VFD(Variable Frequency Drive)의 직류단을 전력버퍼모듈로 통합하여 각 전동기의 보조전력으로 활용함으로써 부하변동에 빠르게 대응할 수 있으며, 주 전원의 느린 응답성을 보상하여 조종성능을 향상시킬 수 있다. 제안된 전력버퍼모듈은 시뮬레이션을 통해 그 유용성을 검증하였다.

• 전기학회논문지P
• /
• 제58권4호
• /
• pp.391-396
• /
• 2009

In this paper, a control algorithm for DC-Link voltage unbalancing compensation of a four-switch inverter for a three-phase BLDC motor drive is proposed. Compared with a conventional six-switch inverter, the split source of the four-switch inverter can be obtained by splitting DC-link capacitor into two capacitors to drive the three phase BLDC motor. The voltages across each of two capacitors are not always equal in steady state because of the unbalance in the impedance of the DC-link capacitors $C_1$ and $C_2$ or the variable current flowed into the capacitor's neutral point in motor control. Despite the unbalance, if the BLDC motor may be run for a long time the voltage across one of the capacitors is more increased. So the unbalance in the capacitors voltages will be accelerated. As a result, The current ripple and torque ripple is increased due to the fluctuation of input current which flows into 3-phase BLDC motor. According to that, the vibration of motor will be increased and the whole system will be instable. This paper presents a control algorithm for DC-Link voltage unbalancing compensation. The sampling from the voltages across each of two capacitors is used to perform the voltage control of DC-Link by using the feedforward controller.

• 한국컴퓨터산업학회논문지
• /
• 제2권3호
• /
• pp.357-362
• /
• 2001

기존의 레이저통신용 스위칭 방식은 변압기 2차측에 정류부 및 평활용 콘덴서가 필수적으로 포함되어 있으며, 이렇게 얻어진 직류전압의 후단부를 스위칭 하게 되므로 시스템장치가 복잡하다. 또한 스위칭에 의한 손실이 크고, 펄스반복율(pulse repetition rate)이 증가할수록 콘덴서에 저장된 에너지가 램프로 충분히 전달되지 못하여 레이저 출력 효율이 저감되는 단점이 있다. 본 연구에서는 스위칭에 의한 손실을 줄여 레이저의 출력 효율을 개선하고자 교류전압의 영점(ZERO)을 ZCC(zero cross control)방식으로 검출하여 변압기 2차측 교류전압의 영점에서 SCR을 턴-온(turn-on)시키는 레이저 시스템을 설계 및 제작하였다. 그 결과 기존의 평활용 콘덴서와 정류부를 사용한 레이저 시스템보다 펄스반복울이 10[pps]씩 증가할수록 레이저 출력 효율 약 3.5$\%$씩 증가하여 60pps에서는 약 25$\%$까지 상승하였다.