• 전기학회논문지
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• 제65권10호
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• pp.1648-1654
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• 2016

This paper analyzes complex vector current control for the enhanced cross-coupling compensation in accordance with parameter variation in grid-connected inverter system, and verifies through simulation and experiment. Complex vector current control is performed in the synchronous reference frame through d-q transformation. It generates cross-coupling components with rotating nominal angular frequency. In general, cross-coupling elements are compensated by decoupling terms added to output of conventional decoupling PI controller. But, it is impossible to compensate them perfectly which transient response is especially deteriorated such as large overshoot and slow tracking, when variation of grid impedance or measurement error occurs. However, complex vector current control can improve stability and response characteristic of current control regardless of the situation as before. Decoupling controller and complex vector controller are represented through complex forms, and these controllers are analyzed by using frequency response in s-domain, respectively. It is verified that complex vector controller has more superior response characteristic than decoupling controller through MATALB, PSIM and experimental in 5kW grid-connected inverter when L filter parameter is varied from 1.1mH to increase double, 2.2mH.

• Journal of Electrical Engineering and Technology
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• 제10권5호
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• pp.2062-2069
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• 2015

In the series hybrid active power filter (SHAPF) with magnetic flux compensation (MFC), the system current oscillate in the experimental results when adding the same phase harmonic current command in current control block. This condition endangers the security of the SHAPF. Taking the digit period average arithmetic as example, this paper explains the inter-harmonics current oscillation in the experiment. The conclusion is that the SHAPF is unstable to the inter-harmonics current in theory. Limited by the capacity of the inverter, the system current and the inverter output current do not increase to infinite. At last, some methods are proposed to solve this problem. From the practical viewpoint, the voltage feed-forward control is easy to achieve. It can suppress the current oscillation problems, and also improve the filtering effect. The feasibility of the methods is validated by both the emulation and experiment results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.266-267
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• 2006

A coupling capacitor voltage transformer (CCVT) is used in extra high voltage and ultra high voltage transmission systems to obtain the standard low voltage signal for protection and measurement. To obtain the high accuracy at the power system frequency, a tuning reactor is connected between a capacitor and a voltage transformer (VT). Thus, no distortion of the secondary voltage is generated when no fault occurs. However, when a fault occurs, the secondary voltage of the CCVT has some errors due to the transient components resulting from the fault. This paper proposes an algorithm for compensating the secondary voltage of the CCVT in the time domain. With the values of the secondary voltage of the CCVT, the secondary and the primary currents are obtained; then the voltage across the capacitor and the tuning reactoris calculated and then added to the measured secondary voltage. The proposed algorithm includes the effect of the non-linear characteristic of the VT and the influence of the ferro-resonance suppression circuit. Test results indicate that the algorithm can successfully compensate the distorted secondary voltage of the CCVT irrespective of the fault distance, the fault inception angle and the fault impedance.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 춘계학술대회 논문집 전기설비전문위원
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• pp.48-50
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• 2006

SC(Static Condenser) in KEPCO is used in voltage control and power factor compensation. Currently KEPCO uses SC to 154kv 50MVA and 23kv SMVA. It is not important in old days because a SC bank accident has no effect on power system. But we are interested in the SC bank for power quality in these days. The SC Bank has a reactor and a condenser using series connection. It is operated in critical point for resonance circuit normally. Therefore the SC bank has a small reliability against other Power instruments. If a 4th harmonic frequency as a resonance frequency is supplied in system, the condenser is damaged because of a resonance current. And a trip and a closing for CB(Circuit Breaker) in many times will have a big influence of SC bank destruction. General OCR(Over Current Relay) observing SC bank is not useful for this protection We think that protection relay must be have the SC bank characteristics. A solution for this problem is active Power, resonance frequency and impedance.

• 한국전기전자재료학회논문지
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• 제26권2호
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• pp.134-139
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• 2013

When the accident occurred in power distribution system, it needs to control efficiently the fault current according to the fault angle and location. The flux-lock type superconducting fault current limiters (SFCL) can quickly limit when the short circuit accidents occurred and be made the resistance after the fault current. The flux-lock type SFCL has a single triggering element, detects and limits the fault current at the same time regardless of the size of the fault current. However, it has a disadvantage that broken the superconductor element. If the flux-lock type SFCL has separated structure of the triggering element and the limiting element, when large fault current occurs, it can reduce the burden of power and control fault current to adjust impedance. In this paper, this system is composed by triggering element and limiting element to analyze operation of limiting current. When the fault current occurs, we analyzed the limiting and operating current characteristics of the two triggering current level, and the compensation characteristics of bus-voltage sag according to the fault angle and location.

• 제어로봇시스템학회논문지
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• 제15권12호
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• pp.1163-1168
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• 2009

The power quality of wind energy becomes more and more important in connecting wind-farms to the grid, especially weak grid. This paper presents the simulation of a wind farm of a permanent magnet synchronous generator (PMSG) and a doubly fed induction generator (DFIG). Flicker mitigation is performed by using PMSG as a static synchronous compensator (STATCOM) to regulate the voltage at the point of common coupling (PCC). A benefit of the measure is that integrating two function of to control the active power flow and to reduce the voltage flicker in a wind farm. Simulation results show that controlling PMSG is an effective and economic measure in reducing the flicker during continuous operation of grid connected wind turbines regardless of short circuit capacity ratio, turbulence intensity and grid impedance angle.

• 한국ITS학회 논문지
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• 제7권2호
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• pp.43-49
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• 2008

본 논문에서는 UHF 대역 RFID에서 송신과 수신신호의 격리도를 개선한 새로운 구조의 방향성 결합기 모듈을 설계 제작하였다. 본 논문에서 제안한 방법은 방향성 결합기자체가 갖는 격리도와 안테나의 부정합으로 인한 TX의 반사를 모두 제거할 수 있는 구조이다. 제안한 방법을 검증하기 위하여 분포소자 및 집중소자로 방향성 결합기를 설계 및 제작하였다. 또한 바렉터 다이오드를 통한 가변회로를 설계하여 안테나의 부정합을 보상할 수 있도록 설계하였다. 제작한 회로의 특성은 모두 910MHz 중심주파수에서 45dB이상의 격리 특성을 보였다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제14권6호
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• pp.733-740
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• 2014

A resistive micro Pirani gauge using amorphous silicon (a-Si) thin membrane is proposed. The proposed Pirani gauge can be easily integrated with the other process-compatible membrane-type sensors, and can be applicable for in-situ vacuum monitoring inside the vacuum package without an additional process. The vacuum level is measured by the resistance changes of the membrane using the low noise correlated double sampling (CDS) capacitive trans-impedance amplifier (CTIA). The measured vacuum range of the Pirani gauge is 0.1 to 10 Torr. The sensitivity and non-linearity are measured to be 78 mV / Torr and 0.5% in the pressure range of 0.1 to 10 Torr. The output noise level is measured to be $268{\mu}V_{rms}$ in 0.5 Hz to 50 Hz, which is 41.2% smaller than conventional CTIA.

• Journal of Electrical Engineering and Technology
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• 제8권4호
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• pp.737-743
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• 2013

The small-scaled onsite generators such as photovoltaic power, wind power, biomass and fuel cell belong to decarbonization techniques. In general, these generators tend to be connected to utility systems, and they are called distributed generations (DGs) compared with conventional centralized power plants. However, DGs may impact on stabilization of utility systems, which gets utility into trouble. In order to reduce utility's burdens (e.g., investment for facilities reinforcement) and accelerate DG introduction, the advanced operation algorithms under the existing utility systems are urgently needed. This paper presents the advanced voltage regulation method in power systems since the sending voltage of voltage regulators has been played a decisive role restricting maximum installable DG capacity (MaxC_DG). For the proposed voltage regulation method, the difference from existing voltage regulation method is explained and the detailed concept is introduced in this paper. MaxC_DG estimation through case studies based on Korean model network verifies the superiority of the proposed method.

• 전기전자학회논문지
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• 제25권1호
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• pp.101-108
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• 2021

본 논문에서는 전기차 충전기용 모듈형 DC/DC 컨버터의 병렬 제어 기법을 제안한다. 전기차 충전기는 모듈형 컨버터를 적용하여 출력 전력 용량이 증가되고 있지만, 모듈간 구성 요소의 차이, 게이트 드라이버의 지연, 센싱 오차 등에 의해 출력 전류 불균형이 발생하며, 이는 전체 시스템의 효율 및 신뢰성 저하를 야기한다. 출력 전류 균등 분배를 위한 기존의 기법들은 전압 강하 또는 시스템 부피 및 비용이 증가한다는 단점을 갖는다. 본 논문에서는 전류 보상 성분을 고려한 병렬 제어 기법을 적용하여 시스템의 하드웨어 변동없이 출력 전류 균등 분배를 달성한다. 시뮬레이션을 통하여 제안하는 병렬 제어 기법의 성능 및 타당성을 검증한다.