• Journal of Power Electronics
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• 제5권3호
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• pp.224-232
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• 2005

A new three phase three-level Pulse Width Modulation (PWM) Switched Voltage Source (SVS) inverter with zero neutral point potential is proposed. It consists of three single-phase inverter modules. Each module is composed of a switched voltage source and inverter switches. The major advantage is that the peak value of the phase output voltage is twice as high as that of a conventional neutral-point-clamped (NPC) PWM inverter. Thus, the proposed inverter is suitable for applications with low voltage sources such as batteries, fuel cells, or solar cells. Furthermore, three-level waveforms of the proposed inverter can be achieved without the switch voltage imbalance problem. Since the average neutral point potential of the proposed inverter is zero, a common ground between the input stage and the output stage is possible. Therefore, it can be applied to a transformer-less Power Conditioning System (PCS). The proposed inverter is verified by a PSpice simulation and experimental results based on a laboratory prototype.

• 전기전자학회논문지
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• 제3권2호
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• pp.268-275
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• 1999

본 논문에서는 CDMA 방식 중계기용 전력증폭기의 선형특성을 향상시키기 위해 기존의 전치왜곡 방식과 전방귀환 방식을 혼합한 전력증폭기를 설계 제작하였다. CDMA방식의 이동통신 시스템은 기존의 아날로그 셀룰라 방식과는 사용 스펙트럼 대역폭이 훨씬 크며 증폭기의 비선형성에 의한 채널사이의 혼변조 왜곡을 충분히 제거하여야만 통신이 가능하기에 선형성이 우수한 전력증특기가 필수적으로 요구된다. 본 논문에서 제작한 전력증폭기는 37dBm, 2-tone 인가시의 IMD 특성이 -50dBc로써 나타났으며, 불요방사 특성도 IS-95 기준을 만족하는 $fc{\pm}\;885kHz$에서 약 -46dBc, $fc{\pm}\;1.98MHz $ 에서는 약 -52dBc로 나타났다.

• 조명전기설비학회논문지
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• 제24권8호
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• pp.48-54
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• 2010

교류 전기철도 시스템은 비선형 단상 부하인 차량의 부하특성으로 인해 고조파 왜곡, 무효전력 발생, 3상 불평형과 같은 전기품질 문제를 가지고 있다. 이 같은 전기품질 문제는 철도 시스템뿐만 아니라 철도와 연계된 다른 건전한 계통에도 악영향을 미치게 된다. 따라서 본 논문에서는 이와 같은 전기철도 급전시스템의 전기품질 문제를 보상하기 위해 철도용 전기품질 보상장치(RPQC; railway power quality conditioner)를 적용하고, SRF(synchronous-reference-frame) 제어를 이용한 RPQC의 제어방법을 제안한다. 제안하는 제어방법을 통해 RPQC는 고조파 왜곡, 무효전력, 부하 불평형과 같은 전기품질 문제를 순시적으로 보상할 수 있으며, 시뮬레이션을 통해 이를 검증한다. 시뮬레이션 결과는 제안한 RPQC 제어방법의 타당성을 보여주고 있다.

• 한국정보통신학회논문지
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• 제14권12호
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• pp.2615-2621
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• 2010

본 논문에서는 메타물질 구조 다중대역 6단자 위상상관기를 설계하고 제작하였다. 이중 주파수 대역에서 신호를 수신 처리할 수 있는 집중소자형 메타물질 구조를 해석하고, 해석된 결과를 기반으로 다중대역 직접변환 수신 전처리기에 적합한 소형화 메타물질 구조 6단자 위상상관기를 제안하고 구현하였다. 다중대역 6단자 위상상관기를 구성하는 저항성 전력 분배기와 메타물질 $90^{\circ}$ 하이브리드 결합기의 산란 계수를 기반으로 동일한 특성을 갖는 6단자 위상상관기 구성 요소를 제작하고 측정하였다. 측정된 메타물질 구조 6단자 위상상관기는 모의실험 결과와 일치하였으며, 이중 주파수 대역에서 -20 dB 이하의 정합과 1 dB 이내의 전달 이득차, 그리고 ${\pm}4.1^{\circ}$ 이하의 전달 위상차 특성으로 양호한 다중대역 6단자 위상상관기 성능을 나타내었다.

• Journal of international Conference on Electrical Machines and Systems
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• 제3권4호
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• pp.383-388
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• 2014

In This paper, the output characteristics and vibrations were compared and analyzed according to operation method in 100W class. The voltage source is applied only two phase in BLDC drive system therefore commutation torque ripple and imbalance of RMF occurred. Due to this efficiency was significantly degraded because mechanical loss is increased, besides the vibration and noise were greatly generated. The vibration and output characteristics were compared and analyzed according to three phase and BLDC drive system.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2000년도 전력전자학술대회 논문집
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• pp.739-743
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• 2000

With significant development of power electronics technology the proliferation of nonlinear loads such as such as static power converters has deteriorated power quality in power transmission distribution systems. Notably voltage harmonics resulting from current harmonies produced by the nonlinear loads have become a serious problem in many systems Moreover momentary interruptions and voltage sags are responsible for many of the power quality problems found in typical industrial plants. Int his paper proposed 3 phase hybrid series active power filter is not only for harmonic compensation but also for harmonic isolation between supply and load and for voltage regulation and imbalance compensation Through computer simulations we have verified the effectiveness of the proposed system.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.1822-1831
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• 2014

Micro-grid is connected to the main power grid through a static switch. One of the critical issues in micro-grids is protection which must disconnect the micro-grid from the network in short-circuit contingencies. Protective methods of micro-grid mainly follow the model of distribution system protection. This protection scheme suffers from improper operation due to the presence of single-phase loads, imbalance of three-phase loads and occurrence of power swings in micro-grid. In this paper, a new method which prevents from improper performance of static micro-grid protection is proposed. This method works based on artificial neural network (ANN) and able to differentiate short circuit from power swings by measuring impedance and the rate of impedance variations in PCC bus. This new technique provides a protective system with higher reliability.

• Journal of Power Electronics
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• 제15권1호
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• pp.288-297
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• 2015

This paper presents a novel approach to diagnose interturn insulation faults in three-phase transformers that operate at different loading conditions. This approach is based on the loci of instantaneous symmetrical components and requires the measurement of three input primary winding currents and voltages to diagnose faults in the transformer. The effect of unbalance supply conditions, load variations, constructional imbalance, and measurement errors when this methodology is used is also investigated. Wing size or length determines the loading on the transformer. Wing travel and area determine the degree of severity of fault. Experimental results are presented for a 400/200 V, 7.5 kVA transformer to validate this method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.2309-2311
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• 2005

A broadband microstrip balun is proposed and designed using a ${\lambda}/4$short-stub in order to compensate phase imbalance. For the demonstration, two baluns are proposed and designed using a ${\lambda}/4$ shorted stub. One is a modified form of the conventional Wilkinson balun, and the other is a modified ring hybrid. Baluns are implemented on TLX-9 substrate of which the dielectric constant is 2.54 and the thickness is 0.5mm. The measurements show a bandwidth of 500MHz at the center frequency of 2GHz.

• Journal of Power Electronics
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• 제17권3호
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• pp.664-673
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• 2017

With the development of multilevel converters, cascaded single-phase H-bridge rectifiers (CHBRs) has become widely adopted in high-voltage high-power applications. In this study, sequence pulse modulation (SPM) is proposed for CHBRs. SPM is designed to balance the dc-link voltage and maintain the smooth changes of switch states. In contrast to phase disposition modulation, SPM balances the dc-link voltage even after removing the load of one submodule. The operation principle of SPM is deduced, and the unbalance degree of SPM is analyzed. All the proposed approaches are experimentally verified through a prototype of a four-module (nine-level) CHBR. Conclusions are drawn in accordance with the results of SPM and its imbalance degree analysis.