• Journal of Power Electronics
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• 제18권3호
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• pp.863-870
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• 2018

The traditional power control theories for the harmonic reduction methods in multilevel inverters are found to be unreliable under unbalanced load conditions. The unreliability in harmonic mitigation is caused by voltage fluctuations, non-linear loads, the use of power switches, etc. In general, the harmonics are reduced by filters. However, such devices are an expensive way to provide a smooth and fast response to secure power systems during dynamic conditions. Hence, the Decoupled Double Synchronous Reference Frame (DDSRF) theory combined with a State Delay Controller (SDC) is proposed to achieve a harmonic reduction in power systems. The DDSRF produces a sinusoidal harmonic that is the opposite of the load harmonic. Then, it injects this harmonic into power systems, which reduces the effect of harmonics. The SDC is used to reduce the delay between the compensation time for power injection and the generation of a reference signal. The proposed technique has been simulated using MATLAB and its reliability has been verified experimentally under unbalanced conditions.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권11호
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• pp.563-571
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• 2003

In this paper, the control algorithm and control method for a combined system of shunt passive filter and series active filter in 3-phase 4-wire system are discussed. Moreover, the three-phase four-wire system is widely employed in distributing electric energy to several office building and manufacturing plants. In such systems, the third harmonic and its 3th harmonics are termed as triple and zero sequence components that do not cancel each other in the system neutral. Consequently, the triple harmonics add together creating a primary source of excessive neutral current. Regarding this concern, this paper presents a new control algorithm for a series hybrid active system, whereas the control approach it adopts may directly influence its compensation characteristics. Hence, the advantage of this control algorithm is direct extraction of compensation voltage reference and the required rating of the series active filter is much smaller than that of a conventional shunt active filter. Some experiments were executed and experimental results from a prototype active power filter confirm the suitability of the proposed approach.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 E
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• pp.1715-1717
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• 1997

This paper deals with the dead operation characteristics of the earth leakage circuit breaker(ELB) caused by impulse voltages. The surge protective devices for electronic circuit and AC power lines are becoming more widely used. It is possible to give rise to the malfunction of ELB due to the operation of surge protective devices, and the interruption of AC power lines brings about several disadvantages such as low reliability of electronic and informational systems, economical loss, and etc. The dead operation characteristics of the ELB from impulse voltages were measured under the conditions of KS C 4613 and the test circuit with a varistor. As a result, the peak current value of the zero-phase sequence circuit of the ELB is increased as the surge voltage and stray capacitance increase. All of the ELBs used in this work were satisfied with the lightning impulse dead operation test condition defined in KS C 4613. However one specimen only did not cause dead operation in the condition of the test circuit with a varistor. There is high possibility that a large portion of the ELBs connected with the AC power lines having the surge protective devices bring about the dead operation.

• 대한전기학회논문지:전력기술부문A
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• 제55권3호
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• pp.116-122
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• 2006

The underground transmission lines is continuously expanded in power systems. Therefore the fault of underground transmission lines are increased every year because of the complication of systems. However the studies dealing with fault location in the case of the underground transmission lines are rarely reported except for few papers using traveling wave method and calculating underground cable impedance. This paper describes the algorithm using fuzzy system and travelling wave method in the underground transmission line. Fuzzy inference is used for fault discrimination. To organize fuzzy algorithm, it is important to select target data reflecting various underground transmission line transient states. These data are made of voltage and average of RMS value on zero sequence current within one cycle after fault occurrence. Travelling wave based on wavelet transform is used for fault location. In this paper, a variety of underground transmission line transient states are simulated by EMTP/ATPDraw and Matlab. The input which is used to fault location algorithm are Detail 1(D1) coefficients of differential current. D1 coefficients are obtained by wavelet transform. As a result of applying the fuzzy inference and travelling wave based on wavelet transform, fault discrimination is correctly distinguished within 1/2 cycle after fault occurrence and fault location is comparatively correct.

• 전력전자학회논문지
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• 제26권5호
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• pp.315-324
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• 2021

A solid state transformer (SST) that can interface an MVAC of three-phase 13.2 kV and a 1.5 kV DC distribution. SST consists of an AC/DC converter and a DC/DC converter with a high-frequency isolation transformer (HFIT). The AC/DC converter consists of cascaded NPC full-bridge to cope with the MVAC. The DC/DC converter applies a quad active bridge (QAB) topology to reduce the number of the HFIT. Topology analysis and controller design for this specific structure are discussed. In addition, the insulation of HFIT used in DC/DC converters is considered. The discussion is validated using a 300 kVA three-phase SST prototype.

• Journal of Power Electronics
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• 제19권1호
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• pp.119-133
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• 2019

Although the dual modulation wave method can solve the low-frequency neutral point potential (NPP) fluctuation problem for three-level neutral point clamped converters, it also increases the switching frequency and limits the zero-sequence voltage. That makes it harmful when dealing with the NPP drift problem if the converter suffers from a long dead time or asymmetric loads. By introducing two degrees of freedom (2-DOF), an NPP control based on a search optimization method can demonstrate its ability to cope with the above mentioned two types of NPP problems. However, the amount of calculations for obtaining an optimal 2-DOF is so large that the method cannot be applied to certain industrial applications with an inexpensive digital signal processor. In this paper, a novel optimal 2-DOF-based NPP control is proposed. The relationships between the NPP and the 2-DOF are analyzed and a method for directly determining the optimal 2-DOF is also discussed. Using a direct calculation method, the amount of calculations is significantly reduced. In addition, the proposed method is able to maintain the strongest control ability for the two types of NPP problems. Finally, some experimental results are given to confirm the validity and feasibility of the proposed method.

• 한국조명전기설비학회지:조명전기설비
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• 제11권5호
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• pp.44-52
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• 1997

반도체와 IC를 포함한 전자회로는 서지 전압 및 전류에 대해 매우 취약하다. 따라서 전자회로와 교류전원선로에 서지보호장치가 널리 사용되고 있다. 이들 서지보호장치의 동작에 의해 누전 차단기가 오동작 할 수 있으며, 누전 차단기의 오동작에 의한 교류전원의 차단은 전자.정보화 시스템의 운전효율 및 신뢰성의 저하와 경제적인 손실 등과 같은 단점을 초래한다. 본 연구의 목적은 서지 전압에 대한 누전 차단기의 오동작 특성을 조사하는 것이다. 10〔kV〕의 1.2/50〔$\mu\textrm{s}$〕서지전압발생기를 제작하였으며, 한국공업규격 KS C 4613의 시험조건과 바리스터를 포함하는 모의 시험회로 조건에 대해 서지 전압을 인가하였을 때 누전 차단기의 오동작 특성을 측정하였다. 그 결과, 서지 전압과 표류정전용량이 증가함에 따라 누전 차단기의 영상전류의 피크값은 증가하였다. 본 연구에서 사용된 모든 누전 차단기는 KS C 4613에 규정된 뇌임펄스 부동작 시험조건에는 적합하였다. 그러나 바리스터를 삽입한 시험회로 조건에서는 단지 1종의 시료를 제외하고 모두 오동작하였다. 서지보호장치를 가지고 있는 교류전원선로에 설치된 누전차단기는 오동작할 가능성이 매우 높다.

• 전력전자학회논문지
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• 제16권3호
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• pp.250-257
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• 2011

본 논문은 병렬 삼상 부스트 컨버터에서 Interleaved PWM에 의해 발생하는 고 주파수 순환전류를 효과적으로 저감시키기 위해서, AC 입력단에 연결되는 삼상 결합 인덕터의 특성을 분석하였다. 제시된 삼상 결합 인덕터 분석은 삼상 결합 인덕터의 구조와 전압 방정식의 해석을 통하여 이루어졌다. 그리고 이것을 바탕으로 기존의 저 주파수 평균화 모델에 삼상 결합 인덕터를 추가하여, 고 주파수 순환전류와 저 주파수 순환전류를 동시에 저감시킬 수 있는 새로운 형태의 평균화 모델을 제안하였다. 새로운 평균화 모델의 영상성분을 이용하면, 삼상 결합 인덕터와 라인 인덕터의 순환전류에 대한 총 인덕턴스를 각각 구해 비교 할 수 있다. 시뮬레이션과 실험결과를 토대로 병렬 삼상 부스트 컨버터에서 사용되는 삼상 결합 인덕터의 유용성을 검증하였다.

• 한국산학기술학회논문지
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• 제10권10호
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• pp.2619-2627
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• 2009

비접지 배전계통에서 전체고장의 약 70%를 차지하는 지락고장 발생시에는 지락전류가 작아 검출이 어렵지만 고장상태로 전원 공급을 지속할 경우 사고 파급 및 기기 소손을 유발할 가능성이 있기 때문에 지락고장 처리는 매우 중요하다. 본 논문에서는 GPT(접지형 계기용 변압기, Ground Potential Transformer)에서 감지하는 영상전압 신호를 이용하여 고장선로를 검출하고, 비상시 연계선로를 이용하여 정전구역을 복구하기 위해 평상시 개폐기가 열려 있는 상태로 배전선로 사이를 연결하는 상시개방점을 이동하며 각 구간을 차례로 분리하면서 GPT 신호의 사라짐 여부를 감시하여 고장구간을 검출하는 방법을 제안한다. 고장구간 탐색 시 전체 정전이 없고, 고장구간 검출과 건전구간 복구가 동시에 가능하며 다양한 형태의 배전계통 구성에 적용 가능하다는 점에서 효율적이다. 본 논문에서 제안하는 고장처리 방법을 프로그램으로 개발하여 베트남 배전자동화 시범사업에 적용함으로써 알고리즘 및 프로그램의 적정성을 검증하였다.