• 전력전자학회논문지
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• 제22권1호
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• pp.82-88
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• 2017

This study proposes a new topology for the performance test of a valve consisting of a modular multilevel converter (MMC)-based static synchronous compensator (STATCOM). The conventional valve performance test equipment requires high-voltage AC source of several kV rating because the number of submodules to be tested in a valve should be at least six or eight. However, the power source of the proposed scheme is DC and not AC source. The DC power source voltage range of the proposed test circuit is from several volts to several tens of volts. Therefore, the size and cost for the performance test equipment can be reduced considerably compared with the conventional method. The proposed scheme satisfies the requirements of the IEC 62927 standard. Simulations are conducted for a valve of 50[MVA] MMC-based STATCOM. Experimental results with a scale-downed setup show the validity of the proposed performance test topology.

• 한국초전도ㆍ저온공학회논문지
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• 제12권1호
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• pp.61-65
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• 2010

To develop the thermal analysis method for the thermal behavior of HTS power cable system, cooled with sub-cooled liquid nitrogen, new thermo dynamic model for HTS cable system is introduced. The introduced thermal model is mainly modified from the thermal circuit following to IEC60287 for underground power cable systems such as XLPE or paper wrapped insulation cables. The thermal circuits for HTS cables are similar to the forced cooled underground cable system but the major thermal parameters and the configuration is apparently different to the normal cable systems so there has been no proposals in this field of analysing method. In this paper, 154kV HTS cable system has been introduced as an aspects of thermal models and a thermal circuit is proposed for the fundamentals on the dynamic rating systems for the HTS cable system. By using the thermal circuit developed in this paper, the optimal controls on the sub-cooling system's capacity become possible and it is expected to make the efficiency of HTS cable higher than conventional static controls.

• 조명전기설비학회논문지
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• 제14권3호
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• pp.6-14
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• 2000

고효율 다중공진형 컨버터는 스위칭 손질을 다중공진 회로를 이용하여 감소시킬 수 있기 때운에 고주파에서 동작이 가능하다. 이려한 고주파 스위칭 동작은 컨버터에 높은 전력 밀도를 제공한다. 그러나 공진 스위치애 걸리는 전압 스트레스는 입력전압의 4~5배 정도여서, 높은 정격의 소자를 필요로 하기 때문에 소자의 온-저항으로 인한 전도 손실을 증가시킨다. 본 문에서는 이러한 문제점 해결하기 위해 제안했던 전압 스트레스를 줄일 수 있는 AT 포워드 MRC는 모델링 해석파 이를 이용한 등가 모드 해석을 하였다. AT 포워드 MRC는 2개의 다중 공전 스위치의 동작 순서에 따라 8개의 등가 모델링이 가능하다. 이 컨버터의 동작 원리는 입력 48[V], 출력 5[V]/50[W]의 실험세트와 PSpice 시뮬레이션을 통해 확인되었으며, 측정된 최대 전압 스트레스는 입력전압의 2.9 배인 170[V]였고 최대 효율은 81.66i%로 측정되었다.

• 경영정보학연구
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• 제20권4호
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• pp.79-96
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• 2018

본 연구는 기술력 평가항목 중 기업의 재무안정성과 관련된 항목을 신용평가모형에 반영하여 중소기업뿐만이 아닌 전체 기업을 대상으로 한 신용평가모형의 부도변별력을 높이기 위한 기술력 평가모형의 신용평가모형 내 내재화에 착안하여 시작되었다. 따라서 기술력 평가모형이 부채비율 기준의 고안정성 중소기업을 사전에 판별하는 데 적용될 수 있는지 검증하는 것을 목표로 한다. 대상 기업을 업종(제조업 vs. 비(非)제조업)과 업력(창업기업 vs. 비(非)창업기업)으로 구분하고, 3개년 동안 해당 군집의 평균 부채비율 1/2 이하를 달성한 기업에 대해 고안정성 중소기업으로 정의한 후, C5.0 기법을 적용하여 모형의 판별력을 검증하였다. 분석결과 소항목 수준에서는 업종과 업력에 따라 중요도 간 차이가 있지만, 중항목 수준에서는 기술개발역량이 고안정성 중소기업을 판별하는 중요변수로 도출되었으며, 기업의 업력에 따라 창업 초기에는 자금조달능력(수익창출능력을 고려한 자본구조, 자본비용 및 자금조달 방법의 다양성)이 미래 고안정성 중소기업 여부를 결정하는 중요변수이지만, 업력이 증가함에 따라 지속적인 성과를 가능하게 하는 기술개발 인프라가 재무안정성에 영향을 미치는 중요 변수로 변화한다는 결론을 도출하였다. 업종과 업력에 따른 모형의 분류 정확도는 71~91% 수준이며, 기술력 평가항목을 이용하여 고안정성 중소기업을 판별할 수 있다는 가능성을 확인하였다.

• 전력전자학회논문지
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• 제26권6호
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• pp.404-410
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• 2021

This paper proposes a high step-up converter with zero-voltage transition (ZVT) cell for fuel cell electric vehicle. The proposed converter applies a ZVT cell to a dual floating output boost converter (DFOBC) so that not only the main switch but also the ZVT switch can achieve full-range soft switching. The current rating of the ZVT switch is 17% of the main switch. The proposed converter has high reliability in that no timing issue occurs. Therefore, online calculation is not required. The minimum turn-on time of the ZVT switch that guarantees soft switching at all loads and input/output voltage is obtained by analysis. In addition, the proposed DFOBC allows the use of a 650 V device even at 800 V output and has the advantage of being able to boost the voltage by 3.5 times with 0.56 duty. Planar coupled inductor with PCB winding was successfully implemented with the converter operated at 300 kHz. The 25 kW prototype achieves peak efficiency of 99% and power density of 63 kW/L.

• 한국생산제조학회지
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• 제8권2호
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• pp.35-43
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• 1999

The paper describes an approach for measuring delivery flow ripple generated by oil hydraulic axial piston pumps. In order to reduce pressure ripple which cause to undesirable noise. vibration and fatigue in hydraulic systems it is indispensible measure a delivery flow ripple from pumps. Since the flow ripple measurement of flow pumps is independent of the dynamic characteristics of the connected hydraulic circuit the measurement of flow ripple is most suitable for pump fluid-borne noise rating. The measurement of flow ripple with high frequencies from axial piston pumps is made by applying the remote instantaneous flow rate measurement method which is based on the dynamic characteristics between pressure and flow rate in hydraulic pipeline. The measured flow ripple waveforms are influenced by the configuration of V-shaped triangular relief groove in the valve plate. It can be seen that the appropriate relief groove in valve plate reduces the pressure and flow ripple amplitude and frequency spectrum for high harmonics.

• 전기학회논문지
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• 제64권9호
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• pp.1306-1314
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• 2015

This paper deals with a switching method of a three-phase interleaved bidirectional DC-DC converter to obtain high efficiency in wide load range. The proposed soft-switching method provides ZVS and ZCS at turn-on, and ZVS at turn-off of the switch as well as considerably reduced conduction loss in light load. Simulation and experiment are carried out with a bidirectional DC-DC converter having the power rating of 3 [kW], and those results show the validity of the proposed switching method.

• 한국철도학회논문집
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• 제9권6호
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• pp.761-765
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• 2006

At present, harmonic currents cause serious problems in power conversion system using the semiconductor switching device. Also some of the conversion system provokes harmonic currents against to the main power supply system and causes hindrances for the system. Main power impedance of the traditional LC passive filter method, influences on the filter characteristics and amplifies the harmonics when resonance phenomenon is occurred. And the traditional existing 2 level inverter systems show the limit in capacity of voltage and current in case of occurring sudden load change. So, to solve this problem active filter which uses cascaded H-bridge multi level inverter has been designed and ex-filter system circuits were totally investigated. With multi level active filtering system not only the size of filter but also the size of filter for transformer can be reduced by half and so as to the weight, while the capacity of inverter can be double sized and wave forms can be compensated exactly and precisely. Also by the benefit of the increase in rating capacity, the various currents owing to the load fluctuation can be dealt more steadily. In order to simulate the wave form of harmonics based on the measured data on the AC 25kV high speed Domestic Commercial railway, it was simulated with PSCAD/EMTDC and PSIM. Based on the results of this demonstration, the power supply system and inverter system would be more stable and also promoting its efficiency.

• 한국전자파학회논문지
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• 제28권5호
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• pp.400-409
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• 2017

고주파 대역에서 삽입 손실을 최소화 하면서 고출력을 견딜 수 있는 결합기에 대해서 연구하였다. 특히, Ku 대역 이상에서는 단위소자 당 낼 수 있는 출력 전력이 저주파 대역에 비해 매우 낮기 때문에, 고출력 SSPA를 만들기 위해서는 많은 반도체 소자를 결합해야만 한다. 마이크로스트립과 같은 평면 결합기는 결합하는 소자의 개수가 증가하면 비례적으로 삽입 손실이 증가하여 전체 시스템 효율이 떨어지고 발열량도 높아지게 된다. 또한 평면 결합기는 낮은 전력 내구성에 따른 문제도 가지고 있다. 이러한 문제점들을 개선하고자 본 논문에서는 cavity radial combiner를 제안하였다. Ku 대역 16-way cavity radial combiner를 제작하여 측정한 결과, 설계 대역에서 반사손실 14 dB 이하, 94.5 % 이상의 출력결합 효율을 얻었다.

• Journal of Power Electronics
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• 제17권3호
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• pp.632-640
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• 2017

Input series output independent (ISOI) dc-dc converter systems are suitable for high voltage input and multiple output applications with low voltage rating switches. This paper proposes a novel control strategy consisting of one output voltage regulating (OVR) control loop and n-1 (n is the number of modules in the ISOI system) input voltage sharing (IVS) control loops. An ISOI system with the proposed control strategy can be applied to applications where the output loads of each module are the same. Under these conditions, IVS can be achieved and output voltages copying can be realized in an ISOI system. In this control strategy there is only one controller for each module and the design process of the control loops is simple. Since no central controller is needed in the system, modularity of the system is improved. The operation principle of the new control strategy is introduced and the control effect is simulated. Then the output power and voltage characteristics of an ISOI system under this new control strategy are analyzed. The stability of the proposed control strategy is explored base on a Hurwitz criterion, and the design guide line of the control strategy is given. A two module ISOI system prototype is fabricated and tested in the laboratory. Experimental results verify the effectiveness of the proposed control strategy.