• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.10
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• pp.1286-1291
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• 2018

In recent years, the proliferation of DER (distributed energy resources) is progressing rapidly. In particular, research on LVDC distribution grid with various advantages has begun. In order to commercialize this LVDC grid, direct current protection method should be established by analysis of DC faults. Recently, the development of HSCB (high-speed circuit breaker) for new ${\pm}750[V]$ LVDC grid has been researched. This paper deals with the calculation of the maximum short-circuit fault current of the HSCB as a part of the development of HSCB for the LVDC distribution grid. First, modeling using PSCAD was carried out for PV array with BESS on the Gochang Power Test Center system. Next, to calculate the rated capacity of HSCB, fault currents were calculated and the characteristics were analyzed through fault simulations. Thus, this study results can help to establish short-circuit capacity calculation of HSCB and protection plan for DC protection relay system.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1211-1222
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• 2018

This study presents a power distribution control scheme for a three-phase interleaved parallel DC/DC converter in a battery energy storage system. To extend battery life and increase the power equalization rate, a control method based on the nth order of the state of charge (SoC) is proposed for the charging and discharging processes. In the discharging process, the battery sets with high SoC deliver more power, whereas those with low SoC deliver less power. Therefore, the SoC between each battery set gradually decreases. However, in the two-stage charging process, the battery sets with high SoC absorb less power, and thus, a power correction algorithm is proposed to prevent the power of each particular battery set from exceeding its rated power. In the simulation performed with MATLAB/Simulink, results show that the proposed scheme can rapidly and effectively control the power distribution of the battery sets in the charging and discharging processes.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.421-422
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• 2014

본 논문에서는 저압 직류 배전 시스템의 구성방법 중 하나인 Bipolar System을 사용할 때 서로 다른 부하용량으로 인하여 발생하는 전압 불균형 문제를 보상하는 전압밸런서와 절연형 양방향 DC-DC 컨버터가 결합된 토폴로지를 제안하였다. 제안하는 DC-DC 컨버터의 1차측은 풀 브릿지 타입, 2차측 하프 브릿지 타입의 밸런싱 회로로 구성하여 따로 밸런서 없이 DC 그리드와 태양광 발전 시스템, ESS 시스템의 연계 및 전압밸런싱이 가능하다. 이와 같은 DC-DC 컨버터를 신재생 에너지와 연계하여 저압 직류 배전 시스템의 분산 전원으로 구성하였고, 시뮬레이션을 통하여 타당성을 검증하였다.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.151-152
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• 2016

최근 저압직류배전에 대한 연구가 급속도로 진행되면서 배전망에 적용되는 구성요소에 대한 연구가 활발히 진행 중이다. 본 논문에서는 대용량 수용가 배전반에 접속된 구성요소 중 배전계통으로부터 직류전력 공급하기 위한 양방향 DC/DC 컨버터, 수용가 직접 전력공급을 위한 직류 저압 태양광 발전시스템용 DC/DC 컨버터, 저압 직류 에너지저장시스템용 DC/DC 컨버터의 운전에 있어서 배전계통간 전력조류를 양방향 운전의 타당성에 대해 비교하고, 운용상 얻어지는 효율 개선 등에 대한 것을 비교 검토하고자 한다.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.5
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• pp.391-396
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• 2022

In this study, a new voltage-balancing dual-active bridge converter that integrates a DAB converter with a voltage balancer is proposed for a bipolar DC distribution system. The proposed converter is configured to connect two loads to the transformer secondary center tap of the DAB converter, and no additional components are added. The proposed converter has the same operation as the conventional DAB converter, and it makes both output voltages similar. Moreover, the imbalanced current offset between the two loads is bypassed only on the secondary side of the transformer. Consequently, the proposed converter integrates a voltage balancer without any additional components, and no additional loss occurs in the corresponding components. Thus, high efficiency and high power density can be achieved. The feasibility of the proposed converter is verified using 3 kW prototypes under 380 V input and 190/190 V output conditions.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.2
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• pp.73-78
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• 2020

In this study, a novel reactive power control scheme is proposed to supply stable reactive power to the distribution line by compensating a ripple voltage of DC link. In a single-phase system, a magnitude of second harmonic is inevitably generated in the DC link voltage, and this phenomenon is further increased when the capacity of DC link capacitor decreases. Reactive power control was performed by controlling the d-axis current in the virtual synchronous reference frame, and the voltage control for maintaining the DC link voltage was implemented through the q-axis current control. The proposed method for compensating the ripple voltage was classified into three parts, which consist of the extraction unit of DC link voltage, high pass filter (HPF), and time delay unit. HPF removes an offset component of DC link voltage extracted from integral, and a time delay unit compensates the phase leading effect due to the HPF. The compensated DC voltage is used as feedback component of voltage control loop to supply stable reactive power. The performance of the proposed algorithm was verified through simulation and experiments. At DC link capacitance of 375 uF, the magnitude of ripple voltage decreased to 8 Vpp from 74 Vpp in the voltage control loop, and the total harmonic distortion of the current was improved.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.6
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• pp.160-168
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• 2010

This paper presents the analysis of the current as stray current and supplied current of the substation, on the DC railway power system. In DC railway power supply system, the running rails are usually used as the return conductor(negative-polarity) for traction load current. This condition mainly focuses on economic considerations, since it does not require the installation of an additional return conductor. But, problems of low resistance between the running rails for the return conductor and earth allows a significant part of the return load current to leak into the earth. This current is normally called to as leakage or stary current. This stary currents creates serious problems for any electrified matter in the underground. Therefore, reduction of stray current of the DC railway power supply system is also of direct benefit to the operational and safety aspects of the DC railway systems. In this paper, deal with the analysis of the current distribution on the DC railway power system applied the common grounding system, using SPLIT of CDEGS program.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.902-904
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• 1993

This paper contains the terminal developement for the feeder remote unit in Korea Distribution Automation System. This terminal unit has serval functions in order to do feeder auotmation as following, the open/close controls and gathering status informations of switchgears, getting line currents and voltages, distribution fault. So FRU has four modules to do those functions-Logic Controller, Relay Controller, Data Acquisition, Display, Power Supply etc. The FRU should be on allays, so AC power is supplied before & behind the switchgear. Power Supply is made up with AC/DC, DC/DC, Battery and/or SOLAR CELLS & CONTROLLER. It is important for the supply to protect against some Surges, because surges are happened so many times. Surge test is fellowing the standard IEC 801-5 or IEEE 587.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.5-6
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• 2016

This paper introduces a high efficiency bidirectional resonant converter using an additional LC auxiliary circuit for dcdistribution applications. The LC auxiliary circuit operates as a variable inductor and the additional LC circuit helps to increase the effective magnetizing inductance, thereby reducing the turn-off and primary circulating current. A 5 kW bidirectional converter for dc-distribution system is implemented to verify the validity of the proposed method. The experimental results show the high efficiency characteristics of the proposed converter over the wide range of load in both direction of power flow. The maximum efficiency of the proposed system was 98.1 % at 3 kW.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.432-433
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• 2018

A new DC-DC converter circuit for LVDC(Low Voltage Direct-Current) distribution is proposed. DC-DC converter consists of two stage which are voltage balancer and converter stage. The balancing circuit adjust balance input voltage of converter circuit and compensate for unbalanced loads and short circuits. The converter circuit control the bipolar output voltage ${\pm}750V$. Simulation is carried out for this DC-DC converter system.